Radiolytic decomposition of oxalic acid in nuclear power plant by gamma irradiation

doi:10.21203/rs.3.rs-3613558/v1

Download PDF

Research Article

Radiolytic decomposition of oxalic acid in nuclear power plant by gamma irradiation

https://doi.org/10.21203/rs.3.rs-3613558/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

The radiation-induced decomposition of oxalic acid was investigated. Co-60 was used for irradiation source and the efficiency of radiolytic decomposition was estimated using G-value and dose constant. Oxalic acid was successfully decomposed by ionizing radiation process of gamma irradiation. The removal of oxalic acid at 10 mM was 16.6, 36.5, 69.5, 83.4, and 92.2% for absorbed dose of 5, 10, 20, 30, and 50 kGy, respectively. The G-value and dose constant for radiolytic decomposition were highly dependent upon the initial concentration of oxalic acid. The G-values for radiolytic decomposition at 5 kGy were 0.82, 2.09, 7.25, 17.02 for initial concentrations of 1, 2, 5, and 10 mM, respectively, but those at 50 kGy were 0.03, 0.04, 0.07, 0.16. The dose constant for 1, 2, 5 and 10 mM were 0.1695, 0.1221, 0.0904, and 0.0536 1/kGy, respectively. The results of this study showed the possibility of ionizing radiation process to decompose decontamination agents in nuclear power plants.

Oxalic acid

Gamma irradiation

Decomposition

G-value

Dose constant

Chemical decontamination is a very effective way to reduce radionuclides and waste in various nuclear power plants. Several organic acids including oxalic acid are used to decontaminate oxide films or oxide deposits. After deploying Siemen’s permanganic acid-complexing organic reduction decontamination process (HP-CORD), oxalic acid was usually used for decontamination of water-cooled reactors such as pressurized power reactor and boiled water reactor. HP-CORD involves several steps accomplishing successive oxidation, complexation, solubilisation and separation of radionuclides (Gordeev et al. 2005; Gurbanov and Guliyeva 2007; Gurbanov et al. 2015). High efficient reduction and complexation potential of oxalic acid enables to reduce the amount of waste with very excellent decontamination results. After decontamination process, the contaminants are disposed into ion exchange resin, transferring low level radioactive water to another decontamination cycle. To perform sustainable decontamination process, oxalic acid should be completely oxidized without any by-product at the final step. Several advanced oxidation processes, including peroxide, ozone, Fenton, UV and ultrasound irradiation, developed and applied to remove decontamination agents (Esplugas et al. 2007; Klavarioti et al. 2009; Mohapatra et al. 2014; Wei et al. 2004). In HP-CORD process, oxidation of oxalic acid by reactive radicals is achieved by UV/peroxide process. However, to reduce complicate decontamination process steps, more efficient oxidation method of oxalic acid is required.

Among various advanced oxidation processes, radiolytic decomposition of organic acids has been studied in many works. With the possibility of radiation technology for wastewater treatment plants, several investigators showed excellent results to remove organic wastes. The ionizing radiation process is a very effective method to eliminate refractory organic matter, showing higher removal efficiency with a simple process step. The ionizing process by gamma irradiation has many advantages in achieving fast and clean, using large amount of reactive radical species and minimizing energy cost with compared to ozone and UV/hydrogen peroxide process. In addition, from the point of view of the formation of final products like water and carbon oxide, it is of interest to study radiolytic decomposition of oxalic acid (Basfar et al. 2005; Kim et al. 2017; Kimura et al. 2012; Mohamed et al. 2009).

In this study, the radiolytic decomposition of oxalic acid by gamma irradiation was investigated. The decomposition efficiency of oxalic acid was estimated by G-values and dose rate constants. This work shows the possibility of application of gamma irradiation to decompose oxalic acid in nuclear power plants.

Chemicals

All of chemicals were high-purity analytical grade. The initial concentrations of oxalic acid prepared at 1, 2, 5 and 10 mM. The initial pH value was adjusted to 2–3 at each test condition. The characteristics of oxalic acid are shown in Table 1. The ultrapure water was obtained from a Milli-Q system (Millipore).

Table 1

Characteristics of oxalic acid investigated in this study
Molecular weight (g/mol)	Solubility (g/L)	pK_a1	pK_a2
90.03	100	H₂C₂O₄↔ H⁺+ HC₂O₄⁻ 1.46	HC₂O₄⁻↔ H⁺+ C₂O₄²⁻ 4.40

Irradiation

Gamma irradiation was performed using a high-level ⁶⁰Co source at the Korea Atomic Energy Research Institute. The radiation activity of source was 1.47ⅹ10¹⁷ Bq with dose rate of 10 kGy/hr. The oxalic acid-containing sample solutions were placed into 15 mL glass screw cap bottles. Absorbed doses were 5, 10, 20, 30 and 50 kGy, and measured by the alanine-EPR dosimetry system. All tests were carried out at room temperature.

G-value calculation

The efficiency of radiolysis was measured by the radiation-chemical yields of target compounds. The G-value is defined as the number of molecules of a product formed or the change in a reactant per 100 eV of absorbed dose. It is calculated using the following equation.

$$\text{G}=\frac{R(6.023\times {10}^{23})}{D(6.24\times {10}^{16})}$$

Where R is the disappearance in the concentration of reactant, oxalic acid (M), D is the absorbed dose (Gy), 6.023x10²³ is Avogadro’s number and 6.24x10¹⁶ is the conversion factor from Gy to 100 eV/L.

Dose constant calculation

Dose constants were used to estimate the decomposition characteristics of oxalic acid by gamma irradiation. Radiolytic decomposition by gamma irradiation is usually considered as pseudo-first order reaction because of large amounts of radicals.

$$\text{C}={C}_{o}{e}^{-kD}$$

$$\text{ln}\frac{C}{{C}_{o}}=-kD$$

Where C is the concentration of oxalic acid after gamma irradiation (mM), C_o is the initial concentration of oxalic acid before gamma irradiation (mM), k is the dose constant (1/kGy) and D is the absorbed dose (kGy). The required dose constant for 50% and 90% decomposition of oxalic acid was calculated using the following equations.

$${D}_{0.5}=\frac{ln2}{k}$$

$${D}_{0.9}=\frac{ln10}{k}$$

Where D_0.5 and D_0.9 were the required doses for 50% and 90% decomposition of oxalic acid (kGy).

Analytical methods

The concentration of oxalic acid was determined by high performance liquid chromatography (Agilent 1200 Series, Agilent Technologies, USA) equipped with Rezex ROA-Organic Acid H+, (8%) 300×7.8 mm column. 0.005N H₂SO₄ was used for eluent and the flow rate of eluent was 0.5 mL/min.

Radiolytic decomposition of oxalic acid

The radiolytic efficiency of oxalic acid was compared between G-value and percentage removal. The G-value and removal of oxalic acid by gamma irradiation is shown in Fig. 1. The G-values for radiolytic decomposition increased with the initial concentration of oxalic acid. The G-values of 10 mM oxalic acid were 17.1, 6.5, 1.6, 0.6, and 0.2 for absorbed doses of 5, 10, 20, 30, and 50 kGy, respectively. Meanwhile, the G-value decreased with accumulated radiation dose but the removal increased. The removal efficiency of oxalic acid by gamma irradiation decreased with exposure time. The removal of oxalic acid at 10 mM was 16.6, 36.5, 69.5, 83.4, and 92.2% for absorbed dose of 5, 10, 20, 30, and 50 kGy, respectively.

Figure 1. The G-value and removal of oxalic acid by gamma irradiation.

When water molecules are radiated by gamma ray, active radicals, some molecular products and ions are generated as a consequence of the interaction between gamma ray and water. This includes oxidizing species such as hydroxyl radical and hydrogen peroxide as well as reducing species such as solvated electron and hydrogen atom. Approximate equal amount of oxidizing and reducing species are generated.

H₂O → [2.7]e⁻ _aq, [0.6]·H, [2.8]·OH, [0.45]H₂, [0.7]H₂O₂, [3.2]H⁺, [0.5]OH⁻

Where the numbers in parentheses show the yield of species production (G-value) in µmol/J at 100 eV. Gross reaction of water radiolysis at pH7 is given in brackets. Radiolytic decomposition of contaminants is usually initiated by radical species generated from water radiolysis. Solvated electron, hydroxyl radical and hydrogen atom radical are very reactive radicals to decompose oxalic acid. Some radical reactions in water by gamma irradiation are shown in Table 2 (Buxton 1998; Carrol and Mather 1992; Getoff 2002; Kartashova et al. 2000; Sato et al. 1978). Because radiolytic reactions are very complicate, almost reactions are competed one another. In addition, most radicals are recombined each other and their oxidizing/reducing power are decreased by radical recombination. Unless air is replaced by inert gas, radical species generated are affected by oxygen in the air. In the presence of oxygen, solvated electron and hydrogen atom radical are converted to oxidizing species (·HO₂ and O₂·⁻). The hydrogen peroxide generated from these species is of importance below pH 8. It is known that the reactivity of hydroperoxyl and superoxide anion radical is very low to decompose many organic contaminants. Nonetheless, it is expected that the remaining radical species after radical recombination are mainly ascribed to decompose oxalic acid. The amount of radical species is proportional to absorbed dose of gamma irradiation, indicating that higher concentration of radicals is generated at higher absorbed dose. However, as shown in Fig. 1, non-specific oxidation of radicals make more complicate reactions, lowering G-value of oxalic acid decomposition. Because many radicals are simultaneously involved in the decomposition of mother and daughter compounds, the fully understanding of oxalic acid removal by gamma irradiation cannot be simplified (Table 2).

Table 2

Radical reactions in water by gamma irradiation
Radical reactions in water	Reaction rate constant (1/M·s)
Radical reactions with ions; H⁺ + OH⁻ → H₂O ·H + OH⁻ → e⁻ _aq+ H₂O e⁻ _aq+ H⁺ → ·H ·OH ↔H⁺+O₂·⁻ H₂O₂↔ H⁺+·HO₂	k = 1.4x10¹¹ k = 2.2x10⁷ k = 2.3x10¹⁰ pK = 11.9 pK = 11.65
Radical recombination reactions; ·OH+·OH→ H₂O₂ ·OH + e⁻ _aq → OH⁻ ·OH+·H→ H₂O e⁻ _aq+ e⁻_aq→ 2OH⁻+ H₂ e⁻ _aq+ ·H → OH⁻ + H₂ ·H+·H → H₂ ·HO₂+·HO₂→ H₂O₂ + O₂	k = 5.5x10⁹ k = 3.0x10¹⁰ k = 7.0x10⁹ k = 5.0x10⁹ k = 2.5x10¹⁰ k = 1.0x10¹⁰ k = 8.3x10⁵
Radical reaction with oxygen; ·H + O₂ → ·HO₂ e⁻ _aq + O₂ → O₂·⁻ ·HO₂ + O₂·⁻→ H₂O₂ + O₂ ·HO₂↔H⁺+ O₂·⁻	k = 2.1x10¹⁰ k = 1.9x10¹⁰ k = 9.7x10⁷ (pH < 7) k = 8.0x10⁵ (pK = 4.8)

Decomposition characteristics of oxalic acid

The dose constants, k, at different initial concentrations of oxalic acid are shown in Fig. 2. The dose constants for 1, 2, 5 and 10 mM oxalic acid were 0.1695, 0.1221, 0.0904, and 0.0536 1/kGy, respectively. It was shown that the dose constant was significantly affected by G-value gap at each initial concentration. The G-values for radiolytic decomposition at 5 kGy were 0.82, 2.09, 7.25, 17.02 for initial concentrations of 1, 2, 5, and 10 mM, respectively, but those at 50 kGy were 0.03, 0.04, 0.07, 0.16. Compared to radiolytic oxidation of oxalic acid at lower initial concentration, it was referred that reactive radicals generated the large amount of intermediates at higher concentration. Non-specific attack of radicals usually leads to lower G-value at radiolytic decomposition. In addition, the dose constant exponentially decreased with the initial concentration of oxalic acid. The decrease of dose constant at lower the initial concentration (below 2 mM) was 5.6 times as high as that at higher the initial concentration (above 2mM). G-value is closely related to the dose constant because G-value implies the efficiency of radiolytic decomposition. The lower efficiency of radiolytic decomposition results in sharp decrease of dose constant. In this investigation, the reflection point concentration for dose constant decrease was 2 mM.

Figure 2. Oxalic acid gamma irradiation at different initial concentrations.

The difference between G-value at each dose and that at 5 kGy for the initial concentration are shown in Table 3 and Fig. 3. The difference of G-value was obtained by subtracting G-value at each dose from that at 5 kGy. Although over 62% difference of G-value was observed at 10 kGy, it was distinctly significant at higher dose. This gave rise to lower dose constant at high the initial concentration of oxalic acid. The greatest difference of G-value at each dose was distributed at different concentration of oxalic acid. As shown in Table 3, the initial concentrations for the greatest difference of G-values were 2, 5, 5 and 10 mM at doses of 10, 20, 30 and 50 kGy, respectively. Interestingly, the decrease of dose rate was inversely proportional to the initial concentration for the greatest difference of G-values. This evidently shows that the dose constant at each the initial concentration was highly affected by G-value. It was referred that the decrease of dose constant was mainly caused by lower G-value at higher the initial concentration of oxalic acid (Buxton 1998; Getoff 2002).

Table 3

Difference between G-value at each dose and that at 5 kGy
Concentration (mM)	Difference of G-value (%)
Concentration (mM)	10 kGy	20 kGy	30 kGy	50 kGy
1	78.0	89.0	92.7	96.3
2	80.9	94.7	96.7	98.1
5	69.7	95.4	98.2	99.0
10	61.7	90.8	96.7	99.1

Figure 3. Relationship between difference of G-value and dose constant.

The dose constant, k, was used to calculate the dose required to produce 50% and 90% oxalic acid degradation (D_0.5 and D_0.9 values). D₅₀ and D₉₀ of oxalic acid gamma irradiation at different initial concentrations is shown in Fig. 4.The variation of D_0.5 values was not too high. D_0.5 values increased from 4.1 to 12.9 kGy for the initial concentration of 1 to 10 mM. Meanwhile, to obtain 90% removal at 10 mM oxalic acid, 43.0 kGy was required. The differences between D_0.9 and D_0.5 values for the initial concentration of 1, 2, 5, and 10 mM were 9.5, 13.2, 17.8, and 30.0 kGy, respectively. This shows that the decomposition of oxalic acid at higher concentration was difficult more than that at lower concentration because of large number of generated intermediates. In this study, most oxalic acid existed as hydrogen oxalate at pH between 1.46 and 4.40. Some reactions of hydrogen oxalate by gamma radiation are shown in Table 4 (Buxton 1998; Carrol and Mather 1992; Getoff 2002; Kartashova et al. 2000; Sato et al. 1978). During gamma irradiation, decomposition of oxalic acid was mainly carried out by oxidizing and reducing radical species. Organic radicals are also involved in the radiolytic decomposition of hydrogen oxalate. The main radiolytic intermediates of hydrogen oxalate are glyoxylic acid, tartaric acid and formic acid. It was guessed that these intermediates significantly decreased G-value and dose constant, especially at higher initial concentration. To fully understand oxalic acid decomposition by gamma irradiation, it is required to involve some computer simulations such as diffusion-kinetic model. Nonetheless, it is expected that the application of gamma irradiation for decomposing oxalic acid can be alternative process for cost intensive UV/hydrogen peroxide process.

Table 4

Some radiolytic reactions of hydrogen oxalate by gamma irradiation
Radical reactions of hydrogen oxalte	Reaction rate constant (1/M·s)
Radical reaction with hydrogen oxalate; HC₂O₄⁻+·OH → H₂O + CO₂ +·COO⁻ HC₂O₄⁻+ e⁻ _aq → HC₂O₂(OH)₂+2OH⁻ HC₂O₄⁻+ ·H → HC₂O₂(OH)₂+OH⁻ ·COO⁻+H⁺→·COOH ·COOH + H₂O₂→·OH + H₂O + CO₂ HC₂O₂(OH)₂+ HC₂O₂(OH)₂→ H₂C₂O₄ + H₂C₂O₃ HC₂O₂(OH)₂+ HC₂O₂(OH)₂→(HC₂O₂(OH)₂) ₂ HC₂O₂(OH)₂+ ·COOH → H₂C₂O₂COOH HC₂O₂(OH)₂+ H₂O₂→ ·OH + H₂O + H₂C₂O₄	k = 1.9x10⁷ k = 3.2x10⁹ k = 1.6x10⁴ k = 1.0x10¹⁰ k = 5.0x10⁷ k = 1.0x10⁸ k = 1.0x10⁸ k = 1.0x10⁹ k = 1.0x10⁵
Recombination radical reaction; ·COO⁻+·COO⁻→C₂O₄²⁻ ·COOH+·COOH→H₂C₂O₄ ·COOH+·COOH→HCOOH + CO₂	k = 1.0x10⁸ k = 4.0x10⁸ k = 5.0x10⁸
Radical reaction with oxygen; ·COO⁻+ O₂→ CO₂ + O₂ ·COOH + O₂→ CO₂+·HO	k = 2.0x10⁹ k = 2.0x10⁹

Figure 4. D₅₀ and D₉₀ of oxalic acid gamma irradiation at different initial concentrations.

Studying the degradation of decontamination agents by gamma irradiation provides insights into fundamental chemical and radiolytical processes in nuclear power plants. It can help elucidate reaction mechanisms, identify intermediate products, and assess the effects of radiation on decontamination agents. Oxalic acid was successfully degraded by gamma irradiation. 92% removal of oxalic acid was obtained at the initial concentration of 10 mM. The dose constant and G-value of radiolytic oxalic decomposition were severely affected by the initial concentration. The dose constant ranged from 0.1695 to 0.0536 1/kGy and decreased with the initial concentration of oxalic acid. G-value was inversely proportional to dose constant, but the difference of G-value at each dose was negligible at higher dose due to the radiolytic intermediates production. These results ensured that the ionizing radiation process by gamma irradiation can be applied for the decomposition of oxalic acid in nuclear power plants.

Acknowledgements

This work was supported by the Technology development Program(S3324880) funded by the Ministry of SMEs and Startups(MSS, Korea).

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Seung Joo Lim and Wang Kyu Choi. The first draft of the manuscript was written by Seung Joo Lim and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.”

Data availability

Enquiries about data availability should be directed to the authors. Data will be made available on request.

Funding

The authors declare that no fund was received for the current research.

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.

Basfar AA, Khan HM, Al-Shahrani AA, Cooper WJ (2005) Radiation induced decomposition of methyl tert-butyl ether in water in presence of chloroform: kinetic modelling, Water Res 39:2085-2095.
Buxton AW (1988) Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals in aqueous solutions. Phy Chem Ref Data 17:513.
Carrol JJ, Mather AE (1992) The system carbon dioxide-water. J Solu Chem 21:607-662.
Criquet A, Leitner NKV (2012) electron beam irradiation of citric acid aqueous solutions containing persulfate. Sep Puri Technol 88: 168-173.
Esplugas S, Bila DM, Krause IGT Dezotti M (2007) Ozonation and advanced oxidation technologies to remove endocrine disrupting chemicals (EDCs) and pharmaceuticals and personal care products (PPCPs) in water effluents. J Hazard Mat 149: 631-642.
Getoff N (2002) Factors influencing the efficiency of radiation-induced degradation of water pollutants. Radia Phy Chem 65: 437-446.
Gordeev AV, Ershov BG, Kosareva IM (2005) A diffusion-kinetic model for radiation-chemical transformations of oxalic acid and oxalate ions in aqueous solutions. Radiat Chem 39: 250-254.
Gurbanov MA, Guliyeva UA (2007) Study of gamma radiolysis of aqueous formic and oxalic acid solutions by UV- spectroscopy. J Radiat Res 55: 4820-4827.
Gurbanov M, Guliyeva U, Mammadov S, Mahmudov H (2015) Radiation-chemical degradation of oxalic acid in water solution. J Chem Chem Eng 9: 353-356.
Kartashova LI, Chulkov VN, Didenko OE, Pikayev AK (2000) Hydrogen peroxide yields in the radiolysis of aerated aqueous solutions of formic acid. High Eng. Chem. 34: 467-469.
Kim HY, Kim T, Cha SM, Yu S (2017) Degradation of sulfamethoxazole by ionizing radiation: Identification and characterization of radiolytic products. Chem Eng J 313: 556-566.
Kimura A, Osawa M, Taguchi M (2012) Decomposition of persistent pharmaceuticals in wastewater by ionizing radiation. Radiat Phys Chem 81: 1508-1512.
Klavarioti M, Mantzavinos D, Kassinos D (2009) Removal of residual pharmaceuticals from aqueous systems by advanced oxidation processes, Environ. Int 35: 402-417.
Mohamed KA, Basfar AA, Al-Shahrani AA (2009) Gamma-ray induced degradation of diazinon and atrazine in natural groundwaters. J Hazard Mat 166: 810-814.
Mohapatra DP, Brar SK, Tyagi RD, Picard P, Surampalli RY (2014) Analysis and advanced oxidation treatment of a persistent pharmaceutical compound in wastewater and wastewater sludge-carbamazepine. Sci Tot Environ 470-471: 58-75.
Sato K, Takmito K, Tsuda S (1978) Degradation of aqueous phenol solution by gamma irradiation. Env Sci Technol 12: 1043-1046.
Wei R, Ge F, Huang S, Wang R (2004) Occurrence of veterinary antibiotics in animal wastewater and surface water around farms in jingsu Province, China. Chemosphere 82: 1408-1414.

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

Radiolytic decomposition of oxalic acid in nuclear power plant by gamma irradiation

Status:

Version 1

Abstract

Figures

Introduction

Materials and methods

Chemicals

Irradiation

G-value calculation

Dose constant calculation

Analytical methods

Results and discussion

Radiolytic decomposition of oxalic acid

Decomposition characteristics of oxalic acid

Conclusions

Declarations

References

Additional Declarations

Status:

Version 1