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Heavy metals in flue gas desulfurization (FGD) gypsum from coal-fired power plants are at risk of releaching during the processes of stockpiling and resource utilization. In this study, the effects of organosulfur chelators dithiocarbamate (DTC) and trisodium trithiocyanate-15 (TMT-15) on the solidification characteristics of heavy metals in desulphurized gypsum under different mass fractions, pH values, water contents and reaction times were investigated. The chemical composition and morphology were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES) and scanning electron microscope (SEM). The experiments showed that both DTC and TMT-15 were effective at stabilizing the heavy metals in the FGD gypsum, with more than a 50% curing effect for all the heavy metals except Pb. DTC showed a better stabilization for Pb, Hg, Cu, Zn, and Cr, and TMT-15 showed a better curing effect for Cd. The solidified gypsum had good heavy metal stability in low-water-content environments. Increasing the mass fraction, reaction time, and pH decreased the heavy metal leaching, and the mass fraction had the greatest effect on the total heavy metal leaching concentration, followed by the reaction time and pH value. [ABSTRACT FROM AUTHOR]

Polysaccharides are functional foods or drugs that can be used to alleviate heavy metal poisoning by cadmium, lead, mercury, and arsenic. Industries generate substantial quantities of toxic heavy metal wastes, such as wastewater discharges, paints, electronic waste, batteries, pigments, and plastics, into the environment that pose a risk to human health. Therefore, it is imperative to eliminate accumulated heavy metal ions from the body and the environment. Heavy metal toxicity can lead to decreased energy levels and impair the functioning of vital organs, such as the brain, lungs, kidneys, liver, and blood. Prolonged exposure can result in progressive physical, muscular, and neurological degeneration that resembles conditions such as multiple sclerosis, Parkinson's disease, Alzheimer's disease, and muscular dystrophy. Polysaccharides operate through mechanisms such as chelation, antioxidant defense, immunomodulation, and tissue repair. Polysaccharides involved in heavy metal removal include methionine and cysteine, together with N-acetylcysteine, an acetylated form of cysteine, S-adenosylmethionine, a metabolite of methionine, α-lipoic acid, and the tripeptide glutathione (GSH). These compounds effectively bind with harmful heavy metals to create a stable complex and defend biological targets from metal ions, thus decreasing their harmful effects and causing them to be excreted from the body. This review also highlights the importance of polysaccharides' ability to mitigate oxidative stress, enhance immune responses, and support tissue repair processes. Polysaccharides are ubiquitous in nature and take part in diverse processes, making them potential natural therapies for heavy metal-related diseases. This review discusses the effectiveness of natural polysaccharides and the mechanisms that allow them to bind with heavy metals to alleviate their effects from the body and the environment. Polysaccharides have inherent features that enable them to function as pharmacological agents and regulate the immune response. [ABSTRACT FROM AUTHOR]

Heavy metals in flue gas desulfurization (FGD) gypsum from coal-fired power plants are at risk of releaching during the processes of stockpiling and resource utilization. In this study, the effects of organosulfur chelators dithiocarbamate (DTC) and trisodium trithiocyanate-15 (TMT-15) on the solidification characteristics of heavy metals in desulphurized gypsum under different mass fractions, pH values, water contents and reaction times were investigated. The chemical composition and morphology were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES) and scanning electron microscope (SEM). The experiments showed that both DTC and TMT-15 were effective at stabilizing the heavy metals in the FGD gypsum, with more than a 50% curing effect for all the heavy metals except Pb. DTC showed a better stabilization for Pb, Hg, Cu, Zn, and Cr, and TMT-15 showed a better curing effect for Cd. The solidified gypsum had good heavy metal stability in low-water-content environments. Increasing the mass fraction, reaction time, and pH decreased the heavy metal leaching, and the mass fraction had the greatest effect on the total heavy metal leaching concentration, followed by the reaction time and pH value.

Polysaccharides are functional foods or drugs that can be used to alleviate heavy metal poisoning by cadmium, lead, mercury, and arsenic. Industries generate substantial quantities of toxic heavy metal wastes, such as wastewater discharges, paints, electronic waste, batteries, pigments, and plastics, into the environment that pose a risk to human health. Therefore, it is imperative to eliminate accumulated heavy metal ions from the body and the environment. Heavy metal toxicity can lead to decreased energy levels and impair the functioning of vital organs, such as the brain, lungs, kidneys, liver, and blood. Prolonged exposure can result in progressive physical, muscular, and neurological degeneration that resembles conditions such as multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, and muscular dystrophy. Polysaccharides operate through mechanisms such as chelation, antioxidant defense, immunomodulation, and tissue repair. Polysaccharides involved in heavy metal removal include methionine and cysteine, together with N-acetylcysteine, an acetylated form of cysteine, S-adenosylmethionine, a metabolite of methionine, α-lipoic acid, and the tripeptide glutathione (GSH). These compounds effectively bind with harmful heavy metals to create a stable complex and defend biological targets from metal ions, thus decreasing their harmful effects and causing them to be excreted from the body. This review also highlights the importance of polysaccharides’ ability to mitigate oxidative stress, enhance immune responses, and support tissue repair processes. Polysaccharides are ubiquitous in nature and take part in diverse processes, making them potential natural therapies for heavy metal-related diseases. This review discusses the effectiveness of natural polysaccharides and the mechanisms that allow them to bind with heavy metals to alleviate their effects from the body and the environment. Polysaccharides have inherent features that enable them to function as pharmacological agents and regulate the immune response.

Due to high metal toxicity, mixed municipal solid waste (MSW) compost is difficult to use. This study detected the presence of heavy metals (Cd, Cu, Pb, Ni, and Zn) in MSW compost through mineralogical analysis using X-ray diffraction (XRD) and performed topographical imaging and elemental mapping using a scanning electron microscope and energy dispersive X-ray analysis (SEM–EDX). Ethylenediaminetetraacetic acid (EDTA), a typical chelator, is tested to remove heavy metals from Indian MSW compost (New Delhi and Mumbai). It deals with two novel aspects, viz., (i) investigating the influence of EDTA-washing conditions, molarity, dosage, MSW compost-sample size, speed, and contact time, on their metal removal efficiencies, and (ii) maximizing the percentage removal of heavy metals by determining the optimal process control process parameters. These parameters were optimized in a batch reactor utilizing Taguchi orthogonal (L25) array. The optimization showed that the removal efficiencies were 96.71%, 47.37%, and 49.94% for Cd, Pb, and Zn in Delhi samples, whereas 45.55%, 79.52%, 59.63%, 82.31%, and 88.40% for Cd, Cu, Pb, Ni, and Zn in Mumbai samples. Results indicate that the removal efficiency of heavy metals was greatly influenced by EDTA-molarity. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of hydroxyl group, which aids heavy metal chelation. The results reveal the possibility of EDTA to reduce the hazardous properties of MSW compost. [ABSTRACT FROM AUTHOR]

Diethylenetriaminepentaacetate (DTPA) is the most widely used chelating agent for Pu and Am. Volunteers were assigned to receive intravenous injections or aerosol inhalations of 1 g of DTPA on days 1-4; volunteers received once daily injections of CaDTPA or ZnDTPA, CaDTPA inhalation as an aerosol, or CaDTPA injection on day 1 and ZnDTPA on days 2-4. CaDTPA injection or inhalation increased the excretion rates of Zn in urine with concomitantly reduced levels of serum Zn. Injection of CaDTPA reduced activities of serum alkaline phosphatase (AP) in parallel with the kinetics of Zn, whereas CaDTPA and ZnDTPA injection reduced activities of lactate dehydrogenase (LDH), and reduced activities of creatinine kinase (CK) were observed upon CaDTPA injection and its inhalation. Intravenous administration of CaDTPA and ZnDTPA enhanced excretion rates of Mn in urine, whereas transient reduction of Mn levels in serum was detected only via CaDTPA injection. Both CaDTPA and ZnDTPA transiently reduced levels of Mg in serum without affecting the excretion rates. On the other hand, both DTPAs increased excretion rates of toxic metals such as Pb and Cd, and CaDTPA also increased the rates of Hg. These results suggest that DTPA, and especially CaDTPA, removes essential metals and that the activities of these metalloenzymes are good indicators for the imbalance of essential metals during the DTPA administration. Our results also show that CaDTPA injection is more potent for removing these metals than ZnDTPA and inhalation of CaDTPA, and DTPA may be useful for the treatment of acute heavy metal poisoning with Pb, Cd, or Hg. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the metal adaptation of Actinobacteria offers a rich source of metal inducible environmentally relevant bio-compounds and molecules. These interact through biosorption towards the unique cell walls or via metal chelating activity of metallophors with trace elements, heavy metals and even with lanthanides to overcome limitations and toxic concentrations. Herein, the purpose is to investigate the adaptation potential of Gordonia rubripertincta CWB2 in dependence of the rare earths and to determine if we can utilize promising metallophore metal affinities for metal separation from aquatic solutions. For details on data interpretation and applicability of siderophores we refer to the related article entitled “Cultivation dependent formation of siderophores by Gordonia rubripertincta CWB2” [1].The respective workflow comprises a metal adaptation method to demonstrate effects on bacterial growth, pH, metallophore production, and metabolic change. All this was evaluated by LC-MS/MS and effects on biosorption of rare earths was verified by ICP-MS. Furthermore, we were able to carry out batch metal adsorption and desorption studies of metallophores entrapped in inorganic polymers of tetramethoxysilane (TMOS) to determine metal chelating capacities and selective enrichment effects from model solutions. The adaptation potential of strain CWB2 at increased erbium and manganese concentrations was verified by increased chelating activity on agar plates, in liquid assays and demonstrated by the successful enrichment of erbium by metallophore-functionalized TMOS-polymers from an aquatic model solution. Furthermore, the number of detected compounds in dependency of rare earths differ in spectral counts and diversity compared to the wild type. Finally, the biosorption of rare earths for the selected adaptation was increased significantly up to 2-fold compared to the wild-type. Overall a holistic approach to metal stress was utilised, integrating a bacterial erbium adaptation, metal chelating, biosorption of lanthanides and immobilization as well as enrichment of metals using metallophore functionalized inorganic TMOS polymers for separation of metals from aquatic model solutions.

The effects of chelating agents on heavy metal activation in Cd- and Pb-contaminated soils were studied through a dynamic activation experiment. An evaluation method for the measuring comprehensive suitability of chelating agent was established by calculating indexes for the degree of activation effect suitability and activated heavy metals' half-life suitability. The following results were obtained: in Cd- and Pb-contaminated soils, heavy metal activation effects reached or approached maximum activating effects within 1 d and subsequently showed different levels of decline in all chelating agent treatment conditions. Declines in activation effects similarly subjected to the law of exponents over time and to the goodness of fit in DTPA, NTA, and GLDA ranged from 0.80 to 0.98. For Cd- and Pb-contaminated soils, chelating agents' levels of comprehensive suitability (H) were recorded as follows: NTA(1.40) > GLDA(1.31) > DTPA(1.14) > EDTA(1.00) > EDDS(0.14) > CA(0.06) and GLDA(1.56) > DTPA(1.48) > EDTA(1.00) > NTA(0.78) > EDDS(0.26) > CA (0.02). GLDA and DTPA are both suitable for Cd and Pb phytoextraction. Moreover, NTA and GLDA are optimal chelating agents for Cd and Pb phytoextraction, respectively. [ABSTRACT FROM AUTHOR]

The ligand, 4-chloro-2,6-dipicolinic acid (H2PDA-Cl), and its two heavy metal complexes, [Ag(HDPA-Cl)(H2DPA-Cl)·2H2O] (1) and {[Cd(μ2-H2O)(H2O)(PDA-Cl)]}n (2), were prepared and then characterized by single-crystal X-ray diffraction. In addition, spectral and thermal correlations with structural results complete their solid-state description and facilitate complex 3 ([Pb(DPA-Cl)]) composition determinations. Complex 1 crystallizes in a monoclinic space group C2/c and each DPA-Cl ligand is tridentate to Ag(I) through the pyridine N and two monodentate carboxyl O atoms. The carboxy group with carbonyl C1 is semideprotonated and forms a symmetric hydrogen bond with a carboxy group of a neighboring complex. Complex 2 crystallizes in a triclinic lattice with space group P . The Cd(II) ions are seven-coordinate and the coordination polyhedra can be described as a distorted pentagonal bipyramid. IR data are consistent with monodentate coordination of the carboxylate to Ag(I), Cd(II), and Pb(II) and observed wavenumber shifts confirm PDA-Cl ligand coordination to Pb(II) in 3. Thermal stability of anhydrous complexes indicates the metal–ligand interactions. The thermal stability of prepared compounds is reflected by the strength of interaction between metal–ligand and hydrogen bonds. [ABSTRACT FROM AUTHOR]

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This review illustrates heavy metals toxicity, currently available therapies and the role and efficacy of chelation therapy for its management. Heavy metals are necessary for various biological processes, but they become harmful in excess. Specifically, they induce oxidative stress by generating free radicals and reducing antioxidant levels. Heavy metals also alter the confirmation of protein and DNA and inhibit their function. Chelation therapy is commonly used to treat metals toxicity. Chelation is a chemical process that occurs when interaction between a central metal atom/ion and ligand leads to formation of a complex ring-like structure. The ligand has a donor ion/molecule, which has a lone pair of electrons and may be monodentate to polydentate. Each metal has a different reactivity with a ligand, so a specific chelation agent is required for each metal. Combination therapy with a chelating agent and an antioxidant led to improved outcome. Heavy metal poisoning is a common health problem because of mining, smelting, industrial, agricultural and sewage waste. Heavy metals can be efficiently excreted from the body following treatment with proper chelation agents. [ABSTRACT FROM AUTHOR]

In this study, amine-terminated hyperbranched PAMAM (polyamidoamine) polymer (AT-HBP) was synthesized as a multifunctional chelating agent to remove two heavy metal ions (Cr(III) and Cu(II)) from the simulated wastewater solutions. The AT-HBP was characterized by Fourier transformed infrared (FTIR), dynamic light scattering (DLS), and proton nuclear magnetic resonance (1H NMR) analysis. The removal process was carried out in two different methods, centrifuged process and ultrafiltration. The concentration of heavy metal ions before and after removal was measured by inductively coupled plasma (ICP) instrument. The removal processes were evaluated by changing different parameters such as solution pH, AT-HBP dosage, and metal ion concentration. To evaluate the extend of binding of heavy metal ions in the presence of AT-HBP the presence of salt in the solution was also examined on the performance of the removal system. The overall results indicated that removal percentages higher than 98% for Cr(III) and 86% for Cu(II) were achieved for heavy metal concentrations of 100 mg/L for both removal process methods. Furthermore, the function of second generation of polypropylenimine (PPI) was compared to AT-HBP. The results reveal that the removal of Cr(III) and Cu(II) ions by AT-HBP were approximately 20% and 10% higher compared to PPI, respectively. Finally, hyperbranched dendritic polymer with lower expenses to synthesize compared to dendrimer underlined favorable properties as a multifunctional chelating agent and enhancement of ultrafiltration process for wastewater treatment. Graphical abstract [ABSTRACT FROM AUTHOR]

The negative effect of excess nickel (Ni) on plants is well investigated but there is only little information on its influence on root anatomy and a possible amelioration by chelating agents. In this study, we utilized light microscopy to observe anatomical changes in canola (Brassica napus) roots and investigated the element content by X-ray microanalysis. Ni-tolerant (Con-II) and Ni-sensitive cultivars (Oscar) were selected for this purpose. The plants were treated with 30 ppm NiSO4. Then, citric acid and ethylene-diamine-tetra-acetic acid (EDTA) (alone or in combination) were applied to observe the influence of chelating agents in metal stress amelioration. Ni treatment led to significant swelling of the roots in the Con-II variety as compared to the cultivar Oscar. Application of EDTA reduced the root radius of Con-II plants and this effect for Ni tolerance is discussed. According to X-ray microanalyses, Ni ions were more dispersed in the sensitive cultivar as indicated by metal adsorption to the cell wall. We investigate the hypothesis that an enhanced capacity of binding metals to the cell wall allows the plants to tolerate more heavy metals. [ABSTRACT FROM AUTHOR]

The remediation of contaminated dredged sediments is necessary to eliminate the risk towards human beings or the environment when there is disposal on land. A greenhouse experiment was carried out to evaluate the chemically assisted phytoextraction to clean up dredged sediment contaminated with Cr, Cu, Pb, and Zn. The ability of castor bean and chicory to absorb, translocate, and accumulate metals from sediment to root and shoot was evaluated by applying EDTA (5 mM), NTA (5 mM), and citric acid (60 mM) to sediment, before the harvest. Citric acid 60 mM was the most effective treatment in increasing Cr, Cu, and Pb in castor bean and chicory shoot. Chicory could accumulate 1730 mg Cr kg−1 in shoot, and had greater values than one for the bioaccumulation and translocation factors when citric acid was added to the sediment. But, the Cr percentages removed per harvest of chicory were 0.05% and were lower for Cu, Pb, and Zn due to low biomass obtained. Citric acid-assisted phytoextraction with chicory can be a promising short time solution to reduce Cr concentration in sediment and reach the Cr level guide for industrial land use only if suitable agronomic practices could be implemented to increase crop yield. [ABSTRACT FROM AUTHOR]

One of the major problems about the chelant-enhanced phytoextraction is the potential metal leaching associated with chelant application. A glasshouse pot experiment was conducted to investigate phytoextraction efficiency of common reed (Phragmites australis (Cav.) Trin. ex Steudel) for Lead and Chromium and to determine EDTA (ethylenediaminetetraacetic acid) enhancement of the mobility and phytoextraction of Pb and Cr and the potential for leaching of metals during the phytoextraction process. The results revealed that the bioconcentration factors of underground organs of the plant species were relatively higher than the bioconcentration factors of shoots and metals concentrations in the plant organs decreased in the order of root› rhizome› leave› stem. Thus, P. australis would be applicable for Pb and Cr phytostabilization. Addition of EDTA (0, 2.5, 5, 10 mmol.kg−1) to polluted pots with Pb and Cr significantly enhanced the mobility of soil metals and led to elevated soil solution concentrations of Pb and Cr. Positive correlation coefficients were found between treatment time and heavy metals concentrations in the plant organs. Optimum phytoextraction was observed when 5mmol. kg−1 EDTA was added in single dosage, 60 days for Pb and double dosage for Cr, after the plant cultivation and, consequently, soil Pb and Cr concentration decreased with the passage of time. It can be concluded that P. australis can remediate Pb-Cr contaminated soils and EDTA had potential to promote the uptake of Pb and Cr for common reed, but with respect to its environmental leaching risk to ground waters, low dose should be used.

The experimental results proved that a liquid and commercial chelating agent (DTCR) with dithiocarbamate (DTC) groups could be used to further remove toxic metal ions from the simulated metallic mine wastewater with trace amount of mixed metal ions. Under the optimized operating conditions, just a little dosage of DTCR (the volume ratio of DTCR to wastewater about 1:104) could make the removal rate of Cr3+, Cu2+, Pb2+, Zn2+ and Cd2+ in the treated water reach 99.70%, 99.28%, 99.10%, 92.33% and 91.49%, respectively. The residual content of the five ions were 0.003, 0.036, 0.009, 0.383 and 0.085 mg/L, which were all obviously lower than the contents required in the emission standard except of Zn2+ and Cd2+. The removal ability followed the order of Cr3+> Cu2+> Pb2+> Zn2+> Cd2+. The characterization revealed that the major functional groups in DTCR were DTC groups (-NCS2) and amino groups (-NH-, -NH2 or -NR2) which were not on DTC groups. The removal mechanisms of these functional groups were investigated by the combination of experimental methods and density functional theory (DFT) calculation, which demonstrated that all the five metal ions could be captured by the metal-ligand bonds between ions and C=S/C-S on DTC groups. But Cr3+, Cu2+ and Pb2+ could be further captured by the electron donation of N atom on -NH2 and -NH- which were not on DTC groups. Moreover, Cr3+ could be further adsorbed by the secondary N atom on DTC group. The relation between the functional groups and metal ions could be calculated quantitatively based on the removal mechanisms. It could well explain the removal ability of DTCR for different metal ions and provide a scientific guideline for the further modification of chelating agent with DTC groups to improve its removal efficiency for Zn2+ and Cd2+ in the depth treatment of wastewater with trace amount of mixed toxic metal ions. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is one of the most common environmental and occupational heavy metals with extended distribution. Exposure to Cd may be associated with several deleterious consequences on the liver, bones, kidneys, lungs, testes, brain, immunological, and cardiovascular systems. Overproduction of reactive oxygen species (ROS) as the main mechanism behind its toxicity causes oxidative stress and subsequent damages to lipids, proteins, and DNA. Therefore, antioxidants along with chelating agents have shown promising outcomes against Cd-induced toxicity. Curcumin with various beneficial effects and medical efficacy has been evaluated for its inhibitory activities against biological impairments caused by Cd. Thus, this article is intended to address the effectiveness of curcumin against toxicity following Cd entry. Curcumin can afford to attenuate lipid peroxidation, glutathione depletion, alterations in antioxidant enzyme, and so forth through scavenging and chelating activities or Nrf2/Keap1/ARE pathway induction. © 2017 BioFactors, 43(5):645-661, 2017 [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide extraction of toxic heavy metals including Uranium (U), Hafnium (Hf), Zirconium (Zr) and Cadmium (Cd) from a synthetic solid waste matrix was carried out using Cyanex 302, Cyanex 301, Cyanex 272, EDTA and TOPO as chelating agents in conjugation with methanol, acetylacetone, MIBK, acetone and acetonitrile as modifier. The dynamic extraction time (10–90 min), pressure (8–35 MPa), temperature (40–100 °C), type of modifier and chelating agent were investigated as the main effective variables on the extraction yield of toxic heavy metal ions. The quantities of toxic heavy metals in the original and extracted samples were determined by ICP analysis. The optimal conditions for the extraction of heavy metal ions were determined by one factor at a time method (OFAT) to be 80 °C, 26 MPa and 70 min (dynamic) using Cyanex 272 as chelating agent and methanol as modifier. The extraction yield of Zr, Hf, U and Cd at optimal conditions was predicted to be 100, 100, 99.1 and 100%, respectively. [ABSTRACT FROM AUTHOR]

1-(2-pyridylazo)-2-naphthol (PAN) is a heterocyclic azo compound that forms inner, mostly reddish colored, water-insoluble chelates with many transition metal ions with metal ion-ligand ratios of 1:1 or 1:2. PAN is rather unselective but it does not form complexes with the alkali and alkaline earth metals, Ge(IV), As, Se and Te. Numerous reported techniques of pre-concentration have been considered for analyzing the role of PAN on the physiochemical outcome of the procedures. PAN been used as a chelating precipitant, flocculant, auxiliary complexing agent, as a ligand for anchoring on other supports with the purpose of introducing chelating property as well as selectivity. The role of PAN in the different techniques of pre- concentration, namely co-precipitation, membrane filtration, micro-extraction, cloud point extraction and solid phase extraction, has been investigated. PAN influences the optimum experimental parameters, namely pH, temperature, time, amount, tolerance limit, etc. [ABSTRACT FROM AUTHOR]

Result for Pb extraction experiments from a contaminated soil performed with citric acid and ethylenediaminetetraacetic acid disodium salt (Na 2 EDTA) indicate that Na 2 EDTA is much more efficient. The Pb removal after 5 successive extractions using 24 mL of 0.1 M Na 2 EDTA solutions and 8 g of soil is close to 100%. Other non-toxic metals such as Ca and Mg, that are present in important concentrations in this soil, are also solubilized, but important differences in the behavior of each metal are observed. A local equilibrium model is used for the interpretation of the results of these batch experiments; the experimental and the model results are in a fairly good agreement. From these results it is concluded that Na 2 EDTA presents almost ideal characteristics for its use as enhancing agent for an electrokinetic remediation of the soil. Therefore, experiments were performed, in which the pH value is controlled at both electrode-compartments using Na 2 EDTA at the cathode and NaOH at the anode, aiming to the recovery of PbEDTA 2– at the anode. Nevertheless, no significant amounts of lead are recovered. The possible negative effects of the electric current over the performance of Na 2 EDTA are studied using a two-compartment cell for electrodialytic remediation with an important electrical current and comparing the results with those obtained under identical conditions without current. It is concluded that the electric current produce no negative effects. Therefore, the cancelling effects of the electromigration and the electroosmotic movement are considered as the most probable explanation for the experimental results. [ABSTRACT FROM AUTHOR]

This study investigated single-step extraction of heavy metals from contaminated sediments collected in the port of Cádiz. Experimental tests of washing with an aqueous solution of a chelating agent were performed at selected solid/liquid (S/L) ratios. Two chelating agents were chosen: 0.3 M EDTA(pH 3.8 and 8) and sodium citrate (1 M). The objective of the tests was to investigate extractive decontamination by the washing treatment. The study was focused on the extraction of Pb, Cu, Zn, and Cd. The experiments showed that the decontamination efficiencies of the extractants were of the order: EDTA (pH 3.8) > EDTA (pH 8) ∼ sodium citrate. EDTAsolution with slightly acid pH was optimal for the extraction of Pb, Cu, Zn and Cd. The data obtained from the thermal analysis of sediments after the decontamination process indicated the success of the extraction procedurewhich is proposed as a technique for controlling the behaviour of the decontamination process. [ABSTRACT FROM AUTHOR]

• The performance of the PCPSS was enhanced using the Taguchi approach (L 9 OA). • Ni was selected as a target heavy metal to maximize the performance of PCPSS. • The effects of chelating agent, applied voltage, and Ni concentration on the performance of PCPSS were studied. • Confirmation experiments were conducted on real soil contaminated with heavy metals. • The simultaneous removal of heavy metals, cations, and anions was investigated. Recently, we have developed a new soil electrokinetic remediation (SEKR) process, hereinafter referred to as the perforated cathode pipe SEKR system (PCPSS), to achieve remediation intensification. Some obstacles, such as the low removal of some heavy metals, particularly Ni, limited our previous PCPCS. We aim to improve the removal efficiency of the PCPSS by adding a chelating agent (i.e., ethylenediaminetetraacetic acid (EDTA)). Given the unsatisfactory remediation results obtained in our previous studies, the Taguchi approach (L 9 OA) was exploited in this work as an experimental design to determine the optimal level of factors that could enhance Ni removal. Results showed that an electric potential of 3 V, addition of 0.5 mol of EDTA, and an initial Ni concentration in the range of 10–20 mg kg−1 could optimize Ni removal. Confirmation experiments conducted on natural contaminated soil showed the following order of removal of heavy metals and other elements: Al (70%) > Co (69%) > Fe (63.5%) > Cu (55%) > Mn (52.8%) > Zn (43.17%) > Cr (41.41%) > Ni (22.26%). Among the studied soil cations, Mg showed the best removal rate, Ba showed moderate removal rate, and Ca showed the lowest removal rate. Notably, the removal rate of V was much higher than that of born (B). [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] PDTA significantly enhanced extraction of Cu from contaminated soil. [•] Complexation-promoted and dissolution of SOM were the mechanisms for Cu extraction. [•] High selectivity of PDTA for Cu2+ avoided unwanted dissolution of soil minerals. [Copyright &y& Elsevier]

Remediation of heavy-metal-contaminated sediment is often hampered by the availability of heavy metals to the added chemical agents because the heavy metals are often shielded by the sediment matrix. Effective heavy-metal extraction technique becomes an important factor in enhancing the treatment efficiency. A novel extraction/washing technique utilizing chelating agent and elevated pressure in consecutive cycles of compression and decompression has been developed for heavy-metal-contaminated sediment washing in the presence of chelating agent. In this study, the optimal operational conditions of pressure-assisted cyclic washing of Cu-contaminated sediments (initial Cu concentration = 23.177 mg/kg) were determined in a laboratory-scale system. The control factors included applied pressure level, washing time, applied chelant [ethylenediamine-tertraacetic (EDTA)] concentration (0.01-0.5 M), pressure times, and application of consecutive batches washing. Results from the bench-scale study showed that up to 70 % of Cu can be removed from the sediments when 10 atm of pressure was applied for washing. The efficiency dropped to 55 % when the pressure dropped to 6 atm. Under the same operational conditions, the optimal cyclic washing time was 60 min. Results from the particle size analyses indicate that the mean particle size dropped from 100 to 50 μm after the pressure-assisted cyclic washing. Thus, cyclic pressure caused the fracture of sediment aggregates resulting in the exposure of Cu to chelating agents. With the assistance of pressure cyclic system, the total washing time and the amount of added chemical agent used can be significantly reduced. [ABSTRACT FROM AUTHOR]

Abstract: Due to the excellent chelating properties of aminopolycarboxylic acid (APCAs), they can be used for the removal of metals from contaminated waters. This paper reviews the research results obtained for both commercial and self-prepared adsorbents functionalized with four most common APCAs: iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The structural characteristics and unique metal binding properties of these chelating adsorbents are presented. The theory of the adsorption phenomena is discussed based on the kinetics of adsorption, equilibrium adsorption isotherm models, and thermodynamic models. The most important applications of APCA-functionalized adsorbents are also described. APCA-functionalized adsorbents are found to be highly promising materials for metal removal from contaminated waters. [Copyright &y& Elsevier]

Highlights: [•] Regular electrolyte refreshment is favorable for maintaining high electric current. [•] EDTA-injection could greatly reduce Pb ecotoxicity. [•] Although adding Tween 80 reduced current, it could enhance microbial growth and biodegradation. [•] Oil biodegradation degree increased toward the anode and cathode. [•] Microbial action was beneficial to metal release from soil matrix. [Copyright &y& Elsevier]

Abstract: The effectiveness and mechanisms of naphthalene and metal removal from artificially contaminated soil by FeEDTA/FeEDDS-activated persulfate were investigated through batch experiments. Using FeEDTA-activated persulfate, higher naphthalene removal from the soil at 7 h was achieved (89%), compared with FeEDDS-activated persulfate (75%). The removal was mainly via the dissolution of naphthalene partitioned on mineral surfaces, followed by activated persulfate oxidation. Although EDDS is advantageous over EDTA in terms of biodegradability, it is not preferable for iron chelate-activated persulfate oxidation since persulfate was consumed to oxidize EDDS, resulting in persulfate inadequacy for naphthalene oxidation. Besides, 55 and 40% of naphthalene were removed by FeEDTA and FeEDDS alone, respectively. Particularly, 21 and 9% of naphthalene were degraded in the presence of FeEDTA and FeEDDS alone, respectively, which caused by electrons transfer among dissolved organic matter, Fe2+/Fe3+ and naphthalene. Over 35, 36 and 45% of Cu, Pb and Zn were removed using FeEDTA/FeEDDS-activated persulfate. [Copyright &y& Elsevier]

A novel complexing membrane containing 8-hydroxyquinoline groups was used for the removal of heavy metal ions (Cd2+ and Ni2+) from aqueous solution. The functionalized membranes were characterized by FTIR–ATR, SEM and EDAX for the presence of functional groups, the physical structure of the membranes and the analysis of the particles deposited on the membrane, respectively. The influence of 8-hydroxyquinoline concentration, feed concentration, pH and temperature of the solution on capture capability was studied. The modified membrane showed a higher affinity to Cd2+ cations than to Ni2+. The metal ion rejection was increased with an increase in concentration of 8-hydroxyquinoline from 0.5 to 2.0 wt%. However at a ligand concentration higher than 2.0 wt%, no significant change was observed in the metal rejection. The experimental results revealed that the metal rejection was decreased with an increase in metal ion concentration in the feed. Moreover the rejection depended on feed pH and is higher for elevated pH. By changing the temperature in the range of 23–28 °C, no considerable effect on metal rejection was observed. However, a higher temperature resulted in a decline in metal rejection. For filtration of a mixture of the two metal ions, the retention was similar to that of the single cations, i.e. Cd>Ni but with smaller absolute rejections. [ABSTRACT FROM PUBLISHER]

Abstract: This study investigated the influence of flushing duration, [S,S]-ethylenediaminedisuccinic acid (EDDS) dosage, humic acid and various combinations of ethylenediaminetetraacetic acid (EDTA), EDDS and tetrasodium pyrophosphate (Na4P2O7) on metal extraction during soil flushing, through column experiments. A lesser extent of enhancement in metal extraction efficiencies was found when the flushing duration and the dosage of EDDS was doubled, compared to their efficiencies measured at pore volume 100. Metal extraction efficiency was mainly influenced by the initial metal distribution in the soils rather than the flushing duration and the EDDS-to-metal molar ratio. Humic acid of less than 10mg/L as dissolved organic carbon (DOC) posed an insignificant effect on metal extraction during EDDS enhanced soil flushing. The extraction rate of Ni by EDTA and EDDS was time dependent, and was initially fast in the case of EDDS, whereas it was slow for EDTA. However, the overall Ni extraction efficiency by EDTA was higher when the flushing time was longer. Na4P2O7 promoted the mineral dissolution which enhanced the metal extraction as a result of soil disruption. The order of metal extraction by Na4P2O7 was Ni>Cr>Cu, probably be due to the different affinities between metals and P2O7 4−. [Copyright &y& Elsevier]

Abstract: This study evaluated the design of step-gradient, single-pulse, multi-pulse, and continuous injection of biodegradable EDDS ([S,S]-ethylene-diamine-disuccinic acid, under the same total dosage) and the significance of pore-water velocities during in situ soil flushing. In view of the metal breakthrough and extraction efficiency of each injection mode, single-pulse injection was found to be the least effective for all metals. Multi-pulse injection was consistently more effective than single-pulse injection, although the efficiency of second and third pulse injections significantly diminished. Continuous injection offered a simple operation and the greatest Ni and Cu extraction, whereas step-gradient injection was the best option for Zn and Pb extraction because it mitigated the influence of metal exchange. Moreover, a rinsing step with a background solution following the initial injection of the multi-pulse injection removed newly formed metal–EDDS complexes from soil pores effectively before further EDDS-flushing. A decrease in pore-water velocity provided a longer residence time for greater Ni and Cu extraction, but also enhanced the rate-limited metal exchange of Zn–EDDS and Pb–EDDS complexes and thus hindered Zn and Pb extraction. These results suggest a slower and continuous injection for the best Ni or Cu removal, but a faster and step-gradient injection for Zn or Pb removal. [Copyright &y& Elsevier]

A highly selective mono-C-allylation of pentaethyl diethylenetriaminepentaacetate was achieved with allyl bromide and potassium carbonate via a newly developed elaborate procedure based on Stevens rearrangement. It is contrastive that the conservative one-pot procedure gave a complicated mixture. [ABSTRACT FROM AUTHOR]

The fly ash from two municipal solid waste incineration plants in Shanghai was treated by the self-developed organic composite chelating agent. The results indicated that the stabilization effect of Pb in the fly ash by the composite chelating agent was the best, and the proportions of its easily leaching form in the two kinds of fly ash decreased from 29.60% and 27.49% to 3.05% and 0.29% respectively. The leaching toxicity of stabilized fly ash was lower than the limits of Standard for Pollution Control on the Landfill Site of Municipal Solid Waste (GB 16889 -2008), so it can be landfilled separately in the landfill site of municipal solid waste. [ABSTRACT FROM AUTHOR]

Abstract: Rhamnolipid, a metal sequestering agent produced by Pseudomonas Sp., has been effective in the removal of metals in soil washing technologies. Rhamnolipid has a strong affinity for cadmium (Cd) compared to some other metals (e.g. cobalt (Co), nickel (Ni)) and might also be useful in chelate-assisted phytoextraction. There have been many studies investigating the formation of metal–rhamnolipid complexes and the ability of rhamnolipid to remove metals from soil. However, to date, the longevity of rhamnolipid in soil has not been measured. Therefore, this study investigated the rate of rhamnolipid degradation in soils of varying physicochemical properties and contaminated with varying concentrations of Cd and zinc (Zn). The rate of rhamnolipid degradation was compared with ethylene diamine tetraacetic acid (EDTA) and citric acid. Our results indicate that citric acid was rapidly degraded, with 20% degradation occurring between 1 and 4 d depending on the level of soil contamination and 70% degradation within 20 d. EDTA was more persistent in the soils; only 14% of the EDTA was degraded after 20 d. Rhamnolipid had cumulative degradation between those of citric acid and EDTA. In most contaminated soils, cumulative degradation of the chelates and ligands were lower than in the uncontaminated soils. These results show that rhamnolipid may remain in the soil long enough to enhance metal phytoextraction, but not remain long enough to raise concerns regarding metal transport in the long-term. [Copyright &y& Elsevier]

Contamination of the environment by waste CCA (Cu, Cr, As) wood, containing the toxic heavy metals, copper, chromium, and arsenic that are hazardous to human health, can be significantly reduced by supercritical fluid extraction (SFE) technology. An environmentally benign solution for the detoxification of these CCA woods is the use of SFE technology for the treatment because no extra pollutant is added. In this work, we studied SFE of Cu, Cr, and As from CCA wood by using supercritical CO2 modified with chelating agents. Effects of pressure and temperature on the extraction efficiency for the heavy metals were studied with organophosphorous chelating agent, Cyanex 302. Some other chelating agents were also compared. Cyanex 302 was the best ligand in our experiments at pressure of 24 MPa and temperature of 333 K. The extraction efficiencies for Cu, Cr, and As were up to 63.5, 28.6, and 31.3%, respectively. [Copyright &y& Elsevier]

• Genome mining reveals a desferrioxamine biosynthetic gene cluster. • Transcriptomics confirms Fe-dependent regulation of desferrioxamine biosynthesis. • Fe-limitation induces siderophore and citrate production and secretion. • Metal stress in succinate containing medium results in high siderophore yields. • First verified siderophore from a Gordonia species: desferrioxamine E. Herein we demonstrate cultivation-dependent siderophore production by the actinomycete Gordonia rubripertincta CWB2. The strain produces mostly citrate, but also desferrioxamine E (DFOE) and new hydroxamate-type siderophores. The production of hydroxamate-like siderophores is influenced by cultivation conditions, for example available carbon sources or presence of metals, such as the rare earth erbium or the heavy metal lead. By cultivation with succinate and extraction with an adsorbing resin (XAD) we purified the G. rubripertincta CWB2 siderophores (yield up to 178 mg L−1). The respective workflow comprises genome mining, cultivation, and overproduction strategies, a rapid screening procedure, as well as traditional structure enrichment and structure elucidation methods. This combination of methods allows the discovery of new natural products with metal complexation capacity, also for lanthanides of commercial value. G. rubripertincta CWB2 carries a desferrioxamine-like biosynthetic gene cluster. Its transcription was proven by a transcriptomic approach comparing expression levels of the selected gene cluster during cultivation in iron-depleted and repleted media. Further investigation of the siderophores of this desferrioxamine producing Actinobacterium could lead to new structures. [ABSTRACT FROM AUTHOR]