Sodium Tungstate Solution Research Articles

Study on removing Mo from tungstate solution using coprecipitation adsorption method based on novel Mo sulphidation process

A coprecipitation–adsorption method based on a novel Mo sulphidation process is proposed for deep removal of molybdenum from tungstate solutions. First, a new sulphur source, P2S5, is used to provide HS− for the Mo sulphidation process. The MoO42− can be thoroughly converted into MoS42− while tungsten still exists as WO42−. Next, in the sodium tungstate solution, 99·4% of MoS42− is removed with precipitated ‘nascent’ CuS under 6 h reaction at 30°C when the molar ratio Cu/Mo is 3. Similarly, in a commercial (NH4)2WO4 solution, by controlling the molar ratio Cu/Mo at 6, 98·4% of MoS42− is removed after 1 h at 30°C. Subsequently, phosphorus introduced during Mo sulphidation is removed using the magnesium ammonium phosphate method allowing the ammonium paratungstate to reach the GB 10116-88 APT-0 standard.On propose une méthode de co-précipitation et adsorption basée sur un nouveau procédé de sulfuration du Mo pour l’enlèvement en profondeur du molybdène de solutions de tungstate. Premièrement, on utilise une nouvelle source de soufre, P2S5, pour obtenir le HS− pour le procédé de sulfuration du Mo. Le MoO42− est entièrement converti en MoS42− alors que le tungstène existe encore sous la forme de WO42−. Ensuite, 99·4% du MoS42− est enlevé de la solution de tungstate de sodium avec le CuS ‘naissant’ précipité, en moins de 6 heures de réaction à 30°C lorsque le rapport molaire de Cu/Mo est de 3. De façon similaire, 98·4% du MoS42− est enlevé d’une solution commerciale de (NH4)2WO4, après une heure à 30°C, en contrôlant à une valeur de 6 le rapport molaire de Cu/Mo. Subséquemment, le phosphore introduit lors de la sulfuration du Mo est enlevé en utilisant la méthode du phosphate ammoniaco-magnésien, permettant ainsi au paratungstate d’ammonium d’atteindre la norme GB de 10116-88 APT-0.

Electrosynthesis and characterization of zinc tungstate nanoparticles

Zinc tungstate nanoparticles with different sizes are produced through an electrolysis process including a zinc plate anode in sodium tungstate solution. The shape and size of the product was found to be controlled by varying reaction parameters such as electrolysis voltage, stirring rate of electrolyte solution and temperature. The morphological (SEM) characterization analysis was performed on the product and UV–Vis spectrophotometry and FT-IR spectroscopy was utilized to characterize the electrodeposited nanoparticles. Study of the particle size of the product versus the electrolysis voltage showed that, increasing the voltage from 4 to 8V, led to the particle size of zinc tungstate to decrease, but further increasing the voltage from 8 to 12V, the particle size of the produced particles increased. The size and shape of the product was also found to be dependent on the stirring rate and temperature of the electrolyte solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR spectroscopy, and photoluminescence, were used to study the structure as well as composition of the nano-material prepared under optimum conditions.

Synthesis and Characterization Of Bismuth (Iii) Iodotungstate, an Exchanger

A number of samples of Bismuth(III) iodotungstate were prepared by mixing the solutions of Bismuth nitrate, Potassium iodate and Sodium tungstate in varying ratios. One of the samples was selected for study because the ion exchange capacity and the yield of the exchanger was found to be satisfactory. The characterization of the exchanger included the determination of the ion exchange capacity of the exchanger by downflow column method and P H titration method. Both the methods exhibited the ion exchange capacity to be 1.0 meq/g. Further studies included the study of IR, TGA, XRD and Distribution studies. IR of the exchanger indicated the presence of the expected components of the exchanger. Thermal gravimetric analysis has clearly shown the loss of weight of exchanger due to the loss of water molecules & other components at different temperatures. X-Ray diffraction pattern proved the exchanger to be amorphous in nature. Chemical stability of the exchanger was studied in different acid and base solutions of different concentrations. The exchanger was heated at different temperatures and after every heating the ion exchange capacity of the exchanger was determined. This shows the decline in the ion exchange capacity on increasing the temperature. Kd values for different metals ion were determined and found the maximum value for Ni ++. Where as minimum value was found to be for Zn ++ . The results appeared to be satisfactory.

Flower-like and hollow sphere-like WO3 porous nanostructures: Selective synthesis and their photocatalysis property

Nanoflake-based flower-like and hollow microsphere-like hydrated tungsten oxide architectures were selectively synthesized by acidic precipitation of sodium tungstate solution at mild temperature. Several techniques, such as X-ray diffraction, scanning electron microscopy, thermogravimetric-differential thermalgravimetric analysis, transmission electron microscopy, and Brunauer–Emmett–Teller N2 adsorption–desorption analyses, were used to characterize the structure and morphology of the products. The experimental results show that the nanoflake-based flower-like and hollow sphere-like WO3·H2O architectures can be obtained by changing the concentration of sodium tungstate solution. The possible formation process based on the aggregation–recrystallization mechanism is proposed. The corresponding tungsten oxide three-dimensional architectures were obtained after calcination at 450°C. Finally, the obtained WO3 three-dimensional architectures were used as photocatalyst in the experiments. Compared with WO3 microflowers, the as-prepared WO3 hollow microspheres exhibit superior photocatalytic property on photocatalytic decomposition of Rhodamine B due to their hollow porous hierarchical structures.

Investigation of solutions of sodium tungstate and D-(+)-tartaric acid by polarimetry, cryoscopy, and potentiometry

Solutions of sodium tungstate and D-(+)-tartaric acid in aqueous 0.01 N HCl and aqueous 0.1 N NaOH are studied by polarimetry, cryoscopy, and potentiometry methods. Equations describing the dependencies of the corresponding properties on concentrations of the solution components are obtained.

A Light‐Assisted Biomass Fuel Cell for Renewable Electricity Generation from Wastewater

A solar-energy-driven biomass fuel cell for the production of electricity from wastewater using only air and light as additional resources is described. The device consists of a photoelectrochemical cell that contains a nanostructured titanium dioxide or tungsten trioxide film as photoanode and a platinum air electrode as cathode, in separate compartments. The TiO(2) or WO(3) films are fabricated from TiO(2) nanocrystals or from sodium tungstate solutions on top of fluorine-doped tin dioxide. Devices were tested with electrolyte only, synthetic wastewater, or with aqueous glucose solution, under irradiation with sunlight, broad spectral illumination, and monochromatic light. Measured light conversion efficiencies were between 0.007 % and 1.7 %, depending on conditions. The highest efficiency (1.7 %) and power output (0.73 mW cm(-2)) are determined for TiO(2) electrodes under 395 nm illumination. In contrast to TiO(2), the WO(3) electrodes are active under visible light (>440 nm), but the IPCE value is low (2 %). Apart from limited visible-light absorption, the overall performance of the device is limited by the substrate concentration in the water and by transport resistance through the cell.

Direct Hydrothermal Precipitation of Pyrochlore-Type Tungsten Trioxide Hemihydrate from Alkaline Sodium Tungstate Solution

Pyrochlore-type tungsten trioxide hemihydrate (WO3·0.5H2O) powder with the average particle size of 0.5 μm was prepared successfully from the weak alkaline sodium tungstate solution by using organic substances of sucrose or cisbutenedioic acid as the acidification agent. The influences of solution pH and acidification agents on the precipitation process were investigated. The results showed that organic acidification agents such as sucrose and cisbutenedioic acid could improve the precipitation of pyrochlore WO3·0.5H2O greatly from sodium tungstate solution compared with the traditional acidification agent of hydrochloric acid. In addition, the pH value of the hydrothermal system played a critical role in the precipitation process of WO3·0.5H2O, and WO3·0.5H2O precipitation mainly occured in the pH range of 7.0 to 8.5. The precipitation rate of tungsten species in the sodium tungstate solution could reach up to 98 pct under the optimized hydrothermal conditions. This article proposed also the hydrothermal precipitation mechanism of WO3·0.5H2O from the weak alkaline sodium tungstate solution. The novel method reported in this study has a great potential to improve the efficiency of advanced tungsten trioxide-based functional material preparation, as well as for the pollution-reducing and energy-saving tungsten extractive metallurgy.

Study on the Removing of Ammonia Nitrogen in Ammonium Paratungstate Crystal Parent Solution

We realize the goal of removing ammonia nitrogen in ammonium paratungstate crystal parent by using strong sodium tungstate liquid to transform-magnesium salt to take off ammonium thoroughly. The results show that removal rate of ammonia can up to 98.88%, ammonia nitrogen contented in the liquid can down to 0.042g/l. Diluting sodium tungstate solution which has been disposed through the above way can be used to confect liquid before the ion exchange,the liquid with the ion exchange can reach the national effluent standard..

Hexagonal nanorods of tungsten trioxide: Synthesis, structure, electrochemical properties and activity as supporting material in electrocatalysis

Tungsten trioxide, unhydrated with hexagonal structure (h-WO 3), has been prepared by hydrothermal method at a temperature of 180 °C in acidified sodium tungstate solution. Thus prepared h-WO 3 has been characterized by X-ray diffraction (XRD) method and using electrochemical techniques. The morphology has been examined by scanning and transmission electron microscopies (SEM and TEM) and it is consistent with existence of nanorods of 50–70 nm diameter and up to 5 μm length. Cyclic voltammetric characterization of thin films of h-WO 3 nanorods has revealed reversible redox behaviour with charge–discharge cycling corresponding to the reversible lithium intercalation/deintercalation into the crystal lattice of the h-WO 3 nanorods. In propylene carbonate containing LiClO 4, two successive redox processes of hexagonal WO 3 nanorods are observed at the scan rate of 50 mV/s. Such behaviour shall be attributed to the presence of at least two W atoms of different surroundings in the lattice structure of h-WO 3 nanorods. On the other hand, in aqueous LiClO 4 solution, only one redox process is observed at the scan rate of 10 mV/s. The above observations can be explained in terms of differences in the diffusion of ions inside two types of channel cavities existing in the structure of the h-WO 3 nanorods. Moreover, the material can be applied as active support for the catalytic bi-metallic Pt–Ru nanoparticles during electrooxidation of ethanol in acid medium (0.5 mol dm −3 H 2SO 4).

Synthesis of Highly Efficient WO<sub>3</sub>-Doped MCF Catalyst and Its Application in the Selective Oxidation of Cyclopentene to Glutaraldehyde

Synthesis of Highly Efficient WO<sub>3</sub>-Doped MCF Catalyst and Its Application in the Selective Oxidation of Cyclopentene to Glutaraldehyde

Large-scale synthesis of hydrated tungsten oxide 3D architectures by a simple chemical solution route and their gas-sensing properties

Square slab-like and flower-like hydrated tungsten oxide three-dimensional architectures were synthesized by acidic precipitation of sodium tungstate solution at mild temperature. Techniques of X-ray diffraction, scanning electron microscopy, thermogravimetric-differential thermalgravimetric analysis, and transmission electron microscopy were used to characterize the structure and morphology of the products. The experimental results show that the square slab-like and flower-like WO3·H2O architectures can be obtained by addition of a varying amount of 10.0 M HCl solution. The corresponding tungsten oxide three-dimensional architectures were obtained after calcinations at 400 °C. Finally, the obtained WO3 three-dimensional architectures were used as sensitive materials in the experiments. Compared with WO3 square slabs, the as-prepared WO3 microflowers exhibit a good response and reversibility to some organic gases, such as toluene and acetone. The responses to 100 ppm toluene and acetone are 16.7 and 17.4, respectively, at a working temperature of 320 °C. In addition, the sensors also exhibit a good response to ethanol, methanol and n-butanol, which indicates that the flower-like WO3 nanostructures are highly promising for applications of gas sensors.

Solution processing of V 2O 5–WO 3 composite films for enhanced Li-ion intercalation properties

We have employed a simple and novel solution processing method to prepare V 2O 5–WO 3 composite films which demonstrate enhanced Li-ion intercalation properties for applications in lithium-ion batteries or electrochromic displays. This solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). The V 2O 5–WO 3 composite films show enhanced Li-ion intercalation properties compared to pure V 2O 5 and WO 3 films. For example, at a high current density of 1.33 A/g, V 2O 5–WO 3 film with a V 2O 5/WO 3 molar ratio of 10/1 exhibits the highest capacities of 200 mA h/g at the first cycle and 132 mA h/g after 50 cycles, while pure V 2O 5 film delivers discharge capacities of 108 mA h/g at the first cycle and 122 mA h/g after 50 cycles. The enhanced Li-ion intercalation properties of the composite films are ascribed to the reduced crystallinity, the increased porosity and thus the enhanced surface area. Both the cyclic voltammogram and chronopotentiometric curves of the V 2O 5–WO 3 film with a molar ratio of 10:1 are distinctively different from those of pure oxide films, suggesting a different Li-ion intercalation process in the V 2O 5–WO 3 film with the molar ratio of 10:1.

Gas sensing properties of nanocrystalline tungsten oxide synthesized by acid precipitation method

WO 3·2H 2O samples were prepared by acidic precipitation of sodium tungstate solution. Nanocrystalline WO 3 powders were obtained after 350 and 600 °C calcinations. XRD patterns of these samples showed a diffraction profile similar to that of monoclinic WO 3. Calcinations at 600 °C yield WO 3 powders with particle sizes ranging from 60 to170 nm whereas that for 350 °C calcinations are in the range of 30–150 nm. The gas sensing properties of these powders in the form of thick film were investigated with and without platinum doping. Gas response of thick films sintered at two different temperatures was measured at four different operating temperatures. We confirm that the sensor elements made from 600 °C calcined powders doped with platinum sintered at 800 °C are highly responsive and selective to ammonia vapour at 350 °C operating temperature as compared to sensor elements made from commercial powders.

Determination of traces of lead and cadmium using dispersive liquid-liquid microextraction followed by electrothermal atomic absorption spectrometry

A procedure is presented for the determination of very low concentrations of lead and cadmium in water samples. Dispersive liquid-liquid microextraction with ammonium pyrrolidine dithiocarbamate is applied. The aqueous sample solution (adjusted to pH 6) is based on the rapidly mixed with of a small volume of a mixture of carbon tetrachloride and methanol. The two phases are separated by centrifugation, and the metals determined in the organic layer using electrothermal atomic absorption spectrometry. An effective chemical modification during the heating cycle is achieved by impregnating the graphite atomizer with a sodium tungstate solution. This allows well defined absorbance time profiles and low background values to be obtained during the atomization stage. The detection limits for lead and cadmium are 10 and 4 ng L−1, respectively. The procedure is applied to the determination of both analytes in bottled water, tap waters, and seawaters.

Vapor−Liquid Equilibria, Density, Speed of Sound, and Refractive Index of Sodium Tungstate in Water and in Aqueous Solutions of Poly(ethyleneglycol) 6000

Vapor−liquid equilibrium data (water activity, vapor pressure, osmotic coefficient, and activity coefficient) of binary aqueous sodium tungstate solutions and ternary aqueous sodium tungstate−poly(ethyleneglycol) (PEG) solutions were obtained through the isopiestic method at T = 298.15 K. Density and speed of sound measurements were carried out on sodium tungstate in pure water and in aqueous solution of mass fraction 0.02 PEG at T = (288.15 to 308.15) K at atmospheric pressure. From the experimental density and speed of sound data, the apparent molar volume and isentropic compressibility values were evaluated and fitted to the Pitzer equation from which the apparent molar volume and apparent molar isentropic compressibility of the solutions at infinite dilution were calculated at each temperature. The results show a positive transfer volume and isentropic compressibility of sodium tungstate from pure water to an aqueous PEG solution. Furthermore, experimental refractive index data were measured for solutions of sodium tungstate in pure water and in aqueous solution of mass fractions 0.02 and 0.04 PEG as well as those for solutions of PEG in pure water and in aqueous solutions of mass fractions 0.02 and 0.04 sodium tungstate at T = 308.15 K.

Synthesis and characterization of a new cation exchanger-zirconium(IV)iodotungstate: Separation and determination of metal ion contents of synthetic mixtures, pharmaceutical preparations and standard reference material

Samples of zirconium(IV)iodotungstate have been synthesized under varying mixing order and ratios of aqueous solution of potassium iodate, sodium tungstate and zirconium oxychloride at pH 1. A tentative formula was proposed on the basis of chemical composition, FTIR and thermogravimetric studies. The material shows a capacity of 0.68 meq g −1 (for K +) which can be retained up to 200 °C. pH titration data reveal its monofunctional behavior. The distribution coefficient values of metal ions have been determined in various solvent systems. A number of important and analytically difficult quantitative separations of metal ions have been achieved using columns packed with this exchanger. In order to demonstrate practical utility of this material, Hg 2+ and Pb 2+ have been selectively separated and determined in the synthetic mixtures. Assay of Al 3+ and Mg 2+ in commercial tablets and analysis of lead in the standard reference material have also been attempted.

Sodium Tungstate on Some Biochemical Parameters of the Parotid Salivary Gland of Streptozotocin-Induced Diabetic Rats: A Short-Term Study

Several studies have shown the antidiabetic properties of sodium tungstate. In this study, we evaluated some biochemical parameters of the parotid salivary gland of streptozotocin-induced diabetic rats treated with sodium tungstate solution (2 mg/ml). The studied groups were: untreated control (UC), treated control (TC), untreated diabetic (UD), and treated diabetic (TD). After 2 and 6 weeks of treatment, parotid gland was removed and total protein and sialic acid (free and total) concentration and amylase and peroxidase activities were determined. Data were compared by variance analysis and Tukey test (p < 0.05). The sodium tungstate treatment modestly decreased the glycemia of streptozotocin-induced diabetic rats. At week 2 of the study, parotid gland of diabetic rats presented a reduction of total protein concentration (55%) and an increase of amylase (120%) and peroxidase (160%) activities, free (150%) and total (170%) sialic acid concentration. No alteration in the evaluated parameters at week 6 of the study was observed. Sodium tungstate presented no significant effect in parotid gland. Our results suggest that diabetes causes initial modification in biochemical composition of parotid. However, this gland showed a recovery capacity after 6 week of the experimental time. Sodium tungstate has no effect in peripheral tissues, such as salivary glands.

Polypyrrole electropolymerized on aluminum alloy 1100 doped with oxalate and tungstate anions

Polypyrrole films doped with oxalic acid and tungstate were potentiostatically electropolymerized on aluminum alloy 1100. Two statistical factorial designs (fractional and complete) were used to study the influence of the synthesis variables on the film performance against corrosion. Corrosion protection of the polypyrrole films doped with oxalate and tungstate anions (PPy/OXA/W) on the aluminum alloy was evaluated by potentiometric and electrochemical impedance spectroscopy (EIS) measurements in a 0.05 mol L−1 NaCl solution. The results obtained showed that the best performance against corrosion was detected with the PPy/OXA/W film synthesized at 1.0 V, 1.5 C in 0.2 mol L−1 pyrrole, 0.1 mol L−1 oxalic acid and 0.05 mol L−1 sodium tungstate solutions provide a protective effect against corrosion.

TEM INVESTIGATIONS ON CNT-ADDED HEXAGONAL WO3 FILMS FOR SENSING APPLICATIONS

In this work, nanocrystalline hexagonal tungsten oxide was prepared by acidic precipitation from sodium tungstate solution. TEM studies of nanopowders showed that the average size of the hexagonal nanoparticles is 30–50 nm. Novel nanocomposites were prepared by embedding a low amount of gold-decorated carbon nanotubes into the hex- WO 3 matrix. The addition of MWCNTs lowered the temperature range of sensitivity of hex- WO 3 nanocomposites to NO 2 hazardous gas. The sensitivity of hex- WO 3 with Au -decorated MWCNTs to NO 2 is at the temperature range between 25°C and 250°C.

How isopolyanions self-assemble and condense into a 2D tungsten oxide crystal: HRTEM imaging of atomic arrangement in an intermediate new hexagonal phase

The structure and structural evolution of tungstic acid solutions, sols and gels are investigated by high-resolution electron microscopy (HRTEM). Acidification of sodium tungstate solutions, through a proton exchange resin, is achieved in a way that ensures homogeneity in size and shape of intermediate polytungstic species. Gelation is shown to involve polycondensation followed by a self-assembling process of polytungstic building blocks leading to sheets with a layered hexagonal structure. Single layers of this new metastable phase are composed of three-, four- and six-membered rings of WO 6 octahedra located in the same plane. This is the first time that a 2D oxide crystal is isolated and observed by direct atomic resolution. Further ageing and structural evolution leading to single sheets of 2D ReO 3-type structure is directly observed by HRTEM. Based on this atomic level imaging, a model for the formation of the oxide network structure involving a self-assembling process of tritungstic based polymeric chain is proposed. The presence of tritungstic groups and their packing in electrochromic WO 3 films made by different techniques is discussed.