China Clay

Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4.

It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra.Rocks that are rich in kaolinite are known as kaolin or china clay.

Intro

China clay occurs in the deposits in the form of china clay rock, a mixture of up to 15 per cent china clay and up to 10 per cent mica, and the remainder being quartz.

The clay itself varies considerably from pit to pit. In some deposits, such as those at Blackpool, Littlejohns and Goonbarrow, the clay is ideally suited for the filling and coating of paper, while in other deposits, such as Treviscoe and Wheal Remfry, the clay is best suited for the making of ceramics.

The formation of china clay

China, the pure white porcelain used by the Chinese, was discovered many thousands of years ago and has always been a much-prized material.

Despite many attempts to find sources elsewhere, it remained elusive until a few deposits were found in some parts of Europe and in America early in the eighteenth century.

As more potteries made use of porcelain, so the demand grew and by the early nineteenth century the kaolin industry had become highly successful, with many of the Potters owning rights to mine the material for themselves.

In addition, by the middle of the nineteenth century, china clay was increasingly being used as a raw material by the developing paper industry.

Development of the China Clay Industry

China clay mining is a complicated process which can be split into three distinct sections - opencast mining, refining and drying

Known as pit operations, this process firstly requires the removal of ground overlying the clay. This is known as overburden, which can vary in depth between one and fifteen metres.

Once the clay is exposed, the method of mining is best described as a hydraulic mining process. This means, quite simply, that a jet of water under enormous pressure is fired at the pit face from a water cannon known in the industry as a monitor.

This liberates from the quarry face the china clay, together with sand and mica.

The material runs in slurry form to the lowest part of the pit, known as the sink, where it is lifted by centrifugal pumps to mechanical sand classifiers, where the more coarse sand elements are removed. The sand is disposed of on belt conveyors, which deposit it on low profile tips that can then be landscaped and seeded with grass.

Having removed the coarsest of the sand, the clay suspension is then transported by underground pipeline to the second process: refining.

China Clay Production

RefiningRefining consists of a series of mineral processing

techniques - predominantly sedimentation - designed to remove the smaller sized waste particles, mainly minerals such as very fine quartz, mica and feldspar, leaving only the required china clay behind.

Value can also be added to the clay at this stage by a variety of processes designed to engineer size and shape of the product, together with the use of a chemical bleaching process that improves its whiteness

Having refined the clay, it is moved on to the final process: drying.

DryingDrying consists of firstly converting the liquid

clay into a solid material by a process known as filtration. The products of filtration normally have a moisture content of about 25%.

Passing the clay through a thermal drier further reduces this moisture content. The driers are fired by natural gas and see a product emerging at around 10% moisture. The product is normally sold in pelletised form - particle size ranges from 6-12mm.

Production

Paper and board, coating clays; fillers; brush coating clays; machine coating clays. Ceramics (excluding refractories), bone china; hard porcelain (including tiles,

tableware, sanitary and electrical porcelain); fine earthenware; earthenware (lower grade); earthenware (sanitary); porous wall tiles; electrical porcelain (England); semi-vitreous china (American); semi-vitreous porcelain (American); hotel china (American); household china (American); belleek (American); glazes (mill additions and frit additions); porcelain enamels; radiants.

Rubber Paint and distemper Leather Cosmetics, insecticides, dusting and medicinal Textiles Linoleum White cement Ultramarine Plastics Miscellaneous, soap; cleaners; inks; fuses; pencils; grinding wheels; welding rods;

boiler coverings; asbestos; dyes; accumulator cases; lubricants (extrusion).

Uses of China Clay

Particle Shape: Platy, with typical aspect ratio of 20:1

Specific Gravity: 2.6 Refractive Index: 1.56 MOH Hardness: 2.5 Moisture: (max %) 1.5 pH: 5-7.5

Properties