Crystalline insoluble acid salts of tetravalent metals—XX Forward and reverse Cs +/H + and Rb +/H + ion exchange on crystalline zirconium phosphate

Abstract

Forward and reverse Cs +/H + and Rb +/H + ion exchange have been investigated by the batch-procedure in 3rder to obtain both the titration and uptake curves, as well as X-ray diffractograms and water contents of the samples at the various Cs + or Rb +-loadings. The interlayer distance of the exchanger increases discontinuously with increasing Cs +-loading and three different phases, ZrHCs(PO 4) 2.2H 2O, ZrH 0·5Cs 1·5(PO 4) 2.3H 2O, and Zr(CsPO 4) 2.6H 2O with interlayer distances of 11·3, 11·7 and 14·2 Å, respectively, have been found in the forward process. For the analogous Rb +-ion exchange process the phases were ZrH 0·5Rb 1·52H 2O (10·6 Å) and Zr(RbPO 4) 2.H 2O (9·2 Å). Reverse ion exchange processes both for Cs + and Rb + ions showed a considerable irreversibility especially in the range of 0–50 per cent Cs + or Rb +-loadings. The replacement of both Cs + and Rb + ions by H + ions occurred together with the formation of solid solutions and therefore the large ion exchange hysteresis loops were ascribed to the formation of different phases in the forward and reverse processes. The X-ray diffraction patterns of the various Rb + and Cs +-phases dried under different conditions are reported. Finally, a general discussion of the Cs + or Rb +-ion exchange behavior on zirconium phosphate at various degree of crystallinity is made. It is concluded that the low, apparent selectivity of crystalline zirconium phosphate towards large monovalent ions is due to steric hindrance and therefore enlarged phases of this exchanger, such as Zr(HPO 4) 2.8H 2O (10·4 Å), are expected to have a high selectivity towards Cs + or even larger cations.