Thermodynamic analysis of sulfur behavior during interaction with copper smelting slag

Abstract

The paper presents the results of a thermodynamic analysis of the distribution of sulfur and copper during the interaction of elemental sulfur with copper smelting slags based on the developed mathematical model and algorithm for its implementation. The model is based on the assumption that at each moment of time when elemental sulfur is fed to the melt, a thermodynamic equilibrium is established between the slag and the gas phase, as well as between the slag, matte (when it appears in the system), and the gas phase. The model consists of two consecutive calculation blocks. The first block describes the distribution of components at the stage of slag sulfidation without the formation of a sulfide phase. The second block describes the distribution of components during slag sulfidation with the formation of a sulfide phase. The satisfactory agreement was shown between the calculated and experimental data obtained during sulfidation of commercial copper smelting slags in the laboratory at a temperature of 1300 °C and elementary sulfur consumption of 3–21% of the mass of the initial slag. Model-based calculations confirmed the high percentage of sulfur released into the gas phase (more than 40%) obtained in laboratory experiments during sulfidation of slag with elemental sulfur without the use of a reducing agent. To analyze the effect of the redox potential on the parameters of slag sulfidation with elemental sulfur, calculations were carried out at different fixed values of CO/CO₂ ratio in the gas phase ranging from 0.15 to 2. It was shown that at increased CO/CO₂ ratios (~ 0.5–0.6), the release of sulfur into the gas phase sharply decreases, while the matte yield increases. The absorption of sulfur by the melt exceeds 98%. The obtained results can be used to select process conditions of depleting copper smelting slags by sulfidation with elemental sulfur.