Studies on the Potential of Nonmodified and Metal Oxide-Modified Coal Fly Ash Zeolites For Adsorption of Heavy Metals and Catalytic Degradation of Organics for Waste Water Recovery

Silviya Boycheva,Denitza Zgureva,Dominika Behunová,Ivan Marinov,Ivalina Trendafilova,Simona Miteva,Margarita Popova,Miroslava Václaviková

doi:10.3390/pr8070778

Abstract

A nanocrystalline zeolite of Na-X type (CFAZ) was synthesized by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion of lignite coal fly ash. Modified CFAZ with magnetic nanoparticles (MNP-CFAZ) was obtained by adding presynthesized magnetic nanoparticles between the synthesis stages. CFAZs loaded by particles of copper (Cu-CFAZ) and cobalt (Co-CFAZ) oxides were prepared by postsynthesis modification of the parent CFAZ, applying a wet impregnation technique. The parent and modified CFAZs were examined for their phase composition by X-ray diffraction, morphology by scanning electron microscopy, and surface characteristics by N2 physisorption. Comparative studies have been carried out on the adsorption capacity of the starting CFAZ and its derivatives with respect to Cd2+- and Pb2+-ions from aqueous solutions. Adsorption isotherms of Cd2+-ions on the studied samples were plotted and described by the adsorption equations of Langmuir, Freundlich, Langmuir–Freundlich, and Temkin. The best correlation between the experimental and model isotherms for the parent and modified CFAZ was found with the Langmuir linear model, assuming a monolayer adsorption mechanism. Parent and modified CFAZs were also studied as catalysts for heterogeneous thermal Fenton oxidation of methylene blue. At 90 °C, the higher catalytic activity exhibits the nonmodified sample, but with the decrease in temperature to 60 °C, the modified samples are more effective catalysts.

Highlights

Coal fly ash (CFA) is a solid byproduct of coal combustion in thermal power plants (TPPs)
For the metal oxide-modified samples, SBET significantly decreases as the lowest of the specific surface values described by values are obtained for Cu-coal fly ash zeolites (CFAZs)
Taking into account that the Langmuir model assumes a uniform distribution of the adsorption sites and surface energy, it could be supposed that the coal ash zeolites prepared by the combination of ultrasonic homogenization and two-step synthesis are characterized by a homogeneous distribution of iron oxide phases and other components transferred from the raw ash, despite the complex composition of the feedstock

Summary

Introduction

Coal fly ash (CFA) is a solid byproduct of coal combustion in thermal power plants (TPPs). As the coal ash in its macrocomposition is predominantly aluminosilicate material, technological approaches to its conversion into zeolites are intensively studied [4]. The synthesis of coal fly ash zeolites (CFAZs). The alkaline conversion of coal ash is most efficiently accomplished by one-stage hydrothermal or two-stage hydrothermal-fusion syntheses [4,6]. The single hydrothermal treatment is usually performed at mild temperatures (below 100 ◦ C), while in the two-step synthesis prealkaline fusion of the reaction mixtures is generally performed at 550 ◦ C, followed by hydrothermal activation in the thermal range of

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Conclusion