Evaluation of phosphate adsorption by porous strong base anion exchangers having hydroxyethyl substituents: kinetics, eq
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RESEARCH ARTICLE
Evaluation of phosphate adsorption by porous strong base anion exchangers having hydroxyethyl substituents: kinetics, equilibrium, and thermodynamics Doina Humelnicu 1 & Ecaterina Stela Dragan 2 Received: 27 July 2020 / Accepted: 21 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Phosphate anions are recognized as the main responsible for the eutrophication of surface waters. In this work, two strong base anion exchangers having either N,N-dimethyl 2-hydroxyethylammonium (SBAEx.2M) or N,N-diethyl 2hydroxyethylammonium (SBAEx.2E) functional groups, as highly efficient sorbents in the removal of phosphate anions, are presented. The influence of the main parameters (pH, contact time, initial concentration of phosphate, temperature) on the adsorption performances was investigated in batch mode. Modeling the kinetics data by Lagergren, Ho and McKay, and Elovich kinetic models indicated chemisorption as the main mechanism of sorption. The sorption at equilibrium was modeled with Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherm models. The experimental isotherms were the best fitted by Langmuir and Sips isotherms, the maximum sorption capacity for phosphate anions being 233.88 mg g−1 SBAEx.2M and 223.5 mg g−1 SBAEx.2E, at pH 3, and 23 °C. Adsorption of phosphate anions in competitive conditions showed that the interference with co-existing anions was low in the case of Cl− ions and much higher with SO42− ions, the ion exchange having an important contribution in the adsorption process. The adsorption was spontaneous and endothermic, the degree of spontaneity increasing with the increase of temperature. The high level of reusability, the adsorption capacity decreasing with only ~ 7% in the case of SBAEx.2E and with ~ 9% in the case of SBAEx.2M, after five sorption/desorption cycles, recommends these SBAEx as promising adsorbents for phosphate removal. Keywords Phosphate . Strong base anion exchangers . Sorption kinetics . Isotherms . Reusability
Introduction Accumulation of toxic anions such as phosphate into the water containing an excess of nutrients determines over growth of algae into water bodies. That constitutes a very serious issue because blue-green algae are toxic and block sunlight to enter into water and use oxygen necessary for the plants and animals in water (Azam et al. 2019; Bunce et al. 2018; Dragan and Dinu 2020; Kumar and Viswanathan 2018). Therefore,
Responsible Editor: Tito Roberto Cadaval Jr * Ecaterina Stela Dragan [email protected] 1
Faculty of Chemistry, “Alexandru Ioan Cuza” University of Iasi, Carol I Bd. 11, 700506 Iasi, Romania
2
“Petru Poni” Institute of Macromolecular Chemistry, Grigore Ghica Voda Alley 41 A, 700487 Iasi, Romania
the phosphate removal in water bodies is highly required. In this respect, the interest in finding efficient and reusable adsorbents for phosphate has lately known a spectacular increase. Various approaches for physico-chemical removal of phosphate have been inspected, such as membrane
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