The electrochemistry of the nickel sulfides—2. Ni3S2

The anodic and cathodic behaviour of Ni₃S₂ (synthetic hazelwoodite) in acid solutions is examined. The presence of a sulfur-rich sulfide layer which passivates the surface is demonstrated. This layer exists in the potential region 0 to 0.6 V sce, and itself dissolves slowly in acid. At higher potentials complex, anion dependent dissolution behaviour involving the formation of elemental sulfur and sulfur oxyanions occurs. At cathodic potentials, non-oxidative acid dissolution with the formation of H₂S is observed, concurrently with the evolution of hydrogen and the production of metallic nickel.