Fluoride Complexes Research Articles

On the Ratio of Cathodic and Anodic Processes during Electroreduction-Electrooxidation of Hafnium in Molten Salts

Investigation of hafnium cathodic and anodic processes in chloride melts containing HfCl4 revealed that two-hafnium electroreduction processes are corresponded two electrooxidation processes. The only difference between these processes was the presence of salt passivation under certain dissolution conditions. In chloride-fluoride melts containing K2HfF6 the number of cathodic and anodic processes can be different due to the amount of hafnium ions passing into the melt during anodic dissolution exceeding the amount of fluorine anions necessary to bind them into fluoride complexes. Based on the experimental data it was found that the conclusion about the mirror reflection of cathodic and anodic processes is invalid in the case of a heteroligand composition of melts. It was determined that the dissolution in the NaCl-KCl-K2HfF6 (10 wt%) melt at the anodic current density of >0.02 А∙cm−2 was accompanied by the formation of Hf(IV) fluoride complexes and Hf(II) chloride complexes. It was shown that the appearance of hafnium complexes with different valence during anodic process in the NaCl-KCl-K2HfF6 (10 wt%) melt is a highly undesirable phenomenon, which leads to the formation of metallic film on the surface of the melt decreasing the current efficiency for coating deposition.

Tuning Corrosion Properties of the Bio-Inspired AZ-Series Mg Alloys Using Electrochemical Surface Treatment under Varying Experimental Regimes

Plasma electrolytic oxidation (PEO) is a preferable process applied to optimize the corrosion and wear properties of metals and their alloys, particularly magnesium (Mg) alloys used in highly demanded medical and aerospace applications. In this project, AZ series alloys (AZ31, AZ61, AZ91), which are the major commercial magnesium alloys, were coated using the PEO process under varying experimental conditions involving electrolyte with Si based ionic chemical networks together with hydroxyl and fluoride functionalities. Surface analysis was carried out using scanning electron microscopy (SEM). Data were further simulated and analyzed using imageJ software. SEM results showed that, increasing the concentration of Al as in AZ91 and AZ61, dendrites-dominated the microstructure at shorter processing times; a cratered-dendritic matrix was obtained at longer processing time. From the composition analysis, fluoride complex peaks were obtained for the higher Al-content alloy (AZ91), due to the localized intensive discharges made regular by the stable β-phases within the Mg matrix. Corrosion analysis was carried out using potentiodynamic polarization. The compact structure, higher growth rate, and stable chemical phases of MgF2 contributed to the highest hardness values ~1271.2 HV and corrosion potential ~−0.18 V for the AZ91 alloy.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

An important problem concerning rare earth metals and molten salts is the reprocessing of nuclear fuel, since lanthanides are always present in spent nuclear fuel. According to the technology being developed for pyroelectrochemical processing of nuclear waste spent fuel is converted into molten salts by anodic dissolution, followed by electrochemical extraction of actinides from lanthanides.Thus a knowledge of the electrochemistry and thermodynamics of lanthanide compounds in molten salt systems is very useful for the understanding the recycling of spent nuclear fuel.The electroreduction of YbCl3 in alkali chloride melts (NaCl-KCl, KCl, CsCl) was studied in the temperature range 973-1173 K by different electrochemical methods. The diffusion coefficients (D) for Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. Decreasing values of D were obtained when the cation in the second coordination sphere changed from Na to Cs. It was shown that such changes are due to the decreasing of counter polarizing effect of cations with increasing cationic radius.The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s approach. The following row of the standard rate constants of charge transfer has been experimentally determined: k s (KCl) < k s (CsCl) < k s (NaCl-KCl).The formal redox potentials E* Yb(III)/Yb(II were obtained in alkali chlorides melts from the linear sweep voltammetry data. From the values of the formal redox potentials were calculated the Gibbs energies and equilibrium constants for the reaction:YbCl2(sol.) +1/2 Cl2(g.) « YbCl3(sol.) (1)It was determined the increasing of the formal entropy for the reaction (1) in transition from NaCl-KCl to CsCl melt that associated with a greater degree of ordering of the reaction products due to the complex formation.Influence of fluoride ions (NaF) on the electrochemical behavior of the Yb(III)/Yb(II) redox couple in an equimolar NaCl-KCl melt was studied. It was determined а decrease of diffusion coefficients and standard rate constants, as well as a shift of the formal redox potentials to the negative region.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of ytterbium in NaCl-KCl, KCl and CsCl melts was studied in the temperature range 973-1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E* Yb(III)/Yb(II) were obtained in alkali chlorides melts from the cyclic voltammetry data. The influence of fluoride ions on the standard rate constants in the NaCl-KCl melt was investigated.

Use of zinc oxide nanoparticles for detection of fluoride in toothpaste gel

This study aimed to investigate the metal-binding effect of fluoride, contained in different commercial toothpaste gels; the study aimed to determine if the toothpastes contained excessive concentrations of fluoride, which result in white spot lesions. A spectrophotometric method that used spectrophotometric reagents, including zinc oxide nanoparticles and iron chloride, was used to determine fluoride distribution; the analysis was based on the selective attack of fluoride ions on metals. Fluoride concentrations between 0 and 1450 ppm were analyzed. Although the iron–fluoride complex was a more sensitive reagent, the zinc–fluoride complex could serve as a suitable alternative to it for fluoride analysis, partly because the method was less time consuming and more stable. The detection and quantification limits obtained from the linear calibration curves of the zinc–fluoride complexes, in deionized water, were 0.191:1 and 0.579:1 w/w ZnO, respectively. A model calibration curve was suggested to detect the unknown products of fluoride degradation. Dentists could use a fluoride treatment similar to the protocol used in this study, to prevent potential enamel demineralization, and exclude physical cavity preparation and restoration.

Multistage leaching of rare earth elements from primary source: a sustainable approach to avoid fluorine contamination by roasting with aluminum hydroxide

ABSTRACT Bastnaesite ore (primary source), with a formula of REE (CO3) F, contains light rare earth type of cerium (Ce) and lanthanum (La) rich content along with 8–10% fluorine. A conventional method such as direct acid leaching causes environmental apprehensions such as the evolution of HF gas which causes adverse effects on the environment. Therefore, a novel and sustainable beneficiationmetallurgy process comprised of roasting the ore with the aluminum hydroxide (Al (OH)3) to deactivate fluorine followed by hydrochloric acid leaching and multistage water leaching was proposed. Leaching from roasted ore was achieved with hydrochloric acid and several parameters affecting REE were optimized. The best results were achieved at a pulp density of 10% w/v, the temperature of 45 °C, 4 mol/L of HCl dosage, 6% of hydrogen peroxide, time of 240 min, and agitation of 280 rpm. Consequently, percentage extraction of Ce and La reached 97.80 and 95.07 % respectively with a high purity of REE oxide product at optimum conditions. Multistage leaching was established at optimum conditions and the percentage recovery of REE was found to be ≥ 99.24%. XRD and SEM-EDX analyses confirmed the formation of metal fluoride complexes (MFx) and recovery of REE.

Structural depolymerization of titanium(IV) fluoride: basis for the formation of titanium(IV) fluoride complexes

Structural depolymerization of titanium(IV) fluoride: basis for the formation of titanium(IV) fluoride complexes

Geology, geochemistry, and genesis of REY minerals of the late Cretaceous karst bauxite deposits, Zagros Simply Folded Belt, SW Iran: Constraints on the ore-forming process

The present study focuses on the geochemistry and occurrence of REY (rare earth elements and yttrium)-bearing minerals in the Late Cretaceous karst bauxite deposits in the central part of the Zagros Simply Fold Belt (ZSFB), SW Iran. The ore bodies comprise a series of individual pods and/or contiguous lenses that occur as infills of deep karst cavities, depressions, and fractures within the upper neritic carbonates of the Cenomanian–Turonian Sarvak Formation. Karst bauxites from the ZSFB show, overall, the same mineral components, which consists of boehmite, hematite (commonly occurring as Al-rich), anatase, and kaolinite, with lesser amounts of diaspore, goethite, chamosite, rutile, and zircon. Among minor constituents, single crystals rich in rare earth elements (REEs) occur mainly in the form of authigenic REY fluorocarbonate, phosphate, and oxide minerals (bastnasite, parisite, rhabdophane, churchite and cerianite). Some textural features, such as spheroidal concretions, pisoids with cortexes lacking radial and circular fractures, growth of simple cortex around earlier pisoids, and pelitomorphic matrix suggest the ores are mostly autochthonous in origin. R-mode factor analysis revealed several significant interelemental relationships including: (i) significant and positive weightings for TiO2, Al2O3, Cr2O3, Ni, Zr, Nb, Hf, Ta, W, and Th, and a significant, negative weighting for SiO2 represent a later bauxitization stage involving silica depletion under drier conditions, promoting formation and stability of a range of minerals including detrital minerals and Al and Ti oxyhydroxides which also control, through scavenging, cations of first-row transition metals such as Ni2+ and Cr6+; (ii) Supergene conditions, mainly acidic pH, probably played an efficient role in the formation of secondary REE-rich phosphates and Ga-hydroxide; (iii) similar and meaningful weightings for U and V suggest that the redox environment would be most important in controlling the U and V mineral phases; and (iv) the scandium co-variance with Fe2O3 represents the control exerted by iron oxy-hydroxides on the critical metal Sc. In the ZSFB bauxites, the most frequent authigenic REE-bearing minerals are light REE (LREE) fluorocarbonates of the bastnaesite group that forms a solid solution series between end members parisite [CaCe2(CO3)3F2] and bastnäsite (CeCO3F). The mode of occurrence of bastnäsite-Ce and parisite-Ce suggests that cerium as fluoride and/or carbonate–fluoride complexes were readily leached by acidic downward solutions and finally precipitated on the geochemical barrier of the carbonate bedrock under alkaline and reducing conditions. Rhabdophane [(Ce, La) PO4·H2O] as an LREE phosphate mineral appears in two generations with different chemical compositions, an early one as irregular and/or acicular particles within the cavities and a later one along the margin of a goethite microvein that cuts the pelitomorphic matrix. Cerianite (CeO2) occurs mainly as sub-micrometer to micrometer grains in the porous aggregates of the aphanitic matrix and as microdomains or microveins that coexist with Al-oxyhydroxide and goethite. Cerianite precipitation may occur due to the predominance of acidic/oxidizing conditions and the dissolution of Ce-rich fluorocarbonates in the bauxitic profile, respectively. The only heavy REE (HREE) phosphate mineral within the ZFSB bauxite deposits is churchite[Y(PO4)·2(H2O)] that forms as single euhedral crystals at the core of the sub-spheroidal structures under an acidic condition.

A Fruitful Decade of Organofluorine Chemistry: New Reagents and Reactions

A Fruitful Decade of Organofluorine Chemistry: New Reagents and Reactions

Nb-Zr enrichment in Jabal Al Bayda A-type granites, western Arabian Shield, Saudi Arabia: interplay of magmatic and hydrothermal processes

Al Bayda’s younger granitic pluton located within the western Arabian Shield, Al Madinah area, KSA, has been studied using collaborative techniques. The collected samples were studied petrographically using a polarizing microscope and geochemically using the XRF technique. Four suites of intrusions can be distinguished based on their mineralogical and geochemical characteristics. A muscovitized epidotize hornblende leucocratic altered granite is the earliest intrusion, followed by perthite alkali feldspar granite. Both are intruded by a chessboard-like texture, Arfvedsonite-aegirine nepheline peralkaline granite. These three types of younger granitoid rocks are intruded by pegmatite-aplite sheets. The metasomatically altered epidotized, muscovitized granite formed during a late magmatic phase that was probably followed by successive co-magmatic and hydrothermal alterations in a closed system. The metasomatic alteration produced enrichment in Zr (up to 699 ppm), Nb (up to 67 ppm), and REE (up to 261 ppm) contents. As a result, residual alkalis, fluoride complexes, and iron-rich mixing fluids contribute to these enrichments. The hypersolvus perthite alkali feldspar exhibited post-orogenic A-type geochemical characteristics, whereas the peralkaline exhibited an anorogenic affinity, and both have been generated within plate-related tectonic settings. An A-type signature is probably the result of melting in the lower crust, whereas tectonic mechanisms shifted from post-orogenic to anorogenic due to the Najd fault system. Utilizing Al Bayda granite placer deposit products in the ceramic industry requires removing zircon minerals. The recorded HFSE, Nb, and REE are also recommended for detailed exploration.

Easy Csp2–Csp2 reductive elimination from organoplatinum complexes by electrophilic fluorinating reagents

Electrophilic fluorination of bisaryl-platinum(II) complexes at RT leads to an exceptionally fast Ar–Ar instead of Ar–F reductive elimination. By reacting bisphosphine bisaryl-platinum(II) complex with NFSI, the biaryl product was formed with >90% yield within <30 minutes at RT. Moreover, by experimental and computational studies, the influence of ancillary ligands on the Ar–Ar reductive elimination reaction was investigated by changing their steric and electronic effects. The stability of some platinum fluoride complexes in the presence of water was also investigated.

Asymmetric Azidation under Hydrogen Bonding Phase-Transfer Catalysis: A Combined Experimental and Computational Study.

Asymmetric catalytic azidation has increased in importance to access enantioenriched nitrogen containing molecules, but methods that employ inexpensive sodium azide remain scarce. This encouraged us to undertake a detailed study on the application of hydrogen bonding phase-transfer catalysis (HB-PTC) to enantioselective azidation with sodium azide. So far, this phase-transfer manifold has been applied exclusively to insoluble metal alkali fluorides for carbon–fluorine bond formation. Herein, we disclose the asymmetric ring opening of meso aziridinium electrophiles derived from β-chloroamines with sodium azide in the presence of a chiral bisurea catalyst. The structure of novel hydrogen bonded azide complexes was analyzed computationally, in the solid state by X-ray diffraction, and in solution phase by 1H and 14N/15N NMR spectroscopy. With N-isopropylated BINAM-derived bisurea, end-on binding of azide in a tripodal fashion to all three NH bonds is energetically favorable, an arrangement reminiscent of the corresponding dynamically more rigid trifurcated hydrogen-bonded fluoride complex. Computational analysis informs that the most stable transition state leading to the major enantiomer displays attack from the hydrogen-bonded end of the azide anion. All three H-bonds are retained in the transition state; however, as seen in asymmetric HB-PTC fluorination, the H-bond between the nucleophile and the monodentate urea lengthens most noticeably along the reaction coordinate. Kinetic studies corroborate with the turnover rate limiting event resulting in a chiral ion pair containing an aziridinium cation and a catalyst-bound azide anion, along with catalyst inhibition incurred by accumulation of NaCl. This study demonstrates that HB-PTC can serve as an activation mode for inorganic salts other than metal alkali fluorides for applications in asymmetric synthesis.

Synthesis, crystal structure and thermal properties of Na2Ti(CF3COO)6(CF3COOH)2

The compound Na2Ti(CF3COO)6(CF3COOH)2 was synthesized as colorless crystals, extremely unstable in air, by the reaction of TiCl4 with trifluoroacetic acid and sodium trifluoroacetate. Crystallographic studies have shown that this sodium trifluoroacetatotitanate is the first example of a tetravalent titanium carboxylate [Ti(RCOO)6]2– containing titanium in an octahedral environment of oxygen atoms of carboxylate groups. Thermal decomposition of Na2Ti(CF3COO)6(CF3COOH)2 in an argon atmosphere results in the complex fluoride Na2TiF6.

An experimental investigation of the solubility and speciation of scandium in fluoride-bearing aqueous liquids at temperatures up to 250 °C

The solubility of ScF3 (solid) and the speciation of scandium in fluoride-bearing aqueous solutions with HF concentrations from 0.53 mmol/kg to 645.12 mmol/kg were investigated at temperatures from 100 to 250 °C and vapor-saturated water pressure. The results of the experiments show that ScF2+ and ScF3o are the dominant species in fluoride-bearing solutions at the conditions investigated. The logarithms of the formation constants (log β) for these species have been determined for 100, 150, 200, and 250 °C and show that scandium fluoride complexes are more stable than scandium hydroxide complexes and Sc3+ at these temperatures in acidic aqueous fluids. Whether this is also the case for near-neutral and alkaline conditions remains to be investigated. Modeling of the transport and deposition of scandium using our experimental data provide evidence that fluoride-bearing aqueous fluids can dissolve up to 2.9 ppm scandium at 250 °C, 500 bar, and a pH of 3, which is more than sufficient to form a hydrothermal ore deposit, given that concentrations of several hundred ppm in a deposit are considered economic. This study reports the essential thermodynamic data needed to understand the factors that control the mobilization of scandium in fluoride-bearing hydrothermal systems and determine whether scandium can be concentrated to exploitable levels.

Exploratory Synthesis for Complex Metal Fluorides Using Solid-State Fluorine Sources

We attempted to synthesize complex metal fluorides via reaction between metal and solid-state fluorine sources and succeeded in preparing trirutile-type Li2MoF6 using LiF, the metal Mo, and CuF2. We also found a new phase of Li2MoF6 that is isostructural with trigonal Li2ZrF6 via a combination of solid-state fluorine sources and high-pressure synthesis. The reaction occurs exothermically and involves conversion and addition associated with redox reaction, and CuF2 then functions as both an oxidizing agent and fluorine source. Because the overall reaction proceeds stoichiometrically, the required amount of fluorine can be controlled by the amount of solid-state fluorine agents. The synthesis route was also applicable for the preparation of other known fluorides, Li2MF6 (M = Ti, Zr, and Nb) and β-Li3MF6 (M = Ti and V). The synthetic route using a solid-state fluorine source is suitable for the exploration of novel inorganic complex metal fluorides.

Fluoride and mixed-ligand fluoride complexes of indium(III): synthesis and structure (review)

Fluoride and mixed-ligand fluoride complexes of indium(III): synthesis and structure (review)

Spectrophotometric Determination of Fe(II) and Fe(III) Using 5-(4-Ethylphenyl azo ) 2-Hydroxybenzaldehyde Oxime Reagent

Spectrophotometric Determination of Fe(II) and Fe(III) Using 5-(4-Ethylphenyl azo ) 2-Hydroxybenzaldehyde Oxime Reagent

Crystallographic evidence of synthesized Ni(II) fluoride complex: Solubilization interaction of fluoride complex in anionic micellar media by conductometric and spectroscopic techniques

The X-ray crystallographic and physicochemical investigation of newly synthesized coordination complex of nickel (Trans-difluorobis(N,N-dimethylethane-1,2-diamine-k2N,N')nickel(II)octahydrate [Ni(dmen)2F2].8H2O is encompassed in this manuscript. The synthesized complex was characterized by elemental analysis, FTIR studies, magnetic measurements, electronic absorption measurements, and single-crystal X-ray diffraction analysis. The crystals are monoclinic in the P2(1)/c space group, with a = 8.0271(4) Å, b = 4.4509(8) Å, c = 15.1013(11)Å, α = 90°, β = 113.2340(10)°, γ = 90°. The crystal structure displays O-H⋯F and O-H⋯O hydrogen-bond interactions. Solubilization of [Ni(dmen)2F2].8H2O (NiDC) by anionic surfactant, sodium lauryl sulfate (SLS), in aqueous solutions in the pre-micellar, micellar and post-micellar concentration ranges was accomplished by UV–Visible spectroscopy and electrical conductivity measurements. The thermodynamic parameters of complex-surfactant interaction including standard entropy (ΔSmic), free energy (ΔGmic), and enthalpy (ΔHmic) of micelle formation were evaluated. The disruption of structured water in the near environment of hydrophobic groups of the surfactant was responsible for the increase in critical micelle concentration (CMC) with increasing temperature. The negative values of ΔGmic and ΔHmic indicate that solubilization of complex in micelles was spontaneous, in addition to enthalpy and entropy-driven. UV–Vis spectroscopy revealed the quantitative measure of interaction of the complex with surfactant in terms of partition constant (Kx), the free energy of partition (ΔGpart), binding coefficient (Kbind), and binding free energy (ΔGbind). The presence of surfactant led to a red-shift in UV–Vis spectra of NiDC which indicates their strong interaction. From the outcomes of the study, it is very clear that CMC in pure surfactants was lower than the CMC found with Ni-complex. The NMR study revealed that the complex is resided at the palisade layer by interacting with the functional moieties of hydrophobic chain. This indication well coincides with results of partitioning study by UV–Vis spectroscopy. The complex also has significant antioxidant and hemolytic activity against DPPH and RBCs respectively but it has no cyctotoxicity against 3 T3 cell lines.

Rees and other critical raw materials in Cretaceous Mediterranean-type bauxite: The case of the Sardinian ore (Italy)

Mediterranean-type bauxite deposits in Sardinia formed during the Upper Cretaceous (Cenomanian–Turonian) due to the emergence of the south European margin of the Alpine Tethys in an area affected by monsoonal climate. The deposits were controlled by the structural frame formed in a transpressive tectonic regime and unconformably overlie carbonate rocks of different age and composition, which led to the formation of different bauxite types. In general, in the Sardinian bauxite deposits, boehmite is the main Al-phase, kaolinite is the main Si-rich mineral, and hematite as well as goethite are the Fe-rich phases. Secondary authigenic anatase and detrital rutile control the Ti contents. Eu/Eu* anomalies show that the bauxite types were derived from the Variscan basement. However, there are differences in Al2O3 and SiO2 contents, which suggest there was localised variability in the extent of epigenetic replacement of kaolinite by boehmite. R-mode factor analysis suggests that most critical raw materials (as defined by the devoted European Union working group), such as Sc, Ga, Nb, Hf, Ta, and W, covary with Al2O3 contents. In the Si-poor bauxite, these metals of economic interest are likely controlled by boehmite, whereas in the Si-rich bauxite they are mostly controlled by weathering-resistant minerals. Rare earth element (REE)-rich minerals, including fluorocarbonates and cerianite, are concentrated in the basal, illuvial horizon, especially in the silica-rich bauxite (ΣREE = 1006–2034 ppm). Cerianite formation required Ce oxidation, whereas fluorocarbonate formation involved mobilisation of trivalent REEs and further fluoride complexation. Both REE-rich mineral phases precipitated under alkaline pH conditions near to the carbonate bedrock. Our evaluation of the critical raw materials distribution in the Sardinian bauxite, coupled with the “economic importance” and “supply risk” parameters, indicate the ore contains large amounts of metals characterised by a “supply risk”, such as light and heavy REEs, and metals of “economic importance”, such as V and W. In this way, the Sardinian bauxite deposits could be reconsidered as a potential source of critical raw materials.

Fluoride Ion-Selective Electrode for Organic Solutions.

Fluoride ions are used in battery electrolytes in fluoride shuttle batteries. Since organic solvents are used in battery electrolytes, there is a growing demand to develop appropriate methods for quantifying fluoride ion concentration in organic solvents. In this study, a fluoride ion-selective electrode (ISE) for organic solutions is proposed as an electrode of the second kind. A Ag|AgF electrode was made via the anodization of a silver wire in propylene carbonate (PC) containing dissolved fluoride ions. The resultant electrode exhibits a stable linear response of the open circuit potential to the logarithm of the fluoride ion concentration in PC solutions over a range of 10-4-10-2 mol dm-3. The lower and upper limits of the linear response were interpreted in terms of the solubility and the formation of a silver fluoride complex. The use of this electrode of the second kind is suitable for the analysis of fluoride ions in organic solutions and is a promising concept for the development of ISEs for the detection of ions in organic solutions under highly restrictive conditions.