Selective transition metal extraction by reverse micelles

In this report we have studied the extraction of a series of heavy metals ions (Cu2+, Ni2+, Fe3+, Cr3+, CrO4(2-)) from water bulk solutions by means of reverse micelles. The parameters explored are the nature and concentration of the accompanying electrolyte, as well as the surfactant nature and its concentration. The extracted metals can be recovered and eventually concentrated in a new water solution carrying out a back extraction. The extracted amount of metal is strongly dependent on the charge of the metal to be extracted. Therefore the extracted water solution is enriched in higher charge metal. Anions of amphoteric metals, like the chromate ions, can be quantitatively separated from their positive cations, like Cr3+ by properly choosing the cationic or the anionic surfactants. The transfer of the metal is essentially controlled by electrostatic forces. A model based on the Poisson-Boltzmann distribution allow us to get the potential profile inside the water pool by determining the concentrations of the surfactant counter ions. From the potential profile and mass balance it is possible calculate the extraction percentage.