Redox chemistry of H2S oxidation by the British Gas Stretford Process Part. II: Electrochemical behaviour of aqueous hydrosulphide (HS?) solutions

Abstract

Electrochemical techniques were used to study the oxidation of HS− ions at pH 9.3. Voltammetry of gold electrodes in HS− -containing solutions showed that multilayers of sulphur and soluble oxidation products were formed. As a known HS− oxidation product, thiosulphate solutions were also studied voltammetrically, but found to be electro-inactive at mildly oxidising potentials. The voltammetric behaviour of polysulphide ions, S n 2− (n = 2 to 5), was similar to that of HS− solutions on oxidation, though they could be reduced to HS− ions at low potentials. Ring-disc electrode experiments, extending the HS− concentration range that had been studied previously, confirmed that polysulphide ions were produced on reduction of anodically deposited elemental sulphur. This was demonstrated in both cyclic Volammetry and potential step experiments. By comparison of the charges passed producing polysulphides from sulphur and reducing them to HS− ions, an average polysulphide chain length of 1.8 was calculated, indicating a mixture of species was produced. Ion chromatography confirmed that polysulphide solutions do contain a number of species, consistent with thermodynamic predictions.