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1.
To investigate the applicability of equilibrium modeling for the estimation of the chemical changes of acid mine waters, the phases predicted to precipitate by equilibrium calculation were compared with what actually precipitates from the stream and acid mine waters in the Dogyae area, Korea. The computer program MINTEQA2 was used for the equilibrium calculations based on the chemical compositional data of the water samples collected in the study area. XRD, IR, thermal and chemical analyses of the collected precipitates were performed to identify their phases.The results of the identification of the collected precipitates are inconsistent with what the equilibrium calculations predict. The equilibrium calculations indicate that ferrihydrite, FeOHSO4, gibbsite, and AlOHSO4 should precipitate from the stream and acid mine waters in the study area. However, the experimental analyses show that only ferrihydrite and Al4(OH)10SO4 are the recognizable precipitates on the bottom of the stream and mine drainage channels. Comparing the stability relations among the possible precipitates with the field occurrence of the precipitates in the study area suggests that FeOHSO4 and AIOHSO4 are kinetically inhibited to precipitate and metastable ferrihydrite and Al4(OH)10SO4 appear in their stability field instead. It indicates that the chemical compositional change of the waters due to the solid phase precipitation in the study area must be interpreted and predicted in terms of the precipitation of not the phases predicted by the equilibrium calculation but the actually identified ones.Assuming that the dissolved species in the aqueous phase are in equilibrium with respect to the currently precipitating solid phases in the study area, the water chemistries are attempted to interpret based on the plot of the theoretically calculated activities of the dissolved species on the stability diagram for the identified precipitates and gibbsite. The plot reveals a few evolution paths of the chemical composition of the acid mine water as the acid generation and neutralization progress. The evolution path producing ferrihydrite and then Al4(OH)10SO4 precipitation suggests that the system including acid producing pyrite has lost significant amounts of its neutralizing capacity and thus, become intolerable to the impacts from acid mine water.  相似文献   

2.
As part of a study of early diagenesis in anaerobic lake sediments the major ions and P, Fe, Mn, pS, p? and pH were measured in interstitial waters of cores from eutrophic Greifensee in north-central Switzerland. A guide for the interpretation of such data is thermodynamic equilibrium between the dissolved species and mineral phases. The results show that CaCO3, which precipitates from the lake water, dissolves rapidly in the CO2-rich interstitial waters resulting in equilibrium with calcite in the top few centimeters of sediment. Siderite, on the other hand, is nearly ten-fold supersaturated 20–30 cm below the surface. Iron monosulfides are metastable in the surface 10–20 cm of sediment and pS and p? results indicate equilibrium between polysulfides and orthorhombic sulfur. Vivianite appears to be limiting the solubility of phosphate below a few centimeters of sediment.The above processes are highly interactive, especially in the case of ferrous iron, with one result being a two order of magnitude decrease in dissolved phosphate in a depth interval of 20cm in the interstitial waters.  相似文献   

3.
As part of an assessment of crystalline rock as a potential host for a nuclear waste repository, water samples were collected from more than 50 locations from the crystalline basement where it is under sedimentary cover in Northern Switzerland and where it is at the surface in the Black Forest. These samples describe the changing chemistry of water in an extended flow system from dilute recharge waters far from chemical equilibrium with its host rock to saline waters at temperatures of 50 to 100°C with residence times far in excess of 105 a that have reached chemical equilibrium with their host rock.This unique set of samples allows an analysis of the chemical evolution of granitic waters from surficial waters far from equilibrium to almost equilibrated waters. Mobile ions, rare gases and isotopic data are used to estimate the extent of reaction between waters and their host rock. The evolution of controlled elements is interpreted as a function of this extent of reaction. Silica contents correspond to approximate equilibrium even in the recharge waters. The relative concentrations of Ca and especially Mg are significantly lower in the borehole waters than in recharge waters indicating a trend towards equilibrium. The Na/K ratios correspond to equilibrium only in the most evolved, older, waters which are shown to be at full equilibrium.  相似文献   

4.
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5.
Detailed mineral and chemical studies of samples of syenite rocks with thick weathering rinds, found in the alkaline massifs on Ilha de São Sebastião, illustrate the complex interplay between variables controlling initial weathering processes. An array of geochemical information was obtained by optical and electron microscopy, X-ray analyses, mass spectroscopy and optical spectrometry. Sericite and metahalloysite are the principal phases nucleating and forming as the perthitic feldspar rock matrix disintegrates. Incipient feldspar dissolution and the formation of submicrometer X-ray opaque secondary phases were observed in “fresh rock” material using transmission electron microscopy. Pore waters, from which secondary phases nucleate and grow are under the constant influence, as alteration proceeds, of physical (e.g., accessibility of mineral surfaces to percolating fluids) and chemical (e.g. chemistry of minerals providing the dominant solutes) controls. Minor- and trace-element signatures do not vary significantly except for Zn, Rb, Sr, Y, REE and Pb. Lathanide mobilities appear related to their host-mineral stabilities with respect to ambient pore waters.  相似文献   

6.
Three sediment cores were collected in the Scheldt, Lys and Spiere canals, which drain a highly populated and industrialized area in Western Europe. The speciation and the distribution of trace metals in pore waters and sediment particles were assessed through a combination of computational and experimental techniques. The concentrations of dissolved major and trace elements (anions, cations, sulfides, dissolved organic C, Cd, Co, Fe, Mn, Ni, Pb and Zn) were used to calculate the thermodynamic equilibrium speciation in pore waters and to evaluate the saturation of minerals (Visual Minteq software). A sequential extraction procedure was applied on anoxic sediment particles in order to assess the main host phases of trace elements. Manganese was the most labile metal in pore waters and was mainly associated with carbonates in particles. In contrast, a weak affinity of Cd, Co, Ni, Pb and Zn with carbonates was established because: (1) a systematic under-saturation was noticed in pore waters and (2) less than 10% of these elements were extracted in the exchangeable and carbonate sedimentary fraction. In the studied anoxic sediments, the mobility and the lability of trace metals, apart from Mn, seemed to be controlled through the competition between sulfidic and organic ligands. In particular, the necessity of taking into account organic matter in the modelling of thermodynamic equilibrium was demonstrated for Cd, Ni, Zn and Pb, the latter element exhibiting the strongest affinity with humic substances. Consequently, dissolved organic matter could favour the stabilization of trace metals in the liquid phase. Conversely, sulfide minerals played a key role in the scavenging of trace metals in sediment particles. Finally, similar trace metal lability rankings were obtained for the liquid and solid phases.  相似文献   

7.
The paper presents a critical analysis of current concepts of the origin of sodic waters. The example of the Datong Basin with widespread sodic waters is employed to demonstrate that these waters typically have salinities of 0.6–4.5 g/l at pH of 7.8–8.8. It was determined that sodic waters are in equilibrium with calcite and clay minerals (montmorillonite and kaolinite) and, sometimes, also with analcime but are never in equilibrium with anorthite, albite, forsterite, microcline, and muscovite; i.e., the water-rock system is in equilibrium-unequilibrium state. The degree of evaporation concentration of salts is in places as high as a few tens. The complex analyses of conditions under which sodic waters are formed indicates that these waters are produced during a certain weathering stage of aluminosilicates, after the groundwaters have reached equilibrium with calcite. The time when this equilibrium can be reached is controlled by the intensity of the water exchange. Original Russian Text ? S.L. Shvartsev, Yanxing Wang, 2006, published in Geokhimiya, 2006, No. 10, pp. 1097–1109.  相似文献   

8.
Chaves thermal waters (76°C) are the most important external manifestations of low-temperature geothermal systems occurring in Portuguese mainland. They are related to crystalline granitic rocks. This paper describes the use of the environmental isotopic composition (oxygen-18, deuterium, and tritium) of hot and cold waters of the Chaves area as an important hydrogeological tool to solve specific problems arising in the appraisal of the geothermal resources of the area (e.g., origin and age of waters, recharge area, and underground flow paths).18O and D analyses seem to confirm the meteoric origin of Chaves thermal waters. The local altitude dependence of meteoric waters was determined by18O and D analyses of superficial and shallow groundwaters of the Chaves plain and its bordering mountains. Chaves thermal waters seem to be related to meteoric waters, infiltrated on the highest topography areas (Bolideira granitic outcrop NE Chaves), that percolate at great depth and emerge in a discharge area at lower altitude (Chaves plain). Chaves thermal waters showing little oxygen-18 shift and low tritium concentrations could be considered external manifestations of an old geothermal system in which the isotopic water-rock interaction is adjusted to equilibrium.  相似文献   

9.
We present the chemical and isotope compositions of the water and gas phases of the unique Mukhen cold high-pCO2 spa. Estimated 518O, 5D, and 513Ctic values and data on geology and hydrogeology of the studied area indicate that the source of the groundwaters is meteoric waters, whereas carbon dioxide is of deep genesis and numerous regional faults are gas-feeding channels. Calculations of equilibrium reactions in the water-rock system show that the upper-aquifer waters (HCO3-Ca-Mg) with low TDS are undersaturated with carbonate minerals, montmorillonites, and aluminosilicates but are oversaturated with kaolinite, whereas the lower-aquifer waters (HCO3-Na) with high TDS are oversaturated with calcite, dolomite, and clay minerals but are undersaturated with main aluminosilicates. We propose a new concept of the formation of these groundwaters, demonstrating that long interaction between rocks and groundwaters in the presence of CO2 and considerable precipitation of secondary minerals are responsible for the high TDS of the lower-aquifer waters (up to 14 g/L) and their geochemical type (HCO3-Na) and unusual isotope composition (518O = -25.2%c, 5D = -69.0%c).  相似文献   

10.
A theoretical study of the system CaCO3-MnCO3-H2O provides evidence that solid solution is limited to three mole fraction ranges corresponding to Mn-calcite, kutnohorite and calcic-rhodochrosite. All these authigenic phases may control the concentration of manganese in suboxic marine pore waters. As a consequence the solubility of manganese cannot be adequately described by a single thermodynamic equilibrium constant.  相似文献   

11.
《Applied Geochemistry》2001,16(9-10):1153-1163
The waters of the thermal springs at Alhama de Granada vary in temperature between 27 and 45°C. Temporal changes in the composition of the principal spring (Baños Viejos) indicate that a small degree of mixing may occur between deep thermal waters and shallow groundwater. Slight compositional variations also occur between the various thermal springs in the study area. These spatial variations are due to the different local hydrodynamic conditions in the springs. Towards the north in less hydraulically transmissive rocks, cooling of the rising water is more noticeable, as are ion exchange and processes of SO4 reduction. The chemical composition of the water is related to the dissolution of evaporites (SO4 and Cl salts), carbonates and silicates, and to the possible existence of sources of S within the rock. Estimates of the mean residence times have been obtained based on 14CDIC and T. The state of thermodynamic equilibrium at the spring discharge was calculated using the SOLMINEQ.88 program. The results indicate that all the samples are supersaturated with respect to quartz, chalcedony, cristobalite, calcite, aragonite and dolomite, and undersaturated with respect to gypsum, anhydrite and halite. The use of different geothermometers and modelling of saturation indices for quartz, albite and anhydrite indicate temperatures of about 110°C.  相似文献   

12.
Due to hydrolysis reactions, iron(III) forms oxyhydroxide precipitates in natural waters that minimise its availability to living organisms. Thermodynamic studies have established equilibrium concentrations of dissolved iron at various pH values, however these studies offer no insight into the kinetics of iron(III) polymerisation and subsequent precipitation. In recent work, the kinetics of iron(III) precipitation and dissolution of the precipitate have been investigated, but there are apparent discrepancies between the equilibrium solubility of iron(III) calculated from the kinetic parameters and its solubility measured by separation of the solid and dissolved phases at equilibrium. In this work, we reconcile kinetic and thermodynamic measurements using a polymer-based mechanistic model of the processes responsible for iron(III) precipitation in aqueous solutions based on a variety of previously published experimental data. This model is used to explain the existence of a solubility limit, including the effect of precipitate ageing on its solubility. We suggest that the model provides a unified approach for examining aqueous systems containing dissolved, solid-phase and surface species.  相似文献   

13.
Clay minerals were reacted with silica-spiked solutions of unbuffered distilled water; water buffered at pH 5.5, 8 and 10; alkali chloride solutions; natural and artificial sea water to assess the influence of pH, silica and cation activities. The data are plotted as silica produced by dissolution or sorption of silica by clay surface as a function of initial silica concentration at a given pH and solution composition. This allows the determination of the dissolved silica value at which the clay mineral surface neither dissolves nor sorbs silica. The values of the various activities in different solutions are used to infer the phase equilibria between solution, clay mineral and the surface phase produced either by dissolution or sorption. Most intensively investigated were sorption reactions of kaolinite in sea water and other ionic solutions to form silica-rich, cation-rich surface phases in cationic solutions and silica-rich phases in cation-free solutions.Inferred equilibrium constants imply that silicate reconstitution is doubtful as a mechanism for partial control of silica and cation composition of sea water but is reasonable in silica-rich interstitial waters.  相似文献   

14.
The oxygen isotope compositions of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel, have been used to identify porewater types during diagenesis. Changes in porewater composition can be related to major geological events within southern Israel. In particular, saline brines played an important role in late (Pliocene-Pleistocene) dolomitization of these rocks. Diagenetic carbonates included early siderite (δ18OSMOW=+24.4 to +26.5‰δ13CPDB=?1.1 to +0.8‰), late dolomite, ferroan dolomite and ankerite (δ18OSMOW=+18.4 to +25.8‰; δ13CPDB=?2.1 to +0.2‰), and calcite (δ18OSMOW=+21.3 to +32.6‰; δ13CPDB=?4.2 to + 3.2‰). The petrographic and isotopic results suggest that siderite formed early in the diagenetic history at shallow depths. The dolomitic phases formed at greater depths late in diagenesis. Crystallization of secondary calcite spans early to late diagenesis, consistent with its large range in isotopic values. A strong negative correlation exists between burial depth (temperature) and the oxygen isotopic compositions of the dolomitic cements. In addition, the δ18O values of the dolomitic phases in the northern Negev and Judea Mountains are in isotopic equilibrium with present formation waters. This behaviour suggests that formation of secondary dolomite post-dates the tectonic activity responsible for the present relief of southern Israel (Upper Miocene to Pliocene) and that the dolomite crystallized from present formation waters. Such is not the case in the Central Negev. In that locality, present formation waters have much lower salinities and δ18O values, indicating invasion of freshwater, and are out of isotopic equilibrium with secondary dolomite. Recharge of the Inmar Formation by meteoric water in the Central Negev occurred in the Pleistocene, and halted formation of dolomite.  相似文献   

15.
《Applied Geochemistry》1994,9(5):583-595
A steady-state geochemical model has been developed to study water-rock interactions controlling metal release from waste rock heaps at the Aitik Cu mine in northern Sweden. The Cu release in drainage waters from the site is of environmental concern. The waste rock heaps are treated as single completely mixed flow-through reactors. The geochemical model includes kinetices of sulphide and primary silicate mineral weathering, heterogeneous equilibrium with secondary mineral phases and speciation equilibrium. Field monitoring of drainage water composition provides a basis for evaluation of model performance.The relative rate of oxidative weathering of sulphides and dissolution of primary silicate minerals, using published kinetic data, are consistent with net proton and base cation fluxes at the site. The overall rate of Fe2+ oxidation within the heap is three orders of magnitude faster than that which could be explained by surface-catalysed reaction kinetics. This suggests significant activity of iron-oxidizing bacteria. The absolute weathering rates of sulphides and silicate minerals, normalized to a measured BET surface area, are approximately two orders of magnitude lower at field scale than published rates from laboratory experiments. Because of the relative absence of carbonate minerals, the weathering of biotite and plagioclase feldspar are important sources of alkalinity.  相似文献   

16.
This article presents the data of studies of ion-salt, microcomponent, gas, and isotopic compositions of water and the equilibrium calculation results for the water-rock system. The Tersinskie carbonic-acid waters are shown to be genetically close to soda waters of the Kuznetsk Basin (Kuzbass) in the zone with slowed water exchange. Taking these data into account, the concept of formation of carbonic-acid mineral waters not connected with magmatic or volcanic activities in the region was developed. According to this hypothesis, carbonic-acid waters are soda waters of regional occurrence, their composition being considerably changed due to CO2 introduction from the deeper zones of the Earth’s crust along the zones of tectonic ruptures.  相似文献   

17.
Given the vital importance of water and energy in desert regions, we undertook a study dealing with the deep reservoirs in Gabes area, which is located in the southeastern part of Tunisia. Geothermal resources are taken from the Intercalary Continental [or Continental Intercalaire (CI)], known as the largest deep aquifer in Tunisia and are used in a number of applications, mainly in agriculture. Previous investigations performed on the thermal waters of this area focused on the genesis of the deep waters with regard to the thermal features of geothermal reservoirs. A more detailed investigation has been carried out, considering both deep and shallow waters. In order to estimate the potential temperatures of deep reservoir in the Gabes area, we developed a synthetic study including chemical geothermometers, multiple mineral equilibrium approach, and other approaches. Chemical types of the thermal waters and effects of mixing between shallow cold waters with deep thermal waters were also discussed. In fact, the application of Na–K–Mg diagram relative to deep geothermal reservoir capitulate estimated temperatures (about 90°C). In addition, the multiple mineral equilibrium approach submits a similar estimated temperature ranging between 65 and 70°C, showing a disequilibrium status which indicates a possibly mixing with surface water. Indeed, wells exploiting the CI aquifer in the south part of the studied area showed the same characteristics, corroborating the reliability of the applied methods.  相似文献   

18.
The thermomineral waters from Massif Central are iron rich waters of sodium bicarbonate type. The aim of this work is to provide more information about the geochemistry of iron, which is clearly related to the redox potential in this type of water. Thermodynamic calculations were used, and the distribution of iron was found to be controlled by the solubility of siderite. The oxidation potential that can be measured with calomel and platinum electrodes corresponds to an electrochemical equilibrium which involves a ferric hydroxide or oxyhydroxide. Finally EPt values measured in the field are in good agreement with values predicted from the equilibrium between siderite and amorphous Fe(OH)3, the association of which acts as a redox buffer. Dissolved oxygen is not in equilibrium with the ferrous-ferric couple and does not affect the measured potential. Even when of local theoretical significance as a thermodynamic variable, this redox potential represents only partial equilibrium conditions.  相似文献   

19.
Using chemical analyses and 25° pH measurements of quenched high-temperature waters, we calculate in situ pH and distribution of aqueous species at high temperature. This is accomplished by solving simultaneous mass action equations for complexes and redox equilibria and mass balance equations, on all components, including a H+ equation with as many as 60 terms (depending on water composition). This calculation provides accurate values for the activities of aqueous ions in a given water at high temperature, which are used to calculate an ion activity product (Q) for each of more than 100 minerals. The value of log(Q/K) for each mineral, where K is the equilibrium constant, provides a measure of proximity of the aqueous solution to equilibrium with the mineral. By plotting log Q/Kvs. T for natural waters, it is possible to determine: a) whether the water was in equilibrium with a host rock mineral assemblage, b) probable minerals in the equilibrium assemblage and c) the temperature of equilibrium. In cases where the fluid departs from equilibrium with a host rock assemblage, it is possible to determine whether this may result from boiling or dilution, and an estimate of amount of lost gas or diluting water can be determined.The calculation is illustrated by application to geothermal waters from Iceland, Broadlands, and Sulphur Bank, hot spring waters from Jemez, Yellowstone and Blackfoot Reservoir (Idaho) and fluid inclusions from the Sunnyside Mine, Colorado. It is shown that most geothermal waters approach equilibrium with a subsurface mineral assemblage at a temperature close to measured temperatures and that some hot springs also approach equilibrium with the host rock at temperatures above outlet temperatures but commonly below the Na-K-Ca temperatures. The log Q/K plots show that some discrepancies between Na-K-Ca temperatures on spring waters and actual temperatures result from a failure of alkali feldspars to equilibrate with the fluid and with each other.Calculations on Sulphur Bank fluids show that boiling probably caused cinnabar precipitation near 150°C and that the boiled fluids equilibrated with secondary minerals near 150° even though temperatures up to 185° have been measured at depth. For the fluid inclusions, the measured bubble temperatures are close to those calculated for equilibration of the fluid with the observed sulfide mineral assemblage.New estimates of stability constants for aluminum hydroxide complexes are included at the end of the paper.  相似文献   

20.
The mineralogy of suspended matter from surface and bottom waters is studied at two sites in the Barents Sea. Along with terrigenous minerals, the suspended matter samples contain authigenic mineral phases of iron and manganese oxyhydroxides. Mn-feroxyhite, Fe-vernadite, goethite, and proto-ferrihydrite were identified in samples from surface waters, whereas birnessite and nonferruginous vernadite were registered in samples from bottom waters. The formation of suspended manganese minerals in bottom waters is explained by an additional Mn supply from underlying reduced sediments during their early diagenesis and oxygen depletion in the near-bottom nepheloid layer. Bacteria are supposed to take part in the authigenic mineral formation.  相似文献   

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