Alissa Cotton

Temperature and pH-dependent dissolution kinetics of natural clinoptilolite and a ‘pure’ heulandite phase have been determined and compared. Si dissolution rates increased with increasing temperature and pH. Heulandite has a slightly higher dissolution rate than clinoptilolite in the pH range 8–10. Measured reaction order was 0.23 and 0.14 for clinoptilolite and heulandite, respectively. This is slightly lower than for other aluminosilicate phases at comparable temperatures. The measured dissolution rates indicate a 1 mm spherical crystal would dissolve in 38 848 years and 17 301 years for clinoptilolite and heulandite, respectively. If solution composition is maintained, and remains unsaturated with respect to Si, Al, etc., the presence of zeolites in the vicinity of an underground nuclear waste repository would be beneficial as a sorption barrier.