Basic Treatment in Natural Clinoptilolite for Improvement of Physicochemical Properties

Abstract

Natural zeolites are low in cost and exhibit interesting properties for applications in adsorption and catalysis. However, the fact that they are natural materials, not obtained in pure form, and can incorporate various compensating ions can compromise their properties and restrict their use. As their textural and chemical properties are of great relevance for adsorption and catalysis applications, this work aims to study the modification of the natural zeolite clinoptilolite to obtain materials with better physicochemical properties. Clinoptilolite was treated with NaOH under various conditions. The treated material was characterized by X-ray diffraction, X-ray fluorescence, N2 adsorption and desorption at 77 K, CO2 adsorption at 273 K, and pyridine adsorption. The treatment allowed the removal of silicon from the material, improving the textural properties and preserving the structural Al. With the removal of Si, the Si/Al ratio decreased, and consequently, the number of acid and adsorptive sites increased. In addition, statistical planning revealed that the concentration of NaOH is the parameter that most influences the improvement of the textural properties.

Mineral Composition and Structural Characterization of the Clinoptilolite Powders Obtained from Zeolite-Rich Tuffs

“…Ukraine-investigated sample >1000 Slovakia-investigated sample >1000 The U.S. Nevada [16] 700 The U.S. Texas [59] 965 The U.S. Idaho [59] 965 Cuba [8] >1000 The U.K. [59] >920 Turkey [65] 800 Austria [66] 720 North Sardinia [57] 450-500 Italy (Modena) [67] >1100…”

“…Clinoptilolite may occur in high-silica or low-silica form, which is determined as Ca-clinoptilolite [3]. The interest in clinoptilolite is not only associated with its abundance in nature but mainly with the most comprehensive physicochemical properties among all of the zeolite-group minerals [7,8].…”

“…The most significant clinoptilolite properties are high sorption and ion exchange capacity, ion exchange selectivity, molecular sieving properties, catalytic activity, acid resistance, and thermal stability up to 750 • C [7]. The latter one distinguished clinoptilolite to the isostructural heulandite, which shows thermal stability up to 400 • C [5,[8][9][10]. Due to the very similar crystallographic structure of the clinoptilolite and heulandite, they were misidentified.…”

Ammonium Sorption from Landfill Leachates Using Natural and Modified Zeolites: Pre-Tests for a Novel Application of the Ion Exchanger Loop Stripping Process

“…First process optimization has already been achieved by NaOH and NaCl pre-treatment of clinoptilolite [24]. NaOH treatment removes Si and preserves Al in the clinoptilolite structure which increases the number of acid adsorptive sites [25].…”

Construction of BiOCl/Clinoptilolite Composite Photocatalyst for Boosting Formaldehyde Removal

“…However, the smaller pore size of NC may hinder the diffusion of BiOCl into the holes. Previous studies have been proved that alkali leaching process could enlarge the pore size significantly [ 18 , 19 ]. Predictably, the NC after alkali leaching treatment would be more feasible for the deposition of BiOCl.…”