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Mining activities have increased the accumulation of heavy metals in farmland soil and in food crops. To identify the key soil properties influencing heavy metal bioavailability and accumulation in food crops, 81 crop samples and 81 corresponding agricultural soil samples were collected from rape, wheat, and paddy fields. Heavy metal (copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), iron (Fe), and manganese (Mn)) concentrations in soils and rape, wheat, rice grains were determined using inductively coupled plasma atomic emission spectroscopy, and soil physicochemical properties (pH, organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium (AK)) were analyzed. Soil extractable metals were extracted using various single extractants (DTPA, EDTA, NH 4 OAc, NH 4 NO 3 , and HCl). The average concentrations of Cu, Zn, Pb, Cd, and Mn in the soil samples all exceeded the local geochemical background value (background values of Cu, Zn, Pb, Cd, and Mn are 43.0, 81.0, 28.5, 0.196, and 616 mg/kg, respectively), and Cd over-standard rate was the highest, at 98%. Furthermore, soil total Cd concentrations (0.1–24.8 mg/kg) of more than 86% of the samples exceeded the soil pollution risk screening value (GB 15618-2018). The sources of Cu, Zn, Pb, Cd, and Mn in soils were mainly associated with mining activities. The key factors influencing heavy metal bioavailability were associated with the types of extractants (complexing agents or neutral salt extractants) and the metals. Cd and Pb concentrations in most wheat and rice grain samples exceeded the maximum allowable Cd and Pb levels in food, respectively, and Cd concentrations in approximately 10% of the rice grain samples exceeded 1.0 mg/kg. Furthermore, rice and wheat grains exhibited higher Cd accumulation capacity than rape grains, and despite the high soil Cd concentrations in the rape fields, the rape grains were safe for consumption. High soil pH and AK restricted Cd and Cu accumulation in wheat grains, respectively. Soil properties seemed to influence heavy metal accumulation in rice grains the most.

This research investigation deals with efficiently removing strontium ions from aqueous solutions, a problem with significant environmental and health implications due to radioactive contamination. The performance and potential of Amberlite XAD-7 resin impregnated with TOPO extractant was evaluated to remove strontium ions from aqueous solutions. The influence of main operating conditions such as the initial pH, initial concentration of strontium in the solution, contact time, impregnation ratio, and adsorbent dosage, was evaluated. The adsorbents were characterized using SEM and FTIR analyses both before and after impregnation, as well as after the adsorption process. The study of the effect of contact time on the adsorption process was carried out in order to achieve the adsorption equilibrium time and determine the appropriate kinetic model. The experimental results showed that the adsorption process reaches equilibrium within 240 min, and the pseudo-second-order kinetic model is very suitable to describe this adsorption process (R 2  > 0.99). Adsorption equilibrium modeling showed that the Langmuir isotherm model can well describe the equilibrium behavior of strontium adsorption by Amberlite XAD-7 resin impregnated with TOPO extractant (R 2  > 0.99). The maximum uptake predicted by the Langmuir model for strontium adsorption using the TOPO impregnated Amberlite XAD-7 was 65.79 mg/g.

In this research work, the adsorption of strontium ions from aqueous solutions was studied using Dowex 50 W-X8 resin loaded with TOPO extractant. This study introduces a novel TOPO-impregnated adsorbent with potential applications for efficient and cost-effective nuclear wastewater treatment. The influence of effective operational parameters such as initial pH of the solution, adsorbent dosage, initial strontium concentration in the solution, and contact time was evaluated. In order to investigate the kinetics of the adsorption process, pseudo-first-order and pseudo-second-order models were used. The results indicated a very good agreement between the experimental data and the pseudo-first-order kinetic model. Langmuir and Freundlich models were used to model the equilibrium of the adsorption. Langmuir isotherm model showed good agreement with the experimental data. The maximum adsorption capacity of Dowex 50 W-X8 resin loaded with TOPO for strontium sorption was obtained 163.43 mg/g of adsorbent calculated by the Langmuir model. The result of the present study showed that Dowex 50 W-X8 resin loaded with TOPO extractant can be an effective adsorbent for the sorption of strontium from aqueous solutions and industrial wastewater.

The growing demand for lithium necessitates the development of an efficient process to recover it from three kinds of solutions, namely brines as well as acid and alkaline leach liquors of primary and secondary resources. Therefore, the separation of lithium(I) from these solutions by solvent extraction was reviewed in this paper. Lithium ions in brines are concentrated by removing other metal salts by crystallization with solar evaporation. In the case of ores and secondary resources, roasting followed by acid/alkaline leaching is generally employed to dissolve the lithium. Since the compositions of brines, alkaline and acid solutions are different, different commercial extractants are employed to separate and recover lithium. The selective extraction of Li(I) over other metals from brines or alkaline solutions is accomplished using acidic extractants, their mixture with neutral extractants, and neutral extractants mixed with chelating extractants in the presence of ferric chloride (FeCl3). Among these systems, tri-n-butyl phosphate (TBP)- methyl isobutyl ketone (MIBK)-FeCl3 and tri-n-octyl phosphine oxide (TOPO)- benzoyltrifluoroacetone (HBTA) are considered to be promising for the selective extraction and recovery of Li(I) from brines and alkaline solutions. By contrast, in the acid leaching solutions of secondary resources, divalent and trivalent metal cations are selectively extracted by acidic extractants, leaving Li(I) in the raffinate. Therefore, bis-2,4,4-trimethyl pentyl phosphinic acid (Cyanex 272) and its mixtures are suggested for the extraction of metal ions other than Li(I).

Heavy metals (HMs) are regarded as a high priority monitoring contaminant and have been identified as a major environmental concern. The forms of land use may have an impact on the movement and accumulation of HMs. The mobility and accumulation of HMs were examined in topsoils of various land use using different soil test methods. Sixty-three soil samples were taken from various land use including garlic, orchard, pasture, potato, vegetable, wheat, and polluted lands. The availability of Cd, Cu, Mn, Ni, Pb, and Zn were determined using CaCl2, HCl, HNO3, EDTA, and DTPA extractants. Amongst all extractants and land use, the mean available contents of Cd, Cu, Mn, Ni, Pb, and Zn were 0.81, 4.95, 58.60, 2.41, 14.94, and 7.95 mg kg−1, respectively. Among the extractants, the mean contents of all HMs in all land use decreased in following order: HNO3 (34.39 mg kg−1) > EDTA (19.41 mg kg−1) > HCl (13.52 mg kg−1) > DTPA (5.26 mg kg−1) > CaCl2 (1.36 mg kg−1). Generally, among the various land use, after polluted land (26.2 mg kg−1) the orchard land (17.3 mg kg−1) presented the highest contents of HMs, and the wheat (8.35 mg kg−1) and pasture (9.94 mg kg−1) lands presented the lowest contents. The results from the geo-accumulation index (Igeo) and the ecological risk index (RI) showed that except for polluted land in other land use the HMs categorized as unpolluted (Igeo < 0) and low risk (RI ≤ 150). The results from the availability ratio (AR) showed that among the extractants, the mean AR calculated for all HMs and land use decreased in the following order: HNO3 (28.08%) > EDTA (26.36%) > HCl (21.55%) > DTPA (7.11%) > CaCl2 (3.19%). It also indicated that the vegetable land (average of all extractants) presented the highest (25.1%) of HMs extractability while the pasture land (average of all extractants) presented the lowest (12.7%). The hazard index (HI) showed that for all HMs in various land use the non-carcinogenic risk were not significant. Generally, Pb and Mn are the main contributors to the total health risks, while Zn and Cu were the least risks. When utilizing the EDTA extractant, Mn and Ni were combined into one cluster by using AR of HMs, but Cu and Pb were combined into one cluster when using the both EDTA and DTPA extractants. The noteworthy feature of this clustering is the use of AR of HMs rather than available ones, which considers both available and total HMs in soil. This study highlights the importance of extractants, land use and AR in assessing risk assessment caused by HMs, bioavailability of HMs and exposure health risk. Lastly, we emphasize the significance of employing AR to evaluate soil enrichments with HMs and suggest considering available background level of HMs rather than the total background levels that is currently utilized to assess soil contamination.

Multivalent cooperativity plays an important role in the supramolecular self-assembly process. Herein, we report a remarkable cooperative enhancement of both structural integrity and metal ion selectivity on metal-organic M 4 L 4 tetrahedral cages self-assembled from a tris-tridentate ligand (L 1 ) with a variety of metal ions spanning across the periodic table, including alkaline earth (Ca II ), transition (Cd II ), and all the lanthanide (Ln III ) metal ions. All these M 4 L 1 4 cages are stable to excess metal ions and ligands, which is in sharp contrast with the tridentate (L 2 ) ligand and bis-tridentate (L 3 ) ligand bearing the same coordination motif as L 1 . Moreover, high-precision metal ion self-sorting is observed during the mixed-metal self-assembly of tetrahedral M 4 L 4 cages, but not on the M 2 L 3 counterparts. Based on the strong cooperative metal ion self-recognition behavior of M 4 L 4 cages, a supramolecular approach to lanthanide separation is demonstrated, offering a new design principle of next-generation extractants for highly efficient lanthanide separation. Lanthanide ions possess similar chemical properties, making their separation from one another challenging. Here the authors show that a tris-tridentate ligand causes high-precision metal ion self-sorting, leading to the selective assembly of tetrahedral M 4 L 4 cages across the lanthanide series.

Usual extraction processes for analyzing foods, supplements, and nutraceutical products involve massive amounts of organic solvents contributing to a negative impact on the environment and human health. In recent years, a new class of green solvents called natural deep eutectic solvents (NADES) have been considered a valid alternative to conventional solvents. Compared with conventional organic solvents, NADES have attracted considerable attention since they are sustainable, biodegradable, and non-toxic but also are easy to prepare, and have low production costs. Here we summarize the major aspects of NADEs such as the classification, preparation method physicochemical properties, and toxicity. Moreover, we provide an overview of novel extraction techniques using NADES as potential extractants of bioactive compounds from foods and food by-products, and application of NADEs in food analysis. This review aims to be useful for the further development of NAES and for broadening the knowledge of these new green solvents in order to increase their use for the extraction of bioactive compounds and in food analysis.

During solvent extraction, amphiphilic extractants assist the transport of metal ions across the liquid–liquid interface between an aqueous ionic solution and an organic solvent. Investigations of the role of the interface in ion transport challenge our ability to probe fast molecular processes at liquid–liquid interfaces on nanometer-length scales. Recent development of a thermal switch for solvent extraction has addressed this challenge, which has led to the characterization by X-ray surface scattering of interfacial intermediate states in the extraction process. Here, we review and extend these earlier results. We find that trivalent rare earth ions, Y(III) and Er(III), combine with bis(hexadecyl) phosphoric acid (DHDP) extractants to form inverted bilayer structures at the interface; these appear to be condensed phases of small ion–extractant complexes. The stability of this unconventional interfacial structure is verified by molecular dynamics simulations. The ion–extractant complexes at the interface are an intermediate state in the extraction process, characterizing the moment at which ions have been transported across the aqueous–organic interface, but have not yet been dispersed in the organic phase. In contrast, divalent Sr(II) forms an ion–extractant complex with DHDP that leaves it exposed to the water phase; this result implies that a second process that transports Sr(II) across the interface has yet to be observed. Calculations demonstrate that the budding of reverse micelles formed from interfacial Sr(II) ion–extractant complexes could transport Sr(II) across the interface. Our results suggest a connection between the observed interfacial structures and the extraction mechanism, which ultimately affects the extraction selectivity and kinetics.

To address the increasing demand for lithium, the recovery of lithium from salt lake brines has garnered significant attention. Techniques have been developed; however, these approaches exhibit drawbacks such as high energy consumption, excessive freshwater usage, and substantial dissolution losses, presenting environmental concerns. This review discusses the application and characteristics of four extractant systems used in solvent extraction: organophosphates, ionic liquids, crown ethers, and β-diketones. Furthermore, we present the optimization of organophosphate systems to make them more environmentally friendly. Optimization encompasses four key aspects: synergistic extractants, coextractants, diluents, and main extractants. Solvent extraction is a simple, cost-effective, and environmentally benign technique for lithium extraction from brine. Modifying the structure of these extractants can reduce dissolution rates and improve extraction efficiencies.

It is critical to understand the risk of element pollution in soils by evaluating their background levels. Phosphorus (P) content in agricultural soils needs to be assessed from agronomic and environmental standpoints. The current study intended to calculate the background levels of available and total P in soils. To achieve this goal, 50 sites without human activities were selected. Soils were sampled from the surface and subsurface of each site (100 soil samples). The available P forms in soils were extracted using the water-extractable P (WEP), calcium chloride-extractable P (CCEP), and Olsen-extractable P (OEP) methods. The first two extractants are being used to evaluate P leaching from soils, while the last one is being used as an agronomic indicator. The methods used to calculate background levels were the iterative 2-δ technique (2-δ) and the calculated distribution function (CDF). Results showed that the upper limits of background levels using 2-δ method were 1.45, 0.92, 8.12, and 424.4 mg kg −1 for WEP, CCEP, OEP, and total P, respectively. Also, the upper limits of background levels using CDF method were 1.42, 1.15, 12.09, and 447.6 mg kg −1 , for WEP, CCEP, OEP, and total P, respectively. It can be concluded that using these background levels, which for the first time were calculated for P, would enable us to have an accurate examination of P excess as a result of human activities.