Electrochemical Depression by Cyanide

Janetski et al. (1977) used voltanunetric method to study the electrochemical behavior of a pyrite electrode in ethyl xanthate solution containing various concentration of sodium sulphide. They observed an additional anodic wave due to the oxidation of the dissolved sulphide species present and that the wave appeared at potential cathodic to xanthate oxidation. Therefore, they concluded that the presence of sulphide in solution introduced an anodic process which occurred in preference to xanthate oxidation and hence dixanthogen would not be formed and the pyrite would not be rendered floatable. 

The depression of pyrite by cyanide has been considered from the electrochemical viewpoint, the formation of ferric ferrocyanide in the surface of pyrite which was perhaps responsible for cyanide depression was proposed by Ball and Richard (1976) to occur by the following electrochemical reaction. 

This equation represents the overall reaction which must occur in several steps. The mineral must produce some ferrous ion in solution which reacts with CFT to form Fe(CN)5 . Using measured oxidation potential and pyrite solubility values, Eligillani and Fuerstenau (1968)delineated the stability domains of the compound 

Janetski et al. (1977) also studied the behavior of a pyrite electrode in a solution of cyanide concentration in the absence and presence of xanthate using voltammetric technique. They reported that on increasing the concentration of cyanide at constant pH and xanthate concentration, the oxidation wave of xanthate is shifted to more anodic potential indicating that the presence of cyanide, which may react with the mineral surface to form an insoluble iron cyanide complex will result in the inhibition of the electrochemical oxidation of xanthate and the depression of pyrite. 

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