Evaluation of biosurfactant-based ion flotation process for metal separation and selective recovery from battery recycling process waters

The process waters generated during the recycling of spent batteries are an important source of various metals such as Al, Li, Mn, Ni, and Co. Despite low metal concentrations, this stream is a promising secondary source of these critical metals. In this work, the recovery of metal ions from battery recycling process waters by the bioionflotation process was investigated with rhamnolipid as a flotation reagent. In this context, the metal binding affinity of rhamnolipid was investigated by means of surface tension analysis, isothermal titration calorimetry (ITC), and zeta potential analysis. The values obtained for the dynamic surface tension analysis and the binding constant from ITC are relatable and considered in relation to the metal binding affinity of rhamnolipids, demonstrating that the affinity order is as Al(III) > Mn(II) > Ni(II) > Co(II) > Li(I). Our findings reveal a rhamnolipid metal interaction and support a surface tension-based approach to predict the metal affinity, thus providing important fundamental information. The bioionflotation results showed an effective recovery of 91 % for Al(III) at pH 8 and 0.85 mM rhamnolipid concentration. Hence, the bioionflotation approach offers an eco-friendly way to selectively recover metals from battery process water, contributing to sustainable resource management and reducing environmental impact.