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 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 concentration distributions of various complex species in solution were evaluated for each ion. The stability constants (log 10 K ML ) of the complexes containing Ni 2+ , Cu 2+, Zn 2+ , Cd 2+ and Pb 2+ ions followed an identical order of log 10 K CuL > log 10 K NiL > log 10 K PbL > log 10 K ZnL > log 10 K CdL when using GLDA (13.03 >12.74 >11.60 >11.52 >10.31) as when using HIDS (12.63 >11.30 >10.21 > 9.76 >7.58). In each case, the constants obtained for metal-GLDA complexes were higher in magnitude than the corresponding constants for metal-HIDS complexes. The conditional stability constants (log 10 K´M L ) of the metal-chelant complexes containing GLDA and HIDS were calculated in terms of pH, and compared with the stability constants for EDTA and other biodegradable chelants.Keywords: stability constant; biodegradable aminopolycarboxylate chelant; GLDA; HIDS; ecotoxic ions. 2Journal of Solution Chemistry, 41(10): 1713Chemistry, 41(10): -1728Chemistry, 41(10): , 2012Chemistry, 41(10): (http://dx.doi.org/10.1007 IntroductionAminopolycarboxylate chelants (APCs) have been and continue to be extensively used in a variety of industrial processes [1,2], including the treatment of toxic metal-contaminated solid waste materials [3][4][5]. APCs are commonly employed to restrict metal ions from playing their normal chemical roles through the formation of stable and water-soluble metal complexes [6,7]. Because ethylenediaminetetraacetic acid (EDTA) forms stable water- Chemistry, 41(10): 1713Chemistry, 41(10): -1728Chemistry, 41(10): , 2012Chemistry, 41(10): (http://dx.doi.org/10.1007 available [25]. The development of the new eco-friendly chelants and the study of their complexation behavior are critical for evaluating the usefulness of these chelants in specific treatment operations [26][27][28][29]. DL-2-(2-carboxymethyl)nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2´-iminodisuccinic acid (HIDS) (Fig. 1) Therefore, we report on the complexation behavior of GLDA and HIDS and divalent ecotoxic ions (Ni, Cu, Zn, Cd, and Pb) in aqueous solutions, which will be useful for the design of eco-friendly waste management processes. Experimental Section InstrumentationKEM AT-610 automatic titrator (Kyoto Electronics, Kyoto, Japan), equipped with a pHcombination electrode and a temperature probe, was used for potentiometric measurements.The electrode system was calibrated with standard buffer solutions (pH 4.0, 7.0 and 9.0 prepared from buffer powders (Horiba, Kyoto, Japan) at 25 ± 0.1°C before and after each serie...

The complex formation equilibria of Cr3+ and Fe3+ ions in aqueous solution with two biodegradable aminopolycarboxylate chelants (dl-2-(2-carboxymethyl)­nitrilotriacetic acid (GLDA) and 3-hydroxy-2,2′-iminodisuccinic acid (HIDS)) were investigated. The potentiometric data obtained at the constant ionic strengths (I) of (0.1 and 1.0) mol·dm–3 KCl and at (25 ± 0.1) °C was processed with the aid of the computer program HYPERQUAD 2008. The formation constants of the proton–chelant and metal–chelant (log K ML) species (M = Fe3+ or Cr3+; L = GLDA or HIDS) were determined, and the concentration distributions of complex species in solution were evaluated for both metal ions. In various pH conditions, the interaction between the chelants (L = GLDA or HIDS) and the metal ions (M = Fe3+ or Cr3+) leads to the formation of different complexes formulated as MH2L+, MHL, ML–, M­(OH)­L2–, and M­(OH)2L3–. The log K ML values at I = 0.1 mol·dm–3 KCl (T = (25 ± 0.1) °C) were 15.27 (log K Fe–GLDA), 14.96 (log K Fe–HIDS), 13.77 (log K Cr–GLDA), 12.67 (log K Cr–HIDS), and at I = 1.0 mol·dm–3 KCl (T = (25 ± 0.1) °C) were 14.79 (log K Fe–GLDA), 14.34 (log K Fe–HIDS), 12.90 (log K Cr–GLDA), 12.09 (log K Cr–HIDS). The conditional stability constants (log K′ML) of the ML complexes were calculated in terms of pH in the range of 2 to 12 and compared with the same for EDTA and other biodegradable chelants (NTA and EDDS).

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Please Cite the article as: H. Hasegawa, Y. Tate, M. Ogino, T. Maki, Z.A. Begum, T. Ichijo and I.M.M. Rahman, Laboratory culture experiments to study the effect of lignite humic acid fractions on iron solubility and iron uptake rates in phytoplankton AbstractThe major fractions of dissolved iron in seawater exist as a complex with organic ligands. A high bioavailability of iron bound to humic acid (HA) compared to the other model ligands, such as desferrioxamine B or ferrichrome, has been reported, which implies the importance of HA to control the geochemical behavior and the transfer of Fe to marine phytoplankton, particularly in estuarine and coastal waters. In the current work, the effect of different HAfractions (>100, 100-30, 30-10, 10-5, and 5-3 kDa), which are extracted from lignite, on the comparative solubility of iron in seawater and the corresponding influence on the iron-uptake and growth rate of the phytoplankton (Prymnesium parvum) has been studied using laboratory cultures. The lower molecular weight (MW) HA fractions, such as 30-10, 10-5 and 5-3 kDa, remained soluble in the simulated seawater medium for a longer time-span compared to the higher MW fractions. The lower MW fractions facilitated higher iron solubility and assisted in achieving a better phytoplankton growth rate. However, a reciprocal impact on phytoplankton growth rates has been observed when the HA concentration increased to a higher range (0.18 to 18 mg-C L -1 ). The highest intracellular Fe uptake in phytoplankton occurred with 30-10 kDa HA in seawater, and the extracellular dissolved Fe concentrations were higher for smaller-sized HA fractions. In a nutshell, our study showed that the controlled addition of lower MW fractions of HA (up to 30-10 kDa) in estuarine waters could ensure the accelerated uptake of Fe in phytoplankton as well as a better growth rate.