Flame tamers: Brucite, huntite and hydromagnesite

By IM Staff
Published: Friday, 08 September 2017

Magnesium minerals boast several unique properties which make them superlative flame retardants, but as Ian Wilson, Consultant*, explains, despite their wide application many of these minerals are only recovered in a handful of places across the world.

Economic deposits of the natural magnesium minerals brucite, huntite and hydromagnesite are found in only a few places in the world and are extracted mainly for use as flame retardants.  

There are two main areas of brucite deposits globally – in Liaoning, China and in Russia, both with significant resources.  

Russian brucite miner Russian Mining Chemical Co. (RMCC) has grown significantly over the last 10 years, largely on the back of international sales to the flame retardant industry. 

Brucite (magnesium hydroxide, or Mg(OH)2), along with huntite (magnesium calcium carbonate) and hyrdromagnesite (hydrated magnesium carbonate), are among the lesser known magnesium minerals. Their chemical compositions are shown in Figure 1.  

Brucite1  

Brucite 

Brucite is distributed in a wide range of rock types, but there are only a few large scale deposits globally.
The mechanism for brucite formation is generally when dolomitic marble, or magnesium-bearing limestone, is subject to contact metamorphism and the mineral pericalse (MgO) is formed and hydrates to brucite in the presence of water.  

The main characteristics of brucite are shown in Table 1 and the principal global resources of brucite are shown in Table 2, with China at 26m tonnes and Russia with 32m tonnes.

Brucite2  

Brucite3

Russia

RMCC

RMCC specialises in the mining, processing and trading of brucite from the Kuldur deposit in the Jewish Autonomous Region of Far East Russia. Kuldur was discovered in 1966 and has reserves of 10m tonnes brucite. The brucite is a crystalline massive rock, white to light grey in colour. The chemistry of the three grades of ore extracted from the mine is shown in Table 3.

RMCC was established in 2002 and started its first production plant in Vyazma, Smolensk Oblast, 220km west of Moscow, in 2006.  

RMCC established Kuldur Mining Company in 2011 and a second processing plant in Vyazma in 2011. RMCC purchased a controlling block of shares in Kuldur Mining in 2012. A view of the Kuldur deposit is shown in Figure 2.

RMCC established a European subsidiary, Europiren BV, in Rotterdam in 2013 and in 2015 opened a polymeric laboratory.

Kuldur’s main business is mining brucite with crushing and sorting.   In 2011 it introduced XRF separators after crushing to separate brucite according to percentage content of MgO, silicon dioxide (SiO2) and iron oxide (Fe2O3). There is also a fully equipped laboratory on site that monitors quality. A view of the facility is shown in Figure 3 with a flowsheet shown in Figure 4.

The Kuldur quarry is located 20km from the railway junction of Izveskovaya, which connects to the Baikal-Amur Mainline (BAM) and Trans-Siberian Railway, which allow Kuldur ore to be railed to several major ports including Saint-Petersburg, Nahodka, Novorossiysk and Vanino.

Once sorted, the best quality material is railed from Kuldur to Vyazma, where it is milled, classified and surface coated by a plant operated by Vyazma Brucite LLC.

The Vyazma plant was upgraded in 2009-2013 to meet increasing demand for brucite. In January 2013, the company received ISO 9001-2008 standard certification for quality management. A flowsheet of the processing plant is shown in Figure 5.

Europiren handles sales of RMCC’s brucite products (see Table 4) to Europe, the Middle East and North Africa, North America and South East Asia. It also provides technical support to RMCC’s customers and manages the company’s polymer research laboratory.

Prior to 2006, there were only sales from Kuldur and overall production that year was 38,714 tonnes. Output has since increased steadily, but the introduction of XRF sorting in 2011 led to a significant increase in production.  

The capacity of each of the two processing plants in Vyazma is 100,000 tpa and sales in 2016 totalled 189,500 tonnes. A third mill is under construction to increase capacity by a further 30,000 tpa.

RMCC acquired the mining rights for the Savinsky deposit, 80km from the Kuldur mine, in January 2017. Savinsky has combined reserves and resources of 22m tonnes brucite and could ship as much as 500,000 tpa. 

Figure 2: Kuldur brucite mine 
Brucite4  
Source: RMCC/Europiren;  Mining at Kuldur is open cast and benched; the mine’s crushing plant can be seen in
the foreground. 

Figure 3: Kuldur crushing and sorting complex 
Brucite5  
Source: RMCC/Europiren 

China

Chinese brucite is found mainly in Liaoning province, in Fengcheng, Kuandian and Xiuyan, with some fibrous brucite operations in Henan, Shaanxi and Hebei provinces. 

Brucite resources in China are around 26m tonnes, 24.3m tonnes of which is whitish-greyish brucite in Liaoning, the remainder being fibrous brucite found elsewhere. There are 13 brucite mines in Liaoning, 10 of which are in the Fencheng area, with two in Kuandian and one in Xiuyan.   

Details of Liaoning’s brucite producers are shown in Table 5.

Four companies in the fibrous brucite areas, which have combined resources of 1.7m tonnes and production capacity of 31,000 tpa, hand mine ore at surface and underground. The brucite is processed as a float material and the resulting product is mainly used as a substitute for asbestos in thermal insulation and sealing and as a friction resistant material in brakes.

Between 2011 and 2016, Chinese export quotas on brucite varied between 400,000 and 500,000 tpa, not all of which was used up each year and these quotas have now been scrapped.

China’s current brucite production levels are unknown, as many mines in Liaoning have been closed due to a wave of environmental inspections to combat air pollution and strict controls on the use of dynamite for blasting (pp50-52).

Liaoning companies produce ultra-fine magnesium hydroxide powder. Brucite is selectively mined, crushed into coarse and fine fractions and then ball milled to produce powder with an 94% minimum Mg(OH)2 content.   

After fine milling, surface treatment – mainly stearic acid and a silane-coupling agent – is applied and the material is then sold as a flame retardant. 

The chemistry of Grade 1 brucite lump from China is compared with equivalent material from Russia’s Kuldur mine in Table 6. The main difference is the very low level of Fe2O3 in the Russian brucite.

Brucite6  

US

The US produces most of its magnesium hydroxide from lake brines, well brines and seawater, but the country also has resources of naturally occurring brucite and brucitic marble.  

Premier Magnesia LLC produces caustic calcined magnesia (CCM) from a magnesite deposit at Gabbs, in Nye County, Nevada. The Gabbs deposit contains a reported 3m tonnes brucite resource, but at present this is not mined. 

Applied Chemical Magnesias Corp. (ACM) used to mine brucitic marble – a mix of brucite and calcite – at Marble Canyon in Van Horn, Texas.  Following legal issues with the mine, ACM-Texas filed for bankruptcy in 2008 and the Marble Canyon operation is now owned by International Brucite Corporation (IBC), which is held by Texas Architectural Aggregate Inc (TAA).  

Garrison Minerals

Garrison Minerals specialises in hydroxide, oxide and carbonate magnesium materials, including Mg(OH)2 which it sells as dry powders and slurry (see box). It imports brucite from Liaoning, China and has 11 slurry distribution terminals located across the US.

Cimbar Performance Minerals partners with Garrison to produce slurry and dry powder. The company’s UltraMag product is used in water treatment, slurries, plastics, rubber and flame retardants and smoke suppressants.  

Brucite7

Brucite8 

Huntite and hydromagnesite

Hydromagnesite and huntite, along with aragonite, are formed in closed lacustrine basins of Tertiary to recent age. 

The two minerals are found in the same deposits and their main characteristics are shown in Table 7. 

The two known operating mines that produce hydromagnesite and huntite are Sibelco Hellas SA Mining Co.’s deposit in Greece and LKAB’s Likya Mining Co. operation in Turkey.  

Sibelco Hellas 

White Minerals SA in Greece was established in 1994 with Dutch company Ankerpoort NV extracting huntite-hydromagnesite from mines and selling it mainly as crude material.  

Belgium’s Sibelco acquired Ankerpoort in 2000 and since 2001 Sibelco has been responsible for mining and marketing both crude and finished products.  

Sibelco Hellas has two quarries, concessions 72 and 74, in the area between the villages of Lefkara and Neraida, southeast of Kozani, in western Macedonia in Greece, with estimated reserves of 250,000 tonnes. Hard porous white plugs located inside the mine are aragonite sinters that feed the basin with magnesium and calcium-rich solutions.

The deposit has an average thickness of 3 metres and selective mining obtains material with 65% huntite and 35% hydromagnesite content. The overburden and ore is soft, meaning that the company does not need to use explosives for mining, which takes place between May and September. Sibelco’s plant at Kerida consists of drying, grinding, classification and bagging.    

Beneath the marlstone is the white huntite-hydromagnesite layer, with huntite:hydromagnesite ratios of between 70:30 and 50:50. After processing, the mixture has a composition of 50:50.  The contact between the marlstone and the underlying layer is irregular, due to the underlying minerals’ expansion.  

Sibelco Hellas has gradually built up its sales of finished products from zero in 2001 to a peak of 24,200 tonnes in 2012, including 7,450 tonnes of processed material and 5,420 tonnes of raw material. Output and sales both declined in 2013 and 2014, and no figures are available for 2015 or 2016 (See Table 8).

Brucite9  

Likya Minerals (LKAB)

In Turkey, reserves of mixed huntite and hydromagnesite are found in South Denizili, Cameli Basin in the southwest of the country. 

One large deposit there was originally mined and processed by Likya Minelco, a joint venture between Likya Mining and Mincelco Specialities. The mine’s current owner, Likya Minerals, is now a joint venture partly owned by Sweden’s LKAB. 

The size of the reserves is reported vaguely by LKAB as being in the "tens of millions of tonnes".  

The company operates a processing plant near Izmir, using a special classification system to achieve a "sharp top cut" grade for coated and uncoated products. Hydromagnesite and huntite are flame retardants on their own, but combined they result in a product which specific properties that can be adjusted by selective mining and processing to fit a variety of applications.

Likya Mining’s products marketed under the trademark Ultracarb and are used as fire retardant fillers in a range of polymers such as polyethylene, polypropylene, PVC and rubber. 

Whereas the classical endothermic flame retardant fillers act by releasing water in a single action process, Ultracarb has a unique three-stage fire retardant mechanism.

First, water is released at temperatures of around 220°C as part of the thermal decomposition phase. Then, carbon dioxide is released at temperatures of around 330°C and then, at temperatures of around 560°C, UltraCarb particles accumulate on the surface of the burning polymer to form a stable char which inhibits the combustion process and thus the propagation of the fire through burning droplets. 

This, like many of the other minerals discussed above, demonstrates the unique performance characteristics of magnesium minerals which makes them suitable substitute flame retardant materials in applications where halogenated or other mineral-based products cannot be used.