Hayato Sato

Effect of silver chloride on the bioleaching of chalcopyrite concentrate

The effect of the addition of silver chloride on the bioleaching of chalcopyrite concentrate, which contained pyrite, sphalerite and galena as sulfide gangue minerals, has been investigated using Thiobacillus ferrooxidans. The addition of silver chloride accelerated the dissolution of copper from the chalcopyrite concentrate. The dissolution rate of Cu was more higher with silver chloride than with the addition of silver sulfate solution at the initial stage of the bioleaching experiments. The recovery of copper increased with increase in the amount of silver chloride. The enhanced dissolution of chalcopyrite did not occur without the contact between silver chloride and chalcopyrite.

Effect of activated carbon on the bioleaching of chalcopyrite concentrate

The effect of the addition of activated carbon on the bioleaching of chalcopyrite concentrate, which contained pyrite, sphalerite and galena as sulfide gangue minerals, has been investigated using Thiobacillus ferrooxidans. The addition of activated carbon accelerated the dissolution of copper from the chalcopyrite concentrate. The recovery of copper increased with increase in the amount of activated carbon and with decrease in particle size of activated carbon. In the chemical control, activated carbon also enhanced the dissolution rate of copper and zinc from the chalcopyrite concentrate. These results indicated that the enhanced rate of leaching could be attributed to the galvanic interactions between activated carbon and chalcopyrite or sphalerite. The presence of Thiobacillus ferrooxidans could accelerate the galvanic interactions.

Bacterial leaching of cobalt-rich ferromanganese crusts

accepted after revision 24 January 1995A study has been made about the possibility of the bacterial leaching of cobalt-rich ferromanganese crusts using Thiobacillus ferrooxidans with elemental sulfur or pyrite as substrate. Ni and Cu in crusts were dissolved rapidly, and then Co, Mn and Fe in crusts were dissolved as pH decreased through the bacterial oxidation of elemental sulfur to sulfate. Ni dissolution depended upon pH condition. However, neither Mn nor Co were extracted with sulfuric acid solution at pH 1.0 in sterile control. Manganese oxide in the crust could be dissolved with reduced sulfur compounds formed during bacterial sulfur oxidation, which led to the dissolution of Co. The dissolution rates of Co and Ni increased with increase in the concentration of elemental sulfur and initial cell number. It was possible to decrease the lag period by using a copper tolerant strain and an adapted strain to the crust. The addition of pyrite increased the cobalt dissolution rate. Pyrite could act as reducing agent toward manganese oxide in the crust.

Fundamental study on the separation of calcite and dickite with sodium oleate.

Flotation behavior of calcite and dickite, alone and 1: 1 mixture, was investigated by a laboratory Denver type flotator at a pH 10.5 using sodium oleate as a collector and sodium silicate as a depressant with the intention of separating calcite from dickite.Both calcite and dickite were negatively charged and therefore neither heterocoagulation nor slime coating took place at an alkaline pH.The following results were obtained.1) In the case of coarse particles system of both calcite and dickite fairly good floatability of calcite was obtained, but for fine particles no satisfactory results were obtained.2) Selective flotation of calcite from dickite at an alkaline pH 10.5 might be explained by the following reasons, hydrophobic flocs of calcite were formed as the result of the increased adsorption of oleate ions on calcite surface and the addition of sodium silicate prevented slime coating.3) Adsorption isotherm of sodium oleate on the surface of calcite and dickite was expressed by the Freundlich type isotherm and the oleate adsorbed on calcite surface forming a multimolecular layer at a high concentration.

Reduction of Hexavalent Chromium with Elemental Sulfur by Sulfur-oxidizing Bacteria.

The reduction of hexavalent chromium (Cr6+) by sulfur-oxidizing bacteria was investigated using elemental sulfur as the substrate for bacteria in 9K medium (without FeSO4). The test bacteria were collected from a neutralization plant at the abandoned Matsuo mine and cultured in iron-free 9K medium with elemental sulfur. The bacteria oxidized elemental sulfur to sulfate, and main strains of them must be Thiobacillus ferrooxidans and Thiobacillus thiooxidans.The results obtained are summarized as follows.1) Cr6+was reduced when the bacteria were cultured on elemental sulfur. It could be due to sulfurous acid formed as a intermediate during the oxidation of elemental sulfur to sulfate by the bacteria.2) Cr6+inhibited the sulfur-oxidizing ability of the bacteria, but the oxidation rate of elemental sulfur increased remarkably after the reduction of Cr6+.3) The rate of Cr6+reduction increased with the inoculum size and the concentration of elemental sulfur, and the optimum initial pH was 2.0.