Selenite Removal from Aqueous Solution Using Silica-Iron Oxide Nanocomposite Adsorbents

Georgiana Mladin; Mihaela Ciopec; Adina Negrea; Narcis Duteanu; Petru Negrea; Paula Svera M Ianăşi; Cătălin Ianăşi

doi:10.3390/gels9060497

Selenite Removal from Aqueous Solution Using Silica-Iron Oxide Nanocomposite Adsorbents

Gels. 2023 Jun 19;9(6):497. doi: 10.3390/gels9060497.

Authors

Georgiana Mladin¹, Mihaela Ciopec¹, Adina Negrea¹, Narcis Duteanu¹, Petru Negrea¹, Paula Svera M Ianăşi², Cătălin Ianăşi³

Affiliations

¹ Faculty of Industrial Chemistry, Environmental Engineering, Polytechnic University of Timişoara, Victoriei Square no. 2, 300006 Timişoara, Romania.
² National Institute for Research and Development in Electrochemistry and Condensed Matter, 144th Dr. A. P. Podeanu Street, 300569 Timisoara, Romania.
³ "Coriolan Drăgulescu" Institute of Chemistry, Bv. Mihai Viteazul, No. 24, 300223 Timisoara, Romania.

Abstract

In recent years, during industrial development, the expanding discharge of harmful metallic ions from different industrial wastes (such as arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, or zinc) into different water bodies has caused serious concern, with one of the problematic elements being represented by selenium (Se) ions. Selenium represents an essential microelement for human life and plays a vital role in human metabolism. In the human body, this element acts as a powerful antioxidant, being able to reduce the risk of the development of some cancers. Selenium is distributed in the environment in the form of selenate (SeO₄^2-) and selenite (SeO₃^2-), which are the result of natural/anthropogenic activities. Experimental data proved that both forms present some toxicity. In this context, in the last decade, only several studies regarding selenium's removal from aqueous solutions have been conducted. Therefore, in the present study, we aim to use the sol-gel synthesis method to prepare a nanocomposite adsorbent material starting from sodium fluoride, silica, and iron oxide matrices (SiO₂/Fe(acac)₃/NaF), and to further test it for selenite adsorption. After preparation, the adsorbent material was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The mechanism associated with the selenium adsorption process has been established based on kinetic, thermodynamic, and equilibrium studies. Pseudo second order is the kinetic model that best describes the obtained experimental data. Also, from the intraparticle diffusion study, it was observed that with increasing temperature the value of the diffusion constant, K_diff, also increases. Sips isotherm was found to best describe the experimental data obtained, the maximum adsorption capacity being ~6.00 mg Se(IV) per g of adsorbent material. From a thermodynamic point of view, parameters such as ΔG⁰, ΔH⁰, and ΔS⁰ were evaluated, proving that the process studied is a physical one.

Keywords: adsorption; iron oxide; nanocomposite; selenite removal; silica matrix; sol–gel.

Grants and funding

This research received no external funding.