Other Effects on Ammonium Paratungstate Production
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- Category: Tungsten Information
- Published on Thursday, 31 December 2015 15:41
Ammonium paratungstate (APT) is an important intermediate product of the production of tungsten metal powder. To ensure the quality of tungsten powder, the average particle size, particle size distribution and crystal morphology should also meet certain requirements while the APT chemical purity does. With the rapid development of modern science and technology, there’re more and more demands for different grain size and shape of tungsten powder production, and thus the requirements of raw material APT are also getting higher and higher.
For APT crystallization conditions, the scholars have carried out extensive exploration and discussion, but the overall reports are rare, and the results are not entirely consistent. In order to investigate the basic conditions of APT production, for the preparation of APT crystallization problems, this article attempts to make some analysis and discussion on theory and the process practice based on a number of experimental studies made recently and some views are put forward by reference.
Evaporation and crystallization is a process that feed liquid and solid of ammonium tungstate to get to oversaturation, which makes the material’s phase change and precipitate purified crystals from the solution.
APT crystals precipitate from ammonium tungstate solution can be achieved, by that to adjust the PH of solution through loss of ammonia and get into the secondary salt formation region. The loss ammonia -adjust PH process can be achieved by evaporation crystallization process and neutralization crystallization process.
(1) It was found that with additional seed crystal, bulk density of APT has declined, which is consistent with the literature. It’s observed under a microscope that the particle size distribution is uneven and most are the coarse-grained polycrystalline. It’s reported that concentrate ammonium paratungstate to a certain proportion, add 1% to 2% the seed. Then constantly supplemented with solution, and prepare coarse APT. Concentrate the ammonium tungstate solution and gradually supplement with a solution to control the oversaturation, to prepared epigranular, large particle size APT.
(2) During the concentrating crystallization process, supplemented with water quantitatively and control oversaturation, the coarse crystalline regular APT can also be prepared. It is noteworthy that no more water in the crystallization terminal stages, or there will be a small amount of ammonium metatungstate with heating and stirring.
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Effect of Gas Stirring on Ammonium Paratungstate Production
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- Category: Tungsten Information
- Published on Thursday, 31 December 2015 15:32
It’s shown in the studies that the main factors controlling ammonium paratungstate particle size are oversaturation, temperature and stirring speed. Preparation of APT fine particles stirred by gas A with a strong intensity. Since the gas is vigorously stirred, crystals were broken into a lot of small nuclei, it is difficult to form large particles. And gas takes away the heat and ammonia, which can control the pot temperature around 70 ℃, while increase the over-saturation of the solution, is conducive to the preparation of APT fine particles.
This approach has been applied in production, the resulting APT is epigranular with surface regularity. Preparation of coarse APT stirred by gas B with a gentle intensity. Since the stirring gas, it’s ensure that the resulting APT will not precipitate and full contact with the solutes. The gas release heat during condensation, not only increase the pot temperature, but also can effectively control the oversaturation of the solution to increase due to the condensation of gas, which is easy to output the coarse particles APT. In this method the test results are obvious, the average particle size of the resulting APT can be more than 50μm, and the particle size distribution is even, particles are regular. The further applications is now in study.
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China Tungsten Industry Development and Changes
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- Category: Tungsten Information
- Published on Thursday, 31 December 2015 11:36
China tungsten industry started mining with unauthorized till gradually orderly management the whole tungsten industry not only annual production increase, but resource protection consciousness also enhance.
On the other hand, after employed a series of reform policy of tungsten industry there are some development and changes in China tungsten industry:
1.Tungsten price go up, economic strength growing
In 1985, China the whole tungsten industry annual sales revenue was less than 2 billion RMB. In 2003, the annual sales revenue was broken through 100 billion RMB. In 2014, annual sale revenue was 740 billion which was 44.3 times than 1985’s.
2.tungsten import and export volume decline, tungsten carbide export volume increase
During Eleventh Five-Year Plan period, tungsten annual gross production was 140,620.00 ton and export volume was 29,000.00 ton. Expected during the 12th five-year plan, the annual gross production will be 130,440.00 ton and export volume will be 26,900.00 ton comparing with 11th five-year plan the export volume of tungsten decline 8.1%
On the other hand, During Eleventh Five-Year Plan period, tungsten carbide annual gross production was 15,800.00 ton and export volume was 3,159.00 ton. Expected during the 12th five-year plan, the annual gross production will reach 24,100.00 ton and export volume will be 24,100.00 ton comparing with 11th five-year plan the export volume of tungsten carbide increase more than 50%.
3. Technology and equipped level increase rapidly
These year China tungsten industry through import, absorb and innovate technology so tungsten carbide production technology and equipped level has significant increase. For example, low-grade tungsten ore, scheelite and wolframite mixture ore extraction technology got new breakthrough. Besides, tungsten melting process and technology and products quality advanced in the world. What’s more, ultra-fine grain, ultra-rough grain, functionally graded material tungsten carbide material, super-large tungsten carbide product and other high-end tungsten carbide product has kept up with the pace of foreign countries and the tungsten series product will develop with high performance, high precision and high added value
4. Accelerating product’s structure adjustment, industrial concentration increased.
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Super Saturation Affects Ammonium Paratungstate Physical Properties 1/3
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 20:18
Super saturation express as concentration driving force △c(△c=c-c0) [Ps: c for the super saturation concentration of the solution, known as concentration of main solution; c0 respective the saturated solubility concentration, means the equilibrium saturation concentration]. It considered that the crystal growth process of ammonium paratungstate is divided into three steps: non-basic element reaction, crystal medium diffusion and interface reaction. Instantaneous super saturation (△c) depends on supersaturated coming into being (polymerization) during the crystallization process and a D-value of eliminate (transformation). Linear growth rate related to △c(r1)and quantity growth rate (rm) can be used to reflect the relationship between them:
r1=K1△c1, (K1means: line rate constant)
rm=Km s△c1, (km means :Quantity rate constant, s means: the existing grain surface area)
So, rm=kms2√ri/k1
Three stages of the whole process of crystallization, the super saturation comes and the changing of elimination rate showed in the picture left:
From the figure, phaseⅠ: induction period, rm=0, the ammonium paratungstate crystallization process rate of super-saturation enlarged, △c1 continue to increasing. Phase II: crystal nucleus, rm>0, the rate of over saturation is always greater than that elimination, the phase transformation reaction to be the limit process of the crystallization. The early stage of the reaction due to the small s , △c still increasing, control by S phase. With the increase of S, △c reaches maximum value and began to decline, controlled by △c. Phase III: s keep increasing, the elimination rate of the super saturation equals to the generation, rm reach the maximum value. Value of rm decreases with the increasing rate of super-saturation, polymerization reaction is the limiting step in the crystallization process. Obviously, RM value of this stage can be used as a measure of the rate of super-saturation.
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Sodium Tungstate Catalyzing Diols and Nitriles Oxidation
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 20:16
According to the number of hydroxyl groups in molecular, the alcohol can be divided into alcohol, glycol and polyols. Two hydroxyl alcohol of molecule is called dibasic alcohol. All alcohol is the same. They can react with organic acid or inorganic acid to form ester. Nitrile is a kind of organic matter containing organic groups-CN. Nitrile can be obtained through the nucleophilic substitution reaction of potassium cyanide and halogenated in water or similar chemical characteristics water solution.
The effect of material loss of electronic called oxidation reaction. Oxidation reaction in its narrow sense refers to the material with oxygen. Oxidation value increases when the oxidation. Oxidation is also called oxidation reaction. The oxidation is a significant reaction in organic chemistry and a core technology for conversion of hydrocarbon to intermediate of organic synthesis. In order to realize clean production, the studies on green oxidant and oxidation process have become the common ground of academia and industry. Hydrogen peroxide is safe, no poisonous, low price, thus is an ideal oxidant.
In the article the oxidations of diols and nitrils catalyzed by sodium tungstate, sodium molybdate and heteropoly acid using H202, Na2C03-H202, and sodium percarbonate as oxidant was studied.
1.The results of catalytic oxidation of l, 2-propanediol and butanediol using sodium tungstate as catalyst and hydrogen peroxide (30%) as oxidant showed that the conversion of substrate increased with the increase of reaction time and temperature, but the selectivity forming hydroxyketone decreased.
2.The increase of amount of catalyst or oxidant would lead to the formation of more by-products acetic acid and formic acid. The increase of acidity of the auxiliary additive would be favorable for the conversion of l,2 propanediol. But the selectivity forming hydroxyacetone decreased.
3.When Na2W04 was used as catalyst under the optimized reaction conditions: temperature is 55℃, time is 60 min, n(sodium tungstate)/(2-hydroxyl phenol)=1, the conversion of l,2-propanediol was 13% and the selectivity of hydroxyacetone could achieve 92.3%. Under similar conditions, the conversions of l,2-butanediol and l,3-butanediol were29.2% and77.5%, and the selectivities forming l-hydroxyl-2-butanone and 4 hydroxy-2-butanone were 65.8 % and 85.3% respectively.
The mechanism of diol oxidation was discussed.The preparation of amides from aryl nicriles and aliphatic nitriles was studied in the presence of sodium tungstate catalyst using sodium percarbonate or sodium carbonate-hydrogen peroxide as oxidant in the solution of methanol and water mixture. The results indicated that aryl nitriles and aliphatic nitriles could transfer to aryl amides with very high selectivity of 95%-100% at room temperature. The comparing study of two oxidants suggested that when sodium carbonate-hydrogen peroxide was used as oxidant, the oxidation rate of nitrile and the selectivity forming amide were better than that percarbonate was used.
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Ion-Exchange Kinetics in Sodium Tungstate Solution
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 20:12
Ion exchange refers that when the water goes across ion exchange column, the cation and anion of the water (HCO - plasma) exchange with the H+ ions of positive resin and OH- ion negative resin in exchange column so as to achieve the purpose of desalination. Ion exchange equipment can achieve automatic continuous detection of water quality, excessive automatic alarm, and automatic complete regeneration process. Spare parts adopt high strength engineering plastic which is of corrosion resistance. This enhances the reliability and durability of equipment. Ion exchange technology was first applied in the preparation of soft water and salt water. Pharmaceutical production water often uses this method. In the biomedical field, ion exchange technology is gradually applied in the separation and extraction of substances such as protein, nucleic acid. Some classic production process is also waiting for ion exchange technology to replace or modify.Tungsten wet smelting with ion exchange process is short and can complete two tasks in removing impurity and transformation at the same time. Equipment is simple and the recovery rate is high.
The kinetics of ion-exchange process between 201x7（Cl- form)strong basic anion-exchange resin and strong concentration WO42-was studied by batch reactor method in this research. The ion-exchange adsorption isotherms in different conditions were determined and double driving-force model was applied to describe the kinetics of ion-exchange process. 
The results indicated that the ion-exchange rate was not affected by the concentration of WO42- and the stirring rate; however it was increased with the increasing of the reaction temperature and the reducing of the bead radius and varied inversely with square of the bead radius. The ion-exchange process was controlled by the grain diffusion. The apparent activation energy of reaction was decreased with the increasing of the concentration of WO42-. The effect of the concentration of Cl- on the ion-exchange process was also studied in this paper.
The results showed that the kinetical rule of the ion-exchange reaction was not changed, the ion-exchange process was still controlled by the grain diffusion, and the concentration of Cl-has little effect on the apparent activation energy of reaction if the total concentration of ion in the solution kept invariableness. The exchange capacity and the adsorption rate of the resin to WO42-were decreased with the increasing of the concentration of Cl-.
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Tungsten Trioxide Content Mensuration in Sodium Tungstate
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 20:10
Tungsten trioxide (chemical formula: WO3) is a kind of yellow powder. It’s insoluble in water, soluble in alkali and slightly soluble in acid. It can be made of tungsten ore and soda ash melting and adding acid. It will sublimate significantly at 850℃. It hardly reacts with inorganic acid except for hydrofluoric acid. It can slowly dissolve in ammonia or a strong alkali solution. It will generate oxychloride after reacting with chlorine gas. But it cannot react with bromine, iodine. Tungsten trioxide also has very wide uses. It is mainly used for calcining reduction in the production of tungsten powder and tungsten carbide powder to produce cemented carbide products, such as tool and mould. At the same time, it can also be used in the manufacture of pure tungsten products, tungsten rod, tungsten bars, tungsten electrode and the shielding materials of counterweight and radiation. In industry, there is a small amount used as colorant of yellow chinaware.
Sodium tungstate is also called sodium tungstate dehydrate. The character of sodium tungstate is colorless crystal or white crystal orthorhombic system. It has the gloss of flaky crystal or crystalline powder. Melting point is 698 ℃ and relative density is 3.25. It effloresces in dry air and loses the crystal water by heating to 100 ℃.Sodium tungstate is soluble in water and aqueous solution is slightly alkaline. But it isn’t insoluble in ethanol and is slightly soluble in ammonia.
How to measure the content of tungsten trioxide in sodium tungstate?Usually we use cinchonine weight method to measure.
1.Reagents: methyl violet indicator 0.1%, hydrochloric acid (1+1), 10%cinchonine hydrochloric acid solution (1+1hydrochloric acid preparation), cinchonine hydrochloric acid lotion 0.2%, solid NaOH, wide strip.
2.The operation steps:
（1）Take sample 0.5 grams in 250 ml beaker with a little water to dissolve. Add 100ml hot water of 60 ~ 80 ℃ and two drops 0.1% methyl orange agent. Use hydrochloric acid to neutralize to red and add 10ml 10% cinchonine under stirring constantly.
（2）Continue stirring to precipitate coagulation and the upper liquid is clear. After precipitate sinking, use the rapid quantitative paper to filtrate. Filter liquor should be carried in the middle of 250 ml volumetric flask.
（3）Use 0.2% cinchonine lotion to wash the precipitation above five times. Then put the precipitation into porcelain crucible with filter paper on the furnace drying coking. At last, carbonize and burn it in the 750～800℃stove for 30 to 45 minutes. Cool and weigh it. The filtrate proceeds by tannins and methyl violet colorimetric method.
Issues worthy of attention in the process of the experiment are as follows:
(1) The sodium ions precipitation must be cleaned. Otherwise, cauterant will become black and the result is on the high side.
(2) 0.1% of methyl orange indicator can be used and the filtrate can proceed by thiocyanate colorimetric method.
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Super Saturation Affects Ammonium Paratungstate Physical Properties 3/3
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 20:06
There are many impurities like: P, As, Mo, Si, they are easily adsorbed on the active point of the crystal, and hinder the growth of crystal to fine APT crystal, then affect the quality. At the same time due to the Cl-、S concentrating after a long time, they enrich on the surface of the ammonium paratungstate to decrease the activity, so that uniform particles of coarse granular products are difficult to formed.
Impurities as P, as, SiO2, Na, Mg, CA, Fe, Mo make influence depending on their interaction properties with paratungstate, the solubility of compounds formed, acid soluble impurities (NH4) H3PW12O40, (NH4) 3AsW12O40, (NH4) 3SiW12O40. These impurities remaining in the mother liquor in the process paratungstate crystallization, concentration more than 1g/L, but the mass fraction no more than 0.005% in the salt. Impurities such as P, As, Si d Si can decrease the crystallization rate of ammonium paratungstate, grain efficiency of other impurities ranking like Mo>Na>Mg>Ca>Fe, depending on the concentration of the original solution.
Impurities are easy to absorb into APT crystal to affect its quality, and even lead to defective goods. So, we can take rate control, increase the concentration of NH4Cl, stirring and add reagents to washing to achieve the purpose of removing impurities.
The above shows that super saturation closely related to the concentration of ammonium chloride solution, ammonium chloride and impurities. So the solution should be controlled in a reasonable range to make a suitable range of concentration of ammonium. People control from the three aspects: the concentration of WO3 in solution, NH4Cl, impurities.
For Super Saturation Affects Ammonium Paratungstate Physical Properties 2/3, please see in
http://news.chinatungsten.com/big5/tungsten-information/81978-ti-10660
http://news.chinatungsten.com/big5/tungsten-information/81978-ti-10660
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Super Saturation Affects Ammonium Paratungstate Physical Properties 2/3
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 20:03
1.Initial concentration of WO3
It was pointed out that increasing the concentration of WO3 lead to the bulk density of ammonium paratungstate decreased. When the concentration of WO3 decreased to a certain degree, the density of ammonium paratungstate was not obvious to saw. It shows that the higher concentration of WO3 in the solution leads to the faster nucleation, and the crystal particles are not easy to grow. When in the lower concentration of WO3, saturation of the solution is changing not obvious, and advantageous to nucleation growth. But when concentration of WO3 is too low, the contact chance of the crystal nucleus and solute molecules is small, and the grain growth is affected. Solution saturation △c decreases resulting in resulting in crystal growth rate (RM) and nucleation rate (rn) decreases. However the slowed down extent of both is different. Supposed that rN slows down larger than rm, in that case nucleation is small, however the growth of the substrate is really large, which is beneficial for preparation of ammonium paratungstate.
2. Concentration of NH4Cl
With NH4Cl added, concentration of NH4 + ion in the solution increases, polymerization and multi-phase reaction balance moves to the right, which will lead to solubility of ammonium paratungstate decreased and △c increased. It is known that the nucleation rate greater than crystal growth rate of APT when increases the super saturation. Ammonium paratungstate crystal size tends to thinner when NH4Cl added. However, ammonium paratungstate generation transformation reaction speed up, low phase velocity, wide area, △c slow to increase, controlled by s for a long time without adding NH4Cl. At the same time, with the increase of NH4+ ion, the same ion effect enhances but the salt effect increase more quickly.
An academic literature pointed out that the higher concentration of NH4Cl in solution, the easier to get small and inhomogeneous crystal. Because the presence of NH4Cl and the same ion effect makes the evaporation crystallization reaction moving to the right, that means, saturation of the solution increases, the nucleation rate accelerated, a large number of fine grains generated at the same conditions. The higher concentration of original NH4Cl, the more fine APT crystal obtained. That may due to the presence of the solution, which may be adsorbed by the crystal grains, but not constituting other substances. Such impurities are adsorbed to the crystal surface, covering the active region of it, and slow down the crystal growth rate which is conducive to obtain smaller particles of crystal.
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China Tungsten Industry Development Situation
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- Category: Tungsten Information
- Published on Wednesday, 30 December 2015 18:28
In the mid-1980, China tungsten ore mining was unauthorized which made international tungsten market turmoil. Tungsten raw material market was oversupply so tungsten price plunged. The price of tungsten fell as lowest as 30 $/mtu and in China tungsten concentrate price fell down to under 10,000.00 RMB/ton. After that, China operated a series of industry regulator policy, for example mining control, resources integration, total amount control and improve industry self-regulation. After China government employed these policies China tungsten industry is now on track.
1. Improving tungsten resources protection
In 2003 to 2012, China total invested 17.2 billion RMB for tungsten ore explored and the new found out tungsten resource (WO3) was nearly up to 30,000,00.00 ton. In 2010, China Ministry of Land and Resources employed strategic action of find tungsten ore which was pay more attention to old mines tungsten ore finding. Beside, the breakthrough has been made in this action. China government not only invested a lot of money in tungsten explored and also emphasis on tungsten resource protection. So the storage of tungsten resource increase every year and in 2009-2011the increase range is the most.
2. Tungsten production capacity keep growing
In 1907, china first time found tungsten ore at west Huashan Mountain in Jiangxi province. After that, in Jiangxi, Hunan, Guangdong and other places found tungsten mines gradually and then input artificial exploitation which formed the early China tungsten industry. In the early 35years before New China establishment, the total production was 237,000.00 ton which accounted for 29.80% of global tungsten production. From 1914 to 2014, global tungsten production was 3,910,000.00 ton and China tungsten production was 1,860,000.00 ton which accounted for 54.08% of global tungsten production.
Especially when China entered new century, tungsten concentrates production has increased rapidly. Due to high-speed development of economy and tungsten price going up so the market demand of tungsten has been grow and the production of tungsten has been increase as well.
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