Continuous prodn. of calcium sulphate dihydrate - from spent sulphuric acid and calcium cpd., involves only one addition of nucleating crystals

摘要

Continuous prodn. of CaSO4.2H2O from spent H2SO4 (e.g. from organic synthesis) and a spent calcium cpd., esp. from carbide mud, with the use of nucleating crystals, is improved in that the nucleating crystals (CaSO42H2O or crystalline gypsum from chemical processes) are added only once, at the beginning of the process. Subsequently, the overflow (contg. suspended CaSO4.-2H2O crystals) is continuously withdrawn and filtered. The coarse CaSO4.2H2O crystals are removed, whilst the filtrate contg. fine CaSO4.2H2O crystals is returned to the reactor where these fine crystals act as nucleating crystals. The product can be dehydrated to CaSO4.O.5H2O and used for various purposes.