Thermal transformation and the ion exchange property of H-formed zeolites

Thermal transformation and ion exchange property were studied in various kinds of H-formed zeolites-synthetic zeolites A, X and Y, synthetic mordenite, natural mordenite and clinoptilolite. H-formed zeolites were produced by the thermal decomposition of NH4-formed zeolites. The thermal decomposition of NH4-formed zeolites was studied by using infrared, differential thermal analyses and X-ray powder diffraction. Deammoniation occurred in the temperature range of 350 -- 5000C followed by hydroxylation, and dehydroxylation took place in the wide temperature range of 500 -- 9000C. These reactions overlapped one another to a considerable extent. H-formed zeolites recrystallized to cristobalite and mullite at a temperature above 9000C for A, X and Y zeolites, and above 10000C for mordenites and clinoptilolite. The distribution coefficient of cesium (K sub(Cs)) decreased with increasing acidity, though the K sub(Cs) values for H-formed synthetic mordenite (HSM) attained about 104 in the acidic region (pH 1 -- 3). As for strontium, the K sub(Sr) values for A, X and Y attained about 104 in the neutral region, but markedly decreased with the increase in acidity. HSM produced by heat treatment below 4000C in air and below 3500C in a vacuum had a good break-through property. (author)