Transporting metal ions using reverse micelles in alcohol modified supercritical carbon dioxide

Metal species including Cd, Co, Cu, Pd and Zn can be extracted from solid materials using reverse micelles (microemulsions) formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and dissolved in supercritical carbon dioxide (ScCO2) containing an alcohol. The cloud-point pressure (CPP) of the microemulsion decreases with increasing amount of alcohol in ScCO2. Below the CPP, two phases co-exist in the system with the bottom phase containing alcohol and the metal loaded microemulsion. After removing the alcohol/microemulsion phase from the high-pressure system, the extracted metal species are recovered by adding a small amount of water and the surfactant can be recycled. The amount of water used to destabilize the microemulsion for metal recovery is much less than that used in solvent-based extraction and acid leaching processes. This solvent-assisted microemulsion dissolution method does not require expensive fluorinated surfactants and may provide an economic and effective method for extraction of metal species from different matrices with minimum liquid waste generation.