Cyclic electrowinning/precipitation (CEP) for the removal of heavy metals from aqueous solution mixtures

The description and operation of a novel cyclic electrowinning/ precipitation (CEP) approach for the simultaneous removal of mixtures of heavy metals from aqueous solutions are presented. CEP combines the advantages of electrowinning in a spouted particulate electrode (SPE) with that of chemical precipitation and redissolution, to remove heavy metals at low concentrations as solid metal deposits on particulate cathodic particles without exporting toxic metal precipitate sludges from the process. The overall result is very large volume reduction of the heavy metal contaminants as a solid metal deposit on particles that can either be safely discarded or further processed to recover particular metals. The performance of this approach is demonstrated with data obtained for the removal of low concentration mixtures of copper, nickel, and cadmium from aqueous solutions, as well as removal from contaminated soil leachates. Separation of these same metals on different sets of cathodic particles is also demonstrated. An analysis of co-electrodeposition of copper and nickel from acidic solution mixtures is also presented, as an example of the processes that occur in the SPE of the CEP system. The quantitative and qualitative behavior of co-electrodeposition of these two metals from their mixtures differs significantly from that of the individual single-metal solutions, primarily due to the metal displacement reaction between NiO and Cu++. A numerical model of co-electrodeposition, corrosion, metal displacement, and mass transfer in the SPE is presented that describes the behavior of the experimental data relatively well. © 2013 American Chemical Society.