A wet phosphoric acid processing process for recovering fluorine

Abstract

The present application discloses a method for wet-process phosphoric acid to recover fluorine, which includes: an acidolysis step: reacting fluorapatite ore powder containing 26%-28% water with concentrated sulfuric acid, maintaining the reaction temperature above 135°C to generate a fluorine-containing gas and a defluorinated slurry containing anhydrous calcium sulfate, wherein the mass fraction of P2O5 in the defluorinated slurry containing calcium sulfate is greater than or equal to 55%, and the fluorine content is 200 ppm to 2000 ppm; an absorption step: absorbing the fluorine-containing gas with an absorption liquid to obtain a fluorine-containing solution, wherein the fluorine in the fluorine-containing solution accounts for more than 95 wt% of the fluorine in the fluorapatite ore powder; a crystal form reconstruction step: performing crystal form reconstruction on the defluorinated slurry containing anhydrous calcium sulfate and filtering to obtain a hemihydrate calcium sulfate filter cake and a filtrate containing phosphoric acid.

Description

Technical Field

[0001] The invention belongs to the field of wet-process phosphoric acid preparation and relates to a new wet-process phosphoric acid process for fluorine recovery. Background Art

[0002] Fluorine is a valuable national strategic resource. In nature, fluorine resources exist in three main forms: fluorite, the main component of which is CaF2; cryolite, the main component of which is Na3AlF6; and fluoroapatite, the main component of which is Ca5(PO4)3F. With the rapid development of my country's fluorine chemical industry, especially the rapid development of the new energy industry, the shortage of fluorite resources has become increasingly prominent. Phosphate ore, which is mainly composed of fluoroapatite, contains 3%-4% fluorine, and contains more than 90% of the fluorine resources in nature. In the process of wet processing of phosphoric acid dihydrate by phosphate ore, the fluorine after acid hydrolysis of phosphate ore is roughly distributed as follows: about 5% to 10% escapes from the gas phase of phosphate ore decomposition, 20% to 25% is taken away by the gypsum solid phase, and 65% to 70% is retained in the liquid phase of phosphoric acid. Among them, the fluorine escaped from the gas phase in the phosphoric acid concentration section accounts for 40% to 45% of the total fluorine in the phosphate ore.

[0003] The prior art (Document 1: "The occurrence form and recovery status and prospects of associated fluorine in wet-process phosphoric acid", He Binbin et al., "Phosphate Fertilizer and Compound Fertilizer", Vol. 38, No. 12, published on December 15, 2023) reported a method for recovering fluorine released from the gas phase during the decomposition of phosphate ore, but the fluorine content released was only 5% to 10% of the total fluorine in the phosphate ore, and the economic benefits after industrialization were difficult to pass. The prior art (Document 2: "Fluorine release and deep defluorination during vacuum concentration of wet-process phosphoric acid", Cheng Defu, "Fertilizer Industry", No. 03, published on June 28, 1997) reported that the release rate of fluorine released from the gas phase is mainly related to the concentration of phosphoric acid in the slurry. As the concentration of phosphoric acid increases, the fluorine release rate increases, and the HF / SiF4 molar ratio in the gas phase changes from small to large. When the phosphoric acid concentration reaches 52% P2O5, the HF / SiF4 molar ratio is greater than 2, and there will be no silica gel precipitation in the fluorine absorption system, which is the most ideal operating state. In addition, the structural form and content of SiO2 in phosphate ore will also affect the release of gaseous fluorine during the decomposition of phosphate ore. When SiO2 exists in a crystalline structure (such as quartz with a regular tetrahedral configuration), it is an inert substance in the process, but when it exists in amorphous SiO2 of clay type, its structure has no specific unit cell parameters and crystal X-diffraction spectrum, and the arrangement between molecules is in an irregular state, which is reactive and is called active SiO2. According to the chemical reaction formula: 2H2SiF6+SiO2→3SiF4↑+2H2O, the fluorosilicic acid solution will react with the active SiO2 in the slurry and quickly release SiF4 gas. Therefore, an increase in the active SiO2 content or a decrease in the water content in the acidolysis slurry will be conducive to the forward reaction, thereby increasing the release rate of fluorine released from the acidolysis gas phase.

[0004] The existing technologies (such as CN110467167B, CN112279231A, CN105236372A, CN104176719B, CN112875662B, etc.; Document 3: "A Brief Analysis of the Principle of Defluorination Reaction in Wet-process Phosphoric Acid", Zhang Haiyan et al., "Inorganic Salt Industry", Vol. 47, No. 01, published on January 10, 2015; Document 4: "Measures for Improving Fluorine Recovery Rate in Wet-process Phosphoric Acid Production", Teng Minghui, "Hebei Chemical Industry", Vol. 35, No. 8, published on August 20, 2012) mainly study the removal and recovery methods of 65% to 70% of fluorine entering the liquid phosphoric acid, including chemical precipitation method, concentration method, gas stripping method and solvent extraction technology. Among them, the chemical precipitation method requires the addition of metal salts as precipitants in the wet-process phosphoric acid solution, Al 3+ It has strong interference with the defluorination method of chemical precipitation; the concentration method consumes a lot of heat to concentrate the dilute phosphoric acid, and the evaporation efficiency is limited. The P2O5 content of concentrated phosphoric acid is less than 53%, and the fluorine yield is less than 50%. Most of the fluorine enters phosphorus chemical products such as phosphate fertilizer, causing resource waste and potential environmental risks; the gas stripping method requires heating the phosphoric acid to a certain temperature and introducing steam to remove the escaped fluorine, which consumes a lot of heat; the solvent extraction method is difficult to recover the solvent and the process flow is complicated.

[0005] About 20% to 25% of fluorine enters phosphogypsum. The existing technology (such as CN102502551A, Document 5: "Experimental Study on the Removal of Water-soluble Phosphorus and Water-soluble Fluorine from Phosphogypsum", Zhang Lizhen et al., "Inorganic Salt Industry", Vol. 54, No. 4, published on April 9, 2022) reported that the lime neutralization process can only achieve the effective removal of water-soluble phosphorus and water-soluble fluorine, with average removal rates of 74.95% and 76.20%, respectively. The mass fractions can be reduced to 0.090% and 0.043% on average. The quality of the treated phosphogypsum only meets the secondary product index requirements of GB / T23456-2018 "Phosphogypsum", which limits the resource quality of phosphogypsum and the quality of deep-processing products. Therefore, it is particularly important to develop a new process for wet processing phosphoric acid that can efficiently and low-costly recover the associated fluorine resources in wet-process phosphoric acid. This can not only provide a large amount of raw material sources for the fluorine chemical industry and avoid the loss of precious fluorine resources, but also efficiently remove harmful impurities in phosphogypsum and realize the comprehensive utilization of phosphogypsum.

[0006] In addition, in the process of wet processing of phosphoric acid from phosphate ore, sulfuric acid decomposing phosphate ore (acid hydrolysis) will generate a large amount of reaction heat. In addition to the heat required to maintain the reaction temperature of the slurry, a large amount of residual heat needs to be removed. SEDahlgren calculated the reaction heat of acid hydrolysis of the dihydrate, hemihydrate, and anhydrous processes. The results showed that at the same sulfuric acid concentration, the reaction heat generated during acid hydrolysis of the anhydrous process was much less than that of the dihydrate process, and there was almost no residual heat that needed to be removed. At the same time, the sulfuric acid concentration also affects the reaction heat of acid hydrolysis. The higher the sulfuric acid concentration used, the greater the reaction heat generated. The prior art (Wu Peizhi, "Wet-process Phosphoric Acid", Chemical Industry Press, 1987: pp. 22-24, 178-183) reported the use of an anhydrous process. When the mass fraction of sulfuric acid used is 98%, the pipeline and the reactor are strictly insulated, the reaction heat is sufficient to maintain the necessary temperature of the reaction materials, and only a small amount of residual heat needs to be removed, and the slurry cooling problem is also better solved. At the same time, the fluorine escape rate during acid hydrolysis can reach more than 80%, and the P2O5 mass fraction of the finished phosphoric acid can reach more than 40%. However, after long-term production and scientific research practice, it has been confirmed that the anhydrous process has fine crystals, difficult liquid-solid phase separation, and is difficult to achieve industrialization. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a new process for wet processing phosphoric acid with efficient fluorine recovery, so as to produce high-concentration phosphoric acid with low fluorine content and high-quality phosphogypsum, and produce high-purity fluorosilicic acid solution as a by-product, thereby achieving efficient recovery of fluorine and comprehensive utilization of phosphogypsum, and improving resource, environmental and economic benefits.

[0008] This application includes the following implementation methods:

[0009] Embodiment 1. A method for wet processing phosphoric acid to recover fluorine, comprising:

[0010] Acid hydrolysis step: directly reacting fluorapatite ore powder containing 26%-28% water with concentrated sulfuric acid, maintaining the reaction temperature above 135° C., generating fluorine-containing gas and a defluorination slurry containing anhydrous calcium sulfate, wherein the mass fraction of P2O5 in the defluorination slurry containing calcium sulfate is greater than or equal to 55%, greater than 58%, greater than 59%, or even greater than 60%, and the fluorine content is 200ppm to 2000ppm;

[0011] Absorption step: absorbing the fluorine-containing gas with an absorption liquid to obtain a fluorine-containing solution, wherein the fluorine in the fluorine-containing solution accounts for more than 95wt% of the fluorine in the fluorapatite ore powder;

[0012] Crystal reconstruction step: The defluorination slurry containing anhydrous calcium sulfate is subjected to crystal reconstruction and filtered to obtain a calcium sulfate hemihydrate filter cake and a filtrate containing phosphoric acid.

[0013] Embodiment 2. The method according to embodiment 1, wherein the D50 of the fluorapatite powder is 200 mesh or higher. The term D50 in this application has the meaning commonly understood by those skilled in the art, indicating the diameter of the cumulative 50wt% point (or 50wt% passing particle size).

[0014] Embodiment 3. The method according to embodiment 1, wherein the concentration of the concentrated sulfuric acid is above 97 wt %, and the amount of the concentrated sulfuric acid used is 105% to 110% of the amount required for the acidolysis step.

[0015] Embodiment 4. A method according to embodiment 1, wherein the mass fraction of P2O5 in the fluorapatite ore powder is 20% to 35%, the mass fraction of fluorine is 3% to 4%, and the content of amorphous silicon dioxide is greater than or equal to 4.8wt%.

[0016] Embodiment 5. The method according to embodiment 1, wherein amorphous silicon dioxide is added to the fluorapatite mineral powder so that the amorphous silicon dioxide content in the fluorapatite mineral powder is greater than or equal to 4.8 wt%.

[0017] Embodiment 6. A method according to embodiment 1, wherein the absorption liquid is an aqueous solution with a fluorosilicic acid content of less than 18 wt %, and in the absorption step, the absorption liquid temperature is controlled at 50°C to 55°C, the vacuum degree is 86.6 kPa to 93.3 kPa, and the fluorine-containing solution is an aqueous solution of fluorosilicic acid.

[0018] Embodiment 7. A method according to embodiment 1, wherein the fluoroapatite ore powder containing 26%-28% water is prepared by the following method: crushing the fluoroapatite into ore with a particle size of less than 25 mm, grinding the ore in a ball mill, and adding water in a certain ratio to obtain a slurry, and then the slurry is settled by a thickener, and the settled slurry is filter-filtered to obtain the fluoroapatite ore powder containing 26%-28% water.

[0019] Embodiment 8. The method according to embodiment 1, wherein the acid hydrolysis step is performed in a polytetrafluoroethylene container.

[0020] Embodiment 9. A method according to embodiment 1, wherein the mass fraction of α-CaSO4·0.5H2O in the calcium sulfate hemihydrate filter cake is greater than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are less than 800 ppm and 200 ppm, respectively; the mass fraction of P2O5 in the filtrate containing phosphoric acid is 40% to 45%, and the mass fraction of water-soluble fluorine is 100 ppm to 1000 ppm.

[0021] Embodiment 10. The method according to embodiment 1, wherein the temperature in the acid hydrolysis reaction is maintained above 135°C, preferably above 145°C, and the temperature in the acid hydrolysis reaction is maintained below 155°C, or below 153°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The method of the present invention is to mix wet phosphate ore powder with concentrated sulfuric acid to undergo acid hydrolysis reaction to obtain a slurry with a P2O5 mass fraction of more than 55%. Due to the increase in phosphoric acid concentration, the gas phase fluorine escape rate is increased from more than 30% to more than 95%. Water is used for countercurrent circulation to absorb fluorine-containing gas, and fluorosilicic acid solution is transferred in time. Fresh water is appropriately added to control the concentration of fluorosilicic acid solution within 18%, ensure that the fluorine-containing gas absorption rate is more than 95%, and realize the efficient recovery and utilization of fluorine resources associated with phosphate ore.

[0024] 2. The heat released by the mixed reaction of the method of the present invention is sufficient to maintain the temperature of the reaction materials at 135°C to 155°C, and the mass fraction of P2O5 in the obtained phosphoric acid product is 40% to 45%, and the mass fraction of water-soluble fluorine is 100ppm to 1000ppm, which can be directly used without concentration, thereby reducing heat energy consumption; at the same time, the residual heat released by the acidolysis reaction is fully utilized to preheat the required air or steam, thereby further reducing energy consumption and reducing production costs.

[0025] 3. The mass fraction of α-CaSO4·0.5H2O in the phosphogypsum product obtained after crystal reconstruction by the method of the present invention is more than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are less than 800ppm and 200ppm respectively. The phosphogypsum has high quality, coarse particles, easy to filter and separate, high strength and can be widely used in building materials, medical materials, functional materials and other fields, thereby realizing the high added value of phosphogypsum.

[0026] In addition, the technical solution of the present invention also brings many other advantages, which will be described in detail in the specific implementation manner.

[0027] It is to be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0029] Figure 1 The process flow chart of the present application method. DETAILED DESCRIPTION

[0030] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The example embodiments can be implemented in various forms and should not be understood as being limited to the embodiments described herein. On the contrary, these embodiments are provided so that the present invention will be comprehensive and complete, and the concepts of the example embodiments will be fully conveyed to those skilled in the art. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without the need for creative work are within the scope of protection of the present disclosure.

[0031] In addition, the described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present invention. However, those skilled in the art will appreciate that the technical solution of the present invention can be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, known methods, devices, implementations or operations are not shown or described in detail to avoid blurring various aspects of the present invention.

[0032] In one aspect, the present invention provides a method for wet processing phosphoric acid for recovering fluorine, comprising:

[0033] Acid hydrolysis step: directly reacting fluorapatite ore powder containing 26%-28% water with concentrated sulfuric acid, maintaining the reaction temperature above 135°C, to generate fluorine-containing gas and a defluorination slurry containing anhydrous calcium sulfate, wherein the mass fraction of P2O5 in the defluorination slurry containing calcium sulfate is greater than or equal to 55%, and the fluorine content is 200ppm-2000ppm;

[0034] Absorption step: absorbing the fluorine-containing gas with an absorption liquid to obtain a fluorine-containing solution, wherein the fluorine in the fluorine-containing solution accounts for more than 95wt% of the fluorine in the fluorapatite ore powder;

[0035] Crystal reconstruction step: The defluorination slurry containing anhydrous calcium sulfate is crystal reconstructed and filtered to obtain a hemihydrate calcium sulfate filter cake and a filtrate containing phosphoric acid. In the method of the present invention, wet phosphate rock powder is mixed with concentrated sulfuric acid to undergo an acidolysis reaction to obtain a slurry with a P2O5 mass fraction of more than 55%. Due to the increase in the concentration of phosphoric acid, the gas phase fluorine escape rate is increased from more than 30% to more than 95%. Water is used for countercurrent circulation to absorb fluorine-containing gas, and the fluorosilicic acid solution is transferred in time. Fresh water is appropriately added to control the concentration of the fluorosilicic acid solution within 18%, and the fluorine-containing gas absorption rate is guaranteed to be more than 95%, thereby achieving the technical effect of efficient recovery and utilization of fluorine resources associated with phosphate rock. The expression "slurry with a P2O5 mass fraction of more than 55%" in this application means that the phosphorus content in the slurry is more than 55wt% based on the mass of P2O5. Similar terms in this application also have similar meanings.

[0036] In some embodiments, the fluorapatite powder has a particle size of 60 wt% to 70 wt% and is past 200 mesh.

[0037] In some embodiments, the concentration of the concentrated sulfuric acid is above 97 wt %, and the amount of the concentrated sulfuric acid used is 105% to 110% of the amount required for the acidolysis step.

[0038] In some embodiments, the P2O5 mass fraction in the fluorapatite ore powder is 20% to 35%, the fluorine mass fraction is 3% to 4%, and the amorphous silicon dioxide content is greater than or equal to 4.8wt%.

[0039] In some embodiments, amorphous silicon dioxide is added to the fluorapatite mineral powder, so that the content of amorphous silicon dioxide in the fluorapatite mineral powder is greater than or equal to 4.8 wt %.

[0040] In some embodiments, the absorption liquid is an aqueous solution with a fluorosilicic acid content of 10 wt% to 18 wt%. In the absorption step, the temperature of the absorption liquid is controlled at 50°C to 55°C, the vacuum degree is 86.6 kPa to 93.3 kPa, and the fluorine-containing solution is an aqueous solution of fluorosilicic acid.

[0041] In some embodiments, the fluoroapatite ore powder containing 26%-28% water is prepared by the following method: crushing the fluoroapatite into crushed ore with a particle size of less than 25 mm, grinding the crushed ore in a ball mill, and adding water in a certain ratio to obtain a slurry, and then the slurry is settled by a thickener, and the settled slurry is filter-filtered to obtain the fluoroapatite ore powder containing 26%-28% water.

[0042] In some embodiments, the acid hydrolysis step is performed in a polytetrafluoroethylene container.

[0043] In some embodiments, the mass fraction of α-CaSO4·0.5H2O in the calcium sulfate hemihydrate filter cake is greater than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are less than 800 ppm and 200 ppm, respectively; the mass fraction of P2O5 in the filtrate containing phosphoric acid is 40% to 45%, and the mass fraction of water-soluble fluorine is 100 ppm to 1000 ppm.

[0044] In some embodiments, the temperature during the acid hydrolysis reaction is maintained above 135°C, preferably above 145°C, and the temperature during the acid hydrolysis reaction is maintained below 155°C, preferably below 153°C.

[0045] The heat released by the mixed reaction of the method described in the above embodiment is sufficient to maintain the temperature of the reaction materials at 135°C to 155°C, and the mass fraction of P2O5 in the obtained phosphoric acid product is 40% to 45%, and the mass fraction of water-soluble fluorine is 100ppm to 1000ppm, which can be directly used without concentration, thereby reducing heat energy consumption; at the same time, the residual heat released by the acidolysis reaction is fully utilized to preheat the required air or steam, thereby further reducing energy consumption and reducing production costs.

[0046] The mass fraction of α-CaSO4·0.5H2O in the phosphogypsum product obtained after the crystal reconstruction by the method described in the above embodiment is more than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are respectively less than 800ppm and 200ppm. The phosphogypsum has high quality, coarse particles, easy to filter and separate, high strength and can be widely used in building materials, medical materials, functional materials and other fields, thereby realizing high added value utilization of phosphogypsum.

[0047] In some embodiments, the temperature in the acidolysis reaction is maintained between 148°C and 152°C. At this temperature, the best reaction effect can be obtained, and the mass fraction of P2O5 in the defluorination slurry containing anhydrous calcium sulfate is greater than or equal to 60%, and the fluorine content is 210ppm to 300ppm. The fluorine escape rate is the highest, so in the absorption step, the fluorine-containing gas is absorbed by an absorption liquid to obtain a fluorine-containing solution, wherein the fluorine in the fluorine-containing solution accounts for more than 99wt% of the fluorine in the fluoroapatite ore powder. This result can be seen from Example 3.

[0048] Glossary: ​​The term "α-CaSO4·0.5H2O" is the chemical molecular formula of calcium sulfate hemihydrate.

[0049] The method of the present invention is described below using specific process steps. It should be noted that the reaction conditions of each step used in the specific process steps can be applied separately to other embodiments without repeated description.

[0050] The novel wet process for processing phosphoric acid for recovering fluorine described in the present invention has the following specific process steps:

[0051] (1) The phosphate rock is crushed into ore with a particle size of less than 25 mm, fed into a ball mill, and water is added quantitatively according to a certain ratio. The resulting slurry is settled through a thickener, and the settled slurry is filtered. The filtrate is recycled in the ball milling process, and the wet ore powder enters the acid hydrolysis reaction process;

[0052] (2) The wet mineral powder and excess concentrated sulfuric acid are subjected to an acid hydrolysis mixed reaction in a polytetrafluoroethylene reactor at a reaction temperature of 135° C. to 155° C. for a reaction time of 4 h to 6 h. The escaping fluorine gas enters the fluorine absorption process, and the defluorinated slurry enters the crystal reconstruction process;

[0053] (3) absorbing the fluorine gas released in step (2) by countercurrent circulation with water, wherein the temperature of the absorption liquid is controlled at 50° C. to 55° C. and the vacuum degree of the absorption system is 86.6 kPa to 93.3 kPa, to obtain a fluorosilicic acid product;

[0054] (4) transporting the defluorinated slurry obtained in step (2) to a crystallization tank, adding a certain amount of water to reconstruct the crystal form of calcium sulfate, the slurry liquid-to-solid ratio is 2.5-4:1, the reaction temperature is 110° C.-120° C., the reaction time is 3 h-4 h, and the anhydrous calcium sulfate is converted into hemihydrate calcium sulfate;

[0055] (5) The slurry obtained in step (4) is filtered, and the filtrate enters a phosphoric acid product collection tank. The filter cake is washed three times in countercurrent with water and dried to obtain a by-product, phosphogypsum.

[0056] In step (1) of the above method, the mass fraction of P2O5 in the phosphate rock is 20% to 35%, and the mass fraction of fluorine is 3% to 4%.

[0057] In step (1) of the above method, the water first added in the ball milling process is fresh water, and the water added thereto is recycled filtrate. The moisture content of the obtained wet mineral powder is 26% to 28%, and the fineness is more than 50% and less than 200 mesh.

[0058] In step (2) of the above method, the amount of sulfuric acid used is 105% to 110% of the chemically measured quota for acid hydrolysis of phosphate rock, and the mass fraction of sulfuric acid is 98%.

[0059] In step (2) of the above method, the reaction equation of the phosphate rock acid hydrolysis process is:

[0060] Ca5F(PO4)3+5H2SO4→3H3PO4+5CaSO4+HF↑①

[0061] The HF generated by the reaction interacts with the active SiO2 mixed in the phosphate rock, and the chemical reaction equation is as follows:

[0062] 4HF+SiO2→SiF4+2H2O ②

[0063] 6HF+SiO2 → H2SiF6+2H2O ③

[0064] 2HF+ SiF4→ H2SiF6 ④

[0065] When the mass fraction of P2O5 in the reaction slurry reaches more than 55% and the reaction temperature is between 135℃ and 155℃, fluorosilicic acid will decompose into the following formula:

[0066] H2SiF6 →2HF↑+ SiF4↑ ⑤

[0067] When the active SiO2 content in the phosphate rock is higher than 4.8%, the decomposition of fluorosilicic acid will intensify, and the chemical reaction equation is as follows:

[0068] 2H2SiF6+SiO2→3SiF4↑+2H2O ⑥

[0069] The heat released by the acidolysis reaction is sufficient to maintain the temperature of the reaction materials at 135°C to 155°C. The escape rate of gaseous fluorine generated by the reaction can reach more than 95%, the mass fraction of P2O5 in the defluorination slurry is more than 55%, and the fluorine content is 200ppm to 2000ppm.

[0070] In step (3) of the above method, the reaction equation of the fluorine-containing gas absorption process is:

[0071] SiF4+2HF+nH2O→H2SiF6+ nH2O ⑦

[0072] 3SiF4+ (2+n)H2O→2H2SiF6+SiO2·nH2O↓ ⑧

[0073] 6HF+ SiO2·nH2O→H2SiF6+(2+n)H2O ⑨

[0074] In order to ensure the absorption rate of fluorine-containing gas, fresh water needs to be appropriately added to control the fluorosilicic acid content of the fluorosilicic acid solution to 10wt%-18wt%, the purity of the fluorosilicic acid solution to be above 95%, and the absorption rate of fluorine-containing gas to be above 95%.

[0075] In step (4) of the above method, the reaction equation for the crystal reconstruction process of calcium sulfate is:

[0076] CaSO4(Ⅱ)+ 0.5H2O→α-CaSO4·0.5H2O ⑩

[0077] Preferably, the water added in the crystal reconstruction process is gypsum washing liquid.

[0078] In step (5) of the above method, the mass fraction of P2O5 in the obtained phosphoric acid product is 40% to 45%, the mass fraction of water-soluble fluorine is 100 ppm to 1000 ppm, the mass fraction of α-CaSO4·0.5H2O in the obtained phosphogypsum product is more than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are less than 800 ppm and 200 ppm, respectively.

[0079] Instructions attached Figure 1 The process flow chart of the present application is schematically described, which can better understand the method and process principle of the present application.

[0080] The process principle of this application is: wet phosphate ore powder is mixed with concentrated sulfuric acid to undergo an acid hydrolysis reaction. The heat released by the reaction is sufficient to maintain the reaction temperature of the reaction materials at 135°C to 155°C, and a slurry with a P2O5 mass fraction of more than 55% is obtained. Due to the increase in the concentration of phosphoric acid, the fluorine escape rate can be increased from more than 30% to more than 95%. Water countercurrent circulation is used to absorb fluorine-containing gases, and the fluorosilicic acid solution is transferred in time, and fresh water is appropriately added to control the fluorosilicic acid content of the fluorosilicic acid solution to 10wt% to 18wt%, ensuring that the fluorine-containing gas absorption rate is more than 95%. A certain amount of water is added to the defluorination slurry, the slurry liquid-to-solid ratio is adjusted to 2.5 to 4:1, the reaction temperature is 110°C to 120°C, and the reaction time is 3h to 4h to convert anhydrous calcium sulfate into hemihydrate calcium sulfate. The generated α-calcium sulfate hemihydrate has large particles, high strength and is easy to separate from phosphoric acid. The mass fraction of P2O5 in the phosphoric acid obtained by filtration separation is 40% to 45%, and the mass fraction of water-soluble fluorine is 100ppm to 1000ppm. The mass fraction of α-CaSO4·0.5H2O in the phosphogypsum product is more than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are respectively less than 800ppm and 200ppm.

[0081] The present application will be more specifically illustrated by the following examples.

[0082] Example

[0083] Example 1

[0084] The raw materials of this embodiment are 1000 kg of fluoroapatite and concentrated sulfuric acid. The mass fraction of P2O5 in the phosphate rock is 27.21%, the mass fraction of fluorine is 3.21%, the mass fraction of active SiO2 is 4.84%, and the mass fraction of sulfuric acid is 98%.

[0085] The process steps of this embodiment are as follows:

[0086] (1) Figure 1As shown in the upper left corner, the phosphate rock is crushed into ore with a particle size of less than 25 mm, fed into the ball mill, and water is quantitatively added according to a certain ratio to obtain slurry. The slurry is settled through a thickener, and the settled slurry is filtered, and the filtrate is recycled in the ball milling process. The moisture content is 26% to 28%, and the fineness is more than 50% and less than 200 mesh wet ore powder enters the next process;

[0087] (2) Wet mineral powder is put into a polytetrafluoroethylene reactor, and 105% sulfuric acid of the stoichiometric amount of acid-hydrolyzed phosphate rock is added. The two are mixed and reacted at a reaction temperature of 140°C and a reaction time of 6 hours. The fluorine gas escapes into the fluorine absorption system to obtain a defluorinated slurry. The fluorine content of the defluorinated slurry is 783ppm, and the mass fraction of P2O5 is 58.97%. The heat released by the acid hydrolysis reaction is sufficient to maintain the temperature of the reaction materials at 140°C;

[0088] (3) absorbing the fluorine gas released in step (2) by countercurrent circulation with water, controlling the temperature of the absorption liquid at 50° C., obtaining a fluorosilicic acid solution with a fluorosilicic acid concentration of 15%, transferring the fluorosilicic acid solution in time and replenishing with fresh water;

[0089] (4) transporting the defluorinated slurry obtained in step (2) to a crystallization tank, adding a certain amount of gypsum-washing liquid to reconstruct the crystal form of calcium sulfate, the slurry liquid-to-solid ratio is 3:1, the reaction temperature is 110° C., the reaction time is 4 h, and the anhydrous calcium sulfate is converted into hemihydrate calcium sulfate;

[0090] It is necessary to further explain here that Figure 1 As shown in the lower right corner, the product obtained by crystal reconstruction is filtered to obtain 40%-45% phosphoric acid, and the solid is calcium sulfate hemihydrate. The calcium sulfate hemihydrate is subjected to three-stage countercurrent washing with water, and washed for the third time with clean water (i.e., the third-stage countercurrent washing). The obtained hemihydrate gypsum is dried to obtain dry hemihydrate gypsum, and the obtained three-washing liquid is used for the second washing step (i.e., the second-stage countercurrent washing). The second-washing liquid obtained by the second washing is used to perform a first washing step (i.e., the first-stage countercurrent washing) on ​​the calcium sulfate hemihydrate solid obtained by filtration, and the first-washing liquid obtained is used to add to the crystal reconstruction step for phosphoric acid recovery;

[0091] (5) The slurry obtained in step (4) is filtered, and the filtrate enters a phosphoric acid product collection tank. The filter cake is washed three times in countercurrent with water and dried to obtain a by-product, phosphogypsum.

[0092] After calculation, the fluorine escape rate of this embodiment is 97.23%, the mass fraction of P2O5 in the phosphoric acid product is 42.78%, the mass fraction of water-soluble fluorine is 314ppm, the mass fraction of CaSO4·0.5H2O in the phosphogypsum product is 96.83%, the mass fractions of water-soluble phosphorus and water-soluble fluorine are 685ppm and 165ppm respectively. The data of the test results related to Example 1 are shown in Table 1.

[0093] Example 2

[0094] The raw materials of this embodiment are 1000 kg of fluoroapatite and concentrated sulfuric acid. The mass fraction of P2O5 in the phosphate rock is 34.67%, the mass fraction of fluorine is 3.83%, the mass fraction of active SiO2 is 4.92%, and the mass fraction of sulfuric acid is 98%.

[0095] The process steps of this embodiment are as follows:

[0096] (1) The phosphate rock is crushed into ore with a particle size of less than 25 mm, fed into a ball mill, and water is quantitatively added according to a certain ratio to obtain ore slurry. The ore slurry is settled by a thickener, and the settled ore slurry is filtered, and the filtrate is recycled in the ball milling process. The wet ore powder with a moisture content of 26% to 28% and a fineness of more than 50% and less than 200 mesh enters the next process;

[0097] (2) Wet mineral powder is put into a polytetrafluoroethylene reactor, and 105% sulfuric acid of the stoichiometric amount of acid-hydrolyzed phosphate rock is added. The two are mixed and reacted at a reaction temperature of 145°C and a reaction time of 6 hours. The fluorine gas escapes into the fluorine absorption system to obtain a defluorinated slurry. The fluorine content of the defluorinated slurry is 451ppm, and the mass fraction of P2O5 is 59.63%. The heat released by the acid hydrolysis reaction is sufficient to maintain the temperature of the reaction materials at 145°C;

[0098] (3) absorbing the fluorine gas released in step (2) by countercurrent circulation with water, controlling the temperature of the absorption liquid at 50° C., obtaining a fluorosilicic acid solution with a fluorosilicic acid concentration of 15%, transferring the fluorosilicic acid solution in time and replenishing with fresh water;

[0099] (4) transporting the defluorinated slurry obtained in step (2) to a crystallization tank, adding a certain amount of gypsum-washing liquid to reconstruct the crystal form of calcium sulfate, the slurry liquid-to-solid ratio is 3.5:1, the reaction temperature is 110° C., the reaction time is 4 h, and the anhydrous calcium sulfate is converted into hemihydrate calcium sulfate;

[0100] (5) The slurry obtained in step (4) is filtered, and the filtrate enters a phosphoric acid product collection tank. The filter cake is washed three times in countercurrent with water and dried to obtain a by-product, phosphogypsum.

[0101] After calculation, the fluorine escape rate of this embodiment is 98.58%, the mass fraction of P2O5 in the phosphoric acid product is 43.63%, the mass fraction of water-soluble fluorine is 173ppm, the mass fraction of CaSO4·0.5H2O in the phosphogypsum product is 97.12%, the mass fractions of water-soluble phosphorus and water-soluble fluorine are 650ppm and 135ppm respectively. The data of the test results related to Example 2 are shown in Table 1.

[0102] Example 3

[0103] The raw materials of this embodiment are 1000 kg of fluoroapatite and concentrated sulfuric acid. The mass fraction of P2O5 in the phosphate rock is 28.62%, the mass fraction of fluorine is 3.92%, the mass fraction of active SiO2 is 5.04%, and the mass fraction of sulfuric acid is 98%.

[0104] The process steps of this embodiment are as follows:

[0105] (1) The phosphate rock is crushed into ore with a particle size of less than 25 mm, fed into a ball mill, and water is quantitatively added according to a certain ratio to obtain ore slurry. The ore slurry is settled by a thickener, and the settled ore slurry is filtered, and the filtrate is recycled in the ball milling process. The wet ore powder with a moisture content of 26% to 28% and a fineness of more than 50% and less than 200 mesh enters the next process;

[0106] (2) Wet mineral powder is put into a polytetrafluoroethylene reactor, and 105% sulfuric acid of the stoichiometric amount of acid-hydrolyzed phosphate rock is added. The two are mixed and reacted at a reaction temperature of 150°C and a reaction time of 6 hours. The fluorine gas escapes into the fluorine absorption system to obtain a defluorinated slurry. The fluorine content of the defluorinated slurry is 289ppm, and the mass fraction of P2O5 is 61.09%. The heat released by the acid hydrolysis reaction is sufficient to maintain the temperature of the reaction materials at 150°C;

[0107] (3) absorbing the fluorine gas released in step (2) by countercurrent circulation with water, controlling the temperature of the absorption liquid at 55° C., obtaining a fluorosilicic acid solution with a fluorosilicic acid concentration of 15%, transferring the fluorosilicic acid solution in time and replenishing with fresh water;

[0108] (4) transporting the defluorinated slurry obtained in step (2) to a crystallization tank, adding a certain amount of gypsum-washing liquid to reconstruct the crystal form of calcium sulfate, the slurry liquid-to-solid ratio is 3:1, the reaction temperature is 110° C., the reaction time is 4 h, and the anhydrous calcium sulfate is converted into hemihydrate calcium sulfate;

[0109] (5) The slurry obtained in step (4) is filtered, and the filtrate enters a phosphoric acid product collection tank. The filter cake is washed three times in countercurrent with water and dried to obtain a by-product, phosphogypsum.

[0110] After calculation, the fluorine escape rate of this embodiment is 99.05%, the mass fraction of P2O5 in the phosphoric acid product is 44.58%, the mass fraction of water-soluble fluorine is 126ppm, the mass fraction of CaSO4·0.5H2O in the phosphogypsum product is 98.58%, the mass fractions of water-soluble phosphorus and water-soluble fluorine are 676ppm and 147ppm respectively. The data of the test results related to Example 3 are shown in Table 1.

[0111] Comparative Example

[0112] The prior art semi-aqueous-dihydrate wet phosphoric acid process is a comparative example, and the fluorine release rate during the acidolysis process is 30% to 40%.

[0113] The raw materials of this embodiment are 1000 kg of fluoroapatite and concentrated sulfuric acid, the mass fraction of P2O5 in the phosphate rock is 28.62%, the mass fraction of fluorine is 3.92%, the mass fraction of active SiO2 is 5.04%, the mass fraction of sulfuric acid is 98%, and the mass fraction of P2O5 in phosphoric acid is 45%.

[0114] The process steps of this embodiment are as follows:

[0115] (1) The phosphate rock is crushed into ore with a particle size of less than 25 mm, fed into a ball mill, and water is quantitatively added according to a certain ratio to obtain ore slurry. The ore slurry is settled by a thickener, and the settled ore slurry is filtered, and the filtrate is recycled in the ball milling process. The wet ore powder with a moisture content of 26% to 28% and a fineness of more than 50% and less than 200 mesh enters the next process;

[0116] (2) Add phosphorus-sulfur mixed acid (wherein the mass fraction of P2O5 is 45%, SO4 2- The mass fraction is 2.5%), the solution is preheated to 80°C, and then phosphate rock powder is added to carry out phosphate rock acid hydrolysis reaction, the slurry liquid-to-solid ratio is 3:1, the reaction temperature is 100°C, the reaction time is 6h, and the fluorine gas escapes into the fluorine absorption system to obtain a semi-aqueous slurry, the fluorine content of the semi-aqueous slurry is 1.22%, and the P2O5 mass fraction is 42.03%;

[0117] (3) After the reaction is completed, the slurry obtained in step (2) is filtered while hot, and the filter cake is washed three times with 90° C. water in reverse flow. The filtered acid is concentrated and defluorinated by a forced circulation vacuum evaporation process. The concentration temperature is 85° C. and the concentration vacuum degree is 15 kPa to 17 kPa. After concentration, the filtered acid enters a phosphoric acid product collection tank;

[0118] (4) absorbing the fluorine gas released from step (2) and step (4) by countercurrent circulation with water, controlling the temperature of the absorption liquid at 55° C., obtaining a fluorosilicic acid solution with a fluorosilicic acid concentration of 15%, transferring the fluorosilicic acid solution in time and replenishing with fresh water;

[0119] (5) The filter cake obtained in step (3) was transported to a crystallization tank, and a certain amount of gypsum washing liquid was added to reconstruct the crystal form of calcium sulfate. The slurry liquid-to-solid ratio was 3:1, the reaction temperature was 65°C, the reaction time was 4h, and the liquid phase SO4 2- The mass fraction is controlled at 6.5%, the mass fraction of P2O5 is controlled at 1.0%, and calcium sulfate hemihydrate is converted into calcium sulfate dihydrate;

[0120] (6) filtering the slurry obtained in step (5), washing the filter cake with water in countercurrent for three times, and drying to obtain the by-product phosphogypsum.

[0121] After calculation, the fluorine escape rate during the acidolysis process of this embodiment is 36.15%, the fluorine escape rate during the concentration process is 54.28%, the total fluorine escape rate is 70.81%, the P2O5 mass fraction in the phosphoric acid product is 52.58%, the water-soluble fluorine mass fraction is 0.58%, the CaSO4·2H2O mass fraction in the phosphogypsum product is 95.50%, the water-soluble phosphorus and water-soluble fluorine mass fractions are 1233ppm and 430ppm respectively. For data on the test effects related to the comparative examples, see Table 1.

[0122] Table 1: Data of Examples and Comparative Examples

[0123]

[0124]

[0125]

[0126] From the above comparison, it can be clearly seen that when the comparative example adopts the semi-water-dihydrate process of the prior art, the fluorine escape rate during the acidolysis process is 36.15%, the fluorine escape rate during the concentration process is 54.28%, the total fluorine escape rate is 70.81%, the P2O5 mass fraction in the phosphoric acid product is 52.58%, the water-soluble fluorine mass fraction is 0.58%, the CaSO4·2H2O mass fraction in the phosphogypsum product is 95.50%, the water-soluble phosphorus and water-soluble fluorine mass fractions are 1233ppm and 430ppm respectively, and calcium sulfate dihydrate is produced;

[0127] The comparative example cannot achieve one of the following effects or conditions listed in the present application, at least in terms of beneficial effects: First: the gas phase fluorine escape rate in the acidolysis reaction stage of the present application is more than 95%, or even higher, which is directly related to the reaction temperature; Second: the heat released by the reaction of the present application is sufficient to maintain the temperature of the reaction materials at 135°C to 155°C; Third: the phosphoric acid obtained in the present application does not need to be concentrated, and the mass fraction of P2O5 in the product is 40% to 45%; Fourth: the mass fraction of α-CaSO4·0.5H2O in the phosphogypsum product obtained after crystal reconstruction by the method described in the present application is more than 95%; Fifth: the method of the present application can achieve water-soluble phosphorus and water-soluble fluorine mass fractions of less than 800ppm and 200ppm, respectively.

[0128] The exemplary embodiments of the present disclosure are specifically shown and described above. It should be understood that the present disclosure is not limited to the detailed structures, configurations or implementations described herein; on the contrary, the present disclosure is intended to cover various modifications and equivalent configurations included in the spirit and scope of the appended claims.

Claims

1. A method for wet processing phosphoric acid for recovering fluorine, comprising: Acid hydrolysis step: reacting fluorapatite ore powder containing 26%-28% water with concentrated sulfuric acid, maintaining the reaction temperature above 135° C. and below 155° C., to generate fluorine-containing gas and a defluorination slurry containing anhydrous calcium sulfate, wherein the mass fraction of P2O5 in the defluorination slurry containing anhydrous calcium sulfate is greater than or equal to 55%, and the fluorine content is 200 ppm to 2000 ppm; Absorption step: absorbing the fluorine-containing gas with an absorption liquid to obtain a fluorine-containing solution, wherein the fluorine in the fluorine-containing solution accounts for more than 95wt% of the fluorine in the fluorapatite ore powder; Crystal reconstruction step: The defluorination slurry containing anhydrous calcium sulfate is subjected to crystal reconstruction and filtered to obtain a calcium sulfate hemihydrate filter cake and a filtrate containing phosphoric acid.

2. The method according to claim 1, wherein the D50 of the fluorapatite powder is 200 mesh or less.

3. The method according to claim 1, wherein the concentration of the concentrated sulfuric acid is above 97wt%, and the amount of the concentrated sulfuric acid used is 105% to 110% of the amount required for the acidolysis step.

4. The method according to claim 1, wherein the P2O5 mass fraction in the fluorapatite ore powder is 20% to 35%, the fluorine mass fraction is 3% to 4%, and the amorphous silicon dioxide content is greater than or equal to 4.8wt%.

5. The method according to claim 1, wherein the absorption liquid is an aqueous solution with a fluorosilicic acid content of less than 18wt%, the temperature of the absorption liquid is controlled at 50°C to 55°C, the vacuum degree is 86.6kPa to 93.3kPa in the absorption step, and the fluorine-containing solution is an aqueous solution of fluorosilicic acid.

6. The method according to claim 1, wherein the fluoroapatite ore powder containing 26%-28% water is prepared by the following method: crushing the fluoroapatite into crushed ore with a particle size of less than 25 mm, grinding the crushed ore in a ball mill, and adding water in a certain ratio to obtain a slurry, then the slurry is settled by a thickener, and the settled slurry is filter-filtered to obtain the fluoroapatite ore powder containing 26%-28% water.

7. The method according to claim 1, wherein the acid hydrolysis step is performed in a polytetrafluoroethylene container.

8. The method according to claim 1, wherein the mass fraction of α-CaSO4·0.5H2O in the calcium sulfate hemihydrate filter cake is more than 95%, and the mass fractions of water-soluble phosphorus and water-soluble fluorine are respectively less than 800 ppm and 200 ppm; the mass fraction of P2O5 in the filtrate containing phosphoric acid is 40% to 45%, and the mass fraction of water-soluble fluorine is 100 ppm to 1000 ppm.

9. The method according to claim 1, wherein the temperature in the acid hydrolysis reaction is maintained above 145°C and the temperature in the acid hydrolysis reaction is maintained below 153°C.

10. The method according to claim 4, wherein the content of amorphous silicon dioxide is greater than or equal to 5 wt%.

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