Anionic Metal Species Research Articles

Self-coagulating polyelectrolyte complexes for target-tunable adsorption and separation of metal ions

Metal-containing wastes in aquatic environments lead to public health hazards and valuable resource lose. Metal-bearing wastewater must be treated to remove heavy metals or recover precious metals. To achieve these, target-tunable adsorbents that bind cationic and anionic metal species were developed through facile polyelectrolyte complexation using polyethylenimine (PEI) and polyacrylic acid (PAA). Utilizing the properties of the two polyelectrolytes and pKa variabilities, stable tunable adsorbents were fabricated in water without additional solvents. The homogenous complex adsorbents were strategically synthesized via dissolution in 0.1 M NaOH and drop-wise addition of 1 M HCl, followed by crosslinking with glutaraldehyde. Consequently, the adsorbents in alternating weight ratios of 4:1 and 1:4 (PEI:PAA) exhibited good tunability and adsorption properties. The maximum single metal adsorption capacities were 1609.7 ± 49.6 and 558.6 ± 9.67 mg/g for gold and cadmium, respectively. The pseudo-second-order model fitted the kinetics data more appropriately and was recognized as the rate controlling step. In a binary mixture, gold selectivity was observed to be influenced by adsorption-reduction mechanism, which was elucidated by XRD and XPS. Moreover, the adsorbents demonstrated NO3– sequestration properties, a feat deemed important for environmental remediation of nitrate ions. Finally, sequential separation was achieved with ethylenediaminetetraacetic acid (EDTA) and acidified thiourea.

Biochar–nZVI nanocomposite: optimization of grain size and Fe0 loading, application and removal mechanism of anionic metal species from soft water, hard water and groundwater

This work for the first time evaluates the efficiency of biochar-supported nanoscale zerovalent iron (nZVI) particles combinedly as a function of biochar grain size and iron loading for the removal of anionic metal species, i.e., HCrO4− and CrO42−. Both the factors are crucial and have to be optimized in order to achieve the highest and fastest removal. Not only that, it is also crucial to check the applicability of that composite in complex aqueous solutions. For that, nZVI particles were supported on biochar grains of different size ranges, i.e., SW (21.54 mg/g) > HW (17.00 mg/g) > DW (16.30 mg/g). Cr(VI) removal mechanisms were chemisorption, reduction and simultaneous coprecipitation as confirmed through various kinetic and isotherm modeling and through pXRD of reaction precipitates.

Comparison of two- and three-compartment cells for electrodialytic removal of heavy metals from contaminated material suspensions.

Electrodialytic remediation can be applied to remove heavy metals from contaminated particulate materials in suspension. The applied electric current is the cleaning agent and the heavy metals are removed by electromigration. In this study, a two-compartment cell was compared to a three-compartment cell, for several contaminated materials such as soils, sediments, mine tailings and ashes and totally 20 experiments were conducted. The pH decrease was faster in the two-compartment cell, but the metal removal was higher in the three-compartment cell since anionic metal species are removed from the material suspension in this cell set-up. For materials with relatively high chloride content, fly ash and harbour sediments, up to 38% of the metals were found in the filtrate in the two-compartment cell. Up to 9% of the current was used to transport heavy metal ions in the experiments and the current was mainly carried by H+ and Ca2+. Even with the lower pH in the two-compartment cell experiments, there was little difference in the percentage of the current carried by the metal ions between the two set-ups. Multivariate analysis showed that the choice of cell set-up depends on the metals targeted by remediation and the material characteristics.

Preparation and characterization of Grafoil/Ni and polyaniline/Ni composites from the controlled electrochemical reduction of NiCl42-

The controlled reduction of a nickel metal anion, NiCl42−, at a carbon (Grafoil) and Polyaniline (PANI) electrode is explored. The incremental increase of Ni deposits is achieved from the reduction of the metal precursor at both electrodes. The normal oxidation/reduction was used to facilitate the uptake and dispersion of the precursor using electrostatic interactions with the positively charged PANI. The controlled in-situ reduction of the dispersed Ni precursor in the polymer was utilized to produce PANI/Ni composites with variable metal content. Scanning electron microscope (SEM) analysis and energy dispersive x-ray (EDX) spectroscopy of both substrates confirm the reduction of the Ni metal precursor at both electrodes. The chemical reactivity of the Ni metal deposited was also confirmed for both substrates using surface specific electrochemical reactions including the formation/reduction of oxidized nickel species and the catalytic oxidation of methanol in alkaline solutions (pH ≈ 14). The electrochemistry associated with NiOOH/Ni(OH)2 and the catalytic oxidation of methanol is resolved in alkaline solution for both electrodes. Furthermore, the electrochemical activity of PANI/Ni composite materials is maintained without acid doping the polymer. Finally, an alternative pathway for the inclusion of anionic transition metal species in PANI that eliminates the competitive uptake of proton and metal cation precursors commonly used in traditional acidic environments is demonstrated.

Improved waste-sourced biocomposite for simultaneous removal of crude oil and heavy metals from synthetic and real oilfield-produced water.

Oil- and gas-produced water (PW) which contains various pollutants is an enormous threat to the environment. In this study, a novel low-cost bio-adsorbent was prepared from shrimp shell and acid-activated montmorillonite. The results of FT-IR spectroscopy, energy dispersive X-ray (EDX) analysis, and SEM-EDX technique indicated that the chitosan-activated montmorillonite (CTS-A-MMT) was prepared successfully. The synthesized CTS-A-MMT was applied to remove simultaneously five cationic and anionic metal species and crude oil from synthetic and real oilfield PW. The adsorption data indicated that crude oil and all studied metals (except As) were adsorbed to CTS-A-MMT in a monolayer model (best fitted by Langmuir model), while As adsorption fits well with Freundlich model. Kinetic models' evaluation demonstrated that the adsorption kinetics of metals on CTS-A-MMT are initially controlled by the chemical reaction (film diffusion) followed by intra-particle diffusion. Application of the prepared CTS-A-MMT in real oilfield PW indicated removal efficiency of 65 to 93% for metals and 87% for crude oil in simultaneous removal experiments. Presence of additional ions in PW decreased the removal of studied metals and crude oil considerably; however, the concentration of the investigated pollutants in treated PW is less than the ocean discharge criteria. It is concluded that the prepared CTS-A-MMT composite is a low-cost and effective adsorbent for treating wastewater contaminated with crude oil and heavy metals (i.e., PW).

Remediation of sandy soil contaminated by heavy metals with Na2EDTA washing enhanced with organic reducing agents: element distribution and spectroscopic analysis

SummaryWashing with Na2EDTA is insufficient to remove both cationic and anionic metal species in contaminated soil. Therefore, washing with Na2EDTA enhanced with organic reducing agents was tested as a means to improve the efficiency of removal of heavy metals and to investigate its effect on the spectroscopic characteristics of contaminated soil. The results indicated that washing with Na2EDTA enhanced with organic reducing agents was effective in removing both arsenic and cationic metals from contaminated soil at the initial pH of the mixed washing agents. The increase in removal efficiencies (compared with a single Na2EDTA washing) under this washing regime was 19–31% for arsenic, 6–19% for cadmium, 3–12% for copper and 6–21% for lead in two samples. The results of metal fractionation indicated that the addition of either oxalic or ascorbic acids could increase the relative proportion of the residual fraction to varying degrees. The spectroscopic analysis demonstrated that these acids were effective in removing metals by dissolving soil minerals, such as amorphous iron oxides, and reducing mineral oxides. The X‐ray photoelectron spectroscopy (XPS) study showed that more Fe(III) was transformed to Fe(II) under Na2EDTA washing enhanced with oxalic acid than with ascorbic acid, and the dissolution of silicon oxides was very limited in the presence of either of these acids. Washing with Na2EDTA enhanced by both oxalic and ascorbic acid of the sampled soils improved removal efficiencies; properties of the washing agent, the physicochemical properties of samples and the pollution characteristics (e.g. the amounts of contamination and metal fractions) combined to influence the effect of washing.HighlightsWashing with Na2EDTA and oxalic or ascorbic acids was effective in extracting arsenic and cationic metals. Oxalic acid was more effective than ascorbic acid in transforming Fe(III) to Fe(II). Addition of organic reducing acids increased the relative proportion of the residual fraction of metals. Metal removal was affected by dissolution of minerals such as scorodite, muscovite and feldspar.

Chiral guanidines and their derivatives in asymmetric synthesis.

Over the past two decades, chiral guanidines and their derivatives have emerged as one of the most powerful organocatalysts mainly on the basis of their strong basicity and/or hydrogen-bond donor ability. Structurally diverse guanidine catalysts (bicyclic, monocyclic and acyclic types) sprang up and enabled numerous fundamental organic transformations to be realized in high efficiency and stereoselectivity. Moreover, chiral guanidinium salts were successfully employed in H-bond donor catalysis, phase-transfer catalysis and others. Recently, several novel chiral guanidine derivatives [e.g., guanidinium salt, pentanidium, bis(guanidino)iminophosphorane] have been designed and used for the synthesis of valuable molecules. In addition, the combination of chiral guanidines and their derivatives with cationic or anionic metal species dramatically expanded their utility and provided solutions to challenging transformations of importance which cannot be achieved with conventional chiral catalysts. This article reviews current achievements of chiral guanidines and their derivatives in organocatalysis, and updates versatile guanidine-metal salt combinations in asymmetric catalytic reactions. In addition, representative examples of achiral guanidine-related catalysis are also covered.

An assessment of strontium sorption onto bentonite buffer material in waste repository.

In the present study, changes occurring in sorption characteristics of a representative bentonite (WIn-BT) exposed to SrCl2 (0.001-0.1M) under the pH range of 1-13 were investigated. Such interaction revealed a significant variation in surface charge density and binding energy of ions with respect to bentonite, and alteration in their physicochemical properties viz., specific surface area, cation exchange capacity, thermal and mechanical behaviour were observed. The distribution coefficients (k d) calculated for sorption onto virgin (UCBT) and contaminated bentonite (CBT) indicated a greater influence of mineralogical changes occurred with variance of pH and strontium concentration. Notably, the sorption mechanism clearly elucidates the effect of structural negative charge and existence of anionic metal species onto CBT, and depicted the reason behind significant k d values at highly acidic and alkaline pH. The maximum k d of UCBT and CBT(0.001M SrCl2) were 8.99 and 2.92L/kg, respectively, at the soil pH 8.5; whereas it was 2.37 and 1.23L/kg at pH 1 for the CBT(0.1M SrCl2) and CBT(0.01M SrCl2), respectively. The findings of this study can be useful to identify the physicochemical parameters of candidate buffer material and sorption reversibility in waste repository.

Stabilization of cationic and anionic metal species in contaminated soils using sludge-derived biochar

Currently, sludge pyrolysis has been considered as a promising technology to solve disposal problem of municipal sewage sludge, recover sludge heating value, sequester carbon and replenish nutrients in farmland soils. The resultant sludge-derived biochar (SDBC) is potentially an excellent stabilizing agent for metal species. This study applied the SDBC into four soils that had been contaminated in field with cationic Pb(II) and Cd(II)/Ni(II), and anionic Cr(VI) and As(III), respectively. The performance of metal stabilization under various operational and environmental conditions was evaluated with acid batch extraction and column leaching tests. Results indicated the SDBC could effectively stabilize these metals, which was favored by elevated temperature and longer aging. Periodic temperature decrease from 45 to 4 °C resulted in the release of immobilized Cr(VI) and As(III) but not Pb(II). However, a longer aging time offset such metal remobilization. This was possibly because more Pb was strongly bound and even formed stable precipitates, as shown by XRD and sequential extraction results. With increasing time, Cr(VI) was sorbed and partly reduced to Cr(III), while immobilized As(III) was co-oxidized to As(V) as indicated by XPS spectra. Column tests revealed that adding SDBC as a separate layer was unfavorable because the concentrated Cd(II) and Ni(II) in localized positions increased the peak levels of metal release under continuous acid leaching. In contrast, uniformly mixed SDBC could effectively delay the metal breakthrough and reduce their released amounts. Yet, a long-term monitoring may be required for evaluating the potential leaching risks and bioavailability/toxicity of these immobilized and transformed species in the SDBC-amended soils.

Heteroatom‐Free Arene‐Cobalt and Arene‐Iron Catalysts for Hydrogenations

75 years after the discovery of hydroformylation, cobalt catalysts are now undergoing a renaissance in hydrogenation reactions. We have evaluated arene metalates in which the low-valent metal species is--conceptually different from heteroatom-based ligands--stabilized by π coordination to hydrocarbons. Potassium bis(anthracene)cobaltate 1 and -ferrate 2 can be viewed as synthetic precursors of quasi-"naked" anionic metal species; their aggregation is effectively impeded by (labile) coordination to the various π acceptors present in the hydrogenation reactions of unsaturated molecules (alkenes, arenes, carbonyl compounds). Kinetic studies, NMR spectroscopy, and poisoning studies of alkene hydrogenations support the formation of a homogeneous catalyst derived from 1 which is stabilized by the coordination of alkenes. This catalyst concept complements the use of complexes with heteroatom donor ligands for reductive processes.

Unimolecular dissociation characteristics of cationic complexes between nicotinic acid and Cu(II) and Ni(II)

Cu2+ and Ni2+ form dimeric ML(L−H)+ complexes with nicotinic acid (M=Cu, Ni; L=nicotinic acid) upon electrospray ionization. Quantum chemical calculations indicate thermochemical preference for coordination of the carboxylate groups rather than the ring nitrogens to the central metal ion in both cases. In analogy to the dimeric metal complexes of amino acids the primary dissociation reaction upon collisional activation of ML(L−H)+ is the loss of CO2 in both cases. Further dissociation of the decarboxylated species show preference for loss of a 3-pyridinyl radical for M=Cu and NiCO2 for M=Ni. This can be understood in light of the redox properties of the two metals and from previous studies of similar complexes with amino acids. Loss of the pyridinyl radical bonded to the carboxylate group in these cationic entities does not lead to M(η2-O2C) structures previously observed for similar anionic metal species.

Ionically modified magnetic nanomaterials for arsenic and chromium removal from water

We describe a method for the removal of arsenic and chromium contaminants from water by using ionically modified magnetic nanoparticles (PPhSi-MNPs). We synthesized and covalently attached a cationic ligand: phosphonium-silane (PPhSi), onto iron oxide magnetic nanoparticles. We exploit the ion-exchange capability of the phosphonium ligand for the removal of the metal ions from water and superparamagnetic nature of iron oxide for physical separation of the sorbent materials for recovery and regeneration. Chemical and physical properties of the phosphonium-coated MNPs are investigated by FTIR, TEM, XPS, EDX, XRD and zeta potential. The highest As(V) and Cr(VI) adsorption efficiency is observed at pH 3. The adsorption of As(V) and Cr(VI) on PPhSi-MNPs is not affected to any considerable extent by the presence of coexisting anions such as chloride, nitrate, and sulfate except phosphate. The adsorption data are best fitted with the Langmuir isotherm model and a pseudo-second-order kinetic model is proposed. Based on the zeta-potential and chemical analyses of the adsorbent surface, we propose that a synergy of electrostatic interaction and ion-exchange between anionic metals and the cation-modified magnetic nanoparticles allow highly efficient removal of the pollutants. A simple pH-triggered desorption and regeneration of the adsorbent is also presented. With adsorption capacities for arsenic (50.5mg/g) and chromium (35.2mg/g), coupled with facile magnetic separation, this nanoadsorbent can be an attractive material for the removal of several anionic metal species from water.

Fractionation analysis of manganese and zinc in beers by means of two sorbent column system and flame atomic absorption spectrometry

In the present article, a method of operational fractionation of Mn and Zn in beer using flame atomic absorption spectrometry was developed. The proposed fractionation scheme was based on use of a hydrophobic adsorbing resin Amberlite XAD7 (first column, 2 g resin bed) connected in a series with a strong cation exchanger Dowex 50Wx4 (second column, 1 g resin bed). After passing the samples of beers through the columns, distinct groupings of Mn and Zn species retained on the sorbents, i.e., hydrophobic fraction of polyphenols bound metal species and cationic metal species fraction, respectively, were determined in respective eluates obtained after complete recovery of Mn and Zn species with 10 ml of 2.0 mol l −1 HNO 3 (first column) and 10 ml of 4.0 mol l −1 HCl (second column). In addition, the effluents collected were analyzed prior to the evaluation of the third, residual fraction, presumably attributed to any hydrophilic anionic and inert metal species. The established fractionation patterns for Mn and Zn were discussed in reference to likely associations of metals with endogenous food bioligands and possible availability of the distinguished metal species classes. The quality of the results was proved by the recovery experiments.

Characteristics of anionic metal species biosorption with waste crab shells

Anionic metal complexes are very effectively bound by biomass types containing an abundance of amine groups. Readily available chitinous materials such as acid-washed Ucides shells (AWUS) sorbed well anionic gold-cyanide (Au(CN) 2 −), selenate (SeO 4 2−), chromate (CrO 4 2−) and vanadate (VO 4 3−) at low pH. Equilibrium biosorption uptakes by AWUS were up to 0.17 mmol Au/g AWUS (pH 3.4), 0.15 mmol Se/g (pH 3.0), 0.54 mmol Cr/g (pH 2.0) and 0.79 mmol V/g (pH 2.5). An increased ionic strength (IS) suppressed the primary anion uptake as chloride ions competed for biosorbent protonated sites and higher IS reduced the activity of ions in solution. The biosorption mechanism was suspected to involve electrostatic attraction.

Competitive transport of toxic metal ions by polymer inclusion membranes

The paper gives a short overview of application of polymer inclusion membranes (PIMs) for separation and removal of metal ions. Investigation of the selective removal of toxic metal ions, i.e. Cr(VI), Cd(II), Zn(II) from acidic chloride aqueous solutions, as well as trace radionuclides, i.e., 137Cs, 90Sr and 60Co from wastewaters using transport across polymer inclusion membranes was studied. The carriers, i.e., tri-n-octylamine for anionic metal species, as well as dibenzo-21-crown-7, tertbutyl-dibenzo-21-crown-7, and dinonylnaphtalenesulfonic acid for metal cations were incorporated into polymer inclusion membranes composed of cellulose triacetate as a support and o-nitrophenyl pentyl ether as a plasticizer. Selective transport of chromium(VI) over zinc(II) and cadmium(II) chloride complexes through PIMs was observed. Competitive transport of trace radionuclide ions, i.e., 137Cs, 90Sr, and 60Co from NaNO3 aqueous solutions across polymer inclusion membranes containing a mixture of dinonylnaphtalenesulfonic acid, and dibenzo-21-crown-7 as the carrier provide the selectivity order Cs(I)>Sr(II)>Co(II).

Experiments on the influence of sediment disturbances on the biogeochemistry of the deep-sea environment

In experiments with large undisturbed sediment cores, stirring the upper centimeters of sediment immediately released dissolved pore-water constituents such as heavy metals and nutrients. Rapid scavenging in the suspension after the disturbance was observed for cationic particle-reactive metals like Mn, Co, Ni, Zn, Cu, Cd, Pb, and Fe, while anionic metal species like Mo, V, and U showed neither strong release nor sorption. Microbial activity, fresh particulate organic carbon and nitrogen, and amino acids and hexosamines increased during the first days after disturbance. The ratios of C and N and of the amino acids also changed with time. Applicability of the results of laboratory experiments to in situ deep-sea conditions supports the necessity of in situ experiments in benthic chambers.

Arsenate sorption by Fe(III)-doped alginate gels

Although cationic metal contaminants can be effectively removed from wastewaters by treatment with biopolymers, application of biopolymers for the removal of anionic contaminants (such as As, Cr(VI), and Se) has been limited. The objective of this study was to examine the fundamental aspects of a possible remediation strategy for removal of anionic metal species employing the biopolymer alginic acid pretreated with Ca and Fe(III). Spherical gel beads (2 mm in diameter) were formed by dispensing the biopolymer solution dropwise into 0.1 M CaCl 2; Ca beads were then washed and equilibrated with 0.1 M FeCl 3 to achieve partial substitution of Fe(III) for Ca. The resulting Ca–Fe beads were found to be effective at removing As(V) from solution on a time scale of approximately 100 h. As(V) sorption was pH dependent; optimal removal and stability of the Ca–Fe beads was achieved at pH 4. At a given initial As(V) concentration, As(V) removal efficiency increased with increasing Fe content (number of beads); at an initial As(V) concentration of 400 μg/l, up to 94% removal was achieved at pH 4 after 120 h. For a given Fe content, uptake of As(V) increased with increasing initial As(V) concentration until saturation was reached. Sorption data was modeled using a single type of As(V) binding site. Data on As(V) sorption as a function of dissolved As(V) concentration and Fe content were used to obtain and validate the site density and conditional affinity constant for As(V) sorption.

Chemical effects on the morphology of supported electrodeposited metals

Copper, zinc, silver and palladium were grown in supports of filter-paper, glass-fibre, nylon membrane and polypropylene membrane. The support has a great effect on both the macroscopic and microscopic habit of the deposits. It was difficult to plate metals from solutions containing completing agents (e.g., cyanide, EDTA) that give anionic metal species. Brighteners and levellers that change the grain size of the deposit also affect the overall morphology. It is clear that the chemical nature of the electrolyte and the support is a major determining factor in the form of the growth.

Kinetics of complexation of metal ions by extractants solubilized in aqueous micellar solutions of cetyltrimethylammonium salts: Effect of the surfactant counterion

Several experiments have demonstrated that the complexation of metal ions by lipophilic extractants solubilized in cationic micelles does occur, although the electrostatic repulsions between the positively charged surface of the micelles and the metal ions are not favourable for the reaction to proceed. Owing to the very high concentration of anion X − which exists close to the micelle surface one may wonder about the possible contribution in this process of species of the type [MX 4] 2−. This problem is addressed here by comparing the kinetics of complexation of four metal extractant couples in different CTA +X − micelles where X − = Br −, Cl − or NO − 3. The existence of anionic metal species is assumed to be less probable with nitrate than with chloride or bromide. The results definitely show a different behaviour in the presence of nitrate when the extractant is known to be strongly partitioned in the micellar pseudophase, but no counterion effect is detected when less hydrophobic complexing agents are considered. These observations further substantiate the distinction previously made between interfacial complex formation reaction and bulk reaction, this being a function of the extractant hydrophobicity.