Ion foam flotation and ion separation of metal cations of different charges, Na+, Li+, Ca2+, Sr2+, Cu2+, Nd3+ and Eu3+ using a sensitive surfactant, nonaoxyethylene oleylether carboxilic acid, was studied as a function of and concentration. We propose here a method to evaluate ion selectivity coefficients using mass and volume balances. This method yields selectivity coefficients in agreement with those obtained with the classical slope method. The ion selectivity obtained by the flotation experiments was found to correlate well with the apparent charge of the surfactant micelles (zeta potential values) in the presence of different salts and is therefore not influenced by the surface curvature. Consequently the ion specificity order has been established according to the surfactant–ion affinity at the air–water and micelle–water interfaces as Na+ &lt; Li+ &lt; Sr2+ &lt; Ca2+ &lt; Cu2+ &lt; Nd3+ &lt; Eu3+. It has been noticed that the selectivity coefficients between the different metal ions, obtained by ion flotation, differ from the ones predicted by using metal ion complexation constants of acetate, which is considered here as the non-surface active complexing part of the surfactant. This discrepancy was attributed to the surface complexation effects at the air–water interface in flotation experiments and at the micelle–water interface. For the separation of lithium and neodymium, a depletion phenomenon of lithium ions from the interface, hence from the foam, has been observed, i.e. once the flotation experiment was finished the lithium concentration in the remaining foaming solution was indeed higher compared to the initial one. This phenomenon was explained by the strong adsorption of Nd3+ that leads Li+ to be repelled from the foam. A general methodology based on the determination of speciation diagrams of the surfactant and the metal ions was also used to highlight the mechanisms involved in ion flotation processes.

Ion foam flotation of metal ions using a carboxylate based surfactant: from speciation to ion separation by foams

254th National Meeting (2017)

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