Results of hydrothermal treatment of the amorphous phases obtained by ballmilling of zeolites A, X and synthetic mordenite

High-energy ball milling of zeolites A, X and synthetic mordenite for an ap propriate time results in the formation of true amorphous aluminosilicate p hases having the same chemical composition as the starting (unmilled) cryst alline materials (zeolites). Since the solubility of thus prepared amorphou s solids in hot alkaline solutions is considerably higher than the solubili ty of the starting zeolites under the same conditions, it can be expected t hat hydrothermal treatment of the amorphous solids would result in their tr ansformation to more stable phases by solution-mediated processes. To evalu ate this thesis, the X-ray amorphous solid phases obtained by high-energy b all milling of zeolites A, X and synthetic mordenite were hydrothermally tr eated at 80 degreesC by 2 M and 4 M NaOH solution, respectively, for 4 h. T he products obtained (zeolites A, P and hydroxysodalite) were characterized by X-ray powder diffraction and particle size distribution measurements. I t was concluded that the nuclei for zeolite crystallization originate from the residual nano-sized quasicrystalline particles (short-range ordering of Si and Al atoms inside amorphous regions that have not been completely des troyed during milling). Type(s) of the zeolite(s) (zeolite A, zeolite Pa) c rystallized by the growth of the nuclei under the given conditions are dete rmined by the chemical composition of the liquid phase (concentrations of S i and Al), and by the chemical composition of the precursor (determined by the type of mechanochemically amorphized zeolite) and the alkalinity of the system (NaOH concentration in the liquid phase), respectively. The results obtained are in agreement with the thermodynamic stabilities of the zeolit e types that may be crystallized under the given conditions and at relative rates of crystallization.