Chemosphere xxx (2014) xxx–xxx

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Chemosphere

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Influence of gamma irradiation on uranium determination by ArsenazoIII in the presence of Fe(II)/Fe(III)

0045-6535/$ - see front matter � 2014 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.chemosphere.2013.12.094

⇑ Corresponding author. Tel./fax: +86 10 6276 5905.E-mail address: liucl@pku.edu.cn (C. Liu).

Please cite this article in press as: Zheng, Z., et al. Influence of gamma irradiation on uranium determination by Arsenazo III in the presence of Fe(II)Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.094

Zhong Zheng a, Mingliang Kang a, Chunli Wang a, Chunli Liu a,⇑, Bernd Grambow b, Lara Duro c,Tomo Suzuki-Muresan b

a Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and MolecularEngineering, Peking University, Beijing 100871, Chinab SUBATECH, Unité Mixte de Recherche 6457, Ecole des Mines de Nantes, CNRS/IN2P3, Université de Nantes, 4 rue Alfred Kastler, BP 20722, 44307 Nantes cedex 03, Francec AMPHOS21, P. Garcia Ifaria 49-51, Barcelona E-08019, Spain

h i g h l i g h t s

� Accurate measurement of uranium iswith great importance in the nuclearfuel cycle.� Fe(II) added to a gamma irradiated

U(VI) solution can give rise to Fentonreaction.� The induced Fenton reaction can

decompose the subsequently addedArsenazo III.� With c radiation and ferrous iron, a

new U measurement method needsto be developed.

g r a p h i c a l a b s t r a c t

U(VI)

Fe(II) Arsenazo(III)

450 500 550 600 650 7000.0

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U(VI)+ars+Fe(II) [U(VI)]ir 0.5 kGy+ars+Fe(II) [U(VI)]ir 1 kGy+ars+Fe(II) [U(VI)]ir 18 kGy+ars+Fe(II) [U(VI)]ir 180 kGy+ars+Fe(II)

a r t i c l e i n f o

Article history:Received 27 September 2013Received in revised form 19 December 2013Accepted 27 December 2013Available online xxxx

Keywords:DecompositionArsenazo IIIGamma irradiationFenton reactionU(VI)Fe(II)/Fe(III)

a b s t r a c t

Arsenazo III is a widely used reagent for the concentration measurement of uranium and other actinidesin aqueous samples. This study indicates that, for routine aqueous samples, due to the strong complexingability with Arsenazo III, Fe(III) can significantly decrease the UV–Vis absorbance of the U(VI)-Arsenazo IIIcomplex, whereas the influence of Fe(II) on the absorbance is negligible. However, when Fe(II) is presentin a gamma-irradiated U(VI) aqueous sample, it can give rise to the Fenton reaction, which produces oxi-dizing radicals that decompose the subsequently added Arsenazo III, leading to a sharp decrease in theabsorbance of the U(VI)-Arsenazo III complex. The decrease in absorbance depends on the iron contentand irradiation dose. Furthermore, the oxidizing radicals from the Fenton reaction induced by gammairradiation can be continually produced. Even if the irradiated solution has been aged for more thanone month in the absence of light at room temperature and without the exclusion of oxygen, the reactiv-ity of the radicals did not decrease toward the subsequently added Arsenazo III. This finding demon-strates that the presence of Fe(II) in gamma-irradiated U(VI) aqueous samples can lead to incorrectU(VI) measurement using the Arsenazo III method, and a new method needs to be developed for thequantitative determination of U(VI) in the presence of gamma radiation and ferrous iron.

� 2014 Elsevier Ltd. All rights reserved.

0

1. Introduction

Bisazo-group reagents for the spectrophotometrically identifi-cation and concentration determination of elements is simple

and selective (Rohwer et al., 1997). In which, Arsenazo III (2,2 -[1,8-dihydroxy-3,6-disulfo-2,7-naphthalene-bis(azo)]dibenzenear-sonic acid), a red organic compound that undergoes reactions witha number of elements forming complexes with different colors, isone of the most widely used indicators for the photometric deter-mination of uranium, thorium, plutonium, barium, strontium, haf-nium, bismuth, manganese, cobalt and the rare earth elements

/Fe(III).

2 Z. Zheng et al. / Chemosphere xxx (2014) xxx–xxx

(Savvin, 1963; Zyryanov and Baykov, 2002; Khan et al., 2006;Dedkova et al., 2008). The unique of Arsenazo III is forming strong,stable metal chelate complexes with the elements mentionedabove. This makes it important for measuring the concentrationsof elements at extreme conditions, such as very basic and acidicmedia, where hydrolysis reactions could occur and polynuclearspecies could be formed. Moreover, Arsenazo III is a suitable re-agent for coordinating elements with various oxidation statesand measuring their concentrations, as is the case for uraniumand plutonium.

The ubiquitous of iron on earth makes it co-exist with most ofthe metal elements. In atmospheric conditions, ferrous ion is oxi-dized to ferric ion by oxygen in many cases. Due to the strong com-plexing ability, ferric ion will form complex with Arsenazo III, thusinfluencing the concentration measurement for those elementsmentioned above. To suppress the interference from Fe(III), areductant is usually used to reduce Fe(III) to Fe(II).

Water radiolysis due to ionizing radiation produces both oxi-dants (�OH, H2O2, HO�2 and O2) and reductants (e�aq, H� and H2) (Nils-son and Jonsson, 2011; Eriksen et al., 2012), and occurs in manysituations, e.g., radiotherapy (Schmid et al., 2010), radiosteriliza-tion (Maquille et al., 2008), sewage treatment (Guo et al., 2008),food irradiation (Katayama et al., 2006), nuclear waste repository(Jonsson et al., 2007), to name only a few. Many studies have con-firmed the effective degradation of refractory organic pollutants bygamma irradiation directly (Gehringer et al., 1988; Arbon et al.,1996; Lee and Lee, 2005; Akiyama et al., 2010; Zheng et al.,2011), and a recent work has demonstrated that the presence ofvarying concentrations of ferrous sulfate can significantly enhancethe degradation (Varghese et al., 2007).

The Fenton reaction is commonly used for advanced oxidationprocesses (AOPs), in particular with organic compounds (Bouniol,2010; Nidheesh and Gandhimathi, 2012). The principle of the Fen-ton reaction is based on a mixture of dissolved iron (Fe(II), catalyst)reacts with hydrogen peroxide (H2O2, Fenton reagent) and pro-duces oxidizing radicals in the following manner:

Fe2þ þH2O2 ! Fe3þ þ �OHþ OH� ð1Þ

Fe3þ þH2O2 ! Fe2þ þHO�2 þHþ ð2Þ

Reaction (1) is the oxidation of ferrous iron Fe(II) to ferric iron Fe(III)by H2O2, which produces strongly oxidizing hydroxyl free radicals(�OH) and hydroxyl anions (OH�). In reaction (2), Fe(III) is reducedto Fe(II) with the formation of perhydroxyl radicals (HO�2). TheHO�2 radical is a relatively weak oxidant, whereas the hydroxyl freeradical (�OH) is a strong oxidant that can react non-selectively withmost organic compounds (Nidheesh and Gandhimathi, 2012).

Thus, an irradiated solution containing Fe(II, III) or the introduc-tion of Fe(II, III) into a gamma-irradiated solution can lead to theFenton reactions, which then produce oxidative radicals that canoxidize organic compounds in the solution. To date, there are con-siderable numbers of studies related to the Fenton reaction, whilefew studies go to the underlying mechanism of the reaction andthe gamma-ray induced reactions are not well-documented (Var-ghese et al., 2007; Bouniol, 2010).

In this paper, we investigated the gamma ray-Arsenazo III–Fe(II,III) reactions in aqueous solutions and discussed how gamma irra-diation can influence the concentration determination of aqueousU(VI) solutions with Arsenazo III spectrophotometric method. Wefound that the Fenton reaction induced by gamma irradiation candecompose Arsenazo III, leading to a sharp decrease in the absor-bance of the U(VI)-Arsenazo III complex. These results will havegreat influence to the analysis of uranium aqueous solutions fromnuclear fuel cycles, and suggest that attention must be paid to the

Please cite this article in press as: Zheng, Z., et al. Influence of gamma irradiatioChemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.094

application of organic compounds, such as Arsenazo III, in gammaradiation-exposed samples.

2. Materials and methods

2.1. Chemicals and reagents

All of the reagents used in this study were of analytical grade.Ammonium ferrous sulfate ((NH4)2FeSO4) and UO2(NO3)2�6H2Owere obtained from Sinopharm Chemical Reagent Co., Ltd.(Shanghai, China). FeCl3�6H2O and Arsenazo III were purchasedfrom J&K chemical Ltd. (Beijing, China). The water used wasdeionized (18.2 MX).

2.2. Gamma irradiation process

Gamma irradiation of the samples was conducted at room tem-perature using a 60Co source in the Fundamental Science Labora-tory on Radiochemistry & Radiation Chemistry at PekingUniversity. Solutions of 0.1 mM of UO2þ

2 (pH � 2.0), with and with-out addition of (NH4)2FeSO4 or FeCl3, were introduced into 10 mLairtight glass vessels and placed into specified positions with dif-ferent distances from the core of the 60Co radiation source toachieve desired absorbed doses ranging from 0.15 kGy to180 kGy. The doses were calibrated with a conventional Frickedosimeter.

2.3. UV–Vis analyses

After irradiation, 1 mL of the irradiated solution was mixed with2 mL Arsenazo III solution (0.1% in w/w). The mixture was then di-luted to 10 mL with a sulfuric acid solution (pH 2.0) in the presenceor absence of the desired concentration of Fe(II). Subsequently, theabsorption spectrum was recorded from 450 nm to 700 nm againsta blank with a UV–Vis spectrophotometer (Lamda-35, Perkin ElmerInc., Waltham, MA, USA). The concentrations of Fe(II)/Fe(III) in theirradiated solution were determined by the phenanthroline meth-od, with and without the reduction step by hydroxylamine hydro-chloride (Viollier et al., 2000).

2.4. ESI–MS measurements

The substances in the mixtures were determined via electro-spray ionization-mass spectrometry (ESI–MS), which is a usefulmethod for identifying the molecular formula to obtain the com-plex information between Arsenazo III and U(VI). All negative-ionelectrospray mass spectra were recorded with a Bruker APEX IV7.0 T Fourier transform ion cyclotron resonance mass spectrometer(Bruker Daltonics, Billerica, MA, USA) equipped with an externalESI source at Peking University. The scan range was from m/z 100to 1200.

3. Results and discussion

3.1. Influence of Fe(II, III) on the absorbance of U(VI)-Arsenazo IIIcomplex

The influence of Fe(II) on the absorption spectra of the ArsenazoIII-U(VI)-complex is shown in Fig. 1a. Free Arsenazo III solutionexhibits an absorption maximum at 540 nm, whereas its complexwith U(VI) shows two intense absorption peaks at 605 and656 nm (Rowatt and Williams, 1989). It has been reported that aslight shift of the absorption band may occur due to differencesin the solution pH and ionic medium used (Rohwer et al., 1997).As observed from Fig. 1a, the influence of Fe(II) on the absorption

n on uranium determination by Arsenazo III in the presence of Fe(II)/Fe(III).

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[U(VI)+0mM Fe(II)]ir+ars [U(VI)+0.01mM Fe(II)]ir+ars [U(VI)+0.03mM Fe(II)]ir+ars [U(VI)+0.05mM Fe(II)]ir+ars [U(VI)+0.07mM Fe(II)]ir+ars [U(VI)+0.1mM Fe(II)]ir+ars

450 500 550 600 650 700

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Abs

orba

nce

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ars U(VI)+ars U(VI)+ars+0.01mM Fe(II) U(VI)+ars+0.1mM Fe(II) U(VI)+ars+1mM Fe(II)

a b

Fig. 1. Influence of Fe(II) on the absorption spectra of U(VI)-Arsenazo III complex: (a) U(VI)+Fe(II) solutions without gamma irradiation; (b) U(VI)+Fe(II) solutions hadreceived 1.8 kGy gamma irradiation dose before recording the UV–Vis spectroscopic data.

Z. Zheng et al. / Chemosphere xxx (2014) xxx–xxx 3

spectra of the Arsenazo III-U(VI)-complex is negligible up to 1 mM.While, when the U(VI) solution with 0.03 mM Fe(II) was irradiatedbefore the addition of Arsenazo III, the absorbance peaks at 605and 656 nm sharply decreased, and the peaks completely disap-peared when the Fe(II) concentration was greater than 0.07 mM(Fig. 1b). There was no discernible change in the absorbance forall of the above solutions after standing for 24 h. These results indi-cate that Fe(II) in a U(VI) solution that had been irradiated by gam-ma rays will lead to an artificially lower measurement result of theU(VI) concentration using the Arsenazo III method.

Fig. 2 shows the influence of Fe(III) on the absorption spectra ofU(VI)-Arsenazo III complex. It indicates that the increase of Fe(III)concentration can significantly decrease the absorbance of theU(VI)-Arsenazo III complex. This is in contrast to a previous obser-vation that Fe(III) can enhance the absorbance of the uraniumArsenazo III complex in 3 M perchloric acid solution (Khan et al.,2006). The reason for this contrast may arise from the differencein solution pH (�2.0) and media (sulfuric acid). Further investiga-tions are needed to understand the underling mechanism.

A previous study indicated that due to the formation of a com-plex with Arsenazo III, Fe(III) acts as an interferent for the determi-nation of manganese, bismuth, magnesium and calcium (Reig et al.,1983; Khan et al., 2006). Therefore, to suppress the interferencefrom Fe(III), a reductant such as Ti(II) chloride (Murty et al.,1997) or L-ascorbic acid (Komersová et al., 2001) is commonly usedto reduce Fe(III) to Fe(II). While, when there is gamma irradiation,aqueous Fe(II) will be oxidized to Fe(III) due to the strong oxidizingradicals produced by water radiolysis (Trumbore and Hart, 1959),and the final speciation iron in the solution would be mainly ferriciron. Fig. 3 shows the dose-dependence of the decrease in absor-

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U(VI)+ars+0mM Fe(III) U(VI)+ars+0.01mM Fe(III) U(VI)+ars+0.03mM Fe(III) U(VI)+ars+0.05mM Fe(III) U(VI)+ars+0.07mM Fe(III) U(VI)+ars+0.1mM Fe(III)

Fig. 2. Influence of Fe(III) on the absorption spectra of U(VI)-Arsenazo III complex.

Please cite this article in press as: Zheng, Z., et al. Influence of gamma irradiatioChemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.094

bance (left) and the corresponding iron speciation evolution inthe irradiated solution (right). The decrease of Fe(II) or the increaseof Fe(III) exhibits a linear correlation with the absorbed dose. Dueto the competitive complexing of Fe(III) and U(VI) with ArsenazoIII, the decrease in absorbance of the gamma irradiated U(VI) +Fe(II) solutions at 605 and 656 nm can be mainly ascribed to theoxidation of Fe(II) to Fe(III).

3.2. Fenton reaction induced by gamma irradiation

To understand the effect of the Fenton reaction on the decreasein absorbance of the U(VI)-Arsenazo III complex, a U(VI) solutionwas irradiated to a designed absorbed dose and then mixed withArsenazo III and Fe(II). The color of the mixed solution changedto blue, which is the characteristic color of the U(VI)-Arsenazo IIIcomplex. However, the mixed solution lost its color gradually afterseveral minutes. The UV–Vis spectra data of the mixed solution re-corded after 24 h is shown in Fig. 4. Fig. 4a shows that the absor-bance decreased significantly upon the introduction of Fe(II) intothe gamma-irradiated U(VI) solution, and the decrease dependson the Fe(II) concentration. With an absorbed dose of 18 kGy, theabsorption at 656 nm disappeared completely in the presence of0.07 mM Fe(II). Furthermore, Fig. 4b shows that the absorbance de-crease is also dose-dependent. To understand the time effect on thereactivity, some irradiated U(VI) solution were allowed to age for 5,10, 20, and 30 d in the absence of light at room temperature with-out the exclusion of air, and then mixed with Fe(II) and ArsenazoIII. Quite the same phenomena were observed as that shown inFig. 4a and b, which indicated that even after 30 d, the oxidizingcapacity of the gamma irradiated U(VI) solution had no discernabledecrease.

Noting that the absorption spectrum in Fig. 4 has a differentprofile from the one in Fig. 1b, e.g., the absorption originating fromArsenazo III at �540 nm is decreased simultaneously in Fig. 4,implying the decomposition of the Arsenazo III structure. The samedecrease of absorbance at �540 nm is also observed for the exper-iments simulating the degradation of Arsenazo III (U(VI) + Arse-nazo III + Fe(II) + H2O2) by the Fenton reaction as shown in Fig. 5,indicating the occurrence of the Fenton reaction in the pre-gammairradiated U(VI) solution with Arsenazo III and Fe(II). Because fer-rous iron is consumed more rapidly than it is regenerated duringthe Fenton reaction process (Zhang et al., 2006; Nidheesh andGandhimathi, 2012), the absorbance decrease in Fig. 4 can beattributed to both the competitive complexing of Fe(III) with Arse-nazo III and the decomposition of Arsenazo III by the Fenton reac-tion. As observed from Fig. 2, the absorbance values at 656 nm are0.671, 0.378 and 0.234 for the 0.01, 0.03 and 0.05 mM Fe(III),

n on uranium determination by Arsenazo III in the presence of Fe(II)/Fe(III).

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irradiated with Fe(II) irradiated without Fe(II)

Fig. 3. Dose dependence of the absorbance (at 656 nm) of U(VI)-Arsenazo III complex (left, [U(VI)] = 0.01 mM, [Fe(II)] = 0.1 mM; and right, the Fe(II)/Fe(III) ratio changed withdose in the solution). During the irradiation process, the dose rate was kept at 30 Gy/min.

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U(VI)+ars+Fe(II) [U(VI)]ir 0.5 kGy+ars+Fe(II) [U(VI)]ir 1 kGy+ars+Fe(II) [U(VI)]ir 18 kGy+ars+Fe(II) [U(VI)]ir 180 kGy+ars+Fe(II)

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[U(VI)]ir+ars [U(VI)]ir+ars+0.01mM Fe(II) [U(VI)]ir+ars+0.03mM Fe(II) [U(VI)]ir+ars+0.05mM Fe(II) [U(VI)]ir+ars+0.07mM Fe(II) [U(VI)]ir+ars+0.1mM Fe(II)

a b

Fig. 4. The absorbance of pre-gamma irradiated U(VI) solution plus Arsenazo III and Fe(II) as a function of: (a) Fe(II) concentration from 0 to 0.1 mM, absorbed dose set at18 kGy; (b) absorbed dose in the range of 0–180 kGy, [Fe(II)]add = 0.1 mM.

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U(VI)+ars+Fe(II)+0.005mM H2O2 U(VI)+ars+Fe(II)+0.01mM H2O2 U(VI)+ars+Fe(II)+0.02mM H2O2 U(VI)+ars+Fe(II)+0.05mM H2O2 U(VI)+ars+Fe(II)+0.1mM H2O2

Fig. 5. The absorption spectra for the U(VI)+Arsenazo III + Fe(II) solution in thepresence of various concentration of H2O2. [U(VI)] = 0.01 mM, [Fe(II)] = 0.1 mM.

4 Z. Zheng et al. / Chemosphere xxx (2014) xxx–xxx

respectively, whereas Fig. 4 shows lower absorbance values of0.576, 0.286 and 0.177 for the equivalent concentrations of Fe(II).

The G-value refers to the number of molecules produced or de-stroyed for every 100 eV dose absorbed by a substance from theionizing radiation. The G-value for H2O2 is 0.76 molecules/100 eV(Draganic et al., 1969). Given the absorbed doses of 1 kGy and18 kGy, 0.008 and 0.14 mM H2O2 are expected to be formed in a10 mL solution, respectively. Based on the theoretical calculations,we compared the difference in the absorbance decrease betweenthe irradiated solution and the solution without irradiation butwith extra H2O2.

The effect of H2O2 on the decomposition of Arsenazo III by theFenton reaction was investigated over the range of 0.005–0.1 mM

Please cite this article in press as: Zheng, Z., et al. Influence of gamma irradiatioChemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.094

(Fig. 5). Because the decomposition of H2O2 is thermodynamicallyfavorable under ambient conditions, the concentration of H2O2 wasre-calibrated using the KMnO4 method (Klassen et al., 1994). Asshown in Figs. 4b and 5, the absorbances at 656 nm for the 1 kGyand 18 kGy irradiated solutions are comparable with the solutionsprepared by adding 0.02 and 0.1 mM H2O2, This confirms the reli-ability of the H2O2 production calculations.

With the increase of the H2O2 concentration, a significant absor-bance decrease at �540 nm occurs after the disappearance of theU(VI)-Arsenazo III complex peaks at 605 and 656 nm. Becausethe symmetrical Arsenazo III molecules contains two groups capa-ble of metal binding and because it can form a 1:1 complex withUO2þ

2 (Rowatt and Williams, 1989; Zyryanov and Baykov, 2002),the results in Figs. 4 and 5 suggest that the complex of ArsenazoIII with U(VI) is more susceptible to oxidation.

3.3. Mass spectrometry analysis

ESI-MS, a powerful technique that enables the identification ofthe molecular formula of complex molecules, was utilized to inves-tigate the binding affinity between Arsenazo III and U(VI). The freeArsenazo III (Fig. 6a) gives rise to a molecular peak at m/z 774.86.After adding 0.01 mM UO2(NO3)2, the ESI-MS spectrum revealstwo main ions at m/z 1105.87 and 1042.88, which can be ascribedto [ars+(UO2NO3)+]� and ½arsþ UO2þ

2 ��

, respectively (Fig. 6b). Thesetwo ions confirm that Arsenazo III forms a 1:1 complex with U(VI)(Rowatt and Williams, 1989; Khan et al., 2011). Nevertheless,when Arsenazo III was introduced into the gamma-irradiatedU(VI) solution (at 1.8 kGy dose) with 0.1 mM Fe(II), the peaks at

n on uranium determination by Arsenazo III in the presence of Fe(II)/Fe(III).

N NNN

O- OH

SO3H SO3H

H2O3AsAsO3H2

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386.93 1042.88

1105.87456.00

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ns.

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386.93

474.86

774.86

638.78

553.80

723.76

274.93

a

Fig. 6. Zoom in the regions of interest for ESI-MS spectra: (a) free Arsenazo III solution (0.02%); (b) 0.01 mM U(VI) + Arsenazo III (0.02%) solution; (c) irradiated U(VI) solution(0.01 mM) at 1.8 kGy + 0.1 mM Fe(II) + Arsenazo III (0.02%); (d) 0.01 mM U(VI) + 0.1 mM Fe(II) + 0.1 mM H2O2 + Arsenazo III (0.02%) solution.

Z. Zheng et al. / Chemosphere xxx (2014) xxx–xxx 5

m/z 1105.87 and 1042.88, as well as the molecular peak of Arse-nazo III at m/z 774.86, disappeared (Fig. 6c). The same result wasobserved for the Arsenazo III solution that contains 0.1 mM Fe(II),0.1 mM H2O2 and 0.01 mM U(VI) (Fig. 1d), in which where the Fen-ton reaction is expected to occur to decompose the Arsenazo III.Therefore, the mass spectral fragmentation patterns further con-firm that the Fenton reaction induced in gamma-irradiated solu-tions in the presence of Fe(II) can decompose subsequentlyadded Arsenazo III reagent.

Based on the discussions mentioned above, the entire processfor Fe(II) to influence the measurement of uranium under gammairradiation can be illustrated as following:

Water Solution ������!c�irradiationH2O2;

�OH; HO�2 ð1Þ

H2O2;�OH; HO�2 þ Fe2þ ! Fe3þ

Fe3þ þ Arsenazo III! FeðIIIÞArsenazo III ð2Þ

Fe2þ þH2O2 ! Fe3þ þ �OHþ OH�

�OHþ Arsenazo III! Decomposition ð3Þ

(1) Water radiolysis due to ionizing radiation produces oxidants(�OH, H2O2 and HO�2).

(2) Oxidants produced by gamma irradiation oxidize the Fe(II)to Fe(III), and then Fe(III) complexes with Arsenazo III toform Fe(III) + Arsenazo III complex. (The experimentalprocess was: U(VI) + Fe(II) + gamma radiation + ArsenazoIII.)

(3) The H2O2 produced by gamma irradiation and the thereafteradded Fe(II) induce the Fenton reaction. The production �OHof the Fenton reaction decomposes Arsenazo III into smallermolecules. (The experimental process was: U(VI) + gammaradiation + Fe(II) + Arsenazo III.)

Please cite this article in press as: Zheng, Z., et al. Influence of gamma irradiatioChemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2013.12.094

4. Conclusions

Arsenazo III is a widely used reagent in spectrophotometricanalysis of elements. Due to the strong affinity with Arsenazo III,Fe(III) can significantly decrease the UV–Vis absorbance of theU(VI)-Arsenazo III complex. Gamma radiation commonly exists inthe nuclear fuel cycle and many other nuclear related occasions,and Fe(II) is ubiquitous in the geosphere. Gamma irradiated solu-tions containing uranium, ferrous iron and other elements arenot few. This study indicates that Fe(II) introduced into gamma-irradiated U(VI) solutions can induce the Fenton reaction, whichcan decompose Arsenazo III, thus leading to a sharp decrease inthe UV–Vis absorbance of the U(VI)-Arsenazo III complex at605 nm and 656 nm. The decrease in the absorbance is positivelyrelated with the iron concentration and the absorbed dose, andthe oxidizing radicals from the Fenton reaction that are inducedby gamma irradiation can be continually produced within onemonth when the samples are kept in the absence of light at roomtemperature and without the exclusion of oxygen. This result sug-gests that attention must be given to the application of Arsenazo IIIin gamma radiation-related fields, and new analytical methodsneed to be developed for the quantitative determination of U(VI)in the presence of gamma radiation and ferrous iron. Moreover, be-cause the Fenton reaction is widely used in the degradation ofrefractory organic pollutants, this study also provides ideas toinvestigate the mechanisms in the degradation of refractory organ-ic pollutants. Further investigations on the influence of gammairradiation to the measurements of other elements with ArsenazoIII method are needed. Meanwhile, the influence on the migrationbehavior of radionuclides in the environment is also essential, forthe mobility of radionuclides in the environment may be highlyinfluence by the natural organic matters.

Acknowledgements

We acknowledge the financial support from the National Natu-ral Science Foundation of China (Grant Nos. 11075006, 91026010),

n on uranium determination by Arsenazo III in the presence of Fe(II)/Fe(III).

6 Z. Zheng et al. / Chemosphere xxx (2014) xxx–xxx

the Ministry of Education of the People’s Republic of China (GrantNos. 10021, 20120001110082), and the State Administration ofScience Technology and Industry for National Defence (GrantNos. 2007-840, 2012-851). The research leading to these resultshas been realized in the framework of the European Union’s Euro-pean Atomic Energy Community’s (Euratom) Seventh FrameworkProgramme FP7-Fission-2010 under grant agreement No. 269688(SKIN project).

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