Pyrolysis enables resource recovery from human feces, yet the mechanisms of release of dissolved organic matter (DOM) from the resulting biochar remain poorly understood. This study investigated how extraction solution pH influences DOM release from feces-derived biochar prepared at different pyrolysis temperatures (280-580 °C), using multispectral techniques, PARAFAC modeling, and two-dimensional correlation spectroscopy (2D-COS). Results showed that dissolved organic carbon (DOC) concentrations ranged from 6.77 to 36.52 mg·g-1, with higher DOM release under alkaline conditions. PARAFAC identified three humic-like components and one protein-like component. Protein-like substances were preferentially released under acidic conditions, while humic-like components dominated under weakly acidic to alkaline environments. 2D-COS analysis further revealed a sequential release of DOM components at the molecular level, influenced by the pyrolysis temperature through modifications in DOM functional groups. These findings provide a theoretical basis and practical insight for employing feces-derived biochars in environmental remediation.

Electrocatalytic nitrate reduction (NO3RR) provides a sustainable pathway for converting nitrate into ammonia (NH3); however, achieving a high NH3 yield while simultaneously enabling its efficient recovery remains challenging. Herein, we develop an exsolved high-entropy perovskite oxide, La0.9 (MnFeCoCuZn)0.2O3 (Ex-LMFCCZ), through in-situ exsolution of multimetallic nanoparticles. The exsolved nanoparticles, together with the enriched oxygen vacancies, create abundant active sites, resulting in an NH3 yield rate of 5.62 mg/cm2/h, which is 2.13 times higher than that of the pristine catalyst Pr-LMFCCZ at-0.4 V vs. RHE. DFT calculations indicate that the downshifted D-band center facilitates the desorption of reaction intermediates, while the enhanced charge polarization promotes electron transfer, thereby enhancing the activity. In addition, the produced NH3 from NO3RR can be effectively captured as solid struvite (MgNH4PO4 & sdot;6 H2O). A closed-loop electrochemical system was further constructed for struvite recovery, in which NH3 originated from NO3RR, and both anodic and cathodic solutions dissolved waste minerals to provide PO43-and Mg2+ without external reagents, yielding struvite with a purity of 57.9%. This integrated system achieves simultaneous nitrate removal, ammonia recovery, and nutrient recycling, offering a green and circular pathway for sustainable wastewater valorization.

Vacancy-engineered Ga 3 In 5− x Ge 2+ x O 16 achieves carrier–phonon decoupling through Ge 4+ induces indium vacancies, enhancing electrical conductivity and suppressing lattice thermal conductivity, achieving a zT of 0.5 at 973 K in an indium-lean oxide.

Electrochemical dehalogenation is a promising approach for removing persistent halogenated organic pollutants from water, but its practical application is often constrained by limited mass transfer and high energy demand in conventional batch reactors. Here, we report a self-separating flow cathode system using Pd-loaded Ti4O7 microparticles (Pd/Ti4O7), integrated with a porous Ti filter that enables in situ particle retention and recycling. With an optimized Pd loading of 0.5 wt %, the system achieved 93- and 13-fold faster diclofenac (DCF) dechlorination than systems without Pd/Ti4O7 and with Ti4O7 alone, respectively, while significantly reducing predicted biotoxicity. Efficient dehalogenation was further demonstrated for multiple chlorinated organic pollutants. Direct electron transfer (DET), rather than atomic hydrogen-mediated reduction, dominates the dehalogenation pathway, which confers strong resistance to common water matrix interferences. A single-pass system removed 99% of DCF from municipal wastewater within 7 min at an energy cost of 0.26 kWh·m-3, comparable to or lower than state-of-the-art technologies. Collectively, these results establish Pd/Ti4O7 self-separating flow cathodes as a robust and scalable platform for electrochemical dehalogenation, while highlighting remaining challenges related to material cost and life-cycle impacts.

Contact-electro-catalysis (CEC) provides a promising route for per- and polyfluoroalkyl substances (PFAS) remediation, yet the mechanistic role of chloride ions (Cl-) in real water matrices remains unclear. Here, we demonstrate that Cl- markedly enhances removal of perfluorooctanoic acid, perfluorooctanesulfonic acid, hexafluoropropylene oxide dimer acid, perfluorononyloxybenzene sulfonate, and 6:2 fluorotelomer sulfonate, achieving 97.04 -99.99% degradation and 96.90 -99.98% defluorination within 120 min at 200 mM Cl-. These rates were 1.43-2.29-fold higher than Cl--free systems. Mechanistic analyses reveal that hydroxyl radicals (•OH) oxidizes Cl- to generate chlorine radicals (Cl•), which selectively attack the carboxylate group of PFAS, enabling thermodynamically favorable decarboxylation followed by mineralization. Unlike conventional electrochemical methods, the Cl•-mediated pathway avoids oxychlorine and chlorinated byproducts. Zebrafish embryo assays further confirmed negligible toxicity of treated solutions. These results establish a sustainable paradigm that achieves high defluorination efficiency and operational safety, offering strong potential for PFAS remediation in saline and industrial waters.

The widespread occurrence of fluoroquinolone antibiotics, particularly ciprofloxacin (CIP), in aquatic environments has raised increasing concerns due to their persistence and potential ecological risks. Developing efficient and sustainable catalysts for advanced oxidation processes remains challenging. Herein, we hypothesize that coupling biomass-derived carbon with Co–Fe bimetallic species can enhance interfacial interactions and promote peroxymonosulfate (PMS) activation for efficient CIP removal. A series of SCF/CoFe-X catalysts were synthesized by integrating Co and Fe species onto strawberry petiole derived carbon fiber (SCF) through solvothermal treatment and calcination. Among them, SCF/CoFe-800 exhibited the best catalytic performance, achieving 92.48% CIP degradation within 30min, along with good pH adaptability and recycling stability. Mechanistic studies revealed that sulfate radicals were the predominant reactive species, while multiple oxidation pathways contributed to CIP degradation. LC-MS analysis identified three possible degradation pathways, and toxicity assessment indicated reduced environmental risks of most intermediates. This work provides insights into the design of sustainable biomass-derived Co-Fe catalysts for PMS activation and antibiotic wastewater remediation.

Phosphorus (P) is the ultimate limiting nutrient for primary productivity on geological timescales, but reconstructing ancient seawater phosphate concentrations in iron-rich sediments is complicated by post-depositional transformations that may obscure primary P signatures. Here, we investigate phosphorus phase partitioning in Late Devonian Ningxiang oolitic ironstones from South China, using a combined approach integrating sequential chemical extractions, solid-state 31P nuclear magnetic resonance (SSNMR), and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The ironstones, composed mainly of hematite, exhibit systematically higher P contents than their siliciclastic host rocks. Our results reveal pronounced stratigraphic variability in P phases: Al/Fe-bound P dominates in the Huangjiadeng Formation, whereas authigenic Ca-phosphates (apatite and carbonate-fluorapatite) prevail in the overlying Xiejingsi Formation. This transition reflects diagenetic transformation of primary Fe-P phases under progressively reducing pore-water conditions, followed by re-precipitation as stable Ca-phosphate minerals. Spectroscopic analyses reveal that Al-bearing minerals constitute a significant, yet previously underappreciated, sink for phosphorus. This redistribution of P among Fe-, Al- and Ca-bound phases challenges the conventional use of bulk P/Fe ratios in Phanerozoic ironstones as direct proxies for paleo-seawater phosphate concentrations. Our study demonstrates that coupling XAFS and NMR spectroscopy with sequential extractions provides a powerful approach to resolve phosphorus phase partitioning and cycling in ancient marine settings.

The electrocatalytic hydrogen evolution reaction (HER) in neutral media is fundamentally limited by sluggish water dissociation. Here we report a Ru single-atom catalyst supported on hydrogen tungsten bronze (Ru & horbar;HxWO3) and show that its high activity originates from strong metal-support interaction (SMSI) at the Ru & horbar;O & horbar;W interface. The strong Ru-support coupling induces pronounced interfacial polarization, which restructures the local hydration layer and enriches activation-relevant interfacial water configurations for the Volmer step. As a result, Ru & horbar;HxWO3 achieves an ultralow overpotential of 14 mV at 10 mA cm-2, delivers a high Ru mass activity of 11.09 A mgRu -1 at 100 mV, and sustains stable HER operation for 80 h at 1 A cm-2 in neutral media. This work elucidates a complete mechanistic pathway, demonstrating how strong Ru-support coupling leverages interfacial electronic modulation to dynamically control hydration-layer structure, thereby accelerating HER kinetics in neutral media.

Alkali-carbonate reaction (ACR) in carbonate aggregates can impair concrete durability, but whether dedolomitization itself can generate expansion remains controversial. This study investigated dedolomitization-induced expansive stress using dolostone-particle compacts exposed to 1 mol/L NaOH solution at 60 degrees C under an initial axial pressure of 5 MPa. Stress evolution in the NaOH-cured compacts exhibited a dormant period followed by rapid growth, reaching 113.9 MPa at 250 days, while the water-cured compact showed no measurable stress growth, indicating that stress development was associated with dedolomitization under alkaline curing. XRD and FTIR confirmed progressive dedolomitization and the formation of brucite and calcite, and the degree of dedolomitization reached 97.2% at 250 days. SEM and pore-structure measurements showed that the products formed polycrystalline aggregates with abundant intercrystalline pores. Quantitative analysis indicated that although dedolomitization caused a stoichiometric decrease in absolute solid volume, the newly formed pore-bearing product skeleton volume was about 17.5% greater than that of the reacted dolomite. The porosity of the product zone was approximately 18.6%, with pore size mainly ranging from 3 to 60 nm. The absence of measurable stress during rewetting ruled out water-uptake swelling of the products as the primary cause. Combined with the confined reaction environment, pore-bearing product structure, and continued stress development, the results support crystallization pressure as the most plausible explanation for the stress generation in compacts. The results also support a fourstage mechanism involving early accommodation in packing voids, progressive loss of accommodation space, crystallization-pressure generation in confined regions, and stress transfer through increasingly connected products. These findings show that dedolomitization under restraint can independently generate expansive stress in dolostone-particle compacts and provide mechanistic insight relevant to ACR-related deterioration in concrete.

Crystalline quartz has a negative effect on the burnability of raw meal in clinker production. However, the causes for the poor burnability of quartz and its impact on clinker performance have not yet been thoroughly investigated. The fundamental mechanism and reaction processes of quartz in raw meal were investigated by calcinating quartz-containing raw meal of various sizes. The quantitative and microstructural analysis of the phase composition was conducted using the X-ray diffraction Rietveld method and scanning electron microscopy (SEM). The results demonstrated that during the calcination of quartz-contained raw meal, alkali ions tend to be absorbed by quartz, resulting in the breaking of Si-O bond in quartz and facilitating the preferential stabilization of alpha '-C2S via K and Na incorporation (potentially forming KC23S12 and NC23S12), which may prevent the conversion of C2S to C3S. Meanwhile, residual SiO2 and limited CaO in quartz region lead to a low CaO/SiO2 ratio, further hindering C3S formation. As a result, quartz crystals prefer to form C2S clusters, resulting in increased f-CaO in non-quartz regions. The high lime saturation ratio in non-quartz region promotes the formation of C3S, but will also lead to excessively high f-CaO in the clinker. A stricter calcination regime should be adopted to reduce the f-CaO content, which will result in over-burning of the clinker and a decrease in its performance. In summary, the fundamental effect of quartz on the burnability is heterogeneous distribution of CaO during clinker calcination.

This study reveals that the intricate sediment compositions, with Li-rich samples characterized by layered clays and layered or needle-like bauxite minerals, form distinct mineral transformation patterns. Mineral co-transformation lags behind the enrichment of Li. AlOOH formed via the desilicification of Li-kaolinite may inherit Li occurrence sites, whereas the transformation of kaolinite to illite potentially leads to the Li loss through K-Li substitution. The Li enrichment shows no selectivity for K, but exhibits a strong coupled enrichment relationship with Al, Mg, and Fe, resulting in dioctahedral minerals transforming into trioctahedral AlMgLiOH. The structure alterations result from inner-complexation of hexa-coordinate Li, differing from previous reports, where Li is bound to the Al-O/OH pseudo-hexagonal cavities (□) of kaolinite and/or AlOOH, exhibiting a more negative 7Li NMR chemical shift of −0.3 ppm, forming Li2O, LiOH, and LiF species. The Li enrichment mechanism induced by reaction of structural OH results in varied acid-base feedback, particularly favoring stronger F-OH substitutions in alkaline samples, which facilitate the retention of Li in ultimate weathering products. 19F NMR results indicate that F bonds with mineral structures to form Al-Al-□ and Mg-Al-□ configurations, exhibiting negative shifted splitting peaks due to Li enrichment in cavity with disappearing upon Li removal. Notably, Li in natural minerals remains significantly unaffected at ambient temperature and even in 200°C-HCl solution but is crucially removed by 200°C-H2SO4, with a leaching efficiency as high as 97.17% while dissolving fewer minerals, highlighting a more eco-friendly method for Li and mineral recovery.

The hydrogen evolution reaction (HER) is a cornerstone of green hydrogen production, yet its efficiency is constrained by the sluggish kinetics of water splitting. High-entropy catalysts (HECs), single-phase materials incorporating multiple principal elements, have emerged as a transformative solution. Their unique attributes including vast compositional flexibility, tunable electronic structures, and synergistic multi-element interactions, enable them to overcome the activity, stability, and cost limitations of conventional catalysts. Despite rapid performance advancements, the rational design of HECs is fundamentally hampered by critical knowledge gaps, particularly in identifying true active sites under operando conditions and predicting long-term stability. This work critically assesses these challenges, systematically summarizing the latest progress in HECs design, synthesis, and structure–activity relationships. By bridging fundamental principles with practical applications, we provide a forward-looking perspective on key research directions. Distinct from recent progress-focused reviews, this work establishes a strategic roadmap by systematically diagnosing seven grand challenges across the science-to-technology pipeline and proposing corresponding countermeasures. This framework aims to guide future research efforts toward the rational design and practical deployments of HECs for practical and cost-effective green hydrogen production.

Zinc (Zn) contamination poses significant risks to soil and water quality, necessitating effective remediation strategies. Palygorskite, a fibrous clay mineral, shows strong potential as an adsorbent, but the molecular-scale mechanisms governing Zn sorption, particularly the role of ionic strength, remain unclear. Here, by integrating batch sorption experiments, surface complexation modeling (SCM), and Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy, this study suggests that ionic strength may act as a key factor influencing Zn(II) sorption mechanisms on palygorskite across varying pH (4.0-7.5) and ionic strength (0.001-0.1 M NaNO3). Macroscopic data revealed that ionic strength strongly suppressed Zn uptake at low pH via competition for permanent-charge sites, but became negligible under alkaline conditions, consistent with SCM quantification of outer-sphere (OS) complexes on basal sites and inner-sphere (IS) complexes on edge sites. XAFS analysis at both 80 and 800 mu M Zn provides direct molecular-scale evidence for a pivotal mechanistic shift: at pH 7.5, elevated ionic strength (0.1 M) promoted the formation of polynuclear IS complexes even at a relatively low concentration (80 mu M), acting as precursors to surface precipitation. This contrasts with the mononuclear species dominant at low ionic strength despite comparable total uptake, and is further corroborated by the formation of polynuclear complexes at higher Zn concentration (800 mu M) even under low ionic strength. We propose that elevated ionic strength may compress the electrical double layer and compete for basal sites, thereby promoting Zn redistribution to reactive edge sites where increased local coverage favors nucleation. This work redefines ionic strength from a competitive background parameter to an active regulator of adsorption-to-nucleation transitions on clay minerals, providing a predictive framework for Zn sequestration in fluctuating ionic environments and guiding the design of palygorskite-based remediation strategies.

Understanding the mechanisms governing Co(II) retention at mineral-water interfaces is critical for predicting its environmental mobility. Here, we investigate Co(II) sorption and surface-induced precipitation on palygorskite using batch experiments, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) mapping, extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray absorption near edge spectroscopy (XANES), and density functional theory (DFT) calculations. Co retention is strongly controlled by pH, ionic strength, and concentration. At pH 6.0, ionic strength effects indicate a shift from outer-sphere to inner-sphere surface complexation. In contrast, at pH 7.5, sorption is dominated by surface-induced precipitation and is associated with a substantially higher activation energy (102.6 kJ mol(-1)) relative to pH 6.0 (9.3 kJ mol(-1)), consistent with a nucleation-controlled process. Spectroscopic analyses reveal the formation of both Co-Al layered double hydroxide (LDH)-like and Co-phyllosilicate-like precipitates form on palygorskite across the concentration range 0.1-3 mM at pH 7.5. Their relative proportions vary with increasing concentrations: LDHlike phases predominate at low Co concentrations, whereas phyllosilicate-like phases increase and become dominant at higher concentrations. STEM-EDS mapping and DFT calculations confirm the nucleation of both LDH-like and phyllosilicate-like phases at palygorskite edge sites. Compared with reported systems such as kaolinite and gamma-Al2O3, palygorskite promotes precipitation at lower Co surface loadings, consistent with its Mgrich composition and fibrous structure. These results demonstrate that mineral composition, particularly Mg/Al ratio, influences the type and relative abundance of secondary Co precipitates, with implications for Co immobilization in both contaminated environments and lateritic weathering systems.

A novel continuous-flow system coupling partial nitrification/Anammox (PN/A), partial denitrification (PD), and Anammox (Amx) biofilm reactors was developed (PN/A-PD-A) to treat mature landfill leachate (MLL). To maximize synergy, the NH4+-N removal in the PN/A reactor was regulated based on the NO2--N accumulation ratio (NAR) in the PD stage, ensuring optimal substrate stoichiometry for the final Amx polishing step. Over 174 days of operation, the system achieved a superior total nitrogen removal efficiency (TNRE) of 98.30 ± 0.14% (effluent TN: 21.80 ± 1.71 mg/L). The PN/A granular sludge, enriched with Candidatus_Kuenenia (5.87%) and Nitrosomonas (9.73%), demonstrated high adaptability to MLL characteristics and contributed to 83.51% of the TN removal. In the PD stage, the dominant genus Thauera (43.91%) facilitated efficient NAR (82.86 ± 1.61%) at a limited COD/NO3--N ratio of 2.32 ± 0.02. The Anammox biofilm (Candidatus_Kuenenia, 27.80%) in the Amx reactor contributed to 13.10% of TN removal, ensuring to meet the MLL discharge standard. Kinetic and metagenomic analyses confirmed that distinct shifts from complete to partial nitrification (and denitrification) in enzymes activity and gene abundance under chronic MLL stress underpinned the robust NO2--N accumulation in both PN/A and PD reactors. Notably, compared to conventional nitrification-denitrification process, the PN/A-PD-A system significantly reduced oxygen demand (60.18%), exogenous organic carbon consumption (91.61%), sludge yield (83.72%), and CO2 emission (94.66%), demonstrating a sustainable pathway for low-carbon nitrogen removal from high-strength wastewater.

Soil organic carbon (SOC) stabilisation by Fe minerals is a major pathway for terrestrial carbon storage, yet redox fluctuations drive Fe mineral transformations that alter mineral-organic interactions. Cerium (Ce) is a highly redox-sensitive rare earth element and often adsorbs onto reactive Fe phases. Whether Ce adsorption influences Fe redox cycling and organic carbon retention in Fe-organic matter associations remains unclear. Here we investigate the effects of Ce, applied at environmentally relevant soil-solution concentrations, on dissolved organic carbon (DOC) release from ferrihydrite-and hematite-humic acid organo-minerals under controlled pH and redox conditions. Batch experiments show that Ce adsorption reduces DOC release across all tested conditions, with maximum decreases of 76 +/- 3% in ferrihydrite-humic acid and 73 +/- 1% in hematite-humic acid organo-minerals. Spectroscopic and microscopic analyses indicate that Ce-mediated DOC retention follows distinct mechanisms in different organo-mineral systems, supported by density functional theory calculations. For ferrihydrite-humic acid, Ce predominantly forms inner-sphere complexes on ferrihydrite surfaces, with spectroscopic and DFT results consistent with interfacial Ce-Fe redox interactions. Under acidic or fluctuating redox conditions, this may help preserve mineral-organic associations by limiting ferrihydrite dissolution and DOC release. In contrast, for hematite-humic acid, Ce adsorption is dominated by ligand complexation with humic acid, while under alkaline conditions Ce-bearing nanoparticles may further enhance mineral-organic cohesion and reduce DOC release. These findings show that Ce enhances organic carbon retention through mineral-specific pathways in controlled Fe-organic matter model systems, with potential implications for SOC stabilisation in Fe-rich soils.

Machine learning (ML) has rapidly emerged as a transformative tool in mineralogy and geochemistry, enabling the modeling of complex nonlinear systems and the integration of heterogeneous datasets. This review synthesizes and critically assesses advances in the application of machine learning to mineral-related tasks, including mineral identification, geological information inversion, behavioral prediction, and mechanism interpretation. We organize modeling paradigms according to data modality, such as imaging, spectroscopy, and structured datasets, and highlight how these approaches have contributed to both fundamental mineralogical understanding and applied geoscience problems. Substantial progress has been achieved in mineral identification and geochemical inversion, where well-established frameworks and datasets support robust modeling. However, persistent challenges remain in linking microscopic mechanisms with macroscopic behavior, integrating heterogeneous modalities, and embedding domain knowledge into machine learning models. Addressing these gaps requires the development of multimodal learning strategies and cross-scale modeling frameworks. Looking forward, we argue that mineralogical research must move beyond purely data-driven approaches toward knowledge-informed machine learning, where physical principles, mechanistic insights, and domain expertise are systematically incorporated into model design and interpretation. Such integration will not only enhance predictive accuracy but also foster mechanistic interpretability and unify mineral process understanding across spatial and temporal scales.

The quantitative identification of nitrate sources is of great significance for water resources management. Stable isotopes combined with Bayesian isotope mixing model (SIAR) model were widely used to identify nitrogen sources. However, limited attention has been paid to how variations in the isotopic composition of nitrate sources affect the estimated source contributions in isotope mixing models. Here, the δ15N-NO3− and δ18O-NO3− isotopes, the SIAR model, and the uncertainty and sensitivity analysis were used to quantify the contributions and uncertainties of nitrate sources in Huashan watershed. 60 surface water (SW) samples and 82 groundwater (GW)samples were collected from November 2021 to October 2022, and atmospheric deposition (AD), chemical nitrogen fertilizer (NF), soil nitrogen (SN), and manure and sewage (M S) were determined as the potential nitrate sources. Source identification by SIAR indicated that in November 2021 the M S was the main contributor of nitrate to SW, while NF was the main contributor to nitrate in groundwater. In April 2022, NF contributed the most to nitrate in surface water, while nitrate in groundwater mainly originated from SN and MS. The variation between November 2021 and April 2022 sources is due to spring fertilization and rainfall. The uncertainty analysis showed that the greatest uncertainties were in SN and NF. Sensitivity analysis showed that the changes in the nitrate isotopic composition of M S had the greatest effect on the results for δ15N, whereas only the mean values of oxygen isotope values of AD had a greater effect on the results for δ18O. Fertilizer application and changes in soil fertility due to agricultural rotations and cropping practices are intrinsic to the high level of uncertainty in SN. Sensitivity analysis highlighted the necessity of accurately measuring the isotopic end-members of potential nitrate sources to reduce the uncertainty in SIAR-based nitrate source apportionment results. Management strategies for the Huashan watershed should focus on domestic sewage treatment, optimization of agricultural practices, and integrated management of strongly connected surface water–groundwater systems to proactively prevent nitrogen pollution risks.

Electrosynthesis of bulk chemicals such as active chlorine depends on the most reactive crystal facets, yet these facets are often thermodynamically disfavored during crystal growth. Here, we present a faceting strategy that integrates 3D printing with electric field inducement to reorient triclinic Ti4O7, realizing a dominant facet transition from (1 - 2 0) to high-energy (0 2 - 2) by storing and releasing strain energy to promote the preferential growth of crystal. Such transition trigger active site switching from O on pristine (1 - 2 0) facet to Ti on the reoriented (0 2 - 2) facet, greatly boosting the active chlorine generation rate to a comparable level (0.19 mg·min-1·cm-2) to benchmark dimensionally-stable anodes while suppressing parasitic water activation. A flow-by reactor reaches high active chlorine generation rates of 0.33-0.35 mg·min-1·cm-2 within 2.9-8.9 s, outperforming industrial dimensionally-stable anodes. This strain-induced faceting approach establishes a general paradigm for controllable crystal reorientation and underscores the potential of 3D printing to expand facet engineering for advanced catalytic systems.

Soil contamination by heavy metals and metalloids poses significant environmental challenges, and iron oxide transformation processes in soils and sediments play a pivotal role in controlling contaminant mobility. While individual metal-ion interactions with Fe oxides have been widely studied, the simultaneous nanoscale effects of coexisting oxyanions and cations during Fe(II)-induced transformations remain poorly understood. Here, we conducted batch extraction experiments to quantify the aqueous, NaOH-extractable arsenic (As(V)), and HCl-extractable cadmium (Cd(II)) during Fe oxide transformation, complemented by nanoscale analyses to resolve the sequestration mechanisms of As(V) and Cd(II). Results showed that Cd(II) slightly increased the extractability of As(V) (from 53.7% to 58.6% at 24 h). In contrast, As(V) strongly promoted lepidocrocite formation (92.7%), which reduced Cd(II) retention and resulted in most Cd(II) being partitioned into the aqueous (79.3%) and extractable (18.5%) fractions at 168 h. Nanoscale observations revealed that As(V) exhibited stronger retention on residual ferrihydrite domains, consistent with its stronger binding affinity with iron oxides, while Cd(II) showed weaker and more evenly distributed associations, often residing on lepidocrocite surfaces. Despite this stronger nanoscale association with ferrihydrite, bulk As(V) partitioning was dominated by lepidocrocite due to its phase abundance (similar to 90%), suggesting the dual control of binding affinity and mineralogical composition. These findings demonstrate that Fe(II)-induced ferrihydrite transformation governs contaminant sequestration pathways and provide mechanistic insights into the mobility of coexisting As and Cd in contaminated systems.