<p>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&#xa0;°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.</p>