A method for recycling raffinate in the process of wet purification of phosphoric acid

Abstract

This article discloses a method for recycling raffinate acid from the wet purification process of phosphoric acid production, belonging to the field of battery raw material technology. This recycling method includes removing sulfur, fluorine, arsenic, and heavy metals from the raffinate acid to be processed to obtain pretreated acid; pre-neutralizing the pretreated acid and then purifying it to obtain a purified liquid and a precipitated residue containing iron, aluminum, and magnesium; and rectifying the purified liquid to obtain industrial-grade phosphoric acid. This method effectively recycles the phosphorus resources in the raffinate acid, and the resulting industrial-grade phosphoric acid can be used as a raw material to produce battery-grade phosphate.

Description

Technical Field

[0001] The present disclosure relates to the technical field of battery raw materials, and in particular to a method for recycling raffinate in a wet purification process for producing phosphoric acid. Background Art

[0002] Industrial-grade phosphoric acid can be produced using two methods: thermal and wet-process phosphoric acid solvent extraction (abbreviated as "wet purification"). The thermal method, also known as the yellow phosphorus method, uses yellow phosphorus as the raw material. The yellow phosphorus is burned and then absorbed into pure water to produce phosphoric acid. The wet-process phosphoric acid solvent extraction method uses wet-process phosphoric acid as the raw material and produces higher-purity phosphoric acid through a series of chemical and organic solvent-assisted purification processes.

[0003] Phosphoric acid produced by the wet-process phosphoric acid solvent extraction method can meet the requirements of most industrial applications. The rapid development of the new energy industry has greatly driven the demand for battery-grade high-purity phosphates, represented by iron phosphate. As the primary raw material for the production of these phosphates, demand for industrial-grade phosphoric acid has also grown rapidly, along with this battery-grade phosphate.

[0004] Raffinate acid is a major byproduct of the solvent extraction purification process for wet-process phosphoric acid, accounting for a significant 40%-45% of the mass of the raw phosphoric acid. During the solvent extraction process, the phosphoric acid molecules in the crude phosphoric acid interact with the extractant and are extracted. Impurity ions in the acid (such as iron, aluminum, magnesium, sulfate, fluoride, arsenic, and heavy metal ions) are partially or completely retained in the raffinate acid due to their low or complete inertness to the extractant. This results in an exponential increase in the impurity ion content of the raffinate acid compared to the original phosphoric acid, significantly limiting its application. Furthermore, the conventional raffinate acid treatment method currently involves mixing the raffinate acid with conventional wet-process phosphoric acid in a mass ratio of 1:2-5 to produce conventional fertilizers, such as monoammonium phosphate, diammonium phosphate, and compound fertilizers. This method produces a large amount of low-grade fertilizer, which is detrimental to the sustainable development of the phosphorus chemical industry.

[0005] In view of this, the present disclosure is proposed. Summary of the Invention

[0006] The purpose of the present disclosure includes providing a method for recycling raffinate in the process of wet purification of phosphoric acid.

[0007] The present disclosure can be implemented as follows:

[0008] The present disclosure provides a method for recycling raffinate acid in a wet purification process for producing phosphoric acid, comprising the following steps: removing sulfur, fluorine, arsenic, and heavy metals from the raffinate acid to be treated to obtain pretreated acid; pre-neutralizing the pretreated acid and then purifying it to obtain a purified liquid and a precipitated residue containing iron, aluminum, and magnesium; and rectifying the purified liquid to obtain industrial-grade phosphoric acid.

[0009] In an optional embodiment, the raffinate acid to be treated is first subjected to rough desulfurization to obtain a first intermediate acid; fluorine, arsenic and heavy metals in the first intermediate acid are removed to obtain a second intermediate acid; and the second intermediate acid is subjected to fine desulfurization to obtain a pretreated acid.

[0010] In an optional embodiment, the raffinate acid to be treated is mixed with a crude desulfurization agent to perform crude desulfurization;

[0011] The crude desulfurizing agent includes at least one of phosphate concentrate, calcium carbonate, calcium hydroxide and calcium oxide.

[0012] In an optional embodiment, the molar ratio of calcium in the crude desulfurizer to sulfate in the raffinate acid is (0.8:1)-(1.0:1).

[0013] In an alternative embodiment, the first intermediate acid is mixed with a defluorinating agent, a sulfide, and a filter aid to remove fluorine, arsenic, and heavy metals.

[0014] In an optional embodiment, the defluorination agent includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate, and activated diatomaceous earth;

[0015] or, the sulfide comprises at least one of sodium sulfide, calcium sulfide, potassium sulfide and phosphorus pentasulfide;

[0016] Alternatively, the filter aid comprises activated carbon.

[0017] In an optional embodiment, the molar ratio of Na in the defluorinating agent to F in the first intermediate acid is (0.4:1)-(0.8:1);

[0018] Alternatively, the molar ratio of As in the first intermediate acid to S in the sulfide is (1:15)-(1:75);

[0019] Alternatively, the filter aid is used in an amount of 0.5 wt % to 5 wt % of the first intermediate acid.

[0020] In an optional embodiment, the second intermediate acid is mixed with an oxidant and a fine desulfurization agent to perform fine desulfurization to obtain pretreated acid and fine desulfurization slag;

[0021] The fine desulfurizing agent includes at least one of barium hydroxide and barium carbonate.

[0022] In an optional embodiment, the oxidant is used in an amount of 0.5 wt% to 1.5 wt% of the second intermediate acid;

[0023] Alternatively, the molar ratio of the barium in the fine desulfurizer to the sulfate in the second intermediate acid is (1.5:1)-(2.5:1).

[0024] In an optional embodiment, the fine desulfurization slag is returned to the rough desulfurization process to be used as a rough desulfurization agent.

[0025] In an optional embodiment, before pre-neutralization, the pretreated acid is concentrated and solid-liquid separated to obtain concentrated pretreated acid and a first precipitated residue containing iron phosphate and aluminum phosphate;

[0026] The content of P2O5 in the concentrated pretreated acid is not less than 40 wt%.

[0027] In an optional embodiment, the concentrated pre-treated acid is mixed with a neutralizing agent for pre-neutralization to obtain a pre-neutralized reaction solution;

[0028] The neutralizing agent includes salts of potassium, sodium, ammonium, and at least one of ammonia, sodium hydroxide, and potassium hydroxide.

[0029] In an alternative embodiment, the salt form of potassium, sodium, or ammonium includes at least one of carbonate, bicarbonate, and phosphate;

[0030] Alternatively, the molar ratio of M in the neutralizing agent to phosphorus in the concentrated pretreatment acid is (0.2:1)-(0.4:1), where M corresponds to ammonia, sodium and / or potassium contained in the neutralizing agent.

[0031] In an optional embodiment, the purification process includes: mixing the pre-neutralization reaction liquid with a first precipitant to perform a first purification, and separating the solid and liquid to obtain a first purified liquid and a second precipitated residue containing iron phosphate, aluminum phosphate, and magnesium phosphate;

[0032] The first purification process includes at least one of the following characteristics:

[0033] Feature 1: The first precipitant includes at least one of methanol, ethanol, propanol, butanol and acetone;

[0034] Feature 2: The amount of the first precipitant used is 1-2.5 times the amount of the pre-neutralization reaction solution;

[0035] Feature 3: The temperature of the first purification is 25℃-65℃.

[0036] In an optional embodiment, the purification process further comprises: mixing the first purification liquid with a detergent to perform a second purification, and separating the solid and liquid to obtain a second purification liquid and a first washing liquid;

[0037] The second purification process includes at least one of the following characteristics:

[0038] Feature 1: The solute in the detergent includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate and potassium phosphate;

[0039] Feature 2: The mass fraction of solute in the detergent is not less than 10%;

[0040] Feature 3: The molar ratio of M in the detergent to P in the first purification solution is (0.15:1)-(0.3:1), corresponding to the sodium and / or potassium contained in the detergent.

[0041] In an optional embodiment, the first washing liquid is returned to the pre-neutralization process to be used as a neutralizing agent.

[0042] In an optional embodiment, the purification process further comprises: mixing the second purified liquid with a second precipitant to perform a third purification, and performing solid-liquid separation to obtain a third purified liquid and a third precipitated residue containing a small amount of magnesium phosphate and alkali metal phosphate;

[0043] The third purification process includes at least one of the following characteristics:

[0044] Feature 1: The second precipitant includes at least one of methanol, ethanol, propanol, butanol and acetone;

[0045] Feature 2: The usage amount of the second precipitant is 20wt%-100wt% of the second purified liquid.

[0046] In an optional embodiment, the third precipitated residue is returned to the first purification process, or the third precipitated residue is mixed with the first precipitated residue and the second precipitated residue and then pulped and recovered.

[0047] In an optional embodiment, industrial-grade phosphoric acid is obtained after the third purification liquid is distilled.

[0048] In an optional embodiment, the third precipitated residue is mixed with the first precipitated residue and the second precipitated residue and then pulped and recovered, comprising:

[0049] The first precipitated residue, the second precipitated residue and the third precipitated residue are mixed with water and a first alkaline substance, neutralized and precipitated to obtain a first slurry; the first slurry is subjected to solid-liquid separation to obtain a separated liquid and phosphate precipitated residue.

[0050] In an optional embodiment, the pulp recovery includes at least one of the following features:

[0051] Feature 1: The water used for mixing with the first sedimentation residue, the second sedimentation residue and the third sedimentation residue is desalted water;

[0052] Feature 2: The mass ratio of water to the total amount of the first precipitated residue, the second precipitated residue, and the third precipitated residue is (2:1)-(5:1);

[0053] Feature 3: The first alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium orthophosphate and potassium orthophosphate;

[0054] Feature 4: The pH value of the first slurry is 5.5-8.0;

[0055] Feature 5: The separated liquid is reused as a detergent in the second purification process, or as a neutralizing agent in the pre-neutralization process, or as a defluorinating agent in the defluorinating process.

[0056] In an optional embodiment, the phosphate precipitation residue is mixed with water to obtain a second slurry; the second slurry is mixed with a second alkaline substance and subjected to secondary cross-current leaching and solid-liquid separation to obtain dephosphorization residue and orthophosphate mother liquor.

[0057] In an optional embodiment, the mass ratio of phosphate precipitate residue to water is (1:4)-(1:9);

[0058] Alternatively, the second alkaline substance includes at least one of sodium hydroxide and potassium hydroxide.

[0059] In an optional embodiment, the secondary cross-flow leaching includes: performing a first-stage leaching on the second slurry and the second alkaline substance to obtain a first-stage leachate and a first sediment;

[0060] The first stage leaching process includes at least one of the following features:

[0061] Feature 1: The pH value of the reaction solution during the leaching process is 13-14;

[0062] Feature 2: Leaching temperature is 50℃-85℃;

[0063] Feature 3: The residence time of the reaction slurry is 25min-45min;

[0064] Feature 4: The mass ratio of the first-stage leachate to the first-stage sediment is (3:1)-(9:1).

[0065] In an optional embodiment, part of the orthophosphate mother liquor obtained from the first-stage leaching is recycled to be mixed with the first precipitated slag, the second precipitated slag and the third precipitated slag.

[0066] In an optional embodiment, the secondary cross-flow leaching further comprises: performing a second-stage leaching on the first sediment and the second alkaline substance to obtain a second-stage leachate and a second sediment;

[0067] The second stage leaching process includes at least one of the following features:

[0068] Feature 1: The pH value of the reaction solution during the leaching process is 14.0-14.3;

[0069] Feature 2: Leaching temperature is 45℃-55℃;

[0070] Feature 3: The residence time of the reaction slurry is 60min-90min;

[0071] Feature 4: The mass ratio of the second-stage leachate to the second sediment is (5:1)-(9:1).

[0072] In an optional embodiment, the second sediment is subjected to alkali washing, and after solid-liquid separation, a first washing liquid and a first slag slurry are obtained;

[0073] The first washing liquid is recycled to the second stage leaching process; the first slurry is washed with water, and the solid-liquid separation is performed to obtain the second washing liquid and the dephosphorization slag.

[0074] In an optional embodiment, the second washing liquid is recycled to the alkali washing process of the second settled slag.

[0075] In an optional embodiment, lime milk is subjected to a first double decomposition reaction with the second-stage leachate to precipitate phosphate in the secondary leachate, and the solid-liquid is separated to obtain a second slurry; the second slurry is subjected to a second double decomposition reaction with the first-stage leachate, and the solid-liquid is separated to obtain alkali solution and calcium hydroxyphosphate.

[0076] In an alternative embodiment, the milk of lime is obtained by mixing a precipitant with water;

[0077] The precipitant includes at least one of calcium oxide and calcium hydroxide.

[0078] In an optional embodiment, the mass ratio of the precipitant to water is (1:3)-(1:5).

[0079] In an alternative embodiment, the molar ratio of calcium in the precipitant to phosphorus in the second stage leachate is (1.5:1)-(1.6:1).

[0080] In an alternative embodiment, the temperature of the first metathesis reaction and the second metathesis reaction are independently 40° C. to 60° C., or the time of the first metathesis reaction and the second metathesis reaction are independently 30 min to 60 min.

[0081] In an optional embodiment, the calcium hydroxyphosphate is washed; and the second washing liquid obtained after washing the calcium hydroxyphosphate is collected and returned to the precipitant slurrying and milking process.

[0082] In an optional embodiment, the suspended solids in the alkali liquor after the double decomposition and dephosphorization are removed and concentrated to obtain a concentrated alkali liquor; and the concentrated alkali liquor is reused to perform leaching treatment on the second slurry.

[0083] The beneficial effects of the present disclosure include:

[0084] The method for recycling raffinate provided by the present disclosure does not require reliance on fertilizer processing plants. Through reasonable process design, phosphorus is selectively extracted from complex phosphate precipitates containing iron, aluminum, and magnesium, and the phosphorus in the raffinate is converted into industrial-grade phosphoric acid to the greatest extent possible, thereby achieving effective recycling of the phosphorus resources in the raffinate. The obtained industrial-grade phosphoric acid can be used as a raw material to prepare battery-grade phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0086] Figure 1 This is a process flow chart of the pretreatment and purification process of the raffinate in Example 1 of the present disclosure;

[0087] Figure 2 This is a process flow chart for recycling the first precipitated residue, the second precipitated residue, and the third precipitated residue in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0088] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0089] The following is a detailed description of the method for recycling raffinate in the wet purification process for producing phosphoric acid provided by the present disclosure.

[0090] The present disclosure provides a method for recycling raffinate acid in a wet purification process for producing phosphoric acid, comprising the following steps: removing sulfur, fluorine, arsenic, and heavy metals from the raffinate acid to be treated to obtain pretreated acid; pre-neutralizing the pretreated acid and then purifying it to obtain a purified liquid and a precipitated residue containing iron, aluminum, and magnesium; and distilling the purified liquid to obtain industrial-grade phosphoric acid.

[0091] It should be noted that if the method of first using a precipitant for purification and then removing sulfur, fluorine, and arsenic is used, in order to avoid contamination of the purified phosphoric acid, barium desulfurization, phosphorus pentasulfide dearsenicization, and steam stripping defluorination are the only options. This purification process is complex and places high demands on the purity and dosage of the chemicals used in the purification process, as well as the operating environment for the purification and impurity removal operations. If the pretreatment and purification processes are combined into a single step, the impurity removal residue and phosphate precipitation residue will be mixed together, complicating the residue composition and making the phosphate precipitation residue separated during the purification process difficult to reuse.

[0092] Therefore, the present disclosure adopts a method of first removing sulfur, fluorine and arsenic, and then pre-neutralizing and purifying. Heavy metal impurity ions (such as lead, cadmium, etc.) can form sulfide precipitates under acidic conditions and are removed together during the arsenic removal process.

[0093] In some embodiments, the raffinate acid to be treated may be subjected to rough desulfurization to obtain a first intermediate acid; fluorine, arsenic and heavy metals in the first intermediate acid may be removed to obtain a second intermediate acid; and the second intermediate acid may be subjected to fine desulfurization to obtain a pretreated acid.

[0094] It should be noted that for phosphoric acid purification enterprises, phosphate concentrate (the main component is calcium fluorophosphate) is the most easily available desulfurizer. However, when crude phosphoric acid is desulfurized with phosphate concentrate, impurity ions such as fluorine and arsenic in the ore will be released into the phosphoric acid. In order to avoid secondary pollution, the present invention adopts a method of rough desulfurization first. The product of calcium salt desulfurization is calcium sulfate, which has a certain solubility in aqueous solution. Therefore, calcium salt can only be used to perform preliminary removal of sulfate impurities; if the calcium salt and barium salt are mixed and the solution is desulfurized, the two desulfurization products produced will interfere with each other, and the purpose of deep desulfurization cannot be achieved. Therefore, the present invention adopts a two-stage method of calcium salt plus barium salt for desulfurization, thereby achieving deep removal of sulfate impurities and obtaining a better desulfurization effect while taking into account the desulfurization cost.

[0095] Fluorine and arsenic do not interfere with each other during the removal process, and since the impurity removal products are all hazardous waste, combining them can simplify the treatment process and remove heavy metal impurities during arsenic removal. The acid solution after arsenic removal also contains a certain amount of non-sulfate sulfides, which also need to be removed. In this disclosure, it is chosen to oxidize them to sulfates before removal.

[0096] As mentioned above, the present disclosure adopts the method of first performing rough desulfurization, then removing fluorine, arsenic and heavy metals, and then oxidizing non-sulfate sulfides before performing deep desulfurization.

[0097] For reference, the raffinate to be treated is mixed with a crude desulfurization agent for crude desulfurization, followed by solid-liquid separation to obtain a first intermediate acid and a crude desulfurization slag (calcium sulfate). The crude desulfurization agent may illustratively include at least one of phosphate concentrate, calcium carbonate, calcium hydroxide, and calcium oxide. Phosphate concentrate contains some calcium phosphate. In some optional embodiments, the crude desulfurization agent is phosphate concentrate.

[0098] The molar ratio of calcium in the crude desulfurizer to sulfate in the raffinate can be (0.8:1) (1.0:1), such as 0.8:1, 0.85:1, 0.9:1, 0.95:1 or 1.0:1, or any other value within the range of (0.8:1)-(1.0:1).

[0099] The crude desulfurization slag obtained above can be used to return to the wet phosphoric acid production system to recover the phosphorus element entrained therein.

[0100] The first intermediate acid is mixed with a defluorinating agent, sulfide and a filter aid to remove fluorine, arsenic and heavy metals.

[0101] In some embodiments, the first intermediate acid can be mixed with the defluorinating agent, sulfide and filter aid at the same time; in other embodiments, the first intermediate acid can be mixed with the defluorinating agent first for defluorination treatment, and the defluorinated reaction liquid is then mixed with the sulfide and filter aid to carry out arsenic removal and heavy metal removal reactions, followed by solid-liquid separation to obtain the second intermediate acid and defluorination, dearsenicization and heavy metal removal slag.

[0102] For reference, the defluorination agent may illustratively include a sodium source and activated diatomaceous earth, wherein the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. In some embodiments, the mass ratio of the sodium source to the activated diatomaceous earth may be (1:0.75) to (1:1.5). If the mass ratio of the sodium source to the activated diatomaceous earth is too low, the desired effect cannot be achieved; if the mass ratio of the sodium source to the activated diatomaceous earth is too high, the defluorination effect is not very helpful.

[0103] The molar ratio of Na in the defluorinating agent to F in the first intermediate acid can be (0.4:1)-(0.8:1), such as 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1 or 0.8:1, or any other value within the range of (0.4:1)-(0.8:1).

[0104] The sulfide may illustratively include at least one of sodium sulfide, calcium sulfide, potassium sulfide, and phosphorus pentasulfide. The molar ratio of As in the first intermediate acid to S in the sulfide may be (1:15) to (1:75), such as 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, or 1:75, or any other value within the range of (1:15) to (1:75).

[0105] The filter aid may illustratively include activated carbon. The amount of the filter aid used may be 0.5 wt% to 5 wt% of the first intermediate acid, such as 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%, or any other value within the range of 0.5 wt% to 5 wt%.

[0106] The second intermediate acid is mixed with an oxidant and a fine desulfurizing agent to perform fine desulfurization, and the reaction liquid obtained by the fine desulfurization is subjected to solid-liquid separation to obtain pretreated acid and fine desulfurization slag.

[0107] The oxidant may include hydrogen peroxide or ozone. The hydrogen peroxide may be, for example, industrial-grade hydrogen peroxide, and its usage amount may be 0.5wt%-1.5wt% of the second intermediate acid, such as 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, or 1.5wt%, or any other value within the range of 0.5wt%-1.5wt%.

[0108] The fine desulfurizing agent is a barium salt, illustratively comprising at least one of barium hydroxide and barium carbonate. The molar ratio of the barium in the fine desulfurizing agent to the sulfate in the second intermediate acid can be (1.5:1) to (2.5:1), such as 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, or 2.5:1, or any other value within the range of (1.5:1) to (2.5:1).

[0109] The above-mentioned fine desulfurization slag is mainly barium slag, which can be returned to the rough desulfurization process to be used as a rough desulfurization agent.

[0110] It should be noted that the above-mentioned desulfurization, defluorination, dearsenicization and heavy metal removal cannot be considered to remove all sulfur, fluorine, arsenic and heavy metals in the raffinate acid 100%, but it can at least remove most of the sulfur, fluorine, arsenic and heavy metals.

[0111] In the present disclosure, before pre-neutralization, the pre-treated acid may be concentrated and solid-liquid separated to obtain concentrated pre-treated acid and a first precipitated residue whose main components are ferric phosphate and aluminum phosphate.

[0112] In some embodiments, the concentrated pretreated acid may be concentrated to a P2O5 content of not less than 40 wt%, such as 40 wt%, 50 wt%, 60 wt%, 70 wt% or 80 wt%, or any other value not less than 40 wt%.

[0113] After the concentrated pretreatment acid is obtained, the concentrated pretreatment acid is mixed with a neutralizing agent for pre-neutralization to obtain a pre-neutralization reaction solution.

[0114] The above-mentioned pre-neutralization can convert the impurity cations into phosphate complex salt precipitates with lower solubility and higher crystallinity, which is beneficial to increasing the removal rate of cationic impurities and improving the separation performance of the precipitated residue.

[0115] For reference, the neutralizing agent may illustratively include salts of potassium, sodium, and ammonium, as well as at least one of ammonia, sodium hydroxide, and potassium hydroxide. The salts of potassium, sodium, and ammonium may include at least one of carbonates, bicarbonates, and phosphates. The molar ratio of M (M includes ammonia, sodium, and potassium) in the neutralizing agent to phosphorus in the concentrated pretreatment acid may be (0.2:1) to (0.4:1), such as 0.2:1, 0.25:1, 0.3:1, 0.35:1, or 0.4:1, or any other value within the range of (0.2:1) to (0.4:1).

[0116] In the present disclosure, the purification process may include: mixing the pre-neutralization reaction liquid with a first precipitant to perform a first purification, and separating the solid and liquid to obtain a first purified liquid and a second precipitate residue whose main components are iron phosphate, aluminum phosphate and magnesium phosphate.

[0117] In the first purification process, the first precipitant is an organic precipitant, which may illustratively include at least one of methanol, ethanol, propanol, butanol, and acetone. The amount of the first precipitant used may be 1 to 2.5 times the amount of the pre-neutralization reaction solution, such as 1, 1.5, 2, or 2.5 times, or any other value within the range of 1 to 2.5 times.

[0118] The temperature of the first purification can be 25°C-65°C, such as 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C or 65°C, or any other value within the range of 25°C-65°C.

[0119] Furthermore, the purification process further includes: mixing the first purification liquid with a detergent to perform a second purification, and separating the solid and the liquid to obtain the second purification liquid and the first washing liquid.

[0120] The solute in the detergent used in the second purification process may illustratively include at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, and potassium phosphate. The mass fraction of the solute in the detergent is not less than 10%, and may be 10%, 20%, 30%, 40%, or 50%, or other values ​​not less than 10%.

[0121] The molar ratio of M (including sodium and potassium) in the detergent to P in the first purification liquid can be (0.15:1)-(0.3:1), such as 0.15:1, 0.2:1, 0.25:1 or 0.3:1, or any other value within the range of (0.15:1)-(0.3:1).

[0122] The first washing liquid can be returned to the pre-neutralization process to be used as a neutralizing agent.

[0123] Furthermore, the purification process also includes: mixing the second purified liquid with the second precipitant to perform a third purification, and separating the solid and liquid to obtain a third purified liquid and a third precipitate residue containing a small amount of magnesium phosphate and alkali metal phosphate.

[0124] During the third purification process, the second precipitant is an organic precipitant, illustratively comprising at least one of methanol, ethanol, propanol, butanol, and acetone. The second precipitant may be used in an amount of 20 wt% to 100 wt% of the second purified solution, such as 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, or 100 wt%, or any other value within the range of 20 wt% to 100 wt%.

[0125] In some embodiments, the third precipitated residue can be returned to the first purification process. In other embodiments, the third precipitated residue can be mixed with the first precipitated residue and the second precipitated residue and then pulped and recovered.

[0126] In the present disclosure, after the third purification liquid is distilled, industrial-grade phosphoric acid, water and regenerated precipitant can be obtained.

[0127] The above-mentioned industrial-grade phosphoric acid can be used as a raw material to prepare battery-grade phosphate (such as iron phosphate), the regenerated precipitant can be reused in the first purification and / or third purification process, and the water can also be recycled as needed.

[0128] As mentioned above, the present invention adopts a three-stage purification method of solvent precipitation-washing-reprecipitation to purify the raffinate acid in view of the high impurity content of the raffinate acid. The staged addition of the solvent can significantly reduce the amount of detergent used and perform a secondary purification on the acid-containing solvent after washing to remove cationic impurities that enter the solvent during the washing process. The acid solution after the three-stage purification meets the requirements of industrial-grade phosphoric acid.

[0129] In the present disclosure, the slurry recovery after mixing the third precipitated residue with the first precipitated residue and the second precipitated residue may include: mixing the first precipitated residue, the second precipitated residue, and the third precipitated residue with water and a first alkaline substance, neutralizing and precipitating to obtain a first slurry; and performing solid-liquid separation on the first slurry to obtain a separated liquid and phosphate precipitated residue.

[0130] In some embodiments, the first precipitated residue, the second precipitated residue, and the third precipitated residue may be mixed and then slurried with water. The obtained slurry is then added with a first alkaline substance to adjust the pH value and then solid-liquid separation is performed to separate the generated phosphate precipitated residue.

[0131] For reference, the water used to mix with the first, second, and third precipitates is desalted water. The mass ratio of water to the total amount of the first, second, and third precipitates can be (2:1) to (5:1), such as 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1, or any other value within the range of (2:1) to (5:1).

[0132] The first alkaline substance may illustratively include at least one of sodium hydroxide, potassium hydroxide, sodium orthophosphate, and potassium orthophosphate.

[0133] The pH value of the first slurry may be 5.5-8.0, such as 5.5, 6, 6.5, 7, 7.5 or 8, or any other value within the range of 5.5-8.0.

[0134] In some embodiments, the separated liquid can be reused as a detergent in the second purification process. In other embodiments, the separated liquid can be reused as a neutralizing agent in the pre-neutralization process. In still other embodiments, the separated liquid can be reused as a defluorinating agent in the defluorination process.

[0135] The obtained phosphate precipitate residue is further mixed with water to obtain a second slurry. The second slurry is mixed with a second alkaline substance and subjected to secondary cross-current leaching to extract phosphorus from the phosphate precipitate residue. The reaction liquid after leaching is subjected to solid-liquid separation to obtain dephosphorized residue and orthophosphate mother liquor.

[0136] The mass ratio of phosphate precipitate to water may be (1:4)-(1:9), such as 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9, or any other value within the range of (1:4) (1:9).

[0137] The second alkaline substance may illustratively include at least one of sodium hydroxide and potassium hydroxide.

[0138] In the present disclosure, the secondary cross-flow leaching may include: performing a first-stage leaching on the second slurry and the second alkaline substance to obtain a first-stage leachate and a first sediment.

[0139] In the first stage leaching, the pH value of the reaction solution can be 13-14, such as 13, 13.5 or 14.

[0140] The first stage leaching process can be carried out at a temperature of 50°C-85°C (such as 55°C, 60°C, 65°C, 75°C, 78°C, 80°C or 85°C, etc.).

[0141] During the first stage leaching process, the residence time of the reaction slurry can be 25 min-45 min, such as 25 min, 30 min, 35 min, 40 min or 45 min.

[0142] The mass ratio of the first-stage leachate to the first sediment can be (3:1)-(9:1), such as 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1.

[0143] The orthophosphate mother liquor obtained from the first stage leaching (which can be understood as the liquid in the first slurry) can be partially reused to be mixed with the first precipitated slag, the second precipitated slag and the third precipitated slag.

[0144] Furthermore, the above-mentioned secondary cross-flow leaching further comprises: performing a second-stage leaching on the first sediment and the second alkaline substance to obtain a second-stage leachate and a second sediment.

[0145] In the second stage leaching, the pH value of the reaction solution may be 14.0-14.3 (eg, 14.0, 14.1, 14.2, or 14.3, etc.).

[0146] The second stage leaching process can be carried out at a temperature of 45°C-55°C (such as 45°C, 48°C, 50°C, 52°C or 55°C, etc.).

[0147] During the second stage leaching process, the residence time of the reaction slurry can be 60 min-90 min, such as 60 min, 70 min, 80 min or 90 min.

[0148] The mass ratio of the second-stage leachate to the second sediment can be (5:1)-(9:1), such as 5:1, 6:1, 7:1, 8:1 or 9:1.

[0149] Furthermore, the second sediment is subjected to alkali washing, and after solid-liquid separation, a first washing liquid and a first slag slurry are obtained.

[0150] The alkali washing process can be performed by leaching the second sediment with a dilute alkali solution (pH of approximately 14). The mass ratio of the dilute alkali solution to the second sediment can be (3:1) to (5:1), such as 3:1, 4:1, or 5:1. The separated first washing liquid can be reused in the second leaching process.

[0151] Furthermore, the first slurry is washed with water and solid-liquid separated to obtain a second washing liquid and dephosphorization slag.

[0152] The water used for washing can be clean water, and the mass ratio of clean water to the first slurry can be (3:1)-(5:1), such as 3:1, 4:1 or 5:1. The separated second washing liquid can be recycled as dilute alkali solution to the alkali washing process of the second sediment.

[0153] Furthermore, the lime milk and the second-stage leachate can be subjected to a first double decomposition reaction (corresponding to the first-stage precipitation) to precipitate the phosphate in the secondary leachate, and the solid-liquid separation is performed to obtain a second slurry; the second slurry is subjected to a second double decomposition reaction (corresponding to the second-stage precipitation) with the first-stage leachate, and the solid-liquid separation is performed to obtain an alkali solution and calcium hydroxyphosphate.

[0154] For reference, lime milk can be obtained by mixing a precipitant with water, wherein the precipitant illustratively can include at least one of calcium oxide and calcium hydroxide.

[0155] The mass ratio of the precipitant to water can be (1:3)-(1:5), such as 1:3, 1:4 or 1:5.

[0156] The molar ratio of calcium in the precipitant to phosphorus in the second-stage leachate can be (1.5:1)-(1.6:1), such as 1.5:1, 1.55:1 or 1.6:1.

[0157] In the present disclosure, the temperature of the first metathesis reaction and the second metathesis reaction is independently 40° C.-60° C., such as 40° C., 45° C., 50° C., 55° C., or 60° C., etc. The time of the first metathesis reaction and the second metathesis reaction is independently 30 min-60 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, etc. Both of the above metathesis reactions can be carried out under strong stirring conditions, and the stirring speed can be illustratively above 270 rpm.

[0158] As mentioned above, the solubility of calcium hydroxyphosphate is much smaller than that of calcium aluminate. When using leachate to prepare calcium hydroxyphosphate, the phosphorus and aluminum elements in the mother liquor can be separated by controlling the amount of calcium oxide or calcium hydroxide added. The two-stage cross-current precipitation method can convert the calcium aluminate generated in the first double decomposition reaction into calcium hydroxyphosphate during the second double decomposition reaction, thereby performing a secondary purification of the precipitated phosphorus product. At the same time, the two-stage double decomposition reaction can effectively improve the conversion rate of soda lime.

[0159] In some embodiments, the calcium hydroxyphosphate obtained by the double decomposition reaction can be washed and then dried to obtain calcium hydroxyphosphate dry powder. This calcium hydroxyphosphate dry powder can be used as a raw material to produce crude phosphoric acid in the wet-process phosphoric acid production process. In addition, this calcium hydroxyphosphate can also be used as a defluorination agent to defluorinate fluoride-containing wastewater. The principle is that calcium hydroxyphosphate easily undergoes ion exchange with fluoride ions in the solution, absorbs fluoride ions to form calcium fluorophosphate, and thus can be used to deeply defluorinate weakly acidic, neutral, and weakly alkaline fluoride-containing wastewater.

[0160] The mass ratio of the above-mentioned calcium hydroxyphosphate to water can be (2:1)-(4:1), such as 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0161] The second washing liquid obtained after washing is collected and can be returned to the precipitant pulping and milking process.

[0162] In some embodiments, the alkali liquor after double decomposition and dephosphorization can be subjected to removal of suspended solids and then concentrated to obtain concentrated alkali liquor.

[0163] The causticity of the dilute alkali solution after dephosphorization is more than 10 times that of the leaching solution. At a higher causticity ratio, aluminate ions are not easy to self-decompose, so the dilute alkali solution after dephosphorization can be directly concentrated.

[0164] The concentrated alkali solution obtained can be used to replenish the lost alkali as needed and then returned to the second slurry for leaching. The above-mentioned replenishment of alkali to the concentrated alkali solution can maintain the alkali balance and water balance of the system.

[0165] When the concentrated alkali solution is used to leach the second slurry again, the aluminate present in the alkali solution has a certain inhibitory effect on the dissolution of aluminum hydroxide. Therefore, in the closed-loop circulation process, the aluminum in the circulating alkali solution does not need to be treated separately.

[0166] In addition, the main component of the dephosphorization slag produced in the present disclosure is a mixture of iron, aluminum and magnesium hydroxides. The dephosphorization slag can be further extracted as needed to recover the valuable elements therein, which helps to achieve the goal of comprehensive utilization of the associated resources of wet-process phosphoric acid.

[0167] Continuing from the above, the present disclosure proposes a new method for utilizing raffinate acid, which cleverly solves the current technical dilemma that the utilization of raffinate acid must rely on fertilizer processing plants, and ensures the integrity and independence of the phosphoric acid purification process. The method proposes a new phosphate precipitate leaching scheme, which achieves the purpose of selectively extracting phosphorus from complex phosphate precipitates containing iron, aluminum, and magnesium. In the open-circuit process, the vast majority of phosphorus (more than 98.5%) and a small proportion of aluminum (less than 30%) in the phosphate precipitate can be transferred to the leachate; in the closed-circuit process, phosphorus can be extracted separately from the complex phosphate precipitate containing iron, aluminum, and magnesium. Through reasonable process design, the method maximizes the conversion of phosphorus in raffinate acid into industrial-grade purified phosphoric acid, while converting the low-utilization-value, essentially useless by-product insoluble phosphate salts into high-value and widely used calcium hydroxyphosphate, thereby achieving comprehensive recovery and efficient utilization of phosphorus resources in raffinate acid.

[0168] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0169] Example 1

[0170] This embodiment provides a method for recycling raffinate in the process of wet purification of phosphoric acid. Figure 1 and Figure 2 , which includes the following steps:

[0171] S1: If Figure 1 As shown, 2000 mL of the raffinate acid to be treated was taken, and 280 g of phosphate concentrate powder was added thereto (the molar ratio of calcium in the phosphate concentrate powder to sulfate in the raffinate acid was 0.95:1. After the reaction was complete, the generated calcium sulfate dihydrate was filtered off to obtain a first intermediate acid.

[0172] The basic information of the above-mentioned raffinate acid to be treated is as follows:

[0173] Item / (g / L) P Fe Al Mg Mn S F Ca As ρ, density Raffinate 172.54 10.09 17.83 23.71 0.79 36.01 17.81 0.11 0.0389 1410.00

[0174] The water content of the phosphate concentrate powder used is 10wt%, and its chemical composition (on anhydrous basis) is as follows:

[0175] <![CDATA[P2O5]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO CaO F <![CDATA[SiO2]]> 34.1％ 1.32％ 1.48％ 0.62％ 47.5％ 2.5％ 15.6％

[0176] S2: 50 g of soda ash (sodium carbonate) and 50 g of activated diatomaceous earth were added to the first intermediate acid of S1, and the acid solution was stirred to fully contact the diatomaceous earth. After the mixed acid solution no longer produced bubbles, 12.5 g of sodium sulfide nonahydrate and 56 g of activated carbon powder were added thereto. After the reaction was complete, the generated precipitate (defluorination, dearsenicization, and heavy metal removal slag) was filtered off to obtain the second intermediate acid.

[0177] The molar ratio of the total amount of Na in sodium carbonate and activated diatomaceous earth to F in the first intermediate acid is 0.56:1; the molar ratio of As in the first intermediate acid to S in sodium sulfide nonahydrate is 1:50; and the amount of activated carbon powder used is 2 wt % of the first intermediate acid.

[0178] S3: Add 29g of hydrogen peroxide to the second intermediate acid of S2, stir to ensure full contact between the two, and then add 115g of barium carbonate to the acid for fine desulfurization. After the reaction is complete, filter the reaction liquid to separate the pretreated acid (fine desulfurization clear liquid) and fine desulfurization slag (barium slag).

[0179] The amount of hydrogen peroxide used is 1 wt % of the second intermediate acid; and the molar ratio of barium in the barium carbonate to sulfate in the second intermediate acid is 2.25:1.

[0180] S4: The pretreated acid obtained in S3 is concentrated, filtered, and separated to obtain concentrated pretreated acid and a first precipitated residue containing iron and aluminum.

[0181] The concentrated pretreated acid is composed of the following:

[0182] <![CDATA[P2O5]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO MnO As <![CDATA[SO3]]> F CaO 43.35％ 1.76％ 0.81％ 3.98％ 0.1％ 0.0001％ 0.009％ 0.21％ 0.03％

[0183] S5: Weigh 500 g of the concentrated pretreated acid in S4, add 50 g of concentrated aqueous ammonia thereto for pre-neutralization reaction, and then place the pre-neutralized solution in a water bath at 55° C. with stirring to obtain a pre-neutralized reaction solution.

[0184] The molar ratio of M (ammonia) in the concentrated ammonia water to phosphorus in the concentrated pretreatment acid is 0.25:1.

[0185] S6: 1000 g of anhydrous ethanol was added to the pre-neutralization reaction liquid (536.12 g) of S5, and the mixture was stirred for a full reaction (reaction temperature: 55° C.). The mixture was filtered to obtain a first purified liquid and a second precipitate containing iron, aluminum, magnesium, and manganese. 130 g of a 15% sodium carbonate aqueous solution (the molar ratio of M in the sodium carbonate aqueous solution to P in the first purified liquid was 0.2:1) was added to the first purified liquid for washing. After full reaction, the mixture was allowed to stand for separation to obtain a second purified liquid and a first washing liquid.

[0186] S7: 800 g of anhydrous ethanol was further added to the second purified liquid (1359.82 g) in S6, stirred to fully react, and filtered to separate to obtain a third purified liquid and a third precipitate residue containing magnesium and alkali metals.

[0187] S8: distilling the third purified liquid in S7 to collect high-concentration ethanol and water, and the remaining liquid is purified phosphoric acid; concentrating the purified phosphoric acid so that the mass fraction of H3PO4 in the acid is ≥85%, thereby obtaining industrial-grade phosphoric acid.

[0188] The composition of this industrial grade purified phosphoric acid is as follows:

[0189]

[0190] Meet the quality requirements of industrial-grade phosphoric acid.

[0191] S9: As Figure 2 As shown, the first precipitated residue, the second precipitated residue, and the third precipitated residue are mixed to obtain a mixed precipitated residue. 1000 g of deionized water is added to the mixed precipitated residue (380.34 g) to prepare a slurry. The obtained slurry is strongly acidic. Sodium hydroxide is added thereto to react and the pH value of the first slurry is adjusted to 6.0. The phosphate precipitated residue and the separated liquid are obtained by filtration.

[0192] S10: 1500 g of deionized water was added to the phosphate precipitate residue (315.67 g) obtained in S9, and the mixture was stirred to prepare a slurry to obtain a second slurry. The second slurry was heated in a water bath at 80° C., and then sodium hydroxide (221 g) was added to the hot slurry to perform a first-stage leaching reaction. During the first-stage leaching reaction, the pH value of the reaction slurry was approximately 13.5. The reaction was stirred for approximately 35 minutes, and then the mixture was separated by sedimentation to obtain a first-stage leachate and a first sediment residue.

[0193] S11: 1500 g of deionized water was added to the first sediment (370.34 g) obtained in S10, and the mixture was stirred evenly. The prepared slurry was heated in a water bath at 50°C. Subsequently, sodium hydroxide (100 g) was added to the preheated slurry to carry out a second-stage leaching reaction. During the second-stage leaching reaction, the pH value of the reaction liquid was approximately equal to 14.1. The mixture was stirred for 75 minutes, and filtered to obtain a second-stage leachate and a second sediment.

[0194] S12: The second sediment from S11 (202.32 g) is washed with 800 g of a 4 wt% aqueous sodium hydroxide solution and then filtered to obtain a first wash solution and a first slurry. The first wash solution is recovered and mixed with the second-stage leachate. The first slurry is washed with 800 g of deionized water, followed by solid-liquid separation to obtain a second wash solution and dephosphorization slag. The dephosphorization slag is then dried and analyzed for composition. The second wash solution can be recycled as a dilute alkali solution to the alkaline washing process of the second sediment.

[0195] The composition of the above-mentioned dephosphorization slag is as follows:

[0196] composition / % Mn Al P Ca Fe K Mg Na Dephosphorization slag 0.4511 10.4231 0.8956 0.6724 8.7621 0.0074 16.7823 1.3201

[0197] It can be seen that the phosphorus element in the phosphate precipitation residue is completely extracted by the alkali solution during the leaching process, the phosphorus leaching rate is >99%, and the dephosphorization residue is a mixture of hydroxides of metal elements.

[0198] S13: 227.16 g of calcium hydroxide was weighed according to a Ca:P = 1.50:1 (molar ratio), and 700 g of deionized water was added thereto to prepare a slurry to obtain a lime slurry. The lime slurry was added to the second leachate from step S11 to precipitate phosphate ions in the solution, and stirred in a 50°C water bath to perform a first metathesis reaction. After the reaction lasted for 55 minutes, the reaction solution was allowed to settle. The lower layer of slurry was separated and added to the first leachate to perform a second metathesis reaction. The reaction was stirred in a 55°C water bath for 40 minutes. After the reaction was complete, the generated calcium hydroxyphosphate was separated by filtration.

[0199] S14: 1300 g of deionized water is added to the calcium hydroxyphosphate obtained in S13 for washing. After washing, the mixture is filtered and dried to obtain calcium hydroxyphosphate powder.

[0200] The composition of the resulting calcium hydroxyphosphate is as follows:

[0201] name P％ Al％ Ca% Na% Calcium hydroxyphosphate 14.84 0.08 34.86 3.67

[0202] According to the results, the separation of phosphorus and aluminum is relatively thorough.

[0203] Example 2

[0204] This embodiment provides a method for recycling raffinate in a wet purification process for producing phosphoric acid, wherein S1 to S4 are the same as those in Example 1, except that:

[0205] S5: Weigh 500 g of the concentrated pretreated acid in S4, add 50 g of sodium carbonate thereto for pre-neutralization reaction, and then place the pre-neutralized solution in a water bath at 55° C. with stirring to obtain a pre-neutralized reaction solution.

[0206] The molar ratio of M (sodium) in the sodium carbonate to phosphorus in the concentrated pretreated acid is 0.31:1.

[0207] S6: To the pre-neutralization reaction liquid (527 g) of S5, 900 g of mixed alcohol (ethanol:isopropanol = 4:1, mass ratio) was added, stirred to allow for full reaction (reaction temperature 60°C), and filtered to obtain a first purified liquid and a second precipitate containing iron, aluminum, magnesium, and manganese. 160 g of a 30% by mass sodium dihydrogen phosphate solution (the molar ratio of M in the sodium dihydrogen phosphate solution to P in the first purified liquid was 0.2:1) was added to the first purified liquid for washing. After full reaction, the solution was allowed to stand and separate, obtaining a second purified liquid and a first washing liquid.

[0208] S7: Add 700 g of mixed alcohol (ethanol: n-butanol = 4:1, mass ratio) to the second purified liquid (1250 g) in S6, stir to fully react, filter and separate to obtain a third purified liquid and a third precipitate containing manganese and alkali metals.

[0209] S8: distilling the third purified liquid in S7 to collect high-concentration alcohol solution and water, and the remaining liquid is purified phosphoric acid; concentrating the purified phosphoric acid so that the mass fraction of H3PO4 in the acid is ≥85% to obtain industrial-grade phosphoric acid.

[0210] The composition of the resulting technical-grade phosphoric acid is as follows:

[0211] <![CDATA[P2O5]]> Cl <![CDATA[SO3]]> <![CDATA[Fe2O3]]> MgO <![CDATA[Al2O3]]> MnO CaO F As 61.83％ 0.0001％ 0.001％ 0.0004％ 0.001％ 0.0011％ 0.0001％ 0.0008％ 0.006％ 0.0001％

[0212] Compared with Example 1, the usage ratio of the mixed alcohol is lower than that of single ethanol, which shows that the mixed alcohol has a better purification effect.

[0213] Comparative Example 1

[0214] This comparative example provides a method for recycling raffinate in the process of wet purification of phosphoric acid, wherein S1 to S4 are the same as those in Example 1, except that:

[0215] S5: Weigh 500 g of the concentrated pretreated acid in S4, add 50 g of concentrated aqueous ammonia thereto for pre-neutralization reaction, and then place the pre-neutralized solution in a water bath at 55° C. with stirring to obtain a pre-neutralized reaction solution.

[0216] The molar ratio of M (sodium) in the sodium carbonate to phosphorus in the concentrated pretreated acid is 0.25:1.

[0217] S6: 1000 g of anhydrous ethanol was added to the pre-neutralization reaction solution (535.84 g) from S5, and the mixture was stirred for a full reaction (reaction temperature: 60° C.). Filtering and separation were performed to obtain a first purified solution and a second precipitate containing iron, aluminum, magnesium, and manganese. 160 g of a 30% by mass sodium dihydrogen phosphate solution (the molar ratio of M in the sodium dihydrogen phosphate solution to P in the first purified solution was 0.2:1) was added to the first purified solution for washing. After full reaction, the solution was allowed to stand for separation to obtain a second purified solution and the first washed solution.

[0218] S7: Add 900 g of anhydrous ethanol to the second purified liquid (1360.13 g) in S6, stir to fully react, filter and separate to obtain a third purified liquid and a third precipitate containing magnesium and alkali metals.

[0219] S8: distilling the third purified liquid in S7 to collect high-concentration ethanol and water, and the remaining liquid is purified phosphoric acid; concentrating the purified phosphoric acid so that the mass fraction of H3PO4 in the acid is ≥85%, thereby obtaining industrial-grade phosphoric acid.

[0220] The composition of this industrial grade purified phosphoric acid is as follows:

[0221]

[0222] The acid meets the quality requirements of industrial-grade phosphoric acid.

[0223] S9: The first, second, and third precipitates are mixed to obtain a mixed precipitate. 1000 g of deionized water is added to the mixed precipitate (383.24 g) to prepare a slurry. The obtained slurry is strongly acidic. Sodium hydroxide is added thereto to react and the pH value of the first slurry is adjusted to 6.5. The phosphate precipitate is separated by filtration to obtain a phosphate precipitate and a separated liquid.

[0224] S10: Add 1500g of deionized water to the phosphate precipitate residue (316.11g) obtained in S9, stir and slurry to obtain a second slurry. Heat the second slurry in a water bath at 85°C, then add sodium hydroxide (230g) to the hot slurry to perform a first-stage leaching reaction. During the first-stage leaching reaction, the pH value of the reaction slurry is about 13.7. Stir and react for about 40 minutes, then settle and separate to obtain a first-stage leachate and a first sediment residue.

[0225] S11: 1500 g of deionized water was added to the first sediment (368.87 g) obtained in S10, and the mixture was stirred evenly. The prepared slurry was heated in a water bath at 50°C, and then sodium hydroxide (96 g) was added to the preheated slurry to carry out a second-stage leaching reaction. During the second-stage leaching reaction, the pH value of the reaction liquid was approximately equal to 14.1. The mixture was stirred for 75 minutes, and filtered to obtain a second-stage leachate and a second sediment.

[0226] S12: The second sediment from S11 (204.44 g) is washed with 800 g of a 4 wt% aqueous sodium hydroxide solution and filtered to obtain a first wash solution and a first slurry. The first wash solution is recovered and mixed with the second-stage leachate. The first slurry is washed with 800 g of deionized water and subjected to solid-liquid separation to obtain a second wash solution and dephosphorization slag. The dephosphorization slag is then dried and analyzed for composition. The second wash solution can be recycled as a dilute alkali solution to the alkaline washing process of the second sediment.

[0227] The composition of dephosphorization slag is as follows:

[0228] composition / % Mn Al P Ca Fe K Mg Na Dephosphorization slag 0.4211 10.1410 0.7956 0.8523 8.8241 0.0142 16.3214 1.6071

[0229] It can be seen that the phosphorus element in the phosphate precipitation residue is completely extracted by the alkali solution during the leaching process, the phosphorus leaching extraction rate is >99%, and the dephosphorization residue is a mixture of hydroxides of metal elements.

[0230] S13: 226.75 g of calcium hydroxide was weighed at a molar ratio of Ca:P = 1.50:1, and 700 g of deionized water was added thereto to prepare a lime slurry. The first-stage leachate, the second-stage leachate, and the alkaline wash solution were mixed. The prepared lime slurry was then added to the mixed leachate. The mixture was stirred in a water bath at 55°C for 70 minutes, and the reaction solution was filtered to separate the generated calcium hydroxyphosphate.

[0231] S14: 1300 g of deionized water is added to the calcium hydroxyphosphate obtained in S13 for washing. After washing, the mixture is filtered and dried to obtain calcium hydroxyphosphate powder.

[0232] The composition of the resulting calcium hydroxyphosphate is as follows:

[0233] name P％ Al％ Ca% Na% Calcium hydroxyphosphate 12.76 1.8 37.98 2.17

[0234] According to the above test results, single-stage precipitation reduces the conversion rate of soda lime and the separation effect of phosphorus and aluminum elements.

[0235] Comparative Example 2

[0236] This comparative example provides a method for recycling raffinate in the process of wet purification of phosphoric acid, wherein S1 to S4 are the same as those in Example 1, except that:

[0237] S5: Weigh 500 g of the concentrated pretreated acid in S4, add 50 g of concentrated aqueous ammonia thereto for pre-neutralization reaction, and then place the pre-neutralized solution in a water bath at 55° C. with stirring to obtain a pre-neutralized reaction solution.

[0238] The molar ratio of M (ammonia) in the sodium carbonate to phosphorus in the concentrated pretreatment acid is 0.25:1.

[0239] S6: Add 1800 g of anhydrous ethanol to the pre-neutralization reaction liquid (536.51 g) of S5, stir to fully react (reaction temperature is 55° C.), filter and separate to obtain the first purified liquid and the second precipitate residue containing iron, aluminum, magnesium and manganese.

[0240] S7: distilling the first purified liquid obtained in S6, collecting high-concentration ethanol and water, and the remaining liquid is purified phosphoric acid; concentrating the purified phosphoric acid so that the mass fraction of H3PO4 in the acid is ≥85%, thereby obtaining purified acid.

[0241] The purified acid is composed as follows:

[0242]

[0243] S7: Take the second precipitated residue separated in S6, add 700g of deionized water to the residue (210.84g) to make a slurry. The obtained slurry is strongly acidic. Sodium hydroxide is added thereto to react and the pH value of the first slurry is adjusted to 5.5 to obtain a phosphate precipitated residue and a separated liquid.

[0244] S8: Add 2000 g of deionized water to the phosphate precipitate residue (201.63 g) obtained in S7, stir and slurry to obtain a slurry. The prepared slurry is heated in a water bath at 75°C, and then sodium hydroxide (210 g) is added to the hot slurry to perform a first-stage leaching reaction. During the first-stage leaching reaction, the pH value of the reaction slurry is approximately 14.1. The reaction is stirred for approximately 120 minutes, and then separated by sedimentation to obtain a leachate and a precipitate residue.

[0245] S9: The sediment in S8 was washed with 1000 g of 4 wt% sodium hydroxide aqueous solution and then filtered. The filter residue was then washed with 1000 g of deionized water. After washing, the filter residue (dephosphorization residue) was dried and its composition was analyzed.

[0246] The composition of dephosphorization slag is as follows:

[0247] composition / % Mn Al P Ca Fe K Mg Na Dephosphorization slag 0.4511 6.2111 2.7956 0.7523 6.2101 0.0142 21.9842 1.85

[0248] S10: 131.12 g of calcium hydroxide was weighed according to a Ca:P = 1.50:1 (molar ratio), and 450 g of deionized water was added thereto to prepare a slurry to obtain a lime slurry. The lime slurry was added to the above-mentioned alkaline wash solution to precipitate the phosphate in the alkaline wash solution, and the solution was stirred in a water bath at 50°C to perform a first double decomposition reaction. After the reaction time was 45 minutes, the reaction solution was allowed to settle, and the lower layer of slurry was separated and added to the first-stage leachate to perform a second double decomposition reaction. The solution was stirred in a water bath at 55°C for 45 minutes. After the reaction was complete, the generated calcium hydroxyphosphate was separated by filtration.

[0249] S11: adding 600 g of deionized water to the calcium hydroxyphosphate obtained in S10 for washing, filtering and drying after washing to obtain calcium hydroxyphosphate powder.

[0250] The composition of the resulting calcium hydroxyphosphate sample is as follows:

[0251] name P％ Al％ Ca% Na% Calcium hydroxyphosphate 14.16 0.5 36.28 2.87

[0252] By comparison with Example 1, it can be seen that:

[0253] ① After removing the acid-containing solvent phase washing step, even if sufficient organic precipitant is added to the purified acid, it still cannot effectively remove the magnesium and calcium ions in the acid. Furthermore, the magnesium ion content in the raffinate acid is too high, which increases the demand for detergent in the washing process. Furthermore, the organic precipitant must be added stepwise to remove the metal ions that enter the acid-containing solvent phase during the washing process.

[0254] ②. During single-stage leaching, the leaching rate of aluminum in phosphate precipitate residue increased, and the leaching extraction rate of phosphorus was around 96%, which was much lower than that of two-stage cross-flow leaching.

[0255] ③. The aluminum-phosphorus ratio of the leachate increases, which increases the aluminum content of the phosphorus precipitation product calcium hydroxyphosphate in the leachate.

[0256] Comparative Example 3

[0257] This comparative example provides a method for recycling raffinate in the process of wet purification of phosphoric acid, wherein S1 to S4 are the same as those in Example 1, except that:

[0258] S5: Weigh 500 g of the concentrated pretreated acid in S4, add 50 g of sodium carbonate thereto for pre-neutralization reaction, and then place the pre-neutralized solution in a water bath at 55° C. with stirring to obtain a pre-neutralized reaction solution.

[0259] The molar ratio of M (sodium) in the sodium carbonate to phosphorus in the concentrated pretreated acid is 0.31:1.

[0260] S6: 1800 g of ethanol was added to the pre-neutralization reaction solution (527 g) from S5, and the mixture was stirred for a full reaction (reaction temperature: 60° C.). The mixture was filtered to obtain a first purified solution and a second precipitate containing iron, aluminum, magnesium, and manganese. 200 g of a 30% by mass sodium dihydrogen phosphate solution (the molar ratio of Na in the sodium dihydrogen phosphate solution to P in the first purified solution was 0.27:1) was added to the first purified solution for washing. After full reaction, the solution was allowed to stand for separation to obtain a second purified solution and the first washed solution.

[0261] S7: distilling the second purified liquid obtained in S6 to collect high-concentration ethanol and water, and the remaining liquid is purified phosphoric acid; concentrating the purified phosphoric acid so that the mass fraction of H3PO4 in the acid is ≥85%, thereby obtaining purified acid.

[0262] The resulting purified acid has the following composition:

[0263]

[0264] Comparison with Example 1 shows that while the combination of a single-stage purification and a single-stage washing method effectively removes the vast majority of cationic impurities in the raffinate acid, the low water mass fraction in the solvent phase during washing requires a relatively large amount of detergent to form a relatively stable solvent-salt solution two-phase system to clean the acid-containing solvent. Furthermore, during this process, sodium ions in the detergent migrate significantly to the solvent phase due to the potential difference between the two phases. After distillation of the solvent phase, all of the sodium ions that enter the solvent remain in the purified acid, resulting in excessive sodium ion content in the purified acid.

[0265] Application Examples

[0266] This application example provides a method for recycling raffinate in a pilot wet purification process for producing phosphoric acid, which comprises the following steps:

[0267] S1: Phosphate concentrate powder is added with water at a mass ratio of 2:1 to prepare a concentrate slurry with a solid content of 60%, and then the concentrate slurry: raffinate acid is prepared at a mass ratio of 1:7 (Ca 2+ :SO4 2- =0.90:1, molar ratio) the two materials were added into a crude desulfurization reactor with stirring for crude desulfurization reaction, the residence time of the materials in the reactor was controlled at 30-40min, and the reaction liquid after sufficient reaction was discharged from the bottom of the reactor and sent to the pretreatment sedimentation tank for sedimentation separation.

[0268] The above-mentioned raffinate acid and phosphate concentrate powder to be treated are the same as those in Example 1.

[0269] S2: The clear liquid in the upper layer of the sedimentation tank is sent to the defluorination tank, and the slurry discharged from the lower layer is sent to the reaction tank of the wet phosphoric acid device to recover the phosphorus entrained therein.

[0270] S3: Add defluorinating agent sodium carbonate and activated diatomaceous earth powder to the defluorinating tank according to 4% of the mass of the clear liquid (Na:F=0.5:1, molar ratio), wherein the mass ratio of sodium carbonate to activated diatomaceous earth is 1:1, stir to evenly mix the defluorinating agent and the acid solution, and then send the mixed slurry to the dearsenicating tank.

[0271] S4: Prepare a 5% mass fraction of sodium sulfide solution for standby use. First, add the prepared sodium sulfide solution (As:S = 1:50, molar ratio) to the arsenic removal tank at a ratio of 2.8% of the acid mass. Then, add 80% activated carbon powder passing through an 80-mesh sieve to the acid at a ratio of 2.5% of the acid mass. After stirring and reacting for 45 minutes, send the reaction solution to a filter press for filtration. Collect the filtrate into the arsenic removal acid collection tank, and collect the filter residue for unified treatment.

[0272] S5: The hydrogen sulfide gas generated during the arsenic removal process is introduced into the scrubbing tower through a forced ventilation system, absorbed by a 5% mass fraction sodium hydroxide solution, and then reused.

[0273] S6: According to the dearsenic acid: hydrogen peroxide: barium hydroxide = 100:1:2.5 (Ba:SO4 2- =2:1, molar ratio) was used to add dearsenic acid, industrial-grade hydrogen peroxide and barium hydroxide into the fine desulfurization reaction tank. After stirring for 45 minutes, the reaction liquid was sent to a filter press for filtration to separate the fine desulfurization slag (barium slag) and pretreatment acid.

[0274] S7: The barium slag is collected and added to the phosphate concentrate slurry to perform coarse desulfurization of the residual acid together with the phosphate concentrate. The amount of phosphate concentrate does not need to be adjusted.

[0275] S8: The pretreated acid is concentrated to a P2O5 content of >40 wt% in the concentrated acid. The concentrated acid solution is filtered to separate suspended solids, yielding concentrated pretreated acid and a first precipitate residue containing iron and aluminum. The concentrated pretreated acid is fed to a pre-neutralization tank, and the first precipitate residue is fed to a phosphate residue slurry mixing tank.

[0276] S9: The concentrated pretreated acid is heated to 55°C in a pre-neutralization tank, and then sodium carbonate powder is added to the pre-neutralization tank according to a molar ratio of Na:P = 0.3:1. After the reaction is complete, the obtained pre-neutralization reaction liquid is sent to the first-stage solvent precipitation tank.

[0277] S10: Add mixed alcohol to the pre-neutralization reaction liquid in a mass ratio of pre-neutralization reaction liquid: mixed alcohol precipitant (ethanol: isopropanol: n-butanol = 8:1:1) = 1:2.5. After stirring for 30 minutes, the reaction liquid is centrifuged to obtain a first purified liquid and a second precipitate containing iron, aluminum, magnesium and manganese. The second precipitate is sent to a phosphate slag slurry mixing tank, and the first purified liquid is sent to the middle of a washing and clarification tank.

[0278] S11: Add 15% sodium carbonate solution to the middle of the washing and clarifying tank at a molar ratio of Na:P=0.18:1, stir and react to obtain a second purified liquid and a first washing liquid. The first washing liquid after washing is discharged from the bottom of the washing and clarifying tank, and the second purified liquid is all recycled to the pre-neutralization reaction tank. The amount of sodium carbonate is deducted according to the amount of sodium ions in the washing liquid, and 0.5 mol of sodium carbonate is deducted for 1 mol of sodium ions.

[0279] S12: The second purified liquid is discharged from the upper part of the washing and clarifying tank and sent to the second-stage solvent precipitation tank. A mixed alcohol precipitant (ethanol: isopropanol: n-butanol = 8:1:1) with a mass ratio of 40% of the solvent is added to the bottom of the second-stage solvent precipitation tank, and the mixture is stirred to allow the solvent to fully react. The solvent after the reaction is filtered through a precision filter to obtain a third purified liquid and a third precipitate residue containing manganese and alkali metals; the third precipitate residue discharged from the precision filter is regularly sent to the first-stage solvent precipitation tank, and the separated third purified liquid is subjected to distillation to separate and purify phosphoric acid, water, and precipitant. The precipitant is collected and recycled, and the phosphoric acid is concentrated and purified so that the mass fraction of H3PO4 in the acid is ≥85%, thereby obtaining industrial-grade purified phosphoric acid.

[0280] The obtained industrial-grade purified phosphoric acid has the following composition (the cycle is repeated 7 times, and the industrial-grade phosphoric acid composition corresponding to each cycle is as follows):

[0281]

[0282] The acid meets the quality requirements of industrial-grade phosphoric acid.

[0283] S13: adding water to the phosphate slag slurry mixing tank at a liquid-solid ratio of 3:1 to prepare slurry, then sending the prepared slurry to a primary neutralization tank, adding sodium hydroxide solution to the primary neutralization tank to adjust the pH value of the slurry to 6.0;

[0284] S14: The slurry after alkali adjustment is sent to the primary leaching sedimentation tank for static sedimentation. The upper phosphate solution is filtered to remove a small amount of suspended matter and then reused in the solvent washing stage, pre-neutralization stage and pre-treatment acid defluorination stage, completely replacing the use of sodium carbonate. The excess phosphate solution is sent to the secondary phosphorus precipitation tank;

[0285] S15: The phosphate precipitated slurry discharged from the lower layer of the sedimentation tank is introduced into the secondary neutralization tank, and is diluted with hot water at a rate of 5 times the mass of the slurry. Subsequently, sodium hydroxide is added to the secondary neutralization tank to maintain the pH of the reaction solution at 13.6-13.8 and the temperature at 78-82°C. After stirring and reacting for 45 minutes, the alkaline reaction solution is transferred to the secondary leaching sedimentation tank for sedimentation and separation of the primary leachate and the primary leach slurry. The primary leachate is sent to the secondary phosphorus precipitation tank and the primary neutralization tank;

[0286] S16: The primary leaching slurry is sent to a tertiary neutralization tank, where water 5 times the mass of the slurry is added to dilute the slurry. Subsequently, sodium hydroxide is added to the tertiary neutralization tank to maintain the pH of the reaction solution at 14.1-14.3 and the temperature at 48-52°C. After stirring and reacting for 70 minutes, the alkaline reaction solution is transferred to a tertiary leaching sedimentation tank for sedimentation to separate the secondary leachate and the secondary leaching slurry. The secondary leachate is sent to the primary phosphorus precipitation tank;

[0287] S17: The secondary leaching slurry is sent to the alkali washing tank, where a 4-6% sodium hydroxide solution with a concentration of 4 times the slurry mass is added to the slurry for rinsing. The rinse liquid is sent to the fourth leaching sedimentation tank for sedimentation and separation of the alkali washing liquid and the alkali washing residue. The alkali washing liquid is returned to the third neutralization tank.

[0288] S18: The alkali-washed residue is sent to a water washing tank, where clean water three times the mass of the residue slurry is added to rinse the residue slurry. The rinse liquid is filtered through a filter press to separate the dephosphorization residue and the washing liquid. A small amount of concentrated alkali liquid is added to the washing liquid to prepare a 4-6% concentration of sodium hydroxide solution, which is then returned to the alkali washing tank. The separated dephosphorization residue is collected and processed uniformly.

[0289] The composition of the dephosphorization slag after leaching is as follows:

[0290]

[0291]

[0292] S19: preparing a lime slurry with a mass fraction of 25%, adding the prepared lime slurry to the primary phosphorus precipitation tank, stirring to fully contact the lime slurry with the secondary leachate to perform a phosphorus precipitation reaction, transferring the primary phosphorus precipitation reaction liquid to the primary phosphorus precipitation settling tank for sedimentation and separation of dilute alkali solution and primary phosphorus precipitation residue; transferring the primary phosphorus precipitation residue to the secondary phosphorus precipitation tank for fully contacting with the secondary leachate to perform a phosphorus precipitation reaction, and separating the dilute alkali solution and secondary phosphorus precipitation residue after the secondary phosphorus precipitation reaction liquid is treated in the secondary phosphorus precipitation settling tank;

[0293] S20: The amount of lime slurry is determined based on the molar ratio of calcium oxide in the lime milk to total phosphorus in the two-stage leachate = 1.50-1.60:1. The amount is appropriately increased or decreased according to the phosphorus and aluminum contents in the secondary phosphorus precipitate to ensure that the phosphorus content in the secondary phosphorus precipitate is greater than 14.0% and the aluminum content is less than 0.1%;

[0294] S21: The secondary phosphorus precipitate residue that does not meet the requirements is returned to the secondary phosphorus precipitation tank for re-conversion. The secondary phosphorus precipitate residue that meets the requirements is sent to the calcium phosphate washing tank and rinsed with clean water three times the mass of the phosphorus precipitate residue. The rinse liquid is filtered and then the hydroxy calcium phosphate is recovered. The washing water is collected and used to prepare lime milk. Part of the hydroxy calcium phosphate is returned to the coarse desulfurization stage to fully replace the phosphate concentrate powder.

[0295] S22: The dilute alkali solution separated from the primary phosphorus precipitation sedimentation tank and the secondary phosphorus precipitation sedimentation tank is sent to the alkali solution collection tank, and a small amount of alkali lost in the process is added to it and the alkali solution is appropriately concentrated. The concentrated alkali solution is returned to the secondary neutralization tank and the tertiary neutralization tank for further use.

[0296] The composition of calcium hydroxyphosphate is as follows:

[0297] name P％ Al％ Ca% Na% ① 14.62 0.07 34.98 1.67 ② 14.21 0.10 35.42 1.82 ③ 14.44 0.09 34.99 2.11 ④ 14.03 0.10 35.84 2.32 ⑤ 14.65 0.06 35.01 1.23 ⑥ 14.35 0.08 34.92 1.11 ⑦ 14.67 0.08 34.78 1.47

[0298] The above results demonstrate that the phosphorus in the phosphate precipitate residue is completely extracted by the alkali solution during the leaching process, with a phosphorus leaching rate exceeding 99%. The dephosphorization residue is a mixture of metal hydroxides. After multiple cycles of alkali solution, the amount of aluminate loaded in the solution no longer changes significantly, indicating that the circulating alkali solution no longer dissolves aluminum from the phosphate precipitate residue, and the dephosphorization residue composition stabilizes.

[0299] During the leaching process, sodium hydroxide solution reacts with carbon dioxide in the air to form sodium carbonate. The ionized carbonate ions are converted into calcium carbonate during the lime milk precipitation stage and enter the hydroxy calcium phosphate product. Therefore, the production of hydroxy calcium phosphate is mainly used for the production of wet-process phosphoric acid and defluorination of fluoride wastewater.

[0300] In summary, the method provided by the present disclosure can effectively recycle phosphorus resources in raffinate acid, and the obtained industrial-grade phosphoric acid can be used as a raw material to prepare battery-grade phosphate.

[0301] Industrial Applicability

[0302] The raffinate acid utilization method proposed in this disclosure cleverly solves the current technical dilemma that the utilization of raffinate acid must rely on fertilizer processing plants, ensuring the integrity and independence of the phosphoric acid purification process. The method proposes a new phosphate precipitate leaching scheme, achieving the purpose of selectively extracting phosphorus from complex phosphate precipitates containing iron, aluminum, and magnesium. In the open-circuit process, the vast majority of phosphorus (about 98.5% or more) and a smaller proportion of aluminum (about 30% or less) in the phosphate precipitate can be transferred to the leachate; in the closed-circuit process, phosphorus can be extracted separately from the complex phosphate precipitate containing iron, aluminum, and magnesium. Through reasonable process design, the method maximizes the conversion of phosphorus in raffinate acid into industrial-grade purified phosphoric acid, while converting the low-utilization-value, essentially useless by-product insoluble phosphate salts into high-value and widely used calcium hydroxyphosphate, achieving comprehensive recovery and efficient utilization of phosphorus resources in raffinate acid.

Claims

1. A method for recycling raffinate in the process of wet purification of phosphoric acid, characterized in that: The method comprises the following steps: mixing the raffinate acid to be treated with a coarse desulfurizing agent to perform coarse desulfurization to obtain a first intermediate acid; mixing the first intermediate acid with a defluorinating agent, a sulfide and a filter aid to remove fluorine, arsenic and heavy metals to obtain a second intermediate acid; mixing the second intermediate acid with an oxidizing agent and a fine desulfurizing agent to perform fine desulfurization to obtain a pretreated acid and a fine desulfurization slag; The pretreated acid is pre-neutralized and then purified to obtain a purified liquid and a precipitated residue containing iron, aluminum, and magnesium, and the purified liquid is distilled to obtain industrial-grade phosphoric acid; The crude desulfurizer includes at least one of phosphate concentrate calcium carbonate, calcium hydroxide and calcium oxide; the fine desulfurizer includes at least one of barium hydroxide and barium carbonate; The purification process includes: mixing the pre-neutralization reaction liquid obtained by pre-neutralization with a first precipitant to perform a first purification, and performing solid-liquid separation to obtain a first purified liquid and a second precipitate residue containing iron phosphate, aluminum phosphate and magnesium phosphate; mixing the first purified liquid with a detergent to perform a second purification, and performing solid-liquid separation to obtain a second purified liquid and a first washing liquid; and mixing the second purified liquid with a second precipitant to perform a third purification, and performing solid-liquid separation to obtain a third purified liquid and a third precipitate residue containing a small amount of magnesium phosphate and alkali metal phosphate.

2. The recycling method according to claim 1, characterized in that: The molar ratio of calcium in the crude desulfurizer to sulfate in the raffinate acid is (0.8:1)-(1.0:1).

3. The recycling method according to claim 1, characterized in that: The defluorination agent includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate, and activated diatomaceous earth; Or, the sulfide includes at least one of sodium sulfide, calcium sulfide, potassium sulfide and phosphorus pentasulfide; Alternatively, the filter aid comprises activated carbon.

4. The recycling method according to claim 3, characterized in that: The molar ratio of Na in the defluorinating agent to F in the first intermediate acid is (0.4:1)-(0.8:1); Or, the molar ratio of As in the first intermediate acid to S in the sulfide is (1:15)-(1:75); Alternatively, the filter aid is used in an amount of 0.5 wt % to 5 wt % of the first intermediate acid.

5. The recycling method according to claim 1, characterized in that: The amount of the oxidant used is 0.5wt%-1.5wt% of the second intermediate acid; Alternatively, the molar ratio of the barium in the fine desulfurizer to the sulfate in the second intermediate acid is (1.5:1)-(2.5:1).

6. The recycling method according to claim 1, characterized in that: The fine desulfurization slag is returned to the rough desulfurization process to be used as a rough desulfurization agent.

7. The recycling method according to any one of claims 1 to 6, characterized in that: Before pre-neutralization, the pre-treated acid is concentrated and solid-liquid separated to obtain concentrated pre-treated acid and a first precipitated residue containing iron phosphate and aluminum phosphate; The content of P2O5 in the concentrated pre-treated acid is not less than 40 wt%.

8. The recycling method according to claim 7, characterized in that: mixing the concentrated pre-treated acid with a neutralizing agent for pre-neutralization to obtain a pre-neutralized reaction solution; The neutralizing agent includes salts of potassium, sodium, ammonium, and at least one of ammonia, sodium hydroxide, and potassium hydroxide.

9. The recycling method according to claim 8, characterized in that: The potassium, sodium, and ammonium salts are in the form of at least one of carbonate, bicarbonate, and phosphate; Alternatively, the molar ratio of M in the neutralizing agent to phosphorus in the concentrated pretreatment acid is (0.2:1)-(0.4:1), where M corresponds to ammonia, sodium and / or potassium contained in the neutralizing agent.

10. The recycling method according to claim 1, characterized in that: The first purification process includes at least one of the following characteristics: Feature 1: The first precipitant includes at least one of methanol, ethanol, propanol, butanol and acetone; Feature 2: The amount of the first precipitant used is 1 to 2.5 times the amount of the pre-neutralization reaction solution; Feature 3: The temperature of the first purification is 25℃-65℃.

11. The recycling method according to claim 1, characterized in that: The second purification process includes at least one of the following characteristics: Feature 1: The solute in the detergent includes at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate and potassium phosphate; Feature 2: The mass fraction of the solute in the detergent is not less than 10%; Feature 3: The molar ratio of M in the detergent to P in the first purification solution is (0.15:1)-(0.3:1), where M corresponds to the sodium and / or potassium contained in the detergent.

12. The recycling method according to claim 11, characterized in that: The first washing liquid is returned to the pre-neutralization process to be used as a neutralizing agent.

13. The recycling method according to claim 1, characterized in that: The third purification process includes at least one of the following characteristics: Feature 1: The second precipitant includes at least one of methanol, ethanol, propanol, butanol and acetone; Feature 2: The usage amount of the second precipitant is 20wt%-100wt% of the second purified liquid.

14. The recycling method according to claim 13, characterized in that: The third precipitated residue is returned to the first purification process, or the third precipitated residue is mixed with the first precipitated residue and the second precipitated residue and then pulped and recovered.

15. The recycling method according to claim 13, characterized in that: After the third purification liquid is distilled, industrial-grade phosphoric acid is obtained.

16. The recycling method according to claim 14, characterized in that: The third precipitated residue is mixed with the first precipitated residue and the second precipitated residue to prepare a pulp for recovery, which includes: The first precipitated residue, the second precipitated residue and the third precipitated residue are mixed with water and a first alkaline substance, neutralized and precipitated to obtain a first slurry; the first slurry is subjected to solid-liquid separation to obtain a separated liquid and phosphate precipitated residue.

17. The recycling method according to claim 16, characterized in that: Pulping recovery includes at least one of the following features: Feature 1: The water used for mixing with the first precipitated residue, the second precipitated residue, and the third precipitated residue is desalted water; Feature 2: The mass ratio of water to the total amount of the first precipitated residue, the second precipitated residue, and the third precipitated residue is (2:1)-(5:1); Feature 3: The first alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, sodium orthophosphate and potassium orthophosphate; Feature 4: The pH value of the first slurry is 5.5-8.0; Feature 5: The separated liquid is recycled as a detergent to the second purification process, or the separated liquid is recycled as a neutralizing agent to the pre-neutralization process, or the separated liquid is recycled as a defluorination agent to the defluorination process.

18. The recycling method according to claim 16 or 17, characterized in that: The phosphate precipitation residue is mixed with water to obtain a second slurry; the second slurry is mixed with a second alkaline substance and subjected to secondary cross-flow leaching and solid-liquid separation to obtain dephosphorization residue and orthophosphate mother liquor.

19. The recycling method according to claim 18, characterized in that: The mass ratio of the phosphate precipitate residue to water is (1:4)-(1:9); Alternatively, the second alkaline substance includes at least one of sodium hydroxide and potassium hydroxide.

20. The recycling method according to claim 18, characterized in that: The secondary cross-flow leaching comprises: performing a first-stage leaching on the second slurry and a second alkaline substance to obtain a first-stage leachate and a first sediment; The first stage leaching process includes at least one of the following features: Feature 1: The pH value of the reaction solution during the leaching process is 13-14; Feature 2: Leaching temperature is 50℃-85℃; Feature 3: The residence time of the reaction slurry is 25min-45min; Feature 4: The mass ratio of the first-stage leachate to the first sediment is (3:1)-(9:1).

21. The recycling method according to claim 20, characterized in that: The orthophosphate mother liquor obtained from the first stage leaching is partially recycled to be mixed with the first precipitated slag, the second precipitated slag and the third precipitated slag.

22. The recycling method according to claim 20 or 21, characterized in that: The secondary cross-flow leaching further comprises: performing a second-stage leaching on the first sediment and a second alkaline substance to obtain a second-stage leachate and a second sediment; The second stage leaching process includes at least one of the following features: Feature 1: The pH value of the reaction solution during the leaching process is 14.0-14.3; Feature 2: Leaching temperature is 45℃-55℃; Feature 3: The residence time of the reaction slurry is 60min-90min; Feature 4: The mass ratio of the second-stage leachate to the second sediment is (5:1)-(9:1).

23. The recycling method according to claim 22, characterized in that: Alkaline washing is performed on the second sediment, and after solid-liquid separation, a first washing liquid and a first slag slurry are obtained; The first washing liquid is recycled to the second-stage leaching process; the first slurry is washed with water, and the solid-liquid separation is performed to obtain the second washing liquid and the dephosphorization slag.

24. The recycling method according to claim 23, characterized in that: The second washing liquid is recycled to the alkali washing process of the second sediment.

25. The recycling method according to claim 22, characterized in that: The lime milk and the second-stage leachate are subjected to a first double decomposition reaction to precipitate phosphate in the secondary leachate, and the solid-liquid separation is performed to obtain a second slurry; the second slurry and the first-stage leachate are subjected to a second double decomposition reaction, and the solid-liquid separation is performed to obtain an alkali solution and calcium hydroxyphosphate.

26. The recycling method according to claim 25, characterized in that: The lime milk is obtained by mixing a precipitant with water; The precipitant includes at least one of calcium oxide and calcium hydroxide.

27. The recycling method according to claim 26, characterized in that: The mass ratio of the precipitant to water is (1:3)-(1:5).

28. The recycling method according to claim 26 or 27, characterized in that: The molar ratio of calcium in the precipitant to phosphorus in the second-stage leachate is (1.5:1)-(1.6:1).

29. The recycling method according to claim 25, characterized in that: The temperature of the first metathesis reaction and the second metathesis reaction is independently 40° C. to 60° C., or the time of the first metathesis reaction and the second metathesis reaction is independently 30 min to 60 min.

30. The recycling method according to claim 25, characterized in that: The calcium hydroxyphosphate is washed; and the second washing liquid obtained after washing the calcium hydroxyphosphate is collected and returned to the precipitant slurrying and milking process.

31. The recycling method according to claim 25, characterized in that: The solid suspended matter in the alkali solution after the double decomposition and dephosphorization is removed, and the solution is concentrated to obtain a concentrated alkali solution; and the concentrated alkali solution is reused to carry out leaching treatment on the second slurry.

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