Abstract
The ion exchange behaviour of crystalline ZrNaH(PO 4) 2. 5H 2O towards alkali metal ions has been investigated. It was found that, in the pH range 3–5, hydrogen ion is not exchanged and only Na +-alkali metal ion exchanges take place. Forward and reverse Na +-K +, Na +-Li +, K +-Li + and Na +-Cs + ion exchange isotherms have been determined and discussed comparatively with the results obtained previously with fully-substituted alkali metal ionic form of zirconium phosphate. The exchanges occur with phase transitions and small hysteresis loops have been observed between the isotherms of the two opposite processes. The sequence of decreasing alkali metal ion preference is K + > Cs + > Na + > Li + and a very high selectivity towards K + or Cs + ion has been found. Thus, differently from Zr(HPO 4) 2. H 2O, the monosodium form exhibits preference for large cations and this different behaviour may be due to the large difference in the interlayer distances of the two ionic forms (7·56 and 11·8 Å respectively). The uptake of large ions by enlarged crystalline zirconium phosphate discloses new practical applications for such an exchanger.
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