Metal-ethylenediaminetetraacetic Acid Complexes Research Articles

Effects of EDTA on the leaching behaviors of Cs(I) and Co(II) from cement waste forms

Cementation is extensively employed for immobilizing radionuclides in low- and intermediate-level radioactive wastes generated during the decommissioning of nuclear power plants. Ethylenediaminetetraacetic acid (EDTA), used as a decontamination agent during the decommissioning process, can be introduced into the cement waste form containing radionuclides. This study investigated the effects of the EDTA present in simulated radioactive decommissioning wastes on the leaching behaviors of Co and Cs immobilized in the cement waste form. Co leaching was facilitated by the formation of highly mobile Co–EDTA complexes. However, Cs leaching was impeded by the competition for leaching with other metal–EDTA complexes. Moreover, the EDTA-induced carbonated layer with a dense pore structure played a crucial role as a retardation barrier for the Cs leaching. The calcite contents of the samples with 8 wt% EDTA were approximately three times higher than those of the samples without EDTA. The introduced EDTA affected the leaching behaviors of both Co and Cs, as well as the microstructure evolution of the cement waste form. Nevertheless, the addition of EDTA had a relatively low positive effect on the efficiency of Cs immobilization, but also an obvious negative effect on the efficiency of Co immobilization, regardless of the concentration of EDTA. Finally, an EDTA dosage of 1 wt% in the cement waste forms containing Co or Cs is suggested as a potential waste acceptance criterion for solidified low- and intermediate-level radioactive waste.

Influence of Transition Metal Electron Configuration on the Structure of Metal–EDTA Complexes

The vibrational spectra of cold complexes of ethylenediaminetetraacetic acid (EDTA) with transition metal dications in vacuo show how the electronic structure of the metal provides a geometric template for interaction with the functional groups of the binding pocket. The OCO stretching modes of the carboxylate groups of EDTA serve as structural probes, informing on the spin state of the ion as well as the coordination number in the complex. The results highlight the flexibility of EDTA in accepting a large range of metal cations in its binding site.

Exploring UiO-66(Zr) frameworks as nanotraps for highly efficient removal of EDTA-complexed heavy metals from water

Metal-organic frameworks (MOFs), an exciting class of porous crystalline materials, are suitable for adsorptive removal of toxic heavy metal-ethylenediaminetetraacetic acid (M-EDTA) complexes from wastewater. In this paper, water-stable UiO-66(Zr) with well-defined morphology was successfully synthesized through a facile microwave-assisted solvothermal method and employed as nanotraps for the efficient capture of the three M-EDTA complexes, Cu-EDTA, Pb-EDTA, and Ni-EDTA. The adsorption behaviors, effects of solution pH and co-existing anions, as well as the eluant and desorption were investigated. The obtained UiO-66(Zr) showed good stability and excellent uptake capacity of M-EDTA in a wide pH range (3.0–10.0). UiO-66(Zr) exhibited a higher removal efficiency of Cu-EDTA (57.56 mg/g), Pb-EDTA (120.6 mg/g), and Ni-EDTA (54.27 mg/g). Based on the overall analysis results, our findings show that EDTA-metal complex ions can be adsorbed inside UiO-66(Zr) mainly through the Lewis‐acid/‐base interactions and possible anion-π interaction with strong binding energies. Size-matching EDTA-metal complexes confined in the UiO-66(Zr) with flexible geometry would also contribute to the fast adsorption kinetics as well as the selective adsorption of different M-EDTA complexes.

Deposition of Metal Oxide Films from Metal–EDTA Complexes by Flame Spray Technique

R2O3 (R = Y, Eu, Er) metal oxides were synthesized from metal–ethylenediaminetetraacetic acid (EDTA) complexes using a flame spray technique. As this technique enables high deposition rates, films with thickness of several tens of micrometers were obtained. Films of yttria, europia, and erbia phase were synthesized on stainless-steel substrates with reaction assistance by H2–O2 combustion gas. The oxide films consisted of the desired crystalline phase with micropores. The porosity of the films was in the range of 6–15%, varying with the metal used. These results suggest that the true density of the metal oxide obtained from metal–EDTA powder through the thermal reaction process plays an important role in achieving film with the desired porosity.

Room Temperature Ferromagnetism in Dual Doped (Mn2+, Ni2+) ZnO Codoped with Li1+ Prepared Using EDTA Sintered at Low Temperature

Nanopowders of Zn1−x−y−zMnxNiyLizO [(x = 0.04, y = 0, z = 0), (x = 0.04, y = 0.03, z = 0) and (x = 0.04, y = 0.03, z = 0.03)] have been synthesized by sol–gel precursor route using ethylene diamine tetraacetic acid (EDTA) as a metal chelating agent. X-ray diffraction analysis confirms the formation of wurtzite hexagonal structure for all the three compositions. Mn2+ doped ZnO exhibits room temperature ferromagnetism (RTFM), and it is found that further Ni2+ doping has decreased Ms because of limit of solid solubility of transition metal in ZnO. But codoping of monovalent Li1+, further increases the ferromagnetism (FM) value, due to introduction of free carriers compared to the dual doped samples. Photoluminescence (PL) spectra of the system, exhibit near band edge (NBE) emission peak at ∼464 nm due to the electron transition from interstitials to the valence band. Recombination of conduction electron with hole trapped at oxygen vacancy, leads to prominent defect emission peaks at ∼482 nm and 532 nm. The evidence of the formation of metal–EDTA complexes are found from the Fourier transform infrared spectra at 2800–3800 cm−1 with shifting, splitting of the peak and also drastic variations in the intensity.

Effects of calcination temperature and solution pH value on the structural and magnetic properties of Ba 2Co 2Fe 12O 22 ferrite via EDTA-complexing process

Y-type hexagonal Ba 2Co 2Fe 12O 22 was prepared via a simple EDTA-complexing process using corresponding metal nitrates as raw materials and ethylene diamine tetraacetic acid (EDTA) as complexing agent. The decomposition process of the precursor, formation process of Ba 2Co 2Fe 12O 22, structure, morphology and magnetic properties of the particles were investigated by thermogravimetric analysis and differential thermal analysis (TGA–DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The effects of calcination temperature and solution pH value on the structure and magnetic properties of the particles were studied. The results showed that the formation of single phase Ba 2Co 2Fe 12O 22 was achieved by controlling the calcination temperature ≥1000 °C. Meanwhile, the pH value ≥8 of initial solution was necessary to form stable metal–EDTA complexes and to produce high quality Ba 2Co 2Fe 12O 22. The magnetic properties showed dependence on the preparation conditions and microstructures. Saturation magnetization ( M s) and coercivity ( H c) were obtained in the range of 30.2–44.8 emu g −1 and 91.7–1953.7 Oe for samples calcined from 700 to 1200 °C, and 28.8–33.4 emu g −1 and 190.1–84.0 Oe for samples from initial solution of pH 3.8–10.1.

An on-line electrodialyzer-ICP-MS analytical system for direct determination of trace metal impurities in KOH

We have developed an on-line electrodialysis system equipped with a cation-permeable membrane that, when coupled to an ICP mass spectrometer, provides a simple and sensitive hyphenated method for the determination of trace metal impurities in concentrated KOH. Because our proposed on-line electrodialysis method allows the quantitative removal of K+ and OH− ions, which may seriously interfere with and potentially damage the ICP-MS system, the safety risks and the analytical errors arising from the presence of extremely high alkalinity KOH are both low. To prevent loss of the analyte cations during the electrodialysis process, a selective chelating agent—ethylenediaminetetraacetic acid (EDTA)—was added to form anionic metal–EDTA complexes. To achieve maximum signal intensities, we optimized the sample flow rate and the amount of EDTA in terms of their effects on the retention and removal efficiencies of the analyte species and K+ ions. Based on the optimized operating conditions, near 100% of trace metal ions in 11.25% KOH solutions—added with 10 mg EDTA L−1 in advance—could pass through electrodialyzer and be delivered to the ICP-MS at a flow rate of 0.1 mL min−1. Because over 99.99% of 11.25% KOH was removed prior to ICP-MS measurement and low blank levels were achieved, this hyphenated method is sufficiently robust for the determination, with detection limits ranging from μg L−1 to sub-μg L−1, of trace Cu, Mn, Zn, Co, Ni, Cd, and Pb impurities in high-alkalinity samples. Because no certified values for the analyte content in KOH were available, the overall analytical method was validated for accuracy and precision by analyzing KOH solutions spiked with known amounts of analytic ions. Based on the analytical data, the analytical accuracy, expressed as spike recovery was found to be at 100 ± 10% for all the elements tested. This method is superior to the reported voltammetric methods for the determination of trace impurities in terms of detection limits, ability of simultaneous multi-elements analysis and speed of analysis. The validated method was successfully applied to determine trace levels of metal impurities in concentrated KOH solutions.

Determination of Low-Level Ethylenediaminetetraacetic Acid in Water Samples by Ion Chromatography with Ultraviolet Detection

A convenient and sensitive ion chromatographic (IC) method for the analysis of ethylenediaminetetraacetic acid (EDTA) in water samples was proposed. Using a fast reversible reaction of free EDTA and metal–EDTA complexes into Fe(III)–EDTA complex in the presence of Fe(III) ions, sample solutions were applied to an ion-exchange column using a mobile phase (pH 2.3), which was composed of 100 μM Fe(III) chloride and 5 mM methanesulfonic acid. The addition of Fe(III) solution (100 μL) containing 10 mM Fe(III) chloride and 0.5 M methanesulfonic acid to the sample solution (10 mL) permitted the injection of a large volume (400 μL) of sample, which allowed for greater sensitivity. The proposed IC method gave a highly linear (r2 > 0.999) calibration curve ranging 0.005–1.0 μM EDTA and had a limit of detection of 1.5 nM. High repeatability (RSD < 2.1%) and recoveries (88–108%) were also obtained. With this method, total EDTA level in raw and drinking waters were analyzed successfully.

Metal composition of Y2O3:Eu powder evaluated using particle analyzer

Y2O3:Eu red phosphor powder was synthesized with powders of metal–ethylenediaminetetraacetic acid (EDTA) complexes as a starting material. The compositional analysis of each metal–EDTA complexes particle and Y2O3:Eu particle was performed using a particle analyzer. In this study, first, the particles of a mixture of Y– and Eu–EDTA complexes were obtained by a spray drying method from solution consisting of Y– and Eu–EDTA$NH4. Then, the metal–EDTA complex powder was fired in obtaining the Y2O3:Eu red phosphor. The metal composition of each particle was scattered for the powder of the metal–EDTA mixture, while it became narrow for the Y2O3:Eu powder. The intensity of cathodoluminescence obtained from the Y2O3:Eu powder increased with increasing the fired temperature. In addition, the maximum intensity was obtained from the sample with xZ0.12 for Y2KxO3:Eux.

Effect of ferric chloride addition on the removal of Cu and Zn complexes with EDTA during municipal wastewater treatment

The presence of the synthetic chelating agent ethylenediaminetetraacetic acid (EDTA) in municipal wastewater has a significant impact on the efficacy of wastewater treatment plants because pollutant metal–EDTA complexes are difficult to remove. To understand the potential of FeCl 3 addition during primary treatment to improve metal removal, laboratory experiments and a full-scale study were conducted. Results of laboratory experiments designed to simulate primary and secondary wastewater treatment indicate that a portion of pollutant metal–EDTA species can be converted into FeEDTA − by addition of FeCl 3 during simulated primary treatment. Addition of FeCl 3 also resulted in improved metal removal by adsorption. The combination of these two processes improved removal of Cu and Zn by 20% during simulated primary treatment. During full-scale treatment, a slight increase in the concentration of FeEDTA − in secondary effluent was observed when FeCl 3 was added during primary treatment. However, FeCl 3 addition had no observable effect on metal concentrations in the wastewater effluent. The most noticeable change in EDTA speciation at full scale occurred during primary treatment, where most of the pollutant metal–EDTA complexes were converted into FeEDTA −, irrespective of whether or not FeCl 3 was added. The formation of FeEDTA − during primary treatment plays a potentially important role in metal removal and should be considered in future evaluations of wastewater treatment plant performance.

Bacterial degradation of EDTA

Degradation of EDTA (ethylenediaminetetraacetic acid) or metal-EDTA complexes by cell suspensions of the bacterial strain DSM 9103 was studied. The activity of EDTA degradation was the highest in the phase of active cell growth and decreased considerably in the stationary phase, after substrate depletion in the medium. Exponential-phase cells were incubated in HEPES buffer (pH 7.0) with 1 mM of uncomplexed EDTA or EDTA complexes with Mg2+, Ca2+, Mn2+, Pb2+, Co2+, Cd2+, Zn2+, Cu2+, or Fe3+. The metal-EDTA complexes (Me-EDTA) studied could be divided into three groups according to their degradability. EDTA complexes with stability constants K below 10(16) (lg K < 16), such as Mg-EDTA, Ca-EDTA, and Mn-EDTA, as well as uncomplexed EDTA, were degraded by the cell suspensions at a constant rate to completion within 5-10 h of incubation. Me-EDTA complexes with lg K above 16 (Zn-EDTA, Co-EDTA, Pb-EDTA, and Cu-EDTA) were not completely degraded during a 24-hour incubation, which was possibly due to the toxic effect of the metal ions released. No degradation of Cd-EDTA or Fe(III)-EDTA by cell suspensions of strain DSM 9103 was observed under the conditions studied.

Adsorption of metal–ethylenediaminetetraacetic acid chelates onto lake sediment

The adsorption of Ethylenediaminetetraacetic acid (EDTA) and its metal complexes, Cu, Fe(III), Hg, Mn and Ni, onto lake sediment was studied. The results reveal that EDTA and metal–EDTA complexes, even though being hydrophilic compounds, are indeed adsorbed within one months' contact time to some extent (6.3–24.8%). Less than 10% of Ni–EDTA, Cu–EDTA and EDTA salt was adsorbed, while the mass amount of Mn–EDTA, Hg–EDTA and Fe(III)–EDTA found in sediment exceeded 15% after the contact period. Thus, adsorption of metal–EDTA chelates might be a relevant process in their removal from the aquatic environment. The metal–EDTA chelates in aqueous and solid phases were determined by gas chromatography–nitrogen phosphorus detection (GC–NPD) system. The complexes were extracted by phosphate solution prior to analysis. The ability of EDTA to desorb adsorbed heavy metals from sediments is also discussed.

Removal of trace metals from contaminated soils using EDTA incorporating resin trapping techniques

A series of experiments was conducted using two urban soils from Montreal contaminated with high levels of trace metals. The experiments were aimed at removing and recuperating trace metals from the contaminated soils using ethylene diamine tetraacetic acid (EDTA) and HCl. Acid washing with 1×10 −3 M HCl was found to be ineffective in removing trace metals from the soils. In contrast, the extraction with EDTA is a promising approach; at a low concentration it removed large amounts of metals. In one soil we were able to decrease Cd concentration from 6.2 to 1.4 mg kg −1; the corresponding results for Cu were 700 to 330 mg kg −1, Pb 800 to 410 mg kg −1, and Zn 2600 to 431 mg kg −1 after 12 times 24-h extraction with 2.74×10 −3 M EDTA. These represent decreases of 76% for Cd, 53% for Cu, 49% for Pb, and 84% for Zn. In a second, less contaminated soil, the Cu concentration was reduced from 130 to 85 mg kg −1 after three 24-h extractions with 2.74×10 −3 M EDTA. We have also developed a procedure to remove metal–EDTA complexes from the leachates using an anion exchange resin. With this technique we were able to trap up to 99% of the Cd, Cu, and Zn, and 93% of the Pb in the soil leachates.