Adsorption of metal-ethylenediaminetetraacetic acid chelates onto lake sediment

Fate of metal-EDTA complexes during ferrihydrite aging: Interaction of metal-EDTA and iron oxides

The widespread presence of ferrihydrite in the environment makes many contaminants including metal-EDTA complexes being adsorbed on it. However, the fate of metal-EDTA complexes during the transformation of ferrihydrite was poorly understood. Understanding the migration and speciation changes of metal-EDTA adsorbed on ferrihydrite during the transformation was helpful to predict its fate in some natural and engineering environments. In this work, the interaction of the two metal-EDTA complexes (Ni(II)-EDTA and Ca(II)-EDTA) and ferrihydrite during the 9-day transformation of ferrihydrite at different pH values was studied. The results showed that part of EDTA complexing metals changed to non-complexed metals during the ferrihydrite transformation, which was due to the fact that metal in the metal-EDTA exchanged with Fe(III) on ferrihydrite. Besides, different speciation of metal ions migrated during the transformation of ferrihydrite. Meanwhile, Fe(III)-EDTA formed in this process, and the exchange of metal in Ca(II)-EDTA with Fe(III) in ferrihydrite was faster than that of Ni(II)-EDTA. Besides, the presence of metal-EDTA affected the transformation rate of ferrihydrite under neutral and alkaline condition, and metal-EDTA accelerated the dissolution of ferrihydrite to form goethite. Therefore, ferrihydrite and metal-EDTA influenced each other during the transformation of ferrihydrite. The results of this work revealed that the process of metal-EDTA dissolving ferrihydrite not only included the dissociation of metal-EDTA, but also involved the migration of metal ions and affected the transformation of ferrihydrite.

Adsorption of lead and antimony in the presence and absence of EDTA by a new vermiculite product with potential recyclability

A new two-step modification method has been proposed where 1.8% HCl and 3.1% HNO₃ were applied to modify the interlayer of vermiculite (VMT). This product was given 90 °C of heat in 30% H₂SO₄ solution that was used for Pb (II) and Sb (III) adsorption. The EDTA presence on the individual adsorption was assessed. X-ray diffraction revealed that the VMT inter-stratified reflection through acid intercalation within the interlayer decreased the parallel gaps between the atoms, witnessing on the outer-sphere adsorption. The driving force was found electrostatic, which fits well with pseudo-second-order kinetics and Langmuir isotherm. The Pb (II) and Sb (III) uptake followed descending order adsorption with increasing concentration of chelating EDTA. Three consecutive desorption cycles revealed that the prepared adsorbent was suitable that may be regarded as a good candidate for complex wastewaters.

Chemical Stability of the Fertilizer Chelates Fe-EDDHA and Fe-EDDHSA over Time

In application conditions, the influence of environmental parameters on used fertilizer chelates and their distribution over time is important. For this purpose, the changes in the content of micronutrient ions and Fe-EDDHA and Fe-EDDHSA chelates in an aqueous medium at different pH values were studied. In the assumed time, changes in the ions content were analyzed using the voltammetry method at pH 3, 5 and 7. The content of isomers and chelate forms was analyzed by ion pair chromatography at pH 3, 5 and 7. These studies allowed us to determine the effect of pH on the stability of iron chelates over time.

Recent Advances of Near-Infrared (NIR) Emissive Metal Complexes Bridged by Ligands with N- and/or O-Donor Sites

Near-infrared (NIR) emissive metal complexes have shown potential applications in optical communication, chemosensors, bioimaging, and laser and organic light-emitting diodes (OLEDs) due to their structural tunability and luminescence stability. Among them, complexes with bridging ligands that exhibit unique emission behavior have attracted extensive interests in recent years. The target performance can be easily achieved by NIR light-emitting metal complexes with bridging ligands through molecular structure design. In this review, the luminescence mechanism and design strategies of NIR luminescent metal complexes with bridging ligands are described firstly, and then summarize the recent advance of NIR luminescent metal complexes with bridging ligands in the fields of electroluminescence and biosensing/bioimaging. Finally, the development trend of NIR luminescent metal complexes with bridging ligands are proposed, which shows an attractive prospect in the field of photophysical and photochemical materials.

Nano-manganese oxides-modified biochar for efficient chelated copper citrate removal from water by oxidation-assisted adsorption process

Removal of chelated copper from wastewater is more difficult than that of copper ions owing to its stable structure, wide range of pH tolerance, and stronger mobility. Copper citrate (CuCA) widely exists in the water system and inevitably poses serious hazards to human health and environment. Biochar as economic functional material has been widely used for environmental applications, especially in wastewater treatment. This study focused on the performance of manganese oxide-modified biochar (BC-MnO_x) toward uptake and removal of CuCA and to understand the related mechanism. The result indicated that the CuCA removal efficiency reached up to 99%. High removal efficiency and low concentration of dissolved Mn over a wide pH range proved that the BC-MnO_x is efficient and chemically stable. Furthermore, the removal mechanism may involve the following processes: First, CuCA was removed via the chemical bonds formed between CuCA and MnO_x on the surface of BC. Second, chemisorption due to the oxygen-containing functional groups or physisorption of porous structure in BC worked synergistically on CuCA. Third, CuCA was partially oxidized into low molecular weight acids by means of MnO_x, while the released Cu ions were retained on the adsorbent surface. This study demonstrates that BC-MnO_x is a promising material for the removal of CuCA from wastewater.

Effect of the competition of Cu(II) and Ni(II) on the kinetic and thermodynamic stabilities of Cr(III)-organic ligand complexes using competitive ligand exchange (EDTA)

The effect of competition of Cu(II) and Ni(II) on the kinetic stability of Cr(III) complexed with natural organic matter (NOM) was characterized using EDTA exchange with single-stage tangential-flow ultrafiltration. For a water sample from Serra de Itabaiana, 3% of spiked Cr(III) was exchanged, while for a sample from the Itapanhaú River, 7, 10, 10, and 21% was exchanged in experiments using Cr(III) alone and in combination with Cu(II), Ni(II), or Cu(II) + Ni(II), respectively. Times required to reach exchange equilibrium with EDTA were less than 360 min. The influence of competition from Ni(II) and Cu(II) on the availability of complexed Cr(III) was low, demonstrating preference of the ligand sites for Cr(III). This was correlated with sample humification, as confirmed by EPR and (13)C NMR analyses. Exchange efficiency was in the order Cu > Ni > Cr, and the process could be readily described by first order kinetics, with average rate constants of 0.35-0.37 h(-1).

The influence of organic ligands on the adsorption of cadmium by suspended matter in natural waters studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and electrochemical methods

Natural water carrying a great amount of suspended particulate matter (SPM) was used as a model system for the study of the competition among organic ligands (dietilentetraamine pentaacetic acid, DTPA, nitrilotriacetic acid, NTA, and citrate, Cit) and natural complexants (SPM) for cadmium adsorption. Speciation diagrams at the pH of the natural sample were obtained by electroanalytical techniques, processing the experimental data with the complexation constants and the mass balance of the system. Results show that the adsorption equilibrium SPM-Cd is completely displaced by DTPA but not completely by NTA or Cit. Furthermore, larger Cit concentrations increase the amount of adsorbed Cd(II). The increment of the complexing capacity may be explained on the basis of SPM-Cit-Cd ternary complexes formation. This hypothesis was supported on the results obtained by applying for the first time the MALDI-TOF technique in a mixture of SPM, Cd(II), organic ligands and their complexes.

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 degrees 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.

Effect of adsorption of Pb(II) and Cd(II) ions in the presence of EDTA on the characteristics of electrical double layers at the ion exchanger/NaCl electrolyte solution interface

The main propose of this work was to describe the basic parameters of electrical double layer structures of the ion exchanger/NaCl before and after the sorption process of Pb(II) and Cd(II) ions from aqueous solutions in the presence of the complexing agent EDTA (ethylenediaminetetraacetic acid). In the studies the following ion exchangers were used: cation exchangers Micro-ionex (in the H(+) and NH(+)(4) forms), Dowex 50W x 4 (in the H(+) form), and Dowex 50W x 12 (in the H(+) form); anion exchangers Dowex 1 x 4 (in the Cl(-) form) and Dowex 1 x 8 (in the Cl(-) form). Study of the physicochemical properties of the sample surface was carried out. The influence of ionic strength, pH, and solution interface was investigated. Electrophoretic mobility, surface charge density, and parameters for different concentrations of the electrolytes under question were presented. pH was changed from 3 to 10. The studies were carried out for the M(II)-EDTA = 1:1 system. The effects of the concentration of the solution containing the above-noted complexes and of the ion exchange/solution phase contact time on sorption capacities of the ion exchangers under consideration were studied. Kinetic parameters of the sorption process were also determined.

Copper(II)-EDTA sorption onto chitosan and its regeneration applying electrolysis

Cu(II)-EDTA (ethylendiaminetetraacetate) complexes are widely used in the manufacture of printed circuit boards. In order to avoid the outlet into the environment the sorption of complexes onto chitosan is proposed. The uptake of both Cu(II) and EDTA proceeds in weakly acidic (pH 3-5) and strongly alkaline (pH > 12) solutions. In acidic solutions EDTA sorption prevails. FT-IR investigations have shown that in acidic solutions the amide bonds between -COOH groups of EDTA and -NH2 groups of chitosan were formed. In alkaline solutions the single EDTA sorption does not proceed. In this media the sorption is enhanced by Cu(II) ions. The possible sorption mechanisms are discussed. The uptake of both Cu(II) and EDTA by chitosan depends on the ratio between them in solutions. EDTA sorption in acidic solutions increases with increase in its concentration while that of Cu(II) decreases. In alkaline solutions the sorption of both Cu(II) and EDTA increases with increase in Cu(II) concentration. The use of electrolysis enables to regenerate chitosan and to reuse it. During electrolysis copper is deposited onto the cathode and EDTA is oxidized onto the anode. The current efficiency depends on the current intensity, the load of chitosan and the pH of the background electrolyte. Electrolysis under the most favorable conditions ensures the 10-cycles regeneration without considerable changes in the sorption properties of chitosan. FT-IR spectra of the initial and regenerated chitosans are similar.

Environmental chemistry of aminopolycarboxylate chelating agents

Aminopolycarboxylate chelating agents are under scrutiny due to their influence on metal availability and mobility and in particular due to their persistence in the environment. In this review chelate adsorption, metal-mobilization, metal-exchange, mineral dissolution, reactive transport, photodegradation, and chemical degradation are all shown to be substantially affected by the chelated metal ion. The different reactivities of the metal-complexes have to be considered when assessing the reactions of chelating agents in the environment because they occur in natural waters predominantly in the form of metal complexes. Knowing the speciation of chelating agents in natural waters is therefore crucial for predicting their environmental fate. Despite this importance, only a few speciation measurements have been reported for natural waters, and model calculations have been frequently used instead. These calculations are, however, complicated by slow metal-exchange reactions that result in a nonequilibrium speciation and by the presence of naturally occurring ligands that compete with the chelating agents for available metals. The basis for a refined risk assessment of aminocarboxylate chelates should be the actual speciation in the natural water directly determined by analytical methods. The discussion of the influence of chelates on metal availability and fate also has to include the potential presence of other aminopolycarboxylate chelating agents besides the well-known EDTA and NTA.