Tungstate Solution Research Articles

Assessment of supercapacitive performance of europium tungstate nanoparticles prepared via hydrothermal method

Nano-sized europium tungstate particles were prepared by reacting europium nitrate hexahydrate and sodium tungstate solutions, and the structures, morphology and optical properties of the product were evaluated by XRD, FT-IR, SEM, and UV–Visible techniques. The Eu2(WO4)3 nanoparticles were evaluated as potential materials for constructing supercapacitor electrodes using the results of cyclic voltammetry, galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy and the electrodes were found to have a specific capacitance (SC) value of 347 F g−1 in a 2.0 M H2SO4 electrolyte at a scan rate of 2 mV s−1. The electrodes were further studied at the GCD at a current density of 1 A g−1, and the SC of the building material was found to be 282 F g−1. The cycling durability of the electrodes was also found to be excellent. After 4000 cycles the SC values of the electrodes were found to reach 129%. The preparation method and the resulting nano-particles, were hence found to be promising for high performance energy applications.

Erratum to: Separation of Molybdenum from Acidic High-Phosphorus Tungsten Solution by Solvent Extraction

Erratum to: Separation of Molybdenum from Acidic High-Phosphorus Tungsten Solution by Solvent Extraction

Optimizing the synthesis procedure and characterization of terbium(III) tungstate nanoparticles as high performance photocatalysts

Through the application of Taguchi robust design (TRD), the operating parameters influencing the synthesis of terbium(III) tungstate nanoparticles via the chemical precipitation reaction were optimized. The overall reaction involved the direct addition of different aqueous terbium(III) solutions to those of tungstate ion solution, and the statistical approach was used to optimize the effects of the operating parameters on the size of the prepared terbium(III) tungstate particles. To this end, analysis of variance (ANOVA) evaluations were performed to evaluate the importance of the different variables including tungstate and terbium ion concentrations, the flow rate at which the cation was added to the tungstate solution (Fc) and the reaction temperature. After optimizing the synthesis procedure, terbium(III) tungstate nanoparticles were prepared under the optimal conditions, and their morphology and chemical composition were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR spectroscopy, and UV–Vis spectrometry. The optimal product was also evaluated as a photocatalyst in the UV-induced catalytic degradation of methyl orange (MO), and was found to possess an excellent activity for catalyzing this reaction, which can be regarded as an indication for its photocatalytic potentials for other similar reactions.

Preparation and electrochromism of pyrochlore-type tungsten oxide film

Pyrochlore-type WO3 powder was synthesized via hydrothermal method using aqueous sodium tungstate solution and oxalic acid as raw materials. The as-prepared powder was made into a soliquoid, from which films were made by dip coating process with indium–tin oxide (ITO). The obtained films were characterized by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), chronoamperometry (CA) and ultraviolet–visible (UV–Vis) absorption. Results show that the crystal of the pyrochlore-type WO3 powder is perfect. When the calcination temperature rises from room temperature to 500 °C, the pyrochlore-type structure first becomes deformed, then it is destroyed and turns into amorphous phase, finally it will completely convert to WO3 with a monoclinic structure. Electrochemical and optical tests demonstrate that the film calcined at 300 °C exhibits the best electrochromic performance and has a coloration efficiency of up to 68.5 cm2·C−1 at 884 nm.

Separation of Molybdenum from Acidic High-Phosphorus Tungsten Solution by Solvent Extraction

A solvent-extraction process for deep separation of molybdenum from an acidic high-phosphate tungsten solution was developed using tributyl phosphate (TBP) as the extractant and hydrogen peroxide (H2O2) as a complexing agent. The common aqueous complexes of tungsten and molybdenum (PMoxW12−xO40 3−, x = 0–12) are depolymerized to {PO4[Mo(O)2(O–O)]4}3− and {PO4[W(O)2(O–O)]4}3− by H2O2. The former can be preferentially extracted by TBP. The extractant concentration, phase contact time, H2O2 dosage, and H2SO4 concentration were optimized. By employing 80% by volume TBP, O:A = 1:1, 1.0 mol/L H2SO4, 1.0 mol/L H3PO4, a contact time of 2 min, and a molar ratio of H2O2/(W + Mo) equal to 1.5, 60.2% molybdenum was extracted in a single stage, while limiting tungsten co-extraction to 3.2%. An extraction isotherm indicated that the raffinate could be reduced to <0.1 g/L Mo in six stages of continuous counter-current extraction.

Facile and Efficient Removal of Tungsten Anions Using Lysine-Promoted Precipitation for Recycling High-Purity Tungsten

We present a facile method for tungsten ion removal using lysine for the development of an environmentally friendly and sustainable recycling technique. Lysine addition to the tungsten solution achieved 100% tungsten removal within 5 min, as a white lysine–tungsten precipitate. Electrospray ionization mass spectrometry analyses of the tungsten and lysine mixed solutions showed that lysine promoted dehydration condensation reactions of anionic tungsten species such as HWO4– and W6O192– through the electrostatic interactions between positively charged lysine and negatively charged tungsten ions. Calcination of the lysine–tungsten precipitate produced tungsten oxide powder of high purity (99.6%) because the lysine is completely decomposed. This facile and useful metal removal method can be used for polyoxometalates of other metals such as molybdenum, tantalum, and niobium.

FTIR-SPECTROSCOPIC INVESTIGATION OF SODIUM TUNGSTATE AND SODIUM MOLYBDATE SOLUTIONS IN WIDE RANGE OF рH

For citation:Matveichuk Yu.V. FTIR-spectroscopic investigation of sodium tungstate and sodium molybdate solutions in wide range of рH. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 56-63. A FTIR spectroscopic study of aqueous solutions of sodium tungstate and molybdate (solution concentration was 0.1 mol/l) over a wide pH range (factor (level) of acidity Z, Z = C (H+)/C (WO42-) or Z = C (H+)/C(MoO42-)) was carried out. In solutions of sodium tungstate complex frequency band at 885-865 cm-1 correspoding to the stretching vibrations ν(W-O-W) was fixed. The frequency bands of 1720-1700 cm-1, 990, 985 and 1025 cm-1 corresponding to bending vibrations δ(W-OH) were fixed that indicates a significant change in composition of the solution as a result of hydrolytic and polycondensation processes. The sodium molybdate solution has not bands corresponding to the stretching vibrations v(Mo-O-Mo). Only the characteristic bands of the deformation vibrations δ(Mo-OH) were recorded. The low intensity complex band in the area of 885-865 cm-1 corresponding to the stretching vibrations ν(W-O-W) even for freshly prepared 0.1 mol/l sodium tungstate solution was appeared as well as the band at 1720-1700 cm-1 attributed to deformation vibrations δ(W-OH) that indicates a fast change in the solution composition. For solutions of sodium molybdate bands of stretching vibrations v(Mo-O-Mo) are fixed at a pH less than 6 after standing for several days. With Hydra/Medusa program diagrams of distribution of molybdate and tungsten particle depending on the pH were calculated. In relatively dilute solutions, the diagrams received with Hydra/Medusa program showed the only protonated (monomeric) form of molybdate ions, where as in the sodium tungstate solution until pH of 9 W6O216- and HW6O215- particles exist that agrees with the results of IR spectroscopy. The results of IR spectroscopy and modeling with Hydra/Medusa program will be used to support the pH operating range for molybdate and tungstate-selective electrodes, since they are an important feature of any analytical ion-selective electrodes. For tungstate-selective electrode it is necessary to maintain the pH less than 9, for molybdate-selective electrode - less than 8 (with dilute ammonia). Considering the changes in the composition of sodium molybdate and tungstate solutions, for the design of molybdate and tungstate-selective electrodes the freshly prepared solutions have to be only used, rather than stored for more than two days.

Size analysis of slag eye formed by gas blowing in ladle refining

The formation of slag eye in a gas stirred ladle was studied through cold models and industrial trials. In the cold model, water and sodium tungstate solution were employed to simulate liquid steel, and silicon oil was employed to simulate slag. The simulation results revealed that the gas flow rate and bath height had strong effects on the slag eye size. In particular, the thickness of slag layer played a strong role in the slag eye size. In addition, the slag eye could not be formed when the thickness of the top layer was more than 4 cm in water-silicone oil model. Besides, the section area of vessel had a great impact on the slag eye size. Industrial trials results showed a similar trend that the gas flow rate was very significant on the slag eye size. The predictions of the existing models showed larger predictions deviations compared with the experimental data. Moreover, a new model without fitting parameters was developed based on force balance and mathematical derivation, and verified by the experimental data. The new model provides the prediction with small deviations by comparing with the data acquired from cold models and industrial trials.

Preliminary study on preparation of ammonium metatungstate from ammonium tungstate solutions using bipolar membrane electrodialysis

A novel process for the preparation of ammonium metatungstate (AMT) from industrial ammonium tungstate solutions using bipolar membrane electrodialysis (BMED) was developed. The preliminary study results showed that the BMED process can be used to effectively prepare the AMT solution from the (NH4)2WO4 solution with the current efficiency of 73.8%. The direct recovery of WO3 reached 99.5% with the power consumption only 864.3kWh/t WO3. The obtained AMT solution can be directly used to produce the AMT crystal. The solubility of the final AMT product reached 650g AMT per 100g H2O at 25°C, which meets the Chinese National Standard on the preparation of petrochemical hydrodesulfurization catalysts. The new process exhibits significant advantages including short flow sheet, low energy consumption, high recovery of WO3 and high quality of product, and environmental friendliness.

STEM analysis of WC-Co coatings modified by nano-sized TiC and nano-sized WC addition

Thermally sprayed hardmetal WC-Co-based coatings are widely applied in order to provide good wear resistance to mechanical components working in demanding environment. The WC-Co coatings are obtained by various spraying methods such as High Velocity Oxygen Fuel (HVOF) or High Velocity Air Fuel (HVAF) techniques. Additional improvement of coatings' properties can be achieved by adding very fine carbides to the WC-Co powder feedstock. The usual approach is the agglomeration and sintering of submicron-sized carbides without or with micro-sized carbides (bimodal distribution). In this work, WC-Co powders were modified by blending them with 5wt% nano-sized TiC (<100nm) or 5wt% nano-sized WC (<100nm). The coatings were deposited by High Velocity Air Fuel (HVAF) on a steel substrate. As reference, pure WC-Co coating was also sprayed. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) were employed for the microstructural characterization of the deposited coatings. The formation of solid solution of tungsten in cobalt with the composition Co0.9W0.1 by selected area electronic diffraction, was detected. W dissolution effect was observed to be lower in the case of nano-sized TiC-added coatings. Microstructural investigation by STEM indirectly indicates that nano-sized WC completely dissolved in the cobalt matrix, inducing solid solution of tungsten in cobalt formation in the 5wt% WC-added coating. The formation of new phases containing Ti, except TiC, was not found in the coating. Obtained results suggest that nano-sized TiC may increase the stability of metallic matrix microstructure in a WC-Co-based coating.

Effect of Microstructural Changes during Annealing on Thermoelectromotive Force and Resistivity of Electrodeposited Ni85.8Fe10.6W1.4Cu2.2 Alloy

Ni85.8Fe10.6W1.4Cu2.2 alloy powder containing nanocrystals of an FCC-structured solid solution of iron, tungsten, and copper in nickel embedded in an amorphous matrix was electrodeposited from an ammonia citrate solution. The alloy exhibits thermal stability in the temperature range between 25°C and 150°C. Over the range 150−360°C, the alloy undergoes intense structural relaxation which considerably increases the electron density of states and, hence, its electrical conductivity. Less intense structural relaxation takes place at temperatures between 360°C and 420°C. In the temperature range of 420°C to 460°C, relatively more intense changes in the electron density of states at the Fermi level occur, as induced by the structural relaxation resulting from the stabilization of larger less mobile tungsten atoms and copper atoms. The large decrease in electrical resistivity and the high increase in the electron density of states at the Fermi level in the temperature range 460−520°C are due to amorphous matrix crystallization and FCC-phase crystal grain growth.

Synthesis of Cr-doped APT in the evaporation and crystallization process and its effect on properties of WC-Co cemented carbide alloy

WC grain size has significant effect on WC-Co cemented carbide alloy properties. In order to inhibit WC grain growth during sintering process, grain growth-inhibitor Cr3C2 is usually added to tungsten carbide powder in advance through mechanical milling. While, homogeneous distribution of Cr3C2 in the tungsten carbide powder is difficult to achieve and result in abnormal growth of WC grains. For this purpose of growth-inhibitor uniform distribution, (CH3COO)3Cr is added into ammonium tungstate solution during evaporation and crystallization process to prepare Cr-doped APT powder, which can be used as precursor for ultrafine-grained WC-Co cemented carbide alloy preparation. Compared with conventional APT powder, the Cr-doped APT has smaller particle size and bulk density, moreover, chromium is evenly distributed within it. The Cr-doped APT is then used to produce Cr-doped tungsten powder, which also has smaller particle size than that of conventional tungsten powder. Cr-doped tungsten powder is subsequently prepared into tungsten carbide powder and WC-Co cemented carbide alloy through carbonization and sintering process, respectively. Compared with conventional WC-Co cemented carbide alloy, the obtained WC-Co cemented carbide alloy has smaller mean WC grain size (0.36μm), and more uniform microstructure. Furthermore, the phenomenon of WC grain abnormal growth during sintering process is not observed, because the grain growth-inhibitor Cr3C2 is well dispersed in tungsten carbide and cobalt composite powder. Results show that the obtained WC-Co cemented carbide alloy presents better mechanical properties (HRA, bending strength, coercive force) than those of conventional WC-Co cemented carbide alloy. Accordingly, the novel addition of (CH3COO)3Cr during the evaporation and crystallization process is the key factor of ultrafine-grained WC-Co cemented carbide alloy production.

Superhard Rhenium/Tungsten Diboride Solid Solutions.

Rhenium diboride (ReB2), containing corrugated layers of covalently bonded boron, is a superhard metallic compound with a microhardness reaching as high as 40.5 GPa (under an applied load of 0.49 N). Tungsten diboride (WB2), which takes a structural hybrid between that of ReB2 and AlB2, where half of the boron layers are planar (as in AlB2) and half are corrugated (as in ReB2), has been shown not to be superhard. Here, we demonstrate that the ReB2-type structure can be maintained for solid solutions of tungsten in ReB2 with tungsten content up to a surprisingly large limit of nearly 50 atom %. The lattice parameters for the solid solutions linearly increase along both the a- and c-axes with increasing tungsten content, as evaluated by powder X-ray and neutron diffraction. From micro- and nanoindentation hardness testing, all of the compositions within the range of 0-48 atom % W are superhard, and the bulk modulus of the 48 atom % solid solution is nearly identical to that of pure ReB2. These results further indicate that ReB2-structured compounds are superhard, as has been predicted from first-principles calculations, and may warrant further studies into additional solid solutions or ternary compounds taking this structure type.

Cyclic voltammetry analysis of copper electrode performance in Na2WO4 solution and optical property of electrochemical synthesized CuWO4 nanoparticles

The electrochemical behavior of copper electrode in sodium tungstate (Na2WO4) solution has been studied through cyclic voltammetry (CV). CV results informed that CuWO4 was formed in kinds of electrochemical processes followed with chemical reaction. A cationic exchange membrane-assisted electrolysis method was developed to synthesize optical nanoparticle CuWO4 for the first time. Anode chamber collected CuWO4 was calcined at 500 °C based on the thermogravimetry test result. The X-ray diffraction (XRD) pattern of calcined CuWO4 showed no impurities. Microstructure of CuWO4 was characterized by transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM). The fourier transform infrared spectroscopy (FTIR) of the sample further confirmed the formation of pure CuWO4 nanoparticle. Furthermore, the optical property of the nanomaterial was studied by ultraviolet visible diffuse reflectance spectrophotometer (UV–vis) and photoluminescence (PL).

Statistically optimized synthesis of dyspersium tungstate nanoparticles as photocatalyst

The parameters affecting the perticipation reaction for the production of dyspersium tungstate nanoparticles were optimized using the taguchi robust design. The parameters studied were the concentrations of dyspersium and tungstate solution, as well as the flow rate of the cation solution and temperature of the reactor, and the outcome under study was the dimensions of the percipitated nanoparticles. Analysis of variance (ANOVA) of the results proved that the flowrate of adding the cation solution (FZ) and the concentration of the solutions of both ions considerablly affect the outcome of the reaction. The synthesized dyspersium tungstate nanoparticles prepared under the optimized factors wereevaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and UV–Vis spectroscopy techniques. Furthermore, the as-synthsized dyspersium tungstate nanoparticles were used as efficient photocatalyst for the photocatalytic degradation of methylene blue under ultraviolet light.

Electrochemical properties of WO3-reduced graphene oxide composite powders prepared by one-pot spray pyrolysis process

In this work, we report the preparation of WO3-reduced graphene oxide (rGO) composite powders by spray pyrolysis process using a stable graphene oxide colloidal solution with ammonium tungstate. The ultrafine WO3 nanocrystals below 10 nm in size are dispersed within the rGO matrix. The bare WO3 powders prepared from the aqueous spray solution of ammonium tungstate are spherical and do not aggregate. The bare WO3 and WO3-rGO composite powders show monoclinic and cubic crystal structures, respectively. The initial discharge capacities of the bare WO3 and WO3-rGO composite powders at a current density of 100 mA g−1 are 771 and 941 mA h g−1, respectively, and their initial Coulombic efficiencies are 67 and 65%, respectively. The discharge capacities of the bare WO3 and WO3-rGO composite powders at the 300th cycle are 282 and 546 mA h g−1, respectively.

Microstructure evolution of the oxide dispersion strengthened CLAM steel during mechanical alloying process

Abstracts Oxide dispersion strengthened Ferritic/Martensitic steel is considered as one of the most potential structural material for future fusion reactor, owing to its high mechanical properties and good irradiation resistance. The oxide dispersion strengthened China Low Activation Martensitic (ODS-CLAM) steel was fabricated by mechanical alloying (MA) and hot isostatic pressing (HIP). The microstructural evolutions during the process of ball milling and subsequent consolidation were investigated by SEM, XRD and TEM. The results showed that increasing the milling time during the first 36 h milling could effectively decrease the grain size to a value of around 30 nm, over which grain sized remained nearly constant. Increasing the rotation speed promoted the solution of tungsten (W) element obviously and decreased the grain size to a certain degree. Observation on the consolidated and further heat-treated ODS-CLAM steel samples indicated that a martensite microstructure with a high density of nano-particles was achieved.

Coordination leaching of tungsten from scheelite concentrate with phosphorus in nitric acid

A hydrometallurgical process for tungsten extraction and recovery from scheelite is reported. The technology includes leaching scheelite using phosphoric acid as chelating agent in nitric acid solutions, extracting tungsten by solvent extraction and reusing leaching agent. In the leaching process, affecting factors, such as temperature, leaching time, nitric acid and dosage of phosphoric acid, were examined on recovery of tungsten. Results show that more than 97% of tungsten could be extracted under conditions of leaching temperature of 80-90 °C, HNO3 concentration of 3.0-4.0 mol/L, liquild-to-soild ratio of 10:1, H3PO4 dosage of 3 stoichiometric ratio and leaching time of 3 h. Solvent extraction was then employed for the W recovery from the leachate with a organic system of 40% (v/v) N235, 30% (v/v) TBP, and 30% sulfonated kerosene. Approximately 99.93% of W was extracted and ammonium tungstate solution containing 193 g/L W was obtained with a stripping rate of 98.10% under the optimized conditions.

Extraction and separation of tungsten from acidic high-phosphorus solution

The utilization of high-phosphorus tungsten ores has attracted extensive attention with the mining and utilization of rich tungsten ores. To extract and separate tungsten from acidic high-phosphorus solution effectively, a novel process was developed. Firstly, tungsten was extracted directly in acid medium by solvent extraction. 99.8% tungsten in acidic high-phosphorus solution was extracted with Aliquat 336 in kerosene by one extraction stage under the conditions of O:A=1, pH=2, 25°C, t=10min, 5% v/v 2-Octanol and 10% v/v Aliquat 336. And then, tungsten and phosphorus were preliminary separated through stripping process. Over 95% tungsten were recovered after five stripping stages under the optimum stripping conditions of 2.5M ammonium bicarbonate, 8min stripping time, O:A=1:1, pH=9, and 60°C, but only about 1.2% phosphorus was recovered from feed liquor. Finally, a small amount of phosphorus left in strip liquor was deeply removed by magnesium salt precipitation method on the optimum conditions of pH=10.0, 25°C, reaction time 1h and Mg/P molar ratio of 1:2 and the ammonium tungstate solution meeting the requirements of producing high-quality ATP can be obtained successfully. Compared to traditional phosphorus removal route, the process in this paper can help extract tungsten directly in acidic medium and decrease the quantity of phosphorus through extraction-stripping process, significantly reducing the consumption of alkali and magnesium salt and improving the separation efficiency of tungsten from acidic high-phosphorus solution.

A novel process for tungsten hydrometallurgy based on direct solvent extraction in alkaline medium

The principle, flow sheet and characteristics of a novel process for tungsten hydrometallurgy based on direct solvent extraction (DSX) with quaternary ammonium salt in alkaline medium were introduced. The pilot tests and industrial tests of the direct solvent extraction process were conducted. The results indicated that, the new technology had excellent adaptability for the treatment of leach solutions from not only autoclave-soda leaching but also caustic soda leaching with different tungsten ores. When proper operational conditions were controlled, the impurities of P, As, Si could almost be removed while sodium tungstate (Na2WO4) solution transformed to ammonium tungstate (NH4)2WO4 solution in the DSX process. The concentration of WO3 in strip liquor could be up to around 170g/L. The raffinate could be returned to leaching step directly or after causticization by lime, the water and alkali could be recycled. Comparing with traditional process, the novel process shows the advantage of higher recovery of WO3, lower consumption of chemicals, and discharge of waste water. Based on pilot tests and industrial tests, an engineering demonstration line of the novel process for treatment of scheelite concentrate had been constructed and ran for more than 1year.