Kinetic transitions during Ag and Cu electrorecovery on reticulated vitreous carbon electrodes in flow-by mode

This paper reports on the kinetics of the galvanostatic electrorecovery of copper and silver from sulphate solutions on a reticulated vitreous carbon cathode in flow-by mode. The influence of applied current and flow rate on the electrorecovery rate was systematically studied. Detailed analysis of the electrorecovery kinetics revealed two regimes. The first one was found to be electron-transfer limited, while the second one appeared to be mass transfer limited. From the relevant kinetic rate constants, a current efficiency of 1.03 ± 0.03 for Ag and 0.88 ± 0.01 for Cu electrorecovery was obtained in the first regime. For the second regime, the characteristic mass transport coefficients were determined as (7.6 ± 0.3) × 10−3 and (22.6 ± 0.03) × 10−3 cm/s for Ag and Cu, respectively. Analysis of the time and concentration at the kinetic transition was shown to allow for an additional, independent calculation of both the current efficiency and mass transport coefficient, and to confirm that the kinetic transitions occur when the limiting current has been reached.