Method for removing arsenic from crude ammonium perrhenate by using ferrous sulfide

Abstract

The invention provides a method for removing arsenic from crude ammonium perrhenate by using ferrous sulfide, and belongs to the technical field of chemical product purification, and the method comprises the following steps: dissolving crude ammonium perrhenate in hot water to obtain an ammonium perrhenate solution; ferrous sulfide is added into the ammonium perrhenate solution for a reaction, and a solid-liquid mixture is obtained; separating the solid-liquid mixture to obtain precipitation slag and an ammonium perrhenate solution subjected to primary arsenic removal; washing the precipitation slag, and combining the washed liquid with the ammonium perrhenate solution subjected to primary arsenic removal to obtain a total ammonium perrhenate solution subjected to primary arsenic removal; diluting the total ammonium perrhenate solution subjected to preliminary arsenic removal, and extracting to obtain an impurity-loaded organic phase and raffinate; carrying out phase back extraction on the organic phase loaded with impurities to obtain a no-load organic phase and a water phase; and carrying out vacuum evaporation and concentration on the raffinate until the raffinate is in a supersaturated state, cooling, adding ammonium perrhenate seed crystals, crystallizing, filtering, and drying to obtain a refined ammonium perrhenate product. The method for removing arsenic from crude ammonium perrhenate by using ferrous sulfide provided by the invention is efficient, low in cost, environment-friendly and capable of deeply removing arsenic.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical product purification, in particular to a method for removing arsenic from crude ammonium perrhenate by using ferrous sulfide. Background Art

[0002] As a key rhenium compound, ammonium perrhenate plays an indispensable role in numerous areas of modern industry. In the aerospace sector, rhenium can significantly enhance the performance of high-temperature alloy components in aircraft engines, such as increasing their strength, hardness, high-temperature resistance, and oxidation resistance, thereby ensuring stable engine operation under extreme conditions. In the electronics industry, ammonium perrhenate is used to manufacture electronic components with special properties, such as highly sensitive sensors and high-performance integrated circuits. Its purity directly affects the performance and reliability of the components. In the chemical industry, ammonium perrhenate, as a catalyst or catalyst precursor, plays a key role in the catalytic efficiency and selectivity of chemical reactions.

[0003] However, in the actual production process of ammonium perrhenate, due to the diversity of raw material sources and the complexity of the production process, crude ammonium perrhenate often inevitably contains arsenic impurities. The presence of arsenic will have a serious negative impact on the quality and application performance of ammonium perrhenate. In the high-temperature alloys used in the aerospace field, even trace amounts of arsenic impurities can cause grain embrittlement of the alloy, reduce the mechanical properties of the alloy, and increase the risk of component failure in high-temperature and high-pressure environments. In the manufacture of electronic components, arsenic impurities can interfere with the electrical properties of electronic components, resulting in unstable conductivity and increased leakage, thereby shortening the service life of the components and reducing the overall quality of electronic products. In chemical catalytic reactions, arsenic can poison the active centers of the catalyst, reducing the activity and selectivity of the catalyst, resulting in a decrease in the conversion rate of the chemical reaction, an increase in by-products, and increased production costs.

[0004] Currently, the methods for removing arsenic impurities in crude ammonium perrhenate mainly include traditional precipitation, adsorption and ion exchange methods.

[0005] Traditional precipitation methods typically use metal ions to form insoluble precipitates with arsenic ions. However, this method often struggles to completely remove arsenic impurities and is prone to introducing new impurities, such as other ions in the precipitant that may remain in the solution. While adsorption methods are relatively simple to operate, the adsorption capacity of the adsorbent is limited, making it less effective for removing high levels of arsenic impurities in crude ammonium perrhenate. Furthermore, the regeneration and recovery costs of the adsorbent are high. While ion exchange methods can reduce arsenic content to a certain extent, their selectivity and service life are also limited. Furthermore, these traditional methods often suffer from complex process flows, high processing costs, and significant environmental impacts.

[0006] Therefore, developing a method that is efficient, low-cost, environmentally friendly and can deeply remove arsenic impurities in crude ammonium perrhenate has important practical significance and application value. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide, which is efficient, low-cost, environmentally friendly and can deeply remove arsenic.

[0008] To solve the above technical problems, the present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide, comprising the following steps:

[0009] Dissolving crude ammonium perrhenate in hot water to obtain an ammonium perrhenate solution;

[0010] adding ferrous sulfide to an ammonium perrhenate solution to react and obtain a solid-liquid mixture;

[0011] The solid-liquid mixture is heated to separate the solid and liquid to obtain precipitated residue and ammonium perrhenate solution for preliminary arsenic removal;

[0012] washing the precipitated residue, and combining the washed solution with the ammonium perrhenate solution for preliminary arsenic removal to obtain a total ammonium perrhenate solution for preliminary arsenic removal;

[0013] The total ammonium perrhenate solution for preliminary arsenic removal is diluted and then extracted to obtain an organic phase loaded with impurities and a raffinate;

[0014] The organic phase loaded with impurities is extracted, and the obtained empty organic phase is washed with water and then returned to the ammonium perrhenate solution for preliminary arsenic removal, and the obtained aqueous phase is treated as wastewater;

[0015] The raffinate is concentrated by vacuum evaporation to a supersaturated state, and after cooling, ammonium perrhenate seed crystals are added for crystallization. After crystallization, the refined ammonium perrhenate product is obtained by filtration and drying.

[0016] 3. Furthermore, the hot water temperature is controlled at 50-80°C.

[0017] Furthermore, the mass percentage concentration of the ammonium perrhenate solution is 15%-35%.

[0018] Furthermore, the amount of ferrous sulfide added is such that the molar ratio of sulfide ions to arsenic ions in the ammonium perrhenate solution is 4:1-6:1, the reaction temperature of the ammonium perrhenate solution and ferrous sulfide is controlled at 50-80° C., and the reaction time is 2-4 hours.

[0019] Furthermore, the temperature of heating the solid-liquid mixture for solid-liquid separation is 55-90°C.

[0020] Furthermore, the washing of the precipitated residue is washing the precipitated residue with deionized water 2-3 times.

[0021] Furthermore, the total ammonium perrhenate solution for preliminary arsenic removal is diluted to a mass percentage concentration of ammonium perrhenate of 1.5% to 3.5%.

[0022] Furthermore, the extractant used for extracting the diluted total ammonium perrhenate solution for preliminary arsenic removal is a mixed solution of methyl isobutyl ketone and tributyl phosphate in a volume ratio of 3:1-5:1, the volume ratio of the diluted total ammonium perrhenate solution for preliminary arsenic removal to the extractant is 1:1-3:1, the oscillation extraction time is 10-20 minutes, and the static stratification time is 15-30 minutes.

[0023] Furthermore, the stripping agent used in the back extraction of the impurity-loaded organic phase is a sodium hydroxide solution with a concentration of 0.5-1.5 mol / L, the volume ratio of the impurity-loaded organic phase to the stripping agent is 1:1-2:1, the oscillation stripping time is 10-20 mins, and the static stratification time is 15-30 mins.

[0024] Furthermore, the temperature of the raffinate during vacuum evaporation and concentration is controlled at 75-95° C., the raffinate is vacuum evaporated and concentrated to a supersaturated state and then cooled to 15-25° C., the amount of the ammonium perrhenate seed crystals added is 0.1%-0.5% of the mass of the supersaturated raffinate after cooling, and the crystallization time is 6-10 hours.

[0025] The present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide. Through the synergistic effect of ferrous sulfide precipitation and extraction processes, arsenic impurities can be deeply removed from crude ammonium perrhenate. Testing has shown that the arsenic content in the ammonium perrhenate product can be reduced to below 0.001% after treatment using the present method, significantly lower than the arsenic removal levels achieved by existing methods. The significant arsenic removal effect meets the extremely stringent requirements for high-purity ammonium perrhenate in high-end applications.

[0026] Furthermore, the method for removing arsenic from crude ammonium perrhenate using ferrous sulfide provided by the present invention features a simple and easy operation, a compact process, and well-coordinated steps, effectively achieving the goals of arsenic removal and purification. Compared with traditional methods, this method eliminates unnecessary intermediate steps and complex operations, has a rational process flow, reduces labor and material inputs during production, achieves high production efficiency, saves production costs, and improves economic benefits.

[0027] Furthermore, the present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide. By strictly controlling the conditions of each step, such as temperature and reagent dosage, throughout the entire arsenic removal process, the introduction of new impurities is avoided. Furthermore, the final refining steps, such as recrystallization, further improve the purity and crystal quality of the product. The resulting ammonium perrhenate product has high purity, good crystallinity, and extremely low impurity content. This superior product quality can meet the demand for high-quality ammonium perrhenate in fields such as aerospace, electronics, and chemical engineering.

[0028] Furthermore, the present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide, minimizing the use and discharge of environmentally harmful chemicals during the reaction process, thereby reducing potential environmental impacts. Furthermore, the recycling of the extractant and stripping agent reduces the generation of chemical waste, thus being environmentally friendly and meeting the requirements of modern green chemistry and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] See also Figure 1 The embodiment of the present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide, comprising the following steps:

[0031] Step 1) Crude ammonium perrhenate is dissolved in hot water to obtain an ammonium perrhenate solution.

[0032] Specifically, crude ammonium perrhenate is dissolved in hot deionized water to prepare an ammonium perrhenate solution with a mass percent concentration of 15%-35%.

[0033] Wherein, the temperature of the hot deionized water is controlled at 50-80°C.

[0034] Step 2) adding ferrous sulfide to the ammonium perrhenate solution to react and obtain a solid-liquid mixture.

[0035] During the reaction, under acidic conditions, the divalent iron in ferrous sulfide is oxidized to trivalent iron by oxygen in the air. The trivalent iron then combines with the arsenate in the crude ammonium perrhenate to form a precipitate, thereby obtaining a solid-liquid mixture. The reaction equation for this process is as follows:

[0036] 4FeS + 3O2 + 12H + = 4Fe 3+ +4S 0 + 6H2O (1)

[0037] Fe 3+ + AsO4 3- = FeAsO4 (s) (2)

[0038] In order to react the arsenic in the crude ammonium perrhenate as completely as possible, the amount of ferrous sulfide added is such that the molar ratio of sulfur to arsenic in the ammonium perrhenate solution is 4:1-6:1.

[0039] In addition, in order to ensure a complete reaction, the reaction temperature of the ammonium perrhenate solution and ferrous sulfide is controlled to be 50-80° C., and the reaction time is 2-4 hours.

[0040] Step 3) The solid-liquid mixture is heated to separate the solid and liquid to obtain a precipitated residue and an ammonium perrhenate solution for preliminary arsenic removal.

[0041] Specifically, when performing solid-liquid separation on the solid-liquid mixture, in order to prevent ammonium perrhenate from crystallizing, the solid-liquid mixture is heated, and the temperature of the solid-liquid separation is controlled to be 55-90°C.

[0042] Step 4) washing the precipitated residue, and combining the washed solution with the ammonium perrhenate solution for preliminary arsenic removal to obtain a total ammonium perrhenate solution for preliminary arsenic removal.

[0043] Specifically, in order to further recover the ammonium perrhenate that may be adsorbed and carried by the precipitated slag and reduce the loss of ammonium perrhenate, the precipitated slag is washed 2-3 times with deionized water, and the washed liquid is combined with the ammonium perrhenate solution for preliminary arsenic removal to obtain a total ammonium perrhenate solution for preliminary arsenic removal, so as to reduce the loss rate of rhenium.

[0044] Step 5) The total ammonium perrhenate solution from which arsenic has been initially removed is diluted and then extracted to obtain an organic phase loaded with impurities and a raffinate.

[0045] In order to avoid the precipitation of ammonium perrhenate crystals during room temperature extraction, which may affect the extraction phase separation and cause rhenium loss, deionized water is first added to the total ammonium perrhenate solution for preliminary arsenic removal to dilute it.

[0046] The total ammonium perrhenate solution for preliminary arsenic removal is diluted with deionized water to a mass percentage concentration of ammonium perrhenate of 1.5% to 3.5%.

[0047] Then, the diluted total ammonium perrhenate solution for preliminary arsenic removal is transferred to a separating funnel, and an extractant is added for oscillation extraction, and then the solution is allowed to stand for stratification, thereby separating the organic phase loaded with impurities and the raffinate.

[0048] The extractant is a mixed solution of methyl isobutyl ketone and tributyl phosphate in a volume ratio of 3:1-5:1.

[0049] The volume ratio of the diluted total ammonium perrhenate solution for preliminary arsenic removal to the extractant is 1:1-3:1.

[0050] The oscillation extraction time during extraction is 10-20 minutes, and the standing stratification time is 15-30 minutes.

[0051] The present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide. Through the synergistic effect of ferrous sulfide precipitation and extraction processes, arsenic impurities can be deeply removed from crude ammonium perrhenate. Testing has shown that the arsenic content in the ammonium perrhenate product can be reduced to below 0.001% after treatment using the present method, significantly lower than the arsenic removal levels achieved by existing methods. The significant arsenic removal effect meets the extremely stringent requirements for high-purity ammonium perrhenate in high-end applications.

[0052] Step 6) The organic phase loaded with impurities is subjected to reverse extraction, and the obtained unloaded organic phase is washed with water and then returned to the ammonium perrhenate solution for preliminary arsenic removal, and the obtained aqueous phase is treated as wastewater.

[0053] The back-extraction agent used in the back-extraction of the organic phase loaded with impurities is a sodium hydroxide solution with a concentration of 0.5-1.5 mol / L.

[0054] The volume ratio of the organic phase loaded with impurities to the stripping agent is 1:1-2:1.

[0055] The oscillation stripping time during stripping is 10-20 minutes, and the standing stratification time is 15-30 minutes.

[0056] Step 7) The raffinate is concentrated by vacuum evaporation to a supersaturated state, and after cooling, ammonium perrhenate seed crystals are added for crystallization. After crystallization, the refined ammonium perrhenate product is obtained by filtration and drying.

[0057] The temperature of the raffinate during vacuum evaporation and concentration is controlled at 75-95°C.

[0058] The raffinate is concentrated by vacuum evaporation to a supersaturated state and then cooled to 15-25° C. before crystallization.

[0059] The amount of ammonium perrhenate seed crystals added to the cooled supersaturated raffinate is 0.1%-0.5% of the mass of the cooled supersaturated raffinate, and the crystallization time is 6-10 hours.

[0060] The present invention provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide. During the entire arsenic removal process, strict control of conditions in each step, such as temperature, pH value, and reagent dosage, prevents the introduction of new impurities. Furthermore, a final refining step, such as recrystallization, further improves the purity and crystalline quality of the product. The resulting ammonium perrhenate product exhibits high purity, excellent crystallinity, and extremely low impurity content. This superior product quality can meet the demand for high-quality ammonium perrhenate in fields such as aerospace, electronics, and chemical engineering.

[0061] Furthermore, the method for removing arsenic from crude ammonium perrhenate using ferrous sulfide provided by the present invention features a simple and easy operation, a compact process, and well-coordinated steps, effectively achieving the goals of arsenic removal and purification. Compared with traditional methods, this method eliminates unnecessary intermediate steps and complex operations, has a rational process flow, reduces labor and material inputs during production, achieves high production efficiency, saves production costs, and improves economic benefits.

[0062] The present invention also provides a method for removing arsenic from crude ammonium perrhenate using ferrous sulfide, minimizing the use and discharge of environmentally harmful chemicals during the reaction process, reducing potential environmental impacts. Furthermore, the recycling of the extractant and stripping agent reduces the generation of chemical waste, making the process environmentally friendly and in line with the requirements of modern green chemistry and sustainable development.

[0063] The following examples illustrate the method for removing arsenic from crude ammonium perrhenate using ferrous sulfide provided by the present invention.

[0064] Example 1

[0065] Dissolution step: Weigh 150 g of crude ammonium perrhenate, add 600 g of deionized water, and dissolve at 50° C. and stirring speed 200 r / min.

[0066] Precipitant addition step: according to the arsenic ion concentration in the solution, the molar ratio of sulfur ion to arsenic ion is 4:1, ferrous sulfide is added, and the mixture is stirred and reacted at 50° C. for 3 hours.

[0067] Filtration step: Filter using a filter membrane with a pore size of 0.1 μm.

[0068] Dilution step: dilute the ammonium perrhenate solution for preliminary arsenic removal to an ammonium perrhenate mass concentration of 3.5%.

[0069] Extraction and impurity removal step: transfer the diluted ammonium perrhenate solution for preliminary arsenic removal to a separatory funnel, add an extractant, which is a mixed solution of methyl isobutyl ketone (MIBK) and tributyl phosphate (TBP) in a volume ratio of 3:1, and the volume ratio of the solution to the extractant is 1:1. Oscillating extraction is carried out for 10 minutes, and the layers are allowed to stand to separate the organic phase loaded with impurities and the raffinate.

[0070] Organic back-extraction step: add a back-extraction agent to the organic phase loaded with impurities. The back-extraction agent is a sodium hydroxide solution with a concentration of 1.5 mol / L. The volume ratio of the organic phase to the back-extraction agent is 1:1. Oscillate and back-extract for 10 minutes. After standing and stratification, collect the aqueous phase for wastewater treatment. The empty organic phase is washed with water to remove sodium ions and then used as the organic phase for extraction and impurity removal.

[0071] Raffinate crystallization step: Vacuum evaporation at 0.05 MPa, 70°C, cooled to 20°C, added with 0.2% ammonium rhenate seed crystals, and crystallized for 12 hours. Testing revealed an arsenic content of 0.0008% in the product.

[0072] Example 2

[0073] Dissolution step: Weigh 200 g of crude ammonium perrhenate, add 800 g of deionized water, and dissolve at 80° C. and a stirring speed of 300 r / min.

[0074] Precipitant addition step: add ferrous sulfide at a molar ratio of sulfide ion to arsenic ion of 6:1, and stir the mixture at 80° C. for 2 hours.

[0075] Filtration step: Filter using a filter membrane with a pore size of 0.3 μm.

[0076] Dilution step: dilute the ammonium perrhenate solution for preliminary arsenic removal to an ammonium perrhenate mass concentration of 2%.

[0077] Extraction and impurity removal step: transfer the diluted ammonium perrhenate solution with preliminary arsenic removal to a separatory funnel, add an extractant, which is a mixed solution of methyl isobutyl ketone (MIBK) and tributyl phosphate (TBP) in a volume ratio of 3:1, and the volume ratio of the solution to the extractant is 1:2. Oscillating extraction is carried out for 10 minutes, and the layers are allowed to stand to separate the organic phase loaded with impurities and the raffinate.

[0078] Organic back-extraction step: add a back-extraction agent to the organic phase loaded with impurities. The back-extraction agent is a sodium hydroxide solution with a concentration of 1 mol / L. The volume ratio of the organic phase to the back-extraction agent is 1:1. Oscillate and back-extract for 10 minutes. After standing and stratification, collect the aqueous phase for wastewater treatment. The empty organic phase is washed with water to remove sodium ions and then used as the organic phase for extraction and impurity removal.

[0079] Crystallization step: Vacuum evaporation pressure of 0.06 MPa, temperature of 80°C, cooling to 25°C, adding 0.5% ammonium rhenate seed crystals, and crystallizing for 10 hours. After testing, the arsenic content of the product was 0.0005%.

[0080] Example 3

[0081] Dissolution step: Weigh 250 g of crude ammonium perrhenate, add 1000 g of deionized water, and dissolve at 70° C. and stirring speed 400 r / min.

[0082] Precipitant addition step: add ferrous sulfide solid according to the molar ratio of sulfide ion to arsenic ion of 5:1, and stir and react at 70°C for 1 hour.

[0083] Filtration step: Filter using a filter membrane with a pore size of 0.5 μm.

[0084] Dilution step: dilute the ammonium perrhenate solution for preliminary arsenic removal to an ammonium perrhenate mass concentration of 1.5%.

[0085] Extraction and impurity removal step: transfer the diluted ammonium perrhenate solution with preliminary arsenic removal to a separatory funnel, add an extractant, which is a mixed solution of methyl isobutyl ketone (MIBK) and tributyl phosphate (TBP) in a volume ratio of 2:1, and the volume ratio of the solution to the extractant is 2:1. Oscillating extraction is carried out for 10 minutes, and the layers are allowed to stand to separate the organic phase loaded with impurities and the raffinate.

[0086] Organic back-extraction step: add a back-extraction agent to the organic phase loaded with impurities. The back-extraction agent is a sodium hydroxide solution with a concentration of 1 mol / L. The volume ratio of the organic phase to the back-extraction agent is 2:1. Oscillate and back-extract for 10 minutes. After standing and stratification, collect the aqueous phase for wastewater treatment. The empty organic phase is washed with water to remove sodium ions and then used as the organic phase for extraction and impurity removal.

[0087] Crystallization step: Vacuum evaporation pressure of 0.08 MPa, temperature of 90°C, cooling to 30°C, crystallization after adding 0.2% ammonium rhenate seed crystals for 8 hours. After testing, the arsenic content of the product was 0.0006%.

[0088] It can be seen from the above examples that the method for removing arsenic from crude ammonium perrhenate using ferrous sulfide provided by the present invention can effectively remove arsenic impurities in crude ammonium perrhenate under different conditions, and the arsenic content in the product reaches an extremely low level, which proves the reliability and effectiveness of the method of the present invention.

[0089] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for removing arsenic from crude ammonium perrhenate using ferrous sulfide, characterized in that: The steps include: Dissolving crude ammonium perrhenate in hot water to obtain an ammonium perrhenate solution; adding ferrous sulfide to an ammonium perrhenate solution to react and obtain a solid-liquid mixture; The solid-liquid mixture is heated to separate the solid and liquid to obtain precipitated residue and ammonium perrhenate solution for preliminary arsenic removal; washing the precipitated residue, and combining the washed solution with the ammonium perrhenate solution for preliminary arsenic removal to obtain a total ammonium perrhenate solution for preliminary arsenic removal; The total ammonium perrhenate solution for preliminary arsenic removal is diluted and then extracted to obtain an organic phase loaded with impurities and a raffinate; The organic phase loaded with impurities is extracted, and the obtained empty organic phase is washed with water and then returned to the ammonium perrhenate solution for preliminary arsenic removal, and the obtained aqueous phase is treated as wastewater; The raffinate is concentrated by vacuum evaporation to a supersaturated state, and after cooling, ammonium perrhenate seed crystals are added for crystallization. After crystallization, the refined ammonium perrhenate product is obtained by filtration and drying.

2. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The temperature of the hot water is controlled to be 50-80°C.

3. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The mass percentage concentration of the ammonium perrhenate solution is 15%-35%.

4. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The amount of ferrous sulfide added is such that the molar ratio of sulfide ions to arsenic ions in the ammonium perrhenate solution is 4:1-6:

1. The reaction temperature of the ammonium perrhenate solution and ferrous sulfide is controlled at 50-80° C., and the reaction time is 2-4 hours.

5. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The temperature for heating the solid-liquid mixture for solid-liquid separation is 55-90°C.

6. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The washing of the precipitated residue comprises washing the precipitated residue with deionized water 2-3 times.

7. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The total ammonium perrhenate solution for preliminary arsenic removal is diluted to a mass percentage concentration of ammonium perrhenate of 1.5% to 3.5%.

8. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The extractant used for extracting the diluted total ammonium perrhenate solution for preliminary arsenic removal is a mixed solution of methyl isobutyl ketone and tributyl phosphate in a volume ratio of 3:1-5:1, the volume ratio of the diluted total ammonium perrhenate solution for preliminary arsenic removal to the extractant is 1:1-3:1, the oscillation extraction time is 10-20 minutes, and the static stratification time is 15-30 minutes.

9. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The stripping agent used in the back extraction of the organic phase loaded with impurities is a sodium hydroxide solution with a concentration of 0.5-1.5 mol / L, the volume ratio of the organic phase loaded with impurities to the stripping agent is 1:1-2:1, the oscillation stripping time is 10-20 minutes, and the static stratification time is 15-30 minutes.

10. The method for removing arsenic from crude ammonium perrhenate using ferrous sulfide according to claim 1, wherein: The temperature of the raffinate during vacuum evaporation and concentration is controlled at 75-95° C. The raffinate is vacuum evaporated and concentrated to a supersaturated state and then cooled to 15-25° C. The amount of ammonium perrhenate seed crystals added is 0.1%-0.5% of the mass of the supersaturated raffinate after cooling, and the crystallization time is 6-10 hours.

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