Process for the production of battery grade ferric phosphate from wet-process phosphoric acid and related acids

Abstract

The present application relates to the production process of battery-grade iron phosphate prepared from wet-process phosphoric acid and its related acid, and belongs to the technical field of wet-process phosphoric acid production. The present application solves the technical problem of providing a production process of battery-grade iron phosphate prepared from wet-process phosphoric acid and its related acid at low cost. The process obtains battery-grade iron phosphate through extraction, defluorination by concentration and chemical defluorination, preparation of NH4H2PO4 solution, reaction, oxidation, adjustment of pH and separation of precipitate, washing and drying. The method of the present application has low production cost and can realize the recycling of fluorine resources. By using specific extraction and stripping methods, or using specific two-step neutralization methods, NH4H2PO4 solution is obtained by extraction and separation from purified wet-process phosphoric acid. The process does not produce raffinate acid, the extractant can be recycled after stripping, and the production quality is not affected by the generation of difficult-to-dissolve substances such as ammonium magnesium phosphate. The two-step method is used to prepare battery-grade iron phosphate, and the cost of preparing iron phosphate by precipitation method is low, which meets the requirements of industrial production.

Description

Technical Field

[0001] This invention relates to the production process of wet-process phosphoric acid and related acids for preparing battery-grade iron phosphate, belonging to the field of wet-process phosphoric acid production technology. Background Technology

[0002] Currently, there are generally two types of batteries used in new energy vehicles: ternary lithium batteries and lithium iron phosphate batteries. Lithium iron phosphate batteries refer to batteries whose positive electrode material is lithium iron phosphate. These batteries exhibit superior performance in terms of thermal stability, safety, production cost, and cycle life, making them the preferred battery choice for many new energy vehicle manufacturers.

[0003] Ferric phosphate, a key material for preparing lithium iron phosphate cathode materials, has seen a surge in market demand driven by the development of new energy vehicles. Ferric phosphate production processes can be categorized into two-step and one-step methods based on production control; sodium salt and ammonium salt methods based on the type of alkali used for pH adjustment; and high-purity ferrous sulfate heptahydrate, iron powder, titanium dioxide slag, and iron salt methods based on the iron source. Currently, the primary industrial production method is precipitation. The principle of precipitation-based ferric phosphate preparation is to utilize a suitable chemical reaction; adding a suitable precipitant to a solution causes the desired precipitate to form. Advantages include controlled precipitate preparation, controllable precipitation rate, fine precipitate particles, and a simple reaction process.

[0004] Patent application number 2023110623563 discloses a process for producing nano-ferric phosphate. This invention uses ammonium phosphate, phosphoric acid, ferrous sulfate, and hydrogen peroxide as raw materials, and employs a three-stage diaphragm reactor, a microchannel reactor, and a three-stage microreactor as partial reaction equipment to prepare nano-ferric phosphate. This method produces high-purity ferric phosphate, but the processing capacity is small and the cost is high, making industrial-scale production difficult.

[0005] Patent application number 2022107964411 discloses a low-cost, continuous method for producing ferric phosphate. This invention uses prepared dilute phosphoric acid to continuously dissolve iron as a raw material. The reaction byproduct, hydrogen, is processed through a pressure swing adsorption (PSA) hydrogen extraction device and a hydrogen peroxide production device to produce hydrogen peroxide. The crude ferrous dihydrogen phosphate solution undergoes solid-liquid separation, pH adjustment, and the addition of hydrogen peroxide to obtain a primary ferric phosphate dihydrate slurry. This slurry is fed into a circulating reactor for continuous recycling, and then sequentially undergoes solid-liquid separation, washing, flash evaporation, and drying to obtain anhydrous ferric phosphate. This method improves ferric phosphate production efficiency, and the byproduct hydrogen can be used to produce hydrogen peroxide, which is ultimately recycled back into the ferric phosphate production process, significantly reducing the production cost of hydrogen peroxide. However, the dilute phosphoric acid used in this method is obtained by diluting 85% industrial phosphoric acid, leaving considerable room for improvement and profit reduction.

[0006] The invention patent with application number 202210937012.1 discloses a method for preparing battery-grade iron orthophosphate. It uses agricultural monoammonium phosphate or wet-process ammonium phosphate neutralized slurry as phosphorus source, and prepares battery-grade iron orthophosphate through dissolution, impurity removal and synthesis steps. In particular, the impurity removal process has been optimized. A large amount of insoluble matter and water-soluble impurities in the phosphorus source are removed by adjusting the pH with an alkaline neutralizing agent, filtration and defluorination, so that the purified phosphorus source can be used to prepare battery-grade iron orthophosphate. This method mixes the phosphorus source slurry with an alkaline neutralizing agent for dissolution and impurity removal, and uses fluoride ion chelating resin for defluorination. However, the processing capacity is small, the cost is high, and it is difficult to realize industrial production. Summary of the Invention

[0007] To address the above deficiencies, the technical problem solved by this invention is to provide a low-cost production process for preparing battery-grade iron phosphate using wet-process phosphoric acid and related acids as raw materials.

[0008] The present invention discloses a wet-process production process for preparing battery-grade iron phosphate from phosphoric acid and related acids, comprising the following steps:

[0009] a. Extraction 1: Wet-process phosphoric acid and its related acids are extracted using extractant A. After extraction, phase separation is performed to obtain oil phase 1 and aqueous phase 1. The extractant A is an extractant for extracting metal cations.

[0010] b. Concentration and defluorination: Aqueous phase 1 is concentrated and defluorinated;

[0011] c. Chemical defluorination: Alkali metal salts are used to perform secondary defluorination on the concentrated defluorinated aqueous phase 1 to obtain defluorinated phosphoric acid;

[0012] d. Preparation of NH4H2PO4 solution: NH4H2PO4 solution is prepared from defluorinated phosphoric acid using method A or method B;

[0013] e. Reaction: NH4H2PO4 solution reacts with ferrous sulfate solution to obtain a mixed solution;

[0014] f. Oxidation: Hydrogen peroxide is added to the mixed solution to carry out the oxidation reaction;

[0015] g. Adjust pH: Use liquid ammonia to adjust the pH of the solution after the oxidation reaction in step f, and separate the precipitate;

[0016] h. Washing and drying: The precipitate is washed and dried to obtain battery-grade iron phosphate;

[0017] Method A includes the following steps:

[0018] A1. Extraction 2: Extract defluorinated phosphoric acid with extractant B, and separate the phases after extraction to obtain oil phase 2 and aqueous phase 2; the extractant B is the extractant for extracting phosphoric acid;

[0019] A2, Back-extraction 2: Liquid ammonia is used to back-extract oil phase 2, and phase separation is performed to obtain oil phase 3 and aqueous phase 3; aqueous phase 3 is NH4H2PO4 solution;

[0020] Method B includes the following steps:

[0021] B1, Neutralization 1: Liquid ammonia is added to defluorinated phosphoric acid to adjust the pH of the solution and a precipitate is generated. The precipitate is separated to obtain aqueous phase 3.

[0022] B2, Neutralization 2: Add liquid ammonia to aqueous phase 3 to adjust the pH of the solution, filter the precipitate, and obtain the filtrate as NH4H2PO4 solution.

[0023] In one embodiment of the present invention, extractant A includes at least one of organophosphorus extractants, organophosphorus extractants, organosulfonic acid extractants, organocarboxylic acid extractants, and tertiary carbonate extractants; extractant B includes at least one of organic basic extractants, organophosphate extractants, organic ketone extractants, and organic alcohol extractants.

[0024] In some specific embodiments, extractant A includes at least one of di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate, di(2,4,4-trimethylpentyl)phosphine, 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester, N,NN-n-octylaminedimethylenephenylphosphonic acid, N,NN-n-hexylaminedimethylenephenylphosphonic acid, toluenesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, cinnamic acid, fatty acids, lauric acid, and naphthenic acid; extractant B includes at least one of trialkylmethylamine, didecylamine, trioctylamine, trinonylamine, ethyl acetate, amyl acetate, butyl acetate, dioctyl sulfoxide, diphenyl sulfoxide, alkyl sulfoxide, di(2-ethylhexyl) hexyl phosphate, dioctyl octyl phosphate, tributyl phosphate, methyl isobutyl ketone, cyclohexanone, isoamyl alcohol, sec-octanol, and substituted primary alcohols.

[0025] In one embodiment of the present invention, the wet-process phosphoric acid and its related acids include, but are not limited to, dilute wet-process phosphoric acid, concentrated wet-process phosphoric acid, residual raffinate acid, and phosphoric acid obtained from the acidolysis of white fertilizer. In some preferred embodiments, the main elements in the wet-process phosphoric acid and its related acids, calculated by their oxides, are: P2O5 content 0.1 wt.%–60 wt.%, Al2O3 content 0 wt.%–10 wt.%, MgO content 0 wt.%–10 wt.%, Fe2O3 content 0 wt.%–10 wt.%, CaO content 0 wt.%–30 wt.%, and F content 0.1 wt.%–5 wt.%.

[0026] In one embodiment of the present invention, in step a, extraction 1, the extraction is a multi-stage three-stage countercurrent extraction, with 1 to 10 stages; preferably 3 stages; the extraction temperature is 25 to 85°C, and the volume ratio O / A is 1 to 10:1.

[0027] In step A1, extraction 2, the extraction is a 1-3 stage countercurrent extraction; the number of extraction stages is preferably 1 stage, the extraction temperature is preferably 25-85℃, and the volume ratio O / A is 1-10:1.

[0028] In step A2, the back-extraction temperature is 25–85°C, with a volume ratio of O / A of 1–10:1; phase separation is preferably carried out at 25–85°C.

[0029] In step B1, the pH of the neutralization solution is adjusted to 3.5–5.0. During neutralization, the mixture is stirred at a speed of 200–500 r / min, and the precipitation temperature is 25–90°C.

[0030] In step B2, the pH of the neutralization solution is adjusted to 5.1–9.0. During neutralization, the mixture is stirred at a speed of 200–500 r / min, and the precipitation temperature is 25–90 °C.

[0031] In one embodiment of the present invention, the method further includes the following steps:

[0032] Processing of oil phase 1: Add back-extraction agent A to oil phase 1 to back-extract the metal cations in oil phase 1 to obtain oil phase 4 and aqueous phase 4. Oil phase 4 is returned to step a as extractant A for recycling, and aqueous phase 4 is returned as back-extraction agent A for recycling.

[0033] In one embodiment of the present invention, the stripping agent A is at least one of ammonium oxalate solution, a mixed solution of ammonium oxalate and ammonium sulfate, and a mixed solution of ammonium sulfate and sulfuric acid. Preferably, in the stripping agent A, the concentration of ammonium oxalate is 1 wt.% to 20 wt.%, the concentration of ammonium sulfate is 0 wt.% to 35 wt.%, and the concentration of sulfuric acid is 0.1 wt.% to 20 wt.%.

[0034] In one embodiment of the present invention, the method further includes an oil-water separation step.

[0035] When using method A, the oil-water separation step includes at least one of the following steps:

[0036] Oil-water separation 1: Separate the oil phase 4 into oil and water, and combine the separated water phase into the water phase 4;

[0037] Oil-water separation 2: Separate the aqueous phase 1 into oil and water, and add the separated oil phase into the oil phase 1. Separate the aqueous phase and proceed to step b.

[0038] Oil-water separation 3: Separate the oil phase 2 into oil and water, and add the separated water phase back into the water phase 2. The separated oil phase is then fed into step A2.

[0039] Oil-water separation 4: The aqueous phase 3 is separated into oil and water to obtain an NH4H2PO4 solution, and the separated organic phase is incorporated into the oil phase 3;

[0040] Oil-water separation 5: Separate the oil phase 3 into oil and water. The separated water phase is added to the NH4H2PO4 solution, and the separated oil phase is returned to be recycled as extractant B.

[0041] When using method B, the oil-water separation step includes at least one of the following steps:

[0042] Oil-water separation 1: Separate the oil phase 4 into oil and water, and combine the separated water phase into the water phase 4;

[0043] Oil-water separation 2: Separate the aqueous phase 1 into oil and water, and add the separated oil phase into the oil phase 1. Separate the aqueous phase and proceed to step b.

[0044] In one embodiment of the present invention, in step b, the concentration temperature is 60-90°C, the phosphoric acid concentration at the concentration endpoint is 40 wt.%-60 wt.%, and the F content is 0.15 wt.%-0.30 wt.%.

[0045] In step c, the F content in the defluorinated phosphoric acid is controlled to be less than 0.15 wt.%.

[0046] In one embodiment of the present invention, aqueous phase 2 is incorporated into step a for extraction;

[0047] When using method A, the filtrate after precipitation in step g or the wash water after washing in step h is incorporated into step A2 for back-extraction;

[0048] When using method B, the filtrate after precipitation in step g or the wash water after washing in step h shall be added to the NH4H2PO4 solution in step B2.

[0049] In one embodiment of the present invention, in step e, the concentration of ferrous sulfate is 0.1 wt.% to 35 wt.%.

[0050] In step f, the hydrogen peroxide is 0.5 to 2.0 times the stoichiometry of ferrous dihydrogen phosphate;

[0051] In step g, the pH of the solution is adjusted to 0.5–2, and the precipitation temperature is 25–90℃.

[0052] In step h, the drying temperature is 300–900℃ and the drying time is 2–8 hours.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. This invention uses an extraction method to remove metal cations from wet-process phosphoric acid and its related acids. Various metal ions in phosphoric acid can be effectively separated, and the extractant can be recycled after back-extraction, reducing production costs.

[0055] 2. This invention uses concentrated defluorination and chemical defluorination to remove fluoride ions from wet phosphoric acid, eliminating the impact of fluoride ions on subsequent processes and realizing the recycling of fluoride resources.

[0056] 3. This invention employs a specific extraction and back-extraction method, or a specific two-stage neutralization method, to extract and separate NH4H2PO4 solution from purified wet-process phosphoric acid. No residual acid is generated during the process, and the extractant can be recycled after back-extraction, avoiding the generation of insoluble substances such as magnesium ammonium phosphate that affect product quality.

[0057] 4. This invention uses a two-step method to prepare battery-grade iron phosphate. The precipitation method for preparing iron phosphate has a lower cost and meets the requirements of industrial production. Attached Figure Description

[0058] Figure 1 The flowcharts are for the production processes of battery-grade iron phosphate prepared by wet-process phosphoric acid and related acids in Examples 1-4 of this invention.

[0059] Figure 2 The flowcharts for the production process of battery-grade iron phosphate by wet-process phosphoric acid and related acids in Examples 5-6 of this invention are shown. Detailed Implementation

[0060] The present invention discloses a wet-process production process for preparing battery-grade iron phosphate from phosphoric acid and related acids, comprising the following steps:

[0061] a. Extraction 1: Wet-process phosphoric acid and its related acids are extracted using extractant A. After extraction, phase separation is performed to obtain oil phase 1 and aqueous phase 1. The extractant A is an extractant for extracting metal cations.

[0062] b. Concentration and defluorination: Aqueous phase 1 is concentrated and defluorinated;

[0063] c. Chemical defluorination: Alkali metal salts are used to perform secondary defluorination on the concentrated defluorinated aqueous phase 1 to obtain defluorinated phosphoric acid;

[0064] d. Preparation of NH4H2PO4 solution: NH4H2PO4 solution is prepared from defluorinated phosphoric acid using method A or method B;

[0065] e. Reaction: NH4H2PO4 solution reacts with ferrous sulfate solution to obtain a mixed solution;

[0066] f. Oxidation: Hydrogen peroxide is added to the mixed solution to carry out the oxidation reaction;

[0067] g. Adjust pH: Use liquid ammonia to adjust the pH of the solution after the oxidation reaction in step f, and separate the precipitate;

[0068] h. Washing and drying: The precipitate is washed and dried to obtain battery-grade iron phosphate;

[0069] Method A includes the following steps:

[0070] A1. Extraction 2: Extract defluorinated phosphoric acid with extractant B, and separate the phases after extraction to obtain oil phase 2 and aqueous phase 2; the extractant B is the extractant for extracting phosphoric acid;

[0071] A2, Back-extraction 2: Liquid ammonia is used to back-extract oil phase 2, and phase separation is performed to obtain oil phase 3 and aqueous phase 3; aqueous phase 3 is NH4H2PO4 solution;

[0072] Method B includes the following steps:

[0073] B1, Neutralization 1: Liquid ammonia is added to defluorinated phosphoric acid to adjust the pH of the solution and a precipitate is generated. The precipitate is separated to obtain aqueous phase 3.

[0074] B2, Neutralization 2: Add liquid ammonia to aqueous phase 3 to adjust the pH of the solution, filter the precipitate, and obtain the filtrate as NH4H2PO4 solution.

[0075] This invention utilizes an extractant to extract metal cations from phosphoric acid, separates the aqueous phase for defluorination, and achieves the recovery and utilization of fluorine resources. An NH4H2PO4 solution is obtained through extraction, back-extraction, or a two-stage neutralization process. Ferrous sulfate and hydrogen peroxide are added to the NH4H2PO4 solution to obtain a primary slurry of ferric phosphate dihydrate. Finally, the precipitate is washed and dried to obtain battery-grade ferric phosphate. This method is simple to operate, has a large processing capacity, produces high-purity products, and has low production costs, achieving comprehensive utilization of wet-process phosphoric acid.

[0076] The method of this invention is applicable to various wet-process phosphoric acid and related acids. In one embodiment of this invention, the wet-process phosphoric acid and related acids include, but are not limited to, dilute wet-process phosphoric acid (i.e., wet-process phosphoric acid with a P2O5 content of 35.% or less based on oxides), concentrated wet-process phosphoric acid (i.e., wet-process phosphoric acid with a P2O5 content greater than 35.% based on oxides), raffinate (i.e., raffinate produced by purifying wet-process phosphoric acid to obtain industrial-grade or food-grade phosphoric acid), and phosphoric acid obtained from the acid hydrolysis of white fertilizer. In some preferred embodiments, the main elements in the wet-process phosphoric acid and related acids, based on their oxides, are: P2O5 content 0.1 wt.%–60 wt.%, Al2O3 content 0 wt.%–10 wt.%, MgO content 0 wt.%–10 wt.%, Fe2O3 content 0 wt.%–10 wt.%, CaO content 0 wt.%–30 wt.%, and F content 0.1 wt.%–5 wt.%.

[0077] The following provides a detailed description of each step of the present invention.

[0078] (1) Step a

[0079] Step a is extraction 1, in which wet-process phosphoric acid and its related acids are extracted using extractant A. After extraction, phase separation is performed to obtain oil phase 1 and aqueous phase 1. Extractant A in this step is an extractant that can extract metal cations.

[0080] Any extractant capable of extracting metal cations can be used as extractant A in this invention. In some embodiments of this invention, extractant A includes organophosphorus extractants, such as di(2-ethylhexyl) phosphate (P204), 2-ethylhexyl phosphate (P507), di(2,4,4-trimethylpentyl)phosphine, etc.; organophosphorus extractants, such as 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester, N,NN-n-octylaminedimethylenephenylphosphonic acid (OADMPPA), N,NN-n-hexylaminedimethylenephenylphosphonic acid (HADMPPA), etc.; organosulfonic acid extractants, such as toluenesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, etc.; and organocarboxylic acid extractants, such as at least one of cinnamic acid, fatty acids, lauric acid, naphthenic acid, etc.

[0081] Step a can employ conventional extraction processes in the art. In some embodiments of the present invention, the extraction is a multi-stage three-stage countercurrent extraction, with 1 to 10 stages. In some specific embodiments of the present invention, the number of stages is 3.

[0082] The extraction temperature and ratio can also be set under conventional conditions in the art. In some embodiments of the present invention, the extraction temperature is 25 to 85°C and the ratio by volume O / A is 1 to 10:1.

[0083] In one specific embodiment, the production process of battery-grade iron phosphate from wet-process phosphoric acid and related acids of the present invention further includes the following steps:

[0084] Processing of oil phase 1: Add back-extraction agent A to oil phase 1 to back-extract the metal cations in oil phase 1 to obtain oil phase 4 and aqueous phase 4. Oil phase 4 is returned to step a as extractant A for recycling, and aqueous phase 4 is returned as back-extraction agent A for recycling.

[0085] In some embodiments of the present invention, the back-extraction agent A is at least one of ammonium oxalate solution, a mixed solution of ammonium oxalate and ammonium sulfate, and a mixed solution of ammonium sulfate and sulfuric acid.

[0086] In some embodiments of the present invention, the concentration of ammonium oxalate in the back-extraction agent A is 1 wt.% to 20 wt.%, the concentration of ammonium sulfate is 0 wt.% to 35 wt.%, and the concentration of sulfuric acid is 0.1 wt.% to 20 wt.%.

[0087] In some embodiments of the present invention, the oil-water separation 1 and / or oil-water separation 2 steps may also be included:

[0088] Oil-water separation 1: Separate the oil phase 4 from the water phase, and merge the separated water phase into the water phase 4; Oil-water separation 2: Separate the water phase 1 from the water phase, and merge the separated oil phase into the oil phase 1, and separate the water phase to proceed to step b.

[0089] The oil-water separation of the present invention can be performed using conventional methods, such as using a common oil-water separator.

[0090] (2) Step b

[0091] Step b is concentration and defluorination, in which aqueous phase 1 is concentrated and defluorinated. Concentration can be performed using conventional methods in this field, such as evaporation concentration.

[0092] In one embodiment of the present invention, the concentration temperature is 60-90°C, the phosphoric acid concentration at the concentration endpoint is 40 wt.%-60 wt.%, and the F content is 0.15 wt.%-0.30 wt.%.

[0093] (3) Step c

[0094] Step c is chemical defluorination, in which the concentrated defluorinated aqueous phase 1 is subjected to secondary defluorination using an alkali metal salt to obtain defluorinated phosphoric acid. Chemical defluorination further reduces the fluoride content in aqueous phase 1, yielding defluorinated phosphoric acid. In one embodiment of the invention, the F content in the defluorinated phosphoric acid is controlled to be less than 0.15 wt.%.

[0095] (4) Step d

[0096] Step d involves preparing an NH4H2PO4 solution, which is obtained from defluorinated phosphoric acid using either method A or method B.

[0097] Method A includes extraction step A1 and back-extraction step A2.

[0098] Extraction 2 involves extracting defluorinated phosphoric acid with extractant B, followed by phase separation to obtain oil phase 2 and aqueous phase 2; the extractant B is the extractant used for extracting phosphoric acid.

[0099] Extractant B is a commonly used extractant in the art capable of extracting phosphoric acid. In one embodiment of the present invention, extractant B includes at least one of the following extractants capable of extracting phosphoric acid: organic basic extractants [organic amines—primary, secondary, and tertiary amines (e.g., trialkylmethylamine, didecylamine, trioctylamine, trinonylamine), lipids (e.g., ethyl acetate, amyl acetate, butyl acetate), sulfoxides (e.g., dioctyl sulfoxide, diphenyl sulfoxide, hydrocarbon sulfoxide), organic phosphate ester extractants (e.g., di(2-ethylhexyl) hexyl phosphate, dioctyl phosphate, tributyl phosphate), organic ketones (e.g., methyl isobutyl ketone, cyclohexanone), organic alcohols (e.g., isoamyl alcohol, sec-octanol, substituted primary alcohols).

[0100] In one specific embodiment of the present invention, in step A1, extraction 2, the extraction is a 1-3 stage countercurrent extraction.

[0101] In one specific embodiment, the number of extraction segments is preferably 1 segment.

[0102] There are no special requirements for the extraction temperature and the ratio; conventional temperatures and ratios in the art can be used. In one embodiment of the present invention, the extraction temperature is preferably 25–85°C, and the ratio (O / A) is 1–10:1 by volume.

[0103] In order to recycle resources and save costs, aqueous phase 2 is returned to step a and mixed with wet phosphoric acid and its related acids for extraction.

[0104] In one embodiment of the present invention, the method further includes oil-water separation 3: oil phase 2 is separated into oil and water, the separated water phase is incorporated into water phase 2, and the separated oil phase is fed into step A2.

[0105] Step A2 is back-extraction 2, in which liquid ammonia is used to back-extract oil phase 2, and phase separation is performed to obtain oil phase 3 and aqueous phase 3; aqueous phase 3 is NH4H2PO4 solution.

[0106] In one embodiment of the invention, the back-extraction temperature is 25–85°C, and the volume ratio O / A is 1–10:1. Preferably, phase separation is performed at 25–85°C.

[0107] In one embodiment of the present invention, the process further includes oil-water separation 4 and / or oil-water separation 5:

[0108] Oil-water separation 4: The aqueous phase 3 is separated into oil and water. The separated aqueous phase is an NH4H2PO4 solution, and the separated organic phase is incorporated into the oil phase 3.

[0109] Oil-water separation 5: Separate the oil phase 3 into oil and water. The separated water phase is added to the NH4H2PO4 solution, and the separated oil phase is returned to be recycled as extractant B.

[0110] Method B includes neutralization step 1 in step B1 and neutralization step 2 in step B2.

[0111] Step B1 is neutralization 1, where liquid ammonia is added to defluorinated phosphoric acid to adjust the pH of the solution to generate a precipitate, and the precipitate is separated to obtain aqueous phase 3.

[0112] In one embodiment of the present invention, the pH value of the solution in this step is adjusted to 3.5 to 5.0.

[0113] In one embodiment of the present invention, stirring is performed while adjusting the pH value, and the stirring speed is controlled at 200-500 r / min.

[0114] As the pH value is adjusted, a precipitate will form in the solution. In one embodiment of the present invention, the precipitation temperature is controlled to be 25–90°C.

[0115] Step B2 is neutralization 2. Liquid ammonia is added to the aqueous phase 3 to adjust the pH of the solution. The precipitate is filtered, and the filtrate is an NH4H2PO4 solution.

[0116] In one embodiment of the present invention, the pH value of the solution in this step is adjusted to 5.1 to 9.0.

[0117] In one embodiment of the present invention, stirring is performed while adjusting the pH value, and the stirring speed is controlled at 200-500 r / min.

[0118] As the pH value is adjusted, a precipitate will form in the solution. In one embodiment of the present invention, the precipitation temperature is controlled to be 25–90°C.

[0119] (5) e Step

[0120] Step e is a reaction in which NH4H2PO4 solution reacts with ferrous sulfate solution to obtain a mixed solution.

[0121] In one embodiment of the present invention, in step e, the concentration of ferrous sulfate is 0.1 wt.% to 35 wt.%.

[0122] (6) f step

[0123] Step f is oxidation, in which hydrogen peroxide is added to the mixed solution to carry out the oxidation reaction.

[0124] In one embodiment of the present invention, in step f, hydrogen peroxide is 0.5 to 2.0 times the stoichiometry of ferrous dihydrogen phosphate.

[0125] (7) g step

[0126] Step g involves adjusting the pH using liquid ammonia to adjust the pH of the solution after the oxidation reaction in step f, and then separating the precipitate.

[0127] In one embodiment of the present invention, the pH value of the solution is adjusted to 0.5 to 2.

[0128] In one embodiment of the present invention, stirring is performed while adjusting the pH value, and the stirring speed is controlled at 200-500 r / min.

[0129] As the pH value is adjusted, a precipitate will form in the solution. In one embodiment of the present invention, the precipitation temperature is controlled to be 25–90°C.

[0130] The precipitate can be separated using conventional methods in the art, such as filtration. For resource recycling, in one embodiment of the invention, when using method A, the precipitated liquid is returned to step A2 and mixed with a back-extraction agent for back-extraction.

[0131] In another embodiment of the present invention, when using method B, the precipitated liquid is returned to step B2 and mixed with NH4H2PO4 solution.

[0132] (8) h steps

[0133] Step h involves washing and drying, followed by precipitate washing and drying to obtain battery-grade iron phosphate.

[0134] Washing and drying can both be performed using conventional methods in this field.

[0135] In one embodiment of the present invention, when using method A, the wash water after washing is incorporated into step A2 and mixed with the back-extraction agent for back-extraction, which can ensure the recycling of resources.

[0136] In another embodiment of the present invention, when using method B, the wash water after washing is incorporated into the NH4H2PO4 solution in step B2, which also ensures the recycling of resources.

[0137] In one embodiment of the present invention, the drying temperature is 300-900°C and the drying time is 2-8 hours.

[0138] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0139] Example 1

[0140] A production process for preparing battery-grade iron phosphate using wet-process phosphoric acid and related acids, employing method A, wherein the wet-process phosphoric acid and related acids used are residual raffinate acids, and the main substances, calculated as oxides, are: P2O5 44wt.%–46wt.%, Al2O3 3wt.%–3.5wt.%, MgO 2.5wt.%–3wt.%, Fe2O3 0.1wt.%–0.5wt.%, CaO 0.1wt.%–0.5wt.%, and F 0.1wt.%–0.5wt.%.

[0141] like Figure 1 As shown, the process includes the following steps:

[0142] (1) Extraction 1: The residual acid was subjected to three-stage countercurrent extraction with 2-ethylhexyl phosphate 2-ethylhexyl ester. The extraction temperature of each stage was 60℃, and the volume ratio O / A was 4:1.

[0143] (2) Back-extraction 1: A mixed solution of ammonium oxalate and ammonium sulfate is used as back-extraction agent A, wherein the concentration of ammonium oxalate is 5 wt.% and the concentration of ammonium sulfate is 35 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0144] (3) Concentration and defluorination: The purified phosphoric acid solution is concentrated and defluorinated in a vacuum evaporator at a concentration of 60°C until the phosphoric acid concentration is 50 wt.%. Fluorides (HF, SiF4) in the vapor are absorbed by water to obtain HF, with an F content of 0.19 wt.%.

[0145] (4) Chemical defluorination: Add sodium carbonate precipitant to the defluorinated phosphoric acid solution to defluorinate until the F content reaches 0.13 wt.%, and then filter and separate the precipitate.

[0146] (5) Extraction 2: Using TBP (tributylphosphine) as extractant B, a single-stage countercurrent extraction was performed on the filtered liquid at an extraction temperature of 60°C and a phase ratio of O / A of 2:1 (volume ratio). After phase separation and oil-water separation, aqueous phase 2 and oil phase 2 were obtained. Aqueous phase 2 was returned to the residual acid for further extraction.

[0147] (6) Back-extraction 2: Liquid ammonia is added to oil phase 2 for back-extraction. The back-extraction temperature is 60℃. The volume ratio of O / A is 1:1. After phase separation and oil-water separation, NH4H2PO4 solution is obtained. The separated oil phase is used as a regenerated extractant for recycling.

[0148] (7) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0149] (8) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0150] (9) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0151] (10) Washing and drying: Wash and dry the precipitate with pure water at a temperature of 500℃ for 4 hours.

[0152] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0153] Example 2

[0154] A production process for preparing battery-grade iron phosphate using wet-process phosphoric acid and related acids, employing method A, wherein the wet-process phosphoric acid and related acids used are concentrated wet-process phosphoric acid, and the main substances, calculated as oxides, are: P2O5 46wt.%–48wt.%, Al2O3 2wt.%–2.5wt.%, MgO 1wt.%–1.5wt.%, Fe2O3 0.1wt.%–0.5wt.%, CaO 0.1wt.%–0.5wt.%, and F 3wt.%–3.5wt.%.

[0155] like Figure 1 As shown, the process includes the following steps:

[0156] (1) Extraction 1: Wet-process concentrated phosphoric acid was extracted with di(2-ethylhexyl) phosphate in two stages of three-stage countercurrent extraction. The extraction temperature of each stage was 60℃, and the volume ratio O / A was 4:1.

[0157] (2) Back-extraction 1: A mixed solution of ammonium sulfate and sulfuric acid is used as back-extraction agent A, wherein the concentration of ammonium sulfate is 35 wt.% and the concentration of sulfuric acid is 1 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0158] (3) Concentration and defluorination: The purified phosphoric acid solution is concentrated and defluorinated in a vacuum evaporator at a concentration of 80°C until the phosphoric acid concentration is 50 wt.%. Fluorides (HF, SiF4) in the vapor are absorbed by water to obtain HF, with an F content of 0.28 wt.%.

[0159] (4) Chemical defluorination: Add sodium carbonate precipitant to the defluorinated phosphoric acid solution to defluorinate until the F content reaches 0.14 wt.%, and then filter and separate the precipitate.

[0160] (5) Extraction 2: Using TBP (tributylphosphine) as extractant B, the filtered liquid was subjected to a single-stage countercurrent extraction at a temperature of 60°C and an O / A ratio of 2:1 (volume ratio). After phase separation and oil-water separation, aqueous phase 2 and oil phase 2 were obtained. Aqueous phase 2 was returned to wet-process concentrated phosphoric acid for extraction.

[0161] (6) Back-extraction 2: Liquid ammonia is added to oil phase 2 for back-extraction. The back-extraction temperature is 60℃. The volume ratio of O / A is 1:1. After phase separation and oil-water separation, NH4H2PO4 solution is obtained. The separated oil phase is used as a regenerated extractant for recycling.

[0162] (7) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0163] (8) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0164] (9) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0165] (10) Washing and drying: Wash and dry the precipitate with pure water at a temperature of 500℃ for 4 hours.

[0166] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0167] Example 3

[0168] A production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids, using method A, wherein the wet-process phosphoric acid and related acids used are wet-process phosphoric acid, and the main contents of the substances, calculated as oxides, are as follows: P2O5 content 24wt.%~26wt.%, Al2O3 content 1wt.%~1.2wt.%, MgO content 0.7wt.%~0.9wt.%, Fe2O3 content 0.2wt.%~0.3wt.%, CaO content 0.6wt.%~0.8wt.%, and F content 1.0wt.%~1.3wt.%.

[0169] like Figure 1 As shown, the process includes the following steps:

[0170] (1) Extraction 1: Wet phosphoric acid was extracted in two stages of three-stage countercurrent extraction with di(2-ethylhexyl) phosphate. The extraction temperature of each stage was 60°C and the volume ratio O / A was 4:1.

[0171] (2) Back-extraction 1: A mixed solution of ammonium sulfate and sulfuric acid is used as back-extraction agent A, wherein the concentration of ammonium sulfate is 35 wt.% and the concentration of sulfuric acid is 1 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0172] (3) Concentration and defluorination: The purified phosphoric acid solution is concentrated and defluorinated in a vacuum evaporator at a concentration of 80°C until the phosphoric acid concentration is 40 wt.%. Fluorides (HF, SiF4) in the vapor are absorbed by water to obtain HF, with an F content of 0.21 wt.%.

[0173] (4) Chemical defluorination: Add sodium carbonate precipitant to the defluorinated phosphoric acid solution to defluorinate until the F content reaches 0.12 wt.%, and then filter and separate the precipitate.

[0174] (5) Extraction 2: Trioctylamine was used as extractant B to perform a single-stage countercurrent extraction on the filtered liquid at an extraction temperature of 60°C and a phase ratio of O / A of 2:1 (volume ratio). After phase separation and oil-water separation, aqueous phase 2 and oil phase 2 were obtained. Aqueous phase 2 was returned to wet phosphoric acid for extraction.

[0175] (6) Back-extraction 2: Liquid ammonia is added to oil phase 2 for back-extraction. The back-extraction temperature is 60℃. The volume ratio of O / A is 1:1. After phase separation and oil-water separation, NH4H2PO4 solution is obtained. The separated oil phase is used as a regenerated extractant for recycling.

[0176] (7) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0177] (8) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0178] (9) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0179] (10) Washing and drying: Wash and dry the precipitate with pure water at a temperature of 500℃ for 4 hours.

[0180] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0181] Example 4

[0182] A production process for preparing battery-grade iron phosphate using wet-process phosphoric acid and related acids, employing method A, wherein the wet-process phosphoric acid and related acids used are phosphoric acid extracted from white fertilizer, and the main substances, calculated as oxides, are: P2O5 content 6 wt.%–8 wt.%, Al2O3 content 2.7 wt.%–3 wt.%, MgO content 0.2 wt.%–0.5 wt.%, Fe2O3 content 2 wt.%–2.5 wt.%, CaO content 0.5 wt.%–0.8 wt.%, and F content 1.3 wt.%–1.5 wt.%.

[0183] like Figure 1 As shown, the process includes the following steps:

[0184] (1) Extraction 1: Phosphoric acid leached from white fertilizer was subjected to two-stage three-stage countercurrent extraction with di(2-ethylhexyl) phosphate. The extraction temperature of each stage was 60℃, and the volume ratio O / A was 4:1.

[0185] (2) Back-extraction 1: A mixed solution of ammonium sulfate and sulfuric acid is used as back-extraction agent A, wherein the concentration of ammonium sulfate is 35 wt.% and the concentration of sulfuric acid is 1 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0186] (3) Concentration and defluorination: The purified phosphoric acid solution is concentrated and defluorinated in a vacuum evaporator at a concentration of 80°C until the phosphoric acid concentration is 40 wt.%. Fluorides (HF, SiF4) in the vapor are absorbed by water to obtain HF, with an F content of 0.24 wt.%.

[0187] (4) Chemical defluorination: Add sodium carbonate precipitant to the defluorinated phosphoric acid solution to defluorinate until the F content reaches 0.13 wt.%, and then filter and separate the precipitate.

[0188] (5) Extraction 2: Trialkylmethylamine was used as extractant B to perform a single-stage countercurrent extraction on the filtered liquid at an extraction temperature of 60°C and a phase ratio of O / A of 2:1 (volume ratio). After phase separation and oil-water separation, aqueous phase 2 and oil phase 2 were obtained. Aqueous phase 2 was returned to the phosphoric acid leaching solution of white fertilizer for extraction.

[0189] (6) Back-extraction 2: Liquid ammonia is added to oil phase 2 for back-extraction. The back-extraction temperature is 60℃. The volume ratio of O / A is 1:1. After phase separation and oil-water separation, NH4H2PO4 solution is obtained. The separated oil phase is used as a regenerated extractant for recycling.

[0190] (7) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0191] (8) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0192] (9) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0193] (10) Washing and drying: Wash and dry the precipitate with pure water at a temperature of 500℃ for 4 hours.

[0194] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0195] Example 5

[0196] A production process for preparing battery-grade iron phosphate using wet-process phosphoric acid and related acids is disclosed, employing method B, with the same wet-process phosphoric acid as in Example 2.

[0197] like Figure 2 As shown, the process includes the following steps:

[0198] (1) Extraction 1: Wet-process concentrated phosphoric acid was extracted with di(2-ethylhexyl) phosphate in two stages of three-stage countercurrent extraction. The extraction temperature of each stage was 60℃, and the volume ratio O / A was 4:1.

[0199] (2) Back-extraction 1: A mixed solution of ammonium sulfate and sulfuric acid is used as back-extraction agent A, wherein the concentration of ammonium sulfate is 35 wt.% and the concentration of sulfuric acid is 1 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0200] (3) Concentration and defluorination: The purified phosphoric acid solution is concentrated and defluorinated in a vacuum evaporator at a concentration of 80°C until the phosphoric acid concentration is 50 wt.%. Fluorides (HF, SiF4) in the vapor are absorbed by water to obtain HF, with an F content of 0.28 wt.%.

[0201] (4) Chemical defluorination: Add sodium carbonate precipitant to the defluorinated phosphoric acid solution to defluorinate until the F content reaches 0.14 wt.%, and then filter and separate the precipitate.

[0202] (5) Neutralization 1: Under the action of the stirring paddle, add liquid ammonia to the filtered clear liquid to adjust the pH of the solution to 4-5, and filter to precipitate.

[0203] (6) Neutralization 2: Under the action of the stirring paddle, liquid ammonia is added to the filtered clear liquid to adjust the pH of the solution to 7-8, and the precipitate is filtered to obtain NH4H2PO4 solution.

[0204] (7) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0205] (8) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0206] (9) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0207] (10) Washing and drying: Wash and dry the precipitate with pure water at a temperature of 500℃ for 4 hours.

[0208] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0209] Example 6

[0210] A production process for preparing battery-grade iron phosphate using wet-process phosphoric acid and related acids, employing method B, with the same wet-process phosphoric acid as in Example 3.

[0211] like Figure 2 As shown, the process includes the following steps:

[0212] (1) Extraction 1: Wet phosphoric acid was subjected to two-stage three-stage countercurrent extraction with di(2-ethylhexyl) phosphate. The extraction temperature of each stage was 60℃, and the volume ratio O / A was 4:1.

[0213] (2) Back-extraction 1: A mixed solution of ammonium sulfate and sulfuric acid is used as back-extraction agent A, wherein the concentration of ammonium sulfate is 35 wt.% and the concentration of sulfuric acid is 1 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0214] (3) Concentration and defluorination: The purified phosphoric acid solution is concentrated and defluorinated in a vacuum evaporator at a concentration of 80°C until the phosphoric acid concentration is 40 wt.%. Fluorides (HF, SiF4) in the vapor are absorbed by water to obtain HF, with an F content of 0.21 wt.%.

[0215] (4) Chemical defluorination: Add sodium carbonate precipitant to the defluorinated phosphoric acid solution to defluorinate until the F content reaches 0.12 wt.%, and then filter and separate the precipitate.

[0216] (5) Neutralization 1: Under the action of the stirring paddle, add liquid ammonia to the filtered clear liquid to adjust the pH of the solution to 4-5, and filter to precipitate.

[0217] (6) Neutralization 2: Under the action of the stirring paddle, liquid ammonia is added to the filtered clear liquid to adjust the pH of the solution to 7-8, and the precipitate is filtered to obtain NH4H2PO4 solution.

[0218] (7) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0219] (8) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0220] (9) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0221] (10) Washing and drying: Wash and dry the precipitate with pure water at a temperature of 500℃ for 4 hours.

[0222] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0223] Comparative Example 1

[0224] A production process for preparing battery-grade iron phosphate using wet phosphoric acid, wherein the wet phosphoric acid used is the same as in Example 3.

[0225] The process includes the following steps:

[0226] (1) Extraction 1: Wet phosphoric acid was subjected to two-stage three-stage countercurrent extraction with di(2-ethylhexyl) phosphate. The extraction temperature of each stage was 60℃, and the volume ratio O / A was 4:1.

[0227] (2) Back-extraction 1: A mixed solution of ammonium sulfate and sulfuric acid is used as back-extraction agent A, wherein the concentration of ammonium sulfate is 35 wt.% and the concentration of sulfuric acid is 1 wt.%. The oil phase 1 loaded with metal ions is subjected to two-stage three-stage countercurrent back-extraction. The temperature of each back-extraction stage is 60℃, and the ratio of O / A is 1:3 (volume ratio). Phase separation and oil-water separation are performed. The oil phase is used as a regenerated extractant and recycled, while the aqueous phase is mixed with the back-extraction agent and recycled.

[0228] (3) Extraction 2: Trioctylamine was used as extractant B to perform a single-stage countercurrent extraction on the filtered liquid at an extraction temperature of 60°C and a phase ratio of O / A of 2:1 (volume ratio). After phase separation and oil-water separation, aqueous phase 2 and oil phase 2 were obtained. Aqueous phase 2 was returned to wet phosphoric acid for extraction.

[0229] (4) Back-extraction 2: Liquid ammonia is added to oil phase 2 for back-extraction. The back-extraction temperature is 60℃. The volume ratio of O / A is 1:1. After phase separation and oil-water separation, NH4H2PO4 solution is obtained. The separated oil phase is used as a regenerated extractant for recycling.

[0230] (5) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0231] (6) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0232] (7) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0233] (8) Washing and drying: Wash and dry the sediment with pure water at a temperature of 500℃ for 4 hours.

[0234] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0235] Comparative Example 2

[0236] A production process for preparing battery-grade iron phosphate using wet phosphoric acid, wherein the wet phosphoric acid used is the same as in Example 3.

[0237] The process includes the following steps:

[0238] (1) Extraction 2: The wet-process phosphoric acid was subjected to a three-stage countercurrent extraction using trioctylamine as the extractant at an extraction temperature of 60°C and an O / A ratio of 2:1 (volume ratio). After phase separation and oil-water separation, aqueous phase 2 and oil phase 2 were obtained. Aqueous phase 2 was returned to the wet-process phosphoric acid for further extraction.

[0239] (2) Back-extraction 2: Liquid ammonia is added to oil phase 2 for back-extraction. The back-extraction temperature is 60℃. The volume ratio of O / A is 1:1. After phase separation and oil-water separation, NH4H2PO4 solution is obtained. The separated oil phase is used as a regenerated extractant for recycling.

[0240] (3) Reaction: Add 35wt.% ferrous sulfate solution (volume ratio 1:1) to NH4H2PO4 solution to react and obtain a mixed solution.

[0241] (4) Oxidation: Add 10% hydrogen peroxide in a volume ratio of 1:1 to NH4H2PO4 to the mixed solution.

[0242] (5) Adjusting pH: Under the action of the stirring paddle, add liquid ammonia to the mixed solution to adjust the pH of the solution to 1.0, control the stirring speed at 300 r / min, and settling temperature at 80℃.

[0243] (6) Washing and drying: Wash and dry the sediment with pure water at a temperature of 500℃ for 4 hours.

[0244] The electrochemical test data for the preparation of iron phosphate in this embodiment are shown in Table 1.

[0245] Table 1. Test data of ferric phosphate in each embodiment and comparative example.

[0246]

[0247]

[0248] Since the main metal ions in phosphoric acid are iron, aluminum, and magnesium ions, and other impurity ions are relatively few, the content of other impurity ions is close to zero after extraction. Therefore, this invention measures the content of iron, magnesium, and aluminum metal ions and fluorine to represent the impurity content. As can be seen from Table 1, the method of this invention yields iron phosphate with low impurity ion content, high purity, and a high iron-to-phosphorus ratio.

Claims

1. A process for the production of battery grade ferric phosphate from wet-process phosphoric acid and related acids, characterized in that, Includes the following steps: a. Extraction 1: Wet-process phosphoric acid and its related acids are extracted using extractant A. After extraction, phase separation is performed to obtain oil phase 1 and aqueous phase 1. The extractant A includes at least one of the following: di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate, di(2,4,4-trimethylpentyl)phosphine, 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester, N,NN-n-octylaminedimethylenephenylphosphonic acid, N,NN-n-hexylaminedimethylenephenylphosphonic acid, toluenesulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, cinnamic acid, fatty acids, lauric acid, and naphthenic acid. In oil phase 1, back-extraction agent A is added to back-extract the metal cations in oil phase 1, resulting in oil phase 4 and aqueous phase 4. Oil phase 4 is returned to step a as extractant A for recycling, and aqueous phase 4 is also returned as back-extraction agent A for recycling. In back-extraction agent A, the concentration of ammonium oxalate is 1 wt.% to 20 wt.%, the concentration of ammonium sulfate is 0 wt.% to 35 wt.%, and the concentration of sulfuric acid is 0.1 wt.% to 20 wt.%. b. Concentration and defluorination: Aqueous phase 1 is concentrated and defluorinated; c. Chemical defluorination: Alkali metal salts are used to perform secondary defluorination on the concentrated defluorinated aqueous phase 1 to obtain defluorinated phosphoric acid; d. Preparation of NH4H2PO4 solution: NH4H2PO4 solution is prepared from defluorinated phosphoric acid using method A or method B; e. Reaction: NH4H2PO4 solution reacts with ferrous sulfate solution to obtain a mixed solution; f. Oxidation: Hydrogen peroxide is added to the mixed solution to carry out the oxidation reaction; g. Adjust pH: Use liquid ammonia to adjust the pH of the solution after the oxidation reaction in step f, and separate the precipitate; h. Washing and drying: The precipitate is washed and dried to obtain battery-grade iron phosphate; Method A includes the following steps: A1. Extraction 2: Defluorinated phosphoric acid is extracted with extractant B, and the oil phase 2 and aqueous phase 2 are obtained after extraction and phase separation; the extractant B includes at least one of trialkylmethylamine, didecylamine, trioctylamine, trinonylamine, ethyl acetate, amyl acetate, butyl acetate, dioctyl sulfoxide, diphenyl sulfoxide, alkyl sulfoxide, di(2-ethylhexyl) hexyl phosphate, dioctyl octyl phosphate, tributyl phosphate, methyl isobutyl ketone, cyclohexanone, isoamyl alcohol, sec-octanol, and substituted primary alcohols; aqueous phase 2 is incorporated into step a for extraction; A2. Back-extraction 2: Back-extraction of oil phase 2 is performed using liquid ammonia, resulting in phase separation to obtain oil phase 3 and aqueous phase 3; aqueous phase 3 is the NH4H2PO4 solution; Method B includes the following steps: B1, Neutralization 1: Liquid ammonia is added to defluorinated phosphoric acid to adjust the pH of the solution and a precipitate is generated. The precipitate is separated to obtain aqueous phase 3. B2, Neutralization 2: Add liquid ammonia to aqueous phase 3 to adjust the pH of the solution, filter the precipitate, and obtain the filtrate as NH4H2PO4 solution; When using method A, the filtrate obtained after precipitation in step g or the wash water obtained after washing in step h is incorporated into step A2 for back-extraction; when using method A, it also includes an oil-water separation step, wherein the oil-water separation step comprises at least one of the following steps: Oil-water separation 1: Separate the oil phase 4 into oil and water, and combine the separated water phase into the water phase 4; Oil-water separation 2: Separate the aqueous phase 1 into oil and water, and add the separated oil phase into the oil phase 1. Separate the aqueous phase and proceed to step b. Oil-water separation 3: Separate the oil phase 2 into oil and water, and add the separated water phase back into the water phase 2. The separated oil phase is then fed into step A2. Oil-water separation 4: The aqueous phase 3 is separated into oil and water to obtain an NH4H2PO4 solution, and the separated organic phase is incorporated into the oil phase 3; Oil-water separation 5: Separate the oil phase 3 into oil and water. The separated water phase is added to the NH4H2PO4 solution, and the separated oil phase is returned to be recycled as extractant B. When using method B, the filtrate after precipitation in step g or the wash water after washing in step h is added to the NH4H2PO4 solution in step B2; when using method B, it also includes an oil-water separation step, which comprises at least one of the following steps: Oil-water separation 1: Separate the oil phase 4 into oil and water, and combine the separated water phase into the water phase 4; Oil-water separation 2: Separate the aqueous phase 1 into oil and water, and add the separated oil phase into the oil phase 1. Separate the aqueous phase and proceed to step b.

2. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 1, characterized in that: The wet-process phosphoric acid and its related acids include wet-process dilute phosphoric acid, wet-process concentrated phosphoric acid, residual raffinate acid, and phosphoric acid obtained from the acid hydrolysis of white fertilizer.

3. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 2, characterized in that: The main elements in the wet-process phosphoric acid and its related acids, calculated by their oxides, are: P2O5 content 0.1 wt.%–60 wt.%, Al2O3 content 0 wt.%–10 wt.%, MgO content 0 wt.%–10 wt.%, Fe2O3 content 0 wt.%–10 wt.%, CaO content 0 wt.%–30 wt.%, and F content 0.1 wt.%–5 wt.%.

4. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 1, characterized in that: In step a, extraction 1, the extraction is a multi-stage three-stage countercurrent extraction, with 1 to 10 stages; the extraction temperature is 25 to 85°C, and the volume ratio O / A is 1 to 10:

1. In step A1, extraction 2, the extraction is a 1-3 stage countercurrent extraction; the extraction temperature is 25-85℃, and the volume ratio O / A is 1-10:

1. In step A2, the back-extraction temperature is 25–85°C, and the volume ratio O / A is 1–10:

1. In step B1, the pH of the neutralization solution is adjusted to 3.5–5.

0. During neutralization, the mixture is stirred at a speed of 200–500 r / min, and the precipitation temperature is 25–90°C. In step B2, the pH of the neutralization solution is adjusted to 5.1–9.

0. During neutralization, the mixture is stirred at a speed of 200–500 r / min, and the precipitation temperature is 25–90℃.

5. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 4, characterized in that: In step a, extraction 1, there are 3 extraction stages.

6. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 4, characterized in that: In step A1, extraction 2, the extraction segment is 1.

7. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 4, characterized in that: In step A2, back-extraction 2, phase separation is carried out at 25–85°C.

8. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 1, characterized in that: In step b, the concentration temperature is 60–90°C, the phosphoric acid concentration at the concentration endpoint is 40 wt.%–60 wt.%, and the F content is 0.15 wt.%–0.30 wt.%. In step c, the F content in the defluorinated phosphoric acid is controlled to be less than 0.15 wt.%.

9. The production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids according to claim 1, characterized in that: In step e, the concentration of ferrous sulfate is 0.1 wt.% to 35 wt.%. In step f, the hydrogen peroxide is 0.5 to 2.0 times the stoichiometry of ferrous dihydrogen phosphate; In step g, the pH of the solution is adjusted to 0.5–2, and the precipitation temperature is 25–90℃. In step h, the drying temperature is 300–900℃ and the drying time is 2–8 hours.

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