A desulfurization process for wet-process phosphoric acid

Abstract

This invention discloses a desulfurization process for wet-process phosphoric acid, belonging to the field of wet-process phosphoric acid desulfurization technology. The method uses wet-process flotation phosphoric acid tailings as raw material. After magnesium removal by leaching with a weak organic acid, the tailings react with excess phosphoric acid under the action of a catalyst. Solid-liquid separation is then performed to obtain a desulfurizing agent whose main component is calcium dihydrogen phosphate. This desulfurizing agent is added to wet-process phosphoric acid, and after the desulfurization reaction, filtration yields desulfurized phosphoric acid and high-purity, high-whiteness, clean gypsum. This invention uses flotation phosphoric acid tailings to prepare a desulfurizing agent for wet-process phosphoric acid desulfurization, developing a new high-value comprehensive utilization pathway for low-value-added solid waste. It fully recovers and utilizes phosphorus and calcium resources in phosphoric acid tailings, resulting in significant economic and social benefits. The reaction of the desulfurizing agent with sulfate ions in wet-process phosphoric acid directly generates high-purity, high-whiteness, clean gypsum, avoiding the generation of difficult-to-treat byproduct phosphogypsum.

Description

Technical Field

[0001] This invention relates to a desulfurization process that is carried out simultaneously with the preparation of a wet phosphoric acid desulfurizing agent, and belongs to the field of wet phosphoric acid desulfurization technology. Background Technology

[0002] Currently, my country's wet-process phosphoric acid production mainly involves the decomposition of phosphate rock using a mixture of phosphoric and sulfuric acids. After the reaction, solid-liquid separation yields wet-process phosphoric acid and phosphogypsum. However, due to the characteristics of the wet-process phosphoric acid production process, to ensure the overall phosphorus yield and the formation of uniform, coarse calcium sulfate crystals, a suitable excess of sulfate ions is often maintained in the liquid phase of the production system. This results in the final phosphoric acid product containing a certain amount of sulfate ions, which can reach 3.0~4.5 wt%. The presence of sulfate ions affects the quality of downstream phosphoric acid products. Therefore, removing sulfate ions from wet-process phosphoric acid is a necessary process step before producing feed-grade phosphates, industrial-grade ammonium phosphate products, and purified phosphoric acid products.

[0003] Currently, the industrial approach to wet phosphoric acid desulfurization involves adding soluble calcium sources to the wet phosphoric acid process. The calcium sources react with sulfate ions to form calcium sulfate precipitate, which removes the sulfate ions. For example, patent CN104495771A discloses a method for desulfurizing dilute phosphoric acid by adding calcium-containing defluorination slag to the dilute phosphoric acid. Patent CN103754850B discloses a method for reducing the sulfate content in dihydrate dilute phosphoric acid by adding fertilizer-grade dicalcium phosphate obtained from phosphorus-containing wastewater through lime precipitation as a desulfurizing agent to the wet phosphoric acid extraction slurry. Patent CN115092898B discloses a method for removing sulfate from wet phosphoric acid using yellow phosphorus slag. This involves re-slurrying the by-product yellow phosphorus slag from the electric furnace yellow phosphorus production process and adding it to the wet dilute phosphoric acid for desulfurization with the help of additives. Patent CN117534046A discloses a method for desulfurizing phosphoric acid using sludge instead of phosphate concentrate by re-slurrying the sludge and adding it to the wet phosphoric acid process for desulfurization. However, the calcium source materials used in these patents are all solid substances with high impurity content and low calcium activity. When used for desulfurization, they not only lead to long desulfurization time and poor desulfurization effect, but also cause soluble impurities in the calcium source materials to enter the wet phosphoric acid, resulting in a decline in the quality of wet phosphoric acid. Insoluble impurities co-precipitate with calcium sulfate crystals to produce phosphogypsum solid waste that is difficult to treat.

[0004] Phosphorus tailings from wet phosphate flotation are solid wastes with low phosphorus content generated during the beneficiation of phosphate rock. Their main components are calcium oxide, magnesium oxide, phosphorus pentoxide, and silicon dioxide, with P2O5 content of 5-8 wt%, CaO ≥ 35 wt%, and MgO ≥ 15 wt%. Phosphorus tailings contain not only soluble calcium that reacts with sulfate ions but also a significant amount of phosphorus. This not only meets the desulfurization requirements of wet phosphoric acid processing but also allows for the full utilization of phosphorus in the tailings. For example, patent CN104555961A discloses a method for defluorination and desulfurization using tailings, directly adding phosphorus tailings in the form of dry powder or slurry to wet phosphoric acid or phosphorus-containing wastewater for desulfurization. However, this patent's direct use of phosphorus tailings for desulfurization results in long desulfurization times and poor desulfurization effects. Furthermore, it leads to a large amount of magnesium from the tailings entering the liquid phase of the wet phosphoric acid process, causing a surge in magnesium impurities. Simultaneously, silicon enters the solid phase, resulting in the formation of large amounts of difficult-to-treat phosphogypsum. Therefore, phosphorus tailings are not suitable for direct use in wet phosphoric acid desulfurization. Summary of the Invention

[0005] To address the shortcomings of existing wet phosphoric acid desulfurization technologies, this invention provides a method for preparing a wet phosphoric acid desulfurizing agent and a desulfurization process. This process uses flotation phosphate tailings to prepare a desulfurizing agent for wet phosphoric acid desulfurization, developing a new high-value comprehensive utilization pathway for low-value-added solid waste. It fully recovers and utilizes phosphorus and calcium resources in phosphate tailings, resulting in significant economic and social benefits. The liquid desulfurizing agent, with calcium dihydrogen phosphate as its main component, has high calcium element activity, simple composition, and few impurities. It has a short desulfurization time and excellent desulfurization effect, and does not increase the content of impurity elements in wet phosphoric acid. The desulfurizing agent reacts with sulfate ions in wet phosphoric acid to directly generate high-purity, high-whiteness, and clean gypsum, avoiding the generation of difficult-to-treat by-product phosphogypsum.

[0006] The technical solution of the present invention is as follows: using wet phosphate flotation tailings as raw material, after leaching with organic weak acid to remove magnesium, it reacts with excess phosphoric acid under the action of a catalyst, and then performs solid-liquid separation to obtain a desulfurizing agent whose main component is calcium dihydrogen phosphate. The desulfurizing agent is added to wet phosphoric acid, and after the desulfurization reaction, it is filtered to obtain desulfurized phosphoric acid and high-purity, high-whiteness cleaning gypsum.

[0007] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0008] (1) Add the wet phosphate flotation tailings to an excess of organic weak acid for leaching reaction. After the reaction is completed, filter to obtain filter residue and filtrate.

[0009] (2) The filter residue obtained in step (1) is subjected to acid hydrolysis reaction with excess phosphoric acid under the action of a catalyst. After the reaction is completed, solid-liquid separation is performed, and the resulting liquid phase is the desulfurizing agent whose main component is calcium dihydrogen phosphate.

[0010] (3) Add the desulfurizing agent obtained in step (2) to wet phosphoric acid to carry out the desulfurization reaction. After the reaction is completed, filter to obtain desulfurized phosphoric acid and high-purity, high-whiteness cleaning gypsum.

[0011] In step (1), the phosphorus tailings have a P2O5 content of 5~8wt%, CaO ≥35wt%, and MgO ≥15wt%.

[0012] The organic weak acid is one or more of benzoic acid, citric acid, oxalic acid, and acrylic acid; the concentration of the organic weak acid is 5-15%.

[0013] Preferably, the concentration of the organic weak acid is 5-10%.

[0014] The mass ratio of phosphorus tailings to organic weak acid is 1:2~5, the leaching reaction time is 30~60 min, and the leaching reaction temperature is 30~50℃.

[0015] In step (2), the initial phosphoric acid is industrial phosphoric acid with a P2O5 content of 40~45wt% and a sulfate content of 3.0~4.5wt%. In subsequent continuous cyclic production, the desulfurized phosphoric acid obtained in step (3) is partially reused.

[0016] The catalyst is a nitrate ester organic compound, including one or more of nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and pentylenetetrazolium nitrate.

[0017] The catalyst addition amount is 0.05~0.10 wt% of the mass of phosphoric acid.

[0018] The mass ratio of filter residue to phosphoric acid is 1:3~6, the acidolysis reaction temperature is 30~75℃, and the acidolysis reaction time is 20~90min. Preferably, the acidolysis reaction temperature is 40~60℃ and the acidolysis reaction time is 20~40min.

[0019] In step (3), the amount of desulfurizer added is such that the molar ratio of calcium content in the desulfurizer to sulfate content in wet-process phosphoric acid is 0.9~1.1:1.

[0020] The wet-process phosphoric acid has a P2O5 content of 40-45 wt% and a sulfate content of 3.0-4.5 wt%.

[0021] The desulfurization reaction temperature is 30~70℃, and the desulfurization reaction time is 30~120min. Preferably, the desulfurization reaction temperature is 30~50℃, and the desulfurization reaction time is 30~60min.

[0022] The desulfurized phosphoric acid (P2O5) content is 43~48wt%, the sulfate content is 0.1~0.2wt%, and the high-purity, high-whiteness cleaning gypsum has a purity greater than 97% and a whiteness greater than 92.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) This invention prepares flotation phosphorus tailings into desulfurizing agent for wet phosphoric acid desulfurization, which develops a new high-value comprehensive utilization path for low-value solid waste, with significant social benefits.

[0025] (2) Phosphorus tailings are solid waste by-products of mineral processing. Using them as raw materials to prepare desulfurizing agents is low-cost and can fully recover and utilize phosphorus and calcium resources in phosphorus tailings, resulting in significant economic benefits.

[0026] (3) The desulfurizing agent prepared by the present invention is a liquid desulfurizing agent. When used for wet phosphoric acid desulfurization, it is a liquid-liquid reaction. The reaction time required is shorter than that of conventional solid desulfurizing agents. The calcium element in the desulfurizing agent has high activity and good desulfurization effect.

[0027] (4) The desulfurizing agent prepared by the present invention removes impurities such as magnesium and silicon contained in phosphorus tailings. It has a simple composition and few impurities, and will not increase the impurity content in wet phosphoric acid during the desulfurization process.

[0028] (5) The desulfurizer prepared by the present invention does not contain other insoluble impurities. It can react with sulfate ions in wet phosphoric acid to directly generate high-purity, high-whiteness, and clean gypsum, avoiding the generation of difficult-to-treat by-product phosphogypsum. Detailed Implementation

[0029] To enhance the understanding of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to specific embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0030] Example 1-1

[0031] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0032] (1) Phosphate tailings with a P2O5 content of 5.6 wt%, CaO content of 36.2 wt%, and MgO content of 15.7 wt% were added to benzoic acid with a concentration of 6.0% for leaching reaction. The mass ratio of phosphate tailings to benzoic acid was controlled at 1:3, the leaching reaction time was 40 min, and the leaching reaction temperature was 45℃. After the reaction was completed, the residue and filtrate were obtained.

[0033] (2) The filter residue obtained in step (1) is added to industrial phosphoric acid with a P2O5 content of 40.9 wt% and a sulfate content of 3.8 wt%. Then, 0.05 wt% of nitroglycerin is added to the industrial phosphoric acid. After mixing evenly, acid hydrolysis reaction is carried out. The mass ratio of filter residue to phosphoric acid is controlled at 1:4. The acid hydrolysis reaction temperature is 60℃ and the acid hydrolysis reaction time is 20 min. After the reaction is completed, solid-liquid separation is carried out. The liquid phase obtained is a desulfurizing agent containing calcium dihydrogen phosphate.

[0034] (3) The desulfurizing agent obtained in step (2) is added to wet phosphoric acid with a P2O5 content of 41.4 wt% and a sulfate content of 4.1 wt% for desulfurization reaction. The amount of desulfurizing agent added is controlled so that the molar ratio of calcium content in the desulfurizing agent to sulfate content in the wet phosphoric acid is 1:1. The desulfurization reaction temperature is 45℃ and the desulfurization reaction time is 58 min. After the reaction is completed, the mixture is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 44.5 wt% and a sulfate content of 0.12 wt% and cleaning gypsum with a purity of 97.3% and a whiteness of 93.4.

[0035] Examples 1-2

[0036] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0037] (1) Phosphate tailings with a P2O5 content of 5.2 wt%, CaO content of 35.7 wt%, and MgO content of 16.5 wt% were added to 7.0% citric acid for leaching reaction. The mass ratio of phosphate tailings to citric acid was controlled at 1:3.5, the leaching reaction time was 35 min, and the leaching reaction temperature was 40℃. After the reaction was completed, the residue and filtrate were obtained.

[0038] (2) The filter residue obtained in step (1) is added to the desulfurized phosphoric acid with a P2O5 content of 44.5 wt% and a sulfate content of 0.1 wt% obtained in Example 1-1, and then 0.06 wt% of industrial phosphoric acid isosorbide nitrate is added. After mixing evenly, acid hydrolysis reaction is carried out. The mass ratio of filter residue to desulfurized phosphoric acid is controlled at 1:4.5, the acid hydrolysis reaction temperature is 65℃, and the acid hydrolysis reaction time is 25 min. After the reaction is completed, solid-liquid separation is carried out, and the liquid phase obtained is a desulfurizing agent containing calcium dihydrogen phosphate.

[0039] (3) The desulfurizing agent obtained in step (2) is added to wet phosphoric acid with a P2O5 content of 40.7 wt% and a sulfate content of 4.2 wt% for desulfurization reaction. The amount of desulfurizing agent added is controlled so that the molar ratio of calcium content in the desulfurizing agent to sulfate content in the wet phosphoric acid is 1.1:1. The desulfurization reaction temperature is 40℃ and the desulfurization reaction time is 55 min. After the reaction is completed, the mixture is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 44.9 wt% and a sulfate content of 0.10 wt% and clean gypsum with a purity of 97.2% and a whiteness of 92.8.

[0040] Examples 1-3

[0041] A wet-process desulfurization process for phosphoric acid follows the same steps as in Examples 1-2, except that 0.09 wt% of industrial phosphoric acid tetranitrophosphate is added in step (2). This process also exhibits significant acidolysis effects; after 22 minutes of acidolysis, solid-liquid separation yields a desulfurizing agent containing calcium dihydrogen phosphate.

[0042] (3) The desulfurizing agent obtained in step (2) is added to wet phosphoric acid with a P2O5 content of 40.7 wt% and a sulfate content of 4.2 wt% for desulfurization reaction. The amount of desulfurizing agent added is controlled so that the molar ratio of calcium content in the desulfurizing agent to sulfate content in the wet phosphoric acid is 1.1:2. The desulfurization reaction temperature is 40℃ and the desulfurization reaction time is 48 min. After the reaction is completed, the mixture is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 44.3 wt% and a sulfate content of 0.09 wt% and clean gypsum with a purity of 97.7% and a whiteness of 93.1.

[0043] Example 2-1

[0044] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0045] (1) Phosphate tailings with a P2O5 content of 6.6 wt%, CaO content of 36.4 wt%, and MgO content of 16.0 wt% were added to acrylic acid with a concentration of 10.0% for leaching reaction. The mass ratio of phosphate tailings to acrylic acid was controlled at 1:5, the leaching reaction time was 50 min, and the leaching reaction temperature was 50℃. After the reaction was completed, the residue and filtrate were obtained.

[0046] (2) The filter residue obtained in step (1) is added to the desulfurized phosphoric acid with a P2O5 content of 44.5 wt% and a sulfate content of 0.1 wt% obtained in Example 1-1. After mixing evenly, an acid hydrolysis reaction is carried out. The mass ratio of filter residue to desulfurized phosphoric acid is controlled at 1:5.5, the acid hydrolysis reaction temperature is 68℃, and the acid hydrolysis reaction time is 65 min. After the reaction is completed, solid-liquid separation is carried out. The liquid phase obtained is the desulfurizing agent whose main component is calcium dihydrogen phosphate.

[0047] (3) The desulfurizing agent obtained in step (2) is added to wet phosphoric acid with a P2O5 content of 44.0 wt% and a sulfate content of 3.3 wt% for desulfurization reaction. The amount of desulfurizing agent added is controlled so that the molar ratio of calcium content in the desulfurizing agent to sulfate content in the wet phosphoric acid is 1.1:1. The desulfurization reaction temperature is 45℃ and the desulfurization reaction time is 120 min. After the reaction is completed, the mixture is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 44.8 wt% and a sulfate content of 1.0 wt% and clean gypsum with a purity of 97.0% and a whiteness of 93.6.

[0048] Example 2-2

[0049] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0050] (1) Phosphate tailings with a P2O5 content of 5.8 wt%, CaO content of 36.1 wt%, and MgO content of 15.6 wt% were added to oxalic acid with a concentration of 5.0% for leaching reaction. The mass ratio of phosphate tailings to oxalic acid was controlled at 1:2.5, the leaching reaction time was 60 min, and the leaching reaction temperature was 50℃. After the reaction was completed, the residue and filtrate were obtained.

[0051] (2) The filter residue obtained in step (1) is added to the desulfurized phosphoric acid with a P2O5 content of 44.5 wt% and a sulfate content of 0.1 wt% obtained in Example 1-1. After mixing evenly, an acid hydrolysis reaction is carried out. The mass ratio of filter residue to desulfurized phosphoric acid is controlled at 1:6, the acid hydrolysis reaction temperature is 60℃, and the acid hydrolysis reaction time is 60 min. After the reaction is completed, solid-liquid separation is carried out. The liquid phase obtained is the desulfurizing agent whose main component is calcium dihydrogen phosphate.

[0052] (3) The desulfurizing agent obtained in step (2) is added to wet phosphoric acid with a P2O5 content of 43.5 wt% and a sulfate content of 3.9 wt% for desulfurization reaction. The amount of desulfurizing agent added is controlled so that the molar ratio of calcium content in the desulfurizing agent to sulfate content in the wet phosphoric acid is 1:1. The desulfurization reaction temperature is 45℃ and the desulfurization reaction time is 240 min. After the reaction is completed, the mixture is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 43.9 wt% and a sulfate content of 0.4 wt% and clean gypsum with a purity of 98.1% and a whiteness of 93.5.

[0053] Example 3

[0054] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0055] (1) Phosphate tailings with a P2O5 content of 6.1 wt%, CaO content of 35.5 wt%, and MgO content of 15.2 wt% were mixed with desulfurized phosphoric acid with a P2O5 content of 44.5 wt% and sulfate content of 0.1 wt% obtained in Example 1-1. Then, 0.07 wt% of industrial phosphoric acid was added to isosorbide mononitrate. After mixing evenly, acid hydrolysis reaction was carried out. The mass ratio of phosphate tailings to phosphoric acid was controlled at 1:5, the acid hydrolysis reaction temperature was 72℃, and the acid hydrolysis reaction time was 55 min. After the reaction was completed, solid-liquid separation was carried out. The liquid phase obtained was the desulfurizing agent with calcium dihydrogen phosphate as the main component.

[0056] (2) The desulfurizing agent obtained in step (1) is added to wet phosphoric acid with a P2O5 content of 41.2 wt% and a sulfate content of 3.8 wt% for desulfurization reaction. The amount of desulfurizing agent added is controlled so that the molar ratio of calcium content in the desulfurizing agent to sulfate content in the wet phosphoric acid is 0.9:1. The desulfurization reaction temperature is 60℃ and the desulfurization reaction time is 60 min. After the reaction is completed, the mixture is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 45.1 wt% and a sulfate content of 0.25 wt% and cleaning gypsum with a purity of 97.8% and a whiteness of 92.5.

[0057] Example 4-1

[0058] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0059] (1) Phosphate tailings with a P2O5 content of 7.0 wt%, CaO content of 36.7 wt%, and MgO content of 15.4 wt% were added to oxalic acid with a concentration of 8.0% for leaching reaction. The mass ratio of phosphate tailings to oxalic acid was controlled at 1:4, the leaching reaction time was 30 min, and the leaching reaction temperature was 35℃. After the reaction was completed, the residue and filtrate were obtained.

[0060] (2) The filter residue obtained in step (1) was added to wet phosphoric acid with a P2O5 content of 42.9 wt% and a sulfate content of 3.6 wt% for desulfurization reaction. The amount of filter residue added was controlled so that the molar ratio of calcium content in the filter residue to sulfate content in the wet phosphoric acid was 0.9:1. The desulfurization reaction temperature was 65℃ and the desulfurization reaction time was 240 min. After the reaction was completed, the filter was filtered to obtain desulfurized phosphoric acid with a P2O5 content of 43.1 wt% and a sulfate content of 0.5 wt% and phosphogypsum with a purity of 80.3% and a whiteness of 30.4.

[0061] Example 4-2

[0062] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0063] (1) Phosphate tailings with a P2O5 content of 6.4 wt%, CaO content of 35.3 wt%, and MgO content of 15.8 wt% were added to a 9.0% concentration of organic weak acid (acrylic acid and citric acid were mixed in a mass ratio of 1:1) for leaching reaction. The mass ratio of phosphate tailings to organic weak acid was controlled at 1:4.5, the leaching reaction time was 45 min, and the leaching reaction temperature was 30℃. After the reaction was completed, the residue and filtrate were obtained.

[0064] (2) The filter residue obtained in step (1) is added to wet phosphoric acid with a P2O5 content of 42.4 wt% and a sulfate content of 4.0 wt% for desulfurization reaction. The amount of filter residue added is controlled to be 1:1 molar ratio of calcium content in filter residue to sulfate content in wet phosphoric acid. The desulfurization reaction temperature is 70℃ and the desulfurization reaction time is 120 min. After the reaction is completed, the filter is filtered to obtain desulfurized phosphoric acid with a P2O5 content of 42.8 wt% and a sulfate content of 1.3 wt% and phosphogypsum with a purity of 75.9% and a whiteness of 31.3.

[0065] Example 5-1

[0066] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0067] Phosphate tailings with a P2O5 content of 6.8 wt%, CaO content of 36.0 wt%, and MgO content of 16.1 wt% were added to wet-process phosphoric acid with a P2O5 content of 43.1 wt% and a sulfate content of 4.2 wt% for desulfurization. The amount of phosphate tailings added was controlled so that the molar ratio of calcium content in the phosphate tailings to sulfate content in the wet-process phosphoric acid was 1.1:1. The desulfurization reaction temperature was 65℃ and the desulfurization reaction time was 240 min. After the reaction was completed, the mixture was filtered to obtain desulfurized phosphoric acid with a P2O5 content of 43.5 wt% and a sulfate content of 0.6 wt% and phosphogypsum with a purity of 72.6% and a whiteness of 29.8.

[0068] Example 5-2

[0069] A desulfurization process for wet-process phosphoric acid includes the following steps:

[0070] Phosphate tailings with a P2O5 content of 7.3 wt%, CaO content of 35.4 wt%, and MgO content of 16.5 wt% were added to wet-process phosphoric acid with a P2O5 content of 40.6 wt% and a sulfate content of 4.7 wt% for desulfurization. The amount of phosphate tailings added was controlled so that the molar ratio of calcium content in the phosphate tailings to sulfate content in the wet-process phosphoric acid was 1.1:1. The desulfurization reaction temperature was 70℃ and the desulfurization reaction time was 120 min. After the reaction was completed, the mixture was filtered to obtain desulfurized phosphoric acid with a P2O5 content of 40.8 wt% and a sulfate content of 1.5 wt% and phosphogypsum with a purity of 73.4% and a whiteness of 30.3.

Claims

1. A desulfurization process for wet-process phosphoric acid, characterized in that, Includes the following steps: (1) Add the phosphorus tailings to an excess of organic weak acid for leaching reaction. After the reaction is completed, filter to obtain filter residue and filtrate. The phosphorus tailings have a P2O5 content of 5~8wt%, CaO ≥35wt%, and MgO ≥15wt%. The organic weak acid is one or more of benzoic acid, citric acid, oxalic acid, and acrylic acid. The leaching reaction time is 30~60min and the leaching reaction temperature is 30~50℃. (2) The filter residue obtained in step (1) is subjected to acid hydrolysis reaction with excess phosphoric acid under the action of a catalyst. After the reaction is completed, solid-liquid separation is performed. The main component of the liquid phase is calcium dihydrogen phosphate desulfurizer. The catalyst is nitrate ester organic matter, including one or more of nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and pentylenetetrazol. The acid hydrolysis reaction temperature is 30~75℃ and the acid hydrolysis reaction time is 20~90min. (3) The desulfurizing agent obtained in step (2) is added to wet phosphoric acid to carry out the desulfurization reaction. After the reaction is completed, the desulfurized phosphoric acid and high-purity, high-whiteness cleaning gypsum are obtained by filtration.

2. The method for preparing a wet-process phosphoric acid desulfurizing agent and the desulfurization process according to claim 1, characterized in that: In step (1), the concentration of the organic weak acid is 5-15%.

3. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (1), the mass ratio of phosphorus tailings to organic weak acid is 1:2~5.

4. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (2), the initial phosphoric acid is industrial phosphoric acid with a P2O5 content of 40~45wt% and a sulfate content of 3.0~4.5wt%. In subsequent continuous cyclic production, the desulfurized phosphoric acid obtained in step (3) is partially reused.

5. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (2), the amount of catalyst added is 0.05~0.10 wt% of the mass of phosphoric acid.

6. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (2), the mass ratio of filter residue to phosphoric acid is 1:3~6.

7. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (3), the amount of desulfurizer added is such that the molar ratio of calcium content in the desulfurizer to sulfate content in wet-process phosphoric acid is 0.9~1.1:

1.

8. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (3), the wet-process phosphoric acid P2O5 content is 40~45wt%, the sulfate content is 3.0~4.5wt%, the desulfurization reaction temperature is 30~70℃, and the desulfurization reaction time is 30~120min.

9. The desulfurization process for wet-process phosphoric acid according to claim 1, characterized in that: In step (3), the content of desulfurized phosphoric acid P2O5 is 43~48wt%, the content of sulfate is 0.1~0.2wt%, and the purity of high-purity, high-whiteness cleaning gypsum is greater than 97% and the whiteness is greater than 92.