U(VI) adsorption mechanisms and behavior of red soil aggregates in typical uranium tailings mining areas in Jiangxi, China

U(VI) adsorption mechanisms and behavior of red soil aggregates in typical uranium tailings mining areas in Jiangxi, China | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article U(VI) adsorption mechanisms and behavior of red soil aggregates in typical uranium tailings mining areas in Jiangxi, China Xuchen Weng, Guangya Kuang, Jiaai Chen, Taoyuan Xiu, Limin Zhou, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7138153/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study investigated the adsorption behavior and mechanisms of uranium on red soil aggregates of different particle sizes from a typical uranium tailings area in Jiangxi Province. Static adsorption experiments were conducted to examine the interaction between uranium and soil aggregates, with the aim of elucidating the characteristics of exogenous uranium contamination. The adsorption kinetics followed a pseudo-second-order kinetic model, indicating chemisorption-dominated processes at equilibrium. Isothermal adsorption analysis revealed that aggregates S1 and S3 adhered to the Langmuir model, suggesting monolayer adsorption, whereas S2 and S4 followed the Freundlich model, implying heterogeneous multilayer adsorption. Scanning electron microscopy (SEM) and spectroscopic analyses demonstrated that the surface morphology of the aggregates remained largely unchanged after adsorption, and their aggregated structure was maintained. Further characterization indicated that uranium adsorption primarily occurred through (i) complexation with surface functional groups (–OH, Si–O, Si–O–Fe, Si–O–Al, Fe–O) and (ii) redox reactions with iron-bearing minerals in the aggregate. These findings provide critical insights into the immobilization mechanisms of uranium in red soils, which are relevant for environmental remediation strategies in uranium-contaminated areas. uranium red soil aggregates adsorption uranium tailings Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Introduction Uranium (U), a naturally occurring radioactive element, is a critical resource for nuclear power generation, however its mining and processing pose significant environmental risks. Owing to its pivotal role in nuclear energy generation, it has garnered increasing global attention. Uranium is present in the Earth's crust at an average concentration of 3 mg/kg(Henner et al., 2018 ) and commonly exists in various forms within rocks and soils, such as uranium ores, carnotite, and pitchblende(Selvakumar et al., 2018 ; Thivya et al., 2016 ; Wu, Wang, & Xie, 2014 ; Yu et al., 2019 ). As reported in the World Nuclear Performance Report (2021), 443 nuclear reactors were operational globally with a total capacity of 3.94 × 10⁵ MWe, alongside 57 reactors under construction with a capacity of 5.88 × 10⁴ MWe. In 2020, global nuclear electricity generation reached 2.55 × 10³ TWh, while the annual demand for uranium surged to 6.25 × 10⁴ tons(You, Dou, Xue, Jin, & Yang, 2022 ). Uranium mining produces substantial amounts of waste rock and tailings, which are often stored in open-air dumps and tailings ponds for long periods. Long-term exposure of uranium tailings to atmospheric erosion and rainwater leaching leads to the gradual release of toxic metals and radionuclides, which subsequently migrate to the surrounding water and soil environment through hydrological and wind-driven processes. This phenomenon has caused severe ecological contamination in areas adjacent to the uranium tailings. Uranium pollution threatens human habitats and health. Thus, it is imperative to implement proactive measures to mitigate the environmental impact of uranium waste and safeguard ecological habitats. The mobility of uranium in groundwater is primarily governed by its oxidation state, with U(IV) being the dominant species. The solubility and transport of uranium in groundwater are highly dependent on water-rock interactions, climatic conditions, and hydrogeochemical factors, including pH, redox potential, ionic strength, and bicarbonate concentration(Chandrasekar et al., 2021 ; Vengosh, Coyte, Podgorski, & Johnson, 2022 ). Elevated uranium levels in groundwater are often associated with uranium mineralization zones or uranium-rich source rocks (e.g., granite)(Sharma, Bajwa, & Kaur, 2021 ). For instance, the average uranium concentration in the Yellow River on China’s Loess Plateau ranges between 2.04 and 7.83 µg/L, significantly exceeding the global average for major rivers, likely due to severe soil erosion in the region(T. Zhang et al., 2023 ). Investigations of groundwater in India have revealed widespread uranium concentrations surpassing the World Health Organization WHO provisional guideline of 30 µg/L, attributed to geological factors such as uranium content in aquifer rocks, oxidation states, and groundwater chemistry favoring the formation of soluble uranyl-carbonate complexes(Coyte et al., 2018 ). Similarly, in Spain’s Ridaura Basin, groundwater uranium levels reached up to 37.7 µg/L, with granite weathering identified as the primary source(Sharma et al., 2021 ). The persistent accumulation of uranium contaminants in aquatic systems poses severe environmental risks and adversely affects the biosphere. According to the (WHO), the recommended guideline for uranium in drinking water, classified as a human carcinogen, should not exceed 15 µg/L(Henner et al., 2018 ). Consequently, the effective purification of uranium-contaminated radioactive water has emerged as a critical socio-environmental challenge. In soil microenvironments, physicochemical processes predominantly occur at the interfaces of the aggregate structural units. Soil aggregates exhibit multiscale heterogeneity in their particle size distribution, resulting in variations in composition, microstructure, and physicochemical properties. Consequently, the environmental behavior of heavy metals (e.g., uranium) differs markedly across different aggregate size fractions. Given the complexity of soil composition and structure, fractionation-based studies of soil aggregates provide more precise insights into the geochemical behavior of uranium than bulk soil analyses. Uranium migration in soils can lead to groundwater infiltration, posing risks to water supplies, ecosystems, and human health in uranium tailing regions. While soils act as natural barriers against uranium migration owing to their adsorption capacity, they also serve as primary receptors of exogenous uranium contamination. Previous research on soil aggregates has primarily focused on stability assessment and particle size distribution, with limited attention paid to microstructural characteristics (e.g., pore morphology, spatial arrangement of minerals, and distribution of organic matter). The aggregate size fractions differed significantly in terms of composition, specific surface area, pore features, and iron/aluminum oxide content. Larger aggregates are enriched in quartz, feldspar, and SiO₂, whereas smaller aggregates contain higher proportions of amphibole, mica, iron or aluminum oxides, and hydroxides. Iron or aluminum oxides contribute to aggregate formation and stability while immobilizing heavy metals through their high surface areas and functional groups. Generally, smaller aggregates exhibit greater organic matter and iron oxide content, higher specific surface area, and more adsorption sites, leading to increased heavy metal accumulation(Xiao et al., 2016 ). Adsorption-desorption dynamics are influenced by the surface area, pore structure, coexisting organic matter, and ions, with mechanisms including electrostatic attraction, hydrogen bonding, pore filling, ion exchange, and complexation. The key factors governing uranium speciation in subsurface environments include soil solution pH, cation types/concentrations, ligand (e.g., carbonate) availability, redox conditions, organic matter content, and mineral composition. These geochemical parameters dictate uranium speciation and modulate soil surface properties, thereby affecting adsorption. Bister et al.(Bister et al., 2015 ) reported higher uranium concentrations in alluvial soils beneath pastures than in farmland in Germany’s Mulde River floodplain. Johnson et al.(De Windt et al., 2025 ) observed depth-dependent uranium variation in alkaline desert soils, with distribution coefficients correlating with clay content and pH. Stojanovic et al.(Izquierdo et al., 2025 ) found no significant relationship between total/available uranium and humus content in Serbian soil types. Li et al.(X. Li et al., 2013 ) demonstrated that uranium adsorption in vadose zone soils was optimal at pH 7.0, with solution pH, contact time, initial concentration, and colloids being major influencing factors. In summary, environmental geochemical factors critically regulate the physicochemical behavior uranium in soils, ultimately governing its subsurface migration. Recent studies have predominantly focused on uranium transport mechanisms in aquifers, leaving a knowledge gap regarding uranium mobility and exogenous contamination in red soils from typical uranium tailings in southern China. To address this issue, a comprehensive investigation of uranium adsorption and transport characteristics within soil aggregates from these regions is urgently warranted. Materials and methods Chemicals and reagents Uranium nitrate hexahydrate and nitric acid were purchased from Shanghai McLean Biochemical Technology Co., Ltd. Azoarsine, Chloroacetic acid and sodium acetate were purchased from Sinopharm Chemical Reagent Co., Ltd. Hydrochloric acid was purchased from Shillong Chemical Co., Ltd. Uranium hexahydrate nitrate is reagent grade, and all other chemicals are analytical grade. Instrumentation The elemental composition, morphology, surface texture, and mapping studies of the prepared biocomposites were investigated using a scanning electron microscope (SEM, JEOL-JSM-5600) and an EDX detector. X-ray diffraction (XRD, Bruker D/8 Discover Plus, GER) analysis was performed using a diffractometer to examine the crystallinity phase, crystal structure, and other physical properties. Identification of important functional groups using Fourier transform infrared spectroscopy (FTIR, Nicolet Magna-550, USA) with a working range of 500–4000 cm − 1 and 40 scans per spectrum. U(VI) analysis was performed by complexation using the Arsenazo-III method and absorbance was recorded on a high-resolution dual-beam Ultraviolet-Visible Spectroscopy (UV-Vis, K8001, JPN). Preparation of red soil aggregates with varying size fractions Ten grams of sample was placed in a 500 mL beaker and diluted to 300 mL with deionized water. The mixture was thoroughly stirred with a glass rod and ultrasonicated for 30 min to achieve complete dispersion of the soil aggregates(Ma, Song, Liu, Kang, & Yue, 2024 ). The well-dispersed suspension was then sequentially passed through 1, 0.25, and 0.053 mm nylon sieves (Quanguan Experimental Instrument Center). The soil fractions retained on each sieve were transferred with deionized water to pre-weighed culture dishes, dried, and weighed to obtain red soil aggregates of > 1, 1-0.25, and 0.25 − 0.053 mm size fractions. For particles < 1 µm, the centrifugation time was calculated according to Stokes' law, and the suspension containing particles < 1 µm was obtained by centrifugation at predetermined speed and duration. This suspension was concentrated by rotary evaporation and freeze-dried to obtain the < 1 µm red soil aggregates, while the pellet in the centrifuge tube represented the 1-0.05 mm fraction. Adsorption experiments and methodology Static adsorption experiments were conducted using 50 mL centrifuge tubes as reaction vessels. The tubes were placed in a constant-temperature shaker set at 25 0 C with a rotation speed of 200 rpm. After reaching the predetermined adsorption time, an aliquot of the supernatant was filtered through a 0.22 µm membrane to determine the uranyl ion concentration in the solution. The uranyl ion concentrations were quantified using UV-Vis spectrophotometry at 650 nm using the arsenazo-III method. The adsorption percentage ( R , %) and equilibrium adsorption capacity ( Qe , mg/kg) of uranium(VI) on red soil aggregates were calculated using the following formulas: \(\:{\text{Q}}_{\text{t}}\text{=}\frac{\text{(}{\text{C}}_{\text{0}}\text{−}{\text{C}}_{\text{t}}\text{)}\text{V}}{\text{m}}\) Eq. (1) \(\:{\text{Q}}_{\text{e}}\text{=}\frac{\text{(}{\text{C}}_{\text{0}}\text{−}{\text{C}}_{\text{e}}\text{)}\text{V}}{\text{m}}\) Eq. (2) \(\:\text{R}\text{(%)}\text{=}\frac{\text{(}{\text{C}}_{\text{e}}\text{−}{\text{C}}_{\text{t}}\text{)}\text{V}}{\text{m}}\text{×}\text{100}\) Eq. (3) The adsorption parameters are defined as follows: R (%) represents the adsorption percentage of uranium(VI) by red soil aggregates; Q t (mg/g) denotes the adsorption capacity of uranium(VI) by red soil aggregates at time t (min); Q e (mg/g) is the equilibrium adsorption capacity of uranium(VI) by red soil aggregates; C 0 (mg/L) indicates the initial mass concentration of uranium(VI); C t (mg/L) represents the concentration of uranium(VI) in solution at reaction time t (min); C e (mg/L) stands for the equilibrium concentration of uranium(VI) in solution; m (mg) and V (mL) correspond to the mass of red soil aggregates and the volume of uranium(VI) solution used in each adsorption experiment, respectively. Error bars were calculated upon duplicate runs of each sorption experiment, and nonlinear regression analysis was conducted using Origin Pro 2021. All experiments were performed in duplicate with the following influencing factors: (1) Adsorption time Red soil aggregates (0.2 g) with different particle sizes were separately placed in 50 mL centrifuge tubes, to which uranium solution with an initial concentration of 10 mg/L was added. The uranium concentrations in the solution were measured after 0.1, 0.5, 2, 4, 6, 8, 10, 16, and 24 h to investigate the effect of adsorption time on U(VI) adsorption by red soil aggregates and to determine the adsorption equilibrium time. (2) Liquid-solid ratio A 0.2 g soil sample was placed in conical flasks with liquid-solid ratios (mL/g) of 20, 50, 100, 200, 300, and 400. The initial uranium concentration was 10 mg/L, and the initial pH of the uranium solution was adjusted to 5.0 using HNO 3 and NaOH. The adsorption time was 10 h to investigate the effects of the liquid-solid ratio and red soil aggregate particle size on U(VI) adsorption. (3) Initial pH Red soil aggregates (0.2 g) with different particle sizes were separately placed in 50 mL centrifuge tubes, to which uranium solution with an initial concentration of 10 mg/L was added. The initial pH of the uranium solution was adjusted to 2, 3, 4, 5, 7, and 8 using HNO 3 and NaOH solutions. The adsorption time was 10 h to investigate the effect of the initial pH on U(VI) adsorption by red soil aggregates of different sizes. (4) Initial uranium concentration At room temperature, red soil aggregates (0.2 g) with different particle sizes were placed in 50 mL centrifuge tubes, to which uranium standard solutions with initial concentrations of 10, 15, 20, 30, 50, and 100 mg/L were added. The pH was maintained at 5.0 with an adsorption time of 10 h to investigate the effect of initial uranium concentration on U(VI) adsorption by different-sized red soil aggregates. (5) Temperature Red soil aggregates (0.2 g) with different particle sizes were separately placed in 50 mL centrifuge tubes, to which uranium solution with an initial concentration of 10 mg/L was added. The initial pH of the uranium solution was adjusted to 5 using HNO 3 and NaOH solution. The experimental temperatures were set at 25, 30, 35, and 40 0 C with an adsorption time of 10 h to investigate the effect of temperature on U(VI) adsorption by red soil aggregates of different sizes. Results and Discussion Effects of particle size and liquid-solid ratio The effects of red soil aggregate particle size and liquid-to-solid ratio (under fixed conditions: t = 24 h, pH = 5.0, T = 25 0 C, C 0 = 10 mg/L, with liquid-to-solid ratios of 50, 100, 150, 200, 300, and 400) on uranium(VI) adsorption are shown in Fig.1 The results indicated that uranium adsorption efficiency increased as aggregate particle size decreased, with significant differences observed between aggregates S1/S2 and S3/S4. Specifically, S1 and S2 exhibited similar U(VI) adsorption rates, as did S3 and S4, following the overall trend of S4 > S3 > S2 > S1. This correlation is attributed to the fact that smaller aggregates possess greater internal porosity and larger specific surface areas, with the total pore volume increasing as the particle size decreases(Y. L. Li et al., 2020). These findings align with those of Li Shiyou et al., who reported enhanced uranium adsorption capacity with reduced clay particle size in wastewater treatment studies, consistent with our observation that the smallest aggregate fraction (S4) achieved maximum uranium adsorption efficiency. With an increasing liquid-to-solid ratio, the uranium adsorption efficiency of the red soil aggregates exhibited an initial sharp decline, followed by gradual stabilization. This trend suggests that increasing the uranium solution volume leads to a relative shortage of available adsorption sites, resulting in reduced adsorption capacity. When the liquid-to-solid ratio exceeded a certain threshold (specifically > 100 in this study), the uranium solution became excessive and the adsorption rate stabilized with minimal further variation. To minimize interference from the liquid-to-solid ratio effects in subsequent adsorption experiments, an optimal ratio of 100 was selected for all further investigations. Medium pH Medium pH significantly influences various factors affecting uranium adsorption, including soil surface charge, chemical speciation of heavy metal ions, degree of metal ion hydrolysis, solubility of organic matter, and nature of functional groups on soil adsorption media. In this study, we investigated the uranium binding capacity of different-sized red soil aggregates (S1-S4) across a pH gradient (2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0) under controlled conditions (t = 24 h, T = 25 0 C, C 0 = 10 mg/L, L/M = 100), with results shown in Fig. 2 Similar to the effects of liquid-to-solid ratio and particle size, S1 and S2 exhibited comparable uranium(VI) adsorption rates, as did S3 and S4 across all pH levels. The adsorption efficiency exhibited strong pH dependence, increasing with pH until it stabilizatd above pH 6. Under acidic conditions (pH < 5), competitive adsorption between H⁺ ions and uranyl cations for surface sites limited uranium uptake, with lower pH values (higher H⁺ concentration) resulting in a poorer adsorption performance. As the pH increased, UO₂²⁺ hydrolysis produced cationic species, including UO₂(OH)⁺, (UO₂)₂(OH)₂²⁺, and (UO₂)₃(OH)₅⁺, while simultaneously enhancing the adsorption capacity of clay minerals and organic matter in the aggregates through increased surface negative charges, facilitating complexation adsorption. Above pH 6, the hydroxyl complexation of uranium(VI) reduces uranyl ion mobility, consequently decreasing adsorption efficiency. To minimize pH interference while maintaining environmental relevance, subsequent experiments were conducted at pH 5 (approximating natural red soil pH) to investigate other factors affecting uranium(VI) adsorption by different aggregate fractions. Uranium initial mass concentration Batch experiments were conducted to investigate the effect of initial uranium(VI) concentration (10, 15, 20, 30, 50, and 100 mg/L) on adsorption by different-sized red soil aggregates under controlled conditions (t = 10 h, T = 25 0 C, pH = 5, L/M = 100 mL/g), and the results are presented in Fig. 3 The data revealed a concentration-dependent adsorption pattern, where uranium(VI) uptake increased with higher initial concentrations. Consistent with previous observations regarding the liquid-to-solid ratio, particle size, contact time, and pH effects, aggregates S1 and S2 showed similar adsorption capacities, as did S3 and S4 across all tested concentrations, following the established size-dependent trend: S4 > S3 > S2 > S1. A rapid increase in uranium(VI) adsorption capacity occurred within the 10-50 mg/L concentration range, followed by progressively diminishing returns at higher concentrations ( C 0 > 50 mg/L). At the maximum tested concentration (100 mg/L), the adsorption efficiency approached equilibrium, demonstrating that lower initial uranium(VI) concentrations yielded greater relative adsorption efficiency but smaller absolute adsorption capacity when using fixed amounts of red soil aggregates. This saturation behavior reflects the finite availability of active adsorption sites on the aggregates at a constant solid-phase mass. Temperature Static adsorption experiments were conducted to investigate the effect of reaction temperature (25, 30, 35, 40 0 C) on U(VI) adsorption by red soil aggregates of different sizes under controlled conditions (t = 10 h, pH = 5, C 0 = 10 mg/L, L/M = 100 mL/g). The removal rates of S1 and S2 aggregates were similar, and S3 and S4 were similar, which showed the same pattern as the above influencing factors, which may be attributed to the small particle size span of S1 and S2 aggregates and the large span of S2 and S3 aggregates. There is a transition particle size between S2 and S3, and the aggregates with particle sizes S1 and S2 are grouped together, and the aggregates of S3 and S4 are grouped together, and the same type of aggregates have similar adsorption properties. As shown in Fig. 4, the adsorption efficiency remained relatively stable with gradual increases in temperature, indicating that temperature had no significant impact on uranium adsorption by the red soil aggregates. Consequently, a room temperature (25 0 C) was selected for all subsequent experiments to maintain operational consistency. U(VI) Adsorption Kinetics To systematically analyze the adsorption kinetics of uranium at the interface of red soil aggregates, the adsorption experimental data obtained at multiple time points were fitted using linear regression analysis with pseudo-first-order (PFONL) and pseudo-second-order (PSONL) kinetic equations. The linear equations for the two models are given by equations Eq. (4) to (5). In the equations, equilibrium and instantaneous sorption capacities of composite materials are denoted by Q e (mg/g) and Q t (mg/g), respectively. The rate constants for PFONL and PSORE are denoted by symbols k 1 (min -1 ) and k 2 (g . mg -1. min -1 ), respectively. The resulting fitting curves are shown in Fig. 5 and 6, and the corresponding kinetic parameters are presented in Table 1. As illustrated in the figures and table, the adsorption kinetics were best fitted by a pseudo-second-order model (R² > 0.93), indicating chemisorption-dominated processes. The theoretical equilibrium adsorption capacity derived from this model closely matched the experimentally measured saturation adsorption capacity. Therefore, the adsorption of uranium by red soil can be more accurately described by the pseudo-second-order kinetic model, which effectively characterizes the adsorption behavior of U (VI) on red soil aggregates of different particle sizes. The adsorption rate is primarily controlled by chemical adsorption. Table 1 Kinetic fitting parameters for uranium adsorption on red soil aggregates with different particle sizes Red soil aggregates PFONL PSONL Q e (mg/kg) K 1 R 2 Q e (mg/kg) K 2 R 2 S1 0.346 0.002 0.931 0.456 0.056 0.978 S2 0.925 0.004 0.652 0.638 0.041 0.939 S3 0.313 0.006 0.978 0.898 0.070 0.998 S4 0.258 0.004 0.953 0.992 0.094 0.998 Adsorption isotherms model Based on the isothermal adsorption experimental data of uranium on red soil aggregates, the relationship between the residual uranium concentration in the solution at adsorption equilibrium and the adsorption capacity of the aggregates was systematically analyzed. The experimental sorption data was fitted into different adsorption models such as Langmuir and Freundlich. The equations for the Langmuir isothermal adsorption model are shown in Eq. (6) and (7), and the equations for the Frenrich isothermal adsorption model are shown in Eq. (8) and (9). In the Langemuir equation, C e (mg.L -1 ) is the equilibrium concentration, Q e (mg.g -1 ) and Q m (mg.g -1 ) are the equilibrium and maximum sorption capacities, respectively. K L (L.mg -1 ) is Langmuir binding constant. In the Freundlich equation, K f (mg/g.(L/mg) 1/ n ) is the Freundlich constant which narrates the relative capacity and n describes the material’s adsorption intensity. The Langmuir and Freundlich models were employed to fit the experimental data to describe the adsorption process of uranium by red soil aggregates. The fitting curves are presented in Fig. 7. The adsorption processes of red soil aggregates S1 and S3 were better fitted to the Freundlich model, as the R² values of the Freundlich model were higher than those of the Langmuir model in Table 2. As a classical nonlinear adsorption model, the Freundlich model is more suitable for describing adsorption phenomena that occur on heterogeneous surfaces or in multiphase systems. This suggests that the adsorption behavior of red soil aggregates S1 and S3 may be influenced by the complexity of the soil's surface physical and chemical properties, demonstrating adsorption characteristics typical of heterogeneous surfaces. The adsorption processes of red soil aggregates S2 and S4 were more closely aligned with the Langmuir model, with significantly better fitting coefficients than the Freundlich model. The Langmuir model is based on the theoretical assumption of monolayer adsorption, where the adsorbent surface possesses uniform adsorption sites, each capable of binding only one molecule, and no interactions occur between the adsorbed molecules. This result indicates that red soil aggregates S2 and S4 likely exhibit a relatively homogeneous adsorption surface, with their adsorption behavior being more consistent with a monolayer adsorption mechanism. In summary, the adsorption behavior of U (VI) on the surface of red soil aggregates was primarily governed by monolayer adsorption, with a maximum adsorption capacity of 8.403 mg/g. Table 2 Isotherm fitting parameters of uranium adsorption by red soil aggregateswith different particle sizes Red soil aggregates Langmuir Freundlich Q m (mg/g) R 2 K L (L·mg/g) n R 2 K F S1 3.625 0.949 0.028 1.760 0.987 0.2187 S2 2.279 0.894 0.048 2.226 0.889 0.266 S3 5.304 0.937 0.078 2.155 0.980 0.718 S4 8.403 0.876 0.048 1.709 0.870 0.641 Mechanisms and behavior The XRD patterns of red soil aggregates with different particle sizes are presented in Fig. 8 The analysis revealed that the primary crystalline minerals in the tested red soil consisted of quartz (SiO₂), kaolinite (Al₂[(OH)₄/Si₂O₅]), hematite (Fe₂O₃), and albite (Na₂O·Al₂O₃·6SiO₂), among others. The surface morphology of red soil aggregates after static adsorption experiments is shown in Fig. 9 Compared with the surface morphology of red soil aggregatesof different sizes before adsorption, no significant changes were observed in the surface morphology of red soil aggregates, which remained predominantly heterogeneous aggregates surrounded by small debris-like and granular particles. The surface elemental composition was obtained by energy-dispersive spectroscopy (EDS) scanning of the surface of red soil aggregates different sizes after adsorption to verify whether uranium was successfully adsorbed onto the surface of red soil aggregates. As shown in Fig. 10 and Table 3, a certain amount of uranium was detected on the surface of the red soil aggregates after uranium adsorption. The mass percentages of uranium(VI) in red soil aggregates S1, S2, S3, and S4 were 1.8%, 2.62%, 3.44%, and 3.93%, respectively, with uranium content increasing as the particle size of the red soil aggregates decreased. This is consistent with the influence of red soil aggregate size on uranium adsorption efficiency, indicating that smaller red soil aggregates exhibit better uranium adsorption. Table 3 EDS components of red soil aggregates with different particle sizes after adsorption Red soil aggregates Element O Na Mg Al Si Fe U S1 Mass percentage (%) 41.24 0.29 0.46 19.56 19.74 16.92 1.8 Element percentage (%) 59.29 0.29 0.43 16.68 16.17 6.97 0.17 S2 Mass percentage (%) 23.73 0.19 0.61 18.28 21.27 33.31 2.62 Element percentage (%) 41.68 0.23 0.71 19.04 21.28 16.76 0.31 S3 Mass percentage (%) 44.14 0.82 0.47 18.91 21.68 10.53 3.44 Element percentage (%) 61.45 0.8 0.43 15.61 17.19 4.2 0.32 S4 Mass percentage (%) 48.68 0.66 0.84 17.6 21.98 6.31 3.93 Element percentage (%) 65.15 0.61 0.74 13.97 16.76 2.42 0.35 The FTIR analysis results (Fig. 11) demonstrated significant variations in the characteristic peaks of the surface functional groups of red soil aggregates of different particle sizes before and after U(VI) adsorption. Specifically, the broad absorption band observed in the 3400-3600 cm -1 wavenumber range can be attributed to the stretching vibrations of hydroxyl groups (-OH) in the aggregate surface structure. The peak near 1630 cm -1 corresponds to the stretching vibrations of C=O and C=C bonds, while the peaks in the 1030-1080 cm -1 range are assigned to C-O stretching in organic compounds or Si-O stretching in silicates(Luo et al., 2017). The peaks at approximately 795 cm -1 , 690 cm -1 , and 463 cm -1 are attributed to Fe-O, Al-O-Si, and Si-O-Si vibrations. After uranium adsorption, the intensity of these peaks decreased significantly, with the -OH peak near 3620 cm -1 shifting to 3623 cm -1 and the C-O stretching vibration peak at 1031 cm -1 undergoing a blue shift to 1080 cm -1 , wheras no noticeable shifts were observed for other characteristic absorption peaks. These phenomena clearly indicate that ion exchange or complexation occurred between the uranyl ions (UO2 2+ ) and the surface hydroxyl groups (-OH) on the aggregates. The characteristic infrared absorption bands of uranium should theoretically appear in the 800-1100 cm -1 range. However, in this experiment, the limited uranium adsorption capacity of red soil aggregates, combined with the strong characteristic vibration peaks of functional groups such as Si-O and C-O from mineral components within the same wavenumber range, resulted in the masking of the vibration signals from trace uranyl ions (U-O). No discernible characteristic absorption peaks for uranium were observed in the infrared spectra. The observed -OH stretching vibrations before and after adsorption may originate from alcohol, phenol, or carboxylic acid functional groups, while the C=O stretching vibration peaks likely arise from conjugated double bonds in the carbonyl groups of aldehydes, ketones, esters, or carboxylic acids. The partial peak shifts observed after adsorption may be attributed to UO2 2+ ions replacing H + in the hydroxyl or amino groups, forming U-O bonds. These findings demonstrate that the abundant functional groups present in red soil aggregates (-OH, Si-O, Si-O-Si, Si-O-Al, and Fe-O) play a crucial role in uranium adsorption. X-ray photoelectron spectroscopy (XPS) analysis was performed to further elucidate the adsorption mechanism between red soil aggregates and uranium (Fig. 12-15), revealing distinct U4f peaks after adsorption, confirming successful uranium uptake, consistent with the EDS results. The characteristic spin-orbit splitting of approximately 10 eV between the U4f 7/2 and U4f 5/2 peaks was observed, with peak positions varying within a narrow range owing to the crystal structure effects and neighboring ions. Minor satellite peaks, resulting from photoelectrons of valence electrons that lost partial initial energy when core-level electrons were ejected (creating electrostatic potentials that simultaneously excited valence electrons to higher empty orbitals or into the continuum), appeared at positions determined by the energy difference between the ground and excited states as well as oxidation state of the element and neighboring ion characteristics(Ilton, Boily, & Bagus, 2007; Van den Berghe, Laval, Gaudreau, Terryn, & Verwerft, 2000). Specifically, uranium satellite peaks emerged near 385 eV, while the main peaks for different samples appeared at 377.77 eV (U4f 7/2 ) and 392.77 eV (U4f 5/2 ) for S1; 378.46 eV and 392.12 eV for S2; 381.08 eV and 391.36 eV for S3; and 382.82 eV and 393.04 eV for S4, corresponding to mixed U(IV) and U(VI) oxidation states that demonstrated redox reactions during adsorption(Scott, Allen, Heard, & Randell, 2005). The systematic shift of the U4f peaks toward higher binding energies indicates that uranium primarily existed as U(VI) on the aggregate surfaces(Rout, Ravi, Kumar, & Tripathi, 2017). The redox reaction between UO2 2+ and the Fe 2+ /Fe 3+ cycle significantly influenced both uranium adsorption and redox transformation on red soil aggregate surfaces(S. Zhang et al., 2022). Post-adsorption XPS analysis revealed systematic shifts in the Fe2p spectra toward higher binding energies: specifically, the Fe2p 3/2 and Fe2p 1/2 peaks shifted from 711.21 to 711.91 eV and from 724.30 to 723.37 eV in S1; from 711.64 to 711.8 eV and from 724.22 to 724.94 eV in S2; from 713.15 to 712.79 eV and from 724.53 to 722.6 eV in S3; and from 712.78 to 713.50 eV and from 724.17 to 725.84 eV in S4. These binding energy transitions demonstrate strong chemical complexation between iron-bearing minerals in red soil aggregates and uranyl ions during adsorption. The observed changes in the peak intensities further confirmed the occurrence of redox reactions that partially reduced U(VI) to U(IV), ultimately forming UO2 2+ precipitates adsorbed on the aggregate surfaces(Chen et al., 2023). The elemental composition and compound content of the experimental red soil are presented in Table 4. As shown in the table, the predominant elemental constituents of the tested red soil were O (50.94%), Si (23.56%), Al (14.39%), Fe (6.78%), and K (2.49%), which is consistent with the EDS spectral analysis results (Fig. 16) The major chemical compounds were identified as SiO₂ (54.07%), Al₂O₃ (28.68%), Fe₂O₃ (10.79%), and K₂O (3.29%), with only trace amounts of alkali metal oxides.' Table 4 The elemental composition and oxide content of red soil obtained from XRF testing Elemental Mass% Oxide content Mass% O 50.94 Na 2 O 0.45 Na 0.32 MgO 0.87 Mg 0.51 Al 2 O 3 28.68 Al 14.39 SiO 2 54.07 Si 23.56 P 2 O 5 0.235 P 0.09 SO 3 0.110 S 0.04 K 2 O 3.29 K 2.49 CaO 0.053 Ca 0.03 TiO 2 1.13 Ti 0.61 Cr 2 O 3 0.027 Cr 0.017 MnO 0.13 Mn 0.09 Fe 2 O 3 10.79 Fe 6.78 NiO 0.013 Zr 0.03 Conclution In this study, red soil aggregates of varying particle sizes were prepared, and their uranium adsorption behaviors were investigated using batch static adsorption experiments. The following conclusions were drawn from the adsorption characteristics under different experimental conditions: The key factors governing uranium adsorption on red soil aggregates include aggregate particle size, liquid-to-solid ratio, solution pH, initial uranium concentration, reaction time, and temperature. As the liquid-to-solid ratio increased, the uranium adsorption rate by the red soil aggregates initially decreased rapidly before it stabilized. Smaller aggregate particle sizes exhibited better uranium adsorption. Higher initial uranium concentrations led to a gradual decrease in the adsorption rate. The effects of different liquid-to-solid ratios, particle sizes, reaction times, pH levels, initial U(VI) concentrations, and temperatures on U(VI) adsorption exhibited two distinct trends: S1 and S2 aggregates showed similar adsorption rate patterns, whereas S3 and S4 displayed comparable adsorption characteristics. This phenomenon may be attributed to the differences in the physicochemical properties of the aggregates. Under ambient temperature conditions, the maximum uranium adsorption rates were achieved when using 0.2 g of red soil aggregates (S1, S2, S3, and S4) with a liquid-to-solid ratio of 100, pH 5, 10-hour adsorption time, and initial uranium concentration of 10 mg/L. The corresponding adsorption capacities were 0.552, 0.709, 0.889, and 0.99 mg/g, respectively. The uranium adsorption kinetics for all aggregate sizes conformed to a pseudo-second-order kinetic model. Isothermal adsorption studies revealed that aggregates S1 and S3 followed the Langmuir isotherm model, whereas S2 and S4 exhibited a better fit with the Freundlich isotherm model. Comparative analysis revealed no significant morphological changes in red soil aggregates of different particle sizes before and after uranium adsorption. The surface morphology remained predominantly heterogeneous, with aggregates, accompanied by debris-like and granular particles. Energy-dispersive spectroscopy detected uranium in the post-adsorption aggregates, with uranium content increasing as particle size decreased. FTIR analysis demonstrated that U(VI) forms strong complexes with surface functional groups (-OH, Si-O, Si-O-Fe, Si-O-Al, Fe-O) for adsorption. XPS spectral analysis before and after adsorption further revealed that the adsorption mechanism involved redox reactions between uranyl ions and iron-bearing minerals in the aggregates. Declarations Author contributions Xuchen Weng: Ideas, investigation, data curation, and writing the original draft. Guangya Kuang: Conceptualization, methodology. Jiaai Chen: Performing the experiments and data collection. Xiu Taoyuan: Investigation, validation and supervision. Limin Zhou: Visualization and investigation. Zhirong Liu: Supervision, writing-review & editing, funding acquisition and project administration Funding Funding financial support from The National Natural Science Foundation of China (No. 12475337, 22266004) and China Uranium Industry Corporation-East China University of Technology State Key Laboratory of Nuclear Resources and Environment Joint Innovation Fund Project (2023NRE-LH-18) are gratefully appreciated. Data availability No datasets were generated or analysed during the current study. Competing interests The authors declare no competing interests. References Bister, S., Birkhan, J., Lüllau, T., Bunka, M., Solle, A., Stieghorst, C., . . . Walther, C. (2015). Impact of former uranium mining activities on the floodplains of the Mulde River, Saxony, Germany. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY, 144 , 21-31. https://doi.org/10.1016/j.jenvrad.2015.02.024 Chandrasekar, T., Sabarathinam, C., Viswanathan, P. M., Rajendiran, T., Mathivanan, M., Natesan, D., & Samayamanthula, D. 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JOURNAL OF SOILS AND SEDIMENTS, 16 (3), 821-830. https://doi.org/10.1007/s11368-015-1274-4 You, Y., Dou, J. F., Xue, Y., Jin, N. F., & Yang, K. (2022). Chelating Agents in Assisting Phytoremediation of Uranium-Contaminated Soils: A Review. SUSTAINABILITY, 14 (10). https://doi.org/10.3390/su14106379 Yu, C. X., Berger, T., Drake, H., Song, Z. L., Peltola, P., & Åström, M. E. (2019). Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton. SCIENCE OF THE TOTAL ENVIRONMENT, 663 , 16-28. https://doi.org/10.1016/j.scitotenv.2019.01.293 Zhang, S., Peiffer, S., Liao, X., Yang, Z., Ma, X., & He, D. (2022). Sulfidation of ferric (hydr)oxides and its implication on contaminants transformation: a review. SCIENCE OF THE TOTAL ENVIRONMENT, 816 , 151574. https://doi.org/10.1016/j.scitotenv.2021.151574 Zhang, T., Jiang, X. Y., Liu, Q., Shang, T. W., Zhong, X. H., & Meng, C. X. (2023). Changes of active particulate uranium under the Water-Sediment Regulation Scheme in the lower Yellow River: Potential impact to the uranium flux into the global ocean. MARINE POLLUTION BULLETIN, 192 . https://doi.org/10.1016/j.marpolbul.2023.115014 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7138153","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492419320,"identity":"a031d0e9-06ee-4508-9171-2f6b34452bad","order_by":0,"name":"Xuchen Weng","email":"","orcid":"","institution":"East China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xuchen","middleName":"","lastName":"Weng","suffix":""},{"id":492419321,"identity":"f5fa4109-e69e-43e0-b56f-21e979b42843","order_by":1,"name":"Guangya Kuang","email":"","orcid":"","institution":"East China University of 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11:41:47","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":99895,"visible":true,"origin":"","legend":"\u003cp\u003eFe2p spectrogram of red soil aggregate S3 before and after adsorption of U(VI): (a); (c) U4f spectrogram of red soil aggregate S3 before and after adsorption of U(VI): (b); (d)\u003c/p\u003e","description":"","filename":"14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7138153/v1/ff55837d37c2c7af00dabdce.jpg"},{"id":87919843,"identity":"f21033a6-1206-40ee-b066-8a5a8eb698f5","added_by":"auto","created_at":"2025-07-30 11:33:46","extension":"jpg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":101579,"visible":true,"origin":"","legend":"\u003cp\u003eFe2p spectrogram of red soil aggregate S4 before and after adsorption of U(VI): (a); (c) U4f spectrogram of red soil aggregate S4 before and after adsorption of U(VI): (b); (d)\u003c/p\u003e","description":"","filename":"15.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7138153/v1/d851b0f124d7abffd4727248.jpg"},{"id":87919856,"identity":"db3898ef-3eec-4346-905b-673afa5b901b","added_by":"auto","created_at":"2025-07-30 11:33:46","extension":"jpg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":98113,"visible":true,"origin":"","legend":"\u003cp\u003eEDS spectra of red soil aggregates with different particle sizes: (a) S1; (b) S2; (c) S3; (d) S4\u003c/p\u003e","description":"","filename":"16.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7138153/v1/1a2c3af72001c3af5605649f.jpg"},{"id":89594516,"identity":"600e1a23-6c98-4564-9137-aeca7b2455df","added_by":"auto","created_at":"2025-08-21 16:31:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2151551,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7138153/v1/c4221ed7-d9b2-482d-876d-65cd47a9adfe.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"U(VI) adsorption mechanisms and behavior of red soil aggregates in typical uranium tailings mining areas in Jiangxi, China","fulltext":[{"header":"Introduction","content":"\u003cp\u003eUranium (U), a naturally occurring radioactive element, is a critical resource for nuclear power generation, however its mining and processing pose significant environmental risks. Owing to its pivotal role in nuclear energy generation, it has garnered increasing global attention. Uranium is present in the Earth's crust at an average concentration of 3 mg/kg(Henner et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and commonly exists in various forms within rocks and soils, such as uranium ores, carnotite, and pitchblende(Selvakumar et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Thivya et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Wu, Wang, \u0026amp; Xie, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Yu et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As reported in the World Nuclear Performance Report (2021), 443 nuclear reactors were operational globally with a total capacity of 3.94 \u0026times; 10⁵ MWe, alongside 57 reactors under construction with a capacity of 5.88 \u0026times; 10⁴ MWe. In 2020, global nuclear electricity generation reached 2.55 \u0026times; 10\u0026sup3; TWh, while the annual demand for uranium surged to 6.25 \u0026times; 10⁴ tons(You, Dou, Xue, Jin, \u0026amp; Yang, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eUranium mining produces substantial amounts of waste rock and tailings, which are often stored in open-air dumps and tailings ponds for long periods. Long-term exposure of uranium tailings to atmospheric erosion and rainwater leaching leads to the gradual release of toxic metals and radionuclides, which subsequently migrate to the surrounding water and soil environment through hydrological and wind-driven processes. This phenomenon has caused severe ecological contamination in areas adjacent to the uranium tailings. Uranium pollution threatens human habitats and health. Thus, it is imperative to implement proactive measures to mitigate the environmental impact of uranium waste and safeguard ecological habitats.\u003c/p\u003e\u003cp\u003eThe mobility of uranium in groundwater is primarily governed by its oxidation state, with U(IV) being the dominant species. The solubility and transport of uranium in groundwater are highly dependent on water-rock interactions, climatic conditions, and hydrogeochemical factors, including pH, redox potential, ionic strength, and bicarbonate concentration(Chandrasekar et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Vengosh, Coyte, Podgorski, \u0026amp; Johnson, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Elevated uranium levels in groundwater are often associated with uranium mineralization zones or uranium-rich source rocks (e.g., granite)(Sharma, Bajwa, \u0026amp; Kaur, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). For instance, the average uranium concentration in the Yellow River on China\u0026rsquo;s Loess Plateau ranges between 2.04 and 7.83 \u0026micro;g/L, significantly exceeding the global average for major rivers, likely due to severe soil erosion in the region(T. Zhang et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Investigations of groundwater in India have revealed widespread uranium concentrations surpassing the World Health Organization WHO provisional guideline of 30 \u0026micro;g/L, attributed to geological factors such as uranium content in aquifer rocks, oxidation states, and groundwater chemistry favoring the formation of soluble uranyl-carbonate complexes(Coyte et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Similarly, in Spain\u0026rsquo;s Ridaura Basin, groundwater uranium levels reached up to 37.7 \u0026micro;g/L, with granite weathering identified as the primary source(Sharma et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe persistent accumulation of uranium contaminants in aquatic systems poses severe environmental risks and adversely affects the biosphere. According to the (WHO), the recommended guideline for uranium in drinking water, classified as a human carcinogen, should not exceed 15 \u0026micro;g/L(Henner et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Consequently, the effective purification of uranium-contaminated radioactive water has emerged as a critical socio-environmental challenge.\u003c/p\u003e\u003cp\u003eIn soil microenvironments, physicochemical processes predominantly occur at the interfaces of the aggregate structural units. Soil aggregates exhibit multiscale heterogeneity in their particle size distribution, resulting in variations in composition, microstructure, and physicochemical properties. Consequently, the environmental behavior of heavy metals (e.g., uranium) differs markedly across different aggregate size fractions. Given the complexity of soil composition and structure, fractionation-based studies of soil aggregates provide more precise insights into the geochemical behavior of uranium than bulk soil analyses. Uranium migration in soils can lead to groundwater infiltration, posing risks to water supplies, ecosystems, and human health in uranium tailing regions. While soils act as natural barriers against uranium migration owing to their adsorption capacity, they also serve as primary receptors of exogenous uranium contamination.\u003c/p\u003e\u003cp\u003ePrevious research on soil aggregates has primarily focused on stability assessment and particle size distribution, with limited attention paid to microstructural characteristics (e.g., pore morphology, spatial arrangement of minerals, and distribution of organic matter). The aggregate size fractions differed significantly in terms of composition, specific surface area, pore features, and iron/aluminum oxide content. Larger aggregates are enriched in quartz, feldspar, and SiO₂, whereas smaller aggregates contain higher proportions of amphibole, mica, iron or aluminum oxides, and hydroxides. Iron or aluminum oxides contribute to aggregate formation and stability while immobilizing heavy metals through their high surface areas and functional groups. Generally, smaller aggregates exhibit greater organic matter and iron oxide content, higher specific surface area, and more adsorption sites, leading to increased heavy metal accumulation(Xiao et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Adsorption-desorption dynamics are influenced by the surface area, pore structure, coexisting organic matter, and ions, with mechanisms including electrostatic attraction, hydrogen bonding, pore filling, ion exchange, and complexation.\u003c/p\u003e\u003cp\u003eThe key factors governing uranium speciation in subsurface environments include soil solution pH, cation types/concentrations, ligand (e.g., carbonate) availability, redox conditions, organic matter content, and mineral composition. These geochemical parameters dictate uranium speciation and modulate soil surface properties, thereby affecting adsorption. Bister et al.(Bister et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) reported higher uranium concentrations in alluvial soils beneath pastures than in farmland in Germany\u0026rsquo;s Mulde River floodplain. Johnson et al.(De Windt et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) observed depth-dependent uranium variation in alkaline desert soils, with distribution coefficients correlating with clay content and pH. Stojanovic et al.(Izquierdo et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) found no significant relationship between total/available uranium and humus content in Serbian soil types. Li et al.(X. Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) demonstrated that uranium adsorption in vadose zone soils was optimal at pH 7.0, with solution pH, contact time, initial concentration, and colloids being major influencing factors.\u003c/p\u003e\u003cp\u003eIn summary, environmental geochemical factors critically regulate the physicochemical behavior uranium in soils, ultimately governing its subsurface migration. Recent studies have predominantly focused on uranium transport mechanisms in aquifers, leaving a knowledge gap regarding uranium mobility and exogenous contamination in red soils from typical uranium tailings in southern China. To address this issue, a comprehensive investigation of uranium adsorption and transport characteristics within soil aggregates from these regions is urgently warranted.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eChemicals and reagents\u003c/p\u003e\n\u003cp\u003eUranium nitrate hexahydrate and nitric acid were purchased from Shanghai McLean Biochemical Technology Co., Ltd. Azoarsine, Chloroacetic acid and sodium acetate were purchased from Sinopharm Chemical Reagent Co., Ltd. Hydrochloric acid was purchased from Shillong Chemical Co., Ltd. Uranium hexahydrate nitrate is reagent grade, and all other chemicals are analytical grade.\u003c/p\u003e\n\u003cp\u003eInstrumentation\u003c/p\u003e\n\u003cp\u003eThe elemental composition, morphology, surface texture, and mapping studies of the prepared biocomposites were investigated using a scanning electron microscope (SEM, JEOL-JSM-5600) and an EDX detector. X-ray diffraction (XRD, Bruker D/8 Discover Plus, GER) analysis was performed using a diffractometer to examine the crystallinity phase, crystal structure, and other physical properties. Identification of important functional groups using Fourier transform infrared spectroscopy (FTIR, Nicolet Magna-550, USA) with a working range of 500\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 40 scans per spectrum. U(VI) analysis was performed by complexation using the Arsenazo-III method and absorbance was recorded on a high-resolution dual-beam Ultraviolet-Visible Spectroscopy (UV-Vis, K8001, JPN).\u003c/p\u003e\n\u003cp\u003ePreparation of red soil aggregates with varying size fractions\u003c/p\u003e\n\u003cp\u003eTen grams of sample was placed in a 500 mL beaker and diluted to 300 mL with deionized water. The mixture was thoroughly stirred with a glass rod and ultrasonicated for 30 min to achieve complete dispersion of the soil aggregates(Ma, Song, Liu, Kang, \u0026amp; Yue, \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e). The well-dispersed suspension was then sequentially passed through 1, 0.25, and 0.053 mm nylon sieves (Quanguan Experimental Instrument Center). The soil fractions retained on each sieve were transferred with deionized water to pre-weighed culture dishes, dried, and weighed to obtain red soil aggregates of \u0026gt;\u0026thinsp;1, 1-0.25, and 0.25\u0026thinsp;\u0026minus;\u0026thinsp;0.053 mm size fractions. For particles\u0026thinsp;\u0026lt;\u0026thinsp;1 \u0026micro;m, the centrifugation time was calculated according to Stokes\u0026apos; law, and the suspension containing particles\u0026thinsp;\u0026lt;\u0026thinsp;1 \u0026micro;m was obtained by centrifugation at predetermined speed and duration. This suspension was concentrated by rotary evaporation and freeze-dried to obtain the \u0026lt;\u0026thinsp;1 \u0026micro;m red soil aggregates, while the pellet in the centrifuge tube represented the 1-0.05 mm fraction.\u003c/p\u003e\n\u003cp\u003eAdsorption experiments and methodology\u003c/p\u003e\n\u003cp\u003eStatic adsorption experiments were conducted using 50 mL centrifuge tubes as reaction vessels. The tubes were placed in a constant-temperature shaker set at 25 \u003csup\u003e0\u003c/sup\u003eC with a rotation speed of 200 rpm. After reaching the predetermined adsorption time, an aliquot of the supernatant was filtered through a 0.22 \u0026micro;m membrane to determine the uranyl ion concentration in the solution. The uranyl ion concentrations were quantified using UV-Vis spectrophotometry at 650 nm using the arsenazo-III method. The adsorption percentage (\u003cem\u003eR\u003c/em\u003e, %) and equilibrium adsorption capacity (\u003cem\u003eQe\u003c/em\u003e, mg/kg) of uranium(VI) on red soil aggregates were calculated using the following formulas:\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{Q}}_{\\text{t}}\\text{=}\\frac{\\text{(}{\\text{C}}_{\\text{0}}\\text{\u0026minus;}{\\text{C}}_{\\text{t}}\\text{)}\\text{V}}{\\text{m}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEq.\u0026nbsp;(1)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{Q}}_{\\text{e}}\\text{=}\\frac{\\text{(}{\\text{C}}_{\\text{0}}\\text{\u0026minus;}{\\text{C}}_{\\text{e}}\\text{)}\\text{V}}{\\text{m}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEq.\u0026nbsp;(2)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{R}\\text{(%)}\\text{=}\\frac{\\text{(}{\\text{C}}_{\\text{e}}\\text{\u0026minus;}{\\text{C}}_{\\text{t}}\\text{)}\\text{V}}{\\text{m}}\\text{\u0026times;}\\text{100}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEq. (3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe adsorption parameters are defined as follows: \u003cem\u003eR\u003c/em\u003e (%) represents the adsorption percentage of uranium(VI) by red soil aggregates; \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e (mg/g) denotes the adsorption capacity of uranium(VI) by red soil aggregates at time t (min); \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e (mg/g) is the equilibrium adsorption capacity of uranium(VI) by red soil aggregates; \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e (mg/L) indicates the initial mass concentration of uranium(VI); \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e (mg/L) represents the concentration of uranium(VI) in solution at reaction time t (min); \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e (mg/L) stands for the equilibrium concentration of uranium(VI) in solution; \u003cem\u003em\u003c/em\u003e (mg) and \u003cem\u003eV\u003c/em\u003e (mL) correspond to the mass of red soil aggregates and the volume of uranium(VI) solution used in each adsorption experiment, respectively. Error bars were calculated upon duplicate runs of each sorption experiment, and nonlinear regression analysis was conducted using Origin Pro 2021.\u003c/p\u003e\n\u003cp\u003eAll experiments were performed in duplicate with the following influencing factors:\u003c/p\u003e\n\u003cp\u003e(1) Adsorption time\u003c/p\u003e\n\u003cp\u003eRed soil aggregates (0.2 g) with different particle sizes were separately placed in 50 mL centrifuge tubes, to which uranium solution with an initial concentration of 10 mg/L was added. The uranium concentrations in the solution were measured after 0.1, 0.5, 2, 4, 6, 8, 10, 16, and 24 h to investigate the effect of adsorption time on U(VI) adsorption by red soil aggregates and to determine the adsorption equilibrium time.\u003c/p\u003e\n\u003cp\u003e(2) Liquid-solid ratio\u003c/p\u003e\n\u003cp\u003eA 0.2 g soil sample was placed in conical flasks with liquid-solid ratios (mL/g) of 20, 50, 100, 200, 300, and 400. The initial uranium concentration was 10 mg/L, and the initial pH of the uranium solution was adjusted to 5.0 using HNO\u003csub\u003e3\u003c/sub\u003e and NaOH. The adsorption time was 10 h to investigate the effects of the liquid-solid ratio and red soil aggregate particle size on U(VI) adsorption.\u003c/p\u003e\n\u003cp\u003e(3) Initial pH\u003c/p\u003e\n\u003cp\u003eRed soil aggregates (0.2 g) with different particle sizes were separately placed in 50 mL centrifuge tubes, to which uranium solution with an initial concentration of 10 mg/L was added. The initial pH of the uranium solution was adjusted to 2, 3, 4, 5, 7, and 8 using HNO\u003csub\u003e3\u003c/sub\u003e and NaOH solutions. The adsorption time was 10 h to investigate the effect of the initial pH on U(VI) adsorption by red soil aggregates of different sizes.\u003c/p\u003e\n\u003cp\u003e(4) Initial uranium concentration\u003c/p\u003e\n\u003cp\u003eAt room temperature, red soil aggregates (0.2 g) with different particle sizes were placed in 50 mL centrifuge tubes, to which uranium standard solutions with initial concentrations of 10, 15, 20, 30, 50, and 100 mg/L were added. The pH was maintained at 5.0 with an adsorption time of 10 h to investigate the effect of initial uranium concentration on U(VI) adsorption by different-sized red soil aggregates.\u003c/p\u003e\n\u003cp\u003e(5) Temperature\u003c/p\u003e\n\u003cp\u003eRed soil aggregates (0.2 g) with different particle sizes were separately placed in 50 mL centrifuge tubes, to which uranium solution with an initial concentration of 10 mg/L was added. The initial pH of the uranium solution was adjusted to 5 using HNO\u003csub\u003e3\u003c/sub\u003e and NaOH solution. The experimental temperatures were set at 25, 30, 35, and 40 \u003csup\u003e0\u003c/sup\u003eC with an adsorption time of 10 h to investigate the effect of temperature on U(VI) adsorption by red soil aggregates of different sizes.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003ch2\u003eEffects of particle size and liquid-solid ratio\u003c/h2\u003e\n\u003cp\u003eThe effects of red soil aggregate particle size and liquid-to-solid ratio (under fixed conditions: t = 24 h, pH = 5.0, T = 25 \u003csup\u003e0\u003c/sup\u003eC, \u003cem\u003eC\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e = 10 mg/L, with liquid-to-solid ratios of 50, 100, 150, 200, 300, and 400) on uranium(VI) adsorption are shown in\u0026nbsp;Fig.1 The results indicated that uranium adsorption efficiency increased as aggregate particle size decreased, with significant differences observed between aggregates S1/S2 and S3/S4. Specifically, S1 and S2 exhibited similar U(VI) adsorption rates, as did S3 and S4, following the overall trend of S4 \u0026gt; S3 \u0026gt; S2 \u0026gt; S1. This correlation is attributed to the fact that smaller aggregates possess greater internal porosity and larger specific surface areas, with the total pore volume increasing as the particle size decreases(Y. L. Li et al., 2020). These findings align with those of Li Shiyou et al., who reported enhanced uranium adsorption capacity with reduced clay particle size in wastewater treatment studies, consistent with our observation that the smallest aggregate fraction (S4) achieved maximum uranium adsorption efficiency.\u003c/p\u003e\n\u003cp\u003eWith an increasing liquid-to-solid ratio, the uranium adsorption efficiency of the red soil aggregates exhibited an initial sharp decline, followed by gradual stabilization. This trend suggests that increasing the uranium solution volume leads to a relative shortage of available adsorption sites, resulting in reduced adsorption capacity. When the liquid-to-solid ratio exceeded a certain threshold (specifically \u0026gt; 100 in this study), the uranium solution became excessive and the adsorption rate stabilized with minimal further variation. To minimize interference from the liquid-to-solid ratio effects in subsequent adsorption experiments, an optimal ratio of 100 was selected for all further investigations.\u003c/p\u003e\n\u003ch2\u003eMedium pH\u003c/h2\u003e\n\u003cp\u003eMedium pH significantly influences various factors affecting uranium adsorption, including soil surface charge, chemical speciation of heavy metal ions, degree of metal ion hydrolysis, solubility of organic matter, and nature of functional groups on soil adsorption media. In this study, we investigated the uranium binding capacity of different-sized red soil aggregates (S1-S4) across a pH gradient (2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0) under controlled conditions (t = 24 h, T = 25 \u003csup\u003e0\u003c/sup\u003eC, \u003cem\u003eC\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e = 10 mg/L, L/M = 100), with results shown in Fig. 2 Similar to the effects of liquid-to-solid ratio and particle size, S1 and S2 exhibited comparable uranium(VI) adsorption rates, as did S3 and S4 across all pH levels. The adsorption efficiency exhibited strong pH dependence, increasing with pH until it stabilizatd above pH 6.\u003c/p\u003e\n\u003cp\u003eUnder acidic conditions (pH \u0026lt; 5), competitive adsorption between H⁺ ions and uranyl cations for surface sites limited uranium uptake, with lower pH values (higher H⁺ concentration) resulting in a poorer adsorption performance. As the pH increased, UO₂\u0026sup2;⁺ hydrolysis produced cationic species, including UO₂(OH)⁺, (UO₂)₂(OH)₂\u0026sup2;⁺, and (UO₂)₃(OH)₅⁺, while simultaneously enhancing the adsorption capacity of clay minerals and organic matter in the aggregates through increased surface negative charges, facilitating complexation adsorption. Above pH 6, the hydroxyl complexation of uranium(VI) reduces uranyl ion mobility, consequently decreasing adsorption efficiency. To minimize pH interference while maintaining environmental relevance, subsequent experiments were conducted at pH 5 (approximating natural red soil pH) to investigate other factors affecting uranium(VI) adsorption by different aggregate fractions.\u003c/p\u003e\n\u003ch2\u003eUranium initial mass concentration\u003c/h2\u003e\n\u003cp\u003eBatch experiments were conducted to investigate the effect of initial uranium(VI) concentration (10, 15, 20, 30, 50, and 100 mg/L) on adsorption by different-sized red soil aggregates under controlled conditions (t = 10 h, T = 25 \u003csup\u003e0\u003c/sup\u003eC, pH = 5, L/M = 100 mL/g), and the results are presented in Fig. 3 The data revealed a concentration-dependent adsorption pattern, where uranium(VI) uptake increased with higher initial concentrations. Consistent with previous observations regarding the liquid-to-solid ratio, particle size, contact time, and pH effects, aggregates S1 and S2 showed similar adsorption capacities, as did S3 and S4 across all tested concentrations, following the established size-dependent trend: S4 \u0026gt; S3 \u0026gt; S2 \u0026gt; S1.\u003c/p\u003e\n\u003cp\u003eA rapid increase in uranium(VI) adsorption capacity occurred within the 10-50 mg/L concentration range, followed by progressively diminishing returns at higher concentrations (\u003cem\u003eC\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e \u0026gt; 50 mg/L). At the maximum tested concentration (100 mg/L), the adsorption efficiency approached equilibrium, demonstrating that lower initial uranium(VI) concentrations yielded greater relative adsorption efficiency but smaller absolute adsorption capacity when using fixed amounts of red soil aggregates. This saturation behavior reflects the finite availability of active adsorption sites on the aggregates at a constant solid-phase mass.\u003c/p\u003e\n\u003ch2\u003eTemperature\u003c/h2\u003e\n\u003cp\u003eStatic adsorption experiments were conducted to investigate the effect of reaction temperature (25, 30, 35, 40 \u003csup\u003e0\u003c/sup\u003eC) on U(VI) adsorption by red soil aggregates of different sizes under controlled conditions (t = 10 h, pH = 5, \u003cem\u003eC\u003csub\u003e0\u003c/sub\u003e\u003c/em\u003e = 10 mg/L, L/M = 100 mL/g). The removal rates of S1 and S2 aggregates were similar, and S3 and S4 were similar, which showed the same pattern as the above influencing factors, which may be attributed to the small particle size span of S1 and S2 aggregates and the large span of S2 and S3 aggregates. There is a transition particle size between S2 and S3, and the aggregates with particle sizes S1 and S2 are grouped together, and the aggregates of S3 and S4 are grouped together, and the same type of aggregates have similar adsorption properties. As shown in Fig. 4, the adsorption efficiency remained relatively stable with gradual increases in temperature, indicating that temperature had no significant impact on uranium adsorption by the red soil aggregates. Consequently, a room temperature (25 \u003csup\u003e0\u003c/sup\u003eC) was selected for all subsequent experiments to maintain operational consistency.\u003c/p\u003e\n\u003ch2\u003eU(VI) Adsorption Kinetics\u003c/h2\u003e\n\u003cp\u003eTo systematically analyze the adsorption kinetics of uranium at the interface of red soil aggregates, the adsorption experimental data obtained at multiple time points were fitted using linear regression analysis with pseudo-first-order (PFONL)\u0026nbsp;and pseudo-second-order (PSONL)\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ekinetic equations. The linear equations for the two models are given by equations Eq. (4) to (5). In the equations, equilibrium and instantaneous sorption capacities of composite materials are denoted by\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003eQ\u003c/em\u003e\u003cem\u003e\u003csub\u003ee\u003c/sub\u003e\u003c/em\u003e (mg/g) and \u003cem\u003eQ\u003c/em\u003e\u003cem\u003e\u003csub\u003et\u003c/sub\u003e\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e(mg/g), respectively. The rate constants for PFONL and PSORE are denoted by symbols k\u003csub\u003e1\u003c/sub\u003e (min\u003csup\u003e-1\u003c/sup\u003e) and k\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(g\u003csup\u003e.\u0026nbsp;\u003c/sup\u003emg\u003csup\u003e-1.\u0026nbsp;\u003c/sup\u003emin\u003csup\u003e-1\u003c/sup\u003e), respectively. The resulting fitting curves are shown in Fig. 5 and 6, and the corresponding kinetic parameters are presented in Table 1. As illustrated in the figures and table, the adsorption kinetics were best fitted by a pseudo-second-order model (R\u0026sup2; \u0026gt; 0.93), indicating chemisorption-dominated processes. The theoretical equilibrium adsorption capacity derived from this model closely matched the experimentally measured saturation adsorption capacity. Therefore, the adsorption of uranium by red soil can be more accurately described by the pseudo-second-order kinetic model, which effectively characterizes the adsorption behavior of U (VI) on red soil aggregates of different particle sizes. The adsorption rate is primarily controlled by chemical adsorption.\u003c/p\u003e\n\u003cp\u003e\u003cimg 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/HYIBAK4fPkyHj58iIMHD9atnDeKEokELl68CMuynECu6zp2yE+SiKhvdkwwhys4SNlsdmCC5uTkJCzLqils0P+/L6gug7hdSzASEQ2zHRXMiYiIRtGO6TMnIiIaVQzmREREQ47BnIiIaMgxmBMREQ05BnMiIqIhx2BOREQ05BjMiYiIhhyDORER0ZBjMCciIhpyDOZERERDjsGciIhoyDGYExERDTkGcyIioiHHYE5ERDTkGMyJiIiGHIM5ERHRkGMwJyIiGnIM5kREREOOwZyIiGjIMZgTERENOQZzIiKiIcdgTkRENOQYzImIiIYcgzkREdGQYzAnIiIacgzmREREQ47BfEik02kEAgHkcjk1iYiIRhyD+YBLp9MIhUI4ffo0NjY21GQiIqLhDOa2bSMUCqm7d6RQKIR0Og3DMNSkkVMsFhGLxdTdREQjbyiD+blz53D48GF19442PT2t7hoptm3jvffew6lTp9QkIqKRN1TBPJfLIRAIYHV1FW+99ZaavKPt2bNH3TUy0uk0Dhw4gP/85z+YmppSk4mIRt7QBPPp6WnMzs46/ca//vWvkUgk1MNoBykWi5icnMTp06dhWRYqlQrGxsY4CJCISDE0wfzJkydIJpMAgGg0CiEEFhYW1MNoB5mamsKLFy8QDAYBAJlMBkIIzMzMqIcSEY20oQnmAHDnzh0AYL/piFldXYWmaZifn1eTiIhomIK5bdvY2NiAruvsNx0ha2trQHVUPxERNTY0wfzevXsA4DS50mi4e/cuAODo0aNqEhERVQ1NMP/iiy8AAIcOHVKTaAdLp9MAgAMHDqhJRERUNTTBfHNzk/2mI6ZYLKJSqSAYDGJ8fFxNJiKiqqEI5mtra6hUKuw3HTG3b98GABw/flxNIiIil6EI5l9//TVQ7Te1bRvFYlE9ZMf79ttv1V073ubmJgDgyJEjKBaLsG1bPYSIiIYlmH/zzTcAgPn5eVy/fh0/+9nP1EN2NNu2ncD217/+VU3esfL5PEzTBKq1dDa1ExE1NhTB/LXXXgMAxGIxXLhwYaQy9UAggN27d8OyLADA0tLSSKyCZts2dF3HixcvcOvWLVy7dk09hIiIqsaEEELdSURERMNjKGrmRERE5I3BnIiIaMgxmBMREQ05BnPqWCwWG8npgkREg4LBnDr2zTff4KefflJ3ExGNjOXl5S3NMsrlckgkEurutjGYExHRwBkbG2tr20og7QbbthEIBPDWW29hZmZGTUYikag717GxMac1c2ZmBgcPHkQgEOhoYSwGcyIiGjhCCFiWBU3TAADxeBxCiLrNsiwYhqH+876Qgfzy5csNX81t2zY+/vhjdTdM06w5fmZmBmfOnOkooI9sMPcqLTXbiIiofyYmJrB//351d42JiQmsrKzg2bNnalLPnTt3DtPT0w1r5ABw69YtXLp0qa4Asr6+rh6KUCgEXddx7tw5NcmXkQ3mCwsLdTe41UZERINnamoKH3zwgbq7p9bW1rC6uur5vbZt489//jPef/99NcnT7373O6yurmJtbU1NammggrlaE97K1k/qd++0TeXVmrGxsYHZ2dm6/Y0+Q03v1UZE1Evnz5+HrusNm9cB4MqVK7AsCwcOHEAsFkOpVFIPqTMzMwNN03D+/Hk1qaWBCub95BWYmm2jzqs1wzRNZLPZuv1szSCiXovFYuouRy6XQygUcvLw6elpLC8vIxAIdDRgLpfLwbIszM3NqUkAgFKphKWlJQCAZVlYXFyEruuIxWIt+8Tn5uZgWVbb030HKpirgWArm19eganZplLTd9rWC+p39Gojop0vl8s5QVOVTqdx7NgxHD58GEIIlMtlnDx5EmfPnsXGxoZ6eFu++uorAMCePXvUJKDajy+EQKFQQCqVct7+uLi4iEAgoB5e48033wSqb4psx0AFcyIiokYuXrxY11o6OzuLSqWiHopcLofTp0/j5s2bTp/2+Pg4FhYWujLyXb6W+5e//KWaVGNqagqhUAjr6+tIpVLQNA35fL7pvPJXX30VcH2HXwzmREQ08BpNTctms87UNberV69C0zSEQiE1qSuv0JY1+127dqlJnkKhED777DMAaDhdTXrjjTcA13f4xWA+wtRxA530IRER9dvMzAzC4XDNPtu2sbGx0XJK23aYn5+HaZqoVCq+BsS1g8F8RKXTacDVhx0OhzE7O7ulgL5v3z688sor6m4iop67du1azd+fP39e8/dB8+677wJA15fAZjAfYQsLC86fb968CQB4+PCh6wh/rl275jk9g4hoO7x48ULdNRBeffVVaJrW9TxzaIK5bdvOlALZLPz6668jFAptqTY56hr1Jem6jp///Ofq7r4qlUqIxWKYnp52nvPk5CQikUjXm6WIaOcolUpYXl52VmOzLKtnsUGOTv/+++/VpJYePHhQ1zXg9uOPPwKu7/BrKIL58vIyfvGLX+DOnTs4f/680zR8//59WJaF2dlZLC8vq/+M2lAqlWBZVsMg3w+2bSMWi0HXdVQqFaysrDjP+caNG0in0zAMo2f/OYlouAWDQRw5csT5MwAcO3asZr52sVjE48ePnb+7LS8v+44j+/btAwB89913ahJQHU0vuzLdisUiNjc3ceHCBTXJ8a9//QtwfYdvYoCVy2URDAYFABGPx9VkIarHaJomAIhsNqsm91WhUBDJZFIEg0ERDofV5IEWj8dFKpVSd/dFoVAQhmEITdNEJpNRk4UQQmSzWQFAaJomyuWymkxEO1A2m3Xy92AwqCYLUc0/TNMUpmk6+yzLcv4dAGEYhjBNU4TDYWGaZl28kPmLut9LoVBoek7yOwzDEKlUSmSzWRGNRoVhGKJQKKiH1wiHw77Pw22gg7m8IV6BXIpGo01vbD/E43HnxwCgJ4HRsiznByG/R9d1EQ6HhWVZ6uG+WZa1bYWPdgpj8rqTyaSaREQ7jDs/9bOpeW6hUHAqg5qmOXGkUTAvl8tC13Wh67rvyoI8vhFZQZHnZppm3fl5afa5zQxsMJcB2l3a8pLJZJwHtt3kj8fvD8KPcrns3I9wOFxTsstkMkLTNKFpWstg6GUrP5xukT/4VgU2MSCFNiIabo2C+VbIuNOqpt0OWeP3aqFsZiCDubvJw8+NSiaTzvHbqVwu+y6A+NXrJujtDOSyNcNvaVgWlLp5f4lotHQrmItqntTNykU4HN7y5w3kALirV68C1UEMfobvv3z5EgAargTUT/fu3QNc8wg7Zds2Dh8+jHw+jy+//BLz8/PqIUB14QTDMFCpVPD555+ryZ4mJyexublZs69fo8Zt23ZWQfrjH//oa1Wm//73vwCA1157TU0iIuq7Tz75BJZlbemVpapisYgnT57gk08+UZN8GbhgXiwWnWXsfvvb36rJDf3tb38DgG1f8efBgwcA4Iyo7FQgEEClUkE8HnemW3iRb++5f/++mtTQ2NgYLMuCrus1q8Ch+pKAXvv888+dNZVPnDihJteRqzrB9SICIqJ22LbtzD+XL0vpxPj4ONbX1/GXv/yl7becuRWLRVy8eBHr6+u+KjaNDFwwd69H61UTdSuVSsjn80AXa8RbJadPTUxM1L0QYGxsrK2HnUgkkM/noeu6r5fbW5YFuGqvrahrHMtNLh7Ta3fu3AGqcyn9/Hhlqwe2MP+SiCiRSGD37t1OXrm4uOhUYDoxPj6OdDqNR48ebWnqbC6Xw6NHjzoK5BjEYP6Pf/wDaCPDls3Kmqb5quH1ytraGiqVilNDlkuk6rqOVCqFcrnsq8sAI9IELQtt77zzjprU0KeffgpUfxd+7yMRkeT12utu+eCDD1q2oDYyMzPjvNmtEwMXzNvhDnqXLl3yFfR65e7duwCAU6dOAdVmEwD45z//iVAo1Na5sQm6Vi6Xc67v8uXLajIR0cgb6mB+/fp1VCoVGIZRs874dtjc3ISu65iamkI6ncbGxgZu3rzZVhCX2ARd68MPPwQARKPRLZV8iYh2uoEL5rLZ1bZtNalGOp3G4uIiNE3DysqKmtxXxWIRlmVhbm4OiUQCkUiko8LFKDRBy0KHnIngJRKJIJ/PwzCMpksgEhGNsoEL5idOnICmacjn856DCdLpNE6fPg1N03D//v1tD2C3b98GADx58gRPnz5FpVLxHOw2OTlZ8wKRTg1rE/T58+cBAEtLS54Ft0gkgqWlJRiG0fHgECKiHU2deD4IUqmUswiKewk89/J8wWDQ10Ij/aDrutA0TViW5awK1GjJUdM0a5ZdlQumqOQCOH5WRZMrqEWjUTVp4Mk1iA3DqFnAIZPJtLUyHBHRqBvIYC6qq5rJwC03wzBENBr1tSqcqK4w1sma5X5YluUULhr93X2cuuKQLLSo5yhXKGoVoN3BcFAKNu1KpVI1axijusJbMpmsuy9ERNTYwAZzUV0eVb51pl2WZTWs9XabXErWfY6ypi55vcRELsOqcq817xWkd0IglwqFgtB13XchjYiIatVHkgFRKBTqmtn90nW9pqan1oi7SdYq3QHV/Qq7ZDLpGWzj8bhnoB+VJuhUKiU0TesokLvfWNePAhwR0aAZyGCeyWTaqqmlUqm6Jlld17dUEGiHV5O6rFmbpukZyIWPl5zs9CboeDzeVstCo8KLXn0FrHA9j51wb4iI2jEmurkEThcsLy/j7NmzNfsMw8D09DTefvtt7N+/31k7XK7jfuLEiZr1xEulEnRd7+rqPt2WSCRw8ODBlvOmi8Ui3nvvPfz973/f9lH73WLbNq5cuYKlpaWa/aZpYt++fTh06BAOHDjgjF5fW1vDv//9b5w4caJmRHskEgEAZwnadDqNy5cvO2svExGNioEK5rZtO5m1bdt4/vw5nj175rxNRq7Brus6DMPA8ePHEQqFlE/5X6b+6aefYn19XU0aCOl0Gt99913LuejpdBqRSKSj6XeJRAIXL14EqvdtEAKd+zmXSiX88MMPePjwIZ4+fYp8Pu+snSwLcb/5zW/qCj25XA6zs7OwLAsTExOYnJyEZVkDXYAjIuoZtaq+E4TD4YZNsoMgm8169pO7sQm6OXc/uRyfQEQ0qgZu0Zhu2NzcxMGDB9Xd2y6Xy+Hq1at1byYLBALOn23bRiQSwcWLF5HP57F7926MjY0hEAggFothbW2tZpGVtbU1LC8v171ZLRKJYG5uzvmux48fQ9f1vrzetB++/fZbpytFCOHU3BOJhHooEdGO939InODPKkAuQQAAAABJRU5ErkJggg==\" width=\"499\" height=\"121\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Kinetic fitting parameters for uranium adsorption on red soil aggregates with different particle sizes\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"604\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 92px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRed soil\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eaggregates\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 211px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePFONL\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"6\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 245px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePSONL\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003ee\u0026nbsp;\u003c/sub\u003e(mg/kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e (mg/kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eS1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.346\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e0.931\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.456\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.056\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.978\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eS2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.925\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e0.652\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.638\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.041\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.939\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eS3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.313\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e0.978\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.898\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.070\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.998\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 92px;\"\u003e\n \u003cp\u003eS4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 79px;\"\u003e\n \u003cp\u003e0.258\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e0.953\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.992\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.094\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.998\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eAdsorption isotherms model\u003c/h2\u003e\n\u003cp\u003eBased on the isothermal adsorption experimental data of uranium on red soil aggregates, the relationship between the residual uranium concentration in the solution at adsorption equilibrium and the adsorption capacity of the aggregates was systematically analyzed. The experimental sorption data was fitted into different adsorption models such as Langmuir and Freundlich. The equations for the Langmuir isothermal adsorption model are shown in Eq. (6) and (7), and the equations for the Frenrich isothermal adsorption model are shown in Eq. (8) and (9). In the Langemuir equation, \u003cem\u003eC\u003csub\u003ee\u0026nbsp;\u003c/sub\u003e\u003c/em\u003e(mg.L\u003csup\u003e-1\u003c/sup\u003e) is the equilibrium concentration,\u0026nbsp;\u003cem\u003eQ\u003c/em\u003e\u003cem\u003e\u003csub\u003ee\u003c/sub\u003e\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e(mg.g\u003csup\u003e-1\u003c/sup\u003e) and \u003cem\u003eQ\u003c/em\u003e\u003cem\u003e\u003csub\u003em\u003c/sub\u003e\u003c/em\u003e (mg.g\u003csup\u003e-1\u003c/sup\u003e) are the equilibrium and maximum sorption capacities, respectively. \u003cem\u003eK\u003csub\u003eL\u003c/sub\u003e\u003c/em\u003e (L.mg\u003csup\u003e-1\u003c/sup\u003e) is Langmuir binding constant. In the\u0026nbsp;Freundlich\u0026nbsp;equation,\u0026nbsp;\u003cem\u003eK\u003csub\u003ef\u003c/sub\u003e\u003c/em\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e(mg/g.(L/mg)\u003csup\u003e1/\u003c/sup\u003e\u003csup\u003en\u003c/sup\u003e) is the Freundlich constant\u0026nbsp;which narrates the\u0026nbsp;relative capacity and\u0026nbsp;n describes\u0026nbsp;the material\u0026rsquo;s adsorption intensity.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Langmuir and Freundlich models were employed to fit the experimental data to describe the adsorption process of uranium by red soil aggregates. The fitting curves are presented in Fig. 7. The adsorption processes of red soil aggregates S1 and S3 were better fitted to the Freundlich model, as the \u003cem\u003eR\u0026sup2;\u003c/em\u003e values of the Freundlich model were higher than those of the Langmuir model in Table 2. As a classical nonlinear adsorption model, the Freundlich model is more suitable for describing adsorption phenomena that occur on heterogeneous surfaces or in multiphase systems. This suggests that the adsorption behavior of red soil aggregates S1 and S3 may be influenced by the complexity of the soil\u0026apos;s surface physical and chemical properties, demonstrating adsorption characteristics typical of heterogeneous surfaces.\u003c/p\u003e\n\u003cp\u003eThe adsorption processes of red soil aggregates S2 and S4 were more closely aligned with the Langmuir model, with significantly better fitting coefficients than the Freundlich model. The Langmuir model is based on the theoretical assumption of monolayer adsorption, where the adsorbent surface possesses uniform adsorption sites, each capable of binding only one molecule, and no interactions occur between the adsorbed molecules. This result indicates that red soil aggregates S2 and S4 likely exhibit a relatively homogeneous adsorption surface, with their adsorption behavior being more consistent with a monolayer adsorption mechanism.\u003c/p\u003e\n\u003cp\u003eIn summary, the adsorption behavior of U (VI) on the surface of red soil aggregates was primarily governed by monolayer adsorption, with a maximum adsorption capacity of 8.403 mg/g.\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\" width=\"469\" height=\"369\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eIsotherm fitting parameters of uranium adsorption by red soil aggregateswith different particle sizes\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"604\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 107px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRed soil\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eaggregates\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 223px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLangmuir\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"6\" style=\"width: 47px;\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 227px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFreundlich\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e\u003cem\u003eQ\u003csub\u003em\u003c/sub\u003e\u003c/em\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e(mg/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003e\u003cem\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003eL\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/sub\u003e(L\u0026middot;mg/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cem\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u003cem\u003eK\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003eS1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e3.625\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003e0.949\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.028\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1.760\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.987\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.2187\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003eS2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e2.279\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003e0.894\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.048\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e2.226\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.889\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.266\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003eS3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e5.304\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003e0.937\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.078\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e2.155\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.980\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.718\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003eS4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e8.403\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 67px;\"\u003e\n \u003cp\u003e0.876\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.048\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e1.709\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.870\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e0.641\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003ch2\u003eMechanisms and\u0026nbsp;behavior\u003c/h2\u003e\n\u003cp\u003eThe XRD patterns of red soil aggregates with different particle sizes are presented in Fig. 8 The analysis revealed that the primary crystalline minerals in the tested red soil consisted of quartz (SiO₂), kaolinite (Al₂[(OH)₄/Si₂O₅]), hematite (Fe₂O₃), and albite (Na₂O\u0026middot;Al₂O₃\u0026middot;6SiO₂), among others.\u003c/p\u003e\n\u003cp\u003eThe surface morphology of red soil aggregates after static adsorption experiments is shown in Fig. 9 Compared with the surface morphology of red soil aggregatesof different sizes before adsorption, no significant changes were observed in the surface morphology of red soil aggregates, which remained predominantly heterogeneous aggregates surrounded by small debris-like and granular particles.\u003c/p\u003e\n\u003cp\u003eThe surface elemental composition was obtained by energy-dispersive spectroscopy (EDS) scanning of the surface of red soil aggregates different sizes after adsorption to verify whether uranium was successfully adsorbed onto the surface of red soil aggregates. As shown in Fig. 10 and Table 3, a certain amount of uranium was detected on the surface of the red soil aggregates after uranium adsorption. The mass percentages of uranium(VI) in red soil aggregates S1, S2, S3, and S4 were 1.8%, 2.62%, 3.44%, and 3.93%, respectively, with uranium content increasing as the particle size of the red soil aggregates decreased. This is consistent with the influence of red soil aggregate size on uranium adsorption efficiency, indicating that smaller red soil aggregates exhibit better uranium adsorption.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e EDS components of red soil aggregates with different particle sizes after adsorption\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"611\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 110px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRed soil\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eaggregates\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003eNa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003eU\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 110px;\"\u003e\n \u003cp\u003eS1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eMass percentage (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e41.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e19.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e19.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e16.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eElement percentage\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e59.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e16.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e16.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e6.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 110px;\"\u003e\n \u003cp\u003eS2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eMass percentage (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e23.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e18.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e21.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e33.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e2.62\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eElement percentage\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e41.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e19.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e21.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e16.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e0.31\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 110px;\"\u003e\n \u003cp\u003eS3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eMass percentage\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e44.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e18.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e21.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e10.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e3.44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eElement percentage\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e61.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e15.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e17.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e4.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 110px;\"\u003e\n \u003cp\u003eS4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eMass percentage\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e48.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e17.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e21.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e6.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e3.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eElement percentage\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e65.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 43px;\"\u003e\n \u003cp\u003e0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e13.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 49px;\"\u003e\n \u003cp\u003e16.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e2.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe FTIR analysis results (Fig. 11) demonstrated significant variations in the characteristic peaks of the surface functional groups of red soil aggregates of different particle sizes before and after U(VI) adsorption. Specifically, the broad absorption band observed in the 3400-3600 cm\u003csup\u003e-1\u003c/sup\u003e wavenumber range can be attributed to the stretching vibrations of hydroxyl groups (-OH) in the aggregate surface structure. The peak near 1630 cm\u003csup\u003e-1\u003c/sup\u003e corresponds to the stretching vibrations of C=O and C=C bonds, while the peaks in the 1030-1080 cm\u003csup\u003e-1\u003c/sup\u003e range are assigned to C-O stretching in organic compounds or Si-O stretching in silicates(Luo et al., 2017). The peaks at approximately 795 cm\u003csup\u003e-1\u003c/sup\u003e, 690 cm\u003csup\u003e-1\u003c/sup\u003e, and 463 cm\u003csup\u003e-1\u003c/sup\u003e are attributed to Fe-O, Al-O-Si, and Si-O-Si vibrations. After uranium adsorption, the intensity of these peaks decreased significantly, with the -OH peak near 3620 cm\u003csup\u003e-1\u003c/sup\u003e shifting to 3623 cm\u003csup\u003e-1\u003c/sup\u003e and the C-O stretching vibration peak at 1031 cm\u003csup\u003e-1\u003c/sup\u003e undergoing a blue shift to 1080 cm\u003csup\u003e-1\u003c/sup\u003e, wheras no noticeable shifts were observed for other characteristic absorption peaks. These phenomena clearly indicate that ion exchange or complexation occurred between the uranyl ions (UO2\u003csup\u003e2+\u003c/sup\u003e) and the surface hydroxyl groups (-OH) on the aggregates.\u003c/p\u003e\n\u003cp\u003eThe characteristic infrared absorption bands of uranium should theoretically appear in the 800-1100 cm\u003csup\u003e-1\u003c/sup\u003e range. However, in this experiment, the limited uranium adsorption capacity of red soil aggregates, combined with the strong characteristic vibration peaks of functional groups such as Si-O and C-O from mineral components within the same wavenumber range, resulted in the masking of the vibration signals from trace uranyl ions (U-O). No discernible characteristic absorption peaks for uranium were observed in the infrared spectra. The observed -OH stretching vibrations before and after adsorption may originate from alcohol, phenol, or carboxylic acid functional groups, while the C=O stretching vibration peaks likely arise from conjugated double bonds in the carbonyl groups of aldehydes, ketones, esters, or carboxylic acids. The partial peak shifts observed after adsorption may be attributed to UO2\u003csup\u003e2+\u003c/sup\u003e ions replacing H\u003csup\u003e+\u003c/sup\u003e in the hydroxyl or amino groups, forming U-O bonds. These findings demonstrate that the abundant functional groups present in red soil aggregates (-OH, Si-O, Si-O-Si, Si-O-Al, and Fe-O) play a crucial role in uranium adsorption.\u003c/p\u003e\n\u003cp\u003eX-ray photoelectron spectroscopy (XPS) analysis was performed to further elucidate the adsorption mechanism between red soil aggregates and uranium (Fig. 12-15), revealing distinct U4f peaks after adsorption, confirming successful uranium uptake, consistent with the EDS results. The characteristic spin-orbit splitting of approximately 10 eV between the U4f\u003csub\u003e7/2\u003c/sub\u003e and U4f\u003csub\u003e5/2\u003c/sub\u003e peaks was observed, with peak positions varying within a narrow range owing to the crystal structure effects and neighboring ions. Minor satellite peaks, resulting from photoelectrons of valence electrons that lost partial initial energy when core-level electrons were ejected (creating electrostatic potentials that simultaneously excited valence electrons to higher empty orbitals or into the continuum), appeared at positions determined by the energy difference between the ground and excited states as well as oxidation state of the element and neighboring ion characteristics(Ilton, Boily, \u0026amp; Bagus, 2007; Van den Berghe, Laval, Gaudreau, Terryn, \u0026amp; Verwerft, 2000). Specifically, uranium satellite peaks emerged near 385 eV, while the main peaks for different samples appeared at 377.77 eV (U4f\u003csub\u003e7/2\u003c/sub\u003e) and 392.77 eV (U4f\u003csub\u003e5/2\u003c/sub\u003e) for S1; 378.46 eV and 392.12 eV for S2; 381.08 eV and 391.36 eV for S3; and 382.82 eV and 393.04 eV for S4, corresponding to mixed U(IV) and U(VI) oxidation states that demonstrated redox reactions during adsorption(Scott, Allen, Heard, \u0026amp; Randell, 2005). The systematic shift of the U4f peaks toward higher binding energies indicates that uranium primarily existed as U(VI) on the aggregate surfaces(Rout, Ravi, Kumar, \u0026amp; Tripathi, 2017).\u003c/p\u003e\n\u003cp\u003eThe redox reaction between UO2\u003csup\u003e2+\u003c/sup\u003e and the Fe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e cycle significantly influenced both uranium adsorption and redox transformation on red soil aggregate surfaces(S. Zhang et al., 2022). Post-adsorption XPS analysis revealed systematic shifts in the Fe2p spectra toward higher binding energies: specifically, the Fe2p\u003csub\u003e3/2\u003c/sub\u003e and Fe2p\u003csub\u003e1/2\u003c/sub\u003e peaks shifted from 711.21 to 711.91 eV and from 724.30 to 723.37 eV in S1; from 711.64 to 711.8 eV and from 724.22 to 724.94 eV in S2; from 713.15 to 712.79 eV and from 724.53 to 722.6 eV in S3; and from 712.78 to 713.50 eV and from 724.17 to 725.84 eV in S4. These binding energy transitions demonstrate strong chemical complexation between iron-bearing minerals in red soil aggregates and uranyl ions during adsorption. The observed changes in the peak intensities further confirmed the occurrence of redox reactions that partially reduced U(VI) to U(IV), ultimately forming UO2\u003csup\u003e2+\u0026nbsp;\u003c/sup\u003eprecipitates adsorbed on the aggregate surfaces(Chen et al., 2023).\u003c/p\u003e\n\u003cp\u003eThe elemental composition and compound content of the experimental red soil are presented in Table 4. As shown in the table, the predominant elemental constituents of the tested red soil were O (50.94%), Si (23.56%), Al (14.39%), Fe (6.78%), and K (2.49%), which is consistent with the EDS spectral analysis results (Fig. 16) The major chemical compounds were identified as SiO₂ (54.07%), Al₂O₃ (28.68%), Fe₂O₃ (10.79%), and K₂O (3.29%), with only trace amounts of alkali metal oxides.\u0026apos;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u003c/strong\u003e The elemental composition and oxide content of red soil obtained from XRF testing\u003c/p\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Elemental\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMass%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOxide content\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMass%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e50.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eNa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eMgO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e28.68\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e14.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e54.07\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e23.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.235\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.110\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e3.29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e2.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eCaO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.053\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e1.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eCr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.027\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eCr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eMnO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e10.79\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e6.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eNiO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.013\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eZr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"Conclution","content":"\u003cp\u003eIn this study, red soil aggregates of varying particle sizes were prepared, and their uranium adsorption behaviors were investigated using batch static adsorption experiments. The following conclusions were drawn from the adsorption characteristics under different experimental conditions:\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eThe key factors governing uranium adsorption on red soil aggregates include aggregate particle size, liquid-to-solid ratio, solution pH, initial uranium concentration, reaction time, and temperature. As the liquid-to-solid ratio increased, the uranium adsorption rate by the red soil aggregates initially decreased rapidly before it stabilized. Smaller aggregate particle sizes exhibited better uranium adsorption. Higher initial uranium concentrations led to a gradual decrease in the adsorption rate. The effects of different liquid-to-solid ratios, particle sizes, reaction times, pH levels, initial U(VI) concentrations, and temperatures on U(VI) adsorption exhibited two distinct trends: S1 and S2 aggregates showed similar adsorption rate patterns, whereas S3 and S4 displayed comparable adsorption characteristics. This phenomenon may be attributed to the differences in the physicochemical properties of the aggregates.\u003c/li\u003e\n \u003cli\u003eUnder ambient temperature conditions, the maximum uranium adsorption rates were achieved when using 0.2 g of red soil aggregates (S1, S2, S3, and S4) with a liquid-to-solid ratio of 100, pH 5, 10-hour adsorption time, and initial uranium concentration of 10 mg/L. The corresponding adsorption capacities were 0.552, 0.709, 0.889, and 0.99 mg/g, respectively. The uranium adsorption kinetics for all aggregate sizes conformed to a pseudo-second-order kinetic model. Isothermal adsorption studies revealed that aggregates S1 and S3 followed the Langmuir isotherm model, whereas S2 and S4 exhibited a better fit with the Freundlich isotherm model.\u003c/li\u003e\n \u003cli\u003eComparative analysis revealed no significant morphological changes in red soil aggregates of different particle sizes before and after uranium adsorption. The surface morphology remained predominantly heterogeneous, with aggregates, accompanied by debris-like and granular particles. Energy-dispersive spectroscopy detected uranium in the post-adsorption aggregates, with uranium content increasing as particle size decreased. FTIR analysis demonstrated that U(VI) forms strong complexes with surface functional groups (-OH, Si-O, Si-O-Fe, Si-O-Al, Fe-O) for adsorption. XPS spectral analysis before and after adsorption further revealed that the adsorption mechanism involved redox reactions between uranyl ions and iron-bearing minerals in the aggregates.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003eXuchen Weng: Ideas, investigation, data curation, and writing the original draft. Guangya Kuang: Conceptualization, methodology. Jiaai Chen: Performing the experiments and data collection. Xiu Taoyuan: Investigation, validation and supervision. Limin Zhou: Visualization and investigation. Zhirong Liu: Supervision, writing-review \u0026amp; editing, funding acquisition and project administration\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eFunding financial support from The National Natural Science Foundation of China (No. 12475337, 22266004) and China Uranium Industry Corporation-East China University of Technology State Key Laboratory of Nuclear Resources and Environment Joint Innovation Fund Project (2023NRE-LH-18) are gratefully appreciated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003eNo datasets were generated or analysed during the current study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBister, S., Birkhan, J., L\u0026uuml;llau, T., Bunka, M., Solle, A., Stieghorst, C., . . . Walther, C. (2015). 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Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton. \u003cem\u003eSCIENCE OF THE TOTAL ENVIRONMENT, 663\u003c/em\u003e, 16-28. https://doi.org/10.1016/j.scitotenv.2019.01.293\u003c/li\u003e\n\u003cli\u003eZhang, S., Peiffer, S., Liao, X., Yang, Z., Ma, X., \u0026amp; He, D. (2022). Sulfidation of ferric (hydr)oxides and its implication on contaminants transformation: a review. \u003cem\u003eSCIENCE OF THE TOTAL ENVIRONMENT, 816\u003c/em\u003e, 151574. https://doi.org/10.1016/j.scitotenv.2021.151574\u003c/li\u003e\n\u003cli\u003eZhang, T., Jiang, X. Y., Liu, Q., Shang, T. W., Zhong, X. H., \u0026amp; Meng, C. X. (2023). Changes of active particulate uranium under the Water-Sediment Regulation Scheme in the lower Yellow River: Potential impact to the uranium flux into the global ocean. \u003cem\u003eMARINE POLLUTION BULLETIN, 192\u003c/em\u003e. https://doi.org/10.1016/j.marpolbul.2023.115014\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"uranium, red soil, aggregates, adsorption, uranium tailings","lastPublishedDoi":"10.21203/rs.3.rs-7138153/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7138153/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigated the adsorption behavior and mechanisms of uranium on red soil aggregates of different particle sizes from a typical uranium tailings area in Jiangxi Province. Static adsorption experiments were conducted to examine the interaction between uranium and soil aggregates, with the aim of elucidating the characteristics of exogenous uranium contamination. The adsorption kinetics followed a pseudo-second-order kinetic model, indicating chemisorption-dominated processes at equilibrium. Isothermal adsorption analysis revealed that aggregates S1 and S3 adhered to the Langmuir model, suggesting monolayer adsorption, whereas S2 and S4 followed the Freundlich model, implying heterogeneous multilayer adsorption. Scanning electron microscopy (SEM) and spectroscopic analyses demonstrated that the surface morphology of the aggregates remained largely unchanged after adsorption, and their aggregated structure was maintained. Further characterization indicated that uranium adsorption primarily occurred through (i) complexation with surface functional groups (\u0026ndash;OH, Si\u0026ndash;O, Si\u0026ndash;O\u0026ndash;Fe, Si\u0026ndash;O\u0026ndash;Al, Fe\u0026ndash;O) and (ii) redox reactions with iron-bearing minerals in the aggregate. These findings provide critical insights into the immobilization mechanisms of uranium in red soils, which are relevant for environmental remediation strategies in uranium-contaminated areas.\u003c/p\u003e","manuscriptTitle":"U(VI) adsorption mechanisms and behavior of red soil aggregates in typical uranium tailings mining areas in Jiangxi, China","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-30 11:33:41","doi":"10.21203/rs.3.rs-7138153/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"571dd45c-9d1b-4ba5-a1f6-8c98e332f4a0","owner":[],"postedDate":"July 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-21T16:23:40+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-30 11:33:41","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7138153","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7138153","identity":"rs-7138153","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}