Effects of impurities from phosphogypsum on the crystal growth of calcium sulfate hemihydrates

The influences of organic compounds, supernatant, calcium phosphate and calcium fluoride on the morphology of calcium sulfate hemihydrate were investigated in hydrothermal conditions by using calcium sulphate dihydrate of analytical grade as the raw material, while the organic compounds and supernatant were obtained from phosphogypsum (PG).The influence of the supernatant on the crystal growth was greater than the organic compounds.The crystal diameter increased and the aspect ratio decreased, while the added amounts of calcium fluoride and calcium phosphate increased.The influence of calcium phosphate on the crystal growth was more obvious than with calcium fluoride.Extremely non-uniform whiskers were observed when the amount of calcium fluoride and calcium phosphate were 5 % and 3 % (w/%), respectively.Key words: phosphogypsum; calcium sulfate hemihydrate; crystal morphology; impurities Avtorji so v pri~ujo~em prispevku raziskovali vplive organskih spojin, plavajo~ih ostankov, kalcijevega sulfata in kalcijevega fluorida na morfologijo kalcijevega sulfat polhidrida v hidrotermalnih pogojih.Kot surovino so uporabili sulfat dihidrat anali-ti~ne ~istosti.S to sintezo so dobili organske spojine in plavajo~e ostanke iz fosfatnega gipsa (PG).Vpliv plavajo~ih ostankov na rast kristalov je bil ve~ji kot vpliv organskih spojin.Premer kristalov je nara{~al, medtem ko je razmerje med dol`ino in premerom kristalov padalo z nara{~anjem dodatka kalcijevega fluorida oz.kalcijevega fosfata.Vpliv kalcijevega fosfata na rast kristalov je bil o~itnej{i kot vpliv