Abstract: A cation exchange membrane manufacturing method in which a film of a blend which consists of a perfluoro carbon polymer having a group transformable into a sulfonic acid group and a perfluoro carbon polymer having a group transformable into a carboxylic acid group or a film of a copolymer which consists of a perfluoro carbon monomer having a group transformable into a sulfonic acid group and a perfluoro carbon monomer having a group transformable into a carboxylic acid group and another film of a perfluoro carbon polymer having a group transformable into a carboxylic acid group are joined together. Following that, the group transformable into a carboxylic acid group and the group transformable into a sulfonic acid group are transformed respectively into the carboxylic acid group and the sulfonic acid group.

Abstract: A cation-exchange membrane for electrolyzing an aqueous solution of an alkali metal halide in the manufacture of an alkali hydroxide and a halogen. The membrane comprises one layer which occupies 5 to 30% of the total thickness of the membrane and has carboxylic acid groups; another layer which occupies 5 to 30% of the membrane thickness and has weakly acidic groups, the weakly acidic groups occupying 10 to 60% of the total exchange group capacity of the layer; and a further layer which has sulfonic acid groups occupying the middle portion of the membrane.

Abstract: An improved method for electrolyzing alkali metal halide. Electrolysis is carried out by supplying an aqueous solution of a halide of alkali metal into an anode chamber partitioned by a cation-exchange membrane and water into a cathode chamber to obtain halogen from the anode chamber and hydrogen and alkali hydroxide from the cathode chamber. The cation-exchange membrane is a fluorocarbon polymer membrane which is prepared by arranging one side thereof to have a cation exchange group concentration lower by 10 to 30% within a depth range of 1 to 100.mu. than that of the other side. The anode chamber is prepared with this side of the membrane which has the lower cation exchange group concentration arranged to face the anode chamber. By this arrangement, a high purity alkali hydroxide can be manufactured at a high rate of decomposition of halide of alkali metal and at a high current efficiency.

Abstract: A dihydrate of calcium hypochlorite of a prismatic crystal shape in which the lengths of axes a, b and c thereof are in the ratios satisfying the following formulas (1), (2) and (3):0.5.ltoreq.b/a.ltoreq.2.0 (1)c/a.gtoreq.1.5 (2)c.gtoreq.5.mu. (3)and a method for the manufacture of the prismatic dihydrate. Further a method for the manufacture of a coarse dihydrate of calcium hypochlorite carried out by using the prismatic dihydrate of calcium hypochlorite as seed crystal.

Abstract: Wet process phosphoric acid prepared by treating phosphate rock with sulfuric acid is purified by extracting said wet process phosphoric acid with an organic solvent containing an equilibrium concentration of phosphoric acid in a first extraction section such that substantial extraction of phosphoric acid from said wet process phosphoric acid is prevented while the organic impurities in said wet process phosphoric acid are substantially extracted and under conditions which prohibit significant extraction of iron impurities into said solvent extractant, extracting the extracted wet process phosphoric acid of reduced organic impurity content with an organic solvent in a second extraction section, returning a portion of the solvent from the second extraction section to the solvent extraction phase of the first section, removing the organic impurities from the solvent phase which is obtained from the first extraction section, and returning at least a portion of the solvent from which the organic impurities have b

Abstract: A method of purifying extracted phosphoric acid containing substantially no metallic impurities which comprises:(a) adjusting the phosphoric acid concentration to from 20 to 65 wt.% as P.sub.2 O.sub.5,(b) adjusting the Si/F atomic ratio in said extracted phosphoric acid to less than 0.2; and(c) contacting said extracted phosphoric acid with silica gel at a temperature of 20.degree.-100.degree. C. to remove the dissolved silica from said extracted phosphoric acid; and(d) recovering extracted phosphoric acid having a reduced silica content.

Abstract: Wet process phosphoric acid prepared by treating phosphate rock with sulfuric acid and separating calcium sulfate, is purified to obtain a purified phosphoric acid by (a) an acid extracting section contacting the wet process phosphoric acid and a phosphoric acid solution containing impurities obtained in the scrubbing section with an organic solvent in the presence of the hydrochloric acid required for extracting a substantial amount of the phosphoric acid component; (b) a scrubbing section contacting the extract obtained in the acid extracting section with aqueous phosphoric acid or water while maintaining the chloride ion concentration in the aqueous phase in the range of 20 to 40 g/liter as Cl; (c) an acid stripping section contacting the purified extract obtained in the scrubbing section with water and (d) an adsorbing section contacting the extracted phosphoric acid obtained in the acid stripping section with an anion-exchange resin.

Abstract: A process for removing sulfate ions from extracted phosphoric acid which is substantially free of metallic ion impurities and which has been prepared by extracting wet process phosphoric acid with an organic solvent which comprises:A. adjusting the extracted phosphoric acid concentration to a concentration greater than 70%;B. adding an amount of a barium compound which is less than the stoichiometric equivalent amount of barium relative to the amount of dissolved sulfate ion to form barium sulfate crystals; andC. separating said barium sulfate from the resulting slurry at a temperature less than 80.degree. C and recovering purified, extracted phosphoric acid;Wherein the amount of barium compound added is such that said purified extracted phosphoric acid contains at least 5 ppm of sulfate ions.

Abstract: A process for removing organic material from extracted phosphoric acid comprises contacting extracted phosphoric acid with a chlorate and hydrochloric acid at a temperature higher than 100.degree. C while maintaining the concentration of the extracted phosphoric acid at a value higher than 90 wt% as H.sub.3 PO.sub.4. Hydrochloric acid may also be included with the chlorate.

Abstract: A process for removing sulfate ions from extracted phosphoric acid which is substantially free of metallic ion contaminants, which comprises adding less than the stoichiometric equivalent of a barium compound relative to the amount of dissolved sulfate ion to said extracted phosphoric acid to form barium sulfate crystals, adding active carbon to the resulting slurry, separating the solid components from the slurry and recovering purified phosphoric acid.