Deep dephosphorization purification method for phosphogypsum

Abstract

The invention relates to the technical field of ardealite dephosphorization, in particular to an ardealite deep dephosphorization purification method which comprises the following steps: step 1, pretreating ardealite; step 2, acidifying the ardealite; step 3, flotation and impurity removal; 4, precipitating and removing impurities; and 5, crystal form transformation. According to the method, the phosphogypsum is subjected to dephosphorization purification by adopting a method of combining secondary acidification, flotation impurity removal and precipitation impurity removal, so that the use amount of nitric acid is reduced; and the superfine dihydrate gypsum seed crystal is used for inducing crystallization, so that the use amount of the dihydrate gypsum seed crystal is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phosphogypsum dephosphorization, and in particular to a method for deep dephosphorization and purification of phosphogypsum. BACKGROUND

[0002] Phosphogypsum is a solid waste produced by phosphorus chemical enterprises in the production of phosphoric acid and phosphate fertilizer by using the wet process. The main phase of phosphogypsum is calcium sulfate dihydrate, which is generally in the form of powdery gray or gray-black. Phosphogypsum contains soluble phosphorus, fluorine, organic matter and other impurities. Organic matter and other impurities adhere to the surface of phosphogypsum, hinder the formation of calcium sulfate dihydrate, delay the setting time, reduce the strength of phosphogypsum, and also increase the water demand of phosphogypsum cementing material, thereby affecting its cohesiveness and fluidity. Soluble phosphorus and fluorine and other impurities will form calcium phosphate and calcium fluoride precipitates in the early stage of hydration, covering the surface of hemihydrate gypsum, hindering its dissolution and hydration, and leading to the decrease of the cementing property of phosphogypsum. Among them, soluble phosphorus usually exists in the form of phosphoric acid and dihydrogen phosphate. On the one hand, it will affect the pH of the system, and on the other hand, it will react with calcium ions during the hydration process of phosphogypsum to form insoluble calcium phosphate, covering the surface of phosphogypsum, hindering the dissolution and hydration of gypsum, prolonging the setting and hardening time of phosphogypsum, and seriously affecting its performance. Soluble phosphorus will also coarsen the crystal of the hydration product, make the structure loose, and reduce the strength of phosphogypsum products.

[0003] The existing technology generally uses acid dissolution method to dephosphorize phosphogypsum. First, strong acids such as hydrochloric acid, sulfuric acid or nitric acid are used to destroy the calcium-phosphorus bond in phosphogypsum, so that the insoluble phosphate is converted into soluble phosphate. Then, alum is added to the reaction solution to form aluminum phosphate seed crystals in the reaction solution. By adjusting the pH, the phosphate is separated from the metal ions (Al 3+ , Fe 3+ , Ca 2+ ) to form a precipitate, so as to obtain a purified solution. Finally, excess sulfate and dihydrate gypsum seed crystals are added to the purified solution to obtain dihydrate gypsum. This method has a large consumption of strong acid. Due to the high concentration of SO4 2- in the system, the supersaturation of dihydrate gypsum is also high, and a large amount of dihydrate gypsum seed crystals need to be added to avoid the formation of small and easy-to-agglomerate gypsum particles due to the high "supersaturation". SUMMARY

[0004] In view of the technical problems of large consumption of strong acid and dihydrate gypsum seed crystals in the existing phosphogypsum dephosphorization process, the present application provides a method for deep dephosphorization and purification of phosphogypsum. The method uses a combination of two-stage acidification, flotation and precipitation to dephosphorize and purify phosphogypsum, thereby reducing the amount of nitric acid used. Ultrafine dihydrate gypsum seed crystals are used to induce crystallization, thereby reducing the amount of dihydrate gypsum seed crystals used.

[0005] The technical scheme of the present application is as follows: A method for deep dephosphorization and purification of phosphogypsum, comprising the following steps: Step one: pretreatment of phosphogypsum, crushing the phosphogypsum; Step two: acidification of phosphogypsum, adding the crushed phosphogypsum into a sulfuric acid solution and mixing uniformly, stirring and reacting at 45-50 DEG C for 20-30 min to obtain a first-stage acidification mixed solution, then mixing the first-stage acidification mixed solution with a nitric acid solution uniformly, continuing to stir and react at constant temperature until the soluble phosphorus concentration has no obvious change, to obtain a second-stage acidification mixed solution; Step three: flotation for removing impurities, using calcium hydroxide suspension to adjust the pH of the second-stage acidification mixed solution to 3-4, then adding a collector and a frother for flotation, to obtain an underflow liquid; Step four: precipitation for removing impurities, adding polyaluminum chloride into the underflow liquid and stirring uniformly, then using calcium hydroxide suspension to adjust the pH of the underflow liquid to 5-6, stirring and reacting at 45-50 DEG C, after the reaction is completed, standing and filtering, to obtain a filtrate; Step five: crystal type conversion, after the filtrate is heated to 50-55 DEG C, adding a sulfate into the filtrate, stirring and reacting, then adding superfine gypsum dihydrate crystal seeds into the filtrate to induce crystallization, separating the crystals and washing the crystals, to obtain gypsum dihydrate.

[0006] Further, in step one, the particle size of the crushed phosphogypsum is 0.1-0.5 mm.

[0007] Further, in step two, the concentration of the sulfuric acid solution is 22wt%-28wt%, and the concentration of the nitric acid solution is 30wt%-40wt%. The crushed phosphogypsum is added into the sulfuric acid solution to mix uniformly, which can dissolve part of the impurities in the phosphogypsum and provide a stable acidic environment for the subsequent reaction of nitric acid and the insoluble impurities in the phosphogypsum.

[0008] Further, in step two, the mass ratio of the crushed phosphogypsum, the sulfuric acid solution and the nitric acid solution is 1:0.9-1.1:0.6-0.8.

[0009] Further, in step two, the soluble phosphorus concentration has no obvious change means that the change amount of the soluble phosphorus concentration within 15-30 min is <1.8 mg / L.

[0010] Further, in step three, the concentration of the calcium hydroxide suspension is 5wt%-10wt%, the collector is alkyl phosphate and / or isooctyl salicylic acid, the collector is preferably alkyl phosphate, and the frother is a polyhydric fatty alcohol or a polypropylene glycol ether, and the frother is preferably a polyhydric fatty alcohol.

[0011] Further, in step three, the flotation temperature is 40-45 DEG C, the flotation time is 20-40 min, and compressed air is introduced during the flotation process, and the flow rate of the compressed air is 0.22-0.28 m3 / h.

[0012] Further, in step four, the adding amount of the polyaluminum chloride is 0.1-0.15g / L, the stirring reaction time is 50-65min, and the standing time is 1-2h.

[0013] Further, in step five, the sulfate is ammonium sulfate or sodium sulfate, preferably ammonium sulfate; the mass of the sulfate is 5%-8% of the mass of the crushed phosphogypsum; and the stirring reaction time is 60-90min. The ammonium sulfate or sodium sulfate can increase the concentration of SO4 2- in the solution, inhibit the dissolution of dihydrate gypsum, and provide sufficient raw materials for the growth of the gypsum crystals.

[0014] Further, in step five, the particle size of the superfine dihydrate gypsum seed is 0.5-2μm; and the mass of the superfine dihydrate gypsum seed is 2%-5% of the mass of the crushed phosphogypsum. The superfine dihydrate gypsum seed has a large specific surface area and high activity, can guide the growth of the gypsum crystals into uniform short columnar or blocky shapes along a specific direction in a small amount, prevents the agglomeration of the gypsum crystals, and is beneficial to improving the strength of the gypsum crystals.

[0015] The present application has the following advantages: The phosphogypsum deep dephosphorization and purification method provided by the present application uses a composite acidification system of sulfuric acid and nitric acid in step two, mixes the crushed phosphogypsum with the sulfuric acid solution, and can inhibit the dissolution of the phosphogypsum to a certain extent, reduce the loss of the gypsum, convert the insoluble phosphate into soluble phosphoric acid, improve the dissolution rate of phosphorus, and reduce the use amount of the nitric acid. Mixing the first-stage acidification mixed solution with the nitric acid solution can oxidize the organic phosphorus or low-valence phosphorus compounds by using the oxidizability of the nitric acid solution, ensure that all the phosphorus forms are converted into soluble phosphate, and further improve the dissolution rate of phosphorus. In step three, the present application uses the calcium hydroxide suspension to adjust the pH of the second-stage acidification mixed solution to 3-4, promotes the formation of the complex of the phosphate and impurities without introducing new metal elements, and then separates the suspended state phosphorus-containing impurities by using the collector with strong adsorption of the phosphorus-containing impurities in the form of foam flotation, to realize the first dephosphorization. In step four, the present application uses the polyaluminum chloride to react with the remaining soluble phosphate to form a stable aluminum phosphate precipitate, and after standing and filtration, the second dephosphorization can be realized, and the content of phosphorus in the filtrate can be reduced to a lower level. DETAILED DESCRIPTION

[0016] In order for those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should fall within the protection scope of the present application.

[0017] Embodiment 1 A phosphogypsum deep dephosphorization purification method comprises the following steps: Step one: phosphogypsum pretreatment, the phosphogypsum is crushed, the particle size of the crushed phosphogypsum is 0.1-0.3mm, and the water content of the crushed phosphogypsum is ≤5%. In the phosphogypsum, the mass percentage of P2O5 is 2.6%.

[0018] Step two: phosphogypsum acidification, the crushed phosphogypsum is mixed with a 28wt% sulfuric acid solution, stirred at 200rpm at 45℃ for 30min to obtain a first-stage acidification mixed solution, then the first-stage acidification mixed solution is mixed with a 30wt% nitric acid solution, and continues to be stirred at 200rpm at constant temperature, during the stirring process, samples are taken every 5min, the soluble phosphorus concentration is determined by molybdenum-antimony anti-spectrophotometry, until the change amount of the soluble phosphorus concentration in 15min is <1.8mg / L, to obtain a second-stage acidification mixed solution. The mass ratio of the crushed phosphogypsum, the sulfuric acid solution and the nitric acid solution is 1:0.9:0.8.

[0019] Step three: flotation impurity removal, the pH of the second-stage acidification mixed solution is adjusted to 3-4 using a 5wt% calcium hydroxide suspension, after the pH adjustment is completed, diisooctyl phosphate and ethylene glycol are added to the second-stage acidification mixed solution, mixed uniformly, then transferred into a mechanical stirring flotation machine, stirred at 2000rpm at 45℃, while 0.2MPa compressed air is introduced for flotation, the flotation time is 40min, wherein the flow rate of the compressed air is 0.22m 3 / h, after the flotation is completed, a bottom flow liquid is obtained.

[0020] Step four: precipitation impurity removal, polyaluminum chloride is added to the bottom flow liquid, stirred uniformly at 300rpm, then the pH of the bottom flow liquid is adjusted to 5-6 using a calcium hydroxide suspension, stirred at 150rpm at 45℃, after the reaction is completed, the liquid is left to stand, filtered to obtain a filtrate; the addition amount of the polyaluminum chloride is 0.1g / L based on the volume of the bottom flow liquid, the stirring reaction time is 50min, and the standing time is 1h.

[0021] Step five: crystal form conversion, after the filtrate is warmed to 50℃, ammonium sulfate is added to the filtrate, the mass of the ammonium sulfate is 5% of the mass of the crushed phosphogypsum, after stirring at 150 rpm for 90 min, superfine gypsum dihydrate seed crystals with a particle size of 0.5 μm are added to the filtrate, the mass of the superfine gypsum dihydrate seed crystals is 2% of the mass of the crushed phosphogypsum, stirring is performed at 100 rpm for 3 h to induce crystallization, the crystals are centrifuged and washed with water, and after drying, gypsum dihydrate is obtained. The total phosphorus content of the gypsum dihydrate is 0.04% (as P2O5), and the fluoride content of the gypsum dihydrate is 0.008%.

[0022] Example 2 A method for deep dephosphorization and purification of phosphogypsum, comprising the following steps: Step one: phosphogypsum pretreatment, the phosphogypsum is crushed, the particle size of the crushed phosphogypsum is 0.5 mm, and the water content of the crushed phosphogypsum is ≤5%. In the phosphogypsum, the mass percentage of P2O5 is 2.4%.

[0023] Step two: phosphogypsum acidification, the crushed phosphogypsum is mixed uniformly with a sulfuric acid solution with a concentration of 22 wt%, stirring is performed at 300 rpm at 50℃ for 20 min to obtain a first-stage acidification mixed solution, then the first-stage acidification mixed solution is mixed uniformly with a nitric acid solution with a concentration of 40 wt%, and stirring is continued at 300 rpm, during the stirring process, samples are taken every 5 min, the soluble phosphorus concentration is determined by molybdenum-antimony anti-spectrophotometry, and the process is continued until the change amount of the soluble phosphorus concentration within 15 min is <1.8 mg / L, to obtain a second-stage acidification mixed solution. The mass ratio of the crushed phosphogypsum, the sulfuric acid solution, and the nitric acid solution is 1:1.1:0.6.

[0024] Step three: impurity removal by flotation, the pH of the second-stage acidification mixed solution is adjusted to 3-4 using a calcium hydroxide suspension liquid with a concentration of 10 wt%, after the pH adjustment is completed, isooctyl salicylic acid and polypropylene glycol methyl ether are added to the second-stage acidification mixed solution, the mixture is uniformly transferred into a mechanical stirring type flotation machine, stirring is performed at 1500 rpm at 40℃, and 0.3 MPa of compressed air is introduced for flotation, the flotation time is 20 min, wherein the flow rate of the compressed air is 0.28 m 3 / h, after the flotation is completed, a bottom flow liquid is obtained.

[0025] Step four: impurity removal by precipitation, polyaluminum chloride is added to the bottom flow liquid, stirring is performed uniformly at 200 rpm, then the pH of the bottom flow liquid is adjusted to 5-6 using a calcium hydroxide suspension liquid, stirring is performed at 100 rpm at 50℃, after the reaction is completed, the liquid is allowed to stand, filtration is performed, and a filtrate is obtained; the addition amount of the polyaluminum chloride is 0.15 g / L based on the volume of the bottom flow liquid, the stirring time is 65 min, and the standing time is 2 h.

[0026] Step five: crystal form conversion, after the filtrate was warmed to 55℃, sodium sulfate was added to the filtrate, the mass of sodium sulfate was 8% of the mass of the crushed phosphogypsum, after stirring at 200rpm for 60min, superfine gypsum dihydrate seed with a particle size of 2μm was added to the filtrate, the mass of the superfine gypsum dihydrate seed was 5% of the mass of the crushed phosphogypsum, the crystal was induced by stirring at 150rpm for 2h, the crystal was centrifuged and washed with water, and the gypsum dihydrate was obtained after drying. The total phosphorus content of the gypsum dihydrate was 0.05% (calculated as P2O5), and the fluoride content of the gypsum dihydrate was 0.01%.

[0027] Example 3 A method for deep dephosphorization and purification of phosphogypsum, comprising the following steps: Step one: phosphogypsum pretreatment, the phosphogypsum was crushed, the particle size of the crushed phosphogypsum was 0.3mm, and the water content of the crushed phosphogypsum was ≤5%. In the phosphogypsum, the mass percentage of P2O5 was 2.8%.

[0028] Step two: phosphogypsum acidification, the crushed phosphogypsum was mixed with a 25wt% sulfuric acid solution, stirred at 300rpm at 48℃ for 28min to obtain a first-stage acidification mixture, then the first-stage acidification mixture was mixed with a 32wt% nitric acid solution, and the stirring reaction was continued at a constant temperature, during the stirring reaction process, the soluble phosphorus concentration was determined every 5min by molybdenum-antimony anti-spectrophotometry, until the change amount of the soluble phosphorus concentration within 20min was <1.8mg / L, to obtain a second-stage acidification mixture. The mass ratio of the crushed phosphogypsum, the sulfuric acid solution and the nitric acid solution was 1:1:0.7.

[0029] Step three: impurity removal by flotation, the pH of the second-stage acidification mixture was adjusted to 3-4 using a 8wt% calcium hydroxide suspension, after the pH adjustment was completed, dodecyl phosphate and octanol were added to the second-stage acidification mixture, and after mixing uniformly, the mixture was transferred into a mechanical stirring flotation machine, stirred at 1500rpm at 43℃, and at the same time, 0.26MPa of compressed air was introduced for flotation, the flotation time was 35min, wherein the flow rate of the compressed air was 0.23m 3 / h, after the flotation was completed, the underflow liquid was obtained.

[0030] Step four: impurity removal by precipitation, polyaluminum chloride was added to the underflow liquid and stirred uniformly at 200rpm, then the pH of the underflow liquid was adjusted to 5-6 using a calcium hydroxide suspension, and the stirring reaction was carried out at 100rpm at 50℃, after the reaction was completed, the underflow liquid was obtained by standing, filtering, the addition amount of the polyaluminum chloride was 0.12g / L based on the volume of the underflow liquid, the stirring reaction time was 60min, and the standing time was 1.5h.

[0031] Step five: crystal form conversion, after the filtrate was warmed to 55℃, ammonium sulfate was added to the filtrate, the mass of ammonium sulfate was 7% of the mass of the crushed phosphogypsum, after stirring at 200rpm for 75min, superfine gypsum dihydrate seed with a particle size of 1μm was added to the filtrate, the mass of the superfine gypsum dihydrate seed was 5% of the mass of the crushed phosphogypsum, the crystal was induced by stirring at 150rpm for 2h, the crystal was centrifuged and washed with water, after drying, gypsum dihydrate was obtained. The total phosphorus content of the gypsum dihydrate was 0.03% (as P2O5), the fluoride content of the gypsum dihydrate was 0.007%.

[0032] Although the present application has been described in detail by preferred embodiments, the present application is not limited to this. Various equivalent modifications or replacements can be made to the embodiments of the present application by those skilled in the art without departing from the spirit and essence of the present application, and these modifications or replacements shall be within the scope of the present application. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, and these changes or replacements shall be within the protection scope of the present application.

Claims

1. A method for deep dephosphorization and purification of phosphogypsum, characterized in that, Includes the following steps: Step 1: Pretreatment of phosphogypsum, which involves crushing the phosphogypsum; Step 2: Acidification of phosphogypsum. Add the crushed phosphogypsum to the sulfuric acid solution and mix evenly. Stir and react at 45-50℃ for 20-30 minutes to obtain a primary acidification mixture. Then mix the primary acidification mixture with the nitric acid solution evenly and continue to stir and react at a constant temperature until the concentration of soluble phosphorus does not change significantly to obtain a secondary acidification mixture. Step 3: Flotation to remove impurities. The pH of the secondary acidified mixture is adjusted to 3-4 using calcium hydroxide suspension. Then, a collector and a frother are added for flotation to obtain the underflow. Step 4: Precipitation and impurity removal. Add polyaluminum chloride to the underflow and stir until homogeneous. Then, use calcium hydroxide suspension to adjust the pH of the underflow to 5-6. Stir the reaction at 45-50℃. After the reaction is complete, let it stand and filter to obtain the filtrate. Step 5: Crystal transformation. After heating the filtrate to 50-55℃, add sulfate to the filtrate, stir and react, then add ultrafine dihydrate gypsum seed crystals to the filtrate to induce crystallization, separate the crystals and wash them to obtain dihydrate gypsum.

2. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step one, the particle size of the pulverized phosphogypsum is 0.1-0.5 mm.

3. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step two, the concentration of the sulfuric acid solution is 22wt%-28wt%, and the concentration of the nitric acid solution is 30wt%-40wt%.

4. The method for deep dephosphorization and purification of phosphogypsum as described in claim 3, characterized in that, In step two, the mass ratio of the pulverized phosphogypsum, sulfuric acid solution, and nitric acid solution is 1:0.9-1.1:0.6-0.

8.

5. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step two, "no significant change in soluble phosphorus concentration" means that the change in soluble phosphorus concentration within 15-30 minutes is <1.8 mg / L.

6. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step three, the concentration of the calcium hydroxide suspension is 5wt%-10wt%, the collector is alkyl phosphate and / or isooctyl salicylic acid, and the foaming agent is polyfatty alcohol or polypropylene glycol ether.

7. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step three, the flotation temperature is 40-45℃, the flotation time is 20-40 minutes, and compressed air is introduced during the flotation process at a flow rate of 0.22-0.28 m³ / min. 3 / h.

8. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step four, based on the volume of the underflow liquid, the amount of polyaluminum chloride added is 0.1-0.15 g / L, the stirring time is 50-65 min, and the standing time is 1-2 h.

9. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step five, the sulfate is ammonium sulfate or sodium sulfate; the mass of the sulfate is 5%-8% of the mass of the pulverized phosphogypsum; the stirring reaction time is 60-90 minutes.

10. The method for deep dephosphorization and purification of phosphogypsum as described in claim 1, characterized in that, In step five, the particle size of the ultrafine dihydrate gypsum seed crystals is 0.5-2μm; the mass of the ultrafine dihydrate gypsum seed crystals is 2%-5% of the mass of the pulverized phosphogypsum.