Metal-citrate Complexes Research Articles

Comparison of phosphorus-based extractants on manganese separation from citrate leach solutions for recycling of lithium-ion batteries

The performance requirements of modern lithium-ion batteries (LIBs) necessitate the use of a number of scarce and strategically sensitive metals such as lithium and cobalt. Recycling end-of-life LIBs reduces the demand on the primary sources of these metals and helps reduce the environmental impact of LIB waste. Citric acid has proven to be an effective environmentally friendly and sustainable lixiviant; however, the formation of metal citrate complexes complicates subsequent metal separation processes such as solvent extraction. This study enhances the understanding of LIB metal separation from citric acid media by comparing the metal separation performance of phosphorus-based liquid-liquid extractants from a citric acid leach. The optimum Mn(II) extraction pH decreases as the extractant’s phosphorus oxidation state increases from phosphinic to phosphonic to phosphoric, due to the oxygen atoms that surround the central phosphorus atom. The maximum Mn(II) separation with Cyanex 272, PC-88A, and D2EHPA was observed at pHs of 6, 3, and 3, respectively. D2EHPA further provided the best separation of Mn(II) over Al, Co, Li, and Ni with separation factors of 137, 191, 118, and 601, respectively. No research is currently available on the metal separation performance of phosphonic (PC-88A) or phosphinic (Cyanex 272) organic extractants from citric acid media.Significance: This study is the first to investigate the use of phosphonic and phosphinic extractants for metal separation from citric acid leach solutions, towards using citric acid as an environmentally friendly lixiviant. The phosphoric extractant, D2EHPA, enabled successful and sequential separation and extraction of aluminium, manganese and lithium, making the process technologically feasible and attractive.

Beneficiation of Nickel from Ultramafic Ores: Using Sodium Citrate as a Green Processing Reagent

The processing of ultramafic ores requires fine grinding, which can result in slime-coating of the nickel-bearing mineral, pentlandite, by the phyllosilicate gangue mineral, serpentine. This lowers nickel recovery and concentrate grade during froth flotation operations. The presence of divalent cations in process water exacerbates the detrimental effects of phyllosilicates on nickel recovery by enhancing the positive surface charge of serpentine and causing charge reversal of pentlandite. To mitigate these issues, an environmentally benign, nontoxic, and biodegradable reagent, sodium citrate, was used in this study to chelate divalent cations on the pentlandite surface and desorb them from the mineral surface. The metal-citrate complexes adsorb onto the positively charged serpentine surface, reversing its charge. Sodium citrate was able to restore the surface charge and hydrophobicity of pentlandite, reverse the charge of serpentine, desorb the divalent cations from the mineral surface, and prevent MgO gangue recovery to the froth phase. Microflotation studies demonstrated that upon the addition of sodium citrate, nickel recovery increased from 74 to 96% and nickel grade was improved from 11 to 15.1% . The hydrophobicity of pentlandite was restored upon conditioning with citrate as evident by increase in water static contact angle from 50° to 70° , DLVO interactions showed that addition of citrate prevents slime coating of pentlandite by serpentine. The results demonstrated the depressive and dispersive action of sodium citrate.

Sub-nanometer ceria-promoted Ni 13X zeolite catalyst for CO2 methanation

Sub-nanometer zeolite 13X-supported Ni-ceria catalysts were synthesized for CO2 methanation. XRD and SEM results show the structure and morphology of 13X zeolite after impregnation and calcination. Ce loading affected the catalysts’ metal dispersion, reducibility, basicity and acidity, and thence their activity and selectivity. STEM-EDX elemental mappings showed that Ce and Ni are predominantly highly dispersed. Ce has a positive effect on the reduction of NiO and leads to a relatively high number of medium basic sites with a low Ce loading. Highly stable 5%Ni2.5%Ce13X had high activity and nearly 100% CH4 selectivity in CO2 methanation at 360 °C, which is mainly due to the high dispersion of metals and relatively high amount of medium basic sites. It can be inferred that this catalyst synthesis strategy has great potential for good catalyst dispersion, since metal uptake by the zeolite is selective for the metal citrate complexes in solution.

Tributylhexadecylphosphonium Modification Strategy to Construct Gold Nanoprobes for the Detection of Aqueous Cr(III)-Organic Complexes.

Most metal probes based on gold nanoparticles (AuNPs) are designed for free metal ions in synthetic waters, and very few are applicable in the detection of metal-organic complexes ubiquitous in real water samples. In this study, we proposed a novel colorimetric nanoprobe strategy for complexed Cr(III) species based on the analyte-induced aggregation of AuNPs, as coated by a cationic surfactant tributylhexadecylphosphonium bromide (THPB) instead of traditional carboxyl modifiers. Such a detection system could be realized via both naked eye and/or UV-vis spectroscopy with detection limits of 8.0 and 0.29 μM, respectively, much lower than its allowable maximum level in industrial effluent as regulated by China EPA (1.5 mg Cr/L, ∼30 μM). The proposed detection system also exhibits high selectivity against various interfering substances including free ions, small organic molecules, and other metal-citrate complexes. The unique hydrolysis and extremely slow decomplexation of Cr(III) are believed to favor the formation of the specific interaction between Cr(III)-citrate and THPB-AuNPs, as verified by X-ray photoelectron spectroscopy characterization, thus endowing the nanoprobe with specific discrimination of the complexed Cr(III) via the aggregation of THPB-AuNPs. Also, the THPB-AuNPs could be stored at room temperature for 30 days and maintain constant detection performance. Moreover, the quantitative detection of Cr(III)-organic complexes with the background of various real water samples agreed well with that based on inductively coupled plasma atomic emission spectrometry, making it an attractive alternative for on-site detection of authentic samples containing Cr(III)-organic species.

Citric Acid-Enhanced Electroremediation of Toxic Metal-Contaminated Dredged Sediments: Effect of Open/Closed Orifice Condition, Electric Potential and Surfactant

Citric acid (CA), a widely used eco-friendly electrolyte, can be employed as an agent for enhancing toxic metal (TM) removal from contaminated dredged sediment using electrokinetic (EK) technology. In this study, dredged harbor sediments co-contaminated by TMs were subjected to enhanced EK treatment using a mixture of chelating agent (CA) and surfactant as an additive in the processing fluids. Several control conditions that may influence the efficiency of TM removal were tested, including open/closed sediment chamber orifices, electric potential gradients (0.5, 1.0, and 1.5 V cm−1), and electrolyte surfactant. Tween 20 (4 mmol L−1) was used as a surfactant within the electrolyte to investigate the extent of TM removal in sediment with high organic matter content. The results showed that an open orifice led to a greater electro-osmotic flow (EOF) with moderate TM removal. In contrast, a closed orifice with a nonionic surfactant electrolyte allowed the highest removal of TMs from the matrix. Moreover, increasing the electric potential gradient led to a higher EOF under the open orifice condition, but no significant increase in TM removal was observed owing to a higher accumulation of TMs in the middle of the matrix, caused by the opposite direction of EOF and electro-migration of metal-citrate complexes.

The rice zebra3 (z3) mutation disrupts citrate distribution and produces transverse dark-green/green variegation in mature leaves

BackgroundRice zebra mutants are leaf variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf variegation mutant in rice, zebra3 (z3), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors.ResultsMap-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves.ConclusionsThese results suggest that leaf variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.

Green synthesis of multi metal- citrate complexes and their characterization

Four new multi metal-citrate complexes have been synthesized through green synthetic pathways. Their synthesis by hydrothermal route in the present research is decorated with features such as, a simple one pot synthesis, cost effectiveness, easy to scale up for commercial production, efficient synthesis conditions like mild temperature and shorter duration which further rules out the possibility of forming byproducts which may cause damage to the environment and being environmental benign as it eliminates the use and recovery of harmful organic solvents such as N, N- dimethyl formamide and N, N- diethyl formamide, used by the researchers in the past during the synthesis of similar metal- organic framework complexes. All four complexes are well defined crystalline materials with polynuclear multi metal-citrate framework having cubic crystal structure as indicated by their Powder X-ray Diffraction patterns. These complexes have been characterized by Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Thermogravimetric analysis and Powder XRD techniques.

Turn‐On Luminescent Probes for the Real‐Time Monitoring of Endogenous Hydroxyl Radicals in Living Cells

AbstractThe utilization of semiconductor quantum dots (QDs) as optical labels for biosensing and biorecognition has made substantial progress. However, the development of a suitable QD‐based luminescent probe that is capable of detecting individual reactive oxygen species (ROS) represents a great challenge, mainly because the fluorescence of QDs is quenched by a wide variety of ROS. To overcome this limitation, a novel QD‐based turn‐on luminescent probe for the specific detection of .OH has been designed, and its application in monitoring the endogenous release of .OH species in living cells is demonstrated. Metal citrate complexes on the surfaces of the QDs can act as electron donors, injecting electrons into the LUMO of the QDs, while .OH can inject holes into the HOMO of the QDs. Accordingly, electron–hole pairs are produced, which could emit strong luminescence by electron–hole recombination. Importantly, this luminescent probe does not respond to other ROS.

Turn-On Luminescent Probes for the Real-Time Monitoring of Endogenous Hydroxyl Radicals in Living Cells.

The utilization of semiconductor quantum dots (QDs) as optical labels for biosensing and biorecognition has made substantial progress. However, the development of a suitable QD-based luminescent probe that is capable of detecting individual reactive oxygen species (ROS) represents a great challenge, mainly because the fluorescence of QDs is quenched by a wide variety of ROS. To overcome this limitation, a novel QD-based turn-on luminescent probe for the specific detection of (.) OH has been designed, and its application in monitoring the endogenous release of (.) OH species in living cells is demonstrated. Metal citrate complexes on the surfaces of the QDs can act as electron donors, injecting electrons into the LUMO of the QDs, while (.) OH can inject holes into the HOMO of the QDs. Accordingly, electron-hole pairs are produced, which could emit strong luminescence by electron-hole recombination. Importantly, this luminescent probe does not respond to other ROS.

Synthesis of LaYbO3 perovskite through modified Pechini method: Structural, electric and magnetic characterization

Single phase LaYbO3 lanthanide-based perovskite powder was synthesized by modified Pechini method, which is based on polyesterification of metal–citrate complexes in aqueous solution. Complexes were formed in aqueous solution and after polyalcohol addition and slow water evaporation, bond formation is allowed and a macroscopic polymeric network was produced, where cations are embedded and uniformly distributed. Finally, through several pyrolysis steps, microcrystalline oxide particles were obtained. Structural characterization was performed by means the powder X-ray diffraction (XRD) technique. The obtained patterns were indexed and refined to reveal that the LaYbO3 simple perovskite crystallizes in an orthorhombic structure, belonging to the Pnma (#62) space group, with lattice constants a = 6.0327 Å, b = 8.4138 Å and c = 5.8307 Å. Studies of electron dispersive X-ray spectroscopy show that the LaYbO3 is free of impurities. Electric response was evaluated by electric polarization measurements as a function of applied electric fields. Obtained curves show evidence of a hysteretic behavior related with dielectric losses which are characteristics of insulator materials. From the saturation values of electric charge, the relative dielectric constant was determined to be 22.6. The magnetic behavior was examined by means of the curves of magnetic susceptibility as a function of temperature. The fit with the Curie equation is in agreement with a typical paramagnetic feature with effective magnetic moment [Formula: see text] = 4.9 [Formula: see text]B, which is close to the theoretical expected value from the Hund’s rules.

Remediation of cadmium- and lead-contaminated agricultural soil by composite washing with chlorides and citric acid.

Composite washing of cadmium (Cd)- and lead (Pb)-contaminated agricultural soil from Hunan province in China using mixtures of chlorides (FeCl3, CaCl2) and citric acid (CA) was investigated. The concentrations of composite washing agents for metal removal were optimized. Sequential extraction was conducted to study the changes in metal fractions after soil washing. The removal of two metals at optimum concentration was reached. Using FeCl3 mixed with CA, 44% of Cd and 23% of Pb were removed, and 49 and 32% by CaCl2 mixed with CA, respectively. The mechanism of composite washing was postulated. A mixture of chlorides and CA enhanced metal extraction from soil through the formation of metal-chloride and metal-citrate complexes. CA in extract solutions promoted the formation of metal-chloride complexes and reduced the solution pH. Composite washing reduced Cd and Pb in Fe-Mn oxide forms significantly. Chlorides and CA exerted a synergistic effect on metal extraction during composite washing.

Theoretical spectroscopic studies and identification of metal-citrate (Cd and Pb) complexes by ESI-MS in aqueous solution

The combined use of ESI-MS, FTIR-ATR and theoretical calculations for the determination of metal-citrate (metal=Cd and Pb) structures are reported. Mass spectrometry allowed to determine the stoichiometry 1:1 and 2:1 of the complexes, corroborating the theoretical calculations. The species found in the ratio 2:1 had their molecular structures readjusted, since the deprotonation of citric acid differed from what was simulated. The calculations of thermodynamic stability (ΔH0(aq.)) for the complexes obtained by B3LYP/LANL2DZ were more exoenergetic than those found by PM6. However, for both methods, the stability of the complexes follows a trend, that is, the lowest-energy isomers in PM6 are also the most stable in B3LYP/LANL2DZ. The infrared analysis suggested that carboxyl groups are complexation sites and hydrogen bonds can help in the stability of the complexes. The vibrational frequencies in B3LYP/LANL2DZ had a good correlation with the experimental infrared results.

Influence of bath concentration and pH on electrodeposition process of ternary Zn-Ni-Mo alloy coatings

The influence of bath pH and also citrate and molybdate concentration, on the electrodeposition process of ternary Zn-Ni-Mo alloy coatings has been examined. The occurrence of the particular forms of the metal-citrate complexes in the electrolytes was analysed using UV-VIS spectroscopy and on the basis of the stability constants of the complexes. In the solutions with lower pH (4·5 and 5·7), in which free metal ions and ZnHCit− and NiHCit− complexes predominate, anomalous codeposition of nickel with zinc took place. In electrolytes with higher pH, containing excess of citrate, in which all the metal ions occur in the form of citrate complexes, and about 20% of the Zn2+ and Ni2+ ions form a ZnNiCit24− mixed complex, the codeposition changes from anomalous to normal. The percentage of Mo in the alloy increases with the increase in concentration of uncomplexed MoO42− ions in the solution. Alloys with much higher Mo content may be obtained from the bath in which preferential deposition of nickel (normal codeposition) takes place.

Polymetallic citric complexes as precursors for spray-pyrolysis deposition of thin LaFeO3 films

A method for the deposition of thin films of the perovskite LaFeO3 on glass is proposed. The films are prepared by spray pyrolysis using an ethylene glycol solution of mixed metal citrate complexes and O2 or N2 as carrier gas at substrate temperatures between 350°C and 400°C and post-deposition annealing at 350–480°C in air. The phase composition, crystal structure, morphology and adhesion of the prepared films (40–600nm thick) are studied by X-ray diffraction, energy dispersive X-ray microanalysis, scanning electron microscopy, and atomic force microscopy. The influence of the conditions of deposition and post-deposition annealing is studied and optimal parameters of the procedure are described. Single phase dense uniform films with crystallites of approx. 30nm are obtained.

Aqueous complexation of citrate with neodymium(iii) and americium(iii): a study by potentiometry, absorption spectrophotometry, microcalorimetry, and XAFS

The aqueous complexation of Nd(III) and Am(III) with anions of citrate was studied by potentiometry, absorption spectrophotometry, microcalorimetry, and X-ray absorption fine structure (XAFS). Using potentiometric titration data fitting the metal-ligand (L) complexes that were identified for Nd(III) were NdHL, NdL, NdHL2, and NdL2; a review of trivalent metal-citrate complexes is also included. Stability constants for these complexes were calculated from potentiometric and spectrophotometric titrations. Microcalorimetric results concluded that the entropy term of complex formation is much more dominant than the enthalpy. XAFS results showed a dependence in the Debye-Waller factor that indicated Nd(iii)-citrate complexation over the pH range of 1.56-6.12.

Presence of Fe3+ and Zn2+ promoted biotransformation of Cd–citrate complex and removal of metals from solutions

The promotion to Cd–citrate complex biotransformation via addition of Fe3+ and Zn2+ was investigated. Single Fe(III)– or Zn–citrate complex was completely degraded by Pseudomonas sp. MBR, Cd–citrate complex was not. In the Cd–citrate media with molar ratio of 1:2 and 1:3, pH increase obtained from the metabolism of excess citrate slightly promoted the biotransformation of Cd–citrate complex, Cd remained in solutions. The presence of Fe3+ and Zn2+ resulted in complete biotransformation of Cd–citrate complex in the 1:1:2 Fe:Cd:citrate and Zn:Cd:citrate and 1:1:1:3 Fe:Zn:Cd:citrate media. Alkaline pH obtained from biotransformation of metal–citrate complexes caused almost complete removal of metals (>98%) through precipitation and co-precipitation. Pseudomonas sp. MBR potentially could be used to treat wastewater containing mixed citrate complexes of Fe(III), Zn and Cd.

A Solid‐State Combustion Method towards Metallic Cu–ZnO Catalyst without Further Reduction and its Application to Low‐Temperature Methanol Synthesis

AbstractA series of Cu–ZnO catalysts were prepared by using a solid‐state combustion method with metal nitrates and citric acid. This method was simple, waste water free, and did not require a reduction step. If the precursors were burnt in an argon atmosphere, H2 and CH4 were emitted in the decomposition of metal citrate complexes and acted as reducing agents to yield metallic Cu from Cu2+ in the chelated compounds. Analysis of XRD patterns revealed that the precursors burnt at 523 K for 1 h in the argon atmosphere were converted into pure Cu species. TPR analysis of the burnt catalysts without further reduction illustrated that almost no hydrogen was consumed. However, a part of amorphous carbon and carboxylates were left in the burnt catalysts. Compared with formerly reported Cu–ZnO catalysts prepared by the sol–gel combustion method, the catalysts prepared by the solid‐state combustion method had higher activity and methanol selectivity.

The Chemical and Electrochemical Activity of Citrate on Pt Electrodes

Citrate is widely used as a complexing agent in electrolytes for deposition of metals and alloys. While the chemistry of metal-citrate complexes is well known, the electrochemical behavior of the citrate ion, particularly on the cathode, was given little attention, although the participation of citrate in the cathodic processes could influence the mechanism of metal deposition and the stability of the plating bath and the properties of the deposits. In the present work, the behavior of on Pt cathodes is investigated by the methods of cyclic voltammetry, anodic stripping voltammetry, HR-XPS and ToF-SIMS. Blocking the Pt electrode surface in contact with solutions is shown by the methods of stripping voltammetry and HR-XPS, the composition of the blocking film being affected by the electrolysis potential. ToF-SIMS investigations show the presence on the cathode surface of species having a high molecular weight, following electrolysis of the solutions containing sodium citrate. The data obtained allow us to suggest a scenario of formation of a film on the electrode surface. Specific adsorption of citrate anions and catalytic transformation of citrate accompanied by decarboxylation and electron transfer to the electrode surface followed by further reduction of the adsorbed species has been observed.

R161, K452 and R460 residues are vital for metal–citrate complex transport in CitSc from Streptomyces coelicolor

Recent discoveries have been made that demonstrate Gram-positive bacteria can transport metal-citrate complexes through the CitMHS family of proteins in symport with H(+) ions. The CitMHS family of transporters investigated to date have the ability to selectively transport only certain metal-citrate complexes. Despite sharing amino acid sequence similarity as high as 73%; predicting what complexes are transported remains difficult. The iron-citrate transporter from Streptomyces coelicolor has been mutated at three postulated critical sites (R161, K452 and R460) based on activity modeling against the LacY permease. All three mutants eliminate or greatly reduce uptake of metal-citrate complexes tested. The implications of this are discussed.

Electrospray ionisation with selected reaction monitoring for the determination of Mn‐citrate, Fe‐citrate, Cu‐citrate and Zn‐citrate

Citrate complexes of Mn and Fe, and potentially those of Cu and Zn, are considered as important low molecular mass species in human serum and cerebrospinal fluid (CSF). For example, Mn is supposed to enter the brain under excess exposure as Mn-citrate leading to neurotoxic effects. Mn-citrate has been characterised in human CSF using chromatography and electrophoresis online with inductively coupled plasma mass spectrometry, but not yet with molecular mass spectrometry. Therefore, this study explores the potential of electrospray ionisation (ESI) with selected reaction monitoring (SRM) for the detection of metal-citrate complexes, in particular Mn-citrate. The collision-induced dissociation of precursor ions with various metal:citrate stoichiometries was studied for Mn-citrate, Fe-citrate, Cu-citrate and Zn-citrate. High selectivity was achieved for Mn(II)-citrate even in respect to Fe(III)-citrate which forms isobaric precursor ions. The limit of detection for Mn-citrate was estimated to be around 250 microg L(-1) (referring to the total Mn content in the standard) using flow injection. The sensitivity was sufficient for the determination of Mn-citrate in standard solutions and in an extract of an Mn-citrate-containing supplement. An improved ESI source design is expected to reduce the limits of detection significantly. The developed ESI-SRM method has the potential to provide complementary data for the quality control of current separation methods for metal citrates using element-selective detection, with application to biomedical samples and further matrices.