Abstract: The disclosure relates to a process and apparatus for the treatment of sodium-nitrate-containing electrolytes during the electrochemical machining of the surfaces of iron-containing workpieces. By adding an oxidizing agent, more particularly ozone, increased production of nitrite in the electrolyte is prevented and, thereby, premature passivation of the surface of the workpiece during the electrochemical metal removal. An apparatus for the oxidation of the electrolyte is comprised of a processing station inserted into the electrolyte circuit, an ozone generator, and a reactor.