Bioprecipitation of copper from a leaching solution by a moderately thermophilic iron-oxidizing bacterium

A moderately thermophilic iron-oxidizing bacterium strain TI-1 produced 74 μmol H₂S extracellularly when grown at 45°C for 15 days in 20 mL of ferrous sulfate-5AAG medium (pH 4.0) containing 1.0 % elemental sulfur and 0.31 % L-glutamic acid. Precipitation of copper from a leaching solution by the H₂S produced by strain TI-1 was investigated. A leaching solution containg Cu²⁺ was prepared by the cultivation of Thiobacillus ferrooxidans AP19-3 on a copper concentrate (5.0 %)-medium (pH 2.5) for 15 days. When strain TI-1 was grown for 8 days in a ferrous sulfate-5AAG medium (pH 4.0) containing 1.0 % elemental sulfur, 0.31 % L-glutamic acid and 5 mM Cu²⁺ from a leaching solution, the Cu²⁺ in the medium was completely precipitated by the H₂S produced by strain TI-1. Growth of strain TI-1 in ferrous sulfate-5AAG medium was not inhibited by 10 mM Cu²⁺. A moderately thermophilic sulfate-reducing bacterium Desulfotomaculum nigrificans IFO 136987 produced 45 μmol H₂S extracellularly when grown at 45°C for 15 days in 20 ml of lactate (0.35 %)-medium. The maximum productivity of H₂S by D. nigrificans was observed in the medium with an initial pH of 7.2. The bacterium did not produce H₂S in the lactatemedium with a pH less than 6.0. Growth of D. nigrificans in the lactate-medium was completely inhibited by 0.56 mM Cu²⁺. These results suggest that strain TI-1 is superior to D. nigrificans in the ability to precipitate copper from the acidic leaching solution containing Cu²⁺.