Selective removal of Gallium from mixed metal solutions with Arsenic by ion flotation using the biosurfactant rhamnolipid

Rhamnolipids have received great attention in various environmental applications in terms of metal complexation and recovery. However, the effect of metal ions on interfacial and foaming properties in relation to flotation are not much studied. To assist, this study investigated the effect of metal ions alone and in a mixed metal system containing Gallium (Ga) and Arsenic (As) on these properties of rhamnolipid, along with isothermal titration calorimetry to study rhamnolipid-metal interactions. Further, the potential of rhamnolipid to recover and separate Ga from As was assessed using bioionflotation. Ga alone and in mixed metal system had a remarkable effect on the interfacial and foaming properties of rhamnolipid as compared to As alone. The effect of operating parameters like pH, rhamnolipid concentration, and airflow rate had a significant influence on the separation performance. Nearly 74% Ga was removed at 0.85 mM rhamnolipid concentration, pH 6, and an airflow rate of 80 ml/min. The selectivity index of Ga over As was highest (17.2) at 0.85 mM rhamnolipid concentration, pH 6, and an airflow rate of 40 ml/min. Also, the selective separation of Ga was dependent on the recovery of water from the foam. Altogether, the results provide new insights on the interfacial and foaming properties of rhamnolipid and its efficiency as an ion collector for Ga and showed that the optimized process parameters could be expected to provide very efficient separation and recovery of target metal via ion flotation.