DETECTION OF SIDE-PRODUCTS ON HEAVY-METAL CATIONS LOADED ZEOLITES BY XRD MEASUREMENTS

During the high loading of A, X, and Y zeolites with heavy metal catio ns by ion-exchange undesired hydroxides are formed at the crystal surf ace. The precipitation is caused by the alkaline reaction of the paren t sodium modification of zeolites in aqueous solutions and the low sol ubility product of heavy metal hydroxides. During the calcination of t he samples the hydroxides are transformed into oxides. Exemplified by zeolite ZnNaA, a stepwise exchange in strongly diluted salt solutions may hinder the formation of hydroxides/oxides. XRD measurements enable a direct monitoring also of smallest amounts of zinc hydroxide/zinc o xide. The framework adopted ZnO causes a change of the symmetry of the zeolite lattice. The side product does not influence the formation of the new crystalline phases during the calcination of ZnNaA.