Anodic Oxidation of Sulfide to Sulfate: Effect of the Current Density on the Process Kinetics

The kinetics of the conversion of sulfide to sulfate by electro-oxidation, using a boron-doped diamond (BDD) electrode was studied. Different applied current densities were tested, from 10 to 60 mA cm(-2). The results showed that the electrochemical conversion of sulfide to sulfate occurs in steps, via intermediate production of other sulfur species. The oxidation rate of the sulfide ion is dependent on its concentration and current density. The reaction order varies with the current intensity, being 2 for the lower applied current intensity and high S2- concentration, which is compatible with a mechanism involving two S-2 ions to give S-2(2). For higher current densities, where current control is less important, reaction order varies from 0.15 to 0.44 for the current densities of 20 and 60 mA cm(-2), respectively. For the formation of SO42- from S2- electro-oxidation, the reaction orders with respect to sulfide concentration and current intensity are 0 and 1, respectively.