Oxidation Of Ethylenediaminetetraacetic Acid Research Articles

Electrochemical treatment of wastewaters containing metal-organic complexes: A one-step approach for efficient metal complex decomposition and selective metal recovery

Metal-organic complexes, especially those of ethylenediaminetetraacetic acid (EDTA) with metals such as copper (Cu) and nickel (Ni) (denoted here as Cu-EDTA and Ni-EDTA), are common contaminants in wastewaters from chemical and plating industries. In this study, a multi-electrode (ME) system using a two-chamber reactor and two pairs of electrodes is proposed for simultaneous electrochemical oxidation of a wastewater containing both Cu-EDTA and Ni-EDTA complexes as well as separation and selective recovery of Cu and Ni onto two different cathodes via electrodeposition. Our results demonstrate that the ME system successfully achieved 90% EDTA removal, 99% solid Cu recovery at the Cu recovery cathode and 56% Ni recovery (33.3% on the Ni recovery cathode and 22.6% in the solution) after a four-hour operation. The system further achieved 85.5% Ni recovery after consecutive five cycles of operation for 20 h. While Cu removal was mainly driven by the direct reduction of EDTA-complexed Cu(II) at the cathode, oxidation of EDTA within the Ni-EDTA complex at the anode was a prerequisite for Ni removal. The oxidation of metal-bound EDTA and free EDTA was driven by •OH and direct electron transfer on the PbO2 anode surface and graphite anode, respectively. We further show that ME system performs well for all pH conditions, treatment of real wastewaters as well as wastewaters containing other metals ions (Cr and Zn) along with Cu/Ni. The separation efficiency of Cu and Ni is dependent on applied electrode potential as well as nature and concentration of binding ligand present with comparatively lower separation efficiency achieved in the presence of weaker binding capacity and/or at lower ligand concentration and lower applied electrode potential. As such, some optimization of electrode potential is required depending on the nature/concentration of ligands in the wastewaters. Overall, this study provides new insights into the design and operation of EAOP technology for effective organic abatement and metal recovery from wastewaters containing mixtures of various metal-organic complexes.

Kinetic Modeling of the Anodic Degradation of Ni-EDTA Complexes: Insights into the Reaction Mechanism and Products

In this study, an electrochemical advanced oxidation process (EAOP) was employed to effectively degrade complexes of nickel and ethylenediaminetetraacetic acid (EDTA) present in electroless nickel plating wastewaters. Our results show that Ni-EDTA complexes can be effectively degraded by an EAOP with degradation of the complexes occurring at/near the anode surface via interaction with hydroxyl radicals generated on water splitting. Our results further show that the rate of Ni-EDTA degradation is not a function of the rate of any particular chemical reaction but, rather, is controlled by the rate of transport of Ni-EDTA to the anode surface. The oxidation of EDTA to smaller noncomplexing entities releases Ni2+, which is subsequently deposited onto the cathode as Ni0. While complete Ni-EDTA removal and Ni recovery are achieved within 2 h, the overall TOC removal by EAOP is limited, with only 50% TOC removal achieved after 2 h of treatment. The low affinity of small molecular weight EDTA degradation products (such as formic acid, glycine, oxamic acid, and acetic acid) for the anode surface limits oxidation of these compounds and overall TOC removal by the anodic oxidation process. We have developed a mathematical kinetic model that satisfactorily describes Ni-EDTA removal, Ni recovery, and TOC removal over a range of Ni and EDTA concentrations and provides a good description of the oxidation of various EDTA degradation intermediates. The mathematical model developed here, when coupled with the hydrodynamics of the electrochemical cell using a computational fluid dynamics tool, can assist in both cell design and the selection of operating parameters such that the performance of the EAOP process for Ni-EDTA degradation and TOC removal is optimized.

Photocatalytic conversion of ethylenediaminetetraacetic acid dissolved in real electroplating wastewater to hydrogen in a solar light-responsive system.

A sustainable and multifunctional photocatalysis-based technology has been established herein for simultaneous hydrogen generation and oxidation of ethylenediaminetetraacetic acid (EDTA) in real electroplating wastewater. When the photocatalyst concentration was 4 g/L and electroplating wastewater pH was 6, optimal adsorptions of EDTA2-, H+, and H2O were observed, while hydrogen generation efficiency reached 305 µmol/(h g). Owing to EDTA oxidation and occupation of the active sites of the photocatalyst by Ni ions or Ni-EDTA chelates, the charge separation and adsorptions of H+ and H2O decreased, reducing hydrogen generation efficiency with time. The lower EDTA and Ni concentrations in treated wastewater showed that photocatalytic conversion of EDTA in real electroplating wastewater to enhance hydrogen generation efficiency can be a practical alternative energy production technology. This study provided a novel idea to enhance the value of electroplating wastewater, to build a hydrogen generation route with no consumption of a valuable resource, and to reduce EDTA and Ni concentrations in electroplating wastewater.

Electrochemical Oxidation of EDTA in Nuclear Wastewater Using Platinum Supported on Activated Carbon Fibers.

A novel Pt/ACF (Pt supported on activated carbon fibers) electrode was successfully prepared with impregnation and electrodeposition method. Characterization of the electrodes indicated that the Pt/ACF electrode had a larger effective area and more active sites. Electrochemical degradation of ethylenediaminetetra-acetic acid (EDTA) in aqueous solution with Pt/ACF electrodes was investigated. The results showed that the 3% Pt/ACF electrode had a better effect on EDTA removal. The operational parameters influencing the electrochemical degradation of EDTA with 3% Pt/ACF electrode were optimized and the optimal removal of EDTA and chemical oxygen demand (COD) were 94% and 60% after 100 min on condition of the electrolyte concentration, initial concentration of EDTA, current density and initial value of pH were 0.1 mol/L, 300 mg/L, 40 mA/cm2 and 5.0, respectively. The degradation intermediates of EDTA in electrochemical oxidation with 3% Pt/ACF electrode were identified by gas chromatography-mass spectrum (GC-MS).

Competitive removal of Cu-EDTA and Ni-EDTA via microwave-enhanced Fenton oxidation with hydroxide precipitation.

Ethylenediaminetetraacetic acid (EDTA) can form very stable complexes with heavy metal ions, greatly inhibiting conventional metal-removal technologies used in water treatment. Both the oxidation of EDTA and the reduction of metal ions in metal-EDTA systems via the microwave-enhanced Fenton reaction followed by hydroxide precipitation were investigated. The Cu(II)-Ni(II)-EDTA, Cu(II)-EDTA and Ni(II)-EDTA exhibited widely different decomplexation efficiencies under equivalent conditions. When the reaction reached equilibrium, the chemical oxygen demand was reduced by a microwave-enhanced Fenton reaction in different systems and the reduction order from high to low was Cu(II)-Ni(II)-EDTA ≈ Cu(II)-EDTA > Ni(II)-EDTA. The removal efficiencies of both Cu(2+) and Ni(2+) in Cu-Ni-EDTA wastewaters were much higher than those in a single heavy metal system. The degradation efficiency of EDTA in Cu-Ni-EDTA was lower than that in a single metal system. In the Cu-Ni-EDTA system, the microwave thermal degradation and the Fenton-like reaction created by Cu catalyzed H2O2 altered the EDTA degradation pathway and increased the pH of the wastewater system, conversely inhibiting residual EDTA degradation.

Micellar Catalytic and Salt Effect on Oxidation of EDTA by MnO4 −

The kinetic oxidation of disodium salt of ethylenediaminetetraacetic acid (EDTA) by permanganate () in 0.005 M NaOH at 25°C in aqueous and/or in and 10 mM of different surfactants; poly(oxyethylene) isooctyl phenyl ether (TX-100), sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) has been studied using a spectrophotometer at 525 nm. The present data show that the reaction is first-order with respect to [EDTA]T and . Also, k obs value is constant within the 0.001 M −0.1 M NaOH range. Values of k obs increase with increasing concentration of CTAB more than TX-100, and decrease with increasing of SDS concentration. The rate of the reaction in the presence of different micelles can be explained using a pseudo-phase model of the kinetics. Association constants of EDTA and with surfactant micelles are reported. The activation parameters ΔH* and ΔS* have also been obtained. The variation of the reaction rate with the nature of the salt is discussed.

Oxidation Studies of Mn(III)–Amino Acid Chelating Agents

The kinetics of oxidation of ethylenediaminetetraacetic acid (Red) and nitrilotriacetic acid (Red) by trisacetatomanganese(III) dihydrate in dilute sulfuric acid and dilute perchloric acid media in nitrogen atmosphere were studied, where Red denotes the reductant in these reactions. At constant [Red], [H+], ionic strength and temperature, a first order dependence with respect to [Mn(III)] was observed. The rate increased with [Red] but was independent at higher [Red]. The rate was unaltered by the changes in [H+], ionic strength and added Mn(II). A suitable mechanism has been proposed to explain the observed kinetic data.

Oxidation of EDTA with H2O2 catalysed by metallophthalocyanines

The oxidation of ethylenediaminetetraacetic acid (EDTA) and Na, Ca, Zn, Fe, and Mn EDTA complexes with hydrogen peroxide was studied in aqueous solution with the use of several metallophthalocyanines (MePcS) as catalysts. The impact of pH, temperature, and catalyst/substrate ratio were investigated. The most effective catalytic system under neutral conditions was FePcS–H2O2. In these laboratory‐scale experiments, a catalyst/substrate/H2O2 molar ratio of 4:100:2000 was found to be optimal, while the effective reaction temperature was 40–60 °C. When the impact of metal speciation was studied, metal‐specific degradation rates in the removal of these compounds were observed: all EDTA–metal complexes except Zn–EDTA were efficiently oxidized within three hours. The most degradable species was Fe(III)–EDTA. Among the catalysts, FePcS was found to be the most active in EDTA degradation. Over 90% of EDTA was removed in the presence of FePcS as catalyst within three hours of reaction time.

Removal of EDTA from low pH printed-circuit board wastewater in a fluidized zero valent iron reactor

Fluidized zero valent iron (ZVI) process was adopted to reduce ethylenediaminetetraacetic acid (EDTA) from low pH printed-circuit board (PCB) wastewater for two reasons: (1) low pH of the wastewater favoring the ZVI reaction; (2) higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. The results showed that the degradation of EDTA was greatly enhanced under acidic pH, longer hydraulic detention time (HRT) and presence of dissolved oxygen (DO). Without addition of oxygen, 65% of EDTA was removed with capacity of 7.33 mg EDTA/g ZVI at pH 2, ZVI dosage of 424 g/L and HRT 10 min. With 6.8 mg/L of DO, 83% of EDTA was reduced with capacity of 19.01 mg EDTA/g ZVI for the same experimental condition. The presence of oxygen/ZVI initiated a Fenton type reaction to reduce EDTA. The end product after EDTA degradation was analyzed by high performance liquid chromoagraphy (HPLC), where propionic acid (C(2)H(5)COOH) was observed, indicating EDTA (oxidation number for carbon is 2) was oxidized to propionic acid (oxidation number for carbon is 3). Nitrogen species was also measured and the nitrogen in EDTA was converted to ammonium instead of nitrate and nitrite.

Submicellar catalytic effect of cetyltrimethylammonium bromide in the oxidation of ethylenediaminetetraacetic acid by MnO 4−

The effects of cetyltrimethylammonium bromide (CTAB), sodiumdodecyl sulphate (SDS) and Triton X-100 (TX-100) on the oxidative degradation of ethylenediaminetetraacetic acid (EDTA) by MnO 4 − have been studied spectrophotometrically at 525 and 420 nm, respectively. It was found that cationic surfactant catalyse the reaction rate while anionic and non-ionic have no effect. The premicellar environment of CTAB strongly catalyses the reaction rate which may be due to the favorable electrostatic binding of both reactants (MnO 4 − and EDTA) with the positive head groups of the CTAB aggregates. The influence of different parameters such as [MnO 4 −], [EDTA], [H +] and [surfactants] were also considered. The reaction follows the first- and fractional-order kinetics with respect to [MnO 4 −] and [EDTA]. The proposed mechanism and the derived rate law are consistent with the observed kinetics.

Incomplete Oxidation of Ethylenediaminetetraacetic Acid in Chemical Oxygen Demand Analysis

Ethylenediaminetetraacetic acid (EDTA) was found to incompletely oxidize in chemical oxygen demand (COD) analysis, leading to incorrect COD values for water samples containing relatively large amounts of EDTA. The degree of oxidation depended on the oxidant used, its concentration, and the length of digestion. The COD concentrations measured using COD vials with a potassium dichromate concentration of 0.10 N (after dilution by sample and sulfuric acid) were near theoretical oxygen demand values. However, COD measured with dichromate concentrations of 0.010 N and 0.0022 N were 30 to 40% lower than theoretical oxygen demand values. Similarly, lower COD values were observed with manganic sulfate as oxidant at 0.011 N. Extended digestion yielded somewhat higher COD values, suggesting incomplete and slower oxidation of EDTA, as a result of lower oxidant concentrations. For wastewater in which EDTA is a large fraction of COD, accurate COD measurement may not be achieved with methods using dichromate concentrations less than 0.1 N.

Hybrid Electrochemical Treatment for Persistent Metal Complex at Conductive Diamond Electrodes and Clarification of Its Reaction Route

The hybrid electrochemical treatment for persistent organometallic complexes [Cu–ethylenediaminetetraacetic acid (EDTA)] that was a combination of the reduction recovery of the center metal as nanoparticles and the oxidative decomposition of the organic ligand was attempted using the potential cycling at the oxygen-terminated boron-doped diamond (BDD) electrode. In the step of the recovery of the center metal of the organo-metal complex in the potential cycling from the reduction potential for , by stepping up the anodic potential limit to the potential region for oxygen evolution reaction, the reionization of electrodeposited Cu could be suppressed in the presence of the dissolved oxygen. Moreover, separation of the electrodeposited Cu as nanoparticles from the electrode surface could be achieved by introducing the oxygen-containing functional groups on the diamond surface. The oxidation of the particle surface by the dissolved oxygen might induce the formation of the insulating layer and accelerate the separation by the electrostatic repulsive force between the oxygen-terminated surface and the insulating layer on the Cu particles. The reaction pathway of the treatment was analyzed using the long-term potential cycling at the potential region between the reduction potential of Cu and the oxidation potential of the EDTA. In flow injection analysis with the UV detector, the formation of the Cu particles by the reduction reaction of the ion from was clarified to mainly occur in the initial stage of the electrolysis. Moreover, in high-performance liquid chromatography analysis with the electrogenerated chemiluminescence detector for the treated solution, ethylenediaminetriacetic acid (ED3A) and ethylenediaminediacetic acid (EDDA) were observed. Therefore, it was confirmed that the liberated EDTA was oxidized to ED3A and EDDA through sequential removal of the acetate groups. An unidentified product (supposed to be the small size of a hydrocarbon) appeared after during the electrolysis. Although the concentration of this unidentified product was not decreased in the electrolysis with anodic potential limit of , the concentration decay for this product was observed for the potential cycling up to , suggesting that for the full oxidation of EDTA to , it might be effective for the electrochemical oxidation by the radical available over at BDD.

Sonochemical destruction of free and metal-binding ethylenediaminetetraacetic acid

This study focused on the sonochemical degradation of ethylenediaminetetraacetic acid (EDTA) and chromium-EDTA complexes. Degradation of the copper(II)-EDTA complex was also investigated as a comparison metal complex. A 90% degradation of a 150-μM EDTA solution with continuous O 2-bubbling was shown for the 20-kHz system in approximately 3 h ( k pseudo-first order=1.22×10 −2 min −1) and less than 1 h for the 354-kHz system ( k pseudo-first order=5.42×10 −2 min −1). These results are consistent with the higher concentrations of hydrogen peroxide found in the higher frequency system and an expected oxidation of EDTA in bulk solution. The presence of a chelated metal decreased the rate of degradation at both frequencies. Cr(III)-EDTA degraded the slowest, supporting the theory that the extremely slow ligand exchange rate of chromium is the determining factor in how fast degradation by hydroxyl radical can occur. The 354-kHz system showed a 17% decrease in the original 150-μM Cr(III)-EDTA complex after 3 h of sonication. All of the chromium from the degraded EDTA complex existed as a combination of oxidized Cr(VI) and possibly small amounts of a new Cr(III)-organic complex (Cr(III)-Y). The 20-kHz system showed a similar extent of degradation (16%) after 3 h of sonication, despite lower hydroxyl radical production. Fifty percent of the chromium from the degraded EDTA complex was found as free Cr 3+ ion, with the remaining 50% existing as both Cr(III)-Y and Cr(VI). Varying degrees of bulk oxidation, near-bubble thermolysis, and perhaps different degradation pathways at the two frequencies are responsible for these differences.

Ruthenium(III) Catalyzed Oxidation Of Ethylenediaminetetraacetic Acid By N-Bromosuccinimide In Aqueous Alkaline Medium – A Kinetic And Mechanistic Study

The Ru(III) catalyzed oxidation of ethylenediaminetetraacetic acid by N-bromosuccinimide in aqueous alkaline medium was found to occur via substrate-catalyst complex formation in equilibrium step followed by the interaction of oxidant species and complex in a slow step to yield the products with regeneration of catalyst. A mechanism involving hypobromate ion as the reactive species of the oxidant has been proposed. The rate constants of individual steps of the reaction mechanism have been evaluated, and used to regenerate rate constants.

Oxidation of Metal−EDTA Complexes by TiO2 Photocatalysis

Ethylenediaminetetraacetic acid (EDTA), a common industrial agent for complexing metal ions in water, frequently inhibits conventional metals-removal technologies used in water treatment. This study investigated the use of TiO2 photocatalysis for the aqueous-phase oxidation of EDTA and several metal complexes of EDTA. Reactions were performed at 0.1 wt % loading of Degussa P-25 TiO2, a solute concentration of 0.8 mM and at a constant pH. The different metal−EDTA complexes exhibited widely different photocatalytic oxidation rates under equivalent conditions of pH = 4 ± 0.1 in an aerobic system: Cu(II)−EDTA > Pb(II)−EDTA >> EDTA > Ni(II)−EDTA ≈ Cd(II)−EDTA ≈ Zn(II)−EDTA >>> Cr(III)−EDTA. Photoefficiency based on the Cu(II)−EDTA initial rate is nearly 60%. The rates of total organic carbon (TOC) removal and formaldehyde generation during photocatalytic EDTA oxidation indicate similarities to electrochemical oxidations of EDTA. Several means were explored to enhance the oxidation of Ni(II)−EDTA, whose behavi...

Anodic Oxidation of Ethylenediaminetetraacetic Acid on Platinum Electrode in Alkaline Medium

The anodic oxidation of ethylenediaminetetraacetic acid (EDTA) was studied in alkaline medium on a smooth platinum electrode. Bulk electrolysis indicated that stable organic intermediates (formaldehyde and glyoxal) are formed during the oxidation of EDTA and that complete oxidation to can be achieved. The proposed pathway suggests that the acetate groups in EDTA are initially oxidized, generating formaldehyde and ethylenediamine. The rest potential of EDTA (0.066 to 0.164 V vs. Hg/HgO) was observed to be higher than for other organic species. In alkaline medium, very little EDTA oxidation was found to occur on bare platinum. Limiting‐current behavior due to PtO formation was observed immediately positive of the rest potential. Tafel behavior (Tafel slope 120 mV/dec) was observed in the potential region positive of the cessation of the bulk of oxide film formation and negative of the onset of evolution. The reaction order of EDTA was determined to be ∼0.5, and that of was close to zero. The reaction mechanism consistent with the experimental data involves Temkin‐type adsorption and a first‐electron‐transfer rate‐determining step.

Kinetics and mechanisms of Co(II) EDTA oxidation by pyrolusite

Monitoring and restoration activities at low-level radioactive waste disposal sites have identified complicated mixtures of inorganic and organic contaminants in soil and groundwater. Metallic contaminants are generally complexed with various chelating agents and organic acids which alter the geochemical behavior of the contaminants in subsurface media. The objective of this study was to provide an improved understanding of the geochemical processes controlling the subsurface transport of radioactive 60Co complexed with ethylenediaminetetraacetic acid (EDTA). Specifically, we investigated the kinetics and mechanisms of Co(II) EDTA 2− oxidation to Co(III)EDTA − by the soil mineral pyrolusite (β-MnO 2). A column displacement technique was utilized to investigate Co(II)EDTA 2− reactivity and oxidation rates through packed beds of pyrolusite-coated SiO 2. The interaction of Co(II)EDTA 2− with the porous media was characterized by a MnO 2-induced oxidation of the Co (II)EDTA 2− to Co(III)EDTA −. The oxidation of Co(II)EDTA 2− appeared to involve the reduction of Mn (IV) to both an aqueous Mn 2+ species and a theorized Mn(III)-oxide solid phase. The redox reaction was catalytic since the reduction products were gradually reoxidized in the presence of dissolved O 2 to form a Mn(IV)-oxide phase. Oxidation of surface-bound Mn 2+ and the theorized Mn(III)-oxide was slow relative to Co(II)EDTA 2− oxidation, and a reversible loss in the oxidative ability of the β-MnO 2 occurred when exposed to CO(II)EDTA 2−. The reduction in catalytic activity of the MnO 2 was not the result of direct surface poisoning by Mn 2+ but rather was believed to result from the formation of an intermediate Mn(III)-oxide solid phase whose oxidative potential was significantly less than MnO 2. Thus, the kinetics of Co(II)EDTA 2− oxidation to Co(III)EDTA − by MnO 2 was dependent on the rate of MnO 2 surface regeneration. The environmental implications of this redox reaction are pronounced, since any Co(III)EDTA − produced is extremely stable, and this enhances the persistence and transport of 60Co in subsurface environments.

Remediation of metal contaminated soil by EDTA incorporating electrochemical recovery of metal and EDTA

AbstractRemoval of toxic heavy metals from a soil matrix by the addition of ethylenediamine tetraacetic acid (EDTA) is an effective means of remediation. The liquid stream containing the metal and chelating agent is amenable to further treatment by electrolysis in which the metal can be separated from the chelating agent. This provides a separated metal that can be removed for reuse or treated for final disposal by conventional technologies and a reclaimed EDTA stream that can be used again for treatment of contaminated soil.Under the diffusion controlled conditions of polarography or voltammetry, we observed reduction of cadmium, copper and lead ions and their protonated EDTA complexes (MHY−), but not of the non‐protonated EDTA complexes (MY2−). Potentials applicable for metal deposition and, consequently, regeneration of the EDTA were established. To prevent electrochemical oxidation of EDTA during electrolysis we used a cell in which the anode and cathode compartments were separated by a cation exchange membrane. Tests with Pb‐EDTA demonstrated that over 95 percent recovery of both EDTA and lead could be achieved by electrolysis. The lead that was deposited onto a copper electrode was a mixture of hydrolysis products and salts and the lead could be recovered by dissolution in acid. EDTA was equilibrated with soil before addition of lead. When electrolyzed, this sample released EDTA and deposited Pb to approximately the same extent as did the samples that had not been equilibrated with soil.

Electrocatalytic Oxidation of Fe/EDTA Complexes at Lead Dioxide Electrodes

The electrolytic oxidation of EDTA (ethylene diamine tetra acetic acid) and the EDTA complexes of Fe2+,3+ was investigated at Pt and pure electrodes and and mixed oxide‐film electrodes deposited on the Pt substrate. The reactivity of the mixed oxide electrodes was significantly greater than for the Pt and electrodes. The application of this phenomena is suggested for reduction of the mass of radioactive wastes generated by the cleaning of steam generators in nuclear power plants.

Kinetics and mechanism of the oxidation of the calcium complex of ethylenediaminetetra-acetic acid by perbenzoic acids

The rate of oxidation of ethylenediaminetetra-acetic acid (EDTA) by perbenzoic acids in aqueous acetate buffers is retarded by added calcium ions. The oxidation of CaEDTA2– proceeds via parallel pathways involving dissociation and subsequent oxidation of the ligand and direct nucleophilic attack of the nitrogen atom of the complex on the outer peroxidic oxygen of the peracid respectively. The mechanism of the latter pathway is discussed. An application of the Ca–EDTA system as a reservoir of EDTA for the inhibition of interfering trace-metal-ion catalysed reactions of peracids is suggested.