Removal of arsenic, lead and bismuth from copper anode slime by a one-step sustainable vacuum carbothermal reduction process

Abstract

A green and efficient method for removing arsenic (As), lead (Pb) and bismuth (Bi) from copper anode slime by a one-step vacuum carbothermal reduction process was proposed. In this paper, the Gibbs free energy and saturation vapor pressure for the reduction process were analyzed theoretically. The effects of temperature and holding time on the reduction and removal ratios for As, Pb and Bi were investigated experimentally. The results showed that the weight loss ratio of the feedstock was 48.28 %, and Pb and Bi decreased to levels below the lower limits for detection with inductively coupled plasma atomic emission spectrometry (ICP–AES), i.e., from 4.81 % and 7.32 %; these values were determined for the optimal vacuum carbothermal reduction conditions, which included a reaction temperature of 1073 K, a holding time of 2 h and a system pressure of 10 Pa. 81.81 % of the As and all of the Pb and Bi were removed. The amounts of Ag and Au recovered in the residue increased from 10.64 % and 510 (g/t) to 15.61 % and 742 (g/t), and the recovery efficiencies were 99.76 % and 99.9 %, respectively. The innovative process proposed in this paper thoroughly separated As, Pb, Bi and precious metals. Volatiles such as As2O3, PbS, and BiSe were placed in lead smelting plants, and the Ag and Au in the residue were placed in copper anode slime for extraction of precious metals, which greatly improved the efficiencies for recovering valuable metals from anode slime and avoided emission of arsenic-containing waste gas and wastewater.