Abstract: Due to numerous impurities carried by sintering flue gas, ammonium sulfate crystallization becomes poor or even fails to occur, which hinders the stable production of the desulfurization system in the new area of Kunming Iron and Steel. To investigate the effect of pH on ammonium sulfate crystallization, NaOH, Ca(OH)₂, Na₂CO₃ and CaCO₃ were adopted to adjust the pH of the first‑effect ammonium sulfate solution, and the influences of pH on crystallization mass and yield‑increase ratio were studied. Sulfuric acid and ammonia water were used to regulate the pH of the second‑effect ammonium sulfate solution, and the effects of pH on crystallization yield, average particle size and coefficient of variation were explored. The results show that when the pH of the first‑effect ammonium sulfate solution is adjusted to approximately 5.25 with NaOH before evaporation, concentration and crystallization, a high ammonium sulfate yield of 63.493 g can be obtained with the minimum NaOH dosage of 0.283 g. The optimal pH for the second‑effect ammonium sulfate solution is 2.5. Under this condition, 61.162 g of ammonium sulfate crystals with large particle size, uniform particle distribution, regular morphology and low impurity content can be obtained, and the crystal morphology is highly consistent with pure ammonium sulfate. These findings can provide a reference for optimizing the crystallization process and increasing the output of ammonium sulfate.

Key words: ammonia process of desulfurization, ammonium sulfate, evaporative crystallization, cooling crystallization