Gallium bioionflotation using rhamnolipid: Influence of frother addition and foam properties

The current study investigated the application of rhamnolipid biosurfactant as an ion collector in bioionflotation. In a top-down approach, the influence of rhamnolipid on gallium (Ga) ion flotation and recovery were investigated followed by detailed studies on the influencing parameters and foam characterization. Rhamnolipid exhibits extensive foaming properties and foam produced by rhamnolipid alone has higher stability making it difficult to collect the flotation concentrates. An addition of 1,2-decanediol introduces instability to this foam and also aids in concentrate collection. Observations during the flotation studies resulted in a series of investigations on rhamnolipid properties such as aggregate size, surface tension, and foam characterization. These results indicated that the addition of Ga and/or 1,2-decanediol affected the molecular aggregation of rhamnolipid. Moreover, the surface activity, foamability, foam drainage, and foam coarsening/coalescence of the rhamnolipid changed in the presence of Ga and/or 1,2-decanediol. In a batch bioionflotation process, rhamnolipid was able to remove nearly 80% Ga at pH 7 in presence of 1,2-decanediol. However, upgrading was higher at pH 6 without 1,2-decanediol, which is important when considering the flotation recovery in presence of other metals. Such biosurfactants have a high potential for wide applications in ion flotation and further optimization of flotation parameters is essential.