NFM_BREF_REVISED_Chap9-Processes to produce

Transcription

Chapter 9
9
PROCESSES TO PRODUCE NICKEL AND COBALT
9.1
Applied processes and techniques
Nickel is produced from oxidic (laterite and saprolite) or sulphidic ore, about 60 % of the nickel
comes from sulphide deposits and 40 % from oxide deposits. There are several variations in the
processes used to produce nickel from these ores and these variations are dependent on the
grade of the concentrate and also on the other metals that are present in the material [ 92, Laine,
L. 1998 ].
Cobalt is usually present in nickel and copper ores and is recovered during their production.
Refining of the recovered by-product that contains cobalt is performed by a combination of
processes governed by the composition of the concentrate and the physical and chemical
characteristics of the final product. Cobalt arsenide ores are also sources of cobalt. These ores
are roasted to remove the majority of arsenic as arsenic oxide [ 104, Ullmann's Encyclopedia
1996 ]. The process however is not used in the EU.
Table 9.1 shows the composition of some ores.
Table 9.1:
Composition of some ores
Source of ore
Type
Murrin Murrin (Australia)
Cerro Matoso (Colombia)
Selebi-Phikwe (Botswana)
Sudbury area (Canada)
Raglan (Canada)
Vale INCO, Copper Cliff
Cosmos (Australia)
Mount Keith (Australia)
Laterite
Laterite
Sulphide
Sulphide
Sulphide
Sulphide
Sulphide
Sulphide
Ni
(%)
1.07
2.16
0.77
1.18
2.56
1.55
5.7
0.6
Cu
(%)
1.73
0.71
2
0.2
0
Co
(%)
0.08
0.04
0.1
Secondary nickel and cobalt are consumed directly in the form of remelted scrap and other
recycled products generally in the production of ferro-nickel and stainless steel [ 92, Laine, L.
1998 ]. Other secondary materials such as catalysts and precipitator dusts are recovered in the
primary smelting processes, usually in the slag furnace.
Because these metals are so closely associated, their production processes are dealt with
together as far as possible [ 92, Laine, L. 1998 ].
9.1.1
9.1.1.1
Nickel production
Oxidic ores
In laterite ores, nickel and cobalt are bound with iron and manganese oxides or silica
compounds and are difficult to upgrade to a concentrate. Smelting of these ores with a source of
carbon in an electric furnace can be used. Ferro-nickel is produced or a nickel matte can be
made after the addition of sulphur. The generic flowsheet is shown in Figure 9.1.
Prior to smelting, the ore is usually preheated or calcined in a rotary kiln [ 106, Raffinot, P.
1993 ]. An electric furnace is then usually used for smelting.
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Laterite
ore
Ammoniacal
leaching
Sulphuric acid
leaching
Drying
Calcining
Hydrogen
reduction
Mixed sulphide to
separate matte
treatment
Smelting in
electric furnace
Nickel rondelles
Nickel oxide
Sinter
Ferronickel
Converter
Ni
matte
Ni cathodes
Ferric chloride
Leaching
Electrowinning
Figure 9.1: Generic flowsheet for nickel production from laterite ores
Saprolite ores can be smelted with sulphur so that the nickel oxide is converted to a nickel
sulphide matte and iron is removed as a slag [ 106, Raffinot, P. 1993 ]. The matte is treated in
the same manner as matte produced from sulphide ores.
Smelting to ferro-nickel accounts for a large proportion of nickel production from laterite ores.
These processes are discussed under ferro-alloys in Section 8.1.4. Leaching of laterite with
ammonia is also used to extract nickel [ 19, HMIP (UK) 1994 ], [ 56, Knuutila, K. 1997 ], [ 94,
Laine, L. 1998 ] and this process is becoming more important. Although conversion of nickel
oxide to impure nickel and then to nickel carbonyl, which is volatile, is used to produce refined
nickel, the nickel oxide is produced from the smelting of a sulphidic ore. The laterite ores
generally have a maximum nickel content of 3 % and are therefore not used directly in this
process.
The pressure leaching of laterites with sulphuric acid is principally a simple and straightforward
process. The temperature, pressure and other parameters may vary from case to case to achieve
the best possible metallurgical conditions depending on the ore and products in question and
other objectives. The temperature of the leaching autoclaves is usually between 230 and 260 °C
and pressures up to 43 bar are used. Oxygen can also be used in the process.
The resultant solution is purified either by modern solvent extraction methods or by traditional
precipitation methods. For example hydrogen sulphide is used to selectively precipitate nickel
and cobalt sulphides which are sent for further metal recovery. The solution can be neutralised
so that iron precipitates. Nickel and cobalt will be precipitated and releached with ammonia.
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Solvent extraction is used to separate nickel and cobalt chlorides or sulphates. Metallic nickel
can be produced by electrowinning and cobalt can be precipitated as cobalt sulphide.
Alternatively nickel and cobalt can be recovered as metal powders using hydrogen reduction.
Table 9.2 shows the processes used in the EU-28.
Table 9.2:
Processes used in EU-28
Company
Name
Location
Industry sector
Process description
Nickel refinery by a hydrometallurgical
process, receiving imported nickel matte
which is ground, dissolved with chlorine,
purified and refined by electrowinning
(NiCl2 salt and Ni metal production)
Metal refinery by a hydrometallurgical
process, receiving matte which is grained,
dissolved with chlorine, purified and
refined by electrowinning (Ni metal
production)
Eramet
Sandouville,
France
Nickel metal
producer, Nickel salts
producer (Ni
chloride, Ni
hydroxycarbonate)
Xstrata
Nickel
Kristiansand,
Norway
Nickel metal
producer
Harjavalta,
Finland
Nickel metal
producer, Ni sulphate
producer, Ni
hydroxycarbonate
producer
Ni refining and Ni salts production.
Refining (electrowinning and hydrogen
reduction)
Harjavalta,
Finland
Nickel Smelting
Sulphidic ore concentrates brought to the
plant. Direct Outotec Nickel flash
smelting (DON process®). Producing
nickel matte from sulphide concentrates.
Boliden also operates a copper flash
smelter in the same site producing copper
anodes from sulphide concentrates. The
emissions of nickel smelter and copper
smelter are inseparable and thus emissions
reported in this exercise originate from
both smelters. The dust emissions are
monitored in three stacks, ventilation
gases, Ni drying plant and Cu drying plant
Clydach
Swansea, UK
Ni metal producer, Ni
sulphate producer (in
China, not in
Clydach), Ni chloride
producer (in China,
not in Clydach)
Imported nickel oxide. Refining of nickel
using the carbonyl process
Norilsk
Nickel
Boliden
Inco Europe
Ltd
9.1.1.2
Sulphidic ores
Nickel-bearing sulphide ores can be concentrated, e.g. by flotation to upgrade the nickel
content. Nickel concentrates that generally contain 7 - 25 % Ni are produced which makes
further processing easier. Sulphide concentrates can also be dried in rotary dryers, steam-heated
coil dryers or fluidised bed dryers. Feeding dry sulphide concentrate to primary smelting
furnace, like flash smelting, enhances process performance and reduces the energy consumption
and exhaust gas flow. Concentrates and sand used as flux are dried to reduce the moisture
content from 7 – 8 % to about 0.2 % prior to smelting process. The nickel concentrates are
usually smelted under oxidising conditions to remove iron sulphide and other gangue materials
from the concentrate to produce a nickel matte. The Outotec flash furnace is used in Europe; the
Outotec and INCO flash furnaces and electric or shaft furnaces are used elsewhere in the world.
The nickel is recovered into a sulphide matte that contains 35 - 70 % Ni, Co and Cu. The matte
can be treated in a Peirce-Smith converter or alternatively it can be granulated or cooled slowly
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before a hydrometallurgical recovery stage [ 139, Riekkola-Vanhanen, M. 1999 ]. The converter
stage is not used in Europe.
Important components of the nickel mattes are cobalt, copper and precious metals. The slag
produced during smelting also contains recoverable metal and is treated in an electric furnace to
produce more nickel matte. This can be granulated and treated separately [ 92, Laine et al. 1998
], [ 94, Laine, L. 1998 ]. Secondary materials are sometimes recovered in the electric furnace.
Figure 9.2 gives an overview of the process options.
Sulphide
concentrate
Roasting
Electric smelting
Flash smelting
Converting
Converting
Flash smelting
Ammoniacal
leaching
Hydrogen
reduction
Nickel powder/
briquettes
Electrolytic
refining
Carbonyl
refining process
Chloride leaching
Electrowinning
Sulphate leaching
Electrowinning/
hydrogen reduction
Ni cathode
Ni pellets/ powder
Nickel cathode
Nickel cathode/
powder/briquettes
Figure 9.2: Generic flowsheet for the production of nickel from sulphide concentrates
9.1.1.2.1
Conventional flash smelting process
Conventional smelting processes are used to remove iron and other gangue materials from
sulphide concentrates to produce nickel matte. Worldwide there are five other smelters, which
use this process. Two of these use a flash smelting furnace designed by BHP Billitonne
(formerly Western Mining Corporation), where the smelting and slag cleaning furnaces have
been built together to form one larger unit.
There are differences in operations between the smelters. The most visible difference is the
matte grade but variations in the raw material composition also cause some differences. The
generic flowsheet is shown below in Figure 9.3.
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Ni concentrate Oxygen + air
Flux
Flash smelting
furnace
Water heat
boiler
Electrostatic
precipitator
Ni matte
Waste heat
boiler
Converter
Slag
Gas to
acid
plant
Slag
High-grade nickel matte
Electric furnace
Ni matte
Figure 9.3: Conventional flash smelting
9.1.1.2.2
Direct Outotec Nickel (DON) process
In Europe only the Direct Outotec Nickel (DON) process is used. The DON process combines
both smelting and converting to produce a high grade matte which is further treated
hydrometallurgically. [ 310, DIRECT OUTOKUMPU NICKEL TECHNOLOGY 2006 ].
Flash smelting furnace is based on utilisation energy contained in the raw material itself to drive
the smelting process. Dried concentrate and flux mixture is fed continuously with oxygen
enriched air through concentrate burner into the vertical reaction shaft of a sealed furnace where
the reactions between oxygen and concentrate particles takes place rapidly in suspension. Part of
the sulphide compounds in the feed ignite, oxidise and release heat, thus acting as a fuel for the
process. Operation uses oxygen enrichment to about 30 – 90 % oxygen in process air. The
degree of oxygen enrichment is determined by the concentrate quality and the heat balance
requirement. Oil burners are used to produce additional energy, when needed.
Molten phases are collected in the horizontal settler part of the flash smelting furnace where
slag and matte form separate layers. The slag is laundered semi-continuously to the electric slag
cleaning furnace where it is treated with coke and a sulphidising agent in order to recover the
valuable metals left in the slag. The matte is periodically tapped and granulated by water
quenching of sprinkled melt. The solid matte granules settle in a bottom section of the tank,
from where they are pumped with water on to a dewatering screen. The granules are lifted in a
bucket elevator into an intermediate bin, from where they are taken on the belt conveyor to
grinding and to the hydrometallurgical nickel plant. The slag passes by launder to an electric
slag-cleaning furnace where it is treated with coke and a sulphidising agent to produce more
nickel matte and a cleaned slag for disposal. The two mattes have different compositions and are
treated separately. The matte is granulated and ground before passing to the leaching stage.
The process is shown in Figure 9.4.
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Concentrate
Silica sand
Secondary
raw materials
Concentrate unloading
Gas to stack
Waste oil
Drying
Gas + dust
Copper
smelter
Gas + dust
Heavy oil
Air O2
Bag filter
ESP
WHB
Smelting by DON
Slag
Coke
Reverts
FSF- matte
Slag cleaning
by EF
Granulation tank
FSF- matte
Grinding
EF- matte
Granulation tank
EF- matte
ESP
Gas ventilation
system process
heat
Slag for
disposal
Acid plant
Slag for sale
Weak acid
H2SO4
Off gas
stack
Hg-sludge to
Further treatment
Liquid SO2
Grinding
Atmospheric leaching
Atmospheric leaching
Figure 9.4: The DON process
9.1.1.2.3
Heap leaching
Open heap leaching is usually carried out at the mine. Material is crushed and ground to allow
intimate particle/acid contact and then formed into natural heaps on an impervious liner. Acid is
sprayed onto the heaps and percolates through the mass. It is collected on the liner and is
recirculated to allow the metal content to build up . Bacteria are used to enhance the leaching
process and improve efficiency and this technique is used for some nickel ores where zinc,
cobalt and copper are leached simultaneously and then separated prior to metal recovery [ 284,
Talvivaara June 2008 ].
9.1.1.3
Matte refining processes
The mattes produced by the smelting processes must be treated further in order to recover and
refine the metal content. Nickel matte must go through a multistage refining process to reject
iron and recover copper, cobalt and precious metals. Matte can be treated pyrometallurgically
but hydrometallurgical processes are more commonly used. A variety of electrorefining,
leaching, reduction and precipitation processes are carried out. Nickel is recovered from purified
solutions by electrowinning or by hydrogen reduction.
Figure 9.5 shows the generic processing routes.
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Roasting
Chlorination
TBRC
converting
Carbonyl
reactors
(Pressure)
acid
Ni matte
Hydrogen
reduction
Nickel
oxide
Nickel
Hydrogen
reduction
Nickel
Electrowinning
Cahode
nickel
H2S
precipitation
Hydrogen
reduction
H2S
precipitation
Copper
Nickel
Ni-Co
Solution
purification
-SX
-Precipitation
Electrowinning
Cathode
Solution
purification
Cu and Co
Ammoniacal
pressure
Chloride
Co and Cu
Figure 9.5: Generic flowsheet for nickel matte refining processes
Nickel containing raw materials are leached in reactors (atmospheric; temperature < 110 °C and
pressure 1 bar) and or in pressure autoclaves (temperature > 100 ° and pressure > 1 bar).
Leaching takes place in chloride (Section 9.1.1.3.1), sulphate (Section 9.1.1.3.2) or ammoniac(see Section 9.1.1.3.3) based solutions and oxygen or chlorine gases are used as an oxidant.
Impurities like copper and iron are precipitated as cake. In most cases Cu-cake is further
processed and iron cake is recycled to smelter or put in the waste areas. Nickel solution is
purified by a combination of solvent extraction and precipitation processes to remove cobalt and
other impurities. Impurities like lead, manganese and gypsum are deposited in a designated
waste area.
9.1.1.3.1
Chloride leaching of matte followed by electrowinning
Matte is leached in a chloride solution in several stages at a high temperature and pressure using
chlorine gas as an oxidant. The chlorine gas is generated in the electrowinning cells and is
returned to the leaching circuit. Copper is precipitated as the sulphide and then iron and arsenic
are precipitated as hydroxides and arsenates to purify the leachate. Copper sulphide is roasted in
a fluidised bed furnace and the resulting calcine is leached with spent copper electrolyte. Copper
is then electrowon.
Cobalt is removed by solvent extraction of the chloride solution using an organic solvent and is
electrowon. The nickel solution is further purified using chlorine to remove lead and manganese
followed by electrowinning of nickel and is then electrowon in diaphragm cells using a
dimensional stable anode (DSA) made with titanium, anodes enclosed in a diaphragm bag to
collect chlorine gas. The cells are sealed to recover the chlorine that is formed at the anode.
This is known as the Falconbridge process and is shown in Figure 9.6.
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Figure 9.6: Falconbridge process
9.1.1.3.2
Sulphate-based atmospheric pressure leaching followed by
electrowinning/hydrogen reduction
Matte is leached in a sulphate-based anolyte recycled from nickel electrowinning[ 57, Knuutila,
K. et al. 1996 ], [ 58, Kojo, I.V. et al. 1997 ]. Nickel sulphide matte is leached in an atmospheric
leaching stage using oxygen or air-sparged leach vessels with the aid of copper ions. Dissolved
iron is oxidised to form iron oxide which precipitates (see Figure 9.7).
Matte
Air
Atmospheric
leach
Atmospheric
leach
Atmospheric
leach
NaOH
Pressure
leach
Oxidation
Ni(OH)2
Cobalt
removal
Nickel
electro winning
Cobalt
precipitate
Nickel
cathodes
Anolyte
Copper
precipitate
Figure 9.7: Sulphate-based leaching process
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The residue from atmospheric leaching is passed to the pressure leaching stage where the nickel
content is dissolved and copper is precipitated as copper sulphide, which is returned to the
copper smelter. The iron oxide precipitate is returned to the nickel smelter. Alternatively the
iron residue is disposed of. The nickel solution from the atmospheric leach is purified by solvent
extraction to remove cobalt and impurities. Cobalt can be electrowon or reduced to cobalt
powder using hydrogen. Nickel can be electrowon from the purified sulphate solution to
produce cathodes [ 310, DIRECT OUTOKUMPU NICKEL TECHNOLOGY 2006 ].
Nickel powder can be produced by adding ammonia and ammonium sulphate to the solution.
The mixture is then reduced in an autoclave using a hydrogen atmosphere. The powder is sold
or can be sintered into briquettes. The sulphuric acid present is neutralised by ammonia. The
ammonium sulphate is recovered for sale or reuse in the process.
This process has been developed into a two-stream process to allow separate treatment of the
mattes produced from the smelter and the slag cleaning furnaces. The flowsheet of the DON
refinery process shown in Figure 9.8.
EF matte
FSF matte
EF = Electric Furnace
FSF = flash smelting furnace
SX = solve extraction
EW = electro-winning
Granulation
Grinding
Co SX
Co
EF- matte
leaching
and Fe
removal
To smelter
Leaching and
Cu/Fe removal
Ni EW
Ni
ATM leaching
Fe residue
(haemethite,
goethite,
jarosite)
Ni pressure
leaching
Cu pressure
leaching
Cu EW
PGM
Cu
Figure 9.8: Flowsheet of the DON refinery process
9.1.1.3.3
Ammonia pressure leach and hydrogen reduction
Matte is leached into ammoniacal ammonium sulphate solution in pressure autoclaves using air
as an oxidant. After the precipitation of copper sulphide, nickel solution is reduced with
hydrogen in the autoclaves to produce metallic nickel powder. The ammonium sulphate formed
in the hydrogen reduction stage is recovered by crystallisation and drying. After the hydrogen
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reduction, the rest of the dissolved nickel and all the cobalt are precipitated with hydrogen
sulphide for further treatment [ 92, Laine, L. 1998 ] [ 94, Laine, L. 1998 ]. This is known as the
Sherritt process and is shown in Figure 9.9.
Ni matte/concentrate
NH3
O2
Adjustment
leach
NH3
Ni
solution
Sº or SO2
Copper boil
H2S
O2 (NH4)2 SO4 or
NH4OH
NH3
Final leach
Residue
wash
H2
Residue
to tailings
CuS/S to smelter
Oxidation &
hydrolysis
Ni/CoS
precipitation
Nickel
reduction
Crystallisation
Ni powder
Ammonium
sulphate
NiS/CoS to
Co refinery
Figure 9.9: Sherritt ammoniacal leaching
9.1.1.3.4
Ferric chloride leaching
Matte is leached in several stages using recycled ferric chloride in the presence of chlorine
(which is generated from the electrowinning cells) near to boiling point. Sulphur remains in the
elemental state and is filtered from the final solution. Iron is then removed by solvent extraction
using tributyl phosphate allowing ferric chloride to be recovered. Cobalt is removed in a further
solvent extraction stage using tri-iso-octylamine. Cobalt chloride solution is sold [ 92, Laine, L.
1998 ], [ 94, Laine, L. 1998 ].
Other minor impurities such as Cr, Al, Pb are removed using a combination of electrolysis, ion
exchange and active carbon. Nickel is then electrowon from the purified solution in diaphragm
cells using titanium anodes and nickel cathodes. Chlorine is collected and returned to the leach
circuit.
9.1.1.3.5
Carbonyl process
The low pressure carbonyl process uses an impure oxide produced by smelting sulphide ore as
the raw material to refine the nickel. This oxide is reduced to an impure metal using hydrogen
and the metal is then activated. Nickel carbonyl is then formed by the reaction of the metal with
carbon monoxide at low temperature and pressure. Nickel carbonyl is volatile and is refined by
separation from the solid impurities. The solid residue is returned for further processing to the
primary smelter to recover other metals that are present [ 19, HMIP (UK) 1994 ], [ 25,
OSPARCOM 1996 ].
Nickel carbonyl gas passes from the reactor and is then decomposed using heat to form powders
and pellets. It can also be decomposed onto other substrates such as carbon fibres to produce
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nickel-coated materials. During decomposition, carbon monoxide is released and is recovered
and reused to produce more nickel carbonyl. Pure nickel salts are produced by the reaction of
nickel pellets with acids. Any exhaust off-gases from the process are incinerated to destroy any
nickel carbonyl and carbon monoxide. Dust from the afterburner is removed using a bag filter.
9.1.1.3.6
Matte electrorefining
Nickel matte can be cast into anodes. These are dissolved in a diaphragm electrolysis cell using
a chloride/sulphate electrolyte. The electrolyte from the anode compartment is purified and
circulated through the cathode bag. The anodes are also bagged to collect the slime that contains
sulphur. Elemental sulphur and precious metals are recovered from the slime. This process is
limited to mattes that have a low copper content [ 94, Laine, L. 1998 ].
9.1.1.3.7
Solvent extraction
Most of the processes described above use a solvent extraction stage to remove iron, calcium
and zinc and to separate nickel and cobalt prior to electrowinning or transformation. Metal ion
complexes are formed using chelating agents so that the desired metal ions can be extracted into
an organic phase. The desired ions are then back extracted into a second aqueous phase by
altering the conditions of a second aqueous phase.
The choice of solvent and chelating (complexing) agent allows specific metal ions to be
removed from aqueous solution and to be concentrated. The solvent/chelating mixture is
recycled between the extraction and winning baths. The baths comprise a mixer/settler to allow
solvent/water contact and then phase separation. Sealed or covered systems are used to prevent
the emission of solvent fumes. Figure 9.10 shows a generic process outline [ 239, ENIA 2008 ].
Stripped organic
Raffinate
Extraction
Pregnant leach
solution
Spent electrolyte
Stripping
Loaded organic
Cu2+ + 2LH  CuL2 + 2H+
aq
org
org
aq
Electro winning
Advanced
electrolyte
CuL2 + 2H+  Cu2+ 2LH
org
aq
aq org
Figure 9.10: Solvent extraction (SX) process outline
9.1.1.3.8
Nickel matte refining process
Eramet has developed a refining process that originated in the nineteen seventies which can:
(See Figure 9.11) [ 239, ENIA 2008 ].



obtain very high purity nickel metal
recover all of the by-products
minimise the solid residue production.
Pyrometallurgical nickel matte is leached by chlorine in a chloride medium in the presence of
recycled ferric chloride near to boiling point. The major constituent of the leaching residue is
elemental sulphur. This by-product, after roasting, allows the production of sulphuric acid.
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The major constituents of the leaching solution are nickel, cobalt and iron chlorides. Impurities
like aluminium, chromium, manganese and lead are also present.
After complementary oxidation of the solution, the iron is first extracted by solvent extraction
using tributylphosphate (TBP) as an extractant. The stripping is performed with water. The iron
chloride solution is sold, after concentrations up to 40 wt – % FeCl3. It is used in water
treatment processes.
The cobalt is extracted from the iron-depleted solution by solvent extraction using tri-isooctylamine as extractant. The stripping is performed with water. The cobalt chloride is sold,
after complementary purification and concentrations up to 27 wt- % CoCl2, as raw material for
chemical specialties production.
In order to obtain a totally pure nickel chloride solution, hydroxides are precipitated to allow the
elimination all the main impurities such as Al, Cr, etc. This is followed by lead removal using
an electrolytic process.
The pure nickel chloride solution is used as raw material to produce high quality nickel salts,
such as nickel chloride solution or crystals, or nickel hydroxycarbonate and high purity nickel
metal (Ni ≥99.99 %) obtained by electrolysis in the chloride medium. Chlorine evolves at the
anode, made of titanium alloy and is collected and directly recycled to the matte leaching step.
Remaining minor impurities such as Al, Cr, Pb are removed using a combination of
precipitation, electrolysis and activated carbon in order to obtain a very pure nickel chloride
solution that is used as a feed material for various production units such as:
•
nickel chloride solution or crystals after concentration, crystallisation and drying;
•
nickel hydroxycarbonate by precipitation, filtration and spray drying;
•
nickel metal (purity >99.99%) by electrolysis in chloride medium on titanium and
nickel cathodes. Chlorine produced at the anodes is recycled at the matte leaching step.
The energy used for the nickel production is in the range of 20 GJ per tonne of nickel which is
in accordance with the energy use of the refining stages.
Emissions to air
The process has the following emissions to air:





Ni 0.025 kg/t Ni
Cl2 0.010 kg/t Ni
VOC
3.6 kg/t Ni
SO2
3.7 kg/t Ni
CO2
600 kg/t Ni
Emissions to water
The process has the following emissions to water:
1. Ni
2. suspended Solids
3. COD
0.017 kg/t Ni
0.18 kg/t Ni
2.0 kg/t Ni
Residues and Waste production
The Eramet nickel refinery using the process described here over does not produce any solid
residue for disposal.
The waste production is 22 kg/t Ni. This data does not include wastes that are not linked to the
production process itself.
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Flowsheet of the Eramet refining process is shown in Figure 9.11.
Ni - Co matte
Chlorine
Chlorine
Leaching
Elemental Sulphur
FeCl3
solvent extraction
Ferric chloride solution
CoCl2
solvent extraction
Cobalt chloride solution
Purification hydroxides
precipitation
By-product sold for metals recovery
Purification
lead removal
By-product sold
Nickel salts
High purity
nickel electrolysis
High Purity Nickel cathodes
Figure 9.11: Flowsheet of the Eramet refining process
9.1.1.4
Nickel alloy production from secondary materials
The process includes raw materials preparation, melting (including tapping and casting), ingot
stripping and dressing, scrap recycling and “electroslag refining” with a throughput about
7000 t/yr.
Raw materials for the process consist of recycled scrap, purchased scrap and virgin material.
Scrap in the form of turnings, swarf off-cuts, etc. is treated to remove oil by centrifuging and/or
degreasing. Raw materials are weighed into charging vessels to the desired alloy composition.
The charging vessels are then transported to the relevant furnace.
Melting is carried out in an induction furnace, with fumes captured by one of two extraction
systems fitted with fabric filters. Some of the metal is further refined in vacuum refining
furnaces. Vacuum induction melting is carried out in a 7.5 tonnes capacity furnace. Casting from
the furnace is carried out either under vacuum or argon. Vacuum arc refining is carried out
producing solid ingots under vacuum. Vacuum is provided by steam ejectors and gases from the
ejectors are cooled using spray condensers. Slag is refined in an electric furnace.
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Three casting techniques are used: top casting, uphill casting and durville casting. Casting
fluxes and anti-piping compounds are used during casting. Ladles used for casting are preheated
by gas-fired burners.
The ingots from casting are stripped of any residual refractory material, etc. Solid waste from the
casting processes, casting/ladle refractories, slags, etc. are collected for the recovery of residual
metal. The stripped ingots may then be subjected to various processes: machining, sawing, grinding
and shot blasting. The scrap from these processes in the form of dust, swarf and turnings is
collected for reprocessing or sale.
9.1.2
Cobalt production
Cobalt is produced during the recovery of nickel after separation by solvent extraction (SX) and
is described above in Section 9.1.1.3.7. Cobalt can be electrowon from the solution to produce
saleable cathodes using diaphragm cells in the same manner as nickel [ 233, Farrell Nordic
Mission 2008 ]. The electrowinning process can be sulphate- or chloride-based.
Cobalt can also be recovered from the solution as a powder by hydrogen reduction.
Alternatively, the solution can be treated to precipitate an impure cobalt by-product for further
refining or may be sold.
Further refining of these and other by-products that contain cobalt, intermediates and recycled
materials is performed using atmospheric and oxygen pressure leaching in a sulphuric or
hydrochloric acid medium. Separation using hydroxides, carbonates and amine or ammonium
complexes is also used [ 104, Ullmann's Encyclopedia 1996 ].
Precipitation, solvent extraction and ion exchange techniques are used to purify the solutions.
Cobalt is then recovered as metal powder, metal oxide or salts. The products are made with a
wide variety of very specific physical and chemical characteristics. Pyrolysis of carboxylates,
high temperature reduction of oxides, precipitation and crystallisation techniques are used
depending on the particle size or other characteristics that are required [ 104, Ullmann's
Encyclopedia 1996 ].
These processes are commercially confidential and very site-specific in nature. A generic
flowsheet is shown in Figure 9.12 and a more specific process is shown in Figure 9.13.
976
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Ore concentrate
Secondary materials
Pre-treatment
Leaching
a) matte
b) treated concentrate
c) alloy
Purification
Bulk Ni or Cu
separation
Leaching
Purification
Purification
Co recovery
Transformation
Sale up to
99.85 % Co
Sale up to
99.99 % Co
Figure 9.12: Generic flowsheet for cobalt production
[ 233, Farrell Nordic Mission 2008 ]
Figure 9.13: A practical cobalt flowsheet
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9.2
Current emission and consumption levels
9.2.1
Energy consumption
The energy consumed for the production of matte from sulphidic concentrates is reported to be
in the range 25 to 65 GJ per tonne of nickel for concentrates that contain 4 to 15 % Ni. The
energy consumed in the various refining stages is reported to be 17 to 20 GJ per tonne of nickel.
9.2.2
Emissions to air
The potential emissions of concern to air from nickel and cobalt production are:







sulphur dioxide (SO2) and other acid gases
oxides of nitrogen (NOX) and other nitrogen compounds
metals and their compounds including As
dust
chlorine
VOCs and odours
CO and carbonyls (alarm levels set at 80 parts per billion).
The relevance of the potential substances emitted from the major sources is given in Table 9.3
and are discussed later in this section.
Solvent Extraction
Sulphuric acid
plant
•••(1)
•
•
•
•••
•
•
Final recovery and
transformation
Electrolysis
Sulphur
dioxide and
trioxide (1)
Leaching and
purification
Component
Significance of potential emissions to air from cobalt and nickel production
Roasting or
smelting
Table 9.3:
HCl
VOCs
(including
CO and
odours)
••
••
Chlorine
Nitrogen
oxides
•(1)
Dust and
metals
•••(1)
••
•
•
•
••
(1) The direct emissions from the roasting or smelting stages of sulphidic ores are treated and/or converted in the gas-cleaning
steps and sulphuric acid plant; the remaining emissions of sulphur dioxide and nitrogen oxides of the sulphuric acid plant are
still relevant. Diffuse or non-captured emissions are also relevant from these sources.
••• More significant – • less significant
The sources of emissions from the process are:



978
roasting
other pretreatment
smelting, converting and slag treatment
July 2014
Chapter 9





leaching and purification
solvent extraction
electrolysis
final recovery or transformation stage
sulphuric acid plant.
9.2.2.1
Sulphur dioxide and other acid gases
The major sources of sulphur dioxide emissions are diffuse emissions from the roaster or
smelter. Uncaptured emissions from the ladle transfer and blowing stages of the converter and
direct emissions from the sulphuric acid plant are also significant. Good extraction and sealing
of the furnaces prevents diffuse emissions and the collected gases are passed to a gas-cleaning
plant and then to the sulphuric acid plant. The gas collection from the converter stages is a
significant source of emissions and this aspect is discussed in Chapter 3.3.5.
After cleaning, the sulphur dioxide in the gas from the roasting stages is converted to sulphuric
acid. Sections 2.11.3.4 and 2.20.6 provide more information about the techniques and emissions
from sulphuric acid plants in this sector.
During start-up and shutdown there may be occasions when weak gases are emitted without
conversion. These events need to be identified for individual installations and many companies
have made significant improvements to process control to prevent or reduce these emissions.
Sulphur dioxide emissions from some processes are shown in Table 9.4.
Table 9.4:
Sulphur dioxide production from some nickel and cobalt processes
Process
Product
Grinding/Leaching
Ni Smelter
Co and Compounds
Ni, Co, Cu
Metal production
(t/yr)
5000
200000
Sulphur dioxide (kg per tonne
of metal produced)
0.01
18
NB: The data refers to specific raw materials - grinding of matte produced from sulphidic ore - smelting of
Cu/Ni sulphidic concentrates.
Source: [ 239, ENIA 2008 ]
During electrolysis, there are emissions of aerosols (diluted hydrochloric and sulphuric acids
and metal salts) to the tank house. These emissions leave the tank house via the (natural)
ventilation or from the cooling towers and are classed as diffuse emissions. Cells can be covered
by foams or plastic beads to reduce the production of mists. Cell room ventilation air can be
demisted and the solution returned to the electrolysis stage.
Chlorine is formed during the electrolysis of chloride solutions. This is collected in the sealed
anode compartment and is returned to the leaching stage. Chlorine monitors are used to detect
leaks and scrubbers are used to remove traces of chlorine from the ventilation air and other
sources.
9.2.2.2
VOCs
VOCs can be emitted from the solvent extraction stages. A variety of solvents are used and they
contain various complexing agents to form complexes with the desired metal that are soluble in
the organic layer. Emissions can be prevented or minimised by using covered or sealed reactors
and in this case, emissions in the order of 30 mg/Nm³ have been reported.
The solvents can be aliphatic or aromatic in nature but usually a mixture is used. VOCs can be
classified according to their toxicity but aromatic and chlorinated VOCs are usually considered
to be more harmful and require efficient removal. Solvent vapours are emitted depending on the
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temperature of the extraction stage and the vapour pressure of the solvent components at that
temperature. VOC concentrations of up to 1000 mg/Nm³ (~1 kg/h) have been reported but the
operating conditions are not known [ 92, Laine, L. 1998 ]. The nature of the solvents and
conditions of use need to be determined so that the hazard can be assessed.
VOCs can be removed using condensers or by cooling the ventilation air and recovering the
solvent for further use. Mass emissions of 0.2 kg per tonne of metal produced have been
reported following condensation [ 92, Laine, L. 1998 ]. Carbon filters or biofilters can also be
used to reduce VOC emissions further but do not allow solvent recovery.
9.2.2.3
Dust and metals
Dust carry-over from the roasting, smelting and converting processes are potential sources of
direct and diffuse emissions of dust and metals. In some processes, the gases are collected and
treated scrubbers and fabric filters or in the gas-cleaning processes of a sulphuric acid plant.
Dust is removed and returned to the leaching process. Fabric filters and scrubbers are used to
remove dust and large particles. Dust and metal emissions from some processes are shown in
Table 9.5 and Table 9.6 but it should be noted that different processes and process stages are
involved and the data is not comparable [ 260, Nyberg et al. 2000 ].
Table 9.5:
Dust and metal emissions from some European processes
Process
Product
Production
(tonnes)
Matte grinding
Refining nickel
matte
Carbonyl
process
DON process
and copper
smelter (1)
Ni
12000
Dust
(kg per tonne
of metal)
0.02
Ni
Ni
(kg per tonne
of metal)
0.005
0.04
Ni
40000
0.01
0.005
Ni, Cu
240000
0.25
0.02
(1) The DON process and copper smelter comprises a site that includes drying, smelting (Cu+Ni), Cu
converting, slag cleaning (Cu+Ni), all Ni matte refining processes and other abatement processes
Source: [ 239, ENIA 2008 ]
Table 9.6:
Emissions to air from some process stages of Co production
Process
Grinding/leaching
Solvent extraction
Final recovery or
transformation
Total
Co
(kg per
tonne of
metal)
0.1
Ni
(kg per
tonne of
metal)
Product
Productio
n (tonnes)
Co
Co
10000
10000
Co
10000
0.8
0.1
Co
10000
0.9
0.1
VOC
(kg per
tonne of
metal)
4.0
4.0
Source: [ 239, ENIA 2008 ]
9.2.2.4
Chlorine
Chlorine is used in some leaching stages and is produced during the subsequent electrolysis of
chloride solutions. The leach vessels are sealed and there is the provision of chlorine gas
scrubbing to remove uncaptured chlorine.
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The anodes in the electrolysis cells are contained in a membrane and enclosed by a collection
hood. The chlorine evolved is collected and reused in the leaching stage. The systems are sealed
and diffuse emissions occur only during membrane or pipework failure. Chlorine alarms are
used extensively in leach and cell rooms to detect such failures and there are normally no
emissions of chlorine [ 233, Farrell Nordic Mission 2008 ].
The presence of chlorine in waste water can lead to the formation of organic chlorine
compounds if solvents, etc. are also present in a mixed waste water.
9.2.2.5
Hydrogen, carbon monoxide and carbonyls
Carbon monoxide and hydrogen are used in the vapometallurgical refining of nickel to produce
crude nickel and then nickel carbonyl. These gases are explosive or very toxic and so sophisticated
reactor seals and control equipment is used to prevent emissions. Comprehensive monitoring and
alarm systems are used. Hydrogen is also used as a reducing agent in hydrometallurgical or
pyrometallurgical recovery or transformation processes. CO is also produced in electric reduction
furnaces if afterburning is not used. Robust process design including scaled equipment and
appropriate gas exhaust systems are used to avoid explosive gas mixtures.
Carbon monoxide is recovered and waste process gases are finally incinerated to destroy any
carbon monoxide or carbonyl that may be present. Nickel carbonyl is converted to nickel oxide
which is recovered.
9.2.2.6
Nitrogen oxides
The roasting and smelting stages are potential sources of nitrogen oxides (NOX). NOX may be
formed out of nitrogen components that are present in the concentrates or as thermal NOX. The
sulphuric acid produced can absorb a large part of the NOX and this can therefore affect
sulphuric acid quality. If high levels of NOX are present after the roasting stages, treatment of
the roasting gases may be necessary for reasons of product quality and environment. Direct
smelting uses oxygen enrichment except for slag fuming and can reduce the thermal NOX. Other
furnaces that use oxy-fuel burners also show a reduction in NOX but the reverse may be true at
lower levels of oxygen enrichment when the temperature increase and the nitrogen content is
significant. The range for all of the processes is 20 to 400 mg/Nm³.
9.2.2.7
Diffuse emissions
Besides process emissions, diffuse emissions occur. The major diffuse emission sources are:






dust from storage and handling of concentrates
leakage from roasters, smelters and converters
dust from the exhaust gases of leaching and purification vessels
exhaust gases (including HCl, Cl2 and VOCs) from the solvent extraction and
electrowinning units
dust from the exhaust gases of casting furnaces
miscellaneous emissions including building ventilation air.
Although diffuse emissions are difficult to measure and estimate, there are some methods that
have been used successfully (see Section 2.3.5). Table 9.7 gives some estimates from a primary
smelter where the smelter and converter ventilation gases are collected and treated with the
dryer gases.
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Table 9.7:
Significance of secondary fume capture and diffuse emissions
Emissions
Sulphur dioxide (1999)
Sulphur dioxide (2004)
Primary capture
(t/yr)
523
630
Secondary capture
(t/yr)
2242
1976
Diffuse
(t/yr)
147
248
Source: [ 239, ENIA 2008 ]
Table 9.7 above shows that diffuse emissions can be significant in primary smelting if
ventilation gases are not collected and treated. The 2004 data was supplied in the industry
response to draft 1 of this document. In this case they would be much higher than abated
emissions. Refining processes are reported to have lower diffuse emissions and the carbonyl
process is particularly well sealed. Action to reduce diffuse emissions may be needed in many
processes.
It is possible to reduce the diffuse emissions arising from granulation fumes by treating the
fumes with NaOH solution. Another way to reduce them, is by using covered, ventilated lids on
the launders. These launders can be heated by using fuel or preferably by using electrically
heated covers, which then allow an efficient collection of diffuse emissions thanks to the small
amount of gas released.
Diffuse emissions from molten material transportation are also significant. In DON process as
well as in flash smelting - flash converting processes there is no ladle transportation of molten
material and thus diffuse emissions are much easier to control.
The collection of diffuse emissions is described in Section 2.12.4.
9.2.3
Emissions to water
Metals and their compounds and materials in suspension are the main pollutants emitted to
water. The metals concerned are Cu, Ni, Co, As and Cr. Other significant substances are
fluorides, chlorides and sulphates.
Possible sources of waste water are:











hydrometallurgical purification processes
matte granulation
waste water from wet scrubbers
waste water from wet electrostatic precipitators
waste water from slag granulation
anode and cathode washing liquid effluent
sealing water from pumps
general operations, including the cleaning of equipment, floors, etc.
discharge from cooling water circuits
rainwater run-off from surfaces (in particular storage areas) and roofs
matte granulation.
Waste water from wet gas-cleaning (if used) of the smelter, converter and fluid bed roasting
stages are the most important sources. Other sources are cleaning and miscellaneous sources.
The leaching stages are usually operated on a closed circuit and drainage systems are isolated
but there are potential problems unless good leak prevention and detection systems are used.
Electrolyte bleed liquors are used in the leaching stage.
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9.2.3.1
Waste waters from abatement plants
If wet scrubbers are used after the leaching and roasting processes, an acidic solution is
produced. The scrubber removes fluorides, chlorine, chlorides, most mercury and selenium and
some particles that pass the mechanical gas treatment. To avoid the build-up of contaminants,
some liquid should be bled continuously from the scrubber and then treated. Dissolved SO2 is
removed prior to the discharge. Weak acid can also be treated by concentrating it and feeding it
back into the uptake shaft of a flash smelting furnace.
Wet electrostatic filters will also produce an acidic scrubber liquid. This is recycled after
filtering or after concentrating it is returned to the uptake shaft of the flash furnace. Some liquid
should be bled from this circuit to remove the build-up of contaminants. This bleed liquor is
treated and analysed before discharge.
Table 9.8 provides an indication of the composition of the gas-cleaning effluents before
treatment.
Table 9.8:
Typical gas-cleaning effluents
Pollutant
Solids
Sulphate
Chloride
Fluoride
Cobalt
Nickel
Copper
Zinc
Cadmium
Lead
9.2.3.2
Concentration
(dissolved)
13 - 25 g/l
1.3 - 1.8 g/l
0.3 - 0.5 g/l
0.1 - 9 mg/l
0.1 - 10 mg/l
5 - 15 mg/l
0.1 - 2.5g/l
1 - 5 mg/l
1 - 3 mg/l
Composition of
suspended solids
250 - 1500 mg/l
5 - 30 % of suspended solids
<0.05 % of suspended solids
Miscellaneous sources
The electrodes and membrane bags used during electrolysis need to be rinsed periodically to
remove deposited material upon the surface. Manganese dioxide can be formed on the surface
of the anodes by the reaction of oxygen with dissolved manganese. After rinsing the anodes, the
manganese is separated from the rinse water for external reuse. Cathodes are cleaned after
removal of the Co or Ni sheets. The anode and cathode washing liquid effluents are acidic and
likely to contain copper, nickel, cobalt and suspended solids.
Granulation water from the granulation of matte or slag is usually recirculated in a closed circuit
system. There have been reports of the formation of persistent organic chlorine compounds and
PCDD/F in some cooling circuits of chlorine leach processes.
Filters and waste water from the hydrometallurgical separation and transformation processes are
treated for metal and suspended solid removal. The products of this treatment may be returned
to upstream operations, depending on their composition and value. The wet ESP can be used for
that purpose. Potential sources of waste waters are reported in Table 9.9.
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Table 9.9:
Summary table of potential waste water sources and treatment options
Process unit
Operation/source
Use/treatment options
Rainwater from roads, yards, roofs
Wet cleaning of roads
Cleaning of lorries, etc.
Cooling water from the furnace,
machinery and equipment
Wet ESP effluent (if needed)
Waste water treatment plant/reuse
Waste water treatment plant
Recirculation, waste water treatment plant
Recirculation
Granulation water
Condensate from gas cooling, wet ESP
Condensate from mercury removal
Cooling water equipment
Leakage
Surface water (rain/wetting)
Scrubber (sinter fine cooling)
Wet gas-cleaning
Recirculation
Removal of suspended dusts and reuse as
feed, waste water treatment plant
After mercury removal to waste water
treatment plant
Recirculation
Recirculation
Wet cleaning of roast gases
General operations including wet gascleaning
General operations
Filter cakes
Cleaning of cells, anodes and cathodes
Maintenance
Effluent treatment
Recovery of metals
General
Smelting
operation
Matte or slag
granulation
Gas cleaning
system
Leakage
Sulphuric acid
plant
Feed storage
Sinter plant
Roast gas
cleaning
Roasting/roast
gas-cleaning
Leaching
Purification
Electrolysis
All process units
Waste water
treatment plant
Recirculation, waste water treatment plant
Recovery of metals
Countercurrent washing
Recovery of metals
Reuse for certain applications/discharge
Table 9.10 and Table 9.11 give data for emissions to water and the mass emissions of nickel per
tonne produced for some European sites [ 239, ENIA 2008 ].
Table 9.10: Examples of waste water analyses
Process
Co
Cl leach
Cl leach
Carbonyl
Smelter + leach (2)
Effluent
(m³/d)
Flow
(m³/t)
200
55
450
10900
Cu
<0.1
0.1
1.0
0.4
10 g/t
Zn
<1.5
1.0
4 g/t
Main components
(mg/l)
As
Co
<0.1 <1.5(1)
0.2
0.25
0.1
2 g/t
Ni
<1.0
0.7
1.0
1.4
10 g/t
COD
25
(1) Co emission is 0.5 kg per tonne of Co produced
(2) The data of Smelter + Leach covers process waters, cooling water, acid plant and rainwater from a
combined Cu and Ni smelter and nickel leaching.
Source: [ 239, ENIA 2008 ]
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Chapter 9
Table 9.11: Mass emissions of nickel per tonne produced for European processes
Emission of nickel
(g Ni per tonne
produced)
15.7
16
29.6
30
Waste water volume
(m³ /d)
Process
Matte grinding and leaching
Matte grinding and leaching
Nickel smelting and matte refining (1)
Carbonyl process
1640
3233
1900
6615
(1) The data of nickel smelter + matte refining covers both Cu and Ni smelter and nickel leaching
process.
Source: [ 239, ENIA 2008 ]
9.2.4
By-products, Process residues and waste
The production of metals is related to the generation of several by-products, residues and
wastes, which are also listed in the European Waste Catalogue (Council Decision 94/3/EEC).
The most important process-specific residues are listed in this section below.
Residues arise as a result of the treatment of liquid effluents. The main residues are gypsum
waste (CaSO4) and metal hydroxides that are produced at the waste water neutralisation plant.
These wastes are considered to be a cross-media effect of these treatment techniques but many
are recycled to the metallurgical process to recover the metals, depending on their value.
Dust or sludge from the treatment of gases are used as raw materials for the production of other
metals such as precious metals and Cu, etc. or can be returned to the smelter or into the leach
circuit for recovery.
9.2.4.1
Precipitates from purification processes
The production of iron-based solids accounts for a significant volume of waste depending on the
process used. The composition is shown in Table 9.12.
Table 9.12: Example compositions of different types of residues
Process
Iron hydroxide residues in the chloride
leaching process
Gypsum residues
Waste water treatment
Fe
(%)
Zn
(%)
40
<10
25
<10
Co
(%)
Cu
(%)
Ni
(%)
0.1
<0.1
1-2
2-3
<0.5
<1
<0.05
The disposal of these residues can be a considerable cost as specially constructed, lined ponds
are used to contain the material. Particular care is taken about leakage and operators of these
ponds have to monitor groundwater. There is a significant cross-media effect. One site deposits
the waste in underground rock caverns.
9.2.4.2
Pyrometallurgical slags and residues
Slags from smelting processes usually contain very low concentrations of leachable metals after
slag cleaning. They are therefore suitable for use in construction, abrasives and other purposes.
The slag output is between 4 and 10 times the weight of the metal produced depending on the
source of the concentrate.
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Table 9.13 gives examples of the composition of some nickel slags. The exact composition will
also depend on the source of the concentrate [ 139, Riekkola-Vanhanen, M. 1999 ].
Table 9.13: Composition of typical nickel slags
Component
Nickel (%)
Cobalt (%)
Copper (%)
Iron (%)
Silica (%)
Lime (%)
Reverberatory furnace
0.2
0.1
0.08
38
36
2
Electric furnace
0.17
0.06
0.01
35
Outotec flash(1)
0.1 - 0.3
0.1 - 0.25
0.05 - 0.25
35 - 43
30 - 39
0.5 - 7
(1)After cleaning in an electric furnace -
A number of standard leachability tests are used by Member States and these are specific to the
Country in question. Nickel slags are listed in the EU on the amber list of the Transfrontier
Shipment of Waste Regulations. The dross and solids, removed during the melting and refining
stages, contain metals that are suitable for recovery. Table 9.14 shows some of the treatment or
reuse options for solid residues from nickel and cobalt processes.
Table 9.14: Some of the treatment or reuse options for solid residues from Ni and Co processes
Process step
Autoclave
Iron removal
Abatement
Pressure leaching
Decopperising
Nickel and cobalt regeneration
Slag treatment
Removal of As, etc.
Effluent treatment
9.2.4.3
Solid output
Residue
Precipitate
Filter dust
Sulphide residue
Cu cement
Impure nickel carbonate
Clean slag
Gypsum ferri-arsenate
Precipitate
Use/treatment options
Smelting furnace
Smelting furnace or disposal
Smelting furnace
Cu recovery
Cu smelter
Pure nickel sulphate production
Construction
Special disposal or As recovery
Recovery of other metals or disposal
Other materials
Other residues or sludges arising from the different process stages or from general waste water
treatment, depending on their composition and value may be recycled or sent for final disposal.
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9.3
Techniques to consider in the determination of BAT
The sections of this document entitled 'Techniques to consider in the determination of BAT' set
out techniques considered generally to have potential for achieving a high level of
environmental protection in the industries within the scope of the document. The background to
the way the techniques are described is given in Section 2.12 and Table 2.10.
This section presents a number of techniques for the prevention or reduction of emissions and
residues as well as techniques reducing the overall energy consumption. They are all
commercially available. Examples are given in order to demonstrate techniques which illustrate
a high environmental performance. The techniques that are given as examples depend on
information provided by the industry, European Member States and the evaluation of the
European IPPC Bureau. The general techniques described in Chapter 2 'common processes'
apply in a large extent to the processes in this sector and influence the manner in which the main
and associated processes are controlled and operated. Techniques used by other sectors are also
applicable particularly those relating to the use of sulphur recovery systems.
The techniques to consider on a site by site basis are strongly influenced by the raw materials
that are available to a site, in particular the type and variability of the concentrate, intermediate
product (e.g. matte) or secondary raw materials. The other metals that they contain can also be
crucial to the choice of process. In a similar manner, the standard of collection and abatement
systems used worldwide in the industry reflects local, regional or long-range environmental
quality standards and direct comparison of the environmental performance of process
combinations is therefore difficult. It is possible however, to judge how a particular process can
perform with the appropriate, modern abatement equipment.
The processes described above are applied to a wide range of raw materials of varying quantity
and composition and are also representative of those used worldwide. The techniques have been
developed by the Companies in this sector to take account of this variation. The choice of
pyrometallurgical or hydrometallurgical technique is driven by the raw materials used, their
quantity, the impurities present, the product made and the cost of the recycling and purification
operation. These factors are therefore site-specific. The basic recovery processes outlined in
Section 9.1 on applied techniques therefore constitute techniques to consider for the recovery
processes when used with appropriate abatement stages. The techniques to consider for
collection and abatement stages and other aspects of process operation and control are covered
in Sections
Note, when discontinuous measurement are performed the reported annual average is an
average of samples obtained during one year
9.3.1
Nickel production
9.3.1.1
Material reception, storage and handling process
9.3.1.1.1
Techniques to prevent and reduce emissions from materials reception,
storage and handling
General techniques applied to reduce diffuse emissions from reception, storage and handling of
raw materials for primary and secondary materials are considered in Chapter 2 (see Section
2.12.4.1) and in the Emissions from Storage BREF [ 290, EC 2006 ]. Within this specific
subsection, only techniques associated with the abatement of diffuse emissions at these stages of
the process will be considered.
Description
The techniques to consider are:

Collection and safety storage of hazardous material.

Extraction gas systems followed by bag filter (see Section 2.12.5.1.4).
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Technical description
Raw materials are concentrates, chlorine, other gases, intermediate products, fluxes and fuel,
other important materials are products, sulphuric acid, slags and process residues.
A list of issues and their management related to the technical processes are given below:

Intermediate products such as matte which have a potential to form dust need to be
handled using appropriate ventilation and dust capture systems; usually in an isolated and
dedicated building.

Chlorine, oxygen and other gases will be handled according to specific safety
requirements to prevent leaks and contain the gases.

Process gases such as oxygen and chlorine are collected and stored in approved pressure
vessels. These gases are usually regenerated and recycled: directly returned to the process
or stored for later reuse.

Acid produced during the process should be stored in double walled tanks and/or tanks
placed in chemically resistant retention bunds. The acid slimes from the sulphuric acid
plant and weak acid from scrubbing systems are treated or processed locally and can be
disposed of as secondary raw materials for other applications.
Achieved environmental benefits

Reduction of dust emissions.

Reuse of dust in the process, where possible.

Prevention of the material leakage.
Environmental performance and operational data
Operational and performance data is summarised in Table 9.15.
Table 9.15:
Plant
Plant E
Dust emissions from loading and on-site transport in a nickel plant
Origin of
Dust (mg/Nm³)
Techniques the
minimum
average
maximum
emission
Bag filter
Loading and
on-site
transport of
Ni matte
0.1
2.1
15.6
Note
Continuous
measurement
(daily averages)
Source: [ 378, Industrial NGOs 2012 ]
Cross-media effects
Increase in energy use.
Technical considerations relevant to applicability
Generally applicable
Economics
Not reported.
Driving force for implementation

Recovery of raw materials.

Environmental and health regulation requirements.
Example plants

Plant D, UK.

Plant E, NO.
Reference literature
[ 291, Competitive Report 2001 ].
988
July 2014
Chapter 9
9.3.1.2
Material pretreatment processes
9.3.1.2.1
Techniques to prevent and reduce emissions from ore preparation and
beneficiation
Description

Bag filter (see Section 2.12.5.1.4) and water spraying

Sedimentation and flotation (thickener)

Drainage system.
Preparation and beneficiation can use processes performed on dry or wet ore. Reducing
emissions focuses on dust suppression, spillage handling and water recovery with the purpose of
reducing the amount of residues and the recycling of water back to the processing plant.
Dust suppression can be managed by the use of dust extractors using fabric filters or abatement
using water spraying systems.
Water recovery is carried-out by using thickeners. Specific tests are required to evaluate which
design is best suited to the material characteristics. The principle is to use gravity to let the
particles settle freely. Flocculants and/or coagulants can be used to improve water recovery.
Dry residues, or those with limited water content, can be easily managed at the on-site residue
storage area.
To control the effects of potential spills, the plant should be built with a drainage system so that
surface water run-off is collected in a sump.

Prevention and reduction of dust and heavy metals emission.

Preservation of raw materials, as filter dust is reused in the process.

Reduction of water use.
The use of a thickener is usually associated with the use of flocculants and/or coagulants.
Flocculants are usually organic polymers while coagulants are either organic or mineral. Dosage
is usually between 5 and 50 g/t of dry residue but in some cases can reach several 100 g/t. If this
step does not provide enough water recovery, the process can be enhanced by the use of
centrifugal machines or filters. Centrifugation will increase the effect of gravity and improve the
settling rate.
Two types of filters can be used to separate solid by liquid: vacuum type filters and pressure
type filters, the latter being more efficient at treating material with a higher fines / clay content
that retains water and which can block vacuum filters products. The use of these technologies
should provide water with low suspended solids that can be recycled into the plant processes.
Cross-media effects

Use of chemicals.
Economics
Not reported.
July 2014
989
Chapter 9


Environmental regulation requirements.
Technical-economic streamlining of processes.
Example plants

Plant F, France.
Not reported.
9.3.1.2.2
Techniques to prevent and reduce emissions from nickel ore and
concentrates drying
Description

Hot ESP (see Section 2.12.5.1.1).

Bag filter (see Section 2.12.5.1.4).
In the rotary dryers, the hot gas produced by the combustion of fuel in the separate chamber or
recycled gas is placed in contact with the wet concentrate or feed mixture and the contained
water is evaporated to the gas. The flame of the burner has no direct contact with feed mixture.
The combustion gas is cooled to thea temperature of 500 °C before going into the drying drum.
Cooling has to be carried out in order to prevent ignition of sulphides. If sulphides ignite and
oxidise, the heat value of concentrates decreases and sulphur dioxide is formed. Thus ignition
has to be prevented by cooling the drying gas in order to minimise the formation of sulphur
dioxide.
Sulphur oxidation prevention may also be carried out using an nitrogen protection and using low
temperature and recycling gases for instance from anode furnace. The flue-dusts from the offgas after rotary dryer are removed using an electrostatic precipitator and a bag filter. Collected
dusts are returned to the process stream as raw material.
In the steam dryers, the operational steam temperature is 130 – 214 °C. The throughput of the
steam dryer is dependent of the pressure/temperature of the steam; by increasing the pressure to
18 – 20 bar the capacity can be raised. A small amount of carrier air or nitrogen (for preventing
of oxidation) is introduced into the dryer to pick up the water of the concentrate. The air/off-gas
amount coming out of a steam dryer is much smaller than that of the rotary dryer and it is
treated for dust removal in a bag filter.
The ESP is the most common dust abatement device for cleaning hot smelter waste gas and the
bag filter for cooled gas.

Reduction of dust and heavy metals emissions.

Recovery of raw materials as collected dust is reused back in the process.

When indirect steam coil dryer is used temperature is so low that no ignition takes place
and thus SO2 formation is prevented.
In order to decrease the fossil fuel energy use the direct rotary drum dryer may use recycled gas
from other parts of the process, but it also needs some fuel to be combusted in order to generate
the heat needed for drying.
Steam coil dryers use the steam recovered in the waste heat boiler from primary smelting and
converting off-gases. The steam consumption is about 150 – 180 kg per tonne of concentrate
depending on the moisture of concentrates and possible secondary feed materials.
990
July 2014
Chapter 9
Dryer off-gases of plant A are dedusted by electrostatic precipitator and bag filter for reducing
particulates release into atmosphere. Operational and performance data is summarised in Table
9.16.
Table 9.16:
Emissions from a rotary dryer in a nickel production plant
Plant
Capacity
Heating
Emissions
Dryer
Off-gas
type
treatment
(min – aver. – max)
Plant A
Rotary
dryer
60 t/h
Heavy oil
Hot-ESP and
~10 kg/t feed
Bag filter.
Continuous
measurements
Gas flows: 53070 66350 - 75510 Nm³/h
as daily average
Dust: 0.02 – 0.21 –
3.59 mg/Nm³ as daily
average
SO2: 8 – 188 – 481
mg/Nm³ as daily
average
Cross-media effects
Bag filter and ESP

Hot ESP and bag filter are generally applicable to new and existing plants with consideration to
the dryer off-gases. The types of dryers used depend on site-specific conditions such as the
reliability of steam supply. Usually smelters are reliable steam supplier, because smelting
processes are continuous processes.
Economics
Not reported

Environmental regulations requirements.

Recovery of raw materials.
Example plants

Plant A, Finland.
[ 310, Makinen T., Taskinen P. 2006 ]
9.3.1.3
Pyrometallurgical transformation processes
9.3.1.3.1
Emission reduction from charging of furnaces in primary nickel
production
Description

Enclosed conveying systems such as pneumatic dense phase conveyor and air slide

Loss-in-weight feeder

Concentrate burner.
July 2014
991
Chapter 9
In the non-ferrous smelter processes it is critical to rely on the feeding system to provide feed as
stable as possible.
In the pneumatic dense phase conveyor, the material is conveyed without fluidisation as
batches. This conveying system has low transport air requirement.
Loss-in weight feeders provide a stable mass flow to the air slide which transports the material
into the concentrate burner. Loss-in-weight feeder is a gravimetric feed system which consists
of a feed bin and a dosing bin provided with an underneath screw conveyor. The feed mixture
drops from the loss-in-weight feeder via a feed chute onto air slide. The air slide transports the
feed mixture in a sealed space to the concentrate burner of flash smelting furnace and evens out
small fluctuations in the feed quantity. The operation of the air slide is noise-free and dust-free.
The slope angle of the air slide can be adjusted and the air slide is provided with an automatic
dome valve. The fluidising air flows together with the feed mixture into the flash smelting
furnace. Air-slide system may works also in two stages, where the first air slides gather feed
mixture feed from loss-in weight unit’s and discharge it to a feed chute where dusts are
introduced. The feed chute is for proper mixing of feed before it is conveyed with the final air
slide to the burner.
Concentrate burners are specifically designed for high oxygen enrichment and even distribution
of concentrate into the reaction flame. The main function of the concentrate burner is to mix
properly the solid feed and process gas. The good combustion of the feed mixture in suspension
is ensured by accurate and simultaneous feed mixture and process gas speed controls, enabled
by the state of the art concentrate burner.

Reduction of diffuse emissions.
In case of Plant A, carrier gas from pneumatic conveyor is directed to concentrate dryer off-gas
treatment (hot ESP and bag filter), see emission data in Section 9.3.2.2.
Cross-media effects
Not reported
Generally applicable.
Economics
The energy usage and the costs for the ventilation are very low.

Prevents dusting into the working atmosphere.
Example plants

Plant A, Finland.
[ 310, Makinen T., Taskinen P. 2006 ]
9.3.1.3.2
Techniques to prevent and reduce emissions from DON process
Description
992
July 2014
Chapter 9




Waste heat boiler and hot ESP (see Section 2.12.5.1.1) followed by wet ESP (see Section
2.12.5.1.2), mercury and arsenic removal system (see Section 2.12.5.5) and sulphuric acid
plant (see Sections 2.12.5.4.1, 2.12.5.4.2)
Wet scrubber (see Section 2.12.5.1.6) or bag filter (see Section 2.12.5.1.4) with lime
injection.
Hot cyclone and venturi scrubber with sodium hydroxide solution.
Covered and hooded launders.
The continuous off-gas flows leaves the furnace through the uptake shaft, is cooled in the forced
circulation heat recovery boiler consisting of a radiation section followed by a convection
section. The boiler is a forced circulation boiler producing saturated steam. Part of the flue-dusts
settles in the boiler. The rest part of flue-dusts is removed in an electrostatic precipitator. Dusts
removed in athe boiler and in the electrostatic precipitator are recycled back into the flash
smelting furnace with the primary feed.
The off-gas has a high, non-fluctuating sulphur dioxide concentration and SO2 is recovered from
the gas mainly by conversion to sulphuric acid at the sulphuric acid plant after dust removal and
gas cleaning. It is possible to recycle weak acid collected in the gas washing section back in to
the furnace by injecting it into the uptake shaft in order to decompose it back to SO 2, oxygen
and water so that the SO2 generated can be recovered in acid plant.
The slag and matte launders, tapping openings and granulating pools are hooded for collection
of diffuse gases. Ventilation gases are cleaned using wet scrubber or with dry lime injection
before bag filters.
Granulation gas is cleaned using sodium hydroxide solution and high pressure multi-venturescrubber. Efficiency of SO2 removing is then mainly depending on pH and solution-gas ratio
and efficiency of dust removing is mainly depending on solution pressure in the scrubbing
nozzle. If gas contains CO2, pH has to be lower than seven, but if gas is CO2 free, pH may be
higher. Bleed out solution from scrubbing is used for neutralisation of granulation water and
bleed out of granulation goes to effluent plant.
Distributed control systems (DCS) are used to control material feed rate, critical process and
combustion conditions and the additions of gases. Several parameters such as temperature,
furnace pressure (or underpressure) and gas volume or flow are measured to allow processes to
be controlled and alarms are provided for critical parameters.
Slag and matte are analysed on the basis of samples taken at intervals so that the control of the
process conditions is possible to keep as smooth.
The DON smelting process is continuous and no ladle transportation is needed, and matte as
well as slag is transferred via covered and hooded launders

Reduction of diffuse emissions.

Reduction of emissions of dust, heavy metals and sulphur dioxide.

The heat recovered by heat recovery boiler is used as steam and electricity. The steam
produced from waste heat boiler is used for drying, other production needs or used for
generation of electrical energy or district heating.

The SO2 is recovered in the form of sulphuric acid product at the acid plants using double
contact process.

Flue-dusts collected in the dust removal systems (boiler and electrostatic precipitator) are
recycled back to the smelting furnace.
July 2014
993
Chapter 9

Oxygen enrichment and utilisation of the feed material’s inherent chemical energy for
smelting allows reduction in the quantity of fuel used and an associated reduction in
greenhouse gas emissions.
Process off-gases from smelting furnace of plant A are cooled in heat recovery boiler; heat is
recovered as high pressure steam that is distributed for other processes use. Cooled off-gas is
then directed to a hot-ESP for particulate capture before entering the acid plant and SO2
fixation.
Ventilation hoods are used at slag tap-holes; ventilation air is directed centralised bag filter
treatment before releasing into atmosphere. Continuous dry lime injection is used to lower SO 2
emission, and to enhance dedusting. Slag launder is covered with lids to reduce environmental
impact (fumes). Slag is further processed in EAF for metals recovery.
Ventilation gases of matte tap-holes are directed to venturi scrubber for SO2 abatement with
sodium hydroxide. A hot cyclone captures coarse particulates before the scrubber; the fines are
captured in scrubbing solution.
Operational and performance data is summarised in Table 9.17.
Plant A
DON FSF,
Single jet
burner
Oxygen
enrichment
1 320 t/d
WHB
and ESP
Steam 40
t/h
Double
contact
acid plant
Ventilation
gases from
slag
tapholes
Bag filter
with dry
lime
injection
80 – 90%
Emissions
Secondary gas
treatment
Secondary gas
collection sources
Primary gas
treatment
Primary gas
handling
Capacity
Emissions from the DON process
Furnace type
Company
Table 9.17:
Dust: (min – ave
- max):
0.005 – 0.098 –
0.550 0.01 –
0.14 – 5 mg/Nm³
(continuous)
SO2 (min – ave max):
40 – 337 – 721
mg/Nm³
(continuous)
Ventilation
gases from
matte
tapholes
Hot
cyclone
Venturi
scrubber
with
NaOH
SO2:
(min. – avg–
max)
50 – 100 - 300
mg/Nm³
(periodic
measurement)
Source: [ 378, Industrial NGOs 2012 ], [ 409, Finland 2013 ]
Cross-media effects

Increase in energy consumption.

Use of chemicals.

Wet gas cleaning systems generate waste and effluent water that requires treatment before
discharge.
994
July 2014
Chapter 9
Economics
Not reported

Reduction of emissions of dust, heavy metals and SO2.

Recovery of sulphur
Example plants

Plant A, Finland
[ 310, Makinen T., Taskinen P. 2006 ], [ 410, Mäkinen et al. 2005 ], [ 411, Taskinen et al. 2001
]
9.3.1.3.3
Techniques to prevent and reduce emissions from EAF
Description

Afterburner (see Section 2.12.5.2.1).

Wet scrubber (see Section 2.12.5.1.6) or bag filter (see Section 2.12.5.1.4) with lime
injection.

Hot cyclone and venturi scrubber with sodium hydroxide solution

Covered and hooded launders.
The slag is tapped periodically from smelting furnace along cooled and covered slag launder
through the already charged coke layer into the electric furnace.
Slag from the electric furnace is tapped into granulation and transported to the slag storage and
used for civil engineering purposes.
Electric furnace off- gas, which contains carbon monoxide, is first incinerated in a water cooled
combustion chamber with excess air and then cooled. Before entering into the stack, gas is
cleaned with Ca(OH)2 injection and bag filter or by scrubbing.

Inert by product slag is produced

CO and SO2 emissions to the atmosphere are prevented by gas cleaning.
Process off-gases from slag cleaning furnace in plant A are incinerated and cooled with dilution
air before directing to centralised bag filter treatment. Ventilation hoods are used at slag tapholes; ventilation air is directed to same centralised bag filter treatment before releasing into
atmosphere. Continuous dry lime injection is used to lower SO2 emission, and to enhance
dedusting.
Discard slag launder is covered with lids to reduce environmental impact (fumes). Discard slag
is granulated with water.
Ventilation gases of matte tap-holes are directed to venturi scrubber for SO2 abatement with
sodium hydroxide. A hot cyclone captures coarse particulates before the scrubber; the fines are
captured in scrubbing solution.
July 2014
995
Chapter 9
Operational and performance data is summarised in Table 9.18 and Table 9.19 [ 378, Industrial
NGOs 2012 ].
Table 9.18:
Company
Plant A
Emissions from an EAF
Feed
Furnace
type
EAF, 3
electrodes
(Söderberg)
Flash
furnace
slag
Off-gas treatment
Emissions
Post combusting
before
Dust (min – ave - max):
centralised bag
filter.
mg/Nm³ (continuous)
0.005 – 0.098 – 0.550 0.01 – 0.14 – 5
SO2 (min – ave - max):
40 – 337 – 721 mg/Nm³
(continuous)
Table 9.19:
Company
Plant A
Emissions from slag taphole and matte taphole granulation gas
Furnace
Emissions
Ventilation Off-gas
source
treatment
EAF
Slag taphole
Centralised bag
filter with dry
lime injection
Dust (min – ave - max):
0.005 – 0.098 – 0.550 0.01 – 0.14 –
5 mg/Nm³ (continuous)
SO2 (min – ave - max):
40 – 337 – 721 mg/Nm³
(continuous)
Matte
taphole
granulation
gas
Hot cyclone
SO2 20 – 80 - 250 mg/Nm³
Venturi scrubber
with NaOH
(periodic measurement)
Cross-media effects


Use of chemicals.

Wet gas cleaning systems generate waste and effluent water that requires treatment before
discharge.
Economics
Not reported.

Example plants

Plant A Finland.

Plant in Fortaleza in Brazil.
[ 310, Makinen T., Taskinen P. 2006 ], [ 410, Mäkinen et al. 2005 ], [ 411, Taskinen et al. 2001
]
996
July 2014
Chapter 9
9.3.1.3.4
Techniques to prevent and reduce emissions from Plant F converting
process
Description

Operation under negative pressure and capture hoods (see Section 2.12.4.3).

Bag filter (see Section 2.12.5.1.4)
The Plant F Nickel Converting Process in France consists of oxidising and sulphurising raw
ferronickel from the smelting furnace to produce Nickel Matte. For this operation, two (2)
Peirce-Smith Converters are used in a two-step operation with slag recycling. The nickel
containing matte is further processed in another French plant for the production of high purity
nickel salts and nickel metal using chloride leaching and electro-winning. Iron is removed as
ferric chloride by solvent extraction and some cobalt chloride is also extracted.
During blowing, the process gas exhausts from the converter and is captured. The extraction fan
control is adjusted to keep a pressure at the mouth of the converter below atmospheric pressure
to avoid gas from escaping outside of the fume extraction system. The fume extraction system is
connected to bag filters further downstream. During settling or tapping periods, the gas exhaust
equipment is also adjusted to avoid emission into the converter bay.
The exhaust gas is then cooled down by a heat exchanger under natural or forced convection
and the collected dust filtered by a bag filter.
SO2 emissions are not an issue as their concentrations in the process fumes are insignificant due
to the thermodynamic equilibrium of the process.

Metal-rich dust can be collected from the air emissions and recycled in the ore smelting
process.

Particulate air emissions are significantly reduced.
Dust emissions level lower than 15 mg/Nm³ was reported.
Liquid effluents are of little importance because the gas treatment process is dry process and the
formulation of liquid waste only results from the cooling of certain parts of the equipment
(condensation).
The largest quantity of waste is solid slag which amounts to some 75 000 tonnes for an annual
Ni matte production of 15 000 tonnes. Slag is tapped from the 60 tonnes converter and then
transported to a dedicated area where it is allowed to cool down to ambient temperature. Finally,
this slag (categorised waste) is transferred to a dedicated storage area.
Dust from the management of air emissions which is collected downstream is also produced.
This dust which is mostly composed of metallic and non-metallic oxides (FeO, NiO, MgO and
SiO2) is collected in bag filters. The dust requires a specific treatment to be consolidated for
further reintroduction into the process (at an earlier step into the ore smelter). Among the
different binder options, concrete may be used as it is easy to handle and operate.
Other solid waste materials which are produced in the converting process are ladle skulls and
scrap. These materials are recycled in the 60 tonne converter.
Cross-media effects

July 2014
997
Chapter 9
Economics
Not reported.

Example plants

Plant F, France.
Not reported.
9.3.1.4
Hydrometallurgical Nickel refining processes
9.3.1.4.1
Techniques to reduce emission from atmospheric and pressure leaching
Description

Sealed or closed process equipment (reactors, settlers and pressure autoclaves / vessels).

Oxygen or chlorine instead of air in leaching stages for minimising process gas flow and
maximising the raw material recovery.

Bag filters (see Section 2.12.5.1.4) or wet scrubbers (see Section 2.12.5.1.6).

Online monitoring and control for critical leaching and abatement equipment parameters.
The leaching process equipment (reactors, settlers, pressure autoclaves/vessels, flush tanks) are
sealed and process gases are collected and treated in abatement equipment like bag filter or wet
scrubbers (see Section 2.9) before the release to atmosphere. The residues from abatement
equipment are releached and effluents are fed to leaching stages to replace or decrease the water
usage.
The online monitoring and controlling of the critical parameters of the leaching process and
abatement equipment is necessary to maximise nickel recovery and at the same time to
minimise emissions.

Reduction of dust and metals emissions.

Higher recovery of nickel by recycling the abatement residues.
Main operational and performance data for atmospheric and pressure leaching plants is
summarised in Table 9.20 and Table 9.21 [ 378, Industrial NGOs 2012 ].
Table 9.20:
998
Emissions from sulphate-based atmospheric and pressure leaching
July 2014
Chapter 9
Process
Plant
type
Atmospheri
c and
pressure
leaching /
sulphate /
oxygen
Plant C
Capacity
66 000 t
Ni/y
Abatement
technique
Nickel (mg/Nm³)
Min.
Average
Max.
0.01
0.2
1.3
Wet gas
Scrubbers
< 1000 kg/yr
Method
to obtain
data
Type of
average
Periodic
(twelve
times per
year)
Average
over the
sampling
period
Table 9.21:
Plant
Plant
E
Emissions from atmospheric and pressure leaching using chlorine gas
Chlorine (kg/h)
Method
Process
Abatement
Type of
Capacity
to obtain
technique
average
type
Min. Average Max. data
Atmospheric
and pressure
leaching –
using chlorine
gas
92 000 t
Ni/y
Wet gas
scrubbers
0.1
0.23
0.87
Periodic
(fifty two
times per
year)
Average
over the
sampling
period
Cross-media effects

Increase in energy use (minor increase in energy consumption when using wet gas
scrubbers).
Bag filters and wet scrubbers are generally applicable.
Economics
Plant C commissioned the new wet gas scrubbers in 2009 roughly at cost of EUR 500 000 each.

Reduction of emissions.

Saving raw materials.
Example plants

Plant C, Finland.

Plant E, Norway.
9.3.1.4.2
Techniques to reduce emissions from solvent extraction refining
(sulphate route)
Description
Techniques to reduce emissions from solvent extraction when refining the solutions coming
from the leaching stage are one or a combination of the techniques mentioned below:
For low shear mixers:

Use of a low shear mixer for the solvent/aqueous mixture to optimise the droplet size and
minimise contact with air reduces the amount of solvent that is evaporated and promote
the dissolution of the metal complex.

Use of covers for the mixer and separator and settlement stages to reduce emissions of
VOCs to air and carry-over in aqueous phase.
July 2014
999
Chapter 9


Use of abatement equipment to treat the ventilation air (condensers, coolers, carbon- and
bio filters).
Use of low shear and variable speed pumping reduces energy consumption of the system
For high shear mixers:
 Conventional mixer-settlers with high-shear pump-mix turbine impellers
 Completely sealed tanks prevent emission, and connected to a central ventilation fan.
 Simple abatement with cooling towers followed by settling duct to recover condensed
VOCs before the fan.
Sealed or covered systems are used to prevent the emission of solvent fumes from the SX shells.
Use of a low shear mixer for the solvent/aqueous mixture to optimise the droplet size and
minimise contact with air, reduces the amount of solvent that is evaporated and promote the
dissolution of the metal complex.
Sophisticated treatment of the ventilation air is also possible, but due to the high air volumes,
low VOC contents and high costs, it is not usually done. A cooling tower is installed in the
ventilation pipe from the loading and stripping area. The water containing VOCs can then be
used as feed water into the SX process. The emission of VOCs from the extraction is
approximately proportional with the amount of ventilation air. To keep the airflow in the
ventilation system as low as possible, without conflicting with working environment for
operators, is therefore important to keep emission as low as possible.

Minimisation of VOCs emission to air.

Low shear and variable speed pumping reduce energy consumption of the system.
Main operational and performance data for solvent extraction plants in nickel production is
summarised in Table 9.22.
Table 9.22:
1000
Emissions of VOCs from solvent extraction refining (sulphate route)
July 2014
VOCs (mg/Nm³) (1)
Plant C
Plant
Process
type
Co-and
CaSX/
sulphate /
Abatement
technique
To treat up
to 140 m³
/h Ni
sulphate
solution
Sealed/cover
ed shells,
low shear,
variable
speed pumps
6000 t
Co/y
Sealed/cover
ed reaction
tanks and
settling
tanks.
Simple
cooling
tower in the
ventilation
system
Plant E
CoSX/chlori
ne
Capacity
Min.
Average
Max
.
3
42
134
< 100 t/yr
2000
900
0
3.5
kg/h
7.0
kg/h
4.9 kg/h
Method to
obtain data
Chapter 9
Type of
average
Periodic
(two
times
per year)
Average
over the
sampling
period
Periodic
(twenty
two
times
per year)
Average
over the
sampling
period
< 70 t/yr
(1) Differences in concentration can be explained because there are differences in flow, both in Ni/Co
solution passing through the extraction and the flow out of the stack
Cross-media effects
Not mentionable.
Shell covers are applicable to new and existing extraction shells.
Economics
No reported data.

Reduction of VOC emissions.
Example plants

Plant C, Finland – Low shear mixing.

Plant E, Norway – High shear mixing
9.3.1.4.3
Techniques to reduce emissions from nickel matte refining process using
ferric chloride leaching with chlorine (chlorine route)
Description
The technique to consider is:

The nickel matte refining process is described in Section 9.1.1.3.8.

By-products (or wastes) are sold-on as chemical intermediates for reuse.

The production of non-usable waste residues from processes is minimised.
July 2014
1001
Chapter 9
The principal environmental performance of the Plant B refining process is outlined as follows:
(Source: Plant B – Data averages from 2007 to 2011)
The energy consumption of the Plant B refining process is in the range of 20 GJ per tonne of
nickel.
Table 9.23:
Process
type
Plant B - Dust emissions from the nickel matte refining process (chlorine route)
Nickel (mg/Nm³)
Abatement
Method to
Type of
technique
average
Min. Average Max. obtain data
Production of
nickel
chloride salts
Bag filter
0.04
0.53
1.4
Periodic
measurements
Average over
the sampling
period
The Plant B refining process does not produce any significant solid residue volumes. The
plant’s solid waste production is 22 kg/t Ni.
Cross-media effects
Not reported.
Not reported.
Economics
Not reported.
Not reported.
Example plants

Plant B, France.
Not reported.
9.3.1.4.4
Techniques to reduce emissions from electrowinning
Description




Online monitoring of critical process parameters like temperature, flow and use of
electricity.
Collection and reuse of chlorine gas and use of a dimensional stable anode (DSA).
Covering of cells using styropor beads to prevent release of aerosols to air.
Foaming agents in order to cover the cells with stable foam layer.
The electrowinning process produces gases at the anode and may produce metal containing acid
mist due to bubbles in the electrolyte that burst at the surface of the solution.
1002
July 2014
Chapter 9
During chloride based electrowinning, the chloride ions will be drawn to the anodes and become
discharged as chlorine gas. The anode, a so called Dimensional Stable Anode (DSA), are
contained in a diaphragm and enclosed by a collection hood. The chlorine gas collected directly
from the anode is blown into a central system and returned to the leaching stage. During the
electrowinning styropor polystyrene beads are used as covering on top of the cells, to prevent
mist from bubbles in the electrolyte solution that burst at the surface, to enter the room
atmosphere and finally air. It is important that the entire cell is continuously covered with
styropor polystyrene beads. The electrolyte is separated into two phases after having passed
through the electrowinning tank. Chlorine containing anolyte from the anodes are transported to
a tank for removal of chlorine, and then mixed with the chlorine-free anolyte from the over fall
in the electrowinning tank. The chlorine gas is finally reused in the process.
During sulphate based electrowinning, the following reaction takes place in sulphate based
electrowinning process: NiSO4 + H2O → Ni + H2SO4 + ½ O2. Nickel sulphate solution is fed in
to the diaphragm bags where cathodes are located. Nickel is precipitated on the cathodes.
Sulphate ions react with water and generate sulphuric acid; which is recycled to the leaching
stage. Oxygen gas from the anode is released to working air and via ventilation to the
atmosphere. Anode gases contain nickel and acid mists. Emission of these substances are
minimised by keeping a stable foam layer on the surface of the solution in the cells.

Reduction of chlorine gas, acid and metals emissions to air.

Reduction of energy use (online monitoring and optimisation of parameters).
Emissions from the electrowinning process
Nickel (mg/Nm³)
Abatement
technique
20 000 t
Ni/y
C
Stable of
foam layer
on the
surface of
the solution
in the cells
Covering of
eletrowinnin
g cells with
styropor
polystyrene
beads to
prevent
acid/metal
mist to air
Plant
Capacity
E
Process
type
Sulphate based
electrowinning
Hydrometallurg
ical purification
process and
chlorine based
electrowinning.
92 000 t
Ni
metal/y
Min.
0.3
Averag
e
Max.
0.5
0.8
1500
kg/yr
2500
kg/yr
0.3
0.5
880
kg/yr
1500
kg/yr
Periodic
(twenty
four
times
per
year)
Periodic
(three
times
per
year)
Type of
average
Table 9.24:
Method to
obtain data
In plant E, collection and reuse of chlorine gas takes place, with no direct emission of chlorine
to air from electrowinning (indirect emissions to air from reuse of chlorine in other leaching or
purification steps will occur, and will be accounted for in the relevant process step). The energy
consumption in the refining process is about 20 GJ/Mt Ni
Averag
e over
the
sampli
ng
period
Cross-media effects

Very minor increase in energy use for collection of chlorine gas.
July 2014
1003
Chapter 9
Very limited number of chlorine based electrowinning sites for Nickel production in Europe (all
known sites are represented in the BREF). This will limit the relevance of chlorine collection
and reuse for other industries or production sites. No other known restrictions.
Economics
DSA anodes imply an additional maintenance and purchase cost.
Internal reuse of chlorine gas and sulphuric acid reduces the need for purchasing them for the
process.

Reduction of chlorine gas, acid and metals emissions to air.
Example plants

Plant C, Finland.

Plant E, Norway.
[ 412, Norwegian Environment Agency 2012 ].
9.3.1.4.5
Techniques to reduce air emissions from Carbonyl process
Description

Collection of off-gases (see Section 2.12.4.3).

Afterburner (see Section 2.12.5.2.1).

The off-gases from the Carbonyl process (containing a carbon monoxide/nickel carbonyl
mixture and hydrogen) and those from system purges and plant blow-down are collected and
piped to a central vent gas manifold. The vent gas manifold then feeds the waste gases in a
controlled manner to the combustion chamber for thermal oxidation.
The combustion chamber comprises an air cooled steel shell, lined with a heat resistant
refractory material. The combustion chamber is heated by two high intensity burners one fuelled
by natural gas (fuel burner) and the other by waste gas (residual hydrogen from the kiln
reduction stage). The gas burners are identical in design and are mounted tangentially to the
furnace, this design promotes a swirling action in the combustion chamber aiding full
combustion. Each of the burners has concentric annuli, one to water-cool the burner and one to
admit induced air for quenching the hot gases if required. In the combustion process, carbon
monoxide and nickel carbonyl are mixed with air in the burner and combusted.
Nickel oxide formed is solid and is in the form of fine dust particulates in the combustion gas
stream. The non-toxic waste (purge) hydrogen is fed into to the manifold as a support fuel to the
waste gas burner. The pressure of the waste hydrogen is monitored and controlled by a water
lute at ground level. In the event of a flame failure, the lute pot is vented to atmosphere via a
discharge point. Hydrogen gas reacts as outlined in the following.
Three basic controls are applied to ensure that the toxic and flammable gases are destroyed
without overheating the combustion chamber:


1004
The primary control is to ensure that a minimum temperature is maintained to oxidise any
toxic gases present; this is done by adjusting the gas flowrate to the fuel burner.
The second control is designed to ensure that the maximum operating temperature of the
combustion chamber does not become too hot for the materials used to construct the
July 2014
Chapter 9
furnace. To control this temperature, the primary air to the return carbon monoxide burner
is increased, and, if that is insufficient, secondary air is admitted to the burner.
The third control ensures that the maximum permitted temperature of the gases leaving
the combustion chamber is not exceeded; as the temperature approaches the maximum
level, a pair of dampers starts to open to admit quench air into the furnace and so dilute
the hot gas with cold air.

The outlet duct of the combustion chamber is fitted with a heat-resistant steel blind. The angle
of the blinds can be changed to control the rate of flow of combustion gases out of the chamber
and if necessary to close the outlet ducting. The outlet duct enters an exhaust. The combustion
gases and particulates flow through the outlet blinds into the exhaust manifold which feeds into
the gas filter system.
The combustion gas stream is passed through a reverse jet filter system, which consists of filter
vessels each with an inlet and outlet damper. Each filter contains filter bags capable of retaining
particles of dust down to sub-micron size, whilst still allowing passage for the main gaseous
stream. The dust filters have a burst bag detection system and are self-cleaning using a reverse
jet pulsing system.
The collected particles descend into bunkers situated below the filters, which are discharged via
rotary valves into slurry pots. Here the dust mixes with a continuous flow of water. The
resultant slurry discharges to the refinery effluent treatment plant.

Reduction of nickel and carbon dioxide air emissions.

Recovery of nickel from the waste gas stream improving natural resource management.

Reuse of hydrogen waste gas from the Carbonyl process as support fuel for the
combustion.

Obtaining a stabilised kiln residue that can be further processed by high-pressure nickel
extraction.

Following high pressure nickel extraction, cobalt/copper extraction can be performed.
Copper/cobalt extraction then leaves a high concentrate of PGMs (Platinum Group
Metals). PGM extraction can then be undertaken resulting in the complete extraction of
metals from the ore
Emission data from the carbonyl process operated at plant D are summarised in Table 9.25.
D
Carbon
yl
proces
s
Afterburne
r followed
by bag
filter
Dust
0.03
0.98
7.4
Ni
0.003
0.06
0.3
CO
265
297
329
SO2
13.6
18.5
23.4
NOx
4.9
6.3
7.7
Type of
average
Method to
obtain data
Max.
(mg/Nm³)
Average
(mg/Nm³)
Min.
(mg/Nm³)
Pollutant
Abatement
technique
Emissions from the Carbonyl process
type
Process
Plant
Table 9.25:
Continuous
measureme
nt
Daily
average
Periodic
(two times
per year)
Averag
e over
the
samplin
g period
July 2014
1005
Chapter 9
Cross-media effects

Increase in energy use (natural gas consumption).
Economics
Not available.

Complete oxidation of toxic nickel carbonyl gas to particulate nickel oxide.

High efficiency recovery of metals from the primary carbonyl process coupled with
further recovery of metals from material recovered by the off-gas and waste water
treatment processes.

Environmental regulations' requirements.
Example plants

Plant D, UK.
9.3.1.4.6
Techniques to reduce emissions from hydrogen reduction processes
when producing nickel powder and nickel briquettes (pressure processes)
Description

Sealed or closed process equipment (reactors, settlers and pressure autoclaves / vessels,
powder conveyors, product silos).

Bag filters (see Section 2.12.5.1.4) or wet scrubbers (see Section 2.12.5.1.6).

Online monitoring and control for critical reduction processes and abatement equipment
parameters.
In general the hydrogen reduction process is as follows (more detailed process descriptions are
presented in Section 9.1.3): Purified nickel solution from the solvent extraction is used as a “raw
material” of the hydrogen reduction process. If needed ammonia and ammonium sulphate is
added to the nickel sulphate solution. The mixed feed solution is reduced with hydrogen in the
autoclaves to produce metallic nickel powder. The powder is sold or can be sintered into
briquettes. The sulphuric acid generated in the reduction process is neutralised by ammonia. The
formed ammonium sulphate solution has a small amount of nickel and cobalt, which are
precipitated with hydrogen sulphide for further treatment. The ammonium sulphate is recovered
by crystallisation and drying.
The reduction process is a batch process and takes place in various autoclaves at high
temperature (about 200 °C) and high pressure (about 30 bar). The hot, water containing
autoclave gases are treated in the gas scrubbers by using sulphuric acid as a washing reagent.
The process conditions make the recovery of ammonia challenging. The continuous monitoring
and control of critical process and scrubber parameters is an essential issue in order to reduce
ammonia emission to air.
The producing of nickel briquettes from powder includes several stages where the dust
formation and release to working air is possible. All the conveyors, silos and process equipment
need to be closed and the gases to be treated at abatement equipment.

Minimisation of the emission of nickel and ammonia to air.
1006
July 2014
Chapter 9
Main operational and performance data for hydrogen reduction processes atmospheric and
pressure leaching plants are summarised in Table 9.26.
C
Average
Max
0.6
3.7
< 1000 kg/yr
0.1
(mg/N
m³)
0.8
3.0
Type of average
NH3
0.05
Method to obtain
data
and wet
scrubbe
rs (for
ammoni
a)
Ni
(mg/N
m³)
Min
Bag
filters
(for
nickel
dust)
Pollutant
Capacity
40 000 t / year
Hydrogen
reduction,
Ni powder
and
briquette
production
Abatement
technique
Emissions from hydrogen reduction processes when producing Ni powder and
type
Plant
Process
Table 9.26:
briquettes
Periodic
measurem
ent
(twelve
times per
year)
Avera
ge
over
the
sampli
ng
period
< 200 t/yr
Cross-media effects

Minor increase in energy consumption when using abatement equipment.
Air abatement techniques are applicable to new and existing hydrogen reduction plants.
Economics

Reduction of emissions.
Example plants

Plant C, Finland.
9.3.1.5
Waste water
9.3.1.5.1
Prevention of waste water
See Section 2.12.6.1.
9.3.1.5.2
Waste water treatment
Description
The techniques to consider to treat effluent water, exception of cooling water, prior to discharge
are:

Pretreatment techniques, in some cases.
July 2014
1007
Chapter 9



Chemical precipitation.
Sedimentation or flotation.
Filtration.
Technical Description
The production of non- ferrous metals is associated with the generation of different liquid
effluents
Pretreatment techniques
In some cases, depending on the sources, it might be necessary to apply a pretreatment to waste
water.
Waste water collected in a sewer system is contaminated with coarse and suspended particles,
dissolved metals and salts. It can consist of rain and sprinkling water running of roofs, roads and
storage yards, of drainage water from groundwater remediation, of cooling towers drains, of
industrial cleaning activities and of neutral process waters.
Coarse floating fractions in the sewer water have to be removed by sieves before further
treatment of the sewer water. Coarse settling fractions in the sewer water are first removed in a
buffering basin or settler by making them settle possibly with addition of a polyelectrolyte. A
rake gathers the settled particles and the gathered sludge is then filtered in a press filter or in a
centrifugal filter. As usually this sludge contains valuable metals, it will be reintroduced in the
production process. The water resulting from this pretreatment is further treated as described for
the waste water generated by production and downstream metal processing.
Waste water from nickel production can contain suspended particles, acids, dissolved metals
and salts. Also the temperature of the water might be a feature of concern, either as incoming
process water or as cooling water.
Chemical precipitation
Dissolved metals and other dissolved elements will be removed by first transferring them into
an insoluble state:

Addition of a base (e.g. sodium or calcium hydroxide) enabling the precipitation of
insoluble metal hydroxides, typically at a pH of 10 - 11.5.

Addition of calcium hydroxide (milk of lime) will co-precipitate the sulphates present in
the waste water as gypsum and the fluoride as calcium fluoride. Applied at a pH of +/- 1,
this can produce a type of gypsum that is clean enough for reuse.

Addition of sulphide (e.g. disodium sulphide, sodium hydrogen sulphide, tri-mercaptosulpho-triazine (TMS)) in alkaline conditions precipitates the metals as insoluble metal
sulphides. This technique can also be used after hydroxide precipitation as a polishing of
the waste water for Tl+ removal.

Addition of iron (iron sulphate or iron trichloride) polishes the water for arsenic;
simultaneous addition of a base might be necessary to maintain an optimal pH of +/- 10.

Precipitation is enabled by the addition of a polyelectrolyte that makes particles collide
and fuse to form larger particles
For complex waste water a multi stage treatment at different pH and with the combination of the
above described techniques might be necessary.
Sedimentation/flotation and filtration
Suspended particles, precipitated metals, gypsum and calcium fluoride are removed from the
waste water by settlers. In order to stimulate this process, a polyelectrolyte is added. The sludge
which is separated from the purified water in the settler is filtered in a press filter or a
centrifugal filter in order to produce a dewatered cake that either can be disposed of or be put in
the metal production process again in order to recover valuable metals. In larger plants, the
treatment of the different waste water flows in an end of pipe installation, where it is grouped
1008
July 2014
Chapter 9
and treated separately in order to maximise the metal recovery by generating two different
sludges.
Before discharging, the pH of the purified water might have to be adjusted by addition of
hydrochloric acid or by injection of CO2.
When the temperature of the purified waste water or the non-contact cooling water is too high
for discharge or reuse, the water should be cooled (cooling towers, heat exchangers). Open
cooling towers should not be applied for cooling of the raw waste water to prevent generation of
metal content. due to this, the conductivity must be taken into account to avoid corrosion and
abrasion.
After treatment, the purified water can be reused for cooling, sprinkling and some processes.
The salt content of the purified water can pose problems for reuse, e.g. calcium precipitation in
heat exchangers. Attention should be paid however to the risk of legionella growth in this
(usually warm) water. This can limit considerably the reuse of water.
The waste water treatment process has to be controlled by adequate measurement of relevant
parameters, in order to dose the additives or to adjust flowrates. Measurements can be on line,
like the measurement of pH, redox-potential, flowrate and conductivity. Such measurements can
steer directly the dosage of additives. Metal content can be determined on a sample taken
proportionally with the flowrate, e.g. of the final control of the effluent or on grab samples taken
during the process for process control. Analysis can be effectuated quickly with AA (atomic
absorption) or ICP (inductive coupled plasma); the latter technique allows for lower detection
limits and a broader range of parameters. Is case of having buffer tank and when the residence
time of the waste water in the process is rather long, point samples and an immediate analysis
could be sufficient to react and to adjust the process.

Removal of suspended and coarse particles, metals, acids, sulphates and fluorides from
waste water, rendering it suitable for discharge or for reuse.

Production of a sludge for reuse (pure gypsum for sale, sludge with valuable metals that
can be put in the production process again) avoids the production of waste to be disposed
of.

Production of a sludge concentrating harmful metals (Cd, As) reduces the amount of
waste to be disposed of.

Production of water suitable for reuse within the plant, e.g. for sprinkling, cooling,
industrial cleaning and for some processes.
The waste water plant from plant D is designed to treat all process effluents (surface drainage
water, plant spillages, washing, roof run-offs, rainwater and road drains) which are collected at
the inlet sump. Filtrate from the operations, together with any return from the emergency tank,
is also collected at this inlet sump.
The effluent treatment plant is designed to treat all process effluents, surface drainage waters,
plant spillages, washing, roof run-offs, rainwater and road drains, which are collected at the inlet
sump. Filtrate from the operations, together with any return from the emergency tank, is also
collected at the inlet sump.
The raw effluent is pumped to a caustic dosing tank where the pH is raised to 10.2 by the
addition of caustic soda. The pH adjusted effluent stream flows to the thickener where the solids
are allowed to settle out of suspension to the base of the thickener.
The clarified water overflows a weir to the clarified water tank where the pH is adjusted, to pH
9.2, using an injection of carbon dioxide. The water is then filtered using graded sand filters.
July 2014
1009
Chapter 9
Each of the sand filters undergoes a washing process every 24 hours using fluidising air to
release the solids collected and to allow the filter wash water from the clarified water tank to
flush the filter. Backwash from the sand filters is collected in the wash water collecting tank and
then pumped via the return pumps to the inlet sump. The filtered water passes to the acid dosing
tank, where it is pH adjusted to between 6 and 9 using carbon dioxide or sulphuric acid, before
being discharged to the river. In the event of a high or low pH, the discharge diverts to the
emergency storage tanks.
The settled solids from the thickeners are transferred to slurry hold tanks prior to being filtered
using a plate and frame filter press. The filtrate is returned back to the inlet sump. The filter
cake is extruded and dried on a band dryer using circulating hot air through the drying strand.
The dried solids are elevated to a product hopper prior to being bagged for transportation and
further processing.
Plant D reports the emissions collected in Table 9.27.
D
Plant
Table 9.27:
Water emissions from plant D
Abatement
technique
Pollutant
Minimum
(mg/l)
Average
(mg/l)
Maximum
(mg/l)
Ni
0.1
0.56
3.2
0.1
0.41
2.5
0.1
0.1
0.1
0.1
0.2
0.2
Soluble
Ni
Co
Cu
Method to
obtain data
Type of
average
Periodic
composite
sampling and
measurement
(two samples per
day to make a
single composite)
Plant C and A are operating in the same area. Plant A has copper and nickel smelters and plant
C has nickel refinery (leaching, solvent extraction, electrowinning, hydrogen reduction) and
chemical plant at site. Both companies have waste water treatment plants. Plant A treats part of
the plant C’s surface and waste area waters.
Plant A waste water treatment plan is described in Section 3.3.6.2. The emission values
associated with this plant can be found in Table 9.28.
1010
July 2014
Chapter 9
A (copper and nickel smelter)
1) Primary settling
2) Precipitation:
Heavy metals are
precipitated as metal
hydroxides with
sodium hydroxide
(pH approx. 10.5) 3)
Actiflo© treatment:
I) Ferric sulphate
(coagulant) is added.
II) Microsand is
injected to the
stream and mixed to
form a uniform
solution.
III) Flocculant is
added to the stream.
<
0.01
0.0
1.8
Ni
<
0.01
0.06
1.9
Zn
<
0.01
0.02
0.4
Pb
<
0.008
0.009
0.05
As
<
0.01
0.02
0.4
Cd
<0.0
01
0.003
0.08
Hg
<
0000
1
0.0002
0.006
Flow
rate
490
m³ /h
1348 m³
/h
3100 m³
/h
Type of
average
Method to
obtain data
Maximum
(mg/l)
Average
(mg/l)
Pollutant
Cu
IV) Heavy flocs are
settled to the bottom
of the settler and
clear water leaves
the settler as the
overflow. The
settlers are equipped
with lamellae to
improve the
separation.
The sludge from the
bottom of the settler
is pumped to
hydrocyclones which
separate the sand
back to the process
and the metal sludge
is removed via the
primary settling
from where it is
pumped to the
sludge basin and
transported to slag
concentration plant.
Minimum
(mg/l)
Water emissions from plant A
Abatement
technique
Plant
Table 9.28:
Continuous
composite
sampling and
measurement
Daily
average
Continuous
measurement
Yearly
average
The feed to plant C´s waste water treatment plant consist of the chemical plant processes waters,
surface waters and refinery process waters. Treatment of the waters is as follows:

pH control by using sodium hydroxide or sodium carbonate

flocculant and coagulant are used if needed

settling: solids are recycled to the leaching stage. Water is sand filtered before going to
settling basins and releasing to river Kokemäenjoki
July 2014
1011
Chapter 9
Table 9.29:
Emissions from plant C
Abatement
technique
Plant
Plant C
(nickel
refinery
and
chemical
plant)
pH control,
flocculant
and
coagulant if
needed,
settlers,
sand filters
Pollutant
Minimum
(mg/l)
Average
(mg/l)
Maximum
(mg/l)
Ni
0.02
0.2
0.9
Cu
<0.01
0.02
0.4
Zn
<0.01
0.2
0.8
U
<0.01
0.2
0.6
Pb
<0.01
0.03
0.6
As
<0.01
<0.01
0.06
Flowrate
33 m³ /h
86 m³ /h
115 m³ /h
Method to
obtain data
Type of
average
Continuous
composite
sampling and
measurement
Daily
average
Continuous
measurement
Monthly
average
Plant B reports the following emissions after the waste water treatment plant (physico-chemical
treatment).
Plant
Table 9.30:
Emissions from plant B
Abatement
technique
B
Physicochemical
treatment
Pollutant
Minimum
(mg/l)
Average
(mg/l)
Maximum
(mg/l)
Ni
0.02
0.55
1.5
Fe
< 0.01
0.2
2
Co
< 0.005
0.05
0.5
Cu
< 0.005
0.03
0.5
Method
to obtain
data
Type of
average
Single
random
sampling
Total
suspended
solids
0.2 kg/t
Ni
Not
reported
TVOC
0.17 kg/t
Ni
Not
reported
Note(1): The presence of chlorides in the effluent interferes with the analysis of the Chemical
Oxygen Demand (COD) parameter; analytical results are therefore not representative. The
Plant B Refining Process analyses Total Organic Carbon (TVOC) instead of COD to flag the
eventual presence of organic compounds in the waste water effluent.
Emissions to water from the waste water treatment plant of plant E are reported in the following
table.
1012
July 2014
Chapter 9
E
Plant
Table 9.31:
Emissions from plant E
Abatement
technique
First step is a
ventilation
tank for
removal of
CO2 by
mixing and
aeration at
low pH (lower
than 5.5).
Second tank is
a precipitation
tank using
NaOH to
precipitate
metals as
hydroxides.
The solid
phase is
filtrated off
and returned
to the process,
the filtrate is
mixed with
cooling water
and sent to
sea.
Pollutant
Minimum
(mg/l)
Average
(mg/l)
Maximum
(mg/l)
Ni
0.06
0.10
0.13
Fe
0.02
0.06
0.13
Co
0.01
0.02
0.04
Cu
0.02
0.03
0.05
As
0.009
0.03
Method to
obtain data
Type of
average
Continuous
composite
sampling and
measurement
Composite
sample of
daily
samples
from one
month
0.11
Plant G is a multi-metal plant using a centralised waste water treatment plant for the generated
waste water (a mixture of sanitary water, process water and rainwater). A description of this
waste water treatment plant, as well as emission values, can be found in Section 3.3.6.2.
Cross-media effects


Use of reagents.

Production of waste for disposal or for recycling in the shaft furnace.

Transfer of heat from water to air.
The techniques to be applied have to take into consideration the specificity of the production
processes, raw materials and the local conditions. Also the size and the flowrate of the receiving
water body can play a role in the choice of the techniques to be applied.
Contact of sulphides with acidic conditions must be avoided in order to prevent the formation of
hydrogen sulphide. Ferric sulphate can be added after precipitation to remove the excess
sulphide.
Economics
Plant C started its waste water treatment plant in 2002. The investment cost was about EUR 3.5
million. Annual operational expenses are about EUR 400 000.
July 2014
1013
Chapter 9
Plant A started the new waste water treatment plant in 2009. The investment cost was about
EUR 4 million €. Annual operational expenses are about EUR 800 000.

Reduction of waste water emissions, driven by the regulation.
Example plants

Plant A, Finland.

Plant B, France.

Plant C, Finland.

Plant D, UK.

Plant E, Norway.

Plant F, France.

Plant G, Belgium.
9.3.1.6
Production Process residues such as waste and by-products
9.3.1.6.1
Prevention and minimisation of residues and wastes
Description

Reuse in the same or other process to recover metals.

Recovery in external plants.

Treatment for other useful applications, as shown in technical description below.
Amount of residues and wastes formed in nickel production depend mainly on composition of
used raw materials. Raw materials contain varying concentrations of impurities that have to be
precipitated and extracted in certain process steps. Some of residues are registered as
transported or on-site isolated intermediate according to REACH-regulation and used as raw or
construction material in own or external processes. The residues that could not be reused are
classified as waste and disposed after appropriate treatment (stabilisation) to landfill according
to the environmental regulation.
Residues formed in smelting processes are mainly iron and silica based slag. Usually slags
contain very low concentrations of leachable metals and therefore they are usable in
construction, abrasives and other purposes. The slag output is 4 – 10 times the weight of the
metal produced. The slag, which cannot be reused is disposed to landfill.
Residues formed in hydrometallurgical leaching and purification route are precipitated in
different process steps. The amount of precipitates is mainly depending on the quality of raw
materials and efficiency of precipitation. One of the main residues fraction in the
hydrometallurgical process route is iron residue (in form of jarosite or goethite). Iron residue is
mainly disposed to landfill. The amount of produced iron residue is fully dependent on the Feconcentration in the raw materials. Elements other than Ni present in the plant feed need to be
extracted and evacuated in order to achieve a pure Ni-product and to avoid a build-up of such
elements in the closed hydrometallurgical circuit. Some of those extracted elements are
concentrated in saleable “On-site Isolated or transported Intermediates” and are registered
according to REACH-regulation.
Residues coming from gases treatment plant are mixed with water (very fine Ni powders are
potentially pyrophoric so wetting them is a safety measure) to form a slurry which is fed directly
to the site waste water treatment plant for treatment and recovery. Dry effluent residue from the
waste water treatment plant is sent to the smelter for metals recovery. Residue from the kilns is
1014
July 2014
Chapter 9
transferred to a nickel pressure extraction system followed by copper and cobalt extraction. The
resulting material is sent for further platinum group metals recovery.

Maximisation of saleable “Intermediates” to be treated and valorised
internally/externally.

Minimisation of wastes that further need to be inertised and landfilled
Typical waste flows and residues formed in nickel production at smelting and refinery stages are
as follows.
Process type
Plant
Residue /
waste
Process
where
formed
Granulated
slag
EAF
Final disposal / construction /
abrasives
Off-gas dust
EAF
Raw material for zinc
production
Matte
Granulation
off-gas dust
DON and
EAF
Raw material for nickel refinery
/ resmelting
Sulphur
residue
Matte
preparatio
n
Raw material for sulphuric acid
production
A
DON- and EAF smelting
B
Further treatment options
Chlorine based leaching.
Electrowinning and chemical
production
Sulphate based leaching,
solvent extraction,
electrowinning, hydrogen
reduction and chemical
production
Chlorine based leaching,
solvent extraction,
Electrowinning
Iron residue
leaching
Stabilisation and final disposal /
Feed to the nickel smelter
Metal (Zn)
carbonate
residue
Solvent
extraction
Stabilisation and final disposal /
Raw material for Zn production
Copper
residue
Leaching
Raw material for copper
production
Copper
residue
Leaching
Raw material for copper
production
Sou
rce:
[
378
,
Ind
ustr
ial
NG
Os
201
2]
E
C
(Filtration)
Cross-media effects

Use of chemicals for precipitation.

Economics
Not reported
Sustainability of the plant operations.
Example plants

Plant A, Finland.
July 2014
1015
Chapter 9



Plant B, France.
Plant C, Finland.
Plant E, Norway.
Not reported
9.3.1.7
Energy efficiency and reduction
Description

Oxygen-enriched air in smelting furnaces and oxygen in converters.

Heat recovery boilers by which high pressure steam is generated from hot and SO2
containing gases produced in the smelting and converting stages.

Use of flue-gas off-gas energy.

Heat exchangers to recover the heat from the warm gas or solution flows.
Increasing the energy efficiency and reduction of external fuel consumption can be achieved by
using techniques to recovery waste heat or to reduce the needed of energy.
Oxygen-enriched air in smelting furnaces and oxygen in converters
Smelting and converting steps: in conventional smelting route, low grade nickel matte is first
produced. The obtained matte is converted into low iron nickel matte in a converters. In both
processing steps oxygen enrichment is used to reach autogenous processing point. The usage of
oxygen enrichment allows melting of returns, scrap and secondaries, especially in converting
step. Also, as the total gas flow is lowered, electricity consumption of fans (process gas,
ventilation, etc) is lowered.
In direct nickel flash smelting (DON) technology high-grade nickel matte with low iron content
is produced in the flash smelting furnace directly without subsequent converting. The dried feed
mixture, oxygen-enriched process air and distribution air are mixed in the effective concentrate
burner. The concentrate ignites and burns in the turbulent gas/solid suspension in the reaction
shaft. The oxidation of concentrate feed is taken further than in conventional process. This
burning process generates a large amount of energy causing the melting of the charge. Flash
smelting is energy efficient process since it makes use of the reaction heat of concentrate, and
therefore external fuel is needed from time to time. The usage of oxygen enrichment in flash
smelting furnace has the significant effect on savings in energy consumption and better
pollution control. Matte produced using this process has a low iron and high nickel content.
DON process has made a separate converting unnecessary, which has an important positive
effect environmentally and on the energy consumption.
Heat recovery boiler
The hot SO2-rich off-gas produced in the smelting furnace, or converting vessel is conducted to
the heat recovery boiler. In the boiler, gas is cooled by generating steam from which energy is
recovered. The steam is used for example in the drying of concentrates and for various process
heating needs, such as in autoclaves. Electricity and district heat may be made from the extra
steam in the power plant.
In indirect steam coil drying the saturated steam produced in the heat recovery boiler connected
to the smelting furnace is utilised.
Use of flue-gas off-gas energy
In the direct drying the hot gas is produced by the combustion of fuel in the separate chamber.
To recovery the energy content of the hot gas from other process steps anode furnace exhaust
off-gases could be partly recycled into the dryer.
1016
July 2014
Chapter 9
Heat exchangers to recover the heat from the warm gas or solution flows
Slag cleaning: The metal values in the smelting/converting slag are removed in an electric
furnace as an iron containing Ni-matte. Electric furnace off-gases are first post-combusted and
then cooled. Heat from gas cooling is removed by a heat exchanger and used in heating and
drying of additives or coke for electric furnace.
Production of sulphuric acid from SO2-containing off-gas produces extra energy, which is
removed and utilised. Oxidation of sulphur dioxide to sulphur trioxide is an exothermic
reaction. Part of the energy produced by this oxidation is transformed by using heat exchanger
to intermediate water and furthermore for heating of other process units or to a second heat
exchangers for district heating.
Cooling of acid is carried out by using heat exchanger where energy is removed to intermediate
water. Energy of the intermediate water moves via the second heat exchanger into district
heating line or to heating of the other process units.
The chlorine leach process is highly exothermic, and steam in the off-gas from the leach tanks is
condensed and heat recovered into a separate glycol circuit, which is distributed for heating
office and plant building.
Before recycle of anolyte in the nickel tank house, the solution has to be cooled. A heat
exchanger is installed to cool down the anolyte before reuse, and the heated water is distributed
to other processes that consume hot water, or used for cleaning purposes in other areas in the
plant.

Reduction of energy consumption.

Reduction of air emissions (the recovered energy replaces, in most cases, fossil fuel).
Plant A:
Direct electricity consumption:
Ni smelter 1 400 – 1 800 kWh/t metal, excluding e.g. oxygen, and pressurised air (over-thefence consumables)
Fuel oil consumption:
Ni smelter 300 - 400 kg/t metal including concentrate drying, flash furnace operational fuel, and
heat-up fuel for FSF and EF
Coke consumption:
Ni smelter 200 - 250 kg/t metal, including coke reductant in slag cleaning electric furnace
Plant C: Refinery electricity consumption is 3 000 – 4 000 kWh/t Ni produced. Heat
consumption is 7 000 – 9 000 kWh/t Ni produced. Plant A copper- and nickel smelters and plant
C refinery are operating in the same site. Companies have common heat recovery systems.
About 50 – 70 % of the heat used in the site is recovered from the different process steps.
Plant E: Refinery electricity consumption is about 5 MWh/t Ni, Cu and Co produced. This plant
delivers 40 000 -45 000 MWh/yr for district heating from the Sulphuric acid plant. From the
exotherm chlorine leach process 12 MW are used for heating of buildings on site. The heat
exchanger used at anolyte cooling, to heat cleaning water, has a capacity of 40 000-50 000
MWh/yr.
Cross-media effects
Not reported.
July 2014
1017
Chapter 9
Economics
Not reported

Sustainability of the plant operation; ecological and economical.
Example plants

Plant A, Finland.

Plant C, Finland.

Plant E, Norway.
[ 413, A.E.M. Warner, C.M. Diaz, A.D. Dalvi, P.J. Mackey, A.V. Tarasov, and R.T.Jones 2007
]
9.3.2
9.3.2.1
Cobalt production
Emission reduction from a cobalt solvent extraction process
Description

Use of low-shear pumping in the liquid-liquid contact mixer-settlers that reduce
evaporation of the organic and aqueous solution. Use of low-shear mixing also reduces
formation of stable emulsion precipitate wastes referred to as cruds in solvent extraction
processes.

Use of a high-shear mixer.

The mixer-settler units are sealed to prevent VOC emissions to the working area
atmosphere.
Hydrometallurgical solvent extraction process in which the cobalt(II) ions in the aqueous feed
solution are selectively separated and concentrated from a process solution typically containing
mainly nickel. Aqueous feed containing the cobalt is mixed in a liquid-liquid contactor with an
organic solution containing an extraction chemical that forms a metal-organic complex with the
cobalt resulting in its dissolution into the organic stream. As the cobalt extraction chemicals are
typically acidic ion exchangers acid is generated during the extraction reaction, which
necessitates a control of pH with an alkaline neutralising agent e.g.. ammonia or sodium
hydroxide. The cobalt-loaded organic phase will contain some co-extracted impurities since the
extraction chemicals are not entirely selective to the target metal and a scrubbing step follows,
where impurities are removed with mixing the organic phase with an aqueous solution typically
containing cobalt. The cobalt is then stripped from the organic phase back to an aqueous
solution by reversing the extraction reaction with mixing with aqueous solution at lowered pH,
which causes the organic complex break up and the cobalt ion liberate. The stripped organic is
then returned to the extraction stage.

Minimisation of emissions of VOCs to air.

Reduced formation of solid waste.
No data was available.
Cross-media effects

Increase of energy consumption.
1018
July 2014
Chapter 9

Use of ammonia for neutralisation of extraction and generation of ammonium sulphate.
Need to make purified water for the wash and strip stages. Use of acid for stripping of
cobalt.
Separation of cobalt by solvent extraction is applied to processes treating nickel-containing raw
materials also containing cobalt. To obtain a high purity product zinc, iron, calcium, manganese
and copper should be removed from the feed solution prior to solvent extraction of cobalt. A
chemical neutralisation is used to adjust pH levels in the extraction and washing stages. Cobalt
is recovered as a high concentration and purity solution suitable e.g. as a feed for cobalt
electrowinning.
Economics
No reported data available.

Selective cobalt separation yielding a high purity product.

Low energy and chemicals consumption.

Low waste generation.
Example plants
Norilsk Nickel Harjavalta (FI), OMG Kokkola Chemicals, Murrin Murrin (Australia), Kasese
Cobalt Company (Uganda), Knightsbridge Cobalt (South Africa), Anglo Platinum Rustenburg
Base Metals Refinery (South Africa)
[ 414, Peek et al. 2009 ].
9.3.2.2
Techniques to reduce emissions from mixed hydroxide and mixed
sulphide precipitation
Description
One or a combination of the following techniques to reduce emissions from mixed hydroxide
and mixed sulphide precipitation of nickel and cobalt containing raw materials are used:

Use of confined process equipment when deemed necessary (reactors, settlers, filters).

Use of confined liquid and slurry transport systems (pipes and covered launders).

Use of high-efficiency solids separation and washing systems to avoid excess usage of
wash water.

Use of high grade hydrogen sulphide gas or other precipitation media to avoid large gas
amounts and to enhance the performance of the precipitation process.

Use of abatement equipment (bag filters, wet scrubbers etc.) for process equipment gas
treatment.

Recycling the abatement residues and effluents.

Use of online monitoring and control for critical leaching and abatement equipment
parameter or other equivalent suitable monitoring method or standard operation
procedure.

Use of online monitoring and control of critical process parameters (e.g. reagent
utilisation rate) to avoid excess chemical consumption and ensure efficient metal recovery
Mixed hydroxide (MHP) and mixed sulphide (MSP) processes consist of following steps:
MHP Process
July 2014
1019
Chapter 9





MHP precipitation is carried out in an atmospheric reactor by adding a basic chemical e.g.
sodium hydroxide.
Precipitation control is based on pH in precipitation reactor and consequently on metal
concentration in the exiting solution.
Slurry from precipitation reactor is thickened and part of the thickened solids are recycled to
precipitation step to act as seeds for further precipitation. Major part of the thickened solids
are further treated in the filtration step.
Precipitated solids are separated from the thickener underflow by filtration and filter cake is
washed with water if necessary.
Prior to shipment the product solids are dried (if required) and packed appropriately.
MSP process

Pre-neutralisation of MSP feed solution may be required.

MSP precipitation is carried out in an atmospheric reactor by adding a sulphide source
such as hydrogen sulphide. Precipitation reactor slurry need to neutralised to knock out
the sulphuric acid, which is generated in the sulphide precipitation reaction.

Precipitation control is based on pH in precipitation reactor and consequently on metal
concentration in the exiting solution. pH control very essential to avoid hydrogen
sulphide gas evolution in the gas phase.

Slurry from precipitation reactor is thickened and part of the thickened solids are recycled
to precipitation step to act as seeds for further precipitation. Seeds recycle increases
precipitate particle size and improves solids separation characteristics thus reducing wash
water consumption. Major part of the thickened solids are further treated in the filtration
step.

Precipitated solids are separated from the thickener underflow by filtration and filter cake
is washed with water if necessary.

Depending on the utilisation of the mother liquor an additional aeration step may be
required to destroy any residual free hydrogen sulphide in the liquor.

Prior to shipment the product solids are dried (if required) and packed appropriately.
In sulphide precipitation processes ventilation gases from the equipment are scrubbed in an
alkaline wet scrubber. On-line or other adequate measurement and control of the most important
process parameters (temperature, pH, metal concentrations) are carries out to secure safe and
reliable operational results (minimum gaseous emissions, high recovery of valuable components
and high precipitate quality)

The environmental benefits are Minimisation of the emission of metals, dust and other
compounds.

and the Higher recovery of nickel and cobalt.
Table 9.32:
Emissions of Kokkola Cobalt plant producing 10 000 t Co/yr
kg Co/t of
metal
Grinding/leaching
0.1
Solvent
extraction
Final recovery or
transformation
Total
cobalt
0.9
production
Process
kg Ni/t of
metal
kg VOC/t of
metal
kg H2S/t of
metal
2
2
0.0.81
0.1
4
2
Cross-media effects
1020
July 2014
Chapter 9
Minor Increase in energy consumption when using wet gas scrubbers.
Economics
Not reported
Reduction of emissions and saving raw materials.
Example plant
Kokkola (SE)
9.3.2.3
Techniques to reduce emissions from electrowinning
Description
The technique to consider for sulphate-based processes is:

Covering of cells using hollow plastic spheres or polystyrene beads to prevent release of
aerosols to air.
The techniques to consider for chloride-based processes are:

Collection and reuse of chlorine gas in the leaching process and use of a dimensional
stable anode (DSA).
In sulphate-based solutions, the main anode reaction generates oxygen bubbles, which may
carry sulphuric acid aerosols into the ambient air (acid mist). Depending on the plant, the airelectrolyte interface is physically blocked using hollow plastic spheres or polystyrene beads.
The cathodes in the sulphate-based process are usually made of stainless steel, and a gelatine dip
is often used as "releasing agent" to help stripping. At the opposite end, some impurities can
cause self-stripping. To overcome this risk, plants produce smaller rounds instead of plates,
using marked or patterned cathodes. The most commonly used anode material is lead alloyed
with antimony.
In chloride-based solutions, chlorine gas is generated at the anode. An electrolyte-permeable
diaphragm cloth anode bag is used to encapsulate the anode, and a chlorine gas extraction
arrangement is typically used to remove (and recover) the chlorine from the top of the bag for
use in the leaching process.
In a chloride-based process, cathodes can be made of titanium, or cobalt starter sheets that have
been grown on titanium mother blanks. The anode material is coated titanium (usually referred
to as dimensionally stable anodes). Typically the coating contains RuO2 as the catalytic
component.

Prevention of diffuse emissions of sulphuric acid mist or chlorine gas.
The only plant electrowinning cobalt in Europe is plant E in Norway (3208 t of cobalt cathode
produced in 2010). It is one only two plants in the world (altogether with Sumitomo, Japan)
using the chloride-based process.
July 2014
1021
Chapter 9
Cross-media effects

Increase in energy use (to remove the acid mist from the cell, in the case of sulphate
solutions, and to operate the chlorine removal, in the case of chloride solutions).
1022
July 2014
Chapter 9
Not reported.
Example plants

Plant E, Norway.
9.4
Emerging techniques
Various developments have been reported for the use of low pressure and atmospheric leaching
for the production of nickel from sulphidic ores. The main processes are [ 139, RiekkolaVanhanen, M. 1999 ]:
Activox leaching: fine grinding and leaching at 100 °C, 10 bar.
CESL process: chloride leaching in sulphate solution using ferric chloride.
The processes have been proven at the pilot stage.




A hydrometallurgical process to produce nickel and cobalt compounds from limonite and
low grade saprolite ore. The technology valorises the ore body profile to a much higher
extent compared to classical processes. It operates in a sulphuric acid medium at
atmospheric pressure using low-risk technologies. The inert solid residue will have to be
stockpiled in a waste dump and the waste water will comply with existing regulations and
requirements. Energy use is reduced and CO2 emissions are low (~ 10 t/t Ni produced).
While demonstrated at pilot scale level, this process is in the final optimisation step for the
Eramet Weda Bay project in 2009
A hydrometallurgical process has been developed and patented to produce nickel and cobalt
compounds from both limonite and saprolite ores for the ERAMET Weda Bay Nickel
project in Indonesia. The process has been designed to specifically accommodate nickel
lateritic ore with a medium to high saprolite ratio. The system is able to process a composite
mix of the different lithological horizons that optimise the recovery of the ore body and thus
significantly reduce the production of waste material.
Over 35 campaigns (more than 86 weeks) of continuous industrial pilot tests (producing
good results) have been carried out by R&D incorporating environmental performance into
the industrial process since 2005. Optimisation of the integrated environmental performance
is the final step before the full industrial scale start-up of the Weda Bay Nickel project.
The hydrometallurgical process operates in a sulphuric acid medium at atmospheric
pressure and at approximately 100°C. Heat from the sulphuric acid production units is
harnessed to produce steam, which will significantly reduce the use of fossil fuels for
energy production. Greenhouse gases produced by the overall process are estimated to be
approximately 5.8 t/ t Ni.
Iron- and manganese-based solid residues will be generated by the process. Both these
residues are classified as non-dangerous and non-harmful to the environment. They will be
separately stockpiled in dedicated and specifically designed dewatered residue stockpiles.
Liquid effluents will be neutralised and passed through on-site sand filters. The precipitates
generated from effluent treatment will be entirely recycled in the hydrometallurgical process
[ 415, Nickel Institute 2013 ].
Three new plants are under construction or are at the commissioning stage for the pressure
leaching of laterites using sulphuric acid [ 139, Riekkola-Vanhanen, M. 1999 ]. The
processes are similar to the established process used in Cuba but different purification
stages are used to remove other metals. An atmospheric chloride leaching process for
laterites is also being developed
A process is being commissioned in Germany to recover nickel and zinc from residues
using an oxy-fuel furnace and a solvent extraction refining system from sulphate solutions.
No data has been reported.
July 2014
1023
Chapter 9
9.4.1
Thermal decomposition of nickel complexes
Description
Production of nickel powder under an inert atmosphere in an electric furnace from the spent
electrolytic bleed from the electrolytic refining of high impurity copper anode.
Metallo-Chimique produces nickel by using the following process.
Nickel is recovered from the “nickel-enriched solution” of the electrolysis, by precipitation.
Nickel (complex) precipitation is carried out by adding an organic complexing agent to the
bleed solution of nickel sulphate in a closed reactor vessel. The solution is obtained from the
electrolytic refining of high impurity copper anodes during copper cathode manufacturing. The
insoluble nickel complex is separated by filtration.
The thermal decomposition of nickel complexes into finely divided powder is carried out under
an inert atmosphere in an electric furnace. The result is a nickel powder, which is cooled and
screwed by a conveyer to a powder press for briquetting. The resulting briquettes are fed into
big bags.
To reduce emissions, a two-step NaOH-scrubber is installed. It has a capacity of 7 500 m³/h.
The scrubber treats the air coming from the reactor vessels and the electric furnace.
 Recovery of nickel metal.
 Reduction of emissions.
Environmental performances and operational data
The operational data of the scrubber, based on spot sample measurements during 2011 – 2012:
Flow: 1 500 –7 500 Nm³/h
Dust: 0.7 – 2.5 mg/Nm³
Cross-media effects
 Increase in investment cost (due to additional equipment to be installed).
 Increase in energy consumption.
 Increase in operational cost by the use of additives.
 Requirement to treat water stream in an appropriate way.
Technical considerations to applicability
No data reported.
Economics
The cost of installing the scrubber is approximately EUR 100 000.
 Reduction of emissions.
 Saving of raw materials.
 Stringent emissions standards and other regulatory requirements.
Example plant
Metallo-Chimique (BE)
1024
July 2014
Chapter 9
[ 415, Nickel Institute 2013 ]
July 2014
1025

NFM_BREF_REVISED_Chap9-Processes to produce

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