Kinetics of sulfide ion adsorption at copper amalgam electrode

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 later al interaction energy, and the results were extrapolated to zero coverage. In the case of a Cu amalgam electrode (7.4 x 10(-4) mol dm(-3) of Cu) kinet ic and thermodynamic parameters of the adsorption/desorption process were d etermined in solutions of different pH (3.6 to 12.8). For pH < 7, the stand ard 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 elect rosorption valency and the activation barrier symmetry-factor were practica lly independent of the pH and equal to -1.32 +/- 0.03 and 0.65 +/- 0.02, re spectively. Study of the effect of Cu concentration revealed the formation of 1:1 (CuS) compound at the interface. It was also found that both Hf and Cu participate in the activated complex. Adsorption of S' on pure mercury i s much faster than on the Cu(Hg) electrode, however the determination of ki netic parameters in this case was obscured by a kinetically controlled tran sition between the two dimensional nuclei of the HgS condensed phase and it s dispersed forms. (C) 1999 Elsevier Science S.A. All rights reserved.