Abstract: The invention relates to a process for the cyclic electrochemical processing of pickle waste liquors containing a maximum 100 g. of sulfuric acid and a minimum of 25 g. of iron ions per liter, combined with the pickling of iron. According to the invention the ammonium, magnesium or alkali-metal sulfate concentration of the waste liquor is adjusted to 0.5-1.0 mol./l. by introducing an appropriate salt, and the acid content of the waste liquor is reduced to a value not exceeding 100 g. of sulfuric acid/liter, then the waste liquir is fed into and passed through the cathode chambers of an electrolysis apparatus consisting of a series of dual electrolytic cells with diaphragms, whereupon the iron content of the waste liquor is reduced to a value of 7-15 g. of Fe.sup.2.sup.+ /liter, thereafter the waste liquor is fed into and passed through the anode chambers of said electrolysis equipment in parallel with the cathode flow, and a current density of 15-22 A/dm.sup.2.