Title: Ionic liquid modified diatomite as a new effective adsorbent for uranium ions removal from aqueous solution
Author: Myroslav Sprynskyy Tomasz Kowalkowski
Hlanganani Tutu Ewa M. Cukrowska Bogusław Buszewski
Reference: COLSUA 19495
To appear in: Colloids and Surfaces A: Physicochem. Eng. Aspects
Received date: 30-8-2014
Revised date: 18-10-2014
Accepted date: 21-10-2014
Please cite this article as: M. Sprynskyy, T. Kowalkowski, H. Tutu, E.M. Cukrowska, B.
Buszewski, Ionic liquid modified diatomite as a new effective adsorbent for uranium ions removal from aqueous solution., Colloids and Surfaces A: Physicochemical and
Engineering Aspects (2014), http://dx.doi.org/10.1016/j.colsurfa.2014.10.042
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Ac ce pte d M an us cri pt 1
Ionic liquid modified diatomite as a new effective adsorbent for uranium ions removal from aqueous solution.
Myroslav Sprynskyya*, Tomasz Kowalkowskia, Hlanganani Tutub, Ewa M. Cukrowskab, Bogusław
Buszewskia aChair of Environmental Chemistry and Bioanalytics, Faculty of Chemistry, Nicolas Copernicus
University, 7 Gagarina Str., 87-100 Toruń, Poland bMolecular Sciences Institute, School of Chemistry, Faculty of Science, University of the
Witwatersrand, Private Bag 3 WITS 2050 Johannesburg, South Africa
Modified diatomite was prepared by chemical treatment with 1–ethyl–3–methylimidazolium chloride solution. The properties of the modified diatomite have been studied using scanning electron microscopy, infrared absorption spectroscopy, thermogravimetric technique, zeta potential and carbon content analyzers. The adsorption of uranium(VI) from aqueous solutions onto the ionic liquid modified diatomite was studied using batch adsorption experiments. The parameters influencing the uranium adsorption, such as contact time, pH of solution, and initial uranium(VI) concentration were studied. Most of uranium is adsorbed in the first 5 minutes. The maximum adsorption of the modified diatomite towards uranium under experimental conditions was 88 mg/g.
The experimental data for uranium adsorption was analyzed using the first-order kinetic model, the
Freundlich, Langmuir, Sips and modified BET isotherm models. The study results showed the multilayer adsorption of uranium ions on modified diatomite.
Keywords: uranium, adsorption, modified diatomite, ionic liquids. *Corresponding author. Tel.:+48566114926, fax: +48566114837
E-mail address: firstname.lastname@example.org (M.Sprynskyy).
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Ac ce pte d M an us cri pt 2 1. Introduction
Environmental pollution due to uranium has largely been as a result of development of the nuclear industry, combustion of coal and other fossil fuels, as well as production and use of phosphate fertilizers. The world’s volume of uranium mining wastes with uranium concentration in the range from several tens of milligrams to a few grams per kilogram accounts for about one billion cubic meters . Nearly 40 million tons of phosphate fertilizers is used worldwide annually . Uranium concentrations in such fertilizers may be from 5 to 150 milligrams per kilogram  compared to the content in natural soil that does not exceed a few milligrams per kilogram.
The release of uranium and the threat of environmental contamination due to its toxicity and radioactivity  promoted the development of various methods and technologies for the treatment of different uranium wastes. Chemical precipitation, lime softening, ion exchange, membrane separation and adsorption methods have been used for treating waste water contaminated with uranium but each of them has its intrinsic advantages and limitations [5, 6]. Various inorganic and organic adsorbents have been investigated including activated carbon, natural and synthetic zeolites, clay minerals, diatomites, hematite, alumina and silica, ion exchange resins, humic acids, coir pith, chitosan, polymeric materials, and different biosorbents.
Modifications of adsorbents has allowed for significant improvement of functional properties. For instance, chemical modification using different organic compounds is extensively used for inorganic adsorbents. This method is widely covered in the literature and is of considerable use currently for modification of different siliceous adsorbents. From one of our previous studies, diatomite modified with a surfactant displayed a high adsorption capacity of 158.8 mg/g of uranium . As a consequence, modification of diatomite using ionic liquids (ILs) looks promising owing to their chemical similarity to organic surfactants .
Ionic liquids have received considerable attention in recent years and their unique properties have been taken advantage of to synthesize polymer nanocomposites  and other new adsorbents [10, 11]. ILs may be a promising alternative to classical organic solvents that are usually used for
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Ac ce pte d M an us cri pt 3 modification of different adsorbents. These compounds are being applied to modify silica , activated carbon , MCM41 and SBA15 mesoporous molecular sieves , aluminum oxide , titanium dioxide , montmorillonite [16, 17], smectite , kaolinite and quartz , halloysite , magnetic nanoparticles , gallocyanine grafted hydrogel  and cellulose .
Among the possible mechanisms of ionic liquids immobilization on the active surface, depending on the nature of the adsorbent, the researchers suggested the interactions to be via cation exchange, electrostatic attraction, hydrogen bonds and covalent grafting.