Studies On Screening And Breeding Of Three Biometallurgical Microorganisms And Their Effect On Minerals

A variety of microorganisms can catalyze the solubilization of minerals in natural environments. Besides Thiobacillus ferrooxidans, which can extract metal from metal sulfides, several other microorganisms such as silicate bacteria Bacillus mucilaginosus and fungi Aspergillus niger have been found to be progress in mineral bioleaching. Bacillus mucilaginosus can dissolve silicate from silicate minerals, and Aspergillus niger can dissolve metal from oxidative minerals. In this study, three types of microorganisms above have been screened from different materials using different isolating methods.In study of Thiobacillus ferrooxidans, 6 strains have been isolated from Dexin Copper mine, Dabaoshan Copper mine, Chengmenshan Copper mine, Tongling Copper mine, Xixiashan Copper mine and Liuyang Pyrite mine using method of enriching culture. Research indicates different strains of Thiobacillus ferrooxidans process different Fe2+ and element sulfur oxidation activities. It has been found that bacterium density in S?medium is higher than that of in 9K Fe2+ medium. The Zinc extracting rate was 100 % when low grade sphalerite was bioleached with DBS strain for 30 days, and 50 % of sphalerite concentrate also can be biooxidized.Two important physiological characteristics of Thiobacillus ferrooxidans, dryness tolerance and high temperature tolerance, have been researched in this study. The results show Thiobacillus ferrooxidans has excellent physiological characteristic of dryness tolerance and bad characteristic of high temperature tolerance because Thiobacillus ferrooxidans rapidly lose its oxidation activity at temperature of 55 ℃. Effects of several factors on oxidation activity of Thiobacillus ferrooxidans have been researched. Experimental results show the lag phase of Thiobacillus ferrooxidans was longer and bacterium density was decreased when 0.25 % pulp density of metal sulfides or 1% element sulfur was added in 9K medium. The research indicates metal sulfides and element sulfur may restrain Fe2+ oxidation activity of Thiobacillus ferrooxidans. It also be found that higher pulp density may decrease bacterial Fe2+ oxidation activity because the collision of mineral particles to bacterial cells will mechanically harm bacterial enzyme system. Experimental results show higher concentration of metal ions, for example [Zn2+]>50 g/L, [Cu2+]>15 g/L and [Mg2+]>15 g/L, mayIVrestrain Fe2+ oxidation activity of Thiobacillus ferrooxidcms although this microorganism can grow in medium containing definite concentrations of metallic ions, and Thiobacillus ferrooxidans was showed to be sensitive to organic substance such as bacterial residue, glucose and peptone.Growth of Thiobacillus ferrooxidans on sphalerite surface and in 9K leach media was studied through estimation of bacterial protein using ninhydrin colorimetric method in the different leach phases. The mineral samples containing adhered bacterium are digested in 0.5 M NaOH in a boiling water bath for 25 min. The digested soup then filtered and the filtrate is neutralised to pH 7 using 0.5 M HC1. Then 1 mL of reagent ninhydrin is added to 2 mL of protein extracted solution and mixed thoroughly. The mixed solution is heated in a boiling water bath for 20 min, then the boiled solution is cooled for 6 min. After development of the color, the absorbance is measured at 562 nm using UV-1100 for the protein content, which provides a measure of the attached cell mass. This study indicated that the attachment of Thiobacillus ferrooxidans to sphalerite mineral is dependent on three factors, namely, particle size, expose period of the sphalerite mineral to the bacteria and as to whether stationary or agitation conditions are used during incubation. The results showed bacterial growth, both in the liquid and on the solid substrate, was found to be increased with increasing incubation periods for two size fractions of sphalerite mineral used. In this study 20 days of incubation were needed for any significant zinc dissolution. Experimental results showed 50 % -80 % of bacterial...