Special clays: Gelling new markets

By IM Staff
Published: Friday, 09 June 2017

Hectorite has attracted significant attention in the last few years as a potential source of lithium, while clays like attapulgite and sepiolite have for decades been important sources of speciality material. Ian Wilson, Consultant*, offers a snapshot of the special clays sector.

Special clays are a group of products derived from a number of different clay minerals found in a wide range of geological environments. 

Two important mineral groups within the special clays field are the smectite group, which includes montmorillonite, saponite and hectorite, generally referred to as bentonites; and the hormite group, which includes palygorskite - more commonly known as attapulgite - and sepiolite.

The smectite group

The smectite group of minerals covers a diverse range of crystal structure, morphology and chemistry.

Bentonite, one of the smectite minerals, is named after Fort Benton in the US and is composed mainly of montmorillonite and other minerals which, depending on the origin of the deposit, can be clays, clastic material from volcanic dusts or other materials.   

Figure 1 outlines bentonite nomenclature and shows the relationship between some smectite minerals, with respect to their structure, chemistry and morphology.

Figure 1: Bentonite nomenclature (smectite group)White bentonite 
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Source: Ian Wilson 
 

A scanning electron microscope (SEM) image of montmorillonite with a rose-like appearance from an arkose in the Madrid Basin in Spain is shown in Figure 2. The main characteristics of smectites are shown in Table 1.

Table 1: Characteristics
of smectites
 
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Source: HH Murray, Applied
Clay Mineralogy, Elsevier

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Figure 2: Montmorillonite from the Madrid Basin
The Clay Minerals Society, London 

White bentonite

White bentonite is mainly montmorillonite and is found in Argentina, China, Greece, Turkey, the US and elsewhere. An example of a high quality white bentonite is found in the Helms deposit, owned by Southern Clay Products Inc. (SCP) near Gonzales in the US state of Texas.

SCP, which became part of Rockwood Holdings Inc. in 2000, was in October 2013 included in the sale of its parent company to German speciality chemical group, ALTANA.  The $635m acquisition included four production sites at Gonzales and Louisville in the US; Widnes in the UK; and Moosburg in Germany. 

Following the deal, ALTANA integrated SCP into its BYK Additives and Instruments division, thereby including rheological additives in its existing wetting and dispersing, air-release, defoaming, surface-improving and wax additives business.  Rheological additives optimise the flow characteristics of various materials.

Once mined, Helms bentonite is passed through optical sorters to separate out the whiter fraction and then undergoes a series of processes to remove any impurities and improve brightness. Bentolite and Gelwhite are two of the trademarked products SCP makes from Helms bentonite.

Bentolite improves plasticity and green strength when used as an additive in ceramic bodies. Helms bentonite is very low in iron (<1%) and when added to a kaolin (perhaps with an iron level of 0.3-0.4%) at the 1-2% level, will only add 0.01-0.02% to the overall iron level of the clay fraction.

The Gelwhite wet processing route gives an extremely pure refined smectite. SCP’s Gelwhite-GP product exhibits excellent thixotropy and enhances suspension stability and viscosity control. It is also effective at reducing syneresis – a process where the gel contracts, causing liquid separation – in home and personal care formulations. Typical chemical analysis of Gelwhite-GP (wt.%) is: 66.5% silicon dioxide (SiO2), 14.7% aluminium oxide (Al2O3), 3.2% magnesium oxide (MgO), 0.8% iron oxide (Fe2O3), 2.2% calcium oxide (CaO), 3.3% sodium oxide (Na2O) and 0.2% titanium dioxide (TiO2).   

Hectorite

Hectorite is a trioctahedral smectite and a magnesium lithium silicate. A hydrophilic swelling clay, hectorite is composed of silicate sheets that delaminate in water to provide an open three-dimensional structure. Viscosity is developed by the combination of electrostatic repulsive forces and Van der Waals attractive forces between the individual platelets. Optimum rheological efficiency requires complete clay dispersion. 

Table 2: Typical characteristics
of hectorite 
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Source: Webminerals.com,
Elementis plc
 

Physically, hectorite is a soft, very pale grey to bluish-grey translucent clay that resembles a piece of wax. An edge cut with a knife will curl in the same way as a candle when trimmed.

Hectorite is mined by UK-based Elementis Plc at its mine near Newberry Springs, California. The company acquired the property with its purchase of the Rheox rheological additives business from US-based NL Industries Inc. in 1998.     

Elementis’ acquisition of Rheox established the company as one of the world’s major suppliers of additives to the coatings industry. In 2000, Elementis amalgamated its Rheox, Daniel Products and Hardman businesses into one to form Elementis Specialties Inc. The group is now a leading producer of organoclay rheological additives.

The company’s hectorite property is located near Mount Pisgah, an extinct volcano, where volcanic ash and dust formed layers within a lake. Subsequent epithermal activity (bubbling springs) helped to form the hectorite. 

The hectorite is mined in an open pit with some blasting to remove the hard olivine basalt cap over the deposit. The clay is both dry and wet-processed. In the dry process, the ore is ground in a Raymond roller mill to yield a 50% hectorite product with much of the remainder being calcite. The dry-processed product is used in water treatment, ceramics, or as a feed for organoclay plants. In the wet process, fine-ground ore from the hammer mill is agitated in hot water. The resulting slurry is cycloned, centrifuged, spray dried and screened to give a 98% hectorite product. 

Characteristics of hectorite are shown in Table 2 with an SEM of clay from Elementis’ Newberry Springs mine in Figure 3.

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Figure 3: SEM of Newberry Springs hectorite Clay
Images, The Clay Minerals Society 

Elementis’ hectorite products are sold under the brand name, BENTON. In 2015, the geographical split of sales revenue for Elementis Speciality Products was: Asia, 32%; North America, 30%; Europe, 28%; and the rest of the world, 10%.   

Market segment split within the group was: industrial coatings, 55%; decorative coatings, 23%; oilfield drilling, 10%; and personal care, 12%. 

Canada-headquartered Lithium Americas Corp., which owns the Lithium Nevada project in northwest Nevada, US, is an emerging hectorite business. Incorporating the Nevada, US-based company formerly known as Western Lithium USA Corp, its Lithium Nevada project until last year was known as the Kings Valley project. 

 Key applications of hectorite
  • Industrial coatings: Protective applications in automotive, containers, furniture, flooring, marine, plastics and construction.
  • Decorative coatings: Homes, offices and similar environments.
  • Oilfield: Drilling and fracking fluids utilised in oil and gas extraction.
  • Personal care: Antiperspirants, nail polish, mascara, make-up, eye shadow, lipsticks, creams, lotions and suncare products.
  • Construction: Concrete, plasters, mortars, renderings, stuccos, flooring systems and building adhesives

Lithium Nevada is a smectite lithium clay project and has been the subject of extensive exploration. Lithium Americas is developing the project with a view to producing lithium carbonate, primarily intended for the lithium battery sector, along with lithium hydroxide for the same market.

Lithium Americas’ subsidiary, Hectatone Inc., has commissioned an organoclay manufacturing plant in Fernley, Nevada, which produces branded Hectatone speciality organoclay products from hectorite and other clays for the oil and gas industry where they are used as viscosifier additives for drilling fluids. Shipments of Hectatone products commenced in January 2015.

In addition to drilling clays for the oil and gas sector, Hectatone is now a certified vendor, via a US Fortune 500 industrial group, of its Hectabind range of products to the animal feed market as mycotoxin binders. Hectatone is also collaborating with other industry participants on a speciality organophilic clay product for environmental applications, capable of removing organic compounds from industrial wastewater effluent. Another of its product, Hectagel, is being tested for use in industrial applications.

In April 2016, Hectatone entered into a strategic alliance with Spanish company TOLSA SA, a global leader in speciality clays. The firms signed a non-exclusive memorandum of understanding to collectively pursue growth opportunities in global clay minerals markets.

Saponite

Saponite is a swelling clay with a low cation exchange capacity, similar to sodium bentonite except that magnesium has replaced most or all of the aluminium as well as the exchangeable sodium. 

Applications for saponite include absorbents, rheological additives and drainage aids for paper processing.   The major market for saponite is the consumer products sector, especially in clumping products for cat litter, but new markets are emerging in nanoclays and modified systems.

There are very few producers of saponite globally, with Spain being the main source thanks to the large operations of companies including Süd-Chemie Espana SL, Bentonitas Especiales SA and TOLSA. Other producers include IMV Nevada in the US.   

TOLSA has the capacity to produce 50,000 tpa saponite from its mine at Cabanas de la Sagra at Toledo in central Spain.   

In Grevena, western Macedonia, northern Greece, local producer Geohellas SA owns a number of sedimentary deposits that contain attapulgite and saponite.

In Ukraine, Veles Agro Ltd has been mining and processing saponite clay since it was established in 1993, with its products going into magnesium mineral fertilisers, animal feed additives, plant protection, aerosols, cleaning agents, water and food, preservatives, feed grain, sorbents for the detoxification of technogenic and radiation-contaminated soil and water, pet litter, deodorising agents, perfumes, cosmetics, ceramics and paint.  

The company’s Varvarovskiy deposit has resources of 34m tonnes saponite.  An image of Veles’ saponite is shown in Figure 4.  Around 10,000 tonnes raw saponite has also been extracted from the company’s Tashkovskiy deposit, the evaluation of which has indicated that the site can be economically developed.

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Figure 4: Veles saponite
Veles Agro 


Hormite (palygorskite-sepiolite) group

The hormite minerals, palygorskite and sepiolite, are elongate clays with many important industrial applications. In the US, the term attapulgite, after the town of Attapulus in the state of Georgia, is used in place of palygorskite, although the International Nomenclature Committee has determined that Palygorskite is the preferred name. 

The main characteristics of palygorskite-sepiolite are shown in Table 3. An SEM of attapulgite from Attapulgus is shown in Figure 5.

Table 3: Main characteristics of
palygorskite-sepiolite 
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HH Murray and Huitang Zhou, SME 7th
Industrial Minerals, 2005
Source: HH Murray, Applied Clay Mineralogy,
Elsevier 2007
 

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Figure 5: SEM of attapulgite from Attapulgus Clay
Images, The Clay Minerals Society 


Some of the main producing areas for attapulgite/palygorskite are in southeast US, China, Greece, Senegal, South Africa and Spain. 

In the US, attapulgite is mainly mined in northern Florida and southwest Georgia. Attapulgite Mining LLC, based in Attapulgus, produces attapulgite clay for use in paints, adhesives, plastics, cosmetic, pharmaceuticals, and agriculture. The company operates as a subsidiary of General Chemical Industrial Products Inc. and was acquired from Zemex Industrial Minerals Inc. in 2007.   

German chemicals conglomerate BASF mines attapulgite over an area of more than 18,000 acres (72.8km2) across Florida’s panhandle and southern Georgia. The operation began as a joint venture (JV) between US firms Engelhard Corp. and ITC Industrials Inc. in 1997 and was acquired by BASF in 2006.  The attapulgite is extracted by surface mining and processing is divided into two production lines – granular and gel – and the refined material is shipped by rail or truck across the US for use in applications from pet litter to pharmaceuticals. Other applications include oil and grease absorbent, pesticide or herbicide carriers, oil filtration, oil well drilling, paint and coating suspension agents, liquid fertiliser, gellants, liquid animal feed, catalyst support and cosmetics. 

Active Minerals International LLC produces high-quality attapulgite products at a production facility in Quincy, Florida. The company makes MIN-U-GEL and Florigel HY-branded attapulgite products from extensive deposits in Georgia and Florida and is the largest producer of gelling attapulgite clay in the world.

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Figure 6: Rod-shaped attapulgite in Acti-Gel 208
Macaulay/James Hutton Institute, Aberdeen 

Typical markets for these products include paint and coatings, building products, oil well drilling mud, agricultural suspensions, catalyst and molecular sieves. An SEM of Active Minerals’ Acti-Gel 208 product, consisting of pure, uniformly sized, rod-shaped mineral particles, is shown in Figure 6.

Attapulgite clays found in the Meigs-Quincy district of southeast US are typically bundles of palygorskite clay particles 2-3microns long and less than 3nm in diameter. The bundles are surrounded by a matrix of smectite clays that are slightly swellable. 

Dry-process grades contain up to 25% non-attapulgite material in the form of carbonates and other mineral inclusions. Processing involves drying and grinding the crude clay to specific particle size distributions with certain ranges of gel viscosity, depending on the end use.  

Oil-Dri Corp. of America produces sorbent products mainly from montmorillonite and attapulgite, which it has mined from deposits in Ochlocknee, Georgia since 1968. 

Attapulgite in China

Anhui Mingmei MinChem Co. Ltd, a Chinese-US JV, was the first company to focus on attapulgite production and development in China. Its Chinese owners established a factory in Mingguang in 1984 and the JV with US-based MinTech International Inc. was formed in 1998. Today, its main products are attapulgite, molecular sieves and other related mineral and chemical products. 

Since 2015, Mingmei’s controlling shareholder has been MinTech International, after the Chinese government transferred its share of the company to private ownership. The current business was built partly on the back of US-led research into sedimentary-type attapulgite clay along the boundary between Mingguang city in Anhui province and Xuyi county in Jiangsu province in east China. In 2009, the company relocated to the Mingguang Development Area and Jianxi Attapulgite Park, forming separate attapulgite and molecular sieve production bases. 

It has three attapulgite mines with over 2m tonnes proven reserves. The attapulgite ore body is four metres thick and is overlain by 10-40 metres of partially weathered basalt. The deposits were formed from the alteration of basaltic ash with minor amounts of smectite, quartz and dolomite associated with attapulgite. 

Mingmei produces around 30,000 tpa attapulgite, of which 40% is exported. The company produces approximately 5,000 tpa of various molecular sieves and other special products that can be used for air separation, refrigeration, automobile and insulating glass. It is also working on new applications for its attapulgite and has developed a mixed palygorskite-montmorillonite product to control the formation of mycotoxins, to detoxify and to decontaminate foodstuffs.

Recently, Mingmei has been struggling to secure enough raw material to meet demand, thanks to government controls on mining for the last four years, forcing Mingmei to source raw material from other countries. 

Attapulgite in Greece

Geohellas owns attapulgite mining and processing operations at Grevena in the north of Greece. The business includes four quarries located in the vicinity of the plant, containing proven reserves of more than 20m tonnes sedimentary, high quality attapulgite-saponite. Mining is generally carried out between May and September in favourable weather conditions.  

Within Geohellas’ deposit, there are distinct attapulgite, saponite and mixed clay beds. A view of the Pilori mine in Figure 7 shows attapulgite, mixed and saponitic beds. The attapulgite is grey to light violet in colour, saponite is green to tan while mixed clay beds have a light tan colour.

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Figure 7: View of attapulgite-saponite beds at the Pilori mine in Greece. The gross
stratigraphic sequence of sediments from bottom up and from the periphery towards
the centre of the basin is saponite>mixed clays>attapulgite. Analysis of Geohellas
samples have identified at least 15 different types of clay.
Geohellas 

Geohellas’ clay is locally sun dried, reducing fuel consumption during processing. The company’s plant produces a range of granular and powder products from three separate production lines. The facility has a capacity of 140,000 tpa, following installation of a new mill in 2015. Geohellas’ sales of attapulgite, saponite and mixed attapulgite/saponite are approximately each a third of the total. Its attapulgite is mainly sold to the absorbent, bleaching and gelling industries, while saponite is mainly sold as cat litter and as construction material.

A view of the Geohellas plant is in Figure 8.

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Figure 8: View of Geohellas plant, Greece. 
Geohellas 


Sepiolite

Sepiolite, formerly known as meerschaum, meaning sea froth, is non-swelling, lightweight, porous clay with a large specific surface area. The individual particles of sepiolite have a needle-like morphology, high surface area and porosity. The shape of the particles accounts for its high sorption capacity and colloidal properties that make it suitable for a wide range of applications.  

Chemistry palygorskite and sepiolite

Palygorskite/attapulgite (MgAl)5(SiAl)8O20. (OH)2. 8H2O

Sepiolite Mg4Si6O15 (OH) 2. 6H2O 
Sepiolite has the highest surface area (BET) of all the clay minerals, at about 300m2/g, with a high density of silanol groups (-SiOH) which explains its hydrophilicity. Sepiolite particles have an average length of 1-2micron, a width of 0.01microns and contain open channels with dimensions of 3.6Åx10.6Å running along the axis of the particle. These particles are arranged to form loosely packed and porous aggregates with an extensive capillary network. This chain-like structure produces the needle-like particles.

Its applications include cat litters, paints, industrial waste, cosmetics, friction control, catalysis, fertilisers, asphalt, drilling mud, acoustics, insulation, water proofing, absorption, filtering, moisture control, supports, bleaching, animal feed, plastics, rubber and construction.

Spain is the largest producer of Sepiolite with leading companies like TOLSA producing more than 620,000 tpa from mines in Toledo and Mineria y Tecnologia de Arcillas (Group SAMCA) mining up to 120,000 tpa from mines in Zaragoza. Tolsa has also been operating a sepiolite mine in Ankara, Turkey since 2012.  In 2013, Tolsa inaugurated its first manufacturing plant in Turkey located in Eskisehir to manufacture consumer products for the pet litter market. 

In Senegal, Senegal Mines SA, which is jointly owned by Spanish company Sepiol SA (51%) and the Senegalise government (49%) has capacity of 100,000 tpa at a location 240km south of Dakar. Société Senegalaise de Phosphates de Thies S.A (SSPT) has mines located at Lam Lam in the country’s Thies region and is owned by TOLSA.

Acknowledgements

Kostas Vythoulkas, Geologist, Geohellas SA, Greece
Dr. Michael Zhou, CEO, Anhui Mingmei MinChem Co. Ltd, China
Alexander Yanchuk, General Manager, VELES Agrarian LLC, Ukraine 

*Ian Wilson is an industrials minerals consultant based in the UK.