Abstract: Arsenic acid is formed from arsenous acid and water under oxygen pressure with catalytic amounts of nitric acid and a halide whereby the nitric oxide by-product is regenerated to nitric acid for contact with fresh arsenous acid.

Abstract: Bromide ions when used as the redox intermediates in the oxidation of arsenic (III) oxide to arsenic (V) acid can be removed from a solution having a major proportion of arsenic acid by treatment with an oxidant selected from H.sub.2 O.sub.2, O.sub.3 or Cr(VI) to oxidize the bromide to bromine followed by purging with air, nitrogen or other inert gas to sweep out the resultant bromine. The bromine can be recovered and recycled to a fresh batch of arsenic (III) oxide.

Abstract: A pulsating potential is applied to the anode in the electrolytic oxidation of arsenic trioxide to arsenic acid to reactivate the anode and increase the current density.

Abstract: A method and apparatus for in situ reduction of cathode overvoltage in electrolytic cells. The method involves introducing low overvoltage or noble metal ions into the catholyte solution and plating those ions on the cathode in situ. The apparatus includes a low overvoltage or noble metal ion generating device for introducing low overvoltage or noble metal ions into the cathode solution so as to plate them in situ on the cathode during or prior to cell operation.

Abstract: A method and apparatus for measuring the overvoltage of a gas producing electrode of a chlor-alkali diaphragm cell is disclosed. The method includes positioning an exposed metal tip of a reference electrode from about 0.2 to about 1.0 mm away from the gas producing electrode within a stream of gas produced by the gas producing electrode. The apparatus includes the reference electrode so positioned. Platinized platinum wire and a RuO.sub.2 --TiO.sub.2 coated Ti wire are preferred as the reference electrodes for cathode and anode, respectively.

Abstract: A method and apparatus for in situ reduction of cathode overvoltage in electrolytic cells. The method involves introducing low overvoltage or noble metal ions into the catholyte solution and plating those ions on the cathode in situ. The apparatus includes a low overvoltage or noble metal ion generating device for introducing low overvoltage or noble metal ions into the cathode solution so as to plate them in situ on the cathode during or prior to cell operation.

Abstract: Electrolysis of alkali metal chloride solutions to produce chlorine and alkali metal hydroxides is accomplished in a cell comprising an anode compartment, a cathode compartment, a cation permeable divider separating the anode compartment from the cathode compartment, where the anode compartment contains an anode separator. The anode separator is comprised of a porous plate of a valve metal having an electrochemically active coating on the face, and an electrochemically non-active barrier layer on the back and a portion of the interior. The anode separator is positioned in the anode compartment so that the back of the anode separator is spaced apart from the cation permeable divider. An alkaline brine zone is formed between the anode separator and the cation permeable divider which increases the service life of the cation permeable divider.

Abstract: An electrolytic cell employing a hydraulically impermeable membrane having a spacing means interposed between the anode and the membrane, is operated by providing a positive pressure differential between the cathode compartment and the anode compartment. The pressure differential is sufficient to maintain contact between the spacer and the membrane to provide uniform spacing between the anode and the membrane. In addition, this process provides sufficient spacing between the membrane and the cathode to provide efficient release of any gas formed and to prevent gas blinding at the cathode. Employing the positive pressure differential enables the cell to be operated at reduced energy costs when producing, for example, concentrated solutions of sodium hydroxide by careful control of the spacing between the membrane and the electrodes.

Abstract: Electrolysis of alkali metal chloride solutions to produce chlorine and alkali metal hydroxides is accomplished in a cell comprising an anode compartment, a cathode compartment, a cation permeable divider separating the anode compartment from the cathode compartment, where the anode compartment contains a porous metal separator. The porous metal separator is comprised of a porous plate of, for example, a valve metal having a porosity of from about 30 to about 75 percent and an air flow value of from about 0.1 to about 60 CFM. The anode separator is positioned in the anode compartment so it is spaced apart from the cation permeable divider and from the anode. During electrolysis, an alkaline brine zone is formed between the porous metal separator and the cation permeable divider which increases the service life of the cation permeable divider. In addition, the porous metal separator provides improved chlorine gas separation properties.

Abstract: Current efficiency in an electrolytic membrane cell for the production of potassium hydroxide from aqueous solutions of KCl is considerably increased by maintaining the anolyte concentration of KCl at 250-350 grams per liter and the catholyte concentration of KOH at from about 410 to about 480 grams per liter. The electrolytic cell employs a cationic permselective membrane comprised of a hydrolyzed copolymer of a perfluoroolefin and a fluorosulfonated perfluorovinyl ether.

Abstract: An electrolytic cell employing a hydraulically impermeable membrane having a spacing means interposed between the anode and the membrane, is operated by providing a positive pressure differential between the cathode compartment and the anode compartment. The pressure differential is sufficient to maintain contact between the spacer and the membrane to provide uniform spacing between the anode and the membrane. In addition, this process provides sufficient spacing between the membrane and the cathode to provide efficient release of any gas formed and to prevent gas blinding at the cathode. Employing the positive pressure differential enables the cell to be operated at reduced energy costs when producing, for example, concentrated solutions of sodium hydroxide by careful control of the spacing between the membrane and the electrodes.