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Bentonite
Uses and Sources
Overview
Made up mainly of montmorillinite,
(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O
Formed from the weathering of volcanic ash beds
Named for Fort Benton, WY, where it was first
described as part of a Cretaceous tuff sequence
Grades vary, but it is generally impure, with
inclusions of other smectite minerals, as well as
quartz, feldspar, calcite, and gypsum
Exhibits a number of unique properties
(IMA-NA 2007)
Properties & Applications
Thixotropy
– Can be semi-solid at rest, but
will be liquid when agitated
– Used as a thickening and suspension agent in
paints, dyes, and varnishes
(KSGS 2002)
Properties & Applications
Cohesion
– Binder and pelletizer
– Ironworks: ore pellets for
feeding into furnaces, and
as a binder in casting sand
molds
(MiningLife 2005)
Properties & Applications
Absorption / Adsorption
– Can absorb several times it dry weight in water
– Pet litter, impermeable clay liners, wastewater
treatment, detergent purification, paper pulp
purification, de-inking
(IMA-NA 2007)
Properties & Applications
Inertness
– Won’t kill you to eat it!
– Filler in pharmaceuticals, animal feed, and
cosmetics
– Purifier and clarifier in beer, wine, and honey
(WSGS 2007)
Properties & Applications
Viscosity and Plasticity
– Drilling: vertical and horizontal
– Lubricates the bit, seals the walls of the borehole,
removes drill cuttings
– Additive in Portland cement,
mortars, and specialized plasters
(WSGS 2007)
Bentonite as a Value-Added Commodity
Bentonite is not often taken straight from the ground
to market.
Much purification is often undergone to specialize
the product
–
–
–
–
–
Sieving (for granular bentonite)
Milling (fine and superfine powdered bentonite)
Removal of associated gangue minerals
Treated with acids (“bleaching earths”)
Treated with organics (“organoclays”)
(IMA-NA 2007)
Bentonite Producers & Refiners
AMCOL International (miner, refiner, large producer
of bentonite products)
Aqua Technologies (organoclay water treatment)
Black Hills Bentonite LLC (miner and 1st-stage
refiner)
BPM Minerals LLC (producer)
CETCO (special-purpose bentonite products)
Montana Bentonite LLC (producer and refiner)
…and MANY others
Production Methods
Drilling & Sampling
Soil Profiling (to aid in
speedy recovery after
reclamation)
Topsoil & Overburden
removal (usual with
scrapers)
Quarrying with loader &
truck
Only economic to mine
bentonite with no more than
50 feet of overburden
(WMA-Minelife 2007)
Simplified Bentonite Mill Flow-Chart
(WMA Minelife, 2007)
World Reserves and Production Statistics
Reserves of all clays used
by man are extremely large,
and are thought to be
inexhaustible on human
timescales
As a result, no concrete
measurements of world
reserves have been
performed
It is still a very lucrative
sector. US production in
2005 amounted to 42
million tons worth $1.7
(Numbers are in thousands of metric tons)
billion
(USGS 2007)
Worldwide Distribution
(Mindat 2007)
End Use Statistics
(USGS 2005)
Works Cited
Industrial Minerals Association of North America, www.ima-na.org, (Accessed March 23, 2007).
Kansas State Geological Survey, http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/bentonite.html,
(Accessed March 27, 2007).
Mindat, http://www.mindat.org/min-9141.html, (Accessed March 27, 2007). MiningLife Media,
http://www.mininglife.com/commodities/Bentonite.asp, (Accessed March 25, 2007).
WMA-Minelife, http://www.wma-minelife.com/bent/bentmine/bentmine.htm, (Accessed March 27, 2007).
Wyoming State Geological Survey, http://www.wsgs.uwyo.edu/minerals/bentonite.aspx, (Accessed
March 27, 2007).
USGS, http://minerals.usgs.gov/minerals/pubs/commodity/clays/, (Accessed March 27, 2007).
USGS, 2005, Bentonite statistics, in Kelly, T.D., and Matos, G.R.,comps., Historical statistics
for mineral and material commodities in the United States: U.S. Geological Survey Data Series
140, available online at http://pubs.usgs.gov/ds/2005/140/ . (Accessed March 27, 2007.)