2019年10月23日星期三

Monoalkyl Phosphate Preparation by Cesium Phosphotungstate

Monoalkyl phosphate is an important surfactant, widely used in chemical fiber, textile, leather, plastics, paper making and cosmetics. 

Monoalkyl phosphate usually synthesized by the esterification of phosphoric acid with aliphatic alcohols by esterification. The commonly used phosphorus agents are three oxychloride (POCl3) and phosphoric acid.

When phosphorus oxychloride is used as an agent for HCL, it is easy to cause environmental pollution, when phosphoric acid is used as a phosphate agent, although it is environmentally friendly, it is difficult to synthesize monoester, diester and three ester because of the low activity of phosphoric acid. Is there a way to improve the activity of phosphoric acid to help balance the benefits of the environment?

monoalkyl phosphate preparation image

Cesium phosphotungstate is a kind of heteropoly acid. It is a new type of multifunctional catalyst. It has not only oxidation reduction property, but also high catalytic activity and good stability, it can be used for homogeneous and heterogeneous reactions, and even can be used as phase transfer catalyst, the most important thing is that it is pollution-free to the environment. Some scholars have studied the synthesis of mono twelve alkyl phosphate by the direct esterification of lauryl alcohol and 85% phosphoric acid with cesium phosphotungstate as catalyst. Through investigation, we found that cesium phosphotungstate in the reaction process showed very high activity during the catalytic reaction, under the catalytic action of cesium phosphotungstate, the selectivity of MAP is 90% with the attraction between lauryl alcohol and phosphoric acid, a single twelve alkyl phosphate has been successfully synthesized. The effect is not weaker than three phosphorus oxychloride (POCl3). The most important is that it is safer and more environmentally friendly with phosphoric acid.

Over the years, cesium phosphotungstate has been recognized more and more by virtue of its excellent catalytic performance and non-toxic and harmless strength. So, when you're not satisfied with the catalytic effect of a certain chemical, you might be able to try cesium phosphotungstate.

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The PK Between Tungsten Trioxide and Titanium Dioxide Photocatalytic Performance

Photocatalysis is a photochemical reaction in the presence of a catalyst, it is a new science and technology.

Common photocatalysts include metal oxides (TiO2, ZnO, Fe2O3, Bi2O3, WO3) and metal sulfides (CdS, MoS2, MoSe2). Titanium dioxide TiO2 is the most white thing in the world, 1 grams of titanium dioxide can paint more than 450 square centimeter area to white. So it's the best paint for making white oil paint. The most well-known is that semiconductor photocatalysis performance of TiO2. TiO2 photocatalysis is widely used because of its high activity, photochemical stability, non-toxic and cheap.

Tungsten trioxide TiO2 is a kind of tungsten compounds that are widely used, It can be used not only for hard alloys, but also for dyes, the most commendable thing is that tungsten trioxide also with excellent photocatalytic performance. Like TiO2, WO3 also has high activity, photochemical stability, non-toxic and so on. If you compare the two, who can be better?

tungsten trioxide and titanium dioxide image

According to the data, TiO2 was the first compound to enter the field of photocatalysis, in 1972, the Japanese discovered that light irradiated TiO2 particles could cause water to undergo a sustained redox reaction, and began the history of photocatalysts. For a long time, TiO2 has been the preferred material for photocatalysis. Until 1983, the scholars in China used WO3 to treat printing and dyeing wastewater for the first time, and achieved very good results. Since then, WO3 has been discovered in application field and application, and gradually catch up from behind, outshining TiO2. How can WO3 compete with TiO2?

TiO2 was used as photocatalyst for a long time. But there are two fatal problems with the performance of TiO2, first, TiO2 has a narrow range of absorption of sunlight, which limits its use of solar energy. Second, photocatalytic reaction efficiency is low, generally not greater than 1%. With the increasingly serious problem of environmental water pollution, TiO2's capacity is too poor, TiO2's weaknesses are the strengths of WO3. From the performance point of view, the activity of WO3 photocatalytic degradation on organic pollutants is higher, the absorption and utilization on sunlight is better.

Tungsten trioxide has better chemical compatibility, WO3 can be mixed with ZnO, Bi2O3, rare earth La, Eu, Y and other elements to form a tungstate photocatalyst, not only pollution control, but also classify the printing and dyeing wastewater, antibiotic wastewater, metal wastewater targeted governance. Therefore, ignoring the price factor, the performance of WO3 undoubtedly has stronger competitiveness.

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Cesium Tungsten Bronze

Cesium tungsten bronze (CsxWO3) is synthesized by solid phase method or liquid phase method with cesium carbonate and sodium tungstate as raw materials.

Cesium tungsten bronze is also called cesium tungstate. CsxWO3 is a non stoichiometric functional compound with a special structure of oxygen eight surface, with low resistivity and low temperature superconducting properties. But in recent years, cesium tungsten bronze is popular for its excellent UV and near infrared shielding performance, with high efficiency, insulation and light reflection effect, this makes it good in the manufacture of special glass, high-end insulation film and LCD screen manufacturing.

In recent years, with the increasing popularity of cesium tungsten bronze, more and more scholars have begun to discuss the liquid phase preparation of cesium tungsten bronze. Some scholars have adopted the hydrothermal method to obtain cesium tungsten bronze, sodium tungstate and cesium carbonate were used as raw materials, in the citric acid solution, the CsxWO3 powder with six square Cs0.33WO3 structure was synthesized by hydrothermal method, and the CsxWO3powder was fully ground and dispersed in a citric acid solution, cesium tungsten bronze film was prepared on glass slide by dipping and dipping method. 

future house image

Through the test of cesium tungsten bronze film, we can draw a conclusion, the CsxWO3 powders obtained by hydrothermal method exhibit strong ultraviolet absorption and short wave near infrared absorption performance, moreover, the absorbance in short wave near infrared region increases with the prolonging of reaction time and the increase of citric acid content. The hydrothermal method failed to solve the cost problem more effectively, but the most important advantage of hydrothermal method is low carbon environmental protection, and the process is easier to control than solid phase method. If more details are to be improved, the large-scale application of cesium tungsten bronze will soon be possible. 

In recent years, with the improvement of people's living requirements, the concept of green house has been popular among people, in the near future, nanotechnology will seep into every detail of live, perhaps our walls, windows, doors, and floors can be made of special glass or paint or film to achieve automatic thermostat adjustment. There is no need to open air-conditioning in summer or open heating installation in winter, real energy saving and environmental protection are achieved, and at that time, such as cesium tungsten bronze and other new materials will certainly have unlimited room for development.

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【Know Tungsten】Sodium Tungstate Applications

Sodium tungstate, Na2WO4•2H2O, a tungstate of sodium, is useful as a source of tungsten. It is prepared from tungsten ores to manufacture tungsten by reducing it. It is often found as dihydrate.
sodium tungstate image
sodium tungstate image

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2019年9月19日星期四

Adipic Acid Catalyzed Preparation by Tungstic Acid

Adipic acid is mainly used for nylon 66 engineering plastics and raw materials, and in the production of various ester products.

Adipic acid is also used for polyurethane elastomer material, acidifier various foods and beverages, sometimes its better than citric acid and tartaric acid. Adipic acid has many functions and a huge demand, but it is a big polluter. The industrial process mainly uses nitric acid to oxidize cyclohexanol and cyclohexanone (KA oil). The method has high yield, but nitric acid seriously damages the equipment and produces a large amount of nitrogen oxides which pollute the environment seriously. With the improvement of human environmental protection consciousness, people urgently need to find environmental protection and pollution-free solutions to solve the problem of adipic acid production.

adipic acid producing equipment image

In recent years, Cao Fabin, a scholar, has proposed that adipic acid is used as catalyst to synthesize adipic acid, according to previous experience, he uses tungstic acid and hydrogen peroxide (H2O2) to make an acidic additive of tungstic acid, in the absence of organic solvent and phase transfer agent, catalyzed 30% hydrogen peroxide oxidation of cyclohexanol to synthetic adipic acid. In the research process, Cao Fabin also found that the addition of suitable active agents could help catalyze the catalytic effect of tungstic acid. After comparing the inorganic substances such as phosphoric acid, phosphorous acid, oxalic acid, resorcinol, sulfonic acid and salicylic acid, he thought that it was most suitable for adding sulfonic acid to an acidic additive of tungstic acid.

The final result shows that when the amount of tungstic acid is 2.5mmol, tungstic acid: acid additive: cyclohexanol: when hydrogen peroxide is 1:1:40:176 (molar ratio), in acid additive, the effect of cyclohexanol oxidation with sulfonic acid and salicylic acid is the best, the yield of reactive adipic acid was 87.8% and the purity was 99.9%. It is worth mentioning that, after the synthesis of adipic acid, acid sulfonic acid and salicylic acid can be put into production again and reused fifth times. The yield of adipic acid separation is still up to 81.5%.

China is a major producer of tungsten, it is feasible to produce an acidic additive of tungstic acid to realize the scale production of adipic acid, using tungstic acid catalyst cyclohexanol method not only has high efficiency, but also to achieve cost control, more importantly is environment friendly. Environmental protection is increasingly valued, enterprises can reduce investment in environmental protection because of the new process, and achieve benefits.

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Why Sodium Silicate Is The Most Common Inhibitor of Scheelite Flotation

There are many inhibitors of scheelite flotation, but the most popular and widely used is sodium silicate, which is recognized by industry as the most effective and cost effective inhibitor.

Sodium silicate, commonly known as water glass, the molecular formula Na2SiO3 is a water-soluble silicate, is a kind of mineral binder, non-sulfide ore, especially a typical inhibitor of silicate minerals. Sodium silicate is selected in the floating scheelite and playing two main functions: one is to make the silica gel modified by physical adsorption on mineral surface, two is the adsorption of SiO32-, HSiO3-, OH- and H+ on the surface of quartz and silicate minerals, which increases the electronegativity and hydrophilicity of the mineral surface.

In scheelite flotation process, sodium silicate was inhibited in quartz, calcite and silicate, generally speaking, sodium silicate is selective when used in low dosage, but using too much will lose the selectivity.

water glass image

Therefore, in order to deal with the complex components of scheelite, people will find helper for sodium silicate, and achieve the ideal effect through the collocation of flotation. The main auxiliary of sodium silicate mainly has the following three members:

1. Metal ions such as AL3+, Mg2+, Cu2+, Fe2+, Ca2+, the combination of sodium silicate with these multivalent metal cations can be effective for fluorite and calcite, the main reason is that sodium silicate and metal cation form metal silicate colloid, and the selectivity of adsorption is enhanced.

2. Sodium silicate combined with Na2CO3. This combination can be used for the separation of scheelite from silicate minerals, its main function is CO32-, HCO3- can be preferentially adsorbed to the surface of calcium minerals, prevent the adsorption of sodium silicate, moreover, silicate minerals can be strongly inhibited by sodium silicate.

3. Temperature. The pulp heated 60-80 °C, can be used for separation of scheelite and calcite, the reason is that the sodium silicate can selectively remove the oleate anion on the calcite surface after heating.

Thus, in the process of scheelite flotation, how to use sodium silicate inhibitors is also a skill, whether it is heated flotation or room temperature flotation, according to the characteristics of sodium silicate can make scheelite flotation to achieve a multiplier effect.

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Nano Cesium Tungsten Bronze Preparation by Solvothermal Method

Cesium tungsten bronze (CsxWO3) is synthesized by solid phase method or liquid phase method with cesium carbonate and sodium tungstate as raw materials.

Therefore, cesium tungsten bronze is also called cesium tungstate. Cesium tungsten bronze CsxWO3 has the function of oxygen compounds in eight face special structure, with low resistivity and low temperature superconducting propertiesaterials. It mainly used to make high-temperature insulation coating, building glass, Low-E glass, automobile insulation film, plant planting shed, LCD screen and so on.

Synthetic of cesium tungsten bronze can be obtained by solid phase method and liquid phase method. In the earlier period, most of cesium tungsten bronze was prepared by solid phase synthesis, such as vapor phase reduction and hydrogen reduction, but the synthesis of solid phase is difficult and the cost is too high. Therefore, with the increasing attention of cesium tungsten bronze, more and more scholars began to study the liquid phase preparation of cesium tungsten bronze and find a way to reduce the manufacturing cost.

cesium tungsten bronze image

Scholars dissolved 400kg sorbitol in a jacketed reactor and dissolved it into tungstate and cesium sulfate, the ratio of the mass ratio of tungstic acid to cesium sulfate is 1 : 0.33, the quality of sorbitol is 3 times the total mass of tungstic acid and cesium sulfate, after high speed stirring 30 min, pump into homogeneous machine to carry on the cycle homogenization, after 60 min, the product is pumped into the high temperature reactor which has been heated to 150 °C, and the high pressure reactor speed is set to 180 r/min. When the above material is completely transferred to the autoclave, turn off the valve of the high-pressure reactor, gradually increase the temperature of the reactor to 350 degrees, and keep 600 min for 150 degrees, release the reaction product, adding deionized water to the filter press, washing with deionized water and absolute ethanol until the sulfate content is below 100 mg/kg, and the content of ethanol is more than 80%, the filter cake is placed in a vacuum oven for drying, and then mechanical pulverization and air flow grinding are carried out to obtain the target product - dark blue cesium tungsten bronze nanometer powder.

The cesium tungsten bronze nano-slurry was added to the acrylic emulsion to coat the film, and the functional film with excellent transparent insulation performance was obtained. The results show that the nanometer tungsten bronze powder with good quality can be prepared by solvothermal method. The transmittance of the functional thermal barrier film at 950 nm is 9.2%, the transmittance of visible light at 550nm is 71%, fog is 0.5%, and the film has excellent infrared absorption characteristics, and it is an excellent transparent thermal insulation material.

Unfortunately, scholars do not seem to solve the cost problem of cesium tungsten bronze by using solvent method. Moreover, the organic solvents in solvent thermal process are volatile and the production process will cause environmental pollution. However, it is certain that the quality of cesium tungsten bronze prepared by solvothermal method is better than hydrothermal method. The results show that the nano cesium tungsten bronze film prepared by solvothermal method not only has good heat insulation effect, but also has a long service life, and the service life is more than 20 years.

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Cesium Tungsten Bronze Preparation by Heat Insulation Film

Cesium tungsten bronze (CsxWO3) is a kind of tungstate powder synthesized by solid phase method or liquid phase method with cesium carbonate and sodium tungstate as raw materials.

Cesium tungsten bronze is also called cesium tungstate. As everyone knows, the sun's heat is mainly concentrated in the two part of the visible light and near infrared light, cesium tungsten bronze CsxWO3 particles can ensure good visible light transmittance, and can cover most of the near infrared caused by heat, and cesium tungsten bronze is an ideal material for manufacturing automotive insulation film.

However, in the manufacture of cesium tungsten bronze CsxWO3 heat insulation film, it is found that CsxWO3 particles are difficult to disperse in solution, and attached to the heat insulation film. In order to realize the near infrared shielding function of cesium tungsten bronze CsxWO3 particles, the dispersion and stability of particles in slurry must be improved, particle dispersion is enhanced by ball milling, ultrasonic addition, dispersant and surface modification.

nano cesium tungsten bronze film image

Some scholars use polyvinyl alcohol (PVA), polyvinyl butyral (PVB) and polyvinyl pyrrolidone (PVP) of the three kinds of membrane material to test cesium tungsten bronze heat insulation film preparation. After the Cs0.33WO3 slurry was obtained by hydrothermal method, the slurry was added into the 15L film solution after 3 hours ball milling and 20 minute ultrasonic wave addition,  at 80 °C, the water was mixed with 10min. Then, the foam 1% was added and the mixture was heated and stirred 20min, finally, three different materials of PVA, PVB, PVP cesium tungsten bronze coating film were prepared.

The results show that the average particle size of Cs0.33WO3 particles decreases after milling 3H with water as solvent. At the same time, the dispersion stability has been greatly improved. After adding polyethylene glycol - 400, the stability of cesium tungsten bronze particle dispersion is further improved, showing excellent near infrared shielding performance, through the transverse contrast of three kinds of film materials, scholars believe that PVA and PVP are Cs0.33WO3 coatings for film-forming substances has good transmittance of visible light and near infrared shielding property, at the same time, the cesium tungsten bronze coating with PVP as film forming material has the best adhesion strength.

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2019年8月15日星期四

GY Chelating Collector

GY chelate collector is the pioneer of the flotation industry in recent years, it is chelate class and fatty acid mixture, there are many categories.

The collection of tungsten ore is mainly made up of benzoic acid and fat collector, GYB and GYR. GY chelating collectors are popular, mainly because they have good selectivity and strong collecting ability. It has good flotation performance for wolframite and scheelite or other nonsulfide etc.. The wolframite and scheelite tungsten ore can be separated without mixing and flotation, which is suitable for the present situation of "lean, thin, miscellaneous and mixed" of the tungsten ore resources in China.

GY chelating collectors image

The most famous applications of GY chelating collector is Hunan shizhuyuan polymetallic ore mining. As everyone knows, shizhuyuan polymetallic ore mining industry is recognized as the most difficult dressing in China, their composition is complex, and the size of the mineral inlay is very fine, and the average size is only 0.01 millimeters - 0.03 millimeters, when grinding ore, it is very difficult to master and difficult to operate. Shizhuyuan tungsten ore is mixture of scheelite and wolframite, the ratio is 3:7, associated with more than 20 minerals, a variety of mineral components are mixed together, and very difficult to separate.

How to separate and recycle shceelite and wolframite mixture? In 1999, Zhang Zhongliu and several other scholars used GY series of chelating collector test in shizhuyuan. According to the mineralogical characteristics of shizhuyuan tungsten molybdenum bismith fluorite polymetallic ore, using the modified water glass selective inhibition of gangue minerals such as fluorite etc., using lead salt to activate wolfram minerals, mixed flotation of wolframite and scheelite with new type of GY chelate collector, the scheelite concentrate is obtained by heating and selecting the mixed coarse ore concentrate. Moreover, the wolframite concentrate is obtained by flotation of the selected tailings with GY collector.

The industrial test results show that the WO3 can reach 70.07% and the total recovery of tungsten can reach 81.62% when the ore is 0.47% WO3 and the GY concentrate is recycled by using a collector. Compared with the traditional 733 oxidation paraffin wax method, the process is simpler and the recycle rate is greatly improved, in addition, 99% of the CaF2 has entered the floating tailings and created favorable conditions for the recycle of fluorite from the tailings. The success of the new flotation process of scheelite and wolframite by GY method is mainly reflected in the effective separation of scheelite and fluorite in mixed flotation, improve the scrambler flotation and inhibition of the active recovery of wolframite in the selection. It can be said that the application of GY series chelating collectors is the savior of many low benefit mines on the verge of bankruptcy. 

In recent years, based on GY series chelating collectors, scholars have also developed many new GY series of drugs and combinations to keep up with the times, such as CF-GY shizhuyuan method, provide many effective mining scheme for increasing tungsten resources in China.

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Wolframite and Scheelite Mixed Flotation -- Shizhuyuan Method

Hunan Shizhuyuan Tungsten Polymetallic Mining Area is a large deposit with a variety of minerals, with up to 143 kinds of mineral varieties.

It is mainly composed of tungsten, tin, bismuth and molybdenum, and is rich in fluorite, copper, lead and zinc , sulfur, iron, gold, silver, beryllium, niobium, tantalum and other minerals, the economic value is difficult to estimate.

Shizhuyuan ore mineral embedded in the complex size of the mineral industry is recognized by the most difficult mineral processing. The ratio of wolframite and scheelite ore is 3:7, and a lot of fluorite, molybdenum and bismuth are associated with it. In the early stage, shizhuyuan using the traditional method of heating and flotation to 733 oxidation of paraffin soap as a collector, the total recovery of tungsten ore is only 40-50%, a large number of waste of resources to make the economic benefits of the mine hesitant.

shizhuyuan method image

In order to get rid of the waste of tungsten resources at an early date, at the beginning of this century, Guangzhou Nonferrous Metals Research Institute, Beijing Institute of mining and Changsha Nonferrous Metallurgy Design Institute and other units jointly tackle key problems, based on the GY chelating collector, a new method of mineral processing, such as molybdenum bismuth and other floatable and bismuth sulfur, and CF-GY combined with the new process of flotation tungsten, a new method of dressing combined with the new technology of CF-GY combined method known as "floating wolfram, shizhuyuan method".

The method is based on the heating flotation method, using highly selective chelating collector CF and GYB mixed flotation wolframite and scheelite and recycle of wolframite slime, a set of processes can realize the difficult technical problems of wolframite and scheelite flotation and difficult separation by flotation of calcium containing minerals. A new flotation process of molybdenum bismuth and other floatable - bismuth sulfur floating - combination inhibitor molybdenum bismuth separation - oxidation bismuth sulfur separation was developed by separating molybdenum, bismuth and so on; Tungsten coarse concentrate combined with sodium sulfide and water glass heating cleaning process, a new process for fluorite flotation by high intensity magnetic separation with combined inhibitors and selective collectors, it provides technical guarantee for the exploitation and utilization of fluorite resources in ores.

The ore of shizhuyuan polymetallic mine in WO3 containing 0.25%-0.45%, belong to low grade complex ore. The industrial test showed that the shizhuyuan tungsten dressing method, the recovery rate can be increased to about 77.70%, nearly 30% increase over the old flotation method, do not underestimate this 30%, for the enterprise, it was tens of millions of economic income.

The recycle rate of tungsten has been greatly improved, and the cost of ore dressing has decreased because of the “shizhuyuan” method, it is a revolutionary breakthrough in the beneficiation technology of tungsten, tin, molybdenum and bismuth in China. It has set a benchmark for many low efficiency mines and pointed out the road.

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Tungsten Carbide Preparation by Sodium Tungstate

Tungsten carbide (W2C) is composed of a tungsten and carbon black compound, six crystal, metal luster, hardness and diamond are similar, extremely difficult to melt.

Tungsten carbide is a good conductor of electricity and heat, mainly used in the production of cemented carbide materials. The traditional tungsten carbide process, must be go through the production of ammonium paratungstate, tungsten powder preparation and carbonation and many other processes, the production cost is high and the process is lengthy. In order to reduce the production cost of tungsten carbide, the approach is to reduce the process from mineral raw materials to product manufacturing processes.

There are many methods for the preparation of tungsten carbide. For example, high temperature melt extraction, carbonization and reduction by aluminum, tungsten carbide is directly obtained from high-purity tungsten concentrates. These methods are simple, crude and effective, but the temperature requirements are particularly high. They need to be realized by the high temperature calcination equipment above 2000 °C, and some enterprises are difficult to achieve. Therefore, we have to explore another new shortcut for the direct reduction of tungsten carbide from sodium tungstate.

tungsten carbide powder image

Sodium tungstate is an intermediate transition from tungsten concentrate to APT. The chemical composition is Na2WO4·2H2O crystal or colorless crystalline powder. Some scholars used calcium acid as carbon source to synthesize tungsten carbide with sodium tungstate.

In the experiment, the sodium tungstate powder was first dried at 120 °C in a vacuum drying chamber for 2 hours, the sodium tungstate powder without crystalline water is obtained, with carbide powder grinding in a planetary ball mill for 15 minutes at the same time, and then the columnar mass is obtained by the briquetting mechanism, after weighing, the graphite crucible was placed in a vacuum reduction furnace for reduction and carbonization. The reduced products obtained by reduction remove the calcium oxide by acid washing.

2NaWO4+6CaC2=W2C+6CaO+2Na2O+11C

After reduction of sodium tungstate by calcium carbide, can obtained purer main phases W2C, tungsten and carbon can produce two kinds of tungsten carbide, WC and W2C. WC is a near normal compound. It can hardly dissolve carbon or tungsten. Therefore, in order to get the WC, the W2C should be obtained with calcination twice, the calcination temperature is 1600 °C, the heat preservation time is 2h. In the two times carbonization process, increasing the heating rate and prolonging the moisture retention time are beneficial to the growth of crystal and decreasing the cooling rate, which is beneficial to refine the grain size of tungsten carbide. Finally, the compound is formed by two times carbonization at high temperature to produce more pure tungsten carbide powder.

The process of converting tungsten sodium tungstate to tungsten carbide eliminates the need for ammonium paratungstate, relatively, it saves a lot of process and cost. Compared with the high temperature melt extraction carbonization and aluminum thermal reduction method, it requires a lower temperature of the reaction furnace, in general, is a law-abiding approach. In industrial practice, however, this shortcut has not attracted much interest, the reason is probably: 1. It is not as straightforward as the high temperature heat reduction method; 2. Tungsten produces tungsten carbide although the cost is slightly higher, its ultimate quality is better controlled.

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Zinc Tungstate Photocatalytic Degradation of Four Chlorophenol Wastewater

Four chlorophenol is a major component of biological pesticides, wood preservatives, dyes and rust removing agents.

Four chlorophenol is also used in Asia, Africa and South America to prevent and control schistosomiasis; In addition, biological treatment of municipal wastewater and industrial waste water also contains chlorophenols. Four chlorophenol wastewater is a kind of three toxic agent, which is carcinogenic, teratogenic and mutagenic. It is easy to cause serious pollution to the environment and is difficult to decompose, therefore, the United States Environmental Protection Agency (EPA) has included it in the list of 129 priority environmental control pollutants.

In recent years, the application of semiconductor photocatalysis technology in environmental management has received extensive attention, among them, the tungstate semiconductor photocatalyst, with its non-toxic and high photocatalytic activity, has gradually replaced the early physical and chemical treatment methods with poor efficiency and high cost, while the zinc tungstate tungstate is four chlorophenol wastewater sniper.

zinc tungstate photocatalytic degradation image

Compared with the traditional physical and chemical methods, the advantage of treating four chlorophenol wastewater with zinc tungstate is simple operation, mild reaction conditions, non-toxic and environmental protection, and the effect is outstanding.

Some scholars used zinc tungstate doped with fluorine to synthesize zinc tungstate photocatalyst, in the test of four chlorophenol, four chlorophenol is firstly adsorbed on the surface of nano ZnWO4, when ZnWO4 absorbs light greater than or equal to the energy of the band gap, photogenerated holes and electrons are produced, four chlorophenol was degraded simultaneously in two ways. During the reaction, the hole and electron move toward ZnWO4, and the photogenerated hole reacts with them directly to form hydroxyl radical, photogenerated electrons are trapped by oxygen molecules adsorbed on the surface to produce superoxide anions, superoxide anion is further protonated to form hydroxyl radicals, and hydroxyl radicals react directly with benzene rings, resulting in CO2 and H2O.

The photocatalytic activity of four chlorophenol wastewater can be obviously improved by using zinc tungstate as photocatalyst, the results show that the total degradation rate of four chlorophenol wastewater reaches 95% after visible light catalysis of 12h, this shows that sodium tungstate has a very good effect on four chlorophenol, and this is also the gospel of the vast population of water pollution areas.

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2019年7月17日星期三

Bismuth Tungstate Preparation by Hydrothermal Method

Bismuth tungstate is a new type of photocatalyst which has attracted much attention in recent years.

It has not only good catalytic performance, stable photocatalytic activity, but also non-toxic environment. It is becoming a new hot spot in the field of photocatalyst.

The liquid phase methods for preparing bismuth tungstate include solvothermal method, precipitation method, microemulsion method, hydrothermal method, etc.. Among the many methods, hydrothermal method has become the most popular method because of its simple operation process, high utilization ratio of raw materials, less energy consumption, and conforms to the policy of energy saving and emission reduction.

bismuth tungstate preparation by hydrothermal method image

The working principle of the hydrothermal method is in a closed reaction vessel special (autoclave), using aqueous solution as reaction medium, heating the reaction vessel, creating a high temperature and high pressure reaction environment, the insoluble substances dissolved in normal temperature and recrystallization.

The main advantages of preparing bismuth tungstate by hydrothermal method: 1. The required reaction equipment is simple; 2. An optimum redox environment can be formed by controlling the reaction atmosphere through an autoclave; 3. The quality of bismuth tungstate is stable; 4. The hydrothermal method can effectively control the grain size and morphology of bismuth tungstate because of isothermal, isobaric and solution conditions; 5. Hydrothermal method does not require calcination and the addition of too many toxic agents, it is more environmentally friendly.

Some scholars used hydrothermal method to produce bismuth tungstate, and sixteen alkyl three ammonium bromide (CTAB) was used as surfactant. By adjusting the pH value in the solution, Bi2WO6 with different structure and morphology was prepared, the samples prepared by XRD, SEM and BET were characterized, the photocatalytic degradation of the prepared samples was also investigated, the optimum temperature of bismuth tungstate prepared by hydrothermal method is 180 °C, and the optimum pH value is 9.5.

bismuth tungstate preparation by hydrothermal method image

Hydrothermal method is the main method for preparing bismuth tungstate at present. Interestingly, the crystal morphology of bismuth tungstate obtained by hydrothermal method is different at different temperatures and different mineralizer, there are square, sheet, spiral, bird's nest shape, plum balls, various forms of bismuth tungstate is different, the range of use is also slightly different. 

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Bismuth Tungstate Preparation by Solid Phase Method

Bismuth tungstate is a new photocatalyst developed in recent years.

It has the characteristics of narrow band gap, good catalytic performance, stable photocatalytic and environmental protection, and has become a new hot spot in the field of photocatalyst.

bismuth tungstate preparation by solid phase method image

The preparation methods of bismuth tungstate mainly include solid phase method and liquid phase method. In general, they are fire process and wet process. Solid phase method is the preparation of bismuth tungstate by sintering at high temperature, compared with the liquid phase method, the solid phase method is more adopted by enterprises. Because most of the smelting enterprises adopt solid phase method to obtain tungsten powder, calcination equipment can be used in conjunction with each other, and the equipment foundation is the reason why solid phase method is more popular. The synthesis principle of bismuth tungstate solid phase method is mechanical processing containing Bi and W elements in the oxide material or its salt, then, the product obtained by mechanical processing and mixing directly through high temperature sintering can obtain bismuth tungstate products.

Some scholars believe that the preparation of solid phase preparation of the ambient temperature is the key to determine the preparation of bismuth tungstate, thus, he tested the 573K, 673K, 773K, 873K, 973K five temperature. Finally, the optimum calcination temperature of bismuth tungstate photocatalyst is 873 K, too low or too high calcination temperature will decrease the activity of bismuth tungstate photocatalyst.

Solid phase process is a relatively mature method for preparing bismuth tungstate, but its inadequacy is also accepted, but its deficiency is also obvious. The main reason is that the process needs to be heated by high temperature, and the energy consumption is greater, what is more serious is the size of the particles, the specific surface area and other factors, the performance of bismuth tungstate catalyst prepared by solid phase method is relative poor to liquid phase. Therefore, in recent years, the use of solid phase method of bismuth tungstate enterprises gradually reduced.

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Bismuth Tungstate--Dyeing Wastewater Treatment with Acrylic Composite Fiber

Dye pollution is one of the most important environmental pollution sources in the world.

Dye wastewater has the characteristics of complex composition, high chromaticity, large amount of emission, toxicity and biochemical degradation. It has been a difficult problem in wastewater treatment.

In recent years, with the development of photocatalytic technology, more and more photocatalysts have been developed. Bismuth tungstate has been widely used for its excellent photocatalytic degradation ability, there is no doubt that bismuth tungstate has better degradation effect on dye wastewater. However, in recent years, it has been found that bismuth tungstate is good, but it is easy to assemble, difficult to separate and difficult to recover. In order to solve this problem, some scholars have proposed a scheme for making composite materials of bismuth tungstate and acrylic fiber.

Acrylic fiber is also called polyacrylonitrile fiber, also known as synthetic wool, and bismuth tungstate does not seem to be related, how are they made of composite materials, and what effect will it have?

wastewater treatment image

The researchers used wet spinning technology to prepare bismuth tungstate-acrylic composite fiber, the general process is as follows:

At room temperature, 20 mL DMSO was added to the conical flask, and five water bismuth nitrate and two sodium tungstate were added into the flask according to the amount of substance 2 to 1, and each ultrasonic was dispersed for a period of time. Adding acrylic fiber, stirring with magnetic force for14 h, prepared into a mass fraction of 10% of the spinning solution, prepared into a mass fraction of 10% of the spinning solution. In 40% dimethyl sulfoxide aqueous solution for wet spinning, after that, the obtained composite fiber is placed in a hot air drying box and dried at 35 °C.

The product began to rise from 40 degrees of temperature, with a certain temperature gradient, heating up to the specified temperature, The bismuth tungstate acrylic fiber with photocatalytic property was obtained by constant temperature reaction for10 h.

What are the advantages of bismuth tungstate acrylic fiber prepared by such a great deal of setbacks? The experimental results show that the bismuth tungstate acrylic fiber not only continues the photodegradation characteristics of bismuth tungstate, the defects of bismuth tungstate for difficult separation and difficult recovery of dye wastewater are also improved, especially for methylene blue wastewater, the photo degradation ability of bismuth tungstate acrylic fiber reaches a small height.

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