The use of electrolyte additives to smoothen cathode deposits
during copper deposition is practised worldwide. These additives
absorb on the cathode surface and take part in the electrochemical
crystallization process. However, these additives also affect the
quality of the cathodes when they are inadequately controlled.
Electrolyte additives used by Palabora are glue, thiourea,
Avitone and chloride. Their effects were determined on cathode
quality, the size of the current density region that gives the desired
compact morphology, and current efficiency. This was done in a
small-scale cell. Small cells have different hydrodynamics from industrial-scale cells, which makes it difficult to simulate the operation of industrial cells in a laboratory. The approach used here was to use a rotating cylinder cathode to attain controlled hydrodynamics. The rotation speed was chosen to give a diffusion layer thickness that is similar to that of an industrial-scale cell.
It was shown that even fairly small changes in the additive
levels can significantly affect the cathode morphology, and the
current density range over which this morphology can be obtained.