共查询到20条相似文献，搜索用时 15 毫秒
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James A. Davis 《Geochimica et cosmochimica acta》1984,48(4):679-691
The adsorption behavior and solution speciation of Cu(II) and Cd(II) were studied in model systems containing colloidal alumina particles and dissolved natural organic matter. At equilibrium a significant fraction of the alumina surface was covered by adsorbed organic matter. Cu(II) was partitioned primarily between the surface-bound organic matter and dissolved Cu-organic complexes in the aqueous phase. Complexation of Cu2+ with the functional groups of adsorbed organic matter was stronger than complexation with uncovered alumina surface hydroxyls. It is shown that the complexation of Cu(II) by adsorbed organic matter can be described by an apparent stability constant approximately equal to the value found for solution phase equilibria. In contrast, Cd(II) adsorption was not significantly affected by the presence of organic matter at the surface, due to weak complex formation with the organic ligands. The results demonstrate that general models of trace element partitioning in natural waters must consider the presence of adsorbed organic matter. 相似文献
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Sofie P. Pasilis 《Geochimica et cosmochimica acta》2008,72(2):277-287
ATR-FTIR spectroscopy is used to understand the adsorption of uranyl-citrate complexes to Al2O3. Spectral data indicate that uranyl-citrate complexes partially dissociate upon adsorption, allowing full or partial hydrolysis of the uranyl ion. Kads values determined for free citrate adsorption are similar to those for citrate in uranyl-citrate complexes, indicating that the complexation of uranyl by citrate does not significantly affect the ability of citrate to bond with the surface. The isotherm data also indicate enhanced citrate adsorption to Al2O3 in the presence of uranyl, suggesting that uranyl may be the central link between two citrate ligands, and that uranyl is associated with the surface through a bridging citrate ligand. Finally, uranyl-citrate complexes interact with citrate adsorbed to Al2O3 through outer sphere interactions. 相似文献
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Sabine Goldberg Scott M. Lesch Donald L. Suarez 《Geochimica et cosmochimica acta》2007,71(23):5750-5762
The constant capacitance model, a chemical surface complexation model, was applied to selenite, Se(IV), adsorption on 36 soils selected for variation in soil chemical properties. The constant capacitance model was able to fit Se(IV) adsorption by optimizing one monodentate Se(IV) surface complexation constant and the surface protonation constant. A general regression model was developed for predicting these surface complexation constants for Se(IV) from easily measured soil chemical characteristics. These chemical properties were inorganic carbon content, organic carbon content, iron oxide content, aluminum oxide content, and surface area. The prediction equations were used to obtain values for the surface complexation constants for four additional soils, thereby providing a completely independent evaluation of the ability of the constant capacitance model to describe Se(IV) adsorption. The model’s ability to predict Se(IV) adsorption was quantitative on one soil and semi-quantitative on three soils. Incorporation of these prediction equations into chemical speciation-transport models will allow simulation of soil solution Se(IV) concentrations under diverse non-calcareous agricultural and environmental conditions without the requirement of soil specific adsorption data and subsequent parameter optimization. 相似文献
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Rare earth element (REE) adsorption onto sand from a well characterized aquifer, the Carrizo Sand aquifer of Texas, has been investigated in the laboratory using a batch method. The aim was to improve our understanding of REE adsorption behavior across the REE series and to develop a surface complexation model for the REEs, which can be applied to real aquifer-groundwater systems. Our batch experiments show that REE adsorption onto Carrizo sand increases with increasing atomic number across the REE series. For each REE, adsorption increases with increasing pH, such that when pH >6.0, >98% of each REE is adsorbed onto Carrizo sand for all experimental solutions, including when actual groundwaters from the Carrizo Sand aquifer are used in the experiments. Rare earth element adsorption was not sensitive to ionic strength and total initial REE concentrations in our batch experiments. It is possible that the differences in experimental ionic strength conditions (i.e., 0.002-0.01 M NaCl) chosen were insufficient to affect REE adsorption behavior. However, cation competition (e.g., Ca, Mg, and Zn) did affect REE adsorption onto Carrizo sand, especially for light rare earth elements (LREEs) at low pH. Rare earth element adsorption onto Carrizo sand can be successfully modeled using a generalized two-layer surface complexation model. Our model calculations suggest that REE complexation with strong surface sites of Carrizo sand exceeds the stability of the aqueous complexes LnOH2+, LnSO4+, and LnCO3+, but not that of Ln(CO3)2- or LnPO4o in Carrizo groundwaters. Thus, at low pH (<7.3), where major inorganic ligands did not effectively compete with surface sites for dissolved REEs, free metal ion (Ln3+) adsorption was sufficient to describe REE adsorption behavior. However, at higher pH (>7.3) where solution complexation of the dissolved REEs was strong, REEs were adsorbed not only as free metal ion (Ln3+) but also as aqueous complexes (e.g., as Ln(CO3)2- in Carrizo groundwaters). Because heavy rare earth elements (HREEs) were preferentially adsorbed onto Carrizo sand compared to LREEs, original HREE-enriched fractionation patterns in Carrizo groundwaters from the recharge area flattened along the groundwater flow path in the Carrizo Sand aquifer due to adsorption of free- and solution-complexed REEs. 相似文献
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A. Gélabert O.S. Pokrovsky J. Schott A. Feurtet-Mazel 《Geochimica et cosmochimica acta》2007,71(15):3698-3716
This work is devoted to the physico-chemical study of cadmium and lead interaction with diatom-water interfaces for two marine planktonic (Thalassiosira weissflogii, TW; Skeletonema costatum, SC) and two freshwater periphytic species (Achnanthidium minutissimum, AMIN; Navicula minima, NMIN) by combining adsorption measurements with surface complexation modeling. Adsorption kinetics was studied as a function of pH and initial metal concentration in sodium nitrate solution and in culture media. Kinetic data were consistent with a two-step mechanism in which the loss of a water molecule from the inner coordination sphere of the metal is rate limiting. Reversible adsorption experiments, with 3 h of exposure to metal, were performed as a function of pH (2-9), metal concentration in solution (10−9-10−3 M), and ionic strength (10−3-1.0 M). While the shape of pH-dependent adsorption edge is similar among all four diatom species, the constant-pH adsorption isotherm and maximal binding capacities differ. Measurements of electrophoretic mobilities (μ) revealed negative surface potential for AMIN diatom, however, the absolute value of μ decreases with increase of [Pb2+]aq suggesting the metal adsorption on negative surface sites. These observations allowed us to construct a surface complexation model (SCM) for cadmium and lead binding by diatom surfaces that postulates the Constant Capacitance of the electric double layer and considers Cd and Pb complexation with mainly carboxylic and, partially, silanol groups. In the full range of investigated Cd concentration, the SCM is able to describe the concentration of adsorbed metal as a function of [Cd2+]aq without implying the presence of high affinity, low abundance sites, that are typically used to model the metal interactions with natural multi-component organic substances. At the same time, Cd fast initial reaction requires the presence of “highly reactive sites” those concentration represents only 2.5-3% of the total amount of carboxylic sites. For reversible adsorption experiments, the dominating carboxylic groups, whose concentration is allowed to vary within the uncertainty of experimental acid-base titrations, are sufficient to reproduce the metal adsorption isotherms. Results of this study strongly suggest that laboratory experiments performed in a wide range of metal to biomass ratios, represent robust and relatively simple method for assessing the distribution of metals between aqueous solution and planktonic and periphytic biomass in natural settings. 相似文献
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高岭石对重金属离子的吸附机理及其溶液的pH条件 总被引：14，自引：0，他引：14
高岭石对Cu^2+,Pb^2+离子的吸附实验及高岭石的溶解实验表明,高岭石对重金属离子的吸附有别于石英单一表面配位模式,离子交换和表面配位模式并存,并随溶液pH由酸性往碱性的变化发生规律性的演替：pH<6.5时主要表现为外圈层配位的离子交换吸附,且在pH<4时由于受到高岭石表层中铝的高溶出及溶液中较高离子强度的影响,高岭石对Cu^2+,Pb^2+离子的吸附率较低,pH为5～6时由于高岭石端面的荷电性为近中性,吸附率则有明显的提升并且表现为一个吸附平台;pH>6.5时离子交换和表面配位均为重要吸附机制,pH再升高时沉淀机制则起着重要作用。研究表明,pH调控高岭石-水界面溶解与质子化-去质子化反应过程,并影响着Cu^2+,Pb^2+离子的吸附行为。最后采用Sverjensky(1993)表面配位的物理模型对吸附结果作了描述。 相似文献
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Tjisse Hiemstra A.M.D. van Rotterdam Willem H. van Riemsdijk 《Geochimica et cosmochimica acta》2010,74(1):59-8428
Information on the particle size and reactive surface area of natural samples and its interaction with natural organic matter (NOM) is essential for the understanding bioavailability, toxicity, and transport of elements in the natural environment. In part I of this series (Hiemstra et al., 2010), a method is presented that allows the determination of the effective reactive surface area (A, m2/g soil) of the oxide particles of natural samples which uses a native probe ion (phosphate) and a model oxide (goethite) as proxy. In soils, the natural oxide particles are generally embedded in a matrix of natural organic matter (NOM) and this will affect the ion binding properties of the oxide fraction. A remarkably high variation in the natural phosphate loading of the oxide surfaces (Γ, μmol/m2) is observed in our soils and the present paper shows that it is due to surface complexation of NOM, acting as a competitor via site competition and electrostatic interaction. The competitive interaction of NOM can be described with the charge distribution (CD) model by defining a ≡NOM surface species. The interfacial charge distribution of this ≡NOM surface species can be rationalized based on calculations done with an evolved surface complexation model, known as the ligand and charge distribution (LCD) model. An adequate choice is the presence of a charge of −1 v.u. at the 1-plane and −0.5 v.u. at the 2-plane of the electrical double layer used (Extended Stern layer model).The effective interfacial NOM adsorption can be quantified by comparing the experimental phosphate concentration, measured under standardized field conditions (e.g. 0.01 M CaCl2), with a prediction that uses the experimentally derived surface area (A) and the reversibly bound phosphate loading (Γ, μmol/m2) of the sample (part I) as input in the CD model. Ignoring the competitive action of adsorbed NOM leads to a severe under-prediction of the phosphate concentration by a factor ∼10 to 1000. The calculated effective loading of NOM is low at a high phosphate loading (Γ) and vice versa, showing the mutual competition of both constituents. Both constituents in combination usually dominate the surface loading of natural oxide fraction of samples and form the backbone in modeling the fate of other (minor) ions in the natural environment.Empirically, the effective NOM adsorption is found to correlate well to the organic carbon content (OC) of the samples. The effective NOM adsorption can also be linked to DOC. For this, a Non-Ideal Competitive adsorption (NICA) model is used. DOC is found to be a major explaining factor for the interfacial loading of NOM as well as phosphate. The empirical NOM-OC relation or the parameterized NICA model can be used as an alternative for estimating the effective NOM adsorption to be implemented in the CD model for calculation of the surface complexation of field samples. The biogeochemical impact of the NOM-PO4 interaction is discussed. 相似文献
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WU Daqing DIAO Guiyi YUAN Peng PENG Jinlian 《《地质学报》英文版》2006,80(2):192-199
The adsorption of pentachlorophenol （PCP） onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values, the position of which is at about pH = 5-6 depending on the mineral species. Based on distribution of both speciation of surface hydroxyls on minerals and PCP in solution a surface reaction model involving surface complexation and surface electrostatic attraction is presented to fit the pH-dependent isotherms, and both reaction constants are calculated. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation, meanwhile both of surface electrostatic attraction and surface complexation are involved on the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders in magnitude, larger than that of surface complexation. The concentration-dependent isotherms can be well fitted by Langmnir equation with the correlation coefficient R〉0.93 for kaolinite and iron oxides. The maximum adsorption is found in the order： hematite 〉 lepidocrocite 〉 goethite 〉 kaolinite 〉 quartz 〉 montmorillonite ≈ illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP onto mineral surfaces suggests that clay and iron oxide minerals will play an important role as HIOCs are adsorbed in laterite or latertoid soil, which is widespread in South China. 相似文献
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Li Ping Weng Luuk K. Koopal Johannes C.L. Meeussen 《Geochimica et cosmochimica acta》2005,69(2):325-339
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微生物参与下的水/粒界面吸附反应研究进展 总被引：3，自引：0，他引：3
回顾了近年来微生物存在下的水/粒界面吸附反应研究进展，包括微生物对金属阳离子的吸附、矿物微粒对微生物的吸附和微生物参与下的水/粒界面吸附；目前，这些吸附反应的定量化模型研究主要有体积分配关系和表面络合模型两种方法。其中，体积分配关系可从野外直接测得；而表面络合模型是采用不受溶液条件变化影响的准热力学常数来描述表面化学反应，能外推至实验室无法直接模拟的条件。随着人们对微生物在环境中重要性认识的加深，微生物参与下的水/粒界面吸附和可预测吸附程度的定量化模型受到人们越来越多的重视。 相似文献
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为更加准确地模拟重金属随泥沙迁移的过程,避免传统模型在描述重金属的吸附解吸时只能片面地考虑简单物理过程的不足,在水沙输移模拟的基础上,同时考虑了重金属随泥沙迁移的物理和化学过程,建立了完整的水动力-泥沙-重金属迁移数学模型。模型利用泥沙颗粒表面复杂形貌与电荷的关系来修正表面络合模型并以此分析了水体中的重金属与泥沙颗粒表面基团间的化学成键作用,同时根据化学反应的不同条件,并结合床面冲淤,将床面泥沙分为有氧层和无氧层分别考虑重金属的沉积与再释放。模型模拟了水槽试验中重金属Ni随泥沙迁移的情况,计算结果与实测数据的对比表明了建立的模型可以合理地反映重金属随泥沙的迁移过程。 相似文献
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The complexation of Cu and Cd by ligands observed in filtered unfractionated lakewaters is compared to the complexation by humic and fulvic acids. Complexation parameters (conditional stability constants and ligand concentrations) of Suwannee River fulvic acids (FA), purified peat humic acids (HA) and of ligands in lakewater samples have been determined using the same methods (ligand-exchange and CSV (cathodic stripping voltammetry) or ASV (anodic stripping voltammetry)), and the same titration ranges of Cu, Cd and organic carbon concentrations. The performance of the used techniques is first evaluated in FA and HA suspensions, and gives comparable results with the literature values for the same materials, according to published models (5-site model, NICA model) and parameters. Model calculations using the WHAM model for FA and HA (Tipping, 1994) are also presented. The comparison of titrations of FA and HA with Cu and Cd with those of lakewater samples indicates that stronger ligands than FA and HA are present at low concentrations in the lakewaters. Specific strong ligands occur in particular in eutrophic lake waters, whereas in a lake with higher metal concentrations and low biological productivity the ligands more closely match the fulvic acid characteristics. 相似文献
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《Applied Geochemistry》2004,19(10):1643-1653
Reactive solute transport simulations in groundwater require a large number of parameters to describe hydrologic and chemical reaction processes. Appropriate methods for determining chemical reaction parameters required for reactive solute transport simulations are still under investigation. This work compares U(VI) distribution coefficients (i.e. KD values) measured under field conditions with KD values calculated from a surface complexation model developed in the laboratory. Field studies were conducted in an alluvial aquifer at a former U mill tailings site near the town of Naturita, CO, USA, by suspending approximately 10 g samples of Naturita aquifer background sediments (NABS) in 17-5.1-cm diameter wells for periods of 3 to 15 months. Adsorbed U(VI) on these samples was determined by extraction with a pH 9.45 NaHCO3/Na2CO3 solution. In wells where the chemical conditions in groundwater were nearly constant, adsorbed U concentrations for samples taken after 3 months of exposure to groundwater were indistinguishable from samples taken after 15 months. Measured in situ KD values calculated from the measurements of adsorbed and dissolved U(VI) ranged from 0.50 to 10.6 mL/g and the KD values decreased with increasing groundwater alkalinity, consistent with increased formation of soluble U(VI)-carbonate complexes at higher alkalinities. The in situ KD values were compared with KD values predicted from a surface complexation model (SCM) developed under laboratory conditions in a separate study. A good agreement between the predicted and measured in situ KD values was observed. The demonstration that the laboratory derived SCM can predict U(VI) adsorption in the field provides a critical independent test of a submodel used in a reactive transport model. 相似文献
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矿物-水界面的表面离子化和络合反应模式 总被引：19，自引：1，他引：19
表面络合模式已广泛应用于研究矿物表面吸附和溶解反应,尤其是(氢)氧化物和层状铝硅酸盐矿物。表面官能团是矿物参与表面络合反应的基本单元,(氢)氧化物矿物只具有表面羟基,而层状铝硅酸盐矿物除表面羟基外还具有离子交换位。矿物的表面电荷由永久结构电荷、配位表面电荷和离解表面电荷组成,各种零表面电荷状态可由不同的零电荷点来表征。恒电容模式、双层模式和三层模式是3种最常用的表面络合模式,它们在双电层结构、表面反应(质子化反应和络合反应)、表面电荷与质量平衡方程及应用范围上存在着一些差异。 相似文献
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F. Ranjbar M. Jalali 《International Journal of Environmental Science and Technology》2014,11(5):1317-1326
This study aimed to evaluate boron (B) adsorption and the capacity of a surface complexation model for simulating this process in calcareous soils. Ten surface soils were collected from different land use areas in Hamedan, Western Iran, to characterize B sorption by soils. The mean B adsorbed by the sample soils varied from 8.9 to 32.8 %. Two empirical models including linear and Freundlich equations fitted well to the experimental data. The linear distribution (K d) values varied from 1.32 to 6.86 L kg?1, while the parameters of Freundlich equation including n and K Fr ranged from 1.16 to 1.33 and 3.31–16.81, respectively. The comparison of two empirical models indicated that B adsorption followed a nonlinear pattern. The soil organic matter had positive correlations with Freundlich and linear distribution coefficients. However, empirical models were not suitable for explaining the mechanism of B adsorption, so a surface complexation model was used to simulate and predict the B adsorption process. B adsorption modeling was conducted using Visual MINTEQ and PHREEQC, based on the assemblage of major surface components (hydrous ferric oxides, aluminum hydroxides, calcium carbonate, and humic acids). B adsorption was successfully modeled by surface complexation. The significant contribution of organic matter to B complexes was resulted from both experimental data and mechanistic modeling. 相似文献