Arsenic removal from copper slag matrix by high temperature sulfide-reduction-volatilization

Arsenic contamination has been a major problem in copper slag utilization. Arsenic is easily incorporated into the silicate-based matrix, making the arsenic difficult to volatilize. In this study, pyrite was selected to depolymerize the matrix structure and volatilize the glassy arsenic by sulfide-reduction-volatilization reaction. The optimum technological parameters and mechanism of glassy arsenic volatilization by pyrite were further studied. The optimum operating parameters for glassy arsenic volatilization by pyrite were determined to be a temperature of 1200 °C, a holding time of 60 min, a heating rate of 5 °C/min, a basicity of 0.3, and a pyrite addition content of 15%. The arsenic volatilization ratio reached 80.9% under these experimental conditions. Besides, the mechanism of glassy arsenic volatilization was elucidated by XRD, XPS, FTIR, and SEM analyses. These results indicate that, with the increase in temperature, the pyrite decomposes to generate a variety of sulfur-based reducing substances (FeS, FeS_1-x, S₂(g)). Through "oxygen capture reaction", these sulfur-based reducing substances depolymerize the bridging oxygen structure from the glass former ([AsO₄], [FeO₄], and [SiO₄]) by the conversion of (Q² +Q³)→(Q⁰ +Q¹) and result in the precipitation of glass former ([AsO₄], [FeO₄] and [SiO₄]) combining with the nearby cation. In this process, the glassy arsenic is released by the glass network and participates in reductive volatilization reaction with sulfur-based reducing substances, converting the glassy arsenic with high thermal stability to volatile arsenic oxide and arsenic sulfide. These findings provide a theoretical support for the in situ volatilization of arsenic in copper smelting and centralized control of arsenic contamination.