Copper export and mobility in acid mine drainage are difficult to understand with conventional approaches. Within this context, Cu isotopes could be a powerful tool and here we have examined the relative abundance of dissolved (<0.22 μm) Cu isotopes (δ⁶⁵Cu) in the Meca River which is an outlet of the Tharsis mine, one of the largest abandoned mines of the Iberian Pyrite Belt, Spain. We followed the chemical and isotopic composition of the upstream and downstream points of the catchment during a 24-h diel cycle. Additional δ⁶⁵Cu values were obtained from the tributary stream, suspended matter (>0.22 μm) and bed sediments samples. Our goals were to 1) assess Cu sources variability at the upstream point under contrasted hydrological conditions and 2) investigate the conservative vs. non conservative Cu behavior along a stream. Average δ⁶⁵Cu values varied from −0.47 to −0.08‰ (n = 9) upstream and from −0.63 to −0.31‰ downstream (n = 7) demonstrating that Cu isotopes are heterogeneous over the diel cycle and along the Meca River. During dry conditions, at the upstream point of the Meca River the Cu isotopic composition was heavier which is in agreement with the preferential release of heavy isotopes during the oxidative dissolution of primary sulfides. The more negative values obtained during high water flow are explained by the contribution of soil and waste deposit weathering. Finally, a comparison of upstream vs. downstream Cu isotope composition is consistent with a conservative behavior of Cu, and isotope mass balance calculations estimate that 87% of dissolved Cu detected downstream originate from the Tharsis mine outlet. These interpretations were supported by thermodynamic modelling and sediment characterization data (X-ray diffraction, Raman Spectroscopy). Overall, based on contrasted hydrological conditions (dry vs flooded), and taking the advantage of isotope insensitivity to dilution, the present work demonstrates the efficiency of using the Cu isotopes approach for tracing sources and processes in the AMD regions.

Porous carbon, which can be functionalized, is considered as a potential carbon material. Herein, two-dimensional (2D) nitrogen-doped magnetic Fe₃C/C (NMC) was prepared by a simple carbonization method using potassium humate (HA-K) as raw material. Remarkably, two templates, g-C₃N₄ and KCl, were formed in situ during the carbonization process, which provide the necessary conditions for the formation of 2D NMC. The NMC was comprehensively studied by different characterization methods. The results show that NMC has a large surface area and mesoporous structure. The prepared NMC-0.50 was used to test the removal performance of Cr(VI). The effects of pH value, coexisting ions and time on Cr(VI) removal performance were investigated, and the adsorption kinetics, isotherm and thermodynamics were studied. The results showed that the adsorption isotherm model of NMC-50 accorded with the Langmuir model, and the maximum adsorption capacity was 423.73 mg g⁻¹. The reaction mechanism of Cr(VI) is adsorption and redox reaction. In addition, NMC-0.50 exhibit high selectivity, separability and regeneration performance. A convenient means for the synthesis of NMC was designed in this work, and demonstrate that NMC has practical value as an adsorbent.

Riverbed sediments are the interface layer in riverine ecosystems connecting the overlying medium of water and the vadose zone. The transport behavior of phosphorus (P), which has been recognized as the primary cause of freshwater eutrophication, in riverbed sediments remains unclear. Understanding the impact of riverbed sediments on P transport is a necessary prerequisite for the development of appropriate strategies to reduce potential groundwater pollution. In this study, riverbed sediments were collected from the upstream, midstream, and downstream sections of the Beiyun River, China, and packed into vertical soil columns to perform leaching experiments to quantify P transport characteristics. In addition, the impact mechanisms were further explored by conducting laboratory batch tests of P adsorption and desorption. The results demonstrated that approximately 80% of P can be adsorbed by riverbed sediments in soil column leaching experiment, and a tailing phenomenon was observed in its desorption. The hydraulic conductivity properties of riverbed sediments were evaluated by the advection-dispersion equation, showing a gradually decreasing adsorption capacity for P from upstream to downstream sections, which was supported by the results obtained from adsorption–desorption thermodynamic and kinetic batch tests. The estimated annual leaching masses of P increased from 60.72 g/(m² a) in the upstream section to 132.31 g/(m² a) in the downstream section. The role of riverbed sediments as a source or sink of P is possibly determined by their coarse sand particles content, and the mean equilibrium P concentration (EPC0). The competitive relationship between P and other forms of nutrients also has an important influence on its source-sink role. These findings suggest that the prevention of the potential P leaching is most needed in the downstream sections of Beiyun River, and corresponding control strategies should be developed to avoid groundwater pollution.

The co-precipitation method was used to synthesize nano-magnetic adsorbent MnFe₂O₄ (nMFO), characterized through XRD, SEM, EDS, and BET techniques. The synthesized nMFO was used for hexavalent and trivalent chromium ions elimination from the aqueous phase. The optimum pH for the adsorption of Cr (VI) and Cr (III) was determined as 2 and 5, respectively. The chromium ions adsorption behavior was well interpreted through the pseudo-second order kinetics model. Furthermore, isotherm studies were conducted, and the obtained results indicated that Langmuir isotherm model could well justify the chromium ions adsorption process. Quick removal (less than 10 min) of both chromium ions and high removal efficiency were occurred using nMFO. The utmost adsorption capacity of trivalent and hexavalent chromium ions were determined as 39.6 and 34.84 mg g⁻¹, respectively. Thermodynamic studies on chromium adsorption revealed positive value for ΔH and negative value for ΔG, representing that chromium ions adsorption was an endothermic and spontaneous process. The multilinearity in the graphs of chromium ions adsorption was observed using intra-particle diffusion model. In this regard, the external mass transfer of chromium ions on synthesized nanoparticles was the important and controlling step in the adsorption process.

The main purpose of current study is accurate prediction of NOx emissions from diesel engines considering in-cylinder ion current. To reach this goal, a validated thermodynamic multi-zone model was used. A modified chemical kinetics mechanism of diesel fuel oxidation was used too. A chemical kinetics mechanism of NOX formation including 103 reactions was added to the main mechanism. A set of ions and ionic reactions was added to the developed chemical kinetics mechanism and finally a modified chemical kinetics mechanism with 445 reactions and 100 species was formed. The developed mechanism was coupled to the multi-zone model and a diesel engine was simulated. The importance of Zeldovich mechanism, prompt mechanism, N₂O mechanism and NNH mechanism were investigated. The progress rates of reactions were calculated and important reactions were identified. The results show that the oxygenated ions, NO⁺, O⁺ and O₂⁺, has more effects on NO production than other ions. The prompt mechanism plays an important role in predicting the ion current inside the chamber. Because this mechanism has reactions that can lead to CH production. The CH radicals produced by this mechanism can be employed by basic ionic reactions and lead to ion production. The results show that using NOx related ionic reactions results in accurate prediction of engine exhaust NOx.

Metal pollution in estuaries represents a serious environmental challenge, especially in areas affected by industrial and mining activities. This study investigates the metal partitioning and availability of rare earth elements (REE), Y and other trace metals (Ag, Tl, U and Cs) in the Ria of Huelva estuary (SW Spain), strongly affected by mining and industrial activities. A 30 h monitoring campaign was performed collecting periodic water samples and deploying diffusive gradient in thin films (DGTs) devices to determine the main factors controlling metal availability. The dissolved concentrations of U (3118–3952 ng/L) and Cs (284–392 ng/L) were in the same order of magnitude than those reported in other estuaries and coastal waters worldwide, however, REE (26–380 ng/L), Y (15–109 ng/L), Ag (14–307 ng/L) and Tl (29–631 ng/L) concentrations exceeded these values for the same salinities. Unlike most metals (i.e. Ag, Tl, U, Cs), which were mainly found in the dissolved form (87–100% of total), REE and Y were found in the particulate phase (22–36% of total). Metal lability was mainly related to the concentration in the water column following this order: U>REE>Y>Ag>Tl. A similar binding mechanism was observed for Tl and Cd, due to its chemical affinity. This relationship between chemical properties and absorption by DGT-resin was also observed for REE (and Y), Rb and Sr, which may cause bioaccumulation upon persistent exposure, considering the ability of these metals to cross the biological membranes. The lability of metals predicted by geochemical codes did not coincide with absorption of labile metals by DGTs due probably to the instability of complexes in contact with the DGT membranes, the inability of metals to form thermodynamically stable complexes or the absorption of colloids. From this work it can be concluded that DGT passive sampling should complement traditional sampling to monitor metal availability in aquatic environments.

Organic contaminants are frequently detected in fresh crops and can cause severe damage to human health. To help control this risk, we introduce a diffusion-based model framework for estimating the removal efficiency for organic contaminants in fresh crops using a simple water soaking method. The framework was developed based on the diffusion coefficient of the organic contaminants, and its application indicates that the removal factor (RF) for organic contaminants has an inverse-exponential relationship with log Kₒw (Kₒw is the octanol-water partition coefficient), which thermodynamically restricts the removal efficiency for chemicals with large steady state log Kₒw. Additionally, the diffusion coefficient of the chemical in water affects the kinetic removal efficiency. For example, the RF simulated for glyphosate, which has a relatively high diffusion coefficient, is 0.592 (61.9% of the steady state RF) after soaking for 1 h, while the RF of lindane is 0.224, which is only 25.0% of the steady state RF. However, if a refreshing method is applied, the RF of lindane can be significantly improved even if more potatoes are used in the water bowl, and this has been demonstrated theoretically with the refreshing function. Model validation indicates that the macro properties of crops, e.g., the active area through which crop tissues interact with water, have a larger impact on the results than do the micro-properties of crops and the physiochemical properties of the organic contaminants. Comparison of our results with those of other studies shows that the simulated ranges for some pesticides compare well with experimental data collected using other household washing methods. However, for other pesticides such as HCB and DDT, the simulated results and current studies are inconsistent due to physical interactions between the water and crop tissues not considered in our model.

Cadmium (Cd) is one of the most harmful and widespread environmental pollutants. Despite decades-long research efforts, the remediation of water contaminated by Cd has remained a significant challenge. A novel carbon material, pinecone biochar, was previously hypothesized to be a promising adsorbent for Cd, while so far, it has received little attention. This study evaluated the sorption capacity of pinecone biochar through isotherm experiments. Based on Langmuir model, the adsorption maximum for Cd(II) was up to 92.7 mg g⁻¹. The mechanism of Cd(II) adsorption on pinecone biochar was also explored through both thermodynamic and kinetics adsorption experiments, as well as both solution and solid-phase microstructure characterization. The solid-solution partitioning behaviour of Cd(II) fitted best with the Tόth model while the adsorption process followed a pseudo-second-order rate, suggesting that the Cd(II) adsorption on the pinecone biochar was mainly a chemisorption process. Microstructure characteristics and mechanism analysis further suggested that coprecipitation and surface complexation were the main mechanisms of Cd adsorption by biochar. Coprecipitation occurred mainly through the forms of Cd(OH)₂ and CdCO₃. Our results demonstrated that pinecone biochar was an efficient adsorbent which holds a huge potential for Cd(II) removal from aqueous solution.

Carbamazepine (CBZ), a widely detected pharmaceutical in wastewaters, cannot currently be treated by conventional activated sludge technologies, as it is highly resistant to biodegradation. In this study, the degradation kinetics and reaction mechanisms of CBZ by hydroxyl radical (OH) and sulfate radical (▪)–based advanced oxidation processes (AOPs) were investigated with a combined experimental/theoretical approach. We first measured the UV absorption spectrum of CBZ and compared it to the theoretical spectrum. The agreement of two spectra reveals an extended π–conjugation system on CBZ molecular structure. The second–order rate constants of OH and ▪ with CBZ, measured by competition kinetics method, were (4.63 ± 0.01) × 10⁹ M⁻¹ s⁻¹ and (8.27 ± 0.01) × 10⁸ M⁻¹ s⁻¹, respectively at pH 3. The energetics of the initial steps of CBZ reaction with OH and ▪ were also calculated by density functional theory (DFT) at SMD/M05–2X/6–311++G**//M05–2X/6–31 + G**level. Our results reveal that radical addition is the dominant pathway for both OH and ▪. Further, compared to the positive ΔGR0 value for the single electron transfer (SET) reaction pathway between CBZ and OH, the ΔGR0 value for SET reaction between CBZ and ▪ is negative, showing that this reaction route is thermodynamically favorable. Our results demonstrated the remarkable advantages of AOPs for the removal of refractory organic contaminants during wastewater treatment processes. The elucidation of the pathways for the reaction of OH and ▪ with CBZ are beneficial to predict byproducts formation and assess associated ecotoxicity, providing an evaluation mean for the feasibility of AOPs application.

The fate of veterinary antibiotics (VAs) in soil environment is determined by the hydrophilic performance and solubility of VAs and the type of soil. In this study, sulfadiazine (SDZ) and chlortetracycline (CTC) were selected as target pollutants, and a batch sorption method was used to find out the single and sorption competitive behavior and mechanism of the target pollutants on loess soil. Kinetic studies showed the apparent sorption equilibrium was reached 0–6 h for CTC and 0–12 h for SDZ. The sorption kinetics of VAs on loess soil were fitted well with a pseudo-second order kinetic model. Sorption thermodynamic data indicated the isotherm sorption of both SDZ and CTC on loess soil was fitted well with Freundlich isothermal (R², 0.960–0.975) and linear models (R², 0.908–0.976). The sorption affinity of CTC (Kd, 290–1620 L/kg for CTC) was much greater than that of SDZ (Kd, 0.6–4.9 L/kg for SDZ). The results also suggest that SDZ may be easily mobilized or leached from loess soil at neutral and alkaline pH, while CTC may be easily mobilized or leached at neutral pH. The sorption of each single target pollutant on the outer layer complex decreased with increasing ionic strength. Higher initial concentrations resulted in greater sorption capacity of target pollutants on loess soil increased. The sorption capacities of CTC and SDZ in the mixed system were lower than the sorption capacity of each single system, showing a competitive sorption behavior of CTC and SDZ during the sorption process. Overall, CTC showed the highest sorption potential in loess soil, whereas SDZ showed a high leaching risk in loess soil. These findings contribute to understanding the fate of different VAs in loess in the natural environment.