Process for the preparation of calcium sulfate-alpha hemi-hydrate

摘要

Production of calcium sulphate- alpha -semihydrate comprises pressing calcium sulphate dihydrate, especially from flue gas desulphurisation, into porous moulded bodies and autoclaving at 125-150 degrees C and 2.5-5 bar under saturation vapour pressure and in the presence of a water-soluble crystallisation auxiliary aid. The crystallisation auxiliary aid is a compound containing K and/or NH4 ions in an amount of 0.02-0.1 wt.% so that long calcium sulphate alpha -semihydrate crystals of length/thickness ratio of 5-15:1 and having a D50 value of 40 mu m are formed.