好酸性・好熱性細菌Ａｃｉｄｉａｎｕｓ ｂｒｉｅｒｌｅｙｉによる黄銅鉱の浸出

Abstract

It is widely accepted in the area of hydrometallurgy that certain microorganisms play a major role in the leaching of base and precious metals from sulfide minerals. Most studies of bioleaching have dealt with the acidophilic mesophilic Thiobacillus species, which grow optimally at around 30 °C and low pH 1 ∼ 2. However, the acidophilic thermophiles, which have temperature optima for activity at 60 ∼ 70 °C, are also candidate microbes for accomplishing metal recovery from mineral resources. Little reports have appeared concerning the bioleaching of sulfides by the thermophilic bacteria at elevated temperatures. This paper describes the bioleaching of high-grade chalcopyrite concentrate (38 ∼ 53 μm) by the acidophilic thermophilic bacterium, Acidianus brierleyi, in a batch stirred reactor. The chalcopyrite leaching was markedly accelerated in the presence of A. brierleyi, and greater than 90 % leaching of copper in the concentrate was achieved at 65 °C within 10 days. However, the chalcopyrite concentrate was scarcely dissolved when the common leaching mesophile, Thiobacillus ferrooxidans, was used at 30 °C. Thus, the thermophile A. brierleyi could solubilize chalcopyrite much faster than the mesophile T. ferrooxidans. The rate of chalcopyrite leaching with A. brierleyi was unaffected by the initial concentration of ferric iron in leach solution, even when the rate of chemical leaching was dependent on the ferric iron concentration. This indicates that the bioleaching of chalcopyrite takes place with a direct microbial attack, the chemical leaching of chalcopyrite by ferric iron being insignificant. Leaching experiments with A. brierleyi were used to examine the dependence of leaching rate on three process parameters, such as solution pH (pH 1.0 ∼ 1.5), temperature (50 ∼ 75 °C), and initial concentrate-liquid loading ratio (2 ∼ 20 kg/m3). The chalcopyrite bioleaching in the batch reactor was carried out most satisfactorily at pH 1.2, 60 ∼ 65 °C, and initial chalcopyrite amount of 20 kg/m3.