Dearsenizing roasting of fine copper-smelting dusts

Fine dust from copper smelting production is processed together with zinc cake in Waelz kilns of a zinc plant to recover non-ferrous and precious metals. The resulting clinker into which copper, precious metals, and most of arsenic pass is used in the smelting of copper-containing raw materials, which causes undesirable accumulation of arsenic in inter-plant circulation. Moreover, the presence of chlorine and fluorine in dust necessitates their removal in the zinc recovery process. It appears rational to use dearsenizing roasting to remove arsenic, chlorine, and fluorine from dust before zinc production. The chemical and phase compositions of dusts are presented. Laboratory studies and pilot tests were performed to determine the optimal roasting conditions. The mode of mixing the starting dust was determined: 90–95% dust, 5–7.5% petcoke, 0–5% calcium oxide, 0–2% pyrite. It was proposed to roast a granulated charge in a rotary tubular kiln at a temperature of 1050 °C for two hours. With these parameters, the degrees of sublimation of arsenic, chlorine, and fluorine were 78–85%, > 95%, and > 97%, respectively, the loss of zinc with sublimates being 4.3–7.2%. The resulting clinker (yield = 51.9–67.4%) can be used to recover zinc at a zinc plant, while sublimates (3.3–4.9% Zn, 23.9–28.0% Pb, 25.4–38.6% As, < 2.6% Cl, < 0.04% F) are additionally processed to separately recover lead cake and transform arsenic to stable form for subsequent utilization.