The electrochemistry of the leaching reactions in the Caron process II. Cathodic processes

The cathodic reactions which are involved in the dissolution of iron alloys in solutions typically used in the Caron Process have been investigated by electrochemical methods. The results have confirmed that cobalt(III) ammine complexes are the main oxidising agents but also highlight the important role of thiosulfate. A solid product is deposited on platinum as well as iron electrodes below −0.75 V/SCE and oxidised at more positive potentials. The product is either Ni or Co metal in the absence of thiosulfate or a metal sulfide when thiosulfate is present. The rate of reactions in the presence of thiosulfate is significantly greater than its absence. The probable chemical reactions taking place during leaching in the Caron Process have been revised on the basis of these observations.

Research highlights
► Co(III) ions are the main oxidising agents in the Caron Process
► Thiosulfate also plays an important role
► Solid metal sulfide is formed from a reaction involving reduction of thiosulfate
► The presence of thiosulfate significantly enhances the rate of dissolution