Optimization of ammonium sulfate crystals based on orthogonal design

Abstract

Orthogonal experiments were performed to explore the influence of various factors and interactions on the crystal size and shape of ammonium sulfate: pH, stirring speed, and the Fe3+ addition amount of ammonium sulfate solution. The influence mechanism was analyzed by combining the characterization results of scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The results show that Fe3+ addition has an effect on the crystallization of ammonium sulfate. pH affects the viscosity of the solution and the width of the metastable zone, potentially influencing the grain size and crystal shape as well as crystal agglomeration. The stirring speed affects the crystal nucleation rate. With increasing stirring speed, the average crystal particle size and its coefficient of variation (C.V.) both increase at first and then decrease. The resulting ammonium sulfate crystals have a broad particle size distribution. The average particle size increases with increasing C.V. value, which is tend to larger particle sizes. Optimal purity of ammonium sulfate crystals is obtained at a liquor pH of 3.4, the stirring speed of 200 r∙min−1, and Fe3+ addition amount of 0.84 g. These results can serve as a reference for related research on the optimization of the ammonium sulfate crystallization process.