Structure and phase changes of nickel slag in oxidation treatment

Abstract

To overcome the difficulty in the direct reduction of Fe2SiO4 in nickel slag, the isothermal oxidation of the nickel slag was conducted between 300 and 1000 °C. Its morphology and phase composition after oxidation at 300-1000 °C for 5-30 min are analyzed by means of Scanning electron microscopy, X-ray diffraction, and thermodynamic calculation. The results show that oxidation can effectively promote the transformation of Fe2+ into Fe3+ in nickel slag. At 900 °C, the oxidation rate of element Fe reaches 95%. Fe2+ in Fe2SiO4 is oxidized to generate Fe2O3, and the unit cell volume decreases from 301.75 Å3 to 297.72 Å3 with the increase in temperature. At the same time, a large number of pores appear in the particle, which reduces the mass transfer resistance of gas in the particle during the reduction process, accelerates the reduction speed, and is conducive to strengthening the reduction. Therefore, the oxidation treatment of nickel slag can improve its phase composition, thus benefiting the subsequent reduction.