Applied Geochemistry最新文献

The presence of organic ligands may exacerbate the mobility of contaminants by stabilizing them in the aqueous phase and reducing their retention on the solid phases, representing an additional environmental hazard.

We investigated the impact of EDTA, citrate and phthalate on the adsorption of four different radionuclides (RN = ¹³⁷Cs, ⁸⁵Sr, ¹⁵²Eu and ²³³U) by a well-characterized smectite clay and evaluated the capability of sorption modeling to incorporate the impact of these organic ligands.

We analyzed the effect of ligand concentration (from 1·10⁻⁶ to 1·10⁻³ M) on RN retention at two different pH values (approximately 5 and 9) to contemplate the occurrence of different adsorption mechanisms in clays (cation exchange or surface complexation) as well as the RN and organic speciation.

The results suggested that phthalate had a minimal effect on the retention of the studied RNs, while EDTA and citrate significantly decreased the adsorption of Eu, Sr and U, even making it drop to zero in some cases. The simulation outcomes demonstrated that, in most cases, the variation in the distribution coefficient (K_d) as a function of the organic concentration could be accurately replicated with the available thermodynamic data, but few relevant discrepancies were identified.

The importance of the possible competitive effects of trace ions in the equilibrium water (notably Ca) for the overall assessment of the role of organic matter on RN retention was highlighted.

Remediation by a composite cover was implemented on partly oxidized sulfide-rich tailings in northern Ontario, Canada to reduce the production and release of acid mine drainage (AMD). The impact of the cover on sulfide oxidation rates and trace element mobility was initiated a decade after cover installation via multi-year measurements of pore-gas concentrations, pore-water and groundwater sampling and analysis, mineralogical studies of the tailings, selective chemical extractions, and synchrotron-based X-ray absorption experiments. Depleted pore-gas O₂ concentrations, circumneutral pH, and improvement in water quality were observed at one detailed sampling location, suggesting that the cover decreased AMD generation and transport. Carbon and sulfur isotope ratios indicate sulfate reduction occurred at the base of the tailings. In contrast, near-atmospheric pore-gas O₂ concentrations, low pH, and elevated aqueous concentrations of Fe, sulfate, Zn, Cu, As, and Pb were observed at another location, suggesting localized sulfide oxidation. Trace elements in the tailings are associated with secondary crystalline and amorphous Fe(III) oxyhydroxides, covellite, and Fe(III) hydroxysulfate phases, formed prior to cover installation. Substantial reductive dissolution of Fe(III) oxyhydroxides due to the isolation of the tailings from the atmosphere by the cover was not observed. Concentrations of Zn and Mn remained elevated due to limited sequestration under the current acidic to circumneutral pH. Although secondary Fe(III) oxyhydroxides contain As(V) and As(III), which were released by arsenopyrite oxidation, dissolved As persists. Due to localized sulfide oxidation, element remobilization, and limited capacity for sulfate reduction, diminished water quality, with elevated aqueous concentrations of sulfate, Zn, As, and Mn, may endure.

Unconventional hydrocarbon production has become the target of an intensive environmental debate due to the risks it poses to water resources. Fracking, while enabling the extraction of oil and gas from ultra-low permeability reservoirs, also possesses the risk of polluting water systems through failures from hydraulic fracturing and its associated procedures. The need to foster national industrial development with a transitional energy matrix has led Brazil to discuss the environmental suitability before producing its large unconventional reserves. Many studies have highlighted the need for a robust environmental characterization before the development of the unconventional industry. In this sense, multiple environmental isotopes may work as a proxy for identifying water contamination right from the early stages. Environmental isotopes may also be applied to enhance the understanding of the natural geochemical processes intrinsic to a given area. This study presents an environmental isotopes baseline for the groundwater and riverine water systems within the São Francisco Basin, a proven tight gas reservoir in Brazil, in a pre-operational context. δ¹⁸O, δ²H, ³H, δ¹³C, and Δ¹⁴C were evaluated in three different seasons in groundwater and surface water samples, along with other auxiliary parameters such as physical-chemical parameters (in situ), major ions, and d-excess. The δ²H and δ¹⁸O in surface water shows an upstream → downstream enrichment trend, with some variations suggesting baseflow interactions in the surface water systems. An evaporation line for the study area was defined as δ²H = 4.6903 δ18O + 10.362. δ¹³C indicates a mutual dissolution of silicates and carbonates in the groundwater system and suggests a group of samples highly related to the recharge areas. Groundwater dating denotes the Serra da Saudade Formation as a modern fractured aquifer with a strong recharge capacity. These findings support stakeholders in environmental monitoring and management of the unconventional gas industry.

Illite, smectite and illite/smectite mixed layers are major phases in various argillaceous rock formations foreseen as potential host rocks for the deep geological disposal of high-level radioactive waste and are important sorbents for cationic radionuclides potentially released in the repository. ²²⁶Ra is a critical radionuclide in the safety analysis and an important source of radioactivity in technically enhanced naturally occurring radioactive materials. A comprehensive study was carried out on the adsorption of Ba and Ra on purified homoionic Na-illite (Illite du Puy) over a wide range of experimental conditions (pH, concentration, ionic strength) allowing for the development of a quasi-mechanistic Ba/Ra adsorption model for illite. Ba adsorption isotherms obtained at fixed ionic strength and pH exhibit a non-linear behaviour in the Ba equilibrium concentration range between ∼10⁻⁷ and ∼10⁻² M. The pH dependent adsorption of trace ²²⁶Ra and Ba was investigated at different ionic strengths and evidenced a more pronounced adsorption of ²²⁶Ra than Ba on illite. Finally, a competition experiment of trace ²²⁶Ra in the presence of increasing Ba concentrations showed an unexpected ²²⁶Ra adsorption behaviour which was not observed for montmorillonite in earlier studies. This large set of experimental data could be successfully modelled by Ba/²²⁶Ra exchange reactions against Na, together with selectivity coefficients, on two different site types, namely planar sites and high affinity sites. The modelling of the pH dependent adsorption of Ba and ²²⁶Ra at high ionic strength and high pH required an additional surface complexation reaction. Two additional exchange sites had to be introduced to quantitatively describe the ²²⁶Ra uptake on illite in the ²²⁶Ra/Ba competition experiment. The nature of these sites, however, remains unclear. The implementation of the ²²⁶Ra adsorption model into predictive transport modelling codes is of key importance for the safety analysis of deep geological disposal of radioactive waste.

Constraining the main sediment sources and pathways across landscapes impacted by anthropogenic activity is essential to limit the dispersal of sediment-borne contaminants, especially in global conservation priority areas. This study examined the provenance, partitioning, and enrichment of metals in the floodplain of the mining-affected Santa Cruz catchment, The Philippines. Composite geochemical fingerprinting of fine sediment samples (n = 36) was performed using a stepwise statistical screening procedure (range test, Kruskal-Wallis H test, discriminant function analysis) to derive the optimum set of tracers. Using a standard unmixing model, flood deposits downstream of the mining areas were shown to be predominantly mining-induced (71.9 ± 7.7 %), followed by natural erosion from gullies and stream banks (15.1 ± 11.0 %) and agricultural sediment (13.0 ± 5.1 %). Element partitioning data (Log K_d = 1.3–6.6) during a high flow event indicated that metals are dominantly associated and transported via suspended particulate matter. Background concentrations of Ni and Cr were found to be orders of magnitude higher than the threshold values set by international sediment quality guidelines (SQGs), emphasizing the need for site-specific SQGs in mineralised areas. Enrichment factor values indicated low to significant contamination of flood deposits relative to natural and agricultural sediment (EF 1.0–5.5). Furthermore, it was demonstrated that using different conservative elements could considerably influence the enrichment factor calculation. Based on tracer screening tests, Th was shown to be the most suitable reference element. The findings provide new insights on the application of geochemical tracers in a mining setting and integrating fingerprinting approaches with traditional assessment techniques to improve the reliability of contamination risk assessment in other areas facing similar sediment pollution problems.

Coastal aquifers, as the interface zone between ocean and land, are highly sensitive and vulnerable to seawater intrusion. This study presents the behavior of radium isotopes and their application to estimate the rate of seawater intrusion in a typical coastal city (Qinhuangdao, China). The hydrochemical results indicated that the coastal aquifers have Na–Cl type water with the lower Na/Cl ratios. The analysis revealed that the formation process of the chemical composition of groundwater was mainly the mixing of seawater and groundwater, while that of inland groundwater was dominated by mineral dissolution and cation exchange and adsorption. Groundwater of intruded aquifers contain significantly higher activities of radium than those of nearshore seawater and inland groundwater. The rates of seawater intrusion were estimated by using equation of the fate and transport of radium in 1–D transient groundwater flow system. In the calculation process, we ignored dissolution and co-precipitation and mainly considered mixing, alpha recoil and decay contribution for radium activity as sources and sinks terms of radium in coastal groundwater based on the characteristics of radium activity and ²²⁴Ra/²²⁸Ra ratio in groundwater. The recoil (P) was determined by the activity ratio of ²²⁴Ra to Th (²³²Th/²³⁰Th), while the retardation (R_f) was calculated from the steady-state radium equilibrium equation. The seawater intrusion rates were obtained by integrating ²²⁴Ra and ²²⁸Ra activities under different thorium ratios (²³²Th/²³⁰Th). The results show that the rate of seawater intrusion varies in a wide range at different locations, which are 0.17–1.03 (²³²Th/²³⁰Th = 0.67) and 0.11–1.01 (²³²Th/²³⁰Th = 1.25) m/d. The method of calculating seawater intrusion rate with radium isotope can obtain the rate of different parts of heterogeneous anisotropic aquifer, which also extends the application of radium isotope in hydrogeology.

The North Tianshan orogen consists of a series of thrust faults and is the most seismic region in China. In this paper, the characteristics of hot springs in the North Tianshan orogen are analyzed. Hydrochemical analysis of 13 hot springs and four mud volcanoes reveals that the cations of most hot springs are mainly Na⁺, while the anions are mainly Cl⁻.Atmospheric precipitation is the main recharge source for the hot springs in the study area, with recharge heights ranging from −9 to 2344 m. Heat storage analysis and trace element results showed deep fluid characteristics, which is consistent with deep circulation processes and regional extrusion pressure background. In addition, continuous measurements of six hot springs were conducted once every three days. The results showed that Cl⁻ and SO₄²⁻ concentration anomalies occurred before several earthquakes of M_L4.0 in the North Tianshan orogen. The hot springs SWQ, HTB, and WS, which have deeper circulation depths, show better responsiveness than X10, which has a shallow circulation depth. The deep circulation of hot springs increases fault sliding friction, which contributes to energy accumulation and strong seismogenesis, and participates in the seismogenesis process. Therefore, continuous monitoring of ion concentrations of deep-circulation hot springs can help identify effective precursor anomalies in the North Tianshan orogen.

The CO₂ preparatory methods implemented during carbonate-clumped isotope analysis for the acid digestion of carbonate with the goal of high sample throughput yielded multiple empirical relationships for the thermometry. These methods varied significantly from its original practice of carbonate reaction at 25 °C using sealed vessel method to automated quick performance acid drip or common acid bath method at 70 °C or 90 °C temperatures, respectively; these approaches differed noticeably. Technical development replacing primitive reaction protocols, introduced different reaction conditions, causing significant differences in the chemical reaction procedure and CO₂ trapping, which caused variation in the values of slope and intercept for the linear regression equations governing carbonate-clumped isotope(Δ₄₇) distribution with carbonate growth temperatures. These studies include the Δ₄₇ measurement and analysis of either laboratory-grown or natural carbonates with precise knowledge of their precipitation/depositional temperatures. However, the discrepancies in the existing universal calibration schemes remained poorly understood despite adopting an identical data correction protocol. This is explained here by the reaction kinetics and CO₂ collection methodologies adopted during experimentation. The present study investigated the slope and intercept values of the published carbonate clumped isotope thermometry equations expressed in the accepted Absolute Reference Frame (ARF in CDES) at 25 °C after accounting for the acid correction factor. We observe a systematic shift in the mean slope and intercept values of 0.0154(±0.007) and 0.153(±0.0686) ‰ for 70 °C reaction experiments and offset of 0.0181(±0.008) and 0.197(±0.079) ‰ for the experiments conducted at 90 °C by using the acid drip and/or Common Acid bath method, respectively from the slope and intercept values of the calibration equations proposed using sealed vessel method at 25 °C reaction temperature. The mean values for slope and intercept are compared using ANOVA and paired f-test. These correction factors for slopes and intercepts will allow the transformation of clumped isotope values at different temperatures into ARF scale at 25 °C and enable accurate deduction of temperature for carbonate samples. Correction factors proposed here account for variations in the sample preparation techniques arising due to different reaction temperatures, mechanisms and vapor pressure in the chamber for isotopic exchange reaction to happen for smaller or prolonged time intervals.

Radioactive nickels are significant environmental concerns because of their long half-lives (⁵⁹Ni = 76,000 years and ⁶³Ni = 100.1 years) and high proportions in nuclear wastes in the repositories. Therefore, the investigation of sorption and mobility of Ni at the disposal facility sites is important for the prediction and evaluation of radiological risks to the public. Herein, the batch sorption and column experiments were performed under various geochemical conditions using site-specific rock and groundwater samples collected at the Wolsong low and intermediate level waste (LILW) disposal facility site in South Korea. The batch sorption results revealed that the sorption of Ni was strongly affected by the pH. Approximately 20% Ni adsorbed at pH 5, which enhanced over 90% at pH > 8. The batch sorption results were used to develop the surface complexation model (SCM) to predict the Ni sorption and its mobility behavior. The non-electrostatic generalized composite (GC) SCM approach simulated the Ni sorption data well. We believe, our study can interpret and extrapolate the sorption and transport behavior of Ni in the underground repository conditions.

High arsenic (As) concentrations in groundwater affected by geothermal activity have been reported worldwide, but the genesis mechanism is not adequately understood. To address this issue, 22 groundwater samples and 69 sediment samples were collected from the Guide basin in northwest China for hydrochemical and geochemical analyses and laboratory experiments. Results indicated that Fe/Mn oxide minerals were the main carriers of As, which was proved by a positive correlation between As and Fe or Mn in sediments. Analysis of hydrologic characteristics showed that direct contribution of As from geothermal water to confined groundwater was probably not significant in the Guide basin. Results of laboratory experiments indicated that As release from aquifer sediments was accelerated by increased temperature under different pH and ORP conditions. Raising temperature may stimulate the release of As by promoting dissolutions of As-bearing Fe (hydr)oxides, weathering of As-bearing silicates and As desorption from sediments into groundwater. The research results can not only increase the understanding of arsenic enrichment mechanism in groundwater under geothermal geological background, but also provide a scientific basis for other high-As groundwater with similar geological background in the world.