Separation and utilization method of arsenic in wet-process phosphoric acid

Abstract

The invention relates to the technical field of wet-process phosphoric acid purification, and discloses a method for separating and utilizing arsenic in wet-process phosphoric acid, which comprises the following steps of: clarifying wet-process phosphoric acid, and feeding supernate into an arsenic removal reaction tank; preparing an induced crystallization agent and a dearsenification agent, firstly adding the induced crystallization agent into the reaction tank, and then adding the dearsenification agent for reaction to obtain dearsenification phosphoric acid A; then heating and dissolving the phosphoric acid C, and cooling and growing crystals to obtain arsenic-removed phosphoric acid C; filtering to obtain arsenic-removed phosphoric acid and arsenic sulfide precipitate; washing and drying the precipitate to obtain an arsenic sulfide product; according to the method, the induced crystallization agent is combined with the dissolution-recrystallization process, so that separated arsenic sulfide is attached to the induced crystallization agent and grows into large-particle precipitates easy to filter, selective separation of arsenic is realized, and generation of arsenic-containing waste residues is avoided; and meanwhile, the separated arsenic is directly converted into a high-purity arsenic sulfide product, so that resource utilization of the arsenic is realized.

Description

Technical Field

[0001] This invention relates to the field of wet-process phosphoric acid purification, and more particularly to a method for separating and utilizing arsenic in wet-process phosphoric acid. Background Technology

[0002] Most domestic wet-process phosphoric acid is produced using the dihydrate process, which involves decomposing phosphate rock with sulfuric acid. Due to the extremely high acidity of sulfuric acid, various impurities from the phosphate rock enter the phosphoric acid during production. Arsenic is a major heavy metal impurity in phosphate rock. In the phosphoric acid purification process, sulfides are typically added to form insoluble arsenic sulfide, thus separating it from the phosphoric acid. The insoluble arsenic sulfide particles formed by traditional arsenic removal methods are extremely fine. These particles mix with other solid precipitates in the phosphoric acid through sedimentation or filtration, forming arsenic-containing sludge. Because of the complex composition of this arsenic-containing sludge, there is currently no suitable treatment process, and it can only be recycled back to the extraction tank. This leads to a continuous increase in the arsenic content in the phosphoric acid, seriously threatening the quality of the phosphoric acid and subsequent products.

[0003] CN112225188A discloses a wet-process phosphoric acid arsenic removal process, in which pressurized H2S gas and wet-process phosphoric acid with a concentration of 35-45% P2O5 are reacted countercurrently in a two-stage arsenic removal tower to generate As2S3 arsenic slag. After the As2S3 arsenic slag crystallizes and grows, it is filtered off by a filter. CN114892027A discloses a method for directly separating arsenic from an arsenic-containing solution, in which the arsenic-containing solution is adsorbed by an adsorption resin to obtain an arsenic-removed solution. The adsorption resin is a strongly basic anion exchange resin. After the resin is saturated, it is eluted with an eluent to obtain an arsenic-containing eluent waste liquid. Specific sampling volumes are used for both adsorption and elution. The arsenic-containing eluent waste liquid is then sulfided, and the oxidation-reduction potential (ORP) is controlled at -100mV to 100mV to obtain sulfided arsenic slag and a sulfided liquid. CN119819239A discloses a deep arsenic removal device for phosphoric acid and its arsenic removal process, which achieves continuous arsenic removal by microwave heating through the cooperation of a temperature-controlled heating component, an arsenic biosensor, a material removal drive motor, a rotating rod, a drying rake blade, and a heat-conducting rod.

[0004] In summary, existing arsenic removal technologies can achieve deep arsenic removal from phosphoric acid, but they cannot separate arsenic sulfide separately. The removed arsenic sulfide mixes with the precipitate in the phosphoric acid to form arsenic slag, which is difficult to utilize. Therefore, it is essential to develop a method for the separation and utilization of arsenic in wet-process phosphoric acid. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for the separation and utilization of arsenic in wet-process phosphoric acid.

[0006] The solution of the present invention is: A method for separating and utilizing arsenic in wet-process phosphoric acid includes the following steps: 1) Clarify the wet-process phosphoric acid; 2) Add the clarified phosphoric acid supernatant from step 1) to the arsenic removal reaction tank; 3) Prepare the crystallizing inducing agent and the arsenic removal agent; 4) First, add the induced crystallizing agent prepared in step 3) to the arsenic removal reaction tank, and then add the arsenic removal agent prepared in step 3) at a certain rate; 5) React the phosphoric acid supernatant obtained in step 2) with the material in the arsenic removal reaction tank to obtain arsenic-removed phosphoric acid A; 6) Add the dearsenic-removed phosphoric acid A from step 5) to a dissolving tank and heat it to obtain dearsenic-removed phosphoric acid B; 7) Add the dearsenic-free phosphoric acid B described in step 6) to the crystallization tank, lower the temperature to grow crystals, and obtain dearsenic-free phosphoric acid C; 8) Filter the arsenic-de-arsenic phosphoric acid C obtained in step 7) to separate arsenic-de-arsenic phosphoric acid and arsenic sulfide precipitate; 9) The arsenic sulfide precipitate described in step 8) is washed and dried to obtain the arsenic sulfide product.

[0007] As a preferred technical solution, the P2O5 concentration of the wet-process phosphoric acid in step 1) is 15% to 45%, and the arsenic content is 15 mg / kg to 200 mg / kg.

[0008] More preferably, the P2O5 concentration of the wet-process phosphoric acid in step 1) is 20% to 42%, and the arsenic content is 20 mg / kg to 100 mg / kg.

[0009] As a preferred technical solution, the arsenic removal agent in step 3) is at least one of Na2S, H2S, P2S5, (NH4)2S, CS2, and Na2S2O3; the concentration of the arsenic removal agent is 2% to 30%; the crystallizing inducing agent is at least one of As2S3, As2S5, FeS, CuS, cysteine, polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG); the amount of crystallizing inducing agent added is 0.5% to 2% of the total mass of the arsenic removal agent. The crystallizing inducing agent mainly provides a ready-made substrate for As2S3 crystallization, making it easier for the As2S3 precipitated in the solution to be adsorbed and arranged in an orderly manner on its surface, thereby effectively promoting the crystallization process, increasing the crystallization rate, reducing fine crystal grains, and increasing the particle size of the precipitated As2S3 particles.

[0010] More preferably, the arsenic removal agent mentioned in step 3) is Na2S, H2S and P2S5; the concentration of the arsenic removal agent is 2% to 15%; the crystallizing inducing agent is As2S3, As2S5 and FeS; and the amount of crystallizing inducing agent added is 0.5% to 1.5% of the total mass of the arsenic removal agent.

[0011] As a preferred technical solution, the rate of adding the arsenic removal agent in step 4) is 20L / min to 150L / min.

[0012] More preferably, the rate at which the arsenic removal agent is added in step 4) is 30 L / min to 120 L / min.

[0013] As a preferred technical solution, step 5) is performed at a rotation speed of 5 r / min to 20 r / min.

[0014] More preferably, step 5) is performed at a rotational speed of 5 r / min to 10 r / min.

[0015] As a preferred technical solution, the dissolution temperature in step 6) is 60℃~90℃, and the dissolution time is 20min~60min.

[0016] More preferably, the dissolution temperature in step 6) is 60℃~80℃, and the dissolution time is 25min~45min.

[0017] As a preferred technical solution, the crystallization temperature in step 7) is 45℃~60℃ and the crystallization time is 60min~180min.

[0018] More preferably, the crystallization temperature in step 7) is 45℃~55℃, and the crystallization time is 60min~150min.

[0019] Raising the solution temperature to 60℃–80℃ promotes the dissolution of fine-particle arsenic sulfide, and the energy cost is acceptable. Cooling to 45℃–60℃ allows the dissolved arsenic sulfide to recrystallize on the surface of the undissolved large-particle arsenic sulfide. This reduces the amount of fine-particle arsenic sulfide and further increases the particle size of the large-particle arsenic sulfide.

[0020] As a preferred technical solution, the filtration method in step 8) is at least one of plate and frame filter press, vacuum belt filter and centrifugal filter.

[0021] Compared with the prior art, the advantages of the present invention are: (1) By adding an inducing crystallizer and an arsenic removal agent in sequence, the arsenic sulfide precipitated in phosphoric acid attaches to the inducing crystallizer, reducing the generation of fine particles and laying the foundation for its separation.

[0022] (2) This invention utilizes the difference in solubility of arsenic sulfide and other precipitates in phosphoric acid at different temperatures. Through dissolution-crystallization technology, a small amount of fine arsenic sulfide particles in dearsenic phosphoric acid A are first dissolved, and then crystallized and grown on larger arsenic sulfide particles, which significantly increases the particle size of arsenic sulfide particles. At the same time, by controlling the appropriate dissolution and recrystallization temperature, the formation of other impurities in phosphoric acid is suppressed. After solid-liquid separation, a high-purity arsenic sulfide product is directly obtained, avoiding the arsenic slag formed by traditional technology. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments. Example 1

[0026] Wet-process phosphoric acid with a P2O5 concentration of 26% and an arsenic content of 45 mg / kg was allowed to stand in a clarifying tank for 4 hours. The supernatant was then added to an arsenic removal reaction tank. After adding 0.5% (by mass) As2S3 as an arsenic removal agent to the arsenic removal reaction tank, a 10% Na2S solution was added at a rate of 50 L / min. The reaction was carried out at a rotation speed of 5 r / min to obtain arsenic-removed phosphoric acid A. Arsenic-removed phosphoric acid A was added to a dissolving tank and dissolved at 75℃ for 30 min to obtain arsenic-removed phosphoric acid B. Arsenic-removed phosphoric acid B was added to a crystallization tank, cooled to 50℃ and kept at that temperature for 90 min to obtain arsenic-removed phosphoric acid C. Arsenic-removed phosphoric acid C was filtered through a plate and frame filter press. The liquid phase was low-arsenic phosphoric acid with an arsenic content of only 3.2 mg / kg, which was used to produce phosphate products. The solid phase was washed and dried to obtain a product with an arsenic sulfide content of 97.8%.

[0027] Comparative Example 1: Wet-process phosphoric acid with a P2O5 concentration of 26% and an arsenic content of 45 mg / kg was allowed to stand in a clarifying tank for 4 hours. The supernatant was then added to an arsenic removal reaction tank. Without adding any crystallizing agent, a 10% Na2S solution was added at a rate of 50 L / min, and the reaction was carried out at a rotation speed of 5 r / min to obtain arsenic-removed phosphoric acid A. Arsenic-removed phosphoric acid A was added to a dissolving tank and dissolved at 75℃ for 30 min to obtain arsenic-removed phosphoric acid B. Arsenic-removed phosphoric acid B was added to a crystallization tank, cooled to 50℃ and held at that temperature for 90 min to obtain arsenic-removed phosphoric acid C. Arsenic-removed phosphoric acid C was filtered through a plate and frame filter press. The liquid phase was phosphoric acid with an arsenic content of 8.7 mg / kg, which was used to produce phosphate products. The solid phase was washed and dried to obtain arsenic sulfide with a content of 45.3%.

[0028] Table 1. Effect of crystallizing agent on arsenic removal efficiency

[0029] Example 2: Wet-process phosphoric acid with a P2O5 concentration of 40% and an arsenic content of 48 mg / kg was allowed to stand in a clarifying tank for 8 hours. The supernatant was then added to an arsenic removal reaction tank. After adding 0.8% (by mass) As2S5 as an arsenic removal agent to the arsenic removal reaction tank, a 5% Na2S solution was added at a rate of 40 L / min and reacted at a rotation speed of 5 r / min to obtain arsenic-removed phosphoric acid A. Arsenic-removed phosphoric acid A was added to a dissolving tank and dissolved at 70℃ for 25 min to obtain arsenic-removed phosphoric acid B. Arsenic-removed phosphoric acid B was added to a crystallization tank, cooled to 55℃ and held at that temperature for 120 min to obtain arsenic-removed phosphoric acid C. Arsenic-removed phosphoric acid C was filtered through a plate and frame filter press. The liquid phase was low-arsenic phosphoric acid with an arsenic content of only 2.9 mg / kg, which was used to produce phosphate products. The solid phase was washed and dried to obtain a product with an arsenic sulfide content of 97.5%.

[0030] Comparative Example 2: Wet-process phosphoric acid with a P2O5 concentration of 40% and an arsenic content of 48 mg / kg was allowed to stand in a clarifying tank for 8 hours. The supernatant was then added to an arsenic removal reaction tank. A 5% Na2S solution was added at a rate of 40 L / min, and the reaction was carried out at a rotation speed of 5 r / min to obtain arsenic-removed phosphoric acid A. Arsenic-removed phosphoric acid A was added to a dissolving tank and dissolved at 70℃ for 25 min to obtain arsenic-removed phosphoric acid B. Arsenic-removed phosphoric acid B was added to a crystallization tank, and then 0.8% (by mass) of As2S5 (arsenic removal agent) was added to the crystallization tank. The mixture was cooled to 55℃ and kept at that temperature for 120 min to obtain arsenic-removed phosphoric acid C. Arsenic-removed phosphoric acid C was filtered through a plate and frame filter press. The liquid phase contained phosphoric acid with an arsenic content of 9.7 mg / kg. The solid phase was washed and dried to obtain an arsenic sulfide content of 63.1%.

[0031] Table 2. Effect of the timing of crystallizing agent addition on arsenic removal efficiency.

[0032] Example 3: Wet-process phosphoric acid with a P2O5 concentration of 35% and an arsenic content of 62 mg / kg was allowed to stand in a clarifying tank for 6 hours. The supernatant was then added to an arsenic removal reaction tank. 0.5% FeS (by mass) of the arsenic removal agent was added to the reaction tank, followed by the addition of a 20% P2S5 solution at a rate of 50 L / min. The reaction was carried out at 10 r / min to obtain arsenic-removed phosphoric acid A. Arsenic-removed phosphoric acid A was added to a dissolving tank and dissolved at 70℃ for 25 min to obtain arsenic-removed phosphoric acid B. Arsenic-removed phosphoric acid B was added to a crystallization tank, cooled to 55℃, and held for 100 min to obtain arsenic-removed phosphoric acid C. Arsenic-removed phosphoric acid C was filtered through a vacuum belt filter. The liquid phase was low-arsenic phosphoric acid with an arsenic content of only 2.5 mg / kg, which was used to produce phosphate products. Solid-phase washing and drying yielded a product with an arsenic sulfide content of 96.8%.

[0033] Comparative Example 3: Wet-process phosphoric acid with a P2O5 concentration of 35% and an arsenic content of 62 mg / kg was allowed to stand in a clarifying tank for 6 hours. The supernatant was then added to an arsenic removal reaction tank. 0.1% FeS (by mass) of the arsenic removal agent was added to the reaction tank, followed by the addition of a 20% P2S5 solution at a rate of 50 L / min. The reaction was carried out at 10 r / min to obtain arsenic-removed phosphoric acid A. Arsenic-removed phosphoric acid A was added to a dissolving tank and dissolved at 70℃ for 25 min to obtain arsenic-removed phosphoric acid B. Arsenic-removed phosphoric acid B was added to a crystallization tank, cooled to 55℃, and held for 100 min to obtain arsenic-removed phosphoric acid C. Arsenic-removed phosphoric acid C was filtered through a vacuum belt filter. The liquid phase was phosphoric acid with an arsenic content of 12.7 mg / kg. The solid phase was washed and dried to obtain arsenic sulfide with a content of 33.4%.

[0034] Table 3. Effect of the amount of crystallizing agent added on the arsenic removal effect.

[0035] High-purity (e.g., 99.9%) arsenic sulfide can be used in high-end fields such as semiconductors and optoelectronics, while arsenic sulfide with a purity of around 97% is mainly concentrated in industrial fields, such as glass, pigments, heat-resistant materials, and alloy preparation.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for separating and utilizing arsenic in wet-process phosphoric acid, characterized in that, Includes the following steps: 1) Clarify the wet-process phosphoric acid; 2) Add the clarified phosphoric acid supernatant from step 1) to the arsenic removal reaction tank; 3) Prepare the crystallizing inducing agent and the arsenic removal agent; 4) First, add the induced crystallizing agent prepared in step 3) to the arsenic removal reaction tank, and then add the arsenic removal agent prepared in step 3) at a certain rate; 5) React the phosphoric acid supernatant obtained in step 2) with the material in the arsenic removal reaction tank to obtain arsenic-removed phosphoric acid A; 6) Add the dearsenic-removed phosphoric acid A from step 5) to a dissolving tank and heat it to obtain dearsenic-removed phosphoric acid B; 7) Add the dearsenic-free phosphoric acid B described in step 6) to the crystallization tank, lower the temperature to grow crystals, and obtain dearsenic-free phosphoric acid C; 8) Filter the arsenic-de-arsenic phosphoric acid C obtained in step 7) to separate arsenic-de-arsenic phosphoric acid and arsenic sulfide precipitate; 9) The arsenic sulfide precipitate described in step 8) is washed and dried to obtain the arsenic sulfide product.

2. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: The wet-process phosphoric acid described in step 1) has a P2O5 concentration of 15% to 45% and an arsenic content of 15 mg / kg to 200 mg / kg.

3. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: The arsenic removal agent mentioned in step 3) is at least one of Na2S, H2S, P2S5, (NH4)2S, CS2, and Na2S2O3; the concentration of the arsenic removal agent is 2% to 30%; the crystallizing agent is at least one of As2S3, As2S5, FeS, CuS, cysteine, polyvinylpyrrolidone, and polyethylene glycol; the amount of crystallizing agent added is 0.5% to 2% of the total mass of the arsenic removal agent.

4. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: The rate at which the arsenic removal agent is added in step 4) is 20 L / min to 150 L / min.

5. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: Step 5) is performed at a rotation speed of 5 r / min to 20 r / min.

6. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: The dissolution temperature in step 6) is 60℃~90℃, and the dissolution time is 20min~60min.

7. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: The crystallization temperature in step 7) is 45℃~60℃, and the crystallization time is 60min~180min.

8. The method for separating and utilizing arsenic in wet-process phosphoric acid as described in claim 1, characterized in that: The filtration method described in step 8) is at least one of plate and frame filter press, vacuum belt filter and centrifugal filter.

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