Bioleaching of clays and iron oxide coatings from quartz sands

Silica sands of low quality contain free iron oxides, clay and silt. These impurities may be removed by biological leaching as well as by industrial washing. The fine fractions obtained from industrial washing of quartz sand from Šastín, Slovakia, with a higher content of iron-bearing minerals and clay minerals were used to study bioleaching of impurities of the quartz sands. The influence of biological leaching by indigenous heterotrophic bacteria and Bacillus spp. bacteria was evaluated by changes in chemical composition of the fine fractions before and after reaction. The bioleaching experiments were performed for 63 days at 24 °C. The extracted iron and clay products were characterized by XRD, FTIR, Mössbauer spectroscopy, chemical and granulometric analyses, SEM, EDX, and nitrogen adsorption techniques. The bacteria assisted in releasing the poorly ordered clay minerals from the surface of quartz particles via dissolution of amorphous Fe oxyhydroxides.