The layer vanadium oxide bronze (CaV₂O₆) was synthesized by the flux method. The ion-exchange reactions with proton (H⁺) and metal cations (Pb²⁺, Cu²⁺, Zn²⁺) were examined at 25°C by the batch method. It was found that the Ca²⁺ between layers was able to exchange easily with H⁺ in aqueous solution. The new bond formation due to H⁺ exchange between layers was studied by FT-IR method. The XRD pattern of CaV₂O₆ did not change upon exchange of Ca²⁺ with H⁺ in aqueous solution. But finally the crystal structure of CaV₂O₆ collapsed when the content of Ca²⁺ between layers decreased over the limit. The critical value of remained Ca²⁺ was identified to be about 0.57 (Ca_0.57H_0.86V₂O₆) .
The selectivity order for Pb²⁺, Cu²⁺ and Zn²⁺ ions in solution was determined by their ion-ex-change reactions, i.e., the removal of Pb²⁺ and Cu²⁺ are excellent due to the concurrently formed products of Pb₃ (VO₄) ₂ and Cu₃ (VO₄) ₂. The removal order for toxic metallic ions was as follow: Pb²⁺>Cu²⁺>>Zn²⁺. Notably, the amount of Pb²⁺ ion retained per 1 g of CaV₂O₆ reached 600 mg.

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Both Cs⁺ and Sr²⁺ have been recognized as serious components of high level radioactive waste. To separate Cs⁺ or Sr²⁺ from other s-block metal ions, the separation of metal ions has been studied by an ion-exchange method. An ion exchanger, composed of dihydrogen tetratitanate hydrate fibers, H₂Ti₄O₉nH₂O, was prepared by synthesizing K₂Ti₄O₉ and converting it to a H⁺ form. Ion-exchange equilibria of alkali and alkaline earth metal ions on the crystalline fibers were measured at 298 K. The separation of Cs⁺ from the aqueous solution containing alkali metal ions, such as Cs⁺, Rb⁺, K⁺, Na⁺ and Li⁺, has been studied by the ion-ex-change method. The ion-exchange reaction is explained in terms of one hydrogen-ion from the fibers being ion exchanged with one alkali metal ion in the aqueous solution. As the selectivity series of the ion-exchange system using dihydrogen H₂Ti₄O₉nH₂O fibers was Cs⁺>Rb⁺>K⁺>Na⁺>Li⁺, Cs⁺ can easily separate from other alkali metal ions. Separation of Sr²⁺ from other alkaline earth metal ions was also studied by the same ion-exchange method. The selectivity series of the ion-exchange system using H₂Ti₄O₉nH₂O fibers was Ba²⁺>Sr²⁺>Ca²⁺>Mg²⁺. The ion-exchange reaction is explained in terms of similar reaction to that for alkali metal ions except the divalent effect. To immobilize Sr²⁺ in the fibers, the structure of SrTi₄O₉nH₂O were changed to a perovskite structure by a heat treatment method.

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A new technique for rare-metal-elements selective-separation using electrodialysis accompanied by metal substitution reaction has been developed. The dialyzer used as a reactor consists of five compartments named Anode, Feed, Reaction, Strip, and Cathode, which are divided with ion-exchange membranes. The Feed solution, the Reaction solution, and the Strip solution contain CuCl₂, rare-metal EDTA complex, and HCI, respectively. When a voltage is applied to the dialyzer, Cu²⁺ transfers from the Feed compartment to the Reaction compartment, and is substituted for the rare-metals complexed with EDTA. The resultant free ions of rare-metal elements move to the Strip compartment at different transfer rates: The rare-metal elements are recovered there, being selectively separated. This separation technique is characterized by preferential transport in the membrane and different rates of metal substitution reaction in the Reactor compartment. In this paper, some experimental results for the separation and the reaction kinetics are presented, and explained by a model proposed.

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Novel porous hollow-fiber membranes containing ion-exchange groups such as sulfonic acid and iminodiacetate groups were prepared by radiation-induced graft polymerization and subsequent chemical modifications. The performance of the membrane for the removal of a trace of metal ions from ultrapure water were evaluated during permeation of the ultrapure water across the membrane. The membrane removed more than 90% of the metal ions after 300-day permeation with a high throughput of ultrapure water and no detectable release of impurities. The ion-exchange porous membranes were found to be effective in improving the quality of the ultrapure water.

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