TALC
Talc is hydrated magnesium silicate. It generally occurs in two morphologies, either macro- or microcrystalline. Talc can have slightly differing compositions subject to the associated minerals in the ore body, but all talcs exhibit to a lesser or greater extent the following unique features: softness, hydrophobicity, platy ness and organophily. These properties can be further enhanced by careful and sometimes propriety processing and bring a number of specific benefits to a wide range of industries including paper, paints, plastics, ceramics, rubber, personal care and roofing. Present annual world talc production is about 5.7 million tonnes, extracted from some 250 deposits scattered across the globe. The term 'talc' covers over 500 products, each distinct by their nature, the proportion of by-minerals they contain and by their properties. Other minerals varying with talc vary according to the user industry: the two principal ones being carbonates and kaolin. People always think of talc as white, but it can also be grey, green, blue, pink and even black.
Extraction and Processing
- Talc Mineralogy:
Talc is a hydrated magnesium sheet silicate with the chemical formula Mg3 Si4 O10 (OH)2. Its elementary sheet is composed of a layer of magnesium-oxygen/hydroxyl octahedra, sandwiched between two layers of silicon-oxygen tetrahedra. The main or basal surfaces of this elementary sheet do not contain hydroxyl groups or active ions, which explains talc's hydrophobicity and inertness. Talc is practically insoluble in water and in weak acids and alkalis. It is neither explosive nor flammable. Although it has very little chemical reactivity, talc does have a marked affinity for certain organic chemicals, i.e. it is organophilic. Above 900°C, talc progressively loses its hydroxyl groups and above 1050°C, it re-crystallises into different forms of enstatite (anhydrous magnesium silicate). Talc's melting point is at 1500°C.
- Talc Geology :
Talc is one of the common minerals in metamorphic rock. Although talc deposits can be found throughout the world in various geological contexts, economically viable concentrations of talc are not that common.
Talc Properties
TALC PROPERTY |
TALC FUNCTION |
USER INDUSTRY |
Platyness |
softness/non abrasiveness |
cosmetics, paper, roofing |
Platyness |
Printability |
coated paper |
Platyness |
Antisticking |
rubber tyres, foundry, food, animal feed, polyethylene antiblocking, fertilizers, paper (pitch and stickies control), roofing |
Platyness |
barrier effect |
paints, joint cements, plastic films, animal feed, fertilizer, rubber hoses |
Platyness & hydrophobicity |
barrier effect |
coated paper, roofing |
Organophilicity |
chemical demand |
coated paper |
Organophilicity |
adsorbing |
cosmetics, paper (pitch control), olive oil |
Organophilicity & hydrophobicity |
softness/feel |
coated paper |
Hydrophobicity |
printing runnability, porosity |
coated paper |
Hydrophobicity |
anticaking |
animal feed, food, fertilizers |
Magnesium content |
flux |
ceramic tiles, sanitaryware, glazes, tableware |
Chlorite content |
low thermal expansion |
refractories |
Magnesium & silicon content |
electro-insulating |
steatites and cordierites |
Molecular structure |
nucleating |
semi-crystalline polymers |
Non-polar |
electro-insulating |
wires and cables |
Inertness |
barrier effect |
rubber (pharmaceutical stoppers) |
Inertness |
carrier |
premixes, pesticides, pharmaceuticals, cosmetics |