Study on Crystallization of Calcium Sulfate Dihydrate under Simulated Conditions of Phosphoric Acid Production

Abstract

The effect of organic and inorganic additin:s on the crystallization of gypsum under simulated conditions of plwsphoric acid production ••Dihydrate Process.. was studied using calcium hydrogen phosphate Cal-11'0 and sulfuric acid as primary nucleation substances in the medium of phosphoric acid and sulfuric acid. Gypsum crystallization occured as reaction taking place. The reaction "•as carried out at 80''C. agitation speed .5.50 rpm. 2.5% !ina! l'cOs conc •ntration and .0% !ina! fi•ee so/• concentration. The cfkct of difll:rcnt additi,•es included citric acid as example of carboxylic acids. 1.2-dihydrnxyhenzene 3..5-disul fonic acid (DIIBDSA) as example of sui !(l!latc compounds. t''o type of surfactant. i.e. cctvl trimethyl ammonium bromide (CTABJ as cationic one and sodium dockcyl sul!:nc (SDS) as anionic one and t\\•o impurities present in phosphat • rocks to expl;1in its dTccts individu:Jily like magnesium oxide ;md aluminum oxide t'l1 the inductillll time and grO\\lh cf!iciency arc sllldied. The obtained results rc\ cakd that the presence of CTAB. Dlll3DSA and AI' decreased the induction time and increased the growth cf!iciency. While the presence of SDS. citric acid. lvlg.::­ increased the induction time and decreased the growth efliciency compared \lith the control test ("•ithout additives). The change on crystal size distribution :md co-crystallized l'cOs in the absence and in the presence of additives arc also measured. The change in the reaction kinetic and the surface energy \\•ere also calculated in the absence and in the presence of additives. Gypsum morphology was investigated using the scanning electron microscope. The studied additiYes were applied individually during leaching of the Egyptian Abu-Tartur phosphate concentrate. The results sho\\•ed that the presence of CT.--\8 and 01-IBDSA improved the liltration rate by 59.76% and 26.92'%_ respectively. On the other hand. the liltration rate is decreased in the presence of citric acid and SDS to 8.88% and 30.18%, respectiwly.