Synthesis of high purity ammonium alum crystallized from solutions containing impurities

Synthesis of high purity ammonium alum crystallized from solutions containing impurities was investigated. It was found that various parameters, including initial Al-2(SO4)(3) concentration, supersaturation, temperature and agitation, have a great effect on the purity of ammonium alum crystals. EDS analysis of crystals indicates that K+ ions were more easily included into ammonium alum crystals than other impurities. Impurities were removed more effectively by non-agitation crystallization than by agitation crystallization. In non-agitation crystallization, the content of K in crystals was drastically decreased and Na, Ca, Mg and Si were almost removed. Ammonium alum crystals with high purity were successfully synthesized by the method of non-agitation recrystallization. Distribution coefficient K-K was much greater than K-Na, which explained that K+ ion was more easily incorporated into ammonium alum crystals than Na+ ion