Abstract
To clarify the anodic dissolution mechanisms of nickel sulfide and pyrrhotite in acid solution, measurements of the electrode potentials and anodic polarization behavior, and galvanostatic anodizing were carried out.
(1) Nickel sulfide dissolved anodically in sulfuric and perchloric acid solutions through the following two simultaneous reactions;
(i) NiS→Ni2++S0+2e,
(ii) NiS+4H2O→Ni2++SO42−+8H++8e.
(2) Pyrrhotite dissolved anodically with high current efficiency in perchloric acid solution through the following principal reaction: FeS→Fe2++S0+2e.
In sulfuric acid solution, however, an anodic film which consisted mainly of anodized elemental sulfur and iron compounds was formed. As a result, the anodic potential of pyrrhotite in galvanostatic anodizing was extremely unstable and the dissolution current efficiency was considerably lower than that in perchloric acid solution.
