Kaolin

The name “kaolin” was adopted from a hill in China (Kao-ling) where it was mined for hundreds of years. Western countries first learned about kaolin when samples of the clay were sent back to Europe by a Jesuit missionary about 1700 as examples of how the Chinese manufactured porcelain. Besides its use in the making of porcelain, kaolin has also found to be necessary in the making of paper, paint and rubber products.

Kaolin, in its natural state, is a soft white powdery substance consisting of the mineral kaolinite that, when examined under an electron microscope, appears to consist of hexagonal, platy crystals measuring from 0.1 to 10 micrometres, sometimes larger. Kaolin crystals sometimes take on book- like and vermicular forms with the occasional macroscopic forms of millimetre size.

Kaolin is found naturally among other minerals such as anatase, feldspar, quartz and muscovite and although it is characterised as being a soft white powder, it can also be found in a yellow colour after being stained by iron hydroxide pigments in the clay surrounding the deposit. When this occurs the clay has to be bleached and washed with water to fully remove the offending minerals to make the isolated kaolin suitable for commercial use.

Kaolin becomes plastic and is able to be moulded into various shapes when it is mixed with around 20 to 35 percent water. When a larger amount of water is added kaolin becomes a slurry, add more and it becomes a watery suspension. The amount of water required to cause kaolin to become plastic is dependant on the size of of the kaolin particles as well as any other chemical that may be present. Most of the world's mines that produce kaolin are in the south eastern states of the United States, others are in the Czech Republic, Germany, England and France.

Australia has six kaolin producers that mainly supply the domestic market. The single largest producer in Australia is Unimin, a fully owned subsidiary of Belgium industrial chemical company Sibelco. Australia produces around 155,000 tonnes of of kaolin a year that comes from all states with the majority coming from Western Australia, New South Wales, Queensland and Victoria. Some of Australia's largest deposits in Western Australia and South Australia are not fully exploited because of the short supply of suitable water. Other deposits, such as those in Skardon River and Broome, are hampered because of their remote location that creates too high a cost regarding transportation that make the mining of kaolin at these sites uneconomical.

Uses of kaolin:

Filling and coating of paper
The manufacturing of glossy white-ware ceramics, particular in the producing of china,
porcelain and refractors
Improving the mechanical strength and resistance to abrasion of of rubber by filling
A flattening and extending agent in paint products
As an ingredient in ink, cosmetics and organic plastics
As an absorbent

Kaolin, as a naturally occurring industrial mineral, is an essential ingredient in many different types of applications. It is widely used as a filler in many variations, in medicines, paint and paper pigment, food products and polymers.