| Abstrakt: |
Natural zeolites, a family of hydrated aluminosilicates, are important raw materials for micro and nano technologies due to their molecular-sieve, ion-exchange and catalytic properties. Their porous crystalline framework is built from alternating SiO4 and AlO4- tetrahedra forming cages and channels, and improvement of zeolite performance is possible by thermal and chemical treatment. The influence of hydrochloric acid and calcination on heulandite-containing tuff from the Georgian Dzegvi-Tedzami deposit was studied by the X-ray energy dispersion spectra and diffraction patterns, thermal analysis, adsorption of water, benzene and nitrogen. It was found that an acidic environment leads to significant dealumination and decationization without amorphization, but with gradual dissolution of the sample; there is also a sharp increase in the surface area and volume of micropores available for large molecules, and in the mesoporous system, pores with a diameter of 4 nm become predominant. Heat treatment leads to dehydration proceeding up to ≈800 °C, amorphization starting at ≈250 °C; the transition to the heulandite B at ≈340 °C is not fixed, at ≈500 °C wairakite is formed; at temperatures above ≈1000 °C, amorphous aluminosilicate contains crystalline inclusions of cristobalite, α-quartz, albite, hematite and magnetite. It is also shown that heat treatment increases the acid resistance of heulandite by reducing the degree of dealumination of acid-treated samples. [ABSTRACT FROM AUTHOR] |
