Ferrihydrite exhibits considerable potential in remediating uranium-contaminated soils and sediments, owing to its excellent adsorption capacity and eco-friendly characteristics. However, how the Fe(II)-catalyzed ferrihydrite transformation influences uranium speciation in the presence of dissolved organic matter (DOM) remains poorly understood. Such understanding is crucial for implementing effective remediation strategies for contaminated environments. This study investigated the roles of DOM in regulating U(VI) reduction during Fe(II)-catalyzed ferrihydrite transformation at the nanoscale and molecular levels, by integrating Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and electrochemical analysis. Our results revealed that DOM inhibited ferrihydrite transformation to goethite, but significantly promoted U(VI) reduction to U(V) (e.g., incorporated forms) and U(IV) (e.g., UO2 precipitates). Moreover, DOM reduced the local aggregation of uranium on Fe minerals, which may create a favorable condition for U(VI) reduction by Fe(II) on the goethite surface. Electrochemical analysis indicated that DOM enhanced electron transfer between Fe(II) and U(VI) at the goethite surface, and served as an electron donor in U(VI) reduction process. Finally, based on FT-ICR-MS analysis, two types of molecules were identified to be closely associated with electron transfer and U(VI) reduction: (1) CHOS and CHONS molecules (present in phenols and polyphenols) characterized by high oxygen content as well as low unsaturation, aromaticity, and molecular weight; and (2) CHON1 molecules (present in phenols) with high unsaturation and molecular weight. These findings provide new insights into uranium sequestration mechanisms in contaminated soils and sediments.

Regenerable cathodes that integrate efficient charge transfer with abundant binding sites are essential for electrochemical U(VI) capture in hybrid capacitive deionization (HCDI) systems. Herein, Ti3C2Tx MXene (MXene), a two-dimensional transition metal carbide, a high-entropy Prussian blue analogue (HEPBA), and their composite, MXene-HEPBA, were evaluated as cathode materials for electro-assisted U(VI) removal. MXene mainly exhibited electric double-layer capacitive behavior, whereas HEPBA and MXene-HEPBA showed pronounced Faradaic redox characteristics. By coupling the conductive MXene scaffold with the multimetal coordination-active HEPBA framework, MXene-HEPBA delivered specific capacitances of 87 F/g at 1.25 A/g and 67 F/g at 6.25 A/g. In synthetic U(VI)-containing solutions, MXene-HEPBA achieved a U(VI) uptake capacity of 56 mg/g under optimized HCDI conditions and exhibited efficient regeneration, with a desorption efficiency of 92% using 0.5 mol/L HNO3 under a reverse voltage of 0.8 V. In actual uranium-bearing groundwater, MXene-HEPBA achieved approximately 59% U(VI) removal, corresponding to an uptake capacity of 47.612 mg/g after pH and flow-rate optimization. Mechanistic analyses revealed that U(VI) was mainly immobilized as coordinated uranyl-like species through coupled electrosorption, surface complexation, and multisite coordination involving MXene surface terminations and HEPBA coordination sites. These results demonstrate its potential as a regenerable HCDI cathode for electrochemical purification of uranium-contaminated groundwater.

Ferrihydrite regulates uranium (U) geochemical behavior and holds great potential for remediating U-contaminated aquatic systems due to its high natural abundance and superior adsorption capacity. However, lighttriggered phase transformation of ferrihydrite and its impacts on U immobilization and stability remain poorly understood. Herein, we investigated U removal during visible-light-induced ferrihydrite transformation at an initial U concentration of 5 mg L-1, pH 5.0-8.0, and under ambient air. Immobilization mechanisms and sequestration stability were further clarified at a representative pH of 6.0 using X-ray diffraction (XRD), highresolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), electron spin resonance spectroscopy, chemical extraction, and kinetic release experiments. Our results showed that 10 mg L-1 ferrihydrite achieved 98% U removal efficiency under illumination at pH 7.0, markedly higher than 72% under dark conditions. XRD and HR-TEM analyses confirmed the light-induced transformation of ferrihydrite to goethite, which proceeded via photoelectron-mediated reductive dissolution of structural Fe(III) and subsequent oxidation of generated Fe(II) by reactive species (e.g., center dot O2- and center dot OH). This mineral transformation facilitated U (VI) immobilization through multiple synergistic pathways: adsorption onto iron minerals, reduction to poorly mobile U(IV) (e.g., 7.1% U(IV) fraction as revealed by XPS), and structural incorporation or physical encapsulation within iron mineral phases. Furthermore, NaHCO3 extraction and kinetic experiments revealed that continuous illumination significantly enhanced the stability of immobilized U relative to dark conditions. This work provides new insights into the photochemical fate of U in Fe-rich systems and offers a sustainable photocatalytic strategy for the remediation of U-contaminated environments.

Soil desertification induced by mineral exploitation has emerged as a critical factor exacerbating environmental deterioration and land degradation. Cellulose derivatives, as highly promising soil remediation materials, have garnered significant attention in the field of desertified soil amelioration. However, their ameliorative effects in uranium mine desertified soils remain unclear. To address this, the remediation effects of sodium carboxymethyl cellulose (CMC), applied at varying concentrations on uranium mine desertified soils and the mechanisms underlying its enhancement of Boehmeria nivea (L.) Gaudich phytoremediation. The results indicated that CMC improved soil structure through adsorption and binding, increasing the composition of macroaggregates in the soil, thereby enhancing soil stability and uranium immobilization capacity. Additionally, CMC addition increased soil nutrient content and facilitated the succession of rhizosphere microbial communities, which in turn improved Boehmeria nivea (L.) Gaudich biomass, stress resistance, and uranium accumulation capacity. Furthermore, CMC amendment enhanced the proportion of bioavailable uranium in the soil by regulating the interactions among soil, rhizosphere microbiota, and Boehmeria nivea (L.) Gaudich. The increase in bioavailable uranium facilitated the absorption and accumulation of uranium by Boehmeria nivea (L.) Gaudich, thereby improving soil remediation efficiency.

The environmental behavior of uranium (U) in soils is predominantly governed by its speciation, which is mediated by soil properties and environmental conditions. Soil water content is a critical driver of soil properties, but the specific mechanisms underlying its impacts on U speciation and stability remain poorly understood. Here, we investigated the mechanisms controlling U fraction and stability in U-contaminated soils under different water content conditions, by employing soil incubation experiments, chemical extraction, stirred-flow experiments, kinetic modeling, and statistical analyses. Results revealed that, relative to soils with a lower water content (e.g., 28 %), those with a higher water content (e.g., 58 %) significantly enhanced U stability, due to the prevalent reducing microenvironments (e.g., low redox potential). Such reducing conditions promoted the transformation of Fe/Mn oxide-U to organic matter-U during the microbial reductive dissolution of Fe minerals (e.g., hematite), and favored U(VI) reduction by Fe(III)-reducing bacteria (e.g., Pseudomonas and Anaeromyxobacter). Furthermore, dry-wet cycle process suppressed U release into soil solution by facilitating the formation of more stable U species (e.g., organic matter-U and residual U), a transformation mediated by Fe(III) reduction under wet conditions and Fe(II) oxidation/Fe mineral precipitation under dry conditions. Statistical analyses identified reactive Fe minerals and soil DOM as the two most critical drivers of U fraction. Additionally, the exchangeable U fraction was the most labile component governing release kinetics, while organic matter-U and carbonate-U fractions dominated U stabilization. Our results provide insights into the migration and transformation behavior of U in contaminated soils surrounding U tailings ponds.

Highly carcinogenic N-nitrosamines are frequently detected in groundwater, posing significant health risks to humans. However, knowledge of their attenuation characteristics and degradation mechanisms in the subsurface environment remains limited. Here, we conducted microcosm experiments to investigate the half-lives (T1/2s) of five representative N-nitrosamines in groundwater-soil systems under varying redox conditions, environmental matrices, and carbon source additions. The results revealed that the T1/2s of N-nitrosamines exceed 150 days in groundwater-soil systems with no contamination history and in groundwater environments without soil matrices. However, environmental matrices with long-term exposure to N-nitrosamine contamination demonstrated a shorter T1/2, ranging from a few to several dozen days. Moreover, N-nitrosamine decay rates under aerobic conditions were approximately twice those under anaerobic conditions. Microbial cometabolism was the primary removal mechanism, producing secondary amines, nitrate, and nitrite observed as intermediates, and ammonium as the main product. Variations in microbial community composition were observed across experimental conditions, underscoring the role of specific microbial taxa such as Nitrospirota, Patescibacteria, and Zixibacteria in the degradation process. By integrating product profiling with microbial analysis, this study offers a comprehensive mechanistic understanding of N-nitrosamine degradation. These findings offer insights for developing targeted remediation strategies to mitigate health risks from groundwater contamination.

The excessive discharge of flue gas degrades air quality, while its injection into coal seams mitigates pollution and enables carbon dioxide storage. This study investigates the adsorption, desorption, and seepage mechanisms of flue gas in coal seams through gas-solid coupling tests under triaxial stress for coal samples with varying water saturation. The results indicate that under constant coaxial and confining pressures, the adsorption capacity, desorption capacity, and seepage rate of flue gas exhibit a significant decline with increasing water saturation. Additionally, the equilibrium times for desorption and seepage are reduced, while the equilibrium time for adsorption is extended. During the processes of adsorption, desorption, and seepage, both axial and radial strains in the coal decrease with increasing water saturation or axial/confining pressure, with the axial strain consistently lower than the radial strain. Gas component analysis reveals nitrogen (N2) dominance during initial desorption, with carbon dioxide (CO2) and methane (CH4) increasing as desorption progresses. Further analysis demonstrates a significant linear relationship between the axial and radial strains of coal and the gas seepage rate. As the effective stress or water saturation increases, both the diffusion coefficient and dimensionless permeability exhibit a declining trend under the same water saturation conditions. Under dry conditions, the effective stress sensitivity coefficient decreases with increasing effective stress. In contrast, under high water saturation conditions, the effective stress sensitivity coefficient displays a more complex pattern, becoming more pronounced as water saturation rises. These studies help to understand the influence of water saturation and stress on the behavior of flue gas in coal and provide a theoretical basis for optimizing coal bed methane extraction and carbon sequestration.

Dissolved organic matter (DOM) is a natural ligand for heavy metal binding. Adsorption and oxidation of DOM by iron and/or manganese oxides may change its molecular composition and affect its binding with heavy metals, but the underlying mechanisms are still poorly understood. In this study, the effects of adsorption and oxidation of DOM by ferrihydrite and/or birnessite on its binding characteristics with copper ions (Cu2+) were investigated using fluorescence spectroscopy and Fourier transform infrared spectroscopies combined with twodimensional correlation analysis. Results showed that the adsorption and oxidation of DOM on birnessite significantly weakened the Cu2+ binding ability of DOM especially in the presence ferrihydrite, which was ascribed to the preferentially adsorption/oxidation of phenolic compounds and the adsorption of carboxylic compounds. Specifically, the reactions of DOM with birnessite enhanced the sensitivity of fulvic-like fraction to Cu2+ binding, being less favorable in the presence of a high concentration of ferrihydrite. Despite the unchanged binding order of Cu2+ with fluorescence components after adsorption and oxidation of DOM on birnessite, the binding of Cu2+ with carboxylic group became later compared with carbohydrate C-O, phenolic and aryl groups and aliphatic C-H. However, with the increase in the content of ferrihydrite, the binding of Cu2+ with carboxylic groups was more advanced. Our results highlighted the importance of the ratio of birnessite and ferrihydrite in controlling the binding characteristics of Cu2+ with DOM fractions, which helps to understand the reactions of heavy metals with natural organic matter under the impacts of complex mineral assemblages.

Both manganese dioxide (MnO₂) and dissolved organic matter (DOM) exert a significant influence on the chemical species of uranium in the contaminated soils, yet the impacts of the interactions between MnO2 and DOM, particularly in the presence of iron oxyhydroxides, on the environmental behaviors of uranium have not been elucidated. In this study, the dynamic behaviors of uranium were investigated during the reactions of DOM with δ-MnO2 in the presence of goethite at different pH values, by employing a combination of kinetic experiments, spectrophotometric titration, X-ray photoelectron spectroscopy, and electrochemical analysis. Our results indicated that the presence of DOM decreased uranium adsorption on MnO2 and promoted the release of uranium bound to DOM and MnO2 through the oxidation of DOM and the reduction of MnO2, respectively. Goethite increased uranium adsorption on its surface and hindered the direct oxidation of DOM by MnO2, but the indirect oxidation of goethite-adsorbed DOM by MnO2 provided an additional route for uranium release. We found that uranium concentration in solution was positively correlated with Mn(II) concentration at pH 4.5, whereas it was positively correlated with the concentration of dissolved organic carbon and negatively correlated with the aromaticity and molecular weight of DOM at pH 6.5. Above results highlighted the significance of the redox process between MnO2 and DOM in regulating the dynamic behaviors of uranium, which contributed to a better understanding of the sequestration and stability of uranium in the contaminated soils around the uranium tailings ponds.

Organic matter retained by reactive minerals constitutes an essential mechanism for long-term storage of carbon in soil, a process that is governed by climate factors. However, how the reactive mineral-associated organic matter affects the composition of soil dissolved organic matter (DOM) across a broad range of climates remains unclear. In this study, the contents of reactive minerals and their associated organic matter were determined by the chemical extraction method. Moreover, the effects of organic matter retained by reactive minerals on soil DOM composition were investigated at molecular level across a wide environmental gradient, by employing Fourier transform ion cyclotron resonance mass spectrometry, solid-state 13C nuclear magnetic resonance and statistical analyses. The results of FT-ICR-MS and correlation analyses indicated that the relative abundances of carbohydrates and proteins/amino sugars decreased, while the relative abundance of condensed aromatics increased with the increase of the content of organic matter retained by reactive minerals per unit mass (i.e., (OC)RN) in soils. We highlighted that the adsorption and dissolution processes of DOM molecules, especially aromatic molecules, on reactive minerals played crucial roles in regulating the molecular composition of DOM in soil solution. Furthermore, (OC)RN was controlled by climate-driven chemical weathering (e.g., precipitation). Our results imply that (OC)RN is a key variable for regulating soil DOM composition under the impacts of climates, and can be used in developing prediction models for carbon cycling.

The abiotic oxidation of divalent manganese (Mn(II)) and the formation of Mn oxides are important geochemical processes, which control the mobility and availability of Mn as well as element cycling and pollutant behavior in soils. It was found that iron (oxyhydr)oxides can catalyze Mn(II) oxidation, but the effects of the coexisting dissolved organic matter (DOM) molecules on the catalysis of different iron (oxyhydr)oxides for Mn(II) oxidation are poorly understood. Herein, we investigated Mn(II) oxidation under the impacts of the interactions between iron (oxyhydr)oxides (i.e., ferrihydrite, goethite and hematite) and DOM molecules. Simultaneously, we elucidated the variations of DOM composition and properties. Our results indicated that the catalysis of iron (oxyhydr)oxides for Mn(II) oxidation was significantly inhibited by DOM. Moreover, DOM had less inhibiting effect on the catalysis of ferrihydrite for Mn(II) oxidation and the formation of Mn oxides (e.g., hausmannite and buserite) relative to goethite and hematite, which was partially because of the higher electron transfer capacities of ferrihydrite. Meanwhile, DOM molecules with high nominal oxidation state of carbon (NOSC), molecular weight, unsaturation and aromaticity were selectively adsorbed and oxidized by Mn oxides, including the oxygenated phenols and polyphenols. The newly formed molecules mainly belonged to phenols depleted of oxygen and aliphatics. Furthermore, NOSC was a key molecular characteristic for controlling DOM composition during DOM adsorption and oxidation by Mn oxides when iron minerals were present. Overall, our research contributes to understanding Mn(II) oxidation mechanisms under heterogeneous systems and behaviors of DOM molecules in the environment.

Particle velocity is an important parameter for analyzing the propagation law of stress waves in a solid medium.Combining the laser Doppler effect and an all-fiber interferometric velocimetry system,a measurement method of stress wave particle velocity in solid medium based on fiber coated probe was proposed.The optical fiber coated probe was embedded in the polymethyl methacrylate(PMMA)at the same radius from the burst center,and the miniature explosive ball with 0.125 g TNT equivalent was used as the explosion source to fill in the center cavity and generate stress wave.Based on the time-frequency analysis method of the short-time Fourier transform,the velocity of the optical fiber end surface could be calculated from the collected signal,and then the medium particle velocity could be deduced.The experimental results show that the velocity of the data measured by different fiber coated probes is 22.648 m/s and 23.505 m/s,respectively.The relative difference between the resulting particle velocity and the data obtained by the traditional circular electromagnetic particle speedometer method is less than 5.00%,which indicates the feasibility of the proposed method.

In the traditional chlorination roasting-water leaching-solvent extraction process for the extraction of rubidium-bearing ore, Rb leaching from the ore and calcium removing from the leachate are conducted separately, and this results in the complicated process and high energy consumption. In order to integrate the Rb leaching and calcium removing processes, Rb-bearing polymetallic ore was firstly treated by chlorination roasting, it was then leached in a micro-reactor with raffinate, and the calcium ions in the leachate were removed in the reactor as carbonate precipitates by passing CO 2 at certain pressure into the reactor. The effects of raffinate alkalinity, CO 2 pressure, and CO 2 reaction time on Rb leaching rate and calcium removing rate were investigated. The experimental results show that when Rb-bearing polymetallic ore was leached for 90 min by stirring with raffinate with 1.125-mol/L alkalinity, and the pulp was made to react with CO 2 at 0.8 MPa for 15 min, the Rb leaching rate and calcium removing rate amounted to 92% and 98.2%, respectively. This integrated process including Rb leaching from Rb-bearing polymetallic ore and calcium removing from leachate could simplify the process for the extraction of Rb-bearing ore and increase its economic benefits.

Amorphous ferrihydrite (Fh) is abundant in aquatic environments and sediments, and often coprecipitates with dissolved organic matter (DOM) to form mineral-organic aggregates. The Fe(II)-catalyzed transformation of Fh to crystalline Fe (oxyhydr)oxides (e.g., goethite) can result in the changes of uranium (U) species, but the effects of DOM molecules on the sequestration and stability of U during Fe (oxyhydr)oxides transformation are poorly understood. In this study, the associations of DOM molecules with U during the coprecipitation of DOM with Fh were evaluated, and the effects of DOM molecules on the kinetics of U release during Fe (oxyhydr)oxides transformation were investigated using a combination of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), X-ray photoelectron spectroscopy (XPS), and kinetic experiments. FT-ICR-MS results indicated that, in addition to phenolic and polyphenolic compounds with higher O/C ratios, portions of phenolic compounds with lower O/C ratios and aliphatic compounds were also contributed to UO22+ binding when Fh coprecipitated with DOM. In comparison, phenolic and polyphenolic compounds with higher O/C ratios and condensed aromatics were preferentially retained on Fe (oxyhydr)oxides during the transformation. XPS results further suggested that the coprecipitated DOM molecules facilitated the reduction of U(VI) to U(IV) during the transformation, possibly through providing electrons or acting as electron shuttles. The kinetic experiment results indicated that the transformation processes accelerated U release from Fe (oxyhydr)oxides, but the coprecipitated DOM molecules slowed down U release. Our results contribute to understanding the behaviors of U and predicting the sequestration of U in the environment.

In this study, a highly dispersed carboxy methyl cellulose stabilized nZVI was synthesized and characterized, showing excellent uranium removal efficiency in acid in situ leach mine water.

The processes of acid in situ leaching (ISL) uranium (U) mines cause the pollution of groundwater. Phosphate (PO43-) has the potential to immobilize U in groundwater through forming highly insoluble phosphate minerals, but the performance is highly restricted by low pH and high sulfate concentration. In this study, hydrogen peroxide (H2O2) and PO43- were synergistically used for immobilizing U based on the specific properties of groundwater from a decommissioned acid ISL U mine. The removal mechanisms of U and the stability of U on the formed minerals were elucidated by employing X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and kinetic experiments. Our results indicated that the removal of U by simultaneously adding H2O2 and PO43- was significantly higher than the removal of U by individually adding H2O2 or PO43-. The removal of U increased with increasing PO43- concentration from 20 to 200 mg L-1 while decreased with increasing H2O2 concentration from 0.003 to 0.3%. Specifically, the removal efficiency of U from groundwater reached 98% after the application of 0.003% H2O2 and 200 mg L-1 PO43-. Amorphous iron phosphate that preferentially formed at low H2O2 and high PO43- concentrations played a dominant role in U removal, while the formations of schwertmannite and crystalline iron phosphates may be also contributed to the removal of U. This was significantly different from the immobilization mechanism of U through the formation of uranyl phosphate minerals after adding phosphate. The kinetic experimental results suggested that the immobilized U had a good stability. Our research may provide a promising method for in situ remediating U-contaminated groundwater at the decommissioned acid ISL U mines.

The dynamic reactions of uranium (U) with iron (Fe) minerals change its behaviors in soil environment, however, how the coexisted constituents in soil affect U sequestration and release on Fe minerals during the transformation remains unclear. Herein, coupled effects of lead (Pb) and dissolved organic matter (DOM) on U speciation and release kinetics during the catalytic transformations of ferrihydrite (Fh) by Fe(II) were investigated. Our results revealed that the coexistence of Pb and DOM significantly reduced U release and increased the immobilization of U during Fh transformation, which were attributed to the enhanced inhibition of Fh transformation, the declined release of DOM and the increased U(VI) reduction. Specifically, the presence of Pb increased the coprecipitation of condensed aromatics, polyphenols and phenols, and these molecules were preferentially maintained by Fe (oxyhydr)oxides. The sequestrated polyphenols and phenols could further facilitate U(VI) reduction to U(IV). Additionally, a higher Pb content in coprecipitates caused a slower U release, especially when DOM was present. Compared with Pb, the concentrations of the released U were significantly lower during the transformation. Our results contribute to predicting U sequestration and remediating U-contaminated soils.

Soil dissolved organic matter (DOM) is composed of a mass of complex organic compounds in soil solutions and significantly affects a range of (bio)geochemical processes in soil environment. However, how the chemical complexity (i.e., heterogeneity and chemodiversity) of soil DOM molecules affects their proton and metal binding ability remains unclear, which limits our ability for predicting the environmental behavior of DOM and metals. In this study, we developed a unified modeling approach for quantifying the proton and metal binding ability of soil DOM based on Cu titration experiments, Fourier transform ion cyclotron resonance mass spectrometry data, and molecular modeling method. Although soil DOM samples from different regions have enormously heterogeneous and diverse properties, we found that the molecules of soil DOM can be divided into three representative groups according to their Cu binding capacity. Based on the molecular models for individual molecular groups and the relative contributions of each group in each soil DOM, we were able to further develop molecular models for all soil DOM to predict their molecular properties and proton and metal binding ability. Our results will help to develop mechanistic models for predicting the reactivity of soil DOM from various sources.

In soil environments, the sequestration and transformation of organic carbon are closely associated with soil minerals. Birnessite (MnO2) is known to strongly interact with soil dissolved organic matter (DOM), but the microscopic distribution and molecular transformation of soil DOM on birnessite are still poorly understood. In this study, the coupled sorption and oxidation of soil DOM on birnessite were investigated at both the microscopic scale and the molecular level. Spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) results revealed, at the nano- to sub-nanoscale, that DOM was located both on the surfaces and within the interflakes or pore spaces of birnessite, and DOM within the interflakes displayed a higher oxidation state than that on the surfaces. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) results suggested that a portion of phenolic compounds were preferentially sorbed and oxidized, resulting in the formation of compounds with higher oxygen contents and polymeric products. Our Cs-STEM and FT-ICR-MS results highlighted the significance of organo-mineral associations in the microscopic mineral structure for the reactivity of organic carbon and provided the molecular evidence for the transformation of soil DOM by birnessite, which contributed to the understanding of the dynamics of soil dissolved organic carbon.

The interactions between dissolved organic matter (DOM) molecules and minerals play significant roles in affecting the fate of carbon and contaminants in soil environment. However, the mechanisms controlling the variations of DOM molecules distribution during the transformation of Fe (oxyhydr)oxides, and the effects of these variations on contaminant behaviors are still largely unknown. In this study, the dynamic variations of DOM properties and distributions, and the kinetics of uranium adsorption on and desorption from Fe (oxyhydr)oxides during the transformation were investigated, employing a combination of Orbitrap mass spectrometry (MS), high-resolution transmission electron microscopy (HR-TEM), and kinetic experiments. Orbitrap MS results indicated that aliphatic molecules and phenolic and polyphenolic molecules with lower O/C values were preferentially released to solution. HR-TEM results indicated that the coprecipitated DOM molecules by ferrihydrite were mainly released to solution rather than sorbed on the newly formed lepidocrocite or goethite during the transformation. Furthermore, the stirred-flow experiment results suggested that soil DOM significantly reduced the adsorption of uranium on, and accelerated the release of uranium from Fe (oxyhydr)oxides, which was ascribed to the changed distribution of DOM molecules and the structure and composition of Fe (oxyhydr)oxides. Our results contribute to predicting contaminant behaviors in soils.