What and Why of Mineral Fillers Mineral filler is ground up rock added to a mix –The mineral filler is an additive and modifier, not the main product. Mineral fillers enhance and alter the product Mineral fillers help control product costs by displacing more expensive ingredients and taking up space in a product matrix.
Factors Typically Considered in Filler Selection Cost Hardness Particle Size and Shape Color Refractive index properties Chemical properties
The Paper Market Paper uses fibers to provide strength, but the smoothness, and reflective properties come from filler. –Kaolin dominates and provides the brightness to the surface Need nice white grades of clay Needs to thin down nice so you can get smooth thin coatings (rheology) –Calcium Carbonate is gaining ground Not making paper with acid chemistry as much so calcium carbonate reactivity not a problem Can get from natural grind Or precipitation from solution –Talc Helps prevent clumping of wood fibers –Amorphous silicates Adsorb and prevent ink strike through –Alumina Tri-hydrate Releases a lot of water at low temperature and makes paper more fire retardent.
Talc Mg 3 Si 4 O 10 (OH) 2 Hardness 1 (softest mineral) S.G. 2.58 - 2.83 Color Colourless, white, pale green, bright emrald-green to dark green, brown, gray Greasy feel
Paint and Ceramics Many filler characteristics similar to paper –Titanium Dioxide provides great whiteness but it is more expensive –Pyrophyllite also used Pyrophyllite is an important ceramic filler –Talc also used –Wollastonite plays similar roles It provides permanent expansion on heating (great if something else is shrinking) –Of course cheapies like calcium carbonate and lesser talc are also valuable
UV Absorbance Titanium Dioxide minerals add UV resistance to plastics Also used in Sun Screen for same reason –Zinc oxide competes in this application
Rutile TiO 2 Hardness 6 - 6½ S.G. 4.23 Color Blood red, bluish, brownish yellow, brown-red, yellow, grayish-black, black, brown, or violet (Rutile means red)
Anatase TiO 2 One of the three common Forms of titanium dioxide S.G. 3.79 - 3.97 Hardness 5½ - 6 Color Brown, yellowish or reddish brown, indigo blue, black; greenish, pale lilac, grey, rarely almost colorless
Brookite TiO 2 One of 3 common forms of Titanium dioxide S.G. 4.08 - 4.18 Hardness 5½ - 6 Color Brown, yellowish brown, reddish brown; dar brown to iron-black; yellowish brown to dark brown in transmitted light
Pyrophyllite Al 2 Si 4 O 10 (OH) 2 Same thing as Talc with Al instead of Mg Hardness 1 - 2 S.G. 2.65 - 2.9 Color White, gray, pale blue, pale green, pale yellow, brownish green
Wallboard White filler powder packed in drywall is usually gypsum –Can be mined but synthetic gypsum is also produced by using limestone to scrub sulfur emissions out of coal flue gas Scrubber gypsum is cheaper than mining gypsum Problem is that location and shipping cost to wallboard plants can negate the cost difference –Building whole new wallboard plants but that’s a lot of at risk capital –The dark side of scrubber gypsum Small amounts of ash can give slight gray tone (acceptance) Need to control salt content or it will corrode drywall screws Countries with a lot of Pyrophyllite fill wallboard with Pryrophyllite
Gypsum Ca[SO 4 ] · 2H 2 O S.G. 2.312 - 2.322 Hardness 2 Color Colorless to white, often tinged other hues due to impurities; colorless in transmitted light.
Plastics and Polymers Ground Powdered calcium carbonate the dominant material –Provides bright coloring –Low absorbance of oil (an expensive glue in plastics) –Provides high gloss –Hardens against gouging and scaring Ground Talc –Soft but gives very smooth surfaces –Makes easier to get out of molds – kind of lubricant like Calcined clay –Absorbs in plasticizers very well Small amounts of mica, silicates and even barites
Adhesives and Sealants Calcium Carbonate and Kaolin –They are cheap and fill a lot of space without messing up flow characteristics. Drilling mud uses barite for density control Kaolin and diatomite prevent caking of ANFO Coal mine rock dust is limestone
Talc and Pyrophyllite Uses
Relative Cost of Mineral Fillers (Lime Price is used as a surrogate for Calcium Carbonate)
Production Reserves of both are large Enough to be a non-issue
Density Modifiers Lightweight Applications –Use rocks that start at normal density but have a tendency to Pop or expand (a lot) when heated –Perlite Good insulator with low thermal conductivty Sound adsorbing Relatively chemically inert Fire retardant –Perlite is used In lightweight and lightweight precast concrete Acoustic ceiling tiles Loosefill insulation As a soil conditioner (from regulatory standpoint do need to check for silica content)
More Lightweight Applications Mica alters and stores lots of water Rapid water expansion pops the mica like worms Vermiculite has more chemically active surfaces than perlite –Is used as a carrier in insecticide sprays –Soaking up and containing oil –Used as a soil conditioner –Also found in lightweight gypsum plasters Fire resistant plaster boards –Can be used as a loose insulator
Barite and the Heavies Barite is used in drilling mud –Its heavy, non-abrasive, and inert It is used in heavy concretes –Concretes needing to weight down pipes in marshy areas –Good neutron adsorber so barite based concrete can reduce lead shielding at nuclear facilities Ground form is a filler and extender –Oil based paints because it does not adsorb oil –Can be used as a tire filler to add weight
Perlite Perlite is a water bearing natural glass That contains Silica, Alumina, Iron, Titanium, Calcium, Magnesium, Sodium and potasium Oxides
Vermiculite (Mg,Fe,Al) 3 (Al,Si) 4 O 10 (OH) 2 ·4H 2 O Hardness 1½ - 2 S.G. 2.3 - 2.7 Color Brown, bronze-yellow
Barite BaSO 4 S.G. 4.5 Hardness 3 - 3½ Color Colourless, white, yellow, brown, grey, blue, etc.; colourless in transmitted light (also tinted yellow, brown, green, blue, etc.)
Uses of Perlite
Uses of Vermiculite
Processing Vermiculite Separating Vermiculite from gangue Minerals is done by a variety of methods The interesting twist is Launching down a wind Tunnel The largest plates settle Out first.
Vermiculite Expansion Drop the flakes right through gas burners (it does not burn) 1000 to 1500 F Water in the weathered mica flashes to steam popping the flakes like pop-corn.
What are They Worth? Vermiculite about $50/ton Barite about $50 to $60/ton Perlite about $140 to $150/ton