A crystal form regulator and application thereof in by-product phosphogypsum of wet-process phosphoric acid

Abstract

The application discloses a crystal form regulator and application thereof in phosphogypsum byproduct of wet-process phosphoric acid, and belongs to the technical field of phosphorus chemical industry.The crystal form regulator is composed of a compound capable of forming aluminum-fluorine complex anions and iron-fluorine complex anions under acidic conditions.The crystal form regulator provided by the application can remove 100% of calcium ions in acidolysis liquid, and can also obtain phosphogypsum with good crystal morphology, and solves the problem that calcium ions in acidolysis liquid after decomposition of phosphate rock by nitric acid or hydrochloric acid cannot be completely precipitated and crystallized from the acid liquid.

Description

Technical Field

[0001] This invention belongs to the field of wet-process phosphoric acid production technology in the phosphate chemical industry, specifically relating to a crystal form regulator and its application in phosphogypsum, a byproduct of wet-process phosphoric acid production. Background Technology

[0002] In current wet-process phosphoric acid production in the phosphate chemical industry, commonly used strong acids include sulfuric acid, nitric acid, and hydrochloric acid. Currently, sulfuric acid is frequently used as the extraction acid in the wet-process phosphoric acid production from phosphate rock. The advantage of this method is that it directly yields well-crystallized calcium sulfate crystals, which facilitates the filtration and separation of phosphogypsum and phosphoric acid. However, the disadvantages are that encapsulation easily occurs during the sulfuric acid decomposition of phosphate rock, leading to incomplete decomposition. Simultaneously, organic matter and impurities from the phosphate rock may adhere to the surface and crystal lattice of the gypsum, resulting in lower whiteness of the phosphogypsum. Furthermore, the limited washing rate results in high impurity content in the phosphogypsum obtained by the sulfuric acid method, leading to significant fluctuations in gypsum quality. For large-scale industrial application, phosphogypsum requires additional pretreatment such as washing and whitening, which significantly increases production costs.

[0003] With the continuous depletion of phosphate rock resources, rich ore is becoming increasingly scarce while lean ore is gradually increasing. Failure to utilize lean ore will result in significant resource waste and ecological damage. By using nitric acid or hydrochloric acid to decompose phosphate rock, flotation can be eliminated, allowing for direct acid hydrolysis to produce phosphoric acid, thus saving on the flotation process and production costs.

[0004] In the decomposition of phosphate rock with nitric acid, due to the lack of technology to control and suppress the crystal morphology of gypsum dihydrate during chemical calcium removal, industrial production enterprises all use sulfate replacement or freezing methods to remove calcium ions. The commonly used reagent in the sulfate replacement calcium removal method is ammonium sulfate. However, due to the lack of technology to control and suppress the crystal morphology of gypsum dihydrate, the resulting gypsum dihydrate produces needle-like whiskers, and the slurry is viscous and difficult to filter and wash. Furthermore, the price of ammonium sulfate is much higher than the price of purchasing sulfuric acid and liquid ammonia separately, making this method costly. The resulting needle-like whisker gypsum dihydrate has limited applications and low economic added value.

[0005] The freezing method for removing calcium ions from acid hydrolysate is currently the mainstream process, with Tianji Coal Chemical Group Co., Ltd. being a representative company. However, the freezing method requires the removal of a large amount of heat, resulting in high energy consumption for refrigeration and significant carbon dioxide emissions. Furthermore, the freezing method only removes 70-80% of calcium ions, leaving 20-30% dissolved in the acid hydrolysate, which significantly reduces the purity of the downstream phosphate and lowers the product grade. The calcium nitrate precipitate formed by cooling crystallization can only be used as an acidic fertilizer in saline-alkali soils, with limited application scope and dosage, resulting in poor economic benefits. Moreover, long-term application of calcium nitrate fertilizer to soil can cause soil compaction, reduce soil permeability, and hinder crop growth.

[0006] When hydrochloric acid is used to decompose phosphate rock, all calcium ions dissolve in the acid hydrolysis solution. Due to a lack of chemical decalcification and crystal form control technology for dihydrate gypsum, industrial enterprises often use sulfuric acid for direct chemical solidification to remove calcium, resulting in needle-like whisker-like dihydrate gypsum. The problems encountered are as described above. Alternatively, some enterprises import organic reagent crystal form control technology from abroad. However, organic reagents have disadvantages such as high price, large usage, toxicity, and reagent residue, which are detrimental to subsequent phosphate production. Summary of the Invention

[0007] Due to a lack of gypsum crystal form control technology, few companies use nitric acid or hydrochloric acid as the extraction acid for phosphate rock decomposition. Most companies choose to directly solidify calcium ions with sulfuric acid, resulting in calcium sulfate dihydrate with poor crystal form for resource utilization. To solve this problem, this invention provides a crystal form control agent that achieves 100% removal of calcium ions from the acid hydrolysis solution, addressing the issue that calcium ions cannot be completely precipitated and crystallized from the acid after phosphate rock decomposition with nitric acid or hydrochloric acid. By adding the crystal form control agent provided by this invention to the acid hydrolysis solution of phosphate rock decomposition with nitric acid or hydrochloric acid, not only are calcium ions completely removed from the acid hydrolysis solution at room temperature, but also gypsum dihydrate with better crystal morphology is obtained.

[0008] The present invention achieves the above objectives through the following technical solutions.

[0009] In a first aspect, the present invention provides a crystal form regulator for use in the wet-process phosphoric acid by-product phosphogypsum process, characterized in that the wet-process phosphoric acid is either nitric acid wet-process phosphoric acid or hydrochloric acid wet-process phosphoric acid.

[0010] The crystal form regulator is composed of one or more pairs of anions and cations, wherein the cations are selected from one or more combinations of lithium ions, sodium ions, potassium ions, ferric ions, ferrous ions, aluminum ions, and ammonium ions; the anions include fluoride ions and hexafluoroferrate ions (FeF6). 3- ), hexafluoroaluminate ion (AlF6) 3- ), tetrafluoroaluminate ion (AlF4) - ), fluorosilicate ions (SiF6) 2- ), fluorophosphate ions (PF6) - ( ), chloride ion, bromide ion, iodide ion, nitrate ion, carbonate ion, oxalate ion, or a combination of two or more of these ions.

[0011] Preferably, the cation is selected from one or more combinations of sodium ions, potassium ions, ferric ions, ferrous ions, aluminum ions, and ammonium ions; the anion includes fluoride ions and hexafluoroferrate ions (FeF6). 3- ), hexafluoroaluminate ion (AlF6) 3- ), tetrafluoroaluminate ion (AlF4) -), fluorosilicate ions (SiF6) 2- One or more of chloride ions.

[0012] Furthermore, the crystal form regulator is composed of compounds that can form aluminum-fluorine complex anions and iron-fluorine complex anions under acidic conditions.

[0013] Preferably, the compound that can form an aluminum-fluorine complex anion under acidic conditions is composed of an aluminum-containing substance and a fluorine-containing substance, wherein the aluminum-containing substance is selected from one or more combinations of alumina, aluminum salts, and fluoroaluminates; and the fluorine-containing substance is selected from one or more combinations of fluoroaluminates, fluorosilicates, fluorophosphates, and fluorine quaternary ammonium salts.

[0014] Preferably, the compound that can form an iron-fluorine complex anion under acidic conditions is composed of an iron-containing substance and a fluorine-containing substance, wherein the iron-containing substance is selected from one or more combinations of iron oxide, ferrous oxide, ferric salt, ferrous salt, and fluoroferrate; and the fluorine-containing substance is selected from one or more combinations of fluoroferrate, fluorosilicate, fluorophosphate, and fluoroquaternary ammonium salt.

[0015] Specifically, the aluminum salt is selected from aluminum chloride and aluminum nitrate;

[0016] The iron salt is selected from ferric chloride and ferric nitrate;

[0017] The ferrous salt is selected from ferrous chloride and ferrous nitrate;

[0018] The fluoroaluminate is selected from sodium fluoroaluminate and potassium fluoroaluminate;

[0019] The fluoroferrate is selected from sodium fluoroferrate and potassium fluoroferrate;

[0020] The fluorosilicate is selected from sodium fluorosilicate and potassium fluorosilicate;

[0021] The fluorophosphate is selected from sodium fluorophosphate and potassium fluorophosphate.

[0022] Specifically, the gypsum crystal form regulator is selected from one or more of the following combinations:

[0023] a) Combinations of fluoroaluminates and fluoroferrates;

[0024] b) Combinations of alumina / aluminum salts and fluoroferrates;

[0025] c) Combinations of ferric / ferrous salts with fluoroaluminates;

[0026] d) Combinations of ferric / ferrous salts and alumina / alumina salts with fluorosilicates;

[0027] e) Combinations of ferric / ferrous salts and alumina / alumina salts with fluoroaluminates;

[0028] f) Combinations of ferric salts / ferrous salts and alumina / alumina salts with fluoroferrates.

[0029] Furthermore, when the decomposition acid of phosphate rock is nitric acid, the gypsum crystal form regulator is selected from one or more of the following combinations:

[0030] I) Combinations of fluoroaluminates and fluoroferrates;

[0031] II) Combinations of alumina / aluminum nitrate and fluoroferrate;

[0032] III) Combinations of ferric nitrate and fluoroaluminate;

[0033] IV) Combinations of ferric nitrate and aluminum oxide / aluminum nitrate with fluorosilicates;

[0034] V) Combinations of ferric nitrate and aluminum oxide / aluminum nitrate with fluoroaluminates;

[0035] VI) Combinations of ferric nitrate and aluminum oxide / aluminum nitrate with fluoroferrate.

[0036] Furthermore, when the decomposition acid of phosphate rock is hydrochloric acid, the gypsum crystal form regulator is selected from one or more of the following combinations:

[0037] I) Combinations of fluoroaluminates and fluoroferrates;

[0038] II) Combinations of alumina / aluminum chloride and fluoroferrates;

[0039] III) Combinations of ferric chloride / ferrous chloride and fluoroaluminate;

[0040] IV) Combinations of ferric chloride / ferrous chloride and alumina / aluminum chloride with fluorosilicates;

[0041] V) Combinations of ferric chloride / ferrous chloride and alumina / aluminum chloride with fluoroaluminates;

[0042] VI) Combinations of ferric chloride / ferrous chloride and alumina / aluminum chloride with fluoroferrates.

[0043] Unless otherwise specified, the " / " in this invention means "or".

[0044] Most preferably, when the decomposition acid of phosphate rock is nitric acid, the gypsum crystal form regulator provided by the present invention is selected from one or more of the following compositions:

[0045]

[0046] When the decomposing acid of phosphate rock is hydrochloric acid, the gypsum crystal form regulator provided by this invention is selected from one or more of the following compositions:

[0047]

[0048] Secondly, the present invention provides the application of a crystal form regulator in phosphogypsum, a byproduct of wet-process phosphoric acid, wherein the wet-process phosphoric acid is nitric acid wet-process phosphoric acid or hydrochloric acid wet-process phosphoric acid.

[0049] Thirdly, the present invention provides a wet-process phosphoric acid by-product phosphogypsum apparatus, characterized in that the apparatus comprises an acid hydrolysis tank, a filtration device 1, a crystallization tank 1, a filtration and washing device, a neutralization tank, a filtration device 2, a nanofiltration membrane 1, a crystallization tank 2, a filtration device 3, and a nanofiltration membrane 2 connected in sequence.

[0050] The acid hydrolysis tank is used for acid decomposition of phosphate rock. The outlet of the acid hydrolysis tank is connected to a filter device 1, through which insoluble matter in the acid hydrolysis solution of phosphate rock is separated. The outlet of the filter device 1 is connected to a crystallization tank 1, through which the acid hydrolysis solution enters the crystallization tank 1 to form phosphogypsum. The outlet of the crystallization tank 1 is connected to a filtration and washing device, through which phosphogypsum is obtained by filtration and washing. The filtrate 1 produced by filtration enters a neutralization tank, where ammonia gas is introduced for neutralization reaction. Liquid ammonia is used to cool the neutralization tank. The outlet of the neutralization tank is connected to a filter device 2, through which industrial monoammonium phosphate and filtrate 2 are obtained. Filtrate 2 passes through a nanofiltration membrane 1, and the purified water produced by nanofiltration can be returned to the acid hydrolysis tank. Filtrate 3 produced by nanofiltration enters the crystallization tank 2 for cooling and crystallization, through which liquid ammonia is used to cool the crystallization tank 2. The outlet of the crystallization tank 2 is connected to a filter device 3, through which the filtrate 4 produced by filtration passes through a nanofiltration membrane 2, and the purified water produced by nanofiltration can be returned to the acid hydrolysis tank. The solid material produced by nanofiltration can be passed back into the crystallization tank 1 for reuse.

[0051] Fourthly, the present invention provides a method for producing phosphogypsum as a byproduct of wet-process phosphoric acid production, characterized in that the method includes: acid hydrolyzing phosphate rock to obtain an acid hydrolysate, filtering to remove insoluble matter, adding a crystal form regulator to the middle of the acid hydrolysate, adding sulfuric acid after the crystal form regulator has dissolved, mixing well, allowing to stand, filtering and washing to obtain phosphogypsum.

[0052] Preferably, the acid used for acid hydrolysis of phosphate rock is nitric acid or hydrochloric acid, with a mass percentage concentration of 25-50% for nitric acid and 15-27% for hydrochloric acid. Based on the calcium ion content in the phosphate rock, the amount of nitric acid or hydrochloric acid added is 1.05-1.15 times the theoretical amount. Specifically, the mass ratio of nitric acid to phosphate rock is (2.18-3.82):1, and the mass ratio of hydrochloric acid to phosphate rock is (1.96-3.50):1.

[0053] The phosphate rock used in the wet-process phosphoric acid has a P2O5 content of 10-30% and a CaO content of 40-70%.

[0054] Preferably, the amount of the crystal form regulator added is 1.0-10.0% of the mass of the acid hydrolysate, specifically selected from 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0%. Depending on the amount of crystal form regulator added, regular rhomboid flakes, flake polycrystalline materials, or granular polycrystalline materials of phosphogypsum can be obtained.

[0055] Preferably, the sulfuric acid concentration is 50-98%, and the amount of sulfuric acid added is based on SO4. 2- With Ca in the acid hydrolysate 2+ The molar mass ratio is 1:1.

[0056] In a specific embodiment of the present invention, the method for producing phosphogypsum as a byproduct of the wet-process phosphoric acid production includes the following steps:

[0057] (1) Add phosphate rock and nitric acid or hydrochloric acid to an acid hydrolysis tank for acid hydrolysis, and filter to remove insoluble substances from the acid hydrolysis solution;

[0058] (2) Transfer the acid hydrolysate to crystallization tank 1, add crystal form regulator, add sulfuric acid after the crystal form regulator dissolves, stir for 0.5-1h, filter and wash to obtain phosphogypsum, enter the neutralization tank, pass ammonia gas, react for 2-3h, filter to obtain industrial monoammonium phosphate and filtrate.

[0059] (3) The filtrate is passed through nanofiltration membrane 1 for nanofiltration. The water produced by nanofiltration is returned to the acid hydrolysis tank. The filtrate is entered into crystallization tank 2 for cooling and crystallization. Ammonium nitrate or ammonium chloride and filtrate are obtained by filtration.

[0060] (4) The filtrate is filtered through nanofiltration membrane 2. The purified water produced by nanofiltration is returned to the acid hydrolysis tank. The resulting concentrated reagent can be passed into crystallization tank 1 for reuse.

[0061] The crystal form regulator provided by this invention has the function of regulating the crystal shape of calcium sulfate dihydrate (phosphogypsum). Those skilled in the art believe that the working principle of the crystal form regulator is as follows: the ions provided by the crystal form regulator couple under acidic conditions to generate aluminum-fluorine complex anions and / or iron-fluorine complex anions, which can reduce the supersaturation of calcium sulfate dihydrate microcrystals in solution and inhibit and slow down the crystallization rate of calcium sulfate dihydrate. Simultaneously, the aluminum-fluorine complex anions and / or iron-fluorine complex anions adhere to the surface of the calcium sulfate dihydrate crystals, inhibiting and slowing down the further crystallization towards SO42-. 2- -Ca 2+ Growth on strong bonds promotes crystal growth towards SO4. 2- -Ca 2+ The growth of secondary strong bonds causes calcium sulfate dihydrate crystals to gradually grow into regular rhomboid plates, plate-like polycrystals, or granular polycrystals.

[0062] The crystal form regulator provided by this invention and the process for producing phosphogypsum as a byproduct of wet-process phosphoric acid production using the crystal form regulator have the following technical advantages:

[0063] 1. This invention solves the problem of preparing phosphoric acid from phosphate rock using the nitric acid and hydrochloric acid methods in the wet-process phosphoric acid production, and directly uses sulfuric acid to chemically solidify Ca. 2+ This study addresses the issue of gypsum crystal form control during the preparation of high-purity purified dihydrate white gypsum by ion exchange, achieving 100% removal of calcium ions from the acid hydrolysate. The production process is characterized by low cost and energy consumption, providing high-quality raw materials for the production and application of downstream gypsum building materials, and yielding significant social and economic benefits.

[0064] 2. The described process flow requires virtually no additional energy to provide heat or utilize secondary energy to cool the acid solution. During the decomposition of phosphate rock with nitric acid, the heat released during nitric acid dilution and the heat of reaction released during phosphate rock decomposition maintain the reaction system temperature between 30-50℃, which meets the optimal temperature requirement for nitric acid decomposition of phosphate rock. Simultaneously, based on the temperature difference between the materials in the neutralization tank and crystallization tank during cooling and crystallization, the heat absorption property of liquid ammonia during vaporization is utilized. By introducing liquid ammonia into the jacketed heat exchange reactor, the neutralization tank can be cooled, reducing ammonia escape rate, while the liquid ammonia also absorbs heat for cooling. This fully utilizes the temperature difference before and after material conversion, meeting production needs while reducing the use of secondary energy and effectively reducing carbon emissions.

[0065] 3. The granular industrial monoammonium phosphate formed by cooling and crystallization in the process provided by this invention has the characteristics of high purity, high economic value, and wide application fields. Compared with the traditional method of monoammonium phosphate, it reduces the physical and chemical drying process of monoammonium phosphate slurry. It utilizes the characteristic of liquid ammonia vaporization to absorb a large amount of heat and uses liquid ammonia to cool and neutralize the monoammonium phosphate slurry in the reaction tank. At the same time, the low temperature is conducive to the cooling and crystallization of monoammonium phosphate, saving a lot of energy consumption. The granular ammonium nitrate formed by cooling can be used as a raw material for the production of high-performance military explosives and agricultural fertilizers. It has the characteristics of high purity, wide application fields, and high economic added value.

[0066] 4. Since the phosphate rock in the wet-process phosphoric acid system already contains ions introduced by the crystal form regulator, the use of the crystal form regulator does not introduce new impurity ions into the system. The crystal form regulator solution concentrated by nanofiltration membrane 2 is returned to crystallization tank 1 to provide crystal form regulation inhibitors for continuous operation in subsequent production. The recycling of the crystal form regulator eliminates the need for further addition of the crystal form regulator in subsequent production; the reagent only needs to be added once.

[0067] 5. This invention uses nanofiltration membranes to concentrate and separate salt solutions, obtaining near-saturated salt solutions and clear water. The nanofiltration membrane has an interception rate of over 90% for divalent and polyvalent salt ions. The clear water obtained by nanofiltration can be returned to the acid hydrolysis tank for recycling in the system. The near-saturated salt solution is beneficial for cooling and crystallization.

[0068] 6. In the method for producing phosphogypsum by-product of hydrochloric acid wet phosphoric acid provided by the present invention, the hydrochloric acid is an industrial waste acid from chemical enterprises such as chlor-alkali industry. The hydrochloric acid method is used to decompose phosphate rock to produce phosphoric acid, which can not only obtain high-quality white dihydrate gypsum, industrial monoammonium phosphate and ammonium chloride products, and improve the economic value of the output materials, but also consume industrial waste hydrochloric acid, reduce environmental pollution, recover useful chemical raw materials, and promote the coordinated development between different chemical industries. Attached Figure Description

[0069] Figure 1 Flow chart of phosphogypsum, a byproduct of the wet process of phosphoric acid production using nitric acid.

[0070] Figure 2 Example 1: SEM image of rhomboid sheet-like single-crystal phosphogypsum.

[0071] Figure 3 Example 2: SEM image of polygonal sheet-like single-crystal phosphogypsum.

[0072] Figure 4 Example 3: SEM image of granular monocrystalline phosphogypsum.

[0073] Figure 5 Example 4: SEM image of spherical polycrystalline phosphogypsum particles.

[0074] Figure 6 Comparative Example 1: SEM image of needle-like whisker phosphogypsum.

[0075] Figure 7 Flow chart of phosphogypsum, a byproduct of the hydrochloric acid wet phosphoric acid process. Detailed Implementation

[0076] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0077] I. Nitric acid wet process for producing phosphogypsum as a byproduct of phosphoric acid production

[0078] The process flow diagram is attached to the instruction manual. Figure 1 As shown.

[0079] The strong acid used in the wet phosphoric acid decomposition of phosphate rock is nitric acid, with a concentration of 30-35%. The phosphate rock has a P2O5 content of 22-28% and a CaO content of 45-50%. The dilution heat released during the dilution with concentrated nitric acid and the reaction heat released during the decomposition of the phosphate rock are utilized. The acidolysis reaction temperature is 42-50℃, requiring no additional heating source.

[0080] Using calcium ions in phosphate rock as the baseline, the amount of nitric acid added is 1.05-1.08 times the theoretical amount. Nitric acid decomposes phosphate rock; the weight ratio of nitric acid added to phosphate rock is 3.03-3.38:1, and the mixture is stirred and held for 1.0-1.5 hours.

[0081] After acidolysis and filtration, a mixed acidolysis solution containing calcium nitrate, nitric acid, and phosphoric acid is obtained. The acidolysis residue is stored in a waste disposal site. The acidolysis solution and crystal form regulator are added to crystallization tank 1. After complete dissolution, sulfuric acid (50% concentration) is added, along with SO42-. 2- With Ca in the acid hydrolysate 2+ When added at a 1:1 ratio, a mixed acid slurry containing dihydrate gypsum is generated in a liquid phase environment. After filtration and washing, phosphogypsum is obtained, which can be directly used in the production of high-end gypsum building materials.

[0082] After high-purity purified white dihydrate gypsum is separated, filtrate 1 containing nitric acid and phosphoric acid is obtained. Filtrate 1 is then passed into a neutralization tank, into which ammonia gas is introduced for neutralization. The neutralization tank is a jacketed heat exchange reactor; liquid ammonia is introduced into the jacket to cool the neutralization tank, maintaining its temperature between 5-14℃. Taking full advantage of the fact that liquid ammonia vaporization requires the absorption of a large amount of heat, liquid ammonia is introduced into the jacketed heat exchange reactor to cool the neutralization tank. Lowering the neutralization tank temperature reduces the amount of ammonia gas that has been heated and leaked out, minimizing raw material loss and facilitating mass transfer during the neutralization reaction. Simultaneously, maintaining the neutralization tank temperature between 5-14℃ promotes the crystallization and precipitation of monoammonium phosphate. After neutralization, filtration is performed to obtain granular industrial monoammonium phosphate and filtrate 2, which is now an ammonium nitrate solution.

[0083] Filtrate 2 is passed through nanofiltration membrane 1 for water-salt separation, yielding clear water and nearly saturated ammonium nitrate filtrate 3. Filtrate 3 is then passed into crystallization tank 2, which also serves as a jacketed heat exchange reactor. Liquid ammonia maintains the temperature in crystallization tank 2 within the range of -10 to -3°C, further cooling the filtrate 3 fed into the crystallization tank, which is beneficial for the cooling and crystallization of ammonium nitrate. Ammonium nitrate is relatively stable at low temperatures, preventing material decomposition or thermal explosion.

[0084] After filtration and separation, granular ammonium nitrate crystals and filtrate 4 are obtained. The granular ammonium nitrate has high purity and can be used as a raw material for the production of high-performance explosives or as agricultural fertilizer. The main component of filtrate 4 is a crystal form regulator. Filtrate 4 is passed through nanofiltration membrane 2 for water-salt separation. The purified water is returned to the acid hydrolysis tank to dilute the concentrated acid, and the concentrated crystal form regulator solution is returned to crystallization tank 1 for recycling.

[0085] (1) The effect of different crystal form regulators on the process of by-product phosphogypsum

[0086] Experimental processes 1-5 were set up, and compositions 1-5 as shown in the table below were added as crystallization agents to crystallization tank 1 of the above-mentioned wet phosphoric acid by-product phosphogypsum process. The amount added was 5.0% of the mass of the acid hydrolysate. After the gypsum precipitated, the Ca content in the acid hydrolysate was measured. 2+ Concentration was recorded, and the crystal form, purity, and whiteness of the by-product phosphogypsum were also recorded. The control group consisted of products without crystal form modifiers.

[0087]

[0088] The results are shown in the table below:

[0089] <![CDATA[Ca in the acid hydrolysis solution 2+ concentration]]> morphology of gypsum crystals Gypsum purity plaster whiteness Process 1 0.02％ flakes 95.47％ 96.9 Process 2 0.00％ flakes 96.04％ 96.3 Process 3 0.01％ flakes 95.52％ 96.5 Process 4 0.00％ flakes 95.57％ 96.3 Process 5 0.01％ flakes 96.61％ 96.4 Comparison process 0.01％ long needle-like 93.81％ 95.2

[0090] The data in the table above shows that when the amount of crystal form regulator added is 5%, any combination of composition 1-5 can be used as the crystal form regulator to prepare flake-shaped phosphogypsum, while the control group without the crystal form regulator can only produce needle-shaped phosphogypsum. This indicates that the crystal form regulator has a good promoting effect on the crystal form regulation of chemically precipitated gypsum.

[0091] Taking the crystal form regulator of Composition 3 as an example, the effect of the amount of crystal form regulator added on the final crystal form and sedimentation rate of phosphogypsum was observed. The acid hydrolysis solution of phosphate rock decomposed by nitric acid was used as the experimental raw material. The CaO content in the acid hydrolysis solution was 23.38%. The reagent of Composition 3 was used as the crystal form regulator, and experiments on the crystal form regulation of dihydrate gypsum were carried out.

[0092] Example 1

[0093] Take 500g of the acid hydrolysis solution and place it in a beaker. Heat it at a constant temperature of 50℃ in a water bath. Add 15g of crystal form regulator (3% of the acid hydrolysis solution mass) to the acid hydrolysis solution. After the regulator is completely dissolved, slowly add 409g of 50% dilute sulfuric acid dropwise to the acid hydrolysis solution. After the dilute sulfuric acid is completely added, continue stirring for 10 minutes. The resulting gypsum dihydrate crystal form is a regular rhombic plate-like single crystal. SEM crystal form image is shown below. Figure 2 As shown, the slurry has good fluidity, and the dihydrate gypsum settles relatively quickly.

[0094] Example 2

[0095] Take 500g of the acid hydrolysis solution and place it in a beaker. Heat it at a constant temperature of 50℃ in a water bath. Add 23g of crystal form regulator (4.6% of the acid hydrolysis solution mass) to the acid hydrolysis solution. After the regulator is completely dissolved, slowly add 409g of 50% dilute sulfuric acid dropwise to the acid hydrolysis solution. After the dilute sulfuric acid is completely added, continue stirring for 10 minutes. The resulting gypsum dihydrate crystal form is a polygonal plate-like single crystal. The SEM image of the crystal form is shown below. Figure 3 As shown, the slurry has good fluidity, and the dihydrate gypsum settles relatively quickly.

[0096] Example 3

[0097] Take 500g of the acid hydrolysis solution and place it in a beaker. Heat it at a constant temperature of 50℃ in a water bath. Add 35g of crystal form regulator (7% of the acid hydrolysis solution mass) to the acid hydrolysis solution. After the regulator is completely dissolved, slowly add 409g of 50% dilute sulfuric acid dropwise to the acid hydrolysis solution. After the dilute sulfuric acid is completely added, continue stirring for 10 minutes. The resulting gypsum dihydrate crystals are granular single crystals. SEM crystal form image is shown below. Figure 4 As shown, the slurry has good fluidity, and the dihydrate gypsum settles relatively quickly.

[0098] Example 4

[0099] Take 500g of the acid hydrolysate and place it in a beaker. Heat it at a constant temperature of 50℃ in a water bath. Add 47g of crystal form regulator (9.4% of the acid hydrolysate mass) to the acid hydrolysate. After the regulator is completely dissolved, slowly add 409g of 50% dilute sulfuric acid dropwise to the acid hydrolysate. After the dilute sulfuric acid is added, continue stirring for 10 minutes. The resulting gypsum dihydrate crystal form is a granular spherical polycrystalline structure. SEM crystal form image is shown below. Figure 5 As shown, the slurry has good fluidity, and the dihydrate gypsum settles relatively quickly.

[0100] Comparative Example 1

[0101] Take 500g of the acid hydrolysis solution and place it in a beaker. Heat the beaker at a constant temperature of 50℃. Slowly add 409g of 50% dilute sulfuric acid to the acid hydrolysis solution. The slurry becomes viscous and loses its fluidity. The resulting dihydrate gypsum crystals are long needle-like whiskers. (SEM image of the crystal structure is shown below.) Figure 6 As shown.

[0102] Due to the large number of pharmaceutical formulations, not all examples are listed in this invention. This does not mean that other combinations of pharmaceuticals cannot be used for crystal form regulation of gypsum dihydrate.

[0103] (2) Effect of different crystal form regulator dosages on the process of by-product phosphogypsum

[0104] Composition 3 was added as a crystallization modifier to crystallization tank 1 in the above-mentioned wet-process phosphoric acid by-product phosphogypsum process. The addition amounts were 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0%, respectively. After the gypsum precipitated, the Ca in the acid hydrolysis solution was measured. 2+ Concentration was recorded, along with the crystal form, purity, and whiteness of the byproduct phosphogypsum. The results are shown in the table below:

[0105] Dosage of crystal form regulator <![CDATA[Ca in the acid hydrolysis solution 2+ concentration]]> morphology of gypsum crystals Gypsum purity plaster whiteness 1.0％ 0.01％ long sheet 95.47％ 96.5 2.0％ 0.00％ Regular rhomboid sheet 96.04％ 96.2 3.0％ 0.01％ Regular rhomboid sheet 95.54％ 96.4 4.0％ 0.00％ Regular rhomboid sheet 95.57％ 96.3 5.0％ 0.01％ polygonal sheet 96.61％ 96.4 6.0％ 0.01％ polygonal sheet 95.81％ 95.2 7.0％ 0.00％ polygonal sheet 96.02％ 96.2 8.0％ 0.02％ Granular single crystal 95.94％ 95.9 9.0％ 0.01％ Granular single crystals and spherical crystals 95.63％ 96.4 10.0％ 0.01％ spherical particles 95.32％ 96.1

[0106] The data in the table above show that as the amount of crystal form regulating agent added increases, the inhibitory effect of the agent on the morphology of calcium sulfate dihydrate crystals gradually strengthens. Based on the experimental results, as the amount of agent added increased from 1.0% to 10.0%, the resulting phosphogypsum crystals gradually changed from long, plate-like shapes to spherical particles.

[0107] II. Hydrochloric acid method for wet-process phosphoric acid production of phosphogypsum as a byproduct

[0108] The process flow diagram is attached to the instruction manual. Figure 7 As shown.

[0109] The strong acid used in the wet phosphoric acid decomposition of phosphate rock is hydrochloric acid, with a concentration of 20-25%. The phosphate rock has a P2O5 content of 22-28% and a CaO content of 45-50%. The dilution heat released during the dilution with concentrated hydrochloric acid and the reaction heat released during the decomposition of the phosphate rock are utilized. The acidolysis reaction temperature is 42-50℃, and no additional heating source is required.

[0110] Using calcium ions in phosphate rock as the baseline, the amount of hydrochloric acid added is 1.05-1.08 times the theoretical amount. Hydrochloric acid is used to decompose phosphate rock, with a weight ratio of hydrochloric acid to phosphate rock of 2.46-2.74:1, and the mixture is stirred and held for 1.0-1.5 hours.

[0111] After acidolysis and filtration, a mixed acidolysis solution containing calcium chloride, hydrochloric acid, and phosphoric acid is obtained. The acidolysis residue is stored in a waste disposal site. The acidolysis solution and crystal form regulator are added to crystallization tank 1. After complete dissolution, sulfuric acid (50% concentration) is added, along with SO42-. 2- With Ca in the acid hydrolysate 2+ When added at a 1:1 ratio, a mixed acid slurry containing gypsum dihydrate is generated in a liquid phase environment. After filtration and washing, phosphogypsum dihydrate is obtained, which can be directly used in the production of high-end gypsum building materials.

[0112] After separation of high-purity purified white dihydrate gypsum, filtrate 1 containing hydrochloric acid and phosphoric acid is obtained. Filtrate 1 is then passed into a neutralization tank, into which ammonia gas is introduced for neutralization. The neutralization tank is a jacketed heat exchange reactor; liquid ammonia is introduced into the jacket to cool the neutralization tank, maintaining the neutralization temperature between 5-14℃. Taking full advantage of the fact that liquid ammonia vaporization requires the absorption of a large amount of heat, liquid ammonia is introduced into the jacketed heat exchange reactor to cool the neutralization tank. Simultaneously, the lower temperature of the neutralization tank reduces ammonia leakage and raw material loss, facilitating mass transfer during the neutralization reaction. Furthermore, the 5-14℃ temperature in the neutralization tank promotes the crystallization and precipitation of monoammonium phosphate. After neutralization, filtration is performed to obtain granular industrial monoammonium phosphate and filtrate 2, which is now an ammonium chloride solution.

[0113] The filtrate 2 is passed through nanofiltration membrane 1 for water-salt separation, yielding clear water and nearly saturated ammonium chloride filtrate 3. The filtrate 3 is then passed into crystallization tank 2, which is also a jacketed heat exchange reactor. Liquid ammonia controls the temperature in crystallization tank 2 within the range of -10 to 0℃, and the liquid ammonia is used to further cool the solution 3 delivered to the crystallization tank, which is beneficial for the cooling and crystallization of ammonium chloride.

[0114] After filtration and separation, granular ammonium chloride crystals and filtrate 4 are obtained. The granular ammonium chloride has high purity and can be used in agriculture, medicine, adhesives, precision casting and other fields. The main component of filtrate 4 is a crystal form regulator. Filtrate 4 is passed through nanofiltration membrane 2 for water and salt separation. The purified water is returned to the acid hydrolysis tank to dilute the concentrated acid, and the concentrated crystal form regulator solution is returned to crystallization tank 1 for recycling.

[0115] (1) The effect of different crystal form regulators on the process of by-product phosphogypsum

[0116] Experimental processes 1-5 were set up, and compositions 1-5 as shown in the table below were added as crystallization agents to crystallization tank 1 of the above-mentioned hydrochloric acid wet process for producing phosphogypsum as a by-product of phosphoric acid. The amount added was 5.0% of the mass of the acid hydrolysate. After the gypsum precipitated, the Ca content in the acid hydrolysate was measured. 2+ Concentration was recorded, and the crystal form, purity, and whiteness of the by-product phosphogypsum were also recorded. The control group consisted of products without crystal form modifiers.

[0117]

[0118] The results are shown in the table below:

[0119]

[0120]

[0121] The data in the table above shows that when the amount of crystal form regulator added is 5%, any one of the crystal form regulators from Composition 1 to Composition 5 can produce flake-like phosphogypsum, while the control group without added crystal form regulator can only produce acicular dihydrate gypsum. This indicates that the crystal form regulator has a good promoting effect on the crystal form regulation of chemically precipitated gypsum.

[0122] The acid hydrolysis solution from the hydrochloric acid method for decomposing phosphate rock was used as the experimental raw material, with a CaO content of 15.83%. Composition 3 was selected as the crystal form regulator, and experiments were conducted to regulate the crystal form of phosphogypsum. The effect of the amount of crystal form regulator added on the final phosphogypsum crystal form and sedimentation rate was observed.

[0123] Example 5

[0124] Take 500g of the acid hydrolysate and place it in a beaker, then heat it at a constant temperature of 50℃ in a water bath. Add 15g of crystal form regulator (3% of the acid hydrolysate mass) to the acid hydrolysate. After the regulator is completely dissolved, slowly add 277g of 50% dilute sulfuric acid dropwise to the acid hydrolysate. After the dilute sulfuric acid is completely added, continue stirring for 10 minutes. The resulting dihydrate gypsum crystals are regular rhomboid plate-like single crystals. The slurry has good fluidity, and the dihydrate gypsum settles quickly.

[0125] Example 6

[0126] Take 500g of the acid hydrolysate and place it in a beaker, then heat it at a constant temperature of 50℃ in a water bath. Add 23g of crystal form regulator (4.6% of the acid hydrolysate mass) to the acid hydrolysate. After the regulator is completely dissolved, slowly add 277g of 50% dilute sulfuric acid dropwise to the acid hydrolysate. After the dilute sulfuric acid is added, continue stirring for 10 minutes. The resulting dihydrate gypsum crystals are polygonal plate-like single crystals. The slurry has good fluidity, and the dihydrate gypsum settles quickly.

[0127] Example 7

[0128] Take 500g of the acid hydrolysate and place it in a beaker, then heat it at a constant temperature of 50℃ in a water bath. Add 35g of crystal form regulator (7% of the acid hydrolysate mass) to the acid hydrolysate. After the regulator is completely dissolved, slowly add 277g of 50% dilute sulfuric acid dropwise to the acid hydrolysate. After the dilute sulfuric acid is completely added, continue stirring for 10 minutes. The resulting dihydrate gypsum crystals are polygonal plate-like single crystals. The slurry has good fluidity, and the dihydrate gypsum settles quickly.

[0129] Example 8

[0130] Take 500g of the acid hydrolysate and place it in a beaker, then heat it at a constant temperature of 55℃ in a water bath. Add 47g of crystal form regulator (9.4% of the acid hydrolysate mass) to the acid hydrolysate. After the regulator is completely dissolved, slowly add 277g of 50% dilute sulfuric acid dropwise to the acid hydrolysate. After the dilute sulfuric acid is completely added, continue stirring for 10 minutes. The resulting dihydrate gypsum crystals are granular and spherical polycrystalline. The slurry has good fluidity, and the dihydrate gypsum settles quickly.

[0131] Comparative Example 2

[0132] Take 500g of the acid hydrolysate in a beaker and heat it at a constant temperature of 50℃ in a water bath. Slowly add 277g of 50% dilute sulfuric acid to the acid hydrolysate. The slurry becomes viscous and loses its fluidity, and the resulting dihydrate gypsum crystals are long needle-like whiskers.

[0133] Due to the large number of pharmaceutical formulations, not all examples are listed in this invention. This does not mean that other combinations of pharmaceuticals cannot be used for crystal form regulation of gypsum dihydrate.

[0134] (2) Effect of different crystal form regulator dosages on the process of by-product phosphogypsum

[0135] Composition 3 was added as a crystallization modifier to crystallization tank 1 in the above-mentioned hydrochloric acid wet process for producing phosphogypsum as a byproduct of phosphoric acid production. The addition amounts were 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0%, respectively. After the gypsum precipitated, the Ca content in the acid hydrolysis solution was measured. 2+ Concentration was recorded, along with the crystal form, purity, and whiteness of the byproduct phosphogypsum. The results are shown in the table below:

[0136]

[0137]

[0138] The data in the table above show that as the amount of crystal form regulating agent added increases, the inhibitory effect of the agent on the morphology of calcium sulfate dihydrate crystals gradually strengthens. Based on the experimental results, as the amount of agent added increased from 1.0% to 10.0%, the resulting phosphogypsum crystals gradually changed from long, plate-like shapes to spherical particles.

[0139] The above specific embodiments are merely illustrative of the invention and do not represent a limitation thereof. Those skilled in the art will recognize that other variations of the specific structure of this invention are possible.

Claims

1. A crystal form regulator, said crystal form regulator being used in the wet-process phosphoric acid by-product phosphogypsum process, characterized in that, The wet-process phosphoric acid is either nitric acid wet-process phosphoric acid or hydrochloric acid wet-process phosphoric acid; The crystal form regulator is composed of a compound that can form aluminum-fluorine complex anions and iron-fluorine complex anions under acidic conditions; the crystal form regulator is composed of one or more pairs of anions and cations, wherein the cations are composed of iron ions and / or ferrous ions, and aluminum ions; the anions include one or more combinations of fluoride ions, hexafluoroferrate ions, hexafluoroaluminate ions, tetrafluoroaluminate ions, fluorosilicate ions, and fluorophosphate ions.

2. The crystal form regulator according to claim 1, characterized in that, Compounds that can form aluminum-fluorine complex anions under acidic conditions are composed of aluminum-containing substances and fluorine-containing substances, wherein the aluminum-containing substances are selected from one or more combinations of aluminum salts and fluoroaluminates; and the fluorine-containing substances are selected from one or more combinations of fluoroaluminates, fluorosilicates, fluorophosphates, and fluorine quaternary ammonium salts. Compounds that can form iron-fluorine complex anions under acidic conditions are groups composed of iron-containing substances and fluorine-containing substances, wherein the iron-containing substances are selected from one or more combinations of ferric salts, ferrous salts, and fluoroferrates; and the fluorine-containing substances are selected from one or more combinations of fluoroferrates, fluorosilicates, fluorophosphates, and fluoroquaternary ammonium salts.

3. The crystal form regulator according to claim 2, characterized in that, The aluminum salt is selected from aluminum chloride and aluminum nitrate; the iron salt is selected from ferric chloride and ferric nitrate; the ferrous salt is selected from ferrous chloride and ferrous nitrate; the fluoroaluminate is selected from sodium fluoroaluminate and potassium fluoroaluminate; the fluoroferrate is selected from sodium fluoroferrate and potassium fluoroferrate; the fluorosilicate is selected from sodium fluorosilicate and potassium fluorosilicate; and the fluorophosphate is selected from sodium fluorophosphate and potassium fluorophosphate.

4. The crystal form regulator according to claim 2, characterized in that, The crystal form regulator is selected from one or more of the following combinations: a) Combinations of fluoroaluminates and fluoroferrates; b) Combinations of aluminum salts and fluoroferrates; c) Combinations of ferric / ferrous salts with fluoroaluminates; d) Combinations of ferric / ferrous salts and aluminum salts with fluorosilicates; e) Combinations of ferric / ferrous salts and aluminum salts with fluoroaluminates; f) Combinations of ferric / ferrous salts and aluminum salts with fluoroferrates.

5. The crystal form regulator according to claim 4, characterized in that, When the decomposition acid of phosphate rock is nitric acid, the crystal form regulator is selected from one or more of the following combinations: I) Combinations of fluoroaluminates and fluoroferrates; II) A combination of aluminum nitrate and fluoroferrate; III) Combinations of ferric nitrate and fluoroaluminate; IV) Combinations of ferric nitrate and aluminum nitrate with fluorosilicates; V) Combinations of ferric nitrate and aluminum nitrate with fluoroaluminates; VI) Combinations of ferric nitrate and aluminum nitrate with fluoroferrates; When the decomposition acid of phosphate rock is hydrochloric acid, the crystal form regulator is selected from one or more of the following combinations: I) Combinations of fluoroaluminates and fluoroferrates; II) A combination of aluminum chloride and fluoroferrate; III) Combinations of ferric chloride / ferrous chloride and fluoroaluminate; IV) Combinations of ferric chloride / ferrous chloride and aluminum chloride with fluorosilicates; V) Combinations of ferric chloride / ferrous chloride and aluminum chloride with fluoroaluminates; VI) Combinations of ferric chloride / ferrous chloride and aluminum chloride with fluoroferrates.

6. The application of the crystal form regulator according to any one of claims 1-5 in the process of producing phosphogypsum as a byproduct of nitric acid wet phosphoric acid or hydrochloric acid wet phosphoric acid.

7. A method for producing phosphogypsum as a byproduct of phosphoric acid production via wet processing, characterized in that, The method includes: acidifying phosphate rock with acid to obtain an acid hydrolysate, filtering to remove insoluble matter, adding the crystal form regulator according to any one of claims 1-5 to the acid hydrolysate, adding sulfuric acid after the crystal form regulator has dissolved, mixing, allowing to stand, filtering and washing to obtain phosphogypsum. Specifically, the acid used for acid hydrolysis of phosphate rock is nitric acid or hydrochloric acid, with a mass percentage concentration of 25-50% for nitric acid and 15-27% for hydrochloric acid. The amount of crystal form regulator added is 1.0-10.0% of the mass of the acid hydrolysis solution.

8. The method according to claim 7, characterized in that, The method for producing phosphogypsum as a byproduct of the wet-process phosphoric acid production includes the following steps: (1) Add phosphate rock and nitric acid or hydrochloric acid to an acid hydrolysis tank for acid hydrolysis, and filter to remove insoluble substances from the acid hydrolysis solution; (2) Transfer the acid hydrolysate to the crystallization tank, add the crystal form regulator, add sulfuric acid after the crystal form regulator dissolves, stir for 0.5-1h, filter and wash to obtain phosphogypsum, enter the neutralization tank, pass ammonia gas, react for 2-3h, filter to obtain industrial monoammonium phosphate and filtrate. (3) The filtrate is passed through a nanofiltration membrane for nanofiltration. The purified water produced by nanofiltration is returned to the acid hydrolysis tank. The filtrate produced enters the crystallization tank for cooling and crystallization. The filtrate is then filtered to obtain ammonium nitrate or ammonium chloride and the filtrate. (4) The filtrate is filtered through a nanofiltration membrane. The purified water produced by nanofiltration is returned to the acid hydrolysis tank, and the resulting concentrate can be passed into the crystallization tank for reuse.

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