Sorption of Uranium on Polyamide and Graphen Oxide Composite Material

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2nd_{Petrus-OPERA Conference on Radioactive Waste Management and Geological Disposal}

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Sorption of Uranium on Polyamide and Graphen Oxide Composite

Material

Z. Tomášová1, V. Brynych1, J. Pospěchová1, P. Ecorchard2, J. Tolasz2 1_{ÚJV Řež, a. s. Waste Management & Fuel Cycle Chemistry Division}

Hlavní 130, 250 68 Husinec-Řež, Czech Republic

2_{Department of Materials Chemistry, Institute of Inorganic Chemistry AS ČR v.v.i,}

Husinec-Řež č.p. 1001, 250 68 Řež, Czech Republic

Abstract

The new synthesized material has been tested as a potential sorbent of uranium for the purpose of treating the liquid radioactive waste. The sorption batch-experiments were performed on polyamide material. The experiments revealed the ability of polyamide-GO to uptake uranium from the solution.

Introduction

The safe treatment and disposal of uranium, the key element for nuclear energy, is a worldwide environmental concern. Sorption is one of the important methods for treatment of liquid radioactive waste, produced in the nuclear industry. Through sorption processes it is possible to transfer the radioactive contaminants from the liquid into a small volume of solid which can be than handled and disposed as a solid waste [1]. One of the potential solutions is using composite materials based on graphen oxide which previously confirmed their ability to remove radionuclides from solution [2,3]. In the presented study, the new nanocomposite material, polyamide-graphen oxide has been tested for potential use as a sorbent of uranium in radioactive liquid waste.

Figure 1: SEM image of synthesized polyamide-GO. Methods

Preparation of the material

Graphen was prepared from natural graphite by exfoliation in ethylene glycole in high intensity cavitation field and pressure of 5 bar. Graphen sheets were subsequently cleansed by dialysis in destilled water and

oxidised to graphen oxide (GO) by modified Hummers method which consist of reaction of graphen with H2SO4 H3PO4 a H3PO4 [4].

For the preparation of the composite polyamide-GO a polyamide PA66 from Sigma-Aldrich s.r.o. was used The commercial PA66 was modified before the reaction with GO in the mixture isopropanol/water in autoclave for 24 hours and the GO water suspension was added at room temperature and mixed for 48 hours. The final product was characterized by scanning electron microscopy (Fig. 1).

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Sorption experiments

Batch sorption experiments were performed on polyamide-GO in order to evaluate the sorption properties of the synthesized material. The sorption kinetic was tested by reaction of 1.5 ml of UO2(NO3)2 solution with 0.01 g of sorbent for various contact time.

Experiments for determining the sorption isotherms were carried out for defined time, being previously determined using sorption kinetic experiments. 1.5 ml solution volume was shaken in the closed vessels with 0.01 g of the studied material. After stirring, the supernatant was analyzed for U remaining in solution by means of UV spectrophotometry, using Arsenazo III method [5].

Sorption behavior was characterized by distribution coefficient Kd, defined by following relationship

d mass

volume∙ mL/g ,

where cmass is the concentration of the sorbate adsorbed onto the solid phase, cvolume is the concentration of the sorbate in solution, V [mL] is the volume of the liquid phase and m [g] is the mass of the sorbent. The data were fitted to the Langmuir isotherm as follows:

e L∙ max∙e

L∙e ,

where qmax is the maximum sorbate uptake [mg/g], KL is the coefficient [L/mol], ce is the equilibrium concentration of the solute [mg/L] and qe is the adsorbed amount of the sorbate on the sorbent [mg/g]. Freundlich isotherm is defined as

e F∙ e, mg/g ,

where KF and n are the characteristic constants.

Results/Discussion

The adsorption of uranium on the polyamide-GO occurs during the first few minutes. Fig. 2 (left) shows the dependence of percentage adsorption on contact time for U(VI). On the basis of previous results, a contact time of 24 h was set for subsequent experiments.

Figure 2: Uranium sorption onto polyamide-GO, sorption kinetics (left), Langmuir and Freundlich isotherm models (right).

The relationship between initial solution concentration and adsorbed amount of uranium is presented in Fig. 2 (right). Sorption of uranium to polyamide-GO is better described by Langmuir model (χ2 =9.4) then by Freundlich (χ2 =12). The parameters of the isotherm models are shown in the Table 1. Maximum sorbate uptake calculated from the Langmuir model corresponds to 21.8 mg/g. The distribution of sorbate between the solid phase and solution is described by distribution coefficient Kd 733.9 ml/g.

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Table 1: Characteristics of Langmuir and Freundlich isotherm models. Langmuir Freundlich

qmax 0.083 n 3.8

KL 5.3 KF 0.068

Conclusion

The new synthesized nanocomposite material has been tested as a potential sorbent for uranium. The sorption batch-experiments were performed on polyamide-GO to determine the sorption kinetics and isotherms. The sorption occurs during the first few minutes. The maximum sorbate uptake was calculated from the Langmuir equation and corresponds to 21.8 mg/g.

Acknowledgments

We thank for support from TAČR project no. TA04020222.

References and Citations

[1] International Atomic Energy Agency (IAEA), “Application of Ion Exchange Processes for the Treatment of Radioactive Waste and Management of SpentIon Exchangers”, IAEA Technical Reports Series No. 408, Austria, 2002.

[2] Z. Zhao, J. Li, T. Wen, C. Shena, X. Wang, A. Xu, “Surface functionalization graphene oxide by polydopamine for high affinity of radionuclides”, Colloids and Surfaces A: Physicochemical and Engineering Aspect, No. 482, pp 258-266, 2015.

[3] L. Chen, S. Lu, S. Wu, J. Zhou, X. Wang, “Removal of radiocobalt from aqueous solutions using titanate/graphene oxide composites”, Journal of Molecular Liquids, No. 209, pp. 397-403, 2015. [4] V. Stengl , “Preparation of Graphene by Using an Intense Cavitation Field in a Pressurized Ultrasonic

Reactor”, Chem. Eur. J. 2012, 18, 14047 – 14054