Crystal modification of calcium sulfate dihydrate in the presence of some surface-active agents

摘要

The effect of surface-active agents(surfactants),as additives,on the crystallization of gypsum was studied under conditions of the simulated dihydrate process of phosphoric acid production.Calcium hydrogen phosphateand sulfuric acid were mixed with dilute phosphire acid at 80 deg C,and the turbidity of the reaction mixture was measured at different time periods to determine the induction time of gypsum crystal formation.Two types of surfactants,namely,cetyltrimethylammonium bromide(CTAB)as a cationic surfactant and sodium dodecyl sulfate (SDS)as an anionic surfactant were added to investigate their effects on the crystallization of gypsum.Addition of CTAB decreased the induction time and increased the growth efficiency,while addition of SDS increased the induction time and decreased the growth effciency compared with the baseline(without additives).The surface energy increased with CTAB and decreased with SDS compared with the baseline.The percentage of fine crystals decreased in the presence of CTAB and increased in the presence of SDS compared with the baseline.Gypsum morphology changed from needle-like in the adsence of additives to tabular in the presence of CTAB.