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. 2.6 Hardness Color White, Brownish white, Grayish white, Yellowish white, Grayish green. Fluorescence None Magnetic 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) 2 Si 4 O 10 (OH) 2 ·n(H 2 O) S.G , Average = 2.35 Hardness Color White, Gray white, Yellow, Brownish yellow, Greenish yellow. Fluorescence None Magnetic 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 Na 0.3 (Mg,Li) 3 Si 4 O 10 (F,OH) 2 S.G , Average = 2.5 Hardness 1-2 Color White. Fluorescence Yes Magnetic 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 equipment And abundant Supplies have taken Price down (and opened up the Cat 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) 2 Si 4 O 10 (OH)·4(H 2 O) S.G , Average = 2.15 Hardness Color White, Gray, Brownish white. Fluorescence None Reported Magnetic No

Sepiolite Micrograph photo Mg 4 Si 6 O 15 (OH) 2 ·6(H 2 O) S.G. 2 Hardness 2 Color Grayish white, Yellowish white, Bluish green white, Reddish white, Gray. Fluorescence None Magnetic No

What is Fuller’s Earth Worth? Easy process and Bulk handle has Again brought down Price (prob also Bentonite 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.