Selective Leaching of Arsenic from Copper Concentrates in Hypochlorite Medium

Abstract

The selective leaching of arsenic using sodium hypochlorite was evaluated in order to reduce its concentration in a copper concentrate. The best conditions achieved in the synthetic concentrate were applied to the industrial concentrate. First, the individual behaviors of pure samples of enargite and chalcopyrite were evaluated under a hypochlorite medium. The enargite reaction is significantly faster than chalcopyrite, allowing for greater selectivity to ClO− (0.1–0.3 M), pH 12–12.5; 20 to 40 °C, reaction time <60 min. Under these conditions, the reagent consumption for pure compounds approaches the stoichiometric consumption and presents a selectivity factor of 5/1. Furthermore, concentrate leaching in a sodium hypochlorite medium, containing enargite, releases arsenic ions into the solution, while copper and iron remain in the solid phase, as CuO and Fe(OH)3, respectively. A novel copper concentrate cleaning process by selective leaching is proposed, which transforms unacceptable copper concentrate for smelters (>0.5%As) into clean concentrates (<0.2%As) or low penalty concentrates (0.2 < %As < 0.5). The estimated consumption for the cleaning process is in the order of 0.4–0.6 kg Cl2 equivalent per kg of concentrate.