Applied Geochemistry最新文献

Aquatic ecosystems are an important source of greenhouse gases (GHGs) released to the atmosphere. However, studies on GHGs fluxes from lacustrine groundwater discharge (LGD) remain limited, particularly for subtropical alluvial-lacustrine plains. This study used the radon (²²²Rn) mass balance model to quantify seasonal variations in LGD rates and fluxes of groundwater-borne GHGs (CH₄, CO₂, N₂O) to the Tian-E-Zhou oxbow lake in Jianghan Plain, central Yangtze. The results showed that the LGD rate in winter was 57.67 ± 28.37 mm/d which was higher than that in summer (24.72 ± 12.16 mm/d). The groundwater-borne fluxes of CH₄, CO₂, and N₂O into the lake in winter were 7.84 ± 6.81 mmol m⁻² d⁻¹, 1.47 ± 1.07 mmol m⁻² d⁻¹, and 3.50 ± 1.90 × 10⁻⁵ mmol m⁻² d⁻¹, respectively, whereas that in summer were 1.48 ± 2.36 mmol m⁻² d⁻¹, 0.72 ± 0.47 mmol m⁻² d⁻¹, and 1.53 ± 1.00 × 10⁻⁵ mmol m⁻² d⁻¹, respectively. High groundwater-borne fluxes of CH₄ across both winter and summer could be attributed to abundant buried organic carbon and strong groundwater reducing environment in this subtropical alluvial-lacustrine plain. Seasonally, fluctuations in water levels mainly affected LGD rates, further resulting in greater groundwater-borne GHGs fluxes in winter than in summer. This study can act as an important reference for future studies on the role of groundwater as an emission pathway for GHGs in lakes of subtropical alluvial-lacustrine plains.

Plant ash, an inexpensive alkaline material containing organic nutrients, can provide electron donors for microbial reactions and neutralize water acidity, making it an excellent candidate for use in preventing acid mine drainage production from tailings. However, the efficacy of using plant ash alone to treat tailings and the role of microorganisms remain unclear. Therefore, the effectiveness of plant ash in acid neutralization, inhibiting oxidation of sulfur-bearing minerals, and reducing acid mine drainage production is compared to that of three other alkaline materials—volcanic ash, limestone, and fly ash—in this study. Their potential microbial mechanisms are also explored. The 63-day experimental results showed that all four alkaline materials effectively neutralized the acidity of the sulfur-bearing tailings and dramatically decreased heavy metal leaching (Fe, Mn, Zn, Pb, As, and Cd). Plant ash had a higher removal efficiency of Fe (99.9%), Mn (94.0%), and Zn (99.7%) than the other three materials, which was related to its ability to provide better precipitation and adsorption conditions. XRD observed gypsum in each treatment column, the formation of a new phase of calcium carbonate was observed in the plant ash column, and SEM showed that precipitation wrapped around the surface of tailings inhibited their oxidation process. 16 S rRNA sequencing confirmed that plant ash could inhibit AMD production through microbial action. The plant ash column had higher biodiversity than the control column, and the eutrophic flora in the plant ash column could use organic matter to consume dissolved oxygen, inhibiting tailing oxidation; however, the growth of some reducing flora resulted in As reduction, causing a slight increase in As in the leachate.

Weathering of basaltic powders was studied experimentally at 35 °C in dilute solutions of oxalic acid and carbonic acid to assess the effect of grain size and reactive surface area for materials under consideration for carbon dioxide reduction (CDR) by enhanced rock weathering (ERW). The basalts chosen for this study (with their mineralogical compositions) are the Blue Ridge (BR) meta-basalt (chlorite > epidote > plagioclase > actinolite) and Pioneer Valley (PV) basalt (plagioclase > augite > quartz > chlorite). Powders of BR and PV basalts were sieved into <45 $\mu$ m, 45–150 $\mu$ m, and >150 μm fractions, and experiments were performed in open-system reactors designed to simulate a 1 mm thick layer of basalt added to agricultural soil in the humid tropics. Weathering rate was assessed by measuring the flux of base cations leached from silicate minerals and results indicate that silt-dominated basaltic powder (<45 $\mu$ m) weathers at approximately double the rate of sand dominated (150–500 $\mu$ m) basaltic powder, both for the BR and PV basalts. This study estimates CDR rates between 2.8 and 6.8 t CO₂/ha/yr across the range of grain size fractions analyzed. Etched primary mineral grains (e.g. plagioclase, augite, actinolite) with depleted base cations observed by SEM-EDS provide morphological and stoichiometric evidence of dissolution, as do the presence of frayed chlorite grains that contain adsorbed Ca and are compositionally intermediate to end-member chlorite and smectite. Small amounts of micron-scale calcite were also observed as a precipitate on mineral surfaces, likely a consequence of localized saturation of Ca and HCO₃ in the matrix of the weathering powders. The results of this study help to constrain differences in weathering flux as a function of grain size, with important implications for effectiveness of CDR via ERW.

Temperature and light are the two most important parameters regulating emissions of biogenic volatile organic compound (BVOC) from plant leaves, yet few field campaigns have been conducted to investigate the light and temperature dependency of BVOC emissions from tropical/subtropical trees. In this study, branch-scale emissions of isoprene and monoterpenes from typical tree species were measured using a dynamic plant chamber in the Pearl River Delta (PRD) region in south China. Our results showed that the temperature- and light-dependent isoprene emissions from the investigated trees could be well captured by the algorithms proposed by Guenther et al. (1993) (G93). However, the previously reported temperature-dependent algorithm for monoterpene emissions with a constant or fitted scaling β factor, could not well simulate monoterpene emissions from the tropical/subtropical trees. The temperature- and light-dependent G93 algorithm for isoprene instead could simulate the monoterpene emissions fairly well, indicating that the emissions of monoterpenes from tropical/subtropical trees depended on both temperature and light like that of isoprene, and that monoterpenes were directly emitted after biosynthesis without storing. This emission pattern was similar to that previously reported for some tropical trees, but different from most temperate and boreal trees. Moreover, when pooling together the measured data of all trees, observed emission rates (normalized to E_s) and the G93 predicted values (normalized to E_s) showed highly significant linear correlations for both isoprene (slope = 0.92; r² = 0.95) and monoterpenes (slope = 0.95; r² = 0.95). The result indicates that the emission model in the tropical/subtropical regions could potentially be simplified to use the G93 isoprene algorithm to formulate both isoprene and monoterpene emissions.

Nitrate is the major component of fine particle matter in recent years, and fog deposition is an important sink form of atmospheric nitrate aerosol. However, evidence shows that high relative humidity, and stable atmosphere condition may lead to the rapid increase of secondary aerosols, including nitrate. Therefore, whether fog event is a sink or a source of nitrate aerosol is still an open question. Simultaneous observations of concentration and isotopes of nitrate both in PM_2.5 and fog water during fog event were conducted during a heavy fog event happened in winter of 2018 in Nanjing, a megacity sited in the Yangzi River Delta, China. Based on nine 12-h time resolution fog water samples and eleven 24-h time resolution PM_2.5 samples, it was found that NO₃⁻ concentration in PM_2.5 increased during the fog event (from 10.4 ± 8.6 μg m⁻³ to 21.2 ± 11.0 μg m⁻³). Compared with Δ¹⁷O–NO₃^- in PM_2.5 before (28.4 ± 3.7‰) and after the fog event (28.6 ± 1.3‰), Δ¹⁷O–NO₃^- in PM_2.5 during the fog event was higher (31.6 ± 1.2‰) and Δ¹⁷O–NO₃^- in fog water was lower (24.3 ± 1.2‰). The increased NO₃⁻ in PM_2.5 during the fog event had a different formation pathway compared with NO₃⁻ in PM_2.5 when there is no fog, and NO₃⁻ in fog water had another formation pathway as well. Explosive growth of NO₃⁻ in PM_2.5 may come from active NO₃ + HC reaction, along with happen of fog event through the reaction of NO₂ with ·OH or H₂O and hydrolysis of N₂O₅. As the fog event finished, the fog water possibly mainly settled NO₃⁻ newly generated during the fog event. It seems the fog event may be a source rather than a sink of atmospheric nitrate aerosols in this case.

Tailings filtration has many advantages (e.g., water recirculation, progressive reclamation, reduction of geotechnical risks and of environmental footprint) and is increasingly used by mining companies to improve the geotechnical stability of tailings storage facilities (TSF). However, low water content also exposes filtered tailings to oxidation thus increasing the risk for acid mine drainage (AMD) generation. Tailings management techniques must therefore be adapted to prevent contamination during operations. More specifically, tailings degree of saturation and exposure time should be controlled so they do not remain exposed too long to oxygen before reclamation work starts. The main objective of this research was therefore to evaluate the combined influence of the mineralogy and the degree of saturation on the time before filtered tailings start generating AMD. This work included (i) physical, chemical, hydrogeological and mineralogical characterization of different tailings, (ii) laboratory kinetic tests, (iii) calibration and validation of reactive transport numerical simulations, and (iv) numerical extrapolations and analysis. Results showed that AMD started when carbonates were depleted and that the critical time (i.e., the time tailings could be left exposed before AMD starts) strongly depended on the mineralogy. Maintaining the degree of saturation above 90% could contribute to delay the generation of AMD, and the greater the degree of saturation, the longer the critical time. However, the critical time became independent of the degree of saturation and depended only on the mineralogy when S_r< 90%. The results of this study tend to show that it should be possible to plan the deposition of reactive filtered tailings to limit the generation of AMD, for example by mixing reactive tailings with other tailings containing a greater neutralization potential and/or by regularly disposing of a new layer of tailings on the surface, with the maximum delay between two layers being shorter than the critical time.

Mineral carbonation through reaction with supercritical CO₂ (scCO₂) is the ultimate pathway to permanent carbon storage for geological sequestration. Whether and how much H₂O is required for the scCO₂-mineral interaction to proceed readily, and the role of H₂O in the reaction have been actively researched topics. We designed and built a novel in situ Raman reactor to study the carbonation product during brucite [Mg(OH)₂]-scCO₂ interaction, and investigated the role of free H₂O by comparing the products in neat, H₂O, and formamide (FM) conditions. We introduced FM to provide a physical polarity environment similar to that of H₂O but without the chemical protonation effect. We further evaluated the role of structural H₂O by conducting experiments with periclase (MgO). The in situ Raman analysis revealed the occurrence of brucite carbonation both in the presence of H₂O and FM, demonstrating the effect of polarity in the reaction; in contrast, carbonation of periclase only occurred in H₂O-saturated scCO₂. The lack of carbonation of periclase with the presence of FM was attributed to the difficulty of magnesite mineralization, as CaCO₃ was able to form in the CaO-FM-scCO₂ system. Post-experimental X-ray diffractometry and Fourier-transform infrared spectrometry of the products showed that brucite carbonation yielded nesquehonite and hydromagnesite in H₂O and FM, respectively; whereas periclase-scCO₂ interaction in H₂O produced a mixture of the two products. Rate calculations suggested that the carbonation reaction was much faster in H₂O; nonetheless, 40–50% carbonation was still achieved in the Mg(OH)₂-FM-scCO₂ system after 330 h. Overall, our results showed that the brucite-scCO₂ reaction could proceed without H₂O under certain conditions – the polarity effect of H₂O/FM was large enough to break the Mg–OH and MgO–H bonds and promote the carbonation process.

Highly saline groundwater limits the availability of freshwater resources, especially in arid/semi-arid inland areas with a growing demand but a scarcity of water resources. Understanding the spatial distribution of groundwater salinity and the factors that control their variability is vital for the scientific management of water resources in these areas. Integrated hydrogeochemistry and environmental isotopes (δD, δ¹⁸O, ³H, ¹⁴C) were used to study the distribution and evolution of fresh and saline groundwater in the Aksu Plain and its links to the paleo-climatic environment since the Late Pleistocene. The results indicated that the sources of groundwater was meteoric water from the Tianshan Mountains. Modern groundwater was found in the piedmont plain and shallow groundwater adjacent to the surface water. The paleo-atmospheric precipitation replenished the deep confined groundwater during the Last Glacial Period. There was no correlation between groundwater salinity and depth. Along the flow path, groundwater salinity has no increasing trend. We found that the paleoclimatic environment and water-rock interaction jointly determine the distribution of groundwater salinity, while evaporation had a slight effect based on the isotopic composition. The long residence time (8–19 ka) and evaporites in sediments (such as halite and gypsum) could provide the conditions for sufficient water-rock interactions, leading to the formation of brackish/saline groundwater. Conversely, the fresh, deep, confined groundwater corresponds to paleo-recharge conditions during the humid Last Glacial Period (21–24.5 ka). Surface water infiltration reduces the salinity of shallow groundwater, but the influence is limited. This study presents a mode that combines hydrogeochemical evolution and paleoclimatic environments to better assess groundwater salinity in the arid inland region.

Topsoils, soil profiles, water, and stream sediments as well as slags and rocks were analyzed to assess the extent and severity of environmental pollution resulting from historical Cu mining and smelting in the vicinity of Leszczyna, Old Copper Basin, SW Poland. Numerous tailings, smelting wastes, and Cu-rich rocks were disposed in the study area, causing long-term leaching and accumulation of various metal(loid)s. Surrounding the anthropogenically impacted area, two types of geochemical background are distinguished, one of which is associated with rocks and soils that are naturally enriched in metal(loid)s and the second one is free of them. The presence of significant anthropogenic changes combined with natural enrichment creates a highly complex environmental situation with regard to different sources of metal(loid)s. Additionally, the ore-hosting carbonate rocks are responsible for specific near-neutral (pH) conditions. With a focus on numerous elements (Cu, Zn, Pb, Ni, As, Cd, Co, Ba, and Cr) we studied spatial and vertical metal(loid)s distributions in soils to determine elements fate under near-neutral conditions. We applied the Synthetic Precipitation Leaching Procedure (SPLP) to evaluate the leaching potential of geogenic and anthropogenic materials and the Acid Neutralization Potential (ANP) test to measure the impact of slags on the pH of local soils. The EDTA extraction indicated high (bio)availability of Cu, Cd, Pb, and Zn, and suggested that metals from Cu-rich rocks are substantially more mobile than these of metallurgical origin. Our data indicate significant metal(loid)s mobility from surface-deposited wastes, especially into soils and stream sediments. The study proves that in the near-neutral conditions wastes are mainly subjected to short-time, rainfall-associated leaching, which is responsible for mobilization of labile metal(loid)s fractions (especially Cu, Pb, Zn, and Cd).

The industrial development of tungsten deposits in Eastern Transbaikalia contributed to a significant deterioration of the environmental situation in the adjacent territories. Heavy-metal water contamination has become a serious problem in the mining areas. The most dangerous are wastes of sulphide ores, the oxidation of which leads to the formation of acidic drains with abnormally high concentrations of heavy metals. The features of the composition of the waters formed in and around the five tungsten deposits were studied and significant differences in their physical and chemical characteristics were shown. The most saline acidic, sulphate waters with the maximum content of heavy metals are recorded in the drainages of the tailings of beneficiation plants and rock dumps and in the ponds of sludge depositories and deposits with an increased ore sulphide content. The groups of elements posing the greatest danger to aquatic ecosystems were identified as Cd, Cu, Zn, Be, Al, Co, Th, Mn in acidic and slightly acidic waters and W, Mo, U, As, Mn in slightly alkaline and alkaline waters. Based on the Eh-pH water parameter ratio, three types of hydrogeochemical environments formed in the mining areas of tungsten deposits were identified. Metal migration in the waters occurs mainly in the form of simple cations, sulphate, fluoride, hydrocarbonate, carbonate and hydroxyl complexes. Geochemical barriers of oxygen, sorption, acidic and alkaline types were studied in the areas around the deposits. The main factors determining the physical and chemical parameters of the waters are shown, including the regional factor, specifically, the ore and host rock composition, the water exchange intensity, and the technogenic factor, which causes a high level of water pollution.