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Kaolin, also known as china clay, is a pigment recovered from kaolinite, a weathering product of feldspar. It is valued as a filler and whitener in many branches of industry. Particularly high-grade kaolin is in high demand by the paper industry because it is ideal as a luminous filler and coating material for high-quality paper.
In the production of kaolin, brightness, opacity, purity and gloss define the pigment quality. These parameters are essentially determined by the particle size distribution. Particles smaller than 0.2 μm are irrelevant in the production of white colour because they no longer diffract the light. Particles larger than 2 μm, by contrast, negatively impact the whiteness. Coarser particles with a diameter above 20 μm in particular must be as few as possible to produce a good paper quality.
High-performance decanters from GEA Westfalia Separator are used in the process shown. Thanks to their accurate classification cut, the particle size distribution can be configured in such a way that the user gets the desired quality with low product losses. In the case of plants which produce many thousands of tones yearly, a yield which is just a few percent higher and a higher degree of whiteness make themselves significantly felt.
With a newly developed recovery process, GEA Westfalia Separator has also succeeded in substantially reducing the losses of the 2 μm fractions. The already minimal product loss can be transformed into the desired higher quality without difficulty by adding on a second classification stage. At the same time, the manufacturer has the possibility to produce two different pigment qualities with the first and second stage.