Abstract: An improved bipolar membrane, a precursor for said membrane and a process for preparing bipolar membranes and precursors are described. In the process a precursor is formed by laminating at least two polymeric layers at least one of which is non-ionic. After the formation of the precursor, the non-ionic layer or layers are chemically treated to form a stable bipolar membrane having high permselectivity and low potential drop. The novel bipolar membrane contains an interfacial layer having anionic and cationic domains.

Abstract: An improved bipolar membrane, a precursor for said membrane and a process for preparing bipolar membranes and precursors are described. In the process a precursor is formed by laminating at least two polymeric layers at least one of which is non-ionic. After the formation of the precursor, the non-ionic layer or layers are chemically treated to form a stable bipolar membrane having high permselectivity and low potential drop. The novel bipolar membrane contains an interfacial layer having anionic and cationic domains.

Abstract: Stable single film bipolar membranes of prolonged life and improved performance particularly for use in electrodialysis water splitting process, are prepared by introducing a more stable interface in the membrane structure. After the cationic exchange groups are preformed on an insoluble cross-linked aromatic polymeric matrix, the dissociable anionic exchange groups may be introduced more intimately chemically bonded in position by using multi-functional compounds containing mixed tertiary, secondary and primary amine groups, so that the resulting interface is comparatively more stable, and is less likely to be neutralized, therefore, attaining longer life-time and a higher level of performance.

Abstract: Superior bipolar membranes are prepared having high performances. The improvement is achieved by (1) using high performance component ion exchange membranes, and (2) controlling the method of joining two component membranes into a bipolar membrane. The method of preparation of high performance component ion exchange membranes is also disclosed.

Abstract: An improved process is described for producing titanium dioxide from ilmenite-type ore. The ore is digested with aqueous hydrogen fluoride, the resulting liquid mixture treated with a water-soluble oxidizing agent, and the ferric iron impurities, in the resulting digestion solution, at a pH between about 1.0 and 6.0, are extracted out with a mono-or dialkyl, or mono- or di-(alkylphenyl) orthophosphoric acid, such as di-(2-ethylhexyl) orthophosphoric acid. The remaining solution is treated with ammonium hydroxide to precipitate hydrated titanium dioxide which is then calcined to form pigmentary titanium dioxide. Alkali metal and ammonium salts of the organophosphoric acid are also useful in the process.

Abstract: An improved process is described for converting aqueous fluosilicic acid waste product into anhydrous hydrogen fluoride and finely divided silica in which aqueous fluosilicic acid is pyrolyzed to produce silica and a dilute aqueous solution of hydrogen fluoride and fluosilic acid. The resulting dilute solution is subjected to electrodialysis, thereby obtaining a hydrogen fluoride concentration greater than that which characterizes the boiling point ridge which divides the phase diagram of the system hydrogen fluoride/fluosilicic acid/water, i.e. HF/H.sub.2 SiF.sub.6 /H.sub.2 O, into two regions. Anhydrous hydrogen fluoride is recovered from the resulting composition by distillation.

Abstract: Novel single film bipolar membranes, of substantially improved efficiency and durability, i.e. having an ion selectivity above 80% in an electrolyte medium of about one mole, are prepared from pre-swollen films containing a relatively high amount, i.e. at least 15% of an insoluble cross-linked aromatic polymer. Under controlled conditions, highly dissociable cationic-exchange groups are chemically bonded to the aromatic nuclei to a desired depth of the film from one side only; subsequently, highly dissociable anion-exchange groups are chemically bonded to the unreacted aromatic nuclei on the other side of the film. The functionalized, densely structured single film ion exchange membrane undergoes negligible degradation, is blister free, and is uniquely suited for electrodialysis particularly water-splitting operations due to its low electrical resistance and low salt leakage.

Abstract: Stable bipolar membranes of high permselectivity and low potential drop are prepared using either an anion or cation preformed first layer upon which a second layer or coating of an ion exchange resin of the opposite charge carried in a matrix polymer is applied. The second layer may be suitably applied such as by casting as a slurry of the ion exchange resin in a solution or by laminating a layer comprising a dispersion of the resin in a solid or fused polymer. Optionally, the surface of the first layer may be treated to increase the resin concentration and/or bonding at the interface, such as by sanding, etching, etc.

Abstract: Removal of sulfur dioxide from an aqueous solution containing the same is effected by subjecting the solution to electrodialytic water splitting. In particular SO.sub.2 is removed from dilute gas streams by means of alkaline solution scrubbing, regeneration of the scrubbing solution and liberation of concentrated SO.sub.2 by means of a membrane water splitter. Waste sulfate produced in the process may be converted to sulfuric acid in a separate membrane water splitter or otherwise processed by conventional means.

Abstract: An improved process is described for recovering TiO.sub.2, useful as a white pigment, from ilmenite-type ores, including the steps of digesting the ore with aqueous hydrofluroic acid, separating out iron impurities from the resulting solution, precipitating hydrated titanium dioxide from the iron-free solution with ammonium hydroxide, and calcining the precipitate to obtain pigmentary TiO.sub.2, wherein the improvement comprises subjecting aqueous solutions of by-product ammonium fluoride, formed in the process, to electrodialytic water-splitting to form an aqueous solution of ammonium hydroxide and an aqueous solution of hydrogen fluoride and recycling said aqueous ammonium hydroxide to the precipitation step and said aqueous hydrogen fluoride to the digestion step.

Abstract: Novel polyelectrolyte membranes of substantially improved efficiency and durability are prepared from a preswollen film containing a relatively high amount of an insoluble cross-linked aromatic polymer. By preswelling the insoluble matrix under controlled conditions preferably to an equilibrium stage, the dissociable ion-exchange groups may be introduced more uniformly onto the aromatic nuclei of the matrix to a desired depth of the film. Controlled penetration of functional groups is important in preparing high performance cationic, anionic membranes as well as bipolar membranes. The membranes so prepared have low electrical resistance, improved current efficiency, undergo negligible degradation and with excellent durability.

Abstract: Sulfur dioxide is separated from an aqueous solution containing the same by subjecting the stream to electrodialytic water splitting. In particular a novel method for removing SO.sub.2 from dilute gas streams by means of alkaline solution scrubbing, regeneration of the scrubbing solution and liberation of concentrated SO.sub.2 effected by means of a two-compartment membrane water splitter is provided. Optionally, waste sulfate produced in the process may be converted to sulfuric acid in a separate membrane water splitter or otherwise processed by conventional means.

Abstract: Improved novel single film bipolar membranes having an ion selectivity above 80% in an electrolyte medium of about one mole, are prepared containing a relatively high amount, i.e. at least 15% of an insoluble cross-linked aromatic polymer. Before the styrenated sheet is chemically functionalized, the film surface is specifically treated, i.e. cleaned to make it more receptive to functional groups, so that the cationic-exchange groups and anion-exchange groups can be introduced homogeneously from each side of the surface-cleaned film, and a single-film bipolar membrane of superior durability, stability, and quality control results.

Abstract: Novel single film bipolar membranes, of substantially improved efficiency and durability, i.e. having an ion selectivity above 80% in an electrolyte medium of about one mole, are prepared from pre-swollen films containing a relatively high amount, i.e. at least 15% of an insoluble cross-linked aromatic polymer. Under controlled conditions, high dissociable cationic-exchange groups are chemically bonded to the aromatic nuclei to a desired depth of the film from one side only; subsequently, highly dissociable anion-exchange groups are chemically bonded to the unreacted aromatic nuclei on the other side of the film. The functionalized, densely structured single film ion exchange membrane undergoes negligible degradation, is blister free, and is uniquely suited for electrodialysis particularly water-splitting operations due to its low electrical resistance and low salt leakage.

Abstract: A system utilizing membrane extraction is provided to recover metal values. The system may be used to separate metal ions from an aqueous solution through the membrane by an organic liquid containing a chelating agent. This invention also contemplates the recovery of metal values from an organic phase, containing the metal complexed with a chelating agent, by an aqueous phase using membrane extraction. In the former case, the metal ion is passed through the membrane from the aqueous phase to the organic phase where it forms a complex with a chelating agent present in the organic phase. In the latter case the metal is extracted from the organic phase into the aqueous phase through the membrane. In both cases a chelating exchange reaction is involved at the interface between the membrane and one of the two phases. This hydro-metallurgical process employs membranes with metal ion diffusivity in the range of about 10.sup..sup.-5 to about 10.sup..sup.-8 cm.sup.2 /sec.

Abstract: A membrane solvent extraction system is utilized to separate two substantially immiscible liquids and extract a solute through a solvent swollen membrane from one solvent liquid phase to the extracting solvent liquid without direct contact between the liquid phases. The membrane extraction method has advantages over conventional solvent extraction and may be applied as the mechanism in separation, purification, pollutant removal and recovery processes.

Abstract: Novel membrane compositions are prepared from polymers comprising tertiary amine containing polyamideamine functional groups. The membranes are durable, highly selective and have excellent homogeneity and high diffusivity. Asymmetric membranes can be prepared by solution casting or melt processing techniques can be used to produce homogeneous, high performance, symmetric membranes. The specific compositions of the membranes can be adjusted so as to achieve a membrane possessing a required degree of hydrophilicity and porosity. These membranes may be used in a variety of separation applications, particularly in two-phase solvent extraction.

Abstract: Novel cross-linked interpolymer membranes of substantially improved efficiency and durability are prepared from a co-mixture of a hydrophilic polymer of [1, .omega.-alkylene(2,6-diketopiperazine)-1,4-dicarboxamide] and a hydrophobic polymer such as polyvinylidene fluoride, by dissolving these polymers in a suitable solvent, forming films of suitable thickness from the solution and thereafter preferably crosslinking the dissolved mixture.