Production Process
The initial materials for obtaining silica by a wet process are solutions of alkali silicate, preferably sodium silicate, from which amorphous silica is precipitated by adding acid. After is has been filtered, washed and dried, the precipitated product consists of 86-88 % SiO2 and 10-12 % water, the latter being present both in the molecular structure and physically bound on the surface.
Metal silicates such as calcium silicate an aluminum silicate are obtained by replacing a part or the total amount of the acid with metal salts, which form relatively insoluble precipitates with waterglass. By varying the main precipitation parameters, such as
- temperature
- pH value
- electrolyte concentration
- duration
it is possible to obtain silica with different surface areas. By changing precipitation conditions it is possible to produce silica with surface areas in the range from approx. 25 to 700 m2/g.
To produce performance silica, there are no fundamental changes to the process set out above. As already mentioned, the acid required for precipitation is replaced in this case by solutions of metal salts. The performance silica suspension obtained from precipitation is transported to filter presses, in which the salt resulting from of the precipitation is washed out and as much water as possible is removed. The filter cake still contains considerable quantities of water, and so at the drying stage it is necessary to evaporate up to six times the amount by weight of water. For this reason, drying accounts for a considerable proportion of the production costs. Drying is practised differently depending on the target properties of the end products. The drying step is often followed by grinding, classifying and/or granulating steps.
Manufacturing Sites
1) Chester, Pennsylvania, USA
2) Zubillaga-Lantaron, Spain
3) Wesseling, Germany
4) Adapazari, Turkey (Joint Venture)
5) Patalganga, India
6) Gajraula, India
7) Maptaphut, Thailand
8) Ta Yuan, Taiwan
9) Akoh, Japan (Joint Venture)
10) Nanping, China (Joint Venture)