Tungstate Solution Research Articles

Effects of molybdenum and cobalt alloying on corrosion resistance of electrochemical coatings based on the Ni–W system

The paper studies coatings of the Ni–W system alloyed with molybdenum and cobalt obtained by electrodeposition. The effect of the concentration of salts of the alloying element in the electrolyte on the chemical composition of the coatings was studied under various synthesis conditions. All the obtained coatings are nanocrystalline or amorphous solid solutions of tungsten, molybdenum or cobalt in nickel with a FCC crystal lattice. Polarization measurements made it possible to establish that the most resistant to corrosion in a 3.5% NaCl solution is a coating containing 35% W and 8% Mo.

An Image-Based Prior Knowledge-Free Approach for a Multi-Material Decomposition in Photon-Counting Computed Tomography.

Photon-counting CT systems generally allow for acquiring multiple spectral datasets and thus for decomposing CT images into multiple materials. We introduce a prior knowledge-free deterministic material decomposition approach for quantifying three material concentrations on a commercial photon-counting CT system based on a single CT scan. We acquired two phantom measurement series: one to calibrate and one to test the algorithm. For evaluation, we used an anthropomorphic abdominal phantom with inserts of either aqueous iodine solution, aqueous tungsten solution, or water. Material CT numbers were predicted based on a polynomial in the following parameters: Water-equivalent object diameter, object center-to-isocenter distance, voxel-to-isocenter distance, voxel-to-object center distance, and X-ray tube current. The material decomposition was performed as a generalized least-squares estimation. The algorithm provided material maps of iodine, tungsten, and water with average estimation errors of 4% in the contrast agent maps and 1% in the water map with respect to the material concentrations in the inserts. The contrast-to-noise ratio in the iodine and tungsten map was 36% and 16% compared to the noise-minimal threshold image. We were able to decompose four spectral images into iodine, tungsten, and water.

Removal of molybdenum by TBP-TRPO extraction in sodium isopolytungstate solution

A new process was proposed for extracting molybdenum from tungsten solutions in acidic tungsten-molybdenum mixed solution. The extraction ratio of molybdenum reached 70 % and the tungsten-molybdenum separation factors reached 400 with the hydrogen peroxide dosage of nH2O2/n(Mo) = 2 (nH2O2/n(W + Mo) = 0.3) for the molybdenum-containing isopolytungstate sodium solution. The experimental conditions resulted in the yield of only 20 % of the traditional method (nH2O2/n(W + Mo) = 1.5–2). The organic phases consisted of 2 % TRPO and 60 % TBP. The saturated extraction capacity of molybdenum was found to be 10 g/L. The solution of 0.3 mol/L sodium bicarbonate was used as the stripping agent. With the temperature of 25 ℃, stripping time of 6 min, and the phase ratio of (O/A)2, the stripping ratio of molybdenum was 90 % and that of tungsten was 70 %. The extraction mechanism of TBP-TRPO and the hydrogen peroxide coordination were analyzed using Raman and infrared analyses. The process has a high industrial potential due to its low hydrogen peroxide dosage, high molybdenum extraction ratio, high separation factor, and low cost.

Preparation of extra coarse-grained WC-Co cemented carbides by doping sodium in the ammonium tungstate solution during evaporation crystallization process

Coarse tungsten powders are usually used as raw material for preparing coarse grained WC-Co cemented carbides. Sodium can effectively promote the growth of tungsten powder during the reduction of tungsten oxide with hydrogen. Conventional addition of sodium salt into tungsten oxide powders by mechanical milling has the disadvantage of uneven distribution of sodium, which leads to abnormal growth of tungsten powders and affects the performance of WC-Co cemented carbides. In this study, uniform sodium doped ammonium paratungstate (APT) was prepared by adding sodium carbonate into ammonium tungstate solution during the evaporation and crystallization process based on the formation of ammonium-sodium paratungstate. Experimental results showed that sodium was uniformly distributed in the APT and promoted the growth of APT crystal. The sodium-doped APT was then used to produce coarse tungsten powders. Compared with tungsten powders obtained from tungsten trioxide with addition of sodium by mechanical milling, the coarse tungsten powders had larger average particle size and more uniform particle size distribution. The coarse tungsten powders were subsequently prepared into tungsten carbide powders and WC-Co cemented carbides by carburization and pressure sintering, respectively. Results showed that the obtained WC-Co cemented carbides had larger average WC grain size (6.8–7.2 μm), higher fracture toughness and transverse ruptures strength, and more uniform microstructure than that of WC-Co cemented carbides obtained by addition of sodium with mechanical milling. Moreover, sodium thoroughly volatilized during hydrogen reduction and carburization process, so that the purity of WC-Co cemented carbides was not reduced. Therefore, this study provided a new route for preparation of extra coarse-grained WC-Co cemented carbides.

The influence of microelements on the yield and its quality of wheat grown under drought conditions on soil with different phosphorus supplies

The results of 2-year vegetation studies devoted to the study of the existing prerequisites for treating seeds (PTS) with solutions of flax selenium, vanadium, tungsten and iodine on the yield and its structure, as well as indicators of the quality of wheat grain are presented. The experimental crop was grown on soil with different supplies of available phosphorus and was grown in an artificially created drought. The effectiveness of microelements was most realized under conditions of low phosphate content in the soil. The use of solutions of sodium selenite, ammonium vanadate, ammonium tungstate and potassium iodide helps to increase the weight of wheat grain by 14, 11, 13 and 7% relative to seed treatment with distilled water. Under stress conditions, persistent sodium selenite has the best effectiveness - grain increase of 11%.

Plastic deformation mechanisms in BCC single crystals and equiatomic alloys: Insights from nanoindentation

Deformation plasticity mechanisms in alloys and compounds may reveal the material's capacity towards optimal mechanical properties. We conducted a series of molecular dynamics (MD) simulations to investigate plasticity mechanisms due to nanoindentation in pure tungsten, molybdenum, and vanadium body-centered cubic single crystals, as well as the body-centered cubic, equiatomic, random solid solutions (RSS) of tungsten–molybdenum and tungsten–vanadium alloys. Our analysis focuses on a thorough, side-by-side comparison of dynamic deformation processes, defect nucleation, and evolution, along with corresponding stress–strain curves. We also checked the surface morphology of indented samples through atomic shear strain mapping. As expected, the presence of Mo and V atoms in W matrices introduces lattice strain and distortion, increasing material resistance to deformation and slowing down dislocation mobility of dislocation loops with a Burgers vector of 1/2 (111). Our side-by-side comparison displays a remarkable suppression of the plastic zone size in equiatomic W–V RSS, but not in equiatomic W–Mo RSS alloys, displaying a clear prediction for optimal hardening response of equiatomic W–V RSS alloys. If the small-depth nanoindentation plastic response is indicative of overall mechanical performance, it is possible to conceive a novel MD-based pathway towards material design for mechanical applications in complex, multi-component alloys.

Prospects of Processing Tungsten Ores from the Akchatau Deposit

An overview of the composition of wolframite ores of the Akchatau deposit and the technologies for processing concentrates using NaOH and Na2CO3 by hydro- and pyrometallurgical methods is given, and the disadvantages associated with both the technology and the equipment are noted. To develop a technology for processing Akchatau wolframite concentrates, samples of ore materials were taken, the chemical and mineralogical composition of the samples was studied, and enrichment was carried out to obtain rich concentrates. The kinetics of the sintering of the wolframite concentrate with soda was investigated, the dependences of the degree of transformation of the tungsten minerals into sodium tungstate were obtained, and the rate constants, the order of the reaction, and the values of the apparent activation energy were calculated. The results of sintering an enlarged sample of wolframite concentrate with soda in a muffle furnace are presented. After the subsequent leaching, studies were carried out to purify the obtained solutions of sodium tungstate from the impurities while eliminating the operations of the neutralizing solutions through the use of electrodialysis with an MK-40 cation-exchange membrane. The scheme of processing the wolframite ores of Akchatau is proposed.

The Plasma Electrolytic Oxidation of Aluminum Using Microsecond-Range DC Pulsing

This manuscript presents the results of our recent work focused on the plasma electrolytic oxidation of aluminum in a sodium tungstate solution using a microsecond-range pulsed DC signal. DC pulses of 50, 300 and 900 μs were followed by 5- and 25-times longer pauses between the pulses, showing the effect of the pulse duration and duty cycle on the morphological, phase and chemical properties of formed oxide coatings. It is shown that all coatings are partially crystalline with gamma-alumina, WO3 and metallic W phases present in formed PEO coatings. A higher duty cycle value results in the higher crystallization of the obtained PEO coatings. Although the chemical composition of the obtained coatings is not very sensitive to processing parameters, their roughness and porosity change significantly, as well as their thickness. The photocatalytic activity and photoluminescence properties of the obtained coatings are dependent on their morphology and chemical composition, i.e., on the processing time. The highest photoactivity and photoluminescence intensity is observed for the coating formed with ton = 300 μs and toff = 25 ton. A comparable application potential is found for the sample processed with ton = 50 μs and toff = 25 ton, which requires considerably less energy for PEO processing.

Effect of SPS frequency on the transformation of diamond to graphite in WC-Co composite

(WC–6wt%Co)/5Vol% diamond composites were successfully fabricated at 1150–1300 °C and 40 MPa for 5 minutes under the thermodynamically unstable conditions of the Spark Plasma Sintering method. The influence of on-off time, and frequency of the DC pulse of SPS on diamond stability, microstructure, and mechanical properties of WC–Co/diamond composites were investigated. The diamond particles are strongly bounded with the cemented carbide matrix by a transition layer composed of a solid solution of tungsten and carbon in cobalt. The amount of graphitization was low in the sintered composites at 1300 °C due to the low temperature and short sintering time. Reduction of SPS frequency effectively inhibited graphite preformation, and no graphite was detected in the sintered composites at 1150 °C. Diamond morphology was not affected during SPS as examined by SEM, and Raman scattering spectra. The uniform dispersion of the super-hard diamond phase in matrix which good bonded, caused the high hardness, fracture toughness and flexural strength of this composite. The reduction of pulse frequency of SPS leads to a significant enhancement in the hardness, fracture toughness, and flexural strength of the composites, overcoming the graphitization of diamond typically observed in SPS. The sample sintered with 4 Hz showed simultaneously the highest hardness (23.6 GPa), the highest fracture toughness (24.6 MPa.m½), and the highest flexural strength (2050 MPa).

An innovative strategy for deeply separating macro amounts of molybdenum from tungstate solutions via vulcanization step-by-step and microbubble floating-extraction: Theoretical and experimental investigation

The gradually increasing demand for high-purity tungsten products has become a key challenge and attracted considerable attention in chemical industry, the premise of which is to achieve the deep separation of molybdenum impurities from tungstate solutions. An innovative separation of molybdenum impurity from tungstate solutions were systematically investigated in this work. On the foundation of the theoretical analysis, a novel strategy named vulcanization step-by-step and the vulcanized trajectory of which were proposed. It was found that the thiomolybdate method is still suitable to separate molybdenum from tungstate solutions (Mo/WO3 > 2 wt%) based on the vulcanization step-by-step, and satisfactory separation results were obtained by microbubble floating-extraction. Under optimized conditions, the separation efficiency of molybdenum can reach over 99 %, and the loss of tungsten is approximately 2 %. As a results, the tungstate solutions with Mo/WO3 less than 2 × 10−6 was obtained. Subsequently, the tungsten products (WO3) with a purity greater than 99.99 % was prepared from purified tungstate solutions. Ultimately, the microbubble floating-extraction mechanisms including the mineralization behaviors of target component, the attachment behaviors of hydrophobic complexes on the surface of rising microbubbles and the mass transfer process at the oil–water phase were comprehensively interpreted at the molecular level. This work can provide an important technical support for the preparation of high-purity tungsten products from tungstate solutions containing macro amount of molybdenum.

Green and low-carbon preparation of ammonium paratungstate by adding ammonia to ammonium metatungstate solution

Since the current industrial method for ammonium paratungstate (APT) production from ammonium tungstate solutions involves evaporative crystallization to remove the excess ammonium, which discharges large amounts of wastewater and consumes considerable energy, a novel method for preparing APT from ammonium metatungstate (AMT) solutions by adding ammonia was developed and investigated systemically in this study. Thermodynamic calculations indicated that the dominant tungsten-containing anions depending upon the solution pH were: metatungstate [H2W12O406−] at pH 2–4, paratungstate [H2W12O4210−] and [W7O246−] at pH 5–8, and tungstate WO42− at pH > 8. The experimental results showed that the temperature, ammonia dosage, stirring speed, reaction time and different ammonium salts added affected the crystallization efficiency and crystalline morphology. The APT crystallization efficiency reached 91.4% with an average particle size of 492.2 μm under the following conditions: a temperature of 85 °C, a 1.6-fold stoichiometric ammonia dosage, a reaction time 5 h, a stirring speed 150 rpm and a C(NH4)2SO4 1 mol/L. The crystallization mechanism involved the transformations of isopolytungstate ion from H2W12O406− to the intermediate H6W12O426− and then to the final H2W12O4210−, which resulted in APT precipitation due to accumulation and combination of the H2W12O4210− and NH4+ ions in solution. The crystallized product exhibited the two primary phases (NH4)6[H6W12O42]·10H2O and (NH4)10[H2W12O42]·10H2O at 40 °C and 55 °C, respectively, while (NH4)10[H2W12O42]·4H2O was formed at temperatures ≥70 °C. Results showed that (NH4)6[H6W12O42] acted as an intermediate in APT crystallization from the AMT solution, which has not been previously reported. Compared with evaporative crystallization, this method for preparing APT product from AMT solutions by adding ammonia exhibits the advantages of (i) less chemical consumption, (ii) minor amounts of discharged wastewater, (iii) low production costs, and (iv) environmental friendliness.

Transition Metal Dichalcogenide WS2 Films Prepared with a Combination of Spin/Dip Coating and CVD

Recently, transition metal dichalcogenides (TMDCs) with 2D structure have attracted interest due to their many unique optical and electrical properties. The primary preparation methods for 2D materials are chemical vapor deposition (CVD), exfoliation, and other vacuum technologies. Large-scale synthesis of WS2 via solution-process is rare due to the higher temperature needed for tungsten-based precursors. Combination of spin coating or dip coating with CVD have been studied recently to make large-area 2D TMDC with good electrical properties. Here, we report a new synthetic route for large WS2 crystal that combined solution coatings and CVD process. A solution of sodium tungstate and hydrazine hydrate with sodium thiosulphate was coated on a silicon wafer via dip and spin coating. The films were then treated with CVD at various positions and temperatures to facilitate crystallization. The double coating conditions and CVD parameters were modified to obtain WS2 crystals. Triangular shaped 44 ± 4 µm WS2 crystals could be obtained with simple annealing above 900oC without gas treatment. The synthesized WS2 was found to be bulk with a triangular shape, as confirmed by Raman and AFM analyses. A PL peak of WS2 at 643 nm was observed at an early crystallization stage.

Enhancement of iron‐based oxygen carriers through alloying with tungsten oxide for chemical looping applications including water splitting

AbstractChemical looping applications offer a variety of options to decarbonise different industrial sectors, such as iron and steel and hydrogen production. Chemical looping with water splitting (CLWS) is a chemical looping technology, which produces H2 while simultaneously capturing CO2. The selection of oxygen carriers (OCs) available to be used in CLWS is finite, due to the thermodynamic limitations of the oxidation with steam for different materials at the relevant process temperatures. Iron‐based materials are one of the most widely studied options for chemical looping combustion (CLC), touted for their relative abundance and low cost; likewise, for CLWS, iron is the most promising option. However, when the reduction of iron oxide (Fe2O3) is extended to wüstite (FeO) and iron (Fe), agglomeration and sintering problems are the main challenge for fluidisation.This work presents iron and tungsten mixed oxides as the OCs for a family of chemical looping applications. The OCs were produced via co‐precipitation; performance assessment was conducted in a thermogravimetric analyser and a lab‐scale fluidised bed reactor over continuous redox cycles. The use of tungsten combined with iron results in a solid solution of tungsten within the Fe2O3 matrix that produced a more mechanically stable material during operation, which performed well during multiple redox cycles with no apparent decrease in the oxygen transport capacity and showed no apparent agglomeration. Furthermore, materials containing tungsten showed a resistance to carbon deposition, whereas the reference Fe2O3 showed peaks of CO and CO2 during the oxidation period, thus indicating carbon deposition. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

The Mechanism of Frabot Test for Uric Acid

Uric acid is an Analyte. Excess uric acid ─ hyperuricemia ─ leads to gout and renal stones. Frabot noted that uric acid added to an alkaline tungstate solution developed an intense blue colour. A colorimetric method widely utilized to quantify uric acid depends on the reduction of the chromogen sodium tungstate by uric acid to produce a measurable colour change. The reaction route from the initial products to the coloured compounds and the oxido-degradation of the organic substance has not been advanced. In this communication the electron flow is given in each step of the series of reactions that take place. These are isomerization to imidol, Michael addition to enone, oxirane formation in a redox step, hydrolysis of imido group, oxirane ring opening, ring contraction to five- member ring, ring opening via alkoxide, and finally assisted decarboxylation to the end product, 5-ureido hydantoin (allantoin).

Highly efficient and selective removal of vanadium from tungstate solutions by microbubble floating-extraction

Highly efficient and selective removal of vanadium from tungstate solutions by microbubble floating-extraction

Adsorption Properties of a Polyamine Special Ion Exchange Resin for Removing Molybdenum from Ammonium Tungstate Solutions

A polyamine special ion exchange resin was used to adsorb Mo from ammonium tungstate solutions. The effects of adsorption time, S2− concentration, adsorption temperature, CO32− concentration, mass ratio of WO3 to Mo, and Mo concentration on the Mo and WO3 adsorption capacities were investigated. Energy dispersive spectrometer plane scans were used to study the distributions of Mo, W, S, and Na on the loaded polyamine special ion exchange resin and the desorbed polyamine special ion exchange resin. The results showed that the polyamine special ion exchange resin performed well during adsorption and desorption. Under the optimum conditions for the static adsorption experiments, the adsorption capacities for Mo and WO3 were 99.29 mg/mL and 31.97 mg/mL, respectively, and the desorption rates for Mo and WO3 were 99.35% and 99.43%, respectively. Adsorption and desorption of molybdenum and tungsten on the polyamine special ion exchange resin were investigated by dynamic adsorption experiments with an ammonium tungstate solution containing 125.0 g/L WO3, 12.50 g/L Mo, 15.65 g/L S2−, and 0 g/L CO32−. The adsorption capacities for Mo and WO3 were 53.48 mg/mL and 9.79 mg/mL, and the adsorption rates for Mo and WO3 were 99.05% and 1.81%, respectively. The loaded polyamine special resin was desorbed with a 45 g/L sodium hydroxide solution, and the dynamic desorption rates for Mo and WO3 were 99.02% and 99.29%, respectively.

Extraction of Sodium Tungstate from Tungsten Ore by Pyrometallurgical Smelting

Tungsten is one of the strategic metals produced from tungsten ores through sodium tungstate. The hydrometallurgical process is a common technology for extracting sodium tungstate from high-grade tungsten concentrates. The grade of tungsten ore is decreasing, and the mineral processing to produce a high-grade concentrate suitable for the hydrometallurgical process is becoming more difficult. It is desirable to develop a new technology to effectively recover tungsten from the complex low-grade tungsten ores. A fundamental study on the pyrometallurgical processing of wolframite was carried out through thermodynamic calculations and high-temperature experiments. The wolframite was reacted with Na2CO3 and SiO2 at 1050–1200 °C and then leached with water to obtain a sodium tungstate solution as a feed for the traditional process of APT (Ammonium paratungstate). The factors affecting the extraction rate of tungsten from wolframite were investigated in air and neutral atmosphere. The extraction rate of tungsten was found to increase with increasing Na2O content and decrease with increasing SiO2 addition and temperature. The extraction rate in argon was higher than that in air for wolframite.

Production of fine-dispersed tungstic acid

The paper presents the results of studies of fine-grained tungstic acid synthesis and research of tungsten trioxide obtained from it. A literature analysis was performed and the direction of the study was formulated. A method of precipitation of tungstic acid from sodium tungstate solutions by hydrochloric acid solution has been proposed. To produce tungstic acid, a continuous operation unit that provided the required draining rates of sodium tungstate and hydrochloric acid solutions, the temperature of draining solutions and their concentrations, was created. The dependence of the specific surface of the obtained tungstic acid on the concentration of the used hydrochloric acid was investigated, and the optimum concentration of hydrochloric acid at 430 grams per liter was determined. Using the mathematical method of simplex-planning experiments, the effect of three parameters on the specific surface area of tungstic acid — the concentration of sodium tungstate solution, the ratio of volume rates of drained solutions, and the temperature of drained solutions, was investigated. The following, close to optimum parameters have been received: concentration of sodium tungstate solution of 35–40 grams per liter, ratio of concentrated (430 g/l) hydrochloric acid to the volume of sodium tungstate solution is (1.9–2.0):1, temperature of solutions is 15–20 °С. Tungstic acid with a specific surface area of 60 m2/gram was obtained. It is determined that for the preparation of tungsten trioxide with a high specific surface area, the heating rate of tungsten acid in its drying must be 40–50 degrees per hour and the final drying temperature must be equal to 400 °C. Figures illustrating the dependence of the specific surface of the obtained tungstic acid on the concentration of sodium tungstate solution, the ratio of the volume velocities of the drained solutions and the temperature of the drained solutions are presented.

A novel method for preparing tungsten and molybdenum peroxy complex solution and its application to tungsten - molybdenum separation

Aiming at the shortcomings of existing separation technology of tungsten (W) and molybdenum (Mo) by hydrogen peroxide (H2O2) complexation, the chemical behaviors of W(VI) and Mo(VI) in aqueous solutions were studied and a new method for preparing W(VI)-Mo(VI)-H2O2 solution was proposed. By using trialkyl phosphine oxide-tributyl phosphate (TRPO-TBP) as a mixed extractant system, the applications of this new method on separation of W and Mo were conducted, including the effect on third phase formation and elimination, satisfactory removal of Mo, and separation efficiency of Mo and W. The results show that the formation and depolymerization of isopoly and heteropoly compounds of W and Mo have an important influence on their separation. The core of the new method lies in the control of pH value when W and Mo begin to complex with H2O2. The formation of metatungstate and heteropoly compounds with high Mo/W atomic ratio could be avoided by adding H2O2 into the mixed solution of tungsten and molybdenum in a high pH range of 5.3–6.5 for complexation. Based on this principle, this method could not only avoid the third phase formation at the source but also effectively improve the satisfactory removal of molybdenum. As the complexation pH value increased from 3.51 to 5.51, after six-stage countercurrent extraction of feed solution containing about 127.8 g/L WO3 and 16.10 g/L Mo, the mass ratio of Mo/WO3 in raffinate decreased from 5.94 × 10−4 to 2.71 × 10−5 and the molybdenum content decreased from 77.50 mg/L to 3.54 mg/L. This study provides a relevant theoretical foundation and feasible improvement for the satisfactory separation of W and Mo from peroxy complex solution system, and is expected to facilitate the industrialization of this technology.

INFLUENCE OF TUNGSTEN AND MOLYBDENUM ON Н2О2 ACCUMULATION IN N.BENTHAMIANA PLANT

The problem of soil pollution with heavy metals is one of the main factors hindering the development of agriculture in Kazakhstan. Soil pollution with heavy metals, especially tungsten, leads to a deterioration in plant growth and development, the formation of active oxygen radicals, and oxidative stress. In plants, tungsten (W) acts as an inhibitor of molybdoenzymes, replacing molybdenum (Mo) in the Mo-cofactor structure. At the same time, Mo itself at high concentrations also negatively affects plant cells. When exposed to tungsten and molybdenum, reactive oxygen species (ROS) accumulate excessively in the plant. When the test plant N. benthamiana is exposed to molybdenum, the accumulation of Н2О2 is sharply reduced compared to the control plant, and in plants treated with a solution of tungsten, the accumulation of Н2О2 is increased by 2 times. The accumulation of Н2О2 in plants treated with a combined solution of molybdenum and tungsten was higher compared to the control plant. An interesting result is an increase in the accumulation of Н2О2 by 3.5 times when exposed to tungsten compared to molybdenum.