The thermodynamics and biodegradability of chelating agents upon metal extraction

Improved methane production of two-phase anaerobic digestion by cobalt: efficiency and mechanism

Two-phase anaerobic digestion (AD) is a promising technology, but its performance is sensitive to methanogen. In this study, the effect of cobalt (Co) on two-phase AD was investigated and the enhanced mechanism was revealed. Though no obvious effect of Co²⁺ was observed in acidogenic phase, the activity of methanogens was significantly affected by Co²⁺ with an optimal Co²⁺ concentration of 2.0 mg/L. Ethylenediamine-N'-disuccinic acid (EDDS) was the most effective for improving Co bioavailability and increasing methane production. The role of Co-EDDS in improving methanogenic phase was also verified by operating three reactors for two months. The Co-EDDS supplement increased the level of Vitamin B12 (VB₁₂) and coenzyme F₄₂₀, and enriched Methanofollis and Methanosarcina, thereby successfully improving methane production and accelerating reactor recovery from ammonium and acid wastewater treatment. This study provides a promising approach to improve the efficiency and stability of anaerobic digester.

Citric acid-based deep eutectic solvent (CA-DES) as a new soil detergent for the removal of cadmium from coking sites

In order to solve the problem of soil pollution caused by excess heavy metals, cadmium (Cd), a novel soil-washing agent organic chelating acid-based deep eutectic solvent (OCA-DES), was investigated for the removal of Cd from the contaminated soil of coking plant. Four kinds of OCA-DES were prepared by mixing choline chloride (Ch-Cl) with four organic chelating acids (citric acid, oxalic acid, tartaric acid, and malic acid), respectively, to compare their washing efficiency of Cd from soil. The effects of washing operation conditions on the Cd removal efficiency were investigated. Side effects of citric acid-based deep eutectic solvent (CA-DES) on soil were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). The results showed that CA-DES had the best Cd removal efficiency and could reach as high as 93.75%, under ideal conditions. CA-DES mainly washed extractable and reducible Cd. The CA-DES washing process has less side effects on soil and hardly eroded the soil or changed the mineral structure of the soil. The main roles of CA-DES washing Cd include (1) hydrogen bonds capturing Cd; (2) the carboxyl group(-COOH) forming soluble chelate with Cd; and (3) releasing H⁺ ions in exchange for Cd. This study demonstrates that CA-DES, a novel soil-washing agent, has excellent removal of cadmium from soil and is environment-friendly.

Predicted structure and selectivity of 3d transition metal complexes with glutamic N,N-bis(carboxymethyl) acid

Structure and selectivity of 3d transition metal complexes with glutamic N,N-bis(carboxymethyl) acid are analyzed and predicted from DFT calculations.

The Early Stages of Mimetite Dissolution in EDTA Studied with Atomic Force Microscopy and Scanning Electron Microscopy

A mineral, mimetite Pb5(AsO4)3Cl, is one of the most insoluble minerals and continues to be considered a viable remedial strategy for immobilization of Pb and As from contaminated soils. It has been recognized that many well-known, naturally-occurring, and synthetic chelators strongly influence dissolution processes in near-surface geological environments. In this study, crystals of mimetite were observed in scanning electron microscopy (SEM) and atomic force microscopy (AFM) before and after dissolution in EDTA (ethylene diamine tetra-acetic acid) solution. Direct in situ observations at room temperature made in an AFM fluid cell revealed that the grain surface roughness has increased due to development of etch pits. Both hexagonal and prismatic walls developed dissolution features between 0.6 and 1.2 µm, respectively, during duration of the experiment. AFM observations suggest surface-controlled dissolution dominated step retrieval on both prismatic and hexagonal surfaces. SEM observations showed the development of rounded edges on hexagonal walls and elongated, oval etch pits on the prismatic wall. These results, representing early dissolution patterns on mimetite surfaces, might suggest that low pH conditions in soils containing organic acids similar to EDTA might contribute to remobilization of Pb and As from mimetite when applied to stabilization of these toxic metals in contaminated soils.

Study on the Methods of Separation and Detection of Chelates

The separation and purification techniques of chelates can improve the accuracy of detecting results of the chelation rate. As a quantitative indicator of metal ion chelates, the chelation rate can not only reflect the completion of chelation but also determine the amount of metal ions in different forms. The determination of chelation rate can help to determine the suitable chelating reaction conditions, make theoretical basis for the fertilizer efficiency, analyze the stability of chelating fertilizers and study the action mechanism of trace elements. In our study, the methods of separation free metal ions from mixture were reviewed first, including gel filtration chromatography, organic solvent precipitation, ion exchange chromatography, membrane separation and high performance liquid chromatography. Then, the qualitative analysis methods of chelates were introduced briefly, including chemical identification, infrared spectroscopy, ultraviolet spectroscopy. A detailed overview of the quantitative determination methods of chelates were also shown, such as ethylenediaminetetraacetic acid titration, chemical titration, atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, spectrophotometric, chemical modified electrode. In addition, the merits and demerits of chelated rate determination methods of various determination methods were analyzed, and summarized the applicability of various methods, which provided a theoretical basis for optimizing chelating process, characterizing the structure of chelates and analyzing the mechanism of chelating fertilizer. The current methods of measuring chelation rate were also summarized and prospected.

Biodegradation of CuTETA, an effluent by-product in mineral processing

Polyamines such as triethylenetetramine (TETA) and other amine chelators are used in mineral processing applications. Formation of heavy metal complexes of these reagents as a by-product in effluent water is a recent environmental concern. In this study, Paecilomyces sp. was enriched from soil on TETA as the sole source of carbon and nitrogen and was found to degrade > 96 and 90% CuTETA complexes at initial concentrations of 0.32 and 0.79 mM respectively, following 96-h incubation. After destabilization, most of the copper (> 78%) was complexed extracellularly and the rest was associated with the cell. Mass spectroscopy results provided confirmation that copper re-complexed with small, extracellular, and organic molecules. There are no reports in the literature that Paecilomyces or any other organism can grow on TETA or CuTETA. This study is the first to show that biological destabilization of CuTETA complexes in mineral processing effluents is feasible.

Greener approach for the extraction of copper metal from electronic waste

Technology innovations resulted into a major move from agricultural to industrial economy in last few decades. Consequently, generation of waste electronic and electrical equipments (WEEE) has been increased at a significant rate. WEEE contain large amount of precious and heavy metals and therefore, can be considered a potential secondary resource to overcome the scarcity of metals. Also, presence of these metals may affect the ecosystem due to lack of adequate management of WEEE. Building upon our previous experimental investigations for metal extraction from spent catalyst, present study explores the concept of green technology for WEEE management. Efforts have been made to recover base metal from a printed circuit board using eco-friendly chelation technology and results were compared with the conventional acid leaching method. 83.8% recovery of copper metal was achieved using chelation technology whereas only 27% could be recovered using acid leaching method in absence of any oxidant at optimum reaction conditions. Various characterization studies (energy dispersive X-ray analysis, scanning electron microscopy, X-ray diffraction, inductive coupled plasma spectrophotometry) of Printed Circuit Board (PCB) and residues were performed for qualitative and quantitative analysis of samples. Significant metal extraction, more than 96% recovery of chelating agent, recycling of reactant in next chelation cycle and nearly zero discharge to the environment are the major advantages of the proposed green process which articulate the transcendency of chelation technology over other conventional approaches. Kinetic investigation suggests diffusion controlled process as the rate determining step for the chelate assisted recovery of copper from WEEE with activation energy of 22kJ/mol.