A method for safe arsenic removal by wet purification of phosphoric acid pretreatment

Abstract

The invention discloses a method for safe arsenic removal by wet purification phosphoric acid pretreatment, wherein a phosphoric acid purifier is added to phosphoric acid, and the reaction production load is 80-110 m 3 / h, the reaction residence time is 60-83min, and the reaction operating temperature is 75-80℃; the phosphoric acid purifier includes polysulfide, sulfide stabilizer and aluminum compound flocculant. By adjusting the amount of phosphoric acid purifier, reverse production load, reaction temperature, reaction time and other conditions, the safe removal of metal ions such as arsenic and iron in the wet purification phosphoric acid pretreatment device can be achieved, while reducing the escape of H2S.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphoric acid dearsenication, and in particular relates to a method for safe dearsenication by wet purification of phosphoric acid pretreatment. Background Art

[0002] With the continuous development of the food, medical and electronic industries, the market demand for phosphoric acid and phosphates is increasing, and the quality requirements for phosphoric acid are getting higher and higher, especially the requirements for arsenic impurities in wet-process phosphoric acid. The arsenic content in wet-process phosphoric acid will directly affect its application in the field of phosphorus fine chemicals. Therefore, the efficient and safe removal of arsenic in wet-process phosphoric acid is a major problem that needs to be solved urgently. The content of arsenic in wet-process phosphoric acid is relatively small, but its presence often has a great impact on the quality of industrial-grade phosphoric acid, food-grade phosphoric acid, electronic-grade phosphoric acid and fine phosphates, and it is one of the key impurities that is more difficult to handle.

[0003] At present, wet phosphoric acid arsenic removal mainly uses chemical precipitation, crystallization and electrodeposition, and there are some new arsenic removal methods in recent years, such as microreactor arsenic removal, vertical zone melting arsenic removal, etc. The Chinese invention patent with publication number CN114804047A discloses a phosphoric acid purification arsenic removal process, which cancels the sodium sulfide addition point in the extraction purification process, adds a precision filtering device after the fine desulfurization phase separation tank, reduces the sodium sulfide addition point, and effectively reduces the risk of hydrogen sulfide leakage; after precision filtration, the small amount of arsenic sulfide precipitate that originally filtered through the pretreatment process is effectively removed; the viscosity of the extraction load solvent is significantly lower than that of phosphoric acid, which is conducive to smooth filtration.

[0004] As for the arsenic removal methods that can be applied industrially, most methods are limited to laboratory research. In the production process, the wet-process phosphoric acid pretreatment device mainly uses chemical precipitation to remove arsenic. Sodium sulfide is used as the arsenic removal agent. Although the cost is not high, a large amount of hydrogen sulfide gas is produced during the arsenic removal reaction, which poses a great safety risk. Therefore, efficient and safe removal of arsenic from wet-process phosphoric acid is a major problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above problems, the present invention aims to provide a method for safe arsenic removal by wet purification of phosphoric acid pretreatment.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for safe arsenic removal by wet purification of phosphoric acid pretreatment, the reaction is carried out in an existing pipeline device, the method is as follows: a phosphoric acid purifier is added to phosphoric acid, the reaction production load is 80-110m 3 / h, reaction residence time is 60-83min, reaction operating temperature is 75-80℃;

[0007] The phosphoric acid purifier comprises polysulfide, sulfide stabilizer and aluminum compound flocculant.

[0008] Furthermore, the mass ratio of the amount of arsenic removed by phosphoric acid to the new phosphoric acid purifier in the reaction is 1:(30-40)

[0009] Furthermore, the reaction is carried out in a phosphoric acid reaction tank, and the phosphoric acid scavenger is added into the phosphoric acid reaction tank via a metering pump.

[0010] Furthermore, after adding the new phosphoric acid purifier, a small amount of hydrogen sulfide gas escaping from the reaction tank is washed with washing liquid in the H2S scrubber and then discharged into the atmosphere, and the H2S discharged into the atmosphere is ≤5ppm.

[0011] Furthermore, the washing liquid of the H2S scrubber is continuously replaced, and when the pH value of the washing liquid is ≤10, it is pumped to the system for recycling.

[0012] Further, the washing liquid includes a low concentration sodium hydroxide solution.

[0013] Furthermore, the As in the phosphoric acid after arsenic removal is ≤0.5ppm.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. Use a new phosphoric acid purifier to replace Na2S. This new phosphoric acid purifier retains the advantages of hydrogen sulfide dearsenic removal, while solving the disadvantage of rapid decomposition of sodium sulfide. The product slows down the decomposition rate of H2S by the dearsenic removal agent in phosphoric acid dearsenic removal. It can quantitatively control the decomposition amount of H2S and the decomposition rate of the dearsenic removal agent according to the arsenic ion content in phosphoric acid, reduce H2S overflow, and is safer. At the same time, the purifier can accelerate the sedimentation rate and completeness of the formed As2S3.

[0016] 2. The arsenic index in the pretreated phosphoric acid after arsenic removal by the new phosphoric acid purifier can meet the control index requirements (As≤1mg / kg), and the acid concentration (P2O5%) after arsenic removal by the new phosphoric acid purifier is as high as 1-1.5% higher than that of the acid concentration of sodium sulfide arsenic removal.

[0017] 3. The new phosphoric acid purifier method can save desalted water consumption, labor costs and hazardous waste treatment costs, and is more economical. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with specific embodiments, but it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above-mentioned technical ideas of the present invention, various modifications, substitutions and changes made according to common technical knowledge and customary means in the field are included in the scope of the present invention.

[0019] Arsenic removal in the conventional wet phosphoric acid pretreatment process is that sodium sulfide is added to phosphoric acid to react with arsenic in the phosphoric acid to produce a precipitate, which is filtered and separated to remove the acid, and then enters the subsequent extraction and purification process, and sodium sulfide is added again to further remove arsenic. In the conventional wet purification phosphoric acid pretreatment process, the present invention uses a new phosphoric acid purifier to replace Na2S. The main component of the new phosphoric acid purifier is polysulfide. According to the principle that H2S reacts with As3+ and As5+ to generate As2S3 and As2S5 precipitation, the new phosphoric acid purifier also contains a sulfide stabilizer component, which can slow down the decomposition rate of the arsenic removal agent, control the decomposition amount of H2S, and reduce the safety risk of H2S overflow. At the same time, an aluminum compound flocculant is added to the product to accelerate the sedimentation rate and completeness of the formed product As2S3.

[0020] This new phosphoric acid purifier retains the advantages of hydrogen sulfide dearsenic removal, while solving the disadvantage of rapid decomposition of sodium sulfide. In phosphoric acid dearsenic removal, the product slows down the decomposition rate of H2S by the dearsenic removal agent, and can quantitatively control the decomposition amount of H2S and the decomposition rate of the dearsenic removal agent according to the arsenic ion content in phosphoric acid, thereby reducing H2S overflow. At the same time, the purifier can accelerate the sedimentation rate and completeness of the formed As2S3.

[0021] The phosphoric acid after desulfurization and defluorination in the wet purification phosphoric acid pretreatment device was taken as the research object. A new phosphoric acid purifier was selected to replace sodium sulfide. The new phosphoric acid purifier in the feed tank was added to the phosphoric acid reaction tank through a metering pump. The mass ratio of phosphoric acid dearsenication amount to the new phosphoric acid purifier was 1: (30-40), and the reverse production load was controlled at 80-110m 3 / h, the reaction residence time is 60-83min, and the operating temperature of the reaction tank is 75-80℃, so that metal ions such as arsenic and iron react and precipitate. After arsenic removal, the As in phosphoric acid is ≤0.5ppm. The finished phosphoric acid slurry after the overflow of the reaction tank will be flocculated, thickened and filtered. After adding the new phosphoric acid purifier, a small amount of hydrogen sulfide (H2S) gas escaping from the reaction tank is washed with a low-concentration sodium hydroxide solution in the scrubber and discharged into the atmosphere. The H2S discharged into the atmosphere is ≤5ppm. The washing liquid of the H2S scrubber adopts continuous replacement. When the pH value of the washing liquid is ≤10, it is pumped to the system for recycling.

[0022] Example 1: Add 80m 3 / h, phosphoric acid, and at the same time add 160L / h, a new type of phosphoric acid purifier, the mass ratio of phosphoric acid dearsenication amount and new type of phosphoric acid purifier is 1:30, and the reverse production load is 80m 3 / h,, the reaction residence time is 83min, the operating temperature of the reaction tank is 80℃, which can reduce the arsenic content in phosphoric acid to 0.3PPM.

[0023] Example 2: Add 90m3 / h, phosphoric acid, and at the same time add 240L / h, a new type of phosphoric acid purifier, the mass ratio of phosphoric acid dearsenication amount and new type of phosphoric acid purifier is 1:40, and the reverse production load is 90m 3 / h,, the reaction residence time is 73min, the operating temperature of the reaction tank is 80℃, which can reduce the arsenic content in phosphoric acid to 0.1PPM.

[0024] Example 3: Add 100m 3 / h, phosphoric acid, and at the same time add 230L / h, a new type of phosphoric acid purifier, the mass ratio of phosphoric acid dearsenication amount and new type of phosphoric acid purifier is 1:35, and the reverse production load is 100m 3 / h,, the reaction residence time is 66min, and the operating temperature of the reaction tank is 80℃, which can reduce the arsenic content in phosphoric acid to 0.3PPM.

[0025] Example 4: Add 110m 3 / h, phosphoric acid, and at the same time add 255L / h, a new type of phosphoric acid purifier, the mass ratio of phosphoric acid dearsenication amount and new type of phosphoric acid purifier is 1:35, and the reverse production load is 110m 3 / h,, the reaction residence time is 60min, the operating temperature of the reaction tank is 75℃, which can reduce the arsenic content in phosphoric acid to 0.4PPM.

[0026] The following is a comparison of the new arsenic removal agent and sodium sulfide arsenic removal under the same conditions.

[0027]

[0028] The arsenic index in the pretreated phosphoric acid after treatment with the two arsenic removal agents can meet the control index requirements (As≤1mg / kg), and the acid concentration (P2O5%) after arsenic removal by the new phosphoric acid purifier is as high as 1.5% higher than that of the acid concentration after arsenic removal by sodium sulfide. This result fully utilizes the new phosphoric acid purifier to complete the removal of metal ions such as arsenic and iron by the wet purification phosphoric acid pretreatment device, while less sodium hydroxide is consumed to treat the generated H2S, and less H2S emissions.

[0029] The above is a detailed introduction to a method for safe arsenic removal by wet purification of phosphoric acid pretreatment provided by the present invention. The structure and working principle of the present invention are described in detail using specific examples herein. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, the present invention can also be improved and modified without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for safe arsenic removal by wet purification of phosphoric acid pretreatment, characterized in that: Add phosphoric acid scavenger to phosphoric acid, the reaction production load is 80-110m 3 / h, reaction residence time is 60-83min, reaction operating temperature is 75-80℃; The phosphoric acid purifier comprises polysulfide, sulfide stabilizer and aluminum compound flocculant.

2. The method for safe arsenic removal by wet purification phosphoric acid pretreatment according to claim 1, characterized in that: The mass ratio of the amount of arsenic removed by phosphoric acid to the new phosphoric acid purifier in the reaction is 1:(30-40).

3. The method for safe arsenic removal by wet purification phosphoric acid pretreatment according to claim 1, characterized in that: The reaction is carried out in a phosphoric acid reaction tank, and a phosphoric acid purifier is added to the phosphoric acid reaction tank via a metering pump.

4. The method for safe arsenic removal by wet purified phosphoric acid pretreatment according to claim 1, characterized in that: After adding the new phosphoric acid purifier, a small amount of hydrogen sulfide gas escapes from the reaction tank and is washed with washing liquid in the H2S scrubber and then discharged into the atmosphere. The H2S discharged into the atmosphere is ≤5ppm.

5. The method for safe arsenic removal by wet purification phosphoric acid pretreatment according to claim 4, characterized in that: The washing liquid of the H2S scrubber is continuously replaced. When the pH value of the washing liquid is ≤10, it is pumped to the system for recycling.

6. The method for safe arsenic removal by wet purification phosphoric acid pretreatment according to claim 3, characterized in that: The washing liquid comprises a low concentration sodium hydroxide solution.

7. The method for safe arsenic removal by wet purification phosphoric acid pretreatment according to claim 1, characterized in that: After arsenic removal, As in phosphoric acid is ≤0.5ppm.

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