Extraction of Heavy Metals from Soils Using Biodegradable Chelating Agents

Abstract

Metal pollution of soils is widespread across the globe, and the clean up of these soils is a difficulttask. One possible remediation technique is ex-situ soil washing using chelating agents. Ethylenediaminetetraacetic acid (EDTA) is a very effective chelating agent for this purpose but has the disadvantage that it is quite persistent in the environment due to its low biodegradability. The aim of our work was to investigate the biodegradable chelating agents [S,S]-ethylenediaminedisuccinic acid (EDDS), iminodisuccinic acid (IDSA), methylglycine diacetic acid (MGDA), and nitrilotriacetic acid (NTA) as potential alternatives and compare them with EDTA for effectiveness. Kinetic experiments showed for all metals and soils that 24 h was the optimum extraction time. Longer times only gave minor additional benefits for heavy metal extraction but an unwanted increase in iron mobilization. For Cu at pH 7, the order of the extraction efficiency for equimolar ratios of chelating agent to metal was EDDS > NTA> IDSA > MGDA > EDTA and for Zn it was NTA > EDDS > EDTA >MGDA > IDSA. The comparatively low efficiency of EDTA resulted from competition between the heavy metals and co-extracted Ca. For Pb the order of extraction was EDTA > NTA >EDDS due to the much stronger complexation of Pb by EDTA compared to EDDS. At higher concentration of complexing agent, less difference between the agents was found and less pH dependence. There was an increase in heavy metal extraction with decreasing pH, but this was offset by an increase in Ca and Fe extraction. In sequential extractions EDDS extracted metals almost exclusively from the exchangeable, mobile, and Mn-oxide fractions. We conclude that the extraction with EDDS at pH 7 showed the best compromise between extraction efficiency for Cu, Zn, and Pb and loss of Ca and Fe from the soil.

Enhanced phytoextraction of Cu, Pb, Zn and Cd with EDTA and EDDS

“…In the EDTA treatments, the concentrations of Pb in the shoots of corn and beans reached up to 270 and 487 mg kg -1 DW, which was 3 and 1.6 times higher than the levels achieved with the EDDS treatments. EDDS has a relatively lower chemical affinity for Pb (log K s = 12.7) (Tandy et al, 2004). Citric acid has a low chemical affinity for Pb (log K s = 6.5) and is easily biodegradable in soil (Römkens et al, 2002), leading to lower effectiveness in increasing concentrations of Pb in shoots.…”

“…These chelating agents included EDTA (Wu et al, 1999;Lombi et al, 2001), EDDS (log Ks = 18.4, Tandy et al, 2004), EGTA (Römkens et al, 2002), HBED (Wu et al, 1999), and NTA (Kulli et al, 1999;Kayser et al, 2000). However, the chelateenhanced Cu uptake by plant shoots was generally minimal (Kulli et al, 1999;Wu et al, 1999;Kayser et al, 2000;Lombi et al, 2001;Römkens et al, 2002) except for the result reported by Blaylock et al (1997).…”

Chelant-induced reclamation of indium from the spent liquid crystal display panels with the aid of microwave irradiation

“…However, such an effect may be suppressed at the high temperature and/or at a pressure-persuaded condition due to the higher dissolution proclivity of indium, or lesser rate of re-sorption of the ML complexes in the active surface sites of the solid matrix, etc. [20,36].…”

“…However, the steric hindrance between DTPA and dissolved metals might play an important role in the mixed matrix solution. A slower rate of interaction between DTPA and the target metal species irrespective of the temperature conditions or at neutral pH can thereby be assumed [18,20]. The lower pH of EDTA in solution is also mentioned as a reason for the lesser metal extraction capability of DTPA than the EDTA [37].…”

“…2013.03.028 from the spent catalysts [16]. However, APCs have rarely been used to treat any vitrified waste [10] in spite of being praised for excellent metal-binding capacities and extensive use in the treatment of contaminated soil solids [17][18][19][20]. Hence, the current report is an effort to comprehend the potential of APCs for indium extraction from the ITO-film composed to a dense vitrified structure.…”