Effect of Annealing Process on Natural Zeolites from Volcanic Ash for Environmental Applications: Structural and Morphological Characterizations

This work presents a study of morphological, structural, and compositional properties of volcanic ash obtained from Nevado del Ruiz volcano in Colombia. The volcanic ash samples were subjected to hydration and annealing processes at atmospheric pressure to obtain zeolite-type natural structures for different applications, like water decontamination and air pollution control. The strong influence of hydration and annealing processes on the formation of zeolite phases was observed. Rietveld refinement was performed with X-ray diffraction (XRD) patterns, obtaining the presence of natural zeolites: gismondine, hydrated calcium aluminosilicate, litosite, clinoplitolite-Na, and phillipsite-K. From scanning electron micrographs, a morphological change of the ash sample was observed with increasing annealing temperature (290 K < T < 673 K). The surface was dominated by the presence of agglomerates or granules around 5 µm in size; other regions with tubular form or flake-type structures were observed with less presence on the surface ash, associated with the formation of the labradorite phase.