Thermodynamic analysis and experimental verification of the green and efficient recycling of waste sulfur slag by airtight sulfuration-vacuum distillation

Abstract

Recovering valuable resources from waste sulfur slag is profoundly significant in terms of making profit and encouraging sustainable development within the tin industry. Sulfur slag is a hazardous waste, and a substantial amount of tin and cuprous sulfide is present in waste sulfur slag. However, tin and cuprous sulfide readily react to form stable metal compounds, which creates a barrier for effective sulfur slag recovery. The separation of copper-tin is essential for the efficient recovery and reuse of sulfur slag. In this paper, the physical composition and structural characteristics of the microstructure of sulfur slag were systematically characterized and confirmed. Thermodynamic calculations were then carried out to analyze the sulfuration reaction mechanism of tin and cuprous sulfide during the airtight sulfuration process and to study the volatilization of stannous sulfide and the decomposition properties of copper sulfide under vacuum conditions. Thermodynamic analysis showed that the products of tin and cuprous sulfide after being sulfided were SnS, SnS2, Sn2S3 and CuS, but they decomposed and existed in the form of SnS and Cu2S. According to the difference of saturated vapor pressure, SnS and Cu2S can be separated under the vacuum condition with high temperature. Finally, experiments were conducted to verify the reliability of the thermodynamic analysis, with good agreement between the two. The extraction purities of stannous sulfide and cuprous sulfide reached 97.87 % and 97.70 %, respectively. The direct yield of tin and copper were 99.66 % and 99.27 %, respectively. The separation efficiency of tin and copper was 99.81 %. The results confirmed that the airtight sulfuration-vacuum distillation method is a feasible alternative for high-value metal resource recovery and reuse from waste sulfur slag. This research contributes to the understanding of the recovery of metal resources from sulfur slag with the airtight sulfuration-vacuum distillation process, showing that it is a significant competitive alternative to existing sulfur slag recovery methods.