Transformation of zeolite A into hydroxysodalite: I. An approach to the mechanism of transformation and its experimental evaluation

Abstract The process of transformation of zeolite A into hydroxysodalite in caustic media is followed by measuring the increase of hydroxysodalite fraction f HS during the heating of the reaction mixture. At a given temperature, the transformation rate strongly depends on the concentration of OH - ions (NaOH) in the reaction mixture. By measuring the change of particle size during the transformation process, it is concluded that transformation of zeolite A into hydroxysodalite takes place by (i) dissolution of zeolite particles, (ii) supersaturation of the liquid phase with “aluminosilicate ions” (Q-species), (iii) nucleation of hydroxysodalite from the solution supersaturated with Q-species, and (iv) crystal growth of primary formed particles (critical nuclei). Following such a model of transformation process it is found that the change of fraction of hydroxysodalite f HS with the transformation time t T , can be described by the equation: f HS = K (ht) t 3 T + K (hm) t 4 T , where K (ht) and K (hm) are constants for a given temperature and a given NaOH concentration. The change of values of constants K (ht) and K (hm) with increase of NaOH concentration is explained in the light of nucleation theories.