The solid dissolves readily in water, and its solutions have a salt-like taste. It could be obtained from ancient dried lake deposits. KCl is used as a fertilizer, in medicine, in scientific applications, and in food processing, where it may be known as E number additive E508.
In a few states of the United States, it is used to cause cardiac arrest, as the third drug in the "three drug cocktail" for executions by lethal injection. It occurs naturally as the mineral sylvite, and in combination with sodium chloride as sylvinite.
The salt is usually obtained as a by-product of copper refining. It is also produced by dissolution of nickel metal or nickel oxides in sulfuric acid.
Aqueous solutions of nickel sulfate reacts 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 precipitates Ni(NH4)2(SO4)2·6H2O. This blue-coloured solid is analogous to Mohr's salt, Fe(NH4)2(SO4)2·6H2O.
Nickel sulfate is used in the laboratory. Columns used in polyhistidine-tagging, useful in biochemistry and molecular biology, are regenerated with nickel sulfate. Aqueous solutions of NiSO4·6H2O and related hydrates react with ammonia to give [Ni(NH3)6]SO4 and with ethylenediamine to give [Ni(H2NCH2CH2NH2)3]SO4. The latter is occasionally used as a calibrant for magnetic susceptibility measurements because it has no tendency to hydrate.
At least seven sulfate salts of nickel(II) are known. These salts differ in terms of their hydration or crystal habit.
The common tetragonal hexahydrate crystallizes from aqueous solution between 30.7 and 53.8 °C. Below these temperatures, a heptahydrate crystallises, and above these temperatures an orthorhombic hexahydrate forms. The yellow anhydrous form, NiSO4, is a high melting solid that is rarely encountered in the laboratory. This material is produced by heating the hydrates above 330 °C. It decomposes at still higher temperatures to nickel oxide.
X-ray crystallography measurements show that NiSO4·6H2O consists of the octahedral [Ni(H2O)6]2+ ions. These ions in turn are hydrogen bonded to sulfate ions. Dissolution of the salt in water gives solutions containing the aquo complex [Ni(H2O)6]2+.
All nickel sulfates are paramagnetic.