Reduction of Copper Smelting Slag by Carbon for Smelting Cu-Fe Alloy

Abstract

An innovative technology for the direct reduction of copper slag was studied while smelting Cu-Fe alloy by carbon to recover the main valuable elements from the copper smelting slag. The melting temperature of samples first decreased, followed by an increase in Fe3O4 content in slag. The melting temperature reached the minimum temperature of 1157 °C once the Fe3O4 content was about 8 wt%. The recovery rate of copper and iron first increased gradually, followed by a rapid increase in the modifier (CaO). Subsequently, the rise in the recovery rate slowed down. The reduction rate of copper and iron only increased by 1.61% and 1.05% from 5 wt% CaO to 10 wt% CaO, but significantly increased by 8.89% and 14.21% from 10 wt% CaO to 25 wt% CaO, and remained almost unchanged beyond 25 wt% CaO. This could be attributed to the reaction between modifier (CaO) and silicate in acidic copper slag to generate low melting point composite oxide while replacing free iron oxides, improving the melting properties and reduction reaction. Meanwhile, the recovery rates of copper and iron increased with the increase of reaction time, reaction temperature, and reduction agent in a certain range. To obtain good element yield, the optimum conditions for reducing copper and iron from the molten copper slag were determined to be 1500 °C, 14 wt% C, 20–25 wt% CaO, and 60–80 min. The recovery rates of iron and copper reached about 90% and 85%, and the contents of iron and copper in alloy reached about 91–93 wt% and 5–7 wt%, respectively. The tailing was mainly composed of Ca3Si3O9, Ca(Mg,Al)(Si,Al)2O6, and SiO2, which could be used as a raw material for cement and pelletizing.