Phosphate-Functionalized Zero-Valent Iron for Efficient Separation of Europium from Acidic Associated Mineral Wastewater

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Here, a zero-acid separation strategy is developed using phosphorylation-engineered zero-valent iron (P–ZVI bm ), which integrates corrosion resistance with selective coordination reactivity. Phosphate functionalization transforms Fe 0 surfaces into chemically stable Fe–O–P frameworks, creating multidentate active sites that drive inner-sphere Eu 3+ complexation and interfacial Eu–phosphate precipitation. Combined experimental and DFT analyses reveal that the Fe–O–P interface facilitates strong chemisorption through hybrid Eu–O–P bonding (E ad up to − 14.7 eV) and electron transfer between Eu 4f/5d and O 2p orbitals, while suppressing Fe⁰ dissolution. In real mine wastewater containing multiple rare-earth and transition metal ions, P–ZVI bm achieves high Eu 3 ⁺ selectivity, stability, and recyclability, maintaining over 85.0% removal efficiency after H 3 PO 4 cycles. This study establishes a zero-acid, phosphate-mediated adsorption–precipitation mechanism for rare-earth recovery, offering a scalable route for sustainable treatment and valorization of radioactive metallurgical effluents within green process metallurgy. Associated radioactive minerals Zero-valent iron Phosphorylation Eu³⁺ Complexation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction The processing of associated mineral resources and the nuclear fuel cycle inevitably generate large volumes of acidic wastewater enriched in uranium, thorium, and rare-earth elements such as europium (Eu 3 ⁺)[1–4]. Although stable europium isotopes are non-radiotoxic, Eu 3 ⁺ often coexists with radionuclides in hydrometallurgical effluents, introducing risks of environmental migration, nuclear safety issues, and long-term management challenges[5]. Furthermore, Eu 3 ⁺ exhibits complex aqueous speciation and strong coordination ability with oxygen-donor ligands, which lead to its high solubility and hinder its selective separation from chemically similar species[6–7]. Therefore, the efficient removal and recovery of Eu 3 ⁺ under highly acidic conditions remains a critical challenge for both environmental protection and resource recycling in radioactive mineral processing. Europium is a strategically important rare-earth element widely used in phosphors[8–12], nuclear detectors[13–14], and advanced energy materials[15–17]. However, its supply is limited due to the low abundance of Eu-bearing minerals and the complex processes required for separation from other lanthanides. Traditional extraction techniques, such as solvent extraction[18–19], ion exchange[20–21], and acid-based adsorption[22–24], have achieved moderate success but face significant limitations, including acid-induced damage to adsorbents, generation of secondary waste, poor selectivity in multi-ion systems, and limited regeneration capability. These challenges underscore the urgent need for environmentally benign, acid-tolerant, and recyclable materials capable of selectively capturing Eu 3 ⁺ from complex metallurgical effluents. Zero-valent iron (ZVI) has gained considerable attention in recent decades as a multifunctional material for the remediation of heavy metals, radionuclides, and organic pollutants, owing to its synergistic adsorption and reduction properties[25–27]. Its unique surface redox reactivity allows for the immobilization of metal ions through electron transfer[28–30] and coprecipitation[31]. However, in acidic environments typical of hydrometallurgical waste streams, pristine ZVI suffers from rapid proton-induced corrosion, excessive hydrogen evolution, and severe particle aggregation, which collectively deteriorates its reactivity and stability. To overcome these limitations, surface engineering strategies have been developed to enhance the acid resistance, reactivity, and functional selectivity of ZVI. Recent advances—including nonmetallic modification[32], chelating-agent stabilization[33], nanoscale structuring[34–35], and vacancy engineering[36–37]—have effectively improved electron transfer, suppressed corrosion, and expanded its applicability to complex aqueous systems. Nevertheless, achieving long-term stability and controlled reactivity in acidic and multicomponent environments remains a key challenge motivating further material innovations such as phosphate-functionalized ZVI. Among them, phosphorylation modification[38–43] offers a particularly promising route. Yet, despite its conceptual appeal, the adsorption behavior, mechanistic pathways, and thermodynamic characteristics of phosphorylation-modified ZVI for Eu 3 ⁺ recovery remain insufficiently elucidated. In this study, we report a zero-acid strategy for europium recovery using phosphorylation-engineered zero-valent iron (P-ZVI bm ) as an adsorbent. The proposed system achieves simultaneous corrosion inhibition and selective Eu 3 ⁺ capture under in an acidic environment, eliminating the need for acidification while maintaining high adsorption efficiency. Through comprehensive kinetic, isotherm, and thermodynamic analyses combined with spectroscopic characterization, we reveal a synergistic mechanism involving Eu 3 ⁺ migration to negatively shifted Fe–O–P surfaces, inner-sphere complexation, and interfacial precipitation of Eu–phosphate species, supplemented by adsorption on secondary Fe oxyhydroxides formed during mild corrosion. This dual-function mechanism adsorption coupled with redox transformation enables robust performance and excellent reusability even under challenging chemical conditions, providing a sustainable and scalable strategy for europium recovery from radioactive mineral effluents and offering new insights into the design of acid-resistant functional materials for green metallurgical processes. 2. Materials and Methods 2.1 Materials Iron powder (Fe, analytical grade, particle size < 50 µm), phosphoric acid (H 3 PO 4 , ≥ 85.0%), nitric acid (HNO 3 , 65.0–68.0%), and sodium hydroxide (NaOH, ≥ 96.0%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous ethanol was obtained from Macklin Biochemical Co., Ltd. Europium nitrate hexahydrate (Eu(NO 3 ) 3 ·6H 2 O, ≥ 99.9%) was supplied by Aladdin Reagent Co., Ltd. All solutions were prepared with deionized water. 2.2 Synthesis of P-ZVI bm Phosphorylated ball-milled zero-valent iron (P-ZVI bm ) was prepared via a mechanochemical approach. Iron powder (3.0 g) and KH 2 PO 4 (0.7309 g) were mixed and placed into an agate ball-milling jar together with a defined amount of agate balls. To avoid oxidation of Fe during milling, nitrogen gas was purged into the jar for 30.0 min prior to sealing. The mixture was then subjected to planetary ball milling at 300.0 rpm for 3.0 h. The resulting material was collected and stored in vacuum-sealed bags and denoted as P-ZVI bm . For comparison, ball-milled Fe powder without KH 2 PO 4 was prepared under identical conditions and denoted as ZVI bm . 2.3 Characterization The crystalline structure of the materials was analyzed using X-ray diffraction (XRD, Rigaku SmartLab SE, Cu-Kα radiation). Surface morphology was observed by scanning electron microscopy (SEM, TESCAN MIRA LMS) and transmission electron microscopy (TEM, JEOL JEM-F200). Surface functional groups were identified by Fourier transform infrared spectroscopy (FTIR, Thermo Nicolet iS5), while microstructural features and defects were investigated by Raman spectroscopy (Renishaw inVia). Elemental composition and chemical states were determined by X-ray photoelectron spectroscopy (XPS, LAUDA Scientific GmbH LSA-100X). P-ZVI bm was prepared using a ball mill (PML10, Netzsch Instruments). The magnetic properties of ZVI bm and P-ZVI bm were measured using a vibrating sample magnetometer (VSM, LakeShore 7404, USA). The surface charges of ZVI bm and P-ZVI bm were determined using a solid surface zeta potential analyzer (SurPASS 3, Anton Paar, Austria). 2.4 Batch Adsorption Experiments for Eu Removal Eu(III) stock solution (1 g·L⁻ 1 ) was prepared as follows: 2.9353 g of Eu(NO 3 ) 3 ·6H 2 O was placed in a beaker, dissolved in 10.0 mL aqua regia under heating and stirring, and subsequently evaporated to dryness in a fume hood. After cooling the residue to room temperature, it was redissolved in 50.0 mL of deionized water and diluted to a final volume of 1.0 L in a volumetric flask. Batch adsorption experiments were conducted using the equilibrium method. Eu(III) solutions of desired concentrations were prepared by dilution of the stock solution and adjusted to target pH using 0.1 mol·L⁻¹ HNO 3 or 0.1 mol·L⁻¹ NaHCO 3 . In a typical run, 5.0 mg of adsorbent was added to 25.0 mL of Eu(III) solution and shaken at 180.0 rpm at a constant temperature for a specified time. The residual Eu concentration was measured by inductively coupled plasma mass spectrometry (ICP-MS). 3. Results and Discussion 3.1 Structural and physicochemical properties of P-ZVI bm The morphological and structural evolution of the zero-valent iron after ball-milling and phosphorylation modification (P-ZVI bm ) was systematically characterized (Figs. 1 A–D). As shown in the schematic illustration (Fig. 1 A), the phosphorylated surface of P-ZVI bm provides abundant adsorption sites and facilitates Eu 3 ⁺ immobilization through inner-sphere complexation and interface nucleation processes. SEM analysis (Fig. 1 B) revealed that P-ZVI bm displayed rougher, flake-like structures with visible surface defects and micro-pores. These morphological changes indicate that phosphate incorporation during mechanical activation promotes surface reconstruction and fragmentation, thereby enlarging the specific surface area and exposing more reactive sites[44–45]. Energy-dispersive X-ray spectroscopy (EDS) further confirmed the presence of Fe (92.08%), O (5.57%), and P (2.35%) in P-ZVI bm , verifying the successful introduction of phosphate groups while maintaining Fe as the predominant component. X-ray diffraction (XRD) patterns (Fig. 1 C) of P-ZVI bm exhibited characteristic reflections at 2θ = 44.5° and 65.0°, corresponding to the (110) and (200) planes of metallic Fe 0 (PDF#65-4899). The absence of new crystalline peaks (2θ = 44.5°) in P-ZVI bm indicates that the Fe 0 core structure was preserved after surface phosphorylation. However, the reduced intensity of Fe 0 peaks suggests partial amorphization induced by high-energy milling and phosphate bonding. Fourier-transform infrared (FTIR) spectra (Fig. 1 D) provide further evidence of chemical modification: absorption bands at 898.0 cm⁻ 1 , 1090.0 cm⁻ 1 , and 1280.0 cm⁻ 1 correspond to P–O, Fe–O–P, and P = O vibrations[45], respectively, confirming stable coordination between phosphate groups and iron atoms. The Fe–O–P linkage is expected to enhance the chemical durability of ZVI in acidic media by forming a protective passivation layer that limits proton attack[46]. 3.2. Adsorption Performance of Eu 3+ Removal The adsorption performance of Eu 3 ⁺ on ZVI bm and P-ZVI bm was systematically evaluated under varying conditions, including pH, solid-to-liquid ratio, contact time, concentration, and temperature (Fig. 2 A). The speciation of Eu varies significantly with pH (Fig. 2 B). At low pH (< 4), Eu 3+ predominantly exists, whereas with increasing pH, hydrolyzed species such as Eu(OH) 2 ⁺ progressively form in solution[47]. Figure 2 C presents the magnetization curves of ZVI bm and P-ZVI bm . The Ms of ZVI bm reaches 225.15 emu·g⁻ 1 , while that of P-ZVI bm decreases to 73.82 emu·g⁻ 1 due to phosphate surface modification. Nevertheless, both materials retain sufficient magnetic responsiveness, allowing efficient separation and recovery from Eu(III)-containing radioactive wastewater under an external magnetic field. To evaluate the electron transfer rate and corrosion resistance of the materials, Tafel tests were conducted using a three-electrode electrochemical system. As shown in Fig. 2 D, the corrosion potentials of ZVI bm and P-ZVI bm are − 0.386 V and − 0.315 V, respectively. The positive shift in corrosion potential indicates that phosphate modification slightly reduces the electron transfer rate but significantly enhances the corrosion resistance of P-ZVI bm . Considering that Eu exists predominantly as cations in aqueous solution, the surface charge of the adsorbent is expected to strongly influence the removal process. Therefore, the zeta potentials of the samples were measured over a pH range of 3–8, as shown in Fig. 2 E. As the pH increased, the zeta potential of ZVI bm decreased from + 28.34 mV to − 3.83 mV, while that of P-ZVI bm exhibited a more pronounced shift from − 2.65 mV to − 50.03 mV. This pronounced negative shift for P-ZVI bm is attributed to the introduction of PO 4 3 ⁻ groups on the surface, which increases overall surface electronegativity[48–49]. The influence of the S/L ratio is presented in Fig. 2 F. Increasing the S/L ratio from 0.1 to 0.6 g·L⁻ 1 enhanced the overall removal efficiency; however, the adsorption capacity per unit mass peaked at S/L = 0.2 g·L⁻ 1 . The subsequent decrease in capacity at higher loadings is attributed to excessive unused sites and a diminished concentration gradient driving force. As shown in Fig. 2 G, both adsorbents exhibited pronounced pH-dependent adsorption behavior within the acidic range (pH 2–6). The removal efficiency increased steadily with pH, reaching a maximum at pH = 3, where adsorption capacities were 7.92 mg·g⁻ 1 for ZVI bm and 121.76 mg·g⁻ 1 for P-ZVI bm . The low uptake under strong acidity was mainly due to proton competition and partial Fe 0 dissolution, while the enhanced performance at higher pH reflected the deprotonation of surface hydroxyls and the increasing contribution of negatively charged Fe–O–P sites[50], which facilitated Eu 3 ⁺ electrostatic attraction and inner-sphere complexation. These observations confirm that phosphate functionalization significantly improves acid tolerance and enhances active-site accessibility. As the initial Eu 3 ⁺ concentration increased (Fig. 2 H), the adsorption capacity rose sharply at low-to-moderate concentrations and then gradually reached saturation, yielding maximum capacities of 48.33 mg·g⁻ 1 for ZVI bm and 152.49 mg·g⁻ 1 for P-ZVI bm . Kinetic experiments (Fig. 2 I) revealed rapid Eu 3 ⁺ uptake during the initial stage, followed by equilibrium at 43.23 mg·g⁻ 1 for ZVI bm and 150.17 mg·g⁻ 1 for P-ZVI bm . Temperature-dependent adsorption results (Fig. 2 J) demonstrated a clear enhancement in Eu 3 ⁺ uptake with rising temperature, reflecting the endothermic nature of the process. The equilibrium capacity of P-ZVI bm increased from 118.64 mg·g⁻ 1 at 293 K to 155.21 mg·g⁻ 1 at 313.0 K, whereas that of ZVI bm increased modestly from 34.11 to 47.65 mg·g⁻ 1 over the same range. 3.3. Adsorption Mechanism Elucidation for Eu 3+ Removal Post-adsorption analyses were conducted to elucidate the structural and chemical evolution of ZVI bm and P-ZVI bm after Eu 3 ⁺ capture (Fig. 3 A–H). SEM-EDS characterization revealed distinct morphological changes in ZVI bm and P-ZVI bm after Eu adsorption, showing surface alteration and discontinuous deposits. Elemental mapping indicated homogeneous distributions of Eu, Fe, O, and P on the ZVI bm surface, whereas Eu on P-ZVI bm appeared sparsely and locally concentrated. EDS quantification further showed that the Eu content on P-ZVI bm (17.92 wt%) was nearly three times that of ZVI bm , confirming the enhanced Eu affinity induced by phosphate functionalization. XRD results (Fig. 3 C) provided structural evidence for distinct immobilization mechanisms. Both materials retained the characteristic Fe⁰ reflections at 2θ = 44.5° and 65.0°, but their intensities weakened after adsorption, indicating partial oxidation of the metallic core. For P-ZVI bm , new diffraction peaks at 2θ = 25.8°, 28.2°, and 31.3° corresponded to crystalline Eu 3 PO 7 phases (PDF#49-1024), confirming that phosphate groups on the surface acted not only as adsorption sites but also as active participants in interfacial precipitation with Eu 3 ⁺. XPS spectra (Figs. 3 D–G) further clarified the chemical states of key elements. The Eu 3d spectrum of P-ZVI bm exhibited two well-defined peaks at 1134.5 eV and 1164.2 eV, characteristic of Eu 3 ⁺. The P 2p signal decreased in intensity and shifted from 133.4 eV to 134.1 eV after adsorption, indicating coordination between phosphate oxygens and Eu 3 ⁺ through Fe–O–P–Eu linkages. Concurrently, Fe 2p spectra showed the disappearance of metallic Fe 0 (706.9 eV) and the emergence of Fe 2 ⁺/Fe 3 ⁺ peaks at 710.8 eV and 724.6 eV, evidencing oxidation of Fe 0 into Fe 2 O 3 , Fe 3 O 4 , and Fe(OH) 3 . The O 1s spectra displayed increased contributions from hydroxyl (Fe–OH) and phosphate (P–O–Fe, P–O–Eu) bonds, confirming the coexistence of redox transformation and chemical complexation during adsorption. Compared with ZVIbm, P-ZVIbm underwent more extensive surface oxidation and formed abundant reactive interfaces enriched with phosphate and iron oxyhydroxides, offering diverse coordination environments for Eu 3 ⁺[44]. 3.4. DFT Elucidation of the Interfacial Adsorption Mechanism Density functional theory (DFT) calculations were employed to gain atomic-level insight into the adsorption mechanism of Eu 3 ⁺ on phosphate-modified Fe–O surfaces (Fig. 4 A–F). The optimized configurations reveal that Eu 3 ⁺ strongly coordinates with surface oxygen atoms from phosphate and Fe–O–P groups, forming inner-sphere complexes with Eu–O bond lengths of approximately 2.1–2.3 Å and O–Eu–O angles between 77.929–79.545°. The corresponding adsorption energies progressively increase from − 8.015 eV for simple bidentate coordination to − 14.709 eV for multidentate bridging complexes, indicating that phosphate functionalization creates high-affinity sites capable of capturing Eu 3 ⁺ through strong chemisorption. The enhanced stability of these configurations suggests that phosphate groups not only serve as anchoring ligands but also promote interfacial nucleation of Eu–phosphate species. Charge density difference analysis (Fig. 4 E) displays pronounced electron accumulation around oxygen and depletion around europium, confirming substantial electron transfer from Eu³⁺ to the phosphate–oxygen framework and the mixed ionic–covalent nature of Eu–O bonding. This charge redistribution stabilizes Eu at the Fe–O–P interface and facilitates partial oxidation of surface Fe atoms. The projected density of states (Fig. 4 F) further supports this conclusion, showing hybridization between Eu 4f/5d and O 2p orbitals near the Fermi level, accompanied by a narrowed band gap and shifted Fe 3d states. Together, these results establish that Eu 3 ⁺ adsorption on P-ZVI bm is dominated by inner-sphere complexation and chemisorptive interaction, wherein phosphate groups create electron-rich, multidentate coordination environments[51] that strongly bind Eu³⁺ and drive the formation of stable Eu–phosphate precipitates. This DFT-supported mechanism coherently explains the experimentally observed high adsorption energy, temperature-enhanced uptake, and structural evolution of the adsorbent, confirming that phosphorylation transforms the Fe 0 surface into a robust, electronically active interface for selective Eu 3 ⁺ immobilization and recovery. 3.5. Application of ZVI bm and P-ZVI bm in real mine wastewater treatment To evaluate the practical applicability of the developed adsorbents, both ZVI bm and P-ZVI bm were tested for Eu 3 ⁺ removal from actual mine wastewater containing multiple coexisting metal ions (Table 1 and Fig. 5 A–D). The wastewater exhibited a complex matrix with high concentrations of competing cations such as Ce (1832.03 mg·L⁻ 1 ), Gd (634.69 mg·L⁻ 1 ), La (541.37 mg·L⁻ 1 ), Sm (361.79 mg·L⁻ 1 ), and other trace elements including Si, Ba, Ni, and Zn. These multicomponent conditions pose a significant challenge for selective adsorption of Eu 3 ⁺, especially under slightly acidic conditions typical of mine drainage systems. As shown in Fig. 5 A, both materials displayed effective Eu 3 ⁺ uptake with increasing contact time, but the removal efficiency of P-ZVI bm was substantially higher across all conditions. At equilibrium, P-ZVI bm achieved a Eu 3 ⁺ removal efficiency of 92.4%, compared with only 48.7% for ZVI bm , confirming that phosphate functionalization significantly enhances adsorption performance in complex aqueous systems. The improvement is attributed to the strong inner-sphere complexation of Eu 3 ⁺ with surface phosphate ligands and the formation of Eu–phosphate precipitates[52–53], which are less susceptible to ionic competition. The selectivity of P-ZVI bm toward Eu 3 ⁺ among the coexisting metal ions is presented in Fig. 5 B. While both adsorbents showed some affinity for light rare-earth elements such as La 3 ⁺, Ce 3 ⁺, and Gd 3 ⁺, the Eu 3 ⁺ adsorption capacity of P-ZVI bm was nearly fourfold higher than that of ZVI bm , with minimal interference from high concentrations of neighboring REEs. This selectivity arises from the specific coordination geometry and bond energy matching between Eu 3 ⁺ and Fe–O–P sites, as confirmed by DFT and XPS results. Furthermore, the negligible adsorption of common transition metals (Ni 2 ⁺, Zn 2 ⁺, Co 2 ⁺) suggests that P-ZVI bm possesses both chemical selectivity and environmental compatibility for rare-earth recovery from metallurgical effluents. The kinetics of Eu 3 ⁺ removal in real wastewater (Fig. 5 C) followed a rapid initial uptake phase, reaching equilibrium within 30.0 mins for P-ZVI bm , compared to nearly 120.0 minutes for ZVI bm . The faster equilibrium rate reflects improved surface accessibility and higher electrostatic attraction due to the negatively charged phosphate groups. In the presence of multiple ions, P-ZVI bm maintained an adsorption capacity of 132.5 mg·g⁻ 1 , representing 86.0% of its performance in simulated single-ion systems, whereas ZVI bm retained only 57.0%. This demonstrates the structural stability and anti-interference ability of the phosphorylated surface in realistic environments. The recyclability of P-ZVI bm was further verified by five consecutive adsorption–desorption cycles using H 3 PO 4 regeneration (Fig. 5 D). The Eu 3 ⁺ removal efficiency remained above 85.0% after five cycles, with only minor declines due to partial surface passivation and loss of active sites. In contrast, ZVI bm exhibited a pronounced capacity drop to below 50% after the third cycle, resulting from severe corrosion and aggregation under acidic regeneration conditions. The retained magnetic response of P-ZVI bm enabled facile separation from treated water by an external magnetic field, further supporting its suitability for practical wastewater applications. In summary, the results demonstrate that phosphorylation effectively transforms conventional ZVI into a highly stable, selective, and recyclable adsorbent capable of capturing and recovering Eu 3 ⁺ from complex mine effluents. The enhanced affinity toward Eu 3 ⁺, high tolerance to competing ions, and strong regeneration capacity confirm that P-ZVI bm bridges the gap between laboratory-scale synthesis and field-scale application. This work provides a feasible pathway for resource recovery from rare-earth-associated radioactive wastewater, aligning with the principles of green metallurgy and sustainable waste valorization. Table 1 Chemical composition of the real wastewater sample Element C x (mg/L) Si 325.927 As 1.530 Au 5.541 B 7.700 Ba 42.162 Be 10.303 Bi 2.817 Cd 0.090 Ce 1832.032 Co 1.317 Ga 8.218 Gd 634.693 Ge 0.970 La 541.373 Ni 11.633 Sm 361.793 Zn 8.525 4. Conclusion In summary, phosphorylation-modified zero-valent iron (P-ZVI bm ) exhibits markedly enhanced physicochemical properties, including reduced particle size, enlarged surface area, more negative surface potential, and superior resistance to corrosion, all of which synergistically improve its Eu³⁺ removal efficiency in acidic media. Under optimized conditions, P-ZVI bm achieves a maximum adsorption capacity of 152.49 mg·g⁻ 1 . Mechanistically, Eu 3 ⁺ migrates toward the negatively shifted interface, undergoes inner-sphere complexation with Fe–O–P groups, and nucleates as Eu 3 PO 7 precipitates. This multi-pathway process not only overcomes the intrinsic instability of ZVI in acidic environments but also establishes a material and mechanistic framework for efficient rare-earth separation in radioactive wastewater treatment. Declarations Conflict of Interest Yuhui Liu is an editorial board member for this journal and was not involved in the editorial review or the decision to publish this article. The authors declare that there is no conflict of interest. Author Contribution Yuhui Liu .Shuang Zhang. and Xiaoyan Li. wrote the main manuscript text and Yu zhang. Jin Li. Zhengquan Zhang prepared figures 1-5. All authors reviewed the manuscript. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (22566002, 22466006), the Natural Science Foundation of Jiangxi Province (20242BAB20107, 20252BAC220002), National Key Laboratory of Uranium Resources Exploration-Mining and Nuclear Remote Sensing (2024QZ-TD-16). 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Water Res, 260 Tuyiringire D, Liu X, Zheng Q, Wang S, Zhang W, Bi F, Zhang Y, Wang Y, Qu J, Zhang Y (2025) Ball-milled phosphate/micro zero-valent iron/biochar for lead and cadmium removal and stabilization in water and soil: Performance, mechanisms, and environmental applications. Sep Purif Technol, 362 Chen ST, Bo T, Zhang Y, Wang YC, Li XY, Zhang S, Liu YH (2025) Biomimetic phosphatization of nano zero-valent iron for thorium removal and waste remediation from rare earth leachates. Environ Res, 285 Stumpf T, Bauer A, Coppin F, Fanghänel T, Kim J-I (2002) Inner-sphere, outer-sphere and ternary surface complexes: a TRLFS study of the sorption process of Eu(III) onto smectite and kaolinite, Radiochim. Acta , 90 No. 6, pp. 345–349 Jing P, Peng L, Xu N, Feng Y, Liu X (2022) Escherichia coli and phosphate interplay mediates transport of nanoscale zero-valent iron synthesized by green tea in water-saturated porous media. Colloids Surf B, 219 Zhang H, Liu X, Zhou B, Chen Z, Cheng J, Zeng K, Zhang L, Sun H, Ai Z (2025) Phosphorylated zerovalent Iron boosts active hydrogen species generation from water dissociation for superior Hg(II) Reduction. Water Res, 283 Bae S, Hanna K (2015) Reactivity of Nanoscale Zero-Valent Iron in Unbuffered Systems: Effect of pH and Fe(II) Dissolution. Environ Sci Technol 49:10536–10543 Patel MA, Kar AS, Kumar S, Tomar BS (2017) Effect of phosphate on sorption of Eu(III) by montmorillonite. J Radioanal Nucl Chem 313(3):537–545 Jordan N, Demnitz M, Lösch H, Starke S, Brendler V, Huittinen N (2018) Complexation of Trivalent Lanthanides (Eu) and Actinides (Cm) with Aqueous Phosphates at Elevated Temperatures. Inorg Chem 57(12):7015–7024 Fan QH, Zhao XL, Ma XX, Yang YB, Wu WS, Zheng GD, Wang DL (2015) Comparative adsorption of Eu(iii) and Am(iii) on TPD, Environ. Sci.: Processes Impacts , 17 No. 9, pp. 1634–1640 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-7932241","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":542110393,"identity":"232522fa-a2fc-4730-8700-20f5c29f2ded","order_by":0,"name":"Yu Zhang","email":"","orcid":"","institution":"East China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Zhang","suffix":""},{"id":542110394,"identity":"3a84d50f-e697-4718-8fd6-ee3fb7beec32","order_by":1,"name":"Jin Li","email":"","orcid":"","institution":"East China University of 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16:13:55","extension":"xml","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":117064,"visible":true,"origin":"","legend":"","description":"","filename":"b82c80a3547e44cd8ba53b3c2f4251311structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/7421ede801f099ddea077e25.xml"},{"id":95569595,"identity":"5551d819-5447-4526-a61b-8fb325b039b3","added_by":"auto","created_at":"2025-11-10 16:40:38","extension":"html","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":126407,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/63dd0fb80ddbf9900b8dbb61.html"},{"id":95569577,"identity":"7e9fcf56-d1cc-44ed-ae12-2b0864c29e58","added_by":"auto","created_at":"2025-11-10 16:40:38","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":956560,"visible":true,"origin":"","legend":"\u003cp\u003eMorphological and structural characterization of P-ZVI\u003csub\u003ebm\u003c/sub\u003e: (A) schematic illustration of phosphate modification and adsorption process. (B) SEM images and EDS elemental mapping. (C) FTIR spectra. (D) XPS spectra.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/7d2488db68ebc390e8aba35c.png"},{"id":95569575,"identity":"c40b9a0c-9ab7-4175-9002-938ef28284d4","added_by":"auto","created_at":"2025-11-10 16:40:38","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":617456,"visible":true,"origin":"","legend":"\u003cp\u003eBatch adsorption behavior of Eu\u003csup\u003e3\u003c/sup\u003e⁺ on ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e: (A) Schematic illustration of the adsorption process and influencing factors. (B) pH. (C) Magnetization curves. (D) Electrochemical polarization curves. (E) Zata. (F) Solid-to-liquid ratio. (G) pH. (H) Concentration. (I) Time. (J) Temperature.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/e3dc7b5530bcc57f8c66eb24.png"},{"id":95569578,"identity":"8e9937bb-d017-422d-bcd5-17820a4aaf60","added_by":"auto","created_at":"2025-11-10 16:40:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":983372,"visible":true,"origin":"","legend":"\u003cp\u003eCharacterization of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e before and after Eu\u003csup\u003e3\u003c/sup\u003e⁺ adsorption: (A–B) SEM images and corresponding EDS elemental mapping showing the distribution of Fe, O, P, and Eu, and (C) XRD patterns of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e before and after adsorption. (D) Full XPS survey spectrum. (F) Fe 2p. (F) O 1s. (G) Eu 3d.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/7f759b899732988d6efe90ac.png"},{"id":95569593,"identity":"d67df768-7408-4d7d-836e-f8b64e86dbe4","added_by":"auto","created_at":"2025-11-10 16:40:38","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":354791,"visible":true,"origin":"","legend":"\u003cp\u003eDFT analysis of Eu\u003csup\u003e3\u003c/sup\u003e⁺ adsorption configurations on Fe–O and Fe–O–P surfaces: (A, B) optimized structures showing Eu (purple) binding with O (red) on ZVI through monodentate and multidentate coordination, respectively. C, D) optimized structures illustrating Eu (purple) interaction with P-ZVI\u003csub\u003ebm\u003c/sub\u003e surfaces via monodentate and multidentate Fe–O–P coordination. (E) charge density difference map and (F) projected density of states (PDOS) of multidentate coordination.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/c4c8dacaf72f7482c8bb684e.png"},{"id":95655497,"identity":"a7cb0c08-333d-42e3-8c35-2100830dcf2a","added_by":"auto","created_at":"2025-11-11 16:16:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":634856,"visible":true,"origin":"","legend":"\u003cp\u003eApplication performance of ZVI\u003csub\u003ebm \u003c/sub\u003eand P-ZVI\u003csub\u003ebm\u003c/sub\u003e in real mine wastewater: (A) Schematic illustration of Eu\u003csup\u003e3\u003c/sup\u003e⁺ recovery from radioactive associated mineral wastewater using P-ZVI\u003csub\u003ebm\u003c/sub\u003e. (B) Efficiency. (C) Adsorption selectivity. (D) Adsorption kinetics. (E) Reusability.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/1cfd7790a6ec6a36383e444d.png"},{"id":97664719,"identity":"130b3475-01d0-41b1-98c8-95b0d4185742","added_by":"auto","created_at":"2025-12-08 09:13:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4250655,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7932241/v1/c231daf2-de77-4bd6-9516-450924a1d2cd.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Phosphate-Functionalized Zero-Valent Iron for Efficient Separation of Europium from Acidic Associated Mineral Wastewater","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe processing of associated mineral resources and the nuclear fuel cycle inevitably generate large volumes of acidic wastewater enriched in uranium, thorium, and rare-earth elements such as europium (Eu\u003csup\u003e3\u003c/sup\u003e⁺)[1\u0026ndash;4]. Although stable europium isotopes are non-radiotoxic, Eu\u003csup\u003e3\u003c/sup\u003e⁺ often coexists with radionuclides in hydrometallurgical effluents, introducing risks of environmental migration, nuclear safety issues, and long-term management challenges[5]. Furthermore, Eu\u003csup\u003e3\u003c/sup\u003e⁺ exhibits complex aqueous speciation and strong coordination ability with oxygen-donor ligands, which lead to its high solubility and hinder its selective separation from chemically similar species[6\u0026ndash;7]. Therefore, the efficient removal and recovery of Eu\u003csup\u003e3\u003c/sup\u003e⁺ under highly acidic conditions remains a critical challenge for both environmental protection and resource recycling in radioactive mineral processing. Europium is a strategically important rare-earth element widely used in phosphors[8\u0026ndash;12], nuclear detectors[13\u0026ndash;14], and advanced energy materials[15\u0026ndash;17]. However, its supply is limited due to the low abundance of Eu-bearing minerals and the complex processes required for separation from other lanthanides. Traditional extraction techniques, such as solvent extraction[18\u0026ndash;19], ion exchange[20\u0026ndash;21], and acid-based adsorption[22\u0026ndash;24], have achieved moderate success but face significant limitations, including acid-induced damage to adsorbents, generation of secondary waste, poor selectivity in multi-ion systems, and limited regeneration capability. These challenges underscore the urgent need for environmentally benign, acid-tolerant, and recyclable materials capable of selectively capturing Eu\u003csup\u003e3\u003c/sup\u003e⁺ from complex metallurgical effluents.\u003c/p\u003e\u003cp\u003eZero-valent iron (ZVI) has gained considerable attention in recent decades as a multifunctional material for the remediation of heavy metals, radionuclides, and organic pollutants, owing to its synergistic adsorption and reduction properties[25\u0026ndash;27]. Its unique surface redox reactivity allows for the immobilization of metal ions through electron transfer[28\u0026ndash;30] and coprecipitation[31]. However, in acidic environments typical of hydrometallurgical waste streams, pristine ZVI suffers from rapid proton-induced corrosion, excessive hydrogen evolution, and severe particle aggregation, which collectively deteriorates its reactivity and stability. To overcome these limitations, surface engineering strategies have been developed to enhance the acid resistance, reactivity, and functional selectivity of ZVI. Recent advances\u0026mdash;including nonmetallic modification[32], chelating-agent stabilization[33], nanoscale structuring[34\u0026ndash;35], and vacancy engineering[36\u0026ndash;37]\u0026mdash;have effectively improved electron transfer, suppressed corrosion, and expanded its applicability to complex aqueous systems. Nevertheless, achieving long-term stability and controlled reactivity in acidic and multicomponent environments remains a key challenge motivating further material innovations such as phosphate-functionalized ZVI. Among them, phosphorylation modification[38\u0026ndash;43] offers a particularly promising route. Yet, despite its conceptual appeal, the adsorption behavior, mechanistic pathways, and thermodynamic characteristics of phosphorylation-modified ZVI for Eu\u003csup\u003e3\u003c/sup\u003e⁺ recovery remain insufficiently elucidated.\u003c/p\u003e\u003cp\u003eIn this study, we report a zero-acid strategy for europium recovery using phosphorylation-engineered zero-valent iron (P-ZVI\u003csub\u003ebm\u003c/sub\u003e) as an adsorbent. The proposed system achieves simultaneous corrosion inhibition and selective Eu\u003csup\u003e3\u003c/sup\u003e⁺ capture under in an acidic environment, eliminating the need for acidification while maintaining high adsorption efficiency. Through comprehensive kinetic, isotherm, and thermodynamic analyses combined with spectroscopic characterization, we reveal a synergistic mechanism involving Eu\u003csup\u003e3\u003c/sup\u003e⁺ migration to negatively shifted Fe\u0026ndash;O\u0026ndash;P surfaces, inner-sphere complexation, and interfacial precipitation of Eu\u0026ndash;phosphate species, supplemented by adsorption on secondary Fe oxyhydroxides formed during mild corrosion. This dual-function mechanism adsorption coupled with redox transformation enables robust performance and excellent reusability even under challenging chemical conditions, providing a sustainable and scalable strategy for europium recovery from radioactive mineral effluents and offering new insights into the design of acid-resistant functional materials for green metallurgical processes.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003eIron powder (Fe, analytical grade, particle size\u0026thinsp;\u0026lt;\u0026thinsp;50 \u0026micro;m), phosphoric acid (H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, \u0026ge;\u0026thinsp;85.0%), nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e, 65.0\u0026ndash;68.0%), and sodium hydroxide (NaOH, \u0026ge;\u0026thinsp;96.0%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous ethanol was obtained from Macklin Biochemical Co., Ltd. Europium nitrate hexahydrate (Eu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, \u0026ge;\u0026thinsp;99.9%) was supplied by Aladdin Reagent Co., Ltd. All solutions were prepared with deionized water.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Synthesis of P-ZVI\u003csub\u003ebm\u003c/sub\u003e\u003c/h2\u003e\u003cp\u003ePhosphorylated ball-milled zero-valent iron (P-ZVI\u003csub\u003ebm\u003c/sub\u003e) was prepared via a mechanochemical approach. Iron powder (3.0 g) and KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e (0.7309 g) were mixed and placed into an agate ball-milling jar together with a defined amount of agate balls. To avoid oxidation of Fe during milling, nitrogen gas was purged into the jar for 30.0 min prior to sealing. The mixture was then subjected to planetary ball milling at 300.0 rpm for 3.0 h. The resulting material was collected and stored in vacuum-sealed bags and denoted as P-ZVI\u003csub\u003ebm\u003c/sub\u003e. For comparison, ball-milled Fe powder without KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e was prepared under identical conditions and denoted as ZVI\u003csub\u003ebm\u003c/sub\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Characterization\u003c/h2\u003e\u003cp\u003eThe crystalline structure of the materials was analyzed using X-ray diffraction (XRD, Rigaku SmartLab SE, Cu-Kα radiation). Surface morphology was observed by scanning electron microscopy (SEM, TESCAN MIRA LMS) and transmission electron microscopy (TEM, JEOL JEM-F200). Surface functional groups were identified by Fourier transform infrared spectroscopy (FTIR, Thermo Nicolet iS5), while microstructural features and defects were investigated by Raman spectroscopy (Renishaw inVia). Elemental composition and chemical states were determined by X-ray photoelectron spectroscopy (XPS, LAUDA Scientific GmbH LSA-100X). P-ZVI\u003csub\u003ebm\u003c/sub\u003e was prepared using a ball mill (PML10, Netzsch Instruments). The magnetic properties of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e were measured using a vibrating sample magnetometer (VSM, LakeShore 7404, USA). The surface charges of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e were determined using a solid surface zeta potential analyzer (SurPASS 3, Anton Paar, Austria).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Batch Adsorption Experiments for Eu Removal\u003c/h2\u003e\u003cp\u003eEu(III) stock solution (1 g\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e) was prepared as follows: 2.9353 g of Eu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO was placed in a beaker, dissolved in 10.0 mL aqua regia under heating and stirring, and subsequently evaporated to dryness in a fume hood. After cooling the residue to room temperature, it was redissolved in 50.0 mL of deionized water and diluted to a final volume of 1.0 L in a volumetric flask. Batch adsorption experiments were conducted using the equilibrium method. Eu(III) solutions of desired concentrations were prepared by dilution of the stock solution and adjusted to target pH using 0.1 mol\u0026middot;L⁻\u0026sup1; HNO\u003csub\u003e3\u003c/sub\u003e or 0.1 mol\u0026middot;L⁻\u0026sup1; NaHCO\u003csub\u003e3\u003c/sub\u003e. In a typical run, 5.0 mg of adsorbent was added to 25.0 mL of Eu(III) solution and shaken at 180.0 rpm at a constant temperature for a specified time. The residual Eu concentration was measured by inductively coupled plasma mass spectrometry (ICP-MS).\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Structural and physicochemical properties of P-ZVI\u003csub\u003ebm\u003c/sub\u003e\u003c/h2\u003e\u003cp\u003eThe morphological and structural evolution of the zero-valent iron after ball-milling and phosphorylation modification (P-ZVI\u003csub\u003ebm\u003c/sub\u003e) was systematically characterized (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA\u0026ndash;D). As shown in the schematic illustration (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), the phosphorylated surface of P-ZVI\u003csub\u003ebm\u003c/sub\u003e provides abundant adsorption sites and facilitates Eu\u003csup\u003e3\u003c/sup\u003e⁺ immobilization through inner-sphere complexation and interface nucleation processes. SEM analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB) revealed that P-ZVI\u003csub\u003ebm\u003c/sub\u003e displayed rougher, flake-like structures with visible surface defects and micro-pores. These morphological changes indicate that phosphate incorporation during mechanical activation promotes surface reconstruction and fragmentation, thereby enlarging the specific surface area and exposing more reactive sites[44\u0026ndash;45]. Energy-dispersive X-ray spectroscopy (EDS) further confirmed the presence of Fe (92.08%), O (5.57%), and P (2.35%) in P-ZVI\u003csub\u003ebm\u003c/sub\u003e, verifying the successful introduction of phosphate groups while maintaining Fe as the predominant component. X-ray diffraction (XRD) patterns (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC) of P-ZVI\u003csub\u003ebm\u003c/sub\u003e exhibited characteristic reflections at 2θ\u0026thinsp;=\u0026thinsp;44.5\u0026deg; and 65.0\u0026deg;, corresponding to the (110) and (200) planes of metallic Fe\u003csup\u003e0\u003c/sup\u003e (PDF#65-4899). The absence of new crystalline peaks (2θ\u0026thinsp;=\u0026thinsp;44.5\u0026deg;) in P-ZVI\u003csub\u003ebm\u003c/sub\u003e indicates that the Fe\u003csup\u003e0\u003c/sup\u003e core structure was preserved after surface phosphorylation. However, the reduced intensity of Fe\u003csup\u003e0\u003c/sup\u003e peaks suggests partial amorphization induced by high-energy milling and phosphate bonding. Fourier-transform infrared (FTIR) spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD) provide further evidence of chemical modification: absorption bands at 898.0 cm⁻\u003csup\u003e1\u003c/sup\u003e, 1090.0 cm⁻\u003csup\u003e1\u003c/sup\u003e, and 1280.0 cm⁻\u003csup\u003e1\u003c/sup\u003e correspond to P\u0026ndash;O, Fe\u0026ndash;O\u0026ndash;P, and P\u0026thinsp;=\u0026thinsp;O vibrations[45], respectively, confirming stable coordination between phosphate groups and iron atoms. The Fe\u0026ndash;O\u0026ndash;P linkage is expected to enhance the chemical durability of ZVI in acidic media by forming a protective passivation layer that limits proton attack[46].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Adsorption Performance of Eu\u003csup\u003e3+\u003c/sup\u003e Removal\u003c/h2\u003e\u003cp\u003eThe adsorption performance of Eu\u003csup\u003e3\u003c/sup\u003e⁺ on ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e was systematically evaluated under varying conditions, including pH, solid-to-liquid ratio, contact time, concentration, and temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). The speciation of Eu varies significantly with pH (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). At low pH (\u0026lt;\u0026thinsp;4), Eu\u003csup\u003e3+\u003c/sup\u003e predominantly exists, whereas with increasing pH, hydrolyzed species such as Eu(OH)\u003csup\u003e2\u003c/sup\u003e⁺ progressively form in solution[47]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC presents the magnetization curves of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e. The Ms of ZVI\u003csub\u003ebm\u003c/sub\u003e reaches 225.15 emu\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e, while that of P-ZVI\u003csub\u003ebm\u003c/sub\u003e decreases to 73.82 emu\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e due to phosphate surface modification. Nevertheless, both materials retain sufficient magnetic responsiveness, allowing efficient separation and recovery from Eu(III)-containing radioactive wastewater under an external magnetic field. To evaluate the electron transfer rate and corrosion resistance of the materials, Tafel tests were conducted using a three-electrode electrochemical system. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD, the corrosion potentials of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e are \u0026minus;\u0026thinsp;0.386 V and \u0026minus;\u0026thinsp;0.315 V, respectively. The positive shift in corrosion potential indicates that phosphate modification slightly reduces the electron transfer rate but significantly enhances the corrosion resistance of P-ZVI\u003csub\u003ebm\u003c/sub\u003e. Considering that Eu exists predominantly as cations in aqueous solution, the surface charge of the adsorbent is expected to strongly influence the removal process. Therefore, the zeta potentials of the samples were measured over a pH range of 3\u0026ndash;8, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE. As the pH increased, the zeta potential of ZVI\u003csub\u003ebm\u003c/sub\u003e decreased from +\u0026thinsp;28.34 mV to \u0026minus;\u0026thinsp;3.83 mV, while that of P-ZVI\u003csub\u003ebm\u003c/sub\u003e exhibited a more pronounced shift from \u0026minus;\u0026thinsp;2.65 mV to \u0026minus;\u0026thinsp;50.03 mV. This pronounced negative shift for P-ZVI\u003csub\u003ebm\u003c/sub\u003e is attributed to the introduction of PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u003c/sup\u003e⁻ groups on the surface, which increases overall surface electronegativity[48\u0026ndash;49]. The influence of the S/L ratio is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF. Increasing the S/L ratio from 0.1 to 0.6 g\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e enhanced the overall removal efficiency; however, the adsorption capacity per unit mass peaked at S/L\u0026thinsp;=\u0026thinsp;0.2 g\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e. The subsequent decrease in capacity at higher loadings is attributed to excessive unused sites and a diminished concentration gradient driving force. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG, both adsorbents exhibited pronounced pH-dependent adsorption behavior within the acidic range (pH 2\u0026ndash;6). The removal efficiency increased steadily with pH, reaching a maximum at pH\u0026thinsp;=\u0026thinsp;3, where adsorption capacities were 7.92 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e for ZVI\u003csub\u003ebm\u003c/sub\u003e and 121.76 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e for P-ZVI\u003csub\u003ebm\u003c/sub\u003e. The low uptake under strong acidity was mainly due to proton competition and partial Fe\u003csup\u003e0\u003c/sup\u003e dissolution, while the enhanced performance at higher pH reflected the deprotonation of surface hydroxyls and the increasing contribution of negatively charged Fe\u0026ndash;O\u0026ndash;P sites[50], which facilitated Eu\u003csup\u003e3\u003c/sup\u003e⁺ electrostatic attraction and inner-sphere complexation. These observations confirm that phosphate functionalization significantly improves acid tolerance and enhances active-site accessibility. As the initial Eu\u003csup\u003e3\u003c/sup\u003e⁺ concentration increased (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH), the adsorption capacity rose sharply at low-to-moderate concentrations and then gradually reached saturation, yielding maximum capacities of 48.33 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e for ZVI\u003csub\u003ebm\u003c/sub\u003e and 152.49 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e for P-ZVI\u003csub\u003ebm\u003c/sub\u003e. Kinetic experiments (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI) revealed rapid Eu\u003csup\u003e3\u003c/sup\u003e⁺ uptake during the initial stage, followed by equilibrium at 43.23 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e for ZVI\u003csub\u003ebm\u003c/sub\u003e and 150.17 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e for P-ZVI\u003csub\u003ebm\u003c/sub\u003e. Temperature-dependent adsorption results (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eJ) demonstrated a clear enhancement in Eu\u003csup\u003e3\u003c/sup\u003e⁺ uptake with rising temperature, reflecting the endothermic nature of the process. The equilibrium capacity of P-ZVI\u003csub\u003ebm\u003c/sub\u003e increased from 118.64 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e at 293 K to 155.21 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e at 313.0 K, whereas that of ZVI\u003csub\u003ebm\u003c/sub\u003e increased modestly from 34.11 to 47.65 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e over the same range.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Adsorption Mechanism Elucidation for Eu\u003csup\u003e3+\u003c/sup\u003e Removal\u003c/h2\u003e\u003cp\u003ePost-adsorption analyses were conducted to elucidate the structural and chemical evolution of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e after Eu\u003csup\u003e3\u003c/sup\u003e⁺ capture (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA\u0026ndash;H). SEM-EDS characterization revealed distinct morphological changes in ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e after Eu adsorption, showing surface alteration and discontinuous deposits. Elemental mapping indicated homogeneous distributions of Eu, Fe, O, and P on the ZVI\u003csub\u003ebm\u003c/sub\u003e surface, whereas Eu on P-ZVI\u003csub\u003ebm\u003c/sub\u003e appeared sparsely and locally concentrated. EDS quantification further showed that the Eu content on P-ZVI\u003csub\u003ebm\u003c/sub\u003e (17.92 wt%) was nearly three times that of ZVI\u003csub\u003ebm\u003c/sub\u003e, confirming the enhanced Eu affinity induced by phosphate functionalization. XRD results (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC) provided structural evidence for distinct immobilization mechanisms. Both materials retained the characteristic Fe⁰ reflections at 2θ\u0026thinsp;=\u0026thinsp;44.5\u0026deg; and 65.0\u0026deg;, but their intensities weakened after adsorption, indicating partial oxidation of the metallic core. For P-ZVI\u003csub\u003ebm\u003c/sub\u003e, new diffraction peaks at 2θ\u0026thinsp;=\u0026thinsp;25.8\u0026deg;, 28.2\u0026deg;, and 31.3\u0026deg; corresponded to crystalline Eu\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e7\u003c/sub\u003e phases (PDF#49-1024), confirming that phosphate groups on the surface acted not only as adsorption sites but also as active participants in interfacial precipitation with Eu\u003csup\u003e3\u003c/sup\u003e⁺. XPS spectra (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD\u0026ndash;G) further clarified the chemical states of key elements. The Eu 3d spectrum of P-ZVI\u003csub\u003ebm\u003c/sub\u003e exhibited two well-defined peaks at 1134.5 eV and 1164.2 eV, characteristic of Eu\u003csup\u003e3\u003c/sup\u003e⁺. The P 2p signal decreased in intensity and shifted from 133.4 eV to 134.1 eV after adsorption, indicating coordination between phosphate oxygens and Eu\u003csup\u003e3\u003c/sup\u003e⁺ through Fe\u0026ndash;O\u0026ndash;P\u0026ndash;Eu linkages. Concurrently, Fe 2p spectra showed the disappearance of metallic Fe\u003csup\u003e0\u003c/sup\u003e (706.9 eV) and the emergence of Fe\u003csup\u003e2\u003c/sup\u003e⁺/Fe\u003csup\u003e3\u003c/sup\u003e⁺ peaks at 710.8 eV and 724.6 eV, evidencing oxidation of Fe\u003csup\u003e0\u003c/sup\u003e into Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and Fe(OH)\u003csub\u003e3\u003c/sub\u003e. The O 1s spectra displayed increased contributions from hydroxyl (Fe\u0026ndash;OH) and phosphate (P\u0026ndash;O\u0026ndash;Fe, P\u0026ndash;O\u0026ndash;Eu) bonds, confirming the coexistence of redox transformation and chemical complexation during adsorption. Compared with ZVIbm, P-ZVIbm underwent more extensive surface oxidation and formed abundant reactive interfaces enriched with phosphate and iron oxyhydroxides, offering diverse coordination environments for Eu\u003csup\u003e3\u003c/sup\u003e⁺[44].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.4. DFT Elucidation of the Interfacial Adsorption Mechanism\u003c/h2\u003e\u003cp\u003eDensity functional theory (DFT) calculations were employed to gain atomic-level insight into the adsorption mechanism of Eu\u003csup\u003e3\u003c/sup\u003e⁺ on phosphate-modified Fe\u0026ndash;O surfaces (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA\u0026ndash;F). The optimized configurations reveal that Eu\u003csup\u003e3\u003c/sup\u003e⁺ strongly coordinates with surface oxygen atoms from phosphate and Fe\u0026ndash;O\u0026ndash;P groups, forming inner-sphere complexes with Eu\u0026ndash;O bond lengths of approximately 2.1\u0026ndash;2.3 \u0026Aring; and O\u0026ndash;Eu\u0026ndash;O angles between 77.929\u0026ndash;79.545\u0026deg;. The corresponding adsorption energies progressively increase from \u0026minus;\u0026thinsp;8.015 eV for simple bidentate coordination to \u0026minus;\u0026thinsp;14.709 eV for multidentate bridging complexes, indicating that phosphate functionalization creates high-affinity sites capable of capturing Eu\u003csup\u003e3\u003c/sup\u003e⁺ through strong chemisorption. The enhanced stability of these configurations suggests that phosphate groups not only serve as anchoring ligands but also promote interfacial nucleation of Eu\u0026ndash;phosphate species. Charge density difference analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE) displays pronounced electron accumulation around oxygen and depletion around europium, confirming substantial electron transfer from Eu\u0026sup3;⁺ to the phosphate\u0026ndash;oxygen framework and the mixed ionic\u0026ndash;covalent nature of Eu\u0026ndash;O bonding. This charge redistribution stabilizes Eu at the Fe\u0026ndash;O\u0026ndash;P interface and facilitates partial oxidation of surface Fe atoms. The projected density of states (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF) further supports this conclusion, showing hybridization between Eu 4f/5d and O 2p orbitals near the Fermi level, accompanied by a narrowed band gap and shifted Fe 3d states. Together, these results establish that Eu\u003csup\u003e3\u003c/sup\u003e⁺ adsorption on P-ZVI\u003csub\u003ebm\u003c/sub\u003e is dominated by inner-sphere complexation and chemisorptive interaction, wherein phosphate groups create electron-rich, multidentate coordination environments[51] that strongly bind Eu\u0026sup3;⁺ and drive the formation of stable Eu\u0026ndash;phosphate precipitates. This DFT-supported mechanism coherently explains the experimentally observed high adsorption energy, temperature-enhanced uptake, and structural evolution of the adsorbent, confirming that phosphorylation transforms the Fe\u003csup\u003e0\u003c/sup\u003e surface into a robust, electronically active interface for selective Eu\u003csup\u003e3\u003c/sup\u003e⁺ immobilization and recovery.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Application of ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e in real mine wastewater treatment\u003c/h2\u003e\u003cp\u003eTo evaluate the practical applicability of the developed adsorbents, both ZVI\u003csub\u003ebm\u003c/sub\u003e and P-ZVI\u003csub\u003ebm\u003c/sub\u003e were tested for Eu\u003csup\u003e3\u003c/sup\u003e⁺ removal from actual mine wastewater containing multiple coexisting metal ions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA\u0026ndash;D). The wastewater exhibited a complex matrix with high concentrations of competing cations such as Ce (1832.03 mg\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e), Gd (634.69 mg\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e), La (541.37 mg\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e), Sm (361.79 mg\u0026middot;L⁻\u003csup\u003e1\u003c/sup\u003e), and other trace elements including Si, Ba, Ni, and Zn. These multicomponent conditions pose a significant challenge for selective adsorption of Eu\u003csup\u003e3\u003c/sup\u003e⁺, especially under slightly acidic conditions typical of mine drainage systems. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA, both materials displayed effective Eu\u003csup\u003e3\u003c/sup\u003e⁺ uptake with increasing contact time, but the removal efficiency of P-ZVI\u003csub\u003ebm\u003c/sub\u003e was substantially higher across all conditions. At equilibrium, P-ZVI\u003csub\u003ebm\u003c/sub\u003e achieved a Eu\u003csup\u003e3\u003c/sup\u003e⁺ removal efficiency of 92.4%, compared with only 48.7% for ZVI\u003csub\u003ebm\u003c/sub\u003e, confirming that phosphate functionalization significantly enhances adsorption performance in complex aqueous systems. The improvement is attributed to the strong inner-sphere complexation of Eu\u003csup\u003e3\u003c/sup\u003e⁺ with surface phosphate ligands and the formation of Eu\u0026ndash;phosphate precipitates[52\u0026ndash;53], which are less susceptible to ionic competition. The selectivity of P-ZVI\u003csub\u003ebm\u003c/sub\u003e toward Eu\u003csup\u003e3\u003c/sup\u003e⁺ among the coexisting metal ions is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB. While both adsorbents showed some affinity for light rare-earth elements such as La\u003csup\u003e3\u003c/sup\u003e⁺, Ce\u003csup\u003e3\u003c/sup\u003e⁺, and Gd\u003csup\u003e3\u003c/sup\u003e⁺, the Eu\u003csup\u003e3\u003c/sup\u003e⁺ adsorption capacity of P-ZVI\u003csub\u003ebm\u003c/sub\u003e was nearly fourfold higher than that of ZVI\u003csub\u003ebm\u003c/sub\u003e, with minimal interference from high concentrations of neighboring REEs. This selectivity arises from the specific coordination geometry and bond energy matching between Eu\u003csup\u003e3\u003c/sup\u003e⁺ and Fe\u0026ndash;O\u0026ndash;P sites, as confirmed by DFT and XPS results. Furthermore, the negligible adsorption of common transition metals (Ni\u003csup\u003e2\u003c/sup\u003e⁺, Zn\u003csup\u003e2\u003c/sup\u003e⁺, Co\u003csup\u003e2\u003c/sup\u003e⁺) suggests that P-ZVI\u003csub\u003ebm\u003c/sub\u003e possesses both chemical selectivity and environmental compatibility for rare-earth recovery from metallurgical effluents. The kinetics of Eu\u003csup\u003e3\u003c/sup\u003e⁺ removal in real wastewater (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC) followed a rapid initial uptake phase, reaching equilibrium within 30.0 mins for P-ZVI\u003csub\u003ebm\u003c/sub\u003e, compared to nearly 120.0 minutes for ZVI\u003csub\u003ebm\u003c/sub\u003e. The faster equilibrium rate reflects improved surface accessibility and higher electrostatic attraction due to the negatively charged phosphate groups. In the presence of multiple ions, P-ZVI\u003csub\u003ebm\u003c/sub\u003e maintained an adsorption capacity of 132.5 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e, representing 86.0% of its performance in simulated single-ion systems, whereas ZVI\u003csub\u003ebm\u003c/sub\u003e retained only 57.0%. This demonstrates the structural stability and anti-interference ability of the phosphorylated surface in realistic environments. The recyclability of P-ZVI\u003csub\u003ebm\u003c/sub\u003e was further verified by five consecutive adsorption\u0026ndash;desorption cycles using H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e regeneration (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD). The Eu\u003csup\u003e3\u003c/sup\u003e⁺ removal efficiency remained above 85.0% after five cycles, with only minor declines due to partial surface passivation and loss of active sites. In contrast, ZVI\u003csub\u003ebm\u003c/sub\u003e exhibited a pronounced capacity drop to below 50% after the third cycle, resulting from severe corrosion and aggregation under acidic regeneration conditions. The retained magnetic response of P-ZVI\u003csub\u003ebm\u003c/sub\u003e enabled facile separation from treated water by an external magnetic field, further supporting its suitability for practical wastewater applications. In summary, the results demonstrate that phosphorylation effectively transforms conventional ZVI into a highly stable, selective, and recyclable adsorbent capable of capturing and recovering Eu\u003csup\u003e3\u003c/sup\u003e⁺ from complex mine effluents. The enhanced affinity toward Eu\u003csup\u003e3\u003c/sup\u003e⁺, high tolerance to competing ions, and strong regeneration capacity confirm that P-ZVI\u003csub\u003ebm\u003c/sub\u003e bridges the gap between laboratory-scale synthesis and field-scale application. This work provides a feasible pathway for resource recovery from rare-earth-associated radioactive wastewater, aligning with the principles of green metallurgy and sustainable waste valorization.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eChemical composition of the real wastewater sample\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eElement\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eC\u003csub\u003ex\u003c/sub\u003e (mg/L)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSi\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e325.927\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.530\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e5.541\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7.700\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e42.162\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10.303\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBi\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.817\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.090\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1832.032\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCo\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.317\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.218\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGd\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e634.693\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.970\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e541.373\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNi\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e11.633\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e361.793\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.525\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn summary, phosphorylation-modified zero-valent iron (P-ZVI\u003csub\u003ebm\u003c/sub\u003e) exhibits markedly enhanced physicochemical properties, including reduced particle size, enlarged surface area, more negative surface potential, and superior resistance to corrosion, all of which synergistically improve its Eu\u0026sup3;⁺ removal efficiency in acidic media. Under optimized conditions, P-ZVI\u003csub\u003ebm\u003c/sub\u003e achieves a maximum adsorption capacity of 152.49 mg\u0026middot;g⁻\u003csup\u003e1\u003c/sup\u003e. Mechanistically, Eu\u003csup\u003e3\u003c/sup\u003e⁺ migrates toward the negatively shifted interface, undergoes inner-sphere complexation with Fe\u0026ndash;O\u0026ndash;P groups, and nucleates as Eu\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e7\u003c/sub\u003e precipitates. This multi-pathway process not only overcomes the intrinsic instability of ZVI in acidic environments but also establishes a material and mechanistic framework for efficient rare-earth separation in radioactive wastewater treatment.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflict of Interest\u003c/h2\u003e\u003cp\u003eYuhui Liu is an editorial board member for this journal and was not involved in the editorial review or the decision to publish this article. The authors declare that there is no conflict of interest.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eYuhui Liu .Shuang Zhang. and Xiaoyan Li. wrote the main manuscript text and Yu zhang. Jin Li. Zhengquan Zhang prepared figures 1-5. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (22566002, 22466006), the Natural Science Foundation of Jiangxi Province (20242BAB20107, 20252BAC220002), National Key Laboratory of Uranium Resources Exploration-Mining and Nuclear Remote Sensing (2024QZ-TD-16).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYin SH, Chen W, Fan XL, Liu JM, Wu LB (2021) Review and prospects of bioleaching in the Chinese mining industry. Int J Min Metall Mater 28:1397\u0026ndash;1412\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDominique G, Dossa KF, Larivi\u0026egrave;re D, Khasa DP (2025) Environmental, health and social acceptability issues associated with rare earth elements: a systematic literature review. 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Sci.: Processes Impacts\u003c/em\u003e, 17 No. 9, pp. 1634\u0026ndash;1640\u003c/span\u003e\u003c/li\u003e\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":"Associated radioactive minerals, Zero-valent iron, Phosphorylation, Eu³⁺, Complexation","lastPublishedDoi":"10.21203/rs.3.rs-7932241/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7932241/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe hydrometallurgical processing of associated radioactive minerals inevitably produces acidic wastewater containing europium (Eu\u003csup\u003e3+\u003c/sup\u003e), a critical rare-earth element whose co-occurrence with radionuclides complicates separation and recovery. Here, a zero-acid separation strategy is developed using phosphorylation-engineered zero-valent iron (P\u0026ndash;ZVI\u003csub\u003ebm\u003c/sub\u003e), which integrates corrosion resistance with selective coordination reactivity. Phosphate functionalization transforms Fe\u003csup\u003e0\u003c/sup\u003e surfaces into chemically stable Fe\u0026ndash;O\u0026ndash;P frameworks, creating multidentate active sites that drive inner-sphere Eu\u003csup\u003e3+\u003c/sup\u003e complexation and interfacial Eu\u0026ndash;phosphate precipitation. Combined experimental and DFT analyses reveal that the Fe\u0026ndash;O\u0026ndash;P interface facilitates strong chemisorption through hybrid Eu\u0026ndash;O\u0026ndash;P bonding (E\u003csub\u003ead\u003c/sub\u003e up to \u0026minus;\u0026thinsp;14.7 eV) and electron transfer between Eu 4f/5d and O 2p orbitals, while suppressing Fe⁰ dissolution. In real mine wastewater containing multiple rare-earth and transition metal ions, P\u0026ndash;ZVI\u003csub\u003ebm\u003c/sub\u003e achieves high Eu\u003csup\u003e3\u003c/sup\u003e⁺ selectivity, stability, and recyclability, maintaining over 85.0% removal efficiency after H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e cycles. This study establishes a zero-acid, phosphate-mediated adsorption\u0026ndash;precipitation mechanism for rare-earth recovery, offering a scalable route for sustainable treatment and valorization of radioactive metallurgical effluents within green process metallurgy.\u003c/p\u003e","manuscriptTitle":"Phosphate-Functionalized Zero-Valent Iron for Efficient Separation of Europium from Acidic Associated Mineral Wastewater","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-10 16:40:33","doi":"10.21203/rs.3.rs-7932241/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":"1c549324-9712-4117-a940-38d6a38a242e","owner":[],"postedDate":"November 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-03T14:28:28+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-10 16:40:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7932241","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7932241","identity":"rs-7932241","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}