Tungstate Solution Research Articles

Solventing out crystallization-basic magnesium carbonate percipitation for thorough phosphorus removal from ammonium tungstate solution.

The ammonium tungstate solution obtained by leaching scheelite with phosphate contains a large amount of phosphorus. For production of qualified ammonium paratungstate products, phosphorus must be deeply removed from the ammonium tungstate solution. In this study, a novel process for ammonium phosphate recovery and deep phosphorus removal from the solution was proposed. First, ammonium phosphate was crystallized and separated from the ammonium tungstate solution by blowing ammonia and cooling. Results showed that the crystallization ratio of phosphorus was above 95% under the conditions of an ammonia concentration of 4.18 mol/L, an initial phosphorus concentration ranging from 15 g/L to 30 g/L, a holding time of 60 min and the temperature of 20°C. Then, the small portion of phosphorus remaining in the ammonium tungstate solution was further deeply removed by basic magnesium carbonate percipitation. The phosphorus removal efficiency was above 99% and tungsten loss was less than 0.22% under the following conditions: the basic magnesium carbonate stoichiometric ratio was 1.5, the initial phosphorus concentration was ranging from 0.5 to 4 g/L, the reaction time was 120 min and temperature was 25°C. After phosphorus removal, the concentration of phosphorus in the ammonium tungstate solution was below 10 ppm, which meant deep phosphorus removal was achieved.

Twin boundaries boost the hydrogen evolution reaction on the solid solution of nickel and tungsten

The development of cost-effective electrocatalysts to produce high-purity hydrogen by electrochemical water splitting is critical to addressing resource and environmental problems. Theoretically, NiW materials are considered to be an excellent HER electrocatalyst. However, current NiW catalysts for HER are not satisfactory. Herein, the NiW solid solution with twin boundaries is successfully fabricated by facile electrodeposition on copper sheet. As compared with Ni, the NiW-0.6A catalyst shows enhanced HER activity in 1 M KOH with the overpotential of 98 mV at 10 mA/cm2. Besides, NiW-0.6A exhibits excellent stability for 100 h at 20 mA/cm2. The excellent HER performance of NiW-0.6A may be attributed to the intrinsic catalytic activity and the defective twin boundaries exposing many active sites. This work could provide feasible suggestions for the design of efficient and high-performance NiW electrocatalysts for HER process..

Cleaner production of ammonium paratungstate by membrane electrolysis-precipitation of sodium tungstate solution

Cleaner production of ammonium paratungstate by membrane electrolysis-precipitation of sodium tungstate solution

Dissolution Behavior of Sodium Phosphate in a Na3PO4–Na2WO4–NaOH Solution System

Sodium hydroxide autoclaving is the main method for smelting scheelite in China. In this method, sodium phosphate is added as an additive to realize the highly efficient decomposition of scheelite, and a crude sodium tungstate solution containing sodium phosphate and sodium hydroxide is obtained. In the subsequent process of ion exchange, phosphorus ions in the solution compete with the resin adsorption of tungstate, which reduces the adsorption capacity of the resin and endangers the purity of the subsequent sodium tungstate solution. To remove the phosphorus from crude sodium tungstate solution, a chemical purification method is usually adopted. The principle of the chemical purification method is to use chemical reagents to react with impurities to form precipitates to achieve the purpose of impurity removal. Because of the advantages of simple industrial implementation and high impurity removal efficiency, it has been widely used in phosphorus removal from crude sodium tungstate solution. However, in the process of phosphate removal in a crude sodium phosphate solution, the chemical purification method has some disadvantages. First, the additional cost of chemical reagents is required, and other metal impurities from chemical reagents would be introduced to crude sodium tungstate solution. Second, phosphate impurity removed by the chemical precipitation method is usually sedimented in other forms but sodium phosphate, which makes the phosphate resource unable to be recycled for tungsten smelting. Therefore, a novel phosphorus removal method needs to be developed. The dissolution behavior of sodium phosphate in a Na3PO4–Na2WO4–NaOH system was investigated in this paper. The results showed that in binary or ternary solution systems of sodium phosphate, sodium tungstate, and sodium hydroxide, the common-ion effect and salt effect exist simultaneously. The common-ion effect decreases the solubility of sodium phosphate, while the salt effect increases the solubility of sodium phosphate. Increasing the concentration of sodium hydroxide or sodium tungstate and lowering the temperature of the solution can greatly reduce the phosphorus concentration in crude sodium tungstate solution, making the crude sodium tungstate solution meet industrial requirements of ion exchange. The results of the study lay a theoretical foundation for the development of new phosphorus removal methods.

Sustainable and efficient leaching of tungsten from scheelite using the mixture of ammonium phosphate, ammonia and calcium fluoride

The traditional scheelite treatment process, which involves the sodium hydroxide decomposition and anion exchange, discharges a large amount of high-salinity wastewater, resulting in severe environmental pollution. In this study, ammonium tungstate solution was prepared directly by scheelite leaching with a mixture of ammonium phosphate, ammonia and calcium fluoride. The effects of ammonium phosphate and calcium fluoride dosages, initial ammonium concentration, temperature, liquid-solid ratio and holding time on the leaching efficiency of scheelite were investigated. The leaching efficiency of scheelite reached 98.6% under the following conditions: the dosages of ammonium phosphate and calcium fluoride were 1.6 and 2 times their theoretical amounts, respectively. Other conditions included: initial ammonia concentration of 30 g/L and L/S ratio of 2:1 at 180 °C and a holding time of 3 h. In addition, the leaching reaction sequence of scheelite and the formation pattern of calcium fluorophosphate were inferred. After purification of the ammonium tungstate solution, a high-purity ammonium paratungstate was prepared by evaporative crystallization. This study presents a new approach for the green and efficient extraction of tungsten from scheelite.

Efficient dissolution of tungstic acid by isopolytungstate solution based on the polymerization theory of tungsten

The rare metal tungsten is a very important strategic metal. The traditional tungsten ore alkaline process has many problems, including the generation of alkali residue, ammonia‐nitrogen wastewater, and industrial wastewater during ion exchange. The feasibility of decomposing scheelite with sulfuric acid has been confirmed due to the economic and environmental pressures faced by scheelite decomposition; however, extracting tungsten from the decomposition residue is a difficult process. This study was based on the polycondensation theory of tungsten, in which tungstic acid (H2WO4) rapidly dissolves in isopolytungstate solution during the acid adjustment process of sodium tungstate solution. Taking advantage of the different polymerization morphologies, a new idea in which tungstic acid selectively enters the solution after the polycondensation reaction between tungstic acid and isopolytungstate is proposed. In this work, the dissolution of tungstic acid in isopolytungstate solution under different experimental conditions were studied. The results indicated that isopolytungstate solution can undergo polycondensation reaction with tungstic acid, and the dissolution of W reached 0.37 g/g under suitable dissolution conditions. Additionally, the residue formed in sulfuric acid decomposition had a satisfactory leaching effect of tungsten in the isopolytungstate solution with a WO3 leaching efficiency of about 98.8%. Tungsten in the hydrochloric acid decomposition residue could also be extracted efficiently in the form of an isopolytungstate solution with a WO3 leaching yield >99%. This work proposes a cleaner and more efficient idea for the selective dissolution of tungsten from the acid decomposition residue of scheelite.

Determination of polyorganosiloxanes (by silicon) in water by extraction high-resolution continuum source electrothermal atomic absorption spectrometry

A method for the determination of polyorganosiloxanes (by silicon) in water using high-resolution electrothermal atomic absorption spectrometry with a continuous spectrum source and preliminary extraction of polyorganosiloxanes by benzene from the analyzed sample is proposed. The quantitative determination of polyorganosiloxanes (by silicon) was carried out on a contrAA® 700 atomic absorption spectrometer in a cross-heating furnace. Natural water was used to optimize the parameters of the temperature – time program of the atomizer. To eliminate chemical interference during silicon determination by proposed method, graphite cuvettes were modified with a permanent modifier to form a carbide coating. A solution of sodium tungstate was used as a permanent modifier. Thermal stabilization of silicon in a graphite furnace was achieved in the presence of a mixed palladium-magnesium modifier in the nitrate form. The accuracy of the results was confirmed by spike test. The developed method of analysis was used to determine the content of polyorganosiloxanes (by silicon) in natural water. The metrological characteristics of the method were assessed in the range of determined silicon contents 0.01 – 100 mg/dm3.

Separation of vanadium and tungsten from synthetic and spent catalyst leach solutions using an ion-exchange resin.

Vanadium and tungsten ion adsorption and desorption characteristics and separation conditions were investigated using a simple porous anion-exchange resin. Initially, systematic experimental research was performed using synthetic aqueous vanadium and tungsten solutions. To evaluate the vanadium and tungsten (50–500 mg L−1) isotherm parameters, adsorption was performed at pH 7.0 using 0.5 g of ion-exchange resin at 303 K for 24 h. Well-known adsorption models such as Langmuir, Freundlich, and Temkin were used. Vanadium was desorbed from the resin using HCl and NaOH solutions. In contrast, tungsten was not desorbed by the HCl solution, which enabled the separation of the two ions. The desorption reaction reached equilibrium within 30 min of its start, yielding over 90% desorption. We investigated the adsorption mechanism and resin stability with the aid of spectroscopic and microscopic analysis, as well as adsorption results. The applicability and feasibility of the resin was tested via recovery of both metals from real spent catalysts. The applicability and reusability results indicated that the resin can be used for more than five cycles with an efficacy of over 90%.

Property and mechanism on sorption of molybdenum from tungstate solution with a porous amine resin

The sustainable development of tungsten and molybdenum resources requires a new clean and recyclable separation technology. This work proposes a recyclable clean separation technology of tungsten and molybdenum with a porous amine resin. The resin was well prepared by assembling amine groups on trioctylamine (TOA) and the porous resin matrix D301 by the dipping method. Here, pH 7.8, temperature 25 °C, and reaction time 240 min was used as optimum condition, resulting in the highest sorption capacity 236 mg g−1, and it has a good cycle performance, exhibiting a retention rate of 90% after five cycles. Experimental spectroscopy combined theoretical calculation confirmed that this sustainable sorption behavior is substantially related to the amine functional groups on the resin. Experimental spectroscopy illustrated that the Cl− ions in the amine resin and the MoS42− ions were subjected to ion exchange. Theoretical investigations further confirm that the sorption site is at the N atoms, the sorption behavior is chemical binding with the binding energy −0.055 Ha, and the bonding method is the s orbit of the N atoms in the amine resin hybridized with the s orbit of the S atoms in the amine resin. Owing to such an excellent performance in the selective sorption of molybdenum from the tungstate solution, the amine resin is greatly promising in the tungsten and molybdenum waste recovery field.

Copper foil after hydrothermal treatment in acidified tungstate solution as conductor- and binder-Free anode electrodes for high performance lithium-ion batteries

Copper foil is commonly used as anode current collector in the battery industry due to its high conductivity, good elasticity and relative abundance. Herein, copper foil was hydrothermally treated in acidified tungstate solution, resulting in the formation of Cu2O and WO3 agglomerated clusters on the copper foil substrate with sufficient open space between neighboring clusters. The copper foil after hydrothermal treatment was directly used as the conductor- and binder-free anode electrode for lithium-ion batteries. Cyclic voltammetry and charge-discharge measurements were performed to investigate the reversible areal capacity, cycling stability and rate capability of the as-prepared electrode. A reversible areal capacity of 357 μAh cm−2 was obtained after 50 cycles at a current density of 60 μA cm−2. Even cycled at a current density of 600 μA cm−2, a reversible capacity of 8 μAh cm−2 remained. When the current density returns to 60 μA cm−2, the conductor- and binder-free electrode exhibits an areal discharge capacity of 430 μAh cm−2.

A Feasible Strategy for Deeply Separating Low Concentrations of Molybdenum from Tungstate Solutions with a High-Efficiency Microbubble Floating-Extraction Concept

A Feasible Strategy for Deeply Separating Low Concentrations of Molybdenum from Tungstate Solutions with a High-Efficiency Microbubble Floating-Extraction Concept

Formation and Properties of Oxide Coatings with Immobilized Zeolites Obtained by Plasma Electrolytic Oxidation of Aluminum

In this paper, we employed plasma electrolytic oxidation (PEO) of aluminum in a water solution of sodium tungstate (Na2WO4∙2H2O) with the addition of the pure and Ce-loaded zeolites clinoptilolite and 13 X for the preparation of oxide coatings. The obtained coatings were characterized with respect to their morphologies and chemical and phase compositions using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray diffraction. The prepared coatings contained γ-alumina, WO3, and metallic tungsten. The surface morphologies of the obtained coatings strongly depended on the PEO processing time; the roughness of all coatings increased with PEO time, while porosity decreased with PEO processing time as a result of microdischarge coalescence and growth. All coatings contained elements originating from the substrate and from the electrolytes. Coatings containing zeolites with Ce showed higher photoactivity than those with immobilized pure zeolites. The highest photocatalytic activity levels were observed for coatings containing immobilized Ce-exchanged clinoptilolite processed for 10 min. It was observed that both clinoptilolite and 13X zeolites improved the features of the PEO coatings in a similar manner, making natural and abundant clinoptilolite an excellent candidate for various applications.

Ultrafine-grain formation and improved mechanical properties of novel extruded Ti-Fe-W alloys with complete solid solution of tungsten

Thermomechanical processing and solid-solution strengthening are effective ways to improve the mechanical properties of Ti alloys with elements such as W and Fe. In this study, we present a novel extruded Ti-Fe-W alloys with improved mechanical properties. To analyze the effect of W on the mechanical properties and microstructure of the alloys, Ti-4Fe-xW (x = 0–3 wt%) alloys were prepared by spark plasma sintering followed by homogenization heat treatment and hot extrusion. The microstructure of the as-sintered specimens included undissolved W particles distributed in the acicular α + β matrix. However, heat treatment at 1300 °C for 1 h led to the complete dissolution of W. After hot extrusion at 850 °C, an ultrafine equiaxed (globular) microstructure was observed, in which Fe and W preferentially diffused into the β phase. The main effect of W on the microstructure was a remarkable grain refinement by activation of dynamic recrystallization and impediment of the grain boundary mobility in Ti-4Fe-(1–3)W (~1 µm) when compared to Ti-4Fe (~3 µm). Additionally, W increment resulted in a gradual decrease of the average size of α grains. The tensile yield strength increased as W content increased so that the Ti-4Fe-3W alloy exhibited a remarkably high tensile strength, yielding at ~1123 MPa with an elongation of ~26%. Finally, theoretical and experimental analyses suggested that grain refinement and solid-solution strengthening were the main mechanisms contributing to the strengthening phenomenon in W-containing alloys.

Determination of the dissolved forms of silicon in natural drinking water using high-resolution continuum-source electrothermal atomic absorption spectrometry

A technique for the determination of dissolved forms of silicon in water using high-resolution continuum-source electrothermal atomic absorption spectrometry (HR-CS-ETAAS) is proposed. The quantitative determination of the dissolved forms of silicon was performed using an atomic absorption spectrometer ContrAA 700 with a graphite cross-heating cuvette. Natural water was selected to optimize the temperature-time program of the atomizer. To eliminate chemical interference during the silicon determination by HR-CS-ETAAS, the graphite cuvettes were modified with a permanent modifier to form a carbide coating. A solution of sodium tungstate was used as a permanent modifier. Thermal stabilization of silicon in a graphite furnace was achieved with a mixed palladium-magnesium modifier present in the nitrate form. The developed method was used for determination of the content of the dissolved forms of silicon in water. The developed technique was certified proceeding from the results of the research and the metrological examination by an organization accredited for this type of the activity and registered in Federal information Fund for ensuring the uniformity of measurements (FIF).

Iron and Manganese Codoped Cobalt Tungstates Co1-(x+y)Fe x Mn y WO4 as Efficient Photoelectrocatalysts for Oxygen Evolution Reaction.

Photoelectrocatalysts are robust materials for the production of energy through different ways such as water splitting. Narrow optical band gaps and high overpotentials are limiting the development of photoelectrocatalysts. In this study, a series of Co1–(x+y)FexMnyWO4 solid solutions of cobalt tungstate codoped with iron and manganese have been synthesized hydrothermally. The synthesized solid solutions have been characterized by powder XRD, UV–visible spectra, cyclic voltammetry (CV), and linear sweep voltammetry (LSV). They all crystallize in a wolframite-type monoclinic crystal system with space group P2/c. Doping of iron and manganese leads to narrowing of the optical band gap of Co1–(x+y)FexMnyWO4 from 2.60 to 2.04 eV. The electrocatalytic activity toward oxygen evolution reaction of all of the samples has been evaluated through LSV measurements. It is found that the sample named C5, which is codoped with manganese and iron, has the lowest onset potential and needs the lowest overpotential to attain the targeted 5 mA cm–2 and standard 10 mA cm–2 current densities as compared with all other synthesized samples. This study shows that the synthesized tungstates can be good candidates for the photoelectrocatalytic oxygen evolution reaction.

Highly efficient sorption of molybdenum from tungstate solution with modified D301 resin.

The separation of molybdenum (Mo) from tungstate solution is a bottleneck problem in tungsten (W) metallurgy, and it hinders the development of high-purity tungsten materials. In this research, a modified D301 resin was used to adsorb and separate molybdenum from tungstate solution. The maximum sorption capacity (Qe) of modified D301 for MoS42− was found to be 428 mg g−1 and the separation coefficient (β) was 108.9 when the contact time was 4 h and the reaction temperature was 25 °C and the pH value of the tungstate solution was 7.2. The sorption process conforms to Langmuir isotherm models and the quasi-second-order kinetic model. The sorption mechanism was also discussed, which was a single layered spontaneous sorption process. Theoretical calculations infer bonding behavior between the N atom on the resin and the S atom on the MoS42− molecule. The sorption energy is −7.67 eV, which indicated that the sorption process is stable chemical sorption. The desorption experiment showed that more than 90% molybdenum could be desorbed from the loaded resin when the concentration of sodium hydroxide solution was 5 w%. Finally, after three-stage sorption–desorption, almost all molybdenum in the solution was adsorbed, achieving better separation of tungsten and molybdenum.

Selective Electrochemical Sensing of NADH and NAD+ Using Graphene/Tungstate Nanocomposite Modified Electrode

AbstractReduced form of β‐nicotinamide adenine dinucleotide (NADH) and its oxidized form (NAD+) are the main cofactors involved in more than 300 dehydrogenase reactions. NAD+ is one of the important oxidizing agent for the oxidation of alcohol, aldehyde and ketones. Similarly, NADH has been used for the treatment of Alzheimer and Parkinson's diseases. Herein, we have reported synthesis of graphene flakes by electrochemical exfoliation of graphite in sodium tungstate solution. It was found that tungstate (WO42−) and hydroxyl (OH−) ions were intercalated into graphite layers and enabled the production of graphene flakes. As‐obtained graphene flakes were characterized by UV‐Visible (UV‐Vis), Fourier transform infrared (FT‐IR), Raman, Field emission scanning electron microscopy (FE‐SEM), Energy dispersive X‐ray (EDX) and High‐resolution transmission electron microscopies (HR‐TEM). FT‐IR, Raman and EDX analysis were confirmed that tungstate (WO42−) ions were present on the surface of graphene flakes. Moreover, graphene‐WO42− (Gr−W) dispersion was prepared by probe‐sonication to form a thin‐film on the surface of glassy carbon electrode (Gr−W/GCE). Interestingly, Gr‐W modified GCE reduced the overpotentials of NADH oxidation and NAD+ reduction. This new senor was also showed linear responses for NADH and NAD+ from 10–270 μM and 100–500 μM, respectively. Furthermore, the selectivity of the Gr−W/GCE was tested in the presence of L‐tyrosine, L‐isoleucine, L‐alanine, glutathione, dopamine (DA), ascorbic acid (AA), uric acid (UA), oxalic acid (OA), glucose, hydrogen peroxide (H2O2), acetaminophen (PA), potassium chloride (KCl) and sodium chloride (NaCl). It was found that selective detection of both NADH and NAD+ could be achieved by using Gr−W/GCE. Finally, the real application of the sensor was demonstrated by accurately detecting spiked NADH concentrations in human blood serum. The recovery analysis was also confirmed that Gr−W/GCE could be useful to detect NADH in biological samples.

Structural Features of Ni–W Alloy Deposited from Pyrophosphate Electrolyte

The composition and structure of Ni–W alloys prepapred from pyrophosphate electrolyte have been studied. It was demionstrated that, regardless of the deposition current density in the range 2–5 A dm–2, alloys are a single-phase system and represent a solid solution of tungsten in nickel with a face-centered cubic lattice. At low deposition current densities in the coating there exists an impurity oxygen-containing phase of tungsten compounds of an intermediate oxidation state. It was found that the oxygen-containing impurity is distributed unevenly over the coating thickness. Impurity grains are formed only at the initial moment of deposition of the coating at the interface with the substrate together with nickel nanocrystals, and only after some time does the formation of the alloy phase begin. The data obtained are explained in term of the cluster mechanism of induced coprecipitation of alloys of refractory metals with metals of the iron group, proposed earlier.

Green separation and recovery of molybdenum from tungstate solution achieved by using a recyclable vulcanizing agent

Separation of molybdenum (Mo) from tungstate solution has become a bottleneck issue in tungsten (W) metallurgy and did hinder the development of high purity tungsten materials. The traditional Mo removal methods using Na2S, NaHS as vulcanizing reagent are suffering the environmental issues of toxic H2S gas and molybdenum trisulfide (MoS3) sludge. To achieve the green separation of Mo from tungstate, a recycle vulcanizing reagent, ethyl thioglycolate (ET) was introduced for the vulcanization of molybdate (MoO42−) from tungstate solution. The vulcanization of Mo by ET, the selective extraction of vulcanized MoO42− from tungstate and the recycling of ET were systematically investigated. The results demonstrated that a high vulcanization efficiency of >98% for MoO42− was achieved and more than 97% of Mo was removed and recovered via vulcanization followed by single-stage solvent extraction, producing a purified tungstate solution with Mo < 5 mg/L (Mo/WO3 < 1 × 10−4) and a byproduct of molybdate solution with 4.1 g/L Mo and <0.01 g/L WO3 under optimal conditions. Additionally, ET exhibited an ideal cycling performance, the regeneration efficiency and the recycled vulcanization efficiency were >95% and >98%, respectively. Compared with traditional vulcanizing reagents, introduction of ET eliminates the emission of toxic H2S gas, significantly decreases the cost caused by the unrecyclable reagent, and transferred the MoS3 sludge into a valuable crude Mo byproduct, which provides an alternative for the green separation and recovery of Mo from tungstate.

Effects of Exogenous Melatonin and ABA on Photosynthetic Characteristics of Naturally Aging Kiwi Seedlings

In this study, the annual yellow kiwi seedlings which were treated with 200μmol/L melatonin (MT), 15μmmol/L abscisic acid (ABA) and 5mmol/L sodium tungstate solution (STD) were used as experimental materials to study the changes in physiological indicators of kiwi fruit under natural aging. After comprehensive analysis, we can speculate that MT may affect the photosynthetic characteristics of aging kiwi by affecting ABA production and keeping its content at a moderate level. The experiment results provided theoretical basis and practical guidance for delaying the production and application of kiwi seedlings.