Research On Isolation And Application In Bioleaching Of Moderate Thermophilic Bacteria

About one third of the world' s gold production comes from ores that are described as refractory, and this proportion is growing as oxidized, near-surface resources become depleted. The three main process routes available for breaking down the sulphide minerals and exposing the gold for subsequent leaching are roasting, pressure oxidation, and bacterial oxidation. Of these,bacterial oxidation appears the most attractive option for many reasons.The microorganisms used for bioleaching are mainly iron-oxidizing or sulfur-oxidizing bacteria which live in acid condition. Thiobacillus ferrooxidans has been proved to be the dominant iron-oxidizing bacterium in mesothermal environment by a lot of research in a long period. The recent studies on microorganism species in the continuous bioleaching system indicates that some moderately thermophilic acidophilic bacteria whose optimum temperature is about 40-45℃, such as Thiobacillus caldus and Leptospirillum ferrooxidans, are the dominant species. The study indicates that moderate thermophilic acidophilic iron-oxidizing or sulfur-oxidizing bacteria play important roles in bioleaching process. Because the temperature in which moderately thermophilic acidophilic bacteria can survival is higher than mesothermal bacteria. They have unable comparative biology predominance.In this research, first, bacterium sourse was obtained from waster water of a pyrite mine. After cultivating in different culture mediums, a group of high iron-oxidizing moderate thermophilic acidophilic bacterium was got. 14g/L FeSO₄·7H₂O can be oxidized by These bacterium in three days.A bacterial species named zyl was isolated after cultivating, separating and purifying. The bacterium community is rotundity, white, semitransparent, heave, lubricity on the Starky—Na₂S₂O₃ solid medium. This bacterial specie is gram-negative and rod-shaped, judged by Gram strain. Analyzed by 16Sr RNA,zyl is similar with Thiobacillus caldus by 99%.The growth and sulfur oxidizing ability of zyl is affected by pH temperature inoculate quantity rotate speed factors. The experimental result shows the optimal cultivating condition is pH 3.0, temperature 45℃, inoculate quantity 1%.The result of leaching mineral experiment shows that though the ability of zyl oxidizing sulfate is strong, they barely oxidized pyrite. After 15 days leaching mineral ,the leaching rate of Fe was just 3.43%, pH hardly dropped. The group of iron-oxidizing moderate thermophilic acidophilic bacterium is better, the leaching rate of Fe was 62.35% after 15 days leaching. Two kinds of bacteria mixed without adding sulfate leaching pyrite ,the effect is a little better than single bacteria. The leaching rate of Fe was 64.59%, pH dropped to 1.65. But the effect of mixed bacterium with adding sulfate was best, the leaching rate of Fe got to 79.89%, pH dropped to 1.41.Based on the result of leaching experiment, the mine leaching mechanism of the mixed bacterium was analyzed,the reason why mixed bacterium leaching effect was better than single bacteria was discussed.