Metal–organic complexation in the marine environment

We discuss the voltammetric methods that are used to assess metal–organic complexation in seawater. These consist of titration methods using anodic stripping voltammetry (ASV) and cathodic stripping voltammetry competitive ligand experiments (CSV-CLE). These approaches and a kinetic approach using CSV-CLE give similar information on the amount of excess ligand to metal in a sample and the conditional metal ligand stability constant for the excess ligand bound to the metal. CSV-CLE data using different ligands to measure Fe(III) organic complexes are similar. All these methods give conditional stability constants for which the side reaction coefficient for the metal can be corrected but not that for the ligand. Another approach, pseudovoltammetry, provides information on the actual metal–ligand complex(es) in a sample by doing ASV experiments where the deposition potential is varied more negatively in order to destroy the metal–ligand complex. This latter approach gives concentration information on each actual ligand bound to the metal as well as the thermodynamic stability constant of each complex in solution when compared to known metal–ligand complexes. In this case the side reaction coefficients for the metal and ligand are corrected. Thus, this method may not give identical information to the titration methods because the excess ligand in the sample may not be identical to some of the actual ligands binding the metal in the sample.     

Comparison of the Complexation of Cu and Cd by Humic or Fulvic Acids and by Ligands Observed in Lake Waters

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.     

Metal Complexation with Different types of Soluble and Adsorbed Freshwater Ligands Followed by DPASV

In order to understand metal speciation in a polluted river (Este River, Northern Portugal) filtrate, freeze dried particles and organics desorbed from surfaces were titrated with Cd(II) and Zn(II), followed by differential pulse anodic stripping voltammetry (DPASV). The obtained results are compared with those previously published for Pb(II) and Cu(II). Due to the heterogeneity of the system, a continuous and a discrete ligand model were used to interpret the titration data. Two types of ligands could be detected and quantified by the discrete ligand model: small molecules with high affinities for cations such as Cd(II), Cu(I), and Zn(II) and macromolecules with higher affinities for Pb(II) and Cu(II). Small ligands were strongly adsorbed onto the particles, as inferred from the desorption of Zn(II) during titration with Pb(II) and Cd(II). The total concentrations of the different ligands and the complex formation constants with the different metals are reported.     

Geochemical factors controlling free Cu ion concentrations in river water

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.     

On-site mercury analysis of soil at hazardous waste sites: by immunoassay and ASV

Two field methods for Hg, immunoassay and anodic stripping voltammetry (ASV), that can provide onsite results for quick decisions at hazardous waste sites were evaluated. Each method was applied to samples from two Superfund sites that contain high levels of Hg; Sulphur Bank Mercury Mine site, Clear Lake, California, and Carson River Mercury site, Nevada. Two laboratory methods were used for comparison purposes; cold vapor atomic fluorescence spectrometry (CVAFS) and inductively coupled plasma-mass spectrometry (ICP-MS). The immunoassay was found to be accurate for high and low Hg concentrations compared to the 5 and 15 μg/g soil sample standards provided with it. Despite poor agreement between immunoassay and confirmatory analysis results at concentrations near the comparison standards, the immunoassay could be used as an effective screening method provided care is taken in identifying an operational screening level. The ASV method had an analytical range of 1–50 μg/g, with a CV of 15%. ASV results were comparable to CVAFS (CV=15%) and more precise than ICP-MS (CV=20%). The lower limit of quantitative results was 3 μg/g for field samples, and is attributed to uncertainty associated with sampling.     

微分电位溶出分析测定配合物稳定常数的研究

报道用微分电位溶出分析法测定配合物在玻炭电极上氧化溶出电位与配位体浓度之间的关系，研究配合物的逐级稳定常数和参与形成配合物的配位体数目。研究了Ｃｕ（Ｈ２Ｓａｌ）２＋２和Ｃｄ（ＳＣＮ）２－４配合物体系，测定结果与文献［３，４］报道结果基本吻合     

Competitive sorption of copper and lead at the oxide-water interface: Implications for surface site density

The competitive sorption of Cu(II) and Pb(II) to colloidal hematite was investigated as a function of pH and total metal concentration. Acid–base titrations of the hematite and single-metal sorption experiments for Cu and Pb at low to medium surface coverages were used to calibrate two surface complexation models, the triple layer model, and a 2-pK basic Stern model with ion-pair formation. The surface site density was systematically varied from 2 to 20 sites/nm². Three different metal surface complexes were considered: (1) an inner-sphere metal complex; (2) an outer-sphere metal complex; and (3) an outer-sphere complex of singly hydrolyzed metal cations. Both models provided excellent fits to acid–base titration and single-metal sorption data, regardless of the surface site density used. With increasing site density, ΔpK of the stability constants for protonation reactions increased and metal surface complexes decreased steadily. The calibrated models based on different site densities were used to predict competitive sorption effects between Cu and Pb and single-metal sorption at higher total metal concentrations. Precipitation of oversaturated solid phases was included in the calculations. Best predictions of competitive sorption effects were obtained with surface site densities between 5 and 10 sites/nm². The results demonstrate that surface site density is a key parameter if surface complexation models are exposed to more complex, multicomponent environments. We conclude that competitive metal sorption experiments can be used to obtain additional information about the relevant surface site density of oxide mineral surfaces.     

A Donnan potential model for metal sorption onto Bacillus subtilis

In this study, we conducted electrophoretic mobility, potentiometric titration, and metal sorption experiments to investigate the surface charge characteristics of Bacillus subtilis and the electrostatic interactions between metal cations and the cell surface electric field. Electrophoretic mobility experiments performed as a function of pH and ionic strength show an isoelectric point of pH 2.4, with the magnitude of the electrokinetic potential increasing with increasing pH, and decreasing with increasing ionic strength. Potentiometric titration experiments conducted from pH 2.4 to 9 yield an average surface charge excess of 1.6 μmol/mg (dry mass). Corresponding cell wall charge density values were used to calculate the Donnan potential (Ψ_DON) as function of pH and ionic strength. Metal sorption experiments conducted with Ca(II), Sr(II), and Ba(II) exhibit strong ionic strength dependence, suggesting that the metal ions are bound to the bacterial cell wall via an outer-sphere complexation mechanism. Intrinsic metal sorption constants for the sorption reactions were determined by correcting the apparent sorption constant with the Boltzmann factor. A 1:2 metal-ligand stoichiometry provides the best fit to the experimental data with log K₂^int values of 5.9 ± 0.3, 6.0 ± 0.2, 6.2 ± 0.2 for Ca(II), Sr(II), and Ba(II) respectively. Electrophoretic mobility measurements of cells sorbed with Ca(II), Sr(II), and Ba(II) support the 1:2 sorption stoichiometry. These results indicate that electrical potential parameters derived from the Donnan model can be applied to predict metal binding onto bacterial surfaces over a wide range of pH and ionic strength conditions.     

大九湖泥炭沼泽源铁有机配合物的络合稳定性及其生态环境意义

为了研究泥炭沼泽源铁有机配合物的络合稳定性,利用pH电位滴定法和荧光淬灭滴定法测定了大九湖泥炭沼泽中不同分子量段的DOM和Fe2+、Fe3+的络合稳定常数.pH电位滴定法结果（4.0~6.1）和荧光淬灭滴定法（1.5~4.1）差异较大,这与高pH条件下OH被脱质子化及Fe2+的氧化有关.相对而言,pH滴定法更适用于探究不同分子量段DOM与铁的络合稳定性,荧光淬灭法不改变样品酸碱条件,更适于研究不同价态铁与DOM的络合稳定性.研究结果表明:DOM与Fe3+的络合稳定常数大于Fe2+,低分子量段（< 3 kDa）的DOM与Fe2+、Fe3+的络合稳定常数更大.泥炭沼泽源铁有机配合物具有较好的络合稳定性,分子量相对较小的DOM与铁的络合能力更强.即便Fe2+氧化为Fe3+,仍能与DOM络合并保持较强的稳定性,这有利于陆源溶解性铁向水生态系统的输出.沼泽源铁有机配合物的络合稳定性还会影响铁的生物可利用性.      

贝叶斯方法在洪水保险费调整中的应用

在洪水保险中,获得的样本信息不符合对统计样本的理论要求.因此,本文运用贝叶斯统计方法,依据先验信息数据确定的保险费,结合新的理赔记录,调整和校正赔款频率和平均赔款额,从而正确估计保险费.使其符合实际的风险水平.并运用实例分析了贝叶斯方法的可行性,本文的方法和结论可供开展洪水保险项目研究和业务工作参考.     

固体汞电极溶出伏安法测定地下水示踪剂中的铜及实验应用

用易溶于水的金属盐类试剂作示踪剂,是岩溶地下水示踪试验中广泛采用的有效方法,通过野外现场测定人工示踪剂中的金属离子可以揭示岩溶地下水的运动特征.传统极谱法所用的液态汞操作不便,且容易造成环境污染.本文制作了固体汞电极,采用溶出伏安法测定地下水示踪剂中的铜,在地下水样品中加入醋酸一醋酸钠缓冲溶液,氯化钾溶液作为支持电解质,采用固体汞电极扫描,记录溶出曲线.实验了氯化钾溶液、醋酸-醋酸钠缓冲溶液用量对100 ng/mL铜标准工作溶液峰电流的影响,在选定最佳实验条件下,铜浓度在0 ～ 1000 ng/mL范围内与峰电流呈现良好的线性关系,相关系数大于0.999,方法检出限为0.58 ng/mL,加标回收率为96.4％ ～ 101.7％.地下水中可能存在的一些离子对测定不产生干扰.该方法应用于地下水示踪试验,铜的测定结果与极谱法基本吻合,且简单快速,适合野外现场测定,同时避免了极谱法液态汞的污染问题.     

Ultraviolet absorbance titration for the determination of conditional stability constants of Hg（Ⅱ） and dissolved organic matter

Strong interaction between natural dissolved organic matter （DOM） and Hg（Ⅱ） may influence the transport, conversion, toxicity and bio-validity of mercury in the environment. In this paper ultraviolet （UV） absorbance titration was employed for the first time for the determination of the conditional stability constants of Hg（Ⅱ） and （DOM）. With increasing Hg（Ⅱ） concentrations, the UV absorbance of fulvic acid, humic acid, and DOM in river increases progressively. By linear and non-linear model fitting, the conditional stability constants （lgK） of Hg（Ⅱ） and DOM were worked out to be 3.54-4.93 and 3.64-4.85, respectively. The results are consistent with those acquired by the typical fluorescence quenching titration method, with the maximum relative error of lgK being 2.6% and the average relative error being 0.2%. The UV absorbance titration method has the advantages of rapid determination, simple performance, and it will probably become a new approach to studying interactions between DOM and trace metallic ions.     

A review of non-conventional metals extracting technologies from ore and waste

In recent years several kinds of gas phase methods/techniques, utilizing organic ligands, have been developed to recover metals from low grade ore or slag, for the removal of heavy metals from industrial waste, as well as solution purification. These methods include, extraction of metals in fluidized bed reactors using organic chelating compounds such as the SERVO process, and metal extraction by supercritical fluid extraction with CO₂ (SFC), followed by a potential method to recycle the metal and regenerate the ligand. These methods are hydrogen reduction, electrochemical separation and acid stripping. This review looks at the extraction of metals by organic ligands, and a brief introduction to the advantages and disadvantages of these two techniques (SERVO and SFC) is presented. A comparison of metal extraction using the two techniques is presented; some conventional methods are discussed, as well as the problems they present. Selected results of the extraction of iron by a gasified ligand in a fluidized reactor are shown to illustrate the potential application and success of this approach. Kinetic models governing such gas–solid state reactions are discussed, and possible ways to recycle the ligand(s) and recover metals in their pure (reduced) state highlighted. Finally, some ideas and suggestions for improvements in the research that had been carried out to date, as well as further future developments deserving attention, are suggested in the conclusion.     

An adaptive sampling approach to reduce uncertainty in slope stability analysis

An adaptive sampling approach is proposed, which can sample spatially varying shear strength parameters efficiently to reduce uncertainty in the slope stability analysis. This approach employs a limit equilibrium model and stochastic conditional methodology to determine the likely sampling locations. Karhunen-Loève expansion is used to conduct the conditional Monte Carlo simulation. A first-order analysis is also proposed to ease the computational burden associated with Monte Carlo simulation. These approaches are then tested using borehole data from a field site. Results indicate that the proposed adaptive sampling approach is an effective and efficient sampling scheme for reducing uncertainty in slope stability analysis.     

多阶多层复杂边坡稳定性的通用上限方法

极限分析上限方法在边坡稳定性评价中受到了广泛关注,但当前所取得的解析成果尚不能直接应用于解决任意多土层分布、多台阶的广义复杂层状边坡。基于组合对数螺线的旋转破坏机制,推导了具有任意坡面几何特征、任意多土层（含非水平土/岩层）边坡的外功率统一积分表达式及相应的虚功率方程,提出了多阶多层复杂边坡稳定性的通用极限分析上限方法;为克服积分式的复杂解析计算,引入了数值积分技术。在此基础上,结合最优化方法和强度折减技术,优化求解了复杂边坡的全局稳定性安全系数及相应的临界滑动面。通过多个典型算例的验证与对比分析,表明该方法具有较高的精度和广泛适用性。最后,针对典型多阶多层边坡实例,开展了上限法的深度拓展与应用研究,其结果为广义复杂层状边坡的稳定性评价提供了新思路。     

Effects of pH and Ca competition on complexation of cadmium by fulvic acids and by natural organic ligands from a river and a lake

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.     

Nonparametric estimation of multivariate joint and conditional spatial distributions

To estimate the recoverable reserves of deposits containing more than one metal, linear combinations of sample grades based on the economic importance of each metal have been employed. These linear combinations, called equivalent grades, have inherent problems at least one of which is that the contribution of an individual metal is confounded with all others. As an alternative to equivalent grades, multivariable joint and conditional spatial distributions may be estimated using indicator variable methods. These spatial distributions may then be used to determine the joint or conditional amounts of the metals in the estimated recoverable reserve.This paper was presented at MGUS 87 Conference, Redwood City, California, 14 April 1987.     

非均质土坡的有限元塑性极限分析

在评价现有边坡稳定分析方法的基础上,提出了边坡稳定的有限元塑性极限分析方法。借助有限单元思想和线性规划,建立了边坡稳定的数学规划模型,由此可以求出安全系数的上下限解,从而,界定了边坡的安全范围,同时,可以给出下限状态下的应力场和上限状态下的速度场。以一个经典非均质土坡的边坡稳定作为算例,比较了多种方法的分析结果,论证了本方法的正确性。