Processing of industrial minerals through bio-leaching of iron

Iron is a common contaminant of industrial mineral products that are valued for their whiteness, including kaolin, silica sand, limestone and chalk. Current refinement technologies for kaolin and silica sands rely on acid washing or chemical treatment to remove iron, generating waste and consuming large amounts of energy. Also, none of these technologies can be applied to carbonates. The ability to remove iron impurities from industrial minerals by other means may reduce costs, allow lower grade material to be exploited and improve the efficiency of mineral processing. The proposed research aims to develop and test practical refining methods based on the microbial reduction of iron to a form readily removable by washing. The proposed project will be completed in 2 years and will involve small scale microcosm experiments through to larger scale bioreactor studies enabling the optimum conditions identified from the microcosm experiments to be scaled up. Microorganisms naturally present in the minerals to be investigated will first be identified and any iron-reducing bacteria found in the minerals will be isolated and cultured in the laboratory. Microcosm experiments will conducted to test the efficiency of indigenous and commercially available iron-reducing bacteria on the rate and extent of iron leaching from kaolin, silica sands and limestones under various externally-controlled conditions, including nutrient supply, pH and chemistry of the growth medium. Bioreactors will then be designed and built for each of the minerals to be investigated and several bioreactor experiments will be conducted to evaluate the quality, commercial and environmental benefits of the newly developed bioleaching technologies. In particular, the achieved outcomes will be compared against success criteria agreed with the industrial partners and the time cost and benefit of achieving certain product characteristics will be assessed. The new refinement technology is expected to lead to financial savings in the order of 7-100M per year, mostly through reduced energy costs. The project is also expected to lead to a reduction in the waste generated by current kaolin processing activities.