CN117098722A

CN117098722A - Recycling method of raffinate acid in phosphoric acid production process by wet purification

Info

Publication number: CN117098722A
Application number: CN202380009641.0A
Authority: CN
Inventors: 王威; 王浩; 阮丁山; 李长东; 郑海洋; 丁代俊
Original assignee: Yichang Bangpu Yihua New Material Co ltd; Hunan Brunp Recycling Technology Co Ltd; Guangdong Brunp Recycling Technology Co Ltd
Current assignee: Yichang Bangpu Yihua New Material Co ltd; Hunan Brunp Recycling Technology Co Ltd; Guangdong Brunp Recycling Technology Co Ltd
Priority date: 2023-07-07
Filing date: 2023-07-07
Publication date: 2023-11-21

Abstract

The invention discloses a recycling method of raffinate acid in a phosphoric acid production process by wet purification, and belongs to the technical field of battery raw materials. The recycling method comprises the following steps: removing sulfur, fluorine, arsenic and heavy metals in the raffinate acid to be treated to obtain pretreatment acid; pre-neutralizing the pretreated acid, purifying to obtain a purified solution and precipitation slag containing iron, aluminum and magnesium, and rectifying the purified solution to obtain the industrial grade phosphoric acid. The method can effectively recycle the phosphorus resources in the raffinate acid, and the obtained industrial grade phosphoric acid can be used as a raw material for preparing battery grade phosphate.

Description

Recycling method of raffinate acid in phosphoric acid production process by wet purification

Technical Field

The disclosure relates to the technical field of battery raw materials, in particular to a method for recycling raffinate acid in a wet purification production process of phosphoric acid.

Background

The production method of industrial grade phosphoric acid is divided into a thermal method and a wet phosphoric acid solvent extraction method (called a wet purification method for short). Wherein, the thermal method is also called yellow phosphorus method, which takes yellow phosphorus as raw material, burns yellow phosphorus and then directly generates phosphoric acid by absorbing the generated phosphorus pentoxide with pure water. The wet phosphoric acid solvent extraction method is to prepare phosphoric acid with higher purity by taking wet phosphoric acid as a raw material and performing a series of chemical-organic solvent synergistic purification treatment.

The phosphoric acid prepared by the wet-process phosphoric acid solvent extraction method can meet the requirements of most industrial application scenes. The rapid development of new energy industry has greatly pulled the demand for battery-grade high-purity phosphates represented by iron phosphate, and the demand for industrial-grade phosphoric acid as a main raw material for producing such phosphates has also been rapidly increased along with the battery-grade phosphates.

The extraction Yu Suan is a main byproduct in the wet-process phosphoric acid solvent extraction purification process, the yield of the extraction Yu Suan is 40-45% of the quality of raw material phosphoric acid, and the yield is large. In the solvent extraction process, phosphoric acid molecules in the crude phosphoric acid interact with an extractant to be extracted by the extractant, and impurity ions (such as iron, aluminum, magnesium, sulfate radical, fluorine, arsenic, heavy metal ions and the like) in the acid are partially or completely left in the raffinate acid due to less or no interaction with the extractant, so that the impurity ion content in the raffinate acid is multiplied compared with that of the original phosphoric acid, and the application range of the raffinate acid is greatly limited. In addition, at present, the traditional raffinate acid treatment mode is to mix raffinate acid and ordinary wet-process phosphoric acid according to the mass ratio of 1 (2-5) to produce traditional fertilizers represented by monoammonium phosphate, diammonium phosphate and compound fertilizer, and the mode can produce a large amount of low-grade fertilizers, which is not beneficial to sustainable development of the phosphorus chemical industry.

In view of this, the present disclosure is specifically proposed.

Disclosure of Invention

The purpose of the disclosure comprises providing a method for recycling raffinate acid in the process of producing phosphoric acid by wet purification.

The present disclosure may be implemented as follows:

the present disclosure provides a method for recycling raffinate acid in a phosphoric acid production process by wet purification, comprising the following steps: removing sulfur, fluorine, arsenic and heavy metals in the raffinate acid to be treated to obtain pretreatment acid; pre-neutralizing the pretreated acid, purifying to obtain a purified solution and precipitation slag containing iron, aluminum and magnesium, and rectifying the purified solution to obtain the industrial grade phosphoric acid.

In an alternative embodiment, the raffinate to be treated is first subjected to crude desulfurization to obtain a first intermediate acid; removing fluorine, arsenic and heavy metals in the first intermediate acid to obtain a second intermediate acid; and (3) carrying out fine desulfurization on the second intermediate acid to obtain the pretreated acid.

In an alternative embodiment, the raffinate to be treated is mixed with a crude desulfurizing agent to effect crude desulfurization;

the coarse desulfurizing agent comprises at least one of phosphate concentrate, calcium carbonate, calcium hydroxide and calcium oxide.

In an alternative embodiment, the molar ratio of calcium in the crude desulfurization agent to sulfate in the raffinate is (0.8:1) - (1.0:1).

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

In an alternative embodiment, the defluorinating agent comprises sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, at least one of 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.

In an alternative embodiment, 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);

or, the filter aid is used in an amount of 0.5wt% to 5wt% of the first intermediate acid.

In an alternative embodiment, the second intermediate acid is mixed with an oxidizing agent and a fine desulfurization agent to perform fine desulfurization to obtain a pretreated acid and a fine desulfurization slag;

the fine desulfurization agent comprises at least one of barium hydroxide and barium carbonate.

In an alternative embodiment, the oxidizing agent is used in an amount of 0.5wt% to 1.5wt% of the second intermediate acid;

or, the molar ratio of barium in the fine desulfurization agent to sulfate in the second intermediate acid is (1.5:1) - (2.5:1).

In an alternative embodiment, the fine desulfurization slag is returned to the coarse desulfurization process for use as a coarse desulfurization agent.

In an alternative embodiment, the pretreatment acid is concentrated and solid-liquid separated prior to preneutralization to yield a concentrated pretreatment acid and a first precipitate slag containing ferric phosphate salts and aluminum phosphate salts;

concentrating P in pretreatment acid ₂ O ₅ The content of (C) is not less than 40wt%.

In an alternative embodiment, the concentrated pre-treatment acid is mixed with a neutralizing agent to perform pre-neutralization to obtain a pre-neutralization reaction solution;

the neutralizing agent includes at least one of potassium, sodium, ammonium salts, ammonia, sodium hydroxide, and potassium hydroxide.

In an alternative embodiment, the salt forms of potassium, sodium, ammonium include at least one of carbonate, bicarbonate, and phosphate;

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

In an alternative embodiment, the purification process comprises: mixing the pre-neutralization reaction liquid with a first precipitator for primary purification, and carrying out solid-liquid separation to obtain primary purification liquid and second precipitate slag containing ferric phosphate salt, aluminum phosphate salt and magnesium phosphate salt;

The first decontamination process includes at least one of the following features:

characteristic one: the first precipitant includes at least one of methanol, ethanol, propanol, butanol, and acetone;

and the second characteristic is: the usage amount of the first precipitant is 1-2.5 times of that of the pre-neutralization reaction liquid;

and (3) the following characteristics: the temperature of the first purification is 25-65 ℃.

In an alternative embodiment, the purification process further comprises: mixing the first purifying liquid with a detergent to perform second purifying and solid-liquid separation to obtain a second purifying liquid and a first washing liquid;

the second decontamination process includes at least one of the following features:

characteristic one: the solute in the detergent comprises at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium dihydrogen phosphate, potassium dihydrogen phosphate and potassium phosphate;

and the second characteristic is: the mass fraction of solute in the detergent is not less than 10%;

and (3) the following characteristics: the molar ratio of M in the detergent to P in the first purifying liquid is (0.15:1) - (0.3:1), which corresponds to sodium and/or potassium contained in the detergent.

In an alternative embodiment, the first wash liquor is returned to the preneutralization process for use as a neutralizing agent.

In an alternative embodiment, the purification process further comprises: mixing the second purifying liquid with a second precipitating agent to perform third purification and solid-liquid separation to obtain a third purifying liquid and third precipitate slag containing a small amount of magnesium phosphate and alkali metal phosphate;

the third decontamination process includes at least one of the following features:

characteristic one: the second precipitant includes at least one of methanol, ethanol, propanol, butanol, and acetone;

and the second characteristic is: the usage amount of the second precipitant is 20wt% to 100wt% of the second purifying liquid.

In an alternative embodiment, the third precipitate is returned to the first cleaning process or, alternatively, the third precipitate is mixed with the first precipitate and the second precipitate and recycled for pulping.

In an alternative embodiment, the third purification liquid is rectified to obtain technical grade phosphoric acid.

In an alternative embodiment, the slurry recovery after mixing the third precipitate with the first precipitate and the second precipitate includes:

mixing the first precipitate slag, the second precipitate slag and the third precipitate slag with water and a first alkaline substance, and neutralizing and precipitating to obtain a first slurry; and carrying out solid-liquid separation on the first slurry to obtain a separation liquid and phosphate precipitation slag.

In an alternative embodiment, pulping recovery includes at least one of the following features:

characteristic one: the water used for mixing with the first sediment, the second sediment and the third sediment is desalted water;

and the second characteristic is: the mass ratio of water to the total amount of the first precipitate slag, the second precipitate slag and the third precipitate slag is (2:1) - (5:1);

and (3) the following characteristics: the first alkaline substance comprises at least one of sodium hydroxide, potassium hydroxide, sodium orthophosphate and potassium orthophosphate;

and four characteristics: the pH value of the first slurry is 5.5-8.0;

and fifth feature: the separated liquid is recycled to the second purifying process as a detergent, or the separated liquid is recycled to the pre-neutralization process as a neutralizing agent, or the separated liquid is recycled to the defluorination process as a defluorination agent.

In an alternative embodiment, the phosphate precipitation slag is mixed with water to obtain a second slurry; and mixing the second slurry with a second alkaline substance, performing secondary cross-flow leaching, and performing solid-liquid separation to obtain dephosphorization slag and orthophosphate mother liquor.

In an alternative embodiment, the mass ratio of phosphate precipitation slag to water is (1:4) - (1:9);

or, the second alkaline substance includes at least one of sodium hydroxide and potassium hydroxide.

In an alternative embodiment, the secondary cross-flow leaching comprises: performing first-stage leaching on the second slurry and a second alkaline substance to obtain first-stage leaching liquid and first sedimentation slag;

the first stage leaching process includes at least one of the following features:

characteristic one: the pH value of the reaction liquid in the leaching process is 13-14;

and the second characteristic is: the leaching temperature is 50-85 ℃;

and (3) the following characteristics: the residence time of the reaction slurry is 25min-45min;

and four characteristics: the mass ratio of the first-stage leaching solution to the first sedimentation slag is (3:1) - (9:1).

In an alternative embodiment, the orthophosphate mother liquor fraction of the first stage leach is recycled to be mixed with the first, second and third precipitants.

In an alternative embodiment, the secondary cross-flow leaching further comprises: performing second-stage leaching on the first sedimentation slag and the second alkaline substance to obtain second-stage leaching liquid and second sedimentation slag;

the second stage leaching process includes at least one of the following features:

characteristic one: the pH value of the reaction liquid in the leaching process is 14.0-14.3;

and the second characteristic is: the leaching temperature is 45-55 ℃;

and (3) the following characteristics: the residence time of the reaction slurry is 60min-90min;

and four characteristics: the mass ratio of the second-stage leaching solution to the second sedimentation slag is (5:1) - (9:1).

In an alternative embodiment, the second sedimentation slag is subjected to alkali washing, and after solid-liquid separation, a first washing liquid and a first slag slurry are obtained;

recycling the first washing liquid to a second stage leaching process; and (3) washing the first slag slurry with water, and carrying out solid-liquid separation to obtain a second washing liquid and dephosphorized slag.

In an alternative embodiment, the second wash liquor is recycled to the alkaline wash process of the second sediment.

In an alternative embodiment, lime milk and the second-stage leaching solution are subjected to a first double decomposition reaction to precipitate phosphate radicals in the second-stage leaching solution, and solid-liquid separation is carried out to obtain second slag slurry; and (3) carrying out a second double decomposition reaction on the second slag slurry and the first stage leaching solution, and carrying out solid-liquid separation to obtain alkali liquor and calcium hydroxy phosphate.

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

the precipitant includes at least one of calcium oxide and calcium hydroxide.

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

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

In alternative embodiments, the temperature of the first metathesis reaction and the second metathesis reaction are independently from 40 ℃ to 60 ℃, or the time of the first metathesis reaction and the second metathesis reaction are independently from 30min to 60min.

In an alternative embodiment, the calcium hydroxy phosphate is washed; and collecting a second washing liquid obtained after washing the calcium hydroxy phosphate, and returning the second washing liquid to the precipitating agent pulping and milk making process.

In an alternative embodiment, removing solid suspended matters in the lye after double decomposition dephosphorization, and concentrating to obtain concentrated lye; and recycling the concentrated alkali liquor to leaching the second slurry.

The beneficial effects of the present disclosure include:

according to the recycling method of the raffinate acid, which is provided by the disclosure, a fertilizer processing factory is not needed, phosphorus elements are selectively extracted from complex phosphate precipitates containing iron, aluminum and magnesium through reasonable process design, phosphorus in the raffinate acid is converted into industrial grade phosphoric acid to the maximum extent, effective recycling of phosphorus resources in the raffinate acid is realized, and the obtained industrial grade phosphoric acid can be used as a raw material to prepare battery grade phosphate.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present disclosure and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person of ordinary skill in the art.

FIG. 1 is a process flow diagram of the pretreatment and purification process of raffinate in example 1 of the present disclosure;

FIG. 2 is a flow chart of a recycling process of the first, second and third sludge in example 1 of the present disclosure.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure more apparent, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

The method for recycling the raffinate acid in the phosphoric acid production process by wet purification provided by the disclosure is specifically described below.

The disclosure provides a recycling method of raffinate acid in a phosphoric acid production process by wet purification, which comprises the following steps: removing sulfur, fluorine, arsenic and heavy metals in the raffinate acid to be treated to obtain pretreatment acid; pre-neutralizing the pretreated acid, purifying to obtain a purified solution and precipitation slag containing iron, aluminum and magnesium, and rectifying the purified solution to obtain the industrial grade phosphoric acid.

If the method of purifying with precipitant and then removing sulfur, fluorine and arsenic is adopted, only barium desulfurization, phosphorus pentasulfide dearsenification and stripping defluorination can be adopted to avoid pollution to the purified phosphoric acid, the purification process is complex and has higher requirements on the purity and the consumption of chemical agents in the purification process and the environment of purifying and removing impurities. If the pretreatment and the purification process are combined into one step, the impurity removal slag and the phosphate precipitation slag are mixed together, so that the composition of the slag is complicated, and the phosphate precipitation slag separated in the purification process is difficult to be reused.

Therefore, in the present disclosure, sulfur, fluorine, and arsenic are removed, and then pre-neutralization and purification are performed, so that heavy metal impurity ions (such as lead, cadmium, etc.) are removed together in the arsenic removal process because sulfide precipitates can be formed under acidic conditions.

In some embodiments, the raffinate to be treated may be first subjected to crude desulfurization to obtain a first intermediate acid; removing fluorine, arsenic and heavy metals in the first intermediate acid to obtain a second intermediate acid; and (3) carrying out fine desulfurization on the second intermediate acid to obtain the pretreated acid.

It should be noted that, for phosphoric acid purifying enterprises, phosphate concentrate (main component calcium fluorophosphate) is the most easily available desulfurizing agent, but when coarse phosphoric acid is desulfurized by phosphate concentrate, impurity ions such as fluorine and arsenic in the ore are released into phosphoric acid, and in order to avoid secondary pollution, the method of coarse desulfurization is adopted in the present disclosure. Based on the fact that the product of desulfurization by using calcium salt is calcium sulfate, the substance has certain solubility in aqueous solution, so that only sulfate radical impurities can be primarily removed by using the calcium salt; if the solution is desulfurized after the calcium salt and the barium salt are mixed, the two desulfurization products can interfere with each other, and the purpose of deep desulfurization cannot be realized. Therefore, the method adopts a two-stage method of removing sulfur by adding calcium salt and barium salt, thereby realizing the deep removal of sulfate radical impurities and obtaining better desulfurization effect while considering desulfurization cost.

The fluorine and the arsenic can not interfere with each other in the removal process, and the impurity removal products are dangerous wastes, so that the treatment process can be simplified by combining the hazardous wastes, and heavy metal impurities can be removed together in the arsenic removal process. The de-arsenic acid solution also contains a certain amount of sulfide in a non-sulfate form, which also needs to be removed, and the sulfide is selectively oxidized into sulfate and then removed in the method.

In this disclosure, the deep desulfurization is performed after the crude desulfurization is performed, then the defluorination, the arsenic and the heavy metals are performed, and then the sulfide in the non-sulfate form is oxidized.

As a reference, the raffinate to be treated is mixed with a crude desulfurizing agent to perform crude desulfurization, and solid-liquid separation is performed to obtain a first intermediate acid and crude desulfurization residue (calcium sulfate). The coarse desulfurizing agent may include at least one of phosphate concentrate, calcium carbonate, calcium hydroxide, and calcium oxide, for example. The phosphate concentrate contains part of calcium phosphate. In some alternative embodiments, the coarse desulfurizing agent selects a phosphate concentrate.

The molar ratio of calcium in the crude desulfurization agent 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, etc., as well as any other value in the range of (0.8:1) - (1.0:1).

The crude desulfurization slag obtained above can be used for returning to a wet process phosphoric acid production system to recover phosphorus element entrained therein.

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

In some embodiments, the first intermediate acid may be mixed simultaneously with the defluorinating agent, sulfide, and filter aid; in other embodiments, the first intermediate acid and the defluorinating agent may be mixed first to perform defluorinating treatment, the defluorinated reaction liquid is mixed with sulfide and filter aid to perform dearsenifying and heavy metal removing reactions, and then solid-liquid separation is performed to obtain the second intermediate acid and the defluorinated, dearsenified and heavy metal removed slag.

For reference, the defluorinating agent may illustratively include a sodium source including at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate, and activated diatomaceous earth. In some embodiments, the mass ratio of sodium source to active diatomaceous earth may be (1:0.75) - (1:1.5), if the mass ratio of sodium source to active diatomaceous earth is too low to achieve the desired effect; if the mass ratio of the sodium source to the active diatomaceous earth is too high, the defluorination is not greatly assisted.

The molar ratio of Na in the defluorinating agent to F in the first intermediate acid may 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, etc., but may also be any other value within the range of (0.4:1) - (0.8:1).

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) - (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, etc., and may be any other value within the range of (1:15) - (1:75).

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

And mixing the second intermediate acid with an oxidant and a fine desulfurizing agent to carry out fine desulfurization, and carrying out solid-liquid separation on a reaction liquid obtained by the fine desulfurization to obtain pretreated acid and fine desulfurization slag.

Wherein the oxidizing agent may include hydrogen peroxide or ozone. The hydrogen peroxide may be, for example, industrial grade hydrogen peroxide, and the amount of the hydrogen peroxide may be 0.5wt% to 1.5wt%, such as 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, or 1.5wt%, etc., of the second intermediate acid, or may be any other value within the range of 0.5wt% to 1.5 wt%.

The fine desulfurization agent is a barium salt, and may include at least one of barium hydroxide and barium carbonate, for example. The molar ratio of barium in the fine desulfurization agent to sulfate in the second intermediate acid may be (1.5:1) - (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, etc., and may be any other value within the range of (1.5:1) - (2.5:1).

The fine desulfurization slag is mainly barium slag, and can be returned to the coarse desulfurization process to be used as a coarse desulfurizing agent.

It should be noted that the above desulfurization, defluorination, dearsenation and heavy metal removal cannot be considered to be one hundred percent removal of all sulfur, fluorine, arsenic and heavy metals in the raffinate, which can at least achieve removal of most of sulfur, fluorine, arsenic and heavy metals.

In the present disclosure, the pretreatment acid may be concentrated and solid-liquid separated prior to preneutralization to obtain the concentrated pretreatment acid and a first precipitate slag whose main components are iron phosphate salt and aluminum phosphate salt.

In some embodiments, P in the pretreatment acid may be concentrated to concentrate ₂ O ₅ The content of (2) is not less than 40wt%, for example, 40wt%, 50wt%, 60wt%, 70wt% or 80wt%, etc., and may be any other value not less than 40 wt%.

After the concentrated pretreatment acid is obtained, the concentrated pretreatment acid is mixed with a neutralizing agent to perform pre-neutralization, to obtain a pre-neutralization reaction liquid.

The pre-neutralization can convert impurity cations into phosphoric acid double salt precipitate with lower solubility and higher crystallinity, which is beneficial to improving the removal rate of cation impurities and the separation performance of precipitated slag.

For reference, the neutralizing agent may illustratively include potassium, sodium, ammonium salts, and at least one of ammonia, sodium hydroxide, and potassium hydroxide. Wherein the salt forms of potassium, sodium, ammonium may include at least one of carbonate, bicarbonate, and phosphate. 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) - (0.4:1), such as 0.2:1, 0.25:1, 0.3:1, 0.35:1 or 0.4:1, etc., or any other value in the range of (0.2:1) - (0.4:1).

In the present disclosure, the purification process may include: mixing the pre-neutralization reaction liquid with a first precipitator for primary purification, and carrying out solid-liquid separation to obtain primary purification liquid and second precipitation slag with main components of ferric phosphate salt, aluminum phosphate salt and magnesium phosphate salt.

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

The temperature of the first purification may be 25℃to 65℃such as 25℃30℃35℃40℃45℃50℃55℃60℃or 65℃or any other value within the range of 25℃to 65 ℃.

Further, the purification process further comprises: mixing the first purifying liquid with a detergent to perform second purifying and solid-liquid separation to obtain a second purifying liquid and a first washing liquid.

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 phosphate, potassium dihydrogen phosphate, and potassium phosphate. The mass fraction of the solute in the detergent is not less than 10%, for example, 10%, 20%, 30%, 40% or 50%, or other values not less than 10% are also possible.

The molar ratio of M (including sodium and potassium) in the detergent to P in the first purge may be (0.15:1) - (0.3:1), such as 0.15:1, 0.2:1, 0.25:1, or 0.3:1, etc., or any other value in the range of (0.15:1) - (0.3:1).

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

Further, the purification process further comprises: and mixing the second purifying liquid with a second precipitating agent to perform third purifying and solid-liquid separation to obtain third purifying liquid and third precipitate slag containing a small amount of magnesium phosphate salt and alkali metal phosphate.

In the third purification process, the second precipitant is an organic precipitant, and may include at least one of methanol, ethanol, propanol, butanol, and acetone, for example. The second precipitant may be used in an amount of 20wt% to 100wt%, such as 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, 90wt% or 100wt%, etc. of the second purified liquid, or any other value in the range of 20wt% to 100 wt%.

In some embodiments, the third precipitate slag may be returned to the first purification process. In other embodiments, the third precipitate can be mixed with the first precipitate and the second precipitate for slurry recovery.

In the present disclosure, after the third purification liquid is rectified, an industrial grade phosphoric acid, water and a regenerated precipitant can be obtained.

The industrial grade phosphoric acid can be used as a raw material for preparing battery grade phosphate (such as ferric phosphate), the regenerated precipitant can be recycled to the first purification and/or the third purification process, and water can be recycled as required.

On the premise of bearing the high impurity content of the raffinate acid, the method of solvent precipitation, washing and reprecipitation is used for purifying the raffinate acid in three stages, the dosage of the detergent can be obviously reduced by adding the solvent in stages, the washed acid-containing solvent can be purified for the second time, the cationic impurities in the solvent during the washing process are removed, and the acid liquor after the three-stage purification meets the requirements of industrial-grade phosphoric acid.

In the present disclosure, the pulping recovery of the third precipitate slag after mixing with the first precipitate slag and the second precipitate slag may include: mixing the first precipitate slag, the second precipitate slag and the third precipitate slag with water and a first alkaline substance, neutralizing and precipitating to obtain first slurry. And carrying out solid-liquid separation on the first slurry to obtain a separation liquid and phosphate precipitation slag.

In some embodiments, the first precipitate slag, the second precipitate slag and the third precipitate slag may be mixed, mixed with water to form slurry, and the slurry may be further added with first alkali matter to regulate pH value and then solid-liquid separated to separate out phosphate precipitate slag.

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

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

The pH of the first slurry may be in the range of 5.5 to 8.0, such as 5.5, 6, 6.5, 7, 7.5 or 8, and the like, and may be any other value in the range of 5.5 to 8.0.

In some embodiments, the separated liquid may be recycled as a detergent to the second purification process. In other embodiments, the separation liquid may be recycled to the preneutralization process as a neutralizing agent. In other embodiments, the separation liquid may be recycled to the defluorination process as a defluorination agent.

Further, the resulting phosphate precipitation slag is mixed with water to obtain a second slurry. And mixing the second slurry with a second alkaline substance, and performing secondary cross-flow leaching to extract phosphorus element in the phosphate precipitation slag, and performing solid-liquid separation on the leached reaction liquid to obtain dephosphorization slag and orthophosphate mother liquor.

The mass ratio of the phosphate precipitation slag to the water can be (1:4) - (1:9), such as 1:4, 1:5, 1:6, 1:7, 1:8 or 1:9, and the like, and can also be any other value within the range of (1:4) (1:9).

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

In the present disclosure, the secondary cross-flow leaching may include: and carrying out first-stage leaching on the second slurry and the second alkaline substance to obtain first-stage leaching liquid and first sedimentation slag.

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

The first stage leaching process may be carried out at a temperature of 50℃to 85℃such as 55℃60℃65℃75℃78℃80℃or 85 ℃.

In the first stage leaching process, the residence time of the reaction slurry may be 25min-45min, such as 25min, 30min, 35min, 40min or 45 min.

The mass ratio of the first stage leach solution to the first precipitate can be (3:1) - (9:1), such as 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1, etc.

The orthophosphate mother liquor of the first stage leaching (which is understood to be the liquid in the first sludge) may be partially recycled for mixing with the first, second and third precipitants.

Further, the secondary cross-flow leaching further comprises: and carrying out second-stage leaching on the first sedimentation slag and the second alkaline substance to obtain second-stage leaching liquid and second sedimentation slag.

In the second stage leaching, the pH value of the reaction solution can be 14.0-14.3 (such as 14.0, 14.1, 14.2 or 14.3).

The second stage leaching process may be carried out at a temperature of 45-55deg.C (e.g., 45deg.C, 48deg.C, 50deg.C, 52deg.C or 55deg.C, etc.).

In the second stage leaching process, the residence time of the reaction slurry may be 60min-90min, such as 60min, 70min, 80min or 90 min.

The mass ratio of the second stage leach solution to the second precipitate can be (5:1) - (9:1), such as 5:1, 6:1, 7:1, 8:1, or 9:1, etc.

Further, the second sedimentation slag is subjected to alkali washing, and after solid-liquid separation, a first washing liquid and first slag slurry are obtained.

The alkaline washing process can be carried out by using dilute alkali solution (the pH value is about 14) to dip and wash the second sedimentation slag, and the mass ratio of the dilute alkali solution to the second sedimentation slag can be (3:1) - (5:1), such as 3:1, 4:1 or 5:1. The separated first washing liquid can be recycled to the second leaching process.

Further, the first slag slurry is subjected to water washing and solid-liquid separation to obtain a second washing liquid and dephosphorization slag.

The water used for the water washing may be clear water, and the mass ratio of the clear water to the first slurry may be (3:1) - (5:1), such as 3:1, 4:1, or 5:1. The separated second washing liquid can be used as a dilute alkali solution to be recycled to the alkaline washing process of the second sedimentation slag.

Further, lime milk and the second-stage leaching solution can be subjected to a first double decomposition reaction (corresponding to first-stage precipitation) to precipitate phosphate radicals in the second-stage leaching solution, and solid-liquid separation is carried out to obtain second slag slurry; and (3) carrying out a second double decomposition reaction (corresponding to second-stage precipitation) on the second slag slurry and the first-stage leaching solution, and carrying out solid-liquid separation to obtain alkali liquor and calcium hydroxy phosphate.

For reference, the lime milk may be obtained by mixing a precipitant with water, wherein the precipitant may include at least one of calcium oxide and calcium hydroxide, for example.

The mass ratio of precipitant to water may be (1:3) - (1:5), such as 1:3, 1:4, or 1:5, etc.

The molar ratio of calcium in the precipitant to phosphorus in the second stage leach solution may be (1.5:1) - (1.6:1), such as 1.5:1, 1.55:1, or 1.6:1, etc.

In the present disclosure, the temperature of the first metathesis reaction and the second metathesis reaction are independently 40 ℃ to 60 ℃, such as 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, or the like. The time of the first metathesis reaction and the second metathesis reaction is independently 30min-60min, such as 30min, 35min, 40min, 45min, 50min, 55min, or 60min, etc. Both of the above-mentioned double metathesis reactions may be carried out under intense stirring conditions, and the stirring speed may be 270rpm or more, for example.

On the premise that the solubility of the calcium hydroxy phosphate is far smaller than that of calcium aluminate, when the calcium hydroxy phosphate is prepared by utilizing leaching liquid, phosphorus and aluminum elements in mother liquor can be separated by controlling the addition of calcium oxide or calcium hydroxide, and the calcium aluminate generated in the first double decomposition reaction can be converted into the calcium hydroxy phosphate in the second double decomposition reaction process by adopting a secondary cross-flow precipitation mode, so that the precipitated phosphorus product is secondarily purified, and meanwhile, the conversion rate of the soda lime can be effectively improved by the two-stage double decomposition reaction.

In some embodiments, the calcium hydroxy phosphate obtained by the metathesis reaction may be washed, and the washed calcium hydroxy phosphate may be dried to obtain a dry powder of calcium hydroxy phosphate. The calcium hydroxy phosphate dry powder can be used as a raw material for producing crude phosphoric acid in the wet-process phosphoric acid production process, and in addition, the calcium hydroxy phosphate can also be used as a defluorinating agent for defluorinating fluorine-containing wastewater, and the principle is that: the calcium hydroxy phosphate is easy to exchange with fluorine ions in the solution, and absorbs the fluorine ions to generate calcium fluoro phosphate, so that the weakly acidic, neutral and weakly alkaline fluorine-containing wastewater can be subjected to deep defluorination treatment.

The mass ratio of the calcium hydroxy phosphate to the water can be (2:1) - (4:1), such as 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.

And collecting a second washing liquid obtained after washing, wherein the second washing liquid can be returned to the precipitating agent pulping and emulsion making process.

In some embodiments, the lye after double-decomposition dephosphorization may be subjected to solid suspension removal and subsequently concentrated to obtain a concentrated lye.

The caustic ratio of the dephosphorized dilute alkali liquor is increased by more than 10 times compared with that of the leaching liquor, and the aluminate ions are not easy to be automatically decomposed under the higher caustic ratio, so that the dephosphorized dilute alkali liquor can be directly concentrated.

The obtained concentrated alkali liquor can be supplemented with the lost alkali according to the need and then returned to the second slurry for leaching treatment. The alkali is supplemented to the concentrated alkali liquor, so that the alkali balance and water balance of the system can be maintained.

When the concentrated alkali liquor is used for leaching the second slurry again, aluminate in the alkali liquor has a certain inhibition effect on the dissolution of aluminum hydroxide, so that the aluminum in the circulating alkali liquor does not need to be treated independently in a closed-loop circulation flow.

In addition, the main component of the dephosphorization slag generated in the method is a mixture of iron, aluminum and magnesium hydroxides, the dephosphorization slag can be continuously extracted according to the requirement, valuable elements in the dephosphorization slag are recovered, and the purpose of comprehensively utilizing the wet-process phosphoric acid associated resources is achieved.

On the premise of bearing the above, the present disclosure provides a new method for utilizing the raffinate acid, which skillfully breaks the technical dilemma that the utilization of the raffinate acid must depend on a fertilizer processing plant, and ensures the integrity and independence of the phosphoric acid purification process. The method provides a new leaching scheme of phosphate precipitation slag, realizes the purpose of selectively extracting phosphorus elements from complex phosphate precipitates containing iron, aluminum and magnesium, and can transfer most of phosphorus (more than 98.5 percent) and less proportion of aluminum (less than 30 percent) in the phosphate precipitation slag into leaching liquid in an open-circuit process; in a closed cycle process, phosphorus can be extracted separately from complex phosphate precipitates containing iron, aluminum, magnesium. According to the method, phosphorus in the raffinate acid is converted into industrial-grade purified phosphoric acid to the maximum extent through reasonable process design, and meanwhile, insoluble phosphate mixed salt which has low utilization value and basically no practical use and is a byproduct is converted into calcium hydroxy phosphate which has higher value and wide use, so that the comprehensive recovery and efficient utilization of phosphorus resources in the raffinate acid are realized.

The features and capabilities of the present disclosure are described in further detail below in connection with the examples.

Example 1

The embodiment provides a method for recycling raffinate acid in a phosphoric acid production process by wet purification, which is shown in fig. 1 and 2, and comprises the following steps:

s1: as shown in FIG. 1, 2000mL of raffinate to be treated was taken, 280g of phosphorus concentrate powder (molar ratio of calcium in the phosphorus concentrate powder to sulfate radical in the raffinate acid was 0.95:1) was added thereto, and after the reaction was completed, the produced calcium sulfate dihydrate was filtered off to obtain a first intermediate acid.

The basic information of the raffinate to be treated is as follows:

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

The water content of the used phosphorus concentrate powder was 10wt%, and its chemical composition (water-free base) was as follows:

P ₂ O ₅

Al ₂ O ₃

Fe ₂ O ₃

MgO

CaO

F

SiO ₂

34.1％

1.32％

1.48％

0.62％

47.5％

2.5％

15.6％

s2: adding 50g of sodium carbonate and 50g of active diatomite into the first intermediate acid of the S1, stirring to enable the acid liquor to fully contact with the diatomite, adding 12.5g of sodium sulfide nonahydrate and 56g of active carbon powder into the acid liquor after the acid liquor is mixed without generating bubbles, and filtering out generated precipitate (defluorination, dearsenation and heavy metal slag removal) after the reaction is completed to obtain the second intermediate acid.

Wherein the molar ratio of the total amount of Na in the sodium carbonate and the active diatomite to F in the first intermediate acid is 0.56:1; the molar ratio of As in the first intermediate acid to S in the sodium sulfide nonahydrate is 1:50; the amount of activated carbon powder used was 2wt% of the first intermediate acid.

S3: 29g of hydrogen peroxide is added into the second intermediate acid of the S2, stirring is carried out to enable the two to be fully contacted, then 115g of barium carbonate is added into the acid to carry out fine desulfurization, after the reaction is completed, the reaction liquid is filtered and pressed, and the pretreated acid (fine desulfurization clear liquid) and the fine desulfurization slag (barium slag) are obtained through separation.

Wherein the hydrogen peroxide is used in an amount of 1wt% of the second intermediate acid; the molar ratio of barium in the barium carbonate to sulfate in the second intermediate acid was 2.25:1.

S4: concentrating the pretreatment acid obtained in the step S3, press-filtering, and separating to obtain the concentrated pretreatment acid and first precipitation slag containing iron and aluminum.

Wherein the concentrated pretreatment acid comprises the following components:

P ₂ O ₅

Al ₂ O ₃

Fe ₂ O ₃

MgO

MnO

As

SO ₃

F

CaO

43.35％

1.76％

0.81％

3.98％

0.1％

0.0001％

0.009％

0.21％

0.03％

s5: 500g of concentrated pretreatment acid in S4 was weighed, 50g of concentrated ammonia water was added thereto for preneutralization, and then the preneutralization solution was stirred in a water bath at 55℃to obtain a preneutralization reaction solution.

Wherein, the molar ratio of M (ammonia) in the concentrated ammonia water to phosphorus in the concentrated pretreatment acid is 0.25:1.

S6: 1000g of absolute ethyl alcohol was added to the preneutralization reaction solution (536.12 g) of S5, and the mixture was stirred to sufficiently react (reaction temperature: 55 ℃ C.), and the mixture was separated by filtration to obtain a first purified solution and a second precipitate containing iron, aluminum, magnesium and manganese. 130g of sodium carbonate aqueous solution with the mass fraction of 15% (the molar ratio of M in the sodium carbonate aqueous solution to P in the first purifying solution is 0.2:1) is added into the first purifying solution for washing, and after full reaction, standing and separating are carried out, so as to obtain a second purifying solution and a first washing solution.

S7: 800g of absolute ethyl alcohol is continuously added into the second purifying liquid (1359.82 g) in the step S6, the mixture is stirred to fully react, and the third purifying liquid and third precipitation slag containing magnesium and alkali metal are obtained through filtration and separation.

S8: rectifying the third purified liquid in the step S7, and collecting high-concentration ethanol and water, wherein the raffinate is purified phosphoric acid; concentrating and purifying phosphoric acid to make H in acid ₃ PO ₄ The mass fraction is more than or equal to 85 percent, and the industrial grade phosphoric acid is obtained.

The industrial grade purified phosphoric acid comprises the following components:

meets the quality requirement of industrial grade phosphoric acid.

S9: as shown in fig. 2, the first, second, and third sludge are mixed to obtain a mixed sludge. 1000g of deionized water is added into (380.34 g) of mixed precipitate slag to prepare slurry, the prepared slurry is strong in acidity, sodium hydroxide is added into the slurry to react, the pH value of the first slurry is regulated to 6.0, and the phosphate precipitate slag and the separating liquid are obtained through filtration and separation.

S10: 1500g of deionized water was added to the phosphate precipitation slag (315.67 g) obtained in S9, and the mixture was stirred to prepare a second slurry. And heating the second slurry in a water bath at 80 ℃, adding sodium hydroxide (221 g) into the hot slurry to perform a first-stage leaching reaction, wherein the pH value of the reaction slurry in the first-stage leaching reaction process is about 13.5, stirring and reacting for about 35min, and settling and separating to obtain a first-stage leaching solution and first settling slag.

S11: adding 1500g of deionized water into the first sediments (370.34 g) obtained in the step S10, uniformly stirring, heating the prepared slurry in a water bath at 50 ℃, then adding sodium hydroxide (100 g) into the preheated slurry to perform a second-stage leaching reaction, wherein the pH value of the reaction liquid in the second-stage leaching reaction process is approximately equal to 14.1, stirring and reacting for 75min, and filtering and separating to obtain a second-stage leaching solution and second sediments.

S12: the second precipitate (202.32 g) in S11 was washed with 800g of a 4wt% aqueous sodium hydroxide solution and then filtered to obtain a first washing solution and a first slurry. The first washing liquid is recycled to be mixed with the second-stage leaching liquid, the first slag slurry is washed by 800g of deionized water, solid-liquid separation is carried out, the second washing liquid and dephosphorization slag are obtained, and the dephosphorization slag is dried and analyzed for composition. The second washing liquid can be used as a dilute alkali liquid to be recycled to the alkali washing process of the second sedimentation slag.

The dephosphorization slag comprises the following components:

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

The phosphorus element in the phosphate precipitation slag is completely extracted by alkali liquor in the leaching process, the leaching rate of the phosphorus is more than 99%, and the dephosphorization slag is a hydroxide mixture of metal elements.

S13: 227.16g of calcium hydroxide was weighed according to Ca: P=1.50:1 (molar ratio), and 700g of deionized water was added thereto to prepare a slurry, thereby obtaining a lime slurry. Adding lime slurry into phosphate ions in the precipitation solution in the second leaching solution in the step S11, stirring in a water bath at 50 ℃ to perform a first double decomposition reaction, standing the reaction solution for settling after reacting for 55min, separating lower-layer slag slurry, adding the lower-layer slag slurry into the first-stage leaching solution to perform the second double decomposition reaction, stirring in the water bath at 55 ℃ to perform the reaction for 40min, and filtering and separating the generated calcium hydroxy phosphate after the reaction is completed.

S14: and (3) adding 1300g of deionized water into the calcium hydroxy phosphate obtained in the step (S13) for washing, and filtering and drying after washing is finished to obtain calcium hydroxy phosphate powder.

The composition of the resulting calcium hydroxy phosphate was as follows:

name of the name	P％	Al％	Ca％	Na％
					Hydroxy calcium phosphate	14.84	0.08	34.86	3.67

From this result, it can be seen that: the phosphorus and aluminum are separated thoroughly.

Example 2

The embodiment provides a method for recycling raffinate acid in a phosphoric acid production process by wet purification, wherein the steps S1 to S4 are the same as those in embodiment 1, and the difference is that:

s5: 500g of the concentrated pretreatment acid in S4 was weighed, 50g of sodium carbonate was added thereto for preneutralization, and then the preneutralization solution was stirred in a water bath at 55℃to obtain a preneutralization reaction solution.

Wherein the molar ratio of M (sodium) in sodium carbonate to phosphorus in the concentrated pretreatment acid is 0.31:1.

S6: to the preneutralized reaction solution (527 g) of S5, 900g of a mixed alcohol (ethanol: isopropanol=4:1, mass ratio) was added, and stirred to sufficiently react (reaction temperature: 60 ℃), and filtered and separated to obtain a first purified solution and a second precipitate slag containing iron, aluminum, magnesium and manganese. 160g of sodium dihydrogen phosphate solution with the mass fraction of 30% (the molar ratio of M in the sodium dihydrogen phosphate solution to P in the first purifying solution is 0.2:1) is added into the first purifying solution for washing, and after full reaction, standing and separating are carried out to obtain a second purifying solution and a first washing solution.

S7: 700g of mixed alcohol (ethanol: n-butanol=4:1, mass ratio) is continuously added into the second purifying liquid (1250 g) in the step S6, the mixture is stirred to fully react, and the third purifying liquid and third precipitate slag containing manganese and alkali metal are obtained through filtration and separation.

S8: rectifying the third purified liquid in the step S7, and collecting high-concentration alcohol liquid and water, wherein the raffinate is purified phosphoric acid; concentrating and purifying phosphoric acid to make H in acid ₃ PO ₄ The mass fraction is more than or equal to 85 percent, and the industrial grade phosphoric acid is obtained.

The composition of the obtained technical grade phosphoric acid is as follows:

P ₂ O ₅

Cl

SO ₃

Fe ₂ O ₃

MgO

Al ₂ O ₃

MnO

CaO

F

As

61.83％

0.0001％

0.001％

0.0004％

0.001％

0.0011％

0.0001％

0.0008％

0.006％

0.0001％

by reducing the proportion of the mixed alcohol compared with the single ethanol, the mixed alcohol has better purifying effect.

Comparative example 1

This comparative example provides a method for recycling raffinate acid in the process of producing phosphoric acid by wet purification, wherein S1 to S4 are the same as example 1, and the difference is that:

Wherein the molar ratio of M (sodium) in sodium carbonate to phosphorus in the concentrated pretreatment acid is 0.25:1.

S6: 1000g of absolute ethyl alcohol was added to the preneutralization reaction solution (535.84 g) of S5, and the mixture was stirred to sufficiently react (reaction temperature: 60 ℃ C.), and the mixture was separated by filtration to obtain a first purified solution and a second precipitate containing iron, aluminum, magnesium and manganese. 160g of sodium dihydrogen phosphate solution with the mass fraction of 30% (the molar ratio of M in the sodium dihydrogen phosphate solution to P in the first purifying solution is 0.2:1) is added into the first purifying solution for washing, and after full reaction, standing and separating are carried out to obtain a second purifying solution and a first washing solution.

S7: 900g of absolute ethyl alcohol is continuously added into the second purifying liquid (1360.13 g) in the step S6, the mixture is stirred to fully react, and the third purifying liquid and third precipitation slag containing magnesium and alkali metal are obtained through filtration and separation.

the acid meets the quality requirements of technical grade phosphoric acid.

S9: and mixing the first precipitate slag, the second precipitate slag and the third precipitate slag to obtain mixed precipitate slag. 1000g of deionized water is added into (383.24 g) of mixed precipitate slag to prepare slurry, the prepared slurry is strong in acidity, sodium hydroxide is added into the slurry to react, the pH value of the first slurry is regulated to 6.5, and the phosphate precipitate slag and the separating liquid are obtained through filtration and separation.

S10: 1500g of deionized water was added to the phosphate precipitation slag (316.11 g) obtained in S9, and the mixture was stirred to prepare a second slurry. Heating the second slurry in a water bath at 85 ℃, adding sodium hydroxide (230 g) into the hot slurry to perform a first-stage leaching reaction, wherein the pH value of the reaction slurry in the first-stage leaching reaction process is about 13.7, stirring and reacting for about 40min, and settling and separating to obtain a first-stage leaching solution and first settling slag;

S11: 1500g of deionized water is added into the first sediment (368.87 g) obtained in the step S10, the prepared slurry is heated in a water bath at 50 ℃ after being stirred uniformly, then sodium hydroxide (96 g) is added into the preheated slurry to carry out a second-stage leaching reaction, the pH value of reaction liquid in the second-stage leaching reaction process is approximately equal to 14.1, the stirring reaction is carried out for 75min, and the second-stage leaching liquid and the second sediment are obtained after filtration and separation.

S12: the second precipitate (204.44 g) in S11 was washed with 800g of a 4wt% aqueous sodium hydroxide solution and then filtered to obtain a first washing solution and a first slurry. The first washing liquid is recycled to be mixed with the second-stage leaching liquid, the first slag slurry is washed by 800g of deionized water, solid-liquid separation is carried out, the second washing liquid and dephosphorization slag are obtained, and the dephosphorization slag is dried and analyzed for composition. The second washing liquid can be used as a dilute alkali liquid to be recycled to the alkali washing process of the second sedimentation slag.

The dephosphorization slag comprises the following components:

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

The phosphorus element in the phosphate precipitation slag is completely extracted by alkali liquor in the leaching process, the phosphorus leaching extraction rate is more than 99%, and the dephosphorization slag is a hydroxide mixture of metal elements.

S13: 226.75g of calcium hydroxide was weighed according to Ca: P=1.50:1 (molar ratio), and 700g of deionized water was added thereto to prepare a slurry, thereby obtaining a lime slurry. Mixing the first-stage leaching solution, the second-stage leaching solution and the alkaline washing solution, adding the prepared lime slurry into the mixed leaching solution, stirring in a water bath at 55 ℃ for reaction for 70min, filtering the reaction solution, and separating the generated calcium hydroxy phosphate.

The composition of the resulting calcium hydroxy phosphate was as follows:

name of the name	P％	Al％	Ca％	Na％
					Hydroxy calcium phosphate	12.76	1.8	37.98	2.17

As is clear from the above test results, the single-stage precipitation reduces both the conversion rate of soda lime and the separation effect of phosphorus and aluminum elements.

Comparative example 2

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

S6: 1800g of absolute ethanol was added to the preneutralized reaction solution (536.51 g) of S5, stirred to be sufficiently reacted (reaction temperature: 55 ℃ C.), and filtered to separate, thereby obtaining a first purified solution and a second precipitate slag containing iron, aluminum, magnesium and manganese.

S7: rectifying the first purified liquid obtained in the step S6, and collecting high-concentration ethanol and water, wherein the raffinate is purified phosphoric acid; concentrating and purifying phosphoric acid to make H in acid ₃ PO ₄ The mass fraction is more than or equal to 85 percent, and the purified acid is obtained.

The composition of the purified acid is as follows:

s7: and (3) taking second precipitate slag separated in the step (S6), adding 700g of deionized water into slag (210.84 g) to prepare slurry, wherein the prepared slurry is strong in acidity, adding sodium hydroxide into the slurry to react, and adjusting the pH value of the first slurry to 5.5 to obtain phosphate precipitate slag and separating liquid.

S8: 2000g of deionized water was added to the phosphate precipitation slag (201.63 g) obtained in S7, and the mixture was stirred to prepare a slurry. And heating the prepared slurry in a water bath at 75 ℃, adding sodium hydroxide (210 g) into the hot slurry to perform a first-stage leaching reaction, wherein the pH value of the reaction slurry in the first-stage leaching reaction process is about 14.1, stirring and reacting for about 120min, and settling and separating to obtain leaching liquid and settling slag.

S9: the sediment in S8 is soaked and washed by 1000g of sodium hydroxide aqueous solution with the concentration of 4wt percent, then is filtered, the filter residue is washed by 1000g of deionized water, and the filter residue (dephosphorization residue) is dried after the washing is finished and analyzed for composition.

The dephosphorization slag comprises the following components:

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

S10: 131.12g of calcium hydroxide was weighed according to Ca: P=1.50:1 (molar ratio), and 450g of deionized water was added thereto to prepare a slurry, thereby obtaining a lime slurry. Adding lime slurry into the alkali washing liquid to precipitate phosphate radical in the alkali washing liquid, stirring in a water bath at 50 ℃ to perform a first double decomposition reaction, standing the reaction liquid for 45min, settling, separating lower-layer slag slurry, adding the lower-layer slag slurry into the first-stage leaching liquid to perform a second double decomposition reaction, stirring in a water bath at 55 ℃ to perform a reaction for 45min, and filtering to separate generated calcium hydroxy phosphate after the reaction is completed.

S11: and (3) adding 600g of deionized water into the calcium hydroxy phosphate obtained in the step (S10) for washing, and filtering and drying after washing is finished to obtain calcium hydroxy phosphate powder.

The composition of the resulting calcium hydroxy phosphate sample was as follows:

name of the name	P％	Al％	Ca％	Na％
					Hydroxy calcium phosphate	14.16	0.5	36.28	2.87

As can be seen by comparison with example 1:

(1) after the washing step of removing the acid-containing solvent phase, magnesium and calcium ions in the acid cannot be effectively removed even if a sufficient amount of organic precipitant is added to the acid with purification. In addition, the magnesium ion content in the raffinate acid is too high, the requirement for the detergent in the washing process is increased, and meanwhile, the metal ions entering the acid-containing solvent phase in the washing process need to be removed by adding the organic precipitant step by step.

(2) When in single-stage leaching, the leaching rate of aluminum element in phosphate precipitation slag is increased, the leaching extraction rate of phosphorus is over 96 percent, and compared with two-stage cross-flow leaching, the leaching rate is more reduced.

(3) The aluminum-phosphorus ratio of the leaching solution is increased, so that the aluminum content of the phosphorus precipitation product calcium hydroxy phosphate of the leaching solution is increased.

Comparative example 3

S6: 1800g of ethanol was added to the preneutralized reaction solution (527 g) of S5, and the mixture was stirred to be sufficiently reacted (reaction temperature: 60 ℃ C.), and the mixture was separated by filtration to obtain a first purified solution and a second precipitate slag containing iron, aluminum, magnesium and manganese. 200g of sodium dihydrogen phosphate solution with the mass fraction of 30% (the molar ratio of Na in the sodium dihydrogen phosphate solution to P in the first purifying solution is 0.27:1) is added into the first purifying solution for washing, and after full reaction, standing and separating are carried out to obtain a second purifying solution and a first washing solution.

S7: rectifying the second purified liquid obtained in the step S6, and collecting high-concentration ethanol and water, wherein the raffinate is purified phosphoric acid; concentratingPurifying phosphoric acid to make H in acid ₃ PO ₄ The mass fraction is more than or equal to 85 percent, and the purified acid is obtained.

The resulting purified acid composition was as follows:

by comparison with example 1, it can be seen that: the adoption of the first-stage purification and the first-stage washing can effectively remove most cationic impurities in the raffinate acid. However, in the process of washing the solvent phase, because the mass fraction of water in the solvent phase is too low, a relatively large amount of detergent is required to be consumed to form a relatively stable solvent-salt solution double-liquid-phase system, so that the purpose of washing the acid-containing solvent is achieved. In the process, sodium ions in the detergent are largely transferred to the solvent phase due to the relation of two phase potential differences, and after the solvent phase is rectified, all sodium ions entering the solvent can remain in the purified acid, so that the sodium ion content of the purified acid exceeds the standard.

Application example

The application example provides a recycling method of raffinate acid in the process of producing phosphoric acid by pilot scale wet purification, which comprises the following steps:

s1: adding water into the phosphorus concentrate powder according to the mass ratio of 2:1 to prepare concentrate pulp with the solid content of 60 percent, and then adding water into the phosphorus concentrate powder according to the mass ratio of the concentrate pulp to the raffinate acid=1:7 (Ca ²⁺ :SO ₄ ^2- =0.90:1, molar ratio) adding the two materials into a stirred coarse desulfurization reaction kettle for coarse desulfurization reaction, controlling the residence time of the materials in the reaction kettle to be 30-40min, and discharging the fully reacted reaction liquid from the bottom of the kettle to a pretreatment sedimentation tank for sedimentation separation.

The above raffinate and phosphorus concentrate powder to be treated were the same as in example 1.

S2: the supernatant fluid of the upper layer of the sedimentation tank is sent to a defluorination tank, and the slag slurry discharged from the lower layer is sent to a wet-process phosphoric acid device reaction tank to recycle the phosphorus entrained in the slag slurry.

S3: adding defluorinating agent sodium carbonate and active diatomite powder into a defluorinating tank according to the mass ratio of 4% (Na: F=0.5:1) of the clear liquid, wherein the mass ratio of the sodium carbonate to the active diatomite is 1:1, stirring to uniformly mix the defluorinating agent with acid liquor, and then conveying the mixed slurry into the defluorinating tank.

S4: preparing 5% sodium sulfide solution for standby, firstly adding the prepared sodium sulfide solution (As: S=1:50, molar ratio) into an arsenic removal tank according to the proportion of 2.8% of the acid liquor, adding 80% of activated carbon powder passing through an 80-mesh sieve into the acid liquor according to the proportion of 2.5% of the acid liquor, stirring and reacting for 45min, then conveying the reaction solution to a filter press for filter pressing, collecting filtrate into an arsenic removal acid collecting tank, and uniformly treating the filter residues after collecting the filter residues.

S5: the hydrogen sulfide gas generated in the arsenic removal process is introduced into a washing tower through a forced draft system, and is absorbed by sodium hydroxide solution with the mass fraction of 5% for recycling.

S6: according to the dearsenic acid, hydrogen peroxide and barium hydroxide=100:1:2.5 (Ba: SO) ₄ ^2- =2: 1, molar ratio), the dearsenic acid, the industrial grade hydrogen peroxide and the barium hydroxide are added into a fine desulfurization reaction tank, the reaction liquid is sent to a filter press for filter pressing after stirring reaction for 45min, and the generated fine desulfurization slag (barium slag) and the pretreatment acid are separated.

S7: and the barium slag is added into the phosphorus concentrate pulp after being collected, and coarse desulfurization is carried out on the raffinate acid together with the phosphorus concentrate, so that the dosage of the phosphorus concentrate does not need to be adjusted.

S8: concentrating the pretreated acid, concentrating the concentrated acid P ₂ O ₅ Content of (3)>And (3) separating solid suspended matters in the acid by pressure filtration from the concentrated acid liquor by 40 weight percent to obtain concentrated pretreated acid and first precipitation slag containing iron and aluminum. The concentrated pretreated acid is sent to a pre-neutralization tank, and the first precipitate slag is sent to a phosphoric acid slag slurry mixing tank.

S9: the concentrated pre-treatment acid is heated to 55 ℃ in a pre-neutralization tank, then sodium carbonate powder is added into the pre-neutralization tank according to the molar ratio of Na:P=0.3:1, and after the reaction is completed, the obtained pre-neutralization reaction liquid is sent to a first-stage solvent precipitation tank.

S10: adding mixed alcohol into the preneutralization reaction liquid according to the mass ratio of the mixed alcohol precipitant (ethanol: isopropanol: n-butanol=8:1:1) =1:2.5, stirring and reacting for 30min, centrifuging the reaction liquid to obtain a first purified liquid and second precipitation slag containing iron, aluminum, magnesium and manganese, conveying the second precipitation slag to a phosphoric acid slag slurry mixing tank, and conveying the first purified liquid to the middle part of a washing clarifying tank.

S11: adding 15% sodium carbonate solution into the middle part of the washing and clarifying tank according to the molar ratio of Na: P=0.18:1, stirring to react to obtain second purifying liquid and first washing liquid, discharging the bottom of the washing and clarifying tank of the washed first washing liquid, recycling the second purifying liquid to the pre-neutralization reaction tank, and deducting the dosage of sodium carbonate according to the amount of sodium ions in the washing liquid, wherein 1mol of sodium ions are deducted to 0.5mol of sodium carbonate.

S12: discharging the second purifying liquid from the upper part of the washing clarifying tank, delivering the second purifying liquid to a second-stage solvent precipitation tank, adding a mixed alcohol precipitant (ethanol: isopropanol: n-butanol=8:1:1) with the mass of 40% of the solvent into the bottom of the second-stage solvent precipitation tank, stirring to fully react the solvent, and filtering the reacted solvent by a precise filter to obtain a third purifying liquid and a third precipitate slag containing manganese and alkali metals; periodically conveying third precipitate slag discharged by the precision filter to a first-stage solvent precipitation tank, rectifying the separated third purifying liquid to separate and purify phosphoric acid, water and precipitant, collecting the precipitant for recycling, concentrating and purifying the phosphoric acid to enable H in acid ₃ PO ₄ The mass fraction is more than or equal to 85 percent, and the industrial grade purified phosphoric acid is obtained.

The composition of the obtained technical grade purified phosphoric acid was as follows (7 cycles were carried out, each cycle corresponding to the technical grade phosphoric acid composition):

the acid meets the quality requirements of technical grade phosphoric acid.

S13: adding water into a phosphate slag pulping tank according to the ratio of liquid-solid ratio=3:1 to prepare slurry, then sending the prepared slurry into a primary neutralization tank, and adding sodium hydroxide solution into the primary neutralization tank to adjust the pH value of the slurry to 6.0;

s14: the slurry after alkali adjustment is sent to a first-stage leaching sedimentation tank for standing sedimentation, a small amount of suspended matters in the phosphate solution on the upper layer are filtered out and removed, and then the phosphate solution is recycled to a solvent washing stage, a pre-neutralization stage and a pretreatment acid defluorination stage, so that the use of sodium carbonate is completely replaced, and the redundant phosphate solution is sent to a second-stage phosphorus sedimentation tank;

s15: introducing phosphate precipitation slag slurry discharged from the lower layer of the settling tank into a secondary neutralization tank, diluting with 5 times of heating water according to the mass of the slag slurry, then adding sodium hydroxide into the secondary neutralization tank, maintaining the pH of the reaction liquid to be 13.6-13.8 and the temperature to fluctuate between 78-82 ℃, stirring and reacting for 45min, transferring alkaline reaction liquid into a secondary leaching settling tank, settling and separating primary leaching liquid and primary leaching slag slurry, and delivering the primary leaching liquid into a secondary phosphorus precipitation tank and the primary neutralization tank;

S16: delivering the primary leaching residue slurry to a tertiary neutralization tank, adding water into the primary neutralization tank for dilution, then adding sodium hydroxide into the tertiary neutralization tank, maintaining the pH of the reaction solution to be 14.1-14.3 and the temperature to be 48-52 ℃, stirring and reacting for 70min, transferring the alkaline reaction solution to a tertiary leaching sedimentation tank for sedimentation and separation of secondary leaching solution and secondary leaching residue slurry, and delivering the secondary leaching solution to a primary phosphorus precipitation tank;

s17: the secondary leaching slag slurry is sent to an alkaline washing tank, 4-6% sodium hydroxide solution with the mass 4 times of the slag slurry is added into the alkaline washing tank to rinse the slag slurry, the rinsing liquid is sent to a four-stage leaching sedimentation tank to separate alkaline washing liquid and alkaline washing slag, and the alkaline washing liquid is completely returned to the three-stage neutralization tank;

s18: the alkaline washing slag is sent to a water washing tank, clear water with the mass 3 times of that of slag slurry is added into the alkaline washing slag to rinse the slag slurry, the dephosphorization slag and the water washing liquid are separated after the rinsing liquid is subjected to filter pressing by a filter press, a small amount of concentrated alkali liquor is added into the water washing liquid to prepare sodium hydroxide solution with the concentration of 4-6%, the sodium hydroxide solution is returned to the alkaline washing tank, and the separated dephosphorization slag is collected and treated uniformly;

the composition of the leached dephosphorized slag is as follows:

s19: preparing lime milk slurry with the mass fraction of 25%, adding the prepared lime milk into a primary phosphorus precipitation tank, stirring to enable the lime milk to fully contact with a secondary leaching solution for phosphorus precipitation reaction, and transferring primary phosphorus precipitation reaction liquid into the primary phosphorus precipitation tank to precipitate and separate dilute alkali liquor and primary phosphorus precipitation slag; delivering the primary phosphorus slag to a secondary phosphorus precipitation tank, fully contacting with a secondary leaching solution to carry out phosphorus precipitation reaction, treating a secondary phosphorus precipitation reaction solution by the secondary phosphorus precipitation tank, and separating dilute alkali solution from the secondary phosphorus slag;

S20: the usage amount of the lime milk slurry is as follows: determining the general dosage according to the molar ratio of total phosphorus=1.50-1.60:1 in the two-stage leaching solution, and properly increasing and decreasing the phosphorus and aluminum contents in the two-stage phosphorus precipitation slag to ensure that the phosphorus content in the two-stage phosphorus precipitation slag is more than 14.0% and the aluminum content is less than 0.1%;

s21: the secondary phosphorus slag which does not meet the requirements returns to the secondary phosphorus precipitation tank to be converted again, the secondary phosphorus slag which meets the requirements is sent to a calcium phosphate washing tank, clear water with the mass 3 times of that of the phosphorus slag is added to be rinsed, the rinsing liquid is subjected to filter pressing treatment, the calcium hydroxy phosphate in the rinsing liquid is recovered, the washing water is collected and used for preparing lime milk, and part of calcium hydroxy phosphate returns to the coarse desulfurization stage to replace the phosphorus concentrate powder comprehensively;

s22: the dilute alkali solution separated in the first-stage phosphorus precipitation sedimentation tank and the second-stage phosphorus precipitation sedimentation tank is sent to an alkali solution collecting tank, the alkali solution is properly concentrated after a small amount of alkali lost in the process is supplemented, and the concentrated alkali solution is returned to the second-stage neutralization tank and the third-stage neutralization tank for secondary use.

The composition of the calcium hydroxy phosphate is as follows:

name of the 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

From the above results, it can be seen that: the phosphorus element in the phosphate precipitation slag is completely extracted by alkali liquor in the leaching process, the leaching rate of the phosphorus is more than 99 percent, and the dephosphorization slag is a hydroxide mixture of metal elements. After the alkali liquor is circulated for many times, the amount of aluminate loaded in the solution is not changed obviously, namely, the circulated alkali liquor is not dissolved out of aluminum element in phosphate precipitation slag, and the dephosphorization slag composition is stabilized.

In the leaching process, sodium hydroxide solution reacts with carbon dioxide in the air to generate sodium carbonate, and ionized carbonate is converted into calcium carbonate in a lime milk precipitation stage to enter a calcium hydroxy phosphate product, so that the prepared calcium hydroxy phosphate is mainly used for producing wet phosphoric acid and removing fluorine from fluorine wastewater.

In summary, the method provided by the disclosure can effectively recycle the phosphorus resources in the raffinate acid, and the obtained industrial grade phosphoric acid can be used as a raw material for preparing battery grade phosphate.

Industrial applicability

The utilization method of the raffinate acid provided by the disclosure skillfully breaks the technical dilemma that the utilization of the raffinate acid is necessary to depend on a fertilizer processing plant, and ensures the integrity and independence of the phosphoric acid purification process. The method provides a new leaching scheme of phosphate precipitation slag, achieves the aim of selectively extracting phosphorus elements from complex phosphate precipitates containing iron, aluminum and magnesium, and can transfer most of phosphorus (more than about 98.5 percent) and less proportion of aluminum (less than about 30 percent) in the phosphate precipitation slag into leaching liquid in an open circuit process; in a closed cycle process, phosphorus can be extracted separately from complex phosphate precipitates containing iron, aluminum, magnesium. According to the method, phosphorus in the raffinate acid is converted into industrial-grade purified phosphoric acid to the maximum extent through reasonable process design, and meanwhile, insoluble phosphate mixed salt which has low utilization value and basically no practical use and is a byproduct is converted into calcium hydroxy phosphate which has higher value and wide use, so that the comprehensive recovery and efficient utilization of phosphorus resources in the raffinate acid are realized.

Claims

1. The method for recycling the raffinate acid in the process of producing the phosphoric acid by wet purification is characterized by comprising the following steps of: removing sulfur, fluorine, arsenic and heavy metals in the raffinate acid to be treated to obtain pretreatment acid; and (3) pre-neutralizing the pretreated acid, purifying to obtain a purified liquid and precipitation slag containing iron, aluminum and magnesium, and rectifying the purified liquid to obtain the industrial grade phosphoric acid.

2. The recycling method according to claim 1, wherein the first intermediate acid is obtained by first performing crude desulfurization on the raffinate to be treated; removing fluorine, arsenic and heavy metals in the first intermediate acid to obtain a second intermediate acid; and (3) carrying out fine desulfurization on the second intermediate acid to obtain the pretreatment acid.

3. The recycling method according to claim 2, characterized in that the raffinate to be treated is mixed with a crude desulfurizing agent to perform crude desulfurization;

the coarse desulfurizing agent comprises at least one of phosphate concentrate calcium carbonate, calcium hydroxide and calcium oxide.

4. The method of claim 3, wherein the molar ratio of calcium in the crude desulfurization agent to sulfate in the raffinate acid is (0.8:1) - (1.0:1).

5. The recycling method according to any one of claims 2 to 4, characterized in that the first intermediate acid is mixed with defluorinating agent, sulfide and filter aid to remove fluorine, arsenic and heavy metals.

6. The recycling method according to claim 5, wherein the defluorinating agent comprises active diatomaceous earth and at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate;

alternatively, the filter aid comprises activated carbon.

7. The recycling method according to claim 6, wherein a molar ratio of Na in the defluorinating agent to F in the first intermediate acid is (0.4:1) - (0.8:1);

8. The recycling method according to any one of claims 2 to 7, characterized in that the second intermediate acid is mixed with an oxidizing agent and a fine desulfurizing agent to perform fine desulfurization, to obtain the pretreated acid and fine desulfurization slag;

9. The recycling method according to claim 8, wherein the amount of the oxidizing agent used is 0.5wt% to 1.5wt% of the second intermediate acid;

10. The recycling method according to claim 8, characterized in that the fine desulfurization slag is returned to a coarse desulfurization process to be used as a coarse desulfurizing agent.

11. The recycling method according to any one of claims 1 to 10, characterized in that, before the preneutralization, the pretreatment acid is concentrated and subjected to solid-liquid separation to obtain a concentrated pretreatment acid and a first precipitate slag containing ferric phosphate salts and aluminum phosphate salts;

p in the concentrated pretreatment acid ₂ O ₅ The content of (C) is not less than 40wt%.

12. The recycling method according to claim 11, wherein the concentrated pretreatment acid is mixed with a neutralizing agent to perform preneutralization to obtain preneutralization reaction solution;

13. The recycling method according to claim 12, wherein the salt forms of potassium, sodium, ammonium include at least one of carbonate, bicarbonate and phosphate;

14. The recycling method according to claim 12 or 13, wherein the purifying process includes: mixing the pre-neutralization reaction liquid with a first precipitator for primary purification, and carrying out solid-liquid separation to obtain primary purification liquid and second precipitation slag containing ferric phosphate salt, aluminum phosphate salt and magnesium phosphate salt;

characteristic one: the first precipitant comprises at least one of methanol, ethanol, propanol, butanol and acetone;

15. The recycling method according to claim 14, wherein the purifying process further comprises: mixing the first purifying liquid with a detergent to perform second purifying and solid-liquid separation to obtain a second purifying liquid and a first washing liquid;

characteristic one: the solute in the detergent comprises at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium dihydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate and potassium phosphate;

and (3) the following characteristics: the molar ratio of M in the detergent to P in the first purifying liquid is (0.15:1) - (0.3:1), and M corresponds to sodium and/or potassium contained in the detergent.

16. The recycling method according to claim 15, characterized in that the first washing liquid is returned to the pre-neutralization process to be used as a neutralizing agent.

17. The recycling method according to claim 15 or 16, wherein the purifying process further comprises: mixing the second purifying liquid with a second precipitating agent to perform third purification and solid-liquid separation to obtain a third purifying liquid and third precipitate slag containing a small amount of magnesium phosphate and alkali metal phosphate;

characteristic one: the second precipitant comprises at least one of methanol, ethanol, propanol, butanol and acetone;

And the second characteristic is: the usage amount of the second precipitant is 20-100 wt% of the second purifying liquid.

18. The recycling method according to claim 17, wherein the third precipitate slag is returned to the first purifying process, or the third precipitate slag is mixed with the first precipitate slag and the second precipitate slag and then pulped for recycling.

19. The recycling method according to claim 17, wherein the third purified liquid is rectified to obtain technical grade phosphoric acid.

20. The recycling method according to claim 18, wherein the pulping recovery after mixing the third precipitate slag with the first precipitate slag and the second precipitate slag comprises:

mixing the first precipitation slag, the second precipitation slag and the third precipitation slag with water and a first alkaline substance, neutralizing and precipitating to obtain a first slurry; and carrying out solid-liquid separation on the first slurry to obtain a separation liquid and phosphate precipitation slag.

21. The recycling method according to claim 20, characterized in that pulping recycling includes at least one of the following features:

characteristic one: the water used for mixing with the first precipitation slag, the second precipitation slag and the third precipitation slag is desalted water;

and four characteristics: the pH value of the first slurry is 5.5-8.0;

and fifth feature: and recycling the separation liquid as a detergent to a second purification process, or recycling the separation liquid as a neutralizing agent to a pre-neutralization process, or recycling the separation liquid as a defluorinating agent to a defluorination process.

22. The recycling method according to claim 20 or 21, wherein the phosphate precipitation slag is mixed with water to obtain a second slurry; and mixing the second slurry with a second alkaline substance, performing secondary cross-flow leaching, and performing solid-liquid separation to obtain dephosphorization slag and orthophosphate mother liquor.

23. The method of claim 22, wherein the mass ratio of phosphate precipitation slag to water is (1:4) - (1:9);

24. The recycling method according to claim 22 or 23, characterized in that the secondary cross-flow leaching comprises: performing first-stage leaching on the second slurry and a second alkaline substance to obtain first-stage leaching liquid and first sedimentation slag;

and the second characteristic is: the leaching temperature is 50-85 ℃;

and four characteristics: the mass ratio of the first stage leaching solution to the first sedimentation slag is (3:1) - (9:1).

25. The method of claim 24, wherein the portion of the orthophosphate mother liquor obtained from the first stage leach is recycled for mixing with the first, second, and third precipitate slags.

26. The recycling method according to claim 24 or 25, characterized in that the secondary cross-flow leaching further comprises: performing second-stage leaching on the first sedimentation slag and a second alkaline substance to obtain second-stage leaching liquid and second sedimentation slag;

and the second characteristic is: the leaching temperature is 45-55 ℃;

27. The recycling method according to claim 26, wherein the second sediments are subjected to alkali washing, and after solid-liquid separation, a first washing liquid and a first slurry are obtained;

recycling the first washing liquid to a second stage leaching process; and washing the first slag slurry with water, and carrying out solid-liquid separation to obtain a second washing liquid and dephosphorization slag.

28. The recycling method according to claim 27, wherein the second washing liquid is recycled to the alkaline washing process of the second sediments.

29. The recycling method according to claim 26, wherein lime milk and the second-stage leachate are subjected to a first double decomposition reaction to precipitate phosphate groups in the second-stage leachate, and solid-liquid separation is performed to obtain second slurry; and (3) carrying out a second double decomposition reaction on the second slag slurry and the first stage leaching solution, and carrying out solid-liquid separation to obtain alkali liquor and calcium hydroxy phosphate.

30. The recycling method according to claim 29, wherein the lime milk is obtained by mixing a precipitant with water;

the precipitant includes at least one of calcium oxide and calcium hydroxide.

31. The method of claim 30, wherein the mass ratio of precipitant to water is (1:3) - (1:5).

32. The method of claim 30 or 31, wherein the molar ratio of calcium in the precipitant to phosphorus in the second stage leach solution is (1.5:1) - (1.6:1).

33. The recycling method according to any one of claims 29 to 32, characterized in that the temperature of the first metathesis reaction and the second metathesis reaction is independently 40 ℃ to 60 ℃, or the time of the first metathesis reaction and the second metathesis reaction is independently 30min to 60min.

34. The method of recycling according to any one of claims 29 to 33, characterized in that the calcium hydroxyphosphate is washed; and collecting a second washing liquid obtained after washing the calcium hydroxy phosphate, and returning the second washing liquid to the precipitating agent pulping and milk making process.

35. The recycling method according to claim 29, characterized in that solid suspended matters in the lye after double decomposition dephosphorization are removed and concentrated to obtain a concentrated lye; and recycling the concentrated alkali liquor to leaching the second slurry.