Effect of in-situ oxidation on the phase composition and magnetic properties of Fe3O4: Implications for zinc hydrometallurgy

Abstract

• Iron precipitates at different oxidation degrees are obtained by H 2 O 2 . • Ms value of Fe 3 O 4 shows a decrease and then recovery with oxidation. • Magnetic properties are affected via a Fe-O bond length-related mechanism. • The “magnetic iron oxides” method is promoted for industrial iron precipitation. Large quantities of hazardous waste are generated in the removal process of iron in zinc hydrometallurgy, which poses a severely permanent threat to the environment. Recently, an innovative magnetite (Fe 3 O 4 ) method for iron precipitation has been proposed. Whereas, the magnetic separation performance and phase composition of Fe 3 O 4 are sensitively disturbed by the oxidizing conditions in the pregnant leach solution from zinc hydrometallurgy. In this work, a series of Fe 3 O 4 samples with different oxidation degrees were in-situ formed. We found that oxidation did not worsen the Fe removal and that all samples have a relatively high iron content (>42.3%). Meanwhile, although the magnetic properties of the samples showed a decrease (from 32.31 to 6.56 emu/g), it could be recovered (10.60 emu/g) by controlling the oxidation to a certain degree. This is correlated with the phase transition of iron oxides as the oxidation degree increase. Furthermore, it is clarified that the mechanism by which the oxidation affects the magnetic properties was the change of Fe-O bond length, as revealed by Raman and Fourier transform infrared spectrometer measurement. This work provides a new strategy for the practical implication of the “magnetic iron” instead of the magnetite precipitation method in zinc hydrometallurgy.