Ability of in situ electrochemical noise techniques was examined to monitor passivation onset regardless of anode impurities in the electrolyte as general tool. This generalization is important to examine the passivation onset phenomenon and its prediction during processing. The passivation of a pure copper as well as a synthesized Cu-Sb and an industrial Cu-Pb anode was studied during simulated electrorefining conditions at laboratory scale. Statistical analysis as well as fast Fourier transform (FFT) and Wavelet analyses techniques were employed to examine the electrochemical noise measurements of active-passive behaviors of copper anodes with Sb or Pb impurities, considering pure Cu as reference. The results showed that these methods of analysis are promising to monitor the copper passivation in simulated refining conditions. Certain parameters of analyses of the measured electrochemical noise (in situ) during the pre-passive region describe the approach of the passive onset during refining. (C) 2010 Elsevier Ltd. All rights reserved.