Bioleaching Of Arsenic-bearing And Refractory Gold Concentrate By Mixed Moderate Thermophiles In Airlift Bioreactor

As China being the biggest country in gold yield and gold resources being lean and complex increasingly, the refractory and low grade gold ores will become the principal materials for gold production in China. The arsenic-containing and refractory gold ores are rich and distributed widely. With the global energy crisis and environmental pollution aggravation, the traditional metallurgical technology will face enormous challenges. The bio-pretreatment-yanidation technique has been paid more attention because of the advantages of resource thrift and environment friendly, as well as higher recovery of gold. However, the long periods of bioleaching has affected its large scale application in industry. Bioleaching of arsenic-brearing and refractory gold concentrate by mixed moderate thermophiles in airlift bioreactor was carried out in this research. The main subjects in this dissertation are as follows:Three bacterial species(Acidithiobacillus caldus, Sulfobacillus thermosulfidoxidans, Leptospirillums ferriphilum) were selected and mixed in the bacterial population ratio of1:1:1. To clarify the adaptation capacity of the mixed moderate thermophiles to increasingly higher pulp densities in bioleaching of an arsenic-bearing gold concentrate, the bioleaching experiments were carried out under different pulp densities from5to20%(w/v) in a laboratory scale airlift bioreactor. Results indicated that it had strong adaptation capacity to the arsenic-bearing concentrate and was feasible to adapt the mixed culture to pulp densities as high as20%(w/v) and can resist the toxicity of arsenic up to15g/L However, the accumulation of iron and arsenic ions in the reactor inhibited severely the activities of bacteria at high pulp density, while the precipitation of iron and arsenic was serious, which hindered the dissolution of the concentrate, resulting in the low removal of iron and arsenic.On the process of adaptation, the structure of microbial communitiy at pulp density of15%was analyzed by PCR-RFLP. The results indicated that Acidithiobacillus caldus, Sulfobacillus sp., Pseudomonas aeruginosa were the main microorganisms in the community, in which At. caldus was S-oxidizing bacteria, Sulfobacillus sp. was S-and Fe-oxidizing bacteria and few literatures reported P. aeruginosa in bioleaching. All of them can resist the toxicity of arsenic strongly.On the base of adaptation, the adapted culture was used to bioleaching of arsenic-bearing and refractory gold concentrate in the airlift reactor. An orthogonal test was performed to investigate the effect of pulp density, inoculum, initial pH and temperature. The results displayed that10%pulp density,5×107cell·mL-1inoculum, initial pH1.6and45℃were the optimal parameters and the temperature was the most significant factor among the parameters researched. Under the optimal condition, the removal of arsenic reached to61.7%within7days.Taking into account of the toxicity of the accumulation of iron and arsenic to the bacteria and severe precipitation of iron and arsenic at high pulp density, ferrous-free9K medium was fed in batches from the fourth day to take away the excess iron and toxic arsenic in the reactor. The flows of the non-ferrous9Kmedium were0.5,1,1.5and2g/L, respectively. The results showed that the removal of arsenic of the flow of w=1g/L was the highest, and the corresponding recovery of gold up to90%which was3times of the original gold concentrate.