| http://www.w3.org/ns/prov#value | - As examples of the cation-exchanging material for use in the present invention, mentioned are gelled or porously-shaped cation-exchanging resins to be produced by introducing sulfonic acid groups or carboxylic acid groups into a polymer or copolymer base of, for example, styrenic polymers or copolymers such as polystyrene and the like, acrylic polymers or copolymers such as polyacrylic resins and
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