Processing of Alumina-Rich Iron Ore Slimes: Is the Selective Dispersion–Flocculation–Flotation the Solution We Are Looking for the Challenging Problem Facing the Indian Iron and Steel Industry?

Beneficiation of alumina rich iron ore slimes is a major challenge for the Indian iron ore industry. Considering the limits of gravity and magnetic separation processes in the relatively finer size range in terms of achieving adequate separation efficiency, selective flotation (with and without selective flocculation) of iron ore slimes, which is being used commercially in several countries for the beneficiation of iron ores, is worth exploring for the beneficiation of Indian iron ores. Based on the extensive work carried out in our laboratories, we have concluded that the design and development of highly selective reagents to achieve satisfactory separation of hematite and goethite from alumina containing minerals (gibbsite or kaolinite) in the ore and ore slimes, is the key to solving the challenging problem of processing alumina rich iron ores. Accordingly our research work has been focused on finding/designing selective reagents for iron oxide–gibbsite–kaolinite separation based on a molecular modeling computational approach developed by us for the design of mineral processing reagents. We present in this paper the results of our density functional theory computations to evaluate the interaction energies of a wide variety of different reagent functional groups such as carboxylic acid, hydroxamic acid, phosphonic acid, iminobismethyl phosphoric acid, xanthate and starch with hematite, gibbsite and kaolinite surfaces. Among all the reagents investigated so far, starch exhibits the highest selectivity towards the hematite surface with a difference in interaction energy of ~63 kcal/mol between hematite and gibbsite surfaces. Based on our earlier work which indicated polyvinyl pyrrolidone (PVP) to be more selective dispersant for kaolinite compared to conventional sodium silicate and sodium hexametaphosphate, we have investigated selective flocculation–dispersion of natural iron ore slimes (three different samples obtained from three different mines in India) with PVP and starch reagent combination. The results are promising. While the work is still in progress, the implications of our recent results are discussed in the context of the challenging problem of processing of alumina rich iron ore slimes in India.