Effect of Mechanochemical Activation in the “Dust–Na2S” and “Dust–Na2S–NaOH” Systems on the Phase Transformations of Arsenic in Copper Smelting Dust

Copper smelting dust is a heterogeneous by-product of pyrometallurgical processing containing sulfate- and arsenic-bearing components, which accounts for its high chemical stability and environmental hazard. In this context, mechanochemical activation is considered a promising approach for initiating structural and phase transformations in such systems. The aim of this study was to investigate the effect of high-energy planetary milling in the “dust–Na2S” and “dust–Na2S–NaOH” systems on changes in the phase composition of arsenic-bearing dust. The samples were prepared by dry mechanochemical activation in a planetary mill for 15 and 30 min with varying reagent contents. According to X-ray diffraction analysis, PbSO4 and ZnSO4·H2O remain the major phases in the binary system, while the formation of elemental sulfur (S6) and the arsenic sulfide phase (As4S4) is observed against a decrease in the As2O3 content. In the presence of NaOH, a more pronounced redistribution of arsenic species is observed, accompanied by the appearance of a Na-containing As–O–S phase, preliminarily identified as Na3AsO2S2, and a further decrease in the proportion of As2O3. Thermodynamic analysis indicates the energetic favorability of arsenic sulfidation when the oxidative contribution of the air atmosphere during milling is taken into account. The obtained results refine the possible mechanochemical pathways of arsenic transformation and may be used to substantiate preliminary activation regimes prior to subsequent leaching.