Dissolution of hematite in acidic oxalate solutions: the effect of ferrous ions addition

Abstract

Studies on the dissolution of hematite in acidic oxalate solutions have shown that there is a strong relationship between dissolution rates and ferrous ion generation in the solution. The effects of temperature, pH of the solution, oxalate and ferrous ions concentration on the dissolution of hematite in acidic oxalate solutions containing ferrous ions were studied. It was found that the pH of the solution is very important for the dissolution as it affects: (1) the activation of hematite surface with adsorbed hydrogen ions; (2) the adsorption of [Fe(C 20 4) 2 ] 2- complex ions on surface active sites and (3) the speciation in oxalate solutions containing ferrous ions. Iron dissolution is highly dependent on temperature and ferrous ion concentration, while it is practically independent of the total oxalate concentration. The dissolution of hematite in oxalate solutions comprises three stages: (1) activation of the solid surface; (2) generation of ferrous ions in the solution (induction period); and (3) an autocatalytic dissolution period. When ferrous ions are added, the induction period is eliminated and dissolution proceeds through the autocatalytic pathway.