阅读说明：本技术 一种钨酸一步氨溶脱磷制取仲钨酸铵的方法 (Method for preparing ammonium paratungstate by one-step ammonia solution dephosphorization of tungstic acid ) 是由 杨正锋 张代彬 张龙辉 刘莉 梁勇 钟志强 徐国钻 于 2021-08-12 设计创作，主要内容包括：本发明提供一种钨酸一步氨溶脱磷砷硅制取仲钨酸铵的方法,具体是将球磨得到的白钨矿细粉用盐酸浸出得到粗制钨酸,再将钨酸转至氨溶釜内,同时加入一定体积的氨水和一定质量的镁盐,反应一段时间后,过滤得到钨酸铵溶液,经蒸发结晶即可得到合格的仲钨酸铵产品。本发明将钨酸氨溶和镁盐除磷砷硅结合在一起,化两步为一步,不仅缩短了工艺流程,还提高了生产效率；充分利用了氨溶渣的促进形核和吸附特性,使除磷砷硅渣与氨溶渣共沉淀,大大提高了反应效率和除杂效果,降低了试剂的消耗,节约了生产成本,适用于大规模工业化生产。(The invention provides a method for preparing ammonium paratungstate by one-step ammonia-dissolving dephosphorized silicon arsenate from tungstic acid, which comprises the steps of leaching fine scheelite powder obtained by ball milling with hydrochloric acid to obtain rough tungstic acid, transferring the tungstic acid into an ammonia-dissolving kettle, simultaneously adding a certain volume of ammonia water and a certain mass of magnesium salt, reacting for a period of time, filtering to obtain an ammonium tungstate solution, and evaporating and crystallizing to obtain a qualified ammonium paratungstate product. The invention combines ammonium tungstate solution and magnesium salt for removing phosphorus, arsenic and silicon, and the two steps are one step, thereby not only shortening the process flow, but also improving the production efficiency; the method makes full use of the characteristics of promoting nucleation and adsorption of the ammonia slag, ensures that the phosphorus, arsenic and silicon removal slag and the ammonia slag are co-precipitated, greatly improves the reaction efficiency and the impurity removal effect, reduces the consumption of reagents, saves the production cost, and is suitable for large-scale industrial production.)

1. A method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorization and desilication of tungstic acid is characterized by comprising the following steps:

step 1: hydrochloric acid leaching of scheelite

Throwing the scheelite fine powder subjected to ball milling into an acid decomposition kettle, adding a certain volume of hydrochloric acid, reacting for a period of time, cooling, filtering, allowing the filtrate to enter an acid filtrate tank, and allowing the tungstic acid to stay in a plate frame;

step 2: dissolving tungstic acid in ammonia and removing impurities

Transferring a certain amount of tungstic acid into an ammonia dissolving kettle, adding a certain volume of ammonia water and a certain mass of magnesium salt, reacting for a period of time, and filtering to obtain an ammonium tungstate solution;

and step 3: evaporative crystallization

And (3) evaporating and crystallizing the ammonium tungstate solution obtained in the step (2) to obtain a qualified ammonium paratungstate product.

2. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: the method comprises the step 1 of ball milling of scheelite, wherein a certain amount of scheelite is added into a ball mill for ball milling, the ball-material ratio is 1.5-4: 1, the diameter of a milling ball is 5-40 mm, the ball milling medium is water, the adding amount of the ball milling medium is 1-3L: 1kg, the ball milling time is 1-15 h, and the average particle size of scheelite fine powder obtained after the ball milling is 10-40 mu m.

3. The method for preparing ammonium paratungstate by one-step ammonia-soluble removal of phosphorus, arsenic and silicon of tungstic acid according to any one of claims 1 or 2, characterized in that: the particle size of the scheelite fine powder is less than 30 mu m.

4. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: in the step 1, the volume of hydrochloric acid/weight of ore is 1.5-4.0 mL:1g, the concentration of hydrochloric acid is 10-31%, the reaction temperature is 60-100 ℃, and the reaction time is 1-5 h.

5. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: the volume mass ratio of ammonia to tungstic acid in the step 2 is 1.5-3.0 mL:1 g.

6. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: the ammonia water concentration in the step 2 is more than 100g/L, preferably more than 210g/L, and more preferably 270 g/L.

7. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: the magnesium salt in the step 2 is one or more of magnesium sulfate, magnesium nitrate and magnesium chloride, and preferably magnesium sulfate.

8. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: the mass ratio of the magnesium salt to the tungstic acid in the step 2 is 0.5-5: 100.

9. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: in the step 2, the reaction temperature is normal temperature to 100 ℃, preferably 50 to 100 ℃, and the reaction time is 0.5 to 4 hours.

10. The method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorizing arsenious silicon tungstate according to claim 1, which is characterized in that: and (3) molybdenum removal treatment is carried out on the ammonium tungstate solution before evaporation and crystallization in the step 3, and the pure ammonium tungstate solution is obtained after filtration.

Technical Field

The invention belongs to the technical field of tungsten smelting, and particularly relates to a method for preparing ammonium paratungstate by one-step ammonia-dissolving purification of tungstic acid.

Background

In the tungsten smelting production process, along with the gradual decrease of the black tungsten concentrate and the gradual increase of the use of the white tungsten concentrate, the finding of an efficient, clean and simple white tungsten smelting process is more important. Tungstic acid is an important intermediate product in the tungsten smelting process, belongs to solid inorganic acid and is easy to dissolve in alkaline aqueous solution. As is well known, solid tungstic acid is prepared from scheelite after being decomposed by hydrochloric acid, ammonium tungstate solution obtained by dissolving ammonium tungstate can be evaporated and crystallized to produce ammonium paratungstate products, although the process has the advantages of short process flow, low production cost and the like, the impurity elements such as potassium, sodium, phosphorus, arsenic, silicon and the like in scheelite concentrate can be circulated to subsequent products along with the production process, and finally the impurity elements of ammonium paratungstate exceed the standard.

In order to remove impurity ions such as phosphorus, arsenic and silicon in the ammonium tungstate solution, magnesium salt is usually added in the ammonium tungstate solution, and the problems of unstable impurity removal, large reagent dosage, high residual magnesium ion in the solution and the like exist in the impurity removal process, so that the problem of Mg standard exceeding exists in the APT product obtained by final evaporation crystallization. Funan university of China (deep removal of magnesium ions in ammonium tungstate solution, rare metals and hard alloy, volume 46, phase 4, pages 1-5) adopts D850 chelating resin to adsorb Mg in ammonium tungstate solution²⁺The method can produce APT products which reach the national standard GB/T10116-88 APT-0, but the process is complex in process, generates more waste water in the adsorption and desorption processes, is high in cost and is not beneficial to being applied to large-scale industrial production.

Therefore, it is very urgent for those skilled in the art how to remove other impurity elements in the ammonia solution process without introducing excessive impurities such as magnesium ions.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a method for preparing ammonium paratungstate by one-step ammonia-dissolving and dephosphorizing tungstic acid, which is characterized in that crude tungstic acid is prepared by decomposing scheelite with hydrochloric acid, then magnesium salt is added when the tungstic acid is dissolved in ammonia, and the dissolution of impurities such as phosphorus, arsenic, silicon and the like can be effectively inhibited by controlling the technological parameters of ammonia dissolving, so that the impurities such as phosphorus, arsenic, silicon and the like can be effectively removed while the tungstic acid is dissolved in ammonia, and the phosphorus, arsenic, silicon and the like can be generated and precipitated and stay in slag. And (3) removing impurities, purifying, evaporating and crystallizing the ammonium tungstate solution to obtain the qualified ammonium paratungstate. The specific technical scheme is as follows:

a method for preparing ammonium paratungstate by one-step ammonia-dissolved dephosphorization and desilication of tungstic acid comprises the following steps:

step 1: hydrochloric acid leaching of scheelite

And (3) pumping the ball-milled scheelite fine powder into an acid decomposition kettle, adding a certain volume of hydrochloric acid, reacting for a period of time, cooling, filtering, feeding the filtrate into an acid filtrate tank, and stopping the tungstic acid in a plate frame.

Step 2: dissolving tungstic acid in ammonia and removing impurities

Transferring a certain amount of tungstic acid into an ammonia dissolving kettle, adding a certain volume of ammonia water and a certain mass of impurity removing agent, reacting for a period of time, and filtering to obtain an ammonium tungstate solution.

And step 3: evaporative crystallization

And (3) evaporating and crystallizing the ammonium tungstate solution obtained in the step (2) to obtain a qualified ammonium paratungstate product.

Further, a step of ball milling the scheelite is included before the step 1, a certain amount of scheelite is added into a ball mill for ball milling, a certain amount of scheelite is added into the ball mill for ball milling, the ball-to-material ratio is 1.5-4: 1, the diameter of a milling ball is 5-40 mm, the ball milling medium is water, the adding amount of the ball milling medium is 1-3: 1, the ball milling time is 1-15 h, and the average particle size of the scheelite fine powder obtained after the ball milling is 10-40 μm.

Further, the volume of hydrochloric acid/weight of ore in the step 1 is 1.5-4.0 mL:1g, the concentration of hydrochloric acid is 10-31%, the reaction temperature is 60-100 ℃, and the reaction time is 1-5 h.

Further, the volume-mass ratio of ammonia to tungstic acid in the step 2 is 1.5-3.0 mL:1 g.

Furthermore, the ammonia water concentration in the step 2 is more than 100g/L, preferably more than 210g/L, and more preferably 270 g/L.

Further, the impurity removing agent in the step 2 is a magnesium salt, specifically one or more of magnesium sulfate, magnesium nitrate and magnesium chloride, and the mass ratio of the magnesium salt to the tungstic acid is 0.5-5: 100.

Further, the reaction temperature in the step 2 is normal temperature to 100 ℃, preferably 50 to 100 ℃, and the reaction time is 0.5 to 4 hours.

Further, molybdenum removal treatment is carried out on the ammonium tungstate solution before evaporation and crystallization in the step 3, and a pure ammonium tungstate solution is obtained after filtration.

The method can realize the short-process preparation of ammonium paratungstate, reduces the dosage of a magnesium salt reagent serving as an impurity removing agent while efficiently removing impurities, reduces residual magnesium ions, and shortens the process flow by changing two processes into one. The process principle of adding magnesium salt to remove impurity ions such as phosphorus, arsenic, silicon and the like is as follows:

Mg²⁺+NH₄ ⁺+PO₄ ^3-→MgNH₄PO₄↓

Mg²⁺+NH₄ ⁺+AsO₄ ^3-→MgNH₄AsO₄↓

from the analysis of the chemical reaction mechanism, it can be found that: the reaction for increasing the ammonia concentration is carried out rightwards, so that magnesium ammonium phosphate sediment is formed, and the phosphorus removal efficiency is improved; according to thermodynamic calculation analysis, the temperature is increased, so that the reaction is favorably carried out rightwards, the formation of magnesium ammonium phosphate and magnesium ammonium arsenate precipitates is favorably realized, and the removal of phosphorus and arsenic is favorably realized; the micro-fine suspended ammonia dissolving slag generated by ammonia dissolving can release seed crystals to promote nucleation and precipitation of magnesium ammonium phosphate and magnesium ammonium arsenate on the one hand, and can adsorb magnesium ammonium phosphate and magnesium ammonium arsenate to form coprecipitation on the other hand, so that the reaction is promoted, and the dephosphorization efficiency is improved.

According to the method, in the step 1, scheelite is added into a ball mill for ball milling, so that the scheelite is crushed into scheelite fine powder, calcium tungstate and other associated silicate minerals can be separated to a certain degree, and the calcium tungstate wrapped by other compounds insoluble in hydrochloric acid is prevented from being dissolved out, so that the yield is reduced; in addition, by controlling the process and parameters in the ball milling process, through experimental optimization, the scheelite fine powder with the average particle size of 10-30 microns is obtained by adopting the ball-to-material ratio of 2-3: 1, the diameter of a milling ball of 5-40 mm, the addition amount of the ball milling medium of water of 1.5-2.5: 1 and the ball milling time of 5-8 h.

In the acid decomposition process, the material ratio and the reaction parameters are controlled, the volume-to-mass ratio of the added hydrochloric acid to the scheelite concentrate fine powder is controlled to be 1.5-4.0L: 1kg, the concentration of the hydrochloric acid is 10-31%, the reaction temperature is 60-100 ℃, and the reaction time is 1-5 hours. In the reaction process, part of calcium impurities in the scheelite fine powder are dissolved by hydrochloric acid and can be removed along with filtration; and part of the silicon dioxide and silicate fine powder particles can not be dissolved by hydrochloric acid, the hydrochloric acid reacts with the scheelite fine powder to generate tungstic acid precipitate which is in a gel state in the solution and is aggregated with the silicon dioxide and silicate particles, unreacted calcium tungstate, phosphorus, arsenic and other impurities, and the mixture stays in the plate frame after being cooled and filtered.

The method is vital to the ammonia dissolving process of rough tungstic acid, is a key link for realizing the preparation of national standard zero-grade products by one-step ammonia dissolving of tungstic acid and taking ammonium paratungstate, adding a tungstic acid crude product obtained by filtering after acid decomposition into an ammonia dissolving kettle, then adding a certain volume of ammonia water and a certain mass of magnesium salt, controlling the adding amount and concentration of the ammonia water, wherein the adding amount of the ammonia water ensures that the tungstic acid can be fully dissolved to generate ammonium tungstate, and is not particularly limited, and the volume-mass ratio of the ammonia water to the tungstic acid is 1.5-3.0 mL:1 g; the concentration of ammonia water can influence the rate of the ammonia dissolving process of the tungstic acid, in the ammonia dissolving process of a crude product of the tungstic acid, insoluble substance fine particles gathered in the tungstic acid in the acid decomposition process can be released, the formed fine suspended ammonia dissolving residue can be used as a seed crystal to accelerate nucleation and crystallization of other precipitation processes, such as magnesium ammonium phosphate and magnesium ammonium arsenate, and mixed crystals can be generated to be separated out together due to the fact that the magnesium ammonium phosphate and the magnesium ammonium arsenate have similar crystal lattices, and enrichment precipitation of phosphorus and arsenic is accelerated and promoted. Meanwhile, the micro-fine suspended ammonia dissolving slag generated in the ammonia dissolving process can also adsorb magnesium ammonium phosphate and magnesium ammonium arsenate to form coprecipitation, so that the removal of impurity elements such as phosphorus, arsenic, silicon and the like is further promoted. According to the invention, the concentration of the ammonia water is controlled to be more than 100g/L, the ammonia water concentration is too low, the ammonia dissolving rate is influenced, the micro ammonia dissolving slag cannot timely generate coprecipitation with magnesium ammonium phosphate, magnesium ammonium arsenate and the like, the adsorption effect is weak, the concentration of the ammonia water is preferably controlled to be more than 210g/L, and a better effect can be achieved; when the concentration of the ammonia water exceeds 270g/L, the generated coprecipitation and adsorption effects are not obviously increased, so that the concentration of the ammonia water is preferably controlled to be 210-270g/L in order to save raw materials and cost.

The impurity removing agent added in the ammonia dissolving process is magnesium salt, the type of the magnesium salt is not particularly limited, the impurity removing agent can be one or more of magnesium sulfate, magnesium nitrate and magnesium chloride, and the magnesium sulfate is preferably used. The invention limits the addition of magnesium salt to fully precipitate impurities such as phosphorus, silicon, arsenic and the like in the ammonia dissolving process, and does not cause the excessive residual in the solution to cause the magnesium content in the ammonium paratungstate product prepared by evaporation crystallization to exceed the standard. According to the indexes, the impurity content in the raw materials and the purity requirement of the final product are comprehensively considered, and the mass ratio of the added magnesium salt to the added tungstic acid is controlled to be 0.5-5: 100.

The reaction temperature and time in the ammonia dissolving process are not particularly limited, but the temperature in the ammonia dissolving process can also certainly affect the removal of impurities in the coprecipitation process, the ammonia dissolving temperature can affect the ammonia dissolving rate, and further affect the formation rate and the coprecipitation effect of the fine ammonia dissolving slag. Finally, adding magnesium salt while dissolving ammonia to remove impurities, optimizing process parameters, and filtering after the ammonia dissolution is finished to obtain WO₃150-300 g/L ammonium tungstate solution, wherein the concentrations of phosphorus, arsenic, silicon and magnesium ions are less than 0.01g/L, and the total weight of the ammonia slag is 3-10% of the weight of the raw ore.

In another technical scheme provided by the invention, molybdenum removal treatment is also carried out before the ammonium tungstate solution after impurity removal is subjected to evaporation crystallization to prepare ammonium paratungstate.

Compared with the prior art, the invention has the following beneficial effects:

1. the process skillfully combines ammonium tungstate solution and magnesium salt phosphorus, arsenic and silicon removal together, and combines two steps into one step, thereby not only shortening the process flow, but also improving the production efficiency.

2. The process fully utilizes the characteristics of the ammonia dissolving process, greatly promotes the efficiency of removing phosphorus, arsenic and silicon from the magnesium salt, reduces the consumption of reagents and saves the production cost.

3. The process utilizes the adsorption characteristic of the ammonia soluble slag to ensure that the phosphorus, arsenic and silicon removing slag and the ammonia soluble slag are coprecipitated, thereby greatly improving the reaction efficiency and the impurity removing effect.

Drawings

FIG. 1 is a schematic diagram of a process for preparing ammonium paratungstate by one-step ammonia-dissolved phosphorus removal, arsenic removal and silicon removal.

Detailed Description

In order to better explain the present invention and to facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.

The invention takes the process of producing tungstic acid by a certain scheelite in China as a research object, and the main components of the scheelite are shown in Table 1.

TABLE 1 composition and content of scheelite

Name (R)	WO3	Mo	SiO2	P	Ca	Others
							Content/wt%	85	0.67	10	0.38	1.7	2.25

According to the technical scheme, the scheelite with the components shown in the table 1 is added into a ball mill for ball milling, the ball-material ratio is 1.5-4: 1, the diameter of a milling ball is 5-40 mm, the ball milling medium is water, the adding amount of the ball milling medium is 1-3: 1, the ball milling time is 1-15 h, and the average particle size of the scheelite fine powder obtained after the ball milling is 10-40 mu m.

In the embodiment of the invention, the scheelite fine powder with the average particle size of 10-30 μm is obtained by preferably adopting a ball-to-material ratio of 2-3: 1, a grinding ball diameter of 5-40 mm, a ball milling medium of water, an addition amount of the ball milling medium of 1.5-2.5: 1 and ball milling time of 5-8 h.

Example 1

Adding 100g of scheelite fine powder into an acid decomposition kettle, adding 200mL of hydrochloric acid, wherein the concentration of the hydrochloric acid is 31%, the reaction temperature is 95 ℃, the reaction time is 4 hours, cooling, filtering and washing, feeding the filtrate into an acid filtrate tank, and stopping tungstic acid in a plate frame for several times to prepare a certain amount of tungstic acid. Adding 100g of tungstic acid into a reaction kettle, adding 300mL of 6mol/L ammonia water, heating to 50 ℃, and reactingFor 2 hours, washing and filtering to obtain 9g of ammonia slag and 320mL of ammonium tungstate solution. In the filtrate: WO₃The concentration was 238g/L and the phosphorus concentration was 146 mg/L. 6g of magnesium sulfate is added into the filtrate, the mixture is stirred for 2 hours, the phosphorus concentration in the solution is 36mg/L, the magnesium ion concentration is 59mg/L, and the ammonium tungstate solution is subjected to impurity removal, evaporative crystallization and other steps to prepare an ammonium paratungstate product, wherein the impurity content is shown in Table 2.

TABLE 2 example 1 ammonium paratungstate product impurity content (mg/kg)

Example 2

Adding 100g of scheelite fine powder into an acid decomposition kettle, adding 250mL of hydrochloric acid, wherein the concentration of the hydrochloric acid is 25%, the reaction temperature is 85 ℃, the reaction time is 3.5 hours, cooling, filtering and washing, enabling filtrate to enter an acid filtrate tank, enabling tungstic acid to stay in a plate frame for several times, and preparing a certain amount of tungstic acid. Adding 100g of tungstic acid into a reaction kettle, adding 150mL of 6mol/L ammonia water, adding 2g of magnesium sulfate, heating to 50 ℃, reacting for 0.5 hour, washing and filtering to obtain 11g of ammonia dissolving residue and 220mL of ammonium tungstate solution. In the filtrate: WO₃The concentration was 340g/L and the phosphorus concentration was 5 mg/L. The concentration of magnesium ions is 23mg/L, and the ammonium tungstate solution is subjected to impurity removal, evaporative crystallization and other steps to prepare an ammonium paratungstate product, wherein the impurity content is shown in Table 3.

TABLE 3 example 2 ammonium paratungstate product impurity content (mg/kg)

Element(s)	Mg	P	As	Si	Others
						EXAMPLE 2 product	<3	5	<3	<3
National standard zero-grade product	10	7	8	8
						Results	Reach the standard	Reach the standard	Reach the standard	Reach the standard	Qualified

Example 3

Adding 100g scheelite fine powder into an acid decomposition kettle, adding 250mL hydrochloric acid with the concentration of 20 percent at the reaction temperature of 75 ℃, reacting for 3.5 hours, cooling, filtering and washing, allowing the filtrate to enter an acid filtrate tank, allowing tungstic acid to stay in a plate frame for several times, and preparing a productAnd (3) quantitative tungstic acid. Adding 100g of tungstic acid into a reaction kettle, adding 250mL of 6.5mol/L ammonia water, heating to 80 ℃, reacting for 4 hours, washing and filtering to obtain 11g of ammonia dissolving residue and 260mL of ammonium tungstate solution. Adding 13g of magnesium sulfate into the ammonium tungstate solution, reacting for 3 hours, and filtering: WO₃The concentration was 240g/L and the phosphorus concentration was 5 mg/L. The concentration of magnesium ions is 82mg/L, and the ammonium tungstate solution is subjected to impurity removal, evaporative crystallization and other steps to prepare an ammonium paratungstate product, wherein the impurity content is shown in Table 4.

TABLE 4 example 3 ammonium paratungstate product impurity content (mg/kg)

Element(s)	Mg	P	As	Si	Others
						EXAMPLE 1 product	55	5	<3	<3
National standard zero-grade product	10	7	8	8
						Results	Out of limits	Reach the standard	Reach the standard	Reach the standard	Qualified

Example 4

Adding 100g of scheelite fine powder into an acid decomposition kettle, adding 300mL of hydrochloric acid, wherein the concentration of the hydrochloric acid is 31%, the reaction temperature is 90 ℃, the reaction time is 2 hours, cooling, filtering and washing, feeding the filtrate into an acid filtrate tank, and stopping tungstic acid in a plate frame for several times to prepare a certain amount of tungstic acid. Adding 100g of tungstic acid into a reaction kettle, adding 300mL of 7.7mol/L ammonia water, adding 1.5g of magnesium sulfate, heating to 100 ℃, reacting for 1 hour, washing and filtering to obtain 11g of ammonia dissolving residue and 310mL of ammonium tungstate solution. In the filtrate: WO₃The concentration was 242g/L and the phosphorus concentration was 7 mg/L. The concentration of magnesium ions is 10mg/L, and the ammonium tungstate solution is subjected to impurity removal, evaporative crystallization and other steps to prepare an ammonium paratungstate product, wherein the impurity content is shown in Table 5.

TABLE 5 example 4 ammonium paratungstate product impurity content (mg/kg)

Element(s)	Mg	P	As	Si	Others
						EXAMPLE 4 product	<3	7	8	<3
National standard zero-grade product	10	7	8	8
						Results	Reach the standard	Reach the standard	Reach the standard	Reach the standard	Qualified

Example 5

Adding 100g of scheelite fine powder into an acid decomposition kettle, adding 250mL of hydrochloric acid, wherein the concentration of the hydrochloric acid is 25%, the reaction temperature is 85 ℃, the reaction time is 3.5 hours, cooling, filtering and washing, enabling filtrate to enter an acid filtrate tank, enabling tungstic acid to stay in a plate frame for several times, and preparing a certain amount of tungstic acid. Adding 100g of tungstic acid into a reaction kettle, adding 300mL of 6mol/L ammonia water, adding 1.5g of magnesium sulfate, reacting for 2 hours at normal temperature, washing and filtering to obtain 13g of ammonia dissolving residue and 330mL of ammonium tungstate solution. In the filtrate: WO₃The concentration was 232g/L and the phosphorus concentration was 16 mg/L. The concentration of magnesium ions is 9mg/L, and the ammonium tungstate solution is subjected to impurity removal, evaporative crystallization and other steps to prepare an ammonium paratungstate product, wherein the impurity content is shown in Table 6.

TABLE 6 example 5 ammonium paratungstate product impurity content (mg/kg)

Element(s)	Mg	P	As	Si	Others
						EXAMPLE 5 product	<3	10	8	12
National standard zero-grade product	10	7	8	8
						Results	Reach the standard	Out of limits	Reach the standard	Out of limits	Qualified

Example 6

Adding 100g of scheelite fine powder into an acid decomposition kettle, adding 250mL of hydrochloric acid, wherein the concentration of the hydrochloric acid is 15%, the reaction temperature is 95 ℃, the reaction time is 4 hours, cooling, filtering and washing, feeding the filtrate into an acid filtrate tank, and stopping tungstic acid in a plate frame for several times to prepare a certain amount of tungstic acid. Adding 100g of tungstic acid into a reaction kettle, adding 300mL of 4mol/L ammonia water, adding 3g of magnesium sulfate, heating to 50 ℃, reacting for 2 hours, washing and filtering to obtain 12g of ammonia dissolving residue and 305mL of ammonium tungstate solution. In the filtrate: WO₃The concentration was 230g/L and the phosphorus concentration was 18 mg/L. The concentration of magnesium ions is 16mg/L, and the ammonium tungstate solution is subjected to impurity removal, evaporative crystallization and other steps to prepare an ammonium paratungstate product, wherein the impurity content is shown in Table 7.

TABLE 7 example 6 ammonium paratungstate product impurity content (mg/kg)

Element(s)	Mg	P	As	Si	Others
						EXAMPLE 6 product	<3	12	11	14
National standard zero-grade product	10	7	8	8
						Results	Reach the standard	Out of limits	Out of limits	Out of limits	Qualified

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.