Diffusion in heteroionic zeolites: part 1. Diffusion of water in heteroionic natrolites

Various heteroionic forms have been prepared of a purified natrolite, from Co. Antrim, UK, using treatments with concentrated nitrate solutions at 333 K. They have been fully analysed with additional characterisation by thermal and X-ray diffraction (XRD) methods. The extent of exchange was limited for many cations. Reasons for this are suggested and for the observance of an apparent new domain in some heteroionic materials, as indicated by both thermal and XRD data. The materials were used as substrates to study the mobility of water in the narrow-pored natrolite framework with a view to its potential use to encapsulate the tritiated water arising from nuclear reprocessing and similar sources. Water mobilities through various heteroionic forms of the zeolite natrolite have been followed radiochemically. Diffusional parameters have been calculated from kinetic plots. The results obtained have been explained in terms of cation and water movements and comparisons are made with similar work in heteroionic analcimes. Although a narrow-pored zeolite, natrolite, unlike analcime, does not offer the same potential for use as a sorbent for the containment of tritiated water. This is because of the ability of the natrolite to expand by distortions of the chains of tetrahedra acting as the structural building blocks of the natrolite framework. (C) 1998 Elsevier Science B.V. All rights reserved.