A filter includes a porous molding, the porous molding being a sintered product of mixed powder containing dry gel powder including an ion exchange resin and thermoplastic resin powder, or a swelled body of the sintered product. When water having an electric resistivity value of 18 MΩ.Math.cm or more is allowed to pass through a space velocity of 1200 hr−1, the electric resistivity value of water after passage is 15 MΩ.Math.cm or more.

To provide a filter that can efficiently remove metal ions in a solution to be treated, and easily acquire a solution having an extremely low content of metal ions.

An ion exchange chromatographic packing material is described that includes support resin particles and a copolymer grafted to the support resin particles. The copolymer includes polymerized functional monomers such as a first ion exchange group monomer and a second ion exchange group monomer. At a first pH, the first ion exchange group monomer is configured to have a first charge at a first pH, and the second ion exchange group monomer is configured to have a net neutral charge. At a second pH, the first ion exchange group monomer is configured to have the first charge at a second pH, and the second ion exchange group monomer is configured to have a second charge at the second pH where the first charge and second charge both have a same polarity.

An ion exchange chromatographic packing material is described that includes support resin particles and a copolymer grafted to the support resin particles. The copolymer includes polymerized functional monomers such as a first ion exchange group monomer and a second ion exchange group monomer. At a first pH, the first ion exchange group monomer is configured to have a first charge at a first pH, and the second ion exchange group monomer is configured to have a net neutral charge. At a second pH, the first ion exchange group monomer is configured to have the first charge at a second pH, and the second ion exchange group monomer is configured to have a second charge at the second pH where the first charge and second charge both have a same polarity.

A composite ion exchange membrane comprising components (a) and (b): (a) a membrane layer comprising ionic groups, two opposing surfaces and optionally a porous support; (b) a layer comprising sulpho groups bound to at least one of the at least two opposing surfaces of the membrane layer (a);
wherein the layer comprising sulpho groups has a thickness of less than 100 nm and the composite ion exchange membrane has a surface zeta potential of 0 to −7.5 mV.

A composite ion exchange membrane comprising components (a) and (b): (a) a membrane layer comprising ionic groups, two opposing surfaces and optionally a porous support; (b) a layer comprising sulpho groups bound to at least one of the at least two opposing surfaces of the membrane layer (a);
wherein the layer comprising sulpho groups has a thickness of less than 100 nm and the composite ion exchange membrane has a surface zeta potential of 0 to −7.5 mV.

Water softening system includes water softening tank, neutralization tank, electrolysis tank, and treatment tank. Water softening tank softens raw water containing a hardness component with weakly acidic cation exchange resin. Neutralization tank neutralizes a pH of soft water that has flowed through water softening tank with weakly basic anion exchange resin. Electrolysis tank generates acidic electrolyzed water for regenerating weakly acidic cation exchange resin of water softening tank and alkaline electrolyzed water for regenerating weakly basic anion exchange resin of neutralization tank. Treatment tank mixes the acidic electrolyzed water that has flowed through water softening tank and the alkaline electrolyzed water that has flowed through neutralization tank, and supplies the mixture of the acidic electrolyzed water and the alkaline electrolyzed water to electrolysis tank.

Water softening system includes water softening tank, neutralization tank, electrolysis tank, and treatment tank. Water softening tank softens raw water containing a hardness component with weakly acidic cation exchange resin. Neutralization tank neutralizes a pH of soft water that has flowed through water softening tank with weakly basic anion exchange resin. Electrolysis tank generates acidic electrolyzed water for regenerating weakly acidic cation exchange resin of water softening tank and alkaline electrolyzed water for regenerating weakly basic anion exchange resin of neutralization tank. Treatment tank mixes the acidic electrolyzed water that has flowed through water softening tank and the alkaline electrolyzed water that has flowed through neutralization tank, and supplies the mixture of the acidic electrolyzed water and the alkaline electrolyzed water to electrolysis tank.

A filter includes a porous molding, the porous molding being a sintered product of mixed powder containing dry gel powder including an ion exchange resin and thermoplastic resin powder, or a swelled body of the sintered product. When water having an electric resistivity value of 18 MΩ.Math.cm or more is allowed to pass through a space velocity of 1200 hr−1, the electric resistivity value of water after passage is 15 MΩ.Math.cm or more. To provide a filter that can efficiently remove metal ions in a solution to be treated, and easily acquire a solution having an extremely low content of metal ions.

A filter includes a porous molding, the porous molding being a sintered product of mixed powder containing dry gel powder including an ion exchange resin and thermoplastic resin powder, or a swelled body of the sintered product. When water having an electric resistivity value of 18 MΩ.Math.cm or more is allowed to pass through a space velocity of 1200 hr−1, the electric resistivity value of water after passage is 15 MΩ.Math.cm or more. To provide a filter that can efficiently remove metal ions in a solution to be treated, and easily acquire a solution having an extremely low content of metal ions.

A method for producing a purified fluoropolymer aqueous dispersion, which includes: (A) bringing a fluoropolymer aqueous dispersion obtained using a hydrocarbon surfactant into contact with an anion exchange resin A or a synthetic adsorbent. The anion exchange resin A has an ion-exchange group represented by the following general formula (A1):

—N+R.sup.1R.sup.2R.sup.3X—

wherein each of R1, R2, and R3 are the same or different, and are each a hydrogen atom or an organic group, and at least one of R.sup.1, R.sup.2, and R.sup.3 is an organic group having 3 or more carbon atoms; and X is a counter ion; or an ion-exchange group represented by the following general formula (A2):

—NR.sup.4R.sup.5

wherein each of R.sup.4 and R.sup.5 are the same or different, and are each a hydrogen atom or an organic group, and at least one of R.sup.4 and R.sup.5 is an organic group having 2 or more carbon atoms.