Zirconium and Hafnium

Zirconium and Hafnium
By Charles Skidmore
MinChem Ltd UK
Zirconium and hafnium are often thought to be rare elements, but they occur
widely in the Earth’s crust, being more plentiful than copper, with a concentration
of 0.028%. They are found in the minerals zircon sand (zirconium silicate
ZrO2.SiO2) and baddeleyite (ZrO2), with zircon being the main source. These
minerals are generally found together with titanium and iron orebodies and are
separated out during the commercial mining of these deposits. All zirconium and
hafnium compounds, including the metal, oxide and salts, are derived from zircon
sand or baddeleyite. Hafnium is always present in 1.5 – 3.0 weight % and has an
almost identical chemistry to zirconium. This makes it difficult to separate the two
and this is only done when absolutely necessary, such as for zirconium nuclear
applications and the preparation of hafnium compounds.
Zircon sand
Events in 2004 continued the trend in 2003, with the undersupply that began in
2002, deepening further and leading to a global shortage approaching 100,000 t.
This has resulted in continuing increases in zircon prices and major uncertainties
in the long-term position. Supply shortages forced up prices almost on a quarterly
basis throughout 2004.
The dramatic price increases have caused major headaches downstream,
including changes in product formulation, a cutback in zirconium chemical output
in China and some substitution by cheaper alternatives.
All zircon markets continued to grow in 2004 but it is the continuing rapid
expansion of the ceramics markets in China that has led to the shortfall in supply.
Zircon sand occurs throughout the world and is the most abundant zirconium
mineral. It is normally recovered from heavy mineral sands (found predominantly
in beach deposits) where the associated titanium minerals, generally rutile and
ilmenite, are recovered separately. Zircon sand is also obtained during rare earth
processing. Australia, South Africa and the US continue to be the main sources
with a world reserve thought to be in excess of 100 Mt.
Zircon is normally produced from heavy mineral sands by dredging and/or dry
mixing operations – the specific method being dependent on the orebody
location, zircon concentration and associated impurities. To achieve the higher
qualities demanded by the various markets, zircon is processed further using
mechanical abrasion, chemical attack and thermal processing (calcination). This
results in zircon with a wide range of physical and chemical properties, which
normally determine its end use. However, owing to the shortages, some
substitution between markets has been occurring.
A considerable volume of zircon sand is used as mined, in a coarse particle size,
for use in abrasives, foundries, refractories (steel, glass, cement, metal), TV
tubes, and for zirconium metal, oxide and chemical production. In these markets,
the lower reactivity of zircon sand, due to its lower surface area, is compensated
for by processing the sand at high temperatures (fusion, sintering, chemical
attack).
In applications where zircon is not attacked so aggressively, and temperatures
are lower, the surface area needs to be increased. This is achieved by milling to
finer particle sizes, as found in zircon flours (generally (<200 or <300 mesh), or in
smaller sizes (5-6 micron and below)) as opacifier grades. These products are
used predominantly in ceramic frits, which are special glasses made to provide
an impervious, long lasting and easily maintained coating on various ceramic
products. The zircon particles reflect light and so impart a white opaque colour to
the final glaze. Generally, zircons with low impurities, finer particle sizes and
narrower particle distribution lead to the best opacifiers. Every day we all come
into contact with the end product, be it in tiles (wall and floor), tableware (plates,
bowls) or sanitaryware (toilets, bidets, washbasins).
Since the desired effect is the formation of an intense white colour, other species
present such as colouring transition metal ions (Fe and Ti) need to be minimised.
Consequently the higher-quality grades (generally referred to as ceramic or
premium grades) have a maximum 0.10% TiO2 and 0.05% Fe2O3. Lower-quality
grades with higher Ti and Fe levels are used in refractory and foundry
applications, although with recent shortages some lower grade has been used to
augment flour and opacifier production.
In 2004, zircon output remained at around 1.1 Mt, similar to 2003. Shipments
from Australia were under 400,000 t (2003: 450,000 t), South African movements
were similar to 2003 level at 370,000 t (the 2002 level of 420,000 t was not
recovered) and US sales remained at 140,000 t, similar to 2003. Output from
Ukraine, India, Vietnam, Brazil, Malaysia, China and Russia also saw little
change, with a combined contribution of around 130,000 t (2002 level).
The ongoing problem of zircon being inextricably linked to titanium minerals and
markets continued. Historically, titanium ores and downstream TiO2 pigments
have been in oversupply. This has led to little price improvement and, with
increasing environmental, social and other operating costs, has led to low
profitability. The heavy mineral sands mining industry has always centred more
on titanium ore recovery than zircon, the latter being considered a by-product.
Hence, with low demand for titanium ores, there has been little incentive to
increase output, and this has resulted in little zircon growth. This situation is
changing with rationalisation in the TiO2 pigment supply market, including a
decrease in TiO2 production capacity (three of the top four suppliers have
decreased capacity in the last year). As a result of this reduced output, and also
because of tighter titanium feedstocks such as rutile, TiO2 selling prices have
been lifted. This higher demand for titanium ores has been benefiting zircon and
several existing mines have lifted output in the latter half of 2004 and into 2005.
The largest world producer is Iluka Resources Ltd, with operations in
Australia/US and production/sales of approximately 375,000 t (similar to 2003).
Considerable work in 2004 centred on cost reduction and operational efficiency
improvements, the return of US profitability and the development of its Lulaton
project in Georgia, US and CRL’s Enterprise deposit in Australia. Developments
in the Murray Basin in southeast Australia are key to Iluka’s long-term position.
Its Douglas and KWR sites in Victoria should lift output by 64,000 t (Douglas in
the fouth quarter of 2005, and KWR in the third quarter of 2007). Other projects
include Jacinth (52% zircon) and Ambrosia (66% zircon) both in South Australia
where reconnaissance is being undertaken.
Iluka continued to increase prices throughout 2004 and asked for a further
increase of approximately US$100/t for the first quarter of 2005. An extra 12.5%
has been requested for the third quarter of 2005. Similar moves have been made
by other producers continuing to quote on a quarterly basis. Also in Australia,
TiWest saw a similar output to 2003 at around 80,000 t.
In South Africa, Richards Bay Minerals (RBM), owned by Rio Tinto and BHP
Billiton plc, is the world’s second-largest producer. In 2004, production difficulties
continued, a serious fire leading to a fall in output, to well under 240,000 t (2003
level).
Anglo American subsidiary, Namakwa, remains in third place with operations in
the Western Cape. A serious fire in the mineral separation plant in October 2003
halted production for three months and led to a fall in output of about 80,000 t in
2003, though some recovery occurred in 2004, bringing output close to 2002’s
level at 100,000 t. Also in South Africa, Ticor SA (Kumba Resources 60%, Ticor
40%) located close to Richards Bay in Kwa Zulu-Natal Province, maintained
output at 50,000 t, similar to2003.
In the US, Du Pont’s Florida plant maintained its 2003 output at around 70,000 t
in 2004.
All zircon markets continued to grow in 2004, with total demand approaching 1.2
Mt. Ceramics (mainly tile and sanitaryware) consumed 52% of total output of
zircon at around 600,000 t. In recent years, the ceramics market has shown
steady annual growth of over 5%, with China taking over 125,000 t and
producing around 36% of the world’s tiles. This has been fuelled by strong
building activity, growth in private home ownership and preparation for the 2008
Olympics. Much of the zircon shortage in Asia is centred on the ceramic tile
demand in China. To meet demand for zircon flour and opacifiers, Shenyang
Astron Mining Industry Ltd (Astron), based in Shenyang but Australian registered,
is increasing its zircon milling capacity by 12,000 t/y, with a new plant in
Shanghai due on stream in 2005. The Italian flour/opacifier-maker, Industrie
Bitossi SpA, part of Colorobbia Group, will also install a plant in Guangdong,
rising to 30,000 t/y. Ceramic tile output is also increasing in other southeast Asia
countries such as Thailand, Malaysia and Indonesia, and also in Eastern Europe,
Turkey and Iran. European ceramics markets remained static at around 270,000
t, with little or no growth, particularly in Italy.
Refractory requirements for zircon saw a dip, falling to 162,000 t in 2004 (2003:
180,000 t). European-based producers continued the trend to move production to
China. All refractory users, and particularly steel makers, have pressed for
increased performance and consequently there has been a continuing fall in
refractory consumption per tonne of product made. For example in China, the
steel industry has seen a fall from 55kg per tonne of steel output to around 20kg/t
in 2002. This increased performance has not been mirrored by increases in
refractory prices, leading to pressures to cut costs and a move to cheaper
manufacturing bases.
Foundry uses for zircon in investment casting (a method of precision-casting of
metals using moulds made from zircon) also remained similar to 2003 levels at
around 166,000 t. This was due to a slower aerospace industry market (turbine
blades). Sports goods, such as golf club production, remained buoyant. The use
of zircon to block X-ray emissions in cathode ray tubes (CRT) found in computers
and TV monitors also continued to rise slowly (94,000 t compared with 90,000 t
in 2003). The development of alternative electronic-display methods, for
example, liquid crystal displays/thin film transistors, may, in the longer term,
temper the growth of zircon usage in this industry.
In addition to the movement in the ceramics industry, the use of zircon in
zirconium chemicals and synthetic zirconia in China jumped significantly (65,000
t in 2004 compared with 45,000 t in 2003). In world terms, this lifted zircon usage
for zirconium metal, oxide and chemical manufacture to over 115,000 t (2003:
110,000 t). This market, like the ceramic opacifiers, needs good-quality zircon
containing low impurity levels. Premium grade is in very short supply and this has
added extra pressure, particularly in China, with some zirconium chemical
producers unable to find material and so chopping output.
Taking all the world markets together, Europe continued to absorb the largest
zircon share (2004: 405,000 t, similar to 2003), with China next at 248,000 t
(225,000 t). North America came next at 175,000 t (similar to 2003) and was
similar to other Asia-Pacific offtake. Japan saw an increase throughout the year
and is now around 63,000 t (55,000 t).
As can be seen from Figure 1, prices moved up with zircon opacifiers in China in
the US$1,200-US$1,600/t range ex plant, depending on sizing.
Figure 1: Zircon sand / flour / opacifier prices
Shipping Terms
Pricing
June 2004
Sand
FOB Australia
US$/t bulk
420-550
FOB South Africa
US$/t bulk
410-550
FOB US
US$/t bulk
400-530
Flour (95% below 45
micron)
US$/t bagged
800-940
FOB Europe
US$/t bagged
800-950
FOB Asia
Micronised (d50 5 micron)
FOB Europe
US$/t bagged
900-1,050
FOB Asia
US$/t bagged
900-1,100
May 2005
550-700
550-700
570-700
950-1,150
950-1,250
1,100-1,500
1,200-1,600
FOB = Free on Board
The prices given are the most up to date at the time of writing
The outlook is for continuing tightness in supply well into 2005and higher pricing,
although the rate of increase may slow. Demand is expected to peak at 1.2Mt in
2005-06 and, with new output starting to emerge in 2005, the year should see a
gradual easing to normality, provided that no other emergencies arise. The
Boxing Day tsunami also contributed to the shortness of zircon by halting the
planned resumption of operations by Lanka Mineral Sands Ltd (LMS). This could
release up to 70,000 t of zircon, which would cut the zircon shortfall considerably.
As all main producers are maximising output, new developments in Australia’s
Murray Basin and the Corridor sands project (CSP) in Mozambique, together with
prospects in Sri Lanka (LMS), India, Canada (Alberta) and the FSU, should
restore supply/demand balance in the next few years.
Baddeleyite
Throughout 2004 and into 2005, the long-established customers for South
African baddeleyite (zirconium ore) continued to reformulate their products using
synthetically-derived feedstock made from zircon sand, namely fused monoclinic
and stabilised zirconias. This trend began in the early 1990s with the closure of
Foskor’s mine and then became irreversible with the curtailment of operations at
PMC, together removing around 18,000-19,000 t/y of output. Markets in
refractory, ceramic, abrasive and other applications were forced to move to
alternative supplies.
Since the 1970s, baddeleyite output was centred on two operators based at
Phalaborwa in the Northern Province of South Africa. Palabora Mining Co (PMC),
a subsidiary of Rio Tinto plc, recovered zirconium ore containing 99% ZrO2+HfO2
as a by-product of its open-pit copper mine. The complex orebody produced a
diverse product mix including high-grade copper, magnetite, precious metal
slimes and naturally-occurring ZrO2, namely baddeleyite. As a result of the
geological changes found as the mine went deeper, and modifications to the
mine geometry, output of baddeleyite came to an end in 2001, with PMC
switching to an underground block-caving mining method. Production of
zirconium sulphate (also known as acid zirconium sulphate – AZST – or
orthosulphate) which was made from baddeleyite, rather than the normal and
now, universally used zircon sand, also came to an end as zirconium ore
feedstock disappeared.
This ended PMC’s position as market leader in zirconium ore and sulphate after
some 30 years. Maximum annual output was achieved by PMC in the late 1980s
when some 13,000 t of oxide and 3,000 t of sulphate were sold. Around this time,
PMC investigated the possibility of building a zirconium chemical plant in the US
but this was shelved when a domestic supplier expanded operations. Instead, a
novel design zirconium basic sulphate (ZBS) plant was completed in the early
1990s based at Phalaborwa (see under zirconium chemical section). This plant
was based on using zircon taken from PMC’s sister company Richards Bay
Minerals (RBM). After significant operational problems, including a serious fire,
PMC sold the plant to black empowerment group, Maxima Investment
Consolidation (Pty) Ltd in November 2004. After a period of closure, this plant is
again being offered for sale by Maxima.
PMC’s main competitor in baddeleyite was the South African state-owned
Phosphate Development Corp Ltd (Foskor). Foskor now has South Africa’s
Industrial Development Corp (IDC) as sole shareholder. Its output declined to
zero in the early 1990s after reaching a maximum yearly output of 6,000-7,000 t.
Unlike PMC, Foskor retained and developed its markets for zirconium ore by
purchasing a synthetic zirconia plant from Fukashina Steel of Japan. After initial
teething problems, this plant has grown and now manufactures monoclinic and
fused stabilised zirconias, and has an annual capacity in excess of 6,500 t. The
products are sold to refractory, abrasive and ceramic pigment markets.
The world’s only remaining commercial source of baddeleyite is in Russia, in the
southwestern part of the Kola Peninsula, close to the Finnish border and
alongside the Russian districts of Apatity, Kandalakha and Polyarnye Zory.
Kovdor town is the administrative centre of the area. This remotely situated mine,
operated by A O Kovdorsky Gok (Kovdor) and 95%-owned by Eurochem Mineral
Chemical Co (Eurochem) based in Moscow, recovers iron ore, apatite
concentrate and baddeleyite from a complex orebody. With a turnover in excess
of £140 million in 2004, Kovdor saw a growth of 8-9% over the previous year’s
results. Output comprised 5.3 Mt of iron ore concentrate, 1.83 Mt of apatite
concentrate (largely sold to other Eurochem enterprises as feedstock for the
manufacture of phosphorus) and some 8,300 t of baddeleyite concentrate. This
latter figure was some 50% higher that the previous year’s sales, a considerable
portion coming from stockpiles and previously worked material.
Currently, Kovdor produces around 6,500 t/y of baddeleyite and expects to
increase this to 8,000 t/y over the next few years. Kovdor’s main sales continue
to be directed towards the abrasive and refractory markets, particularly in the
East, and some 90% of production exported. In recent years Kovdor has also
been developing pigment grades of baddeleyite to replace PMC’s Zirconium Ore
Grade 5, which was used to make lower-cost blue/yellow ceramic colours.
Although synthetic zirconias are used in this market, the colour, shade and
strength found in PMC’s Zirconium Ore Grade 5 has been difficult to replicate
without using baddeleyite.
As well as increasing baddeleyite output, Eurochem also plans a number of
large-scale investments centred on ore-beneficiation, new mining equipment,
larger mining trucks and a major modernisation of the mill and concentrator. The
main aim is to lift mined volumes and reduce costs. It is expected that
baddeleyite and other product output will continue for a further 20-30 years. The
mine operates around the year despite the harsh winters, using feedstock from
the open pit and part-processed tailings. As further developments occur in ore
recovery, separation and purification, new products and applications may be
developed.
The Norwegian fusion plant Nako Narvik AS, built to take baddeleyite feedstock
from Kovdor, remains closed, despite attempts by the bank owners to find a
partner or buyer. It was thought that, with increasing zirconia prices and
developing shortages, the plant might re-open, either based on baddeleyite or
zircon-sand feed. However, as both of these feedstocks are in tight supply, this
seems unlikely.
Technical matters relating to the uranium and thorium content of baddeleyite and
synthetic zirconia (fused monoclinic and stabilised grades) continue to be
debated at specific radioactivity conferences and related mineral user-group
meetings. There is a continuing trend by the legislators to tighten up on
acceptable levels of U + Th contained in baddeleyite (and zircon sand) from a
production, shipment, bulk storage and end-use consideration. Specifically this is
controlled with regard to worker, environment/waste and transport regulations.
Work has been focused on the education of likely problem sites, with emphasis
on risk assessment. Varying levels of legislation around the world have been
subject to comparison and attempts are being made to harmonise the variations.
In general, synthetic zirconias are less radioactive than baddeleyite but this is
dependent on the zircon sand feedstock used.
Figure 2 outlines the market position for baddeleyite and synthetic zirconia,
including both fused monoclinic and stabilised zirconia.
Figure 2: Markets for baddeleyite / synthetic zirconia in 2004
Refractories
Ceramic
pigments
Abrasives
Electronics
Oxygen sensors
Glass/gemstone
s
Advanced
ceramics/catalys
t
Total
Baddeleyite
(t)
6,800
500
Synthetic
zirconia (t)
14,000
14,000
Total (t)
Growth
20,800
14,500
Increase
Increase
1,000
0
0
0
2,500
3,000
850
650
3,500
3,000
850
650
Level
Level
Level
Level
0
5,500
5,500
Increasing
8,300
40,500
48,800
Around 70% of refractories produced worldwide are used in the steel industry
(with cement, chemicals, ceramics, glass, others each 4-6%). Despite a
continuing rise in world steel output, the use of baddeleyite/synthetic zirconia
increased only marginally in 2004. This was due to the continuing reduction in
the rate of refractory consumption per tonne of steel output. Refractory
production continued to grow in China in line with the huge increase in steel
making. Western producers reinforced their position in the market by establishing
wholly-owned or joint-venture companies and transferred some manufacturing to
these plants. Similar moves are happening in the glass, ceramic and other
refractory fields. Ceramic and plastic colour pigment output increased further in
2004, with Asia, specifically China, showing gains. This demand is being fuelled
by China’s insatiable growth in ceramic tile output.
Alumina-zirconia (AZ) abrasives were manufactured first by Norton in the US. AZ
alloy can contain up to 40% zirconia and is made by fusing alumina, zircon and
baddeleyite/fused monoclinic zirconia in an electric arc furnace. These products
offer an exceptional cutting action and increased lifetime. These facts, together
with changes in the metal forming market (more precise, near net casting), have
led to almost zero growth.
Electro-ceramic markets utilising zirconia’s insulator or conductor properties,
continued to grow slowly in filter, buzzer, spark generator and other lead
zirconate titanate (PZT) applications.
In glass applications there have been new developments in frit and other surface
coatings. This has been offset by market saturation in the cubic zirconia field,
and some replacement by alumina, leading to little or no growth in this sector.
The varied uses of zirconia in the advanced ceramic, fuel cell and catalyst
(industrial and autocatalyst) areas continue to grow. Zirconia of much higher
purity (and price) can be made in partially (PSZ) or fully stabilised (FSZ) forms by
careful chemical processing under controlled conditions. These grades offer
novel mechanical and electrical properties.
The advanced ceramics field saw continuing interest in fuel cells and industrial/
automotive catalysts. Other applications using zirconia’s superior mechanical
properties continued to grow slowly – although volumes remain relatively small.
(See later in zirconium metal, oxide and chemicals section.)
Prices for baddeleyite and synthetic zirconia (see Figure 3) moved up in 2004,
reflecting increased prices for zircon sand, shipping rates, other raw materials,
fuel and Chinese export tax rebates. Additional zirconia output, particularly in
China (see later), led to more fierce competition, which tempered the increases,
and some grades were more affected than others.
Figure 3: Prices for fused monoclinic ZrO2 / stabilised ZrO2 and baddeleyite
US $ / t CIF Main Ports EC, US, Japan
June 2004
May 2005
Monoclinic zirconia
* Refractory / Abrasive 2,200 – 2,800
2,500 – 3,200
Grade
* Ceramic Pigment Grade
2,700 – 3,700
3,000 – 3,800
Structural / Electronic Grade 3,300 – 4,800
3,300 – 4,800
High
Purity
Advanced 15,000 – 25,000
15,000 – 25,000
Ceramic Grade
Stabilised Zirconias
Refractory Grade
3,400 – 4,200
3,300 – 4,800
High
Purity
Advanced 25,000 – 75,000
25,000 – 75,000
Ceramic Grade
* Baddeleyite price levels in the lower half
The prices given are the most up to date at the time of writing
Zirconium metal, oxide and chemicals
As the zircon feedstock shortages deepened throughout 2004 and into 2005,
some Chinese producers of various zirconium chemicals were forced to cut
production and this led to price increases over and above the increment caused
by the zircon-sand price hikes. Overall demand for metal, oxide and chemicals
continued to grow and key markets are given in figure 4.
Figure 4: Major zirconium and hafnium chemical production and application
Product
Abbreviation
Formula
World
Production
Capacity in
tonnes
Application
Zr silicate
ZrO2.SiO2
1,100,000
Zr oxychloride
ZOC
ZrOCl2.8H2O
80,000
Zr sulphate
ZOS
Zr(SO4)2.4H2O
10,000
Zr basic sulphate
ZBS
Zr5O8(SO4)2
H 2O
Zr basic carbonate
ZBC or BZC
ZrOCO3 x H2O
25,000
(NH4)3ZrOH(CO3)
15,000
Ammonium
carbonate
Zr acetate
Zr
AZC
x
25,000
32H2O
ZAC
H2ZrO2(C2H3O2)2
2,000
KFZ
K2ZrF6
1,000
ZrO2
45,000
Zr metal
Zr
10,000
Hf metal
Hf
N/A
Hf dichloride
Hf dibromide
Hf oxide
Hf carbide
Hf nitride
HfCl2
HfBr2
HfO2
HfC
HfN
N/A
N/A
N/A
N/A
N/A
Potassium
hexafluorozirconate
Zr oxide
Opacifier in ceramic tiles, sanitary
ware and table ware
Steel/glass refractories
Foundry/investment casting
TV/Computer glass
Production of Zr chemicals/oxides
Manufacture of Zr/Hf metal/
chemicals
Manufacture of other Zr chemicals
Titania coating
Antiperspirant
Oil field acidising agent
Manufacture of other Zr chemicals
Titania coating
Leather tanning reagent
Manufacture of other Zr chemicals
Titania coating
Leather tanning reagent
Manufacture of other Zr chemicals
Paint driers (siccatives)
Antiperspirant
Catalyst
Paper coating (insolubiliser)
Fungicidal treatment of textiles
Manufacture of other Zr chemicals
Water repellent in textiles/paper
Catalyst production
Grain refiner - Mg/Al alloys
Flame proofing of textiles
Refractories
Ceramic colours
Abrasives
Electronics
Oxygen sensors
Glass/gemstones
Catalyst
Advanced ceramics
See Fig 2&5
Chemical processing plant
Nuclear fuel rod/core components
Explosives
Alloys
Pyrotechnics
Military
Orthopaedics
Aerospace
alloys,
nuclear
refractories, control rods, cutting
tips, sputtering agent, plasma
coating, military
Catalyst
Special refractories
Optical coatings, electronics
Nuclear control rods
Cutting tools, coatings
N/A = information Not Available
Zirconium metal is an important refractory material and is used in alloyed and
unalloyed forms. Its outstanding metallurgical properties, such as resistance to
high temperatures and chemical attack, lead to its use in challenging engineering
applications such as chemical reactors with hot, corrosive environments. More
recently, zirconium has been used in professional flute manufacture due to its
ability to lift the musical quality. In 2001, Smith and Nephew introduced its
biocompatible zirconium alloy knee replacement to the world of orthopaedics,
with thousands now in use. The same alloy containing zirconium in an oxidised
form was applied to the bearing surface in artificial hip joints in 2003. This new
technology addresses two primary concerns surgeons have about hip implants:
wear and fracture. Both can lead to premature implant failure and additional
surgery. Future potential includes shoulder and hip fracture implants. Hafnium’s
ability to capture neutrons means that hafnium has to be removed where the
zirconium metal is used in nuclear applications eg, nuclear fuel rod claddings,
reactor cores and related engineering. With the slowdown in new nuclear reactor
installations worldwide, zirconium metal producers have concentrated on
developing new markets.
Zirconium oxide occurs naturally as the mineral baddeleyite but the majority of
the worlds’ supply is made synthetically by removing silica from zircon sand
(zirconium silicate) using a variety of techniques based on thermal dissociation
(where the resulting product is referred to as fused monoclinic zirconia) or
chemical splitting (resulting in zirconium being converted to chemical-grade
zirconia). Thermal dissociation techniques include electric arc fusion to dissociate
ZrO2 from SiO2 and plasma dissociation followed by leaching. Chemical splitting
can involve attack with carbon at 2,000°C or carbon/chlorine to make carbide
tetrachloride, and then hydrolysis/calcinations. An alternative chemical splitting
process involves reaction with alkali or alkali earth oxide (sodium
hydroxide/carbonate or lime) followed by hydrolysis/calcination/acid leaching.
Chemical-grade (monoclinic) zirconia are usually made by onward processing
and calcination of zirconium oxychloride (ZOC), basic carbonate (ZBC) or other
species.
Monoclinic zirconia undergo an 8% volume change when they are heated to
1,170°C, at which temperature the tetragonal form occurs. Continued heating
results in a further change to the cubic phase at 2,370°C. This catastrophic
volume change in the monoclinic/tetragonal transformation is avoided by the
addition of a cubic oxide (eg, MgO, CaO or Y2O3) to baddeleyite and fused
monoclinic zirconia during processing at high temperatures. This results in fused,
fully stabilised zirconia (FSZ) in the cubic phase, which is stable from room
temperature to its molten state. This material has a uniform thermal expansion
curve, hence rapid volume changes are eliminated, which means the ceramic
article being produced, eg, a refractory nozzle, does not crack or shatter on
cooling.
Similar cubic additions are used in chemical-grade zirconia, particularly yttria,
though these tend to be added during chemical processing to result in an
intimate contact of cubic oxide/zirconia. Where the stabilised oxide is present in
concentrations less than those required for complete stabilisation in the cubic
phase, then the resulting zirconia will be a combination of cubic and tetragonal
and/or monoclinic phases – so-called partially stabilised zirconia (PSZ). The
development of PSZ in the 1970s led to the start of the zirconia advanced
ceramics markets. It was realised that these new materials offered superior
mechanical properties to metals (stronger, better heat and wear resistance) and
had a novel electrical make up (conductor as well as insulator). This led to a wide
range of applications, which are shown in Figure 5.
Figure 5: Applications for zirconia in advanced ceramics
A. Utilising ZrO2’s superb mechanical properties
USE
APPLICATION
Structural ceramics
Various components, pumps, bearings, seals, valves, optical
fibre connectors.
Hip and knee replacement joints, dental ceramics.
Grinding medias, engine components, textile thread guides,
printer heads.
Extrusion of copper / wire.
Removal of impurities during casting.
Blades, scissors, cutting tools.
Plasma spray.
Zirconia single crystal in various colours.
Lenses, glass fibre, laboratory equipment.
Scratch resistant bracelets/faces.
Bioceramics
Low wear ceramics
Forming dies
Metal filtration
Cutting applications
Coatings
Gemstones
Glass
Jewellery/Watches
B. Utilising ZrO2’s interesting electrical properties
USE
Fuel Cells
Oxygen sensors
H2
from
electrolysis
MHD electrodes
APPLICATION
ZrO2 is used in solid oxide fuel cells as the electrolyte.
Oxygen concentrations affect yttria stabilised ZrO2
conductivity and this property can be used to control
emissions in auto engines, furnaces and gas boilers.
water This is the reverse of the fuel cell.
Magneto-hydrodynamic generators for current generation
where zirconium electrodes are used
Filters, transducers, Use in mobile phone filters, acceleration and underwater
resonators, other PZT detection sensors. Production of buzzers for clocks, timers,
uses
automobiles etc. Ultrasonic motors (utilising sound rather
than electrical power).
Catalysts
For industrial and automobile exhaust applications using
ceria-doped ZrO2.
The range of applications for zirconium chemicals, as seen in Figure 4, continues
to diversify with major uses in catalysts, chemical manufacturing, healthcare,
metals, as a paint drier (siccative), and in paper, textile and titania coatings. Key
items made are zirconium acetate (ZAC), zirconium basic carbonate (ZBC),
ammonium zirconium carbonate (AZC), zirconium oxychloride (ZOC), zirconium
acid sulphate (ZOS/ZST) and zirconium basic sulphate (ZBS). Over recent years,
China has added significant new capacity and remains the powerhouse of
zirconium chemical production, with a total annual capacity of over 100,000 t.
Smaller volumes emanate from India, South Africa, the UK and the US.
ZOC continues to be the basic building-block chemical used to make other
species, and Chinese capacity now exceeds 60,000 t. Several producers have
been unable to purchase enough zircon-sand feed to maintain output, and
production volumes have fallen in the latter half of 2004 and into 2005. In China,
zircon sand has been selling at prices up to US$1,000/t and this has led to big
increases in ZOC prices, almost double those of 1-2 years ago.
Since ZOC is used to make ZBS, ZBC and chemical grade zirconia, the price
increases have been pushed down the line, leading to large cost increases for
the various customers.
ZOC continues to replace ZOS/ZST in pigment (TiO2) coating due to its lower
cost and higher solubility, with the choice being dependent on the manufacturing
process and type of scrubber used in the acid treatment system. Antiperspirant
markets also moved ahead as personal hygiene sales grew in markets outside
the EC and the US. The use of ZOS/ZST in leather tanning saw little or no
growth possibly because of substitution by synthetics and low fashion interest.
ZBS continued to be used primarily as an intermediate for ZBC, AZC and other
products, with China again a major source. As noted, PMC sold its ZBS plant in
South Africa during 2004 to Maxima Investment. After consideration, this group
decided not to run the plant and has offered it for sale.
Major consumers of ZBC all pushed ahead. The use of ZBC in paint driers is
closely linked to catalytic action, the zirconium compound speeding up the
physical change from the liquid to the solid state (O2 is absorbed leading to
oxidative cross-linking). The catalyst industry uses ZBC as a precursor to other
zirconium compounds/special oxides.
AZC is mainly used in paper coating to improve print adhesion and in textiles to
fix antifungal species such as Cu, Cr or Hg to the cellulose fibre.
As mentioned, China continued to increase capacity in zirconium product output.
Shenyang Astron Mining Industry Ltd (Yingkou Astron Chemical Co Ltd) saw
further growth in fused and stabilised zirconium oxides (additional furnaces
installed in 2003 lifted annual capacity to 13,000 t) and chemicals (new ZOC
production being added during the second quarter of 2005). Although based in
Shenyang, Astron is an Australian public-listed company. Being a major importer
and user/seller of zircon sand into the Chinese market, Astron has also been
working to secure long-term supplies. In a joint venture with Carnegie Corp Ltd of
Australia, zircon concentrate from the old British Titan Products mineral sand
deposit in Gambia has been shipped to China for processing. Despite water
shortages in Gambia, which has hindered the operation of mining equipment, this
project continues to develop. Astron has also acquired 100% of Zirtanium Ltd,
which owns large zircon deposits in the Murray Basin in western Victoria. The
117 Mt Horsham deposit, discovered in the 1980s by CRA/Rio Tinto, but
relinquished by CRA owing to separation problems with the very fine grain size,
should yield 30,000 t/y of zircon, together with other titanium minerals, once
large-scale mining begins. Astron is also planning to enter the titania business by
processing feedstock from Zirtanium and other interests, and has been courting
London’s AIM (Alternative Investment Market) to raise funds.
Asia Zirconium Ltd (Jiangsu Xinxing Chemicals Group), one of the first Chinese
makers of zirconium chemicals in the 1970s, was successfully floated on the
Hong Kong Stock Exchange last year. With total annual capacity of 35,000 t ZOC
and 6,000 t ZBC, it is one of the largest manufacturers. Recent developments
include nanometric zirconium oxide and further plant expansions. There are now
a total of approximately 40 zirconium chemical plants in China although lack of
adequate zircon-sand feedstock has pushed some close to going out of
business.
Canadian-based rare-earth producer AMR continued to develop its Chinese and
Thailand plants in 2004, producing zirconium oxide and chemicals for the
catalyst, fuel cell and electronic markets. Sydney based rare-earth company
Lynas Corp, increased its shareholding in AMR to approximately 20%.
In Japan, four companies were involved in fused zirconia/chemical production:
Daiichi Kigenso Kagaku (DKK), Fukushima, Tosoh Corp and Sumitomo Osaka
Cement (SOC). DKK, has its headquarters in Osaka and a relatively new plant in
Gotsu on the northern coast of Honshu, well away from the earthquake zone. It
continued to developed its catalyst, fuel cell and advanced ceramic grades of
PSZ. In May 2005, DKK announced the building of a new plant devoted to
zirconia manufacture for SOFC (solid oxide fuel cells). This 16,500m2 plant will
be situated in Fukui Technoport in Fukui Prefecture on the Sea of Japan’s coast,
north of Nagoya, and also remote from the threat of earthquakes. Final annual
manufacturing capacity of 2500 t will be achieved within three years and involves
an investment of US$40 million. Products will include yttrium, scandium and
stabilised zirconias. The decision to expand further comes after DKK’s successful
float on the Tokyo Stock Exchange in December 2004.
In the US, Southern Ionics Inc (SII) further reinforced its position in the chemical,
catalyst and renal dialysis markets. In the latter market, SII is close to FDA
approval in the US for a new home dialysis kit to be made by Renal Solutions
Inc. This will reduce the need for regular hospital visits and also compete with
other systems used at home such as CAPD (Continuous Ambulatory Peritoneal
Dialysis). Eka (part of Akzo Group and Formerly Hopton Technical),
strengthened its paper coating markets and ATI Wah Chang based in Albany,
Oregon, pressed ahead in aerospace, chemical, automotive, nuclear and medical
applications for its range of speciality materials such as zirconium and hafnium
metal/alloys. Working with Smith and Nephew, a significant improvement in knee
and hip replacements has been made. MEI continued to refocus on advanced
technology markets.
In the UK, MEL (sister company to MEI US) moved further away from commodity
zirconium chemicals – concentrating on higher added value products such as
fuel cell and catalyst markets. UCM Group (formerly Universal Abrasives and
incorporating Unitec Ceramics UK and Universal America, US) has manufactured
electro-fused zirconia for over 30 years. It has consolidated production in the US,
having closed its UK site. Advanced ceramic grades of zirconia continue to be
made in Stafford, UK, with sales/marketing being split between the UK and US,
depending on the market.
In India, Bhalla Chemical continued to increase output, with the announcement of
a new plant in Rajastan. In Tamil Nadu, the 500 t/y zirconia and 250 t/y zirconium
sponge plant being developed by Nuclear Fuel Complex (NFC) of Hyderabad
moves closer to completion at Tuticoru. Ukraine-based Vilnihorsk State Mining
and Metallurgical Plant (VSMMP) began offering yttria-stabilised zirconia to
augment the zirconium oxide, zircon and related mineral range.
In Australia, Australian Fused Materials (AFM) once again sold all of its 4,500 t
output of fused zirconia in 2004, and continues to press for an additional furnace
to lift volumes. This expansion has been prevented thus far by shareholder
differences.
The largest zirconia producer is the French industrial giant, Saint Gobain, with
plants in Australia, the US, China and France. Total production capacity for
zirconium chemical and zirconia production is thought to be approximately
40,000 t/y, of which around one third is fused monoclinic and chemical-grade
zirconia.
In South Africa, Geratech Beneficiation Ltd continued to develop its factory in
Krugersdorp, which is only 20% utilised, by the addition of more zirconium
sulphate output. Geratech would like to process locally most of the South African
produced zircon sand now shipped to China for zirconium chemical production.
This goal for the country to convert its mineral output into high added value
products rather than selling the basic mineral has been raised several times
before in Australia and China. As ocean shipment becomes more costly due to
fuel increases, and more difficult due to security constraints, there is strong
pressure for this to happen. However, environmental costs play a key role in
zirconium chemical production and China still has the lowest cost per tonne in
this regard, although things are changing.
All producers of zirconium metal, oxides and chemicals have been affected by
the continuing shortage of zircon sand and resulting price increases. Over
100,000 t/y of zircon is consumed in making these products, some 10% of world
output. Security of supply is now paramount and large consumers such as Astron
have bought into the zircon-mining industry to ensure adequate feedstock and
also to develop business in the related titanium minerals field. With higher raw
material, fuel and freight costs, particularly in China, zircon metal, oxide and
chemicals are now considerably more expensive than in 2003.
Hafnium metal and chemicals
Hafnium is normally present at 1.5-3.0% by weight in zircon sand and
baddeleyite, and is removed when zirconium is used for nuclear applications. All
hafnium compounds derive from this difficult extraction process based on the
Kroll process. Hafnium is found in various alloyed and unalloyed forms such as
plate, strip, sheet, rod, wire and tube – similar to zirconium metal. It is also
converted into the oxide and other reactive chemical species (see Figure 4).
Hafnium’s strong ability to absorb neutrons led to its use in controlling nuclear
reactors. Rods containing hafnium are raised or lowered to regulate the nuclear
reaction. Hafnium metal finds extensive use in aerospace alloys, in medical and
other special products.
Hafnium metal and compounds are produced in the US (Westinghouse Electric
Co, ATI Wah Chang), in Europe (Cezus, France) and in Russia, China and
Ukraine. Additional nuclear-related material is no doubt produced clandestinely.
World output of hafnium compounds is similar to 2003 but the higher zircon
feedstock cost has led to increased pricing.