Bioionflotation: Biotechnical approach for metal recovery from low concentrated waters

Ion flotation is a well-known process for the separation or removal of metal ions at a low concentra-tion from aqueous solutions. The use of various flotation agents is well documented, yet there is a high demand for new flotation agents. The new ion flotation agents need to be highly selective, effi-cient, and environmentally friendly. Microbial biosurfactants with high surface activity and metal complexation ability are molecules of interest in this regard. The use of these biomolecules as flota-tion reagents in the ion flotation process can be termed as ‘bioionflotation’. This biotechnological approach for metal recovery from low concentrated waters is still dawning and more research is required to improve the selectivity and process efficiency. This study investigated the separation of gallium (Ga) from aqueous solutions using rhamnolipid biosurfactant as the flotation reagent. The systematic study showed the influence of metal ions on surface activity and foaming properties of the biosurfactant. Further effects of various operating parameters on the metal recovery and selec-tivity were studied. The flotation results of the mixed metal solutions (containing Ga and As at 1 mM concentration), showed nearly 60% and 3.5% of Ga and As recovery, respectively, at 0.85 mM rhamnolipid concentration at pH 6 and air flow rate of 40 ml/min. Further, the selectivity index for Ga over As was 17.2 for the studied system. These results provide insights on the parameters influ-encing the properties of flotation collectors and provide the basis for the development of the bioion-flotation process for effective and selective separation of metal ions from low concentrated waters. These results also indicate the role of biosurfactants as a promising green flotation reagent.