Study of the Interaction of Factors Affecting Ammonium Sulphate Crystallization Based on Orthogonal Design

Aiming at the problems of low crystallization rate and uneven particle size during evaporative crystallization of ammonium sulfate mother liquor (a by-product of ammonia desulfurization of sintered flue gas), this study investigated via orthogonal tests the effects of evaporation temperature, pH, stirring rate, and calcium sulfate addition on crystallization amount, average particle size, and coefficient of variation (C.V.). The results showed: For crystallization amount, the influence degree was evaporation temperature>pH>stirring rate>calcium sulfate addition; for average particle size, it was stirring rate>pH>evaporation temperature>calcium sulfate addition; for C.V. value, it was stirring rate>pH>calcium sulfate addition>evaporation temperature. Crystal morphologies included hexahedral, columnar, lamellar, etc., with aggregation under some conditions. Crystals contained calcium, nitrogen, oxygen, and sulfur elements(Ca, N, O, S); Ca content increased with calcium sulfate addition. Ammonium sulfate crystals' diffraction peaks matched pure ammonium sulfate, with the highest peaks at pH 5.0, 250 rpm stirring, 3500 mg·L −1 calcium sulfate, and 333.15K.