A method for removing impurities from ammonium paratungstate crystal mother liquor

Abstract

A method for removing impurities from ammonium paratungstate crystal mother liquor of the present invention comprises alkalization, evaporation and ammonia expulsion, and acidification. Alkalization is to add alkali liquid to the ammonium paratungstate crystal mother liquor, react under normal temperature and slight negative pressure, stop adding alkali liquid when the pH value of the reaction liquid is 11-13, and obtain alkalized liquid and ammonia gas; evaporation and ammonia expulsion is to contact steam with the alkalized liquid in a stripping tower in countercurrent, so that the ammonia in the alkalized liquid is converted into ammonia gas, and after the ammonia gas is removed, a deammonified liquid is obtained; acidification is to send the deammonified liquid to a reaction tank for stirring, add an acidifier to the reaction tank without heating, acidify to a solution pH value of 1.5-1.2, and obtain an acidified liquid after filtering. The method of the present invention can obtain a low-content ammonia nitrogen and low COD ammonium paratungstate crystal mother liquor conversion liquid, which can be reused in the main process, optimize the process flow, and improve the workshop's ability to treat ammonium paratungstate crystal mother liquor.

Description

Technical Field

[0001] The invention belongs to the technical field of impurity removal of tungsten smelting crystallization mother liquor, and relates to a method for removing impurities from ammonium paratungstate crystallization mother liquor, and in particular to a method for removing impurities from ammonium paratungstate crystallization mother liquor in a process for producing ammonium paratungstate by tungsten ore salt / alkali decomposition-acid extraction-evaporation crystallization. Background Art

[0002] With the country's emphasis on rare metal materials, environmental protection, green development, and high-quality development in recent years, in the process of producing ammonium paratungstate using tungsten ore salt / alkali decomposition-acid extraction-evaporation crystallization, tungsten has undergone a series of reactions in alkaline and acid environments throughout the process. Compared with the ammonium paratungstate products produced by the mainstream production process ion exchange process, it has the characteristics of low chemical element content and low total amount, and good physical properties. It is deeply favored by downstream companies that manufacture high-end products, and is highly consistent with the current national advocacy of high-quality development.

[0003] The ammonium tungstate produced by the extraction method is evaporated and crystallized to produce ammonium paratungstate product and the remaining 30%-40% volume of crystallization mother liquor. The mother liquor COD is 60000-120000mg / L, contains 10-15g / L ammonia, and contains 50-100g / L WO3. The high content of COD is affected by the ammonia in the mother liquor, the residual organic phase of extraction, the low-valent tungsten and molybdenum homo / heteropoly acid salts, sulfide ions and their derivatives and other reducing components. During the crystallization process, many components interact with each other to form more complex substances. For example, the organic phase components of the extraction interact with the sulfur derivatives of sulfide ions, making the phase composition of the crystallization mother liquor complex and difficult to handle. If the mother liquor is directly refluxed to the main process, there are great limitations for the following three reasons:

[0004] (1) High ammonia (ammonium) directly returns to the main process and releases a certain amount of ammonia after contacting with alkaline solution or alkaline salt solution, resulting in unorganized emission of ammonia waste gas and high ammonia nitrogen content in wastewater;

[0005] (2) COD from mineral flotation agents and extracted organic phase directly affects the filtration of tungsten slag separation and purification;

[0006] (3) The tungsten in the mother liquor is highly polymerized, usually tungsten and impurity elements or itself are highly polymerized, and the valence of tungsten and molybdenum becomes lower after acid adjustment, and the simple tungstate WO4 2- The properties of the products vary greatly, making it difficult to control their state during the production process.

[0007] Preliminary research found that after the mother liquor was added into the process at a volume fraction of 25%, the COD of the entire process solution soared from about 4000mg / L to 15000mg / L-28000mg / L, which seriously impacted the treatment capacity of the wastewater treatment station. Compared with the wastewater COD discharge standard of 100mg / L, the environmental risk increased sharply. When it is lower than 25%, the mother liquor is accumulated. At present, the main methods and shortcomings of the industry for treating mother liquor are:

[0008] 1. Alkali conversion-precipitation synthesis of scheelite: ① It is difficult to completely drive out the ammonia in the mother liquor with alkali, and the synthetic scheelite and waste liquid contain high ammonia; ② Calcium salt precipitant generally uses calcium chloride, which leads to the introduction of chloride ions in the production process and the risk of equipment corrosion; ③ The discharge of three wastes is large, the reagent consumption is high, and the cost is high.

[0009] 2. Acidified mother liquor - ion exchange / extraction method - alkali conversion: ① The ion exchange / extraction process is long and requires many equipments; ② The acidified mother liquor enters the ion exchange / extraction process to recover tungsten. The mother liquor after acidification is an ammonia solution, which needs to be alkalized and then deammoniated to meet the discharge standards.

[0010] 3. Alkali conversion - ammonia stripping method: ① The alkalinity of the mother liquor needs to be adjusted to 1-2 mol / L, which consumes a lot of alkali; ② The amount of waste gas generated by stripping is large, the stripping time is long, and it is difficult to treat thoroughly.

[0011] 4. Alkali conversion - directly added to the main process: ① The mother liquor has high alkali consumption, incomplete alkalization, and high ammonia content; ② The alkalized liquid contains high COD.

[0012] Therefore, it is urgent to develop a method for reducing impurities in the ammonium paratungstate crystallization mother liquor, so as to achieve the requirements of treating and recovering ammonia, reducing COD, and digesting highly polymerized tungsten, and to return it to the main process quickly and at low cost. Summary of the invention

[0013] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for removing impurities from the ammonium paratungstate crystallization mother liquor, which can reduce the contents of ammonia nitrogen and COD in the crystallization mother liquor, and digest highly polymerized tungsten so that the mother liquor conversion liquid can be quickly and low-cost returned to the main process.

[0014] In order to solve the above technical problems, the present invention adopts the following technical solutions.

[0015] A method for removing impurities from ammonium paratungstate crystallization mother liquor comprises the following steps:

[0016] (1) Alkalization: add alkali solution to the ammonium paratungstate crystal mother liquor and stir, and react under normal temperature and slight negative pressure (i.e., normal temperature and vacuum), wherein the slight negative pressure (i.e., vacuum degree) is 0.1 kPa to 0.3 kPa. When the pH value of the reaction liquid reaches 11 to 13, stop adding alkali solution, stir, and obtain alkalized liquid and ammonia gas, and absorb the ammonia gas by water spraying and recover the ammonia gas by ammonia condensation;

[0017] (2) Evaporation and ammonia drive: First, introduce 0.2MPa~0.5MPa steam from the bottom of the stripping tower to preheat the stripping tower. After preheating the stripping tower temperature to 90℃~100℃, the alkalized liquid is heated at 2m 3 / h~8m 3 / h flow rate from the top of the stripping tower, the gas and liquid in the tower form countercurrent direct contact, the top temperature of the stripping tower is controlled to be 90°C to 95°C, the steam micro-positive pressure is 1kPa to 5kPa, so that the ammonia in the alkalized liquid is converted into ammonia gas, and after the ammonia gas is removed, a deammonified liquid is obtained, the ammonia nitrogen concentration of the deammonified liquid is 5mg / L to 200mg / L, and the ammonia gas is subjected to water spray absorption and ammonia condensation recovery;

[0018] (3) Acidification: The deammoniation liquid is sent to a reaction tank and stirred. Without heating, an acidifier is added to the reaction tank to acidify the solution to a pH value of 1.5 to 1.2, so that the soluble sulfur-containing compounds are acidified to generate insoluble sulfur. After filtration, an acidified liquid is obtained, i.e., the ammonium paratungstate crystal mother liquor conversion liquid, and impurity removal is completed.

[0019] The above method for removing impurities from the ammonium paratungstate crystal mother liquor is preferably such that in step (1), the alkali solution is added at a speed of 1 m / s. 3 / h~4m 3 / h, the alkali solution includes sodium hydroxide solution and / or industrial liquid alkali, the concentration of sodium hydroxide in the alkali solution is 300g / L-400g / L, and the stirring time after stopping adding the alkali solution is 20min-40min.

[0020] In the above method for removing impurities from the ammonium paratungstate crystal mother liquor, preferably, in step (1), when the pH value of the reaction solution is 12 to 12.5, the addition of alkali solution is stopped.

[0021] In the above method for removing impurities from the ammonium paratungstate crystallization mother liquor, preferably, in step (2), the alkalized liquid is introduced from 2m above the top of the stripping tower, and the ammonia nitrogen concentration of the deammoniation liquid is 5mg / L to 100mg / L.

[0022] The above method for removing impurities from the ammonium paratungstate crystal mother liquor is preferably, in step (3), the reaction tank is a stainless steel reaction tank or a plastic reaction tank, the volume of the deammoniation solution is 75% to 80% of the designed volume of the reaction tank, and the speed of adding the acidulant to the reaction tank is 0.1 m / s. 3 / h~5m 3 / h, the acidifying agent is H2SO4 solution, and the concentration of the H2SO4 solution is 2.5mol / L~10mol / L.

[0023] The above-mentioned method for removing impurities from the ammonium paratungstate crystal mother liquor is preferably that in step (3), during the acidification process, when the pH value of the solution is greater than 4 (usually 13≥pH value>4), a pH meter or 5-0.5 precision pH test paper is used to measure the pH value of the solution; when the pH value of the solution is between 4 and 1, a 5-0.5 precision pH test paper is used to measure the pH value of the solution or a pH meter is used to measure the pH value of the solution after filtering with filter paper.

[0024] In the above method for removing impurities from the ammonium paratungstate crystal mother liquor, preferably, in step (3), the speed at which the acidulant is added to the reaction tank is 0.5 m / s. 3 / h~3m 3 / h, the concentration of the H2SO4 solution is 2.5mol / L~5mol / L.

[0025] The above method for removing impurities from the ammonium paratungstate crystallization mother liquor preferably further comprises step (4) returning to the main process: sending the crude sodium tungstate solution and the acidified liquid obtained in step (3) to a purification step in the main production process for treatment.

[0026] In the above-mentioned method for removing impurities from the ammonium paratungstate crystal mother liquor, preferably, in step (4), the purification process is implemented in a purification tank, the volume ratio of the crude sodium tungstate solution to the acidifying solution is 2 to 5:1, the total volume of the crude sodium tungstate solution and the acidifying solution is 70% to 80% of the designed volume of the purification tank, the alkalinity of the crude sodium tungstate solution is 18 g / L to 30 g / L, and the concentration of WO3 in the crude sodium tungstate solution is 100 g / L to 150 g / L.

[0027] The above-mentioned method for removing impurities from the ammonium paratungstate crystallization mother liquor is preferably such that, in step (1), the alkalization is carried out in a negative pressure tank with a negative pressure system, and the volume of the ammonium paratungstate crystallization mother liquor accounts for 75% to 80% of the designed volume of the negative pressure tank.

[0028] The terms of the present invention are explained as follows:

[0029] Crude sodium tungstate solution: refers to the solution obtained by boiling the slurry of scheelite or mixed scheelite with salt and alkali and then filtering it through a filter press.

[0030] Industrial liquid caustic soda: The main ingredient is sodium hydroxide. Depending on the production process and raw materials, it may contain other ingredients such as sodium carbonate and sodium sulfide.

[0031] Depolymerization: A large molecule decomposes into one or more small molecules through certain chemical reactions.

[0032] The main innovative points and principles of the present invention are as follows:

[0033] The applicant has conducted research on the crystallization mechanism of ammonium paratungstate, the properties of the crystallization mother liquor, the behavior of impurities, the principle and operating parameters of the alkaline ammonia drive process of the tube-type ammonia conversion tower, and the correlation between the formation mechanism of various reducing sulfates and substances. It was found that the impurity group in the mother liquor is mainly composed of ammonia / ammonium, sulfide, organic matter and other substances, which are concentrated in the COD indicators of the solution or wastewater, especially the latter two.

[0034] 1. COD composition

[0035] 1. Mother liquor COD in the form of sulfur

[0036] (1) Unoxidized sulfide ions;

[0037] (2) Sulfide ion oxidation products such as sulfur, sulfide ions, sulfite, and thiosulfate are reducing substances;

[0038] (3) Sulfide ions, sulfur and sulfur acid radicals produce polysulfates under high temperature and high alkalinity during the ammonia drive process;

[0039] (4) The product sulfur and the carboxylic acids of the mineral flotation agent, the alcohols / amines and other organic substances in the extracted organic phase interact with each other through intermolecular forces to form substances with a certain degree of water solubility.

[0040] 2. Mother liquor COD in the form of organic matter: It comes from the flotation agent and extraction system phase components in the production raw material scheelite, dissolved or entrained in the ammonium tungstate solution and mother liquor.

[0041] (1) Dissolved and entrained extraction system phase components such as alcohols and tertiary amines;

[0042] (2) As the crystal volume concentrates and the pH decreases, the alcohols and tertiary amines entrained in the ammonium tungstate solution interact more strongly with the inorganic acid salts, generating ionic substances with a certain solubility.

[0043] 3. Other forms of COD

[0044] It is reduced by sulfide ions to intermediate valence substances such as tungstate and residual ammonia / ammonium.

[0045] 2. Evolution of sulfide, an important component of COD

[0046] Sulfide ions come from sodium sulfide, a molybdenum removal agent in the front-end process, which remains in the solution and enters the ammonium tungstate solution through the extraction-stripping process. Sulfide ions come from ammonium sulfide ions added to inhibit the precipitation of molybdenum during the crystallization of ammonium paratungstate, and their oxidation products during the crystallization and ammonia expulsion process.

[0047] Sulfide ions undergo a series of oxidation and polymerization reactions in the ammonium paratungstate crystals, evolving from -2 valence to 0, +2, +4, and +6 valence, generating water-insoluble sulfur and highly water-soluble subsalts, thiosalts, disalts and other reducing substances. These substances are the main components of COD because they belong to the intermediate valence state, are unstable in nature, and are difficult to handle.

[0048] The industry generally adopts the high temperature and high alkali ammonia drive method of the tube-type ammonia conversion tower. Although it has the effect of reducing the ammonia nitrogen in the mother liquor of ammonium paratungstate crystallization, the problem that comes with it is that under high temperature and high alkali, sulfide ions, sulfur and their derivatives are more complexly intertwined to generate larger molecules of polythionate (hypersulfate), which is more difficult to handle and is also part of the composition of COD.

[0049] 3. The entry point of the present invention

[0050] At present, the main research direction of ammonium paratungstate crystallization mother liquor is how to recover the valuable metal-tungsten and the ammonia and ammonium treatment of ammonia nitrogen related to environmental protection work. Few people have studied the behavior of sulfide ions and their derivatives in the ammonium paratungstate crystallization process and mother liquor treatment process and their impact on COD, and there are few studies on removal processes. There are few related or similar literature and related technologies, which has brought great inconvenience to the preliminary research work of the corresponding work.

[0051] In the process of studying the crystallization, the applicant found that the first evolution of sulfide ions occurred in the crystallization of ammonium paratungstate, and the products were subsalt, thiosalt, disalt, etc.; the second evolution occurred in the ammonia drive stage, and under the action of high temperature and high alkali, the product was disalt. These products flowed unimpeded in the ammonium paratungstate production process and directly entered the wastewater system, causing high COD.

[0052] The conventional method of reducing COD in the form of sulfur is not feasible and difficult to implement. For example, the calcium salt precipitation method will precipitate together with the valuable metal tungsten. The large amount of iron salt precipitation method causes the main process product ammonium paratungstate to be unqualified. The sodium hypochlorite oxidation method is incompatible with the main process equipment mainly composed of carbon steel. The hydrogen peroxide oxidation method is large in amount and incomplete, and the cost is high. Through a large number of experiments in different directions, the applicant found that sulfide ions and their derivative salts have a characteristic: in alkaline or neutral environments such as alkaline liquid and mother liquor, they have high solubility, can be highly stable, and have certain complexation; in acidic environments, as the pH decreases, the stability becomes worse and worse, and is gradually decomposed. The products are either volatile, such as hydrogen sulfide and sulfur dioxide; or are precipitates, such as elemental sulfur, which can reduce the content of low-valent sulfur in the solution, which is ultimately reflected in the reduction of COD, achieving the purpose of simple process and high efficacy.

[0053] Based on the above research of the applicant, the applicant coordinated the alkalization, evaporation and ammonia expulsion and acidification steps, so that the ammonium paratungstate crystallization mother liquor can be quickly and low-cost treated and the crystallization mother liquor can be refluxed to the main process. The specific principle is as follows:

[0054] (1) Ammonium paratungstate crystallization process:

[0055] Ammonium sulfide decomposes when heated: (NH4)2S=NH3+H2S

[0056] The product hydrogen sulfide is oxidized by O2 in the air: 2H2S+O2=2S↓+2H2O

[0057] (2) Alkalization

[0058] [PW 12 O 40 ] 3- +24OH - =PO4 3- +12WO4 2- +12H2O (tungstate heteropoly acid ion alkalization, [PW 12 O 40 ] 3- For example)

[0059] [H2W 12 O 40 ] 6- +18OH - =12WO4 2- +10H2O (Alkalinization of tungsten isopolyacid ions)

[0060] 6NaOH+(2n+4)S=2Na2S·S n +Na2S2O3+3H2O

[0061] NH4 + +OH - =NH3·H2O

[0062] (3) Evaporation and ammonia drive

[0063] NH3·H2O=NH3↑+H2O

[0064] (4)Acidification

[0065] 6H + +2S·S n 2- +S2O3 2- =(2n+4)S↓+3H2O

[0066] 2H + +S2O3 2- =S↓+SO2+H2O

[0067] It can be seen from the above reaction principle that before the final acidified liquid enters the main process, the present invention has already well carried out deep reduction of ammonia nitrogen and COD on the ammonium paratungstate crystallization mother liquor, preventing the enrichment of pollution factors such as thiosulfate, sulfide, dithionate, trithionate, etc. in the main process and causing side reactions.

[0068] Compared with the prior art, the advantages of the present invention are:

[0069] (1) The present invention provides a method for removing impurities from the mother liquor of ammonium paratungstate crystallization, which can achieve the effect of short-process, efficient and quick removal of COD and reduction of ammonia nitrogen. Sulfur-containing substances such as nitrite, thiosalt and dithionite have similar chemical properties and are difficult to remove at one time. The present invention can achieve a one-time and overall reduction of their content, preventing pollution factors such as thiosulfate, sulfide, dithionite and trithionite from being enriched in the main process and causing side reactions.

[0070] (2) The present invention adopts a direct countercurrent contact method between steam and alkalized liquid, which realizes uniform and rapid heating of the alkalized liquid, completely drives out ammonia, and realizes an overall reduction in the amount of ammonia nitrogen in the deammonification liquid, avoiding the risk of uneven heat exchange and the defect of high residual ammonia in the conventional tube process.

[0071] (3) Although sulfuric acid is introduced in the present invention, sulfate is the most common anion in the process of producing ammonium paratungstate, that is, in a broad sense, no new impurities are introduced, and the present invention is compatible with the entire production process. The sulfuric acid introduced in the present invention has no effect on the valuable metal tungsten anion, and tungsten always exists in the solution in a soluble ionic state without forming a precipitate, and the yield of the valuable metal tungsten is not reduced.

[0072] (4) The purification step of the main process requires the removal of impurities by adjusting the pH of the solution by adding a large amount of sulfuric acid. The acidified solution in the present invention can be quickly and unimpededly added to the acid adjustment tank and enter the main process. DETAILED DESCRIPTION

[0073] The present invention is further described below in conjunction with specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are commercially available, and the room temperature is usually 20°C to 30°C.

[0074] Example 1

[0075] A method for removing impurities from ammonium paratungstate crystallization mother liquor of the present invention comprises the following steps:

[0076] (1) Alkalization: 10m 3 Ammonium paratungstate crystal mother liquor (containing COD 101921mg / L, ammonia nitrogen 13g / L, WO389g / L) was heated to 3m 3 / h speed to add industrial liquid alkali and stir, the concentration of sodium hydroxide in the industrial liquid alkali is 350g / L, the reaction is carried out under room temperature and slight negative pressure conditions, the slight negative pressure can be provided by a negative pressure system, the slight negative pressure (vacuum degree) is 0.1kPa, during the reaction, ammonium ions react with alkali to generate ammonia and escape from the mother liquor, and the macromolecular tungsten hetero (iso) polyacid ions are depolymerized, when the pH value of the reaction liquid is 12.5, stop adding liquid alkali, which is the end point of adding alkali, stir for 30min, and obtain alkalized liquid and ammonia. The ammonia is successively absorbed by water spraying and recovered by ammonia condensation, and ammonia is recovered. The alkalization process can be implemented in a negative pressure tank, the negative pressure tank is equipped with a negative pressure system, the negative pressure system can provide slight negative pressure, the volume of ammonium paratungstate crystal mother liquor pumped into the negative pressure tank accounts for 75% of the designed volume of the negative pressure tank, the ammonia is absorbed by water spraying in the water spraying absorption system, and condensed and recovered in the ammonia condensation recovery system.

[0077] (2) Evaporation and ammonia drive: First, introduce 0.4MPa steam from the bottom of the stripping tower to preheat the stripping tower. After the stripping tower temperature reaches 95°C, the alkalized liquid is 3 / h flow rate from the top of the stripping tower 2m, the gas and liquid in the tower form countercurrent direct contact, the top temperature of the stripping tower is controlled at 92℃~94℃, the steam micro-positive pressure is 2.4kPa, the ammonia dissolved in the alkalized liquid is turned into gaseous ammonia, and the ammonia is evaporated to drive ammonia, and the deammonified liquid is obtained. The ammonia nitrogen concentration of the deammonified liquid is 84mg / L, the COD is 96825mg / L, and the WO3 concentration is 85g / L, and it flows out from the water outlet at the bottom of the stripping tower. The obtained ammonia is absorbed by water spraying and recovered by ammonia condensation.

[0078] (3) Acidification: Pump the deammoniation liquid into a stainless steel reaction tank for stirring. The volume of the deammoniation liquid is 75% of the designed volume of the reaction tank. Without heating, add the acidifier at a rate of 1.2 m 3 / h is added to the reaction tank. The acidifier is H2SO4 solution. The concentration of H2SO4 solution is 4mol / L. The solution is acidified to a pH value of 1.3, so that the soluble sulfur-containing compounds are acidified to generate insoluble sulfur. During the acidification process, when the solution pH value is greater than 4 (usually 13≥pH value>4), a pH meter is used to measure the solution pH value. When the solution pH value is between 4 and 1, a pH meter is used to measure the solution pH value after filtering with filter paper to prevent the yellow-white solid product from covering the pH meter probe. After acidification, filter to obtain the acidified liquid, i.e., the conversion liquid of the ammonium paratungstate crystal mother liquor, containing 8395mg / L COD, 76mg / L ammonia nitrogen, and 72g / L WO3. After impurities are removed, the acidified liquid is stored in a stainless steel or plastic storage tank for standby use. Among them, the WO3 concentration decreases because the tungsten is diluted by the industrial liquid alkali added during the alkalization process and the dilute sulfuric acid added during the acidification process, but the total amount is stored in the solution without loss.

[0079] (4) Return to the main process: send the crude sodium tungstate solution and the acidified solution obtained above to the purification process in the main production process for stirring treatment. The purification process is implemented in the purification tank. The volume ratio of the crude sodium tungstate solution to the acidified solution is 3:1. The total volume of the crude sodium tungstate solution and the acidified solution is 75% of the designed volume of the purification tank. The alkalinity of the crude sodium tungstate solution is 22g / L. The concentration of WO3 in the crude sodium tungstate solution is 117g / L. The conventional operation of purifying the phosphorus, arsenic, silicon and other elements of the sodium tungstate solution by magnesium sulfate is carried out.

[0080] Example 2

[0081] A method for removing impurities from ammonium paratungstate crystallization mother liquor of the present invention comprises the following steps:

[0082] (1) Alkalization: 10m 3 Ammonium paratungstate crystal mother liquor (containing COD 98937mg / L, ammonia nitrogen 14g / L, WO3 96g / L) was heated to 3m 3 / h speed to add industrial liquid alkali and stir, the concentration of sodium hydroxide in the industrial liquid alkali is 350g / L, the reaction is carried out under slight negative pressure at room temperature, the slight negative pressure can be provided by a negative pressure system, the slight negative pressure (vacuum degree) is 0.12kPa, during the reaction, ammonium ions react with alkali to generate ammonia and escape from the mother liquor, and the macromolecular tungsten hetero (iso) polyacid ions are depolymerized, when the pH value of the reaction liquid is 11, stop adding liquid alkali, which is the end point of adding alkali, stir for 30min, obtain alkalized liquid and ammonia, and the ammonia is successively absorbed by water spraying and recovered by ammonia condensation, and the ammonia is recovered. The alkalization process can be implemented in a negative pressure tank, the negative pressure tank is equipped with a negative pressure system, the negative pressure system can provide slight negative pressure, the volume of ammonium paratungstate crystal mother liquor pumped into the negative pressure tank accounts for 75% of the designed volume of the negative pressure tank, the ammonia is absorbed by water spraying in the water spraying absorption system, and condensed and recovered in the ammonia condensation recovery system.

[0083] (2) Evaporation and ammonia drive: First, introduce 0.4MPa steam from the bottom of the stripping tower to preheat the stripping tower. After the stripping tower temperature reaches 90℃, the alkalized liquid is heated at 3.5m 3 / h flow rate is introduced from 2m on the top of the stripping tower, the vapor and liquid in the tower form countercurrent direct contact, the top temperature of the stripping tower is controlled at 92℃~92.5℃, the steam micro-positive pressure is 2kPa, the ammonia dissolved in the alkalized liquid is converted into gaseous ammonia, and evaporation and ammonia drive are realized to obtain deammoniation liquid. The ammonia nitrogen concentration of the deammoniation liquid is 152mg / L, the COD is 89043mg / L, and the WO3 concentration is 86g / L. The deammoniation liquid flows out from the water outlet at the bottom of the stripping tower, and the obtained ammonia is absorbed by water spraying and recovered by ammonia condensation.

[0084] (3) Acidification: Pump the deammoniation liquid into a stainless steel reaction tank for stirring. The volume of the deammoniation liquid is 75% of the designed volume of the reaction tank. Without heating, add the acidifier at a rate of 1.2 m3 / h rate into the reaction tank, the acidifier is H2SO4 solution, the concentration of H2SO4 solution is 4mol / L, acidification to the solution pH value of 1.5, so that the soluble sulfur-containing compounds are acidified to generate insoluble sulfur, during the acidification process, when the solution pH value is greater than 4 (usually 13≥pH value>4), the solution pH value is measured by a pH meter, and when the solution pH value is between 4 and 1, the solution pH value after filtering with filter paper is measured by a pH meter to prevent the yellow-white solid product from covering the pH meter probe. After acidification, filter to obtain the acidified liquid, i.e., the ammonium paratungstate crystal mother liquor conversion liquid, containing COD 12116mg / L, ammonia nitrogen 140mg / L, WO3 79g / L, complete impurity removal, and the acidified liquid is stored in a stainless steel or plastic storage tank for use.

[0085] (4) Return to the main process: send the crude sodium tungstate solution and the acidified solution obtained above to the purification process in the main production process for stirring treatment. The purification process is implemented in the purification tank. The volume ratio of the crude sodium tungstate solution to the acidified solution is 3:1. The total volume of the crude sodium tungstate solution and the acidified solution is 75% of the designed volume of the purification tank. The alkalinity of the crude sodium tungstate solution is 20g / L. The concentration of WO3 in the crude sodium tungstate solution is 109g / L. The conventional operation of purifying the phosphorus, arsenic, silicon and other elements in the sodium tungstate solution by magnesium sulfate is carried out.

[0086] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for removing impurities from ammonium paratungstate crystal mother liquor, characterized in that: The following steps are involved: (1) Alkalization: add alkali solution to the ammonium paratungstate crystal mother liquor and stir, and react under normal temperature and slight negative pressure conditions, wherein the slight negative pressure is 0.1 kPa to 0.3 kPa. When the pH value of the reaction liquid reaches 11 to 13, stop adding alkali solution, stir, and obtain alkalized liquid and ammonia gas, and absorb the ammonia gas by water spraying and recover the ammonia gas by ammonia condensation; (2) Evaporation and ammonia drive: First, introduce 0.2MPa~0.5MPa steam from the bottom of the stripping tower to preheat the stripping tower. After preheating the stripping tower temperature to 90℃~100℃, the alkalized liquid is heated at 2m 3 / h~8m 3 / h flow rate from the top of the stripping tower, the gas and liquid in the tower form countercurrent direct contact, the top temperature of the stripping tower is controlled to be 90°C to 95°C, the steam micro-positive pressure is 1kPa to 5kPa, so that the ammonia in the alkalized liquid is converted into ammonia gas, and after the ammonia gas is removed, a deammonified liquid is obtained, the ammonia nitrogen concentration of the deammonified liquid is 5mg / L to 200mg / L, and the ammonia gas is subjected to water spray absorption and ammonia condensation recovery; (3) Acidification: The deammoniation liquid is sent to a reaction tank and stirred. Without heating, an acidifier is added to the reaction tank to acidify the solution to a pH value of 1.5 to 1.2, so that the soluble sulfur-containing compounds are acidified to generate insoluble sulfur. After filtration, an acidified liquid is obtained, i.e., the ammonium paratungstate crystal mother liquor conversion liquid, and impurity removal is completed.

2. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 1, characterized in that: In step (1), the alkali solution is added at a speed of 1m 3 / h~4m 3 / h, the alkali solution includes sodium hydroxide solution and / or industrial liquid alkali, the concentration of sodium hydroxide in the alkali solution is 300g / L-400g / L, and the stirring time after stopping adding the alkali solution is 20min-40min.

3. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 1, characterized in that: In step (1), when the pH value of the reaction solution is 12 to 12.5, stop adding the alkali solution.

4. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 1, characterized in that: In step (2), the alkalized liquid is introduced from 2 m above the top of the stripping tower, and the ammonia nitrogen concentration of the deammoniation liquid is 5 mg / L to 100 mg / L.

5. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 1, characterized in that: In step (3), the reaction tank is a stainless steel reaction tank or a plastic reaction tank, the volume of the deammoniation liquid is 75% to 80% of the designed volume of the reaction tank, and the speed of adding the acidulant into the reaction tank is 0.1 m / s. 3 / h~5m 3 / h, the acidifying agent is H2SO4 solution, and the concentration of the H2SO4 solution is 2.5mol / L~10mol / L.

6. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 5, characterized in that: In step (3), during the acidification process, when the pH value of the solution is greater than 4, the pH value of the solution is measured using a pH meter or 5-0.5 precision pH test paper; when the pH value of the solution is between 4 and 1, the pH value of the solution is measured using 5-0.5 precision pH test paper or a pH meter is used to measure the pH value of the solution after filtering with filter paper.

7. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 5, characterized in that: In step (3), the acidulant is added to the reaction tank at a speed of 0.5 m / s. 3 / h~3m 3 / h, the concentration of the H2SO4 solution is 2.5mol / L~5mol / L.

8. The method for removing impurities from ammonium paratungstate crystal mother liquor according to any one of claims 1 to 7, characterized in that: The method further includes step (4) returning to the main process: sending the crude sodium tungstate solution and the acidified liquid obtained in step (3) to the purification step in the main production process for treatment.

9. The method for removing impurities from ammonium paratungstate crystal mother liquor according to claim 8, characterized in that: In step (4), the purification process is carried out in a purification tank, the volume ratio of the crude sodium tungstate solution to the acidified solution is 2 to 5:1, the total volume of the crude sodium tungstate solution and the acidified solution is 70% to 80% of the designed volume of the purification tank, the alkalinity of the crude sodium tungstate solution is 18 g / L to 30 g / L, and the concentration of WO3 in the crude sodium tungstate solution is 100 g / L to 150 g / L.

10. The method for removing impurities from ammonium paratungstate crystal mother liquor according to any one of claims 1 to 7, characterized in that: In step (1), the alkalization is carried out in a negative pressure tank with a negative pressure system, and the volume of the ammonium paratungstate crystallization mother liquor accounts for 75% to 80% of the designed volume of the negative pressure tank.