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STUDIES ON THE MODIFICATION OF SOME NATURAL ZEOLITE FROM ROMANIA AFTER ACID AND BASIC TREATMENTS
Abstract
The natural zeolites (NZs) are low-cost natural materials, available in large quantities in different parts of the world, with good mechanical and thermal properties, ion exchange capacity, ability to adjust pH, high surface area and adsorption capacity. Despite their wide range of applications, the use of NZs is limited in industrial processes (where synthetic zeolites are preferred) due to presence of impurities in their structure and the properties which could not be optimized by nature. These limitations can be overwhelmed by modifying the structure of NZ. Dealumination and desilication are the most commonly used methods to change the properties of NZs such as Si/Al ratio, specific surface, pore size, acidity, etc. In this study, a NZ collected from Cluj County, Romania was used. NZ with particles size up to 0.5 mm was treated with various concentrations of (i) acidic (0.25, 0.75 and 1.25 N HCl ? NZ-H) and (ii) basic (0.25, 0.75 and 1.25 N NaOH ? NZ-Na) solutions, for 60 min. The characterization of both NZ and modified zeolites (NZ-H and NZ-Na) was conducted using different techniques including conventional analytical methods, inductively coupled plasma-optical emission spectrometry (ICP-OES), powder X-ray diffraction (pXRD) and scanning electron microscopy (SEM). Considering that Si/Al > 4 and, predominant alkaline cations (Na + K > Ca) the used raw zeolite sample is included to earth alkali clinoptilolite class. As expected, the removal of major and minor elements was higher for acid treatment (NZ-H) compared to alkali treatment (NZ-Na). The high cation exchange capacity (CEC) of investigated zeolites may be due to the higher percentage purity of clinoptilolite mineral content in these samples. pXRD analysis revealed a high content of clinoptilolite in the raw natural zeolite and that the structure of zeolite was not significantly altered by acid and basic treatments. However, the crystallinity decreases with acid treatment, due to the dealumination of clinoptilolite. According to SEM, the surface of NZ-H and NZ-Na samples is disordered, the small particles exhibited a tendency to form agglomerates.
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