Abstract: A bipolar membrane which exhibits a low water dissociation voltage for an extended period of time under a high current density condition, and a high current efficiency, without developing blister. The bipolar membrane comprises a cation-exchange membrane and an anion-exchange membrane which are joined together, wherein ion-exchange resin particles having ions exchanged with ions of a metal of an atomic number 20 to 90, such as titanium, zirconium, tin, iron, ruthenium or palladium, or with complex ions of said metal are existing on the junction interface between the cation-exchange membrane and the anion-exchange membrane.

Abstract: A bipolar membrane which exhibits a low water dissociation voltage for an extended period of time under a high current density condition, and a high current efficiency, without developing blister. The bipolar membrane comprises a cation-exchange membrane and an anion-exchange membrane which are joined together, wherein ion-exchange resin particles having ions exchanged with ions of a metal of an atomic number 20 to 90, such as titanium, zirconium, tin, iron, ruthenium or palladium, or with complex ions of said metal are existing on the junction interface between the cation-exchange membrane and the anion-exchange membrane.

Abstract: To reuse ashes that are left after burning components contained in a black liquor obtained by digesting wood chips in the step of producing kraft pulps. Acids and alkalis are produced by burning components contained in a black liquor obtained by digesting wood chips and by decomposing an aqueous solution of the thus obtained ashes through the electrodialysis by using a bipolar membrane and a cation-exchange membrane and/or an anion-exchange membrane.

Abstract: Disclosed is a bipolar membrane comprising a cation-exchange membrane in which a cation-exchange group present at least at its adhered surface has been ion-exchanged with a heavy metal ion, which is adhered closely to an anion-exchange membrane at a peel strength of not less than 0.2 kg f/25 mm, and having a water-splitting current efficiency of not less than 80% and a water-splitting membrane potential of not more than 2.0 V.

Abstract: Disclosed is an anion-exchange membrane prepared by subjecting a membrane composed of a resin containing a high-molecular-eight compound having haloalkyl groups chemically bound thereto to ultraviolet radiation or ionizing radiation to thereby decrease the amount of the haloalkyl groups present in its surface portion less than 0.1 micrometer deep from its surface by 10 to 95% from that of the haloalkyl groups present in the interior of the membrane, and the converting the haloalkyl groups present in the membrane into anion-exchange groups.