Study On Leaching Of Chalcopyrite By Moderate Thermophiles

Bioleaching is paid the increasing attention due to low cost, no pollution and simple operation, especially for low-grade and complex composition of mineral resources in China. Moderate thermophiles have great application prospect in the leaching of minerals and provide more advantages owing to reduced cooling equipment for industrial reactor. Despite some progress has been made in the industrial application of copper sulfide ores leaching by moderate thermophiles, but mechanism of microbiologies is not enough and the leaching efficiency of copper need to be improved. In this paper, moderate thermophilic isolates and enrichment with a high capacity of leaching chalcopyrite were obtained from a number of copper areas in China; the community composition of the enrichment was analysed; chalcopyrite leaching parameters by the enrichment in the reactor were investigated; microbial community structure and population dynamics in the reactor were studied. By artificially building bioleaching microbial communities, the bioleaching performance and microbial community varieties were surveyed. The research work enhances the understanding of leaching characteristics of moderate thermophiles and provides reference data and experience for industrial applications.The specific research contents and results are summarized as follows:1 Moderate thermophilic enrichment and community analysis1.1 In this paper, under the moderate high temperature and acidic conditions, with addition of the pyrite, chalcopyrite, a mixture of ferrous sulfate and elemental sulfur as the main energy sources, moderate thermophilic microbial community structure in the stable phase was investigated by PCR-RFLP method, and community compositions of three culture systems were compared. Results showed that Sulfobacillus thermotolerans, Acidithiobacillus caldus and Leptospirillum ferriphilum had a high abundance in the three culture systems.1.2 Different energy sources had a significant effect on microbial community compositions. In the culture system with pyrite as the main energy source, L. ferriphilum accounted for the highest proportion. In both culture systems culture system with a mixture of ferrous sulfate and elemental sulfur as energy sources, L ferriphilum accounted for about 50%, and differences in the proportion of bacteria were mainly the varieties of S. thermotolerans and A. caldus. In the former culture system the ratio of S. thermotolerans and A. caldus was about 1:1. And in the latter, the ratio of S. thermotolerans, and A. caldus was nearly 4:1. Most members of archaeal community in moderate thermophilic chalcopyrite leaching system were related to the genena of Ferroplasma.2 Isolation and identification of moderate thermophilic bacteria2.1 Moderately thermo-acidophilic and iron-oxiding strains ZW-1 was isolated from acid mine drainage in Dexing Mine, Jiangxi Province and its morphological, physiological and biochemical characteristics,16S rRNA sequences and leaching properties were studied. Results revealed that the strain was G- and rod-shaped, size (0.8-1.5)μm×0.4μm and with optimum temperatures and pH of 48℃and 1.9. The strain grew autotrophically by using ferrous and elemental sulfur as energy sources and heterotrophically by using yeast powder and peptone, but it can not use glucose. Phylogenetic tree based on 16S rRNA gene sequences revealed that the strain ZW-1 and Sulfobacillus acidophilus were at the same evolutionary branch with a similarity of 99.0%. Leaching performance studies showed that the strain ZW-1 had a high oxidation capacity of Fe2+ up to 0.295 g/L-h, and could tolerate a high concentration of 25 g/L Fe3+ and 35 g/L Cu2+. When leaching chalcopyrite (12 g/L pulp density), percentage copper released by the strain ZW-1 increased to 46.4% after 20 days.2.2 Six moderate-thermophilic sulfur-oxidizing strains with similar morphological, physiological and biochemical characteristics were isolated from the four typical acidic environments in China. Their optimum growth temperatures and pH were 45-50℃and 2.5-3.5, respectively. They can grow autotrophically by using elemental sulfur, sodium thiosulfate and potassium tetrathionate as energy sources and trace glucose can stimulate their growth. Phylogenetic analysis showed that all six bacteria had high homology with Acidithiobacillus caldus in Genbank (more than 99%), and were initially identified as Acidithiobacillus sp.。 3 Bioleaching of chalcopyrite with moderate thermophilic enrichment3.1 Moderate thermophilic microorganisms with strong chalcopyrite leaching capability were enriched from several acid mine drainage in China. By domestication, tolerance of pulp concentration increased from 10 g/L to 50 g/L. Under the conditions of 0.4 g/L yeast powder and 180rpm rotational speed, moderate thermophilic enrichment can leach 74% copper of chalcopyrite. Through agitation leaching experiments in the reactor, leaching of chalcopyrite by the consortia was further improved. When leaching chalcopyrite, the leaching rate of chalcopyrite in 50 g/L pulp density was 81% after 8 days. Acid consumption experiments showed that it was necessary to the high leaching of chalcopyrite by adding a large number of acid during leaching. In the small-scale column leaching reactor, the moderate thermophilic enrichment has a certain ability to low-grade chalcopyrite leaching, and the leaching rate of chalcopyrite was 40.8% after 60 days.3.2 In the pre-mid-late three stages of 60d leaching, there were similar bacterial populations including:L. ferriphilum, S. thermotolerans and At. caldus. In the initial stages (20 d), L. ferriphilum had a high proportion of 81% in the leaching system of chalcopyrite. With leaching, the proportion of L. ferriphilum decreased gradually. In the 60 d, L. ferriphilum decreased to 13%. In the initial stages, S. thermotoleran had the proportion of 16%. In the late stages of leaching (60 d), the proportion of S. thermotolerans increased to 79%.4 Bioleaching of chalcopyrite by "artificial design" of consortia of moderate thermophiles4.1 We utilized the isolated microorganisms to construct effective moderate thermophilic consortia. The consortia including At. caldus S2, L. ferriphilum YSK and Sulfobacillus sp.TPY had higher leaching efficiency when processing the recalcitrant chalcopyrite containing basic gangue.4.2 It had also shown that consortia containing autotrophic and heterotrophic acidophiles tend to show cooperation between different groups. Moderately thermophilic F. thermophilum and Sufobacillus sp. may enhance mineral oxidation by removing soluble organic materials that might inhibit some chemolithotrophic bacteria. Mutualistic interactions between physiologically distinct moderately thermophilic acidophiles, including transformations of iron and sulfur and transfer of organic compound, were considered to play a critical role in promoting chalcopyrite dissolution. The results provided the information to the design of effective moderate thermophilic acidophiles consortia.In order to enhance the dissolution rate, reduce cost, develop and popularize the moderate thermophilic bioleaching technology, we should carry out these studies on strain screening, correlation on community structure and leaching efficiency, leaching systems and process optimation and additives.