Ion flotation of Co2+, Ni2+, and Cu2+ using dodecyldiethylenetriamine (Ddien)

Ion flotation is a separation process involving the adsorption of a surfactant and counterions at an air/aqueous solution interface. It shows great promise for removing toxic heavy metal ions from dilute aqueous solutions. It was found that a chelating surfactant, dodecyldiethylenetriamine (Ddien), could selectively remove one metal ion over others at different pH values. Selectivity was attributed to the formation of surface-active chelated species at specific pH. Surface tension data show that [M-(Ddien)2]2+ is more surface-active than [M-(Ddien)]2+ and other Ddien species, thus the relative fraction of [M-(Ddien)2]2+ in the solution determined the metal ion flotation efficiency. The ion flotation results were consistent with the surface tension data and the relevant speciation diagrams. Theoretical discussion reveals that DeltaG0ads and DeltaG0chelation for the Ni(II) and Co(II) ions in the Ddien-Ni(II) and Ddien-Co(II) systems are more negative than those for Cu(II) in the Ddien-Cu(II) system.