PHASE TRANSITION PROCESS IN THE HYDROTHERMAL ZEOLITIZATION OF VOLCANIC ASHES INTO LTA AND FAU STRUCTURES

MONZÓN, JORGE DANIEL; GONZALEZ, MAXIMILIANO R.; MUÑOZ, MERCEDES; PEREYRA, ANDREA M.; BASALDELLA, ELENA I.

CLAYS AND CLAY MINERALS

CLAY MINERALS SOC

Año: 2020

0009-8604

A natural volcanic ash, accessible as an aluminosiliceous resource in southern Argentina, was transformed into crystalline zeolites A and X. Starting from a collected sample (VA), an amorphous fraction (VA40, retained on #40 mesh) was separated from the natural ash by sieving. Both were distinctly used for zeolite production. These solids were alkaline-treated separately, aged, and reacted under controlled conditions of temperature at autogenous pressure. Along the whole process the solid phases were characterized by X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), and scanning electron microscopy (SEM). It was observed that after the activation treatment and alkaline aging, reactive crystalline NaAlSiO4 polymorphs appeared, whose presence markedly enhanced the posterior zeolite crystallization. After activation, the presence of quartz and plagioclase minerals in the natural ash seemed to improve the production of polymorphs, indicating that the structural features of the ash influence the hydrothermal transformation. Even under adequate pretreatment and suitable synthesis conditions, the coarse non-crystalline fraction led to low conversions, while the highest conversions in zeolite A and X were obtained from the natural ash.