Comparative Study on Refractory Gold Concentrate Kinetics and Mechanisms by Pilot Scale Batch and Continuous Bio-Oxidation

Abstract

Most studies conducted have focused on the pulp density, Fe3+ concentration and sulfuric acid concentration, etc., of bio-oxidation, and few have reported on the influence of different bio-oxidation methods on kinetics. In this study, a comparative investigation on refractory gold concentrate by batch and continuous bio-oxidation was conducted, with the purpose of revealing the kinetics influence. The results showed that improving the removal rates of the gold-bearing pyrite (FeS2) and arsenopyrite (FeAsS) yielded the best results for increasing gold recovery. The removal rates of S, Fe and relative gold recovery linearly increased when compared to the second-order equation increase of the As removal rate in both batch and continuous bio-oxidation processes. The removal kinetics of S and Fe by continuous bio-oxidation was 12.02% and 12.17% per 24 h day, approximately 86.64% and 51.18% higher than batch bio-oxidation, respectively. The higher removal kinetics of continuous bio-oxidation resulted from a stepwise increase in microbe growth, a larger population and higher dissolved Fe3+ and H2SO4 concentration compared to a linear increase by batch bio-oxidation. The cyanidation gold recovery was as high as 94.71% after seven days of continuous bio-oxidation, with the gold concentrate sulfur removal rates of 83.83%; similar results will be achieved after 13 days by batch bio-oxidation. The 16sRNA sequencing showed seven more microbe cultures in the initial residue than Acid Mine Drainage (AMD) at genus level. The quantitative real-time Polymerase Chain Reaction (PCR) test showed the four main functional average microbe populations of Acidithiobacillus, Leptospirillum, Ferroplasma and Sulfobacillus in continuous bio-oxidation residue as 1.08 × 103 higher than in solution. The multi-microbes used in this study have higher bio-oxidation activity and performance in a highly acidic environment since some archaea co-exist and co-contribute.