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

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.