Dissolution of aluminosilicates and Fe-oxyhydroxideminerals from granitic eluvium using bacteria of Bacillus genus was monitoredwith solution chemistry, granulometric and X-ray analyses as well as microscopictechniques to determine the effects of these bacteria on crystal surface andreleasing mechanism of K, Si, Fe, and Al from minerals. Feldspars, quartz andmicas are dominant minerals in granitic eluvium (GE). Oxyhydroxides of Fe arefound in the intergranular spaces of minerals, contaminating and making mostfeldspar raw materials unsuitable for commercial applications. Bacteria ofBacillus spp. decrease pH of leaching medium by production of organic acids.These organic acids are directed by glycocalyx of adherent bacteria to specificsites on mineral surface (e.g. to crystal defects). The impregnated ironminerals are released by bacterial destruction of intergranular and cleavagespaces of silicate grains. This bacterial activity results in the release of Fe,Si, and K from feldspar and Fe oxyhydroxides. However, pH of leaching medium isadjusted to neutral value in regular intervals during bioleaching to maintainbacterial activity. The decrease of fine-grained fraction is the result ofbacterial destruction of GE. Despite the impoverishment of the distribution offine-grained fraction, there was observed the increase of the surface area offeldspar grains from the value 3.65 m2/g to value 4.82 m2/g. This fact confirmsthe activity of bacteria of Bacillus genus together with hydrolysis in pointcorrosion of mineral grains. After 120 days of bioleaching, 31 % Fe extractionfrom granitic eluvium was observed. It was also possible to accelerate thisprocess by using 0.1 M oxalic acid after 1 month's bacterial pretreatment.Moreover, the bacterial pretreatment facilitated the access of oxalic acid toFe-bearing minerals and showed a possibility to use the oxalic acid in lowerconcentration. This fact is important especially from the view of producingless-agressive effluent to the environment and decreasing of costs in subsequentrecyclation of oxalic acid.
