Cadmium Incorporation in the Crystallization of Calcium Sulfate Hemihydrate from Phosphoric Acid

Semi‐batch crystallization experiments of CaSO4 · 1/2H2O(HH) were performed in concentrated phosphoric acid at various H2SO4 contents in the absence and presence of additives. The influence of the operating conditions and additives on the cadmium and phosphate incorporation in the HH lattice were determined. The Cd uptake increased with raising H2SO4 content. Addition of HNO3 caused a reduced cadmium and phosphate incorporation. Addition of iodide also lowered the cadmium incorporation. The obtained results fits into a model for the incorporation of foreign ions during crystal growth. According to this model the incorporation is primarily a kinetically controlled process.