29 августа, 2015 
Pokraskin The filter cake can be oven dried, after which it requires crushing into small lumps prior to calcination. To reduce manual handling, the cake is often extruded into noodles onto a belt drier, where a flow of hot air through the pigment bed dries the product into small pellets.
3.4.8
Calcination
Calcination is one of the most important steps in cadmium pigment manufacture, since not only does the product become a pigment at this stage, but conditions used greatly affect the resultant pigmentary properties.
As stated previously for yellows, cubic cadmium and zinc sulfides are converted into hexagonal forms. Cadmium sulfoselenides are formed on calcining reds.
Rotary, tunnel, and static kilns using crucibles or “saggars” have all been used, with calcining sometimes carried out in a molten salt bath [5]. In the calcining process, sulfur dioxide, and (in the case of reds) selenium and some selenium dioxide are emitted, which requires careful fume removal through a gas scrubber or similar equipment. Temperature, residence time and calcining atmosphere all affect color properties and pigment texture. Ideally, cadmium pigments should be soft in texture, not too light or deep, have sufficient tinting power (strength) and chroma (brightness).
Generally, increased temperatures produce lighter and brighter shades, but with less strength, while lower temperatures have the opposite effect. The temperature range used is typically 500-650 °C, with deeper shades requiring a higher temperature. Slight changes in calcination temperatures are regularly made to obtain a balance of the required properties.
During calcination, cadmium and zinc sulfides are converted to their hexagonal form and cadmium selenide is formed. This is normally produced by reacting an insoluble cadmium salt with an equimolar amount of selenium. The cadmium selenide then forms a solid solution with the cadmium sulfide. For example:
3 CdS + CdCO3 + Se ^ 3 CdS. CdSe + CO2T + SO2T
3.4.9
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