Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

doi:10.1016/j.jes.2018.03.010

Journal of Environmental Sciences

Volume 75, January 2019, Pages 115-123

https://doi.org/10.1016/j.jes.2018.03.010 Get rights and content

Abstract

Sorption of U(VI) onto TiO₂ as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO₂ was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO₂ below pH 4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO₂ was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO₂ was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO₂ particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed.

Graphical abstract

Introduction

Uranium, one of the most important elements in the nuclear industry (Krepelova et al., 2008), is easily released during the cycling of uranium, such as in mining, processing and waste treatment. It is thus of great importance to investigate the migration and diffusion behavior of uranium in the natural environment due to its chemotoxicity combined with radiotoxicity. Sorption is among the important factors affecting the migration of U(VI) in environmental media (Wang et al., 2017a). In recent decades, scholars have paid increasing attention to the sorption/desorption process of uranium at the solid/solution interface (Fan et al., 2012; Li et al., 2014a; Qian et al., 2014; Sheng et al., 2015; Zhu et al., 2016). Previous research has proved that the mineral composition is indeed complicated, and the mechanism of U(VI) is difficult to accurately elaborate, especially at the molecular scale (Bachmaf and Merkel, 2011; Campos et al., 2013; Nair et al., 2014; Wang et al., 2017b). Kowal-Fouchard et al. (2004) found that U(VI) adsorbed on montmorillonite through ion exchange and on edge sites, and could form at least four kinds of species, including triple bond X₂UO₂, Al(OH)₂UO₂^2 +, SiO₂UO₂ and SiO₂(UO₂)₃(OH)₅⁻. Ligands such as phosphate and humic acid could promote U(VI) sorption by forming ternary surface complexes on adsorbent surfaces (Guo et al., 2009, Tan et al., 2017). For U(VI) sorption on pyrrhotite, inner-sphere surface complexation occurred first, and with the increase of time, reductive co-precipitates of U(VI) on pyrrhotite/pyrite were observed (Liu et al., 2017).

Titanium oxide is widely used as a model mineral for sorption studies due to its high chemical stability, high sorption capacity, radiation stability, wide availability and good recyclability (Romuald et al., 2007, Yan et al., 2016). Several previous studies have focused on the sorption of metal ions (such as Cu(II), Mo(VI), Co(II), Cr(VI), Pb(VI), Se(IV), Eu(III), Th(IV), Pu(VI)) on the TiO₂ surface (Tan et al., 2009a). It was found that differences in sorption properties were related to the morphology, crystallographic form, surface area, and grain size, and have nothing to do with the degree of impurity or surface charge of different TiO₂ materials (Comarmond et al., 2011). Ye et al. (2016) found that the interactions between fulvic acid with U(VI) at TiO₂ surface mainly took place via surface complexation and electrostatic attraction. Vandenborre (2005) reported similar surface complexes for U(VI) on different crystallographic planes of rutile and anatase in the pH range of 2.0–4.5. The enhancement of U(VI) sorption by fulvic acid was also reported by Guo et al. (2004), and the sorption was found to be increased with increasing ionic strength.

In this work, the effects of environmental factors, such as pH, ionic strength, soil humic acid (SHA), and temperature on U(VI) sorption on TiO₂ were studied; and spectroscopic investigations were performed in parallel to further explore the sorption mechanism of U(VI).

Section snippets

Materials

All chemicals used were of analytical grade. TiO₂ was purchased from Aladdin. The stock solution of UO₂(NO₃)₂ was prepared by dissolving UO₂(NO₃)₂·6H₂O in distilled-deionized water. SHA extracted from Gannan soil has been characterized in our previous work (Fan et al., 2008).

Characterization

The samples for X-ray photon-electron spectroscopy (XPS) and X-ray diffraction (XRD) detection were prepared as follows: 0.048 g TiO₂, 10 mL of 4 mol/L NaNO₃ solution, and 0.8 mL of 1.0 × 10^− 3 mol/L U(VI) stock were added into a

Sorption kinetics

The sorption of U(VI) on TiO₂ as a function of contact time is shown in Fig. 1. As can be seen from Fig. 1, sorption equilibration of U(VI) on TiO₂ was reached quickly within 20 hr. Therefore, 24 hr was selected in the following experiments to ensure sorption equilibration. It is interesting to note that, in the first 3 hr, the sorption of U(VI) in 0.5 mol/L NaNO₃ solution was lower than that in 0.01 mol/L NaNO₃ solution. Afterward, the sorption in 0.5 mol/L NaNO₃ solution increased sharply and

Conclusions

Sorption of U(VI) to TiO₂ was studied under various physicochemical conditions. The sorption process conforms to the pseudo second-order kinetics model. The presence of SHA could slightly enhance U(VI) sorption under acidic conditions, while U(VI) removal was strongly hindered by SHA. U(VI) uptake on TiO₂ was confirmed to be a spontaneous and endothermic process, which could be well-described by the Langmuir isotherm model. Interestingly, U(VI) sorption on TiO₂ was promoted at high ionic

Acknowledgements

This work was supported by the Natural National Science Foundation of China (Nos. 21601169, 41573128, 21601179 and 21647009), the Natural National Science Foundation of Gansu Province (No. 17JR5RA309), the Key Laboratory Project of Gansu Province (No. 1309RTSA041); CAS “Light of West China” Program and the “100-Talent” Program from the Chinese Academy of Sciences in Lanzhou Center for Oil and Gas Resources, Institute of Geology and Geophysics, CAS.

References (53)

B. Campos et al.
Adsorption of uranyl ions on kaolinite, montmorillonite, humic acid and composite clay material
Appl. Clay Sci.
(2013)
Q.H. Fan et al.
Effect of pH, ionic strength, temperature and humic substances on the sorption of Ni(II) to Na-attapulgite
Chem. Eng. J.
(2009)
F.L. Fan et al.
Rapid removal of uranium from aqueous solutions using magnetic Fe₃O₄@SiO₂ composite particles
J. Environ. Radioact.
(2012)
Z.J. Guo et al.
Sorption of U(VI) and phosphate on gamma-alumina: binary and ternary sorption systems
Colloids Surf. A Physicochem. Eng. Asp.
(2009)
Y.S. Ho et al.
The kinetics of sorption of divalent metal ions onto sphagnum moss peat
Water Res.
(2000)
A. Krepelova et al.
Structural characterization of U(VI) surface complexes on kaolinite in the presence of humic acid using EXAFS spectroscopy
J. Colloid Interface Sci.
(2008)
F. Lian et al.
Effect of humic acid (HA) on sulfonamide sorption by biochars
Environ. Pollut.
(2015)
H.B. Liu et al.
Mechanical investigation of U(VI) on pyrrhotite by batch, EXAFS and modeling techniques
J. Hazard. Mater.
(2017)
T. Missana et al.
On the applicability of DLVO theory to the prediction of clay colloids stability
J. Colloid Interface Sci.
(2000)
Z.W. Niu et al.
Effect of pH, ionic strength and humic acid on the sorption of uranium(VI) to attapulgite
Appl. Radiat. Isot.
(2009)

S. Bachmaf et al.

Sorption of uranium(VI) at the clay mineral–water interface

Environ. Earth Sci.

(2011)

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Sorption of uranyl ions on TiO2: Effects of pH, contact time, ionic strength, temperature and HA

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Characterization

Sorption kinetics

Conclusions

Acknowledgements

Appl. Clay Sci.

Chem. Eng. J.

J. Environ. Radioact.

Colloids Surf. A Physicochem. Eng. Asp.

Water Res.

J. Colloid Interface Sci.

Environ. Pollut.

J. Hazard. Mater.

J. Colloid Interface Sci.

Appl. Radiat. Isot.

J. Mol. Liq.

J. Mol. Liq.

Appl. Radiat. Isot.

J. Hazard. Mater.

Chem. Geol.

J. Hazard. Mater.

Chem. Eng. J.

J. Mol. Liq.

Water Sci. Technol.

Appl. Geochem.

J. Environ. Sci.

Chem. Eng. J.

Environ. Pollut.

J. Environ. Sci.

J. Mol. Liq.

Sorption of uranium(VI) at the clay mineral–water interface

Environ. Earth Sci.

Sorption of uranyl ions on TiO₂: Effects of pH, contact time, ionic strength, temperature and HA