Dealumination of sodium Y zeolite with hydrochloric acid

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Abstract
The dealumination of sodium Y zeolite with hydrochloric acid solution has been studied. The amount of aluminium removed from the framework was found to be proportional to the hydrogen ion concentration of the acid solution. Dealumination does not occur when the pH of the acid solution is > 2.30, while complete dealumination was observed at pH values of < 0.46. Aluminium was removed from the framework, behaved as a trivalent cation in the lattice initially and then was released into the solution phase at higher hydrogen-ion concentrations. Four hydrogen ions were required to remove one aluminium from the zeolite framework. X-Ray diffraction indicated that the crystallinity of the aluminium-deficient zeolites decreased with increasing degree of dealumination until finally they became amorphous. However, the supercage and small cages sodium cationexchange capacities were shown to decrease linearly with the decrease in framework aluminium, indicating that the channel network remains intact. Experimental results suggest that exchangeable sodium ions will be present in the supercage only when the dealuminated zeolite contains twelve or fewer framework aluminiums per unit cell.

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