Formation and Stability of Binary Complexes of Divalent Ecotoxic Ions (Ni, Cu, Zn, Cd, Pb) with Biodegradable Aminopolycarboxylate Chelants (dl-2-(2-Carboxymethyl)Nitrilotriacetic Acid, GLDA, and 3-Hydroxy-2,2′-Iminodisuccinic Acid, HIDS) in Aqueous Solutions
Abstract:The protonation and complex formation equilibria of two biodegradable aminopolycarboxylate chelants (DL-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2´-iminodisuccinic acid (HIDS)) with Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ and Pb 2+ ions was investigated using the potentiometric method at a constant ionic strength of I = 0.10 mol·dm -3 (KCl) in aqueous solutions at 25 ± 0.1°C. The stability constants of the proton-chelant and metal-chelant species for each metal ion were determined, and the concen… Show more
“…Both the P 3 O 10 and P 3 O 8 (NH) 2 ligands show their greatest stabilities in the corresponding Cu complexes, and also clearly show a similar r M dependence in terms of their log 10 β ML values, despite the difference in the bridging atoms of the different ligands. Furthermore, the order of the log 10 β ML values for the first-row transition metal ions is in accordance with the Irving–Williams order [47–49]. These results suggest that only the non-bridging oxygen atoms are coordinating directly to the different metal ions, and that the imino groups do not participate in the coordination to the metal ions.Fig.…”
The stability constants of ML-type complexes of the two linear triphosphate ligand anion analogues triphosphate (\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$\end{document}) and diimidotriphosphate (\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$\end{document}) were investigated thermodynamically using potentiometric titrations according to Schwarzenbach’s procedure. The stability constants of the ML-type complexes of different divalent metal ions with \documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$\end{document} are larger than those of the corresponding complexes with \documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$\end{document} because of the greater basicity of the imino group. The order of the stability constants for the ML-type complexes follows the Irving–Williams order, indicating that only non-bridging oxygen atoms are coordinated directly to the different metal ions in both ligands, and that the imino groups cannot participate in coordination to the metal ions. In the complexation reactions of the Ca2+, Sr2+, Ba2+–\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$\end{document} and Cu2+, Zn2+, Ni2+–\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$\end{document} systems, each metal ion forms an enthalpically stable complex, and there was no suggestion of a conspicuous entropic effect based on the chelate effect. Monodentate complexes that are strongly coordinated with the ligands were there...
“…Both the P 3 O 10 and P 3 O 8 (NH) 2 ligands show their greatest stabilities in the corresponding Cu complexes, and also clearly show a similar r M dependence in terms of their log 10 β ML values, despite the difference in the bridging atoms of the different ligands. Furthermore, the order of the log 10 β ML values for the first-row transition metal ions is in accordance with the Irving–Williams order [47–49]. These results suggest that only the non-bridging oxygen atoms are coordinating directly to the different metal ions, and that the imino groups do not participate in the coordination to the metal ions.Fig.…”
The stability constants of ML-type complexes of the two linear triphosphate ligand anion analogues triphosphate (\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$\end{document}) and diimidotriphosphate (\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$\end{document}) were investigated thermodynamically using potentiometric titrations according to Schwarzenbach’s procedure. The stability constants of the ML-type complexes of different divalent metal ions with \documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$\end{document} are larger than those of the corresponding complexes with \documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$\end{document} because of the greater basicity of the imino group. The order of the stability constants for the ML-type complexes follows the Irving–Williams order, indicating that only non-bridging oxygen atoms are coordinated directly to the different metal ions in both ligands, and that the imino groups cannot participate in coordination to the metal ions. In the complexation reactions of the Ca2+, Sr2+, Ba2+–\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$\end{document} and Cu2+, Zn2+, Ni2+–\documentclass[12pt]{minimal}
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\begin{document}$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$\end{document} systems, each metal ion forms an enthalpically stable complex, and there was no suggestion of a conspicuous entropic effect based on the chelate effect. Monodentate complexes that are strongly coordinated with the ligands were there...
“…The same constants for GLDA and HIDS were calculated from the experimental potentiometric data using the HYPERQUAD 2008 program (Gans et al, 1996), and described in detail elsewhere (Begum et al, 2012).…”
Section: Protonation Constants Of Chelants and Stability Constants Ofmentioning
Ex situ soil washing with synthetic extractants such as, aminopolycarboxylate chelants (APCs) is a viable treatment alternative for metal-contaminated site remediation. EDTA and its homologs are widely used among the APCs in the ex situ soil washing processes. These APCs are merely biodegradable and highly persistent in the aquatic environments leading to the post-use toxic effects.Therefore, an increasing interest is focused on the development and use of the eco-friendly APCs having better biodegradability and less environmental toxicity. The paper deals with the results from the lab-scale washing treatments of a real sample of metal-contaminated soil for the removal of the ecotoxic metal ions (Cd, Cu, Ni, Pb, Zn) using five biodegradable APCs, namely [S,S]-ethylenediaminedisuccinic acid, imminodisuccinic acid, methylglycinediacetic acid, DL-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2'-iminodisuccinic acid. The performance of those biodegradable APCs was evaluated for their interaction with the soil mineral constituents in terms of the solution pH and metal-chelant stability constants, and compared with that of EDTA. Speciation calculations were performed to identify the optimal conditions for the washing process in terms of the metal-chelant interactions as well as to understand the selectivity in the separation ability of the biodegradable chelants towards the metal ions. A linear relationship between the metal extraction capacity of the individual chelants towards each of the metal ions from the soil matrix and metal-chelant conditional stability constants for a solution pH greater than 6 was observed. Additional considerations were derived from the behavior of the major potentially interfering cations (Al, Ca, Fe, Mg, and Mn), and it was hypothesized that use of an excess of chelant may minimize the possible competition effects during the single-step washing treatments.Sequential extraction procedure was used to determine the metal distribution in the soil before and after the extractive decontamination using biodegradable APCs, and the capability of the APCs in removing the metal ions even from the theoretically immobilized fraction of the contaminated soil was observed. GLDA appeared to possess the greatest potential to decontaminate the soil through ex situ washing treatment compared to the other biodegradable chelants used in the study.
KeywordsSoil remediation; Toxic metals; Ex situ washing; Aminopolycarboxylate chelants; Biodegradable; Sequential extraction 3
IntroductionSoil contamination with heavy metals derived from various anthropogenic activities, including agricultural practices, industrial activities and waste disposal is a worldwide concern. Soil washing is one of the few enduring treatment alternatives, which uses either or both physical and chemical processes, to confine the contaminants in soils (Peters, 1999;Dermont et al., 2008). Soil decontamination by washing treatment can be accomplished through either in situ or ex situ operations. Aminopolycarboxylate c...
“…The effectiveness of NTA, EDTA, IDSA (iminodisuccinic acid) and MGDA (methylglycine diacetic acid) as potential alternatives of EDTA was investigated by for the extraction of Cu, Zn, and Pb from contaminated soils, which indicate EDDS as the best option among all. The DL-2-(2-carboxymethyl) nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2 0 -iminodisuccinic acid (HIDS) have been introduced as the biodegradable alternatives to EDTA, along with EDDS, IDSA, and MGDA by Begum et al (2012a). The DL-2-(2-carboxymethyl) nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2 0 -iminodisuccinic acid (HIDS) have been introduced as the biodegradable alternatives to EDTA, along with EDDS, IDSA, and MGDA by Begum et al (2012a).…”
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