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1.
Weathering processes affecting pyritic wastes may generate huge amounts of acid waters with high concentrations of potentially toxic contaminants (acid mine drainage). Acid mine drainage is mainly produced in the vadose zone. In the present study, a coupled non-isothermal multiphase flow and reactive transport model of the vadose zone of sulfide mine tailings was developed. The geochemical model included kinetically controlled reactions for Fe(II)-oxidation and for the dissolution of sulfide and aluminosilicate phases and the Pitzer ion-interaction model to describe the behavior of the pore-water solutions. Model results were compared with experimental observations in unsaturated column experiments under strongly evaporative conditions similar to arid or semiarid climates. Evolution trends for temperature, water saturation, evaporation rates, pore-water hydrochemistry and mineral phases observed during the drying experiment were adequately reproduced. The coupled model reproduced the increase of solute concentrations in the column top and the precipitation of a crust of secondary mineral phases. This crust became a barrier for water vapour diffusion to the atmosphere and modified the thermohydraulic behavior of the tailings. Enhanced downward migration of water vapour and its condensation in this colder end of the column were correctly taken into account by the model, which reproduced the dilution observed in the lower part of the column during the experiments.  相似文献   

2.
地震作用下尾矿坝有液化失稳的危险,尾矿动孔压的演化规律可以间接体现其液化过程。为研究尾矿动孔压的演化规律,开展了一系列的动三轴试验。结果表明：尾矿动孔压演化具有明显的阶段性,在等压固结时可用S形反正弦函数曲线描述,在偏压固结时可用J形指数函数曲线描述;尾矿材料在等压固结条件下临界孔压接近于围压,在偏压固结条件下临界孔压小于围压,且随围压及固结应力比的增大而减小,随尾矿平均粒径的增大而增大。基于极限平衡理论推导了等压固结和偏压固结条件下的临界孔隙水压力方程,从理论上阐释了试验结果所揭示的动孔压演化规律,可以为地震区上游式尾矿坝的抗震设计提供参考。  相似文献   

3.
. This paper deals with sorption and anaerobic biodegradation of the soluble aromatic fraction of jet fuel and how it is influenced by pore-water velocity during transport in a groundwater aquifer. The study was carried out as controlled laboratory column experiments. A binary mixture of toluene and 1,2,4-trimethylbenzene with a concentration ratio of 2:1 was used through the entire investigations. The column experiments were conducted with contaminated sediments and groundwater, taken from wells at a field research site. The columns were operated anaerobically under continuous-flow conditions at 10 °C in a temperature-controlled refrigerator. Two percent sodium azide was added to the injection solution of two of the columns to prevent biodegradation of the studied organic mixture. Chloride was used as a conservative tracer to characterize the hydrodynamic parameters such as dispersivity and porosity of the columns. The results showed that both compounds in the mixture were attenuated because of sorption and biodegradation processes in the columns. 1,2,4-trimethylbenzene was attenuated more significantly than toluene. Biodegradation of toluene was coupled mainly with the microbial reduction of ferric iron, whereas 1,2,4-trimethylbenzene, in contrast, was mostly sorbed. Their sorption and biodegradation were studied with different pore-water velocities, and a mass balance approach was applied to calculate biodegradation rates. The biodegradation rates of toluene were –0.16, –0.21, and –0.26 (unit: mM day–1) for pore-water velocities of 96, 82.4, and 54.9 (unit: cm day–1), respectively. This indicates that a decrease in the pore-water velocity significantly enhanced the biodegradation of toluene, consistent with other reports in the literature. For 1,2,4-trimethylbenzene the biodegradation rates were –0.05, –0.13 (unit: mM day–1) for pore-water velocities of 96 and 82.4 (unit: cm day–1), respectively. The biodegradation rate of 1,2,4-trimethylbenzene did not increase at the lowest pore water velocity as expected. This might be a result of substrate competition.  相似文献   

4.
Microbial sulfidogenesis plays a potentially important role in Fe and As biogeochemistry within wetland soils, sediments and aquifers. This study investigates the specific effects of microbial sulfidogenesis on Fe mineralogy and associated As mobility in mildly acidic (pH 6) and mildly basic (pH 8) advective-flow environments. A series of experiments were conducted using advective-flow columns, with an initial solid-phase comprising As(III)-bearing ferrihydrite-coated quartz sand. Columns for each pH treatment were inoculated with the sulfate-reducing bacteria Desulfovibrio vulgaris, and were compared to additional abiotic control columns. Over a period of 28 days, microbial sulfidogenesis (as coupled to the incomplete oxidation of lactate) caused major changes in Fe mineralogy, including replacement of ferrihydrite by mackinawite and magnetite at the in-flow end of the inoculated columns. At pH 8, the Fe2+ produced by electron transfer between sulfide and ferrihydrite was mainly retained near its zone of formation. In contrast, at pH 6, much of the produced Fe2+ was transported with advecting groundwater, facilitating the downstream Fe2+-catalyzed transformation of ferrihydrite to goethite. At both pH 6 and pH 8, the sulfide-driven reductive dissolution of ferrihydrite and its replacement by mackinawite at the in-flow end of the inoculated columns resulted in substantial mobilization of As into the pore-water. At pH 8, this caused the downstream As concentrations within the inoculated columns to be greater than the corresponding abiotic column. However, the opposite occurred under pH 6 conditions, with the Fe2+-catalyzed transformation of ferrihydrite to goethite in the inoculated columns causing a decrease in downstream As concentrations compared to the abiotic column. Although thermodynamically favorable at intermediate times and depth intervals within the inoculated columns, solid As sulfide phases were undetectable by As XANES spectroscopy. Our findings show that microbial sulfidogenesis can trigger significant As mobilization in subsurface environments with advective groundwater flow. The results also demonstrate that formation of mackinawite by sulfidization of ferric (hydr)oxides is not effective for the immobilization of As, whereas the Fe2+-catalyzed transformation of ferrihydrite to goethite under mildly acidic conditions may mitigate As mobility.  相似文献   

5.
This study appraised the use of phosphate fertilisers in immobilising metals in mine tailings to prevent their uptake into Curly Mitchell grass (Astrebla lappacea), when grown on capped, phosphate-amended tailings. Leaching experiments showed that Pb mobility was reduced by both bone meal and superphosphate amendment. Bone meal amendment also reduced Cd mobility. By contrast, Cd, Mn and Zn mobility increased in superphosphate-amended tailings due to increased acid production and, Cu was mobilised in bone meal-amended tailings possibly through the formation of soluble metal-complexing organic compounds. Arsenic and Sb were mobilised in both treatments due to phosphate ligand exchange. Greenhouse trials used Curly Mitchell grass grown on 1-m-high columns stacked with waste materials and different amendments overlain by clean topsoil. Curly Mitchell grass showed substantial uptake of Cd, Mn, Pb and Zn from unamended tailings and waste rock, where these were penetrated by the plant’s root system. Addition of phosphate fertilisers to the surface of tailings did not result in reduced metal uptake by Curly Mitchell grass. In tailings capped with limestone, the limestone layer formed an effective physical barrier preventing root penetration into the tailings and led to substantially reduced metal uptake in grass. The study demonstrates that thorough mixing of waste materials and fertilisers as well as irrigation may be required for successful phosphate immobilisation of metals in base metal tailings. Alternatively, the placement of a thin layer of crushed limestone on top of the tailings pile prior to capping may lead to the formation of a chemical and physical barrier and prevent the transfer of environmentally significant elements into the above-ground biomass of Mitchell grasses.  相似文献   

6.
Mine tailings discharged to river systems have the potential to release significant quantities of major and trace metals to waters and soils when weathered. To provide data on the mechanisms and magnitudes of short- and long-term tailings weathering and its influence on floodplain environments, three calendar year-long column leaching experiments that incorporated tailings from Potosí, Bolivia, and soil from unaffected downstream floodplains, were carried out. These experiments were designed to model 20 cycles of wet and dry season conditions. Two duplicate columns modeled sub-aerial tailings weathering alone, a third modeled the effects of long-term floodplain tailings contamination and a fourth modeled that of a tailings dam spill on a previously contaminated floodplain. As far as was practical local climatic conditions were modeled. Chemical analysis of the leachate and column solids, optical mineralogy, XRD, SEM, EPMA, BCR and water-soluble chemical extractions and speciation modeling were carried out to determine the processes responsible for the leaching of Al, Ca, Cu, K, Na, Mg, Mn, Sn, Sr and Ti. Over the 20 cycles, the pH declined to a floor of ca. 2 in all columns. Calcium, Cu, Mg, Mn and Na showed significant cumulative losses of up to 100%, 60%, 30%, 95% and 40%, respectively, compared to those of Al, K, Sr, Sn and Ti, which were up to 3%, 1.5%, 5%, 1% and 0.05%, respectively. The high losses are attributed to the dissolution of relatively soluble minerals such as biotite, and oxidation of chalcopyrite and Cu-sulfosalts, while low losses are attributed to the presence of sparingly soluble minerals such as svanbergite, cassiterite and rutile. These results strongly suggest that the release of tailings to floodplains should be limited or prohibited, and that all tailings should be removed from floodplains following dam spills.  相似文献   

7.
Historical gold mining operations in Nova Scotia, Canada, resulted in numerous deposits of publicly accessible, arsenic (As)-rich mine waste that has weathered in situ for 75–150 years, resulting in a wide range of As-bearing secondary minerals. The geochemical heterogeneity of this mine waste creates a challenge for identifying a single remediation approach that will limit As mobility. A 30-cm-thick, low-organic content soil cover was evaluated in a laboratory leaching experiment where, to simulate natural conditions, the equivalent of 2 years of synthetic rainwater was leached through each column and two dry seasons were incorporated into the leaching protocol. Each column was a stratigraphic representation of the four major tailings types found at the historical Montague and Goldenville gold mine districts: hardpan tailings, oxic tailings, wetland tailings, and high Ca tailings. Hardpan tailings released acidic, As-rich waters (max 12 mg/L) under the soil cover but this acidity was buffered by surrounding oxic tailings. Leachate from the oxic tailings was circumneutral, with average As concentrations between 4.4 and 9.7 mg/L throughout the experiment. The presence of carbonates in the high Ca tailings resulted in near-neutral to weakly alkaline leachate pH values and average As concentrations between 2.1 and 6.1 mg/L. Oxidation of sulfides in the wetland tailings led to acidic leachate over time and a decrease in As concentrations to values that were generally less than 1 mg/L. This study shows that the use of a low-organic content soil cover does not create reducing conditions that would destabilize oxidized, As-bearing secondary phases in these tailings. However, oxygen penetration through the cover during dry seasons would continue to release As to tailings pore waters via sulfide oxidation reactions.  相似文献   

8.
尾矿料的动力特性试验研究   总被引：10，自引：0，他引：10  
通过对某铜矿的尾矿料进行动三轴和共振柱试验,研究了尾矿材料动力变形特性,提出了简单实用的孔隙水压力模型,给出了能更加准确地预测尾矿材料的动孔隙水压力的公式,并将其与Seed提出的预测公式进行了比较。在不同密度尾矿料的动三轴试验基础上,分析了相对密度对液化特性的影响,得出了相对密度小于70 %时抗液化强度随相对密度的增加而明显增加的结论。在不同围压下进行动三轴试验,结果表明：在相同的液化振次条件下,围压越高,动剪应力比越低。由共振柱试验可知,尾矿料的阻尼比随着动剪应变幅的增大而增大,而动剪模量随动剪应变幅的增大而减小,动剪模量和阻尼比与动剪应变幅的关系受围压影响不太敏感。  相似文献   

9.
 The oxidation and the subsequent dissolution of sulfide minerals within the Copper Cliff tailings area have led to the release of heavy metals such as Fe, Ni, and Co to the tailings pore water. Dissolved concentrations in excess of 10 g/l Fe and 2.2 g/l Ni have been detected within the shallow pore water of the tailings, with increasing depth these concentrations decrease to or near analytical detection limits. Geochemical modelling of the pore-water chemistry suggests that pH-buffering reactions are occurring within the shallow oxidized zones, and that secondary phases are precipitating at or near the underlying hardpan and transition zones. Mineralogical study of the tailings confirmed the presence of goethite, jarosite, gypsum, native sulfur, and a vermiculite-type clay mineral. Goethite, jarosite, and native sulfur form alteration rims and pseudo-morphs of the sulfide minerals. Interstitial cements, composed of goethite, jarosite, and gypsum, locally bind the tailings particles, forming hardpan layers. Microprobe analyses of the goethite indicate that it contains up to 0.6 weight % Ni, suggesting that the goethite is a repository for Ni. Other sinks detected for heavy metals include jarosite and a vemiculite-type clay mineral which locally contains up to 1.6 weight % Ni. To estimate the mass and distribution of heavy metals associated with the secondary phases within the shallow tailings, a series of chemical extractions was completed. The experimental design permitted four fractions of the tailings to be evaluated independently. These four fractions consisted of a water-soluble, an acid-leachable, and a reducible fraction, as well as the whole-rock total. Twenty-five percent of the total mass of heavy metals was removed in the acid-leaching experiments, and 100% of the same components were removed in the reduction experiments. The data suggest that precipitation/coprecipitation reactions are providing an effective sink for most of the heavy metals released by sulfide mineral oxidation. In light of these results, potential decommissioning strategies should be evaluated with the recognition that changing the geochemical conditions may alter the stability of the secondary phases within the shallow tailings. Received: 9 April 1997 · Accepted: 21 July 1997  相似文献   

10.
Speciation and colloid transport of arsenic from mine tailings   总被引：2，自引：0，他引：2  
In addition to affecting biogeochemical transformations, the speciation of As also influences its transport from tailings at inoperative mines. The speciation of As in tailings from the Sulfur Bank Mercury Mine site in Clear Lake, California (USA) (a hot-spring Hg deposit) and particles mobilized from these tailings have been examined during laboratory-column experiments. Solutions containing two common, plant-derived organic acids (oxalic and citric acid) were pumped at 13 pore volumes d−1 through 25 by 500 mm columns of calcined Hg ore, analogous to the pedogenesis of tailings. Chemical analysis of column effluent indicated that all of the As mobilized was particulate (1.5 mg, or 6% of the total As in the column through 255 pore volumes of leaching). Arsenic speciation was evaluated using X-ray absorption spectroscopy (XAS), indicating the dominance of arsenate [As(V)] sorbed to poorly crystalline Fe(III)-(hydr)oxides and coprecipitated with jarosite [KFe3(SO4, AsO4)2(OH)6] with no detectable primary or secondary minerals in the tailings and mobilized particles. Sequential chemical extractions (SCE) of <45 μm mine tailings fractions also suggest that As occurs adsorbed to Fe (hydr)oxides (35%) and coprecipitated within poorly crystalline phases (45%). In addition, SCEs suggest that As is associated with 1 N acid-soluble phases such as carbonate minerals (20%) and within crystalline Fe-(hydr)oxides (10%). The finding that As is transported from these mine tailings dominantly as As(V) adsorbed to Fe (hydr)oxides or coprecipitated within hydroxysulfates such as jarosite suggests that As release from soils and sediments contaminated with tailings will be controlled by either organic acid-promoted dissolution or reductive dissolution of host phases.  相似文献   

11.
  Time-of-flight laser-ionization mass spectrometry was applied to study the chemical composition of mineral particle surfaces in a sulphide-rich mine-tailings impoundment. This surface-sensitive technique provides chemical information from surfaces of irregularly shaped mineral particles (both conductive and insulators) less than 100 μm in diameter, which are considered to be representative of particle surface coatings in the tailings pile (after drying). In addition, depth profiles in the mineral particles were obtained. The combination of speed of analysis (1 min), small beam-diameter (2–4 μm), surface sensitivity (2–10 nm), trace-element sensitivity, and capability to analyze rough surfaces makes this method useful as a complement to studies of pore-water geochemistry and tailings mineralogy. As an example, the behavior of Pb and As in the Kidd Creek tailings dam near Timmins, Ontario, Canada, was studied, using a combination of surface analyses, and pore-water geochemical data. Received: 22 February 1995 / Accepted: 6 January 1996  相似文献   

12.
《China Geology》2021,4(3):476-486
The groundwater level has been continuously decreasing due to climate change and long-time overexploitation in the Xiong’an New Area, North China, which caused the enhanced mixing of groundwater in different aquifers and significant changes in regional groundwater chemistry characteristics. In this study, groundwater and sediment pore-water in drilling cores obtained from a 600 m borehole were investigated to evaluate hydrogeochemical processes in shallow and deep aquifers and paleo-environmental evolution in the past ca. 3.10 Ma. Results showed that there was no obvious change overall in chemical composition along the direction of groundwater runoff, but different hydrochemical processes occurred in shallow and deep groundwater in the vertical direction. Shallow groundwater (< 150 m) in the Xiong’an New Area was characterized by high salinity (TDS > 1000 mg/L) and high concentrations of Mn and Fe, while deep groundwater had better water quality with lower salinity. The high TDS values mostly occurred in aquifers with depth < 70 m and >500 m below land surface. Water isotopes showed that aquifer pore-water mostly originated from meteoric water under the influence of evaporation, and aquitard pore-water belonged to Paleo meteoric water. In addition, the evolution of the paleoclimate since 3.10 Ma BP was reconstructed, and four climate periods were determined by the δ18O profiles of pore-water and sporopollen records from sediments at different depths. It can be inferred that the Quaternary Pleistocene (0.78–2.58 Ma BP) was dominated by the cold and dry climate of the glacial period, with three interglacial intervals of warm and humid climate. What’s more, this study demonstrates the possibilities of the applications of pore-water on the hydrogeochemical study and further supports the finding that pore-water could retain the feature of paleo-sedimentary water.© 2021 China Geology Editorial Office.  相似文献   

13.
Recycling the mine waste (tailings) into cemented tailings backfill has economical and environmental advantages for the mining industry. One of the most recent types of cemented tailings backfill is gelfill (GF), a backfill that contains sodium silicate as chemical additive. GF is typically made of tailings, water, binder and chemical additives (sodium silicate gel). It is a promising mine tailings backfill technology. From a design point of view, the environmental performance or durability of GF structures is considered as a key factor. Due to the fact that GF structures are cementitious tailings, their durability and environmental performance depend on their ability to resist the flow of aggressive elements (water and oxygen). Thus, understanding the unsaturated hydraulic properties of GF is essential for a cost-effective, environmentally friendly and durable design of GF structures. However, there is a lack of information with regards to unsaturated hydraulic properties of GF, the factors that affect them and their evolution with time. Hence, the unsaturated hydraulic properties (water retention curve (WRC) or water characteristic curve, air entry value (AEV), residual water content, unsaturated hydraulic conductivity) of GF are investigated in this paper. GF samples of various compositions and cured in room temperature for different times (3, 7, 28, and 90 days) are considered. Saturated hydraulic conductivity and microstructural tests have been conducted; WRCs are measured by using a WP4-T dewpoint potentiameter and the saline solution method. Unsaturated hydraulic conductivity is predicted using the van Genuchten (1980) equation. The water retention curve (WRC) is determined as the relationship between volumetric water content and suction for each GF mix and curing time. The van Genuchten (1980) equation is used to simulate the WRC to best-fit the experimental data. AEV and residual water content are also computed for each mix and curing time. Furthermore, functions are developed to predict the evolution of AEVs, residual water content and fitting parameters of the van Genuchten model with degree of hydration. Important outcomes have been achieved with regards to unsaturated hydraulic properties. The unsaturated hydraulic conductivity of GF was calculated to decrease when the suction, binder content, and degree of hydration increase. The effects of binder content and degree of hydration are more obvious at low suction ranges. The obtained results would contribute to a better design and assessment of the durability and environmental performance of GF structures.  相似文献   

14.
Tailings generated during processing of sulfide ores represent a substantial risk to water resources. The oxidation of sulfide minerals within tailings deposits can generate low-quality water containing elevated concentrations of SO4, Fe, and associated metal(loid)s. Acid generated during the oxidation of pyrite [FeS2], pyrrhotite [Fe(1−x)S] and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate, (oxy)hydroxide, and silicate minerals. The extent of acid neutralization and, therefore, pore-water pH is a principal control on the mobility of sulfide-oxidation products within tailings deposits. Metals including Fe(III), Cu, Zn, and Ni often occur at high concentrations and exhibit greater mobility at low pH characteristic of acid mine drainage (AMD). In contrast, (hydr)oxyanion-forming elements including As, Sb, Se, and Mo commonly exhibit greater mobility at circumneutral pH associated with neutral mine drainage (NMD). These differences in mobility largely result from the pH-dependence of mineral precipitation–dissolution and sorption–desorption reactions. Cemented layers of secondary (oxy)hydroxide and (hydroxy)sulfate minerals, referred to as hardpans, may promote attenuation of sulfide-mineral oxidation products within and below the oxidation zone. Hardpans may also limit oxygen ingress and pore-water migration within sulfide tailings deposits. Reduction–oxidation (redox) processes are another important control on metal(loid) mobility within sulfide tailings deposits. Reductive dissolution or transformation of secondary (oxy)hydroxide phases can enhance Fe, Mn, and As mobility within sulfide tailings. Production of H2S via microbial sulfate reduction may promote attenuation of sulfide-oxidation products, including Fe, Zn, Ni, and Tl, via metal-sulfide precipitation. Understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings.  相似文献   

15.
Water and dissolved ion transport in mineral tailings was studied at laboratory scale with three different tailings samples. Percolation rate, determined in column experiments, depends mainly on the granulometric distribution of the solid and varies between 3.0×10–4 cm/s for a tailings sample with coarser particles (d90>700 m) to 4.0×10–5 cm/s for the tailings sample with higher content of fine particles (d90<200 m). In stationary conditions, the ascending rate of water by capillarity through the solid bed is controlled by the evaporation rate at the top surface of the tailings. Rates between 2.6×10–5 cm/s (2.2 mm/day) and 8.1×10–5 cm/s (7.0 mm/day) have been obtained under forced evaporation at 40 °C. Ion transport in the percolation process is mainly controlled by the hydraulic diffusion of the solution through pores in the solid bed. In the capillarity process, ion transport is controlled by chemical diffusion of the dissolved ion in the ascending solution.  相似文献   

16.
This study focuses on the reclamation work being performed on two former acid-generating tailings sites, located in Quebec, Canada. At both sites, the tailings were partially oxidized due to extended exposure, and the pore water is acidic. The reclamation solution applied to control acid mine drainage is a monolayer cover, made of non acid-generating tailings in one case and a till in the other. The goal of this project was to assess the response of the tailings-cover systems under various conditions. Tailings samples were collected in situ and characterized in the laboratory. Large column tests were conducted to evaluate the hydrogeological and geochemical behaviour of the covered tailings following wetting and drying cycles. The instrumented columns were designed to reproduce some of the existing site conditions and provide representative results for longer term analyses. Volumetric water content, suction, and oxygen concentrations were also monitored over time. The experimental data were used to validate different numerical models including those constructed with Vadose/W (GeoSlope Int.). Additional simulations were conducted under field conditions to evaluate the effect of various influence factors such as the depth of the water table, climatic conditions and the thickness of the cover. The combination of experimental and numerical results show how the behaviour and efficiency of a monolayer cover placed over reactive tailings depend on these factors, highlighting the importance of hydrogeological properties and water table depth. In many instances, the cover materials were prone to desaturation, especially when the water table was deeper than about 2 m below the tailings-cover interface. These results tend to indicate that relatively thin monolayer covers would not be able to prevent oxygen ingress under some of the conditions observed in the field. Desaturation of the cover and/or reactive tailings is due to a combination of drainage and evaporation. In such cases, increasing the thickness of the monolayer cover only has a limited effect. A discussion follows on the practical implications of these laboratory experiments and the numerical simulations for field design of reclamation measures at these two tailings impoundments.  相似文献   

17.
Intrinsic biodegradation of toluene coupled with the microbial reduction of ferric iron (Fe(III)) as the terminal electron acceptor was studied by using laboratory column experiments under continuous flow conditions. Columns were packed with contaminated aquifer sediment and N2-purged groundwater taken from the western part of the Gardermoen aquifer. The columns were operated anaerobically at 8 °C (in-situ temperature). Chloride was initially used to characterize flow properties of the columns. Intrinsic biodegradation of toluene, including abiotic loss and biological loss, was estimated by comparing breakthrough curves of toluene for live columns and sterilized control columns based on mass balance in steady-state conditions. The column experiments were run at two different flow velocities. The estimated average intrinsic rate was -0.73 and -0.53 mM day-1 for pore-water velocities of 1.75 and 2.68 cm h-1, respectively, corresponding to -0.27 and -0.22 mM day-1 in biological loss rate. The results indicate that intrinsic biodegradation of toluene could be used as an efficient remediation approach for contaminated groundwater at the Gardermoen fire-fighting training site.  相似文献   

18.
The chemistry of pore water is an important property of clayrocks being considered as host rocks for long-term storage of radioactive waste. It may be difficult, if not impossible, to obtain water samples for chemical analysis from such rocks because of their low hydraulic conductivity. This paper presents an approach for calculating the pore-water compositions of clayrocks from laboratory-measured properties of core samples, including their leachable Cl and SO4 concentrations and analysed exchangeable cations, and from mineral and cation exchange equilibria based on the formation mineralogy. New core sampling and analysis procedures are presented that reduce or quantify side reactions such as sample oxidation (e.g. pyrite) and soluble mineral dissolution (celestite, SrSO4) that affect measured SO4 concentrations and exchangeable cation distributions. The model considers phase equilibria only with minerals that are observed in the formation including the principal clay phases. The model has been used to calculate the composition of mobile pore water in the Callovo-Oxfordian clayrock and validated against measurements of water chemistry made in an underground research laboratory in that formation. The model reproduces the measured, in situ pore-water composition without any estimated parameters. All required parameters can be obtained from core sample analysis. We highlight the need to consider only those mineral phases which can be shown to be in equilibrium with contacting pore water. The consequence of this is that some conceptual models available in the literature appear not to be appropriate for modelling clayrocks, particularly those considering high temperature and/or high pressure detrital phases as chemical buffers of pore water. The robustness of our model with respect to uncertainties in the log K values of clay phases is also demonstrated. Large uncertainties in log K values for clay minerals have relatively small effects on modelled pore-water compositions.  相似文献   

19.
论壳内韧性流层及其构造表现   总被引：11，自引：0，他引：11  
地球物理探测表明,在上地壳之下有一不均匀分布的壳内低速层,中地壳之中还有一些局部的低速层。现代破坏性地震震源主要集中于10～15km深处,相当于这一低速层之顶部,处于脆韧性过渡带内。从岩石变形的角度看,这个低速层是一个壳内的韧性流变层,以发育近水平的韧性剪切带和褶叠层构造为其特征。它在纵向上和横向上都是不均一的,代表了地壳尺度的韧性剪切带,在地壳构造的演化中起着极重要的作用。  相似文献   

20.
A series of laboratory column tests on reactive mine tailings was numerically simulated to study the effect of high water saturation on preventing sulfide mineral oxidation and acid mine drainage (AMD). The approach, also known as an elevated water table (EWT), is a promising alternative to full water covers for the management and closure of sulfidic tailings impoundments and for the long term control of acid mine drainage. The instrumented columns contained reactive tailings from the Louvicourt mine, Quebec, and were overlain by a protective sand cover. Over a 13–19 month period, the columns were exposed to atmospheric O2 and flushed approximately every month with demineralized water. A free draining control column with no sand cover was also used. During each cycle, water table elevations were controlled by fixing the pressure at the column base and drainage water was collected and analyzed for pH and Eh, major ions, and dissolved metals (Fe, Zn, Cu, Pb, and Mg). The columns were simulated using the multi-component reactive transport model MIN3P which solves the coupled nonlinear equations for transient water flow, O2 diffusion, advective–dispersive transport and kinetic geochemical reactions. Physical properties and mineralogical compositions for the material layers were obtained from independent laboratory data. The simulated and observed data showed that as the water table elevation increased, the effluent pH became more neutral and SO4 and dissolved metal concentrations decreased by factors on the order of 102–103. It is concluded that water table depths less than or equal to one-half of the air entry value (AEV) can keep mine tailings sufficiently saturated over the long term, thus reducing sulfide oxidation and AMD production.  相似文献   

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