Special clays are a group of products derived from a number
of different clay minerals found in a wide range of geological
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
Figure 1 outlines bentonite nomenclature and shows the
relationship between some smectite minerals, with respect to
their structure, chemistry and morphology.
Bentonite nomenclature (smectite group)White
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
|Source: HH Murray, Applied
Clay Mineralogy, Elsevier
|Figure 2: Montmorillonite from the
The Clay Minerals Society, London
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
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 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
|Table 2: Typical characteristics
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
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
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.
|Figure 3: SEM of Newberry Springs hectorite
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
Key applications of hectorite
- Industrial coatings: Protective applications in
automotive, containers, furniture, flooring, marine,
plastics and construction.
- Decorative coatings: Homes, offices and similar
- 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
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
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 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
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
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
|Figure 4: Veles saponite
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
|HH Murray and Huitang Zhou, SME
Industrial Minerals, 2005
Source: HH Murray, Applied Clay Mineralogy,
|Figure 5: SEM of attapulgite from
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.
|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
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
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
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.
|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
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
|Figure 8: View of Geohellas plant,
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
Chemistry palygorskite and sepiolite
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
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.
Kostas Vythoulkas, Geologist, Geohellas SA, Greece
Dr. Michael Zhou, CEO, Anhui Mingmei MinChem Co. Ltd,
Alexander Yanchuk, General Manager, VELES Agrarian LLC,
*Ian Wilson is an industrials minerals consultant based
in the UK.