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1.
It is challenging to predict the degree to which shallow groundwater might be affected by leaks from a CO2 sequestration reservoir, particularly over long time scales and large spatial scales. In this study observations at a CO2 enriched shallow aquifer natural analog were used to develop a predictive model which is then used to simulate leakage scenarios. This natural analog provides the opportunity to make direct field observations of groundwater chemistry in the presence of elevated CO2, to collect aquifer samples and expose them to CO2 under controlled conditions in the laboratory, and to test the ability of multi-phase reactive transport models to reproduce measured geochemical trends at the field-scale. The field observations suggest that brackish water entrained with the upwelling CO2 are a more significant source of trace metals than in situ mobilization of metals due to exposure to CO2. The study focuses on a single trace metal of concern at this site: U. Experimental results indicate that cation exchange/adsorption and dissolution/precipitation of calcite containing trace amounts of U are important reactions controlling U in groundwater at this site, and that the amount of U associated with calcite is fairly well constrained. Simulations incorporating these results into a 3-D multi-phase reactive transport model are able to reproduce the measured ranges and trends between pH, pCO2, Ca, total C, U and Cl− at the field site. Although the true fluxes at the natural analog site are unknown, the cumulative CO2 flux inferred from these simulations are approximately equivalent to 37.8E−3 MT, approximately corresponding to a .001% leak rate for injection at a large (750 MW) power plant. The leakage scenario simulations suggest that if the leak only persists for a short time the volume of aquifer contaminated by CO2-induced mobilization of U will be relatively small, yet persistent over 100 a.  相似文献   

2.
The potential for metal release associated with CO2 leakage from underground storage formations into shallow aquifers is an important consideration in assessment of risk associated with CO2 sequestration. Metal release can be driven by acidification of groundwaters caused by dissolution of CO2 and subsequent dissociation of carbonic acid. Thus, acidity is considered one of the main drivers for water quality degradation when evaluating potential impacts of CO2 leakage. Dissolution of carbonate minerals buffers the increased acidity. Thus, it is generally thought that carbonate aquifers will be less impacted by CO2 leakage than non-carbonate aquifers due to their high buffering potential. However, dissolution of carbonate minerals can also release trace metals, often present as impurities in the carbonate crystal structure, into solution. The impact of the release of trace metals through this mechanism on water quality remains relatively unknown. In a previous study we demonstrated that calcite dissolution contributed more metal release into solution than sulfide dissolution or desorption when limestone samples were dissolved in elevated CO2 conditions. The study presented in this paper expanded our work to dolomite formations and details a thorough investigation on the role of mineral composition and mechanisms on trace element release in the presence of CO2. Detailed characterization of samples from dolomite formations demonstrated stronger associations of metal releases with dissolution of carbonate mineral phases relative to sulfide minerals or surface sorption sites. Aqueous concentrations of Sr2+, CO2+, Mn2+, Ni2+, Tl+, and Zn2+ increased when these dolomite rocks were exposed to elevated concentrations of CO2. The aqueous concentrations of these metals correlate to aqueous concentrations of Ca2+ throughout the experiments. All of the experimental evidence points to carbonate minerals as the dominant source of metals from these dolomite rocks to solution under experimental CO2 leakage conditions. Aqueous concentrations of Ca2+ and Mg2+ predicted from numerical simulation of kinetic dolomite dissolution match those observed in the experiments when the surface area is three to five orders of magnitude lower than the surface area of the samples measured by gas adsorption.  相似文献   

3.
A small scale and temporally limited CO2 injection test was performed in a shallow aquifer to investigate the geochemical impact of CO2 upon such aquifers and to apply and verify different monitoring methods. Detailed site investigation coupled with multiphase simulations were necessary to design the injection experiment and to set up the monitoring network, before CO2 was injected over a ten-day period at three injection wells, at a depth of 18?m below surface level into a quaternary sand aquifer located close to the town of Wittstock in Northeast Germany. Monitoring methods comprised groundwater sampling and standard analyses, as well as trace element analyses and isotope analyses; geoelectrical borehole monitoring; passive samplers to analyse temporally integrated for cations and multi-parameter probes that can measure continuously for dissolved CO2, pH and electrical conductivity. Due to CO2 injection, total inorganic carbon concentrations increased and pH decreased down to a level of 5.1. Associated reactions comprised the release of major cations and trace elements. Geoelectrical monitoring, as well as isotope analyses and multi-parameter probes proved to be suitable methods for monitoring injected CO2 and/or the alteration of groundwater.  相似文献   

4.
In assessing the feasibility of widespread deployment of CO2 geological storage, it is prudent to first assess potential consequences of an error or accident that could lead to CO2 leakage into groundwater resources above a sequestration interval. Information about the sensitivity of the groundwater system to introduction of CO2 is needed in order to design groundwater monitoring program. A laboratory-batch experiment was conducted to explore the range of CO2 impact on groundwater quality of a spectrum of representative aquifers, in the Gulf Coast region, USA. Results show that CO2 elevated concentrations of many cations within hours or days. Two types of cations were recognized according to their concentration trends. Type I cations—Ca, Mg, Si, K, Sr, Mn, Ba, Co, B, Zn—rapidly increased following initial CO2 flux and reached stable concentrations before the end of the experiment. Type II cations—Fe, Al, Mo, U, V, As, Cr, Cs, Rb, Ni and Cu—increased at the start of CO2 flux, but declined, in most cases, to levels lower than pre-CO2 concentrations. Dissolution of dolomite and calcite caused the largest increase in concentrations for Ca, Mg, Mn, Ba and Sr. Cation release rates decreased linearly as pH increased during mineral buffering. Experiment results suggest that carbonate minerals are the dominant contributor of changes in groundwater quality. Risk assessments of potential degradation of groundwater and monitoring strategies should focus on these fast-reacting minerals. Mobilization risk of Type II cations, however, may be self-mitigated because adsorption occurs when pH rebounds.  相似文献   

5.
Practical geologic CO2 sequestration will require long-term monitoring for detection of possible leakage back into the atmosphere. One potential monitoring method is multi-spectral imaging of vegetation reflectance to detect leakage through CO2-induced plant stress. A multi-spectral imaging system was used to simultaneously record green, red, and near-infrared (NIR) images with a real-time reflectance calibration from a 3-m tall platform, viewing vegetation near shallow subsurface CO2 releases during summers 2007 and 2008 at the Zero Emissions Research and Technology field site in Bozeman, Montana. Regression analysis of the band reflectances and the Normalized Difference Vegetation Index with time shows significant correlation with distance from the CO2 well, indicating the viability of this method to monitor for CO2 leakage. The 2007 data show rapid plant vigor degradation at high CO2 levels next to the well and slight nourishment at lower, but above-background CO2 concentrations. Results from the second year also show that the stress response of vegetation is strongly linked to the CO2 sink–source relationship and vegetation density. The data also show short-term effects of rain and hail. The real-time calibrated imaging system successfully obtained data in an autonomous mode during all sky and daytime illumination conditions.  相似文献   

6.
Deep saline aquifers in sedimentary basins are considered to have the greatest potential for CO2 geological storage in order to reduce carbon emissions. CO2 injected into a saline sandstone aquifer tends to migrate upwards toward the caprock because the density of the supercritical CO2 phase is lower than that of formation water. The accumulated CO2 in the upper portions of the reservoir gradually dissolves into brine, lowers pH and changes the aqueous complexation, whereby induces mineral alteration. In turn, the mineralogical composition could impose significant effects on the evolution of solution, further on the mineralized CO2. The high density of aqueous phase will then move downward due to gravity, give rise to “convective mixing,” which facilitate the transformation of CO2 from the supercritical phase to the aqueous phase and then to the solid phase. In order to determine the impacts of mineralogical compositions on trapping amounts in different mechanisms for CO2 geological storage, a 2D radial model was developed. The mineralogical composition for the base case was taken from a deep saline formation of the Ordos Basin, China. Three additional models with varying mineralogical compositions were carried out. Results indicate that the mineralogical composition had very obvious effects on different CO2 trapping mechanisms. Specific to our cases, the dissolution of chlorite provided Mg2+ and Fe2+ for the formation of secondary carbonate minerals (ankerite, siderite and magnesite). When chlorite was absent in the saline aquifer, the dominant secondary carbon sequestration mineral was dawsonite, and the amount of CO2 mineral trapping increased with an increase in the concentration of chlorite. After 3000 years, 69.08, 76.93, 83.52 and 87.24 % of the injected CO2 can be trapped in the solid (mineral) phase, 16.05, 11.86, 8.82 and 6.99 % in the aqueous phase, and 14.87, 11.21, 7.66 and 5.77 % in the gas phase for Case 1 through 4, respectively.  相似文献   

7.
The assessment of the environmental impacts of CO2 geological storage requires the investigation of potential CO2 leakages into fresh groundwater, particularly with respect to protected groundwater resources. The geochemical processes and perturbations associated with a CO2 leak into fresh groundwater could alter groundwater quality: indeed, some of the reacting minerals may contain hazardous constituents, which might be released into groundwater. Since the geochemical reactions may occult direct evidence of intruding CO2, it is necessary to characterize these processes and identify possible indirect indicators for monitoring CO2 intrusion. The present study focuses on open questions: Can changes in water quality provide evidence of CO2 leakage? Which parameters can be used to assess impact on freshwater aquifers? What is the time scale of water chemistry degradation in the presence of CO2? The results of an experimental approach allow selecting pertinent isotope tracers as possible indirect indicators of CO2 presence, opening the way to devise an isotopic tracing tool.The study area is located in the Paris Basin (France), which contains deep saline formations identified as targets by French national programs for CO2 geological storage. The study focuses on the multi-layered Albian fresh water aquifer, confined in the central part of the Paris Basin a major strategic potable groundwater overlying the potential CO2 storage formations. An experimental approach (batch reactors) was carried out in order to better understand the rock–water–CO2 interactions with two main objectives. The first was to assess the evolution of the formation water chemistry and mineralogy of the solid phase over time during the interaction. The second concerned the design of an isotopic monitoring program for freshwater resources potentially affected by CO2 leakage. The main focus was to select suitable environmental isotope tracers to track water rock interaction associated with small quantities of CO2 leaking into freshwater aquifers.In order to improve knowledge on the Albian aquifer, and to provide representative samples for the experiments, solid and fluid sampling campaigns were performed throughout the Paris Basin. Albian groundwater is anoxic with high concentrations of Fe, a pH around 7 and a mineral content of 0.3 g L−1. Macroscopic and microscopic solid analyses showed a quartz-rich sand with the presence of illite/smectite, microcline, apatite and glauconite. A water–mineral–CO2 interaction batch experiment was used to investigate the geochemical evolution of the groundwater and the potential release of hazardous trace elements. It was complemented by a multi-isotope approach including δ13CDIC and 87Sr/86Sr. Here the evolution of the concentrations of major and trace elements and isotopic ratios over batch durations from 1 day to 1 month are discussed. Three types of ion behavior are observed: Type I features Ca, SiO2, HCO3, F, PO4, Na, Al, B, Co, K, Li, Mg, Mn, Ni, Pb, Sr, Zn which increased after initial CO2 influx. Type II comprises Be and Fe declining at the start of CO2 injection. Then, type III groups element with no variation during the experiments like Cl and SO4. The results of the multi-isotope approach show significant changes in isotopic ratios with time. The contribution of isotope and chemical data helps in understanding geochemical processes involved in the system. The isotopic systems used in this study are potential indirect indicators of CO2–water–rock interaction and could serve as monitoring tools of CO2 leakage into an aquifer overlying deep saline formations used for C sequestration and storage.  相似文献   

8.
Proper characterizations of background soil CO2 respiration rates are critical for interpreting CO2 leakage monitoring results at geologic sequestration sites. In this paper, a method is developed for determining temperature-dependent critical values of soil CO2 flux for preliminary leak detection inference. The method is illustrated using surface CO2 flux measurements obtained from the AmeriFlux network fit with alternative models for the soil CO2 flux versus soil temperature relationship. The models are fit first to determine pooled parameter estimates across the sites, then using a Bayesian hierarchical method to obtain both global and site-specific parameter estimates. Model comparisons are made using the deviance information criterion (DIC), which considers both goodness of fit and model complexity. The hierarchical models consistently outperform the corresponding pooled models, demonstrating the need for site-specific data and estimates when determining relationships for background soil respiration. A hierarchical model that relates the square root of the CO2 flux to a quadratic function of soil temperature is found to provide the best fit for the AmeriFlux sites among the models tested. This model also yields effective prediction intervals, consistent with the upper envelope of the flux data across the modeled sites and temperature ranges. Calculation of upper prediction intervals using the proposed method can provide a basis for setting critical values in CO2 leak detection monitoring at sequestration sites.  相似文献   

9.
Geological sequestration of CO2 into depleted hydrocarbon reserviors or saline aquifers presents the enormous potential to reduce greenhouse gas emission from fossil fuels. However, it may give rise to a complicated coupling physical and chemical process. One of the processes is the hydro-mechanical impact of CO2 injection. During the injection project, the increase of pore pressures of storing formations can induce the instability, which finally results in a catastrophic failure of disposal sites. This paper focuses mainly on the role of CO2-saturated water in the fracturing behavior of rocks. To investigate how much the dissolved CO2 can influence the pore pressure change of rocks, acoustic emission (AE) experiments were performed on sandstone and granite samples under triaxial conditions. The main innovation of this paper is to propose a time dependent porosity method to simulate the abrupt failure process, which is observed in the laboratory and induced by the pore pressure change due to the volume dilatancy of rocks, using a finite element scheme associated with two-phase characteristics. The results successfully explained the phenomena obtained in the physical experiments.  相似文献   

10.
Miller field of the North Sea has had high concentrations of natural CO2 for ~70 Ma. It is an ideal analog for the long-term fate of CO2 during engineered storage, particularly for formation of carbonate minerals that permanently lock up CO2 in solid form. The Brae Formation reservoir sandstone contains an unusually high quantity of calcite concretions; however, C and O stable isotopic signatures suggest that these are not related to the present-day CO2 charge. Margins of the concretions are corroded, probably because of reduced pH due to CO2 influx. Dispersed calcite cements are also present, some of which postdate the CO2 charge and, therefore, are the products of mineral trapping. It is calculated that only a minority of the reservoired CO2 in Miller (6–24%) has been sequestrated in carbonates, even after 70 Ma of CO2 emplacement. Most of the CO2 accumulation is dissolved in pore fluids. Therefore, in a reservoir similar to the Brae Formation, engineered CO2 storage must rely on physical retention mechanisms because mineral trapping is both incomplete and slow.  相似文献   

11.
Deep brine recovery enhanced by supercritical CO2 injection is proposed to be a win–win method for the enhancement of brine production and CO2 storage capacity and security. However, the cross-flow through interlayers under different permeability conditions is not well investigated for a multi-layer aquifer system. In this work, a multi-layer aquifer system with different permeability conditions was built up to quantify the brine production yield and the leakage risk under both schemes of pure brine recovery and enhanced by supercritical CO2. Numerical simulation results show that the permeability conditions of the interlayers have a significant effect on the brine production and the leakage risk as well as the regional pressure. Brine recovery enhanced by supercritical CO2 injection can improve the brine production yield by a factor of 2–3.5 compared to the pure brine recovery. For the pure brine recovery, strong cross-flow through interlayers occurs due to the drastic and extensive pressure drop, even for the relative low permeability (k = 10?20 m2) mudstone interlayers. Brine recovery enhanced by supercritical CO2 can successfully manage the regional pressure and decrease the leakage risk, even for the relative high permeability (k = 10?17 m2) mudstone interlayers. In addition, since the leakage of brine mainly occurs in the early stage of brine production, it is possible to minimize the leakage risk by gradually decreasing the brine production pressure at the early stage. Since the leakage of CO2 occurs in the whole production period and is significantly influenced by the buoyancy force, it may be more effective by adopting horizontal wells and optimizing well placement to reduce the CO2 leakage risk.  相似文献   

12.
Among the risks of CO2 storage is the potential of CO2 leakage into overlaying formations and near-surface potable aquifers. Through a leakage, the CO2 can intrude into protected groundwater resources, which can lead to groundwater acidification followed by potential mobilisation of heavy metals and other trace metals through mineral dissolution or ion exchange processes. The prediction of pH buffer reactions in the formations overlaying a CO2 storage site is essential for assessing the impact of CO2 leakages in terms of trace metal mobilisation. For buffering the pH-value, calcite dissolution is one of the most important mechanisms. Although calcite dissolution has been studied for decades, experiments conducted under elevated CO2 partial pressures are rare. Here, the first study for column experiments is presented applying CO2 partial pressures from 6 to 43 bars and realising a near-natural flow regime. Geochemical calculations of calcite dissolution kinetics were conducted using PHREEQC together with different thermodynamic databases. Applying calcite surface areas, which were previously acquired by N2-BET or calculated based on grain diameters, respectively, to the rate laws according to Plummer et al. (Am J Sci 278:179–216, doi:10.2475/ajs.278.2.179, 1978) or Palandri and Kharaka (US Geol Surv Open file Rep 2004–1068:71, 2004) in the numerical simulations led to an overestimation of the calcite dissolution rate by up to three orders of magnitude compared to the results of the column experiments. Only reduction of the calcite surface area in the simulations as a fitting procedure allowed reproducing the experimental results. A reason may be that the diffusion boundary layer (DBL), which depends on the groundwater flow velocity and develops at the calcite grain surface separating it from the bulk of the solution, has to be regarded: The DBL leads to a decrease in the calcite dissolution rate under natural laminar flow conditions compared to turbulent mixing in traditional batch experiments. However, varying the rate constants by three orders of magnitudes in a field scale PHREEQC model simulating a CO2 leakage produced minor variations in the pH buffering through calcite dissolution. This justifies the use of equilibrium models when calculating the calcite dissolution in CO2 leakage scenarios for porous aquifers and slow or moderate groundwater flow velocities. However, the selection of the thermodynamic database has an impact on the dissolved calcium concentration, leading to an uncertainty in the simulation results. The resulting uncertainty, which applies also to the calculated propagation of an aquifer zone depleted in calcite through dissolution, seems negligible for shallow aquifers of approximately 60 m depth, but amounts to 35 % of the calcium concentration for aquifers at a depth of approximately 400 m.  相似文献   

13.
Hyperspectral plant signatures can be used as a short-term, as well as long-term (100-year timescale) monitoring technique to verify that CO2 sequestration fields have not been compromised. An influx of CO2 gas into the soil can stress vegetation, which causes changes in the visible to near-infrared reflectance spectral signature of the vegetation. For 29 days, beginning on July 9, 2008, pure carbon dioxide gas was released through a 100-m long horizontal injection well, at a flow rate of 300 kg day−1. Spectral signatures were recorded almost daily from an unmown patch of plants over the injection with a “FieldSpec Pro” spectrometer by Analytical Spectral Devices, Inc. Measurements were taken both inside and outside of the CO2 leak zone to normalize observations for other environmental factors affecting the plants. Four to five days after the injection began, stress was observed in the spectral signatures of plants within 1 m of the well. After approximately 10 days, moderate to high amounts of stress were measured out to 2.5 m from the well. This spatial distribution corresponded to areas of high CO2 flux from the injection. Airborne hyperspectral imagery, acquired by Resonon, Inc. of Bozeman, MT using their hyperspectral camera, also showed the same pattern of plant stress. Spectral signatures of the plants were also compared to the CO2 concentrations in the soil, which indicated that the lower limit of soil CO2 needed to stress vegetation is between 4 and 8% by volume.  相似文献   

14.
Underground geological storage of CO2 in deep saline aquifers is considered for reducing greenhouse gases emissions into the atmosphere. However, some issues were raised with regard to the potential hazards to shallow groundwater resources from CO2 leakage, brine displacement and pressure build-up. An overview is provided of the current scientific knowledge pertaining to the potential impact on shallow groundwater resources of geological storage of CO2 in deep saline aquifers, identifying knowledge gaps for which original research opportunities are proposed. Two main impacts are defined and discussed therein: the near-field impact due to the upward vertical migration of free-phase CO2 to surficial aquifers, and the far-field impact caused by large-scale displacement of formation waters by the injected CO2. For the near-field, it is found that numerical studies predict possible mobilization of trace elements but concentrations are rarely above the maximum limit for potable water. For the far-field, numerical studies predict only minor impacts except for some specific geological conditions such as high caprock permeability. Despite important knowledge gaps, the possible environmental impacts of geological storage of CO2 in deep saline aquifers on shallow groundwater resources appears to be low, but much more work is required to evaluate site specific impacts.  相似文献   

15.
A field facility located in Bozeman, Montana provides the opportunity to test methods to detect, locate, and quantify potential CO2 leakage from geologic storage sites. From 9 July to 7 August 2008, 0.3 t CO2 day−1 were injected from a 100-m long, ~2.5-m deep horizontal well. Repeated measurements of soil CO2 fluxes on a grid characterized the spatio-temporal evolution of the surface leakage signal and quantified the surface leakage rate. Infrared CO2 concentration sensors installed in the soil at 30 cm depth at 0–10 m from the well and at 4 cm above the ground at 0 and 5 m from the well recorded surface breakthrough of CO2 leakage and migration of CO2 leakage through the soil. Temporal variations in CO2 concentrations were correlated with atmospheric and soil temperature, wind speed, atmospheric pressure, rainfall, and CO2 injection rate.  相似文献   

16.
This study focused on the target injection layers of deep saline aquifers in the Shiqianfeng Fm. in the Carbon Capture and Sequestration (CCS) Demonstration Projects in the Ordos Basin, northwestern China. The study employed a combination method of experiments and numerical simulation to investigate the dissolution mechanism and impact factors of CO2 in these saline aquifers. The results showed (1) CO2 solubility in different types of water chemistry were shown in ascending order: MgCl2-type water < CaCl2-type water < Na2SO4-type water < NaCl-type water < Na2CO3-type water < distilled water. These results were consistent with the calculated results undertaken by TOUGHREACT with about 5% margin of error. CO2 solubility of Shiqianfeng Fm. saline was 1.05 mol/L; (2) compared with distilled water, the more complex the water’s chemical composition, the greater the increase in HCO3 ?concentration. While the water’s composition was relatively simple, the tested water’s HCO3 ?concentrations were in close accord with the calculated value undertaken by the TOUGHREACT code, and the more complex the water’s composition, the poorer the agreement was, probably due to the complex and unstable HCO3 ? complicating matters when in an aqueous solution system including both tested HCO3 ?concentration and calculated HCO3 ?concentration; (3) the CO2 solubility in the saline at the temperature conditions of 55 °C and 70 °C were 1.17 and 1.02 mol/L. When compared with the calculated value of 1.20 and 1.05 mol/L, they were almost the same with only 1 and 3% margin of error; concentrations of HCO3 ? were 402.73 mg/L (0.007 mol/L) and 385.65 mg/L (0.006 mol/L), while the simulation results were 132.16 mg/L (0.002 mol/L) and 128.52 mg/L (0.002 mol/L). From the contrast between the tested data and the calculated data undertaken by the TOUGHREACT code, it was shown that TOUGHRACT code could better simulate the interaction between saline and CO2 in the dissolution sequestration capacity. Therefore, TOUGHREACT code could be used for the inter-process prediction of CO2 long-term geological storage of CO2; (4) The Ca2+ concentration and SO4 2?concentration in saline water had less effect on the solubility of CO2 and HCO3 ?concentration. In addition, TDS and pH values of saline affected not only the solubility of CO2, but also the conversion of CO2 to HCO3 ? due to that they can affect the activity and acid-base balance. So in fact, we just need to consider that the TDS and pH values are main impact factors in the dissolution sequestration capacity of CO2 geological sequestration in deep saline aquifers.  相似文献   

17.
CO2 is a greenhouse gas, whose emissions threaten the existence of human beings. Its inherently safe sequestration can be performed via CO2 mineralization, which is relatively slow under natural conditions. In this work, an energy-saving membrane electrolysis technique was proposed for accelerating the CO2 mineralization of wollastonite into SiO2 and CaCO3 products. The electrolysis process involved splitting NH4Cl into HCl and NH3·H2O via hydrogen oxidation and water reduction at the anode and cathode of the electrolytic system, respectively. In contrast to the chlor-alkali electrolysis, this method did not involve Cl? oxidation and the standard potential of the anode was reduced. Additionally, NH4Cl was used as the electrolyte instead of NaCl; as a result, the generation of NH3·H2O instead of NaOH occurred in the catholyte and the cathodic pH dramatically decreased, thus reducing the cathodic potential for hydrogen evolution. The observed changes led to a 73.5% decrease in the energy consumption. Moreover, after the process of CO2 mineralization was optimized, SiO2 with a specific surface area of 221.8 m2 g?1 and CaCO3 with a purity of 99.9% were obtained.  相似文献   

18.
The rates of Fe(II) oxidation and precipitation from groundwater are highly pH dependent. Elevated levels of dissolved CO2 can depress pH and cause difficulty in removing dissolved Fe and associated metals during treatment of ferruginous water. This paper demonstrates interdependent changes in pH, dissolved inorganic C species, and Fe(II) oxidation rates that occur as a result of the removal (degassing) of CO2 during aeration of waters discharged from abandoned coal mines. The results of field monitoring of aeration cascades at a treatment facility as well as batchwise aeration experiments conducted using net alkaline and net acidic waters in the UK are combined with geochemical modelling to demonstrate the spatial and temporal evolution of the discharge water chemistry. The aeration cascades removed approximately 67% of the dissolved CO2 initially present but varying the design did not affect the concentration of Fe(II) leaving the treatment ponds. Continued removal of the residual CO2 by mechanical aeration increased pH by as much as 2 units and resulted in large increases in the rates of Fe(II) oxidation and precipitation. Effective exsolution of CO2 led to a reduction in the required lime dose for removal of remaining Fe(II), a very important factor with regard to increasing the sustainability of treatment practices. An important ancillary finding for passive treatment is that varying the design of the cascades had little impact on the rate of CO2 removal at the flow rates measured.  相似文献   

19.
About 500 well and spring waters were collected on an approximately 1-km spacing in an area centered on six small U and Cu-U occurrences near Monticello, N.Y., as an orientation survey in the NURE program. Rocks of the area belong to the Devonian Catskill Group and are predominantly red sandstones and shales of fluvial origin. The sediments dip 0–5° in the main part of the area, but steepen to 45° in the east. The ground waters were analyzed for 46 elements plus several other water properties.An R-mode factor analysis extracted 10 factors. The strongest factor, termed “Dissolved solids”, has heavy loadings on most major elements, plus U, B, Li, Sr, and Zn. This factor is attributed to varying degrees of interaction between original rainwater and rocks. Recognition of anomalies for elements loaded on this factor is aided by evaluation of ratios or plots against total dissolved solids or conductivity. Three weaker factors apparently represent admixtures with two types of deep brine and with waters of enhanced Fe-Mn resulting from reducing conditions. Other factors include an assemblage of insoluble trace metals and a Zn-Cu-P factor, both possibly related to contamination and/or analytical problems, a rare earth group, and an Se-As-Ag factor. The waters are clearly complex mixtures of effects.The geographic distribution of high U values shows some correlation with the distribution of U occurrences, but many equally high values occur outside the known mineralized area. When the data are projected to a vertical section normal to the strike, high U values define two gently dipping aquifers. The upper anomalous aquifer contains the known occurrences but extends downdip. Samples within this aquifer show patterns in U, dissolved O2, and conductivity, apparently related to influx of fresh water from updip, along major rivers, and along possible fractured zones. High He values are also most numerous near the occurrences and define the deeper U-rich aquifer. The interpretation of the data is greatly clarified by separation of individual aquifers.Saturation indices are generally −3.4 to −5 and show patterns similar to dissolved U, except for values of −6 to −9 in a few samples with high phosphate. Predominant U species are usually UO2(CO3)22−, or less commonly UO2CO30 or UO2(HPO4)22−.  相似文献   

20.
The CO2 migrated from deeper to shallower layers may change its phase state from supercritical state to gaseous state (called phase transition). This phase transition makes both viscosity and density of CO2 experience a sharp variation, which may induce the CO2 further penetration into shallow layers. This is a critical and dangerous situation for the security of CO2 geological storage. However, the assessment of caprock sealing efficiency with a fully coupled multi-physical model is still missing on this phase transition effect. This study extends our previous fully coupled multi-physical model to include this phase transition effect. The dramatic changes of CO2 viscosity and density are incorporated into the model. The impacts of temperature and pressure on caprock sealing efficiency (expressed by CO2 penetration depth) are then numerically investigated for a caprock layer at the depth of 800 m. The changes of CO2 physical properties with gas partial pressure and formation temperature in the phase transition zone are explored. It is observed that phase transition revises the linear relationship of CO2 penetration depth and time square root as well as penetration depth. The real physical properties of CO2 in the phase transition zone are critical to the safety of CO2 sequestration. Pressure and temperature have different impact mechanisms on the security of CO2 geological storage.  相似文献   

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