Method for direct purification and separation of wet-process phosphogypsum slurry and purified phosphogypsum and phosphoric acid

Abstract

The application provides a method for directly purifying and separating phosphogypsum slurry, and belongs to the technical field of solid waste treatment. The method comprises the following steps: adding phosphogypsum slurry obtained in the production of phosphoric acid into a flotation device, then adding a silane type activator and mixing uniformly, then adding a dual-function collector and stirring uniformly, and then performing reverse flotation by aeration; taking the reverse flotation froth as tailings, and performing solid-liquid separation to obtain organic waste residue and phosphoric acid; performing solid-liquid separation on the concentrate obtained by the reverse flotation to obtain crude phosphogypsum and phosphoric acid; performing leaching purification on the crude phosphogypsum to obtain purified phosphogypsum, and combining the phosphoric acid obtained by two times of separation as a by-product. The dual-function collector is composed of 10-50 wt% ether type surfactant, 30-60 wt% oil and 10-30 wt% cosolvent. The phosphogypsum obtained by the method meets the quality standard of the first grade product in GB / T 23456-2018, and the gypsum recovery rate reaches more than 80%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid waste treatment, and particularly relates to a method for directly purifying and separating phosphogypsum slurry in a wet-process phosphoric acid production process and purified phosphogypsum and phosphoric acid prepared by the method. BACKGROUND

[0002] Phosphogypsum is a by-product solid waste produced in the production of phosphoric acid by using sulfuric acid to decompose phosphate concentrate. It is estimated that 5-8 tons of phosphogypsum are produced for every ton of phosphoric acid. The main component of phosphogypsum is CaSO4·2H2O, which has a wide range of uses, such as cement retarder, block, veneer gypsum board, road filling, building materials, etc. However, untreated phosphogypsum contains a large amount of impurities, such as organic matter, soluble phosphorus, insoluble phosphorus, soluble fluorine, insoluble fluorine, quartz, silicates, and heavy metals, which greatly affect the gelation performance and strength of the gypsum, becoming a major problem in the resource utilization of phosphogypsum.

[0003] China is the world's largest producer of phosphate fertilizer, but the actual utilization rate of phosphogypsum is only 30%. China's annual increase in phosphogypsum storage is about 50 million tons. The storage of a large amount of phosphogypsum not only occupies a large area of land, but also may cause environmental problems such as dust, groundwater and soil pollution, and disasters such as landslides, becoming a major bottleneck restricting the development of the phosphate fertilizer industry.

[0004] In the prior art, the purification treatment of phosphogypsum is generally to add a large amount of water to the by-product phosphogypsum solid obtained in the production of phosphoric acid, and then add various reagents for flotation purification treatment. For example, the patent application publication CN114308398A discloses a phosphogypsum flotation washing and decolorization purification method, which adds ether diamine to the phosphogypsum slurry for three times of continuous reverse flotation. The CaSO4·2H2O content in the obtained phosphogypsum is 80-90%, and the whiteness of the phosphogypsum is 30-40%. CN112871457A discloses a method for purifying and removing impurities from phosphogypsum, which adds water to the phosphogypsum ore to a slurry concentration of 25-35%, then adds lime and water glass to solidify soluble phosphorus and fluorine, then adds a decolorizing agent containing -OH functional groups to remove black organic matter, and finally adds a dephosphorizing agent containing -NH3 +The functional group reagent collects gypsum, separates gypsum from silicate, fluorine and phosphorus, and obtains purified gypsum with whiteness of 60% or more and purity of 98% or more. In these methods, on the one hand, a large amount of water needs to be added for slurry adjustment, and flotation wastewater is obtained, causing secondary pollution. In industrial production, new facilities such as slurry adjustment tanks need to be built, increasing production costs. On the other hand, most of them need to be classified for flotation to remove organic matter and silicate impurities, and the purification process is long and the cost is high. A small number of methods use one-step flotation removal, and amine cationic collectors are used as desilicon collectors. The production cost of such collectors is high, and they are not suitable for strong acid systems (pH <1, under this condition, gypsum and quartz are positively charged or not charged, and are not easy to be collected by cationic collectors). Moreover, these methods are not used with wet-process phosphoric acid production processes. The phosphorus recovered from phosphogypsum is left in the flotation wastewater and cannot be directly and effectively returned to the wet-process crude phosphoric acid. The wet-process crude phosphoric acid is not purified and impurities are removed.

[0005] Therefore, how to improve the purification effect of phosphogypsum while reducing the consumption of fresh tap water in the phosphogypsum purification process and avoiding secondary pollution, and directly obtaining high-quality phosphoric acid, developing a dual-functional collector suitable for strong acid conditions to achieve one-step flotation removal of organic matter and silicate impurities, shortening the purification process, and reducing the cost of industrial production, has become a technical problem to be solved. SUMMARY

[0006] To solve the above problems, the present application provides a method for direct purification and separation of wet-process phosphogypsum slurry, which uses a dual-functional collector to directly remove organic matter and silicate impurities from phosphogypsum slurry obtained in the industrial wet-process phosphoric acid production process by one-step reverse flotation. Purified phosphogypsum meeting the requirements of first-grade product in GB / T23456-2018 is obtained, and high-quality phosphoric acid is also obtained.

[0007] To achieve the above purpose, the present application adopts the following technical solutions:

[0008] A method for direct purification and separation of wet-process phosphogypsum slurry, comprising the following steps:

[0009] S1, transferring the phosphogypsum slurry obtained in the wet-process phosphoric acid production into a flotation device and stirring uniformly;

[0010] S2, adding a silane activator to the flotation device, then adding a dual-functional collector, and stirring uniformly; the dual-functional collector is composed of 10wt%-50wt% ether surfactant, 30wt%-60wt% oil and 10wt%-30wt% cosolvent;

[0011] S3, aerating the flotation device for reverse flotation; the reverse flotation time is preferably 5-15min;

[0012] S4, the reverse flotation froth in step S3 is separated as tailings to obtain organic waste residue and phosphoric acid; the concentrate obtained in step S3 is subjected to solid-liquid separation to obtain crude phosphogypsum and phosphoric acid;

[0013] S5, the crude phosphogypsum is sequentially leached with dilute sulfuric acid and clean water to obtain purified phosphogypsum.

[0014] In the prior art, organic matter and silicate impurities are mostly removed by two-step reverse and direct flotation, while the dual-functional collector in the present application can simultaneously remove organic matter and silicate impurities by one-step reverse flotation. The surfactant in the dual-functional collector can promote the formation of a uniform bubble layer in the slurry, and the organic matter, after being captured by the oil collector, interacts with the formed bubbles to form an organic matter bubble layer on the surface of the bubbles; and the silane activator combines with the silicate through hydrogen bonding and dehydration condensation to form silica gel particles, which are then assembled with the organic matter bubble layer to float up, obtaining an organic waste residue containing silicate; thus, the purposes of simultaneously removing organic matter and silicate are achieved.

[0015] In the phosphogypsum slurry, there is a small amount of un-decomposed apatite covered with silicate, which will increase the total phosphorus content in the phosphogypsum. The silane activator in the present application can strip the silicate covering the surface of the apatite to form organosilicate, which is then self-assembled with the dual-functional collector to float up and removed, and the exposed apatite is further decomposed by phosphoric acid in the system to form phosphoric acid, effectively recovering the phosphorus in the phosphogypsum and increasing the mass concentration of the phosphoric acid.

[0016] Preferably, the mass ratio of the slurry to the liquid in the phosphogypsum slurry in step S1 is 1:(2-4).

[0017] Preferably, the mass of the silane activator accounts for 0.01%-0.03% of the dry mass of the phosphogypsum slurry.

[0018] Preferably, the silane activator comprises at least one of γ-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

[0019] Preferably, the mass of the dual-functional collector accounts for 0.02%-0.05% of the dry mass of the phosphogypsum slurry.

[0020] Preferably, the ether surfactant comprises at least one of sodium lauryl polyoxyethylene ether sulfate, allyloxy polyoxyethylene ether, fatty alcohol polyoxyethylene ether (such as isomeric decanol polyoxyethylene ether, dodecanol polyoxyethylene ether, isooctanol polyoxyethylene ether), and nonylphenol polyoxyethylene ether.

[0021] Preferably, the oil is a C10-C22 non-polar hydrocarbon oil; for example, the oil includes at least one of kerosene, diesel oil, pine oil, transformer oil, and tar oil.

[0022] Preferably, the co-solvent includes at least one of n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, dodecanol, tetradecanol, and hexadecanol.

[0023] Preferably, the mass fraction of the dilute sulfuric acid is 10%-30%. Under other conditions being the same, when the mass concentration of the dilute sulfuric acid is 10%-30%, better effects can be achieved for purifying the phosphogypsum.

[0024] The application also provides the purified phosphogypsum and phosphoric acid prepared according to the above method.

[0025] Preferably, the purified phosphogypsum has a whiteness of ≥70%, a CaSO4·2H2O content of ≥95%, a water-soluble phosphorus content of ≤0.1%, and a water-soluble fluorine content of ≤0.1%; and meets the quality standard of the first-grade product in GB / T 23456-2018 "Phosphogypsum".

[0026] Preferably, the mass concentration of the phosphoric acid is 10%-40%.

[0027] Compared with the prior art, the application has the following beneficial effects: (1) In the prior art, the phosphogypsum is slurried with water to a mass concentration of 25%-35% and acid is added to adjust the pH, and 1.86-3 tons of flotation wastewater are generated per ton of phosphogypsum produced; in the application, the phosphogypsum slurry generated in the process of producing phosphoric acid by the wet method is directly purified and separated, and the phosphogypsum does not need to be slurried with water; thus, a large amount of fresh tap water is avoided, secondary pollution is avoided, and a large amount of water resources and wastewater treatment costs are saved in industrial production. The method can purify the phosphogypsum and the phosphoric acid at the same time, the mass concentration of the phosphoric acid is increased by 0.5%-2.0% compared with the phosphoric acid produced by the traditional wet method, and the removal rate of acid-insoluble substances in the phosphoric acid is more than 95%. (2) In the application, the organic matter and silicate impurities do not need to be removed by the two-step method of reverse flotation and positive flotation, but only need to be removed by one reverse flotation to simultaneously remove the organic matter and silicate impurities. (3) The purified phosphogypsum prepared by the method of the application has a whiteness of ≥70%, a CaSO4·2H2O content of ≥95%, a water-soluble phosphorus content of ≤0.1%, and a water-soluble fluorine content of ≤0.1%; and meets the quality standard of the first-grade product in GB / T 23456-2018 "Phosphogypsum"; and the gypsum recovery rate is more than 80%. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a process flow chart for directly purifying and separating the wet-process phosphogypsum slurry in the application.

[0029] Figure 2 Appearance comparison chart of the phosphoric acid obtained in Example 1 and the phosphoric acid produced by wet-process phosphoric acid production;

[0030] Figure 3 Appearance comparison chart of the purified phosphogypsum obtained in Example 1 and the phosphogypsum separated from the phosphogypsum slurry according to the solid-liquid separation method. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described clearly and completely in combination with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application. Any equivalent transformation or substitution made by those skilled in the art according to the following embodiments falls within the scope of protection of the present application.

[0032] Example 1

[0033] The present embodiment provides a method for preparing phosphogypsum by directly purifying wet-process phosphogypsum slurry, which comprises the following steps (process flow chart as shown in Figure 1

[0034] S1, the phosphogypsum slurry obtained in the wet-process phosphoric acid production with a solid-liquid mass ratio of 1:2 is transferred into a flotation device and stirred uniformly; the water-soluble phosphorus content in the phosphogypsum dry basis separated from the phosphogypsum slurry is 0.23%, the water-soluble fluorine content is 0.19%, the CaSO4·2H2O content is 85.49%, and the whiteness is 23.9%.

[0035] S2, 0.02% of γ-aminopropyltrimethoxysilane based on the dry mass of the phosphogypsum slurry is added into the flotation device and stirred uniformly; then 0.035% of a bifunctional collector based on the dry mass of the phosphogypsum slurry is added and fully stirred uniformly; the bifunctional collector is composed of 50wt% isomeric decanol polyoxyethylene ether, 40wt% diesel oil and 10wt% n-pentanol.

[0036] S3, the aeration switch is opened, and air is supplied to the flotation device for 10 minutes of reverse flotation.

[0037] S4, the reverse flotation foam in step S3 is taken as tailings, and after solid-liquid separation, silicate-containing organic waste residue and phosphoric acid are obtained; the obtained concentrate is subjected to solid-liquid separation to obtain phosphogypsum crude product and phosphoric acid. The phosphoric acid obtained twice is combined, and the mass concentration is 16.98%. Referring to Figure 2 , Figure 2 ​The phosphoric acid in the left beaker is produced by the wet-process phosphoric acid process, and the phosphoric acid in the right beaker is obtained in the present example. The removal rate of acid-insoluble substances in the phosphoric acid obtained in the present example is 95.60%, and the mass fraction of the phosphoric acid is increased by 1.20% compared with the phosphoric acid produced by the wet-process phosphoric acid process.

[0038] S5, the obtained crude phosphogypsum is washed with a small amount of 20% sulfuric acid, and then washed with a small amount of clean water twice to obtain purified phosphogypsum. The content of CaSO4·2H2O in the purified phosphogypsum is 96.68%, the whiteness is 75.8%, the water-soluble phosphorus content is 0.04%, and the water-soluble fluorine content is 0.02%; the gypsum recovery rate is 81.50%. Referring to Figure 3 , Figure 3 The left side in the middle is phosphogypsum separated from phosphogypsum slurry according to the solid-liquid separation method, and the right side is phosphogypsum obtained by directly purifying the phosphogypsum slurry in the present example. As can be seen from the figure, the whiteness of the phosphogypsum prepared in the present example is significantly higher than that of the phosphogypsum obtained by the solid-liquid separation method from the original phosphogypsum slurry.

[0039] Example 2

[0040] The present example provides a method for preparing phosphogypsum by directly purifying wet-process phosphogypsum slurry, which comprises the following steps (process flow chart as Figure 1 shown):

[0041] S1, the phosphogypsum slurry with a solid-liquid mass ratio of 1:3 obtained in the production of wet-process phosphoric acid is transferred into a flotation device and stirred uniformly; the water-soluble phosphorus content in the phosphogypsum dry basis separated from the phosphogypsum slurry is 0.23%, the water-soluble fluorine content is 0.19%, the CaSO4·2H2O content is 85.49%, and the whiteness is 23.9%.

[0042] S2, 0.01% of the silane activator based on the dry mass of the phosphogypsum slurry is added to the flotation device and stirred uniformly; then 0.05% of the bifunctional collector based on the dry mass of the phosphogypsum slurry is added and stirred uniformly; wherein the silane activator is composed of 50wt% 3-aminopropyl triethoxysilane and 50wt% 3-aminopropyl trimethoxysilane; the bifunctional collector is composed of 5wt% lauryl polyoxyethylene ether sodium sulfate, 5wt% allyloxy polyoxyethylene ether, 30wt% diesel oil, 30wt% kerosene, 10wt% n-butanol and 20wt% n-hexanol.

[0043] S3, open the aeration switch, and aerate the flotation device for 15 minutes.

[0044] S4, the reverse flotation froth in step S3 is taken as tailings, and after solid-liquid separation, silicate-containing organic waste residue and phosphoric acid are obtained; the obtained concentrate is subjected to solid-liquid separation to obtain crude phosphogypsum and phosphoric acid. The phosphoric acid obtained twice is combined, the mass concentration is 16.90%, the removal rate of acid-insoluble substances in phosphoric acid is 96.4%, and the mass fraction of phosphoric acid is increased by 1.09% compared with the crude phosphoric acid produced by the wet-process phosphoric acid production.

[0045] S5, the obtained crude phosphogypsum is eluted with a small amount of 10% sulfuric acid once, and then eluted with a small amount of clean water twice to obtain purified phosphogypsum. The content of CaSO4·2H2O in the purified phosphogypsum is 95.10%, the whiteness is 73.9%, the water-soluble phosphorus content is 0.05%, and the water-soluble fluorine content is 0.03%; the gypsum recovery rate is 80.30%.

[0046] Example 3

[0047] The embodiment provides a method for directly purifying and separating wet-process phosphoric acid gypsum slurry, which comprises the following steps (as shown in the process flow chart): Figure 1

[0048] S1, the phosphogypsum slurry with a solid-liquid mass ratio of 1:4 obtained in the production of wet-process phosphoric acid is transferred into a flotation device and stirred uniformly; the water-soluble phosphorus content in the phosphogypsum dry basis separated from the phosphoric acid gypsum slurry is 0.28%, the water-soluble fluorine content is 0.14%, the CaSO4·2H2O content is 88.80%, and the whiteness is 34.2%.

[0049] S2, a silane activator accounting for 0.03% of the dry mass of the phosphogypsum slurry is added to the flotation device and stirred uniformly; then a bifunctional collector accounting for 0.02% of the dry mass of the phosphogypsum slurry is added and stirred uniformly; wherein the silane activator is composed of 30wt% γ-(2,3-epoxypropoxy) propyl trimethoxysilane and 70wt% γ-methacryloyloxypropyl trimethoxysilane; the bifunctional collector is composed of 30wt% allyloxy polyoxyethylene ether, 10wt% dodecanol polyoxyethylene ether, 10wt% pinol oil, 20wt% transformer oil, 20wt% n-heptanol and 10wt% n-octanol.

[0050] S3, open the aeration switch, and aerate the flotation device for 5 minutes.

[0051] S4, the reverse flotation froth in step S3 is taken as tailings, and after solid-liquid separation, silicate-containing organic waste residue and phosphoric acid are obtained; the obtained concentrate is subjected to solid-liquid separation to obtain crude phosphogypsum and phosphoric acid. The phosphoric acid obtained twice is combined, the mass concentration is 16.90%, the removal rate of acid-insoluble substances in phosphoric acid is 96.4%, and the mass fraction of phosphoric acid is increased by 1.09% compared with the crude phosphoric acid produced by the wet-process phosphoric acid production.

[0052] ​S5, the obtained crude phosphogypsum is washed with a small amount of 30% sulfuric acid, then washed with a small amount of water twice to obtain purified phosphogypsum. The CaSO4·2H2O content of the purified phosphogypsum is 96.25%, the whiteness is 72.2%, the water-soluble phosphorus content is 0.05%, and the water-soluble fluorine content is 0.02%; the gypsum recovery rate is 83.39%.

[0053] Example 4

[0054] The present embodiment provides a method for direct purification and separation of wet-process phosphogypsum slurry, comprising the following steps (process flow chart as shown in Figure 1

[0055] S1, the phosphogypsum slurry with a solid-liquid mass ratio of 1:2 obtained in the production of wet-process phosphoric acid is transferred into a flotation device and stirred uniformly; the water-soluble phosphorus content in the phosphogypsum slurry is 0.50%, the water-soluble fluorine content is 0.86%, the CaSO4·2H2O content is 80.62%, and the whiteness is 35.1%.

[0056] S2, a silane activator accounting for 0.02% of the dry mass of the phosphogypsum slurry is added to the flotation device and stirred uniformly; then a bifunctional collector accounting for 0.035% of the dry mass of the phosphogypsum slurry is added and stirred uniformly; the silane activator is composed of 10wt% γ-mercaptopropyl triethoxysilane and 90wt% N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane; the bifunctional collector is composed of 10wt% isooctanol polyoxyethylene ether, 10wt% nonylphenol polyoxyethylene ether, 20wt% polyoxyethylene lauryl ether, 20wt% kerosene, 10wt% diesel, 10wt% tar, 5wt% dodecanol, 5wt% tetradecanol, and 10wt% hexadecanol.

[0057] S3, open the aeration switch and aerate the flotation device for 10 minutes.

[0058] S4, the reverse flotation foam in step S3 is taken as tailings, and after solid-liquid separation, silicate-containing organic waste residue and phosphoric acid are obtained; the obtained concentrate is subjected to solid-liquid separation to obtain crude phosphogypsum and phosphoric acid. The two obtained phosphoric acids are combined, and the mass concentration is 40.00%; the removal rate of acid-insoluble substances in the phosphoric acid is 96.50%; the mass fraction of the phosphoric acid is increased by 2.00% compared with the crude phosphoric acid obtained in the production of wet-process phosphoric acid.

[0059] S5, the obtained crude phosphogypsum is washed with a small amount of 40% sulfuric acid, then washed with a small amount of water twice to obtain purified phosphogypsum. The CaSO4·2H2O content of the purified phosphogypsum is 95.10%, the whiteness is 70.8%, the water-soluble phosphorus content is 0.06%, and the water-soluble fluorine content is 0.05%; the gypsum recovery rate is 92.65%.

[0060] ​The above merely provides the preferred embodiments of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement or improvement made by any person skilled in the art based on the present application should be included in the protection scope of the present application.

Claims

1. A method for direct purification and separation of wet-process phosphate gypsum slurry, characterized in that, Includes the following steps: S1. Transfer the phosphate gypsum slurry obtained in the wet process of phosphoric acid production into the flotation unit and stir it evenly; S2. Add a silane activator to the flotation device, then add a bifunctional collector and stir until homogeneous; the bifunctional collector is composed of 10wt% to 50wt% ether surfactant, 30wt% to 60wt% oil and 10wt% to 30wt% cosolvent. S3. Introduce air into the flotation device to perform reverse flotation; S4. The reverse flotation foam from step S3 is used as tailings. After solid-liquid separation, organic waste residue and phosphoric acid are obtained. The concentrate obtained in step S3 is subjected to solid-liquid separation to obtain crude phosphogypsum and phosphoric acid. S5. The crude phosphogypsum is rinsed with dilute sulfuric acid and then rinsed with water to obtain purified phosphogypsum.

2. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The solid-liquid mass ratio of the phosphate gypsum slurry in step S1 is 1:(2-4).

3. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The silane activator accounts for 0.01% to 0.03% of the dry phosphate gypsum slurry by mass.

4. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The silane activators include at least one of γ-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

5. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The mass of the bifunctional collector is 0.02% to 0.05% of the dry mass of phosphate gypsum slurry.

6. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The ether surfactants include at least one of sodium lauryl polyoxyethylene ether sulfate, allyloxy polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and nonylphenol polyoxyethylene ether.

7. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The oil is a C10 to C22 nonpolar hydrocarbon oil.

8. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The co-solvent includes at least one of n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, dodecanol, tetradecanol, and hexadecylol.

9. The method for direct purification and separation of wet-process phosphate gypsum slurry according to claim 1, characterized in that, The mass fraction of the dilute sulfuric acid is 10% to 30%.

10. The purified phosphogypsum and phosphoric acid prepared by the method for direct purification and separation of wet-process phosphogypsum slurry according to any one of claims 1 to 9.

Images