Recovery of high-grade copper matte by selective sulfurization of CuO–Fe2O3–SiO2–CaO system

The separation of Cu from the CuxO-FexO containing waste (such as copper slag and electroplating sludge) is always intractable by using pyrometallurgy method. The carbothermic reduction methods, as well as the conventional sulfurization technology by using sulfurization agent FeS2, will introduce lots of iron into the prepared Cu–Fe alloy or Cu–Fe–S matte, and this results in the difficulty in further separation of Cu from Fe. In this work, CaS is utilized as the new sulfurization agent, and the iron content of prepared Cu–Fe–S matte is lower than 5%, while the copper grade is improved to about 76–79%. Such products could be used as the raw materials for producing metallic copper. According to the experimental results, at 1450 °C, the copper oxides in CuO–Fe2O3–SiO2–CaO system is selectively sulfurized by CaS, and Cu2S dominated product is formed and separated from slags. The recovery extent of copper reaches 98% when the CaS addition is 1.15 times (1.15CaS) of the stoichiometric quantity required. However, the increase of CaS addition (1.6CaS) will lead to the sulfurization of iron oxides, and make the iron content in Cu–Fe–S matte increase to 15%. Besides, when the Cu/Fe ratio (in mass) of synthetic waste is 0.5, part of the CaS is oxidized by Fe2O3, which results in the recovery extent of Cu to only about 73.30%. However, the copper recovery extent could be improved to 97% by adding extra reductant carbon.