Foam Separation of Metal Ions and the Potential 'Green' Alternative to Solvent Extraction

Foam separation has been applied to recover or remove various substances from dilute aqueous solutions in various industries because it is an environment- and cost-friendly process. The literature has been reviewed focusing on the separation of metal ions. From an operational point of view, various methods are discussed for the removal of metal ions from solution, and on the selective recovery of a specific target metal ion. The former applications are designed to purify industrial effluents, and the performance of foam separation is well proven. The latter examples are aimed at recovering valuable metals, which has been shown to be difficult due to the inherent problem of contamination in foam separation. An operation mode was developed to overcome this problem and to enhance the selectivity for separating a specific target metal from solutions containing multi-metals. The method, called continuous counter-current foam separation, was developed, and its performance was demonstrated by the experimental results for Ga(III) separation. Since both high selectivity and recovery was obtained by this method, foam separation is potentially a "solvent-free" alternative to solvent extraction.