Liquid-liquid extraction of molybdenum(VI) and uranium(VI) by LIX 622

The order of extraction of Mo(VI) from 1M acid solutions by 5% (v/v) LIX 622 (HL) in benzene is HCl>HNO₃>HClO₄>H₂SO₄, and extraction decreases with increasing concentration of HCl and H₂SO₄, and increases slightly with increasing concentration of HNO₃ and HClO₄. The extracted species is shown to be MoO₂L₂ as established by IR data of organic extracts and the extracted species in the solid form. Extraction is almost quantitative at and above 10% LIX 622, and is found to be independent of [Mo(VI)] in the range of 10^–4 to 10^–3 M. The diluents CCl₄, CHCl₃ and C₆H₆ are found to be superior to solvents of high dielectric constant for extraction of Mo(VI). Extraction of uranium(VI) by 10% (v/v) LIX 622 in benzene was found to increase with increasing equilibrium pH (3.0 to 6.0), and becomes quantitative at pH 5.9. Tributyl phosphate acts as a modifier up to 2% (v/v). Thorium(IV) is almost not extracted by LIX 622 or its mixture. Separation of Mo(VI) and U(VI) is feasible.     

Extraction of U(VI), Zr(IV) and Th(IV) from perchlorate media, by PC-88A

Extraction of U(VI), Zr(IV) and Th(IV) has been investigated from perchlorate media using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) dissolved in toluene. The extraction of U(VI), Zr(IV) and Th(IV) was found to be quantitative in the pH range 1.6 to 3.2, 2.0 to 4.7 and 2.3 to 3.8, respectively, with 3.0^.10^-3, 5.6^.10^-4 and 1.0^.10^-2M PC-88A dissolved in toluene. U(VI) was stripped with 4.0M HCl, Zr(IV) with 2.5M NaF and Th(IV) with 8.0M HCl from the metal loaded organic phase containing PC-88A dissolved in toluene. The probable extracted species have been ascertained by plotting log D vs. log [HR] as UO₂R₂ ^.2HR, ZrR₄ ^.2HR and ThR₄ ^.4HR, respectively. U(VI) was separated from Zr(IV) and Th(IV) and from other associated metals. This method was proved by the determination of U(VI) in some real samples.     

Gas-phase coordination complexes of U(VI)O2(2+), Np(VI)O2(2+), and Pu(VI)O2(2+) with dimethylformamide

Electrospray ionization of actinyl perchlorate solutions in H₂O with 5% by volume of dimethylformamide (DMF) produced the isolatable gas-phase complexes, [An^VIO₂(DMF)₃(H₂O)]²⁺ and [An^VIO₂(DMF)₄]²⁺, where An = U, Np, and Pu. Collision-induced dissociation confirmed the composition of the dipositive coordination complexes, and produced doubly- and singly-charged fragment ions. The fragmentation products reveal differences in underlying chemistries of uranyl, neptunyl, and plutonyl, including the lower stability of Np(VI) and Pu(VI) compared with U(VI).     

Synergistic extraction studies of uranium(VI) and plutonium(VI) with some β-diketones and heterocyclic N-oxides

The equilibrium constants for coordination of methyl substituted pyridine N-oxides with plutonium(VI) thenoyl trifluoroacetonate in chloroform (K_s) follow an order similar to those of the analogous uranium(VI) complexes indicating steric hindrance to bonding in the case of ortho substituted pyridine N-oxides. The extraction constants (k) of Pu(VI) chelates with various β-diketones are found to be only marginally higher than the values for the corresponding uranium(VI) chelates which is in conformity with the close similarity of the ionic radii of PuO ₂ ²⁺ and UO ₂ ²⁺ .     

Extraction and separation of Th(IV) and U(VI) from nitric acid media using PIA-8 and HDEHP

Extraction behavior of Th(IV) and U(VI) has been investigated with bis(2-ethylhexyl) phosphinic acid (PIA-8) and bis(2-ethylhexyl) phosphoric acid (HDEHP) from nitric acid media in toluene. The optimum conditions for extraction of these metals have been established by studying various parameters like acid concentration, pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.3-2.5M HNO₃ by 2.5^.10^-2M HDEHP and in the pH range 0.1-2.5 with 2.3^.10^-2M PIA-8 in toluene. U(VI) was completely extracted in the acidic range of 0.1-2.0M HNO₃ with 2.2^.10^-2M HDEHP and in the pH range of 1.0-3.0 with 2.0^.10^-2M PIA-8 in toluene. The probable extracted species have been ascertained by log D-log c plot as UO₂ R₂ ^.2HR with both the reagents and Th (NO₃)₂R₂ ^.2HR with PIA-8 and Th (NO₃)₃R^.3HR with HDEHP, respectively. Temperature dependence of the extraction equilibrium is examined by the temperature variation method. Separation of U(VI) and Th(IV) was also carried out from commonly associated metals.     

Nitrosyl-pentafluorotellurat(VI)

Nitrosyl pentafluorotellurate(VI) . NO+OTeF₅^? is prepared from NOCl and Hg(OTeF₅)₂. It is ionic NO+OTeF₅^? in the solid state and in acetonitrile solution, in the gaseous state however a covalent molecule ON–OTeF₅.     

Synthesis,structural studies and biological activity of dioxomolybdenum(VI), dioxotungsten(VI), thorium(IV) and dioxouranium(VI) complexes with 2-hydroxy-5-methyl and 2-hydroxy-5-chloroacetophenone benzoylhydrazone

New complexes of MoO₂(VI), WO₂(VI), Th(IV) and UO₂(VI) with aroyl hydrazones have been prepared and characterized by various physicochemical methods. Elemental analysis suggested 1 : 1 metal : ligand stoichiometry for MoO₂(VI), WO₂(VI), and UO₂(VI) complexes whereas 1 : 2 for Th(VI) complexes. The physicochemical studies showed that MoO₂(VI), Th(IV) and UO₂(VI) complexes are octahedral. The electrical conductivity of these complexes lies in the range 1.00 × 10⁻⁷−3.37 × 10⁻¹¹Ω⁻¹ cm⁻¹ at 373 K. The complexes were found to be quite stable and decomposition of the complexes ended with respective metal oxide as a final product. The thermal dehydration and decomposition of these complexes were studied kinetically using both Coats-Redfern and Horowitz-Metzger methods. It was found that the thermal decomposition of the complexes follow first order kinetics. The thermodynamic parameters of the decomposition are also reported. The biological activities of ligands and their metal complexes were tested against various microorganisms.     

Kinetic Determination of Nanogram Amounts of Mo(VI) in Solution

A new inhibitory reaction is proposed and a kinteic method developed for the determination of ultra‐micro amounts of Mo(VI) on the basis of its inhibitory activity in oxidation of trimethylenediamine ‐N,N,N′,N′‐tetraacetic acid (TDTA) by KMnO₄ in the presence of hydrochloric acid. Under optimal conditions the sensitivity of the method is 0.5 ng/cm³. The probable relative error is 2.9–3.5% for the concentration range 7.5–2.0 ng/cm³ of Mo(VI). The effect of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. The selectivity of the method is relatively good. Kinetic equations were proposed for the investigated process. A method has been applied for determination of Mo(VI) in a certain kind of steel.     

Wolfram(VI)-fluorid-pentafluorotellurate(VI): WFn(OTeF5)6-n

Tungsten(VI) Fluoride Pentafluorotellurates(VI): WF_n(OTeF₅)_6-n In WF₆ fluorine can be replaced by F₅TeO groups by means of B(OTeF₅)₃ to form WF_n(OTeF₅)_6-n. Isolation was achieved for WF₅OTeF₅ and cis-WF₄ (OTeF₅)₂. Compounds with n > 2 have been identified by ¹⁹F-nmr spectroscopy. The ligand behaviour of the F₅TeO group is compared to OMe and OPh.     

Synthesis and structure of mononuclear molecular complexes of molybdenum(VI) and tungsten(VI) oxy- and dioxyhalides

Specific features of the synthesis and structure of mononuclear molecular halide oxide complexes of Group VI d ⁰ metals molybdenum(VI) and tungsten(VI) are surveyed. Various methods of synthesis of adducts based on MOX₄ and MO₂X₂ (M = Mo, W; X = F, Cl, Br) are described, such as direct interaction, ligand exchange, and the method of nascent reagents. The principles of formation of a particular geometric isomer are discussed: according to the self-consistency rule, the coordination of a neutral donor ligand L trans to a multiply bonded oxo ligand is preferable to that of acido ligands X⁻ (anions). Rare exceptions are mentioned.     

Extraction of U(VI) by cyanex-272

Extraction of U(VI) from HNO₃, HCl and HClO₄ media using cyanex-272 (bis[2,4,4 trimethyl pentyl] phosphinic acid)/n-dodecane has been carried out. In the case of HNO₃ and HClO₄ media, the distribution ratio (D) value first decreases and then increases, whereas from HCl medium it first decreases and then remains constant with increase in H⁺ ion concentration. At lower acidities, U(VI) was extracted as UO₂(HA₂)₂ by an ion exchange mechanism, whereas at higher acidities as UO₂(NO₃)₂ ^.2(H₂A₂) following a solvation mechanism. The D for U(VI) by cyanex-272, PC-88A and DEHPA at low acidities follows the order cyanex-272 > PC-88A > DEHPA. Also, cyanex-272 was found to extract U(VI) more efficiently than TBP at 2M HNO₃. The effect of diluents on the extraction of U(VI) by cyanex-272 followed the order cyclohexane > n-dodecane > CCl₄ > benzene. The loading of U(VI) into cyanex-272/n-dodecane from 2M HNO₃ has shown that at saturation point, cyanex-272 was 78% loaded. No third phase was observed at the saturation level. The stripping of U(VI) from the loaded organic phase was not possible with water, it was poor with acetic acid and sodium acetate but quantitative with oxalic acid, ammonium carbonate and sodium carbonate.     

Tungsten(VI) and mixed tungsten,molybdenum(VI) complexes of tartaric acid

A number of studies of species formed in the tungsten(VI) oxide-R,R-(+)-tartaric acid-water system have been carried out(^1–3). While various species have been proposed, it is generally accepted that three main ones predominate. Two have tungsten: (+)-tartaric acid [(+)-tartH₄] ratios of 11 and the third has the same ratio of 12. This latter species cannot be that proposed by Avaloset al. ⁽³⁾ since both ligands in their structure would have to be present as unidentates.Recently we have shown⁽⁴⁾ that high resolution¹H and¹³C n.m.r. studies were particularly useful in delineating the complexes formed in aqueous solution in the analogous molybdenum(VI) system. Thus, we turned our attention to the corresponding tungsten(VI) complexes, especially in view of the controversy surrounding the nature of the species formed in aqueous solution with (+)-tartH₄. The results of our studies, presented below, indicate that only a few species are formed, and that these are quite analogous, as might be expected, to the previously described molybdenum(VI) species⁽⁴⁾. In addition we have observed the formation of a mixed dimeric species [MoWO⁴{(+)-tart}₂]^4–, whose structure is akin to the mono-metallic complexes, as well as the well-characterized antimony(III) and arsenic(III) dimers of (+)-tartH₄ ⁽⁵⁾.     

On the synthesis of ammonium xenon(VI) hexafluoromanganate(IV)

The reaction between NH₄MnF₃ and xenon hexafluoride yields ammonium xenon(VI) hexafluoromanganate(IV). The persistance of the NH⁺₄ in the environment of the XeF₆, during the synthesis of the salt, can be attributed to the positive charge because XeF₆ is electrophylic and will oxidize neutral or negatively charged species but not cations. Ammonium xenon(VI) hexafluoromanganate(IV) was characterized by chemical analysis, magnetic susceptibility measurements, thermogravimetric studies and vibrational spectroscopy. The spectroscopic evidence supports the formulation NH⁺₄XeF⁺₅MnF²₆^?.     

Synthesis and ROMP activity of aminophenol-substituted tungsten(VI) and molybdenum(VI) complexes

Tungsten(VI) and molybdenum(VI) complexes [MO(L¹)Cl₂] and [M(X)(L²)Cl₃] (X = O, NPh) with tridentate aminobis(phenolate) ligand L¹ = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) and bidentate aminophenolate ligand L² = 2,4-di-tert-butyl-6-((dimethylamino)methyl)phenolate) were prepared and characterised. These complexes are principally stable in open atmosphere under ambient conditions. When activated with Et₂AlCl, they exhibited high activity in ring-opening metathesis polymerisation (ROMP) of 2-norbornene (NBE) and its derivatives. Especially complexes [M(NPh)(L²)Cl₃], which are easily available from corresponding metal oxides MO₃ by a simple three-step synthesis, were found very efficient ROMP catalysts for NBE (M = Mo, W) and 2-norbornen-5-yl acetate (M = Mo).     

Adsorption of U(VI) on montmorillonite pillared with hydroxy-aluminum

Hydroxy-aluminum pillared Na-montmorillonite(OH–Al-MT) was prepared for studying sorption of U(VI) in the existence of soluble calcium (Ca²⁺), carbonate ion (CO₃^2?) and humic acid. Various characterizations confirm that hydroxy-aluminum was successfully pillared into Na-montmorillonite (Na-MT). The effects of pH, concentration of Ca²⁺ and CO₃^2? as well as HA on the sorption capacity of Na-MT and OH–Al-MT for U(VI) has been investigated by batch experiments. Additionally, the kinetics, isotherms and thermodynamics of adsorption of U(VI) were discussed in detailed. The study indicates that OH–Al-MT can be a potentially promising low-cost adsorbent for removal of U(VI) in wastewaters.     

Neutron activation analysis for chromium(III) and (VI) in lixiviated liquid through a calcined chromium(VI) adsorbed hydrotalcite

Summary Electrophoresis followed by neutron activation analysis was utilized to determine chromium(III) and (VI) in mixed solutions. These solutions proceeded from Cr(VI) adsorbed hydrotalcites heated at 800 °C to partially immobilize Cr in the Mg-Al oxide solid solution. Immobilization was studied by Cr lixiviation with NaCl solutions through the heated hydrotalcites. The results have shown that Cr lixiviated was in the form of CrO₄^2- ions, mainly because some Cr(VI) was not completely reduced to Cr(III) during heating. Chromium lixiviated from HT-Cr sample, heated at 800 °C and γ-irradiated at 1000 kGys, was found, as well, in the form of CrO₄^2- ions. Although γ-irradiation increases Cr immobilization in the solid, it does not reduce completely all CrO₄^2- ions present in the solid and, therefore, some Cr is lixiviated through the solid in the form of CrO₄^2- ion.     

Rapid chemical synthesis of four ferrate(VI) compounds

The preparation of four novel Fe(VI) salts, including PbFeO₄, ZnFeO₄, CdFeO₄ and HgFeO₄ is demonstrated. These Fe(VI) salts were synthesized from a solid phase reaction merely by grinding K₂FeO₄ with M (C₂H₃O₂)₂.nH₂O (M = Pb²⁺, Zn²⁺) or M (NO₃)₂.nH₂O (M = Cd²⁺, Hg²⁺) at room temperature. A rapid and efficient reaction occurred upon grinding the solid reactants to afford high yield ferrate(VI) salts which were characterized by XRD, EDS and FTIR techniques. All of the synthesized ferrates were rather stable and could be stored at room temperature for more than a month with no significant decomposition.     

Protocol for Extraction and Determination of Cr(VI) in Solid Materials with a High Cr(III)/Cr(VI) Ratio Using EDDS as a Leaching Agent for Cr(VI) and a Masking Agent for Cr(III)

A sensitive and selective protocol for the extraction of all forms of Cr(VI) from solid materials followed by determination by catalytic adsorptive stripping voltammetry has been elaborated. Cr(VI) was leached to a solution with 0.2 mol L^?1 (NH₄)₂SO₄/NH₄OH+0.1 mol L^?1 EDDS (pH 9.5) and simultaneously Cr(III) was transferred to a nonactive electrochemical complex with EDDS. The method allows for Cr(VI) determination in solid samples containing even a 1000–2000 fold excess of extractable Cr(III) without its noticeable influence. The effects of several experimental variables such as the composition and pH of the extractant, the time and temperature of the solid sample mixing with the extractant were studied. At the optimized conditions more than 95% of total Cr(VI) recoveries from solid samples were achieved. The validation of the proposed procedure was carried out by Cr(VI) determination in certified reference material CRM 019 Ash, spiked and unspiked with Cr(III), and by comparing the obtained results with those obtained using other common extraction procedures.     

Insoluble Fe(VI) compounds: effects on the super-iron battery

Cathodes composed of Fe(VI) salts are capable of three-electron reduction, and are useful for energetic super-iron batteries. This study investigates the solubility of BaFeO₄ and K₂FeO₄ Fe(VI) salts. Electrolytes are determined in which Fe(VI) has a low aqueous or non-aqueous solubility, or is insoluble. Insoluble Fe(VI) salts have the duel benefits of preventing Fe(VI) solution-phase (i) decomposition and (ii) diffusion to the anode; thereby preventing super-iron battery self-discharge. BaFeO₄ is insoluble in water, and has a solubility of less than 2×10⁻⁴ M in 5 M KOH containing Ba(OH)₂. A BaFeO₄ super-iron battery has a high discharge efficiency when containing an electrolyte of either 12 M KOH, or 6 M KOH saturated in Ba(OH)₂. Fe(VI) cathodes in non-aqueous media may be useful in providing a high-capacity Li or Li-ion super-iron battery. We illustrate that Fe(VI) salts are insoluble and chemically unreactive with a range of organic electrolytes, and can be discharged as cathodes in non-aqueous electrolytes. In acetonitrile containing 1 M LiClO₄, the discharge of an Fe(VI) cathode is demonstrated to a capacity over 394 mAh g⁻¹ K₂FeO₄.