On the Assumed Mechanism of the Pressure Oxidation of Pyrrhotine during the Pressure Oxidation Leaching of a Low-Nickel Pyrrhotine Product Using Iron(III) Ions as an Oxidant

—The influence of the Fe(III) content in the solutions of the sulfuric acid leaching of a pyrrhotine concentrate on the features of the reaction mechanism of its desulfurization is analyzed. Owing to the hydrolysis of ferrisulfate (iron(III) sulfate) in the solution, the active surface of the concentrate is blocked by the formed basic iron hydrosulfate, whose chemical decomposition is accompanied by the oxidation of pyrrhotine sulfur to form elemental sulfur. The organization of the two-stage direct-flow leaching of the pyrrhotine concentrate is shown to be important for extracting nonferrous metals and components of the gangue to the pyrrhotine concentrate and fabricating a concentrated cake containing nickel, copper, and cobalt.