Thin-Layer Chromatography Method for the Investigations of Re(VII), Mo(VI)

Abstract

The benavicur of Re(VII), Mo(VI) and V(V) ions was studied chromatographically in aliphatic alcohol -HC1 systems on Al ₂O₃ as an adsorbent. Changes in the chromatographic process with the changes of the kind and composition of mobile phase were analysed.

It was also attempted to describe theoretically the results of chromatograpnic separation by using the thermodynamic theory of adsorption from multicomponent solutions.     

Interaction of Molybdenum(VI) Oxyanions with +2 Metal Cations

The association of molybdenum(VI) oxyanions with metal cations was investigated in solutions of low ionic strength, such as those prevailing in most natural waters. Potentiometric titrations were carried out for the systems containing molybdenum(VI) anions and divalent metal cations (M = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb). This selection includes the major cations and some other cations of high environmental relevance. The interaction of iron(III) with Mo(VI) anions was also studied. At neutral and basic pH values and for those systems where the solubility of the molybdate salt is high enough, ionic species pairs such as [M(MoO₄)] predominate. At acidic pH values, [M(HMoO₄)]⁺ and [M(Mo₇O₂₄)]^4– are formed, the latter species are only relevant for total molybdenum concentrations higher than 1 mmol·L^?1. These results provide the basis for molybdenum speciation in natural aquatic systems, on which the environmental fate, bioavailability and toxicity of the element depend.     

Micro-determination of As(V), V(V), Mo(VI), W(VI) in the presence of Cu(II), Ni(II) and Zn(II)

A rapid procedure is described for the separation and determination of 0.025 mg to 1.0 mg quantities of As(V), V(V), Mo(VI) and W(VI) from small quantities of Cu(II), Ni(II), and Zn(II) using silica gel as the selective sorbent for the cations. The individual anionic components, which remain in the supernatant solution after separation from the cations, are determined by colorimetric methods. The complete recovery of As(V) in supernatant solution has also been tested radiometrically using⁷⁶As as the radioactive indicator. The sorbed cations after extraction with dilute hydrochloric acid are determined by EDTA titrations.     

Reactions between technetium(VII) and some hydrazones and the spectrofluorimetric determination of technetium(VII) with 2,2′-dipyridylketone hydrazone

The reactions between pertechnetate and five hydrazones are described. Of these, the technetium(VII)/2,2′-dipyridylketone hydrazone system was found to be most sensitive, and is studied in detail. Spectrofluorimetric procedures for the determination of technetium(VII) over the range 0.01–12 mg l^?1 are reported. The reaction proceeds most favourably under acidic conditions (1.4 M hydrochloric acid). For 1 mg l^?1 technetium(VII), 100 mg l^?1 levels of U(VI), Re(VII), Mo(VI) or W(VI) do not interfere when the reaction proceeds at room temperature. Sensitivity improves at higher temperatures.     

Adsorption Behavior of U(VI) and Re(VII) on Iron Sulfide Nanoparticles Modified with Titanate Nanotubes: Mechanism and Performance Insights

A novel nanocomposite (TNTs-FeS) was developed by anchoring ferrous sulfide (FeS) nanoparticles immobilized on titanate nanotubes (TNTs) by hydrothermal method to remove U(VI) and Re(VII) from aqueous solution, and the removal mechanism and efficiency were examined. The experimental results showed that the TNTs can effectively improve the dispersibility and stability of FeS. The environmental conditions, including initial solution pH, initial concentration, equilibrium time, and dosage, played an important role in the remediation process, which can affect the immobilization efficiency significantly. The maximum quantity removal of U(VI) and Re(VII) was 291.67 and 226.23 mg/g at pH of 6.0 and 12.0. The adsorption kinetics and the equilibrium isotherms of U(VI) and Re(VII) all fitted well with the pseudo-second-order model (R²>0.99) and the Freundlich model (R²>0.99). The main mechanism of removal by TNTs-FeS was electrostatic attraction, chemical reduction, and surface complexation. Thus, TNTs-FeS composites exhibited a high potential to remove U(VI) and Re(VII) heavy metal ions from the surface and groundwater.     

Sensitive Differential Pulse Polarographic Determination of Molybdenum Using The New Catalytic System Mo(VI)‐Phenantroline‐Chlorate

It was found that in acidic chloride media the complex of Mo(VI) with 1,10‐phenantroline induces catalytic reduction of KClO₃. This catalytic effect can be utilized for sensitive differential pulse polarographic determination of Mo(VI) with a low detection limit of 2.9×10^?11 M (2.8 ng/L). The optimal Mo(VI) response was obtained at pH 2.8, in the presence of (6–12)×10^?5 M 1,10‐phenantroline and 2×10^?2 M KClO₃. The sensitivity was 1.73 nA/nM and the catalytic response was linear up to 7.5×10^?7 M Mo (VI). The interferences from inorganic ions and surface‐active substances were investigated. The results of the determination of Mo(VI) in CRM water sample showed good reproducibility (R.S.D. for standard solution is below 1.2% and for water samples is 8.9%) and accuracy of the elaborated catalytic polarographic method.     

Chelating behavior of macroreticular hydroxamic acid resin towards molybdenum(VI), tungsten(VI), uranium(VI) and vanadium(V)

Summary The properties and behaviour of the hydroxamic acid resin have been studied and shown to be an highly selective resin for molybdenum(VI), tungsten(VI), uranium(VI) and vanadium(V) ions. The stability constants of these metal ion complexes with the resin have been determined. The sorption and desorption characteristics of these metal ions on this resin and the methods for the separation of these metal ions from each other on a short column of such resin were also developed.

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Komplexierungsverhalten von makroretikularem Hydroxamsäureharz gegenüber Molybdän(VI), Wolfram(VI), Uran(VI) und Vanadium(V)

Zusammenfassung Die Eigenschaften und das Verhalten von Hydroxamsäureharz wurden untersucht. Das Harz erwies sich als hochselektiv für Mo(VI), W(VI), U(VI) und V(V). Die Stabilitätskonstanten der Komplexe wurden bestimmt, die Sorptions- und Desorptionscharakteristica wurden untersucht und Trennungsmethoden für die genannten Ionen an einer kurzen Säule entwickelt.

     

Liquid-liquid extraction of Mo(VI) and V(V) by Primene JMT

The extraction equilibrium of pentavalent vanadium and hexavalent molybdenum with a benzene solution of primary amine Primene JMT sulphate has been investigated. The comparison of the extraction of aqueous solutions containing the salts of the elements and the solutions containing the mixture of Mo(VI) and V(V) was carried out. The attention was directed to the pH 2–6 region in which the heptamolybdates and decavanadates in prevail aqueous phase and to the region ≈1M H₂SO₄ which was suitable for the extraction separation of Mo(VI). The mechanism of extraction is discussed.     

A Fluorescence Quenching Method for the Determination of Chromium(VI) with L-Tyrosine

Abstract

A fluorescence quenching method for the determination of Cr(VI) in aqueous solution is described. The fluorescence intensity of the system is linear ever the range 5×10^?6 - 1.0×10^?4 M Cr(VI). The method has been applied to the determination of Cr(VI) In cast iron and waste water.     

Construction of a new solid-state U(VI) ion-selective electrode based on polypyrrole conducting polymer

In this study, a potentiometric sensor based on a pencil graphite electrode (PGE) coated with polypyrrole doped with uranyl zinc acetate (termed PGE/PPy/U) have been prepared for potentiometric determination of uranyl in aqueous solutions. Electropolymerization reaction for preparing of U(VI) sensor electrode was carried via applying a constant current of 1.0 mA on PGA working electrode in a solution containing 8.0 mM pyrrole and 0.8 mM ZnUO₂(CH₃COO)₄ salt. The constructed electrode displayed a linear and near Nernstian response (22.60 ± 0.40 mV/decade) to U(VI) ions in the concentration range of 1.0 × 10^?6–1.0 × 10^?2 M. A detection limit of 6.30 × 10^?7 M and a fast response time (≤12 s) was observed during measurements. The working pH range of the electrode was 4.0–8.0 and lifetime of the sensor was at least 60 days. The electrode revealed good selectivity with respect to many cations including alkali, alkaline earth, transition and heavy metal ions. The introduced uranyl electrode was used for measurement of U(VI) ion in real samples without any serious inferences from other ions.     

LIX 84 as an extractant for throium(IV), uranium(VI) and molybdenum(VI)

The extraction order of Th(IV), U(VI) and Mo(VI) based on pH_0.5 values is Mo(VI)>U(VI)>Th(IV). Quantitative extraction has been observed for U(VI) by mixture of 10% (v/v) LIX 84 and 0.1M dibenzoylmethane at pH 4.2 and by mixture of 10% LIX 84 and 0.05M HTTA in the pH range 5.5–7.3 and for Mo(VI) by 10% LIX 84 from chloride media at pH 1.5. The order of extraction of Mo(VI) from 1N acid solutions is HCl>H₂SO₄>HNO₃>HClO₄ and extraction decreases very rapidly with increase in the concentration of HCl as compared to that from H₂SO₄, HNO₃ and HClO₄ acid solutions. The diluents C₆H₆, CCl₄ and CHCl₂ are found to be superior ton-butyl alcohol and isoamyl alcohol for extraction of Mo(VI). Influence of concentration of different anions on the extraction of U(VI) and Mo(VI) has been studied. Very little extraction has been observed in case of Th(IV) by LIX 84 or its mixtures with other chelating extractants or neutral donors.     

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.     

Removal, preconcentration and determination of Mo(VI) from water and wastewater samples using maghemite nanoparticles

Removal and recovery of Mo(VI) from aqueous solutions were investigated using maghemite (γ-Fe₂O₃) nanoparticles. Combination of nanoparticle adsorption and magnetic separation was used to the removal and recovery of Mo(VI) from water and wastewater solutions. The nanoscale maghemite with mean diameter of 50 nm was synthesized by reduction coprecipitation method followed by aeration oxidation. Various factors influencing the adsorption of Mo(VI), e.g. pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within <10 min and was independent of initial concentration of Mo(VI). Studies were performed at different pH values to find out the pH at which maximum adsorption occurred. The maximum adsorption occurred at pHs between 4.0 and 6.0. The Langmuir adsorption capacity (q_max) was found to be 33.4 mg Mo(VI)/g of the adsorbent. The results showed that nanoparticle (γ-Fe₂O₃) is suitable for the removal of Mo(VI), as molybdate, from water and wastewater samples. The adsorbed Mo(VI) was then desorbed and determined spectrophotometrically using bromopyrogallol red as a complexation reagent. This allows the determination of Mo(VI) in the range 1.0–86.0 ng mL⁻¹.     

Determination of uranium(VI) in sea water by cathodic stripping voltammetry of complexes with catechol

Polarographic (d.c.) measurements showed that complex ions of uranium(VI) with catechol adsorb on the dropping mercury electrode. This effect is used to determine uranium(VI) directly in sea water. Optimal conditions include pH 6.8, 2 × 10^?3 M catechol, and a collection potential between ?0.1 and ?0.4 V (vs. Ag/AgCl) at a hanging mercury drop electrode. The cathodic scan is made with the linear-scan or differential-pulse mode (d.p.c.s.v.). The detection limit with the d.p.c.s.v, mode is 3 × 10^?10 M after a collection period of 2.5 min. Between pH 6 and 8, the peak height increases with pH and with catechol concentration up to 5 × 10^?3 M. There is linear relationship between the collection time and the measured peak height until the drop surface becomes saturated. With a collection period of 3 min, the reduction current increases linearly with the metal concentration up to about 5 × 10^?3 M U(VI). The maximum adsorption capacity of the mercury drop is 4.4 × 10^?10 mol cm²; each complex ion then occupies 0.38 nm², equivalent to the size of about one catechol molecule. Interference by high concentrations of Fe(III) is overcome by selectively adsorbing U(VI) at a collection potential near the reduction potential of Fe(III). Organic surfactants reduce the peak height for uranium by up to 75% at unnaturally high concentrations only (4 mg l^?1 Triton X-100). Competition by high concentrations of Cu(II) for space on the surface of the drop is eliminated by addition of EDTA.     

Adsorption of metal anions of vanadium(V) and chromium(VI) on Zr(IV)-impregnated collagen fiber

The metal anions of vanadium (V) and chromium (VI) in aqueous solution can be effectively adsorbed by Zr(IV)-impregnated collagen fiber (ZrICF). The maximum adsorption capacity of V(V) takes place within the pH range of 5.0 to 8.0, while that of Cr(VI) is within the pH range of 6.0 to 9.0. When the initial concentration of metal ions was 2.00 mmol L⁻¹ and the temperature was 303 K, the adsorption capacity of V(V) on Zr-ICF was 1.92 mmol g⁻¹ at pH 5.0, and the adsorption capacity of Cr(VI) was 0.53 mmol g⁻¹ at pH 7.0. As temperature increased, the adsorption capacity of V(V) increased, while that of Cr(VI) was almost unchanged. The adsorption isotherms of the anionic species of V(V) and Cr(VI) can be fit by the Langmuir equation. The adsorption rate of V(V) follows the pseudo-first-order rate model, while the adsorption rate of Cr(VI) follows the pseudo-second-order rate model. Furthermore, ZrICF shows high adsorption selectivity to V(V) in the mixture solution of V(V) and Cr(VI). Practical applications of ZrICF could be expected in consideration of its performance in adsorption of V(V) and Cr(VI).     

The adsorption behaviour of99Mo(VI),238U(VI),95Zr(IV) and95Nb(V) on alumina

The distribution of Mo(VI) and the interfering radiocontaminants U(VI), Zr(IV) and Nb(V) have been investigated between chromatographic alumina and aqueous hydrochloric acid solutions of concentrations ranging from 0.5M to 11M. At low acidities (less than 1M HCl) the distribution coefficients increase with the decrease of acid concentration, while in the region of 2–4M they increase with the increase of the acid concentration. Above 4M HCl, the increase inK _D continues with the acid concentration for both Zr(IV) and Nb(V), but constant values are reached for U(VI) and Mo(VI).     

A solid state Cr(VI) ion-selective electrode based on polypyrrole

We report on a graphite electrode onto which polypyrrole was electrodeposited and then doped with chromate ion. This electrode can serve as a Cr(VI)-selective solid-state electrode. Electropolymerization of pyrrole was performed potentiostatically at 0.80?V (vs. SCE) using battery graphite as the working electrode in a solution containing 0.10?M of pyrrole and 20?mM of chromate. A platinum wire was used as an auxiliary electrode. The new electrode displays high selectivity, a very wide dynamic range, a sufficiently fast response time and a good shelf lifetime. It shows a linear Nernstian response over 1.0?×?10^?6 to 1.0?×?10^?1?M concentration range (with a slope of 26.55?±?0.20?mV per log of concentration). The detection limit is 0.5?μM, and the pH optimum is 7.0.

Simultaneous Determination of Antimony(III) and Molybdenum(VI) by Adsorptive Stripping Voltammetry Using Quercetin as Complexing Agent

A sensitive and selective voltammetric method for simultaneous determination of Sb(III) and Mo(VI) using Quercetin (Q) as complexing agent is described. Optimal conditions were found to be: pH 3.7, C_Q=6.0 µmol L^?1 and E_acc=?0.10 V. The LOD (3σ) for Sb(III) are 0.076 and 0.040 µg L^?1, whereas for Mo(VI) are 0.086 and 0.048 µg L^?1 with t_acc of 60 and 120 s, respectively. The method was validated using synthetic sea water (ASTM D665) and was applied to the determination of Sb(III) and Mo(VI) in natural waters with satisfactory results.     

Dimerization of electrogenerated Mo(V) in sulphuric acid solutions

The electrochemical behaviour of molybdenum(VI) in sulphuric acid solutions was investigated by cyclic voltammetry. In the reduction of Mo(VI) to Mo(III) a dimerization reaction of Mo(V) is involved; the rate constant for the reaction was estimated to be 2.79×10² M⁻¹ s⁻¹ and the activation energy was ca. 35 kJ mol⁻¹ in 0.1 M H₂O₄. Oxidation of the monomer and dimer Mo(V) species take place at −0.31 and +0.18 V (vs. SCE), respectively.     

Re(VII) extraction and separation from Mo(VI) by levextrel resins containing trialkyl amine

A synthetic method of novel trialkyl amine (N235, R₃N, R = C₈–C₁₀) Levextrel resin was described in this paper. The extraction behavior of rhenium(VII) and molybdenum(VI) with this N235 Levextrel resin has been studied. The mechanism of extraction of Re(VII) with the N235 Levextrel resin has been discussed briefly through equi-molar series method and the conventional slope analysis method. The optimal conditions of extraction and separation Mo(VI) and Re(VII) with the N235 Levextrel resin were determined. Also, its excellent extraction characteristics for Re(VII) were confirmed by extraction and stripping tests in a analog liquid solution containing Mo(VI) and Re(VII).