Abstract: In order to investigate the effects of adding different proportions of ammonium chloride and am-monium nitrate on the solubility, metastable zone and crystallization of ammonium sulfate, the solubilityand metastable zone of the mixed solution were measured by laser method. The solution was cooled andcrystallized. The thermodynamics of mixed solution is calculated by using Van't Hoff equation. Themixed solution was cooled and crystallized. The average particle size and distribution of the crystals wereinvestigated by sieving method, and the crystal morphology was analyzed by macro. The results showthat NH₄⁺can reverse the hydrolysis of ammonium sulfate, resulting in a significant decrease in solubilityof the mixed solution compared with that in pure water; Cl and NO, also affect the solubility of ammo-nium sulfate, and Cl^- has a more obvious effect. When the ratio of ammonium chloride to ammoniumnitrate was 1:2, the width of ammonium sulfate metastable zone became wider, indicating that ammoni-um nitrate could inhibit ammonium sulfate nucleation to a certain extent. When the ratio of ammonium chloride to ammonium nitrate was 2:1, the metastable zone width of ammonium sulfate was narrower thanthat of pure ammonium sulfate. No matter how the proportion of ammonium chloride and ammonium ni-trate was adjusted, the crystallization amount of ammonium sulfate increased. When the ratio of ammonium chloride to ammonium nitrate was 1:1, the crystallization capacity and average particle size were thelargest. The related research results can provide a new idea for optimizing the crystallization of ammonium sulphate mother liquor obtained by ozone denitrification and ammonia desulfurization.

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