The effect of various process variables on anode passivation in copper electrorefining was investigated by combining conventional electrochemical techniques, laser-based visualization, and digital image processing in a laboratory scale copper electrorefining cell. High current density operation causes early anode passivation; in the range of 0.23 to 1.50 kA m(-2), the effect of current density on the onset of passivation was found to be constant. The higher the temperature the longer the time required for the onset of anode passivation. When the electrolyte is circulated, anode passivation occurs earlier than in the absence of circulation, but the effect also depends on the direction of circulation.