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Clays
©2009 Dr. B. C. Paul
Credit is given to Industrial Minerals (SME), USGS,
A Geologist – Mining Discontinuity(Or Should I Say Market Discontinuity)
• Geology has a specialty for Clay Mineralogists who detail every structural and chemical aspect of clay
• The market rarely deals in pure clays– Our clays are normally concoctions of clay minerals
that either lack deleterious impurities or contain impurities that make them do interesting things
• Clays are Feldspar and Alumino silicate weathering products– They often develop a charged plate like structure at
the atomic level
Kaolin Clay Family
• Chemically it is a plate structure– 1 layer if silica tetrahedrons– 1 layer of alumina octahedrons
• Typical commercial properties– It is very fine grained – soft and non-abrasive– Clay is white– A mixture of course and fine plate sizes
makes a slurry that is thin and non-viscous even at high solids
Kaolin/ Kaolinite Size and Character
Al2Si2O5(OH)4 S.G. 2.6Hardness 1.5-2 Color White, Brownish white, Grayish white, Yellowish white, Grayish green.Fluorescence NoneMagnetic No
Uses
• Filler and coating for paper– Wood fiber just acts as a web to hold things together– Want bright reflective white– Low viscosity for easy handling
• Filler in paints and plastics– Conductivity and salt impurities also become
important• Ceramics
– How well it holds together– Fusing and melting temperatures
• Ball Clay– Used for making China (not the country)
Processing
• Dry process depends on original deposit pretty well being right for market– Crush material to size of egg– Dry it (rotary dryer)– Pulverize– Air sort for size and minor impurity removal
Wet Process
• Clay slurries are settled to get the grit out• Clay slurries are finely sized so exact size
consists can be blended back• Clay slurries may be leached or
magnetically separated to get out iron or other impurities
• Can flock and float to remove iron impurities
• Spray dried.
What is Kaolin Worth
Around $100 to$120/ton
Bentonite• Mostly made of geologist’s Montmorillanite
– Smectite clay group– A layer of octahedrons– 2 layers of coordinating ions in-between– Can allow 1 or 2 layers of water
• Structure gives bentonite a lot of ion exchange capabilities
Bentonite / Montmorillinite
(Na,Ca)0,3(Al,Mg)2Si4O10(OH)2·n(H2O) S.G. 2 - 2.7, Average = 2.35 Hardness 1.5-2 Color White, Gray white, Yellow, Brownish yellow, Greenish yellow. Fluorescence NoneMagnetic No
Applications and Ion Exchanges
• If sodium exchanges out there is expands more– Drilling applications usually want something thick at
low solids – usually not too much expansion• Bentonite is the opposite of Kaolinite
– Kaolin is thin and high solids – Bentonite is thick at low solids
– Another application is sticking sand together for foundary castings
• Low expansion is usually desirable• Calcium bentonite more suitable here
Hectorite
• A special lithium bearing smectite– Can produce a thixotropic property– That means it can liquefy when agitated
• Can hold up fines when drilling stops and the mud goes thick
• Then thins down when drilling resumes
Hectorite
Na0.3(Mg,Li)3Si4O10(F,OH)2 S.G. 2 - 3, Average = 2.5 Hardness 1-2 Color White. Fluorescence YesMagnetic No
More Applications
• Pelletizing Iron ore– Glue pellets together with bentonite – want
something thick with a strong bond
• Absorbent granuals– Layer structure was designed to soak up– Sodium bentonite which expands more has
found a new market• Scoopable cat litter
Processing
• Break up Clay Chunks – sometimes done with “slicer”
• Dry the Clay
• Crush to size
• Screen and bag
What is Bentonite Worth?
Easy processing,Big equipmentAnd abundantSupplies have takenPrice down(and opened up theCat litter market)
About $20-$30/ton
The Hormite Clays
• Palygorskite (attapulgite)• Sepiolite• It has a needle and fiber like structure that
gives it great adsorbent surface area• Super adsorbant• Also can have excellent filtering potential
– Fuller’s earth can be special bentonite or a hormite clay blend.
• Processing is similar to bentonite
Palygorskite
(Mg,Al)2Si4O10(OH)·4(H2O) S.G. 2.1 - 2.2, Average = 2.15 Hardness 2-2.5 Color White, Gray, Brownish white. Fluorescence None ReportedMagnetic No
Sepiolite
Micrographphoto
Mg4Si6O15(OH)2·6(H2O) S.G. 2Hardness 2Color Grayish white, Yellowish white, Bluish green white, Reddish white, Gray. Fluorescence NoneMagnetic No
What is Fuller’s Earth Worth?
Easy process andBulk handle hasAgain brought downPrice (prob alsoBentonite competition)
About $80-$100/ton
Common Clays
• Natural break down product– Local potters find clay mixes that suit their
particular firing needs
• Brick makers may not always be able to find suitable clays– May mine and process shales to get clay for
use in brickmaking• One of the major reasons that shale is mined• Its usually to flakey and layered to be a durable
aggregate.