Model of multiple metal electrodeposition in porous electrodes

An electrochemical process is being developed for recovering metals from shredded waste electrical and electronic equipment by leaching and electrowinning. In a membrane-divided electrochemical reactor, chlorine is generated at the anode and used as oxidant in an external leach reactor, in which the metals are dissolved in an acidic chloride solution. As the resulting metal ion concentrations are relatively low, a porous (e.g.,graphite felt) cathode with a large specific surface area and high mass-transport rates is required to achieve acceptable rates and efficiencies of electrodeposition, the counter reaction to the anodic evolution of chlorine. Hence, as a design tool, a mathematical model was developed to predict potential, concentration, current density, and current efficiency distributions for individual metals within the (flow-through) porous cathode, as well as cell voltages and specific electrical energy consumptions of the electrochemical reactor as functions of cathode feeder potential, cathode thickness, porosity, concentrations, and flow rate and direction. To maximize current efficiencies and productivities of the predominant metal, copper, simulations suggest using an initial cathodic feeder electrode potential of -0.5V (standard hydrogen electrode) to metallize the felt, followed by electrodeposition of the bulk of the metal at -0.3V (standard hydrogen electrode), optimal felt thicknesses depending on reactant concentrations. (c) 2006 The Electrochemical Society