Ion Concentration In Pore Water Research Articles

Investigation on ion concentration of pore water in compacted bentonite after infiltrated by salt solutions

The behavior of salt solutions infiltrated into compacted bentonite was investigated in this study, with particular attention paid to the ion concentration in the pore water, in order to improve the understanding of the bentonite behavior in geological disposal projects. A Japanese bentonite, Kunigel V1 (K_V1), was used to prepare specimens with a thickness of 2 mm and an initial dry density of 1.4 to 1.7 Mg/m3. For each density case, salt solutions (NaCl, KCl, and CaCl2) of different amounts (0 to 2 mol/L) were supplied to the specimens. After infiltration, the basal spacing (d001) and exchangeable cations of the montmorillonite in the bentonite and the leached cations from the bentonite were measured. Based on the test results, the ion concentration in the interlayer pore water of the montmorillonite or the interparticle pore water was discussed. The findings indicated that the infiltration capacities of the various salt solutions into the compacted K_V1 bentonite were in the order of KCl > CaCl2 > NaCl. The K_V1 specimen with the highest initial dry density exhibited the strongest resistance to salt solution infiltration. After the infiltration of the NaCl solution into the compacted K_V1 bentonite, the increased sodium ions mainly remained in the interparticle pores, leading to an increase in the sodium ion concentration in the interparticle pore water. During the infiltration of the KCl and CaCl2 solutions into the compacted K_V1 bentonite, the infiltrated potassium ions in the case of KC1 and the calcium ions in the case of CaCl2 tended to penetrate the interlayer pore preferentially, thereby displacing the exchangeable sodium ions. After most of the exchangeable sodium ions that had initially existed in the montmorillonite had been replaced, the infiltrated potassium or calcium ions remained in the interparticle pores.

Physical and chemical characteristics analysis of hydrate samples from northern South China sea

In this paper, the gas-hydrate-bearing cores were analyzed for giving a good insight into the exact reserves of natural gas hydrate. The cores were collected from the China National Offshore Oil Corporation (CNOOC) drilling expeditions in 2015 at the LW3-1 area, closed to China's first trial production of natural gas hydrate in 2017. The gas composition of natural gas hydrate and their origin were mainly investigated. The results showed that the gas is mainly methane, up to 98.30%–99.20%. It also contains a small amount of carbon dioxide and other hydrocarbons, which are 0.58%–1.31% CO2, and trace of C2 ~ C4 (less than 0.5%). Gas is generated by mixed-genetic actions dominated by microbial origin. C1 is generated by microbial actions, while C2 is generated by thermogenic actions. Meanwhile, the surface morphology, composition, and distribution of grain size of the host sediments were also studied. The results showed that, the percentage of silty sand is up to 83.57%, where the content of coarse silts is up to 25.12%. There are a preponderance of microfossils and pore structures in the host sediments which consists of silica (SiO2), calcite (CaCO3) and illite, providing a space for the accumulation of gas hydrates. The chloride ion concentration in pore water is 349.09–364.41 mmol/L, which suggested that the hydrate saturation is in a range of 42.81%–45.58% with a good exploitation potential.

A new theory for membrane efficiency coefficient of compacted clay

A new method for calculation the membrane efficiency coefficient w of compacted clay is proposed in this paper. The influence of fixed negative charge on the surface of clay minerals is considered. What’s more, the change of porosity during deformation is considered. Based on the chemical potential of specimens, the true ion concentration in pore-water is obtained. Based on the true ion concentration in pore water, the disjoining pressure considering fixed negative charge inside soils and the change of void ratio is proposed. A new calculation method for the membrane efficiency coefficient of compacted clay is established. The test data of w considering different porosity are calculated and the calculated results are compared with the traditional calculation methods. The new calculation methods of w provide a more physical-based theory for environmental geotechnical engineering.

Formation of authigenic carbonates at a methane seep site in the middle Okinawa Trough, East China Sea

The formation of authigenic carbonates at cold seep is closely related to underlying methane seepage and anaerobic oxidation of methane (AOM), and these processes can be reflected in the geochemical characteristics of pore water in the sediments. In terms of petrological, mineralogical and geochemical analyses of research materials, including authigenic carbonates and pore water samples from the middle Okinawa Trough, East China Sea,these results show that authigenic carbonate minerals are mainly composed of high-magnesium calcite, low-magnesium calcite, dolomite, and iron dolomite and exhibit extremely negative carbon isotopic compositions (δ13C = −52.30‰ to −31.10‰ V-PDB) and positive oxygen isotopic compositions (δ18O = 3.36‰ to 7.27‰ V-PDB). Geochemical analyses of pore water suggest linear sulfate gradients and steep increase of methane and total alkalinity concentrations with depth, which indicate sulfate-induced AOM activities. Based on the sulfate concentration reduction, carbon isotope characteristics of dissolved inorganic carbon (DIC) and increased methane concentration, the sulfate-methane interface (SMI) is considered to be shallow. These data, combined with the variations in ion concentrations in pore water, suggest that the leakage of biogenic methane and intense AOM resulted in the formation of abundant authigenic carbonates, which inherited light carbon (12C)-enriched isotopic signature of methane in the shallow sediments. Combined geochemical characteristics of pore water and authigenic carbonates, intense methane seep activities and associated AOM can be inferred both in present-day and ancient geological records on the western slope of the middle Okinawa Trough.

Coupled THMC models for bentonite in an argillite repository for nuclear waste: Illitization and its effect on swelling stress under high temperature

Subsurface manipulations such as those expected from the disposal of heat-emanating radioactive waste in deep repositories can induce strongly coupled Thermal (T), hydrological (H), mechanical (M) and chemical (C) processes. Adequate coupled THMC models are highly desirable or even indispensable for performance assessment of such repositories, for examples for the analysis of bentonite-based engineered barrier system (EBS) surrounding the emplaced waste. In this study, we present coupled THMC model simulations of a generic nuclear waste repository in an argillite with a bentonite-based buffer. The objective is to evaluate the chemical changes in the EBS bentonite and their effect on mechanical behavior under high temperature, attempting to shed light on whether EBS bentonite can sustain temperatures higher than 100°C without significant impact on barrier's performance.Two scenarios were simulated for comparison: a case in which the temperature near the waste canister peaks at 200°C and a case in which the temperature at the same spot culminate with about 100°C. Simulations for a generic case with Kunigel-VI bentonite as backfill and Opalinus Clay as host rock were conducted for 1000years and reported in the previous study (Zheng et al., 2015). In this paper, simulations for 100,000years have been done for two types of bentonite-based buffer materials: Kunigel-VI and FEBEX bentonite. This enables us to evaluate how different types of bentonite behave in terms of the illitization and its impact on swelling stress and whether we can generalize these results to support decision making. The simulations show the occurrence of illitization in the bentonite buffer and the enhancement of illitization under high temperature. However, FEBEX bentonite undergoes less illitization mainly due to the higher ion concentration in pore water and the lower content of K-feldspar in the bentonite mineral composition. Moreover, the reduction of swelling stress by chemical changes is more pronounced for Kunigel-VI bentonite than for FEBEX bentonite. Overall, the results of our model simulations suggest that an argillite repository with a bentonite-based EBS that is similar to FEBEX bentonite could sustain temperatures much higher than 100°C as far as illitization concerns. Model results also reveal that illitization is stabilized after about 2000years in bentonite near the waste package, but continues in bentonite near the bentonite-argillite interface, which manifests the strong effect of geochemical interaction between EBS bentonite and host rock on long term illitization in bentonite.

Effects of sediment-associated CuO nanoparticles on Cu bioaccumulation and oxidative stress responses in freshwater snail Bellamya aeruginosa.

Copper oxide nanoparticles (CuO-NPs) may pose high ecological risks to aquatic ecosystems. While sediments are the final destinations for CuO-NPs, little is known about the potential ecotoxicity of sediment-associated CuO-NPs on freshwater deposit-feeding macroinvertebrates. The gastropod Bellamya aeruginosa was chosen as an ecotoxicological test species. Adult snails were exposed to Cu (180μg/g dry weight (DW)) added to sediments in the form of CuO-NPs, CuO microparticles (CuO-MPs, size control), and CuSO4 (solubility control) for 7, 14, and 28days, Cu burdens in different tissues and biomarkers of oxidative stress were determined to understand Cu accumulation differences among tissues, potential mechanisms of Cu uptake, time-effect relationships, particle size effects, and the relative contribution of toxicity from CuO-NPs and its soluble Cu ions. There was no difference in Cu ion concentrations in porewaters between the CuO-NPs and CuO-MPs treatments. In addition, relatively low Cu ion concentrations in porewater might indicate their remarkably low solubility. The hepatopancreas and gonad of B. aeruginosa are the primary target tissues for Cu accumulation. Cu accumulation in the hepatopancreas and gonad from CuSO4 treatments was consistently higher than that from the CuO-NPs and CuO-MPs treatments. After long-term exposure, Cu accumulation was higher from CuO-NPs than from CuO-MPs, especially, the Cu accumulation rate from CuO-NPs was greater than that from CuSO4. Short-term exposure to the three Cu forms caused oxidative stress to the hepatopancreas. CuO-MPs did not cause oxidative damage. Long-term exposure to CuO-NPs and CuSO4 resulted in oxidative damage. Overall, prolonged exposure to CuO-NPs will increase the ecotoxicity risk to B. aeruginosa. Although there was no difference in Cu accumulation between the CuO-NPs and CuO-MPs treatments after 14days of exposure, pronounced oxidative damage was caused by exposure to CuO-NPs but not to CuO-MPs, implying that toxicity of CuO-NPs could be attributed to specific nanoparticulate effects.

Influence of soil pH on the toxicity of zinc oxide nanoparticles to the terrestrial isopod Porcellionides pruinosus

The effects of soil pH on the toxicity of ZnO nanoparticles (NPs) to the terrestrial isopod Porcellionides pruinosus were evaluated. Isopods were exposed to a natural soil amended with CaCO3 to reach 3 different pH(CaCl2) levels (4.5, 6.2, and 7.3) and to standard LUFA 2.2 soil (pH 5.5) spiked with ZnO NPs (30 nm), non-nano ZnO (200 nm), and ionic Zn as ZnCl₂. Toxicity was expressed based on total Zn concentration in soil, as well as total Zn and free Zn²⁺ ion concentrations in porewater. Compared with ZnO-spiked soils, the ZnCl₂-spiked soils had lower pH and higher porewater Ca²⁺ and Zn levels. Isopod survival did not differ between Zn forms and soils, but survival was higher for isopods exposed to ZnO NPs at pH 4.5. Median effect concentrations (EC50s) for biomass change showed similar trends for all Zn forms in all soils, with higher values at intermediate pH. Median lethal concentration (LC50) and EC50 values based on porewater Zn or free Zn ion concentrations were much lower for ZnO than for ionic zinc. Zn body concentrations increased in a dose-related manner, but no effect of soil pH was found. It is suggested not only that dissolved or free Zn in porewater contributed to uptake and toxicity, but also that oral uptake (i.e., ingestion of soil particles) could be an important additional route of exposure.

Stable Isotopes Reveal Widespread Anaerobic Methane Oxidation Across Latitude and Peatland Type

Peatlands are an important source of the atmospheric greenhouse gas methane (CH4). Although CH4 cycling and fluxes have been quantified for many northern peatlands, imprecision in process-based approaches to predicting CH4 emissions suggests that our understanding of underlying processes is incomplete. Microbial anaerobic oxidation of CH4 (AOM) is an important CH4 sink in marine sediments, but AOM has only recently been identified in a few nonmarine systems. We used (13)C isotope tracers and followed the fate of (13)C into CO2 and peat in order to study the geographic extent, relative importance, and biogeochemistry of AOM in 15 North American peatlands spanning a ∼1500 km latitudinal transect that varied in hydrology, vegetation, and soil chemistry. For the first time, we demonstrate that AOM is a widespread and quantitatively important process across many peatland types and that anabolic microbial assimilation of CH4-C occurs. However, AOM rate is not predicted by CH4 production rates and the primary mechanism of C assimilation remains uncertain. AOM rates are higher in fen than bog sites, suggesting electron acceptor constraints on AOM. Nevertheless, AOM rates were not correlated with porewater ion concentrations or stimulated following additions of nitrate, sulfate, or ferric iron, suggesting that an unidentified electron acceptor(s) must drive AOM in peatlands. Globally, we estimate that AOM could consume a large proportion of CH4 produced annually (1.6-49 Tg) and thereby constrain emissions and greenhouse gas forcing.

Theoretical Model Study of Micro-Electric Field Effects on Seepage in Micro Particle Clays

Electric charges exist on the clay particle surfaces and induce a micro-electric field which leads to the formation of adsorbed water surrounding clay particles and exerts an influence on the movement pattern of ions in pore water, resulting in the ion effect of seepage in clay. The two factors above will obviously change the characteristics of seepage in micropore of clays. The change of seepage property caused by the factors mentioned above is defined as micro-electric field effect on seepage (MEFES) in clay. The electric potential on the surface of micro particles of clay amounts to tens or hundreds of mV, and then the electric field on the particle surface greatly affects the regulation of seepage. Using theoretical analyses, MEFES in micro particle clays is discussed in this paper. A theoretical model of seepage is proposed for the quantitative description of MEFES. The theoretical model shows the influences of particle surface electric potential, pore sizes, soil conductance, ion concentration in pore water, ion valence , viscosity etc. on seepage characteristics. The equivalent permeability coefficient derived from the theoretical model can be also simplified to that of Darcy’s law without regard to MEFES.

Experiment Probe on Micro-Electric Field Effects on Seepage in Micro Particle Clays

Using laboratory experiment method, the micro-electric field effect on seepage in micro particle clays is discussed in this paper. A series of micro-and mesoscopic parameters and seepage consolidation tests are conducted for the samples of micro particle clays with different ion concentrations in pore water or particle surface electric potentials. The test results show that an increase in particle surface electric potential or a decrease in ion concentration will result in the decrease of equivalent permeability coefficient, consolidation rate and consolidation displacement, revealing the existence of micro-electric field effect on seepage in micro particle clays.

Thermally and chemically induced failure in geomaterials

ABSTRACT Failure conditions in soils occurring during or as a result of heating or by altering their chemical environment appear to be strongly dependent on the history of the application of stress and temperature and or the chemical change. Several cases of such history leading to various modes of failure are identified and interpreted in terms of Thermal and Chemical Cam-Clay models. Particular attention is given to the influence of thermal variability on the coefficient of the critical state, M, or the angle of internal friction. A detailed analysis of the material history offers an explanation of an apparent confusion about whether the soil strength is decreased or increased by temperature. Dependence of failure conditions of clay on the ion concentration in pore water and on its acidity in the context of a landslide trigger mechanism are also discussed.

The influence of superficial deposits on groundwater quality in the Vale of York

Summary Borehole samples were obtained from the glacial, lacustrine and fluviatile sands and clays which overlie the Permo-Triassic sandstone aquifer in the Vale of York. Mineralogical and chemical analyses were undertaken for 26 samples from which pore water was also extracted and analysed. Ion concentrations in pore water were found to change as a function of depth and permeability. Most of the ions present in pore water are thought to be derived from the drift and the source minerals have been identified. The superficial deposits are thought to have an important influence on the chemistry of ground water in the underlying Permo-Triassic sandstones. Comparison with ground water from similar aquifers, but drift free, indicates that in these cases the sandstone exerts an important influence on ground water chemistry.