SOLID-PHASE HYDRATION EFFECT ON THE SELEC TIVITY OF ALKALI-METAL IONSFOR INORGANIC-ION EXCHANGERS - SOLID-STATE NMR-STUDY

The ion exchange reactions of alklai metal ions on inorganic ion excha ngers were examined with solid state NMR technique in related with the hydration phenomenon of metal ions. H-1, Li-7, Na-23 NMR spectra were measured on lithium ion selective tin antimonate and titanium antimon ate. According to the NMR study as well as ion exchange study, it was found that these exchangers had two types of ion exchange sites, one w as favorable for lithium ions and the other had poor selectivity for l ithium and sodium ions. In the former site, lithium ions were adsorbed by dehydrating water molecules. The second and the third exchangers e xamined were monoclinic antimonate and cubic niobate, both are very se lective for lithium ions. It was found that only lithium ions were sel ectively adsorbed on these ion exchangers by dehydrating their hydrate d water molecules. Small space of ion exchange site result in the sele ctivity. The last ion exchanger was cubic ammonium molybdate, in which potasium ions as well as ammonium ions are very selective. Two types of ion exchange sites were found to present due to the H-1 NMR study. One site, the population was about 25%, was found to adsorb any kind o f univalent ions. The other site was very favorable for potassium ions and could not adsorb hydrogen ions. The phenomenon was well accountab le from the analogy of hydration properties of metal ions in aqueous s olution.