E-Journal of Advanced Maintenance Vol.9-2 (2017) 145-151
Japan Society of Maintenology

Treatment of spent radioactive cationic exchange resins used in nuclear
power plants by Fenton-like oxidation process
Xu Lejin1,2*, Sui Zengguang1, Yang Jun1, Wan Zhong2 and Wang Jianlong2
1

Nuclear Engineering and Technology Department, School of Energy and Power Engineering,
Huazhong University of Science & Technology, Wuhan 430074, PR China
2
Collaborative Innovation Center for Advanced Nuclear Energy Technology, INET, Tsinghua
University, Beijing 100084, PR China
ABSTRACTFenton and Fenton-like oxidation processes have been developed to effectively disintegrate and mineralize spentradioactive ion exchange resins from nuclear power plants. In this paper, the degradation of spent cationic resins
by Fenton-like process for chemical oxygen demand (COD) removal and weight reduction was investigated.
The effects of initial pH, Cu2+ concentration and H2O2 dosage on resin degradation by the Cu2+/H2O2 oxidation
process was studied. The results showed that lower initial pH value brought higher COD removal rate. With theincreasing amount of Cu2+ concentration and H2O2 dosage, the COD removal rate of resins first increased andthen decreased. The degradation efficiency (in term of COD removal rate) and weight reduction percentages
were 99% and 39%, respectively, at pH 0.75 and T 95 C with 0.2 M Cu2+, and 35 mL 30% H2O2. The scanningelectron microscopy images provided the information of morphological changes of resin during the dissolution
process, which clearly revealed the degradation of resins.
KEYWORDS

ARTICLE INFORMATION

Spent radioactive resin, Fenton-like oxidation, Treatment, COD removal,
Weight reduction, Morphological change

Article history:
Received 7 November 2016
Accepted 27 April 2017

1.

Introduction

During the operation of the nuclear facilities in the nuclear power plants, ion-exchange resins(IERs) are used for removing the radioactive contaminants such as neutron activation products andfission products leaked from fuel elements, recycling of nuclear fuel, purification of radioactive
wastewater and so on [1‒3]. The spent radioactive IERs should be properly treated and disposed tominimize their potential hazard to the environments.
Various technologies have been developed for the treatment and disposal of spent radioactive
resins, including super compaction, immobilization (such as cementation and bituminization) andadvanced oxidation processes (such as supercritical water oxidation, Fenton reactions and plasmatechnology) [4]. The application of these technologies is limited because of the properties of spentradioactive resins, such as containing radionuclides, inflammability, diffusion, swellability, and so on.
The common treatment of resins, i.e. immobilization [5,6], will cause the volume increase, leading to
the high expense of transportation and management. Thus, several methods to reduce and stabilize theradioactive waste before immobilization have been studied, e.g. incineration [7], pyrolysis [8], Fenton
reactions [2,3].
Used as the pretreatment method before immobilization, the process flow diagram of the wet
catalytic oxidation is shown in Fig. 1 [9]. The spent resins are transformed from a solid phase into aliquid phase by the reaction of H2O2 with catalyst. After evaporation or concentration, the condensed
solution is further immobilized in cement. The off-gas produced from the process does not containradioactive contamination, which can be vented directly. Catalyst (metal ion, represented as M2+)
reacts with H2O2 (namely Fenton-like process) producing various short-lived oxidative species, viz.
*Corresponding author, Tel.: 027 87540164, E-mail: xulejin@hust.edu.cn
Present address: Power Energy Building, 1037 Luoyu Road, Wuhan 430074, China

ISSN-1883-9894/10 © 2010 – JSM and the authors. All rights reserved.

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L. J. Xu, et al./ Treatment of spent radioactive cationic exchange resins
Used in nuclear power plants by Fenton-like oxidation process•OH and HOO•, as described in reactions (1) and (2) [3]. These radicals attack on the polymer matrix
for dissolution of cationic resins, as described in Eqs. (3) and (4) [10]. Functional groups of cationicresins, represented as C8H8SO3, are dissolved and decomposed into low molecular organics such as
styrene monomer and divinyl benzene by reactive oxidants (Eq. 3). The reactions of divinyl benzene
and styrene monomer are presented in Eqs. (6) and (7), showing that these low molecular organics areeven mineralized to carbon dioxide and water.
Off gas emission

Condenser

H 2O 2Reactor

Condensed solution

Catalyst

Immobilization (e.g. cement solidification)

Fig. 1. Schematic diagram of the wet catalytic oxidation process for resin treatment.

M(n-1)+ + H2O2 → Mn+ + •OH + OH– (M = Fe, Cu…)
Mn+ + H2O2 → M(n-1)+ + HOO• + H+
•OH + HOO• + resin → linear polystyrene (soluble) + CO2↑ + SO42- + H2O•OH + HOO• + linear polystyrene → simple organic substrates + CO2↑ + H2O
C8H8SO3 + 20H2O2 → 8CO2 + 23H2O + H2SO4
C8H8 + 20H2O2 → 8CO2 + 24H2O
C10H10 + 25H2O2 → 10CO2 + 30H2O

(1)
(2)
(3)
(4)
(5)
(6)
(7)

In this work, the disintegration and dissolution of cationic resins by Fenton-like process wasstudied. The effects of initial pH and concentrations of Fenton reagents (i.e. Cu2+ and H2O2) on
cationic resin dissolution were investigated. The morphological changes of the cationic resins during
the dissolution process were also observed by scanning electron microscope (SEM).

2.

Materials and Methods

2.1. Resins and Chemicals
Amberlite INR77 cationic resin was supplied by ROHM & HAAS, which is the strong acidstyrene-divinylbenzene copolymer as shown in Fig.2. The characteristics of cationic resin are asfollows: physical form: amber translucent beads; functional group: sulfonic acid; particle size: 0.6‒0.7mm; degree of cross-linking: 8%; total volume capacity: 1.8 eq/L; moisture content: 49.5% (w/w).
After usage, the typical performances of the spent resins from a nuclear power plant were listed inTable 1.
H3C

CH

SO3H

CH2

H3C

CH

CH3

CH

CH2

CH

CH3

SO3H

Fig. 2. Structure of cationic exchange resin.

Analytical grade chemicals, including H2O2 (30% v/v in water), CuSO4·5H2O and NaOH, wereobtained from the Beijing Chemical Factory. Distilled water was used throughout this study.

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L. J. Xu, et al./ Treatment of spent radioactive cationic exchange resins
Used in nuclear power plants by Fenton-like oxidation process

Table 1 Typical performance of the spent radioactive ion-exchange resins from a nuclear power plant

Water content

52%

Wet density

1.110 g/mL

Cs-1373.510 × 103 Bq/kg

Co-60

0.3335 × 103 Bq/kg

Sr-90

0.5200 × 103 Bq/kg

2.2. Experimental Procedures
All experiments were conducted in a four-necked round-bottom flask (250 mL), which wasplaced in a water bath controlled at a constant temperature (95 °C). A mixture of 20 g resins and 30mL CuSO4·5H2O solution was added into the reactor, and its initial pH was adjusted by NaOH. Resins
were violently stirred by a mechanical stirrer with the speed of 150 rpm. The experiments wereinitiated by adding a given amount of H2O2 at flow rate of 1.25 mL/min to the solution, andCuSO4·5H2O solution was continuously added at 0.58 mL/min. Samples were taken at a given timeintervals during the reaction. After 100 min, the reaction was stopped. The weight of residue wasmeasured after dried in a vacuum oven at 100 °C for three days.
2.3. Analytical Methods
The chemical oxygen demand (COD) is an indicative measure used to quantify the amount oforganics in water. According to the basis of the COD test, nearly all organic compounds can be fully
oxidized to carbon dioxide with a strong oxidizing agent under acidic conditions. The COD
measurement for the dissolved resin solution was based on digestion with potassium dichromate inconcentrated sulphuric acid for 15 min at 165 °C with DRB200 of HASH, USA. The absorbance wasobtained with a LAMBDA 25 UV/vis spectrophotometry made in PerkinElmer, USA. The pH value
was measured by a Thermo Orion 8103BN pH-meter, USA. The scanning electron microscopy (SEM)
observation was done by using FEI Quanta 200 FEG ESEM instrument of FEI Company.
The weight reduction rate was calculated by the following equation:(8)
Weight reduction rate = (1 - w/w0)  100%
where w is the weight of residue, and w0 is the weight of original dry resin. After dried for three days,
the weight of 20 g cationic resin is 10.16 g.

3. Results and Discussion
3.1. Effect of Initial pH
With the initial temperature of reactor maintained at 95 °C, the influence of pH on resin
degradation by the Cu2+/H2O2 oxidation process was studied at three different pH values of 0.75, 1.50
and 2.25, as shown in Fig. 3. When the resins were decomposed completely after 30 min reaction,
samples were taken, and COD values were analyzed to represent the degree of resin degradation. It
can be seen that COD value was the lowest at pH 0.75, indicating that the degradation of resin was
more efficient at lower pH value. The final COD value was about 5 g/L (corresponding to about 0.25
g resin [2]) at pH 0.75, and the COD removal rate was about 99%. When initial pH values are 0.75
and 1.50, COD values increased from 30 min to 50 min, which could be ascribed to the continuous
dissolution of resins.

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L. J. Xu, et al./ Treatment of spent radioactive cationic exchange resins
Used in nuclear power plants by Fenton-like oxidation process

1000.75
1.50
2.25

COD (g/L)

8060402002030405060708090100110Time (min)Fig. 3. Effect of pH on resin decomposition (35 mL 30% H2O2, [Cu2+] = 0.2 M, T0 = 95 C)

The mechanism through which the Cu2+/H2O2 system produces oxidants involves strikingly
similar redox reactions like Fe2+/H2O2 system [11]. Both the divalent (Cu2+) and monovalent (Cu+)
oxidation states react easily with H2O2 (Equations 9 and 10), generating reactive oxidants, mainlyhydroxyl radicals (•OH). According to reaction (9), with the increase of initial pH value, theconcentration of OH– increases, resulting in less •OH formed in the solution. Moreover, higher pH
values enhance the decomposition of H2O2, lower the oxidation potential of •OH, and reduce theproduction of •OH, which finally decrease the dissolution and degradation of resins [12].
Cu+ + H2O2 → Cu2+ + •OH + OH– (k = 1.0 × 104 M-1s-1)(9)
2+++2-1 -1
Cu + H2O2 → Cu + HOO• + H (k = 4.6 × 10 M s )(10)
3.2. Effect of Catalyst Concentration
The effect of catalyst concentration on resin degradation was investigated using Cu2+ as catalyst
over a range of 0.1‒0.3 M at pH 0.75 and T 95 C with 35 mL 30% H2O2 (Fig. 4). As the Cu2+concentration increased from 0.1 M to 0.2 M, COD values decreased, suggesting that the resin
degradation was enhanced, because of the increasing reactive free radicals formed. However, when
the Cu2+ concentration was increased to 0.3 M, resin degradation was not further enhanced but
decreased, attributed to the scavenging of reactive free radicals through undesirable reactions (11‒13)[3]. Hence, the best Cu2+ concentration of 0.2 M for the effective resin degradation was obtained.
Cu+ + •OH → Cu2+ + OH–(11)(12)
Cu+ + HOO• → Cu2+ + HO2–
Cu2+ + HOO• → Cu+ + O2 + H+(13)148

L. J. Xu, et al./ Treatment of spent radioactive cationic exchange resins
Used in nuclear power plants by Fenton-like oxidation process

100

0.1 M
0.2 M
0.3 M

COD (g/L)

8060

40

2002030405060

70

80

90100

110

Time (min)Fig. 4. Effect of Cu2+ concentration on resin decomposition (pH 0.75, 35 mL 30% H2O2, T0 = 95 C)

3.3. Effect of H2O2 Dosage
The obtained results for resin degradation as a function of H2O2 dosage at various reaction times
with pH 0.75 and 0.2 M Cu2+ at 95 C are displayed in Fig. 5. It should be noted that after 30 min
reaction when the H2O2 dosages are 20 mL and 50 mL, there were still some solid resin beads left inthe solution obviously. Thus, when the reaction time increased from 30 min to 45 min, the continuous
dissolution of resins could lead to the increase of COD value. When H2O2 dosage increased from 20mL to 35 mL, the resin oxidation was obviously accelerated, mainly due to the increasing amount ofreactive oxidants produced. Nevertheless, for a higher dosage (50 mL), the degradation degree was
not enhanced but a little decreased, due to the scavenging effect of •OH by H2O2. As expressed by Eq.
(14), although other radicals (HOO• and O2•-) are formed, they are much less reactive than •OH,
which may be neglected [13]. Thus, the optimum H2O2 dosage was 35 mL in this experiment.
H2O2 + •OH → HOO•/O2•- + H2O(14)10020 mL
35 mL50 mL

COD (g/L)

8060

402002030405060708090100110Time (min)Fig. 5. Effect of H2O2 dosage on resin decomposition (pH 0.75, [Cu2+] = 0.2 M, T0 = 95 C)

3.4. Morphological Change of Resin
The SEM analyses were performed before and after resin disintegration process at the optimized
condition (pH 0.75, 35 mL 30% H2O2, [Cu2+] = 0.2 M, T0 = 95 C). As shown in Fig. 6a, resins are thesmooth spherical uniform beads with the diameter of 425‒475 µm. After 10 min Fenton-like oxidation

149

L. J. Xu, et al./ Treatment of spent radioactive cationic exchange resins
Used in nuclear power plants by Fenton-like oxidation process(Fig. 6b), the individual beads stuck together, and the solidified resins were split and dissolved,
resulting from the attack of hydroxyl radicals. After about 30 min reaction, resins were almost
completely dissolved. At last (100 min), the weight of residue was 6.2 g with the weight reduction rateof 39%.

(a)

(b)

Fig. 6. SEM images of resin (a) before and (b) after 10 min reaction (pH 0.75, 35 mL 30% H2O2, [Cu2+] =0.2 M, T0 = 95 C)

4.

Conclusions

Fenton-like oxidation process using Cu2+ as catalyst has proven to be effective for thedecomposition of cationic exchange resins. The experimental results showed that the degradation ofspent cationic resins was affected by initial pH, Cu2+ concentration and H2O2 dosage, and the best
reaction conditions were obtained as follows: pH 0.75, 0.2 M Cu2+, and 35 mL 30% H2O2. Under theabove conditions, percentages of COD and weight reduction were 99% and 39%, respectively. SEM
images provided an intuitive way to observe the morphological changes of resin during the dissolution
process. This process is very efficient for the disintegration and dissolution of cationic resins, which
can be used as the pretreatment method before immobilization for volume and weight reduction.

Acknowledgement
The research was supported by the National Natural Science Foundation of China (Grant No.
51348008) and the General and Special Financial Grant from the China Postdoctoral Science
Foundation (Project No. 2012M520302, 2013T60131).

References[1] N. E. Bibler, E. G. Orebaugh: ''Iron-catalyzed dissolution of polystyrenesulfonate cation-exchange resin inhydrogen peroxide'', Ind. Eng. Chem. Prod. Res. Dev., Vol. 15, No. 2, pp. 136‒138 (1976).
[2] Z. Wan, L. J. Xu, J. L. Wang: ''Disintegration and dissolution of spent radioactive cationic exchange resinsusing Fenton-like oxidation process'', Nucl. Eng. Des., Vol. 291, pp. 101‒108 (2015).
[3] Z. Wan, L. J. Xu, J. L. Wang: ''Treatment of spent radioactive anionic exchange resins using Fenton-likeoxidation process'', Chem. Eng. J., Vol. 248, pp. 733‒740 (2016).
[4] J. L. Wang, Z. Wan: ''Treatment and disposal of spent radioactive ion-exchange resins produced in thenuclear industry'', Prog. Nucl. Energy, Vol. 78, pp. 47‒55 (2015).
[5] J. F. Li, J. L. Wang: ''Advances in cement solidification technology for waste radioactive ion exchange
resins: A review'', J. Hazard. Mater, Vol. 135, No. 1‒3, pp. 443‒448 (2006).
[6] I. Plecas, A. Peric, S. Glodic, A. Kostadinovic: ''Comparative leaching studies of 60Co from spentradioactive ion-exchange resin incorporated in cement'', Cement Concrete Res., Vol. 25, No. 2, pp.
314‒318 (1995).

150

L. J. Xu, et al./ Treatment of spent radioactive cationic exchange resins
Used in nuclear power plants by Fenton-like oxidation process[7]

K. Kinoshita, M. Hirata, T. Yahata: ''Treatment of ion-exchange resins by fluidized bed incinerator
equipped with copper oxide catalyst fundamental studies'', J. Nucl. Sci. Technol., Vol. 28, No. 3, pp.
228‒238 (1991).
[8] U. Chun, K. Choi, K. Yang, J. Park, M. Song: ''Waste minimization pretreatment via pyrolysis andoxidative pyrolysis of organic ion exchange resin'', Waste Manage., Vol. 18, No. 3, pp. 183‒196 (1998).
[9] Y. C. Ye, S. N. Yu: ''Stabilization and volume reduction of radioactive spent ion exchange resins'', Nucl. Sci.
Tech., Vol. 12, No. 1, pp. 68‒72 (2001).
[10] X. C. Jian, T. B. Wu, G. C. Yun: ''A study of wet catalytic oxidation of radioactive spent ion exchange
resin by hydrogen peroxide'', Nucl. Saf., Vol. 37, No. 2, pp. 149‒157 (1996).
[11] A. D. Bokare, W. Choi: ''Review of iron-free Fenton-like systems for activating H2O2 in advanced
oxidation processes'', J. Hazard. Mater, Vol. 275, No. 2, pp. 121‒135 (2014).
[12] L. J. Xu, J. L. Wang: ''A heterogeneous Fenton-like system with nanoparticulate zero-valent iron foroxidation of 4-chloro-3-methyl phenol'', J. Hazard. Mater., Vol. 186, No. 1, pp. 256‒264 (2011).
[13] Q. Liao, J. Sun, L. Gao: ''Degradation of phenol by heterogeneous Fenton reaction using multi-walledcarbon nanotube supported Fe2O3 catalysts'', Colloids Surf. Physicochem. Eng. Aspects, Vol. 345, No. 1‒3,pp. 95‒100 (2009).

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