Effects of Fe and cost-effective media composition on arsenopyrite bioleaching by Sulfobacillus thermosulfidooxidans

Bioleaching of arsenopyrite (FeAsS) is considered a cost-effective technology for the recovery of gold. The mineral dissolution is significantly affected by the generation of secondary products, which is often influenced by Fe and medium composition. This study aims to clarify the mechanisms by which Fe²⁺/Fe³⁺ and major medium components affect arsenopyrite bioleaching via changes in the mineral surface structure, phase composition, and Fe/As/S speciation. The results show that 71.9, 57.5, 75.1, 67.8, and 69.4% As was extracted from arsenopyrite after 10 days of bioleaching in a basal salts medium (BSM), 9K, BSM supplemented with Fe³⁺, K⁺- and NH₄⁺-free BSM (amended BSM), and dilute H₂SO₄, respectively. Fe²⁺ in the 9K medium supported the bacterial growth, but also enhanced jarosites and tooeleite formation at later bioleaching stages, which lowered the dissolution of arsenopyrite (as well as oxidation of As(III) to As(V)). Arsenopyrite was not detected in the bio-oxidized residue collected from BSM after 10 days, and As(V) (occurring as 52.3% amorphous ferric arsenate and 16.6% scorodite) was a dominant As species in the residue. In contrast, mainly As(III) (>60% present as tooeleite) was observed in the other bioleaching assays. The costs of arsenopyrite bio-processing can be reduced when the amended BSM or dilute H₂SO₄ are used, as indicated by the limited formation of jarosites, amorphous ferric arsenate, and scorodite in the bioleaching systems.