Ammonium Paratungstate Research Articles

Regulating oxygen vacancies to optimize the electronic structure and catalytic activity of tungsten oxides for hydrogen evolution reaction

The undesirable intrinsic activity of tungsten oxides derived from poor conductivity and adverse hydrogen absorption energy is insufficient for their practical application. Herein, the tungsten oxides with adjustable oxygen vacancies were synthesized by a facile pyrolysis of ammonium paratungstate hydrate in controllable atmospheres. The structural characterizations confirmed that oxygen vacancies and crystalline phases in tungsten oxides depend on the pyrolysis atmosphere. The electrochemical test indicated a strong dependence between catalytic activity and oxygen vacancies in tungsten oxides. Combining experimental results and density functional theory calculations verified that introducing oxygen vacancies into tungsten oxides effectively modulates the surface electronic structure. The enhanced electronic conductivity by reducing band gap accelerates the electron transfer from catalysts into the reactive species. The optimized hydrogen adsorption energy by electron migration from O into W promotes the activation of reactive species at W sites and the desorption from O sites, thereby accelerating the reaction kinetics.

Chitosan and Its Derivatives as a Barrier Anti-Corrosive Coating of 304 Stainless Steel against Corrosion in 3.5% Sodium Chloride Solution

This study investigates the corrosion resistance of chitosan and its crosslinked form coatings applied on stainless steel as substrate using various analytical techniques. Fourier transform infrared spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed for surface characterization. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques were used to analyze the electrochemical behavior. Four coatings were evaluated along with naked stainless steel (ss): chitosan (Chi), chitosan crosslinked with ammonium paratungstate (Chi/PTA), chitosan crosslinked with polyethylene glycol (Chi/PEG), and chitosan crosslinked with polyvinylpyrrolidone (Chi/PVP). Electrochemical measurement parameters analysis assessed the coating corrosion resistance, such as impedance modulus (|Z|) and corrosion potential (Ecorr). Results indicate varying degrees of corrosion resistance among the coatings. Chi/PTA exhibited notable characteristics in the electrochemical tests, showing promising polarization resistance (Rp) and impedance behavior trends. Conversely, Chi/PEG showed differing electrochemical responses, suggesting higher susceptibility to corrosion under the study conditions. These findings contribute to understanding the electrochemical performance of chitosan-based coatings on stainless steel, highlighting their potential in corrosion protection applications.

Kinetic study of reaction formation of phosphate products from thermal dissolution of wolframite using fusion technique

This study examined an alternative technique of extracting tungsten from wolframite ore using a fusion method with ammonium phosphate salt. Current techniques use alkali salts to decompose tungsten ores and use various purification methods to produce ammonium paratungstate, which is a key intermediate precursor in the extraction of tungsten. In this study, a two-step extraction process, which involves thermal decomposition of the ore using fusion and a separation stage, is examined. The novelty of this technique is the ability to completely decompose wolframite ore and form an unstable tungsten oxide phosphate (WO2(PO3)2) compound. The instability of WO2(PO3)2 in deionized water enables selective isolation of tungsten as insoluble precipitates of WO3 and WO2. The decomposition reaction of WO2(PO3)2 is influenced by the presence of oxygen and determined to be first order under ambient conditions. Scanning electron micrographs and X-ray diffraction analysis showed above 80% of the tungsten precipitated compared with the amount that remained in the filtrate solution.

A Fundamental Study on the Preparation of Sodium Tungstate from Wolframite via the Smelting Process

Tungsten is a high-value resource with a wide range of applications. The tungsten metal is produced via ammonium paratungstate, which is a multi-stage process including leaching, conversion, precipitation, calcination, and reduction. A short process to produce tungsten metal from the electrolysis of molten sodium tungstate has been demonstrated. However, sodium tungstate cannot be directly produced from wolframite in the conventional hydrometallurgical process. There was no information reported in the literature on producing sodium tungstate directly from tungsten concentrates. The present study proposed a simple and low-cost process to produce sodium tungstate by high-temperature processing of wolframite. The mixtures of wolframite, sodium carbonate, and silica were melted in air between 1100 and 1300 °C. High-density sodium tungstate was easily separated from the immiscible slag, which contained all impurities from wolframite, flux, excess sodium oxide, and dissolved tungsten oxide. The slag was further water leached to recover sodium tungstate in the solution. Effects of Na2CO3/Ore and SiO2/Ore ratios, temperature, and reaction time on the recovery of tungstate and the purity of sodium tungstate were systematically studied. Sodium tungstate containing over 78% WO3 was produced in the smelting process, which is suitable for the electrolysis process. The experimental results will provide a theoretical basis for the direct production of sodium tungstate from wolframite. The compositions of the WO3-containing slags and sodium tungstate reported in the present study fill the knowledge gap of the tungsten-containing thermodynamic database. Further studies to use complex and low-grade tungsten concentrates to produce sodium tungstate are underway.

Refining mechanisms of arsenic during preparation process of ultrafine WC powder by nitridation−carbonization method

To simplify the preparation process and prepare ultrafine WC powder, a certain amount of As element was added to the ammonium paratungstate precursor. The mechanism of As in the preparation process of ultrafine WC powder by nitridation−carbonization method was systematically discussed. The results show that when the carbonization temperature was 1400 °C, the nitridation temperature increased from 500 to 600 °C, and the As content increased from 0 to 0.3 wt.%, the average particle size of the prepared WC powder decreased from 2.23 to 0.22 μm, and the particle uniformity was significantly improved. The As element in the nitrided product was in the form of W2O3(AsO4)2, which was easily enriched or distributed between the two phases on the surface of the nitrided products (NH4)0.42WO3 and WN, hindering the growth of WC grains during the carbonization process. Consequently, ultrafine WC powder was prepared.

Study on agglomeration mechanism of ammonium paratungstate pentahydrate and controllable preparation of pure monodisperse crystals

Ammonium paratungstate (APT) is an important intermediate for the production of tungsten-containing products. However, its morphology problems caused by crystal agglomeration affect its properties. In this paper, the mechanism of agglomeration during the evaporative crystallization of APT was studied. The experimental result reveals that the temperature, as a critical parameter, significantly affects hydrates purification of crystallization. Combined with on-line and off-line analysis, it is proposed that the crystal agglomeration mainly results from hydrate transformation from heptahydrate to pentahydrate. Furthermore, based on this agglomeration mechanism, the strategy of adding seeds was applied to control the supersaturation within the metastable region and to avoid the nucleation of heptahydrates. The effect of seeds properties, such as the effect of its mass and size on the particle size distribution and agglomeration degree of the products, were investigated in batch crystallization. Finally, we obtained monodisperse crystals of pure APT·5H2O with better performance.

Solid-State 183W NMR Spectroscopy as a High-Resolution Probe of Polyoxotungstate Structures and Dynamics.

Polyoxometalates such as ammonium paratungstate (APT) constitute an important class of metal oxides with applications for catalysis, (opto)electronics, and functional materials. Structural analyses of solid polyoxometalates mostly rely on X-ray or neutron diffraction techniques, which are largely limited to compounds that can be isolated with long-range crystallographic order. While 183W NMR has been shown to probe polyoxotungstate structures and dynamics in solution, its application to solids has been extremely limited. Here, state-of-the-art methods for the detection of solid-state 183W NMR spectra are tested and compared for APT in different hydration states. The highly resolved solid-state spectra distinguish each crystallographically distinct site in the tungstate structure. Furthermore, the 183W chemical shifts are shown to be highly sensitive to the local structure, dynamics, and symmetry of APT, establishing solid-state 183W NMR spectroscopy as a potent probe for analysis of polyoxotungstates and other tungsten-derived materials to complement solution NMR and diffraction-based techniques.

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.

Электрохимическая переработка отходов ренийсодержащих сплавов на основе вольфрама в аммиачно-карбонатных растворах

The electrochemical behavior of rhenium-containing tungsten alloys waste of the type WRe (wt. %: W — 80–95, Re — 5–20) in a solution of (NH4)2CO3 1,0 M was studied using the method of linear voltammetry in potentiodynamic mode and potentiostatic electrolysis. Separation of tungsten and rhenium from the resulting electrolyte was carried out by crystallization of ammonium paratungstate and concentration of rhenium in the mother liquor. A basic technological scheme for the processing of rhenium-containing tungsten alloys is proposed.

Development of chitosan base graphene oxide/ WO3 hybrid composite for supercapacitor application

The use of non-renewable energy has brought to serious environmental problems for the planet. The amount of greenhouse gases rose immediately as the combustion of fossil fuels increased. As a result, sea levels are steadily rising and the Earth is becoming warmer. Research on renewable energy sources has been done extensively to provide a solution. However, in order to maximise energy utilisation, renewable energy needs an energy storage system, such as a super capacitor. For the development of sustainable supercapacitors for future energy systems, electrode material is a prospective target. The formation of desired electrode material is essential in order to fabricate supercapacitor with higher power density and longer life cycle than secondary batteries in electronic application. In this study, chitosan (CS) was isolated from crab shells, and graphene oxide (GO) was synthesized using a modified Hummers' process, followed by a chemical reduction approach. Based on the results, the synthesized GO exhibited higher capacitance as compared to GO that synthesized through single-step modified Hummers’ method. Continuous efforts have been exerted to further improve the electrochemical performance of GO/WO3 nanocomposite by incorporating an optimum content of WO3. In this manner, comprehensive investigations on different parameters, such as loadings of ammonium paratungstate (APT), hydrothermal temperature and reaction time were conducted in order to study the formation of GO/WO3 nanocomposite. WO3 and GO/WO3 nanocomposite were successfully synthesized through a simple hydrothermal method.

Efficient extraction of tungsten from isopolytungstate using anion exchange resin

ABSTRACT Isopolytungstate is considered an important intermediate product in scheelite metallurgy. However, extracting tungsten from the isopolytungstate solution and producing the conventional commodity ammonium paratungstate is challenging. This study is based on the polymerisation of tungsten to various polytungstates in acid solutions. Using the different morphologies of polymerisation, different types of anion exchange resin were used to extract tungsten from the isopolytungstate solution. The results indicated that the D301 resin had a better adsorption efficiency than the other resins. The tungsten adsorption efficiency reached 99.62% under suitable adsorption conditions. Additionally, tungsten loaded by resin could effectively be desorbed through the alkali desorbent. Under optimal desorbing conditions, the desorption efficiency reached up to 98.94%. This work proposes promising routes for extracting tungsten from isopolytungstate solutions.

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.

Chitosan-Based Sustainable Coatings for Corrosion Inhibition of Aluminum in Seawater

Metals are widely used in various industrial applications due to their advantageous properties, but they often exhibit signs of degradation over time because of prolonged exposure to environmental conditions. To prevent corrosion, coatings have gained popularity owing to their practicality in maintaining the original shape and dimensions of the object being protected. Nevertheless, traditional coatings may pose significant toxicological and environmental concerns, leading researchers to explore eco-friendly alternatives such as chitosan-based coatings. Chitosan, a biopolymer derived from chitin, is abundant in nature and has been extensively studied for its physicochemical properties, including its potential in the development of new materials. Chitosan-based coatings have shown promise as effective corrosion inhibitors, and this study aims to develop a crosslinked chitosan-based coating from shrimp waste as an alternative to expensive, commercial coatings. Chitosan, and chemically modified polyethylene glycol, polyvinylpyrrolidone, and ammonium paratungstate chitosan coatings of high- and medium molecular weight prepared by the sol-gel technique, were used for the study of corrosion protection of aluminum in 3.5% synthetic seawater. The molecular interactions and structural alterations following cross-linking of chitosan-based coatings was supported by FTIR-ATR. Surface morphology analysis by AFM indicated good coating adsorption on aluminum surfaces. Contact angle measurements showed hydrophilic properties with contact angles >62° and <90°. Physicochemical characterization (molecular weight (kDa), deacetylation (%), humidity (%), and ash (%)) was also carried out. The corrosion inhibition effectiveness was assessed by gravimetric tests after immersion studies, and the results highlighted the MMW-Chi-based coating’s performance.

Influence of the Precursor Structure on the Formation of Tungsten Oxide Polymorphs.

Understanding material nucleation processes is crucial for the development of synthesis pathways for tailormade materials. However, we currently have little knowledge of the influence of the precursor solution structure on the formation pathway of materials. We here use in situ total scattering to show how the precursor solution structure influences which crystal structure is formed during the hydrothermal synthesis of tungsten oxides. We investigate the synthesis of tungsten oxide from the two polyoxometalate salts, ammonium metatungstate, and ammonium paratungstate. In both cases, a hexagonal ammonium tungsten bronze (NH4)0.25WO3 is formed as the final product. If the precursor solution contains metatungstate clusters, this phase forms directly in the hydrothermal synthesis. However, if the paratungstate B cluster is present at the time of crystallization, a metastable intermediate phase in the form of a pyrochlore-type tungsten oxide, WO3·0.5H2O, initially forms. The pyrochlore structure then undergoes a phase transformation into the tungsten bronze phase. Our studies thus experimentally show that the precursor cluster structure present at the moment of crystallization directly influences the formed crystalline phase and suggests that the precursor structure just prior to crystallization can be used as a tool for targeting specific crystalline phases of interest.

Electrochemical assessment of refractory metallic catalysts for application in oxygen evolution reaction

The development of electrocatalysts for water splitting is a challenging issue for researchers in the field, because the oxygen evolution reaction (OER) occurs in multiple stages and with slow kinetics. In this study, Tungsten (W) and Molybdenum (Mo) (refractory metals) particles with a Body-Centered Cubic (BCC) structure were obtained through the high-energy milling of precursors Ammonium paratungstate (APT) and Ammonium heptamolybdate (AHM)) followed by reduction/decomposition in hydrogen (H2) atmosphere. It was found that particle size and oxygen vacancies strongly influence the catalytic activity of refractory metals. In fact, the W smaller particle/crystallite size, confirmed by Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) techniques, as well as the larger ratio O2/O1 = 0.81 determined by X-ray photoelectron spectroscopy (XPS), leads to a sharp increase in current density compared to Mo that have O2/O1 = 0.75. The W particles only require 322 mV vs. RHE to generate a current density of 10 mA cm−2, against 334 mV vs. RHE for Mo. The W showed superior electrocatalytic performance, with low overpotential, Tafel slope of 53 mV dec−1, CDL of 1.79 mF cm−2, ECSA of 44.75 cm2, the specific activity of 10.72 mA cm−2, and mass activity of 2400 A g−1. Therefore, this two-step synthesis method is highly effective in producing catalysts with excellent electrochemical responses for energy applications.

Synthesis and characterization of tungsten trioxide (WO3) as photocatalyst against wastewater pollutants

In this work, crash precipitation technique was employed to synthesize a visible light-responsive tungsten trioxide (WO3) photocatalyst using ammonium paratungstate as tungsten precursor. The spray-dried (120 °C) and calcined (600 °C) WO3 powder was characterized by analyzing methods of XRD, PSD, BET and BJH, Raman, FESEM/EDX, FTIR, UV–vis DRS and XPS spectroscopy. X-ray diffraction (XRD) and Raman studies confirm the well crystalline monoclinic crystal structure. Scanning electron microscopy (SEM) images showed micron-sized spherical bulks of WO3 particles with needle-like morphology. A normal distribution with a d50 (median diameter) value of 6.0 μm was observed with particle size analysis. Much enhanced BET surface area of 102 g/m2 with wide pore size 1.8 nm is measured compared to commercially available WO3 that results in increased pollutants surface adsorption. Fourier transform infrared spectroscopy (FTIR) study demonstrated that the calcined sample surface is enriched with bonded hydroxyl groups, beneficial for powder particles activity. Photocatalyst band gap was calculated by considering the absorbance measurements recorded on UV–vis diffuse reflectance spectroscopy (DRS). The energy value of 2.6 eV was calculated which lies in the visible light region while X-ray photoelectron spectroscopy (XPS) analysis showed 6 + oxidation state for tungsten. Bulk WO3 sphere photocatalytic activity was evaluated through the exertion of synthetic textile methylene blue (MB) dye and sulfamethoxazole (SMX) pharmaceutical antibiotic. The obtained activity results showed 85% and 100% degradation for MB and SMX under 100 min visible light irradiation. We expect that our work may provide a new sample for energy production (H2) through water photolysis, gas sensing and soft matter research.

OVERVIEW OF THE GLOBAL TUNGSTEN MARKET. PART 2. COMMODITY FLOWS OF RAW TUNGSTEN PRODUCTS

Link for citation: Boyarko G.Yu. Overview of the global tungsten market. Part 2. Commodity flows of raw tungsten products. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.37-53. In Rus. The relevance of the work is caused by the need to study the problems of quite volatile world market of tungsten raw materials. Objective: to study the dynamics of global commodity flows (production, import, export, consumption) of raw tungsten products (tungsten ores and concentrates, ammonium paratungstate, tungsten waste and scrap); to assess the criticality of the world market of raw tungsten products. Methods: statistical, graphical, logical. Results. The raw tungsten product global market is very complex. The world production of primary tungsten raw materials increased from 4 to 7 kt 100 % W/year in 1913–1915, from 75 to 90 kt 100 % W/year in 2011–2020 with a growth rate of +2,9 %/year. Utilization of secondary tungsten raw materials in the world increased from 2–3 kt 100 % W/year in 1970s to 14–23 kt 100 % W/year in 2008–2020 with an increase rate of +4,3 %/year. The share of global utilization of tungsten waste from the amount of primary and secondary tungsten raw materials increased from 5–6 % in 1970s to 21 % in 2019. In 1970–1980, there was a period of usual low-growth global consumption of tungsten products with the growth rate of tungsten raw materials demand for +3,4 %/year. There was a strong decrease in demand for tungsten products (–6,9 %/year) in the military sphere (the end of the Cold War) and priority shift in the trade of tungsten raw material comodities (increase in the role of ammonium paravolframate trade), reducing the role of Russia in the tungsten market (the consequences of the stagnation of the Russian economy, primarily metalworking) in the 1990s. In the 2000–2010s, there was a rapid growth in global demand for final tungsten commodity products and, accordingly, global demand and supply of tungsten raw materials, with an increase in demand of +6,4 %/year. At the same time, there is a trend of decreasing share in world trade in tungsten raw materials from the amount of extracted primary and recycled secondary raw materials by volume and cost, respectively, 39 and 47 % in 1970 to 21 and 27 % in 2020. The share of raw materials in world trade in tungsten products decreased from 70–80 % by volume and 60–70 % of the cost in 1970–1980s, respectively, up to 42–55 and 15–20 % in the 2010s. China dominates in the global production, processing and consumption of raw tungsten products, therefore, its trade policy to restrain (quota) exports of these goods determines the dynamics of the world market of tungsten raw materials. In international trade, China has changed the strategy of exporting raw materials to importing them, while becoming the leader in importing tungsten concentrates. Other industrialized countries – consumers of tungsten raw materials – the USA, Germany, Britain, France, Japan and South Korea – have become critically dependent on tungsten raw material imports (the share of imports is over 50 % of consumption) and will remain so in the foreseeable future.

Preparation ultrafine WC based on the new tungsten metallurgy system of “no ammonia transformation - no hydrogen reduction”

The preparation of ultra-fine tungsten carbide (WC) is a difficult and hot topic in tungsten industry. The industrial production process requires the need to transform tungsten concentrates to produce ammonium paratungstate (APT) intermediate products followed by hydrogen reduction to produce W, and finally carburization to produce WC. Due to the formation of H2O in the hydrogen reduction process, it is difficult to obtain <100 nm tungsten powder materials. Therefore, in this study, a novel method was introduced that synthesizes ultrafine WC via hydrothermal synthesis of ZnWO4 followed by a carbothermic reduction–carburization process. The findings of this study showed that ZnWO4 with a particle size of 29 nm was synthesized from Na2WO4 solution. This can solve the problem of ammonia‑nitrogen wastewater discharge in the process of APT preparation, and prepare nano-scale raw material. In addition, zinc is volatile at high temperature, which has been widely used in the field of recycling waste cemented carbide. Based on this, the WC mixed powder was obtained by carbothermic reduction of ZnWO4 under the condition of excess C addition, which can inhibit the agglomeration of particles and avoid the production of H2O. Then the single-phase WC with a particle size of 60 nm was obtained by a carburization reaction process at 1300 °C for 3 h. The research intersects tungsten metallurgy with tungsten material preparation, shortens the production process and reduces waste water discharge.

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.

Direct transformation of tungsten trioxide monohydrate into ammonium paratungstate tetrahydrate in ammonium salt solutions

Direct transformation of tungsten trioxide monohydrate into ammonium paratungstate tetrahydrate in ammonium salt solutions