The effect of copper, acid, and temperature on the diffusion coefficient of cupric ions in simulated electrorefining electrolytes

Deposition and dissolution processes involved in copper electrorefining are significantly affected by the diffusion coefficient of copper within an electrolyte. It is believed that the diffusion coefficient of cupric ions under conditions similar to those encountered in commercial electrolytes is not precisely known. The effects of copper, acid, and temperature on copper diffusivity were measured for simulated industrial electrolytes. Copper and acid concentrations tested were 35¯70 and 160¯250 g L-1, respectively. Temperature was varied from 40°C to 65°C. Increasing the copper and acid concentrations slightly decreased the diffusivity of copper. The diffusion coefficient of cupric ions increased with increasing temperature according to the Arrhenius relationship. An activation energy of 19.2 kJ mol-1 was calculated from the data. The diffusivity data was utilized in a simple one-dimensional finite difference model. The model indicates that saturation of copper sulfate occurs very rapidly at the high current densities (3820 A m-2) used in accelerated passivation experiments.