Kinetics of Lead Remobilization from Montmorillonite by Glutamate Diacetate (GLDA), Methylglycine Diacetate (MGDA), and Ethylenediamine Tetraacetate (ETDA) Chelating Agents

Green chelating ligands are being increasingly produced and commercialized globally because conventional ligands such as ethylenediamine tetraacetate (EDTA) are poorly biodegradable and persistent in the environment. The study of toxic metal remobilization processes from minerals by new chelating ligands is crucial to better understand the fate and transport of metals in soil and sediment environments. In this research, the effects of two green alternatives of EDTA, i.e., glutamate diacetate (GLDA) and methylglycine diacetate (MGDA), on lead (Pb) remobilization kinetics from Pb-loaded montmorillonite (MMT) were studied at two ligand concentrations of 0.25 and 1.0 mM. The effects of a 30-day residence time on the rate and quantity of Pb remobilization were also evaluated. The results showed that the time-dependent Pb remobilization was biphasic with an initial rapid phase lasting 3 h followed by a slow phase taking 12 h. The degree of Pb remobilization was governed by the nature and concentration of the chelating ligands presented in the systems. The capacity of the ligands to remobilize Pb from MMT was in the order EDTA > > MGDA > GLDA, according to the decreasing order in the stability constants of their complexes with Pb ions. The aging of the MMT systems caused a significant reduction in both Pb remobilization quantity and rate parameters. The results suggest that GLDA and MGDA have a significantly lower Pb-remobilizing impact than EDTA in contaminated soil and sediments containing MMT as a major clay constituent. Article highlights Pb remobilization kinetics from MMT by EDTA, MGDA and GLDA ligands are biphasic. Ability of the ligands to remobilize Pb from MMT is in the order EDTA > > MGDA > GLDA. The Pb remobilization is governed by the concentration of the ligands applied. A 30-day aging period significantly decreases the Pb remobilization quantity and rate.