China Nonferrous Metallurgy

The annual output of copper slag in China has exceeded 20 million tons. The main mineral phases in copper slag are fayalite and magnetic iron oxide, and the iron content is more than 30 %. Due to the high thermodynamic stability of fayalite, the current recovery method needs to consume a lot of energy and the cost is high. Magnetohematite (γ-Fe₂O₃) is a metastable magnetic material with cation vacancies, which has been widely used in the fields of wastewater treatment, biomedicine and catalysis. In this paper, high purity γ-Fe₂O₃ was obtained by low temperature alkali fusion-hydrolysis-calcination process using copper slag as raw material. The results showed that the iron-bearing phase (fayalite, magnetite) in copper slag could be converted into α-NaFeO₂ precursor by calcination at 550℃; after hydrolysis and calcination, γ-Fe₂O₃ with a band gap of 2.20eV was obtained, which exhibited good photocatalytic activity in the visible light range; the specific surface area, average pore diameter, pore volume and saturation magnetization of γ-Fe₂O₃ were 9.354m²/g, 14.88nm, 0.0348cm³/g and 19.13emu/g, respectively. The photocatalytic-degradation tests of MB at room temperature showed that the photocatalytic process obeyed pseudo-first-order reaction with a degradation rate constant K value of 1.29×10^-2min^-1(20mg/L); adding H₂O₂ could improve the photodegradation efficiency; owing to its superparamagnetic, γ-Fe₂O₃ could be reused via magnetic separation and showed excellent stability in cycle photodegradation performance tests. The process uses low temperature alkali fusion and consume low energy, which provides a new way for the resource utilization of copper slag.