Research On Bioleaching Of Chalcopyrite By Alicyclobacillus Spp

Chalcopyrite is not only the most abundant copper ore, but also the most refractory copper sulfide by environmentally hydrometallurgy way due to its special crystal structure, therefore it is the industrial target. The genus Alicyclobacillus is a kind of acidophilic and moderately thermophilic bacteria, researches show that the genus Alicyclobacillus have great potential in the leaching of chalcopyrite, despite there are only a few of researches and reports about this genes in biohydrometallurgy. Our laboratory has successfully isolated three novel Alicyclobacillus species from Dexing mine in China. This paper characterized the physiological and biochemical features of the three Alicyclobacillus strains and carried out the bioleaching experiment of chalcopyrite with three Alicyclobacillus strains and other moderately thermophilic microorganisms.The physiological and biochemical features of the three Alicyclobacillus strains were characterized. The results show that the three Alicyclobacillus strains are all short rod shaped and gram-positive. Three Alicyclobacillus strains can use extensive organic and inorganic substrates such as yeast extract, typotone, glucose and xylitol for heterotrophilic growth and ferrous ions, element sulfur for autotrophic growth.50mM ferrous ions are oxidized completely by strain A, strain B, strain AP-AC in120hours,110hours and90hours, respectively. Anaerobic and microoxic growth also occur in the media containing organics and ferric ions or element sulfur, as result, the ferric ions and element sulfur are reduced to ferrous ions and H2S, respectively. About10%of ferric ions in the medium containing15mM ferric sulfate are reduced to ferrous ions after12days of cultivation under microoxic condition.The structure and dynamics of the microbial populations are monitored by16S rDNA clone library and real-time PCR. The results of16S rDNA clone library show that the original consortia after domestication contains Acidithiobacillus caldus, Leptospirillum ferriphilum, Sulfobacillus thermosulfidooxidans and Ferroplasma cupricumulans. The analysis results of real-time PCR indicate that S. thermosulfidooxidans is the dominant species in the early period during the bioleaching, At.caldus and L.ferriphilum are the dominant species at middle and last period, the proportion of F.cupricumulans increases in the latter phase of the leaching process. The proportion of Alicyclobacillus strains in total microorganism is high in former stages and gets lower with time, until Alicyclobacillus strains vanish in the last stages. Alicyclobacillus species can affect the proportion of other microbes, for example, Alicyclobacillus species could promote the growth of At.caldus and Lferriphilum, and further inhibit the growth of S. thermosulfidooxidans.The bioleaching of chalcopyrite was performed by Alicyclobacillus species along with other typical moderately thermophilic microorganisms at temperature of45℃. The pH value, redox potential of the leachate and the concentration of the cupric ions, ferrous and total iron ions in the leachate are measured, and the chalcopyrite residues are also observed by scanning electron microscope and detected by energy dispersive spectrometer (SEM-EDS) and by X-ray diffraction (XRD). The results show that Alicyclobacillus species can leach chalcopyrite a little more efficiently than typically acidophilic microorganisms. After30days of bioleaching,47.5%of copper is leached by Alicyclobacillus species, higher than46.6%by typical bioleaching microorganisms. However, the mixture of Alicyclobacillus spp. and typical leaching microorganisms is weaker in bioleaching chalcopyrite, only40.6%of copper is released from the ore. Alicyclobacillus strains have significant influence on the formation of jarosite in the process of chalcopyrite bioleaching. A large quantity of granular potassium jarosite formed on the surface of chalcopyrite in the leaching system containing only typical leaching microorganisms, and a relatively less jarosite formed in the leaching system containing mixed culture of Alicyclobacillus species and typical leaching microorganisms than containing only typical leaching microorganisms. However, only a little flocculent potassium jarosite formed in the leaching system containing only Alicyclobacillus species. So the Alicyclobacillus spp. isolated from Dexing mine by our laboratory can inhibit the formation of potassium jarosite in the bioleaching process of chalcopyrite.