| Protein colloid (glue), thiourea, Avitone and chloride ion are the most common additives used electrorefining copper. The polarization behavior of these additives, single and combined, was studied by cyclic voltammetry techniques in conjunction with stationary and rotating disc electrodes. In the stationary electrode work, different protein colloids give substantially different results in polarization or interaction with other additives. The role played by Avitone is not clear, but it does somewhat modify other additives in the electrolyte. Thiourea can cause a depolarized peak and a polarized plateau depending on the concentration, the other additives present and the potential selected. Chloride ion causes some changes in polarization behavior and morphology, but the most significant effect is the interaction with other organics. It was found that an improper balance among the additives, especially the ratio of thiourea to chloride ion, could cause rough, irregular deposits, due to a very localized variation of these additives. In the rotating disc work, it was found that the polarization behavior of these additives strongly depended on the mass transfer conditions. The polarization curve for an additive-free electrolyte is independent of the rotation speed in the potential scan range studied. The current tends to decrease with an increase of rotation speed for a glue-containing electrolyte, except in certain potential regions where a current maximum is observed. The plot of current versus rotation speed at a selected potential seemed to provide a means of detecting the concentration variation of a protein colloid in the copper electrolyte. The correlation between thiourea content, rotation speed and scan rate has been established by using the onset of the thiourea plateau as the criterion. The calculation of the pseudo limiting current indicates the formation of a passive film is the reason for the presence of the current plateau. Thiourea content in a mixture with protein colloid TPC IV can be estimated from the slope of the reverse scan curve, and the concentration of protein colloid then intimated by the potential shift of the thiourea peak. |
