Abstract
This study investigated a low-energy-consuming procedure for the synthesis of zeolite materials from coal fly ash (CFA). Materials containing zeolite phases, namely Na–X, Na–P1, and zeolite A, were produced from F–class fly ash, using NaOH dissolved in distilled water or in wastewater obtained from the wet flue gas desulphurization process, under atmospheric pressure at a temperature below 70 °C. The influence of temperature, exposure time, and alkaline solution concentration on the synthesized materials was tested. In addition, chemical, mineralogical, and textural properties of the obtained materials were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and cation exchange capacity (CEC). Cd(II), Ni(II), NH4+ cation, and Se(VI) anion sorption experiments were conducted to compare the sorption properties of the produced synthetic zeolites with those of the commercially available ones. Zeolitization resulted in an increase of CEC (up to 30 meq/100 g) compared to raw CFA and enhanced the ability of the material to adsorb the chosen ions. The obtained synthetic zeolites showed comparable or greater sorption properties than natural clinoptilolite and synthetic Na–P1. They were also capable of simultaneously removing cationic and anionic compounds. The structural, morphological, and textural properties of the final product indicated that it could potentially be used as an adsorbent for various types of environmental pollutants.
Highlights
Zeolites are microporous, crystalline hydrated aluminosilicates composed of tetrahedral SiO4 and AlO4 − units [1]
The synthesized products matched the characteristic peaks of zeolite Na–X at 14.49, 4.24, 2.89, 3.83, 8.87, 7.57, and 5.76 dhkl (6.10, 20.94, 30.85, 23.24, 9.97, 11.69, and 15.39 2θ, respectively), when compared with the X-ray diffraction (XRD) standard pattern of zeolite X from the PDF-2 release of the 2010 database formalized by the International Centre for Diffraction Data (ICDD) and the IZA-SC Database of Zeolite Structures
The type of zeolite obtained in the experiment is comparable with another study, in which zeolite X was synthesized at a low temperature from coal fly ash (CFA) with seawater [48]
Summary
Crystalline hydrated aluminosilicates composed of tetrahedral SiO4 and AlO4 − units [1]. Their essential structural feature is a three-dimensional tetrahedral framework, in which each oxygen atom is shared by two tetrahedra. The structure of zeolites is characterized by a regular construction of channels and chambers, which confers them a number of unique qualities including large sorption capacity as well as ion-exchange, molecular-sieve, and catalytic properties. Due to these features, zeolites have gained a great deal of attention from researchers. The demand for rare and specific minerals, such as zeolites, has been increasing in recent years, and finding a low-cost and effective method for their synthesis remains a challenging issue
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