Recovery of Cu, Pb, Cd and Zn from synthetic mixture by selective electrodeposition in chloride solution

Secondary fly ash, resulting from thermal treatment processes, leads to a highly concd. chloride soln. with Cu, Pb, Cd and Zn as main heavy metals when dissolved in water. The selective electrodeposition of these heavy metals was studied. The goal was to recover, under potentiostatic conditions, each heavy metal with high purity, yield and reaction rates. By changing the parameters pH and overpotential, an optimum of the three requirements was looked for. In general, Cu, Pb and Cd could be sepd. with purities of 99 mol% or higher. Underpotential deposition probably is the main reason for the impurities in case of Cu and Pb deposition. H+ redn. as side reaction could be kept small for Cu, Pb and Cd even at lower pH by carefully selecting the overpotential. The quality of the deposits obtained depended strongly on the overpotential, but hardly on the pH. The deposits of Cu, Pb and Cd were easily removable from the cathode due to a dendritic growth mechanism. Zn deposits showed compact growth and adhered to the electrode surface. In addn., the structure of the deposits, revealed by scanning electron microscope (SEM), was compared with the current transients during electrodeposition. An enhancement factor r was introduced to compare the different deposition rates. [on SciFinder (R)]