A SIMPLE SULFUR ELECTRODE FOR AQUEOUS SULFIDE MINERAL STUDIES

The behavior of an electrode made by pressing a mixture of 90% w/w sulfur and 10% w/w graphite into a pellet was studied by cyclic voltammetry. The electrode has a large electrochemical window between -0.3 V and +0.7 V (vs. the standard sodium chloride calomel electrode) where there is little chemical reaction. At potentials more negative than -0.5 V hydrogen sulfide is produced. Reduction at the electrode in copper(II) solutions produces covellite which can be reoxidised to copper(II) ion and sulfur. Leaving covellite on the electrode reduces the potential for the reduction of sulfur to hydrogen sulfide. The formation of covellite occurs by a mixed controlled mechanism and the modified form of the Levich equation gives the diffusion coefficient for copper(II) ion as 3.9 x 10(-10) m2 s-1 at 298 K. It is believed the "sulfur electrode" could be useful in studying the reactions of metal ions with sulfur and in interpreting the electrochemical reactions of mineral ores during leaching.