Mineral bio-processing: an option for recovering strategic

Mineral bio-processing:
an option for recovering strategic metals?
D. Barrie Johnson
College of Natural Sciences,
Bangor University, UK
Bangor
Acidophile
Research
Team
• Professor of Environmental Biotechnology at Bangor University
• also Guest Professor at Exeter University (UK) and Changsha University (China)
• Director of Research & Head of BART(Bangor Acidophile Research Team)
• Royal Society Research Fellow, Fellow of the Learned Society of Wales &
Distinguished Lecturer of the Mineralogical Society (UK)
• research going research collaboration with groups (universities, research organisation
and industries) throughout the world (Chile, China, South Africa, France…..)
Topics covered in this talk:
• Brief outline of the development and current status of biomining
technologies
• The roles of microorganisms in mobilizing and immobilizing metals
•
• Recent and projected developments in biomining technologies
• “Strategic metals” defined and their potential for extraction and recovery
using biohydrometallurgical approaches
Biohydrometallurgy
•
A sub-division of hydrometallurgy (“the use of aqueous chemistry for the
recovery of metals from ores, concentrates, and recycled or residual
materials”) that uses microorganisms in one or more stages of a process
•
Usually (but not always) constrained to operate in conditions where
microorganisms are metabolically active
Biomining
Technology based on the oxidative dissolution of sulfide minerals by
prokaryotic microorganisms that facilitates the recovery of metals
•
Bioleaching: metals are brought into solution (e.g. Cu)
•
Bio-oxidation: metals are made accessible for chemical extraction
(e.g. Au)
1. A brief history of biomining
Late 1940’s:
A novel bacterium isolated from water
draining an abandoned coal mine that
could oxidize both iron and sulfur at low pH
“Thiobacillus ferrooxidans”
Early 1950’s:
Other similar bacteria isolated; also found
that these bacteria could solubilize pyrite
Fe2+ + 0.25 O2 + H+ → Fe3+ + 0.5H2O
S0 + 1.5 O2 + H2O → SO42- + 2H+
8 FeS2 + 30 O2 + 18 H2O → Fe8O8(OH)6SO4 + 30 H+ + 15 SO42-
Some milestones in the development of bioprocessing of mineral ores
using acidophilic prokaryotes ("biomining")
Date
Location
Operation
18th & 19th centuries
Spain, U.K.
Leaching of copper ores in
“precipitation ponds”
1960s
U.S.A.
Copper dump leaching
(Kennecott Corporation)
1960s-1990s
Ontario, Canada
In situ mining of uranium
1980-1996
Lo Aguirre, Chile
Bioheap leaching of copper
(with SX/EW)
1986-
Fairview, South Africa
Bioprocessing of gold ore concentrate
in aerated stirred tanks.
1995-
Nevada, U.S.A.
Bioheap leaching of gold ore.
1999-2013
Kasese, Uganda
Bioprocessing of cobaltiferous ores in
stirred- tank bioreactors
2004-2005
Chuquicamata, Chile
Thermophilic leaching of chalcopyrite
concentrate
2008-
Talvivaara, Finland
Bioheap leaching of a polymetallic
black schist (Ni, Zn, Cu)
First “biomining” operation, mid 1960’s: Bingham copper mine, Utah
“Dump” leaching of low grade (run-of-mine) waste rock
acid irrigation
Pregnant
Leach
Solution
Dexing copper mine, China
Kennecott Chino
Mine, New Mexico
ROM dumps
irrigation
PLS stream
Cu2+
Cementation:
+ Fe0  Cu0 + Fe2+
1970’s: in situ bioleaching of uranium (Canada)
• Used to extract uranium from otherwise worked-out mines
• Underground workings blasted, flooded for a period and then drained
• UO22+ recovered from leach liquors
In situ biomining had been used long before the discovery of bacteria:
Periodic flooding of underground working at the Mynydd Parys copper mine
(Wales) allowed Cu to be recovered for >100 years after active mining had ended
1980’s: heap bioleaching of copper (mostly Chile)
5 km
2 km
Escondida, copper mine, Chile
Typical circuit design: copper bioheap operation
inoculation
copper metal
raffinate
acid irrigation
electrowinning
copper ore heap
Pregnant
Liquor
Solution
air blowers
impermeable membrane
solvent extraction
Irrigation and inoculation: Talvivaara Ni Mine (Finland)
Sb. acidophilus YTF1
Sb. thermosulfido
Acidicaldus
Heap aeration
Talvivaara
Escondida
Stirred tank leaching
•
Used for mineral concentrates (chiefly refractory gold) and at pulp densities of
~20%
•
Most stirred tanks operate at between 35 and 45C; cooling is a major
operating cost
•
Tanks are generally constructed of high-grade stainless steel
•
Tanks are actively aerated
•
Agitation (stirring) is another major operational cost
•
Minerals are processed in a matter of days (~3-6)
1980’s: tank leaching of refractory gold (Fairview: South Africa)
Initially processed14 tons concentrate/day, now 55 t/day
Gold Biomining in Asia
Suzdal BIOX plant
(Kazakhstan): 192 t gold
concentrate/day in sub-zero
temperatures
A more recent operation at Kokpatas (Uzbekistan) is designed to
process over 160,000 t of refractory gold concentrate/year
2. Using microorganisms to mobilize and immobilize metals
•
by effecting redox transformations
•
by mediating changes in pH
•
via production of metabolic products/wastes
Many transition metals form hard and dense sulfide minerals
Pyrite
Talc
Diamond
Goethite
Hardness
(Mohs scale)
6.5
1
10
5.25
Density (g/cm3)
5.0
2.7
3.5
3.8
The reduced sulfur present in these minerals (oxidation state of -2 in
chalcocite (Cu2S) and -1 in pyrite (FeS2) represents a potential
energy source for some highly specialised bacteria and archaea)
In iron-containing sulfide minerals (e.g. pyrite and chalcopyrite
(CuFeS2) the iron is present in its reduced (Fe2+) form, which again is
a potential energy source for some life forms
The problem is how to access this energy!
→ sulfide mineral-degrading bacteria use ferric iron (Fe3+) as the tool
to unlock the energy-rich sulfides
Abiotic dissolution of pyrite at low pH by ferric iron
6H+
7Fe2+
FeS2
6Fe3+
3H2O
S2O32-
Dissolution of pyrite at low pH: role of primary* microorganisms
2Fe2+
Fe2+
FeS2
O2
Fe3+
Fe3+
*Fe-oxidizing acidophiles
Dissolution of pyrite at low pH: role of primary* microorganisms
2Fe2+
Fe2+
Fe3+
Fe3+
FeS2
Contact leaching
Non-contact leaching
*Fe-oxidizing acidophiles
Dissolution of pyrite at low pH: role of secondary* microorganisms
2Fe2+
Fe2+
FeS2
O2
Fe3+
Fe2+
Fe3+
Fe3+
S2O32-
Polythionates, S0
O2
SO42-, H+
*S-oxidizing acidophiles
Dissolution of pyrite at low pH: self inhibition by autotrophs
X
2Fe2+
Fe2+
Fe3+
Fe3+
FeS2
DOC*
X
Fe3+
Fe2+
Polythionates, S0
S2O32-
X
DOC*
DOC*
SO42-, H+
*Dissolved Organic Carbon
Dissolution of pyrite at low pH: role of tertiary* microorganisms
CO2
2Fe2+
Fe2+
Fe3+
Fe3+
FeS2
DOC
Fe3+
Fe2+
S2O32-
Polythionates, S0
DOC
DOC
SO42-, H+
*heterotrophic acidophiles
Microorganisms that can be anticipated to be found* in mineral
bioleach liquors 1.
Primary Group: iron-oxidisers (autotrophs)
2.
Secondary Group: sulfur-oxidisers (autotrophs)
3.
Tertiary Group: heterotrophic acidophiles
- iron-oxidisers
- iron-reducers
- sulfur-oxidisers
*occurrence does not imply that the organism(s) is fulfilling a useful function,
so far as the commercial objective is concerned
Lithotrophic (“rock eating”) prokaryotes
Unexposed rock
Pitted rock due to selective dissolution of sulfidic minerals
Bioleaching of base metal sulfides:
target metals are solubilised
Ni2+
(Fe,Ni)9S8
FeS2
SiO2
SiO2
Fe/S bacteria
FeS2
Fe3+
SO42-
Bio-oxidation of refractory gold ores:
dissolution of sulfide minerals exposes metallic gold
FeAsS
FeS2
FeS2
Fe/S bacteria
Au
Au
CN-
FeS2
Au(CN)4-
Bioleaching of uranium ores:
ferric iron oxidizes insoluble U(IV) to soluble U(VI)
UO2 2+
Fe2+
UO2
Fe3+
Acidithiobacillus spp.
Leptospirillum spp.
etc.
Physiological restrictions in using microorganisms for mineral
processing
• Temperature
• pH
• Pressure
• Osmotic/salt stress
Sulfolobus sp.
Leptospirillum ferrooxidans
Acidithrix ferrooxidans
Temperature/pH
Metallosphaera spp.
75
Ac. brierleyi
S.metallicus
Temperature (oC)
65
Sc. yellowstonensis
55
Sb. thermosulfidooxidans/acidophilus
Am.ferrooxidans
45
L. thermoferrooxidans
Fp. acidarmanus
L. ferrooxidans
Fp. acidiphilum
T. prosperus/"Fm.acidiphilum"
35
At. ferrooxidans
Sb.montserratensis
0.0
2.0
1.0
pH
3.0
4.0
Metal recovery via biosulfidogenesis
• Bacteria can generate H2S from inorganic S-sources (sulfate, elemental sulfur
etc.)
• They require an electron donor (energy source) to do this
• H2S reacts with many metals to produce highly insoluble metal sulfides
4 C3H8O3 + 7 SO42- + 14 H+ → 12 CO2 + 7 H2S + 16 H2O
H2S + Me2+ → MeS↓ + 2 H+
Acidophilic sulfidogenic system using an
Upflow Biofilm Reactor (UBR)
pump
Feed in
(pH 1.5‐4)
meter
pH electrode
Effluent out
(pH 2‐5)
Packed bed
(immobilized SRB)
Can be used for off-line and in-line metal precipitation
pump
Feed in
(pH 1.8-4)
meter
pH
electrode
H2S stream →
Effluent out
(pH 2-5)
Colonised
beads
(immobilised
SRB)
In-line metal precipitation bioreactor
Off-line metal precipitation vessel
Selective on-line and off-line precipitation of metals
using a single acidophilic sulfidogenic bioreactor
In line
precipitation of
ZnS and CoS
Off-line
precipitation
of CuS
3. Some more recent developments in biomining technologies
- thermophilic bioleaching
- indirect bio-oxidation of sulfide minerals
- reductive dissolution of oxidized ores
- selective removal of metals from leach liquors using biomineralization at
low pH
2004-2005:
Thermophilic (70-80C) stirred tanks for processing chalcopyrite
concentrates (Chuquicamata, Chile)
Objectives:
• efficient bioleaching of chalcopyrite (CuFeS2)
• faster rates of mineral dissolution
• reduced cooling costs
Indirect leaching of mineral concentrates
• mineral oxidation (by ferric iron: abiotic) is separated from ferrous iron
oxidation (biological) in a two-stage process
• each process can be operated at optimum conditions of temperature, pH and
oxygen concentration
• demonstrated at pilot-scale for processing zinc sulfide concentrates (BioMinE
project)
Two-stage (“indirect leaching) of zinc sulfide concentrate
Fe3+
Fe2+
Mineral leaching reactor
(anoxic; 80-90˚C)
ZnS
bacteria
PLS
Zn2+ & Fe2+
Zn stripping
Fe3+ regeneration
reactor
(aerated; ~45˚C)
Ferric iron-regenerating bioreactor
The BioMOre project (2015-): deep in situ (bio)leaching of a sulfidic ore body
• an indirect bioleaching process is envisaged, whereby acidic ferric iron-rich leach
liquors are regenerated in surface bioreactors and injected through boreholes into
the fractured ore deposit
Bio-processing of oxidized ores using reductive dissolution
“biomining in reverse gear”
•
a process for using bacteria to extract metals from ores and waste materials in
which the primary reaction is that of ferric iron reduction rather than ferrous iron
oxidation
Ni-laterite ore,
Western Australia
In contrast to conventional mineral bio-processing, “reverse gear”
biomining uses acidophilic bacteria to catalyse the reductive dissolution of
oxidized minerals at low pH
Ni FeO.OH
FeO.OH Ni
FeO.OH Ni
FeO.OH Ni
FeO.OH Ni
FeO.OH Ni
Ni FeO.OH
Ni FeO.OH
FeO.OH Ni
FeO.OH Ni
FeO.OH Ni
FeO.OH Ni
FeO.OH Ni
Ni FeO.OH
Ni FeO.OH FeO.OH Ni
S0
SO42-
Fe2+, Ni2+ , OH-
Selective precipitation of metal sulfides by using acidophilic SRB
•
The solubility products of chalcophilic metal sulfides show great variation
•
The concentration of the key reactant (S2-) varies with pH
([Me2+ ] [S2-] > Ksp for MeS to form)
•
This facilitates selective recovery of transition metals as their sulfide phases,
by varying and controlling pH
Log Ksp
pH 2
pH 4
Fe2+
Fe2+
Fe2+
Zn2+
Zn2+
ZnS
Cu2+
CuS
pH 7
FeS
Cu2+
-35.9
Cd2+
-28.9
Zn2+
-24.5
Co2+
-22.1
Ni2+
-21.0
Fe2+
-18.8
Mn2+
-13.3
Modular units for treating and recovering metals from mine-impacted
waters and mine process waters
Zn-capturing reactor
Cu-capturing reactor
schwertmannite-generating reactor
4. Where do “strategic metals” fit into this?
(i) E-tech elements (in bold & italics), from Critical Metals in Strategic Energy
Technologies, Critical Metals Strategy and Critical Metals for the EUS
(ii) EU Raw Materials Initiative COM (2008) 699. Critical raw materials for the EU
Science opportunity
(ii) “E-tech elements”; Natural Environment Research Council (UK), 2013.
Importance to environmental technologies
(a) Cobalt has already been successfully biomined from pyritic
tailings (via oxidative bioleaching) in Kasese (Uganda)
Acid mine drainage
Tailings waste (from copper mining)
Stirred tank bioleaching: Kasese
Bioleaching of cobaltiferous pyrite in tanks is followed by electrowinning,
producing a high-quality product (~99.9% Co)
Ni laterites also contain significant amount of Co (mostly associated with Mn(IV)
minerals); this too can bioleached using a reductive approach
anaerobic
aerobic
Mn
Time (days)
(Ni,Co)xMn(O,OH)4.nH2O
asbolane
Fe2+
Ni2+ , Co2+ , Mn2+
Fe3+
Cobalt solubilised (mg L-1)
Manganese solubilised (mg L-1)
Co
A variety of biological options exist for downstream capturing of Co from PLS
Oxidative
(bio)leaching
Reduced ores
(sulfides)
fungi
CoC2O4
oxalate
Fungal leaching
urea
carbonate
Other solubilized metals
PLS
Abiotic (chemical) leaching
CoCO3
H2S
SRB
CoS
Reductive
(bio)leaching
Oxidized ores (laterites etc.)
Direct reductive bio‐conversion
Bio‐nanomaterials
• Low carbon/energy (“green”) extractive technologies
• Cobalt products may be sourced for the metal or used directly in other applications (as nanoparticles)
(b) Indium:
•
Found in association with ZnS in sulfide ore bodies
•
ZnS is readily bioleached (directly or indirectly), potentially facilitating the extraction
and recovery of In
(c) Gallium:
• By product of the production of Al (bauxite) and Zn (sulfide ores)
• Extraction/recovery of Ga from bioleached ZnS ores is a possibility
(d) REE (and PGM):
• Unlikely to be susceptible to bioleaching
• Biooxidation and/or bioreduction could be used to remove encapsulating minerals
Removal of ferric iron deposits coating valuable minerals/precious metals
- rare earth element (REE) minerals (monazite etc.)
- silver, gold, PGMs
bio-reduction
+ Fe2+
ferric oxyhydroxide
monazite
(REE phosphates)
Process analogous to bio-oxidation of refractory gold ores
Summary:
1.
Biohydrometallurgical processes are long established for extracting metals
from primary ores and mineral wastes, and also for recovering metals from
leachate liquors
2.
With the exception of Co, none of the metals on the “critical lists” have so far
been targeting for bio-extraction/recovery
3.
Innovations in biohydrometallurgy, such as reductive bioprocessing, open up
new opportunities for metal extraction and recycling
4.
“Urban (bio)mining” (extraction and recovery of metals from waste electrical
and electronic equipment:WEEE) provides another opportunity to develop and
used biohydrometallurgy. Downstream (selective) recovery of metals would
probably be the major technological challenge
Underground workings, Mynydd Parys copper
mine (Wales); abandoned for 200 years
Diolch yn fawr!
Bangor
Acidophile
Research
Team