The phosphorite dissolution and aqueous species release play a pivotal role in the global phosphorus (P) cycle. To elucidate differences in dissolution mechanisms between phosphorite of different weathering degrees, three phosphorite samples (with high, moderate, and low weathering degrees) were collected from field environments; then, a series of mineralogical characterizations coupled with dissolution experiments were conducted. Compared to primary phosphorite, weathered phosphorite exhibited substantial depletion of carbonate minerals, while silicate minerals and phosphate minerals were relatively enriched, and secondary minerals (e.g., FePO4 and CaF2) were formed. Furthermore, the dissolution rates of phosphorite samples within a pH range of 3–7 were determined using a mixed-flow reactor. The results demonstrated a negative linear relationship between the logarithm of dissolution rate and pH (R2 = 0.54–0.94). The P release rate constant (from 0.7 to 1.52 mol g−1 s−1) and kinetic reaction order (from 0.58 to 0.74) of weathered phosphorite were significantly higher than those of primary phosphorite. We modeled the co-dissolution behavior of associated minerals with fluorapatite using transition state theory. Calcite exhibited the strongest inhibitory effect on fluorapatite dissolution, whereas the effects of other minerals were relatively weak. In the column leaching experiment, compared to the primary phosphorite, the elements released from weathered phosphorite were predominantly present in ionic forms with a higher migration capability. During the leaching process, phosphate minerals in phosphorite were mainly converted to Exchangeable/loosely bound P (Ex-P), Iron-bound P (Fe–P), and Calcium-bound P (Ca–P); Ca2+ and CO32− were mainly converted to dolomite, and F− was mainly converted to fluorite and fluorapatite. This systematic investigation provides critical insights into weathering-driven mineralogical evolution and its mechanistic control on phosphorite dissolution. © 2025 Elsevier Ltd

Hydrogen gas (H2) is naturally produced by biological and non-biological reactions in various environmental niches. However, the influence of H2 on microbial processes that cause the mobilization and release of arsenic from solid phase into groundwater remains to be resolved. Given that dissimilatory arsenate [As(V)]-respiring prokaryotes (DARPs) have been demonstrated to significantly contribute to the formation of As-contaminated groundwater, our study specifically examined the interactions between H2 and DARPs. We prepared an enriched DARP population from As-contaminated soils. Metagenomic analyses of the DARP population revealed that approximately 46.7 % of the qualified DARPs' MAGs contain at least one type I Ni-Fe hydrogenase. The Ni-Fe hydrogenase proteins in DARPs show unique diversity. Functional assays indicate that the DARP population exhibited notable activity in oxidizing H2 while concurrently reducing As(V) under strictly anaerobic conditions. Arsenic release assays indicate that the DARP population is highly proficient at catalyzing the reductive mobilization of arsenic in scorodite, using hydrogen as the electron donor. These findings offer the initial evidence that H2 can directly promote the formation of arsenic-contaminated groundwater mediated by DARPs, a biogeochemical process that has long been overlooked. Therefore, this study increases our insight into the microbial mechanisms involved in the formation of arsenic-contaminated groundwater. © 2025 Elsevier B.V.

The Mg/Al hydrotalcite (Mg/Al HT) was firstly used as a heterogeneous ozonation catalyst and 2,4-dichlorophenoxyacetic acid (2,4-D) was efficiently degraded by Mg₃/Al HT with a COD removal of 68 %. It was higher than that of α-FeOOH with a COD removal of 50 %. The effects of Mg/Al atomic ratio, phosphate and pyrrole on the ozonation performance of Mg/Al HTs were also investigated. The X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption experiment and temperature programmed desorption of adsorbed CO₂ or NH₃ were used to characterize the surface properties of Mg/Al HT. The surface acidity and basity was proven to be responsible to the excellent ozonation activity of Mg/Al HT. The results of electron spin resonance (ESR) analysis and probe experiments confirmed that ^[rad]OH, O₂^[rad]− and ¹O₂ were involved in the 2,4-D degradation process and their contributions are as followed: ^[rad]OH > O₂^[rad]- > ¹O₂. The synergistic effect of surface acid (ozone adsorption center) and base sites (catalytic center) determines Mg/Al HT in the enhanced catalytic ozone decomposition into reactive species. More important, the transition metal free based Mg/Al HTs is steady, non-toxic, naturally abundant and environment friendly, which provided a promising alternative in practical water treatment by catalytic ozonation.
© 2020 Elsevier B.V.

In this work, bimetallic iron and copper co-doped graphitic carbon nitride catalysts (FeCu-g-C3N4) exhibited pH-dependency in the activation of peroxymonosulfate (PMS) for ofloxacin (OFX) degradation, and the mechanism of the generation of reactive oxygen species (ROS) was correlated to the pH of reaction system. The degradation efficiency of OFX reached to 91% within 120 min at pH of 3.1, while only 70% OFX was removed at pH of 9.0. Furthermore, the mainly generated ROS were identified with quenching experiments and electron spin resonance (ESR). Under acidic condition (pH 3.1), center dot OH and O-1(2) made a major contribution for OFX degradation, while O-1(2) was the dominant ROS at alkaline condition (pH 9.0). The bimetallic Fe and Cu and the cyano groups on g-C3N4 were revealed to play critical roles in the activation of PMS. Also, Fe and Cu species were suppressed for PMS activation at alkaline condition, and cyano groups in g-C3N4 were active at both acidic and alkaline conditions. This work provides useful information for the influence on the performance of PMS activation under different conditions for the removal of recalcitrant organic compounds in water.

Karst water, with constituting major sources for water supply worldwide, is vulnerable and prone to be polluted. In this study, it is reported that karst water polycylic aromatic hydrocarbons (PAHs) pollution is caused by the infiltration of surface runoff in the bared carbonate areas, which is of universal significance for the protection of groundwater resources in karst region. Hydro-geochemistry, stable isotopes (delta D, delta O-18 and Sr-87/Sr-86) and characteristic ratio method were conducted together to illustrate the concentration, distribution, sources and pollution path of polycyclic aromatic hydrocarbons in groundwater in the Liulin karst water system of northern China. The results showed that total concentration of polycyclic aromatic hydrocarbons ranged from 39.25 to 16,830 ng/L in groundwater, with Naphthalene being the dominant component, and the median value increased gradually along the flow path. The highest polycyclic aromatic hydrocarbons concentrations in karst water were mainly observed in the coal mining and the discharge areas. Based on the characteristic ratios, the polycyclic aromatic hydrocarbons in the study area mainly come from local incomplete combustion of woods, fossil fuels, coal and liquid fuels. The slight shift of 8D and delta O-18 and moderate Sr-87/Sr-86 ratios suggest that the polycyclic aromatic hydrocarbons in karst water is mainly polluted by surface runoff during rain events in the bared karst region. The leakage of river water may partly contribute to the polycyclic aromatic hydrocarbons in some karst water, which normally located close to the karst water-river water mixing line. This study provides a new technical method for tracing the sources and identifying the pollution paths of organic pollution in a karst water system.

Improper exploitation and massive coal mines closures without proper solutions bring about the extensive occurrence of goaf water in China where over 3500 coal mines have been shut down in the last 30 years. Discharge of goaf water poses severe environmental impact, especially in fragile karst areas. Based on the extensively literatures reading, field investigation combined with hydrogeochemical and isotopic (delta S-34) analysis, this paper reviewed the distribution, characteristics and formation of coal mine goaf water in karst areas in China. The occurrence of goaf water is reported in over 50% of the coal fields, with more than 30 water discharges. Distinct major ion chemistry in goaf water (low pH, high total dissolved solids, SO42- and negative delta S-34 values) are closely related to a combination of comprehensive physical, chemical and biological interactions. Recharge water, water filling channels and storage space constitute hydrogeological conditions necessarily for the produce of goaf water. Oxidation of sulfides minerals with air and water, acidic dissolution of minerals (e.g., gypsum, calcite and dolomite) and cation exchange, under the action of bacteria, are major processes in the genesis of goaf water. A case study on the environmental impact of goaf water is also done at Jinci, northern China. Our research suggests that goaf water in Jinci (TDS: 3595 mg/L - 9841 mg/L, SO42-: 2463 mg/L - 3256 mg/L; negative delta S-34 values < -5 parts per thousand) may pollute the surface and karst water via fractures or faults evidenced by the high SO42- and low delta S-34 values in these waters. Finally, a conceptual model is established to demonstrate the influences of goaf water on karst water-surface water environment in karst areas. (C) 2020 Elsevier Ltd. All rights reserved.

Long-term deposition of coal spoil piles may lead to serious pollution of soil and water resources in the dumping sites and surrounding areas. Karst aquifers are highly sensitive to environmental pollution. In this study, the occurrence and release/mobilization of polycyclic aromatic hydrocarbons (PAHs) in coal waste and coal spoils fire gas mineral (CSFGM) were evaluated by field and indoor investigations at Yangquan city, one of the major coal mining districts in the karst areas of northern China. Field investigations showed that dumping of coal waste over decades has resulted in soil and water pollution via spontaneous combustion and leaching of coal spoil piles. Indoor analysis revealed that the 2-ring and 3-ring PAHs contribute to 65-80% of the total PAHs in coal spoils, with naphthalene (Nap), Chrysene (Chr), and Phenanthrene (Phe) as the dominant compounds. Based on a heating/burning simulation experiment, the production of PAHs is temperature-dependent and mainly consists of low-ring PAHs: 2-ring, 3-ring, and part of the 4-ring PAHs. The PAHs in the leachate are light-PAHs (Nap, 20.06 ng/L; Phe, 4.76 ng/L) with few heavy-PAHs. The distribution modes of PAHs in two soil profiles suggest that the precipitation caused downward movement of PAHs and higher mobility of light-PAHs.

Characterization of the spatial distribution and speciation of iron (Fe) in Fe-modified biochars is critical for understanding the mechanisms of contaminant removal. Here, synchrotron-based techniques were applied to characterize the spatial distribution and speciation of Fe in biochars modified by FeCl3 or FeSO4 and pyrolyzed at 300, 600, and 900 degrees C, respectively. Confocal micro-X-ray fluorescence imaging (CMXRFI) results indicated Fe, sulfur (S), and chlorine (Cl) diffused into the basic porous structure of the biochars and aggregated to the surface as pyrolysis temperature increased. Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra revealed maghemite (gamma-Fe2O3) as the primary Fe species in the modified biochars and Fe(0) was observed when pyrolyzed at 600 or 900 degrees C. Unmodified and FeCl3-modified biochars pyrolyzed at 900 degrees C were evaluated in the removal of arsenate (As(V)), arsenite (As(III)), hexavalent chromium (Cr(VI)) and Hg(II) from aqueous solution and Fe-modification enhanced the removal efficiency from 42.0%, 62.5%, 19.6%, and 97.0%, respectively, to all 99.9%. X-ray absorption spectroscopy results indicate both adsorption and redox reaction contributed to the removal mechanisms. The present study provides a prospective and sustainable material and offers information relevant to tailoring Fe-modified biochars to specific environmental applications.

An efficient strategy for enhancing iron efficiency in heterogeneous Fenton reaction via the pyrolysis of ferrocene chemically modified sepiolite (Sep) was proposed in this study. Highly dispersed FeC6 on sepiolite (Fe-Dis@Sep) was synthesized as an efficient photo-Fenton catalyst for the visible light degradation of ofloxacin (OFX). It exhibits an excellent Fenton activity and stability towards OFX degradation. The pseudo-first order reaction rate constant of Fe-Dis@Sep was 5.1-fold higher than that of the supported catalyst with aggregated iron oxides prepared by traditional impregnation method (Fe-Agg@Sep). Based on TEM images and density functional theory (DFT) calculation, the enhanced Fenton activity of Fe-Dis@Sep was attributed to the unique incorporation of FeC6 on Sep via Si-O-C-Fe bond which not only favor the high dispersion of FeC6 with an electron deficiency but also promote Fe(III) to Fe(II) cycle via the formation of surface Fe-H2O2 complex. center dot OH and O-2(-)center dot were identified as active species for OFX degradation in Fe-Dis@Sep-H2O2-Vis system. 98.7% of F and 97.0% of N in OFX was converted into F- and NO3- with a TOC removal efficiency of 89.35%. The possible degradation pathway of OFX was also proposed according to HPLC-MS results. Finally, the Fenton reaction mechanism over Fe-Dis@Sep was discussed. (C) 2020 Elsevier B.V. All rights reserved.

Contamination of groundwater with fluoride and arsenic in deep aquifers poses new health challenges worldwide. Integrated hydrogeochemical parameters with multiple isotopes (delta O-18, delta H-2, delta C-13, delta S-34, Sr-87/Sr-86 and C-14) is applied to demonstrate the origins and evolutions of deep groundwater and mobilization of groundwater solutes, fluoride and arsenic at Yuncheng Basin, northern China. Over 80% of deep samples have elevated fluoride (up to 3.73 mg/L) and/or arsenic values (up to 24.3 mu g/L) above the WHO guideline of 1.5 mg/L and 10 mu g/L, respectively. Deep saline groundwater normally belongs to Na-SO4-(Cl) type and is characterized by distinctly depleted delta O-18 and delta H-2 values (as low as -10.4%o and -78.5%o, respectively) than deep fresh water and shallow groundwater, indicating palaeo-climatic effect. Results of ionic ratios and isotopes reveal that three types of solute sources are delineated for deep aquifers. Deep saline groundwater with old residence times of ~ 11000 yrs showed the most depleted delta O-18 and delta H-2 values, high B/Cl and low Br/Cl, pointing towards the palaeo-saline water for the locally distributed groundwater solutes in the Qiji and Wenxi County. Saline sample near the faults with residence time of 7403 yrs showed strong evidence of a geothermal origin. In the central basin, some deep groundwater yield modern ages (3696 yrs and 4348 yrs), higher salinities (up to 1200 mg/L) and lower delta S-34 values (8.74%o-9.96%o), indicating the vertical leakage of shallow groundwater suffering from pyrite oxidation. High F-As fresh groundwater, characterized by Na-HCO3(-SO4) type with diverse hydrogeochemical and isotopic compositions, are evolved in closed reducing environment and semi-closed facultative environment and controlled by palaeo-recharge and shallow leakage, respectively. Organic degradation mainly controls the enrichment of arsenic and fluoride in groundwater.