ION-EXCHANGE IN BERYLLOPHOSPHATE-G .1. ION-EXCHANGE EQUILIBRIA

Ion-exchange isotherms and selectivity plots are presented for beryllophosphate-G, the synthetic beryllophosphate analogue of the zeolite gismondine. Exchange reactions involving Na+ and K+ or NH4+ were accompanied by changes in crystal symmetry and hysteresis loops were seen in the isotherms. Exchange of K+ by NH4+ was fully reversible without hysteresis and the two end members were found to have very similar symmetry. Only limited exchange of Na+ by Ca2+ or Mg2+ could be achieved under the conditions used and no symmetry change was observed. The phases present across the Na+-K+ exchange field were studied in depth using X-ray powder diffraction, solid-state NMR and scanning electron microscopy. Unit-cell parameters were calculated for fully K-exchanged beryllophosphate-G.