好酸性・好熱性古細菌<i>Acidianus Brierleyi</i> による 海底熱水鉱床鉱石のバイオリーチング<b> </b>

Abstract

This article describes the bioleaching of deep-sea hydrothermal ore deposits by the acidophilic and thermophilic archaeon Acidianus brierleyi at 65℃. Bioleaching experiments with A. brierleyi were used to examine the dependence of leaching rates on three process parameters such as solution pH (pH 1.2–2.0), initial cell concentration (1×1013–1×1014 cells/m3), and initial ore-liquid loading ratio (5–40 kg/m3). The leaching of copper and zinc was markedly accelerated in the presence of A. brierleyi, and greater than 80 % extraction of copper and zinc in the ore sample (38–53 μm) was achieved at 65℃ within 10 days of batch operation. Nearly identical bioleaching rates of zinc and copper were obtained for the deep-sea hydrothermal sulfide (ore sample A) and terrestrial sulfide concentrates (sphalerite and chalcopyrite) by the thermophilic archaeon A. brierleyi. However, the bioleaching of lead was practically negligible because of precipitation of insoluble anglesite. The bioleaching of gallium tended to be suppressed as the initial ore-liquid loading ratio was increased from 5 to 40 kg/m3. The bioleaching of the ore sample (45.4 % SiO2) yielded less than 5 % extraction of gallium in 10 days of batch operation at an initial ore-liquid loading ratio of 40 kg/m3, and gallium in the bioleaching residue was concentrated 1.8-fold of its initial content. Moreover, the concentration of gold in the bioleaching residue was increased by a factor of 1.9 after 10 days of batch operation. It can be concluded that bioleaching is an attractive processing route to recover valuable metals from deep-sea hydrothermal ore deposits.