首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 78 毫秒
1.
The form or speciation of a metal in natural waters can change its kinetic and thermodynamic properties. For example, Cu(II) in the free ionic form is toxic to phytoplankton, while copper complexed to organic ligands is not toxic. The form of a metal in solution can also change its solubility. For example, Fe(II) is soluble in aqueous solutions while Fe(III) is nearly insoluble. Natural organic ligands interactions with Fe(III) can increase the solubility by 20-fold in seawater. Ionic interaction models that can be used to determine the activity and speciation of divalent and trivalent metals in seawater and other natural elements will be discussed. The model is able to consider the interactions of metals with the major (Cl-, SO4 2-, HCO3 -, CO3 2-, Br-, F-) and minor (OH-, H2PO4 -, HPO4 2-, PO4 3-, HS-) anions as a function of temperature (0 to 50 °C), ionic strength [0 to 6 m (m = mol kg-1)] and pH (1 to 13). Recently, it has been shown that many divalent metals are complexed with organic ligands. Although the composition of these ligands is not known, a number of workers have used voltammetry to determine the concentration of the ligand [L n ] and the stability constant (K ML) for the formation of the complex  相似文献   

2.
Adsorption and Desorption of Phosphate on Calcite and Aragonite in Seawater   总被引：3，自引：0，他引：3  
The adsorption and desorption of phosphate on calcite and aragonite were investigated as a function of temperature (5–45 °C)and salinity (0–40) in seawater pre-equilibrated with CaCO3. An increase in temperature increased the equilibrium adsorption; whereas an increase in salinity decreased the adsorption. Adsorption measurements made in NaCl were lower than the results in seawater. The higher values in seawater were due to the presence of Mg2+ and Ca2+ ions. The increase was 5 times greater for Ca2+ than Mg2+. The effects ofCa2+ and Mg2+ are diminished with the addition of SO4 2- apparently due to the formation of MgSO4 and CaSO4 complexes in solution and/or SO4 2- adsorption on the surface of CaCO3. The adsorbed Ca2+ and Mg2+ on CaCO3 (at carbonate sites) may act as bridges to PO4 3- ions. The bridging effect of Ca2+is greater than Mg2+ apparently due to the stronger interactions of Ca2+ with PO4 3-.The apparent effect of salinity on the adsorption of PO4 was largely due to changes in the concentration of HCO3 - in the solutions. An increase in the concentration of HCO3 - caused the adsorption of phosphate to decrease, especially at low salinities. The adsorption at the same level of HCO3 - (2 mM) was nearly independent of salinity. All of the adsorption measurements were modeled empirically using a Langmuir-type adsorption isotherm[ [PO4]ad = KmCm[PO4]T/(1 +Km [PO4]T) , ]where [PO4]ad and [PO4]T are the adsorbed and total dissolved phosphate concentrations, respectively. The values of Cm (the maximum monolayer adsorption capacity, (mol/g) and Km (the adsorption equilibrium constant, g/(mol) over the entire temperature (t, °C) and salinity (S) range were fitted to[ Cm = 17.067 + 0.1707t - 0.4693S + 0.0082S2 ( = 0.7) ][ ln Km = - 2.412 + 0.0165t - 0.0004St - 0.0008S2 ( = 0.1) ]These empirical equations reproduce all of our measurements of[PO4]ad up to 14 mol/g and within ±0.7 mol/g.The kinetic data showed that the phosphate uptake on carbonate minerals appears to be a multi-step process. Both the adsorption and desorption were quite fast in the first stage (less than 30 min) followed by a much slower process (lasting more than 1 week). Our results indicate that within 24 hours aragonite has a higher sorption capacity than calcite. The differences between calcite and aragonite become smaller with time. Consequently, the mineral composition of the sediments may affect the short-term phosphate adsorption and desorption on calcium carbonate. Up to 80 % of the adsorbed phosphate is released from calcium carbonate over one day. The amount of PO4 left on the CaCO3 is close to the equilibrium adsorption. The release of PO4 from calcite is faster than from aragonite. Measurements with Florida Bay sediments produced results between those for calcite and aragonite. Our results indicate that the calcium carbonate can be both a sink and source of phosphate in natural waters.  相似文献   

3.
During equilibration of K-feldspar, quartz and muscovite with dilute KCl-solutions, the change in pH of the solution was measured as a function of time. The resulting equilibrium constant, K T = aK + /aH +, is 104.21±0.06, 105.86±0.03 and 106.01±0.03 at 300, 60 and 30° C respectively (standard states at 1 bar) and are consistent with the best higher temperature data. At 30° C this constant is consistent with the aK + /aH + ratio of seawater. From K T and the activity of K + in seawater, a pH of 8.2 is calculated, essentially identical with the pH which results from dissolution of CaCO3 under atmospheric CO2-pressure. Consequently, detrital K-feldspar, quartz, muscovite, and calcite are stable in seawater. Apparently, the seawater pH is controlled by CaCO3 as well as K-feldspar, quartz and muscovite. Independently both equilibria show virtually the same pH, within the variability due to disordering, solid solution and surface energy effects.Assuming that the K-concentrations of pore solutions vary between about 4000 and 40 ppm, these solutions have alkalic pH-values in the temperature range between 30 and 300° C if K-feldspar, quartz and muscovite are present. In limestones the pH is fixed by the dissociation of CaCO3; the occasionally observed formation of K-feldspar in these rocks requires a minimum K-concentration of approximately 4 ppm.

Die Untersuchungen wurden am Department of Mineralogy and Geochemistry der Pennsylvania State University durchgeführt. Der erste Autor (H. E. Usdowski) bedankt sich für die freundliche Aufnahme und die ausgezeichneten Arbeitsmöglichkeiten. Besonderer Dank gilt Dr. George Helz für viele Diskussionen und manche Hilfe im Labor. Die Deutsche Forschungsgemeinschaft hat die Untersuchungen durch einen Forschungsauftrag unterstützt.  相似文献   

4.
Recent stability constant data for ferrous complexation by chloride, hydroxide and sulphate ions are used to recalculate the equilibrium distribution of soluble ferrous species at pH 7 and 8 in fresh- and seawater. Contrary to previous calculations hydroxy complexes are negligible and the aquated Fe2+ ion is the dominant species for all conditions. In seawater up to 15% of the iron might be present as chloride complexes, and 9% as sulfate complexes. The implications of these results to mineral formation are discussed.  相似文献   

5.
样品测试是研究岩溶区水工环问题的重要手段。岩溶区交通不便利、样品运输困难以及测试单位处理样品不及时,导致样品测试存在不同程度的滞后,现有研究还不能有效解释"测试滞后"对岩溶水样性质有何影响。为此,本文以云南宣威市一典型岩溶泉水为研究对象,通过离子色谱仪、原子发射光谱仪等测试手段,对同一时间点采集的泉水样品按照时间序列对K+、Na+、Ca2+、Mg2+、Cl-、SO2-4、HCO-3、pH、NO-3、CO2(fs)共10项指标进行对比实验,探讨"测试滞后"对岩溶水样性质的影响。结果表明:岩溶水样放置过程中,各指标A类标准不确定度为0. 02～1. 83,HCO-3、Ca2+不确定度值显著高于其他指标; Shapiro-Wilk正态性检验结果显示pH、K+、Mg2+、Cl-、NO-3服从正态分布;随着时间变化,各指标相对偏差变化范围0%～57. 38%,其中pH、Ca2+、SO2-4、NO-3的相对偏差在允许误差范围之内; 10项指标均值含量与变异系数总体呈显著负相关性(Spearman相关系数为-0. 709,P 0. 05),变异系数为Na+ K+ CO2(fs) Mg2+ Cl-SO2-4 Ca2+ HCO-3 p H NO-3,揭示测试滞后对不同指标的影响程度不同,其中对质量分数低的指标影响尤为突出。在整个实验期间内,水样水质变化可分为5个阶段:以各项指标未出现明显变化的初期稳定阶段(0～3d),以Na+、K+、Mg2+三项指标出现显著变化的初步变化阶段(3～5d),以多项指标发生较为显著变化的混合变化阶段(5～17d),以微生物作用为主的细菌潜在影响阶段(17～35d),以水质趋于稳定的相对平衡阶段(35～75d),其中"细菌作用"和"碳酸平衡作用"是岩溶水样放置过程中存在的两个重要作用机制。研究结果可为提高岩溶水样测试质量提供科学指导。  相似文献   

6.
A theoretical model was developed to study the chemical speciation of the trace elements Zn, Cd, Cu and Pb aqueous solutions and their responses to variations in ionic strength and complexation. Two mixing solutions were investigated, a freshwater-seawater system and a freshwater-brine system. The brine was a calcium, sodium-chloride solution with a molal ionic strength of two. Trace element associations with the ligands OH?, Cl?, CO2?3, SO2?4, and HCO?3 were considered at pHs from 3.5 to 11.0 at 25°C. In general, the relative importance of the various ligand-trace element complexes can be predicted from a comparison of their stability constants. However, the effect of pH on the importance of a given complex is not readily apparent from the stability constants. Freshwater-seawater mixtures, as might be found in a totally mixed estuary, show that seawater composition is the dominant control on chemical complexing. Chloride complexing is similar for lead and zinc in the freshwater-brine mixtures. This similarity may account in part for the association of lead and zinc in strata-bound ore deposits.  相似文献   

7.
Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)3 and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from <0.4 μmol L−1 at pH > 7 to 1941 μmol L−1 at pH < 4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al3+ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)3 minerals (e.g. gibbsite or amorphous Al(OH)3), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater.  相似文献   

8.
Pollution of groundwater by seawater intrusion poses a threat to sustainable agriculture in the coastal areas of Korea. Therefore, seawater intrusion monitoring stations were installed in eastern, western, and southern coastal areas and have been operated since 1998. In this study, groundwater chemistry data obtained from the seawater intrusion monitoring stations during the period from 2007 to 2009 were analyzed and evaluated. Groundwater was classified into fresh (<1,500 μS/cm), brackish (1,500–3,000 μS/cm), and saline (>3,000 μS/cm) according to EC levels. Among groundwater samples (n = 233), 56, 7, and 37% were classified as the fresh, brackish, and saline, respectively. The major dissolved components of the brackish and saline groundwaters were enriched compared with those of the fresh groundwater. The enrichment of Na+ and Cl− was especially noticeable due to seawater intrusion. Thus, the brackish and saline groundwaters were classified as Ca–Cl and Na–Cl types, while the fresh groundwater was classified as Na–HCO3 and Ca–HCO3 types. The groundwater included in the Na–Cl types indicated the effects of seawater mixing. Ca2+, Mg2+, Na+, K+, SO4 2−, and Br− showed good correlations with Cl− of over r = 0.624. Of these components, the strong correlations of Mg2+, SO4 2−, and Br− with Cl− (r ≥ 0.823) indicated a distinct mixing between fresh groundwater and seawater. The Ca/Cl and HCO3/Cl ratios of the groundwaters gradually decreased and approached those of seawater. The Mg/Cl, Na/Cl, K/Cl, SO4/Cl, and Br/Cl ratios of the groundwaters gradually decreased, and were similar to or lower than those of seawater, indicating that Mg2+, Na+, K+, SO4 2−, and Br−, as well as Cl− in the saline groundwater can be enriched by seawater mixing, while Ca2+ and HCO3 − are mainly released by weathering processes. The influence of seawater intrusion was evaluated using threshold values of Cl− and Br−, which were estimated as 80.5 and 0.54 mg/L, respectively. According to these criteria, 41–50% of the groundwaters were affected by seawater mixing.  相似文献   

9.
The technique of competitive ligand-exchange/anodic stripping voltammetry (CLE-SV) was used to investigate effects of pH and Ca concentration on cadmium complexation by fulvic acid (FA), as well as Cd speciation in two different freshwaters, a hardwater Lake Greifen and a softwater River Wyre. Binding of Cd to Suwannee river FA (10 mg/l) was determined at different pH (7–8.5) and in the presence of various concentration of Ca2+ (0–2 mmol/l). The results from one-ligand discrete models were compared to simulations by the WHAM VI model. In Lake Greifen, the determined dissolved [Cd2+] ranged from 10−13 to 10−12 mol/l, and the conditional stability constant with natural ligands was log K CdL about 9.5–10.5 (pH 8.6–8.8) with ligand concentrations of 1.2–7.8 × 10−6 mol/g C. In the softwater River Wyre, dissolved [Cd2+] ranged from 4 × 10−12 to 1 × 10−11 mol/l, and the ligands were weaker (log K CdL 8.9–9.8, pH 8.0) with lower ligand concentrations (0.9–2.3 × 10−6 mol/g C). The titration curves of FA samples were close to the simulated curves by the WHAM VI model at pH 8.0–8.5, but deviated more from the model at lower pH, indicating that the results determined with CLE-SV for Cd-FA complexation are relevant to the data base in the model. Calculation of the Ca competition for Cd binding by FA showed a competition effect of similar strength as the measured one, but indicated a systematic difference between measured and modeled data at pH 7.5. Using the WHAM model for comparison with FA, the complexation of Cd by the River Wyre ligands was close to that of FA, whereas stronger complexation was observed in the Lake Greifen water. These differences may originate from different ligand composition in the lake and the river.  相似文献   

10.
Adsorption of divalent metal ions, including Cu2+, Pb2+, Zn2+, Cd2+ and Ni2+, on quartz surface was measured as a function of metal ion concentration at 30°C under conditions of solution pH= 6. 5 and ion strength I = 0. 1mol/L. Results of the experimental measurements can be described very well by adsorption isotherm equations of Freudlich. The correlation coefficients (r) of adsorption isotherm lines are > 0. 96. Moreover, the experimental data were interpreted on the basis of surface complexation model. The experimental results showed that the monodentate-coordinated metal ion surface complex species (SOM+) are predominant over the bidentate-coordinated metal ion surface complex species [(SO)2M] formed only by the ions Cu2+, Zn2+ and Ni2+. And the relevant apparent surface complexation constants are lgKM = 2.2–3.3 in order of KCd≥KPb > KZn > KNi≥KCu, and lgβM = 5.9-6.8 in order of βNi > βZn > βCu. Therefore, the reactive ability of the ions onto mineral surface of quartz follows the order of Cd > Pb > Zn > Ni> Cu under the above-mentioned solution conditions. The apparent surface complexation constants, influenced by the surface potential, surface species and hydrolysis of metal ions, depend mainly on the Born solvation coefficient of the metal ions. This project was financially supported by the National Natural Science Foundation of China (No. 49572091).  相似文献   

11.
The oxidation of Fe(II) with H2O2 at nanomolar levels in seawater have been studied using an UV-Vis spectrophotometric system equipped with a long liquid waveguide capillary flow cell. The effect of pH (6.5 to 8.2), H2O2 (7.2 × 10−8 M to 5.2 × 10−7 M), HCO3− (2.05 mM to 4.05 mM) and Fe(II) (5 nM to 500 nM) as a function of temperature (3 to 35 °C) on the oxidation of Fe(II) are presented. The oxidation rate is linearly related to the pH with a slope of 0.89 ± 0.01 independent of the concentration of HCO3−. A kinetic model for the reaction has been developed to consider the interactions of Fe(II) with the major ions in seawater. The model has been used to examine the effect of pH, concentrations of Fe(II), H2O2 and HCO3− as a function of temperature. FeOH+ is the most important contributing species to the overall rate of oxidation from pH 6 to pH 8. At a pH higher than 8, the Fe(OH)2 and Fe(CO3)22− species contribute over 20% to the rates. Model results show that when the concentration of O2 is two orders of magnitude higher than the concentration of H2O2, the oxidation with O2 also needs to be considered. The rate constants for the five most kinetically active species (Fe2+, FeOH+, Fe(OH)2, FeCO3, Fe(CO3)22−) in seawater as a function of temperature have been determined. The kinetic model is also valid in pure water with different concentrations of HCO3− and the conditions found in fresh waters.  相似文献   

12.
天山乌鲁木齐河源1号冰川融水径流水化学特征研究   总被引：3，自引：2，他引：1  
冯芳  冯起  刘贤德  李忠勤  刘蔚  金爽 《冰川冻土》2014,36(1):183-191
2006年和2007年的整个消融期内,在天山乌鲁木齐河源1号冰川末端水文控制点逐日定时采集融水径流样品,对样品的主要可溶离子、pH、电导率EC、总溶解固体TDS和悬移质颗粒物SPM进行了分析. 结果表明：天山乌鲁木齐河源1号冰川融水径流离子类型为Ca2+-HCO3--SO42-,呈弱碱性. 融水径流中TDS变化受日径流量调节显著,表现为消融初期和末期浓度较高,消融强烈时浓度较低;SPM以细颗粒物质为主,各粒度组分含量变化幅度较大,且质量浓度SSC年内变化与TDS呈相反的变化趋势. 融水径流中离子组成主要受岩石风化作用影响,离子摩尔比值和Piper图分析表明,控制冰川径流离子组成的主要过程是碳酸盐、黄铁矿和长石类矿物风化作用.  相似文献   

13.
Theory is derived from the work of Urey (Urey H. C. [1947] The thermodynamic properties of isotopic substances. J. Chem. Soc. 562-581) to calculate equilibrium constants commonly used in geochemical equilibrium and reaction-transport models for reactions of individual isotopic species. Urey showed that equilibrium constants of isotope exchange reactions for molecules that contain two or more atoms of the same element in equivalent positions are related to isotope fractionation factors by α = (Kex)1/n, where n is the number of atoms exchanged. This relation is extended to include species containing multiple isotopes, for example 13C16O18O and 1H2H18O. The equilibrium constants of the isotope exchange reactions can be expressed as ratios of individual isotope equilibrium constants for geochemical reactions. Knowledge of the equilibrium constant for the dominant isotopic species can then be used to calculate the individual isotope equilibrium constants.Individual isotope equilibrium constants are calculated for the reaction CO2g = CO2aq for all species that can be formed from 12C, 13C, 16O, and 18O; for the reaction between 12C18O2aq and 1H218Ol; and among the various 1H, 2H, 16O, and 18O species of H2O. This is a subset of a larger number of equilibrium constants calculated elsewhere (Thorstenson D. C. and Parkhurst D. L. [2002] Calculation of individual isotope equilibrium constants for implementation in geochemical models. Water-Resources Investigation Report 02-4172. U.S. Geological Survey). Activity coefficients, activity-concentration conventions for the isotopic variants of H2O in the solvent 1H216Ol, and salt effects on isotope fractionation have been included in the derivations. The effects of nonideality are small because of the chemical similarity of different isotopic species of the same molecule or ion. The temperature dependence of the individual isotope equilibrium constants can be calculated from the temperature dependence of the fractionation factors.The derivations can be extended to calculation of individual isotope equilibrium constants for ion pairs and equilibrium constants for isotopic species of other chemical elements. The individual isotope approach calculates the same phase isotopic compositions as existing methods, but also provides concentrations of individual species, which are needed in calculations of mass-dependent effects in transport processes. The equilibrium constants derived in this paper are used to calculate the example of gas-water equilibrium for CO2 in an acidic aqueous solution.  相似文献   

14.
A natural Ca-poor pigeonite (Wo6En76Fs18) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal X-ray diffraction. The sample, monoclinic P21/c, was annealed up to 1,093°C to induce a phase transition from P21/c to C2/c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections (h + k = 2n + 1, present only in the P21/c phase) showed a displacive phase transition P21/c to C2/c at a transition temperature T Tr = 944°C, first order in character. The Fe–Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in a range of temperatures between the closure temperature of the Fe–Mg exchange reaction and the transition temperature. Isothermal disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression of ln k D versus 1/T yielded the following equation: ln k\textD = - 3717( ±416)/T(K) + 1.290( ±0.378);    (R2 = 0.988) \ln \,k_{\text{D}} = - 3717( \pm 416)/T(K) + 1.290( \pm 0.378);\quad (R^{2} = 0.988) . The closure temperature (T c) calculated using this equation was ∼740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s of the atomic fractions used to define the Fe–Mg degree of order, performed according to Mueller’s model, allowed us to retrieve the disordering rate constants C 0 K dis+ for all three temperatures yielding the following Arrhenius relation: ln( C0 K\textdis + ) = ln K0 - Q/(RT) = 20.99( ±3.74) - 26406( ±4165)/T(K);    (R2 = 0.988) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = \ln \,K_{0} - Q/(RT) = 20.99( \pm 3.74) - 26406( \pm 4165)/T(K);\quad (R^{2} = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe–Mg exchange process was obtained. The above relation was used to calculate the following Arrhenius relation modified as a function of X Fe (in the range of X Fe = 0.20–0.50): ln( C0 K\textdis + ) = (21.185 - 1.47X\textFe ) - \frac(27267 - 4170X\textFe )T(K) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = (21.185 - 1.47X_{\text{Fe}} ) - {\frac{{(27267 - 4170X_{\text{Fe}} )}}{T(K)}} . The cooling time constant, η = 6 × 10−1 K−1 year−1 calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late cooling history of the ureilite parent body after impact excavation.  相似文献   

15.
We discuss the nature of the ore-forming hydrothermal fluid in the Noya gold-bearing calcite-quartz-adularia veins of central Kyushu, Japan on the basis of oxygen, carbon, and strontium isotope ratios, and aqueous speciation calculations for the present-day geothermal fluid. The isotopic values of the Noya ore-forming fluid were estimated to be −6.5‰ for δ13C and −7.5‰ for δ18O. The oxygen isotopic equilibrium temperatures for vein calcite are more than 180°C at the bottom of the Noya mineralization zone, and decrease with increasing elevation. As the temperature decreased, the dominant carbon species in the fluid changed from H2CO3 to HCO3- at about 120°C. The equilibrium temperatures for vein quartz are consistent with the calcite calculations. The carbon and oxygen isotope trends of the Noya vein calcite and the isotope ratios of strontium suggest that the fluids that precipitated the Noya veins were controlled by an andesite-dominated geology. Chondrite-normalized REE patterns for the white-colored veins from wells 51-WT-1 and 51-WT-2 displayed a light REE-rich pattern with positive Eu anomalies, suggesting the existence of a reducing environment for the fluid. The pyrite-rich gray-colored veins and a silicified rock from well 51-WT-2 showed higher REE concentrations than did the white veins. Altered host andesitic rocks have similar REE patterns to that of the silicified rock, and have higher REE contents than the others in the drill cores. Aqueous speciation calculations showed that the fluid in the hydrothermal reservoir is currently in muscovite stability. The fluid at the ore-mineralization stage may have contained more potassium or have had a higher pH, so that adularia precipitated with calcite and quartz, as well as gold. Fluid boiling at depth in the system produced the gold-bearing calcite-quartz-adularia veins.  相似文献   

16.
Carbonate cementation in the surface layer of reefs and beachrock eliminates porosity and partially replaces detrital quartz grains. The uptake and release of CO2 by photosynthesis and respiration in reef communities cause a shift in the carbonate buffer system of seawater. Field studies and experimentation simulating the natural settings show minimum values of CO2 (1.9 mmoles 1?1) and HCO3? (2.4 meq 1?1) in association with maximum values of pH (9.8) and O2 (> 100% oxygen saturation) in waters covering corals and algae prior to sunset. The converse is true for these variables prior to sunrise, when minimum values of pH (7.6) and O2 (<66% oxygen saturation) occur with maximum values of CO2 (2.7 mmoles 1?1) and HCO3? (2.7 meq 1?1). Experimental tanks containing plain seawater showed almost no diurnal variability in pH (a constant 7.5–7.6) or O2 (80–90% oxygen saturation) measurements. Seawater adjacent to reef biomass, with elevated pH and supersaturated with calcium carbonate, is periodically pumped into the underlying reef and beach sediments due to pressure-buildups between the reef framework or algal zones and open waters. Carbonate precipitation and quartz dissolution follow. As the system equilibrates, pH values progressively decrease.  相似文献   

17.
Humic Ion-Binding Model V, which focuses on metal complexation with humic and fulvic acids, was modified to assess the role of dissolved natural organic matter in the speciation of rare earth elements (REEs) in natural terrestrial waters. Intrinsic equilibrium constants for cation-proton exchange with humic substances (i.e., pKMHA for type A sites, consisting mainly of carboxylic acids), required by the model for each REE, were initially estimated using linear free-energy relationships between the first hydrolysis constants and stability constants for REE metal complexation with lactic and acetic acid. pKMHA values were further refined by comparison of calculated Model V “fits” to published data sets describing complexation of Eu, Tb, and Dy with humic substances. A subroutine that allows for the simultaneous evaluation of REE complexation with inorganic ligands (e.g., Cl−, F−, OH−, SO42−, CO32−, PO43−), incorporating recently determined stability constants for REE complexes with these ligands, was also linked to Model V. Humic Ion-Binding Model V’s ability to predict REE speciation with natural organic matter in natural waters was evaluated by comparing model results to “speciation” data determined previously with ultrafiltration techniques (i.e., organic acid-rich waters of the Nsimi-Zoetele catchment, Cameroon; dilute, circumneutral-pH waters of the Tamagawa River, Japan, and the Kalix River, northern Sweden). The model predictions compare well with the ultrafiltration studies, especially for the heavy REEs in circumneutral-pH river waters. Subsequent application of the model to world average river water predicts that organic matter complexes are the dominant form of dissolved REEs in bulk river waters draining the continents. Holding major solute, minor solute, and REE concentrations of world average river water constant while varying pH, the model suggests that organic matter complexes would dominate La, Eu, and Lu speciation within the pH ranges of 5.4 to 7.9, 4.8 to 7.3, and 4.9 to 6.9, respectively. For acidic waters, the model predicts that the free metal ion (Ln3+) and sulfate complexes (LnSO4+) dominate, whereas in alkaline waters, carbonate complexes (LnCO3+ + Ln[CO3]2−) are predicted to out-compete humic substances for dissolved REEs. Application of the modified Model V to a “model” groundwater suggests that natural organic matter complexes of REEs are insignificant. However, groundwaters with higher dissolved organic carbon concentrations than the “model” groundwater (i.e., >0.7 mg/L) would exhibit greater fractions of each REE complexed with organic matter. Sensitively analysis indicates that increasing ionic strength can weaken humate-REE interactions, and increasing the concentration of competitive cations such as Fe(III) and Al can lead to a decrease in the amount of REEs bound to dissolved organic matter.  相似文献   

18.
A hydrogeochemical study of surface water of the West Bokaro coalfield has been undertaken to assess its quality and suitability for drinking, domestic and irrigation purposes. For this purpose, fourteen samples collected from rivers and ponds of the coalfield were analysed for pH, conductivity, total dissolved solids (TDS), major cations (Ca2+, Mg2+, Na+ and K+), major anions (HCO3-, F-, Cl-, SO42- and NO3-) and trace metals. The pH of the analysed water samples varied from 7.3 to 8.2, indicating slightly alkaline in nature. The electrical conductivity (EC) value varied from 93 μs cm-1 to 906 μs cm-1 while the TDS varied from 76 mg L-1 to 658 mg L-1. HCO3- and SO42- are the dominant anion and Ca2+ and Na+ the cation in the surface water. The concentration of alkaline earth metals (Ca2+ + Mg2+) exceed the alkali metals (Na+ + K+) and HCO3- dominates over SO42- + Cl- concentrations in the majority of the surface water samples. Ca2+ -Mg2+ -HCO3- and Ca2+ -Mg2+ -Cl- are the dominant hydrogeochemical facies in the surface water of the area. The water chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources. For quality assessment, analyzed water parameter values compared with Indian and WHO water quality standard. In majority of the samples, the analyzed parameters are well within the desirable limits and water is potable for drinking purposes. However, concentrations of TDS, TH, Ca2+, Mg2+ and Fe are exceeding the desirable limits in some water samples and needs treatment before its utilization. The calculated parameters such as sodium absorption ration, percent sodium, residual sodium carbonate, permeability index and magnesium hazard revealed good to permissible quality and suitable for irrigation purposes, however, higher salinity, permeability index and Mg-ratio restrict its suitability for irrigation at few sites.  相似文献   

19.
The variation of adsorption constants and isotope fractionation with pH and temperature during the adsorption of B from seawater onto marine clay have been examined. The controls over adsorption are similar to those exhibited by pure clay minerals (Bassett, 1976; Keren and Mezuman, 1981). The isotope fractionations are the result of equilibrium processes, not kinetic effects. Variations in the measured fractionation factor with pH arise from the differences between the isotope fractionation associated with adsorption of B(OH)3 and B(OH)4− and the pH dependence of B speciation. The implications of these results for the distribution of B isotopes in seawater and sediment porewaters are briefly discussed.  相似文献   

20.
Cupric carbonate and cupric bicarbonate complexation constants were determined in natural seawater and in a variety of synthetic media. The formation constants of CuHCO3+, CuCO30 and Cu(CO3)22? at 25°C and zero ionic strength are: log βH0 = 1.8, log β10 = 6.82 and log β02 = 10.6. Formation constants of these species appropriate to 0.7 molar ionic strength and 25°C are log βH ～- 1, log β1 = 5.73, log β2 = 9.3. Our results indicate that the inorganic speciation scheme of Cu(II) in seawater is dominated by CuCO30 and that the ternary species, CuCO3OH?, is of substantial importance.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号