Zirconium(IV) selenophosphate, a three-component inorganic ion-exchanger was synthesized. In most cases, it was found that the ion-exchange capacity of three-component inorganic ion-exchangers was greater than those of two-component inorganic ion-exchangers. A theoretical explanation was given for the enhancement of ion-exchanger capacity of three-component materials and was found to be in good agreement with the experimental value.

Various synthetic inorganic ion-exchangers have been developed so far mostly based on arsenate, phosphate, tungstate, molybdate and selenite of metals (Qureshi and Rawat, 1968; Dyer and Gill, 1970; Qureshi et al., 1970; Qureshi et al., 1971; Qureshi and Nabi, 1971 and 1972; Singh et al., 2003; and Gupta et al., 2004 and 2005). Three-component inorganic ion-exchangers which were reported earlier (Qureshi et al., 1976; Qureshi and Kaushik, 1977; Varshney and Khan, 1979; Nabi et al., 1982; and Berardelli et al., 1985) showed an increased ion-exchange capacity as compared to the two-component materials (Nunes et al., 1961; Amphlett, 1964; Inoue, 1964; Clearfield et al., 1968; Qureshi and Varshney, 1968; Qureshi et al., 1970; Qureshi et al., 1977; and Qureshi and Rahman, 1987). However, no attempt has been made to explain the increased ion-exchange capacity of these materials. In this paper, a preliminary study has been done to explain the enhanced ion-exchange capacity in terms of: (a) three-dimensional skeleton comprising three different elements; (b) pK values of acid anionic group incorporated into the lattice structure; and (c) pH titration. The values so obtained are in good agreement with experimentally reported ion-exchange capacities.

An Elico model Li-10 pH meter (India) was used to measure pH of the solutions. A Bausch and Lomb Spectronic 20 D⁺ (USA) and a Perkin Elmer 137 spectrophotometer (USA) were used for absorbance and IR studies respectively.The synthesis of zirconium(IV) selenophosphate ion-exchanger has been synthesized in the laboratory (Qureshi and Rahman, 1987). Samples of zirconium(IV) selenophosphate ion-exchangers were synthesized by adding an aqueous solution which was 0.05 M (1M = 1 mol dm^-3) in sodium selenite and 0.05 M in orthophosphoric acid to an aqueous solution of zirconium(IV) bis (nitrate) oxide. The desired pH was adjusted by adding dilute HNO₃ or NaOH solution. The gel so formed was allowed to settle down for 24 h, washed several times with distilled water to remove excess reagents, and filtered under suction. It was then dried at 40 °C for seven days in an oven. The dried material was then treated with distilled water, which resulted in the cracking of the substance into smaller particles with slight evolution of heat. To convert the sample into H⁺ form, the material was kept for 24 h in 1.0 M HNO₃ solution. It was then washed with distilled water to remove excess acid.

A Theoretical Approach to Increased Ion-Exchange Capacity to Three-Component Ion-Exchange Materials, Zirconium, selenophosphate, ion-exchanger, selenite of metals, three-dimensional skeleton, ion-exchange capacities, three-component inorganic ion-exchanger, three-component materials.