Sillimanite supply surge

Some good news in the mineral sector at last. It would appear that prospects are promising for the sillimanite group minerals and alusite, kyanite, sillimanite, and mullite whose key market is refractories, followed by casting, abrasives, and ceramics (see panel for definitions p.35).

At the expense of bauxite, and with the refractories market showing some signs of initial recovery, those active in the supply of sillimanite minerals might be forgiven for some cautious optimism not long after the dark days of 2009.

Indeed, if truth be told, sillimanite mineral suppliers were already “on the case” as it were in 2008 with Imerys unveiling its €30m. investment in new and expanded aluminosilicate refractory raw materials supply, and the much awaited Peruvian andalusite source beginning (at last) to show serious signs of coming to fruition.

However, the rapidly unfolding financial debacle of late 2008-2009 squandered any hope of anticipated market demand for 2009, and unsurprisingly, some plans were placed on hold.

But it was hoped to be only a temporary setback. Come the latter months of 2009, as the steel market, and China especially, started to recover, optimism returned with the same signs of anticipated buoyancy in the market. This trend has reassured and strengthened continued plans for increasing production capacity for sillimanite minerals supply.

Andalusite dawn: South African andalusite
output is set to rise significantly by 2014.
Courtesy Andalusite Resources (Pty) Ltd


Supply overview

The global sillimanite minerals supply market is a relatively limited one, owing to avery few deposits being commercially developed (see map p.29).

The natural sillimanite mineral supply sector is restricted in the main to just two primary geographic sources of andalusite (France and South Africa) and one primary source of kyanite (the USA).

On a smaller scale, kyanite is produced in India (five mines), Ukraine (one miner, one processor), captively in Brazil by a refractories producer, and produced intermittently as a by-product of mineral sands mining in Australia.

Sillimanite is rarely produced in any large volumes and production appears restricted to India (four mines) and China.

Data on Chinese sillimanite group production is sparse. Aside from the established Yilong, Xinjiang andalusite mine, kyanite and sillimanite supply is certainly small scale: in 2003 China operated three mines producing 28,000 tonnes kyanite and 19 mines producing 36,000 tonnes sillimanite.

From a corporate viewpoint, of significance is the ownership by Imerys, France, through subsidiaries, of the dominant andalusite producing mines in France, South Africa, and China.

However, in recent years, Andalusite Resources (Pty) Ltd, South Africa, has emerged as the one independent andalusite supplier to Imerys. Towards the end of 2009, a second independent emerged in the form of Andalucita SA, of Peru.

In Ukraine, Ukraine Minerals Ltd intends to increase kyanite processing and develop a new kyanite deposit and plant.

With regard to synthetic mullite production, this is concentrated in the USA, Brazil, Europe, China, India, and Japan. With the exception of C-E Minerals, USA, and a few Chinese producers, most sintered production units are <20,000 tpa, while fused mullite units are <10,000 tpa.

Again, it is worth noting that significant mullite production capacity comes under Imerys in the USA, Germany, and Brazil (see producer tables for summary of main sillimanite mineral producers p.42-43).

Andalusite Resources’ Maroeloesfontein mine and plant, Thabazimbi, Limpopo
province, South Africa; very close to Samrec's Rhino mine. Production capacity
at 50,000 tpa has been a limiting factor, and has prompted expansion plans
for 2012. Courtesy Andalusite Resources (Pty) Ltd.


Supply highlights

Andalucita

For many years, the andalusite within unconsolidated sands and gravels of the Tablazo Mancora flood plain of northern Peru, and the as yet unproven resource of in situ andalusite in nearby shales and schists, has been under evaluation.

In 2006, Andalucita SA, owned by Refractarios Peruanos SA, was formed to develop the 10m. tonne 58-60% Al₂O₃ alluvial andalusite deposit 20km south of the port of Paita, north-west Peru.

After a series of studies, September 2009 saw production start for an initial operating phase of 30,000 tpa, with, at that time, eventual production for export planned for 60,000 tpa.

In January 2010, plans were revised slightly. Carlos De Ferrari, managing director at Andalucita told IM: “This new state-of-the art andalusite operation in Peru is presently scheduled to reach its initial first phase full capacity production level of 40,000 tpa by mid-year 2010.”

The primary andalusite grade being produced and intended for shipment contains a minimum of 58 % Al₂O₃ and a maximum of 0.8 % Fe₂O₃.

“Works trial production samples are now being distributed to key world refractory markets. Markets presently placing initial orders for Paita andalusite involve refractory consumers in Europe, Asia, and North America.” said de Ferrari.

In September 2009, Andalusite Resources (Pty) Ltd, announced plans to increase its andalusite production from 50,000 tpa up to 100,000 tpa by 2012.

Andalusite Resources’ Maroeloesfontein mine, Thabazimbi, Limpopo province, is about 220km north-west of Johannesburg. “We are mining the same strike line as Rhino Minerals [Samrec’s Thabazimbi mine]. We are mining the southern tail end of this ore body.” said Andreas Pabst, sales and marketing director Andalusite Resources.

Andalusite Resources’ main markets are in Europe, South Africa, China, and India.Ê “We also sell into Russia, Japan, Korea, Taiwan and other countries in Asia and the Middle East, but our production capacity so far has been the main limiting factor when selling into these territories.” Pabst told IM.

The company is producing at almost its full capacity of 50,000 tpa, and at this rate the mine life is about 20 years.

Andalusite Resources’ has licenses to mine all the farms north of its site up to the Rhino mine (except for one farm). The immediate extension which borders onto Maroeloesfontein has already been found to add at least another 25 years of life to the mine (at 50,000 tpa).

At the end of 2009, the company completed its latest drilling programme, which encompassed the remaining six farms between Maroeloesfontein’s northern extension and Samrec’s concessions to the north. “We have found bigger reserves there than expected; which will add an additional 25 years of life. So in total, Maroeloesfontein has reserves to last at least 70 years at 50,000 tpa.” said Pabst.

Given the proven large reserves, Andalusite Resources has decided to aim for a production expansion in the region of 80,000-100,000 tpa by the end of 2012.

Imerys

Imerys, the Paris based world leader in industrial minerals, over the years has steadily built up its portfolio of impressive aluminosilicate producing subsidiaries, and has made no secret of its expansion plans.

In October 2008, in response to customer demand and as a strategic move for the future, Imerys launched a €30m. investment programme to secure near and medium term supply of aluminosilicate minerals primarily for the refractories market.

The programme included: adding a new 70,000 tpa sintered mullite rotary kiln to C-E Minerals’ plant at Andersonville, Georgia in February 2009; debottlenecking at Samrec’s Krugerspost and Thabazimbi andalusite mines in South Africa, adding 30,000 tpa; ongoing work to start a new andalusite mine at Segorong; adding 25,000 tpa capacity to the existing 15,000 tpa capacity at Imerys Yilong Andalusite Mineral Co., Xinjiang province (Imerys acquired a 65% stake in 2007); and a new 20,000 tpa white fused alumina furnace at Treibacher Schleifmittel Zschornewitz GmbH.

At that time, the management of Minerals for Refractories, Imerys, told IM: “We are very bullish about mid-term prospects [for aluminosilicates].”

Some 15 months on, despite the recession slowing things somewhat, Imerys is still on course to bring these developments to fruition.

Talking to IM in January 2010, Damien Chauveinc, general manager Imerys Andalusite Business Unit, said: “Our debottlenecking investments at Thabazimbi and Krugerpost are now nearly completed and will be fully commissioned during Q1 2010. Our Capex in China at Yilong in Xinjiang was commissioned late 2009 and is ready to start up after the winter break. As for the so called Segorong project, involving village relocation and opening up of a new mine, we are still in line with the plan announced at that time, and start building up the new village beginning of 2010.”

The Segorong project has clearly taken more time than Imerys initially expected, with inhabitants of Segorong village proposed to be relocated at a new village at Praktiseer, a few kilometres distant. Imerys secured final approval from the South African government for this development in July 2009.

The new Segorong mine, expected to produce 85,000 tpa by 2014, is to be located between Samrec’s existing Havercroft and Annesley mines, and will apparently extend reserves currently exploited by these mines by 15 years.

Andalucita SA’s new operation near Paita, Peru
is scheduled to reach its initial first phase full
capacity production level of 40,000 tpa by mid-year
2010. Courtesy Andalucita SA.


Kyanite Mining Corp.

The world’s unsurpassed leader in kyanite production and development is Kyanite Mining Corp. (KMC) which has been exploiting the kyanite deposits in central Virginia, USA, since 1945. The company produces both kyanite and mullite.

KMC’s operations are concentrated around Dillwyn, Virginia and produce one kyanite grade, Virginia Kyanite ranging between 55-60% Al₂O₃, and a second product, Virginia Mullite, which KMC describes as “a true mullite, and not a synthetic blend”.

Variations of the two products are limited to their particle sizes offered, which are mesh sizes 35, 48, 100, 200, 325, and micronised kyanite and mullite with a d₅₀ value of around 4.7 microns.

Hank Jamerson, vice president, director of sales and marketing, KMC, told IM: “The key markets for KMC are refractories for steel production, investment casting flours and grains, kiln furniture, ceramic parts, and metal foundries. We also participate in the brake shoe/abrasive market, electrical insulating porcelains and the sanitaryware/whiteware markets.”

Although KMC is confident of its kyanite reserve base, the company continues to actively invest in the exploration of suitable deposits around the world.

“Given the current consumption levels for kyanite, we conservatively feel that the reserves from Willis Mt. and East Ridge will last for 50-75 years, which does not include our reserves in Canada.” Jamerson commented.

That said, KMC is still keen to boost production capacity at Dillwyn. KMC used the slowdown in the market during 2009 to completely re-engineer and replace the critical iron reduction stage of its beneficiation process.

“This significant plant renovation will allow us to produce a higher quality kyanite through significant removal of the current existing iron in our product while also increasing our recovery of kyanite.” said Jamerson.

KMC is hopeful that these upgrades and re-designs will permit an increase in production capacities at this stage of the process.

KMC has also completed its automated processing and bagging facility, which included construction of additional warehouses that allows KMC to have >5,000 s.tons of “certified and pre-qualified” material bagged in inventory which is available to be shipped at a moment’s notice.

Togni SA

Brazilian refractories producer Togni S/A Materiais Refratarios, which celebrates its centenary in 2010, mines kyanite for captive use and produces sintered mullite based on Brazilian gibbsitic clays containing 72% Al₂O₃ at its plant in Sacramento, Minas Gerais.

Togni also produces 15,000 tpa chamotte (45-60% Al₂O₃) at its Plant 1 at Pocos de Caldas, Minas Gerais, where a wide range of refractories are produced. By mid-2011 Togni expects to expand this plant to 120,000 tpa. The expansion will include a new milling facility, a mixing facility for unshaped products,ÊaÊline ofÊeightÊautomaticÊhydraulic presses and a tunnel kiln for high temperature operation.Ê

The company is augmenting its aluminosilicate portfolio by expanding its Plant 2 in Pocos de Caldas, Minas Gerais. The plant currently comprises two kilns for dead burned magnesia production, and Togni has bought a new rotary kiln for the production of 45-60% Al₂O₃ chamotte to be in operation by mid-2011.

“The total production capacity of raw materials [at Plant 2] will be in the range of 40,000 tpa. This facility is also equipped with a milling plant and a concentration plant for kyanite.” said Livio Togni, operation vice president, at Togni.

Regarding markets, Togni told IM: “As with other refractories producers, iron and steel is the most important market to our company (45%), but we also supply to non-ferrousÊmetalsÊ(15%), cement, lime and non-metallic mineralsÊ(15%), glass (10%), petrochemical, ceramics, and others (15%).

Ukraine Minerals

Ukraine Minerals Ltd (Umin) was formed in 2008, and owns several mineral processing plants in Ukraine, and exports worldwide. Umin’s key minerals processed include kyanite, and also kaolin, ilmenite, rutile, zircon, staurolite, foundry and glass sands, and aggregates.

Based in Dnepropetrovsk, Umin operates a processing plant in Volnogorsk (Ukraine trans. = Vilnohirsk), which it acquired from mineral sands producer Vilnohirsk Mining & Metallurgical Plant (VMMP), itself once state owned, but owned by Ukrainian titanium dioxide producer (80,000 tpa) CJSC Crimea Titan since November 2004.

Umin was effectively born out of DVS Co. Ltd, a trading company founded in May 1994, specialising in Ukrainian minerals and chemicals, and distributing VMMP products.

VMMP operates a huge open pit mine complex producing ilmenite, rutile, zircon, staurolite, and kyanite (in the past, latter was <20,000 tpa). Umin has a license to process certain VMMP tailings resources as well as some new deposits yet to be developed by Umin as mining operations. The Volnogorsk deposit is claimed to host 2m. tonnes of aluminosilicates.

Umin processes 25,000 tpa aluminosilicate minerals, including kyanite, and 25,000 tpa titanium-zircon minerals. The natural grain size of the products is about 140-200 microns, and it is milled up to 45-60 microns.

Umin’s kyanite-sillimanite has found application in the production of high-alumina refractories and in non-stick coatings in the foundry industry. Key markets are in Ukraine, Russia, Belorussia, Turkey, Italy, Germany, India, and Iran.

Umin is also looking to expand its kyanite production. “In the near future, in Prosyana [site of Umin’s kaolin mine and plant], we plan to quarry another deposit that contains kyanite.” Denis Prohorov, export manager, Umin Ltd told IM.

Umin also plans to increase mineral production by 300% through expanding its processing plant in Volnogorsk.

Prospects elsewhere

In China, there were unconfirmed reports that Hainan Chansheng Mineral Industry Co. Ltd was investing $146m. into developing a possible 200,000 tpa andalusite and sericite resource near Danzhou city, Hainan island, south China.

The company plans to construct an initial 20,000 tpa processing facility near the 6.38m. tonne deposit, before implementing further expansion to the reach 200,000 tpa at a later date.

In Russia, Moscow-based miner, Kianit LLC, a subsidiary of JSC Granit, has announced plans to mine 100,000 tpa kyanite ore from the Khysovaarskoe deposit in the Republic of Karelia, north-west Russia.

The company intends to construct a mill, in addition to an open pit kyanite mine, with processing capacity to produce 20,000 tpa kyanite concentrate. Mining is expected to start in 2011, with metallurgical tests of bulk samples currently in process.

Market outlook

Refractory markets, especially steel refractories, consume the vast majority of sillimanite minerals, although they are also used in casting, abrasive, and ceramic applications.

Consumption of sillimanite minerals generally reflects the geographic distribution of mineral sources. For example, consumption of andalusite is relatively low in the USA, around 15,000 tpa, compared to Europe’s approximate 150,000 tpa. This is mainly owing to the distance the North American markets are from established andalusite sources, creating high freight costs, and thus encouraging US refractory formulations to use alternative aluminosilicates such as bauxites, mullite, and kyanite.

Towards the end of 2009, refractory mineral markets were showing some signs of recovery, with traders and consumers reporting healthy signs of some returning demand.

The World Steel Association reported that global steel production grew to 107.5m. tonnes in November 2009, representing the third consecutive year-on-year growth since September 2009, and a 24.2% rise on November 2008 levels.

Perhaps not surprisingly, China led the way with a steel output of 47.3m. tonnes in November a 37.4% growth on November 2008 figures, and almost half of total world production.

Across the board production rises were seen throughout Asia, Europe and North America, with the most promising increases coming from Russia (up 42.6% year on year), Ukraine (up 67.1%), and the USA (up 26.9%).

Meanwhile, total crude steel production for the first 11 months of 2009 was 1,090m. tonnes; almost 11% lower than steel production during the same period last year.

In India, CUMI , which is mostly a captive producer of fused mullite, reported that its Q2 2009 (to 30 September 2009) fused minerals business continued with strong performance, with a 11% growth in sales over Q2 of 2008 (to Rs.400m.($8.7m.)). CUMI has expanded markets for its mullite in glass and carbon black refractory applications.

Most sillimanite producers would have experienced a tough 2009, and many will hope that 2010 will provide some welcome relief.

Denis Prohorov, export manager, Umin Ltd, told IM: “The market situation of the refractory industry in 2009 was not good. The downturn started in the first quarter of 2009, and only in September-October 2009 did we see some positive trends in that industry. Production capacities of refractory plants in Ukraine and Russia were functioning only at 40% of their capacity.”

Andreas Pabst, director, Andalusite Resources, echoed the trials of 2009: “Last year was obviously a tough trial for Andalusite Resources. Many of our traditional markets contracted sharply, whilst India and China performed much better overall and thus really proved their value to us. Very recently, we have seen a solid resurgence of demand across the board, from our long-standing customers as well as new ones whom we have not supplied recently (or only with limited volumes).”

Certainly, owing the range of activity in production expansions and upgrades reported earlier in the article, it seems that recovery is anticipated, although caution is still the watchword.

Damien Chauveinc, general manager Imerys Andalusite Business Unit, commented: “As far as 2010 market trends are concerned, we have been experiencing a pick-up in demand for a few months, since November, but it’s far too early to be able to give any forecasts.”

Phlippe Bourg, sales & marketing manager - Minerals for Refractories Division at Imerys, added: “The situation both on the end users demand side, mainly steel producers, and Chinese supplies, mainly bauxite, needs to be clarified first.”

Regarding kyanite, there are some new market directions, as Hank Jamerson, vice president, director of sales and marketing, KMC, explained: “We are currently experiencing success in new markets such as ceramic foam filters for metal production, and refractories for aluminium production. In general, the performance of our key markets is weaker than it was 18 months ago, but much more lively than it was 8-12 months ago. We look to the near term future with cautious optimism.”

The bauxite question

Perhaps the greatest talking point surrounding the outlook for sillimanite minerals is whether they can make any inroads into markets supplied by bauxite. This topic, while a traditional talking point, has been increasingly in discussion over the last two years, and is now generating even more interest.

The key driver for this has been the steady decline of cheap and readily available refractory bauxite from China. Indeed, many refractory manufacturers had actually used sillimanite minerals before being wooed to cheap Chinese bauxite exports from the 1980s. They were further lured to China by intermittent supply of RASC bauxite from Guyana and limited, specific grade bauxite production from Par‡, Brazil, which eventually halted in December 2003.

Since then the tables have turned, with Chinese government policies reducing bauxite (and other mineral) exports, increased demand for bauxite within China, and Bosai Minerals Group, of Chongqing, China acquiring the RASC Guyana operations.

Matters have been compounded with government restrictions and closures in bauxite mining in Shanxi, and closures of shaft and round kilns, owing to environmental and safety controls.

Pre-recession, this created tight availability of refractory bauxite worldwide with a consequent rise in its price. Then the recession provided somewhat of a breathing spot, as global consumers cleared their inventories and battened down the hatches to ride out the crisis.

With market recovery underway, and, critically, no change in China’s position on bauxite exports nor domestic bauxite mining (the former likely to remain unchanged, the latter might possibly change in H2 2010), a return to tight supply and high prices is anticipated.

Jack Gao, general manager of mineral processor and exporter Refmin China Co. Ltd told IM: “The alternative material for bauxite we are now selling is low grade bauxite with 75-84% Al₂O₃, plus mullite, Alpha Star bauxite [a calcined high alumina aggregate produced in Xiuwen, Guizhou, by Guizhou Star Minerals, a C-E Minerals j-v], and brick grog. Shanxi material is quite short and a new source is Guizhou, where some refractory grade is now coming out. Supply [of refractory grade] is very short due to strong demand at the end of 2009, and it is very difficult to get 85-89% Al₂O₃ bauxite, and also the price keeps increasing.”

Owing to this situation, consumers are researching the economic and technical suitability of using andalusite. This has very much helped to oil the wheels of the expansion plans of Imerys and Andalusite Resources, but has also prompted Andalucita to emerge as a new player in Peru.

Traditionally, andalusite has not competed directly with bauxite in refractories. Indeed, it is not always a straightforward substitution of sillimanite minerals for bauxite. For certain applications it is possible, but not for others.

In his paper “Andalusite in Peru, South America”, presented at UNITECR’09 last October, Bill McCracken discussed that certain performance factors of andalusite (eg. high degree of mullitisation at 1,400¼C, high thermal conductivity, small expansion coefficient, low porosity, and increased spalling resistance) could be favourably compared to 85-90% Al₂O₃ refractories, and not directly compared favourably nor equivalent to other 60% Al₂O₃ mullitised refractory materials.

However, McCracken noted that: “The iron content in refractory grade andalusite is a major negative factor, with global usage specifications calling for less than 1%.”

The bottomline appears to be that alumina content is not everything, with sillimanite minerals offering key properties, and the outcome against bauxite coming down to price versus performance (see panel left) as outlined by Bernd Durstberger, former Head of Minerals for Refractories Division, Imerys, in his presentation “Alternative solutions to non-metallurgical metallurgical bauxite and alumina in a tight supply scenario”, at the 15^th International Bauxite & Alumina Seminar, 11-13 February 2009 .

Durstberger was of the opinion that the price/performance ratio in many refractory applications is favorable for mullite/chamotte versus Chinese bauxite. Significantly, influencing risk factors for continued bauxite reliance by consumers include currency fluctuations, freight market developments, and most crucially, the unpredictability of Chinese bauxite supply (exports and actual mining).

Durstberger considered that there is taking place a revision of previous “overshooting” by refractory manufacturers, ie. where they “overshot” their initial replacement of aluminosilicates with Chinese bauxite, especially in lower temperature uses.

The upshot is that low-temperature applications are leaning to chamotte/flint clay usage and high temperature applications to mullite/andalusite usage. There is also a trend in blending in of lower alumina raw materials.

Talking to IM in January 2010, Damien Chauveinc, general manager Imerys Andalusite Business Unit confirmed: “We still believe our capacity expansions make sense in light of our assessment of the demand trends for our minerals in refractories and of the development of Chinese bauxite pricing and availability.”

Some sillimanite mineral producers are already reaping the benefits of consumers looking to alternative aluminosilicate sources.

KMC has enjoyed raw material substitutions of its Virginia Kyanite in place of bauxite fines, andalusite fines, calcined alumina, and fumed silica. “The utilisation of Virginia Kyanite as a substitute for the [previously mentioned] raw materials has been driven by a number of factors such stable/reasonable pricing, consistent/repeatable quality, as well as the fact that Virginia Kyanite has always been readily available while other materials were in limited supply.” said Jamerson.

Clearly, there is potential for sillimanite minerals like andalusite and kyanite to benefit from refractory bauxite’s predicament. But it still requires a bit of a leap on the part of the consumers, many of which remain to be “converted”.

Andreas Pabst, Andalusite Resources, observed: “With regard to bauxite, I truly believe that andalusite’s potential to act as substitute or added product, is not fully grasped yet by the industry.”

Pabst makes the point that the larger refractory groups, such as RHI and Vesuvius, which enjoy well funded research and development programmes, are very much clued up about what andalusite can and cannot do in refractory applications. However, many of the mid-sized and smaller refractory companies are not yet fully in this position.

“We often encounter real reluctance of technological departments to change their approach. They stick to what they know and that is it. However, if one looks at the price development of andalusite versus bauxite for instance, it needs to be noted that bauxite has more than quadrupled in price over the last 5-6 years, while andalusite’s price levels have only increased by about 20-30% over the same time period.” said Pabst

It appears that although there is much interest in andalusite’s potential as a refractory raw material, particularly with regard to the bauxite supply situation, only a few consumers seem willing to test to the water.

For its part, Andalusite Resources, in co-operation with its chief marketing agent Cofermin Rohstoffe GmbH is looking into commissioning more research into the technical aspects of andalusite replacing bauxite, and thus expanding its market share.

Pabst concluded: “This expansion [at Maroeloesfontein] will depend very much on the market situation of steel, ceramics, refractories, and bauxite; but from our point of view we believe strongly in the long term growth and viability of the andalusite market.”

Indeed, another keen observer of the market is emerging new producer Andalucita SA of Peru. Carlos De Ferrari, Andalucita SA, recognises the interest in andalusite from the refractories market and is hopeful. “On a steel production comparative basis, the western hemisphere consumes roughly 20% of the andalusite refractories used in Europe. Based on the above, the western hemisphere industrial world could be consuming at minimumÊ100,000 tpa of Peruvian quality andalusite.”

For Brazilian refractories producer Togni SA, the bauxite issue has played an important role in its development. “It forced us to find viable alternatives; we can now produce synthetic bauxite in our Plant 3 with a Brazilian source of raw materials without depending on imports anymore, especially with the monopoly that is being created by the Chinese suppliers. For synthetic bauxite, we use some synthetic additions, decreasing the amount of iron oxide to 0.8% and the alkalis to very low amounts, with improved physical properties, giving us a much better product compared to natural calcined bauxite.” said Livio Togni, operation vice president, Togni.

Togni also underlined that Brazil is a very rich country regarding aluminosilicate minerals “which gives us some good possibilities to supply refractories production.”

Certain high grade sillimanites remain largely unaffected by the bauxite debate. Sintered and fused mullites made from higher purity raw materials mean predominately higher application temperatures and longer life cycles of refractories ie. very specific niche market applications.

Jan Kupfer, director Business Division Technical Ceramics, Nabaltec AG, told IM: “That’s basically the reason why Nabaltec expects a further increase in demand and consumption for its synthetic sintered mullites in the future.”

Nabaltec’s Symulox^® products find application mainly in high alumina refractory products, typically in steel and glass manufacture, incinerator linings, and kiln furniture production. “Due to their high purity, M72 and Z72 products are used rather in high performance refractories, than as a substitute for refractory bauxite. Nabaltec does not expect any significant impact from the shortage of these minerals on its own business.” said Kupfer.

In conclusion, with the future of Chinese bauxite supply very much in doubt, and already emerging trends of increasing sillimanite mineral use in certain refractory applications, it would appear that there are good prospects for market penetration for these minerals.

The next bridge to cross, given market recovery continues, will be to reassure consumers of a quality consistent, stable supply of high quality sillimanite minerals at attractive prices. (see p42-43 for producer tables).

World production of andalusite, kyanite, sillimanite & mullite (tonnes)

A: andalusite

K: kyanite

M: mullite, ie. synthetic: fused & sintered

S: sillimanite

cap. estimated production capacity where production unknown

Note: figures are in tonnes, and refer to most recent production estimates, usually 2008; planned production for 2010 only indicated, see producers’ table for post-2010 plans

Sillimanite minerals in brief

Andalusite, kyanite, sillimanite, and mullite are all aluminium silicate, or aluminosilicate minerals, typically occuring in metamorphic rocks such as gneiss or schist, and their weathered derivatives, including some mineral sand deposits.

They are also referred to as the sillimanite group of minerals, since supply was originally dominated by Indian sillimanite output. In the USA, owing to kyanite’s predominance, the group is referred to as kyanite and related minerals.

Their commercial development is limited to just a few producers worldwide (see map and producer table).

In the case of mullite, natural occurrences are uneconomic to mine and thus all commercially produced mullite is synthetic, ie. produced from natural minerals by calcination and fusion (see ‘Mullite matters’ panel).

With the exception of mullite, these minerals are mined using open pit methods. Drilling and blasting for hard rock deposits, followed by primary and secondary crushing, high intensity dry or wet magnetic separation, sometimes heavy media separation, possibly flotation and gravity separation, and acid leaching for concentrate upgrades.

Kyanite and sillimanite are also produced as by-products from mining of certain mineral sands.

When these minerals are subject to high temperatures they undergo mullitisation, a chemical reaction of their consituents to form a mullite phase. The mullite imparts superior refractory properties and high strength. Thus, the main market applications for these mineral are in refractories, ceramics, abrasives, and foundries.

Mullite matters

Mullite is rare in nature, and is named from one locality on the Isle of Mull, Scotland, where argillaceous sediments have been fused by igneous intrusion.

Mullite, 3Al₂O₃-2SiO₂, is a mineral phase much sought after as a major constituent of refractory and ceramic products owing to its extremely high refractoriness and strength (the latter owing to the interlocking of its needle-like crystals). Mullite is very refractory, breaking up into corundum and liquid silica at 1,810ºC.

Since mullite does not naturally occur in deposits of commercial value, the mineral is produced synthetically by either sintering or fusing carefully selected aluminosilicate raw materials.

Sintered mullite maybe produced by calcining kyanite (as produced by KMC), calcining a bauxitic kaolin (as produced by C-E Minerals), or by calcining carefully selected blends of alumina, kaolin, and bauxite (as in China).

Commercial sintered mullite grades have alumina contents in the 45-50%, 60%, and 70+% Al₂O₃ categories. Other important properties are low iron (<1% Fe₂O₃) and low cristobalite, and of course, the all important mullite phase, which can range from 65-90%.

Fused mullite grades, which include so-called white fused mullite grades, can be produced from fusing Bayer process alumina and high purity silica (eg. Washington Mills), or by fusing certain blends of bauxite, aluminas, and refractory kaolins (eg. in China).

There are a range of commercial grades of sintered and fused mullite on offer. A typical analysis would be: 71.7-76.2% Al₂O₃, 23.0-23.6% SiO₂, 0.11-3.0%, TiO₂, 0.13-1.17% Fe₂O₃, 0.04-0.06% CaO, 0.05-0.06% MgO, 0.05-0.44% alkalies.

Mullite has a melting point of 1,810¡C, softens at 1,650ºC, and has a specific gravity of 3.156.

Fused zirconia mullite, with a melting point of 1,750¡C and specific gravity of 3.5-3.6 is produced by fusing calcined alumina and zircon sand. During melting, the zircon and alumina react to yield a mixture of mullite and zirconia.

Fused zirconia mullite is composed of large, needle-like mullite crystals, containing co-precipitated monoclinic zirconia. Average crystal width is 100 microns, with an average length of 10,000 microns. Traces of dendritic, monoclinic zirconia and about 5% glass is present in the interstices between the mullite crystals.

Sillimanite minerals in refractories

Key Properties

Refractoriness
Thermal stability Flow resistance
Shock resistance
Abrasion resistance
Hot load and hot strength
Porosity
Alkali content

Market penetration

Mullite
Mullite 47 (M47) in blast furnace tap-hole clays
Chamotte/M47 and Mullite 60 (M60) in tundish backup linings
M60 and Mullite 70 (M70) used in steel lances
M60 and M70 in electric arc furnace delta sections
M60 and M70 in slide gate formulations
M60 in construction grade plastics
M47-70 used to replace fine grain calcined bauxite in mortars, plaster, and plastics
M60 in iron runners
M60 grain of choice in torpedo ladle applications
M70 and M60 in various pressed brick shapes.

Andalusite
in steel ladles
in hot stove bricks
in bricks for cement rotary kilns
Andalusite-SiC in iron ladles

Aluminosilicate raw materials in refractories

Price comparisons

Major natural sillimanite mineral producers*

Major mullite producers (fused & sintered)