Study on the effect of ammonium (NH4+) as impurity and seed ratio on batch cooling crystallization of nickel sulfate hexahydrate

Abstract

This research examines the influence of NH4+ impurities and seed ratio on growth mechanisms and characteristics of nickel sulfate hexahydrate in batch cooling crystallization. The kinetic behavior, thermal properties, and functional groups were also studied under the influence of NH4+ impurities. At low concentrations of impurities, competing process between Ni2+ and NH4+ ions to bind with SO42− causes the crystal output yield and growth rate to decrease and the crystallization activation energy increases. At high concentrations of impurities, NH4+ ions incorporate into crystal structure and produce double salt (NH4)2Ni(SO4)2 6H2O. The formation of double salt causes the crystal output yield and growth rate to increase and the crystallization activation energy decreases. The presence of NH4+ ions, whether in low or high concentrations, induces structural distortion in the crystal lattice and the crystals could exhibit heat stability up to 80 °C. Furthermore, crystal growth mechanisms can change significantly affected by NH4+ impurities rather than seed ratio. Impurity tends to attach to the crystal when the impurity concentration is low and impurity can be incorporated when the concentration is high. The seed ratio significantly increases crystal output yield and slightly increases crystal purity.