Abstract: The invention relates to method of producing chlorine dioxide comprising the steps of: providing a reactor with an aqueous acidic reaction medium containing chlorate ions; reacting said chlorate ions with hydrogen peroxide as a reducing agent in such proportions that chlorine dioxide is formed; withdrawing the chlorine dioxide from the reaction medium; wherein the content of tin in the reaction medium at steady state is maintained below 20 mg Sn per kg reaction medium.

Abstract: An increasing problem with the pulping chemical recovery system, is the presence of chloride and potassium in the recovery boiler. Chloride and potassium increase inter alia the stickiness of carryover deposits and dust particles to the recovery boiler tubes, which accelerate fouling, corrosion and plugging of the recovery boiler. As the environmental legislation becomes more stringent, the degree of system closure increases. The present invention relates to a process by which the collected precipitator dust is leached, at a temperature exceeding 50.degree. C., for a residence time sufficient to get a chloride and potassium enriched leach solution and to remove at least a part of the content of metal ions in a solid phase. Said leach solution is electrochemically treated, preferably in an electrodialysis cell, in order to remove at least a part of the chloride and potassium therein. By the present process, the problem of sticky deposits in the recovery boiler can be substantially reduced.

Abstract: This invention is related to a process for producing pulp from a cellulosic starting material, wherein an aqueous process effluent is purified from metal impurity cations. This process comprises that the effluent is purified by an electro-chemical membrane treatment in an electrochemical membrane device comprising a unit cell through which an electric current is passed between an anode side and a cathode side of said cell, said cell comprising at least two ion permeable membranes forming between them at least one compartment, said effluent being fed into an effluent feed compartment in said cell, in which the effluent is purified by removing with the electric current metal impurity cations from the effluent through a cation selective membrane on the cathode side of said compartment, and withdrawing from said compartment the purified effluent. The purified effluent may be recirculated to the pulp mill process, e.g. as washing water.

Abstract: The invention relates to a method of producing pulp comprising a step of forming green liquor containing alkali metal sulfide and alkali metal carbonate. The method further comprises a step of electrochemically treating the green liquor to oxidize at least part of the sulfide therein.

Abstract: Sulphide-containing white liquor is treated in a continuously operating electrolytic cell having separate anode and cathode compartments separated by a partially permeable barrier. White liquor is introduced into the anode compartment of the cell, and an aqueous solution of alkali metal hydroxide is introduced into the cathode compartment of the cell so that sulphide is oxidized in the anode compartment, while at the same time alkali metal cations are transported through the barrier into the cathode compartment, where water reacts to form hydroxide ions. An electrolytic cell suited for implementing the method is also disclosed.

Abstract: The invention relates to a process for treating a low-concentrated aqueous feed solution which includes at least one aqueous process stream from a pulp mill. The process includes concentrating the feed solution by evaporation to form an evaporation concentrate, and subjecting at least a part of the concentrate to a first electrodialysis treatment, thereby forming a first electrodialysis concentrate containing salt removed from the evaporation concentrate and at least one diluate depleted in the salt. The invention also relates to a plant for carrying out the above process.

Abstract: Disclosed is a process of producing chlorine dioxide having the steps of providing a reactor with an aqueous acidic reaction medium containing alkali metal chlorate and phosphate; reducing chlorate ions in the reaction medium to form chlorine dioxide; withdrawing chlorine dioxide gas from the reaction medium; withdrawing reaction medium from the reactor and transferring it to an electrochemical cell; treating the reaction medium electrochemically to increase the acidity and decrease the content of alkali metal ions; recycling the acidified reaction medium to the reactor; and adding make up alkali metal chlorate to the reaction medium before or after the electrochemical cell.

Abstract: The invention relates to a process of producing chlorine dioxide using, in a first alternative atmospheric pressure and hydrogen peroxide in the reaction medium optionally with an electrolytic cell. In a second alternative, either atmospheric or subatmospheric pressure is used in the reaction medium together with an organic or inorganic reducing agent and an electrolytic cell.

Abstract: The invention relates to a method of producing an acidified aqueous solution containing alkali metal sulfate and chlorate comprising the steps of introducing an aqueous solution containing alkali metal sulfate and chlorate into an electrochemical cell and electrochemically increasing the acidity of said aqueous solution, wherein the current efficiency of the cell is maintained below 70%.

Abstract: Process water from pulp manufacture is purified in a separator device by mechanical or a combination of mechanical and chemical methods and is thereafter evaporated, at least part of the concentrate resulting from the evaporation being recycled and mixed with the process water fed into the separator device. In a preferred embodiment, a precipitant is added to the mixed water comprising the process water and the concentrate. The part of the concentrate not recycled and mixed with the process water is supplied, optionally after further evaporation, with an acid to a pH of 1-5, whereupon resulting flocs and precipitates are removed in a separator device.

Abstract: A process for producing chloric acid, which involves introducing a metal chlorate solution and an acid into separate compartments of an electrodialysis cell to produce a chloric acid solution.