| 摘要 |
<p>A process for the preparation by aqueous means of purified calcium sulphate, of marked whiteness, realised, as required, in the form of long-limbed polymorphous or monomorphous crystalline structures, is characterised by the fact that it includes (a) the formation of an aqueous solution through the dissolving of impure semihydrated calcium sulphate, with a concentration of at most 13 grams per litre (expressed in dissolved Ca SO4) and with a pH of at least 5.5; (b) the separation of the aqueous solution containing the dissolved calcium sulphate from the insoluble solid phase formed by the impurities which are to be eliminated; (c) the recrystallization of the purified calcium sulphate in dehydrated form based on the aqueous solution resulting from stage (b), if necessary, in the presence of a germination starter which has been introduced into the reaction medium; (d) the separation, after recrystallization, of the aqueous phase, which has lost the dissolved calcium sulphate, from the solid phase constituted by the recrystallized purified calcium sulphate; (e) the recycling of the aqueous phase, which has lost the dissolved sulphate, through the stage (a) where the impure calcium sulphate source is dissolved. The purified crystalline structures obtained through this process are particularly intended for application in such diverse fields as cement and plaster, and more especially, paper, paint and plastics.</p> |
