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. 2026 Mar 3;17:3369. doi: 10.1038/s41467-026-70043-9

UV-activated assisted electrochemical process for mine water deep mineralization and resource recovery

Xiangyun Liu 1, Youzheng Chai 1, Yuwei Gu 1, Yongqi Li 1, Xiao Wang 2, Qiancheng Wang 3, Gong Zhang 1,4,✉, Huijuan Liu 1,4, Jiuhui Qu 1
PMCID: PMC13066401  PMID: 41775716

Abstract

High-salinity mine water generated during membrane concentration of mine water contains structurally stable complex organic matter that resists removal and mineralization by conventional advanced oxidation processes, ultimately producing low-value by-product salts that hinder the resource utilization pathway. Leveraging the ultraviolet sensitivity of inherent chromophore groups and conjugated structures, this study developed an ultraviolet-activated assisted electrochemical process. By harnessing ultraviolet/oxidant synergies, this approach achieves ~89.9% total organic carbon removal, with minimal performance decay over 1000 hours. Combined with ultraviolet-visible spectroscopy, fluorescence excitation-emission-matrix spectroscopy, fourier transform ion cyclotron resonance mass spectrometer, and model contaminant experiments, this study elucidates an ultraviolet activation and radical attack synergistic mechanism driving organic mineralization. The direct integration of purified brine with bipolar membrane electrodialysis successfully produces acid, high-purity alkali (>99%), and reusable water, thereby closing the loop of impurities removal and resource recovery. This integrated system offers a strong strategy for high-value resource recovery and sustainable mine water management.

Subject terms: Pollution remediation, Sustainability

A UV-assisted electrochemical process achieves ~89.9% total organic carbon removal from high-salinity mine water with stable 1,000 h performance. The bipolar membrane electrodialysis produces acid, high-purity alkali (>99%), and reusable water.

Introduction

Coal, as a key raw material for various fuels and chemical production, holds a particularly significant strategic position in countries with relatively scarce natural resources of natural gas and oil1. However, the discharge of mine water resulting from coal mining activities has evolved into a global environmental challenge, evident in major coal-producing countries such as the United States, the United Kingdom, India, Hungary, Italy, and the former Soviet Union2–4. China, as the world’s foremost coal producer and consumer, confronts especially acute challenges. Approximately 1.87 tons of mine water are produced per ton of coal mined5, with an annual total of up to 6.02 billion tons. Unfortunately, the current utilization rate of these mine waters is only 35%, resulting in a severe waste of water resource6,7. Among the mainstream technologies for increasing utilization rate, membrane concentration desalination is a commonly used method8–10. However, while producing fresh water, they also generate complex components and difficult-to-treat high-salinity mine water, which has become the key bottleneck restricting the efficient utilization of mine water resources.

The crystallization technique for high-salinity mine water can recover water and salt7, but the main product, sodium sulfate, has low economic value and poor marketability, and the system’s operation is highly dependent on purchased chemicals, incurring high costs11. Bipolar membrane electrodialysis (BMED) offers a promising alternative, converting concentrated brine directly into valuable acids and alkalies (e.g., H2SO4, NaOH), thereby enhancing product value while reducing chemical dependence12–14. However, the successful application of BMED is highly dependent on strict feedwater requirements for deep pretreatment15,16. Among them, the membrane contamination problem caused by organic contaminants is particularly prominent17–20. Hence, efficient removal of organic substances from high-salinity mine water is critical.

These organic contaminants primarily derive from groundwater and industrial activities, including the dissolved organic matter (DOM), the release of lubricants and rubber particles21,22. Typically characterized by structural stability, strong hydrophobicity, and poor biodegradability, they resist effective removal by traditional advanced oxidation processes (e.g., ozone or electrochemical oxidation) in high-salinity mine water23–25. However, the aromatic and heterocyclic compounds within this organic fraction demonstrate significant ultraviolet (UV) sensitivity due to their inherent chromophore groups and conjugated structures26,27. When absorbing light, they may directly photolysis into small molecules organic or act as photosensitizers by generating reactive intermediates (e.g., 3DOM*, 1O2,) that facilitate the degradation and mineralization of organic matter26,28–32. This prompts us to propose the innovative idea of using UV to augment the electrochemical process for the efficient mineralization of organic contaminants in mine water.

Here, this study constructs a UV-activated assisted electrochemical process (UAEP) based on the precise coupling of UV and electrochemical (EC) processes, achieving ~89.9% total organic carbon (TOC) removal and 57.9% total nitrogen (TN) removal in high-salinity mine water. Characterization involved ultraviolet-visible (UV-Vis) spectroscopy, fluorescence excitation-emission-matrix (EEM) spectroscopy, and fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) reveals the composition and transformation differences of DOM in high-salinity mine water during UV, EC, and UAEP treatment. Combined with FT-ICR MS and model contaminant experiments, this study further elucidates a UV activation and radical attack synergistic mechanism driving organic mineralization from the perspectives of organic compounds and free radicals. Integrated bipolar membrane electrodialysis (BMED) concurrently produces freshwater, acid, and high-purity alkali (>99%), closing the loop of impurities removal and resource recovery. This work paves the way for the sustainable treatment of high-salinity mine water.

Results

UAEP for high-efficiency TOC removal

Commercial RuIrSn/Ti anode and self-made Pd/Ti cathode were employed in both the conventional electrolytic cell and the UAEP reactor. Characterization confirmed uniform RuIrSn distribution in the anode (Supplementary Fig. 1). For the cathode, highly uniform Pd nanoparticles were deposited onto Ti by magnetron sputtering, followed by calcination in a H₂/Ar atmosphere to enhance stability (Supplementary Fig. 2). Optimized operation (40 mA/cm2; cycle time: 1 min, pH = 7.1) enabled deep TOC mineralization of actual high-salinity mine water with low energy consumption in both the UAEP reactor and scale-up reactor (Supplementary Figs. 3, 4, Supplementary Table 1).

Under these established conditions, the initial characterization of the raw water by UV-Vis absorption spectrum showed a distinct UV absorption (Fig. 1a), which may correspond to organic substances containing conjugated double bonds or aromatic structures33. The decrease in absorbance after UV treatment indicates that UV has degraded some of the organic matter. However, both EC treatment and UAEP treatment were affected by the UV absorption of free active chlorine (Supplementary Fig. 5), resulting in an increase in absorbance in the range of 220 nm < λ < 255 nm. Despite this interference, the UAEP treatment significantly reduced the absorbance of the solution and dramatically improved TOC removal efficiency compared with the EC treatment. After 0.5 h treatment with UV and EC, the TOC removal rates were approximately 11.7% and 7.7%, respectively, while the UAEP treatment could reach 56.0% (Fig. 1b). This phenomenon indicates that UV not only enhances the degradation of contaminants with characteristic functional groups, but also effectively promotes the deep mineralization process of organic contaminants, thereby achieving a more thorough water purification effect.

Fig. 1. TOC removal performance of UAEP.

Fig. 1

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a UV-Vis absorption spectra and b TOC removal efficiency following ultraviolet (UV), electrochemical (EC), and UV-activated assisted electrochemical process (UAEP) treatment. c Comparative TOC removal by Fenton oxidation, ozone oxidation, and UAEP. d Chemical oxygen demand (COD) degradation rate after 1.0 h treatment across processes. Experimental conditions: 100 mL actual high-salinity mine water, initial TOC = 114 mg/L, initial COD = 280 mg/L, [SO42−] = 35 g/L, [Cl−]=3 g/L, cycle time: 1 min, and the initial pH was different (Fenton: pH = 3, COD: Fe2+: H2O2 = 3:1:3, Ozone: pH = 9.0, O3: COD = 10:1, and others: pH = 7.1). Data are presented as mean ± s.d. (standard deviation) from n = 3 independent experiments. Error bars represent the standard deviation calculated using the STDEV function in Excel. Source data are provided as a Source data file.

Additionally, this process has significant advantages over ozone oxidation (TOC: 36%) and Fenton oxidation (TOC:46%) (Fig. 1c, d, Supplementary Fig. 6). The equipped Pd electrode achieved rapid mineralization of organic matter and improved energy efficiency in the early stage of the reaction (Supplementary Fig. 7a)34,35. Further comparisons were made with typical direct oxidation processes (represented by titanium dioxide Ti4O7 and BDD)36,37, the low mineralization efficiency of Ti4O7 (TOC: 52%) and BDD (TOC: 68%) further confirmed the effectiveness of the strategy adopted in this study, reducing the chloride ion at the source and increasing the hydroxyl radicals (·OH) at the end (Supplementary Fig. 7 b–d).

Overall molecular composition changes of UAEP

To understand the enhanced TOC removal performance of UAEP, the fluorescence characteristics of treated samples were first analyzed using the parallel factor method38. The fulvic-acid-like substance, protein tryptophan-like substance, and protein tyrosine-like substance were identified (Supplementary Fig. 8), which were consistent with those of typical components in mine water23.

Both UV and EC have significant removal effects on fluorescence substances (>40%), indicating that UV and EC can effectively destroy the aromatic structures or functional groups of organic substances. Compared to EC, UAEP increased the removal rate of protein tryptophan-like substances by approximately 14.6–20.1%, directly demonstrating the enhancement from UV. However, the removal efficiency of fulvic-acid-like substance, protein tyrosine-like substance did not significantly improve, which could have two possible reasons for this39–41, 1) it may be related to the re-release of intermediate products or the recombination of photolytic products, 2) the oxidant competes with organic matter for UV, thereby affecting the removal efficiency of organic matter (Supplementary Fig. 3).

To further elucidate how UV works in conjunction with EC to enhance the contaminant removal performance, FT-ICR MS analysis was employed to examine changes in DOM composition at the molecular level42. Highly unsaturated phenols and aliphatic compounds remained the dominant DOM categories across all treatments, with their distribution remaining relatively stable (Supplementary Fig. 9). Furthermore, the change in the number of detected DOM molecules closely paralleled the observed TOC removal (Fig. 2a), confirming the mineralization trend.

Fig. 2. Molecular characteristics of raw and treated high-salinity mine water via FT-ICR MS analysis.

Fig. 2

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a Organic molecule counts, pH, and TOC levels. b The molecular mass (Masswa) and molecular count distribution across defined mass ranges. c The elemental ratios: H/Cwa, O/Cwa. d The modified aromaticity index (AImodwa) and nominal oxidation state of carbon (NOSCwa). e the double bond equivalent (DBEwa). All “wa” subscripts denote intensity-weighted averages. Source data are provided as a Source data file.

Crucially, their molecular characteristics underwent significant and distinct transformations depending on the treatment. UV treatment primarily attacked double bonds, resulting in the fragmentation of large molecules to generate small molecular organic substances and mineralization43, specifically manifested as the decrease of Masswa, NOSCwa, DBEwa, AImodwa, and O/Cwa, as well as an increase of H/Cwa and pH (Fig. 2, Supplementary Table 2). While EC treatment relied on the oxidation effect to transform different molecular weight organic matter from high activity to high oxidation state until mineralization, specifically manifested as a decrease of H/Cwa, AImodwa, and DBEwa, the increase of NOSCwa and O/Cwa, and pH (Fig. 2). It was noteworthy that the selective removal of different molecular weights by EC and UV led to a lower average molecular weight after UV treatment (Fig. 2b). The UAEP led to rapid changes in the organic mineralization rate, the removal amount of different molecular weight organic substances, and molecular indicators (such as DBE), presenting a synergistic mechanism of oxidation dominance and reduction assistance.

Building on the distinct molecular transformations induced by UV and EC treatments, FT-ICR MS analysis revealed significant selectivity in DOM composition changes (Supplementary Tables 3, 4). UV treatment preferentially cleaves heteroatomic bonds (e.g., C–S, C–Cl) within complex molecules like CHONS, converting them into simpler CHO or CHON substances, evidenced by a marked decrease in CHONS species alongside increased relative abundance of CHO and CHON compounds44–46. Conversely, both EC and UAEP treatments effectively mineralized most organic species (including CHO and CHON), but critically generated stable chlorinated byproducts through electrochlorination reactions (Cl− → Cl2 → ClO−), leading to aromatic/aliphatic chlorination and a significant increase in chlorine-containing compounds (Supplementary Fig. 10)47.

Furthermore, the number of precursors and products in UV and EC is significantly lower than in UAEP, as indicated by van Krevelen diagrams (Supplementary Fig. 11), suggesting that more transformation reactions occur in the latter reaction systems. And extending the time has little effect on it. Analysis of oxidized compounds (Ox) further reveals (Supplementary Fig. 12) that the Ox precursors are mainly O7~O9 in the raw water, which are normally distributed. UV treatment retained low-oxygen compounds (O/C < 0.5, O5~O7). But EC treatment is dominated by free active chlorine oxidation, generating high-oxygen compounds (O/C ≥ 0.5, O8~O11), indicating that organic matter mineralization is more inclined to generate carboxylic acid-like molecules. Notably, during the UAEP treatment, the Ox distribution is more extensive (O4~O16), and the difference in product distribution between 1 h and 2 h of reaction is not significant, suggesting that Ox reached dynamic equilibrium in the later stage of the reaction.

Molecular mechanism of UAEP

Venn diagram analysis quantifies that a total of 1881–4052 precursor compounds and 1682–2360 product compounds were identified after different treatments (Fig. 3a, b). A substantial overlap was observed among the removed compounds in the UV, EC, and UAEP processes, with only 77, 67, and 546 being uniquely removed in each system (Fig. 3a). Additionally, the unique precursors mainly suggest that UV preferentially targeted medium molecular (MM) and large molecular (LM) weight (Mass ≥ 300 Da), unsaturated, oxygen-containing aromatic compounds ((DBE-O)/C ≤ 0.00, NOSC ≥ 0.00, H/C: 0.70 ~ 1.25, AImod: 0 ~ 0.56), EC was more inclined towards small molecular (SM) and medium molecular (MM) weight (Mass < 450) saturation oxygen-containing aliphatic compounds ((DBE-O)/C ≤ 0.00, NOSC ≥ 0.00, H/C: 1.25–2.20, AImod: 0.00 ~ 0.56) (Fig. 3c). Hence, the UAEP significantly expanded the coverage range of precursor compounds through complementary and synergistic effects, especially for saturated reduced substances ((DBE-O)/C ≤ 0.00, NOSC ≤ 0.00), indicating that the synergistic system broke through the kinetic limitation of a single treatment.

Fig. 3. DOM transformation pathways.

Fig. 3

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Venn diagrams of a precursors and b products during UV, EC, and UAEP treatments. Colors represent the UAEP (purple), UV (blue), and EC (pink) groups, and numbers indicate the count of features in unique or overlapping regions. The distribution diagrams of unique c precursors and d products for the three treatment ways. e, f The number of possible precursor-product pairs between the precursors and products during different treatments. (DBE-O)/C, Oxygen-corrected Double Bond Equivalent per Carbon atom, H/C, atomic ratios, SM/MM/LM, small (Mass < 300 Da)/medium (300 Da ≤ Mass < 450 Da)/large molecules (Mass ≥ 450 Da), AImod, modified aromaticity index. The related transformation reactions and data are listed in Supplementary Table 5. Source data are provided as a Source data file.

Interestingly, the number of common compounds in products significantly decreased (1659 precursors in versus 223 in products) (Fig. 3b), and the proportions of the unique products rose to 72.6%, 43.3%, and 49.9% in UV, EC, and UAEP treatment, suggesting the distinct mechanisms of the three treatments exerting on the common compounds. As evident from Fig. 3d, the unique products for UV were primarily concentrated in the range of NOSC ≤ 0.00 and H/C > 1.25, implying that oxidized state molecules were more readily decomposed into saturated reduced state molecules during UV. Similar results were reported that halonitromethanes, chlorinated and brominated/iodinated haloacetic acids were removed by UV photolysis48,49. However, for EC and UAEP, molecules with higher NOSC and mass, and lower H/C ratios are observed. And it is most likely due to the oxidation and chlorination addition reactions that occurred in the organic molecules.

To further understand the difference among the three transformation processes, the mass difference analysis difference analysis was employed based on 45 types of transformation reactions that have been reported in advanced oxidation processes (Supplementary Table 5)42,50,51. As depicted in Fig. 3e, UV mainly adopts the photolysis pathway (+2H, −CO, −SO3), selectively degrading double bonds and heteroatoms (C-S: 272 kJ/mol, C–N: 306 kJ/mol) to reduce toxic products44,49,52. While EC relies on the oxidation pathway (+3O, +2Cl, −SH2), driving the accumulation of highly oxidized carboxylic acid compounds. However, the different reaction type (+OH+Cl increase and other reactions decrease) for UAEP indicates that the enhanced effect is not a linear superposition of the effects of individual conditions (Fig. 3f), but rather results from the dynamic construction of the oxidation network and the selective reconfiguration of reaction pathways, achieving more selective and deeper mineralization of diverse organic contaminants (Supplementary Fig. 13)40,53. Moreover, this does not change with the different types of organic contaminants and the extension of the reaction time (Supplementary Fig. 14).

Insights into the mineralization mechanism of UAEP

To clarify the deep mineralization mechanism of UAEP, caprolactam (CL), identified by UHPLC Q Orbitrap HRMS in high-salinity water samples, was chosen as the model contaminant (Supplementary Fig. 15). Comparative experiments showed that whether chloride ions were present or not, UV treatment had no direct effect on degrading CL (Fig. 4a). However, UAEP overcame the EC bottleneck of low-concentration degradation and achieved nearly 100% removal of CL, along with 63.8% TOC removal and 97.1% TN removal (Supplementary Fig. 16).

Fig. 4. Mechanistic insights into UAEP mineralization.

Fig. 4

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a UAEP performance. b UV-Vis absorption and c fluorescence emission spectra at varying caprolactam (CL) concentrations. d Radical quenching experiments. e EPR tests in the UAEP reactor. Changes in fluorescence intensity f during oxidation and g during reduction. h Intermediate relative intensity variations during UAEP treatment. Experimental conditions: 70 mL synthetic water, CL = 20 mg/L, [SO42−] = 35 g/L, [Cl−] = 3 g/L, [DMPO] = 100 mM, [coumarin] = 400 mg/L, [7-azido-4-methylcoumarin] = 100 mg/L, cycle time: 1 min, and the initial pH = 7.1. Data are presented as mean ± s.d. (standard deviation) from n = 3 independent experiments. Error bars represent the standard deviation calculated using the STDEV function in Excel. Source data are provided as a Source data file.

Additionally, the UV-Vis absorption spectrum indicated that a certain degree of UV absorption occurred at 254.0 nm for high-concentration CL (Fig. 4b). At the given excitation wavelength of 254.0 nm, a fluorescence signal was emitted at 308.6 nm (Fig. 4c). Therefore, it was speculated that the CL in the ground state absorbed UV energy and produced a higher-energy excited state, increasing the reaction probability with active molecules, thereby accelerating the subsequent reactions and explaining the effect of UAEP treatment on the degradation of low-concentration CL. Moreover, when the given UV wavelength was lower than the absorption wavelength of the organic compound, the UV direct photolysis effect could not be ignored (Supplementary Fig. 17), but deep mineralization still relied on the changes in free radicals under UV regulation (Supplementary Fig. 18)49.

The radical scavenging experiments further confirmed that atomic hydrogen (H*) and hydroxyl radical (·OH) in the solution are the key active species in the degradation process (Fig. 4d). And the electron paramagnetic resonance (EPR) experiment confirmed that UV activation reduced the amount of active chlorine species and increased the amount of ·OH, which is also one of the reasons for the breakthrough of the bottleneck through UAEP (Fig. 4e). Coumarin reacts with ·OH to form 7-hydroxy coumarin, and the change in fluorescence signal reflects the influence of UV, EC, and UAEP treatment on the transformation path of organic matter (Fig. 4f, Supplementary Fig. 19). The cyclic voltammetry (CV) and the experiment with 7-azido-4-methylcoumarin to 7-amido-4-methylcoumarin further confirmed that H* can participate in the reduction of organic matter, which provides a theoretical basis for explaining the acceleration of TOC removal by the Pd cathode (Fig. 4g, Supplementary Fig. 20). Furthermore, during the UAEP treatment process, the dynamic changes in the relative intensity of the intermediate products further confirmed the synergistic process of multiple free radicals working together (Fig. 4h, Supplementary Figs. 21, 22)54–58.

Practical applications of the UAEP

The high-salinity mine water was treated by pretreatment, membrane concentration, and UAEP, after which the clarified water entered the BMED process for water, acid, and alkali recovery (Fig. 5a, Supplementary Fig. 23). The continuous operation for 1000 h demonstrated that UAEP treatment maintained stable removal rates of TOC (~89.9%) and TN (~57.9%) in the pretreated feed water, and the electrode morphology and elemental valence showed almost no change (Fig. 5b, Supplementary Fig. 24).

Fig. 5. Application of UAEP-BMED.

Fig. 5

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a Schematic of mine water treatment process. b UAEP stability assessment in high-salinity mine water. The inset is the total carbon organic (TOC) and total nitrogen (TN) of the raw water and the treated water. Lines inside the box represent the average value, boxes represent the interquartile range, and whiskers represent the minimum and maximum values. c Recovery of fresh water, purified NaOH, and acid from UAEP, electrodialysis (ED), and bipolar membrane electrodialysis (BMED). Inset table: water quality of desalinated water from ED. The purple shaded area in the graph shows the change in conductivity of ED during a thirty-day operation. Data are shown as mean (solid purple line) ± s.d. (shaded area) derived from n = 32 independent cycles. The purity of liquid alkali (pi chart), as-produced NaOH (photo), and concentrations of liquid alkali and acid (histogram) from BMED are shown. TDS, total dissolved solids. Experimental conditions: the initial pH = 7.1. Source data are provided as a Source data file.

After UAEP decontamination, electrodialysis (ED) isolates the salt from the purified water. This step achieved a 98.4% removal ratio for Na2SO4 with a current efficiency of 94.9% (Supplementary Table 6, Supplementary Fig. 25a, b), and there was almost no contamination before and after the reaction (Supplementary Fig. 26). Crucially, the downstream BMED unit simultaneously recovered three valuable products with a current efficiency of 48.2% (Fig. 5c, Supplementary Fig. 25c, d), 1) almost non-toxic fresh water meeting reuse standards, 2) NaOH (purity > 99%), and 3) acid, suitable for reuse in industrial processes. This strategy not only reduces the overall operating costs of the zero-emission system compared to the ozone oxidation - salt crystallization methods but also enhances resource utilization and economic performance, demonstrating considerable potential for practical application (Supplementary Fig. 27, Supplementary Table 7). Furthermore, the subsequent vaporization yielded solid NaOH, supporting circular economy principles and sustainable development.

Discussion

This study is the first to elucidate, from an organic matter perspective, the critical role of the UV activation effect in promoting the deep mineralization of organic compounds in high-salinity mine water. Through FT-ICR MS molecular trajectory tracking and model contaminant experiments, this study further elucidates a synergistic mechanism of UV activation and radical attack driving organic mineralization from the perspectives of organic compounds and free radicals. Based on this, this work ultimately achieved the dual goals of deep mineralization and resource recovery of high-salinity mine water by constructing a UAEP coupling the BMED technique. Future optimization of UV wavelength and EC processes to achieve the optimal combination is expected to further enhance mineralization efficiency. This advancement will accelerate the evolution of mine water treatment technology, transitioning from traditional methods towards the UAEP deep mineralization process coupled with BMED for simultaneous acid and alkali production.

Methods

Materials and reagents

High-salinity mine water was collected from CHN Energy in Beijing, China. The water compositions are shown in Supplementary Table 1. The porous titanium (Ti) electrodes with a diameter of 30 mm are obtained from Baoji Yingkehui Metal Products Co., Ltd. (China). All chemical reagents, including sodium sulfate (Na2SO4), sodium chloride (NaCl), caprolactam (CL), tert-butyl alcohol (TBA), methanol (MeOH, high-performance liquid chromatography grade, 99.90% purity), benzoic acid (BA), nitrobenzene (NB), 1,4-dimethoxybenzene (DMOB), sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3), phosphate (H3PO4) and hydrofluoric acid (HF), are procured from Shanghai Aladdin Biochemical Technology Co., Ltd. (China). Coumarin and 7-hydroxycoumarin (98% purity) were provided by Meryer Biochemical Technology Co., Ltd. (Shanghai, China), while 7-azido-4-methylcoumarin and 7-amino-4-methylcoumarin (99% purity) were commercially obtained from Sigma-Aldrich Trading Co. (Shanghai, China). DMPO (97% purity) was purchased from Beiren Chemical Technology (Beijing) Co., Ltd. (China). All reagents are of analytical grade and used without further purification.

Preparation of electrodes

The Ti electrodes were cleaned by ultrasonication in acetone, absolute ethanol, a mixed acid solution (70% deionized water + 20% HNO3 + 10% HF), and deionized water, followed by complete drying in a vacuum oven at 60 °C. A 20 nm palladium (Pd) thin film was deposited onto the Ti substrate via magnetron sputtering (KJLC system, Kurt J. Lesker Co., China) to fabricate the Pd/Ti cathode, which was subsequently annealed at 300 °C for 1 h in H2/Ar (10%/90%) atmosphere. The RuIrSn/Ti anode was obtained from Baoji Longsheng Nonferrous Metals Co., Ltd. (Baoji, China).

Characterization of electrodes

Scanning electron microscopy (SEM, Zeiss, Merlin, Germany) equipped with an energy dispersive spectrometer (EDS) and Transmission electron microscopy (TEM, Tecnai Spirit, Czechia) equipped with energy-diffusive X-ray spectroscopy (EDS), X-ray diffraction (XRD, Bruker D8 Discover), X-ray photoelectron spectroscopy (XPS, Shimadzu, AXIS Supra + ) were used to analyses the morphology and elemental composition of Pd/Ti and RuIrSn/Ti. Materials characterization for the catalysts is provided in the Supporting Information (Supplementary Figs. 1, 2).

Electrochemical measurements

Electrochemical experiments were conducted at ambient temperature using a standard three-electrode configuration connected to an Autolab potentiostat (PGSTAT302N, Metrohm) controlled with NOVA software. An Ag/AgCl electrode served as the reference for all aqueous measurements. Cyclic voltammetry (CV) was performed in a potential window of −1.2 to 0.4 V vs. Ag/AgCl at varying scan rates. The electrochemical generation of atomic hydrogen (H*) and hydroxyl radicals (·OH) at a current density of 40 mA/cm2 was investigated in a three-electrode assembly segregated by a proton exchange membrane (PEM). Electron paramagnetic resonance (EPR) measurements were conducted on a Bruker E500 spectrometer after reaction for 1 min in the UAEP reactor. Spectral simulations and data fitting were performed using the EasySpin toolbox (version 5.2.35) within MATLAB software (R2022b, MathWorks).

Resource recycling experiments

The experimental treatment was carried out using high-salinity mine water, with volumes of 100 mL and 0.1 m3. The process operated under a cycle time of 1 min, an initial TOC concentration of 114 mg/L, an initial COD concentration of 280 mg/L and a reaction time of 2.0 h. The UAEP reactor comprised the following core components: 1) a flow-through electrochemical reactor with RuIrSn/Ti anode and Pd/Ti cathode, 2) a flow-by UV reactor containing a UV lamp (254 nm, 6 W), 3) a DC supply (DH1750-1, Beijing Dahua Radio Instruments Co., China), and 4) a peristaltic pump. The distance between the two electrodes was set at 4 mm, and all electrochemical degradation experiments were conducted at pH 7.1 using a DC power source. Fenton oxidation and ozone oxidation parameters strictly adhered to standard methods HJ 1095–2020 and T/CECS 1347-2023, respectively, resulting in the following operating conditions: Fenton oxidation employed a COD: Fe2+: H2O2 mass ratio of 3:1:3 at pH = 2, pH = 3, pH = 4. Ozone oxidation utilized an O3: COD mass ratio of 10:1 at pH = 8, pH = 9, pH = 10 and an O3: COD mass ratio of 1:1 and 4:1 at pH = 9. During the reaction process, samples were periodically withdrawn from the reactor and filtered (polysulfone, 0.45 µm, Anpel Laboratory Technologies (Shanghai) Inc.) before analysis. A detailed description of other effluents is available in Supplementary Text 1.

High-salinity mine water processed by UAEP underwent sequential treatment, sodium sulfite to eliminate free active chlorine, deep calcium and magnesium removal via ion-exchange resin, pH adjustment with sulfuric acid, and final concentration through electrodialysis (ED). The ED stack comprises 10 identical membrane pairs arranged in series between the anode and cathode. Each membrane pair unit incorporates a cation exchange membrane (CEM), an anion exchange membrane (AEM), and two isolation channels forming a concentrate chamber and a dilute chamber, respectively. The ED process produces concentrated brine, which is subsequently fed into a bipolar membrane electrodialysis (BMED) device. The BMED configuration represents a specialized adaptation of conventional ED, where a bipolar membrane is inserted between each CEM/AEM pair, creating a CEM/BPM/AEM repeating unit. All membranes possess an effective area of 18 cm2. Both the anode and cathode consist of RuO2-coated Ti plates. A uniform flow rate of 300 mL/min is maintained across all compartments, including the electrode compartments, which utilize a circulating 4% Na2SO4 solution. A detailed description of the ED-BMED is available in Supplementary Fig. 25, Supplementary Table 6.

Sample analytical methods

The ultraviolet absorption spectra of the water samples were tested using the U-3900 ultraviolet-visible spectrophotometer (Hitachi). The concentrations of caprolactam (CL), benzoic acid (BA), nitrobenzene (NB), and 1,4-dimethoxybenzene (DMOB) were measured in triplicate using high-performance liquid chromatography (HPLC, Alliance e2695, Waters, USA) coupled with UV detection. Separations were achieved by a C18 column (4.6 × 250 mm, 5 μm, XBridge, Waters). The degradation intermediates of CL were analyzed by ultra-high performance liquid chromatography Q Exactive hybrid quadrupole-orbitrap high-resolution accurate mass spectrometry (UHPLC Q Orbitrap HRMS, Thermo Fisher Scientific, USA). The concentration of free active chlorine was measured by the N, N-diethyl-p-phenylenediamine (DPD) method offered by USEPA. Total organic carbon (TOC) was determined in triplicate with a Shimadzu TOC analyzer (TOC-L, Shimadzu, Japan), and chemical oxygen demand (COD) was measured in triplicate by the commercial Hach® kit. EEM spectra were obtained by a fluorospectrophotometer (F-7000, equipped with 980 lasers, Hitachi, Japan). Additionally, the samples were analyzed by a 15 T FT-ICR MS (SolariX, Bruker) equipped with an electrospray ionization (ESI) source in negative ionization mode. To quantitatively probe radical dynamics, coumarin and 7-azido-4-methylcoumarin were employed as molecular probes, enabling specific detection of transient radical species via their characteristic adduct formation mechanisms. The detailed descriptions of the measurement conditions and toxicity evaluation experiment are available in Supplementary Texts 2–4.

Supplementary information

Supplementary Information (9.5MB, pdf)
Transparent Peer Review file (2.8MB, pdf)

Source data

Source Data (2MB, xlsx)

Acknowledgments

We gratefully acknowledge the financial support from the Major Program of the Ministry of Science and Technology (MOST) of China (no. 2023YFC 3210300).

Author contributions

X.L. and G.Z. conceived the idea. X.L. performed the experimental studies. X.W. provided the actual high-salinity mine water samples. X.L., Y.C., Y.G., Y.L., Q.W., G.Z., H.L., and J.Q. carried out the analysis. X.L. and G.Z. wrote the manuscript. All authors contributed to its preparation and approved the final version.

Peer review

Peer review information

Nature Communications thanks the anonymous reviewers for their contribution to the peer review of this work. A peer review file is available.

Data availability

All the data supporting the findings of this study are available within the Article and its Supplementary Information files. Source experimental data are available via figshare (10.6084/m9.figshare.31220905)59. All the raw data relevant to the study are available from the corresponding author upon request. Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-026-70043-9.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Information (9.5MB, pdf)
Transparent Peer Review file (2.8MB, pdf)
Source Data (2MB, xlsx)

Data Availability Statement

All the data supporting the findings of this study are available within the Article and its Supplementary Information files. Source experimental data are available via figshare (10.6084/m9.figshare.31220905)59. All the raw data relevant to the study are available from the corresponding author upon request. Source data are provided with this paper.

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