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1.
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   

2.
The exceptional ability of dendrimers to coordinate metal ions yields the potential for many applications including wastewater remediation, which is the focus of this study. Here, the comparison of metal ion removal rate from simulated wastewater by generation 4 dendrimers with external hydroxyl functional groups (G4-OH) is evaluated for Ni2+, Fe2+, and Fe3+ ions. Ni2+ to amine complexation occurred more rapidly than Fe3+, which was more rapid than Fe2+ complexation. These results indicate that both charge density and d-electron configuration are important toward the chelation rate. The impact of both factors is discussed in light of existing models in which precursor aquation rates have been proposed as a key intermediate step. Additionally, the application of the dendrimers as chelation agents is further advanced by immobilizing the dendrimer to titania and re-evaluating its chelation ability for Ni2+ removal. The dendrimer immobilization decreased the pseudo-first-order rate coefficient for Ni2+—amine complexation at a pH of 7 by a factor of 7.5. This result is significant as it suggests that mass transfer becomes important following immobilization of the dendrimer to titania.  相似文献   

3.
Conditional surface binding constants and complexation capacities for Zn, Pb, Cd, and Cu were determined from surface titration experiments of heterogeneous natural aquatic particulate matter of different origin and composition. Metals and particles were evaluated in naturally occurring concentration ranges in river water.The adsorption of trace metals can be adequately described with a single conditional binding constant over a wide range of metal : particle ratios. Binding constants for aquatic particles at pH 8.0 are remarkably independent from particle composition and are specific for each metal: log Kads Zn = 8.39, log Kads Pb = 9.67, log Kads Cd = 8.61, log ads Cu = 9.84. From competition experiments with Ca and Pb we extracted a sorption coefficient for Ca of log Kads Ca = 2.5 (pH 8.0). Maximum surface binding capacities for all metal ions were found for particles containing high fractions of Mn-oxides which are associated with large specific surface areas. Generally, we found sorption capacities to decrease in the sequence Cu Pb, Zn > Cd.The experiments suggest that the conditional surface binding constants and complexation capacities are applicable to model trace metal adsorption in the concentration ranges of natural waters under conditions similar to the experiments. Results also imply that the chemical nature of particle surface sites is rather uniform in the intermediate concentration range or that the array of binding sites averages out differences in sorption strength over the prevailing concentration range of metal ions, respectively.  相似文献   

4.
Removal of Lead,Copper, Zinc and Cadmium from Water Using Phosphate Rock   总被引：2，自引：0，他引：2  
Removal of Pb^2＋, Cu^2＋, Zn^2＋ and Cd^2＋ from aqueous solutions by sorption on a natural phosphate rock （FAP） was investigated. The effects of the contact time and initial metal concentration were examined in the batch method. The percentage sorption of heavy metals from solution ranges generally between 50% and 99%. The amount of sorbed metal ions follows the order Cu〉Pb〉Cd〉Zn. Heavy metal immobilization was attributed to both surface complexation of metal ions on the surface of FAP grains and partial dissolution and precipitation of a heavy metal-containing phosphate. The very low desorption ratio of heavy metals further supports the effectiveness of FAP as an alternative and low-cost material to remove toxic Pb^2＋, Cu^2＋, Zn^2＋ and Cd^2＋ from polluted waters.  相似文献   

5.
Pb2+, like Cu2+, forms strong complexes with fulvic acids (Cd2+-fulvate complexes are much weaker), but Pb-fulvate precipitates at a much lower mole ratio of metal ion to fulvic acid than either Cu-fulvate or Cd-fulvate does. Physical association of Pb2+ with Pb-fulvate solids as well as complexation by sites still available in the precipitates probably causes the increased removal of free Pb2+ from solution after precipitation begins.  相似文献   

6.
《Geochimica et cosmochimica acta》1999,63(19-20):3311-3319
Copper speciation was determined monthly at seven sites on four rivers in southern New England to understand which geochemical factors control free metal ion concentrations in river water. Samples were conventionally filtered (<0.45 μm) and then ultrafiltered (3.000 molecular weight cut-off) to determine Cu speciation in the truly dissolved size fraction. Differential pulse anodic stripping voltammetry (DPASV) was used to quantify natural organic complexation and cathodic stripping square wave voltammetry (CSSWV) to measure directly both Cu sulfide complexes and total EDTA concentrations. The results showed both dissolved organic matter (DOM) and sulfide complexation dominate Cu speciation and control the concentrations of free ion. Free Cu2+ was calculated to be in the subnanomolar range for the majority of the year. Only in the winter months, when concentrations of DOM and metal sulfides complexes were at a minimum were free metal ions directly measurable by DPASV at low nanomolar concentrations. The extent of sulfide complexation appears to be dominated by the size of headwater marshes (upstream sampling sites) and by the amount of sewage treatment plant effluent (downstream sites). DOM complexation was related to the organic matter composition and followed model organic ligands. Indirect evidence suggests variations in river water pH and Ca2+ (metal competition) has only a minor role in Cu complexation. Measured concentrations of total EDTA suggest this synthetic ligand can control Cu speciation in some highly developed watersheds; however, competition from Ni (and possibly Fe) limits the extent of this complexation.  相似文献   

7.
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8.
The diffusion coefficients of aquo metal ions (Mz+) and their EDTA complexes (M-EDTA(z−4)+) were compared to understand the effect of EDTA complexation on the diffusion of metal ions by the diffusion cell method for Co2+, Ga3+, Rb+, Sr2+, Ag+, Cd2+, Cs+, Th4+, , and trivalent lanthanides. Most studies about ionic diffusion in water have dealt with free ion (hydrated ion). In many cases, however, polyvalent ions are dissolved as complexed species in natural waters. Hence, we need to study the diffusion behavior of complexes in order to understand the diffusion phenomenon in natural aquifer and to measure speciation by diffusive gradient in thin films (DGT), which requires the diffusion coefficients of the species examined. For many ions, the diffusion coefficients of M-EDTA(z−4)+ are smaller than those of hydrated ions, but the diffusion coefficients of M-EDTA(z−4)+ are larger than those of hydrated ions for ions with high ionic potentials (Ga3+ and Th4+). As a result, the diffusion coefficients of EDTA complexes are similar among various metal ions. In other words, the diffusion of each ion loses its characteristics by the complexation with EDTA. Although the difference is subtle, it was also found that the diffusion coefficients of EDTA complexes increase as the ionic potential increases, which can be explained by the size of the EDTA complex of each metal ion.  相似文献   

9.
《Geochimica et cosmochimica acta》1999,63(13-14):1955-1967
The investigation of the Cu2+ uptake by the calcium carbonate minerals vaterite and calcite with continuous wave and pulse electron paramagnetic resonance (EPR) yields information on a molecular scale about the relevant complexation reactions at the mineral–water interface. The structural assignment is based on changes in the coordination geometry of the copper complexes. Magnetic interactions of the unpaired Cu2+ electron with nuclei of 13C-labeled carbonate ligands and protons from water or hydroxyl ligands in the first and second coordination spheres of the cation are detected by pulse EPR techniques. Our results show that the Cu2+ ions are rapidly dehydrated upon adsorption on the mineral surface. The strong surface binding is due to monodentate coordination to three or four carbonate surface ions, comparable to chelate complexation in solution. The formation of square-planar or square-pyramidal copper complexes at exposed surface sites like kinks and steps yields a convincing explanation for the inhibition of calcium carbonate growth and dissolution. Upon recrystallization the Cu2+ ions are integrated into the calcite lattice where they exhibit a dynamic Jahn–Teller effect. The resulting local lattice distortions are expected to destabilize the CuxCa(1−x)CO3(s) solid solution. Our results support the concept of a dynamic calcium carbonate surface, covered by a thin, structured surface layer. The detailed structural information obtained for Cu2+ provides a better understanding of the interaction of other metal ions with calcium carbonate minerals.  相似文献   

10.
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   

11.
In this study, the speciation of Zn2+, Pb2+, and Cu2+ ions sorbed at the calcite surface was monitored during a 2.5-year reaction period, using extended X-ray absorption spectroscopy to characterize metal speciation on the molecular scale. Experiments were performed using pre-equilibrated calcite-water suspensions of pH 8.3, at metal concentrations below the solubility of metal hydroxide and carbonate precipitates, and at constant metal surface loadings. The EXAFS results indicate that all three metals remained coordinated at the calcite surface as inner-sphere adsorption complexes during the 2.5-year ageing period, with no evidence to suggest slow formation of dilute metal-calcite solid solutions under the reaction conditions employed. All three divalent metals were found to form non-octahedral complexes upon coordination to the calcite surface, with Zn2+ adsorbing as a tetrahedral complex, Cu2+ as a Jahn-Teller distorted octahedral complex, and Pb2+ coordinating as a trigonal- or square-pyramidal surface complex. The non-octahedral configurations of these surface complexes may have hindered metal transfer from the calcite surface into the bulk, where Ca2+ is in octahedral coordination with respect to first-shell O. The use of pre-equilibrated calcite suspensions, with no net calcite dissolution or precipitation, likely prevented metal incorporation into the lattice as a result of surface recrystallization. The results from this study imply that ageing alone does not increase the stability of Zn2+, Pb2+, and Cu2+ partitioning to calcite if equilibrium with the solution is maintained during reaction; under these conditions, these metals are likely to remain available for exchange even after extended sorption times.  相似文献   

12.
Aqueous iodine species occur mainly as iodide (I−) and iodate (IO3−), depending on redox conditions. The adsorption of IO3− on naturally occurring oxides under oxic conditions is of environmental concern. The adsorption behaviors of IO3− by hydrous ferric oxide (HFO), α-FeOOH, and γ-Al2O3 were examined in this study as functions of pH, ionic strength, and solid concentration. Adsorption data were analyzed using an extended triple-layer model (ETLM) for surface complexation modeling to infer IO3− adsorption reactions and equilibrium constants. Results of ETLM analysis suggest that adsorption of IO3− is both an outer-sphere and an inner-sphere process, as expressed by the following complexation reactions, which are consistent with the independent pressure jump kinetic results and adsorption enthalpy measurements
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13.
The adsorption behavior of Zn2+ ions onto the surface of amorphous aluminosilicates was studied using both potentiometric and spectroscopic methods (XANES: X-ray Absorption Near-Edge Structure). The aluminosilicates were prepared with different Al/Si ratios in order to compare the reactivities of surface aluminol and silanol groups toward Zn2+ ions. Potentiometric experiments were performed by maintaining the reacting suspensions at constant pH, ionic strength, and solid concentration, while Zn concentration was increased by stepwise addition. Our results showed that the surface aluminol and silanol groups possess significantly different reactivities toward Zn2+ ions. The reaction of Zn2+ ions with aluminol groups occurs through three processes: (i) surface complexation, (ii) dissolution, and (iii) re-sorption. A stoichiometric relationship was confirmed for the surface complexation between the aluminol groups and Zn2+ ions: two moles of H+ ions were released for one mole of Zn2+ ion adsorption. Following the surface complexation process, measurable amounts of zinc and aluminum ions were found to be mobilized from the surface of the solid to the liquid phase; subsequently, these ions precipitated on the solid surface, and possibly formed a co-precipitate with the hydrotalcite-type structure. On the other hand, a stoichiometric relationship was not obtained for the sorption of Zn2+ ions on silanol groups, and therefore, it was concluded that Zn2+ ions are retained on the surface of amorphous aluminosilicates by two different reactions. One reaction involves the surface complexation between Zn2+ ions and surface aluminol groups, which proceeds rapidly. The other reaction is the slow retention of Zn2+ ions onto silanol and/or aluminol groups, which could be the surface precipitation of Zn(OH)2 or the co-precipitation of Zn2+-Al3+ hydroxides. It can be suggested that the total sorption behavior of Zn2+ ions on amorphous aluminosilicates with different Al/Si ratios can be represented as the sum of the individual reactions of Zn2+ ions toward the aluminol and silanol groups. The potentiometric results were confirmed by XANES data. It was clearly evident that only the aluminol groups were responsible for surface complexation of Zn2+ ions. An equilibrium constant was calculated for this reaction.  相似文献   

14.
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   

15.
A new organic/inorganic composite based on polyacrylonitrile and stannic molybdophosphate (PAN–SMP) as an adsorbent was synthesized under various conditions. The physicochemical properties of this material were specified by elemental analysis, scanning electron microscopy, infrared spectroscopy and thermogravimetry studies. The synthesized material was found to be stable in demineralized water, in dilute acids, under gamma radiation up to the total radiated of 100 kGy doses and in high temperature up to 500 °C. Ion exchange capacity of the synthesized composite and its distribution coefficient (K d) for several metal ions were determined. The results showed that PAN–SMP has a great affinity toward some metal ions such as Tl+, Sr2+, Ba2+, UO2 2+ and La4+. Based on the determined K d values, two binary quantitative separations of metal ions (Cr6+ from Cu2+ and Pb2+ from Cu2+) have been achieved on columns of this ion exchanger. The ability of PAN–SMP to decontaminate low-level liquid waste was also investigated.  相似文献   

16.
In environmental studies, it is necessary to be able to predict the behaviour of contaminants in more or less complex physico-chemical contexts. The improvement of this prediction partly depends on establishing thermodynamic models that can describe the behaviour of these contaminants and, in particular, the sorption reactions on mineral surfaces. In this way, based on the mass action law, it is possible to use surface complexation models and ion exchange models. Therefore, the aim of this study is (i) to develop an ion-exchange model able to describe the sorption of transition metal onto pure clay minerals and (ii) to test the ability of this approach to predict the sorption of these elements onto natural materials containing clay minerals (i.e. soils/sediments) under various chemical conditions. This study is focused on the behaviour of Zn(II) in the presence of clayey sediments. Considering that clay minerals are cation exchangers containing multiple sorption sites, it is possible to interpret the sorption of Zn(II), as well as competitor cations, by ion-exchange equilibria with the clay minerals. This approach is applied with success to interpret the experimental data obtained previously in the Zn(II)–H+–Na+–montmorillonite system. The authors’ research team has already studied the behaviour of Na+, K+, Ca2+ and Mg2+ versus pH in terms of ion exchange onto pure montmorillonite, leading to the development of a thermodynamic database including the exchange site concentrations associated with montmorillonite and the selectivity coefficients of Na+, K+, Ca2+, Mg2+, and Zn2+ versus H+.  相似文献   

17.
The sorption of ferrous iron to a clay mineral, nontronite (NAu-2, a ferruginous smectite), was investigated under strictly anoxic conditions as a function of pH (3-10), Fe2+ concentration (0.01-50 mM), equilibration time (1-35 days), and ionic strength (0.01-0.5 M NaClO4). The surface properties of NAu-2 were independently characterized to determine its fixed charge and amphoteric site density in order to interpret the Fe2+ sorption data. Fe2+ sorption to NAu-2 was strongly dependent on pH and ionic strength, reflecting the coupled effects of Fe2+ sorption through ion exchange and surface complexation reactions. Fe2+ sorption to NAu-2 increased with increasing pH from pH 2.5 to 4.5, remained constant from pH 4.5 to 7.0, increased again with further increase of pH from pH 7.0 to 8.5, and reached a maximum above pH 8.5. The Fe2+ sorption below pH 7.0 increased with decreasing ionic strength. The differences of Fe2+ sorption at different ionic strengths, however, diminished with increasing equilibration time. The Fe2+ sorption from pH 4.5 to 7.0 increased with increasing equilibration time up to 35 days and showed stronger kinetic behavior in higher ionic strength solutions. The kinetic uptake of Fe2+ onto NAu-2 is consistent with a surface precipitation mechanism although our measurements were not able to identify secondary precipitates. An equilibrium model that integrates ion exchange, surface complexation and aqueous speciation reactions reasonably well describes the Fe2+ sorption data as a function of pH, ionic strength, and Fe2+ concentration measured at 24 h of equilibration. Model calculations show that the species Fe(OH)+ was required to describe Fe2+ sorption above pH 8.0 satisfactorily. Overall, this study demonstrated that Fe2+ sorption to NAu-2 is affected by complex equilibrium and kinetic processes, likely caused by surface precipitation reactions.  相似文献   

18.
A. A. Borisov 《Petrology》2012,20(4):391-398
Using published experimental data an expression was derived for the Ti4+/Ti3+ ratio as a function of temperature, oxygen fugacity, and melt composition. The equation can be used to estimate Ti3+ content in lunar basaltic melts. It was shown that the Ti3+ content in melts is probably no higher than the Fe3+ content even under the reduced conditions typical of lunar magmas. Trivalent Ti can lead to some decrease in $f_{O_2 }$ during melt cooling under closed-system conditions, but it cannot reduce Fe2+ in melt to metal, because it will be completely consumed by Fe3+ reduction to Fe2+. The presence of additional reducers, such as Cr2+, can be favorable for the formation of metal during melt cooling.  相似文献   

19.
X-ray absorption fine structure (XAFS) measurements was used at the U L3-edge to directly determine the pH dependence of the cell wall functional groups responsible for the absorption of aqueous UO22+ to Bacillus subtilis from pH 1.67 to 4.80. Surface complexation modeling can be used to predict metal distributions in water-rock systems, and it has been used to quantify bacterial adsorption of metal cations. However, successful application of these models requires a detailed knowledge not only of the type of bacterial surface site involved in metal adsorption/desorption, but also of the binding geometry. Previous acid-base titrations of B. subtilis cells suggested that three surface functional group types are important on the cell wall; these groups have been postulated to correspond to carboxyl, phosphoryl, and hydroxyl sites. When the U(VI) adsorption to B. subtilis is measured, observed is a significant pH-independent absorption at low pH values (<3.0), ascribed to an interaction between the uranyl cation and a neutrally charged phosphoryl group on the cell wall. The present study provides independent quantitative constraints on the types of sites involved in uranyl binding to B. subtilis from pH 1.67 to 4.80. The XAFS results indicate that at extremely low pH (pH 1.67) UO22+ binds exclusively to phosphoryl functional groups on the cell wall, with an average distance between the U atom and the P atom of 3.64 ± 0.01 Å. This U-P distance indicates an inner-sphere complex with an oxygen atom shared between the UO22+ and the phosphoryl ligand. The P signal at extremely low pH value is consistent with the UO22+ binding to a protonated phosphoryl group, as previously ascribed. With increasing pH (3.22 and 4.80), UO22+ binds increasingly to bacterial surface carboxyl functional groups, with an average distance between the U atom and the C atom of 2.89 ± 0.02 Å. This U-C distance indicates an inner-sphere complex with two oxygen atoms shared between the UO22+ and the carboxyl ligand. The results of this XAFS study confirm the uranyl-bacterial surface speciation model.  相似文献   

20.
《Applied Geochemistry》2000,15(7):953-973
The enhancement of mobility of radionuclides in the geosphere through complexation by humic substances is a source of uncertainty in performance assessment of radioactive waste repositories. Only very few data sets are available which are relevant for performance assessment of an underground repository for radioactive waste. Using the equilibrium dialysis-ligand exchange method developed at the Paul Scherrer Institut, conditional stability constants for the formation of complexes of Aldrich humic acid with Ca2+, NpO2+, Co2+, Ni2+, UO22+ and Eu3+ and complexes of Laurentian soil- and Suwannee River fulvic acid with Co2+, UO22+ and Eu3+ were measured. pH was varied between 5 and 10 and ionic strength between 0.02 and 0.2 M. The data are presented as equilibrium coefficients that are free from any model assumptions. The equilibrium coefficients increased in the order Ca2+≅NpO2+<Co2+< Ni2+<UO22+< Eu3+. The quality of the data is assessed in an extended discussion of statistical and systematical errors, and by a critical ‘rereview’ of the auxiliary stability constants used for the calculation of the equilibrium coefficients. An approximate overall uncertainty of 0.5 log-units is estimated for the stability data reported. The conditional stability constants were found to increase markedly with increasing pH in the case of Co2+, UO22+ and Eu3+. For Ni2+, Ca2+ and NpO2+ this effect was less pronounced. For all metal ions tested, the influence of ionic strength was of less importance, and the conditional stability constants did not show a significant dependence on the type of humic substances investigated.  相似文献   

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