Soaking it up: Bentonite’s global reach

By IM Staff
Published: Saturday, 21 May 2016

Recent growth in bentonite consumption has been driven largely by foundry, oil drilling and iron ore pelletising markets. However, the latest downturn in oil and steel prices is likely to see volumes in the latter two markets decrease in the short to medium term. Andrew Scogings* gives an overview of worldwide bentonite production and consumption.

The name bentonite was first suggested in 1898 for clay hosted by the Benton Shale in Wyoming. It was initially described as clay formed by the alteration of volcanic ash, but the most widely used commercial definition is that bentonite is clay consisting essentially of smectite minerals (usually montmorillonite) regardless of occurrence or origin.

In geological terms, bentonite is essentially a rock composed of smectite plus variable amounts of impurities, or 'inert minerals’ such as quartz, feldspar, kaolinite, illite, gypsum, zeolite, and opaline silica.  Interestingly, minerals such as zeolite may complement the smectite component in products such as cat litter, where zeolite helps with odour control. 

Most economic bentonite deposits are of Cretaceous age or younger and associated with marine shale and marl (Wyoming), calcareous sands and marls (Morocco), carbonaceous shales and coal (South Africa), sandstone and conglomerate (Australia), dacitic pyroclastics and tuffs (Milos), andesite (China) or rhyolite and obsidian/perlite (China and Mozambique).

Bentonite is characterised by exchangeable cations such as Ca2+, Mg2+, Na+ or Li+ which affect its designation and properties. For example, bentonite is typically described as either swelling or non-swelling bentonite.  Swelling bentonite (also known as western bentonite) is sodium bentonite that swells in water and is generally used in its natural state.  Non-swelling bentonite is calcium bentonite (also known as southern bentonite) that is used as mined, after treatment with soda ash to produce sodium-exchanged bentonite, or treated with acid to produce bleaching clay.  Li-rich bentonite is known as hectorite and is commercially mined only in the US.

Bentonite is truly 'a mineral of a thousand uses’ and is utilised for its high surface area, bonding, swelling, sorptive, sealing and rheological properties.  These properties may be modified by treatment with acids, soda ash or other chemicals in addition to calcination, milling and sieving.  Bentonite finds application in diverse markets including metalcasting, oil well drilling, iron ore pelletising ('IOP’), edible oil purification, paper, ceramics, detergents, cat litter and civil engineering.

Figure 1 Estimated global bentonite production,
percentage by country in 2013

BENT1 

Source: BGS (Brown et al., 2015)

Table 2 Bentonite trade by leading exporting and importing countries

Exports (1,000 tonnes)

Country

HS Code

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

India

3803

 437 

 415 

 503 

 582 

 440 

 117 

 886 

 973 

 1,447 

 1,258 

USA

250810

 848 

 1,274 

 1,432 

 1,089 

 710 

 947 

 1,029 

 1,035 

 892 

 902 

Greece

250810

 876 

 974 

 1,119 

 1,177 

 746 

 992 

 1,007 

 931 

 920 

 850 

Turkey

250810

 238 

 293 

 279 

 244 

 250 

 308 

 319 

 338 

 394 

 370 

Italy

250810

 247 

 274 

 298 

 281 

 187 

 242 

 215 

 226 

 225 

 236 

China

250810

 254 

 286 

 319 

 368 

 255 

 321 

 193 

 194 

 215 

 219 

Slovakia

250810

 76 

 118 

 99 

 94 

 73 

 33 

 87 

 98 

 185 

 160 

Netherlands

250810

 186 

 132 

 130 

 121 

 136 

 178 

 187 

 142 

 137 

 121 

Imports (1,000 tonnes)

Country

HS Code

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Canada

250810

 384 

 491 

 560 

 443 

 354 

 486 

 459 

 539 

 467 

 476 

Germany

250810

 319 

 411 

 352 

 362 

 336 

 386 

 448 

 435 

 489 

 475 

Netherlands

250810

 200 

 281 

 305 

 314 

 84 

 238 

 290 

 277 

 216 

 264 

Sweden

250810

 49 

 125 

 184 

 178 

 120 

 200 

 214 

 232 

 190 

 238 

Poland

250810

 115 

 154 

 165 

 175 

 122 

 156 

 208 

 227 

 209 

 191 

Japan

250810

 204 

 223 

 210 

 253 

 122 

 201 

 211 

 246 

 202 

 185 

UK

250810

 152 

 186 

 160 

 197 

 143 

 137 

 200 

 174 

 173 

 152 

Brazil

250810

 168 

 138 

 221 

 216 

 124 

 205 

 197 

 160 

 128 

 116 

Thailand

250810

 50 

 50 

 39 

 54 

 42 

 65 

 104 

 83 

 103 

 101

Source: UN Trade Statistics 



Global production 

Global bentonite production was estimated by the United States Geological Survey (USGS) at 16m tonnes in 2015. 

The US and China are the world’s foremost bentonite producers and are estimated to account for 50-60% of overall supply, or around 8-10m tpa (Figure 1). The main discrepancy in global estimates concerns Chinese production and, whereas the USGS 2013 Minerals Yearbook Clay and Shale report doesn’t include any Chinese bentonite production for 2013, the USGS 2013 Minerals Yearbook China (Tse, 2015), the USGS Clays report (Flanagan, 2016) and the BGS (Brown et al., 2015) each reported approximately 3.5m tonnes for 2013. 

According to data from the China Non Metallic Industry Association (CNMIA) China’s bentonite production had increased from 4m to 8m tpa by 2014; however the Chinese bentonite industry currently faces difficulties such as low demand and fierce competition mainly in the IOP space. This is because imported lumpy iron ore has reduced demand for IOP-grade bentonite as a binder for Chinese iron ore fines such as magnetite.  The CNMIA reported recently that Chinese IOP production was approximately 130m tonnes, consuming some 2.5m tpa of bentonite at an addition rate of about 2% bentonite per tonne of iron ore. 

Professor Lei, Suzhou SINOMA Design and Research Institute of the Non-metallic Minerals Industry Co., recently estimated that current Chinese bentonite consumption exceeds the 5m tpa mark, with 2.2m tpa going into the IOP market, 1.5m tpa going into machine casting, 500,000 tpa consumed by drilling muds, 300,000 tpa going into activated clays and the remaining 0.5m tpa being taken up by other, smaller markets. 

Leading global exporters of sodium and calcium bentonite include India, US and Greece, while leading importers include Canada, Germany, Netherlands and Japan (Table 2). The US is the leading global producer of sodium bentonite and is also a significant producer of calcium bentonite.  Elsewhere in locations such as Europe, China and India, calcium bentonite is the predominant mineral and is used either in its natural state or after sodium-exchange or acid activation.

Figure 2 Estimated global bentonite
demand by market

BENT2 

Source: BGS Various industry sources; Shaw (2014)


Table 4 Geology of Kunimine Group mines

Mine Name

Tsukinuno

Kawasaki

Dobuyama

Hosogoe

Shirosaki

Prefecture

Yamagata 

Miyagi 

Miyagi 

Niigata 

Niigata 

Geological Age

Miocene 

Miocene 

Miocene 

Miocene 

Miocene 

Geological origin

Diagenesis

Diagenesis

Hydrothermal /Diagenesis

Hydrothermal

Hydrothermal

Ore Shape

1-7m bedded

20-30m bedded

Massive

Massive

Massive 

Bentonite Type

Sodium

Calcium-sodium

Calcium

Sodium-calcium

Sodium-calcium

Source: Masakazu Ito, Kunimine Industries


BENT3 

Figure 3 MTI drying pads, stockpiles and plant at
Colony, Wyoming 
Source: Masakazu Ito, Kunimine Industries 

Global consumption

The main bentonite markets are foundry, cat litter, IOP, drilling mud and civil engineering, which together account for >80% of sales by volume (Figure 2). Bentonite markets such as IOP and drilling mud are directly related to steel production and oil/gas drilling activity, both of which have declined in the past year – therefore sales to these markets are believed to have decreased during 2015 and into 2016. 

Consumption patterns vary from region to region, depending on the composition of the industrial base and population demographics.  For example, cat litter consumption is higher in wealthier economies; therefore demand is concentrated in areas such as North America, Japan and Europe.  Similarly, bentonite consumption for iron ore pelletising is greatest in countries that produce iron ore 'fines’ that need to be agglomerated, such as in China, Russia and the US.

Foundry sands probably have the widest geographic distribution of bentonite applications; however castings production has increasingly transitioned from high-cost locations such as Western Europe, to lower-cost production bases in Eastern Europe, India, S.E. Asia and China. Conversely, the US remains a major producer of iron castings due mainly to its large automotive and heavy equipment manufacturing industry.

Industrial-grade bentonite prices range from as low as approximately $30/tonne for cat litter dried crudes to $220/tonne for foundry-grade dried crudes, according to IM data. Other specialised grades for paper, wine fining, detergents and edible oil clarification markets command higher prices.

BENT4 

Figure 4 Sodium bentonite (2 metres thick) overlain
by tuff and sandstone.
Gurulmundi, Australia Source: MTI


BENT5 

Figure 5 Calcium bentonite overlain by andesite.
Jianping, Liaoning Province, China  Source: A. Scogings

Exploration and production methods

Bentonite exploration generally follows a similar path to other minerals, often from discovery of an outcrop, which is then explored by methods such as field mapping, trenching, drilling and lab testing.  Data generated in this way, if successful, could lead to the estimation of a mineral resource which defines the geometry, tonnage and quality of a deposit. 

Bentonite deposits are often large, shallow dipping and tend to have greater lateral than vertical extent.  Most deposits are mined from open pits using bulldozers and scrapers to remove overburden, followed by selective extraction of the bentonite using excavators or front end loaders.

After mining, the clay is often stockpiled or laid out on 'drying pads’ to allow for natural drying before blending into product stockpiles (Figure 3). Bentonite is typically made into final products via a process of drying, crushing, milling or screening.  Some producers supply dry crudes in bulk (also known as 'dried and crushed’) to processors who may blend with local bentonite and then mill into final products.

Although bentonites are generally described as being calcium (southern) or sodium (western), in fact a complete range of calcium to sodium varieties exist throughout the world.  This even applies to the 'western’ bentonites in Wyoming, Montana and South Dakota, which are traditionally described as sodium bentonites. Calcium and magnesium bentonites may be sodium activated and this is usually achieved by the addition of sodium carbonate (soda ash), in the process replacing exchangeable Ca and Mg cations with sodium cations. Soda ash may be added as powder or a solution to bentonite drying pads, or added to bentonite in mixing and shearing equipment such as pan mills, paddle mixers or extruders.

Because of the wide variety of applications in which bentonite is used, there is no optimum level of sodium that meets all requirements, nor is sodium activation always desirable.  Therefore as a general rule, bentonites require different levels of sodium activation (typically less than 4% soda ash), depending on the amount of exchangeable calcium and magnesium cations present in the clay and the final properties desired.  

The addition of too much sodium, also known as 'over-activation’, can result in decreased thermal durability in foundry clays and in increased fluid loss in drilling muds. On the other hand, too little soda ash may result in low swelling, low viscosity and low water absorption, which could adversely affect performance in drilling muds and IOP. 

Calcium bentonite that is destined for edible oil purification is treated with HCl or H2SO4 (acid activation).  This treatment removes impurities such as calcite, replaces exchangeable cations with hydrogen and opens up the clay platelets to increase the surface area.

BENT6 

Figure 6 White calcium bentonite associated with
rhyolite. Anhui Province, China 
Source: A. Scogings 


BENT7 

Figure 7 Laviosa’s white bentonite mine at Bakirgoel
near Unye in the Black Sea area, Turkey 
Source: Laviosa Chimica Mineraria 


BENT9 

Figure 9 Mining operations at LLC Bentonite
Company’s Khakasia deposit near Abakan in Russia 
Source: LLC Bentonite Company 

Leading global bentonite producers

AMCOL International was acquired by Minerals Technologies Inc. (MTI) in 2014 and is the leading producer, accounting for an estimated 15% of global bentonite production, most of which is produced in the US in Wyoming (Colony and Lovell) and Alabama (Sandy Ridge). MTI also produces bentonite from mines and plants in Australia (Gurulmundi), China (Jianping area), Mexico and Turkey (Enez area) and in addition has plants in other countries including Australia, China, India, Poland, South Korea, Thailand and the UK where imported and/or local bentonite is processed. MTI has numerous blending plants in the US where specialised foundry blends are produced; these products are known as Additrol which are custom bentonite blends that may also include carbonaceous products, cereals, iron oxides and starches.  MTI supplies most bentonite markets and also has plants producing geosynthetic clay liners in the US, Poland and other global locations.

Imerys acquired S&B Industrial Minerals in 2015 and is considered to be the second largest bentonite producer in the world, with an estimated 10-12% market share in volume terms. The S&B acquisition brought numerous mineral assets to the company, including bentonite, perlite, and wollastonite. Imerys now has has bentonite mines and plants in Greece (Milos), Bulgaria (Propast, Dobrovoletz and Enchetz mines in the Kardzhali area), Hungary (Egyhozasheszo), Georgia (Mtspiri mine in the Ozurgeti area), Morocco (Trebia mine in the Nador area), South Africa (near Heidelberg), the US (Tennessee), India and China (Jianping area). Imerys supplies many different applications such as foundry, iron ore pelletising, civil engineering, drilling fluids, pet litter, animal feed and other specialities. 

Clariant AG bought private equity-owned Süd-Chemie AG in April 2011 to expand into chemical catalysts used in the oil and automotive industries. Süd-Chemie was a long established German-based global producer of industrial grade bentonites, catalysts and specialised bentonite-based products for markets including metal casting, civil engineering, drilling, paper, detergents, edible and non-edible oils, fat and wax purification. Clariant has bentonite mining and production facilities in several countries including China, Germany, Indonesia, Mexico and Turkey.

The Taiko Group, based in Malaysia, is reportedly the largest producer of bleaching earths after Clariant.  Its operations include mining and processing in China, India, Indonesia and Malaysia.

BENT8 

Figure 8 Kunimine’s opencast sodium-calcium bentonite mine at Shirosaki 
Source: Kunimine Industries Co Ltd 


BENT10 

Figure 10 Calcium bentonite being mined from G&W’s
Blaaubosch pit at Koppies, South Africa 
Source: G&W Mineral Resources 


BENT11 

Figure 11 Trial mining of calcium bentonite at
Namaacha Mining’s project in Mozambique 
Source: Namaacha Mining 

Bentonite production in selected countries

Examples of bentonite production in selected countries are outlined below. These examples are not an exhaustive list, but aim to highlight some global activities across a spectrum of locations and bentonite types.

Australia is estimated to produce between 100,000 and 200,000 tpa of bentonite from several mines. Sodium-magnesium bentonite is mined in New South Wales near Mildura (Arumpo Bentonite) and near Gurulmundi north of Miles in Queensland (MTI and Sibelco).   MTI’s Gurulmundi mine has several sodium bentonite beds ranging up to three metres in thickness and varying in colour from blue grey, olive grey, greyish yellow green to yellowish grey. Each bed is characterised by a distinctive mineralogical and chemical fingerprint, but in the main they consist of montmorillonite associated with variable amounts of other minerals including zeolite and feldspar. The bentonite beds are often capped by volcaniclastic rocks such as tuff or volcanogenic sandstone (Figure 4) and products are supplied to foundry, drilling, civil engineering, cat litter, agriculture and other markets both locally and overseas. 

Calcium-magnesium bentonite was previously mined near Scone in New South Wales and a significant deposit of calcium bentonite at Mantuan Downs in northern Queensland was discovered in the 1960s; this was mined on a trial basis within the last few years by Australian Pacific Coal Ltd. Sodium-magnesium bentonite has been produced during coal mining operations near Ipswich, west of Brisbane and the stockpile is currently processed by Bentonite Products Pty Ltd for supply to civil engineering markets amongst others.

China is probably the leading global producer of bentonite, though estimates vary widely from 3.5m tonnes (USGS; BGS) to between 4-8m tonnes (CNMIA) of which a large proportion goes into iron ore pelletising.  Most Chinese bentonite is calcium dominant; a wide range of colour and purity means that a wide range of markets can be supplied, from IOP, foundry, civil engineering and drilling through to desiccants, oil purification, paper and detergents.

The main source of industrial grade bentonite in China for foundry, civil engineering and drilling markets is near Jianping in western Liaoning Province, where international companies MTI, Clariant and Imerys have mining, processing and distribution facilities. The bentonite is predominantly calcium-magnesium type and usually associated with andesite, sometimes in very thick beds (Figure 5).  The low iron (off-white to pale yellowish) clays from this area are noted for high thermal durability after soda ash treatment. White bentonite is mined and processed in several provinces including Anhui (Figure 6), Hebei and Inner Mongolia for specialised paper and detergent markets.  

India produces well in excess of 1m tpa calcium and sodium bentonite and is recorded as exporting about 1m tpa, being a leading supplier to global IOP markets. There are numerous bentonite producers including Ashapura, Gimpex and Star Bentonite, with the majority of India’s bentonite sourced from deposits in Gujarat State in western India.

Star Bentonite was founded in 1979 and has numerous mines in Lakhpat, Mandvi and Abdasa counties in Kutch, western Gujarat and processing centres at Bhuj, Faradi and Gandhidham. The company claims to handle a volume of approximately 250,000 tpa, with total capacity of 250,000 tpa lumpy (dried and crushed) and 100,000 tpa milled powders for export. Star recently moved from field activation (spreading soda ash in solution onto bentonite) to automated activation, so that the process includes mixers, blenders, pug mills and extruders in addition to roller mills and rotary driers.

Italy was recorded by the USGS as producing about 100,000 tpa of bentonite in 2013, down from 500,000 tonnes recorded in 2005. Exports are reportedly more than 200,000 tpa, therefore it is considered likely that Italian annual production is a lot higher than recorded by the USGS and BGS.  Italy has number of bentonite producers including long-established Laviosa Chimica Mineraria which mines and processes over 250,000 tonnes of materials every year. Laviosa markets into a broad range of applications, both for industrial markets (e.g. paint additives, paper industry, detergents, ceramics, plastics, civil engineering, foundry and waterproofing in the environmental and construction sectors) and for the consumer market (cat litter) in more than 80 countries worldwide.

The company has three plants in Italy; two in Livorno and one near Cagliari in Sardinia. Laviosa has several foreign subsidiaries which are in Turkey (Laviosa Sanayi ve Ticaret Ltd.Sti., 100% owned), India (Laviosa Trimex Industries Pvt. Ltd., a joint venture, 55% subsidiary, in partnership with the Indian company Trimex Industries) and France (Laviosa MPC SAS, 80% owned). The Bakirgoel deposit in Turkey has a resource of around 2m tonnes of white and pink bentonite and was opened in August 2015, ready to extract 10,000 tonnes for the year (Figure 9). In addition to its own operations, Laviosa holds a stake in the Spanish bentonite processor Laviosa Promasa SA and, in 2014, it took a minority share in Zhejiang Hongyu New Materials, a leading Chinese producer of organoclays. Laviosa continues to make significant investments in order to secure 60% of its raw material requirements for the next 15 years, with the goal of reaching reserves of at least 3m tonnes.

Japan is a significant producer of around 400,000 tpa calcium and sodium bentonite, most of which is consumed domestically and supplemented by imports of about 200,000 tpa.  Kunimine Industries and Hojun Kogyo are the two main miners and producers of industrial products that are sold into foundry and civil engineering markets, while Mizusawa Industrial Chemicals is an important  producer of acid activated bentonite (under the Galleon trademark) for refining edible oils.

Kunimine is the biggest Japanese bentonite producer with an output of 150,000 to 200,000 tpa of calcium, sodium and sodium-calcium bentonites from five mines known as Tsukinuno, Kawasaki, Dobuyama, Hosogoe and Shirosaki (Table 4; Figure 8). The bentonite is mined both underground and from opencast pit. Kunimine imports sodium bentonite from Black Hills Bentonite, Wyoming, for blending with its local production.

Russia is estimated to produce about 500,000 tpa calcium bentonite mostly for local consumption. The leading producer is LLC Bentonite Co. which has mining operations at the 10th Khutor calcium bentonite deposit near Abakan in Khakassia eastern Russia (Figure 9), at the Zyryanskoje calcium bentonite deposit near Kurgan in central Russia and at the Dash-Salakhly sodium bentonite deposit near Qazakh in western Azerbaijan.  Bentonite reserves are claimed to exceed 35m tonnes in Russia and 86m tonnes in Azerbaijan.

LLC Bentonite supplies markets including foundry, IOP, cat litter, civil engineering and drilling, and sales have reportedly grown from 45,000 tonnes in 2001 to more than 450,000 tonnes in 2015. The company estimates that it supplies 75% of the Russian market overall, with 96% share in metallurgy (IOP),   34% in drilling and 74% in metalcasting.

South Africa and Mozambique are estimated to collectively produce about 200,000 tpa bentonite. G&W Mineral Resources mines and activates high purity calcium-magnesium bentonite from a large deposit near Koppies (Figure 10) while Imerys mines sodium bentonite near Heidelberg in the Western Cape, South Africa.  Products from both mines find their way into a wide spectrum of markets including foundry, civil engineering, drilling and chromite pelletising. Midden Mining was reported earlier in 2015 to have identified sodium bentonite east of Heidelberg, in the Mossel Bay district.

Calcium bentonite derived from the alteration of obsidian (volcanic glass) within a rhyolitic sequence is currently mined by G&W in southern Mozambique.  A mine and milling plant previously owned by G&W is now operated by Mimoc, while Namaacha Mining Limitada has delineated a deposit estimated at >0.5m tonnes north of Mimoc’s operation. Namaacha Mining recently conducted trial mining (Figure 11) and a bulk sample was successfully tested on a plant scale at a South African chromite pelletising plant. Most Mozambique bentonite is sold into the chromite pelletising market.

The US is the leading global producer of sodium bentonite and although significant tonnages are exported, a large part is consumed locally by foundries, oil drilling, IOP and cat litter markets.  Calcium bentonite is sold into a range of markets including foundry and acid activated bleaching earth. The largest sodium bentonite producers are MTI, Bentonite Performance Minerals, and Black Hills Bentonite and Wyo-Ben.

MTI is the world’s largest producer of sodium bentonite from mines and plants at Colony and Lovell, Wyoming which supply cat litter, drilling muds, IOP, foundry and other applications. MTI is a world leading supplier of high-durability bentonite blends for foundry greensands and also produces calcium bentonite at Sandy Ridge, Alabama.

Bentonite Performance Minerals, a subsidiary of Halliburton Co., began its history in 1928 and mines and processes sodium bentonite at Colony and Lovell, Wyoming. 

Black Hills Bentonite LLC is controlled by the Thorson Family, with the rest of the ownership divided amongst The Clorox Co., Kunimine Industries and Sojitz Corp. Black Hills Bentonite operates mines and plants near Kaycee, Tensleep and Upton, Wyoming that produce a variety of natural sodium bentonite products for use in cat litter, drilling muds, IOP, foundry and other applications.

The US is unique in commercial production of hectorite from two localities.  The major producer is Elementis Specialties which has been a global supplier of high performance drilling mud products to the oil services industries since 1949.  The company mines and processes white hectorite at Hector, California, producing clay and polymeric additives under the Bentone and Thixatrol trade names.  Hectatone Inc., a wholly-owned subsidiary of Western Lithium USA Corp., reportedly shipped its first Li-hectorite based drilling grade product known as Hectatone in early 2015. The plant sources hectorite from the Kings Valley deposit, Nevada.

*Dr Andrew Scogings

Industrial Minerals Magazine Consultant

Principal Consultant, CSA Global Pty Ltd

Perth, Australia

Acknowledgments

The following industry sources are thanked for their assistance: Don Eisenhour and Dougal Scott (MTI), Vincent Gouley (Imerys), Larry Washow and Olimpia Laviosa (Laviosa Chimica Mineraria), Leonid Voevodin (Bentonite Company LLC), Masakazu Ito (Kunimine Industries), Nikunj Thakkar (Star Bentonite), Richard da Silva (Matsopa Minerals / G&W Mineral Resources), Robert Barnett (Namaacha Mining) and Robert Parsons (Black Hills Bentonite).

Bibliography

Brown, T., et al., 2015. World mineral production 2009-13. British Geological Survey, Keynorth, Nottingham, UK.

Eisenhour, D. and Reisch, F., 2006. Bentonite, in Industrial Minerals & Rocks, 7th edition, 1487-1494. Society for Mining, Metallurgy, and Exploration, Inc. Colorado, USA. 

Flanagan, D. M., 2016. Clays. United States Geological Survey.  http://minerals.usgs.gov/minerals/pubs/commodity/clays/mcs-2016-clays.pdf 

Harben, P.W. and Kuzvart, M., 1996. Clays: Bentonite and Hectorite, in Industrial Minerals - A Global Geology, 33-42. Industrial Minerals information Ltd. 

Li, A., 2016. China’s bentonite industry has room to grow. Industrial Minerals Magazine, February 2016. http://www.indmin.com/Article/3523658/Chinas-bentonite-industry-has-room-to-grow.html

Shaw, S., 2014. Bentonite as an oilfield mineral in North America. Oilfields Minerals Outlook, Industrial Minerals Events. 24-26 June 2014, Houston, USA. 

Tse, P-K., 2015. The Mineral Industry of China. 2013 Minerals Yearbook. China (Advance Release). United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/country/2013/myb3-2013-ch.pdf