Ceramics-Silikáty 51, (4) 202 - 209 (2007)

Naturally occurring iron oxides are often coated on silicate grains or are impregnated in the matrix in silicates of industrial importance. These Fe-rich impurities can be removed from industrial minerals such as granite through bioleaching. Heterotrophic bioleaching may substantially reduce the need of aggressive chemical bleaches treat industrial silicate minerals. This process involves a siliceous matrix, which is why silicate heterotrophic bacteria of the genus Bacillus are of potential use. These organisms are noted for their ability to reduce ferric iron coupled with dissolution. Solution phase assays were used to monitor iron reduction activity by a Bacillus sp. during the bioleaching of natural feldspar raw materials under various experimental conditions. The rate of reductive iron dissolution was dependent on the presence of yeast extract, nitrate and sulphate in the medium. Quinone stimulated the Fe(III) reduction in feldspars raw materials in cell suspensions. The dissolution of iron was enhanced in the presence of technical-grade sucrose and molasses. The amendment of the medium with river water and indigenous bacteria increased the bacterial reduction of iron. The Fe content in granite samples treated by bioleaching decreased by about 60 %. The process needs controlled conditions for the bacterial iron reduction and is dependent on the mineralogical composition of non-metallic ores.