Journal Search Engine

to

Search Advanced Search Adode Reader(link)
View PDF Download PDF Export Citation Korean Bibliography PMC Previewer
ISSN : 1738-1894(Print)
ISSN : 2288-5471(Online)
Journal of Nuclear Fuel Cycle and Waste Technology Vol.22 No.2 pp.159-171
DOI : https://doi.org/10.7733/jnfcwt.2024.020

An Efficient Sulfuric Acid- and Hydrazine-based Process for Recycling Wastewater Generated From U(VI)-Contaminated Soil-Washing

Hyun-Kyu Lee, Byung-Moon Jun, Tack-Jin Kim, Sungbin Park, Seonggyu Choi, Jun-Young Jung, Hee-Chul Eun*
Korea Atomic Energy Research Institute, 111, Daedeok-daero 989beon-gil, Yuseong-gu, Daejeon 34057, Republic of Korea
* Corresponding Author. Hee-Chul Eun, Korea Atomic Energy Research Institute, E-mail: ehc2004@kaeri.re.kr, Tel: +82-42-868-2712

March 26, 2024 ; May 13, 2024 ; June 11, 2024

Abstract


This study aimed to develop an efficient recycling process for wastewater generated from soil-washing used to remediate uranium (U(VI))-contaminated soil. Under acidic conditions, U(VI) ions leached from the soil were precipitated and separated through neutralization using hydrazine (N2H4). N2H4, employed as a pH adjuster, was decomposed into nitrogen gas (N2), water (H2O), and hydrogen ions (H+) by hydrogen peroxide (H2O2). The residual N2H4 was precipitated when the pH was adjusted using sulfuric acid (H2SO4) to recycle the wastewater in the soil-washing process. This purified wastewater was reused in the soil-washing process for a total of ten cycles. The results confirmed that the soil-washing performance for U(VI)-contaminated soil was maintained when using recycled wastewater. All in all, this study proposes an efficient recycling process for wastewater generated during the remediation of U(VI)-contaminated soil.


Soil-washing , Uranium precipitation , Hydrazine decomposition , Wastewater treatment , Water recycling

초록

    1. Introduction

    The predominant greenhouse gases in Earth’s atmosphere include carbon dioxide (CO2), methane, nitrous oxide, and fluorinated gases [1, 2]. Particular focus has been placed globally on reducing CO2 emissions [3]. CO2 is generated through the combustion of fossil fuels such as coal, natural gas, and oil. Therefore, the use of alternative energy sources to replace fossil fuels, such as nuclear energy and renewable energy (e.g., solar, hydro, and wind), is critical for the sustainability of both humanity and ecosystems [4- 7]. Nuclear energy has a high energy density and provides a more stable electricity source compared with renewable energy [8-10]. However, one of the environmental problems associated with nuclear energy production is the generation of radioactive waste. The toxic nature of uranium (U), used as fuel in nuclear power generation, is widely known to cause various health issues in the human physiological system (e.g., liver and kidney) [11].

    In oxidizing environments, U typically exists as the soluble uranyl (UO22+) ion, which exhibits notable mobility [12]. Consequently, it easily migrates into media such as soil and water through pathways such as adsorption, ion exchange, and solubilization. Hence, in the event of unexpected incidents such as nuclear leakage, improper disposal, or abnormal system operation during nuclear power generation, the risk exists for U to easily disperse into the surrounding environment. This study focuses on methods to remediate environments contaminated with U. To this end, a series of treatment processes are proposed to purify U(VI)-contaminated soil and to treat U(VI) effluents. The selection of radioactive waste treatment methods should be based on factors such as the radioactive composition and the release procedure in the process flow [13] because radioactive materials, even with very low concentrations of radioactive isotopes compared with nonradioactive contaminants, exhibit high radiotoxicity and different behaviors [14]. Various studies on remediation methods for Ucontaminated soil, including soil-washing, electrokinetic extraction, vitrification, and phytoremediation, have been reported [15-17]. Although several treatment methods for cleaning U-contaminated radioactive soil have been developed, a method that minimizes the generation of secondary radioactive waste during the treatment process should be selected [18]. Meanwhile, the U oxidation states range from +0 (unstable) to +3 (red), +4 (green), and +6 (yellow). U ions are soluble in water; however, their solubility varies depending on the presence of inorganic ligands such as OH−, HCO 3 - , CO 3 2 - , and PO 4 3 - [19, 20]. The recovery of U from aqueous solutions has been extensively researched, and various methods, including solvent extraction, coprecipitation, ion-exchange, and sorption, have been explored for this purpose [21-24].

    We have reported several research outcomes in which U-contaminated soil was remediated using the soil-washing method, where U(VI) ions in a U(VI)-containing effluent were precipitated and removed [25-28]. Under acidic conditions, U is leached from U(VI)-contaminated soil and the leached U ions (i.e., UO22+) are separated as precipitates through a neutralization treatment using sodium hydroxide (NaOH). In the present study, we advanced previous research findings to establish a more efficient treatment process for U(VI)-contaminated soil. Our primary focus was on reducing the volume of effluent generated from soil-washing and minimizing the generation of secondary solid waste. To achieve these objectives, we used decomposable hydrazine (N2H4) as a precipitant for U(VI) ions. Several studies applying acidified hydrazine to soil decontamination have been reported, but it is difficult to find cases of using hydrazine to treat soil decontamination wastewater [29, 30]. By using N2H4 as a precipitant instead of NaOH, only OH− is supplied, and N2H4 can be decomposed with H2O2. This method reduces the amount of solid waste generated by preventing the accumulation of salts such as Na+. We explored a recycling process in which the effluent generated during the washing process of U(VI)-contaminated soil is purified and subsequently reused as the washing effluent in the soil-washing step. After comprehensively reviewing the experimental results, we proposed an efficient recycling process concept for the remediation of U(VI)-contaminated soil, including the effluent treatment process.

    2. Materials and Methods

    2.1 Materials

    Sulfuric acid (H2SO4, 98%), H2O2 (30%), and NaOH (98%) were obtained from Duksan Chemicals (South Korea). Hydrazine monohydrate (N2H4∙H2O, 98%) was purchased from KANTO (Japan). Deionized water was obtained from a water purification system (aquaMAX Basic 360, Younglin, South Korea). The U(VI)-contaminated soil used in the study was sampled from soil accumulated in the waste storage facility of the Korea Atomic Energy Research Institute. The initial concentration of U(VI) in the contaminated soil varied from 50 to 169 Bq∙g−1, depending on the soil particle size.

    2.2 U(VI)-contaminated Soil-Washing

    The U(VI)-contaminated soil intended for soil washing was prepared by blending soils with various initial U(VI) concentrations and particle sizes (Fig. 1). The initial U(VI) concentration of the mixed soil was 91.5 Bq·g−1 (7,412 mg·L−1). The uranium concentration of 1 Bq·g−1 was converted to 81 mg·L−1) (Table 1). The U(VI)-contaminated soil-washing process was based on our previous research [25]. Briefly, it was conducted as follows: A washing agent of 0.5 M H2SO4 (approximately pH 0) was used to leach U(VI) from the soil, and the U(VI)-contaminated soil was mixed with sulfuric acid solution in a 1:5 w/w ratio. The acid leaching reaction was carried out by stirring the mixture using a combi-D24 stirrer (FINEPCR, Korea) at 25°C for 1 h. The supernatant was then completely separated by centrifugation at 3,000 rpm for 10 min to be used in subsequent purification experiments.

    Fig. 1

    U(VI)-contaminated soil particles of various sizes used in the present study.

    JNFCWT-22-2-159_F1.gif
    Table 1

    Weight content and U(VI) concentration according to the particle size of U(VI)-contaminated soil

    Particle size (mm) Content* (wt%) U(VI) (Bq·g−1) U(VI) (mg·L−1)
    0.85–2.0 28.0 50 4,050
    0.5–0.85 32.0 74 5,994
    0.2–0.5 35.4 117 9,477
    <0.2 4.6 169 13,689
    Mixed soil 100 91.5 7,410

    *Weight content of U(VI)-contaminated soil corresponding size in mixed soil.

    2.3 Purification of U(VI)-contaminated Wastewater

    2.3.1 Precipitation of leached U(VI) ions

    To adjust the pH of the acidic U(VI) effluent to 7.2 ± 0.2, N2H4 solution was added to the U(VI)-contaminated wastewater and the pH was measured using a pH meter (OrionStar T910, Thermo Scientific, USA). The U(VI) precipitate was filtered through a 0.2 μm filter using a vacuum filtration apparatus. The U concentration in the filtrate was measured using a portable X-ray fluorescence (XRF) spectrometer (X-200, SciAps, USA). The morphology and elemental composition of the precipitate were analyzed by scanning electron microscopy with energy-dispersive Xray spectroscopy (SEM-EDX) (SU8010, Hitachi, Japan). The particle size distribution of the U(VI) precipitate was analyzed using a particle size analyzer (S3500, Microtrac, USA).

    2.3.2 Decomposition of hydrazine

    Since soil decontamination is performed under acidic conditions, in order to reuse the wastewater for soil decontamination, it is necessary to adjust the wastewater from neutral conditions to acidic conditions by decomposing N2H4. Therefore, the decomposition of N2H4, including N2H5+, which was used as a precipitant for U(VI) ions, was carried out by adding H2O2 to the filtrate after the removal of the U(VI) precipitate. The effluent was heated to 50°C, and H2O2 was gradually added to the effluent over a period of 30 min to decompose N2H4 and N2H5+. The H2O2 addition was continued until the pH reached a stable value (i.e., pH 1.5–2.0). The total concentration of H2O2 injected for N2H4 decomposition basically depends on the residual concentration of N2H4 after precipitation of leached U(VI) ions, but H2O2 can also spontaneously decompose [31]. For this reason, H2O2 is injected based on pH value of wastewater. The residual concentration of N2H5+ over time was analyzed using an ultraviolet–visible (UV–vis) spectrophotometer (DR1900, HACH, USA). Hydrazine concentration was measured according to the hydrazine analysis method (Method 8141) provided by HACH.

    2.3.3 Testing the efficiency of the wastewater recycling process

    To evaluate the efficiency of the recycling process for the treated effluent, we conducted a recycling experiment following the procedure. In brief, the experiment involved injecting N2H4 into the effluent generated from U(VI)-contaminated soil-washing to precipitate leached U(VI) ions. H2O2 was subsequently added to decompose the remaining N2H4 (including N2H5+). Continuously, H2SO4 was used to adjust the pH of the effluent to that corresponding to the original soil-washing conditions (i.e., pH ~0), and the adjusted effluent was recycled into the soil-washing process.

    3. Results and Discussion

    3.1 U(VI)-contaminated Soil-Washing and Precipitation of U(VI) Ions

    U(VI) in the contaminated soil was effectively extracted with a 98% leaching efficiency achieved through soil washing with a 0.5 M H2SO4 solution. The remaining U(VI) concentration in the soil was determined to be 1.8 Bq·g−1. The fact that U was sufficiently leached from the soil under acidic conditions suggests, on the basis of the Pourbaix diagram for U in H2SO4 solution (Fig. 2), that the predominant form of U in the contaminated soil is mainly UO22+. However, achieving the recommended U residue concentration of 1.0 Bq·g−1 in treated soil, as suggested by the International Atomic Energy Agency [32], would necessitate iterative soil-washing [33]. Because the focus of the present study is recycling soil-washing effluent, the U(VI)-contaminated soil was not subjected to repeated washing and the effluent containing U(VI) ions generated from a single acid washing was used in the subsequent steps of the experiment.

    Fig. 2

    Pourbaix diagram of uranium in sulfuric acid medium [56].

    JNFCWT-22-2-159_F2.gif

    To precipitate the leached U(VI) ions, N2H4 was injected into the U(VI) effluent until the pH of the effluent was adjusted to neutral (i.e., pH = 7.2 ± 0.2). According to previous studies, under neutral conditions, UO22+ predominantly exists as UO2(OH)2(s) [34, 35]. Because N2H4 hydrolyzes in water, thereby generating OH− ions (Eq. (1)), adjusting the pH of the U(VI) effluent to neutral with N2H4 can induce the precipitation of U(VI) ions (Eq. (2)) [36]:

    N 2 H 4 + H 2 O → N 2 H 5 +  + OH −
    (1)

    UO 2 2+  + 2OH −  →UO 2 (OH) 2
    (2)

    UO22+ can also precipitate in the form of compounds containing metal ions such as K+ and Ca2+ (e.g., K2(UO2)6 O4(OH)6·7H2O and Ca(UO2)6O4(OH)6·8H2O) [37]. In the present study, the performance of N2H4 as a pH adjuster was evaluated by comparing the results of U(VI) effluent treatment using NaOH, commonly used as a pH adjuster, with those of effluent treatment using N2H4. As shown in Fig. 3(a), the U(VI) ion concentration decreased as the pH of the effluent increased with the addition of N2H4. Notably, at pH levels greater than 6.5, a sharp decrease in the U(VI) ion concentration was observed with the addition of N2H4. This phenomenon is assumed to result from the equilibrium concentration distribution among N2H4, N2H5+, and N2H62+ with respect to pH, as considered in previous studies [38]. We speculate that, at pH levels greater than 6.5, N2H5+ becomes the dominant chemical species, ensuring a stable and sufficient supply of OH− ions for the precipitation of U(VI) ions (Eq. (2)). Overall, when U(VI) wastewater was neutralized using N2H4 or NaOH, U(VI) ions were stably precipitated at pH 7.2 ± 0.2 and EDX analysis showed that the precipitate contained 23.3wt% of U(VI) (Fig. 4).

    Fig. 3

    Residual rates of (a) U(VI) and (b) Fe ions according to pH, which was adjusted by the addition of N2H4 or NaOH.

    JNFCWT-22-2-159_F3.gif
    Fig. 4

    SEM-EDX analysis results for the dried U(VI) precipitate.

    JNFCWT-22-2-159_F4.gif

    The predominant cations in the soil-washing effluent, Fe ions, completely precipitated under neutral conditions (i.e., pH 7.2 ± 0.2) during the effluent treatment with NaOH. However, when the effluent was treated with N2H4, 10–20% of the Fe ions remained in the effluent (Fig. 3(b)). The residual Fe content in the supernatants tended to be higher when N2H4 was used as a neutralizing agent than when NaOH was used. In particular, all of the Fe species were efficiently precipitated at neutral pH in the aqueous solutions where NaOH was utilized, whereas 10–20% of the Fe stably remained in a dissolved state in the N2H4 reaction batches; this tendency can be explained by the additional formation of soluble Fe(II) species under the reducing condition induced by N2H4. Aqueous Fe(II) species presumed to be present in the supernatants include iron(II) sulfides (e.g., FeHS+, Fe(HS)2(aq), etc.) [39-44] and iron(II) hydrazine complexes; the direct interaction and formation of soluble complexes between Fe(II) and a simple ammine group (NH3) have been studied in previous works [45, 46]. Meanwhile, the particle size distribution of the U(VI) precipitate ranged from 4.6 μm to 248 μm, with the smallest 4.6 μm particles accounting for 0.5% of the total (Fig. 5). Hence, we infer that the U(VI) precipitate can be readily separated in large quantities by commercial filtration systems, such as filter presses and metal filters [47, 48].

    Fig. 5

    Particle size distribution for the U(VI) precipitate.

    JNFCWT-22-2-159_F5.gif

    3.2 Decomposition of N2H4

    After the leached U(VI) ions were precipitated, H2O2 was injected to decompose the remaining N2H4 (including N2H5+). The spontaneous decomposition reactions of N2H4 and N2H5+ by H2O2 proceeded as described by Eqs. (3) and (4), respectively [36]:

    N 2 H 4  + 2H 2 O 2   →   N 2 (g) + 4H 2 O       Δ G = − 204.9   kcal
    (3)

    N 2 H 5 +  + 2H 2 O 2  → N 2 (g) + 4H 2 O + H +  Δ G  = −188.9 kcal
    (4)

    In the U(VI) precipitation reaction under the pH 7.2 ± 0.2 condition, the injected N2H4 exists predominantly as N2H5+ (the theoretical molar fraction of N2H5+ is at least 80%) [38]. Consequently, as N2H5+ decomposes in the effluent, the concentration of H+ increases, leading to a decrease in the effluent pH. Therefore, the characteristics of the decomposition of N2H5+ in the effluent by H2O2 over time were confirmed through changes in the pH and in the concentration of N2H5+ (including N2H4). As depicted in Fig. 6, N2H5+ rapidly decomposed within 0.2 h after the injection of H2O2, leading to the generation of H+ and, consequently, to a decrease in the pH from 7.2 to 1.53. Despite the N2H5+ decomposition reaction continuing for 24 h, no substantial further decrease was observed in the N2H5+ concentration or the pH. These results suggest that the decomposition of N2H5+, which generates H+, diminishes when the pH is less than 2 because N2H62+ is simultaneously generated [36, 38]. Although the pH did not reach the initial soil-washing condition of pH 0, we propose that a slight pH adjustment might be sufficient for recycling the effluent in the acidic soil-washing process.

    Fig. 6

    Residual rates of (a) U(VI) and (b) Fe ions according to pH, which was adjusted by the addition of N2H4 or NaOH.

    JNFCWT-22-2-159_F6.gif

    3.3 Testing the Efficiency of the Wastewater Recycling Process

    A series of tests for recycling process was conducted to assess the efficiency of reusing the effluent generated from U(VI)-contaminated soil-washing as a washing agent for U(VI)-contaminated soil after the effluent had been purified through processes such as U(VI) precipitation, filtration, N2H4 decomposition, and pH adjustment. Fig. 7 depicts the concentrations of released U(VI) and Fe ions during soilwashing using the recycled effluent. Despite the use of recycled treated effluent, U(VI) continued to leach steadily from the U(VI)-contaminated soil, with an average concentration of 608 mg·L−1. Similar to the leached U(VI) concentration, the leached Fe concentration showed no substantial decrease compared with the initial leaching concentration. The concentrations of leached Fe ions were in the range 30–100 mg∙L−1. Meanwhile, the slight variations in the concentrations of U(VI) and Fe ions leached from the soil with the number of recycling cycles is attributable to the heterogeneous nature of the soil particles introduced during soil-washing [49].

    Fig. 7

    Concentration of U(VI) and Fe ions eluted during the recycling process.

    JNFCWT-22-2-159_F7.gif

    The pH range of U(VI)-contaminated wastewater was observed to be 7.2–7.5, 1.0–1.8, and −0.2 to −0.4 during the U(VI) precipitation, N2H4 decomposition, and pH adjustment processes, respectively. Throughout the ten recycling cycles, the pH of the treated effluent in each processing step remained within the expected and appropriate ranges (Fig. 8). Fig. 9 shows photographs of the effluent during the effluent treatment processes. Injecting H2O2 into the effluent during the N2H4 decomposition process initially resulted in a brownish color, which gradually turned colorless. This observation is attributed to the attack by H2O2 on Fe ions with six water molecules as ligands. The Fe ions are oxidized to Fe(IV), which is an unstable state. As the decomposition reaction progresses, the Fe(IV) ions are expected to revert to oxidation states of +3 or +2, resulting in transformation of the treated effluent to colorless [50, 51]. To recirculate the treated effluent in the soil-washing process, we finally adjusted the pH of the effluent to the pH corresponding to the soil-washing conditions (i.e., pH ~0) using H2SO4; in this process, a white precipitate, considered to be hydrazinium hydrogen sulfate (N2H6SO4, [N2H5]+[HSO4]−), was formed. Fig. 10 shows the results of the composition analysis of the precipitate. The main elemental components of the precipitate were O (47.6wt%), S (32.2wt%), and N (17.0wt%). We also confirmed that U and Fe removed in the previous processing step were not included. In the pH adjustment process, N2H5+, which was not removed during the process of N2H4 decomposition using H2O2, was eliminated as N2H6SO4. As a result, when the treated wastewater was recycled in the soil-washing process, only H2SO4 remained in the wastewater, which ultimately enabled the maintenance of soil-washing efficiency without interference from N2H4, which was used as a neutralizing agent.

    Fig. 8

    pH value in each wastewater treatment process according to the number of recycling cycles.

    JNFCWT-22-2-159_F8.gif
    Fig. 9

    Actual photos of wastewater during each wastewater treatment process.

    JNFCWT-22-2-159_F9.gif
    Fig. 10

    SEM-EDX analysis results for the dried precipitate generated during the pH adjustment process.

    JNFCWT-22-2-159_F10.gif

    The critical aspect in evaluating the applicability of the effluent recycling process is confirming whether U(VI) is consistently leached from the U(VI)-contaminated soil through the recycling of the effluent. Hence, we investigated the U(VI) concentration in the soil with respect to the number of recycling cycles (Fig. 11). Excluding the second recycling cycle, U(VI) was consistently leached from the U(VI)-contaminated soil through ten cycles of effluent recycling. The residual concentration of U(VI) in the treated soil ranged from 1.2 to 2.3 Bq·g−1, corresponding to a leaching rate in the range 97.5–98.6%. Meanwhile, it was confirmed that Fe ions that were not completely precipitated upon N2H4 injection did not reduce U(VI) leaching efficiency during ten cycles of effluent recycling. On the basis of these results, we concluded that consistently maintaining the pH conditions of the recycled effluent at the initial value of soil-washing (i.e., pH ~0) promoted the leaching of U(VI). In addition, the injection of excessive H2O2 can induce the precipitation of U(VI) ions. Therefore, it is recommended to inject more than ~1.5 times the stoichiometric amount of H2O2 required for the decomposition of N2H4 (equations (3) and (4)) to compensate for the spontaneous decomposition of H2O2 [36, 38]. In the second recycling cycle, the unexpectedly high U(VI) concentration in the soil after soilwashing is attributed to excess injected H2O2. We speculate that the excess H2O2 remaining after the decomposition of N2H4 and N2H5+ could have reduced the leached U(VI) ions to U(IV) [52], resulting in the precipitation of U(IV), which was incorporated into the washed soil.

    Fig. 11

    U(VI) concentration in soil according to the number of recycling cycles.

    JNFCWT-22-2-159_F11.gif

    3.4 Proposed Recycling Process for Efficient Treatment of U(VI)-contaminated Soil- Washing Effluent

    On the basis of the experimental findings from this study, we have proposed a process for the recycling of wastewater in U(VI)-contaminated soil-washing (Fig. 12). The proposed recycling process involves using several physicochemical processes (e.g., precipitation, filtration, and chemical decomposition) to purify wastewater generated after soil-washing. The purified effluent is then reused in the soil-washing process. In the soil-washing process, the leached U(VI) ions are removed as a U(VI)-precipitate through neutralization using N2H4. The N2H4 used as a pH adjuster is decomposed into N2, H2O, and H+ by H2O2. This simultaneous process lowers the pH of the wastewater to the acidic range because of the generated H+. To facilitate the recycling of the treated wastewater in the soil-washing process, a final pH adjustment is carried out using H2SO4. During this process, any remaining N2H5+ from the N2H4 decomposition forms a precipitate in the shape of N2H6SO4. Consequently, the ultimate chemical composition of the treated solution is dominated by the initial washing agent, H2SO4. This wastewater recycling process can contribute to the economics and efficiency by enabling the continuous treatment of large volumes of U(VI)-contaminated soil with small-scale equipment and a washing solution [53].

    Fig. 12

    Conceptual flow diagram for the efficient recycling process of wastewater generated from U(VI)-contaminated soil-washing.

    JNFCWT-22-2-159_F12.gif

    4. Conclusions

    In the present study, soil-washing was selected as the method for remediating U(VI)-contaminated soil. To purify the soil-washing effluent, water treatment methods such as neutralization–precipitation, solid–liquid separation, and chemical decomposition were applied. The proposed efficient recycling process for wastewater in this study involves using N2H4 to precipitate and remove U(VI) ions through neutralization. The residual N2H4 is then completely eliminated via decomposition by H2O2 and precipitation by H2SO4, which enables the purified wastewater to be reused in the soil-washing process. The proposed recycling process can reduce the amount of radioactive wastewater generated during the soil-washing of U(VI)-contaminated soil by enabling the treatment of large quantities of U(VI)-contaminated soil with a small volume of washing agent. However, because all substances generated within the radioactive management zone are subject to more stringent regulations than general industrial waste and the treatment costs are higher [54, 55], future research should focus on optimizing the conditions in the proposed wastewater recycling process, particularly during the pH adjustment step using H2SO4, to avoid or minimize the formation of N2H6SO4 precipitate.

    Acknowledgements

    This work was supported by a research grant from the Korea Atomic Energy Research Institute (KAERI) [Grant No. 522230-24, Republic of Korea].

    CRediT author statement

    Hyun-Kyu Lee: Writing-original draft, investigation. Byung-Moon Jun: Investigation, validation. Tack-Jin Kim: Project administration, validation. Sungbin Park: Project administration, supervision. Seonggyu Choi: Investigation, data curation. Jun-Young Jung: Investigation, resources. Hee-Chul Eun: Conceptualization, investigation, validation, writing-review & editing.

    Conflict of Interest

    The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

    Figures

    Tables

    References

    1. A. Razmjoo, L.G. Kaigutha, M.A.V. Rad, M. Marzband, A. Davarpanah, and M. Denai, “A Technical Analysis Investigating Energy Sustainability Utilizing Reliable Renewable Energy Sources to Reduce CO2 Emissions in a High Potential Area”, Renew. Energy, 164, 46-57 (2021).
    2. K.O. Yoro and M.O. Daramola, “CO2 Emission Sources, Greenhouse Gases, and the Global Warming Effect”, in: Advances in Carbon Capture, M.R. Rahimpour and M. Farsi, eds., 1st ed., 3-28, Woodherad Publishing, Sawston, UK (2020).
    3. C. Graves, S.D. Ebbesen, M. Mogensen, and K.S. Lackner, “Sustainable Hydrocarbon Fuels by Recycling CO2 and H2O With Renewable or Nuclear Energy”, Renew. Sustain. Energy Rev., 15(1), 1-23 (2011).
    4. G.E. Halkos and E.C. Gkampoura, “Reviewing Usage, Potentials, and Limitations of Renewable Energy Sources”, Energies, 13(11), 2906 (2020).
    5. Y. Lu, Z.A. Khan, M.S. Alvarez-Alvarado, Y. Zhang, Z. Huang, and M. Imran, “A Critical Review of Sustainable Energy Policies for the Promotion of Renewable Energy Sources”, Sustainability, 12(12), 5078 (2020).
    6. C. Pelletier, Y. Rogaume, L. Dieckhoff, G. Bardeau, M.N. Pons, and A. Dufour, “Effect of Combustion Technology and Biogenic CO2 Impact Factor on Global Warming Potential of Wood-to-Heat Chains”, Appl. Energy, 235, 1381-1388 (2019).
    7. C. Tortajada, “Contributions of Recycled Wastewater to Clean Water and Sanitation Sustainable Development Goals”, NPJ Clean Water, 3(1), 22 (2020).
    8. M.D. Mathew, “Nuclear Energy: A Pathway Towards Mitigation of Global Warming”, Prog. Nucl. Energy, 143, 104080 (2022).
    9. M. Usman and M. Radulescu, “Examining the Role of Nuclear and Renewable Energy in Reducing Carbon Footprint: Does the Role of Technological Innovation Really Create Some Difference?”, Sci. Total Environ., 841, 156662 (2022).
    10. S.Z. Zhiznin, V.M. Timokhov, and A.L. Gusev, “Economic Aspects of Nuclear and Hydrogen Energy in the World and Russia”, Int. J. Hydrog. Energy, 45(56), 31353-31366 (2020).
    11. P. Bangotra, M. Sharma, R. Mehra, R. Jakhu, A. Singh, A.S. Gautam, and S. Gautam, “A Systematic Study of Uranium Retention in Human Organs and Quantification of Radiological and Chemical Doses From Uranium Ingestion”, Environ. Technol. Inno., 21, 101360 (2021).
    12. R. Selvakumar, G. Ramadoss, M.P. Menon, K. Rajendran, P. Thavamani, R. Naidu, and M. Megharaj, “Challenges and Complexities in Remediation of Uranium Contaminated Soils: A Review”, J. Environ. Radioact., 192, 592-603 (2018).
    13. M. Dulama, M. Iordache, and N. Deneanu, “Treatment of Uranium Contaminated Wastewater–A Review”, Proc. of Nuclear 2013 the 6th Annual Internationl Conference on Sustainable Development Through Nuclear Research and Education, 80-87, May 22-24, 2013, Rumania.
    14. J. Li, X. Wang, G. Zhao, C. Chen, Z. Chai, A. Alsaedi, T. Hayat, and X. Wang, “Metal–Organic Frameworkbased Materials: Superior Adsorbents for the Capture of Toxic and Radioactive Metal Ions”, Chem. Soc. Rev., 47(7), 2322-2356 (2018).
    15. G. Dermont, M. Bergeron, G. Mercier, and M. Richer- Laflèche, “Soil Washing for Metal Removal: A Review of Physical/Chemical Technologies and Field Applications”, J. Hazard. Mater., 152(1), 1-31 (2008).
    16. R. Mahinroosta and L. Senevirathna, “A Review of the Emerging Treatment Technologies for PFAS Contaminated Soils”, J. Environ. Manage., 255, 109896 (2020).
    17. Y. Ma, X. Li, H. Mao, B. Wang, and P. Wang, “Remediation of Hydrocarbon–Heavy Metal Co-Contaminated Soil by Electrokinetics Combined With Biostimulation”, Chem. Eng. J., 353, 410-418 (2018).
    18. R.O.A. Rahman, H.A. Ibrahium, and Y.T. Hung, “Liquid Radioactive Wastes Treatment: A Review”, Water, 3(2), 551-565 (2011).
    19. C. N. Trung, G.M. Begun, and D.A. Palmer, “Aqueous Uranium Complexes. 2. Raman Spectroscopic Study of the Complex Formation of the Dioxouranium(VI) Ion With a Variety of Inorganic and Organic Ligands”, Inorg. Chem., 31(25), 5280-5287 (1992).
    20. S.J. Markich, “Uranium Speciation and Bioavailability in Aquatic Systems: An Overview”, Sci. World J., 2(1), 707-729 (2002).
    21. J. Hernández and D. Ruiz, “Removal of Chloride Ions From a Copper Leaching Solution, Using Electrodialysis, to Improve the Uranium Extraction Through Ion-Exchange”, J. Hazard. Mater., 420, 126582 (2021).
    22. Y. Pan, D. Li, R. Feng, E. Wiens, N. Chen, R. Chernikov, J. Götze, and J. Lin, “Uranyl Binding Mechanism in Microcrystalline Silicas: A Potential Missing Link for Uranium Mineralization by Direct Uranyl Co-Precipitation and Environmental Implications”, Geochim. Cosmochim. Acta, 292, 518-531 (2021).
    23. A. Massoud, A.M. Masoud, and W.M. Youssef, “Sorption Characteristics of Uranium From Sulfate Leach Liquor by Commercial Strong Base Anion Exchange Resins”, J. Radioanal. Nucl. Chem., 322(2), 1065-1077 (2019).
    24. M. Zhu, L. Liu, J. Feng, H. Dong, C. Zhang, F. Ma, and Q. Wang, “Efficient Uranium Adsorption by Amidoximized Porous Polyacrylonitrile With Hierarchical Pore Structure Prepared by Freeze-Extraction”, J. Mol. Liq., 328, 115304 (2021).
    25. H.K. Lee, S. Chang, W. Park, T.J. Kim, S. Park, and H. Jeon, “Effective Treatment of Uranium-contaminated Soil-Washing Effluent Using Precipitation/Flocculation Process for Water Reuse and Solid Waste Disposal”, J. Water Process Eng., 48, 102890 (2022).
    26. H.K. Lee, W. Park, S. Chang, H. Jeon, and S. Park, “Uranium Recovery From Sulfate-based Acidic Soil Washing Effluent Using Ion-Exchange Resins”, Water Air Soil Pollut., 233, 453 (2022).
    27. H.K. Lee, I. Kim, I.H. Yoon, W. Park, S. Chang, H. Jeon, and S. Park, “A Simple and Effective Purification Method for Removal of U(VI) From Soil-Flushing Effluent Using Precipitation: Distillation Process for Clearance”, J. Radiat. Prot. Res., 48(2), 77-83 (2023).
    28. H.K. Lee, B.M. Jun, I. Kim, H.C. Eun, W. Park, W.H. Jang, T.J. Kim, S.N. Nam, Y. Yoon, and S. Park, “Design and Applicability of a Water Recycling System to Treat Wastewater Generated From Real Uranium-contaminated Soil”, Chem. Eng. J., 472, 144927 (2023).
    29. Y. Ma, F. Li, Y. Jiang, W. Yang, L. Lv, H. Xue, and Y. Wang, “Remediation of Cr(VI)-Contaminated Soil Using the Acidified Hydrazine Hydrate”, Bull. Environ. Contam. Toxicol., 97, 392-394 (2016).
    30. T. Fu, B. Zhang, X. Gao, S. Cui, C.Y. Guan, Y. Zhang, B. Zhang, and Y. Peng, “Recent Progresses, Challenges, and Opportunities of Carbon-based Materials Applied in Heavy Metal Polluted Soil Remediation”, Sci. Total Environ., 856(Part 1), 158810 (2023).
    31. E. Koubek, M.L. Haggett, C.J. Battaglia, K.M. Ibne- Rasa, H.Y. Pyun, and J.O. Edwards, “Kinetics and Mechanism of the Spontaneous Decompositions of Some Peroxoacids, Hydrogen Peroxide and t-Butyl Hydroperoxide”, J. Am. Chem. Soc., 85(15), 2263- 2268 (1963).
    32. International Atomic Energy Agency. Clearance Levels for Radionuclides in Solid Materials: Application of Exemption Principles: Interim Report for Comment, IAEA Waste Management Section Report, IAEATECDOC- 855 (1996).
    33. S. Chang, H.K. Lee, H.B. Kang, T.J. Kim, S. Park, and H. Jeon, “Decontamination of Uranium-contaminated Soil by Acid Washing With Uranium Recovery”, Water Air Soil Pollut., 232, 415 (2021).
    34. V.N. Rychkov, A.L. Smirnov, S.Y. Skripchenko, A. Pastukhov, and N.A. Poponin, “Precipitation of Yellowcake From Pregnant Regenerate by Various Reagents”, J. Radioanal. Nucl. Chem., 314(3), 1741-1746 (2017).
    35. M.J. Kang, B.E. Han, and P.S. Hahn, “Precipitation and Adsorption of Uranium(VI) Under Various Aqueous Conditions”, Environ. Eng. Res., 7(3), 149-157 (2002).
    36. H.C. Eun, J.Y. Jung, S.Y. Park, J.S. Park, N.O. Chang, S.B. Kim, and B.K. Seo, “Decomposition of a High- Concentration Hydrazine in Wastewater From A Chemical Decontamination Process of A Nuclear Facility”, Int. J. Environ. Res., 14, 385-391 (2020).
    37. N. Perdrial, A. Vázquez-Ortega, G. Wang, M. Kanematsu, K.T. Mueller, W. Um, C.I. Steefel, P.A. O’Day, and J. Chorover, “Uranium Speciation in Acid Waste-weathered Sediments: The Role of Aging and Phosphate Amendments”, Appl. Geochem., 89, 109-120 (2018).
    38. H. Nakui, K. Okitsu, Y. Maeda, and R. Nishimura, “The Effect of pH on Sonochemical Degradation of Hydrazine”, Ultrason. Sonochem., 14(5), 627-632 (2007).
    39. G.W. Luther III and T.G. Ferdelman, “Voltammetric Characterization of Iron(II) Sulfide Complexes in Laboratory Solutions and in Marine Waters and Porewaters”, Environ. Sci. Technol., 27(6), 1154-1163 (1993).
    40. J.Z. Zhang, and F.J. Millero, “Investigation of Metal Sulfide Complexes in Sea Water Using Cathodic Stripping Square Wave Voltammetry”, Anal. Chim. Acta, 284(3), 497-504 (1994).
    41. D. Wei and K. Osseo-Asare, “Formation of Iron Monosulfide: A Spectrophotometric Study of the Reaction Between Ferrous and Sulfide Ions in Aqueous Solutions”, J. Colloid Interface Sci., 174(2), 273-282 (1995).
    42. G.W. Luther, D.T. Rickard, S. Theberge, and A. Olroyd, “Determination of Metal (Bi)Sulfide Stability Constants of Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+ by Voltammetric Methods”, Environ. Sci. Technol., 30(2), 671-679 (1996).
    43. R. Al-Farawati and C.M. Van Den Berg, “Metal–Sulfide Complexation in Seawater”, Mar. Chem., 63(3-4), 331-352 (1999).
    44. W. Davison, N. Phillips, and B.J. Tabner, “Soluble Iron Sulfide Species in Natural Waters: Reappraisal of Their Stoichiometry and Stability Constants”, Aquat. Sci., 61, 23-43 (1999).
    45. D.J. Klocke and A.N. Hixson, “Solubility of Ferrous Iron in Aqueous Ammoniacal Solutions”, Ind. Eng. Chem. Process Des. Dev., 11(1), 141-146 (1972).
    46. S.E. Ziemniak, M.E. Jones, and K.E.S. Combs, “Magnetite Solubility and Phase Stability in Alkaline Media at Elevated Temperatures”, J. Solution Chem., 24(9), 837-877 (1995).
    47. F. Amini and H.V. Truong, “Effect of Filter Media Particle Size Distribution on Filtration Efficiency”, Water Qual. Res. J., 33(4), 589-594 (1998).
    48. A.D. Stickland, E.H. Irvin, S.J. Skinner, P.J. Scales, A. Hawkey, and F. Kaswalder, “Filter Press Performance for Fast‐Filtering Compressible Suspensions”, Chem. Eng. Technol., 39(3), 409-416 (2016).
    49. D. Grasso, M.A. Butkus, D. O’Sullivan, and N.P. Nikolaidis, “Soil-Washing Design Methodology for a Lead-contaminated Sandy-Soil”, Water Res., 31(12), 3045-3056 (1997).
    50. C. Walling and K. Amarnath, “Oxidation of Mandelic Acid by Fenton’s Reagent”, J. Am. Chem. Soc., 104(5), 1185-1189 (1982).
    51. W. Lin, C. Gong, R. Chen, X. He, J. Nan, G. Li, H.H. Ngo, and A. Ding, “In-situ Utilization of EPS Improves the Directional Oxidation Ability of Fe (III)/H2O2 and Enhances Sludge Dewaterability”, Chem. Eng. J., 475, 146123 (2023).
    52. Y. Ohashi, Y. Tanaka, Y. Tsunashima, and Y. Ikeda, “Development of Methods for Recovering Uranium From Sludge-like Uranium Generated in Decontamination of Metal Wastes”, J. Nucl. Sci. Technol., 54(3), 382-390 (2017).
    53. Y. Wang and L. Serventi, “Sustainability of Dairy and Soy Processing: A Review on Wastewater Recycling”, J. Clean. Prod., 237, 117821 (2019).
    54. K.W. Han, J. Heinonen, and A. Bonne, “Radioactive Waste Disposal: Global Experience and Challenges”, IAEA Bulletin, 39(1), 33-41 (1997).
    55. W. Belter and D. Pearce, “Radioactive Waste Management”, in Reactor Technology: Selected Reviews, L.E. Link, ed., 149-248, Springfield, Virginia (1965).
    56. M.J. Lottering, L. Lorenzen, N.S. Phala, J.T. Smit, and G.A.C. Schalkwyk, “Mineralogy and Uranium Leaching Response of Low Grade South African Ores”, Miner. Eng., 21(1), 16-22 (2008).

    Editorial Office
    Contact Information

    - Tel: +82-42-861-5851, 866-4157
    - Fax: +82-42-861-5852
    - E-mail: krs@krs.or.kr

    SCImago Journal & Country Rank