© The Author(s) 2025. Published by EDP Sciences and China Science Publishing & Media Ltd.

1 Introduction

With the development of nuclear industry, the prevention and control of radioactive environmental risks associated with radioactive contamination has become increasingly urgent. Radioactive wastewater produced by activities such as nuclear power plant operation, radioactive mineral mining, nuclear medicine procedures, uncontrolled nuclear testing, and accidental discharges of radioactive effluent poses a critical threat to ecosystems and human health [1]. Radioactive wastewater mainly contains radionuclides such as ⁹⁰Sr, ¹³⁷Cs, ²³⁹Pu, ¹³¹I, ⁹⁹Tc, and ⁷⁹Se [2]. Achieving efficient purification and recovery of radionuclides from radioactive wastewater is of crucial for the safe use of nuclear energy and mitigation of environmental risks related to radionuclide contamination. Radioactive wastewater purification technologies mainly include adsorption, membrane separation, electrochemical treatment, evaporation, precipitation, and phytoremediation [2]. Among these, adsorption has attracted growing attention due to its efficiency and energy-saving properties in radioactive wastewater purification, making it a research hotspot in recent years. The total research output of various purification technologies over the past decade is shown in Figure 1. The data were sourced from the Web of Science Core Collection. Adsorbent materials used for radioactive wastewater treatment primarily include natural adsorbents, composite adsorbents, and novel functionalized adsorbents. This paper reviewed the research progress of adsorption materials in radioactive wastewater purification, analyzing their advantages, limitations, and future application prospects.

Fig. 1 Annual number of publications on radioactive wastewater treatment using adsorption, membrane technologies, electrochemical methods, evaporation systems, phytoremediation, and precipitation from 2014 to 2024. Data were obtained from the Web of Science Core Collection.

2 Research progress of adsorption methods in the purification of radioactive wastewater

2.1 Natural adsorbents

Renewable natural resources, such as clay, minerals, and biopolymers, due to its abundant resources and low cost, it is widely used for the purification of radioactive wastewater [3]. For instance, clay minerals are considered ideal adsorbents due to their high availability, low production costs, non-toxicity, large specific surface area, excellent adsorption capacity, and strong ion exchange potential [4, 5]. Zeolite, a low-cost and easily accessible porous silicate material, exhibits exceptional adsorption capacity and ion-exchange properties due to its abundant pores and high surface area. These properties make zeolite widely used for adsorbing potentially toxic elements (PTEs) [6] and radioactive nuclides. For instance, El-Kamesh investigated the adsorption of ¹³⁷Cs and ⁹⁰Sr by zeolite [7]. Under conditions of 298 K and pH = 6, after 3 h of contact, the adsorption capacity of zeolites for ¹³⁷Cs reached 77 mg/g, with a radionuclide removal efficiency of 95.66%. Under the same conditions, the adsorption capacity for ⁹⁰Sr was 95 mg/g [8]. Meanwhile, Abdollahi et al. also studied the adsorption characteristics of natural zeolite for Cs-137 and ⁹⁰Sr, and it was found that under pH = 7.23, the adsorption efficiency of natural zeolite for ¹³⁷Cs was 67.8%, while at pH = 7.9, the adsorption efficiency for ⁹⁰Sr reached 93.5% [9]. This suggests that pH is a key factor influencing the adsorption capacity of zeolites for radionuclides. Identifying the optimal pH conditions is crucial for enhancing the adsorption efficiency of zeolite [5].

Bentonite is a natural clay mineral with a high surface area and good cation exchange capacity, which enables it to provide numerous adsorption sites. The adsorption mechanism of natural bentonite materials for radioactive nuclides is illustrated in Figure 2a. According to the study by Wang et al. [10], pH and ion strength are critical factors influencing the adsorption capacity of bentonite for Uranium(VI) [U(VI)], with ion exchange playing a pivotal role in the adsorption process. The study also demonstrated that bentonite has considerable adsorptive capability for U(VI), with an adsorption capacity reaching 9.124 mg/g. In addition, Chen et al. studied the adsorption performance of natural bentonite for Eu(III) and found that its adsorption capacity depended on the pH of the solution, and the adsorption capacity of bentonite for Eu(III) can reach 4.52 mg/g, indicating that bentonite shows promising potential for treating Eu(III)-containing radioactive wastewater [11]. Moreover, bentonite minerals, as a natural adsorbent, exhibit excellent performance in treating radioactive wastewater containing ¹³⁷Cs, achieving a removal rate of up to 98% [12]. The adsorption effect of bentonite, attapulgite, and kaolinite for ¹³⁷Cs are shown in Figure 2b. As seen, besides bentonite, attapulgite and kaolinite also exhibit high adsorption capacities due to their unique internal surface areas and pore sizes. By comparing and analyzing the adsorption performance of two clay minerals, attapulgite and kaolinite, with other modified adsorbents for ¹³⁷Cs, it was found that attapulgite exhibited exceptional adsorption efficiency, achieving a removal rate of up to 97%, while the removal efficiency of kaolinite was 75% [13]. In contrast to synthetic adsorbents, attapulgite and kaolinite clays serve as naturally occurring, economical, and eco-friendly adsorbents [13]. Montmorillonite is a hydrous aluminosilicate mineral with a layered silicate sheet structure, as shown in the cross-sectional model in Figure 2c, and this structure makes montmorillonite suitable for application in the treatment of radioactive nuclides [11]. Yılmaz et al. demonstrated that montmorillonite has excellent adsorption capacity for the radioactive isotope ¹⁷⁷Lu, achieving a removal of approximately 90% of ¹⁷⁷Lu and reaching adsorption equilibrium within 90 min [14]. Additionally, montmorillonite clay, as an abundant and sustainable adsorbent, is also suitable for treating various radioactive medical waste, such as ¹³¹I and Tc(99-m) [14].

Fig. 2 (a) Main adsorption mechanisms of bentonite-based materials for radionuclides [11]; (b) (1): Adsorption capacity (qe) (2): Adsorption distribution coefficient (Kd), A: Attapulgite, B: Bentonite, K: Kaolinite [13]; (c) Cross-sectional model of montmorillonite layered silicate sheets [11].

Biological adsorbents, such as bacteria, fungi, algae, and plants, demonstrate excellent potential in the treatment of radioactive wastewater due to their efficient adsorption capacity, adaptability to specific pH values, and excellent selectivity and stability towards radioactive nuclides. For example, Takehiko et al. found that the adsorption capacity of Streptomyces for uranium (U) reaches 380 μmol/g [15]. Additionally, studies have shown that the red winter yeast, as a natural organic adsorbent, can achieve an adsorption efficiency of up to 95% for ¹³⁷Cs at pH 6 and 25 °C [16]. Biomass adsorbent materials are promising candidates for radioactive nuclide adsorption due to their wide availability, strong renewability, and environmental friendliness. Furthermore, biomass-based adsorbents, with their exceptional high specific surface area and complex porous structure, provide abundant active sites for adsorption, resulting in a substantial increase in their adsorption efficiency. For instance, Ahmadpour et al. used almond shells as a biosorbent to remove radioactive strontium (Sr²⁺), achieving an adsorption capacity of 116.3 mg/g [17]. Additionally, leaves exhibit promising effectiveness in the removal of radioactive wastewater. For example, Benalia et al. used unmodified oak leaf powder to directly treat strontium-containing simulated wastewater. Under neutral conditions, oak leaves demonstrated good adsorption performance, with an adsorption rate exceeding 80% [18]. Moreover, Sharma et al. studied the adsorption performance of poplar leaves for the removal of radioactive thorium (Th(IV)) and found that after alkaline modification, the surface-negative functional groups of poplar leaves increased, thereby enhancing their adsorption efficiency for thorium ions [19]. Overall, in the past few years, the efficacy and properties of natural adsorbents in capturing radioactive isotopes have garnered extensive interest. The performance and characteristics of various types of natural adsorbents for wastewater purification are summarized in Table 1. Although natural adsorbent materials exhibit potential in the purification of radioactive nuclides, their adsorption capacity is generally lower than that of the composite adsorbent materials.

2.2 Composite adsorbents

Due to the common drawbacks of natural adsorbent materials, such as low adsorption capacity, poor selectivity, and poor regeneration performance, researchers have turned their attention to composite adsorbents. Composite adsorbents refer to materials synthesized by chemical or physical methods that exhibit specific adsorption properties. These materials can be designed with tailored pore structures, surface functional groups, and chemical compositions to achieve efficient adsorption of specific gases, liquids, or solid pollutants. For example, potassium hexacyanoferrate (PBAFe) [21], silver-loaded activated carbon fiber composites (Ag@ACF) [22], and carboxymethyl chitosan gel titanium phosphate (TiP) aerogels [23], these materials typically have a high specific surface area and pore volume, providing more adsorption sites to achieve higher adsorption capacities. Additionally, through molecular design, they can achieve high selectivity for specific pollutants, reducing adsorption of other substances. Many composite adsorbents exhibit good chemical and thermal stability, maintaining their adsorption capacity under variable environmental conditions. Furthermore, they can be regenerated through simple physical or chemical methods, restoring their adsorption properties for repeated use. For example, alginate@polymeric beads (alg@PB) exhibits good adsorption stability under various pH conditions, particularly at pH 10, indicating that it has good adsorption performance across a wide pH range [24]. In contrast, the adsorption performance of citric acid-activated magnesium-aluminum-iron composite (CAA@MgAlFe) is critically influenced by pH [25]. Under acidic conditions (pH 2–4), the adsorption capacity is low due to the dissolution effect of layered double hydroxides (LDHs). Under neutral to mildly alkaline conditions (pH 4–10), the adsorption capacity for uranium decreases with increasing pH, limiting its application range in different pH environments. The preparation process and adsorption mechanism diagram of CAA@MgAlFe are shown in Figures 3 and 4.

Fig. 3 Schematic diagram of the preparation process for CAA@MgAlFe [25].

Fig. 4 Adsorption mechanism diagram of CAA@MgAlFe [25].

The adsorption targets, conditions, performance, and characteristics of composite materials in the purification of radioactive wastewater are shown in Table 2. It can be observed that both Ag@ACF and CAA@MgAlFe composite materials achieve their maximum adsorption capacities after hydrothermal treatment. Chen et al. [22] synthesized Ag@ACF composite materials by using hydrothermal modification and vacuum reduction techniques, which allowed for the uniform distribution of silver nanoparticles on the surface and in the pores of the activated carbon fibers (ACF), providing a large number of active sites for iodine ions. On the other hand, after hydrothermal treatment [25], the combination between layered double hydroxides (LDHs) and calcium alginate gel in the CAA@MgAlFe composite material became more compact, forming a more stable composite structure. Under high-temperature conditions, the crystal structure of LDHs was further refined, and the connections between particles became stronger. This not only improved the mechanical strength and durability of the material but also made it less prone to structural damage or particle detachment under complex environmental conditions, thus extending the material’s lifespan.

The preparation of composite adsorbent materials is a challenging and complex process, involving the selection of various materials, optimization of synthesis methods, and tuning of performance. Precise control of the material’s microstructure is crucial to ensure that the prepared composite materials exhibit favorable adsorption performance under various environmental conditions. Li et al. [21] developed a Fe-Co framework Prussian Blue Analogue (PBA) adsorbent–potassium ferrocyanide cobalt (PBAFe)–using a simple chemical synthesis method, which effectively adsorbs cesium ions. The adsorption mechanism of PBAFe for Cs⁺ is shown in Figure 5. The material demonstrates excellent adsorption stability and selectivity under mildly acidic conditions. In practical applications, it can efficiently remove Cs⁺ in complex water environments, with a removal efficiency of up to 83.59%. On the other hand, Ye et al. [26] developed hollow porous composite nanofibers (HPN) that enhance the interface exposure of nanocatalysts through electrospinning and phase separation techniques, which effectively reduces mass transfer resistance, enabling rapid adsorption and efficient reduction of uranium. The uranium removal mechanism is shown in Figure 6, with removal efficiency reaching 98.86% within 4.5 h. However, the preparation of these materials typically requires precise synthesis conditions and complex process control (the preparation process of HPN is shown in Fig. 7). Researchers combine different types of adsorbent materials to leverage the unique advantages of each material and utilize their synergistic effects to achieve efficient removal of pollutants. While enhancing the adsorption capacity of composite materials, attention should be given to the development of regeneration technologies. Promoting research into efficient material regeneration techniques can enable the reuse of adsorption materials, reduce operational costs, and minimize potential secondary environmental risks.

Fig. 5 Schematic diagram of the Cs+ adsorption mechanism by PBAFe [21].

Fig. 6 Schematic diagram of the uranium removal process using HPN [26].

Fig. 7 Schematic diagram of the HPN preparation process [26].

2.3 Engineered adsorbents¹

Engineered adsorbents refer to materials whose adsorption functionality is artificially tailored through structural design, surface modification, or nanoscale engineering, with performance governed by human intervention rather than the intrinsic properties of raw components. The materials of metal-organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes and graphene have demonstrated substantial potential for the treatment of radioactive wastewater. MOFs and COFs have become widely studied due to their high specific surface areas and tunable porous architectures, which allow for the rational design of adsorption behavior. Post-synthetic modifications, including targeted surface functionalization, can further increase their adsorption capacity by introducing specific binding sites. MXenes exhibit excellent electrical conductivity and hydrophilicity, features that make them highly effective in capturing heavy metal ions and organic pollutants when combined with deliberate surface engineering. Similarly, graphene offer exceptional mechanical strength and chemical stability, and its surface chemistry can be engineered to improve affinity toward targeted contaminants in complex wastewater matrices.

Currently, research on the engineered adsorbent materials focuses on developing new synthesis strategies to enhance their adsorption efficiency, selectivity, and long-term stability. The PPFM composite material, composed of nitrogen-rich fibers as the inner layer and porous Zr-MOFs as the outer layer [30], exhibits excellent performance in iodine adsorption and the degradation of the nerve agent simulant DMNP due to its unique core-shell structure. The dual functionality of the PPFM composite material in treating toxic compounds is illustrated in Figure 8. This material demonstrates a high iodine adsorption capacity of 609 mg/g without the need for additional co-catalysts, and can eliminate 80% of DMNP within 7 min, indicating rapid response and high efficiency. Furthermore, MOF materials also exhibit outstanding performance in removing Co(Ⅱ) [31]. The UiO-66-Lys/PAN nanofiber membrane, prepared via electrospinning, shows a pure water flux of 872 Lm⁻² h⁻¹ and a Co(Ⅱ) retention rate of 45.4%, with a maximum adsorption capacity reaching up to 41.4 mg/g, along with good radiation stability [31].

Fig. 8 Dual functionality of PPFM composites in the treatment of toxic compounds [30].

COFs and their composites show broad application prospects in addressing radioactive wastewater. Yang et al. focused on the simultaneous removal of ${\mathrm{UO}}_2^{2+}$ and ${\mathrm{ReO}}_4^{-}$ using electrostatic adsorption technology [32]. Their study found that COF-1 and COF-2 exhibited exceptionally high adsorption capacities, which were 2.5 times and 2.1 times higher, respectively, than those achieved by physicochemical adsorption methods. Li et al. highlighted the extensive application potential of COFs in water treatment, providing an overview of the classification and synthesis methods of COFs [33], and summarizing the development history of COFs, as detailed in Figure 9.

Fig. 9 Development history of covalent organic frameworks (COFs) [33].

Currently, research on MXene materials found that MXene had favorable adsorption performance for Eu(III) [34]. The synthesis process and structural characteristics of MXene are shown in Figure 10. MXene was modified by citric acid and alkali treatment to form CA-Alk-Ti₃C₂T_x [35], and the structure of the TiO₂/MXene composite material is shown in Figure 11. Under optimized conditions, this material exhibits a maximum adsorption capacity of 117.87 mg/g for Eu³⁺, demonstrating high adsorption efficiency and good reusability. Liu et al. outlined the characteristics and properties of MXene materials and provided a comprehensive summary of the research progress on MXenes, and they also proposed potential future research directions to address the challenges MXene materials face in practical applications [34].

Fig. 10 Synthesis process and structural characteristics of MXene [34].

Fig. 11 Structure of TiO2/MXene composites [34].

In the field of uranium adsorption, graphene materials after modification have shown promising application potential. Li’s group used density functional theory (DFT) simulations to investigate the adsorption performance of single-side fluorinated graphene (ssFG) [36]. The findings revealed that the ssFG exhibits a strong adsorption capacity for uranium atoms, particularly the C₂F structure, which demonstrates a high adsorption energy of 3.45 eV. Shao et al. successfully developed a graphene electrode modified with amidoxime groups (PAO-N-rGO/CF), which achieves efficient adsorption of radionuclides through chemical bonding between the amidoxime groups and U(Ⅵ). The study found that under specific conditions, the removal efficiency for U(VI) reached 99.93%, with excellent cycling stability [37].

Carbon nanotubes (cCNTs) have become a subject of widespread interest for their potential in purifying nuclear wastewater. The cCNTs show remarkable adsorption efficiency for Co²⁺ ions, which is attributed to their large specific surface area and optimal isoelectric point, with a maximum adsorption capacity of 25.1 mg/g. The adsorption capacities of cCNTs for different metal ions, as well as a comparison with other functionalized carbon nanotubes (fCNTs), are presented in Figure 12 [38]. Meanwhile, the Fe₃O₄/CNT nanocomposite has shown outstanding adsorptive properties for U(VI), reaching a theoretical maximum adsorption capacity of 287.53 mg/g [39].

Fig. 12 Comparison of adsorption capacities of cCNT and fCNT for different metal ions [38].

The performance and features of engineered adsorbent materials applied in radioactive wastewater purification are shown in Table 3, and it can be found that the engineered adsorbent materials have favorable adsorption performance broad application prospects for in radioactive wastewater treatment. The future research is suggested to focus on performance optimization, cost reduction, and preparation processes simplification.

The key functional groups, adsorption mechanisms, and representative materials employed for the sequestration of four classes of radioactive nuclides (Sr²⁺, Cs⁺, I⁻/${\mathrm{IO}}_3^{-}$, and Co²⁺/Co³⁺) are summarized in Table 4. Ligand selection may be optimized according to ionic radius, charge, and coordination preferences. For Sr²⁺ and Cs⁺, crown ethers and phosphate moieties facilitate host–guest complexation and ion exchange to form M–PO₄ linkages, while carboxylate groups further enhance Sr²⁺ uptake via electrostatic attraction and chelation. Adsorption of Co²⁺/Co³⁺ relies predominantly on polyamine and thiol functionalities forming stable coordination complexes. Anionic species (I⁻/${\mathrm{IO}}_3^{-}$) are sequestered through anion exchange using quaternary ammonium or protonated amine groups or by AgI precipitation on Ag⁺-loaded substrates.

The equilibrium adsorption capacities of Sr²⁺ across natural, composite, and engineered adsorbents exhibit a distinct increasing trend from low to high. Natural adsorbents generally demonstrate low capacities, typically within the range of 5–20 mg/g. Composite adsorbents show improved performance, with capacities predominantly ranging from 10–105 mg/g. Engineered adsorbents perform the best, with most samples exceeding 100 mg/g, and several reaching values between 200 and 320 mg/g, as illustrated in Figure 13. Concurrently, adsorption performance variability increases with material-design complexity, primarily owing to increased specific surface area, optimized pore architecture, and synergistic interactions among multiple phases, all of which enhance adsorption efficiency. These findings indicate that composite and engineered modifications can significantly enhance the Sr²⁺ removal efficiency of adsorbents, offering a strong rationale for the development of next-generation high-performance adsorption materials.

Fig. 13 Comparison of equilibrium adsorption capacities of Sr2+ among natural, composite, and engineered adsorbents. Data were obtained from the Web of Science Core Collection.

2.4 Adsorption membrane materials

Adsorption membranes are typical composite membranes, which combine the advantages of traditional adsorption methods and filtration technology, allowing for the design of membranes targeted at specific pollutants, demonstrating high selectivity in the adsorption of radionuclides [41]. The performance and features of adsorption membranes in radioactive wastewater treatment are shown in Table 5. Compared to traditional separation techniques, adsorption membrane technology does not require high temperature or pressure for pollutant removal, thereby reducing energy consumption. Once saturation is reached, the membrane material can be regenerated and recycled through a desorption process.

Metal-Organic Frameworks (MOFs) have become a research focus in the development of adsorption membranes. For example, Long et al. [41] developed a PVDF/ZIF-8 nanocomposite adsorptive membrane, which uses reverse diffusion to precisely control the crystal growth on the metal ion side of the membrane. The PVDF/ZIF-8 exhibited efficient and durable iodine ion adsorption with a maximum adsorption capacity of 73.33 mg/g. The preparation process of the composite membrane and the mechanism for iodine removal from water are shown in Figure 14.

Fig. 14 Preparation process of PVDF/ZIF-8 nanocomposite membrane and schematic diagram of iodine removal from water [41].

Polypyrrole-based materials utilize the redox properties of polypyrrole to impart controllable surface charge to the membrane. Chen’s team [42] developed a microfiltration membrane adsorbent material for the rapid and efficient adsorption of radioactive nuclides. This micro-membrane material is composed of zeolitic imidazolate framework-67 (ZIF-67) nanoparticles combined with polyamide microporous membranes (PA), which was prepared using the permeation method and in situ synthesis. In batch adsorption experiments, the ZIF-67@PA microfiltration adsorption membrane demonstrated exceptionally high adsorption efficiency for thorium ions (Th(IV)), with a saturation adsorption capacity of 703.59 mg/g within 50 min, and good reusability, indicating its great potential for industrial applications. In ceramic membrane materials, Janus electro-controlled adsorption membranes can be designed by constructing functional layers on both sides of the membrane. Xiao et al. [43] firstly utilized microporous ceramic membranes to assemble two-dimensional (2D) imidazolate framework-L (ZIF-L) for the preparation of ZIF-L@SiC membrane (Fig. 15), which can effectively remove iodine. Under optimal flux and concentration conditions, the iodine removal efficiency approached 100%, with the iodine adsorption process shown in Figure 16. This study clearly demonstrates the strong selective adsorption capability of ceramic membranes for iodine.

Fig. 15 Schematic diagram of the preparation process for ZIF-L@SiC membrane [43].

Fig. 16 Schematic diagram of iodine adsorption process by ZIF-L@SiC membrane [43].

Similarly, using the seed-assisted secondary growth method, Xu et al. [44] developed a columnar double-walled MOF adsorption membrane made of lac-Zn, with its preparation process and dynamic adsorption shown in Figure 17. The lac-Zn polycrystalline film exhibited excellent stability and strong adsorption capacity in irradiation experiments, with an iodine adsorption capacity of up to 755 mg/g in cyclohexane solution. In contrast, its dynamic adsorption capacity for iodine ions in aqueous solution was relatively weaker, at 31.72 mg/g. The adsorption efficiency of lac-Zn membranes for iodine is not only influenced by pore size and specific adsorption interactions, but also by membrane permeability, mass transfer rate, ion diffusion pathways, and separation time.

Fig. 17 Schematic diagram of the preparation process and dynamic adsorption process of lac-Zn columnar double-walled MOF adsorption membrane [44].

Adsorption membranes can also be used for radioactive wastewater treatment through simple filtration methods. This approach not only retains the high efficiency of adsorbents and filtration technology in purifying radioactive wastewater, but also enables the separation and recovery of low-cost powder adsorption materials, making it suitable for large-scale and high-repetition industrial applications. Cheng et al. [45] prepared a nickel-metal oxide-graphene oxide composite membrane (GO/Ni-MOF) using electrostatic self-assembly technology. The schematic diagram of the adsorption mechanism of GO/Ni-MOF for Sr₂O₃ is shown in Figure 18. Under optimal conditions, the maximum adsorption efficiency for Sr₂O₃ reached 32.99%, with an adsorption capacity of 72 mg/g. Additionally, electrochemical-switching ion extraction (ESIE) technology, which primarily utilizes electrochemical methods to control the adsorption and desorption processes of ions, enables efficient separation and purification of target ions [46]. Luo’s team [47] investigated a highly selective BiOI membrane based on Electrochemical Surface Ion Exchange (ESIE) technology. By triggering the formation of iodine vacancies on the adsorptive membrane through electrochemical reactions, this membrane exhibits high selectivity for iodine ions due to the ion vacancy trapping effect. Even in the presence of many competing anions, the membrane maintains a high iodine ion adsorption capacity of 328.3 mg/g. Furthermore, the iodine vacancy BiOI membrane maintains high extraction efficiency and stability, while allowing for easy desorption of captured iodine ions without introducing secondary environmental risks. The mchematic diagram of iodine vacancy BiOI film for adsorption and extraction of iodine ions from solutions containing radioactive elements is shown in Figure 19.

Fig. 18 Schematic diagram of the adsorption mechanism of GO/Ni-MOF for Sr2O3 [45].

Fig. 19 Schematic diagram of iodine vacancy BiOI film for adsorption and extraction of iodine ions from solutions containing radioactive elements [47].

The application of adsorption membrane materials combines the multiple advantages of adsorption and membrane filtration methods, enabling efficient removal of radioactive nuclides while maintaining excellent adsorption capacity in highly saline radioactive waste solutions. Some adsorption membranes show a marked increase in adsorption capacity compared to pure adsorbents of the same material and can recover valuable elements such as uranium, enabling resources recycling. After saturation, adsorption membranes can restore their adsorption capacity through appropriate regeneration processes, enabling the repeated use of the membrane material, which reduces the treatment costs.

2.5 Evaporation adsorption materials

Traditional radioactive wastewater purification technologies mainly focus on the enrichment of radioactive nuclides, while the reduction of wastewater volume is equally important. Therefore, there is an urgent need for an efficient treatment method that can simultaneously reduce wastewater volume and enrich nuclides. Solar-driven interfacial evaporation is an effective treatment method that can reduce wastewater volume and concentrate nuclides, providing benefit of energy saving. Yu et al. synthesized a three-dimensional porous structural monomer sponge (KGS) using konjac glucomannan (KGM) and reduced graphene oxide (rGO), which exhibited excellent evaporation performance under single sunlight exposure. The preparation process of KGS is shown in Figure 20a, and the SEM images of the porous structure of KGS are shown in Figures 20b–20d. KGS exhibited a rapid evaporation rate of 1.60 kg/m² h and an interfacial water evaporation efficiency of up to 92%. This performance is attributed to its outstanding absorbance, photothermal properties, thermal insulation, and efficient water transport. Additionally, the purification process reduced the concentration of radioactive elements (strontium, cesium, and uranium) in wastewater. KGS also exhibited outstanding durability and stability, with no noticeable decline in performance even after 20 cycles. These results indicate that KGS, utilizing solar-driven interfacial evaporation, can effectively treat radioactive wastewater and concentrate radioactive nuclides [52]. Solar-driven light evaporation adsorption materials have broad application prospects in the field of radioactive wastewater purification due to their energy efficiency, environmental friendliness, and ease of operation.

Fig. 20 (a) Schematic diagram of the preparation process of KGS; (b–d) SEM images of KGS porous structures with different cations [52].

3 Conclusion

This review summarizes the current research status and characteristics of adsorption methods in the field of radioactive wastewater treatment, providing an in-depth analysis of the advantages and disadvantages of various adsorption materials. As one of the most important technologies for treating radioactive wastewater, adsorption methods have achieved numerous groundbreaking research results in the field of radioactive wastewater purification. In the future, to further promote the coordinated and sustainable development of environmental protection and the safe use of nuclear energy, further researches are still needed in the following areas:

1. As for natural adsorbents, their adsorption capacity and selectivity should be further enhanced through modification and activation methods.

2. Composite adsorbents and engineered adsorbents offer advantages such as high adsorption capacity and strong selectivity, but further research is needed to reduce preparation costs and simplify the preparation processes.

3. Adsorption membrane materials combine the advantages of traditional adsorption methods and advanced membrane technologies, demonstrating high selectivity in purifying radioactive nuclides. It is important to further enhance the adsorption capacity and recyclability of adsorption membranes.

4. Novel light evaporation adsorption materials provide notable energy savings and minimize the risk of secondary environmental impacts. However, the purification mechanisms of light evaporation adsorption materials for radioactive nuclides require further investigation. Kinetic and thermodynamic studies could be used to further explore the mechanisms of the purification process.

Funding

This research received no external funding.

Conflicts of interest

The authors declare no conflict of interest.

Data availability statement

No data are associated with this article.

Author contribution statement

Gao Junkai: Writing – Original Draft, Integration and Revision of the manuscript. Lv Anyuan: Writing – Section 2.4 “Adsorption Membrane Materials”. Zhao Ziru: Writing – Section 2.3 “Engineered Materials”. Luo Xiaoyue: Writing – Section 2.5 “Evaporation Adsorption Materials”. Li Zhaoyu: Writing – Section 2.2 “ Composite Absorbents”. Wang Huimin: Writing – Section 2.1 “Natural Absorbents”. Wang Runjie: Data Curation, Visualization, Figure Preparation. Chen Yan: Review and Editing. Hou Li’an: Supervision, Conceptualization, Methodology.

References

All Tables

All Figures

	Fig. 1 Annual number of publications on radioactive wastewater treatment using adsorption, membrane technologies, electrochemical methods, evaporation systems, phytoremediation, and precipitation from 2014 to 2024. Data were obtained from the Web of Science Core Collection.
In the text

	Fig. 2 (a) Main adsorption mechanisms of bentonite-based materials for radionuclides [11]; (b) (1): Adsorption capacity (qe) (2): Adsorption distribution coefficient (Kd), A: Attapulgite, B: Bentonite, K: Kaolinite [13]; (c) Cross-sectional model of montmorillonite layered silicate sheets [11].
In the text

	Fig. 3 Schematic diagram of the preparation process for CAA@MgAlFe [25].
In the text

	Fig. 4 Adsorption mechanism diagram of CAA@MgAlFe [25].
In the text

	Fig. 5 Schematic diagram of the Cs+ adsorption mechanism by PBAFe [21].
In the text

	Fig. 6 Schematic diagram of the uranium removal process using HPN [26].
In the text

	Fig. 7 Schematic diagram of the HPN preparation process [26].
In the text

	Fig. 8 Dual functionality of PPFM composites in the treatment of toxic compounds [30].
In the text

	Fig. 9 Development history of covalent organic frameworks (COFs) [33].
In the text

	Fig. 10 Synthesis process and structural characteristics of MXene [34].
In the text

	Fig. 11 Structure of TiO2/MXene composites [34].
In the text

	Fig. 12 Comparison of adsorption capacities of cCNT and fCNT for different metal ions [38].
In the text

	Fig. 13 Comparison of equilibrium adsorption capacities of Sr2+ among natural, composite, and engineered adsorbents. Data were obtained from the Web of Science Core Collection.
In the text

	Fig. 14 Preparation process of PVDF/ZIF-8 nanocomposite membrane and schematic diagram of iodine removal from water [41].
In the text

	Fig. 15 Schematic diagram of the preparation process for ZIF-L@SiC membrane [43].
In the text

	Fig. 16 Schematic diagram of iodine adsorption process by ZIF-L@SiC membrane [43].
In the text

	Fig. 17 Schematic diagram of the preparation process and dynamic adsorption process of lac-Zn columnar double-walled MOF adsorption membrane [44].
In the text

	Fig. 18 Schematic diagram of the adsorption mechanism of GO/Ni-MOF for Sr2O3 [45].
In the text

	Fig. 19 Schematic diagram of iodine vacancy BiOI film for adsorption and extraction of iodine ions from solutions containing radioactive elements [47].
In the text

	Fig. 20 (a) Schematic diagram of the preparation process of KGS; (b–d) SEM images of KGS porous structures with different cations [52].
In the text