Abstract: An aqueous medium containing contaminant ions such as hexavalent chromium ions is treated by introducing electrolytically generated ferrous ions which are preferably generated in water acidified to a low enough pH to prevent the formation of flocculent material. The ferrous ions reduce the hexavalent chromium ions to a trivalent state, and thereafter alkaline material is introduced into the medium to raise its pH high enough to cause insoluble chromic hydroxide and ferric hydroxide to precipitate. The apparatus includes a ferrous ion generator for recirculating liquid through an electrolytic cell and a receptacle, from which receptacle liquid for end use can be withdrawn and to which makeup water and acid can be added.

Abstract: Contaminating ions are removed from an aqeuous medium, e.g. hexavalent chromium ions from cooling tower waters, by an electrochemical method which includes formation of an insoluble iron compound or complex of the contaminant ion, utilizing an anode of iron, iron alloy or insoluble iron compound. The electrodes are treated with an acid solution at regular intervals to remove any substances formed on or lodged between the electrodes. The electrolytic cell includes a plurality of closely spaced generally parallel plate electrodes with electric potential applied to the two end electrodes, and an electrode near each end electrode is of a size protecting the end electrode from flux field effects.

Abstract: Contaminating ions are removed from an aqueous medium, e.g. hexavalent chromium ions from cooling tower waters, by an electrochemical method which includes formation of an insoluble iron compound or complex of the contaminant ion, utilizing an anode of iron, iron alloy or insoluble iron compound. The electrodes are treated with an acid solution at regular intervals to remove any substances formed on or lodged between the electrodes. The electrolytic cell includes a plurality of closely spaced generally parallel plate electrodes with electric potential applied to the two end electrodes, and an electrode near each end electrode is of a size protecting the end electrode from flux field effects.