Effect of Temperature, Stirring Rate, and pH on Ammonium Sulfate Crystallization Under the Action of Ammonium Fluoride and Ammonium Chloride

ABSTRACT To investigate the influencing factors and mechanisms of ammonium sulfate mother liquor crystallization under the action of ammonium fluoride and ammonium chloride, this study employed laser diffraction and evaporation crystallization methods. Under varying ratios of ammonium fluoride to ammonium chloride, temperatures, stirring speeds, and pH conditions, the width of the ammonium sulfate crystallization metastable zone, crystallization yield, particle size distribution, and crystal morphology were examined. Results indicate that increasing the ammonium chloride ratio accelerates ammonium sulfate precipitation, increases crystal number, inhibits crystal growth, reduces mother liquor crystallization efficiency, and decreases crystallization yield. Conversely, increasing the ammonium fluoride ratio accelerates ammonium sulfate crystal nucleation and growth, shortens crystallization time, enhances mother liquor crystallization efficiency, and improves crystallization yield. At 333.15 K, the average particle size was larger, and the coefficient variation (C.V.) value was smaller. At a stirring speed of 250 rpm, changes in solute molecular diffusion and migration lead to a more uniform solute distribution in the solution. At pH values of 4.5 or 5.0, ion movement in the solution becomes more active. This promotes enhanced binding between NH 4 + and SO 4 2− ions, accelerating ammonium sulfate nucleation. Crystal surface growth rates increase, ultimately forming more regular ammonium sulfate crystals.