Kinetic speciation of nickel in mining and municipal effluents

This study presents the results of kinetic speciation of nickel in undiluted mining and municipal effluents and effluents diluted with receiving freshwaters from the surrounding environment. The dilution ratios used for the dilution of the effluents were arbitrarily chosen, but were representative of the prevailing mining practices. The purpose of the this dilution was to mimic dilution with natural waters that result from dilution of the mining and municipal effluents with receiving freshwaters, so that this study would reveal environmental realities that are of concern to the managers and regulators of water resources. Ligand exchange kinetics using the competing ligand exchange method (CLEM) was studied using two independent techniques: graphite furnace atomic absorption spectrometry (GFAAS) with Chelex 100 resin as the competing ligand, and adsorptive cathodic stripping voltammetry (AdCSV) with dimethylglyoxime (DMG) as the competing ligand to determine the percentage of Ni metal released from Ni(II)–DOC complexes and the rate of dissociation of Ni(II)–DOC complexes. Using a sample containing a mixture of 30% Copper Cliff Mine effluent, 40% Sudbury municipal effluent and 30% Vermillion River water, both techniques gave results showing that the dilution of the effluent samples increased the percentage of nickel released from Ni(II)–DOC complexes. This increase in the release of nickel from the Ni(II)–DOC complexes may be of concern to managers and regulators of water resources. Agreement between the results of these two techniques has enhanced the validity of the competing ligand exchange method used by both techniques.     

Investigation of DGT as a metal speciation technique for municipal wastes and aqueous mine effluents

This paper reports the results of an investigation on the performance of the Diffusive Gradient in Thin Films (DGT) Technique in speciation of metals in aqueous samples of municipal wastes and mine effluents. The DGT was assessed regarding its suitability for in situ determination of metal speciation in municipal wastes and aqueous mine effluents. As the thickness of the diffusive gel layer of the DGT was increased to 0.40, 0.80, and 1.60 mm, a decrease in the amount of accumulated metal mass was observed for most of the metals studied in all the effluent samples. However, the results were different from one field-study site to another. Effect of kinetics also was observed in the amount of accumulated metal mass by the DGT. The computer speciation code, Windermere Humic Aqueous Model (WHAM VI), was used to predict the metal speciation of Cd, Cu, Ni, Pb, Co, and Zn, and WHAM predictions were compared with those of the experimentally determined metal speciation by the DGT technique (free and labile metal ions). This comparison showed good similarities between the theoretically predicted WHAM VI values and the experimentally measured values by DGT. The DGT technique was found to be simple and useful for investigating chemical speciation of trace metals in aqueous samples of municipal wastes and aqueous mine effluents.     

Trace metal speciation measurements in waters by the liquid binding phase DGT device

The speciation measurements of trace metals by the diffusive gradients in thin-films technique (DGT) using a poly(4-styrenesulfonate) (PSS) aqueous solution as a binding phase and a cellulose dialysis membrane (CDM) as a diffusive layer, CDM-PSS DGT, were investigated and showed good agreement with computer modelling calculations. The diffusion coefficients of ethylenediaminetetraacetic acid (EDTA) complexes with Cd²⁺ and Cu²⁺ were measured and compared with those of the inorganic metal ions. CDM-PSS DGT device was tested for speciation measurement in sample solutions containing EDTA, tannic acid (TA), glucose (GL), dodecylbenzenesulfonic acid (DBS) and humic acid (HA) as complexing ligands forming organic complexes with varying stability constants. Lower percentages of DGT labile copper concentrations over total filterable copper concentrations obtained from the deployments in freshwater sites indicated that copper complexes with organic matter were basically not measured by the devices.     

Speciation of Charged Complexes by Donnan Dialysis

Abstract

The assignment of metal complexes to various regimes on the basis of their dissociation kinetics is one type of metal speciation study. The most common scheme, which involves column ion-exchange as a means of separating free metal ions and metals in the form of highly labile complexes from other forms of metals in the sample, is demonstrated to categorize incorrectly stable, charged complexes such as iron(II) and nickel(II) o-phenanthroline as labile. Donnan dialysis is an alternative ion-exchange method for metal speciation studies. Data are provided which demonstrate that the above complexes are correctly assigned by the Donnan dialysis method. The relative labilities of ethylenediamine and triethylenetetramine complexes of iron (II) and nickel (II) are also correctly determined by Donnan dialysis.     

Determination of Dynamic Metal Complexes and their Diffusion Coefficients in the Presence of Different Humic Substances by Combining Two Analytical Techniques

The combined use of a competing ligand exchange (CLE) method and a diffusive gradient in thin films (DGT) technique in a quasi-labile system provides a better understanding of dynamic metal (Cu and Ni) complexes in the presence of humic substances of different origins. The CLE and DGT techniques provide total labile (dynamic) metal complexes (Cu and Ni) and their dissociation rate constants in environmental systems. DGT was found to estimate lower concentrations of labile metal complexes than CLE. These discrepancies were caused by diffusion controlled metal flux (towards the binding resin gel) in the diffusive gel of DGT. The interactions of Cu and Ni with humic acids are stronger than their interactions with fulvic acid and natural organic matter. Changes in the lability of Ni and Cu complexes (complexed with humic substances of different origins) with the changing analytical detection window indicate that the complexes of these metals were formed with different binding sites with diverse binding energies in the humic substances. The combination of these two techniques was found to be very useful in determining diffusion coefficients of labile metal-humate complexes in quasi-labile systems. The values of diffusion coefficients of labile Ni and Cu complexes determined in this study are in good agreement with limited results from the literature. This finding is novel and can be very useful in further improving our understanding of the metal-humate interactions in natural environments.     

Application of permeation liquid membrane and scanned stripping chronopotentiometry to metal speciation analysis of colloidal complexes

The potential of permeation liquid membrane (PLM) to obtain dynamic metal speciation information for colloidal complexes is evaluated by measurements of lead(II) and copper(II) complexation by carboxyl modified latex nanospheres of different radii (15, 35, 40 and 65 nm). The results are compared with those obtained by a well characterized technique: stripping chronopotentiometry at scanned deposition potential (SSCP). Under the PLM conditions employed, and for large particles or macromolecular ligands, membrane diffusion is the rate-limiting step. That is, the flux is proportional to the free metal ion concentration with only a small contribution from labile complexes. In the absence of ligand aggregation in the PLM channels, good agreement was obtained between the stability constants determined by PLM and SSCP for both metals.     

Chemical speciation of Co, Ni, Cu, and Zn in mine effluents and effects of dilution of the effluent on release of the above metals from their metal-dissolved organic carbon (DOC) complexes

The paper explores the lability of DOC complexes of Co, Ni, Cu, and Zn in the mining effluent, and investigates the effects of dilution of the effluent on the release of metals from the metal-DOC complexes. This study was done using competing ligand exchange method in conjunction with adsorptive cathodic stripping voltammetry on effluent samples from Copper Cliff Mine, Sudbury, Canada, using two samples of the effluent: one, undiluted (100%) effluent, and the other, diluted (45%) effluent. The dilution was done with tap water in order to determine the effects of dilution on the metal complexes in the effluents when they were discharged into receiving streams of freshwaters. The dilution of the effluent had a small effect on release of Cu from the Cu-DOC complexes, but had a much greater effect on the release of Zn from the Zn-DOC complexes. The release of Ni and Co from their DOC complexes decreased drastically on dilution of the effluent. The much greater release of Cu from the Cu-DOC complexes compared to the release of Ni, Co, and Zn from their DOC complexes in both the undiluted and the diluted effluent was probably due to the higher absolute concentration of Cu and the higher [Cu]/[DOC] ratio. The drastic decrease in the release of Ni and Co from the Ni- and Co-DOC complexes in the diluted (45%) effluent compared with the undiluted (100%) effluent probably resulted from strengthening of the metal-DOC bond due to the reduced screening of charges by a smaller concentration of Ca²⁺ in the diluted (45%) effluent. This work also shows that change in the ionic strength produces conformational changes in and in aggregation and precipitation of the DOC and also changes in electrostatic interactions between the metal cations and the humate polyanions.     

Online coupling of ultraviolet titanium dioxide film reactor with poly(methyl methacrylate) solid phase extraction–inductively coupled plasma mass spectrometry for speciation of trace heavy metals in freshwater

To rapidly discriminate dissolved labile and stable organic-complexed metal ions, a fully automated approach comprising a photocatalyst-assisted digestion reactor (PADR), a non-functionalized poly(methyl methacrylate) (PMMA) solid-phase extraction (SPE) column, and inductively coupled plasma-mass spectrometry (ICP-MS) instrumentation was developed. To separate labile dissolved metals from other concomitant metal complexes, a non-functionalized PMMA bead was used as the SPE adsorbent because of its selective interaction with labile metal ions. The PMMA SPE–ICP-MS hyphenated system was optimized, and its analytical reliability was confirmed by using it to analyze the certified reference material—NIST 1643e (artificial saline water). Detection limits (σ = 3, n = 7) for all analyte ions (Ni, Cu, Zn, Cd, and Pb), which ranged from 0.005 to 0.186 μg L^{− 1}, could be reached; therefore, this technique appeared uniquely suited to determining levels of trace elements in most natural freshwater samples. To determine the total quantity of dissolved metals, a new digestion reactor (PADR) was developed for online conversion of metal–organic complexes to their labile forms. Compared to conventional photolysis methods, the digestion time improved considerably and the digestion efficiency for organic substances was excellent (> 90%) in the PADR format, with a very short resident time of 10 min. After construction of the PADR–PMMA SPE–ICP-MS hyphenated system, the speciation potential of our developed method was evaluated by analyzing three intentionally contaminated water samples. Results indicated that our developed hyphenated system is effective for online determination of total, labile, and metal–humic complexes in freshwater samples and that is capable of providing representative metal speciation patterns for different aquatic systems.     

Investigation of bis(carboxymethyl)dithiocarbamate complexes by the extraction method

The extraction of copper, lead, cadmium, nickel and zinc dithizonates was investigated in the presence of ammonium bis(carboxy-methyl)dithiocarbamate. For all metals studied, except zinc, masking of extraction was observed, depending on the amount of the dithio-carbamate in the aqueous phase. From the shift of the pH(1 2 ) values for dithizonate extraction, the stability constants beta(2) for the metal complexes with bis(carboxymethyl)dithiocarbamate were calculated. The logarithms of the constants are 21.46, 15.45,11.24 and 7.93 for the copper, lead, cadmium and nickel complexes respectively.     

The determination of all the platinum group elements and gold in rocks and ore by neutron activation analysis after preconcentration by a nickel sulphide fire-assay technique on large samples

The noble metals are inhomogeneously distributed in sulphide ores and their host rocks. It is therefore necessary to analyse large sample sizes to obtain representative analyses. A nickel sulphide fire assay technique has been adapted to extract the noble metals from a large sample size (50 g) into a nickel sulphide button. Subsequently the fire assay button is dissolved in hydrochloric acid and the solution is filtered. The noble metal residue retained on the filter paper is analysed quantitatively by i.n.a.a. techniques. This method is rapid, relatively inexpensive and has better sensitivities for all the noble metals than other analytical techniques.     

Speciation of Cu(II) with a flow-through permeation liquid membrane: discrimination between free copper, labile and inert Cu(II) complexes, under natural water conditions

Metal toxicity is not related to the total metal ion concentration, but to those of some specific Cu(II) species. The Permeation Liquid Membrane technique is based on the carrier-mediated transport of the test metal across a hydrophobic membrane and enables discrimination between various trace metal species in solution. The present work shows how the labile and inert Cu(II) complexes can be determined selectively, by varying the flow-rate of the test solution, in a flow-through cell. A mathematical model of metal flux through the PLM, based on diffusion-limited transport under steady-state conditions, is described. The model and the performance of the technique were studied in well-defined synthetic solutions containing simple organic hydrophilic ligands forming either inert (nitrilotriacetic acid), or labile complexes with Cu(II) (tartaric acid, malonic acid). The results were compared with theoretical predictions of thermodynamic species distribution in solution. Uncertainties on stability constants for copper speciation calculation were taken into account. The detection limits of the device are discussed. This work demonstrates that the flow-through cell is a reliable tool for copper speciation measurements in natural waters.     

金属离子的光催化去除研究进展

利用光催化剂表面的光生电子或空穴等活性物种，通过还原或氧化反应去除水相中的金属离子，是与环境保护、贵金属回收或金属担载催化剂制备相关的重要过程。笔者结合半导体的结构特征，综述了利用光催化还原反应或氧化反应，对铬、汞、铜、镍、银及铂、钯等贵金属和锰、铀等的光催化去除效果，介绍了该技术在处理金属离子混合体系实现金属分离过程的应用。结合有关实验数据，对一些可能反应机制进行了探讨。对与环境保护及其它相关工艺过程的应用进行了介绍。     

Evaluation of humic complexes of trace metals in river water by adsorption on indium-treated XAD-2 resin and DEAE-Sephadex A-25 anion exchanger

A combined adsorption procedure for the analytical fractionation of humic/metal complexes in river water is described. It is based on an indium-loaded XAD-2 resin and a DEAE-Sephadex A-25 anion exchanger, respectively. After the separation of suspended particles, an aliquot of the water sample to be analysed is passed through an indium-loaded XAD-2 resin column to collect the metal-humic complexes. A second aliquot is directly passed through a DEAE-Sephadex A-25 anion exchanger column to collect humic complexes and other negatively charged metal species. Both column effluents are analysed by inductively coupled plasma-mass spectrometry or by graphite-furnace atomic absorption spectrometry for various trace metals (e.g., Al, Mn, Fe, Co, Ni, Cu, Zn, Sr, Ba). According to this fractionation procedure, significant amounts of iron, aluminium and copper in river water are found to be humic complexes, and less than 15% of nickel, cobalt and zinc are complexed with humic substances. Manganese, strontium and barium are hardly associated with humic substances.     

Electrochemical synthesis,magnetic, spectral and cyclic voltammetric studies on lactic acid complexes

Summary Complexes of iron, cobalt, nickel and copper with lactic acid (H₂LA) were prepared by electrochemical oxidation of the metal in non-aqueous solution; this new method gives a high yield (73–87%). The reaction mechanism and the electrochemical efficiency show that cobalt, nickel and copper give divalent complexes and the iron complex is trivalent. The isolated complexes were characterized by physicochemical techniques. C.v.s of the complexes indicate the irreversibility of the electrode processes and confirm the oxidation state of the metals.     

Electrospray mass spectrometric studies of L-carnosine (beta-alanyl-L-histidine) complexes with copper(II) or zinc ions in aqueous solution

Electrospray ionization mass spectrometry (ESI-MS) was used for the speciation of supramolecular assemblies formed between equimolar amounts of carnosine and copper or zinc ions in dilute aqueous solutions. In the case of pure carnosine and carnosine/copper systems, the effect of pH changes, in the range 2-9, on the complexes surviving in solution was also explored. ESI data, besides supporting previous reported results on the formation of dimeric carnosine/copper and carnosine/zinc complexes, allowed a more complete speciation of the examined systems, bringing to light the existence of bis-complex species and, in the zinc case, the formation of oligomeric species. The data obtained for the systems investigated show that ESI-MS is not only a reliable and fast technique for the analysis of the metal/ligand systems, but also an interesting tool to obtain stoichiometric information on metal complexes formed in very low concentration solutions.     

Free and bound phenolic compounds in barley (Hordeum vulgare L.) flours. evaluation of the extraction capability of different solvent mixtures and pressurized liquid methods by micellar electrokinetic chromatography and spectrophotometry

The solution speciation of metals is a critical parameter controlling the bioavailability, solution-solid phase distribution and transport of metals in soils. The natural metal-complexing ligands that exist in soil solution include inorganic anions, inorganic colloids, organic humic substances, amino acids (notably phytosiderophores and bacterial siderophores) and low-molecular mass organic acids. The latter two groups are of particular significance in the soil surrounding plant roots (the rhizosphere). A number of analytical methodologies, encompassing computational, spectroscopic, physico-chemical and separation techniques, have been applied to the measurement of the solution speciation of metals in the environment. However, perhaps with the exception of the determination of the free metal cation, the majority of these techniques rarely provide species specific information. High-performance liquid chromatography (HPLC) coupled to a sensitive detection system, such as inductively coupled plasma mass spectrometry (ICP-MS) or electrospray ionisation mass spectrometry (ESI-MS), offers the possibility of separating and detecting metal-organic acid complexes at the very low concentrations normally found in the soil environment. This review, therefore, critically examines the literature reporting the HPLC separation of metal-organic acid complexes with reference to thermodynamic equilibrium and kinetic considerations. The limitations of HPLC techniques (and the use of thermodynamic equilibrium calculations to validate analytical results) are discussed and the metal complex characteristics necessary for chromatographic separation are described.     

Comparison of physicochemical speciation procedures with metal toxicity to chlorella pyrenoidosa

Metal speciation as measured by anodic stripping voltammetry (ASV), adsorption on a resin with adsorbed hydrated aluminium oxide, and dialysis with receiving resins is compared with the toxicity of the metals to the freshwater green alga Chlorella pyrenoidosa Chick. In the presence of natural and synthetic ligands, similar labile fractions of metals were obtained for ASV at three electrodes (hanging mercury drop electrode, mercury film electrode and Nafion-coated mercury film electrode). The toxic fractions determined by ASV and bioassay were in reasonable agreement for zinc, cadmium and copper, and alteration of the analytical conditions provided some measure of agreement for lead. The resin with adsorbed hydrated aluminium oxide correlated well with bioassay for copper, but over-estimated lead toxicity and under-estimated cadmium toxicity. Dialysis with receiving resins under-estimated metal bioaccumulation in the presence of ligands. Metal speciation analysis for water samples gave higher toxic fractions for metals in samples of polluted river water and road runoff samples than those found in pristine river water.     

Effects of competitive binding on the amperometric determination of copper with electrodes modified with chromotrope 2B

Electrodes modified with Chromotrope 2B incorporated by ion-exchange into a polycationic film of electropolymerized [Ru(v-bpy)(3)](2+) (v-bpy = 4-vinyl-4'-methyl-2,2'-bipyridyl) have been employed in the amperometric determination of copper in solution and exhibit very high sensitivity as well as linear calibration curves in the concentration range 7 x 10(-8)-1 x 10(-4)M. The effects of competing ligands, including chloride, bromide, oxalate, ammonia, acetate, citrate, borate, humic and fulvic acids, or the presence of competing metal ions such as cobalt or nickel on the uptake of copper by the modified electrodes have also been studied. The presence of competing ligands or metal ions decreases the analytical signal due to copper incorporation. The magnitude of this effect is dependent on the relative strength of coordination of the competing ligands for copper ions or of Chromotrope 2B for the competing metals, and also on the concentration of the interferents. The relevance of this work to speciation studies is discussed.     

Metal speciation measurement by diffusive gradients in thin films technique with different binding phases

Since its invention in the mid-1990s, the diffusive gradients in thin films (DGT) technique has rapidly become one of the most promising in situ sampling techniques for trace metal measurement in natural waters. We investigated here the possibility of using DGT devices with different binding phases to determine different DGT labile fractions of Cd and Cu in laboratory solutions and in natural waters. Several binding phases were studied, including conventional Chelex 100 resin imbedded polyacrylamide hydrogel (Chelex) and several recently developed binding phases, poly(acrylamide-co-acrylic acid) (PAM-PAA) gel, poly(acrylamidoglycolic acid-co-acrylamide) (PAAG-PAM) gel, Whatman P81 cellulose phosphate ion-exchange membrane (P81), and poly(4-styrenesulfonate) (PSS) aqueous solution. Laboratory testing in metal solutions spiked with EDTA or humic acid suggested that all the DGT devices measured only free metal ions and inorganic metal complexes. Upon field testing at both freshwater and seawater sites it was found that the DGT labile metal concentrations measured by different binding phases can be significantly different, suggesting that the DGT labile metal fractions were dependent on binding strength of the binding phase. By designing binding phases that can compete with different natural water complexing ligands to varying extents, it is possible to use these different DGT devices to measure metal speciation in natural waters.     

Complexation of Ni, Cu, Zn, and Cd by DOC in some metal-impacted freshwater lakes: a comparison of approaches using electrochemical determination of free-metal-ion and labile complexes and a computer speciation model, WHAM V and VI

Complexation of Ni(II), Cu(II), Zn(II), and Cd(II) by dissolved organic carbon (DOC) in some freshwater lakes in Rouyn-Noranda, Québec, Canada, where they were impacted by effluents from a nearby copper smelter, was measured by kinetic and equilibrium methods using cathodic and anodic stripping voltammetry. The measured free-metal-ion and labile metal-complex concentrations were compared with the predictions made by a widely-used computer speciation model, the Windermere Humic Aqueous Model (WHAM): WHAM V and its improved version WHAM VI. If it is assumed that 65% of the DOC is “active”, i.e. behaving as isolated humic substances such as fulvic acid, both versions of WHAM are able to predict the labile and free-metal-ion concentrations of Ni, Zn, and Cd reasonably well; however, both underestimate the free-copper-ion concentration by one to two orders of magnitude. WHAM VI is generally better than or equal to WHAM V for successfully predicting most of the free-metal-ion concentrations. The modelled competition by Al(III) and Fe(III) in the lake surface waters showed that in most cases Cu(II) was most affected by this competition. WHAM VI predicts a larger effect from the Al(III) and Fe(III) competition than does WHAM V.