Applied Geochemistry最新文献

The current study is devoted to the determination of the SIT coefficients at 298.15 K for interactions, involving $C{O}_2\left(\text{aq}\right)$, $\text{HC}{O}_3^{-}$, and $C{O}_3^{2‐}$, with mostly Na⁺ and K⁺ ions. The SIT model is a simple yet physically sound model for activity coefficients in aqueous solutions, that has just one parameter for each cation-anion or a dissolved gas – electrolyte interaction. Among the issues that were met for carbonate systems are the side reactions of hydrolysis and disproportionation in the carbonate solutions, that complicate the analysis of data and lead to unusually large difference, up to 9%, in the values of activity coefficients, determined in different authoritative laboratories. For ${\text{Na}}_{2}C{O}_3$ and $K_{2}C{O}_3$ solutions, it was necessary to take into account the reaction of formation of the ionic pair $M^{+}+C{O}_3^{2‐}=\text{MC}{O}_3^{-}$, with the equilibrium constants ${\beta }_1^o$ equal to ${\log }_{10}{\beta }_1^o=$ 0.75 ± 0.08 for $M^{+}=N{a}^{+}$ and to ${\log }_{10}{\beta }_1^o=$ 0.67 ± 0.11 for $M^{+}=K^{+}$. In all, there are values for more than 20 binary SIT interaction coefficients. All results are valid at 298.15 K, 0.1 MPa.

The Quaternary sediments preserved within the Thirlmere Lakes system, Greater Blue Mountains World Heritage Area, Australia, are an important regional environmental record representing at least the last two interglacials. Understanding the source and evolution of these sediments, both temporally and spatially, is an essential component of the site's reconstruction. In this study, we evaluate this question using physical, mineralogical, elemental, and isotopic analytical techniques. Four distinct lake sediment facies all show bi-modal distributions of coarse sand and clay to fine silts, representing various mixtures of catchment Hawkesbury Sandstone and Ashfield Shale. Clays are predominantly kaolinite-dickite, however, the 7 Å dehydrated form of halloysite is prominent in an orange-yellow oxidised lake facies unit. The relative distribution and concentration of rare earth elements, including yttrium (REY), is heterogeneous across all the lake facies, varying between both lakes and with depth. This variability suggests a geochemical signature reflecting a combination of mixed sources and secondary mineral precipitation, driven by catchment geomorphology and specific site conditions. Slightly positive Ce anomalies in the oxidised lake facies, combined with the greater halloysite representation, represents a period of dry conditions and sub-aerial exposure. Evaluation of catchment, regional and continental REY ratios, Eu anomalies and εNd data implies a predominant internal catchment source signature, with any external contributions restricted to the local Bringelly Shale and the immediate south-eastern Australia, including the Murray River Basin. Geochemical and isotopic values for these proposed internal and external sediment sources predicts that an aeolian source from outside the immediate catchment represents a maximum of 30% of the fine-grained sediment fraction.

Tangquan hot springs is one of the three well-known geothermal systems in Nanjing, Jiangsu Province, eastern China. Previous studies have shown its high flow rate and ideal water chemistry favorable for utilization. Here we further examine the potential of the hot springs using gas geochemistry in this paper. 35 water samples and 16 gas samples were collected for chemical isotopic analyses. The geothermal gases are found to be primarily atmospheric in origin, containing high nitrogen, oxygen and carbon dioxide gases. Carbon isotope shows that the origin of CO₂ and CH₄ are thermal metamorphic in the upper crust. The isotope ratio of helium is 3.47–4.73 Ra, indicating that mantle He accounts for 44–60% in total of geothermal gases. These findings furnish the grounds to infer geothermal potential at the deeper part of the geothermal system. The immediate geothermal reservoir has a temperature of 90 °C, but the temperature of deeper part of the system could reach 150–205 °C, using the carbon gas isotope geothermometer. These findings show a promising future of deep geothermal resources in the region.

Cementitious matrices are considered for the immobilisation of radioactive aluminium. The processes occurring at the interface between both materials are relevant for the long-term stability of the repository. The present study compares Ordinary Portland cement (OPC), CEM I-type, with alternative Portland blended cement (CEM IV and CEM I + 50% silica fume) and magnesium potassium phosphate cement (MKPC). Al A1050 and Al AA5754, with 3.5% Mg, have been used as reactive metal alloys. Two exposure conditions were employed: (1) water immersion and (2) isolated in sealed plastic films. Long-term corrosion monitoring (E_corr, i_corr and V_corr) was evaluated to understand the effect of Al reactivity in the matrix. The associated H₂ release was quantified to understand the changes at the metal/matrix interface. Furthermore, pore ion concentrations and the pore microstructure were evaluated. The metal/matrix interface alterations were analysed at the end of the tests. The study revealed that after 300 days of water immersion, the CEM I + 50% of silica fume matrix had reduced the pore solution pH down to 10.5 compared to CEM I, which remained high alkaline (pH 12.9), and CEM IV with no significant decreases (pH 12.3). In contrast, MKPC showed the lowest pH (7–9.8). Low Al corrosion rates were found with MKPC, followed by CEM I + 50% SF according to their lower pH. A corrosion product layer of 90-50 μm thickness was observed at the Al/CEM I matrix interface constituted of aluminium and oxygen. Furthermore, enrichment in Al was detected in the matrix (around 1 mm depth), causing the formation of ettringite nodules. Voids were detected at the interface level associated with the high volume of H₂ released. The MKPC matrix showed no alteration at the metal/matrix interface due to the lower reactivity of the matrix and lower H₂ release. A homogeneous and dense region (30 μm) rich in phosphorous, potassium and magnesium was observed near the metal surface.

The significance of examining groundwater quality is highlighted by the fact that 75% of the European Union population relies on groundwater for their water supply. In the Republic of Serbia, over 50% of the groundwater used for public water supply comes from alluvial aquifers, with 80–90% of this water originating from river water infiltration. This study investigates the origin of increased ammonium concentrations (up to 4.7 mgN/l) in the Danube alluvial aquifer near Kovin-Dubovac area, Serbia, a potential future regional water supply source surrounded by intensive agricultural production and an open coal mine. Comprehensive research involved statistical processing of physicochemical data (13 parameters from 33 sampling sites), isotopic analyses (δ¹⁵N–NH₄ – 12 samples; δ³⁴S–SO₄, δ¹⁸O–SO₄ in 5 samples), and microbiological tests (denitrifying, sulphate-reducing, iron-related, and heterotrophic aerobic bacteria in 15 samples). Factor analysis revealed significant positive loadings (>0.5) among indicators of autochthonous organic matter origin (Fe²⁺, Fe_tot, and TOC), geological matrix components (Na, H₂S, Cl), and groundwater state parameters (pH, Eh, and NH₄⁺). This multifaceted approach and the spatial concentration gradients of parameters associated within extracted principal components revealed the predominance of two NH₄⁺ sources. The riparian zone is characterized by sediment organic matter mineralization, increased iron content, and natural ammonium origin (δ¹⁵N–NH₄⁺ from +4.82‰ to +6.93‰) accompanied by conditions suitable for DNRA and sulphate reduction. Approaching to the hinterland lower iron and total organic matter content, accompanied by increased redox values revealed the signature of fertilizers application (δ¹⁵N–NH₄⁺ −0.84‰ and −0.33‰), associated with denitrification influence. This multifaceted approach reduces ambiguity, providing a clearer interpretation of results when discerning the origin of nitrogen and aquifer potential for nitrogen loss or conservation in a reducing groundwater environment.

Globally, groundwater contamination by fluoride (F⁻) is a threat to the safe drinking water supply. Nevertheless, our understanding of the geochemical processes of F⁻ mobilization to the groundwater by linking groundwater and aquifer material chemistry is limited. We therefore characterized that in the hard-rock aquifers of Central India, an area that has not been investigated thoroughly despite the known severity of the problem. Exploratory drilling of boreholes (n = 45) and lithostratigraphic modeling identified weathered basalt, vesicular basalt, fractured basalt, sandstone of Lameta, and fractured granite as major aquifers in the study area. The groundwater contamination by F⁻ (concentration >1.5 mg/L) mainly occurred at depths >35 m bgl (at elevations <500 m amsl) of the fractured basalt and fractured granite aquifers, while samples collected from the shallow basalt, sandstone of Lameta, and shallow granite were mostly safe. The F⁻ contamination of groundwater was primarily governed by the chemical evolution of groundwater along the flow path. Solute mass balance in groundwater, in conjunction with the mineralogical characterization of the aquifer materials, suggests that weathering of silicate and carbonate minerals was the dominant form of mineral dissolution in aquifers, which consumed dissolved CO₂ along the flow path and resulted in an alkaline pH (>8) in groundwater of the deeper aquifers. The mobilization of F⁻ in the groundwater could primarily be attributed to the ion exchange between OH⁻ in water and structural F⁻ in fluorapatite and F-bearing mica/amphibole. By assessing water quality and aquifer properties, this study suggests that primarily, the sandstone of Lameta and weathered and vesicular basalts can be targeted for F-safe drinking water supply in the study area. Targeting shallow aquifers can be an option for F-safe drinking water supply in other affected areas with similar geological and environmental settings.

This study investigates contemporary freshwater contamination originating from old mine workings in the Thames-Coromandel region of Te Ika-a-Māui (North Island), Aotearoa New Zealand. We employed a multi-method approach, including stable H and O isotope determinations of surface water, geochemical modelling, and diffusive gradients in thin films (DGT) deployments. Atypically, spring-summer (Sept–Nov) surface water stable oxygen isotope ratios (δ¹⁸O) were negatively displaced from meteoric values (ca. −0.28 ± 0.13 ‰), indicating a remarkable degree of low-temperature water-rock interaction, likely enhanced by dry antecedent conditions. Isotope ratios in tributaries showed less alteration than the main stem, suggesting greater meteoric inputs and shorter residence times in areas of high topographic relief. Conversely, in the main stem, isotope ratios revealed higher mineral weathering, accompanied by elevated dissolved metal concentrations, consistent with dominant inputs from shallow groundwater. Weathering of primary sulfides contributed pronounced acidity in one tributary (pH ca. 3.8), but overall, carbonate buffering ameliorated acid mine drainage across the catchment (pH ca. 7–8). Nevertheless, our results confirm exceedances of ecological guideline values (>80% protection threshold) for several toxic metals including Al, Zn, Cd and Pb; with implications for fresh and coastal water quality in Tikapa Moana-o-Hauraki, the Firth of Thames.

Geochemical primary halos play a crucial role in mineral exploration as they provide valuable insights into the dispersion of ore materials, identification of concealed deposits, and determination of ore deposit dimensions. The Naruo mining area in the Duolong mineral district, northern Tibet, China well-known for its worldclass porphyry-epithermal Cu–Au deposits is currently chosen as the study area. We employ statistical and nonlinear methods to analyze geochemical data from drill holes. Specifically, R-type cluster analysis is utilized to evaluate element affinity and concentration index, while an improved Grigorian zoning index is employed to delineate the vertical zoning sequence of the primary halo. These methodologies significantly enhance our understanding of element enrichment within geological contexts and greatly contribute to mineral resource evaluation. Based on these results, we have constructed a vertical zonation index model of denudation coefficient tailored to the geological characteristics of mineralization within the study area. This model effectively represents the vertical variation of the ore body. Our findings reveal a decrease in this zoning index towards the central region of deep ore bodies which correlates with deep granodiorite porphyry occurrences. Furthermore, we observe increasing concentrations of Cu, Ag, and Au with depth in specific sections of drill holes indicating promising exploration potential. Supplementary short-wave infrared data suggests the presence of a deep hydrothermal center in drill hole RNZK2404 which tentatively infers concealed porphyry bodies. Notably, the reversal observed at 4200 m on RNZK2404's zoning index hints at a possible hidden ore body at great depths. Finally, three-dimensional visualization techniques effectively illustrate spatial patterns for elements thereby paving way for future endeavors in mineral exploration.

The transport parameters of radionuclides, the diffusion coefficient and the retardation factor, in clay-rich host rocks investigated for deep geological disposal, can be determined using various types of laboratory experiments. The present study aimed at comparing three types of laboratory experiments commonly used in the context of radioactive waste for the determination of the transport properties of two non-reactive tracers, HTO and ¹²⁵I, in Boom Clay. Two Boom Clay samples with orientation parallel and perpendicular to the bedding were selected to assess the role of sample heterogeneity and anisotropy. Each sample/orientation was subjected to through-diffusion experiments, pulse injection experiments with pressure differences over the clay core ranging from 5 to 19 bars and a back-to-back experiment.

In the case of HTO, the three types of experiments led to a consistent set of transport parameters for each Boom Clay sample. Over the three types of experiment, the average apparent diffusion coefficients and accessible porosity vary at maximum a factor 1.4 and 1.3, respectively for a same sample type/orientation. The porosity accessible to HTO was similar to the porosity calculated from the water content. In the case of ¹²⁵I, the three types of experiments also showed consistency for the determination of the apparent diffusion coefficients with values varying within a factor 1.7 for the same sample type/orientation. However, variation in accessible porosity between the experiments revealed a physical modification of the Boom Clay sample occurring during the pulse injection experiments and affecting ¹²⁵I transport.

Transport anisotropy was consistently observed in all the types of experiment and for both HTO and ¹²⁵I with a higher anisotropy observed in the samples richer in clay. Slightly higher total porosity and lower ¹²⁵I accessible porosity were noticed in the clay-rich samples in comparison to silt-rich samples.