Kinetics of sulfide ion adsorption at copper amalgam electrode

Abstract

Convolutive voltammetry was employed in studies of the kinetics of sulfide ion adsorption at copper amalgam and mercury electrodes. Measurements were carried out for low electrode coverages to minimize the effect of the lateral interaction energy, and the results were extrapolated to zero coverage. In the case of a Cu amalgam electrode (7.4×10 −4 mol dm −3 of Cu) kinetic and thermodynamic parameters of the adsorption/desorption process were determined in solutions of different pH (3.6 to 12.8). For pH<7, the standard rate constant of the process was independent of the pH and equal to 92±7 s −1 , but in basic solutions it decreased with an increase in the pH down to 11±2 for pH 10 and to 3.1±0.5 s −1 for pH 12.8. The electrosorption valency and the activation barrier symmetry-factor were practically independent of the pH and equal to −1.32±0.03 and 0.65±0.02, respectively. Study of the effect of Cu concentration revealed the formation of 1:1 (CuS) compound at the interface. It was also found that both H + and Cu participate in the activated complex. Adsorption of S 2− on pure mercury is much faster than on the Cu(Hg) electrode, however the determination of kinetic parameters in this case was obscured by a kinetically controlled transition between the two dimensional nuclei of the HgS condensed phase and its dispersed forms.