Effect of Ammonium (NH4+) Impurity on the Crystallization of Cobalt Sulfate Hexahydrate from Aqueous Solutions Using Cooling Method

This research examines the influence of ammonium (NH4+) impurities on the kinetic behavior, activation energy, crystal structure, morphology, and purity of cobalt sulfate hexahydrate using the cooling crystallization method. Characterization results indicate that ammonium at all concentrations affects the crystallization process, with a minimum concentration required to alter crystal characteristics. At ammonium concentrations up to 3.75 g/L, the crystal growth rate decreases, while activation energy increases. Furthermore, the crystal structure does not change, and crystal purity decreases by approximately 0.2%. This decline is insignificant and tends to stagnate, suggesting a maximum adsorption limit of impurities onto the crystal. At ammonium concentrations of 5 g/L, the crystal growth rate increases, and activation energy decreases. This shift in behavior is caused by the formation of Tutton’s salt, (NH4)2Co(SO4)2·6H2O, which significantly reduces crystal purity by 1%. Additionally, the presence of ammonium does not alter the crystal shape.