Method for multi-effect synergistic production of clean gypsum in wet-process phosphoric acid process

Abstract

The invention relates to a method for multi-effect synergistic production of clean gypsum in a wet-process phosphoric acid process, and belongs to the technical field of wet-process phosphoric acid and solid waste recycling. The method comprises the following steps: carrying out a reaction on phosphorite and industrial wet-process phosphoric acid in acidolysis equipment, inhibiting leaching of impurities such as iron, magnesium and aluminum by using relatively weak acidity of phosphoric acid, and eliminating sulfuric acid dilution heat to reduce gas phase escape, so that more than 90% of fluorine is retained in a liquid phase, thereby obtaining a fluorine-rich crude phosphoric acid solution containing monocalcium phosphate; replenishing sulfuric acid into the crude phosphoric acid solution and controlling crystallization conditions to produce high-purity clean gypsum with extremely low fluorine content (less than or equal to 0.05%); one part of the obtained fluorine-rich crude phosphoric acid solution is taken as a product to be extracted, so that efficient fluorine recovery and phosphoric acid purification are facilitated, and the other part of the fluorine-rich crude phosphoric acid solution is circularly used for countercurrent treatment of residues before acidolysis to further enrich residual phosphorus and fluorine. According to the method, the phosphorus and fluorine recovery rate is remarkably increased, and solid waste source decrement and resource synergistic appreciation are achieved.

Description

Technical Field

[0001] This invention belongs to the field of phosphoric chemical technology, specifically relating to a method for producing wet-process phosphoric acid, and particularly a method for producing high-quality clean gypsum through multi-effect synergistic production during the wet-process phosphoric acid production process, and for efficiently recovering residual phosphorus and fluorine resources from acid-insoluble residues. Background Technology

[0002] Phosphoric acid is a core intermediate in the phosphate chemical industry, with over 80% of global production achieved through wet processes. The traditional "sulfuric acid process" produces approximately 4-5 tons of phosphogypsum as a byproduct for every ton of phosphoric acid (calculated as P2O5), resulting in a global stockpile exceeding 6 billion tons. Phosphogypsum contains phosphorus, fluorine, and heavy metals, and long-term stockpiling can easily cause soil and water pollution, becoming a key bottleneck for the industry's green development. In the traditional one-step sulfuric acid process, the heat of sulfuric acid dilution during acid hydrolysis causes a large amount of fluoride to vaporize and escape, resulting in low fluorine recovery rates. The strong acid environment causes a large amount of metallic impurities such as iron, magnesium, and aluminum to leach out, increasing the burden on subsequent purification. Furthermore, the large quantity and poor quality of the byproduct phosphogypsum lead to the loss of phosphorus and fluorine resources.

[0003] To reduce phosphogypsum at its source, researchers proposed a two-step "phosphoric acid-sulfuric acid" method: first, phosphate rock is decomposed with phosphoric acid to produce soluble calcium dihydrogen phosphate; after solid-liquid separation to remove acid-insoluble residue, sulfuric acid is added to the filtrate to precipitate gypsum. Theoretically, this process can avoid co-precipitation of impurities, yielding clean gypsum. However, practical applications still face several challenges: for example, when using industrial wet phosphoric acid acid hydrolysis of phosphate rock containing sulfate ions, the reaction efficiency and final gypsum yield will further decrease. Moreover, as the sulfate content of phosphoric acid increases during the initial acid hydrolysis process, the yield of acid-insoluble residue becomes increasingly higher, leading to a decrease in the clean gypsum yield. Additionally, the residual phosphorus content in the acid-insoluble residue produced by the reaction will further increase.

[0004] While patent CN103626143A proposes a process for producing by-product white gypsum, it uses pure phosphoric acid without sulfate ions, which is inconsistent with the actual industrial practice of recycling sulfate-containing mother liquor, and it does not address the efficient recovery of phosphorus from the residue. Patent CN106044730B discloses a method for producing wet-process phosphoric acid using high-grade phosphate rock, in which 5%~55wt% dilute sulfuric acid is used to acid-wash the residue, and the acid-washing liquid is then recycled back to the acidolysis step. This would significantly reduce the yield of clean gypsum, which is inconsistent with the concept of this invention.

[0005] Therefore, there is an urgent need to develop a green value-added process to achieve synergistic recovery of phosphorus and fluorine, source improvement of phosphogypsum, and low impurity reduction of phosphoric acid solution, ultimately forming a complete wet-process phosphoric acid solution that couples efficient resource utilization with clean production. Summary of the Invention

[0006] To address the technical problems identified in this invention, the technical solution is as follows: A method for producing clean gypsum through multi-effect synergistic process in wet phosphoric acid production includes the following three steps: (1) Low-impurity acid hydrolysis and fluorine enrichment: Phosphate rock and industrial wet phosphoric acid aqueous solution are added to the acid hydrolysis reaction equipment at a mass ratio of 1:(10~15) and the reaction is carried out at a temperature of 80~100℃ for 8~12 minutes to make fluorine highly enriched in the liquid phase; after the reaction, the slurry is separated into solid and liquid to obtain a crude phosphoric acid solution rich in fluorine and containing calcium dihydrogen phosphate and acid-insoluble residue; (2) Preparation of clean gypsum: Add calcium sulfate dihydrate seed crystals to the crude phosphoric acid solution containing fluorine and calcium dihydrogen phosphate obtained in step (1) and add sulfuric acid to maintain the mass concentration of sulfate in the solution within the range of (1.0%~3.0%)±0.1% for aging and crystallization (the addition rate of sulfate can be controlled by using a peristaltic pump for feeding). Filter to obtain clean gypsum and fluorine-rich crude phosphoric acid solution. (3) Residual phosphorus and fluorine recovery: Part of the fluorine-rich crude phosphoric acid solution obtained in step (2) is extracted as a product, and the other part is recycled to re-acidify and recrystallize the acid-insoluble residue generated in step (1) to deeply extract residual phosphorus and fluorine elements from the residue. After the treatment is completed, solid-liquid separation is performed, and the crude phosphoric acid solution is returned to step (1) for recycling.

[0007] The main chemical components and reactions involved are as follows: The main component of phosphate rock is Ca5F(PO4)3, and the main chemical reactions involved in step 1 are as follows: Ca5F(PO4)3+ 5 H2SO4+ n H2O → 3 H3PO4+ 5 CaSO4·nH2O↓+ HF↑ Ca5F(PO4)3+ 7 H3PO4→ 5 Ca(H2PO4)2+ HF↑ The main chemical reaction equations involved in step 2 are as follows: Ca(H2PO4)2+ H2SO4+ 2 H2O= CaSO4·2H2O↓+ 2H3PO4 The main chemical reaction equations involved in step 3 are as follows: Ca5F(PO4)3+ 5 H2SO4+ n H2O → 3 H3PO4+ 5 CaSO4·n H2O↓+ HF↑ Preferably, in the above process, the mass fraction of P2O5 in the industrial wet-process phosphoric acid solution in step (1) is 20%~40%, and the SO4 content in the solution is... 2- The mass concentration is 0.5%~3%.

[0008] Preferably, the mass of the calcium sulfate dihydrate seed crystals added in step (2) is 1 to 3 times the theoretical mass of the clean gypsum to be generated.

[0009] Preferably, the temperature of the acid-insoluble residue in the countercurrent treatment of circulating phosphoric acid in step (3) is 80~110℃.

[0010] Preferably, the acid hydrolysis reaction temperature in step (1) is 80°C and the reaction time is 10 minutes.

[0011] Preferably, the crystallization process in step (2) is carried out at 80°C for 60 minutes.

[0012] Preferably, the mass ratio of the amount of fluorine-rich crude phosphoric acid solution extracted and the amount of solution recycled in step (3) is 1:9.

[0013] The present invention achieves selective decomposition of phosphate rock through mild acid hydrolysis (without adding sulfuric acid), and has the following outstanding advantages: (1) It utilizes the weak acidity of phosphoric acid to inhibit the leaching of impurities such as iron, magnesium, and aluminum, and obtains a crude phosphoric acid solution with low impurities from the source; (2) By strictly controlling the content of sulfate, the heat of sulfuric acid dilution is eliminated, and more than 90% of the fluorine is efficiently enriched in the liquid phase, which facilitates the efficient recovery of fluorine resources in the future. (3) The acid-insoluble residue is treated by countercurrent phosphoric acid circulation, which reduces the P2O5 content in the residue to below 0.5% and increases the total phosphorus recovery rate to over 98%. The high-purity clean gypsum (fluorine content ≤ 0.05%) prepared accounts for more than 50.0 wt% of the total solid products and is of higher quality than building material standards. This can greatly improve economic benefits and completely solve the environmental pressure of phosphogypsum stockpiling, realizing a green closed loop of phosphorus and fluorine co-recovery, solid waste source reduction and resource value-added. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the preparation method of the present invention. Detailed Implementation

[0015] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0016] In the following embodiments, the phosphate rock used by Hubei Yihua Group Co., Ltd. for producing phosphate compound fertilizer (containing 32.43% P2O5) and the industrial wet-process phosphoric acid raw material of Hubei Yihua Group are used as examples (P2O5 mass concentration 20~40%, sulfate mass concentration 0.5%~3%). The selection requirements for phosphate rock are: rich phosphate rock containing more than 30% P2O5; medium-grade phosphate rock containing 20%~30% P2O5; and low-grade phosphate rock containing 10%~20% P2O5 can all be used in this invention.

[0017] Phosphate rock sold by other companies and industrial wet-process phosphoric acid feedstocks that meet the above component requirements can be used in this invention.

[0018] Example 1 A method for the synergistic production of clean gypsum in a wet-process phosphoric acid process includes the following steps: Step 1: Add 40 g of phosphate rock and 400 g of industrial wet-process phosphoric acid aqueous solution with 40% P2O5 to the acid hydrolysis reaction tank and carry out intermittent operation. The operating conditions are: temperature 80 ℃, linear velocity of the acid hydrolysis reaction tank 12.56 m / s; reaction time of the reactants in the acid hydrolysis reaction tank is 10 minutes to obtain the generated material slurry. Perform solid-liquid separation to obtain 420 g of filtrate.

[0019] Step 2: First, determine the calcium ion concentration (1.67% by mass) and sulfate concentration (0.75% by mass) in the filtrate obtained in Step 1. Based on the calcium ion concentration, calculate the theoretical mass of calcium sulfate dihydrate (cleaning gypsum) to be generated as 30.2 g. Then, calculate the amount of sulfate required based on this theoretical generation. Simultaneously, considering that the sulfate mass concentration in the solution needs to be maintained at 3.0% ± 0.1% after the reaction, and combining this with the initial sulfate concentration, calculate the required amount of sulfuric acid to be added using material balance (this step uses a 10 mol / L sulfuric acid aqueous solution for addition; this concentration is prepared by diluting concentrated sulfuric acid, at which point the heat of dilution has been largely released, avoiding the impact of local overheating on the crystallization process). Add 46.3 g of sulfuric acid solution and calcium sulfate dihydrate seed crystals (the mass of the seed crystals is 3 times the theoretical mass of the clean gypsum to be generated) to the filtrate, react at 80 ℃ for 60 min, filter after the reaction, and obtain filter cake clean gypsum.

[0020] The method for calculating the amount of sulfuric acid to be added by reverse calculation is as follows: The total mass of the solution after the reaction is M (420g), C 目标 The target sulfate concentration is 3.0% (i.e., C). 目标 =0.03 g / g solution). According to the law of conservation of mass, the mass of sulfate added is m. add = Mass of sulfate ions needed to maintain sulfate concentration + Mass of sulfate ions consumed for complete precipitation of calcium ions in the solution, i.e.: m add = M × (C 目标 - C0) + ((M × C Ca2+ () / 40) × 96 Where, m add M represents the mass of sulfate added, M represents the total mass of the solution after the reaction, and C represents the total mass of the solution. 目标 C is the target sulfate mass concentration, C0 is the initial sulfate mass concentration, and C Ca2+ 40 represents the calcium ion concentration in the solution, 40 represents the relative atomic mass of calcium, and 96 represents the relative molecular mass of sulfate.

[0021] Step 3: Take 90% (by mass) of the filtrate after the reaction in Step 2 to treat the filter cake after filtration in Step 1. Operating conditions: temperature is 80 ℃, reaction time is 60 min. Filter to obtain acid-insoluble residue with low residual phosphorus content. The treated filtrate is returned to Step (1) for recycling.

[0022] Acid-insoluble residue and cleaned gypsum were dried at 80 °C for 10 hours. The content of non-water-soluble P2O5 in the gypsum was determined by the quinoline phosphomolybdate gravimetric method (GB / T1871.1-1995), and the building material indicators of white gypsum were determined by GB / T 23456-2018. Their respective masses were weighed. The fluoride concentration in the crude phosphoric acid solution was determined by a fluoride ion selective electrode, and the total fluoride content in the crude phosphoric acid solution after step 3 was calculated.

[0023] Example 2 A method for the synergistic production of clean gypsum in a wet-process phosphoric acid process includes the following steps: Step 1: Add 40 g of phosphate rock and 600 g of 20% P2O5 industrial wet-process phosphoric acid aqueous solution to the acid hydrolysis reaction tank and carry out intermittent operation. The operating conditions are: temperature 80 ℃, linear velocity of the acid hydrolysis reaction tank 12.56 m / s; reaction time of the reactants in the acid hydrolysis reaction tank is 10 minutes to obtain a slurry of the product. After solid-liquid separation, 620 g of filtrate is obtained.

[0024] Step 2: First, determine the calcium ion concentration (1.13% by mass) and sulfate concentration (0.80% by mass) in the filtrate obtained in Step 1. Add 52.7g of 10 mol / L sulfuric acid aqueous solution and calcium sulfate dihydrate seed crystals to the filtrate to continue the reaction. The added sulfuric acid aqueous solution should ensure that the sulfate concentration in the solution is 3.0% ± 0.1% after the reaction (calculation method is the same as in Example 1). The mass of the added calcium sulfate dihydrate seed crystals is twice the theoretical mass of clean gypsum to be produced (60.4g). Operating conditions: temperature 80℃, reaction time 60min, reaction completed, filtered to obtain filter cake white gypsum.

[0025] Step 3: Take 90% (by mass) of the filtrate after the above reaction and use it to treat the acid-insoluble residue filter cake after filtration in Step 1. Operating conditions: temperature 90 ℃, reaction time 60 min. Filter to obtain acid-insoluble residue with low residual phosphorus content.

[0026] Acid-insoluble residue and cleaned gypsum were dried at 80 °C for 10 hours. The content of non-water-soluble P2O5 in the gypsum was determined by the quinoline phosphomolybdate gravimetric method (GB / T1871.1-1995), and the building material indicators of white gypsum were determined by GB / T 23456-2018. Their respective masses were weighed, and the results are shown in Table 2. The fluoride concentration in the crude phosphoric acid solution was determined by a fluoride ion selective electrode, and the total fluoride content in the crude phosphoric acid solution after step 3 was calculated. The results are shown in Table 1.

[0027] Example 3 A method for the synergistic production of clean gypsum in a wet-process phosphoric acid process includes the following steps: Step 1: Add 40 g of phosphate rock and 400 g of industrial wet-process phosphoric acid aqueous solution with 30% P2O5 to the acid hydrolysis reaction tank and carry out intermittent operation. The operating conditions are: temperature 80 ℃, linear velocity of the acid hydrolysis reaction tank 12.56 m / s; reaction time of the reactants in the acid hydrolysis reaction tank is 10 minutes to obtain a slurry of the product. After solid-liquid separation, 425 g of filtrate is obtained.

[0028] Step 2: First, determine the calcium ion concentration (1.78% by mass) and sulfate concentration (0.55% by mass) in the filtrate obtained in Step 1. Add 34.7 g of 10 mol / L sulfuric acid aqueous solution and calcium sulfate dihydrate seed crystals to the filtrate to continue the reaction. The added sulfuric acid aqueous solution should ensure that the sulfate concentration in the solution is 1.0% ± 0.1% after the reaction (calculation method is the same as in Example 1). The mass of the added seed crystals is 1.5 times (48.8 g) of the theoretically generated clean gypsum. Operating conditions: temperature 80℃, reaction time 60 min, reaction completed, filtered to obtain filter cake white gypsum.

[0029] Step 3: Take 90% (by mass) of the filtrate after the above reaction and use it to treat the filter cake after filtration in Step 1. Operating conditions: temperature 110 ℃, reaction time 60 min. Filter to obtain acid-insoluble residue with low residual phosphorus content.

[0030] Acid-insoluble residue and cleaned gypsum were dried at 80 °C for 10 hours. The content of non-water-soluble P2O5 in the gypsum was determined by the quinoline phosphomolybdate gravimetric method (GB / T1871.1-1995), and the building material indicators of white gypsum were determined by GB / T 23456-2018. Their respective masses were weighed, and the results are shown in Table 2. The fluoride concentration in the crude phosphoric acid solution was determined by a fluoride ion selective electrode, and the total fluoride content in the crude phosphoric acid solution after step 3 was calculated. The results are shown in Table 1.

[0031] Example 4 A method for the synergistic production of clean gypsum in a wet-process phosphoric acid process includes the following steps: Step 1: Add 40 g of phosphate rock and 400 g of industrial wet-process phosphoric acid aqueous solution with 30% P2O5 to the acid hydrolysis reaction tank and carry out intermittent operation. The operating conditions are: temperature 80 ℃, linear velocity of the acid hydrolysis reaction tank 12.56 m / s; reaction time of the reactants in the acid hydrolysis reaction tank is 10 minutes to obtain a slurry of the product. After solid-liquid separation, 428 g of filtrate is obtained.

[0032] Step 2: First, determine the calcium ion concentration (mass concentration 1.80%) and sulfate concentration (mass concentration 0.50%) in the filtrate obtained in Step 1. Add 32.0 g of 10 mol / L sulfuric acid aqueous solution and calcium sulfate dihydrate seed crystals to the filtrate to continue the reaction. The added sulfuric acid aqueous solution should ensure that the sulfate mass concentration in the solution after the reaction is 0.5% ± 0.1% (calculation method is the same as in Example 1). The mass of the added seed crystals is twice the theoretical mass of clean gypsum to be produced (33.1 g). Operating conditions: temperature 80 ℃, reaction time 60 min, filter to obtain filter cake white gypsum.

[0033] Step 3: Take 90% (by mass) of the filtrate from the reaction in Step 2 and use it to treat the filter cake from Step 1. The operating conditions are: temperature 90 ℃, reaction time 60 min. Filter to obtain an acid-insoluble residue with low residual phosphorus content.

[0034] Acid-insoluble residue and cleaned gypsum were dried at 80 °C for 10 hours. The content of non-water-soluble P2O5 in the gypsum was determined by the quinoline phosphomolybdate gravimetric method (GB / T1871.1-1995), and the building material indicators of white gypsum were determined by GB / T 23456-2018. Their respective masses were weighed, and the results are shown in Table 2. The fluoride concentration in the crude phosphoric acid solution was determined by a fluoride ion selective electrode, and the total fluoride content in the crude phosphoric acid solution after step 3 was calculated. The results are shown in Table 1.

[0035] Example 5 A method for the synergistic production of clean gypsum in a wet-process phosphoric acid process includes the following steps: Step 1: Add 40 g of phosphate rock and 400 g of industrial wet-process phosphoric acid aqueous solution with 30% P2O5 to the acid hydrolysis reaction tank and carry out intermittent operation. The operating conditions are: temperature 80 ℃, linear velocity of the acid hydrolysis reaction tank 12.56 m / s; reaction time of the reactants in the acid hydrolysis reaction tank is 10 minutes to obtain a slurry of the product. After solid-liquid separation, 425 g of filtrate is obtained.

[0036] Step 2: First, determine the calcium ion concentration (1.78% by mass) and sulfate concentration (0.55% by mass) in the filtrate obtained in Step 1. Add 34.7 g of 10 mol / L sulfuric acid aqueous solution and calcium sulfate dihydrate seed crystals to the filtrate to continue the reaction. The added sulfuric acid aqueous solution should ensure that the sulfate concentration in the solution is 1.0% ± 0.1% after the reaction (calculation method is the same as in Example 1). The mass of the added seed crystals is 1.5 times (48.8 g) of the theoretically produced clean gypsum. Operating conditions: temperature 80℃, reaction time 60 min, reaction completed, filtered to obtain filter cake white gypsum.

[0037] This embodiment omits step 3 and compares it with embodiments 1-4.

[0038] The experimental results of Examples 1-5 above and the index detection parameters of the generated cleaning plaster are shown in Tables 1 and 2: Table 1 Experimental Results Table 2 Requirements for Gypsum Building Materials (GB / T 23456-2018)

[0039] In summary, the water-soluble P2O5 content in the clean gypsum prepared by the method of this invention is all below 0.3%, and the residual phosphorus content in the acid-insoluble residue is all less than 0.5%, significantly lower than the above 3.25% before the cyclic phosphoric acid treatment. The fluorine content in the liquid-phase phosphoric acid is above 90%, and the quality of the by-product clean gypsum meets the requirements for gypsum building materials. Furthermore, the experimental results show that the water-soluble phosphorus content tends to increase as the sulfate concentration decreases. Example 4 illustrates that when the sulfate concentration is too low (equal to 0.5%), the prepared clean gypsum may not meet the building material index requirements.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for the multi-effect synergistic production of clean gypsum in a wet-process phosphoric acid process, characterized in that, Includes the following steps: (1) Low-impurity acid hydrolysis and fluorine enrichment: Phosphate rock and industrial wet-process phosphoric acid aqueous solution are added to the acid hydrolysis reaction equipment at a mass ratio of 1:(10~15) and the reaction is carried out at a temperature of 80~100℃ for 8~12 minutes to make fluorine highly enriched in the liquid phase; after the reaction, the slurry is separated into solid and liquid to obtain a crude phosphoric acid solution rich in fluorine and containing calcium dihydrogen phosphate and acid-insoluble residue. (2) Preparation of clean gypsum: Add calcium sulfate dihydrate seed crystals to the crude phosphoric acid solution containing fluorine and calcium dihydrogen phosphate obtained in step (1) and add sulfuric acid. Maintain the mass concentration of sulfate in the solution after the reaction within the range of (1.0%~3.0%)±0.1% for aging and crystallization. Filter to obtain clean gypsum and fluorine-rich crude phosphoric acid solution. (3) Residual phosphorus and fluorine recovery: Part of the fluorine-rich crude phosphoric acid solution obtained in step (2) is extracted as a product, and the other part is recycled to re-acidify and recrystallize the acid-insoluble residue generated in step (1) to deeply extract residual phosphorus and fluorine elements from the residue. After the treatment is completed, solid-liquid separation is performed, and the crude phosphoric acid solution is returned to step (1) for recycling.

2. The method according to claim 1, characterized in that, The industrial wet-process phosphoric acid solution in step (1) has a P2O5 mass fraction of 20%~40%, and the solution contains SO4. 2- The mass concentration is 0.5%~3%.

3. The method according to claim 1, characterized in that, The mass of calcium sulfate dihydrate seed crystals added in step (2) is 1 to 3 times the theoretical mass of clean gypsum to be generated.

4. The method according to claim 1, characterized in that, In step (3), the temperature of the acid-insoluble residue in the countercurrent treatment of circulating phosphoric acid is 80~110℃.

5. The method according to claim 1, characterized in that, The acidolysis reaction in step (1) is carried out at a temperature of 80°C for 10 minutes.

6. The method according to claim 1, characterized in that, The crystallization process in step (2) is carried out at 80°C for 60 minutes.

7. The method according to claim 1, characterized in that, The mass ratio of the output and circulation of the fluorine-rich crude phosphoric acid solution in step (3) is 1:9.

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