Industrial minerals, with or without modification, play a
key role in removing and sequestering harmful waste
A number of recent developments including Swedens
plans for utilising bentonite in nuclear waste disposal have
highlighted this growing trend in the industry (see IM July
09, p.24: Bentonites nuclear disposal
There are many end uses including the well known flue gas
desulphurisation (FGD) to the lesser know application in acid
mine drainage and land remediation.
Nuclear disposal techniques utilise minerals
with absorbing properties, particularly bentonite.
Courtesy Steve Morgan/Greenpeace
Flue gas desulphurisation
Power plants emit large amounts of sulphuric oxide gases,
derived from the sulphur in the fuel. These gases cause acid
rain that damages foliage and leads to eutrophication of lakes
Sulphur trioxide is also generated as a by-product from
Selective Catalyst Reduction (SCR) used in some power plants to
Coal has the highest sulphur content, followed by oil, which
may be high in sulphur, like Venezuelan crude. Natural gas can
be sweet with low sulphur or can be high in
Sulphur compounds are removed from the flue gases by
treatment with limestone or lime. The utility power plant
category dominates the FGD market at 90%.
In the USA in 2007, Flue Gas Desulphurisation (FGD) consumed
14.5m. tonnes of limestone and 3.73m. tonnes of lime
both products add carbon dioxide to the atmosphere.
Gypsum is formed by the reaction. Where the power plant is
near a wallboard plant, it is used as a substitute for mined
One such new project is Bulgaria where Balkanstroy Group AD
has started construction of a gypsum board and gypsum mortar
facility near Stara Zagora. The $55m. plant will consume
360,000 tpa of FGD gypsum (IM 4 June 2009: Bulgarian gypsum
In the USA last year, 8m.tonnes of this synthetic gypsum
were used out of a total consumption of 18.7m. tonnes, the rest
being mined gypsum. Some magnesium hydroxide slurry is also
used in FGD. The advantage is that the magnesium sulphate
produced is soluble and thus solid waste problems are
Wollastonite reacts with sulphuric, carbonic and
hydrochloric acids, so can substitute for lime and limestone.
Diopside, a by-product of some wollastonite sources, should
also be useful in FGD.
Acid Mine Drainage
Pollution by toxic heavy metals, including arsenic, cobalt,
copper, cadmium, chromium, lead, silver and zinc , and by
aluminium and manganese, occurs when rock excavated or exposed
in an underground mine, is leached out by water. Leaching is
accelerated in the low pH conditions created by Acid Mine
Drainage (AMD) from sulphide ores.
Pollution also occurs when chemicals such as cyanide,
sulphuric acid and flotation reagents spill, leak, or leach
from the mine site into nearby water bodies. These chemicals
can be highly toxic.
The US Toxic Release Inventory (TRI) requires mining, among
other industries, to report on their release of toxic
chemicals. In 2005, although mining represented less than 0.5%
of the industrial activity, it produced 27% of all toxic
chemicals reported, an amount of 530m. tpa. Of this, 97% was
from drainage from mine tailings.
Some 80 facilities are not reporting tailings and waste rock
to NPRI so the actual release of toxics could be much higher.
Remediation of AMD is performed mainly by adding limestone and
lime, but also by caustic soda, and hydrogen sulphide.
In 2007, in the USA, 3.74m. tonnes of limestone and 104,000
tonnes of lime were used in AMD remediation.
The use of both these products results in the release of
carbon dioxide into the atmosphere. An environmentally
preferred alternative is the use of wollastonite.
Wollastonite has a neutral pH but this rises to an alkaline
10.4 in contact with water due to the hydrolysis to lime and
In acid waters, this process is accelerated and a surface
layer of amorphous silica remains on the wollastonite particle.
The lime captures the sulphuric acid in AMD as insoluble
calcium sulphate, with potential use in gypsum wall board.
The amorphous silica is porous and has a high surface area.
For wollastonite milled to 63 microns in size, the reactive
surface area increases from 1.19 to 47.6 m²/g after 15
days in mine drainage fluid.
This silica has been shown to adsorb arsenic, copper, zinc,
iron and aluminium.
Liners and caps
Swelling bentonite is also used as an admix 3 to 5:1 with
native soil in layers 1.5 to 3 cm thick to form an impermeable
liner for tailings ponds, in the same way that it is used in
landfills. It may also be used to cap waste rock piles.
Sodium-bentonite swells when contacted by water, thus
forming an impermeable self-healing barrier.
Around 139,000 tonnes of bentonite were used in
waterproofing and sealing applications in 2007.
India and China are he most promising markets for
geosynthetic clay liners (GSL). Amcol International Corp.
currently has GCL production facilities Australia, China, India
(via a j-v with Ashapura), Poland, South Korea, and the UK.
Amcol produces bentonite GCLs for landfill protection from
its six plants worldwide, and it has nearly a 50% market share.
The company is eyeing China, India and Brazil as the major
Nuclear waste disposal
Disposal of nuclear waste and dealing with spills, is an
on-going problem, which is likely to increase with the
replacement of carbon dioxide generating fossil fuels by
There have been a number of nuclear waste spills
notably in Chernobyl (Ukraine), Windscale (UK), Chalk River
(Canada ) ,Savannah River Site (USA) , Maxey Flat (USA), and
the Areva plant in Tricastin (France).
Solid nuclear wastes are encapsulated in glass, copper or
special cements. Liquid wastes are concentrated by ion-exchange
Deep well burial is one method to dispose of spent fuel. To
prevent damage of containers and release of radioactive
nuclides, SKB of Sweden, places the copper capsules in holes
backfilled with bentonite. This cushions the capsules against
crushing by rock movement, and seals against leakage in or
Radioactive elements are released by nuclear accidents and
in the course of normal activities.
These elements are long lived and can persist for a lifetime
in the body when inhaled or ingested. The result is often
Radioactive caesium, 137 Cs products of the Chernobyl
disaster were carried by air streams and have been detected as
far west as Vermont.
It has been shown that radioactive chemicals can be removed
from waste streams and sequestered by various minerals. The
minerals are mainly clays, micas, zeolites, silicas and
Bentonites role in nuclear waste
Adapted from SKB
Finnish group Kemira Oy discovered that phlogopite can
extract and sequester radioactive elements from contaminated
waters by ion exchange.
Sridhar Komarneni and Rustum Roy of Pennsylvania State
University discovered that phlogopite acts as a highly
selective sieve for capturing radioactive isotopes of ceasium,
cobalt and strontium from liquid wastes. These are immobilised
in a solid form that can be disposed of as solid waste.
Mica can be used by dispersing it in water or soil and then
filtering out the caesium-laden product or by letting
caesium-contaminated humans or animals ingest the material,
which extracts the caesium from the body and is then
Phlogopite is 30 times more effective than muscovite and 6
times more effective than biotite, in the sequestration of
radioactive cobalt, 60Co.
When the finely ground phlogopite is converted to the sodium
form by ion exchange, the 60Co, radioactive cobalt,
uptake is doubled. Phlogopite is also 16 times more effective
in the sequestration of radioactive strontium, 85
However natural muscovite is 13 times more effective than
phlogopite in sequestering radioactive cesium,
The Savannah River Site, Aitken, South Carolina, USA was
built by E.I. du Pont de Nemours now chemicals giant
Dupont for the Atomic Energy Commission in the 1950s as
a site to produce weapons grade nuclear materials.
The site is highly contaminated due to dumping and releases
of chemicals in the 1950s. Over 500 Curies - of Caesium 137
were released into cooling water. This has contaminated the
canals and wetlands to the extent of 3,000 acres.
The ceasium winds up in the sediment but rises to the
surface annually. Since ceasium replaces potassium, it is
concentrated in the wetlands plants and garden vegetables and
thence into foraging animals.
Residents in the area are advised not to eat dear meat and
home grown vegetables.
Caesium isotope 137Cs with a half-life of 30 years, is the
most prevalent radioactive isotope in people exposed to nuclear
radiation. Offsite people in the SRS area have high levels of
137Cs. SRS has the highest 137Cs concentration ratio in the
world 6.8+/- 2.3. The recommended maximum level is
The river covers 310 square miles. Remediation is on-going
and the major sites are planned to be remediated by 2025.
A 2002 study was made, on an area of 8 acres with one canal,
of the use of various minerals to decontaminate wet lands at
the Savannah River. Various clays were evaluated; kaolin gave
poor results and illite mica the best.
The conventional method is to dig out the sediment and truck
it to a dump. The cost, for an 8 acre site, was estimated to be
Tests were conducted using illite (fine grained muscovite )
as an on-site additive, in a layer 0.1 inch thick, consuming
about 100 tonnes.
The illite absorbs the 137Cs and sinks to the bottom of the
wetland and stays there, holding the cesium tenaciously. It is
reported not to release it over time or exposure to ammonium
The cost to decontaminate the 8 acres on site by
illite was estimated to be only $19m. The illite price used was
$450/tonne delivered, this the illite needed to remediate 3,000
acres would be 37,500 tonnes.
The best of the illite minerals tested was Todd Light ball
clay produced by KT Clay, TN, specification 89% < 5 microns
and 46% < 0.5 microns.
Mineralite 3X and 4X from MMC also demonstrated good results
these have 95-98% -325 mesh.
Saponite is a magnesium-containing clay similar to a
non-swelling bentonite. It is produced by IMV Nevada.
Saponite from the Khmelknytsky saponite deposit in the
Ukraine, is being used mainly as a detoxicant for animals in
the Chernobyl region that have ingested radioactive elements in
Zeolites, both naturally occurring and synthetic, are used
in the decontamination and disposal of radioactive wastes.
After the Chernobyl nuclear accident, mordenite zeolite was
added to animal feed in Sweden to remove 137Cs from the
gastrointestinal tracts of contaminated animals.
Minerals in mercury removal
Mercury is released into the atmosphere from cement kilns,
but it is coal burning plants that are the largest source of
mercury emissions, about 40 tonnes annually 40% of the
total emissions. The top 50 power plant polluters in the US
emit over 18,000kg of mercury annually.
This has resulted in Environmental Protection Agency (EPA)
regulations which call for 80% reduction by 2010 and 90% by
The conventional flue gas treatment is Activated Carbon
Injection (ACI), at a cost of about $2,530/tonnes, which can
reduce mercury emissions by 90%.
Activated carbon is made by pyrolysis of nutshells, wood, or
coal. It has very high surface area of 500 1500 sq. m/g.
It may contain graphene layers to account for the high surface
area. It is often treated with sulphur or iodine to increase
efficiency. Activated carbon, iodine treated, can absorb up to
5kg mercury for each tonne
When used, ACI adds carbon to the fly ash produced from the
power plants. The carbon in the fly ash can cause problems when
used in the manufacture of concrete. Millions of tons of fly
ash are used in the USA and Canada for the production of
concrete. The presence of too much carbon into the fly ash in
some instances makes the fly ash unusable in this
Indias Ashapura Minechem mine bentonite from
state for use in Geosynthetic Clay Liners which it
through subsidiary Ashapura Volclay.
Geosynthetic Clay liners - a lining material filled with
bentonite clay - are one of the largest uses of
minerals in the waste disposal market.
EPA now estimates mercury emissions in the US from cement
clinker production at 10,500 kg/year. Part of it is from the
coal fuel used, but it is also present in the limestone and
shale feed. EPA legislation is pending to regulate feed or
emissions concentration limits to 120 microgramme/ dry standard
The goal is to reduce mercury emissions by 81- 93%.
Other mercury remediation methods
Zeolites are being proposed for the extraction of mercury.
Large scale tests, in power plants, are underway, using
chabazite zeolite from Canada based Zeox Corporation.
A US patent has been applied for by Millenium Inorganic
Chemicals now part of Cristal Global for
precipitated silica, which has been treated with copper or
other transition elements and with sulphur-containing silane
which gives better results in removing mercury from gaseous
Highly porous silica has been developed by the researchers
at the Pacific North-west National Laboratory. This, when
treated with thiol a sulphur/hydrogen compound
has the ability to capture mercury ions in wastewater. The
thiol attracts mercury ions, but ignores other ions in the
The synthetic silica from decomposition of wollastonite
and/or diopside has a high porosity and surface area and may
also be able to sequester mercury.
Prior patents (US 6,719,828 and 7,048,781) use silicates
such as montmorillonite and vermiculite, treated with metal
sulfides, for the same purpose.
It is possible that high aspect ratio wollastonite, treated
the same way, could also sequester mercury. Also expanded
graphite, with its high surface area, and graphene content may
behave like activated charcoals and absorb mercury.
Obama minerals bounce
The use of industrial minerals in environmental remediation
is likely to grow with the growth of legislation, especially
during the presidency of Barack Obama. The new US Fuel
Efficiency Policy which could spell an end to gas
guzzling vehicles, is the most sweeping environmental act
since the Clean Air Act of the 1970s which is the basis for
todays pollution regulations.
Passing such an act within the first six months of his
presidency, Obama has given a strong environmental statement of
intent to the world which is expected to pave the way for the
use of many minerals in waste remediation and emissions
The minerals most likely to be affected by such trends will
be limestone, lime, magnesium hydrate, micas, clays, zeolites,
activated carbon, graphite, wollastonite, diopside and
Contributor: George Hawley, of George C.
Hawley & Associates, Canada, is an industrial minerals