Definition and Uses:
At least seven sulfate salts of nickel (II) are known. These salts differ in their hydration or crystal habits.
The common tetragonal hexahydrate crystallizes from aqueous solution between 30.7 and 53.8 °C. Below these temperatures, a heptahydrate crystallizes, and above these temperatures an orthorhombic hexahydrate forms. The yellow anhydrous form, NiSO4, is a high-melting solid rarely encountered in the laboratory. This material is produced by heating hydrates above 330 °C. At higher temperatures, it decomposes to nickel oxide.
The salt is usually obtained as a byproduct of copper refining. It is also produced by dissolving nickel metal or nickel oxides in sulfuric acid.
Aqueous solutions of nickel sulfate react with sodium carbonate to precipitate nickel carbonate, a precursor to nickel-based catalysts and pigments. Addition of ammonium sulfate to concentrated aqueous solutions of nickel sulfate results in the precipitation of Ni (NH4) 2 (SO4) 2 6H2O.
Nickel sulfate occurs as a hexahydrate, the rare mineral retgersite. The second hexahydrate is known as nickel hexahydrite (Ni, Mg, Fe) SO 4 6H 2 O. The heptahydrate, which is relatively unstable in air, occurs as morainosite.