Synergistic enhancement effect of Ag+ and organic ligands on the bioleaching of arsenic-bearing gold concentrate

Bio-oxidation of arsenic-bearing gold concentrate is generally slow and prone to passivation. To alleviate this concern, it is pivotal to explore the possible catalysts to reduce passivation during bio-oxidation. In the present work, the enhancing effects of Ag+, ethylenediamine tetraacetic acid (EDTA) and oxalate (Ox) on bio-oxidation of arsenic-bearing gold concentrate and the possible mechanisms were investigated by the leaching experiments, thermodynamic calculation, XRD and SEM analyses. Results indicated that the addition of Ag+ and organic ligands could effectively accelerate the bioleaching process. Especially, under the synergistic action of Ag+ and EDTA, the leaching efficiency of As reached the highest value of 87.4% after 10 days. Thermodynamic calculations demonstrated that from the onset of bio-oxidation, the leaching rate was significantly retarded due to the formation of S0, As2S2, As2S3 and jarosite. However, As2S2 and As2S3 could be dissolved in the presence of Ag+ by the formation of Ag2S intermediate that was easily dissolved by Fe3+. Moreover, the addition of EDTA and Ox further facilitated the As extraction, for the possible reason that the presence of organic ligands inhibited the formation of jarosite on the mineral surface by forming corresponding complexes. This possible mechanism was further confirmed by XRD and SEM analyses. Overall, this work demonstrated that organic ligands bind to Ag+ can substantially enhance the efficiency of bioleaching of arsenic-bearing gold concentrate. •Organic ligands for enhancing bio-oxidation is investigated.•The combination of Ag+ and organic ligands can promote the bio-oxidation process.•The mechanism mainly relies on the reduction of passivation products.•The low pH and high Eh can lead to a higher bio-oxidation rate.