Mechanism of the enhancement of bioleaching of copper from enargite by thermophilic iron-oxidizing archaea with the concomitant precipitation of arsenic

Abstract

Bioleaching of enargite by the thermophilic iron-oxidizing archaea, Acidianus brierleyi, at 70 °C for 27 days yielded a 90.9% recovery of Cu and 5.9% recovery of As. The preferential dissolution of Cu compared to As was mainly achieved by the formation of crystalline scorodite (FeAsO 4·2H 2O). Although the chemical valence of As in enargite was confirmed to be As(III), most of the dissolved As was in the compound H 3As VO 4. This indicates that the H 3As IIIO 3 released from the enargite was immediately oxidized to H 2As VO 4 − in solution via a catalytic reaction on the surface of the enargite. During the bioleaching process, dissolved Fe 3+ was consumed through the formation of precipitates, such as scorodite and jarosite ((M +)Fe 3(SO 4) 2(OH) 6), as well as the oxidation of enargite. Even after the formation of scorodite had stopped due to the consumption of Fe 3+, As was further passivated in the absence of Fe 3+. The co-sorption of Cu 2+ and H 2As VO 4 − on jarosite led to the formation of copper arsenate by a seed-forming effect. Subsequent secondary mineral precipitation resulted in the formation of multi-precipitation layers consisting of scorodite, potassium jarosite, elemental sulfur and copper arsenate, after most of the Cu had been recovered from the enargite by microbially induced leaching.