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.