Stabilization of Uranium in Acid Ore Wastewater through Hydrothermal Mineralization-Induced Crystallization.

Uranium [U(VI)] mining activity resulted in the discharge of uranium containing acid wastewater. It is necessary for immobilizing the uranium from wastewater to avoid its environmental pollution. In this work, a novel hydrothermal mineralization strategy is proposed for uranium stabilization. Three reaction systems such as Mg3(PO4)2 + UO22+, Mg2+ + PO43- + UO22+, and Mg2+ + PO43- + Mg3(PO4)2 + UO22+ were designed to investigate the uranium mineralization and stabilization performance. The consumed molar quantities of magnesium and phosphate were calculated to understand the mineralization mechanisms. The molar ratios of Mg/U and P/U in the experimental results were in agreement with those of thermodynamic calculation in the presence of dissolved Mg2+ and PO43- under the hydrothermal process. The calculated saturated index indicated the facile crystallization of uranium into the saleeite and chernikovite through hydrothermal mineralization at the pH value of 5 and 473 K. Crystallization into saleeite and chernikovite contributed to uranium stabilization, resulting in the negligible leaching rate of 5% due to the high crystallinity of 97.23%. Thus, hydrothermal mineralization of uranium crystallization into saleeite and chernikovite was promising for uranium stabilization with long-term stability.

Enhanced cadmium removal by a magnetic potassium ferrocyanide framework: Performance and mechanism study.

Polluted environments often contain large amounts of toxic metals, such as cadmium, which pose a major threat to ecosystems and public health. Contamination by cadmium and its compounds is often observed in areas surrounding zinc mining sites and electroplating factories, and the control of cadmium pollution is essential for environmental safety and health. In this study, a highly efficient and straightforward separation strategy for K4Fe(CN)6@Fe3O4 nanocomposites is successfully developed to capture the Cd ions in the water environment. Batch adsorption experiments revealed that K4Fe(CN)6@Fe3O4 exhibited a high cadmium removal rate (greater than 98 %) at a pH level of 6.0 and solid-liquid ratio of 1.0 g/L at room temperature (298 K). Kinetic analysis revealed that the adsorption process followed a pseudo-second-order model and cadmium was rapidly removed in the first 10 min, with chemisorption dominating the capture of Cd2+ by K4Fe(CN)6@Fe3O4. Adsorption isotherms revealed a heterogeneous adsorption behavior, with a maximum adsorption capacity of 40.78 mg/g. The intrinsic adsorption of Cd2+ by K4Fe(CN)6@Fe3O4 occurring primarily through electrostatic interaction and ion exchange. In addition, K4Fe(CN)6@Fe3O4 exhibited an excellent regeneration capacity. Therefore, integrating Fe3O4 into the metal cyanide not only provided the composite material with excellent chemical stability and selective adsorption sites for Cd2+, but also facilitated subsequent sorbent collection and recovery. Overall, this study presents a simple and feasible approach for integrating Fe3O4 into potassium ferrocyanide frameworks for efficient cadmium removal from contaminated water.

Novel biocompatible N-rich AIE fluorescent probe for live cell imaging and visual onsite detection of uranium.

A sensitive and biocompatible N-rich probe for rapid visual uranium detection was constructed by grafting two trianiline groups to 2,6-bis(aminomethyl)pyridine. Possessing excellent aggregation-induced emission (AIE) property and the advantages to form multidentate chelate with U selectively, the probe has been applied successfully to visualize uranium in complex environmental water samples and living cells, demonstrating outstanding anti-interference ability against large equivalent of different ions over a wide effective pH range. A large linear range (1.0 × 10-7-9.0 × 10-7 mol/L) and low detection limit (72.6 nmol/L, 17.28 ppb) were achieved for the visual determination of uranium. The recognition mechanism, photophysical properties, analytical performance and cytotoxicity were systematically investigated, demonstrating high potential for fast risk assessment of uranium pollution in field and in vivo.

Statistically and visually analyzing the latest advancements and future trends of uranium removal.

Uranium contamination and remediation is a very important environmental research area. Removing radioactive and toxic uranium from contaminated media requires fundamental knowledge of targets and materials. To explore the-State-of-the-Art in uranium contamination control, we employed a statistical tool called CiteSpace to visualize and statistically analyze 4203 peer-reviewed papers on uranium treatment published between 2008 and 2022. The primary content presentations of visual analysis were co-authorships, co-citations, keyword co-occurrence analysis with cluster analysis, which could offer purposeful information of research hots and trends in the field of uranium removal. The statistical analysis results indicated that studies on uranium removal have focused on adsorption of uranium from aqueous solution. From 2008 to 2022, biochar and biological treatment were firstly used to sequester uranium, then adsorption for uranium removal dominates with adsorbents of graphene oxide, primary nanofiber magnetic polymers and metal-organic frameworks (MOFs). In recent years, photocatalysts and metal-organic frameworks are expected to be two of the most popular research topics. In addition, we further highlighted the characteristics and applications of MOFs and GOs in uranium removal. Overall, a statistical review was proposed to visualize and summarize the knowledge and research trends regarding uranium treatment.

Fabrication of highly efficient hydroxyapatite microtubes for uranium sequestration and immobilization.

Uranium-containing wastewater is a common by-product of uranium mining. Phosphate and phosphate minerals can interact with uranyl ions [U(VI)], impeding the migration of these ions by forming relatively stable uranium-containing crystalline phase(s). In this study, hydroxyapatite microtubes (HAP-T) were fabricated to sequester uranyl ions from simulated radioactive wastewater. HAP-T had excellent adsorption and stability properties; over 98.76% of U(VI) could be sequestrated by 0.25 g/L HAP-T within 5 min at pH = 4.0. The isotherms and kinetics data could be suitably reflected by the Freundlich and the pseudo second-order kinetic models, respectively. The maximum adsorption capacity of HAP-T was 356.42 mg/g. The adsorption ability of HAP-T for U(VI) was inhibited when Mg2+ or SO42- ions or fulvic acid (FA) substances existed in the simulated radioactive wastewater. The inhibition by FA was attributed to its negative charges, which caused competition between FA and HAP-T for uranium sequestration. The primary mechanisms of U(VI) sequestration by HAP-T were electrostatic interactions and surface complexation. The effectiveness of HAP-T, HAP-B (bio-hydroxyapatite synthesized from fish bone), and HAP-C (commercially available synthesized hydroxyapatite) for uranium immobilization was compared; HAP-T was more effective than HAP-B or HAP-C in immobilizing uranium. HAP-T, which has a micron-sized tubular structure, is likely less mobile in groundwater than are HAP-B and HAP-C, which have nanoscale granular structures. In conclusion, HAP-T can be used to sequester and immobilize uranyl ions.

Dual light-driven p-ZnFe2O4/n-TiO2 catalyst: Benzene-breaking reaction for malachite green.

Heterocyclic aromatic compounds such as malachite green can cause immense harm to the environment and mankind because of their toxic bio-accumulation and insufficient biodegradation. ZnFe2O4/TiO2 (ZF-T) has attracted attentions as a visible-light-driven catalyst because it can break and mineralize benzene through photolysis. Compared with TiO2, which photodegrades only 53.5% malachite green, anatase TiO2 loaded with ZnFe2O4 has greater photocatalytic activity and can degrade up to 90.1% malachite green. Furthermore, a photocatalytic efficiency above 80% can be obtained through five consecutive cycles with a duration of 4 h. In this study, ZF-T was characterized, and its photolytic parameters, including dosage, pH, time, and ionic strength, were optimized. The photolytic products of malachite green were analyzed by ultraviolet-visible spectroscopy and liquid chromatography-mass spectrometry, which confirmed that ZF-T can drive visible light to produce •O2- and H+ free radicals that can efficiently degrade heterocyclic aromatic hydrocarbons and cleave benzene rings. These outcomes deepen our understanding of the development and applications of visible-light-driven ZF-T composites in the field of wastewater purification.

Effectiveness and mechanism of uranium adsorption on size-graded red mud.

As a type of useful solid waste, red mud (RM) should be reused to achieve waste-to-resource strategies. Additionally, the fast development of nuclear industry requires effective and reliable materials for treating uranium (U)-containing wastewater. This study attempted to remove uranyl ions [U(VI)] from mimic radioactive wastewater by various RM particles with different size fractions (e.g., >75, 45-75, 20-45, 10-20, 5-10, and <5-µm). Sorption data confirmed that the RM with a size fraction of <5-µm exhibited the largest adsorption capacity. The U removal behavior was favorably described by the pseudo-second-order model and Langmuir model. The mineral phases in the RM remarkably influenced U(VI) removal. Cancrinite, katoite, grossular, calcite, and calcium aluminum silicate phases made contributions to U(VI) adsorption. In addition, redox precipitation with iron-bearing minerals on RM surface also led to U(VI) adsorption. The findings of this work offer fundamental knowledge on the potential application of RM for clean-up of U(VI) from contaminated sites.

Highly selective adsorption and lattice process of cesium by cubic cyanide-based functional materials.

Cesium (Cs) is a byproduct of nuclear bombs, nuclear weapons testing, and nuclear fission in nuclear reactors. Cs can enter the human body through food or air and cause lasting damage. Highly efficient and selective removal of 137Cs from low-level radioactive effluents (LLREs), which contain many radionuclides and dissolved heavy metal species, is imperative for minimizing LLRE volume, and facilitating their final disposal. Prussian blue analogs (PBAs) have received much attention as materials for the removal of radioactive Cs because of their affinity for adsorbing Cs+. In this study, an inexpensive and readily available cyanide-based functional material (PBACu) exhibiting high efficiency and excellent selectivity toward Cs capture was designed through a facile low-temperature co-precipitation process. Nano-PBACu, crystallizing in the cubic space group (Fm-3m (225)), has an average pore size of 6.53 nm; consequently, PBACu can offer abundant atomic occupation sites for capturing and incorporating Cs. Here, the pseudo-second-order kinetic model and Langmuir model fitted well with the adsorption of Cs + on PBACu, with a maximum capture capacity of 95.75 mg/g within 5 min, confirming that PBACu could rapidly capture Cs ions. PBACu strongly and selectively interacted with Cs even in a simulant containing large Na+, NH4+, Ca2+, and Mg2+ ion concentrations in an aqueous solution. The process of Cs + adsorption by cyanide-based functional crystals was confirmed to involve the entry of Cs+ into cyanide-based functional crystals to replace K+ and finally achieve the lattice incorporation of Cs. The current results broaden the lattice theory of radionuclide Cs removal and provide a promising alternative for the immobilization of Cs from radioactive wastewater.

Highly-efficient and easy separation of γ-Fe2O3 selectively adsorbs U(⠥) in waters.

The migration and transformation of uranyl [U (Ⅵ)] ions in the environment are quite dependent on the geological condition in particular with the site enriched in Fe. In this study, the interfacial interaction of U (Ⅵ) ions with maghemite (γ-Fe2O3) particles was studied and the interaction mechanism was explored as well. Batch experiments confirm that γ-Fe2O3 can effectively remove U (Ⅵ) from an aqueous solution within a relatively short reaction time (R% > 92.01% within 3 min) and has a considerable capacity for U (Ⅵ) uptake (qt: 87.35 mg/g). γ-Fe2O3 displays an excellent selectivity for U (Ⅵ) elimination. Results on the effects of natural organic matter such as humic acid (HA) indicated that HA could promote the interfacial interaction between γ-Fe2O3 and U (Ⅵ) under acidic conditions. Compared with other radionuclides (e.g., Sr(Ⅱ) and Cs(Ⅰ)), U (Ⅵ) was more effectively removed by γ-Fe2O3. The U (Ⅵ) removal by γ-Fe2O3 is primarily due to electrostatic interactions and precipitation that result in the long-term retardation of uranium. γ-Fe2O3 not only can fast and selectively adsorb U (Ⅵ) but also can be magnetically recycled, demonstrating that γ-Fe2O3 is a cost-effective and promising material for the clean-up of uranyl ions from radioactive wastewater.

Highly efficient uranium (VI) capture from aqueous solution by means of a hydroxyapatite-biochar nanocomposite: Adsorption behavior and mechanism.

The exploration and rational design of easily separable and highly efficient sorbents with the sufficient capability of retaining radioactive and toxic uranium U(VI) is paramount. In this study, a hydroxyapatite (HAP) biochar nanocomposite (BR/HAP) was successfully fabricated from rice straw biochar (BR), to be used as a new and efficient adsorbent for removing U(VI) from aqueous solution. Both BR and the BR/HAP composite were characterized via Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photo electron spectroscopy (XPS) techniques. Batch test results showed that BR/HAP exhibited remarkably higher adsorption capacity than the raw BR. A pseudo-second order kinetic model thoroughly explained the adsorption kinetics, providing the maximum U(VI) adsorption capacities (qe) of 110.56 mg g-1 (R2 = 0.98) and 428.25 mg g-1 (R2 = 0.99), for BR and BR/HAP, respectively, which was indicative of the rate-limited sorption via diffusion or surface complexation after rapid initial adsorption steps. The Langmuir isotherm model fitted the experimental data to accurately simulate the adsorption of U(VI) onto BR and BR/HAP (R2 = 0.97 and R2 = 0.99). The thermodynamic results showed negative values for ΔG°, clearly indicating that the reaction was spontaneous, as well as positive values for ΔH° (11.04 kJ mol-1 and 28.86 kJ mol-1, respectively) and ΔS° (88.97 kJ mol-1 K-1, and 183.42 kJ mol-1 K-1), making clear the endothermic nature of U(VI) adsorption onto both sorbents, with an increase in randomness at a molecular level. FTIR spectroscopy and XPS spectrum further confirmed that the primary mechanisms were ion exchange with UO22+ and surface complexion by -OH and -COOH. In addition, BR/HAP showed an excellent reusability, making it a promising candidate as a new sorbent for U(VI) removal from wastewater. In view of that, it would be interesting to perform future research to explore practical implications of this sorbent material regarding protection from environmental and public health issues related to that pollutant.

Adsorption of arsenic (III) from aqueous solution by a novel phosphorus-modified biochar obtained from Taraxacum mongolicum Hand-Mazz: Adsorption behavior and mechanistic analysis.

A novel phosphorus (P) modified biochar (PLBC) was produced by pyrolyzing biomass of the dietic herb Taraxacum mongolicum Hand-Mazz (TMHM) and treating it with monopotassium phosphate (KH2PO4). This phosphorous loaded biochar was then assessed as adsorbent for As(III) removal from contaminated water. In the current research, the adsorbent was characterized before and after P loading by means of SEM-EDX, TEM, FTIR and XRD techniques. It was evidenced that the presence of P on the surface of the biochar (BC) could improve its efficiency to remove As(III) from contaminated environments. Adsorption kinetics were evaluated by performing batch-type experiments at varied times and pH values (5, 7 and 9). The kinetic study revealed that a contact time of 24 h was required to attain equilibrium and the experimental data were best fitted to the pseudo-second-order kinetic model (qe = 17.1 mg g-1). In addition, several batch experiments were conducted with varied arsenic concentrations. During the adsorption tests, the maximum adsorption of As(III) was found at pH 5. The adsorption study further showed that compared to BC, PLBC depicted increased removal of As(III) from contaminated solutions. The adsorption experimental data showed the best fit to the Langmuir isotherm model (with R2 = 0.84), with maximum As(III) adsorption capacity reaching 30.76 mg g-1 for PLBC.

Heterostructured Bi2O2CO3/rGO/PDA photocatalysts with superior activity for organic pollutant degradation: Structural characterization, reaction mechanism and economic assessment.

Compared with conventional methods for organic pollutant degradation, photocatalysis is a promising treatment technology with broad application prospects. Bi2O2CO3 is often used for organic pollutants degradation but greatly restricted by having drawbacks of large band gap and high electron-hole recombination rate. Herein, heterostructured Bi2O2CO3 (BOC)/reduced graphene oxide (rGO)/polydopamine (PDA) (BGP) photocatalysts were first designed through a green chemical method. By incorporating rGO and PDA in BOC, the kinetic constant of BGP to catalytically degrade methyl orange (MO) was significantly increased; over fourfold elevated rather than that of BOC (kapp/BOC = 0.0019, kapp/BGP = 0.0089) due to the high electron transfer capability of rGO and superior adhesive force and semiconducting properties of PDA. DRS and photoelectrochemical results confirmed the improvement of the light absorption range and charge transfer capability because of the synergistic effect of rGO and PDA. Results of trapping experiment and ESR unraveled the catalytic mechanism that both holes (h+) and superoxide radicals (•O2-) were the main oxidative species for MO degradation. Economic assessment results demonstrated that Bi2O2CO3/rGO/PDA heterojunctions have great potentials in the field of organic wastewater purification. This study developed a low-cost and highly efficient BGP material and provided a deep understanding of the structure-performance relationships of materials for organic pollutant degradation.

Persistent thallium contamination in river sediments, source apportionment and environmental implications.

The adverse impacts of detrimental thallium (Tl) contamination are of increasing concerns to sustainable development. Herein, the contents, distributions and sources of Tl and potential toxic elements (PTEs) (Pb, As, Cr, Cu, Ni, Co, Sb, Cd and U) were investigated in sediments collected in Gaofeng River, which has been contaminated by long-term mining activities, located in Yunfu City, Southern China. Results indicated that excessive Tl levels were found in sediments (1.80-16.70 mg/kg). Sequential extraction procedure indicated that despite a large amount of Tl entrapped in residual fraction, a significant level of Tl (0.28-2.34 mg/kg) still exhibited in geochemically labile fractions, which was easy for Tl mobilization and availability. Pb isotope tracing method further confirmed that the pyrite exploitations may be the prime contaminated contributor (47-76%) to these sediments. These findings highlight that it is essential to establish more effective measures for Tl contamination control and call for engineered remediation countermeasures towards polluted river sediments.

Incorporation of Cadmium and Nickel into Ferrite Spinel Solid Solution: X-ray Diffraction and X-ray Absorption Fine Structure Analyses.

The feasibility of incorporating Cd and Ni in hematite was studied by investigating the interaction mechanism for the formation of CdxNi1-xFe2O4 solid solutions (CNFs) from CdO, NiO, and α-Fe2O3. X-ray diffraction results showed that the CNFs crystallized into spinel structures with increasing lattice parameters as the Cd content in the precursors was increased. Cd2+ ions were found to occupy the tetrahedral sites, as evidenced by Rietveld refinement and extended X-ray absorption fine structure analyses. The incorporation of Cd and Ni into ferrite spinel solid solution strongly relied on the processing parameters. The incorporation of Cd and Ni into the CNFs was greater at high x values (0.7 < x ≤ 1.0) than at low x values (0.0 ≤ x ≤ 0.7). A feasible treatment technique based on the investigated mechanism of CNF formation was developed, involving thermal treatment of waste sludge containing Cd and Ni. Both of these metals in the waste sludge were successfully incorporated into a ferrite spinel solid solution, and the concentrations of leached Cd and Ni from this solid solution were substantially reduced, stabilizing at low levels. This research offers a highly promising approach for treating the Cd and Ni content frequently encountered in electronic waste and its treatment residues.

Novel Viologen Derivative Based Uranyl Coordination Polymers Featuring Photochromic Behaviors.

A series of novel uranyl coordination polymers have been synthesized by hydrothermal reactions. Both complexes 1 and 2 prosess two ipbp- ligands (H2 ipbpCl=1-(3,5-dicarboxyphenyl)-4,4'-bipyridinium chloride), one uranyl cation, and two coordination water molecules, which can further extend to 2D networks through hydrogen bonding. In complex 1, two sets of equivalent nets are entangled together, resulting in a 2D + 2D → 3D polycatenated framework. In complex 2, the neighbouring equivalent nets interpenetrate each other, forming a twofold interpenetrated network. Complexes 3 and 4 are isomers, and both of them are constructed from (UO2 )2 (OH)2 dinuclear units, which are connected with four ipbp- ligands. The 3D structures of complexes 3 and 4 are similar along the b axis. Similar to other viologen-based coordination polymers, complexes 3 and 4 exhibit photochromic and thermochromic properties, which are rarely observed in actinide coordination polymers. Unlike the monotonous coordination mode in complexes 1-4, the ipbp- ligands feature a µ3 -bridge through two kinds of coordination modes in complex 5. Notably, complex 5 presents a unique example in which terminal pyridine nitrogen atom is involved in the coordination.

Distribution and migration of uranium, chromium, and accompanying metal(loid)s in soil-plants system around a uranium hydrometallurgical area.

The extraction and utilization of uranium (U) ores have led to the release of significant amounts of potentially toxic metal(loid)s (PTMs) into the environment, constituting a grave threat to the ecosystem. However, research on the distribution and migration mechanism of U, chromium (Cr), and their accompanying PTMs in soil-plant system around U hydrometallurgical area remains insufficient and poorly understood. Herein, the distribution, migration, and risk level of PTMs were evaluated in soil and plant samples around U hydrometallurgical area, Northern Guangdong, China. The results demonstrated that the maximum content of U and Cr found in the analyzed soils were up to 84.2 and 238.9 mg/kg, respectively. These values far exceed the soil background values in China and other countries. The highest content of U (53.6 mg/kg) was detected in Colocasia antiquorum Schott, and the highest content of Cr (349.5 mg/kg) was observed in Pteridium aquilinum, both of which were enriched in their roots. The risk assessment of PTMs demonstrated that the study area suffered from severe pollution (PN > 3), especially from U, Cr, Th, and As, suggesting the non-negligible anthropogenic impacts. Hence, in light of the significant ecological hazard posed by the U hydrometallurgical area, it is imperative to implement appropriate restoration measures to ensure the human health and maintain the stability of the ecosystem.

Risk assessment and strontium isotopic tracing of potentially toxic metals in creek sediments around a uranium mine, China.

The contamination of creek sediments near industrially nuclear dominated site presents significant environmental challenges, particularly in identifying and quantifying potentially toxic metal (loid)s (PTMs). This study aims to measure the extent of contamination and apportion related sources for nine PTMs in alpine creek sediments near a typical uranium tailing dam from China, including strontium (Sr), rubidium (Rb), manganese (Mn), lithium (Li), nickel (Ni), copper (Cu), vanadium (V), cadmium (Cd), zinc (Zn), using multivariate statistical approach and Sr isotopic compositions. The results show varying degrees of contamination in the sediments for some PTMs, i.e., Sr (16.1-39.6 mg/kg), Rb (171-675 mg/kg), Mn (224-2520 mg/kg), Li (11.6-78.8 mg/kg), Cd (0.31-1.38 mg/kg), and Zn (37.1-176 mg/kg). Multivariate statistical analyses indicate that Sr, Rb, Li, and Mn originated from the uranium tailing dam, while Cd and Zn were associated with abandoned agricultural activities, and Ni, Cu, and V were primarily linked to natural bedrock weathering. The Sr isotope fingerprint technique further suggests that 48.22-73.84% of Sr and associated PTMs in the sediments potentially derived from the uranium tailing dam. The combined use of multivariate statistical analysis and Sr isotopic fingerprint technique in alpine creek sediments enables more reliable insights into PTMs-induced pollution scenarios. The findings also offer unique perspectives for understanding and managing aqueous environments impacted by nuclear activities.

Microbial features with uranium pollution in artificial reservoir sediments at different depths under drought stress.

The uranium (U) containing leachate from uranium tailings dam into the natural settings, may greatly affect the downstream environment. To reveal such relationship between uranium contamination and microbial communities in the most affected downstream environment under drought stress, a 180 cm downstream artificial reservoir depth sediment profile was collected, and the microbial communities and related genes were analyzed by 16S rDNA and metagenomics. Besides, the sequential extraction scheme was employed to shed light on the distinct role of U geochemical speciations in shaping microbial community structures. The results showed that U content ranged from 28.1 to 70.1 mg/kg, with an average content of 44.9 mg/kg, significantly exceeding the value of background sediments. Further, U in all the studied sediments was related to remarkably high portions of mobile fractions, and U was likely deposited layer by layer depending on the discharge/leachate inputs from uranium-involving anthoropogenic facilities/activities upstream. The nexus between U speciation, physico-chemical indicators and microbial composition showed that Fe, S, and N metabolism played a vital role in microbial adaptation to U-enriched environment; meanwhile, the fraction of Ureducible and the Fe and S contents had the most significant effects on microbial community composition in the sediments under drought stress.

The latest research trends in the removal of cesium from radioactive wastewater: A review based on data-driven and visual analysis.

The widespread adoption of nuclear energy has increased the amount of radioactive cesium (Cs) that is discharged into waste streams, which can have environmental risks. In this paper, we provide a comprehensive summary of current advances in aqueous Cs removal by employing a bibliometric analysis. We collected 1580 articles related to aqueous Cs treatment that were published on the Web of Science database between 2012 and 2022. By applying bibliometric analysis combined with network analysis, we revealed the research distribution, knowledge base, research hotspots, and cutting-edge technologies in the field of aqueous Cs removal. Our findings indicate that China, Japan, and South Korea are the most productive countries with respect to Cs removal research. In addition, both historic events and environmental threats might have contributed to research in Asian countries having a higher focus on Cs removal as well as strong international cooperation between Asian countries. A detailed keyword analysis reveals the main knowledge base for aqueous Cs removal and highlights the potential of the adsorption-based method for treating Cs contamination. Furthermore, the results reveal that exploration of functional materials is a popular research topic in the field of Cs removal. Since 2012, novel materials, including Prussian blue, graphene oxide, hydrogel and nanocomposites, have been widely investigated because of their high capacity for Cs removal. On the basis of the detailed information, we report the latest research trends on aqueous Cs removal, and propose future research directions and describe the challenges related to effective Cs treatment. This scientometric review provides insights into current research hotspots and cutting-edge trends in addition to contributing to the development of this crucial research field.

Reply to the comments on "Facilely synthesized cobalt doped hydroxyapatite as hydroxyl promoted peroxymonosulfate activator for degradation of Rhodamine B" by Zuo et al.

In a Co-HAP/PMS system, catalytic degradation process of RhB was accompanied by the gradual leaching of cobalt ion. The results of additional experiments showed that leached cobalt ion indeed contributed to active PMS for RhB degradation, which was not addressed in the previous study. The finding of the contribution from leached cobalt ion to PMS activation was reported due to the valuable comments of Zuo et al., what will be concerned in the future work. Importantly, Co-HAP still showed a significant contribution to PMS activation for RhB degradation at the initial stage. Fortunately, the release of Co2+ from Co-HAP was slow, the secondary pollution could not be addressed due to the slightly release of Co2+ ion that the Co2+ concentration is lower than the standard of the discharge wastewater. Furthermore, the mechanism of non-radical reaction in the Co-HAP/PMS system was reported to confirm the heterogeneous catalysis of a Co-HAP/PMS system.