Abstract: Alkali metal chlorite, particularly sodium chlorite, is produced with a low carbonate level by combining a chlorine dioxide generating system operating at subatmospheric pressure with a chlorite formation reactor in which the chlorine dioxide reacts with hydrogen peroxide in the presence of aqueous alkali metal hydroxide, particularly sodium hydroxide.

Abstract: An in-situ procedure is described for measuring chlorate ion concentration in aqueous media containing the same by employing electrodes, particularly microelectrodes which generate a sigmoidal-type response at high chlorate ion concentration, and which exhibit catalytic properties toward chlorate ion electroreduction or electrooxidation.

Abstract: Chlorine dioxide is produced by reaction of chlorate ions, usually provided by sodium chlorate, with a persulfate in an aqueous acid reaction medium containing sulfuric acid. By-product sodium sulfate, sulfuric acid feedstock or mixture may be electrolyzed to form the persulfate for the reaction.

Abstract: Chlorine dioxide is produced by reaction of sodium chlorate, a reducing agent, preferably methanol or hydrogen peroxide, and sulfuric acid at the boiling point of the reaction medium under a subatmospheric pressure. Present in the reaction medium is a component which suppresses the solubility of by-product sodium sulfate and thereby increases the concentration of free hydrogen ions in the reaction medium available for reaction to form chlorine dioxide. The solubility-depressing component generally is an inert alkali metal salt, preferably an inert sodium salt, such as perchlorate or nitrate. By increasing the concentration of hydrogen ions available for reaction, it is possible to achieve an improvement in the rate of production of chlorine dioxide.

Abstract: Sodium sesquisulfate produced in crystalline form in a high acidity highly efficient chlorine dioxide generating process is converted by metathesis to crystalline anhydrous neutral sodium sulfate and the acid recovered as a result is recycled to the chlorine dioxide generating step. The metathesis is effected by contacting the crystalline sodium sesquisulfate with aqueous sodium chlorate solution, aqueous sodium chloride solution, aqueous methanol or water alone. The metathesis is effected in such manner as to minimize the additional evaporative load imposed on the chlorine dioxide generating process by the metathesis medium.

Abstract: Solid sodium sesquisulfate is metathesized by water to neutral anhydrous sodium sulfate and to recover the acid values therefrom by employing a dynamic leaching of the solid phase sodium sesquisulfate, to provide an acid medium for recycle to a chlorine dioxide generating process producing the sodium sesquisulfate without significantly increasing the evaporative load on the generator.

Abstract: Chlorine dioxide is continuously produced at high efficiency in a single vessel process by reduction of chlorate ions with hydrogen peroxide in an aqueous acidic medium. The hydrogen peroxide is pre-mixed with at least a portion of the aqueous chlorate solution feed or the sulfuric acid feed or a mixture thereof. By pre-mixing the hydrogen peroxide feed, the occasional decomposition of hydrogen peroxide and the resulting foaming of the generator liquor is eliminated.

Abstract: Chlorine dioxide, useful as a pulp mill chemical, is produced without producing sodium sulfate effluent for disposal, by effecting reduction of chloric acid in an aqueous reaction medium in a reaction zone at a total acid normality of up to about 7 normal in the substantial absence of sulfate ion and in the promence of a dead load of sodium chlorate added to and subsequently removed from the reaction medium. Chloric acid for the process is produced electrolytically from an aqueous solution of the deadload sodium chlorate and make-up quantities of sodium chlorate. The chloric acid reduction to produce chlorine dioxide may be effected using methanol or electrolytically.

Abstract: Scale is removed from within cation-exchange membranes by operating the cathode compartment of a cell divided by the cation-exchange membrane with a mildly-acid catholyte while effecting transfer of cationic species from the anode compartment to the cathode compartment.

Abstract: The voltage requirements of a membrane-divided cell are decreased by operating the cell with a catholyte temperature significantly in excess of the anolyte temperature, generally at least 10.degree. C. greater and preferably at least 20.degree. C. greater. The invention is particularly useful in an electrochemical acidification process whereby aqueous sodium chlorate and sodium sesquisulfate solution is acidified for use in a chlorine dioxide generating process and aqueous sodium hydroxide is produced as a by-product.

Abstract: Sodium sesquisulfate produced in crystalline form in a high acidity methanol-based highly efficient chlorine dioxide generating process is converted by metathesis to crystalline anhydrous neutral sodium sulfate and the acid recovered as a result is recycled to the chlorine dioxide generating step. The metathesis is effected by contacting the crystalline sodium sesquisulfate with aqueous sodium chlorate solution, aqueous sodium chloride solution, aqueous methanol or water alone. The metathesis is effected in such manner as to minimize the additional evaporative load imposed on the chlorine dioxide generating process by the metathesis medium.