Reduction of Ferric Iron in Hydrometallurgical Solutions Using Zero-Valent Iron

Most hydrometallurgical solutions usually contain high levels of ferric iron, which is often regarded as a major and problematic impurity. Precipitation of Fe(III) by raising the solution pH results in a voluminous amorphous residue that is particularly difficult to handle. Prior complete or partial reduction of Fe(III) to the divalent state facilitates the precipitation of crystalline iron oxides such as magnetite or goethite. The aim of this research was to investigate the effectiveness of zero-valent iron (ZVI) for the reduction of Fe(III) to Fe(II), which is a crucial pretreatment step for the efficient removal of iron. The effects of pH, reaction time and type of coexisting anions, i.e., sulphates or chlorides, were evaluated by conducting batch tests in an agitated reactor. It was found that using ZVI, Fe(III) is rapidly reduced to Fe(II), with higher reduction kinetics achieved in sulphate solutions at acidic pHs of 0.5–1.