In the industry, synthetic white tungsten or ammonium paratungstate is generally precipitated from the purification liquid, and then tungstic acid or tungsten oxide is produced. The process is as follows.

1. Synthetic white tungsten. Precipitation and synthesis of white tungsten generally use calcium chloride as a precipitant (sometimes with calcium hydroxide or calcium sulfate) to precipitate calcium tungstate. The reaction formula is:

Na2WO4+CaCl = CaWO4↓+2NaCl

Calcium chloride also produces calcium salt precipitates for impurities such as silicon, phosphorus , arsenic , molybdenum and the like, and thus has no purification effect, and only purifies sulfur. The quality and precipitation rate of synthetic white tungsten are mainly related to the tungsten content of the cleaning liquid, the alkalinity, the type of precipitant and the amount of addition. The tungsten content affects the fineness of the synthetic white tungsten and the filtration and washing performance.

Regarding the comparison of precipitants: calcium chloride can obtain high-grade synthetic white tungsten: (WO3 reaches 70-76%), the precipitant has little pollution to the product, and the disadvantage is that calcium chloride is easily deliquescent, and transportation packaging is difficult. Lime is cheap, but the obtained synthetic white tungsten has a low grade, generally only 60-68% WO3. It is difficult to filter and wash, the mother liquid has high tungsten content, and the synthetic white tungsten grade WO3 obtained by calcium sulfate, but the product is highly polluted (sodium sulfate, calcium sulfate) ), and the reaction time is long. Therefore, calcium chloride is preferred.

When synthetic white tungsten is used as the final product, it is filtered and dried, and then packaged; if tungstic acid or tungsten oxide is used as the final product, the synthetic white tungsten is filtered and washed and sent to prepare tungstic acid.

2. Preparation of tungstic acid. Industrially, hydrochloric acid or nitric acid is often used to decompose and synthesize white tungsten to prepare tungstic acid. A commonly used synthetic white tungsten hydrochloric acid decomposition method, the reaction formula is:

CaWO4+2HCl = H2WO4↓+CaCl2

The impurities of silicon, phosphorus and arsenic in the synthesis of white tungsten have a great influence on the preparation of tungstic acid, which makes the size of tungstic acid fine and gelatinous, which is difficult to precipitate and filter. At the same time, it also forms heteropoly acid with tungsten to increase the tungsten content in the mother liquor. .

The main influencing factors for the preparation of tungstic acid are: (1) Temperature: high temperature is conducive to the preparation of coarse-grained tungstic acid. The decomposition of impurities is complete, but the acid loss is large, the working environment is poor, and the initial temperature is usually 70-80 degrees. After the addition, boil for another 10-15 minutes; (2) hydrochloric acid concentration: high concentration is favorable for coarsening of tungstic acid particle size, complete decomposition of impurities, 30% hydrochloric acid concentration is generally used in production; (3) residual acidity: low acidity at the end of decomposition The tungstic acid has a small particle size and a low purity, and generally has a residual acidity of 70-80 g/l. In addition, the addition of an appropriate amount of nitrate (nitrate) during acid decomposition is beneficial to accelerate the decomposition process and oxidation of impurities. And it is beneficial to increase the total recovery of tungsten.

The filtered tungstic acid should be washed. The quality of tungstic acid meets the standard before it can be shipped or sent to produce tungsten oxide. Otherwise, it should be cleaned. The ammonia method is commonly used for the purification of tungstic acid, that is, the tungstic acid solution is dissolved in ammonia water to be converted into an ammonium tungstate solution, and most of the impurities such as silicon, iron , manganese remain in the precipitate.

3. Preparation of ammonium paratungstate. The ammonium paratungstate is prepared from the ammonium tungstate solution by concentrated crystallization, and the tungstic acid is first dissolved in the ammonia water, and the tungsten is separated from some impurities, and the reaction formula is:

H2WO4+2NaOH=(NH4)2WO4 +2H2O

Certain impurities such as iron, manganese, and calcium chlorides simultaneously form hydroxide precipitates and tungsten separation. The solution was filtered through sedimentation and the filtrate was an ammonium tungstate solution.

The tungsten leaching solution is treated with a strong alkaline or weakly basic anion exchange resin, and the tungsten-loaded resin is rinsed with an ammonium chloride solution, and the resulting eluent is used to prepare ammonium paratungstate; in addition, an ammonium tungstate solution can also be obtained by solvent extraction. Sodium tungstate as a stock solution, tertiary amine or quaternary amine as kerosene organic phase was extracted at pH = 2-4 under conditions tungsten, then 2-4% ammonia stripping available ammonium tungstate solution.

The preparation of ammonium paratungstate from the ammonium tungstate solution can also be carried out by a neutralization method. When the ammonium tungstate solution is neutralized to pH=7-7.4 by using 10-20% hydrochloric acid, the form of tungsten in the form of needle-like ammonium paratungstate is precipitated, and the crystallization rate is up to 85-90%, but the neutralization method can not recover ammonia and consume hydrochloric acid, and has been replaced by the evaporation method.

When the ammonium tungstate solution is concentrated, a part of ammonia can be evaporated. After cooling (greater than 50 degrees), the plate-like ammonium paratungstate crystal is crystallized: ie:

12(NH4)2WO4 = 5(NH4)2O·12WO3 ·5H2O↓+14NH3↑+2H2O

Since the solubility of ammonium paratungstate is smaller than that of ammonium paramolybdate, in order to prevent the product from being contaminated by molybdenum, the tungsten and molybdenum can be separated by a stepwise crystallization method. For example, if 60% of the liquid is evaporated, the crystallization rate of tungsten is 55%, and the crystallization rate of molybdenum is only 12%, so the ammonium arsenate which is initially crystallized contains little molybdenum. The late stage ammonium tungstate precipitated with higher molybdenum.

The ammonia gas volatilized during evaporation is recovered by the washing tower, and the obtained ammonia water is returned for use; the mother liquid rich in impurities is recovered for tungsten.

4. Preparation of tungsten trioxide. Industrial tungsten oxide powder can be obtained by calcining dry pure tungstic acid or ammonium paratungstate. The reaction formula is:

H2WO4 = WO3+H2O↑

5(NH4)2O·12WO3 ·nH2O =12WO3 +10NH3↑+(5+n)H2O(calcined)↑

When the calcination temperature is 500 degrees, the tungstic acid can be completely dehydrated, and the temperature above 250 degrees can completely decompose the ammonium paratungstate. The tungsten trioxide used for the production of tungsten and tungsten carbide should have a certain purity, but also meet certain particle size requirements. The particle size of tungsten trioxide is closely related to the particle size and calcination temperature of tungstic acid such as ammonium paratungstate.

Four: Preparation and equipment required for concentrate

The main equipment concentrate processing equipment includes roasting kiln, decomposition tank, pressure cooker, melting furnace, purification tank, ion exchange column, solvent extraction tank, continuous centrifugal filter, evaporation crystallization tank or continuous evaporation crystallizer. The powder preparation equipment includes a rotary tube furnace, a tungsten trioxide baking furnace, a blue oxygen furnace and a reduction furnace. The press molding equipment includes a hydraulic press and a cold isostatic press. The sintering and smelting equipment includes a pre-sintering furnace, a high-temperature sintering furnace, a vertical melting furnace, various vacuum melting furnaces, and the like.

The workshop consists of a general tungsten smelting plant, such as tungsten wet smelting, tungsten powder production, tungsten (ingot) preparation, comprehensive recovery (recovery of calcium chloride, tungsten iron, strontium, bismuth , antimony, etc.), and other auxiliary facilities such as hydrogen production. composition. Depending on the nature and scale of the production, workshops can be set up separately or combined. As will be integrated hydrometallurgical recovery of tungsten incorporated into the workshop, prepared tungsten powder, tungsten (ingots) into a powder metallurgical workshop.

Factory configuration and characteristics Chemical processes such as acid, alkali and organic reagents are used in the wet smelting production process, and harmful emissions are required to be treated. Therefore, when the factory is configured, the wet smelting workshop should be located in the downwind direction of the plant, and the raw and auxiliary materials should be transported and the tungsten slag removed. The tungsten powder metallurgy part has dustproof, explosion-proof and fireproof requirements, and should be placed in an area that is relatively clean and free from external dust.

The recovery rate of main technical and economic indicators: tungsten wet smelting is 90% to 98%; pure tungsten powder is 98% to 99%; pure tungsten (ingot) is 98% to 99.5%. Technical and economic indicators depend on factors such as the raw materials used, the production process and the price of raw and auxiliary materials. In Japan, a company such as wolframite concentrates as raw material the classical alkaline process, product consumption per ton of caustic soda paratungstate 2.46t; 3.2t hydrochloride; China factory in scheelite as raw material the classical acid method process per ton The ammonium paratungstate product consumes 4 to 5 tons of hydrochloric acid and 1.7 to 2.3 tons of ammonia water.

A higher purity tungsten compound must be prepared prior to the preparation of the metal tungsten. Therefore, impurities in the crude sodium tungstate solution and crude tungstic acid obtained by decomposing the tungsten mineral raw material are removed. Purification of crude sodium tungstate solution and crude tungstic acid can produce tungsten pure ammonium paratungstate tungsten oxide. These two pure tungsten compounds are the most commonly used raw materials for industrial production of tungsten powder.

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