Process for the hydrothermal conversion of gypsum from flue-gas desulphurization into alpha semihydrate calcium sulphate

摘要

Industrial waste gypsum is hydrothermally converted into calcium sulphate alpha -hemihydrate by heating an aqueous suspension of gypsum under pressure to temperatures of 130-180 DEG C, with addition of acids, flue gas desulphurisation gypsum in a concentration of 20-55 and preferably 40-50 % by weight being reacted with 0.02-1.0 and preferably 0.1-0.5 % by weight of sulphuric acid and 0.02-1.0 and preferably 0.1-0.6 % by weight of an organic acid at temperatures from 145 DEG C to 170 DEG C, preferably 155-165 DEG C, for times of 3-20 minutes, the reaction preferably being carried out continuously.