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Removal of uranium (VI) from aqueous systems by nanoscale zero-valent iron particles suspended in carboxy-methyl cellulose Article in Journal of Nuclear Materials · November 2013 DOI: 10.1016/j.jnucmat.2013.07.018
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Journal of Nuclear Materials 443 (2013) 250–255
Contents lists available at ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Removal of uranium (VI) from aqueous systems by nanoscale zero-valent iron particles suspended in carboxy-methyl cellulose Ioana-Carmen Popescu (Hosßtuc) a,⇑, Petru Filip b, Doina Humelnicu c,⇑, Ionel Humelnicu c, Thomas Bligh Scott d, Richard Andrew Crane d a
R&D National Institute for Metals and Radioactive Resources – ICPMRR Bucharest B-dul Carol I No. 70, Sector 2, 202917 Bucharest, Romania C. D. Nenitescu Institute of Organic Chemistry, Splaiul Independentei 202B, Sector 6, 71141 Bucharest, Romania Al.I. Cuza University of Iasi, The Faculty of Chemistry, Bd. Carol-I No. 11, Iasi 700506, Romania d Interface Analysis Centre, University of Bristol, 121 St. Michael’s Hill, Bristol BS2 8BS, UK b c
a r t i c l e
i n f o
Article history: Received 25 March 2013 Accepted 7 July 2013 Available online 18 July 2013
a b s t r a c t Carboxy-methyl-cellulose (CMC), a common ‘‘delivery vehicle’’ for the subsurface deployment of iron nanoparticles (INP) has been tested in the current work for the removal of aqueous uranium from synthetic water samples. A comparison of the removal of aqueous uranium from solutions using carboxymethyl-cellulose with and without iron nanoparticles (CMC–INP and CMC, respectively) was tested over a 48 h reaction period. Analysis of liquid samples using spectrophotometry determined a maximum sorption capacity of uranium, Qmax, of 185.18 mg/g and 322.58 mg/g for CMC and CMC–INP respectively, providing strong evidence of an independent aqueous uranium removal ability exhibited by CMC. The results point out that CMC provides an additional capacity for aqueous uranium removal. Further tests are required to determine whether similar behaviour will be observed for other aqueous contaminant species and if the presence of CMC within a INP slurry inhibits or aids the reactivity, reductive capacity and affinity of INP for aqueous contaminant removal. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction Nanoscale zero-valent iron particles (INP) have been identified as a novel, effective and low-cost alternative to other more established methods for the treatment of contaminated water and soil. Compared to bulk scrap metal (granular or powdered Fe0 > 0.1 lm in diameter) more commonly used in permeable reactive barriers, INP have a significantly greater surface area to volume ratio, higher surface energy and, resultantly, a significantly improved reactivity with regard to contaminants [1]. Their colloidal size also makes their deployment flexible due to their conceptually high mobility through porous media and their potential for injection at almost any location and depth in terrestrial groundwater systems [2,3]. The remediation mechanism depends on the nature of the contaminant but in all cases is driven by the oxidation of Fe(0) [4]. To date, nanoscale zero-valent iron particles (INP) have been shown to be effective decontaminators of a range of contaminants including chlorinated organics [5–11] and inorganic anions [12– 16], amongst others [4,9,17–19]. In addition, INP have also been shown to successfully remediate solutions contaminated with a ⇑ Corresponding authors. Tel.: +40 232201136; fax: +40 232201313 (D. Humelnicu). E-mail addresses:
[email protected] (I.-C. Popescu (Hosßtuc)), doinah@ uaic.ro (D. Humelnicu). 0022-3115/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2013.07.018
range of metals, including lead [20–22], chromium [4,12,19, 22,23], copper, [12,21,19], arsenic [15,24,25], nickel [21], zinc [21], cadmium [21] and silver [21]. The application of INP for the remediation of radionuclides remains less widely researched than for the aforementioned heavy metals and organic contaminants. Studies are limited to the radioisotopes of Ba [23,26,27], and U [28–31]. In order to improve the performance of nanoscale zero-valent iron particles (INP) for in-situ contaminated water treatment much emphasis has been placed in recent years on the development of surface modifications and ‘‘delivery vehicles’’ to facilitate nanoparticle mobility within porous networks. As an alternative to surfactants, the use of polyelectrolyte coatings such as carboxymethyl-cellulose (CMC) has received a great deal of interest [32,33] in order to increase the nanoscale zero-valent iron particles (INP) stability and mobility in contaminated soils and water [34]. Despite such widespread interest, to date there have been a limited number of studies on reactions between the ‘‘delivery vehicle’’ and the aqueous contaminant species [35,36]. At present it remains unclear whether they act to increase or decrease contaminant removal efficacy. The current study, using uranium as an example contaminant, INP as reactive material, and CMC as a ‘‘delivery vehicle’’ seeks to cover this knowledge gap. It also aims to point out the mechanism of the interaction between CMC molecules
I.-C. Popescu (Hosßtuc) et al. / Journal of Nuclear Materials 443 (2013) 250–255
and uranyl ions originated from its nitric salt in the presence and absence of INPs respectively, in a carbonate-free model solution in the pH range 5–7 specific to the polluted environment.
The uranium elution was performed using acidic solutions (HNO3 0.1 M, HCl 0.1 M) for a solid sample and basic ones (0.1 M Na2CO3) for another one. Percentage of radionuclide desorbed [39] was calculated with:
2. Materials and methods
Re covered% ¼ All chemicals, carboxy-methyl-cellulose (CMC), iron sulphate (FeSO47H2O), hydrochloric acid (HCl), sodium dihydrogen phosphate (NaH2PO4), sodium hydroxide (NaOH), nitric acid (HNO3), uranyl(VI) nitrate (UO2(NO3)26H2O), sodium carbonate (Na2CO3), and solvents (ethanol, acetone) used in this study were of reagent grade and all solutions were prepared using Milli-Q purified water (resistivity > 18.2 MX cm). 2.1. Nanoparticle synthesis The nanoscale zero-valent iron particles (INP) were synthesized following an adaptation of the method first described by other authors Wang [11], using sodium borohydride to reduce Fe(II) to a metallic state. Briefly, 7.65 g of FeSO47H2O was dissolved in 50 ml of Milli-Q water (18.2 MX cm) and then a 4 M NaOH solution was used to adjust the pH to the range 6.2–7.0. The salts were reduced to metallic nanoparticles by the addition of 3.0 g of NaBH4. The nanoparticle product was isolated through centrifugation and then sequentially washed with water, ethanol and acetone (20 ml of each). The nanoparticles were dried in a desiccator under low vacuum (10–2 mbar) for 48 h and annealed under vacuum (
