Elsevier

Journal of Hazardous Materials

Volume 262, 15 November 2013, Pages 464-471
Journal of Hazardous Materials

Chelant extraction of heavy metals from contaminated soils using new selective EDTA derivatives

https://doi.org/10.1016/j.jhazmat.2013.08.069Get rights and content

Highlights

  • Two EDTA derivatives were synthesized to enhance the selectivity of chelators.

  • PDTA had the highest stability constants for Cu2+ and Ni2+.

  • PDTA had the highest overall selectivity for trace metals over major cations.

Abstract

Soil washing is one of the few permanent treatment alternatives for removing metal contaminants. Ethylenediaminetetraacetic acid (EDTA) and its salts can substantially increase heavy metal removal from contaminated soils and have been extensively studied for soil washing. However, EDTA has a poor utilization ratio due to its low selectivity resulting from the competition between soil major cations and trace metal ions for chelation. The present study evaluated the potential for soil washing using EDTA and three of its derivatives: CDTA (trans-1,2-cyclohexanediaminetetraacetic acid), BDTA (benzyldiaminetetraacetic acid), and PDTA (phenyldiaminetetraacetic acid), which contain a cylcohexane ring, a benzyl group, and a phenyl group, respectively. Titration results showed that PDTA had the highest stability constants for Cu2+ and Ni2+ and the highest overall selectivity for trace metals over major cations. Equilibrium batch experiments were conducted to evaluate the efficacy of the EDTA derivatives at extracting Cu2+, Zn2+, Ni2+, Pb2+, Ca2+, and Fe3+ from a contaminated soil. At pH 7.0, PDTA extracted 1.5 times more Cu2+ than did EDTA, but only 75% as much Ca2+. Although CDTA was a strong chelator of heavy metal ions, its overall selectivity was lower and comparable to that of EDTA. BDTA was the least effective extractant because its stability constants with heavy metals were low. PDTA is potentially a practical washing agent for soils contaminated with trace metals

Introduction

Heavy metal contamination of soils, resulting from rapid industrialization, increased urbanization, modern agricultural practices, and inappropriate waste disposal methods, has become a serious problem worldwide [1], [2], [3]. The available remediation technologies for heavy metal-contaminated soils are mainly divided into two groups: namely immobilization, such as in situ chemical fixation, and separation, such as soil washing. Chelant-enhanced soil washing is a technology that is potentially useful for the economically feasible remediation of contaminated soils [4], [5], [6], [7], [8].

The chelating agent ethylenediaminetetraacetic acid (EDTA) and its salts have been extensively studied for their potential use in soil washing [9], [10], [11], [12]. They have been reported to appreciably increase the dissolution and mobilization of cationic heavy metals [13], [14]. EDTA has low biodegradability in soil and a high efficiency of metal extraction through the formation of thermodynamically stable and soluble metal–EDTA complexes [15], [16]. In addition, recent advances in recovery and recycling techniques of used EDTA have enhanced its appeal [17].

A majority of the literature focused on demonstrating the remediation capabilities of EDTA has found that extraction of heavy metals was faster and more complete with increased quantities of added EDTA. Competition between the major cations of the soil (e.g., Ca2+, Mg2+, and Fe3+) and minor cations for chelation by EDTA may be one of the factors affecting the efficiency of trace metal extraction [18], [19], [20], [21], [22], [23]. As illustrated in previous studies [24], [25], when Ca solubility in calcareous soils is raised, the effectiveness of EDTA extraction is diminished significantly, increasing the cost of remediation. For non-calcareous soils, Fe and Al dissolution may be more crucial, in view of their high tendency for complexation (i.e., large stability constants). Excessive addition of chelating agent can cause extensive dissolution of soil minerals and organic matter, leading to alteration of soil physical and chemical properties and even disintegration of soil structure, which could render the soil unfit for future use for vegetation or construction. Therefore, there has been a growing need to develop highly selective chelating agents for the extraction of heavy metal ions from polluted soils.

In previous studies, EDTA has been modified to improve its selectivity in chelating target metal ions [26], [27], [28]. Highly selective EDTA derivatives have a wide range of application in the fields of analytical chemistry, biology and medicine, as well as in many industrial processes. In this study, two new EDTA derivatives were designed and synthesized with the goal of enhancing its selectivity as a chelating agent. These EDTA derivatives contain a phenyl or benzyl group directly bonded to the nitrogens of the ethylenediamino group, and thus potentially are more sterically constrained than the parent compound. The objective of this study was to characterize these EDTA derivatives in aqueous solution and assess their potential as selective washing agents. Batch experiments were conducted to determine their efficacy in the simultaneous extraction of trace metal ions and major cations from contaminated soils and to investigate the extraction mechanisms.

Section snippets

Soil Characteristics

Soil samples were collected from 0.7 to 1.7 m below the ground surface at a demolished industrial site in South China, air-dried at room temperature (20–30 °C), and passed through a 2 mm sieve. The soil properties in Table 1 were the average of three replicates.

Various soil physical and geochemical characterization tests were carried out. The physical and chemical characteristics of the soil are shown in Table 1. The metal concentrations in soil were determined by acid digestion with HF–HClO4–HNO3

Acid–base properties of EDTA derivatives

The protonation constants of PDTA and BDTA in water were determined with a view to assessing their acid–base properties, since these properties control what species exist in solution at various pH values. Both PDTA and BDTA have six potential sites that can bind with a proton, including the two nitrogens of the ethylenediamino groups and the four carboxyl groups. However, only three deprotonation events were observed by potentiometry (Table 2). For comparison, Table 2 also includes the

Conclusions

Two new EDTA derivatives, BTDA and PDTA, were synthesized and their metal–ligand complexation equilibrium constants and selective capabilities in aqueous media were investigated, along with those of EDTA and CDTA. Titration results showed that PDTA had the highest stability constants for Cu and Ni and the highest overall selectivity for trace metals over major cations. Equilibrium batch experiments were conducted to evaluate the efficacy of the EDTA derivatives at extracting Cu, Zn, Ni, Pb, Ca,

Acknowledgements

The project was supported by National Natural Science Foundation (No. 41171374), National Funds for Distinguished Young Scientists of China (No. 41225004), Guangdong Province Higher Vocational Colleges & Schools Pearl River Scholar Funded Scheme, the Ministry of Environmental Protection of China (No. 201109020) and the Research Fund Program of Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (No. 2011K0007).

References (46)

  • R.S. Tejowulan et al.

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

    Environ. Pollut.

    (1998)
  • C.E. Martinez et al.

    Solubility of lead, zinc and copper added to mineral soils

    Environ. Pollut.

    (2000)
  • M.A.M. Kedziorek et al.

    Solubilization of lead and cadmium during the percolation of EDTA through a soil polluted by smelting activities

    J. Contam. Hydrol.

    (2000)
  • A. Polettini et al.

    The effect of operating variables on chelant-assisted remediation of contaminated dredged sediment

    Chemosphere

    (2007)
  • L. Di Palma et al.

    Heavy metals mobilization from harbor sediments using EDTA and citric acid as chelating agents

    J. Hazard. Mater.

    (2007)
  • L. Di Palma et al.

    Copper leaching from a sandy soil: mechanism and parameters affecting EDTA extraction

    J. Hazard. Mater.

    (2005)
  • M.A. Santos et al.

    Bis(3-hydroxy-4-pyridinone)–EDTA derivative as a potential therapeutic Al-chelating agent. Synthesis, solution studies and biological assays

    J. Inorg. Biochem.

    (2005)
  • C.F.G.C. Geraldes et al.

    Preparation, physic-chemical characterization, and relaxometry studies of various gadolinium (III)–DTPA–bis (amide) derivatives as potential magnetic resonance contrast agents

    Magn. Reson. Imaging

    (1995)
  • J.D. Martin-Ramos

    Copper(II) and Nickel(II) chelates with dihydrogen trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetate(2−) ion (H2CDTA2−). Synthesis, XRD structure and properties of [Cu(H2CDTA)]·H2O and [Ni(H2CDTA)(H2O)]·4H2O

    Polyhedron

    (1996)
  • M.X. Wang et al.

    A novel selective fluorescent chemosensor for Cu(II)

    Chinese Chem. Lett.

    (2007)
  • Z.L. Zou et al.

    The study of operating variables in soil washing with EDTA

    Environ. Pollut.

    (2009)
  • M.D. Andrade et al.

    Optimizing the molarity of a EDTA washing solution for saturated-soil remediation of trace metal contaminated soils

    Environ. Pollut.

    (2007)
  • X.P. Li et al.

    Environment impact of heavy metals on urban soil in the vicinity of industrial area of Baoji city, P.R. China

    Environ. Geol.

    (2007)
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