Two-stage leaching of copper-zinc concentrate containing tennantite

The goal of the present work was to evaluate the possibility to improve bioleaching of Cu-Zn concentrate containing tennantite by means of using alkaline sulfide leaching (ASL). Concentrate contained 18.1% Cu, 6.2% Zn, and 1.7% As. ASL allows removing arsenic by means of destruction tennantite (Cu12As4S13) that results in the formation of dissolved thioarsenite and CuS and CuS2 in solid residues. ASL was performed under the following conditions: 95 degrees C, pulp density 20%, residence time 6 h, NaOH concentration 3.5M, Na2S concentration 1.5M. ASL residue contained 17.8% Cu, 6.4% Zn, and 0.2% As. Bioleaching of the concentrate and ASL solid residue was performed in stirred tank reactor under the following conditions: 40 degrees C, pulp density 10%, residence time 20 d. Cu extraction reached 21 and 37%, while Zn extraction was 38 and 47% during concentrate and ASL residue bioleaching. The results obtained demonstrated that ASL pretreatment of the concentrate containing tennantite led to significant increase in copper extraction. Therefore, two-stage leaching including ASL and bioleaching may be considered as promising approach for processing tennantite-containing products since it allows avoiding emission of toxic gases and providing comparatively high copper and zinc extraction.