The special features of the kinetics of oxidation of divalent iron during sulfuric acid leaching of pyrrhotine with the participation of nitrous acid

Abstract

The kinetics of oxidation of divalent iron ions with molecular oxygen during pyrrhotine leaching in sulfuric acid solutions with the participation of nitrous acid as an activator was studied. The oxidation of Fe²⁺ to Fe³⁺ only occurred at the second slow stage of the process, when the degree of solid phase stripping reached almost 80% of the value maximum under given conditions. The order of the reaction with respect to sulfuric acid was negative (−1.1 ± 0.1), as is characteristic of sulfate media. A substantial change in effective activation energies from 7 ± 5 kJ/mol at $c_{H_2 SO_4 }^O$ = 0.25 mol/l to 31 ± 5 kJ/mol at $c_{H_2 SO_4 }^O$ = 1.02 mol/l could be caused by different contents of the pyrrhotine solid phase in the system at the beginning of the second leaching stage. It was assumed that the oxidation of Fe²⁺ to Fe³⁺ occurred with much lower energy expenditures in the presence of a sulfide solid phase.