The continued growth in demand for mineral resources has led to a large amount of mining wastes, which is a major challenge in the context of carbon neutrality and climate change. In this study, runoff migration, batch leaching, and column experiments were used to investigate the short-, medium-, and long-term leaching of heavy metals from legacy tailings, respectively; the cumulative metal release kinetic equations were established, and the long-term effects of tailings leaching were verified by HYDRUS-1D. In runoff migration experiments, surface dissolution of tailings and the co-migration of adsorbed soil particles by erosion were the main carriers in the early stages of leachate formation (Mn ∼ 65 mg/L and SO42- up to 2697.2 mg/L). Batch leaching tests showed that the concentration of heavy metals in soil leached by acid rain were 0.1 ∼ 22.0 μg/L for Cr, 0.7 ∼ 26.0 μg/L for Cu, 4.8 ∼ 5646.0 μg/L for Mn, 0.3 ∼ 232.4 μg/L for Ni, and 1.3 ∼ 448.0 μg/L for Zn. The results of column experiments indicated that some soluble components and metals with high mobility showed a significant decreasing trend at cumulative L/S ≤ 2. Additionally, the metals have higher leaching rates under TCLP conditions, as shown by Mn > Co > Zn > Cd > Ni > Cu > Pb > Cr. The fitting results of Langmuir equation were closer to the cumulative release of metals in the real case, and the release amounts of Mn, Zn, Co, and Ni were higher with 55, 5.84, 2.66, and 2.51 mg/kg, respectively. The water flow within tailings affects the spatial distribution of metals, which mainly exist in relatively stable chemical fractions (F3 + F4 + F5 > 90 %) after leaching. Numerical simulation verified that Mn in leachate has reached 8 mg/L at a scale of up to 100 years. The research results are expected to provide technical basis for realizing the resource utilization of tailings in the future.

Advanced oxidation methods (AOPs) are frequently used to remove stubborn pollutants from the aquatic environment, and developing an eco-friendly and high-performance catalyst is an effective strategy to enhance the efficiency of AOPs. In this study, Mn nanoparticle-loaded nitrogen-doped kelp biochar catalysts were synthesized at varying temperatures to activate peroxymonosulfate (PMS) and degrade acetaminophen (ACT). The findings show that, under ideal circumstances, the Mn@NBC-800/PMS system can fully remove ACT (20mg/L) in 10min. Electrochemical tests, electron paramagnetic resonance (EPR) analysis and quenching experiments reveal that the primary mechanism of ACT degradation was a non-radical pathway dominated by electron transfer and singlet oxygen (1O2). In addition, mechanism studies indicate that Mn species, C=O groups and graphite N were possible catalytically active sites. The Mn@NBC-800/PMS system demonstrates excellent catalytic activity across various pH values, inorganic anions, and water conditions, making it highly suitable for practical applications. This study emphasizes the significant potential of Mn/N co-doped biochar and provides invaluable insights for designing efficient carbon-based catalysts for wastewater treatment.

The activation of peroxymonosulfate (PMS) using metal-organic frameworks (MOFs) has garnered significant interest in the field of wastewater treatment. However, the environmental challenges associated with traditional methods for synthesizing MOFs precursors, such as the requirement for high temperatures and pressures, remain. Furthermore, the catalytic performance and stability of mono-metallic materials are areas needing enhancement. This work successfully synthesized a novel magnetic Fe-Ce bimetallic N-doped porous MOF material (Fe/Ce@5MNC). The optimized Fe/Ce@5MNC exhibited a higher specific surface area and a more extensive pore structure, as verified by various characterization techniques. Moreover, the synthesis process of the precursor is simpler, energy-saving, and relatively environmentally friendly. Notably, the synergistic effect between Fe and Ce, coupled with the presence of multiple active sites such as FeNx and graphite N, enabled Fe/Ce@5MNC to decompose 86.4 % of TCH within 30 min, marking a 31.4 % increase over Ce@NC. After four cycles, the catalyst maintained good surface stability, with the degradation efficiency remaining at 67.7 %. Quenching and electron paramagnetic resonance (EPR) experiments confirmed that the main degradation mechanisms are singlet oxygen (1O2) generation and electron transfer. This study presents a new method for synthesizing efficient Fe, N co-doped magnetic bimetallic PMS activators and designing carbon catalysts for deep oxidation.

Heavy metals in industries such as electroplating plants and semiconductor industries usually exist in the form of heavy metal organic complexes, and the removal of heavy metal organic complexes is troubled by the difficulty of decomplexation as well as the complexity of the treatment process of the free heavy metal ions after decomplexation. In this study, we proposed a synergistic strategy for the removal and secondary utilization of Cu(II) organic complexes (Cu-EDTA) in wastewater through mixed pyrolysis of carbon nitride precursor and Cu-EDTA, and the resulted product was used for the efficient degradation of tetracycline (TC). The unique electronic structure of carbon nitride and abundant surface defects anchor Cu during pyrolysis, which effectively realizes the removal of Cu-EDTA from wastewater. In addition, the Cu and O co-doped carbon nitride (Cu/O-CN) catalyst constructed by this strategy was proved to be effective in peroxydisulfate activation TC degradation, with a removal efficiency of 91.5% in 20min, a degradation rate of 0.1643 min-1, and a TOC removal efficiency of 53%. X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculation revealed Cu+ active center constructed by the strong metal support interaction between Cu and carbon nitride in Cu/O-CN and the 1O2 dominated nonradical degradation pathways of TC. This study demonstrated a synergistic strategy for the efficient removal and secondary utilization of Cu-EDTA in wastewater, providing new insights into the use of environmentally friendly and cost-effective methods for the removal and recovery of heavy metal organic complexes from wastewater.

Traditional sludge treatment methods have problems in terms of environmental safety and cost-effectiveness. In this study, we followed the principle of "waste for waste" to synthesize magnetic sludge biochar (FSBC800) from biochemical sludge and Fenton sludge to activate persulfate (PMS) to remove persistent pollutants. Tetracycline hydrochloride (TC-HCl) was degraded up to 90.9% by FSBC800 using an active PMS system in just 30minutes. This removal rate is higher than that of Fenton sludge biochar and biochemical sludge biochar by 2.7 and 1.8 times, respectively. The self-contained Fe in Fenton sludge formed evenly distributed Fe3O4 particles, while the biochemical sludge provided a large number of oxygen-containing functional groups, which increased the reactive active sites of FSBC800 and improved the catalytic performance. The dominant role of SO₄•⁻, •OH, and ¹O₂ in the degradation of TC-HCl was demonstrated by the identification of reactive oxygen species and electron paramagnetic resonance (EPR) analysis. By examining the intermediates, a potential TC-HCl degradation pathway was postulated. The catalyst has good reusability and practical application, and the removal of TC-HCl was still 84.8% after four replicated experiments. This study establishes a cost-effective, efficient, and recyclable biochar-based catalyst for water remediation, and at the same realizes resourceful utilization of sludge.

The proposed possible mechanisms of As( iii ) removal by Mn–Ce/AC 3 .

The efficient removal of hexavalent chromium (Cr(VI)) with high toxicity has attracted widespread concern since it causes serious harm to ecological environment and public health. Herein, we report a novel nitrogen-functionalized graphene aerogel with stereoscopic structure through a simple hydrothermal method and freeze drying for Cr(VI) removal from water. Graphene oxide (GO) and nitrogenous organics polyethyleneimine (PEI) and pyrrole are used as raw materials for preparing PEI/polypyrrole/GO aerogel (PPGA) adsorbent. PEI and pyrrole act as nitrogen sources to introduce nitrogenous functional groups, and also take on the role of cross-linkers for helping GO sheets to form stereoscopic structure. The obtained PPGA has a fast adsorption rate, excellent reusability, and shows a remarkable adsorption capacity for Cr(VI) up to 458.24 mg/g under the optimal conditions (pH 2.0, 298 K, Cr(VI): 600 mg/L, dosage: 0.4 g/L). The adsorption process of Cr(VI) on PPGA can fit the pseudo-second-order kinetic model well. Analysis of intraparticle diffusion shows that the Cr(VI) removal process is a multi-step process. Adsorption thermodynamic and isotherm results demonstrate Cr(VI) adsorption on PPGA is a spontaneous endothermic process. The adsorption mechanism involves electrostatic attraction, redox, and chelation. In general, this work provides a simple and eco-friendly way to prepare PPGA, which has a great potential for actual application of Cr(VI) removal in effluent.

Soil aggregate size plays an important role in controlling the distribution and transport of metals. Metals immobilized in soil particles will pose potential risks through production/sink flow and infiltration. This study explored the distribution behavior of metals based on soil aggregate size in a restored coastal mining area by establishing Structural Equation Model (SEM) and column experiments. The results showed that hydrological factors and a high degree of weathering accelerated the dissolution of metals from the mine, the desorption of Wa-NH4+-N, the release of F-, and the leaching of NO3-. Driven by soil properties, natural factors, and anthropogenic activities, the total metal content (Totalmetal) of Cr, Ni, Zn, Mn, and As showed significant spatial heterogeneity compared to Cd, Co, Cu, and Pb. The geochemical fraction of metals (Geometal) indicated that Cd, Co, Pb, Zn, As, and Cu are mainly present in iron‑manganese oxidation bound, organically bound, and residual fractions. The results of SEM showed that the physicochemical properties, Wa-NH4+-N, nitrate nitrogen, and inorganic anions of the soil could explain 69.1 %, 76.4 %, 97.1 %, and 80.0 % of the variation in Kd-Mn, Kd-Pb, Kd-Ni, and Kd-Zn, respectively. While Kd-Cd, Kd-Cu, and Kd-Cr could be predicted by the Totalmetal, but the Geometal seemed to have little influence on metal Kd. The results of column experiments showed that macroaggregates (>0.25 mm) significantly affected the distribution of Co, Cr, Cu, Mn, Ni, Pb, and Zn in the topsoil. The severe disruption of soil aggregate structure resulted in small fluctuations of anthropogenic Cu, Mn, Pb, Zn, and As in different layers of deep soil. In addition, mineral composition in >0.15 mm particle size was more likely to change. Overall, the hydrological cycle of coastal mines increases the uncertainty of their response to risk. Our study provides a basis for future strategies for priority control and risk prevention.

In this work, a series of Fe@NC catalysts were facilely fabricated by one pot pyrolysis of Zn-Fe-MOFs precursors which was ingeniously designed by incorporating of NH2-group N and doping Zn2+ into Fe-based MOF to solve the problem of Fe aggregation. The results indicated that the reasonable design of the precursor significantly improved catalytic performance of the catalysts. As the optimized catalyst, Fe@NC-1 exhibited outstanding catalytic activity in the activation of PMS for paracetamol degradation. In Fe@NC-1/PMS system, paracetamol was completely degraded in 8 min and the degradation constant was 204 times of that for Fe@NC. The quenching and electron paramagnetic resonance (EPR) experiment results confirmed that SO4- & BULL; and & BULL;OH occurred during the reaction, while SO4- & BULL; was identified as the main reactive species in the Fe@NC-1/PMS system. Furthermore, graphite N, Fe-Nx and Fe0 were possible catalytically active sites. This research provides a new idea for the rational design of carbon-based catalysts in the field of advanced oxidation.

Efficient and robust photocatalysts for environmental pollutants removal with outstanding stability have great significance. Herein, we report a kind of three dimensional (3D) photocatalyst presented as Z-scheme heterojunction, which combining TiO2 and ZnxCd1-xS with graphene aerogel to contrast TiO2-ZnxCd1-xS graphene aerogel (TSGA, x=0.5) through a moderate hydrothermal process. The as-prepared Z-scheme TSGA was used to remove aqueous Cr(VI) via a synergistic effect of adsorption and visible light photocatalysis. The adsorption equilibrium can be reached about 40 min, then after about 30 min irradiation under visible light (wavelength (λ) > 420 nm) the removal rate of Cr(VI) almost reached 100%, which is much better than the performance of pristine TiO2 and Zn0.5Cd0.5S, as well as TiO2 graphene aerogel (TGA) and Zn0.5Cd0.5S graphene aerogel (SGA). The virulent Cr(VI) was reduced to Cr(III) with hypotoxicity after photocatalysis on TSGA, meanwhile the as-synthesized TSGA presented a good stability and reusability. The reduced graphene oxide (rGO) sheets between TiO2 and Zn0.5Cd0.5S played a role as charge transfer mediator, promoting the photoinduced electrons transfer and photocatalysis ability of TSGA was enhanced significantly. Hence, such photocatalyst exhibits a potential application on removing heavy metals with high efficiency and stability from polluted aqueous environment.

The environmental problems caused by mining are continuous and multifaceted, in order to help manage and plan restored mining areas, the bioavailability of metals is an effective tool for measuring the potential risks to human health. This study analyzes the geochemical fractions of eight metals (As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) to compare their bioavailability and establishes a Hierarchical health risk (HHR) model to assess the human health risks of the mine area after restoration. The results indicated that children have the highest non-carcinogenic risks exposed through ingestion (HI-ingestion) due to their special behaviors; HI-dermal may be enriched in the body; and HI-inhalation is lowest, as it is related to soil particle size. Affected by local economic development, environmental climate, soil type, and mining, the carcinogenic risk of exposure through the skin (CR-dermal) for adults significantly exceeds the acceptable safety level (ASL). The spatial distribution shows that the harm of mining to human health is a continuous process. There was still a significant CR for adults after remediation, and the HI of tailings exposure was more serious. The Classification and Regression Tree (CART) model of metal bioavailability was developed by integrating the extrinsic and intrinsic factors of metals to explore the effects of different factors on metal bioavailability and predict. The results showed that the bioavailability of metals was a dynamic process that combined land use, the distance to traffic roads, physicochemical properties of soil, and geochemical fractions of metal, and that it affects human health both directly and indirectly. Due to the fragility and sensitivity of the ecosystem after the mining area is restored, it may face greater environmental health risks.

Carbon doped strategy has been recognized as an efficient strategy to enhance photo-Fenton degradation performance. However, the preparation of high efficiency C-doped photocatalyst has been a significant challenge. Herein, we synthesized magnetic carbon-doped ZnFe2O4 via a facile solvothermal-calcination route. The photo Fenton activity of C-doped ZnFe2O4 under visible light (lambda > 420 nm) was evaluated by degradation of tetracycline hydrochloride. C-doped sample, CZF-2 (0.5 g L-1) presented excellent removal performance for TC-HCl (20 mg L-1) in presence of H2O2 (10 mM) and could remove 90.8% of TC-HCl within 50 min. The C-doping modulates crystal defects and generates surface oxygen vacancies simultaneously, thus building a new C-doping level near valence band and a defect level under the conduction band. Meanwhile, surface oxygen vacancies bring photo-generated electrons and electrons generated from itself to surface to accelerate photo-Fenton reaction, and the holes are rapidly transferred to the surface to participate in the degradation of pollutants.

The efficient removal of heavy metal by rationally designed carbon-based adsorbents is a key challenge in the field of water purification. Herein, we report a nitrogen-enriched lignosulfonate exfoliated graphene oxide (NLEGO) for hexavalent chromium (Cr(VI)) removal from aqueous solution. The nitrogen content of N-LEGO reached 13.28%, and the ratio of N-bonding configurations (pyri-N:amine-N:pyrro-N:grap-N) was 2.3:1.6:1:2.3. For Cr(VI) with initial concentration of 70 mg L-1 under pH= 2, the residuary concentration after treated by NLEGO was close to 0.004 mg L-1, which meets the industrial wastewater discharge standard. The Cr(VI) adsorption behavior on N-LEGO can be fitted with the pseudo-second-order kinetics and Freundlich isotherm model well. The adsorption mechanism of Cr(VI) on N-LEGO includes anions electrostatic attraction, reduction and surface chelation. Density functional theory (DFT) simulations showed that N atoms doping was feasible and thermodynamically stable, meanwhile the N-doped system was easier to adsorb Cr2O72-than HCrO4-. The findings of this work can provide a new idea for the development of N-doped carbon-based adsorbents for the removal of highly toxic Cr(VI) from aqueous solutions.

Developing high-efficient, low-cost and environmentally friendly catalysts is essential for activating peroxymonosulfate (PMS) but remains a challenge. Recently, novel catalysts of transition metal-nitrogen co-doped carbon materials, especially Fe-N-C, have attracted much attention due to their superior performance for PMS activation. Herein, FeSO4 and ZnSO4 were added during the synthesis of ZIF-8, obtained concave N, S co-doped iron-based carbon materials (Fe-S@NC) with mesoporous structure through high-temperature pyrolysis. This porous carbon material with a depressed surface not only promoted the exposure of active sites, but also accelerated mass transfer. The synergistic effect of Fe atoms and heteroatoms significantly enhanced the activation ability of the material to PMS. Benefiting from these advantages, only 2 mg/L Fe-S-1@NC and 0.5 mM PMS was required to achieve the rapid degradation of acetaminophen (ACT) (99.7%, 0.7290 min(-1)). Besides, the activation system has a wide pH adaptability and low leaching iron concentration. Then the reaction mechanism of Fe-S-1@NC/PMS system was investigated by quenching experiments and electron paramagnetic resonance technique (EPR), it was proposed that singlet oxygen (O-1(2)) was the primary reactive species responsible for the degradation of ACT. This study provides new insight for the design of carbon catalysts in advanced oxidation field.

Contamination of drinking water with heavy metals, particularly arsenic (As), is a persistent problem with serious public health implications worldwide. In this study, we present a zinc based metal-organic framework (Zn-MOF-74) and polyacrylamide polymer (PAM) coated on reduced graphene oxide (rGO) as an effective adsorbent for the removal of arsenite (As(III)) from water. Zn-MOF-74 nanoparticles were prepared by room temperature precipitation and these were immobilized on rGO surface grafted PAM by a free-radical polymerization method, (Zn-MOF-74/rGO/PAM nanocomposites). The experimental data correlates well with the pseudo-second-order kinetic model and Langmuir isotherm, and the maximum adsorption capacity (q(max)) was 282.4 mg g(-1) at pH 10, 298 K. The removal efficiency was rapid, removing more than 99.8% of As(III) from a 0.2 mg L-1 solution and achieving drinkable levels in 15 min. Thermodynamic data revealed that the process was spontaneous and endothermic. Furthermore, the adsorbent revealed high stability in pH range 4-10 and could be reused at least four times. Adsorption mechanism involved a synergistic combination of chemisorption and physisorption. FTIR and XPS analyzes revealed that the amide group (-NH2) and hydroxyl group (-OH) on ZnMOF-74/rGO/PAM dominate in their adsorption.

Although the mining area has been restored, the environmental problems caused by years of large-scale oil shale mining are still continuing, coupled with the intensive distribution of the surrounding petrochemical industry, posing a serious threat to the local ecological environment. In this study, we investigated eight heavy metals (Cu, Ni, Pb, Cd, As, Cr, Mn and Zn) contamination and distribution around mining area, evaluated the potential risks of environment, identified the main sources of metal pollution and performed source apportionment. The results showed that the original north and south dumps were seriously polluted, and the CF values were significantly higher than other sampling sites. Ni, Zn and Mn have high coefficients of variation, which may be greatly affected by human factors and especially the waste slag piled up. The concentration of heavy metals in the water was lower than in the soil; soil particles, pH, Eh and acid mine drainage influence the variation of heavy metal concentrations. As and Cd have very high RAC values, and accordingly they were mainly present in the exchangeable and reduced fractions. Mn was exposed to higher ecological risks, followed by Pb, although there were high loads on carbonate bound and oxidizable fractions. APCS-MLL receptor model was used to identify and apportionment three main sources of contamination. The mean contribution rates of industrial activity, atmospheric deposition and mixed sources accounted for 39.77%, 22.24% and 37.99%, respectively. Cluster analysis further classified the metal pollution sources according to the spatial distance of sampling points.

Making adsorbent with high adsorption efficiency and wide application is the most economical and effective method to remove arsenic from water. A simple in-situ synthesis method was used to combine the highly oxidized delta-MnO2 with the modified Fe/Co-MOF-74 structure of the metal organic framework. The new composite materials obtained have high adsorption rates in the pH range of 2-10. The isotherm and kinetic parameters of arsenic removal on Fe/Co-MOF-74 were well-fitted by the Langmuir and pseudo-second-order models. At room temperature, the maximum adsorption capacity of As(III) is 300.5 mg/g. Most common substances in water, such as carbonate, sulfate and humic acid, have no effect on As(III) adsorption, and only the presence of phosphate can inhibit the adsorption process of arsenic. The main adsorption mechanism is electrostatic adsorption and complexation. In conclusion, delta-MnO2@Fe/Co-MOF-74 is a kind of adsorbent with excellent performance in the removal of As (III) in water, which has a wide application prospect and a value of further study.

Compounding a single component with a specific function into a composite material that can fully exert synergy effects according to demand is the key to achieving the expected function and expanding emerging applications. Herein, anchoring delta-MnO2 with strong oxidizing ability on the surface of Fe/Mg-MIL-88B with superior uptake ability for As(V) to form an amorphous nanocomposite with multiple functions for removing more toxic As(III). Due to special construction and rational design, the fabricated nanocomposite demonstrated an excellent As(III) removal performance over a very broad pH range of 3 to 10. Impressively, the adsorption efficiency of the obtained delta-MnO2@Fe/Mg-MIL-88B on As(III) is greatly improved, and the maximum adsorption capacity under laboratory conditions is as high as 221.04 mg/g in room temperature. Notably, the residual concentration of arsenic will drop below 10 mu g/L, as long as the initial As(III) concentration is not higher than10 mg/L, which is very critical for further promotion. In general, the delta-MnO2@Fe/Mg-MIL-88B exhibits excellent promise in removing As(III) from sewage, and its applicability in practical complex water treatment deserves further study.

Arsenite (As(iii)) is more toxic and more difficult to remove from water than arsenate (As(v)).

For further understanding leaching characteristics of heavy metals in tailings and better immobilization on heavy metals against acid rain, batch experiments were conducted. The leaching results of Cu(II), Zn(II), Cd(II) and Mn(II) can be well fit by second-order kinetics equation, and Pb(II) can be well fit by two-constant equation. The leaching intensity of heavy metals in tailings was ranged as: Mn(II)> Cu(II)> Cd(II)> Zn(II)> Pb(II). Triethylenetetramine functioned montmorillonite (TETA-Mt) was successfully synthesized and can obtain simultaneous immobilization effect compared with Mt and TETA, and immobilization rates on Cu(II), Cd(II), Mn(II) and Zn(II) can reach above 90%, the immobilization rate on Pb(II) can reach more than 75%. The mechanisms for efficient immobilization of heavy metals on TETA-Mt included buffering and adsorption abilities. The mechanism for TETA-Mt adsorption of heavy metals included physical absorption, chelation and chemical sedimentation. The results showed that TETA-Mt can be applied to effective immobilization of heavy metals in tailings and efficient remediation of acid mine drainage (AMD) in acid rain area.