Tungstate Solution Research Articles

The effect of annealing and frequency of the external magnetic field on magnetic properties of nanostructured electrodeposit of the Ni86,0Fe9,8W1,3Cu2,9 alloy

A nanostructured powder of the Ni86,0Fe9,8W1,3Cu2,9 alloy is deposited on a titanium cathode by electrodeposition from the citrate bath, at the current density of 400 mA cm−2. The powder particles are of a cauliflower and dendritic shape and composed of nanocrystals of the FCC phase of the solid solution of iron, tungsten and copper in nickel, captive in an amorphous matrix. The freshly deposited powder is thermally stable up to 160 °C. The annealing of the powder in the temperature range from 160 °C to 460 °C results in its structure relaxation. At temperatures higher than 460 °C, the amorphous phase in the powder is crystalizing and crystal grains of the FCC solid solution are growing. The structural changes caused by annealing, affect magnetic properties of the alloy. The cooled powders after the structure relaxation have higher magnetization, a lower loss of the active power and a lower coercive field. Crystallization of the amorphous phase and crystalline grain growth of the FCC phase causes a decrease in magnetization, an increase in the power loss and the power of coercive field.

UV-Induced Photocatalytic Reduction of Methylene Blue Dye in the Presence of Photochromic Tungsten Oxide Sols

In spite of the wide application of nanodisperse tungsten oxide (from photo- and electrochromic devices to biomedical materials), its physicochemical properties were studied insufficiently. In this work, we have performed a comparative analysis of photochromic and photocatalytic properties of polyvinylpyrrolidone-stabilized tungsten oxide nanoparticles prepared by ion exchange and precipitation from sodium tungstate solution. Reversible UV-induced reduction of Methylene Blue dye in the presence of photochromic tungsten oxide sol has been shown, the dependence of photochromic properties of tungsten oxide sols on sodium cation concentration in solution has been revealed.

Continuous solvent extraction operations for the removal of molybdenum from ammonium tungstate solution with quaternary ammonium salt extractant

The continuous solvent extraction operations for the removal of molybdenum from ammonium tungstate solution was conducted using a solvent extraction system consisting of 10% (v/v) N263 as extractant and 30% (v/v) isooctanol as modifier in sulfonated kerosene for 63 h under optimized conditions in mixer-settlers. The concentration of Mo in raffinate was less than 10 mg/L with mass ratio of Mo/WO3 less than 6.0 × 10−5 and the concentration of Mo in strip liquor reached 30 g/L with mass ratio of WO3/Mo less than 1.0 × 10−2, which was consistent with the results of batch tests. The loaded organic solution and the oxidized organic solution were characterized by infrared spectroscopy and the results demonstrated that molybdenum exists in the form of [Mo2O11(H2O)2]2− in oxidized organic solution. The theoretical calculation of temperature change of the organic solution in oxidation process was conducted. The oxidant of 7 wt% H2O2 was recommended to be used during industrial production and a cooling water system has to be installed around the oxidation tank at the same time.The new process exhibited significant advantages of low overall costs, large value increase due to molybdenum producibility of MSA and environmental friendliness without wastewater and residue generation.

Exfoliated, mesoporous W18O49/g-C3N4 composites for efficient photocatalytic H2 evolution

Rapid recombination of photogenerated carriers and lack of active sites have always been the problems for enhancing the H2 evolution performance of semiconductor-based photocatalysts, which can be solved promisingly by co-catalysis and lifting specific surface area, respectively. In this work, a simple two-step green route is developed to synthesize novel exfoliated and mesoporous W18O49/g-C3N4 composites through calcining the precursors of g-C3N4 powder impregnated with ammonium tungstate solution in a reductive atmosphere produced by the pyrolysis of polyacrylonitrile powder. With the optimal loading amount of W18O49, the obtained W18O49/g-C3N4 composite presents an excellent photocatalytic performance for H2 production in triethanolamine aqueous solution under visible light. The H2 evolution rate at 7 °C was 912.3 μmol⋅g−1h−1, 9.7-fold higher than that of pure g-C3N4. In addition, the mechanism of the H2 production over the obtained W18O49/g-C3N4 photocatalysts was also proposed. This work will provide a new strategy for improving the specific surface area of nanomaterials and constructing the heterojunctions between different nanostructures simultaneously.

Study of a Hydrogen Inhibition Method with Sodium Tungstate for Wet Aluminum Dust Removal Systems

Hydrogen, which can be produced due to the accumulation of aluminum dust that reacts with water in wet dust removal systems, is a fire and explosion hazard. To reduce hydrogen production, sodium tungstate is used in hydrogen inhibition experiments to inhibit the reaction between aluminum dust and water. The purity of the aluminum powder was 95.15%, analyzed with X-ray fluorescence spectrometry (XRF). Each of the hydrogen inhibition experiments lasted for 12 h. In addition, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology and composition of particles before and after the experiments. There was nearly no hydrogen produced when the concentration of the sodium tungstate solution reached 100 g/L. The results show that a protective coating containing W element was formed on the surface of the aluminum particles after the reaction with sodium tungstate, and the coating prevented the aluminum particles from contacting with water.

Recovery of valuable metals from molybdenum-removal sludge by reverse sulfurization leaching

Selective precipitation is the main process used to remove molybdenum from tungstate solutions by the tungsten industry in China. The process exploits the fact that molybdenum is a sulfophile whereas tungsten is an oxyphile. First, the sulfur ions replace oxygen and convert the molybdate to thiomolybdate, then a moderate amount of additives (copper compounds) are reacted with the thiomolybdate to form complex precipitates. We call the filtered wet precipitate “molybdenum-removal sludge”. The main components of the sludge are molybdenum, copper and sulfur, infiltrated by some amount of tungsten due tomechanical entrainment. Based on the fact that copper is a typical sulfophile, it is possible that copper ions can react withthe sulfur of the thiomolybdate, thus converting it to soluble molybdate. This is actually the reverse of molybdenum sulfuration process, so we therefore call it the “reverse sulfuration process.” Based on the leaching thermodynamics and structure characteristics of this kind of sludge, a new treatment process was developed in this work. About 90% of tungsten and 15% of molybdenum were washed out with ammonia water when the pH > 9. The recovery rate of molybdenum was close to 70% when a stoichiometric amount of copper ions (with sodium hydroxide 4 mol/L) were utilized for the reverse sulfurization leaching. The leaching rate of molybdenum obtained on leaching with 2 mol/L sodium hydroxide for 120 min at 80 °C and then fixing with copper chloride was 94.4%, and 87.67% of sulfur ions were fixed in the form of an amorphous CuS compound.

Corrosion Resistance of Structural Materials in Tungstate Solutions

It is shown that the corrosion activity of tungstate solutions is caused by the presence of fluoride ions and by the total alkalinity. We determine the optimal mode of welding of carbon, chromium, and nickel-chromium steels. In the original tungstate solution, the maximum corrosion rate is recorded for specimens of VSt3sp carbon steel with welded joints. The electrochemical studies show that, in the original solution at room temperature, this type of steel corrodes in the passive state. As temperature or the concentrations of components of the solution increase to the values corresponding to the evaporated solution, the analyzed steel begins to corrode in the active state. Chromium and nickel-chromium steels (08Kh13, 08Kh22N6T, and 12Kh18N10T) preserve their passive state both in the original solution and in the evaporated solutions. The PON-A, PON-B, and PON-V paronites and TMKShch rubber are chemically stable and, therefore, suitable for the production of gaskets intended for operation in the original Na2WO4 solutions.

Process development for the recovery of high grade calcium tungstate from alkaline leach liquor of spent [sbnd]HDS catalyst

Molybdenum is often associated with nickel-tungsten based spent HDS catalyst and must be removed from tungstate solution to obtain commercially acceptable tungsten products. In order to address this problem, a different approach has been proposed in the present work. A two step process based on selective thionization of Mo using Na2S at alkaline condition followed by W precipitation as calcium tungstate (CT) using lime (Ca(OH)2) was studied. Various operating parameters were tested and optimum conditions for Mo thionization and W precipitation were developed. The CT produced by the conventional process was used as a reference to check the improvement in the proposed process with respect to Mo impurity. Under the optimum conditions, 92.7% Mo was rejected to the CT filtrate and 99.7% W converted to CT. The CT obtained from the proposed process contained 0.53% Mo, which was much less as compared to the CT obtained from the conventional process having 2.5% Mo using the same leach solution. High-grade ammonium paratungstate (APT) containing <100 ppm Mo was obtained by treating the CT, which can be used for the tools industry and other applications.

Mechanism of Selective Precipitation of Molybdenum from Tungstate Solution

Selective precipitation of molybdenum (Mo) is a widely utilized method for separation of Mo from tungstate solution; however, the corresponding mechanism is still unclear. The aim of the work presented herein is to investigate the effects of the reaction time, temperature, and CuS dose on the precipitation of Mo and characterize the obtained precipitates via powder x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) analyses. The results demonstrate that sulfurized molybdenum ($$ {\text{MoS}}_{ 4}^{{ 2 {-}}} $$) can be selectively precipitated as NH4CuMoS4 or Cu2MoS4 on addition of CuS depending on the reaction temperature and CuS dose, and a corresponding reaction mechanism is proposed. Under the optimum conditions of CuS/Mo = 1.5, T = 35°C, and t = 8 h, up to 99% of the Mo was selectively precipitated. The present study elucidates the mechanism of Mo precipitation and provides basic and robust guidelines for separation of Mo from tungstate solution.

Hydrogen peroxide coordination-calcium salt precipitation for deep phosphorus removal from crude sodium tungstate solution

In the traditional alkali smelting process of tungsten ore，a small amount of the associated phosphorus will enter the sodium tungstate solution. In order to produce a qualified tungsten product, phosphorus must be removed in depth. Conventional methods for removing phosphorus, such as magnesium salt precipitation, ion exchange, etc., are difficult to efficiently remove high concentrations of phosphorus from sodium tungstate solution. In this paper, a method for deep phosphorus removal from crude sodium tungstate solution by hydrogen peroxide coordination‑calcium salt precipitation is proposed due to the coordination ability of hydrogen peroxide with tungstate to form peroxytungstate which is difficult to be precipitated by calcium. The paper mainly explores the theoretical feasibility of this method, the influence of time, calcium addition, pH value, initial phosphorus concentration and other factors on P removal. The best phosphorus removal condition has been obtained: under the condition of adding hydrogen peroxide, when the reaction time is 10 min; the molar ratio of calcium to phosphorus added is 3; the pH value is 9.5, and the phosphorus concentration is higher than 1 g/L, the phosphorus removal effect has been basically stable. The phosphorus removal ratio can reach 99.9% which means that phosphorus concentration in solution is <10 ppm after phosphorus removal, and the tungsten loss is as low as 0.1%. This method can remove phosphorus deeply from sodium tungstate solution containing different initial phosphorus concentration.

Orthophosphoric acid solutions of sodium orthovanadate, sodium tungstate, and sodium molybdate as potential corrosion inhibitors of the Al2Cu intermetallic phase

Orthophosphoric acid solutions of sodium orthovanadate, sodium tungstate, and sodium molybdate are tested as potential corrosion inhibitors of the Al2Cu intermetallic phase. Corrosion inhibition is observed for 0.2 M solutions of Na3VO4 and Na2WO4 by increasing the pH to > 2. When the pH is < 2, the aforementioned salts increase the corrosion rate of the intermetallic phase. A 0.2 M solution of Na3VO4 causes the precipitation of vanadium phosphate on the surface of the Al2Cu phase at pH = 1.

Термодинамическое моделирование распределения редких элементов при растворении отходов жаропрочных никелевых сплавов в минеральных кислотах

This work is aimed at studying the possibility of heat-resistant alloys waste processing, in particular, to determine the distribution of elements of a heat-resistant nickel alloy in solutions of mineral acids. The aim of the work was to predict the behavior of alloy components using the method of thermodynamic analysis. The research results can serve as a scientific basis for the development of promising technologies for the processing of metal wastes of heat-resistant alloys, allowing the extraction and separation of valuable rare and non-ferrous metals. Thermodynamic modeling of the interaction for the heat-resistant nickel alloy containing refractory rare metals with hydrochloric, sulfuric and nitric acids was carried out within a temperature range of 20-100 °C and concentration from 50 to 150 g/dm3 under a pressure of 1 atm. According to the results of calculations, it was revealed that nickel transfers into sludge, both in the form of a metal and in the form of a Ni4W compound. A temperature growth of more than 60 °C and an acid concentration from 50 to 150 g/dm3 do not affect predominant distribution of tantalum and niobium pentoxides into the slurry and contributes to the transition to a solution of non-ferrous metals. The obtained data of thermodynamic modeling were confirmed in experiments on the anodic dissolution of the alloy in sulfate solutions. According to the results of X-ray phase analysis of sludge, it was found that the highest intensity of the diffractogram peaks corresponded to a solid solution of tungsten in nickel. The oxide phases of tantalum were also detected. In the electrolyte solution transferred, mainly Re, Co, Cr. Thus, it was shown the possibility of using the method of thermodynamic modeling to predict the behavior of elements in the processing of waste heat-resistant nickel alloys.

Numerical investigation of the WC re-precipitation impact on the residual stress state in WC20 wt.-%Co hardmetal

In WC-Co hardmetals severe micro stresses form between the carbide and binder phases during the cooling stage of the liquid phase sintering process. The main cause of these micro residual stresses is the difference in the coefficients of thermal expansion in each of the constituent phases. There have also been discussions as to whether or not the solution and re-precipitation of elemental tungsten may be an additional driver for the temperature-dependent formation of residual stresses [1, 2]. To further investigate the influence of the re-precipitation effect on the residual stress state in hardmetals, a numerical approach combining the diffusion modelling capabilities of thermocalc/DICTRA [3] is applied in conjunction with temperature-dependent nonlinear mechanical analysis utilizing the finite element method. This combination allows for a qualitative estimate of the re-precipitation effect on the final residual stress state in hardmetals. Additionally, the temperature dependence of the residual stress state in hardmetals is investigated, with and without consideration of the solution and re-precipitation of W and C in the binder.A detailed 2.5D representative volume element based on EBSD images of a WC20wt.-%Co hardmetal has been derived for use in mechanical FE simulation. In the mechanical analysis, the cobalt binder is modelled as temperature-dependent elastic-viscoplastic isotropic material with isotropic hardening. Carbides are modelled as purely orthotropic elastic materials with temperature-dependent description of the elastic constants. The DICTRA results are applied as additional internal loads to the mechanical model via two equivalent coefficients of thermal expansion. A comparison of model results obtained with and without re-precipitation effect permits the impact of the re-precipitation effect on the residual stress state to be examined qualitatively.Finally, the model results are compared to experimental measurements of the residual stress state in WC20wt.-%Co hardmetal specimens, obtained via neutron diffraction.

Equilibrium WO3 concentration in the Ca2+-(NH4)2CO3-(NH4)2WO4-NH3-H2O system

The Ca2+-(NH4)2CO3-(NH4)2WO4-NH3-H2O system is a typical system in tungsten extractive metallurgy used in the preparation and purification of ammonium tungstate solution. To determine an appropriate solution composition to optimize these processes, a thermodynamic model combined with the Pitzer activity equations was developed. This model allowed us to predict the dependence of the equilibrium WO3 concentration on the compositions of the solution in the Ca2+-(NH4)2CO3-(NH4)2WO4-NH3-H2O system. Thermodynamic analyses clarified the stable regions of CaCO3 and CaWO4 in the Ca2+-(NH4)2CO3-(NH4)2WO4-NH3-H2O system and indicated that increasing both the total NH3 and total CO2 concentrations is beneficial for increasing the equilibrium WO3 concentration. The experimental results confirm that the thermodynamic model offers a means of predicting the equilibrium concentrations of species in the system. Furthermore, the equilibrium WO3 concentrations of the solution of the Ca2+-(NH4)2CO3-(NH4)2WO4-NH3-H2O system at 298.15 K have been predicted at different total CO2 concentrations, as well as different total NH3 to total CO2 concentration ratios. Thus, the findings of this study will not only help determine the appropriate composition of the leaching system for preparing ammonium tungstate solutions, but also provide a reference for purifying ammonium tungstate solutions.

A novel Tungsten-based fiducial marker for multi-modal brain imaging

BackgroundMulti-modal brain image registration is a prerequisite for accurate mapping of brain structure and function in neuroscience. Image registration is commonly performed using automated software; however, its accuracy decreases when images differ in modality, contrast, uniformity, and resolution. This limitation could be overcome by using an external reference point; however, high-contrast agents in multi-modal imaging have not been previously reported. New methodsHere, we propose a novel multi-modal fiducial marker that contains Tungsten solution and provides high contrast in magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET). The basic characteristics of this multi-modal marker were investigated by assessing major sources of image contrast in the following modalities: density and T1-, T2-relaxivity in comparison with conventional contrast agents. ResultsTungsten solution had lower T1- and T2-relaxivity and high solubility, and showed high contrast in T1- and T2-weighted MR and CT images at a high-density concentration (˜3.0 g/mL), whereas other conventional solutions did not show sufficient contrast in either CT or MRI. Comparison with existing methodsThe use of this Tungsten-based multi-modal marker allowed more accurate registration than a software-only method in phantom and animal experiments. Application of this method demonstrated accurate cortical surface mapping of neurotransmitter function (dopamine transporter, DAT) using PET and MRI, and provided a neurobiologically relevant cortical distribution consistent with previous literature on histology-based DAT immunoreactivity. ConclusionsThe Tungsten-based multi-modal fiducial marker is non-radioactive, easy to handle, and aids precise registration across different modalities of brain imaging.

Effect of iron valence on hydrothermal preparation of pyrochlore-type tungsten oxide

Abstract Pyrochlore-type tungsten oxide (PTO), WO3·0.5H2O, is an emerging material with very wide potential applications. The influences of iron valences and the additive amount of ferrous ion on tungsten crystallization ratio and the acceleration mechanism of ferrous ion were investigated when PTO was hydrothermally prepared in aqueous ammonium tungstate solution containing ammonium carbonate. The results show that ferrous ion can remarkably accelerate tungsten crystallization while both elemental iron and ferric ion have little influence on the crystallization. Moreover, the tungsten crystallization ratio increases with increasing the amount of ferrous ions added and reaches the maximum of about 60% with ferrous ion concentration of 16 g/L. FTIR analysis of the spent solution after PTO crystallization shows that ferrous ion can accelerate the conversion of WO4 tetrahedral to WO6 octahedron. Combined with XPS and XRD analyses of the hydrothermal product, the acceleration effect of ferrous ion on tungsten crystallization could basically be attributed to the increase in the interplanar spacing of PTO lattice caused by the incorporation of ferrous ion into PTO crystal lattice. The results presented is conducive to the efficient preparation of PTO powder and cleaner tungsten metallurgy.

Study on removal of molybdenum from ammonium tungstate solutions using solvent extraction with quaternary ammonium salt extractant

A new process for the removal of molybdenum from ammonium tungstate solutions using solvent extraction with quaternary ammonium salt extractant was proposed. The molybdenum can be selectively extracted over tungsten using a solvent extraction system consisting of 10% (v/v) N263 as extractant and 30% (v/v) isooctanol as modifier in sulfonated kerosene. The separation coefficient βMo/W reached 1 × 104.A continuous operation test was conducted using an industrial feed containing 2.2 g/L Mo and 258 g/L WO3. The concentration of Mo in raffinate decreased to <1 mg/L with mass ratio of Mo/WO3 <4.0 × 10−6 in four-stage counter current batch-continuous extraction at an A/O ratio of 3:1. After scrubbing, the loaded organic solution was first oxidized using 7% H2O2 followed by stripping using a mixed solution of 3 mol/L NH4HCO3 and 3 mol/L NH3·H2O in six counter current stages at an A/O ratio of 1:8. The stripping of molybdenum reached almost 100%, resulting in 62.1 g/L Mo and 0.96 g/L WO3 in the strip liquor with the WO3/Mo mass ratio of 0.015.This new process exhibited big advantages of wide adaptability, low tungsten loss, high value of molybdenum products, low cost and environmental friendliness.

Palladium enriched tungsten oxide thin films: an efficient gas sensor for hazardous gases

Palladium enriched tungsten trioxide thin films were prepared by spraying solution of ammonium tungstate as a precursor on glass substrates using spray pyrolysis deposition technique. Palladium chloride as a precursor for palladium was introduced in the precursor solution during refluxing process before deposition. The catalyst Pd with different concentrations was introduced on series of WO3 films. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy were applied to analyze structure and morphology of the deposited thin films. The effect of Pd enrichment on the microstructure, electrical and gas sensing properties of the as-synthesized WO3 thin films was studied. Variation in the electrical conductivity of pure and Pd supplemented WO3 films was measured in air and in the presence of hazardous gases such as NO2, SO2 and NH3. The addition of 3 w/o Pd in WO3 raised the gas response of the film to 1.1 towards NO2 at lowest operating temperature of 100 °C. The film shows adequate response towards SO2 (0.32) and NH3 (0.27) at 200 °C and 225 °C, respectively. The response and recovery time ranged in 0.5–1.25 s and 1–6.7 s respectively even for high gas concentrations upto 750 ppm.

Interactive effects of abscisic acid and nitric oxide on chilling resistance and active oxygen metabolism in peach fruit during cold storage.

Cold conditions can accelerate the production of reactive oxygen species (ROS), and excessive ROS may attack biological macromolecules, disrupt related signal pathways, induce oxidative stress and influence plant metabolism. The cross-talk between nitric oxide (NO) and abscisic acid (ABA) and the inhibitions by NO or ABA on oxidative damage have been reported in fruits. However, there are few reports about the roles of NO-ABA interactions in chilling stress and antioxidant defense in fruits during cold storage. This study was conducted to investigate the roles of NO, ABA and interactions between NO and ABA in response to chilling stress on peach fruit (Prunus persica (L.) Batsch, cv. 'Xintaihong'). Treatments with 15 µmol L-1 NO, 100 µmol L-1 ABA and 15 µmol L-1 NO + 5mmol L-1 sodium tungstate solution could reduce ROS content, alleviate lipid peroxidation and enhance antioxidant enzyme activities and antioxidant capacities. However, treatments with 5µmol L-1 potassium 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), 5mmol L-1 sodium tungstate and 100 µmol L-1 ABA + 5µmol L-1 c-PTIO differentially blocked these protective effects and significantly increased ROS content and lipid peroxidation of peaches under low-temperature conditions. Application of exogenous ABA could increase the resistance to cold-induced oxidative stress by enhancing the efficiency of enzymatic and non-enzymatic systems, which were partially mediated by NO. © 2018 Society of Chemical Industry.

Leaching of synthetic Ca3WO6 with ammoniacal ammonium carbonate solution under atmospheric pressure: A fundamental study

In (NH4)2CO3 solution, leaching Ca3WO6-bearing product converted from tungsten concentrate can directly obtain ammonium tungstate solution, and thus eliminates high-salinity wastewater discharge in ammonium paratungstate manufacture. Possible reactions of Ca3WO6 leaching in aqueous ammoniacal ammonium carbonate solution under atmospheric pressure were investigated thermodynamically and experimentally. The results show that tungsten in Ca3WO6 can be efficiently leached out by forming CaCO3(s) and (NH4)2WO4 (aq) in aqueous ammoniacal ammonium carbonate solution, while raising ratio of total ammonia to total carbon in solution and forming calcite are beneficial to increase the WO3 leaching ratio. Whereas the secondary reactions of Ca3WO6 with H2O and/or Ca (OH)2/CaCO3 with (NH4)2WO4 may occur and thus CaWO4 forms in the leaching, decreasing WO3 leaching ratio especially in concentrated (NH4)2WO4 solution and in case of forming vaterite. In addition, a three-layer cover was observed on the unreacted Ca3WO6 and hinders the leaching process. Through simultaneous grinding and leaching, both high WO3 leaching ratio and high WO3 concentration leachate can be achieved by increasing ratio of total ammonia to total carbon in NH3-(NH4)2WO4- (NH4)2CO3-H2O system. These results are helpful to optimize the leaching process of the converted product with Ca3WO6 by roasting tungsten-containing materials.