Nickel (II) sulfate is highly toxic and carcinogenic. It has two known phases. Alpha-form (blue tetragonal) converts to beta-form (green monoclinic) at 127.9°F. It becomes blue and opaque at room temperature and greenish-yellow anhydrous salt is formed at 536°F.
Method 1: Nickel (II) sulfate is produced by dissolution of nickel metal or nickel oxides in sulfuric acid.
Method 2: Reacting nickel carbonyl, sulfur dioxide and oxygen together to form a mixture of nickel sulfate, nickel sulfite and nickel oxide. Nickel sulfite and nickel oxide are further converted to nickel sulfate all the nickel sulfate are collected.