The soils contaminated by toxic metals are often remediated using EDTA and similar non-biodegradable chelators. Most chelators are in fact synthetic amino acid derivatives, whereas natural proteinogenic amino acids (PAAs) have not been systematically explored as remediation agents, despite their well-known metal chelating abilities and environmental benefits. Our study represents a comprehensive research exploring 16 structurally and functionally different PAAs as potential remediating agents, applied to 3 different heavy metal-contaminated samples. The study was mostly focused on extracting Cd, Cu, Ni, and Zn. The reaction parameters were screened and optimized. It was found that the efficiencies of extracting Cu, Ni, and Zn by Threonine, Aspartic acid and Histidine were comparable to those by EDTA, whereas non-polar side chain-containing PAAs demonstrated consistently lower PTM extraction rates compared to other PAAs. The sulfur-containing Cysteine appeared to be efficient to extract Cd (to some extent), Ni and Zn, but not Cu, due to chemical reasons. The structure-functional correlations were identified, described, and found to be independent on the specific samples. Possible molecular mechanisms of metal extraction from soils by PAAs are discussed. In contrast to EDTA, the soil-essential elements are almost not extracted by PAAs. This important feature of the PAAs, along with their availability, observed selectivity, competitive efficiency, non-toxicity and even fertilizing properties, make them particularly soil-friendly, and thus, potentially applicable chelators in certain remediation processes.

A systematic study of extraction of various organic pollutants from highly contaminated solid media (e.g., sludge) by applying a phase transition of a benign partially miscible solvent system composed of water/ethyl acetate/ethanol was conducted. This solvent system possesses an upper critical solution temperature of about 55 °C. The efficiency of the phase transition extraction (PTE) process is found to be higher and much faster compared to those obtained without phase transition (at ambient temperature). The influence of various operating conditions on the process efficiency was investigated. The performance of the phase transition extraction when applied on contaminated sludge is much better than the extraction with ethyl acetate only, although the latter is shown to be a very efficient solvent for extracting various organic contaminants (e.g., pharmaceuticals, persistent organic pollutants) from aqueous solutions. The efficiency of phase transition extraction from the aqueous solution was somewhat lower than that achieved with ethyl acetate, but it shows a clear advantage in the presence of detergents, as emulsion formation is prevented. © 2019, Springer Nature Switzerland AG.

As part of the project of developing a “green” and highly feasible soil remediation process, recycling an eco-friendly chelating agent, glycine, using Chelex-100 chelating resin, was studied. Two model complexes, copper and nickel glycinates, were tested under various conditions, including equivalent viscosity but different temperature conditions. Two similar complexes demonstrated very different reactivity towards Chelex-100. An in-depth study led to the discovery of unusual metal-dependent mechanisms of the complex-to-resin metal transfer. Particularly, nickel transfer proceeds via a dissociative mechanism, whereas copper transfer does not require pre-dissociation of the complexes, and proceeds via the associative ligand-exchange mechanism. Both processes result in the recovery of the used chelator. The glycine solution was applied on the spiked soil, then recovered on Chelex-100 resin and successfully reused, thus demonstrating a proof of the concept. These findings contribute to the science, strategies, and methodology of both water purification and chelator recycling fields. © 2018 Elsevier Ltd