Simultaneous Determination of Cu-EDTA and Its Degradation Intermediates by Capillary Electrophoresis with a Capacitively Coupled Contactless Conductivity Detector

Direct analysis of biodegradable chelating agents based on liquid chromatography/electrospray ionization mass spectrometry using a metal-free hydrophilic interaction liquid chromatographic column

Recently, biodegradable aminopolycarboxylic acid chelating agents have attracted attention as an alternative to environmentally persistent chelating agents such as ethylenediamine-N,N,N',N'-tetraacetic acid. However, the detection of chelating agents requires complexation with metals or derivatization by esterification reagents, and their direct detection using the currently available analytical methods still represents a challenge. Herein, we describe a direct analytical method for the biodegradable chelating agents ethylenediamine-N,N'-disuccinic acid, 3-hydroxy-2,2'-iminodisuccinic acid, methylglycine-N,N'-diacetic acid, and N,N-bis(carboxymethyl)-L-glutamic acid, via ultra-performance liquid chromatography/electrospray ionization quadrupole/time-of-flight mass spectrometry. Satisfactory retention and separation with a good peak shape were successfully achieved using a metal-free hydrophilic interaction liquid chromatographic column. The calibration curves showed good linearity in the range of 1.0-50 μM with correlation coefficients greater than 0.9988. The detection limits ranged from 0.04 to 0.12 μM. Furthermore, the developed method could be applied to the quantitative analysis of the four chelating agents in biodegradation and photodegradation experiments at the laboratory level. The proposed method, which offers the advantages of quickness, sensitivity, and requiring no complicated pretreatment steps, is expected to contribute significantly to the practical analysis of chelating agents in environmental water samples.

Electrochemical Ni-EDTA degradation and Ni removal from electroless plating wastewaters using an innovative Ni-doped PbO2 anode: Optimization and mechanism

In this work, a novel Ni-doped PbO₂ anode (Ni-PbO₂) was prepared via a co-electrodeposition method and used to remove Ni-ethylenediaminetetraacetic acid (Ni-EDTA) from solutions typical of electroless nickel plating wastewater. Compared with a pure PbO₂ electrode, Ni doping increased the oxygen evolution potential as well as the reactive surface area and reactive site concentration and reduced the electron transfer resistance thereby resulting in superior Ni-EDTA degradation performance. The 1% Ni-doped PbO₂ electrode exhibited the best electrochemical oxidation activity with a Ni-EDTA removal efficiency of 96.5 ± 1.2%, a Ni removal efficiency of 52.1 ± 1.4% and an energy consumption of 2.6 kWh m^-3. Further investigations revealed that 1% Ni doping enhanced both direct oxidation and hydroxyl radical mediated oxidation processes involved in Ni-EDTA degradation. A mechanism for Ni-EDTA degradation is proposed based on the identified products. The free nickel ion concentration initially increased as a result of the degradation of Ni-EDTA complexes and subsequently decreased as a consequence of nickel electrodeposition on the cathode surface. Further characterization of the cathode deposits by X-ray diffraction and X-ray photoelectron spectra indicated that the deposition products were a mixture of Ni⁰, NiO and Ni(OH)₂ with elemental Ni accounting for roughly 80% of the deposited nickel. Results of this study pave the way for the application of anodic oxidation processes for efficient degradation of Ni-containing complexes and recovery of Ni from nickel-containing wastewaters.

A technique for the speciation analysis of metal-chelator complexes in aqueous matrices using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry

Chelators, capable of creating soluble complexes with metals, may disrupt the natural speciation of metals in environmental matrices. Detection of environmental speciation of such complexes has remained challenging as obtaining the precise inherent nature of metal-chelator complexes is difficult by using routine techniques. Herein, we report a rapid and sensitive technique for the speciation analysis of complexes of five metal ions (Ni, Pb, Co, Fe and Ca) with two aminopolycarboxylate chelator variants, namely, EDTA (ethylenediaminetetraacetic acid) and EDDS (ethylenediamine-N,N'-disuccinic acid), including the simultaneous quantification of those complexes. EDTA is characterized as environmentally persistent among the chelators used in the current work whereas EDDS is biodegradable. The speciation analysis was performed using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The separation was achieved by using hydrophilic interaction liquid chromatographic column. The effect of various operating parameters on analytes such as mobile-phase composition, buffer concentrations and pH, sample diluents, sample injection volume, and column temperature on the peak shape and sensitivity were systematically optimized. The dilution was the only requirement for preparing the samples for analysis. The average relative uncertainty was 2.4% with the average precision (as RSD, n= 7) of 3.5%. For the metal-EDTA complexes, LOD range was 3 to 76 nmol L-1 with satisfactory recovery from a simulated mix matrix (recovery: 79-97%) and river water by standard addition (recovery: 82-94%). For metal-EDDS complexes, LOD range was 66 to 293 nmol L-1 with recovery from a simulated mix matrix (recovery: 56-97%) and river water by standard addition (recovery: 61-91%). The proposed method will be applicable in speciation analysis and simultaneous detection of metal-chelator complexes from environmental samples.

Decomplexation efficiency and mechanism of Cu(II)-EDTA by H2O2 coupled internal micro-electrolysis process

Internal micro-electrolysis (IE) coupled with Fenton oxidation (IEF) was a very effective technology for copper (Cu)-ethylenediaminetetraacetic acid (EDTA) wastewater treatment. However, the mechanisms of Cu²⁺ removal and EDTA degradation were scarce and lack persuasion in the IEF process. In this paper, the decomplexation and removal efficiency of Cu-EDTA and the corresponding mechanisms during the IEF process were investigated by batch test. An empirical equation and the oxidation reduction potential (ORP) index were proposed to flexibly control IE and the Fenton process, respectively. The results showed that Cu²⁺, total organic carbon (TOC), and EDTA removal efficiencies were 99.6, 80.3, and 83.4%, respectively, under the proper operation conditions of iron dosage of 30 g/L, Fe/C of 3/1, initial pH of 3.0, Fe²⁺/H₂O₂ molar ratio of 1/4, and reaction time of 20 min, respectively for IE and the Fenton process. The contributions of IE and Fenton to Cu²⁺ removal were 91.2 and 8.4%, respectively, and those to TOC and EDTA removal were 23.3, 25.1, and 57, 58.3%, respectively. It was found that Fe²⁺-based replacement-precipitation and hydroxyl radical (•OH) were the most important effects during the IEF process. •OH played an important role in the degradation of EDTA, whose yield and productive rate were 3.13 mg/L and 0.157 mg/(L min^-1), respectively. Based on the intermediates detected by GC-MS, including acetic acid, propionic acid, pentanoic acid, amino acetic acid, 3-(diethylamino)-1,2-propanediol, and nitrilotriacetic acid (NTA), a possible degradation pathway of Cu-EDTA in the IEF process was proposed. Graphical abstract The mechanism diagram of IEF process.

Co-N-doped MoO2 modified carbon felt cathode for removal of EDTA-Ni in electro-Fenton process

Metal ions removal is inhibited in aqueous solution containing ethylenediaminetetraacetic acid (EDTA). In this study, the non-noble metals-based Co-N-doped MoO₂ nanowires (Co-N-MoO₂) were successfully synthesized using cyanamide and Co(Ac)₂ as precursors by pyrolysis, then immobilized on carbon felt (CF), and firstly used as cathode to remove EDTA-Ni complex through oxygen reduction reaction (ORR) in electro-Fenton (EF) process. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that a synergetic coupling effect of doping of N and Co induced structural modifications of MoO₂ lattice, and produced more lattice defects. The electrochemical analysis results showed that the superior ORR electrochemical catalysis activities were obtained at pH = 3 with the lowest cathodic peak potentials (- 0.157 V vs. Ag/AgCl), the highest electrochemical active surface area (EASA: 3.971 mC cm^-2), the extraordinarily high of the ring current (35.5 μA) and high H₂O₂ yield (> 20%). Under the optimum conditions, about 68% of EDTA-Ni was removed with the Co-N-MoO₂/CF as cathode after 120 min with lower specific energy consumption (0.0226 kW h mg^-1 (DOC)) in EF system. Mechanism analysis indicated that the production of strong oxidizing property of hydroxyl radical (•OH) on the cathode played an important role in the removal of EDTA-Ni in the EF process, synergetic effect of cobalt and nitrogen co-doped could facilitate the high generation of H₂O₂, which greatly promote the formation of •OH. The EF system with Co-N-MoO₂/CF cathode has a potential for breaking metal-complex with good stability, showing that this cathode is a candidate for application for applications in EAPOs.

Treatment of Ni-EDTA containing wastewater by electrocoagulation using iron scraps packed-bed anode

The unique electrocoagulator proposed in this study is highly efficient at removing Ni-EDTA, providing a potential remediation option for wastewater containing lower concentrations of Ni-EDTA (Ni ≤ 10 mg L^-1). In the electrocoagulation (EC) system, cylindrical graphite was used as a cathode, and a packed-bed formed from iron scraps was used as an anode. The results showed that the removal of Ni-EDTA increased with the application of current and favoured acidic conditions. We also found that the iron scrap packed-bed anode was superior in its treatment ability and specific energy consumption (SECS) compared with the iron rod anode. In addition, the packed density and temperature had a large influence on the energy consumption (ECS). Over 94.3% of Ni and 95.8% of TOC were removed when conducting the EC treatment at an applied current of 0.5 A, initial pH of 3, air-purged rate 0.2 L min^-1, anode packed density of 400 kg m^-3 temperature of 313 K and time of 30 min. SEM analysis of the iron scraps indicated that the specific area of the anode increased after the EC. The XRD analysis of flocs produced during EC revealed that hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) were the main by-products under aerobic and anoxic conditions, respectively. A kinetic study demonstrated that the removal of Ni-EDTA followed a first-order model with the current parameters. Moreover, the removal efficiency of real wastewater was essentially consistent with that of synthetic wastewater.