Behavior of As, Pb, Cu, and Zn under conditions of reduction roasting of fine dust generated by a copper smelter with natural gas

The processing of fine dust from copper smelters in Kazakhstan is an urgent task. The currently used technology of hydrometallurgical dust processing, which involves leaching with sulfuric acid to produce lead cake and a solution containing copper and zinc, fails meet modern requirements. The significant content of arsenic in the dust (up to 15%) hinders the production of high-quality products. In this study, fine dust from a copper smelter in Kazakhstan, obtained following conversion of copper mattes from autogenous smelting in Vanyukov furnaces, was used. Comprehensive analytical studies of the elemental and phase composition of dust were carried out using a Bruker D 8 ADVANCE X‑ray diffractometer and a scanning electron microscope with a JED-2300 energy dispersive X‑ray spectrometer (JEOL). This ensured the reliability of the data on the elemental composition of the initial dust, which were subsequently used to examine the behavior of arsenic and other non-ferrous metals under conditions of reduction roasting with natural gas.

In order to gain a deeper understanding of the mechanism of the reduction roasting, a detailed thermodynamic analysis was carried out to examine the interactions between dust components and natural gas within the temperature range of 500–1000 K. Thermodynamic calculations were carried out using Outotec HSC Chemistry 8.1.5 software. It was established that favorable conditions are created for the reduction of zinc and copper ferrites, as well as arsenic oxide (As⁵⁺) when roasting dust with natural gas. It was demonstrated that the preliminary roasting of dust with natural gas ensures the most effective reduction of arsenic oxide (As⁵⁺) and the production of arsenic-free calcine with the subsequent high selective separation of Pb, Cu, and Zn from it into commercial products.

The use of this method will significantly improve the technological performance of leaching fine dust with sulfuric acid due to the preliminary maximum removal of arsenic from the general technological scheme and the destruction of copper and zinc ferrites, which are relatively insoluble in acid, to their readily soluble oxides, with their subsequent dissolution.