Arsenate Adsorption on Fly Ash, Chitosan and Their Composites and Its Relations with Surface, Charge and Pore Properties of the Sorbents.

Agnieszka Adamczuk,Weronika Sofinska-Chmiel,Grzegorz Jozefaciuk

doi:10.3390/ma13235381

Agnieszka Adamczuk, Weronika Sofinska-Chmiel + Show 1 more

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https://doi.org/10.3390/ma13235381

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Abstract

One of the ways to recycle millions of tons of fly ash and chitin wastes produced yearly is their utilization as low-cost sorbents, mainly for heavy metal cations and organic substances. To improve their sorption efficiency, fly ashes have been thermally activated or modified by chitosan. We aimed to deeply characterize the physicochemical properties of such sorbents to reveal the usefulness of modification procedures and their effect on As(V) adsorption. Using low temperature nitrogen adsorption, scanning electron microscopy, mercury intrusion porosimetry, potentiometric titration and adsorption isotherms of As(V) anions, surface, pore, charge and anion adsorption parameters of fly ash activated at various temperatures, chitosan, and fly ash modified by chitosan were determined. Arsenate adsorption equilibrium (Langmuir model), kinetics (pseudo-second order model) and thermodynamics on the obtained materials were studied. Neither temperature activation nor chitosan modifications of fly ash were necessary and profitable for improving physicochemical properties and As(V) adsorption efficiency of fly ash. Practically, the physicochemical parameters of the sorbents were not related to their anion adsorption parameters.

Highlights

Among the basic problems of today’s civilization is the utilization of municipal, industrial, and agricultural wastes
SEM images of the studied adsorbents: (a) initial fly ash (FA) with encircled spongy structures; (b) fly ash activated at T = 1173 K (FA900); (c) initial fly ash modified by structures; (b) fly ash activated at T = 1173 K (FA900); (c) initial fly ash modified by chitosan (FACS); (d) magnification of the encircled fragment in the (c) image
In the flyfly ash (FA) image, spherical particles dominate, which may belong to two groups: cenospheres and/or plerospheres produced at temperatures of 1723 to 2023 K during coal burning in thermal power plants

Summary

Introduction

Among the basic problems of today’s civilization is the utilization of municipal, industrial, and agricultural wastes. A recently developing direction is the reuse of waste products for sorption of dyes, heavy metals, and other environmental pollutants [3,4,5]. Fly ash has been applied in the production of sorbents for water, sewage, soil, and exhaust fumes treatment to remove heavy metals [2,6,7], phosphates [8,9], humic acid [10,11], pesticides [12,13,14], dyes [15,16,17], fluoride [18], boron [19], ammonium [20], tannic acid [21], petroleum compounds [22,23], radioactive pollutants [23], chemical oxygen and suspended solids [24,25]. A frequent procedure applied to fly ash, aiming at improving its sorption properties, is a heat treatment called thermal activation [26,27]

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