Removal of Cd2+, Zn2+, and Sr2+ by Ion Flotation, Using a Surface-Active Derivative of DTPA (C12-DTPA)

Ion flotation was studied for the removal of cadmium, zinc, and strontium ions from aqueous solutions at pH 5-9 in a customized flotation cell, using an aminopolycarboxylic chelating surfactant, 2-dodecyldiethylenetriamine pentaacetic acid (C-12-DTPA) in combination with two foaming agents: dodecyltrimethylammonium chloride (DoTAC) and dimethyldodecylamine-N-oxide (DDAO). The results from experiments showed that both Zn2+ and Cd2+ could be removed via ion flotation to 100% at pH 5, and Sr2+ could be removed via ion flotation to 60%-70% at pH 7-9. The removal of metal ions from the flotation cell was seen to vary with pH, but this was not exclusively related to the magnitudes of the formed metal ion-chelating surfactant conditional stability constants. The removal was also dependent on the foam properties of the samples that were found to vary over the investigated pH interval. The outcome of the investigation points to the chelating surfactant C-12-DTPA having excellent chelating properties for all of the studied ions above pH 7. In combination with correctly chosen foaming agents, the optimized surfactant system could be expected to provide very efficient remediation of waters polluted with metal ions via ion flotation.