Nucleation thermodynamics and nucleation kinetics of (NH4)2SO4 under the action of NH4Cl

•The dissolution process of (NH4)2SO4 under the action of NH4Cl is an endothermic reaction.•The ammonium chloride has a significant effect on the salting out of ammonium sulfate.•The classical 3D nucleation theory can better explain (NH4)2SO4 nucleation kinetics.•The activation energy obtained by the self-consistent Nývlt-like equation and the classical 3D nucleation theory is similar. This study aims to explore nucleation thermodynamics and kinetics of (NH4)2SO4 during cooling under the action of NH4Cl. For this purpose, (NH4)2SO4 was added to the NH4Cl solution in different proportions. The solubility and supersolubility of the mixed solution were measured using a laser method. Then, the (NH4)2SO4 metastable zone width was obtained under different NH4Cl addition and cooling conditions. Studies have shown that the dissolution process of (NH4)2SO4 is an endothermic reaction. Increasing the NH4Cl concentration narrows the (NH4)2SO4 metastable zone width because NH4Cl provides more NH4+ and promotes crystal nucleation, whereas increasing the cooling rate widens the (NH4)2SO4 metastable zone width because the change in the size of the solute molecular clusters in the solution lags behind the transition of the solution state. Additionally, the nucleation kinetics of (NH4)2SO4 under the action of NH4Cl was studied based on the self-consistent Nývlt-like equation and the classical 3D nucleation theory, indicating that the classical 3D nucleation theory can better explain (NH4)2SO4 nucleation kinetics, and the activation energy Esat of the nucleation process obtained by the two models is similar. The study results can provide a reference for the optimization of nucleation of (NH4)2SO4 mother liquor under the condition of high chlorine content.