Abstract: Chlorine dioxide is produced electrolytically in the cathode compartment of an electrolytic cell using a three-dimensional high surface-area cathode. The cathode compartment is separated from an anode compartment by a cation-exchange membrane. Sodium chlorate is reacted with hydrogen ions and chloride ions in the cathode compartment and chlorine dioxide is vented from the cathode compartments. Chlorine co-produced with the chlorine dioxide is reduced at the cathode to provide chloride ions for the reaction while electrolytically-produced hydrogen ions are transferred across the membrane from the anode compartment to the cathode compartment to provide hydrogen ions for the reaction.

Abstract: Dichromate values, or other soluble hexavalent chromium values, are removed from cell liquor or other aqueous media containing the same by cathodically reducing the same to trivalent chromium, which deposits on the cathode as chromium hydroxide. The cathode has a high surface area three-dimensional structure which exposes the electrolyte to electrolysis for a relatively long period of time. An electrode potential of about 0 volts vs. SCE is applied to the cathode. Once the electroconductive sites on the cathode become exhausted, the cathode is regenerated chemically or electrochemically for reuse in further dichromate removal.

Abstract: Peroxydisulfuric acid and its salts are produced electrochemically from an aqueous acid sulfate solution using a glassy carbon anode in the presence of fluoride ions dissolved in the anolyte. A low cost alternative to platinum is provided and high current efficiencies are obtained.

Abstract: Hypochlorite present in cell liquor or other aqueous chlorate solution is reduced electrolytically in the presence of dischromate using a high surface area cathode having a three-dimensional electrolyte-contacting surface. An electrode potential more positive than -1 volts vs. SCE is applied to the cathode.

Abstract: Chlorine dioxide is formed by an autocatalytic electrochemical process from highly acidic chlorate solution containing a residual concentration of chlorine dioxide. Cathodic current is applied to the solution by an electrode which does not otherwise catalyze the chemical formation of chlorine dioxide from the acidic chlorate solution. High purity chloride dioxide is obtained while half the acid is consumed and half the water is produced as compared with a conventional chemical chlorine dioxide generating process.

Abstract: Chlorine is selectively cathodically electrolytically removed from aqueous solutions of chlorine dioxide and chlorine by the application of an electrode potential at a pH of the aqueous solution of up to about 4. Chlorine is electrolytically reduced to chloride ions while the concentration of the chlorine dioxide remains substantially the same in the treated solution. The chlorine reduction is effected directly at pH values up to about 2 using a low overpotential cathode and indirectly at pH values up to about 4 using a high overpotential cathode.

Abstract: Soluble hexavalent chromium values are removed from aqueous chlorate solutions by employing a critical effective ratio of OH.sup.- :Cr.sub.2 O.sub.7.sup.= ions of at least 3:1 in the aqueous chlorate solution and by employing a dithionite to reduce the hexavalent chromium to trivalent chromium, preferably in the mole ratio of S.sub.2 O.sub.4.sup.= :Cr.sub.2 O.sub.7.sup.= of at least 3:1. The trivalent chromium forms chromic hydroxide (Cr(OH).sub.3) with the hydroxyl ions and precipitates from the aqueous chlorate solution. The process is rapid and effective in quantitative removal of hexavalent chromium from the aqueous chlorate solutions and is especially useful for the removal of sodium dichromate from cell liquor which is intended to be employed in chlorine dioxide production and which is produced by diaphragmless electrolysis of sodium chloride.

Abstract: Dichromate values, or other soluble hexavalent chromium values, are removed from cell liquor or other aqueous media containing the same by cathodically reducing the same to trivalent chromium, which deposits on the cathode as chromium hydroxide. The cathode has a high surface area three-dimensional structure which exposes the electrolyte to electrolysis for a relatively long period of time. An electrode potential of about 0 volts vs. SCE is applied to the cathode.