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.