The recovery of critical metal Gallium (Ga) using biosurfactant rhamnolipid by bioionflotation process was attempted in this project. The project was divided into four work packages. The first work package deals with the complexation studies of surface active biomolecules and target metals. Rhamnolipid biosurfactant was chosen as the best substitute for marinobactin considering the similar properties. Ability of rhamnolipid biosurfactant to form complex with target metal Ga, in presence or absence of 1,2 decanediol as common non-ionic frother was confirmed by Dynamic light scattering studies. Aggregate size was found to be higher at lower pH and smaller at higher pH values. Increase in aggregation size for rhamnolipid solutions with Ga and/or 1,2 decanediol suggests the influence of Ga and 1,2 decanediol on the molecular aggregation behaviour of the biosurfactant which may also affect the adsorption kinetics and foaming ability.
In the second work package, rhamnolipid was investigated for its potential as flotation agent. Various properties of rhamnolipid biosurfactant like interfacial properties and foam characterization were studied. It was observed that rhamnolipid plays a dual role of frother and collector when applied in the flotation process. Moreover, the effect of addition of 1,2 decanediol was also studied on the properties of rhamnolipid. Presence of Ga had a strong impact on surface activity of rhamnolipid resulting in the shifting of surface activity curve. The rhamnolipid-Ga complexation that makes the Ga ions hydrophobic and aids their attachment to bubbles, also affects the apparent surface tension.
The foam characteristics of rhamnolipid were evaluated from the the water content of foam (foam drainage), bubble size and bubble shape. Foams with Ga had higher liquid drainage as compared to those without Ga. Smaller bubbles were found in the foam of samples without Ga and the bubble size tends to increase in the presence of Ga. the circularity of bubbles for the foams without Ga was more than that of the foams with Ga.
In the third work package, rhamnolipid biosurfactant was evaluated for its ability to recovery Ga by flotation (bioionflotation process). The flotation experiments were carried out using rhamnolipid at different pH and in absence and presence of 1,2 decanediol. The foam produced by rhamnolipid alone was too stable and is disadvantageous for the flotation process when it comes to the downstream processing. Addition of 1,2 decanediol provided the appropriate stability to the foam. The recovery of Ga was highest at pH 7 in presence of 1,2 decanediol. However, the upgrading value was higher for pH 6 in absence of 1,2 decanediol. The value of upgrading factor is important parameter when considering the flotation recovery in presence of other metals. For the flotation process with metal mixture, higher the upgrading factor for target metal as compared to other metals, higher is the selectivity and process efficiency. Moreover, the new bioionflotation set-up was designed and constructed for use in further experiments.
Work package four dealt with the recovery of Ga from mixed metal system using rhamnolipid by bioionflotation process. Effect of mixed metal system on various properties of rhamnolipid as flotation agent were investigated and the results reaveled that the presence of Arsenic (As), did not affect the complexation of rhamnolipid with Ga. Further, results from various flotation experiments suggested that the rhamnolipid was able to selectively recover Ga from mixed metal systems by rhamnolipid. Rhamnolipid was able to selectively recovery 88% Ga in presence of As with an upgrading value of 1.7429 at pH 6 and air flow rate of 0.02 L/min. The selectivity index was 1.7402.
