NATURAL ZEOLITES AND THEIR ION-EXCHANGE BEHAVIOR TOWARDS CHROMIUM

In this work studies have been performed which demonstrate that trivalent chromium cations may be retained by naturally occuring zeolites. The experimental work perfomed on the natural zeolite clinoptilolite, which is found in abudant quantities in Greece, showed that the ion exchange process is quite rapid and high quantities of chromium ions are removed from the aqueous solutions in a short period of time. Also, the actual exchange capacity of the zeolites is much smaller, about 50%, of the theoretical one. Despite the regeneration conditions used, significant amounts of chromium is retained by the zeolite. It was also shown that loading and regenerating die zeolite greatly improves the ion exchange capacity of the zeolite, since a very small amount of chromium is released during regeneration and an almost constant amount is taken after each loading cycle.