China Clay –Definition, Processing, Properties & Uses

Find the china clay definition, processing, properties & uses here. China clay, also known as kaolin and white clay, can be used to make the required shape in the ceramic production process.

What is china clay?

China clay is also known as kaolin & white clay. Primary clay is formed during the natural kaolinisation process. It is formed by the decomposition of a portion of the feldspar mineral. It has a white colour and is used as a body former in the ceramic slip casting, pressing, and forming processes.

Table of Contents

China Clay: Definition, Processing, Properties & Uses 3

The chemical formula of China clay is Al₂Si₂O₅(OH)₄.

Formation of China Clay:

Many theories are put forth for the formation of China clay; some of them are accepted widely. We will see some of the methods in detail: 1) The igneous emanation theory. 2) The surface weathering theory. 3) The bog or moor water theory.

The igneous emanation theory:

As per the igneous emanation theory, igneous gases from the centre of the earth and superheated steam, carbon dioxide, fluorine compounds, and boron are the active agents that decompose some of the feldspar. According to this theory, clay is formed at significant depths below the surface. Clays found in China support this theory.

The Surface Weathering Theory:

Clays formed by this surface weathering theory are found near to the surface. This theory explains that feldspar is decomposed by water containing carbon dioxide. Clay found in France is created by this theory.

The bog or moor water theory:

This theory forms clay, which is found near the lignite beds. This theory explains that water from bogs is an active agent for kaolinization as it contains ammoniacal salts and organic acids. This theory forms the German clays.

Processing of China Clay:

Processing of china clay differs from place to place, but the essential steps are the same. i) Excavating china clay. ii) Sieving process. iii) The settling process. iv) The filter press process. v) Drying process. vi) Packing and transportation.

Excavation of china clay:

China clay is extracted from the deposits by mixing with water using a jet water splashier. Forced water is sprayed on clay and mixed with water; this water-plus-clay slurry is pumped to ground level. In this slurry, the clay content is very low, generally below 10 percent. Then this slurry is sent to the next process.

Sieving process:

The slurry mix from the deposit passed through a series of sieves. Usually 40 mesh, 100 mesh and 200 mesh are kept in series to remove all other materials from the slurry. In this process, from small stones to sand, materials were removed by sieves. The sieved slurry will be sent to the settling process.

Settling Process:

Then this slurry is sent to a series of settling tanks. Clay particles are allowed to settle in settling tanks. In this process, the clay percentage in the slurry is increased by 50 to 60 percent. The settling tank is designed in a zigzag way, as demonstrated by the below picture. The design aims to make the clay particles settle quickly by restricting the flow.

Filter Press Process:

Then the clay slurry is sent to the filter press by a pump. After the filter press process, the clay will have around 15% to 20% moisture content. The cake-like material is taken out from the filter press.