Chelant extraction of heavy metals from contaminated soils.

Leaching of heavy metals from contaminated soils using EDTA

Aminopolycarboxylate chelating agents are under scrutiny due to their influence on metal availability and mobility and in particular due to their persistence in the environment. In this review chelate adsorption, metal-mobilization, metal-exchange, mineral dissolution, reactive transport, photodegradation, and chemical degradation are all shown to be substantially affected by the chelated metal ion. The different reactivities of the metal-complexes have to be considered when assessing the reactions of chelating agents in the environment because they occur in natural waters predominantly in the form of metal complexes. Knowing the speciation of chelating agents in natural waters is therefore crucial for predicting their environmental fate. Despite this importance, only a few speciation measurements have been reported for natural waters, and model calculations have been frequently used instead. These calculations are, however, complicated by slow metal-exchange reactions that result in a nonequilibrium speciation and by the presence of naturally occurring ligands that compete with the chelating agents for available metals. The basis for a refined risk assessment of aminocarboxylate chelates should be the actual speciation in the natural water directly determined by analytical methods. The discussion of the influence of chelates on metal availability and fate also has to include the potential presence of other aminopolycarboxylate chelating agents besides the well-known EDTA and NTA.

Environmental Chemistry of Aminopolycarboxylate Chelating Agents

http://ira.lib.polyu.edu.hk/bitstream/10397/2547/1/B5%20Grass%20AP%202005.pdf

The use of vetiver grass (Vetiveria zizanioides) in the phytoremediation of soils contaminated with heavy metals

Arsenic in the Environment: A Global Perspective

Chelating agents such as EDTA, when present in water percolating through polluted soils, are capable of solubilizing heavy metals, increasing their downward mobility to groundwater as they form water-soluble and negatively charged complexes. The mobilization and movement of heavy metals in an EDTA flux is investigated with both laboratory experiments and mathematical modeling. The solubilization of Cd and Pb is monitored during the percolation of EDTA, in both pulse and step modes, through columns filled with a contaminated soil. The experimental breakthrough curves (BTCs) are used to validate a numerical model that links solute transport of EDTA and EDTA−metal chelates to the metal solubilization process. An implicit difference scheme is used to solve advection−dispersion equations for free and complexed EDTA with, for both, inclusion of a second-order kinetic law to express the extraction reaction. The hydrodispersive parameters of the column are calculated using the bromide BTCs. The ability of the mod...

Leaching of Cd and Pb from a polluted soil during the percolation of EDTA: Laboratory column experiments modeled with a non-equilibrium solubilization step

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

A 3 year study of the infiltration of Lot River water into a well field located in an adjacent gravel and clay alluvial aquifer was conducted to assess the importance of organic matter regarding the redox processes which influence groundwater quality in a positive (denitrification) or negative (Mn dissolution) manner. Chloride was used to quantify the mixing of river water with groundwater. According to modeling with PHREEQC, the biodegradation of the infiltrated dissolved organic carbon (DOCi) is not sufficient to explain the observed consequences of the redox reactions (dissolved O2 depletion, denitrification, Mn dissolution). Another electron donor source must therefore be involved: we propose solid organic carbon (SOC) as a likely candidate, if made available for degradation by prior hydrolysis. Its contribution to redox reactions could be significant (30-80% of the total organic carbon consumed by redox reactions during river bank filtration). We show here also that even though the first few meters of infiltration are highly reactive, significant redox reactions can take place further in the aquifer, possibly affecting groundwater quality away from the river bank.

Organic matter and modeling redox reactions during river bank filtration in an alluvial aquifer of the Lot River, France.

Electron trapping capacity of dissolved oxygen and nitrate to evaluate Mn and Fe reductive dissolution in alluvial aquifers during riverbank filtration.

Monika A.M. Kedziorek

Papers

Leaching of Cd and Pb from a polluted soil during the percolation of EDTA: Laboratory column experiments modeled with a non-equilibrium solubilization step

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

Organic matter and modeling redox reactions during river bank filtration in an alluvial aquifer of the Lot River, France.

Electron trapping capacity of dissolved oxygen and nitrate to evaluate Mn and Fe reductive dissolution in alluvial aquifers during riverbank filtration.

Acidification and solubilisation of heavy metals from single and dual-component model solids