Production process for preparing iron phosphate from lithium extraction byproduct sodium phosphate

Abstract

The invention discloses a production process for preparing iron phosphate from a lithium extraction byproduct sodium phosphate, and belongs to the field of new energy production. The process comprises the following steps: dissolving sodium phosphate dodecahydrate with water to obtain a sodium phosphate solution; carrying out ultrafiltration impurity removal on the sodium phosphate solution, and then sequentially carrying out iron removal and hardness removal treatment through a manganese sand filter material and chelate resin; the treated solution is introduced into a three-compartment bipolar membrane system, and phosphoric acid and sodium hydroxide products are generated through an electrolytic reaction. According to the invention, a three-compartment bipolar membrane electrodialysis system and related matched pre-treatment (a filtering system and an ion exchange system) are utilized to recycle sodium phosphate in the mother liquor of the original lithium precipitation section, and the original treatment is replaced to enter a sewage treatment section and a solid waste treatment section, so that the recycling is realized to the greatest extent. Meanwhile, phosphoric acid obtained by the bipolar membrane can replace sodium phosphate to synthesize ferric phosphate, so that the pure water amount for washing is greatly reduced. And a green circulating process is realized under the condition of low operation cost.

Description

Technical Field

[0001] The present invention belongs to the field of new energy production, and its main application field is to transform sodium phosphate, a byproduct in precipitated lithium phosphate, and sodium phosphate, a byproduct obtained when recycling waste lithium iron phosphate, into a production process for first preparing phosphoric acid and sodium hydroxide and then preparing iron phosphate by using three-compartment bipolar membrane electrodialysis. Background Art

[0002] At present, when lithium is extracted in the new energy field in the market, when lithium phosphate is produced by precipitation method (CN117105190A), sodium phosphate waste liquid will be generated accordingly. For enterprises, this waste water cannot be used.

[0003] Similarly, when recycling waste lithium iron phosphate batteries, sodium phosphate salts will also be produced when sodium hydroxide is added to precipitate iron hydroxide. Under the original process, the sodium phosphate salts will react with ferrous sulfate to produce crude iron phosphate, and then because it contains a large amount of sodium ions, it needs to be washed three or more times, consuming a large amount of pure water in the process, and then pure iron phosphate can be obtained as a precursor for making lithium iron phosphate batteries.

[0004] Therefore, there is an urgent need to provide a new production process for preparing iron phosphate from sodium phosphate, a byproduct of lithium extraction. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a production process for preparing iron phosphate from sodium phosphate, a byproduct of lithium extraction. The present invention can make use of production waste liquid as a resource, prepare phosphoric acid and sodium hydroxide from the sodium phosphate byproduct; the obtained phosphoric acid reacts with ferrous sulfate to generate iron phosphate, and since the phosphoric acid contains a low sodium ion content, the amount of pure water used for washing iron phosphate can be greatly saved; the obtained sodium hydroxide can be used as the alkali solution used in the recycling of waste lithium iron phosphate batteries.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] The present invention provides a production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, which is as follows:

[0008] Sodium phosphate dodecahydrate is dissolved in water to obtain a sodium phosphate solution; the sodium phosphate solution is subjected to ultrafiltration to remove impurities, and then iron removal and hardness removal are performed in sequence through a manganese sand filter material and a chelating resin; the treated solution is passed into a three-compartment bipolar membrane system to generate phosphoric acid and sodium hydroxide products by electrolysis reaction; the phosphoric acid is reacted with ferrous sulfate to obtain a crude iron phosphate filter cake, which is washed with water to obtain pure iron phosphate; the sodium hydroxide is used for recycling waste lithium iron phosphate batteries to obtain a mixed salt solution of disodium hydrogen phosphate and sodium phosphate.

[0009] Preferably, the sodium phosphate dodecahydrate comes from lithium precipitation mother liquor or waste lithium iron phosphate batteries.

[0010] Preferably, the mass fraction of sodium phosphate dodecahydrate in the sodium phosphate solution is 13%-40%.

[0011] Preferably, the ultrafiltration impurity removal treatment is performed through a hollow fiber membrane.

[0012] Preferably, the contents of calcium ions and magnesium ions in the solution obtained after the hardness removal treatment are reduced to below 1 ppm.

[0013] Preferably, the setting parameters of the three-compartment bipolar membrane system are as follows:

[0014] Current density is 600A / m 2 -800A / m 2 The acid chamber uses potentiometric titration to control the hydrogen ion concentration between 0.8mol / L and 2mol / L, the alkali chamber uses acid-base neutralization titration to control the hydroxide ion concentration between 0.8mol / L and 2mol / L, the sodium ion content in the acid chamber is between 200-1000ppm, and the phosphorus content in the alkali chamber is between 200-1000ppm.

[0015] Preferably, the pure iron phosphate is used as a precursor for lithium iron phosphate batteries, and a mixed salt solution of disodium hydrogen phosphate and sodium phosphate is used as a raw material in the production process of preparing iron phosphate from sodium phosphate, a by-product of lithium extraction.

[0016] Preferably, the three-compartment bipolar membrane system comprises an anode plate, a cathode plate and a membrane stack sandwiched between the anode plate and the cathode plate connected to a DC power supply, wherein the membrane stack is composed of at least one electrodialysis unit and both ends of the membrane stack are bipolar membranes; the electrodialysis unit is a three-compartment structure composed of a bipolar membrane, an anion exchange membrane, a cation exchange membrane and a bipolar membrane arranged in sequence, and the three compartments are respectively an acid chamber composed of a bipolar membrane and an anion exchange membrane, a salt chamber composed of an anion exchange membrane and a cation exchange membrane, and an alkali chamber composed of a cation exchange membrane and a bipolar membrane.

[0017] Furthermore, pure water, solution after iron and hardness removal treatment and pure water are introduced into the acid chamber, salt chamber and alkali chamber respectively. Under the action of electric field force, phosphoric acid solution and sodium hydroxide solution are obtained in the acid chamber and alkali chamber respectively.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) Sodium phosphate waste liquid can be processed for resource utilization without generating pollution and achieving clean production;

[0020] 2) The acid and alkali produced by three-compartment bipolar membrane electrodialysis can be reused in the lithium iron phosphate battery process;

[0021] 3) When the acid produced by three-compartment bipolar membrane electrodialysis is used instead of sodium phosphate to generate iron phosphate, a large amount of pure water for washing can be saved;

[0022] 4) The alkali-producing waste lithium iron phosphate batteries obtained by three-compartment bipolar membrane electrodialysis are recycled. The process can be used to adjust the pH and precipitate iron hydroxide, and the obtained disodium hydrogen phosphate and sodium phosphate mixed salt solution can continue to be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the schematic diagram of sodium phosphate three-compartment bipolar membrane electrodialysis;

[0024] Figure 2 The figure is the overall process flow chart. DETAILED DESCRIPTION

[0025] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0026] like Figure 2 As shown, a production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, is provided in the present invention. The production process mainly comprises dissolving sodium phosphate dodecahydrate, removing impurities by ultrafiltration, removing iron by manganese sand, removing hardness by chelating resin, preparing phosphoric acid and sodium hydroxide by three-compartment bipolar membrane electrodialysis, reacting phosphoric acid with ferrous sulfate to generate ferric phosphate, and recycling waste lithium iron phosphate batteries by sodium hydroxide.

[0027] Each step of the production process will be described in detail below.

[0028] Step 1) dissolving sodium phosphate salt: adding sodium phosphate dodecahydrate obtained from lithium precipitation mother liquor or sodium phosphate dodecahydrate obtained from recycling waste lithium iron phosphate batteries into pure water to dissolve and obtain a sodium phosphate solution.

[0029] As a preferred embodiment of the present invention, the mass fraction of sodium phosphate dodecahydrate in the sodium phosphate solution can be 13%-40%.

[0030] Step 2) Ultrafiltration to remove impurities: After the sodium phosphate dodecahydrate is completely dissolved in water, the obtained sodium phosphate solution is subjected to ultrafiltration to remove impurities, and the obtained clear solution enters the next step.

[0031] As a preferred embodiment of the present invention, the ultrafiltration impurity removal treatment can be performed by a hollow fiber membrane.

[0032] Step 3) Manganese sand iron removal: The ultrafiltration clear liquid obtained after impurity removal contains a small amount of iron ions. Manganese sand filter material is used to remove iron from the ultrafiltration clear liquid.

[0033] Step 4): Chelating resin for de-hardening: The solution after iron removal is treated with chelating resin for de-hardening to reduce the calcium and magnesium ion content in the solution to below 1 ppm.

[0034] Step 5): the solution after the de-hardening treatment with the chelating resin is passed into a three-compartment bipolar membrane system to generate phosphoric acid and sodium hydroxide products by electrolysis reaction.

[0035] As a preferred embodiment of the present invention, the setting parameters of the three-compartment bipolar membrane system during the reaction are specifically as follows:

[0036] Current density is 600A / m 2 -800A / m 2 The acid chamber uses potentiometric titration to control the hydrogen ion concentration between 0.8mol / L and 2mol / L, the alkali chamber uses acid-base neutralization titration to control the hydroxide ion concentration between 0.8mol / L and 2mol / L, the sodium ion content in the acid chamber is between 200-1000ppm, and the phosphorus content in the alkali chamber is between 200-1000ppm.

[0037] like Figure 1 The figure shows a schematic diagram of the structure of a three-compartment bipolar membrane system, which mainly includes an anode plate, a cathode plate and a membrane stack sandwiched between the anode plate and the cathode plate connected to a DC power supply. The membrane stack is composed of at least one electrodialysis unit, and both ends of the membrane stack are bipolar membranes. The electrodialysis unit is mainly composed of a three-compartment structure consisting of a bipolar membrane, an anion exchange membrane, a cation exchange membrane and a bipolar membrane arranged in sequence. The three compartments are an acid chamber composed of a bipolar membrane and an anion exchange membrane, a salt chamber composed of an anion exchange membrane and a cation exchange membrane, and an alkali chamber composed of a cation exchange membrane and a bipolar membrane.

[0038] In actual use, pure water, solution after iron and hardness removal treatment and pure water are respectively introduced into the acid chamber, salt chamber and alkali chamber. Under the action of electric field force, phosphoric acid solution and sodium hydroxide solution are obtained in the acid chamber and alkali chamber respectively.

[0039] Step 6): The phosphoric acid obtained by the three-compartment bipolar membrane system is reacted with ferrous sulfate to obtain a crude iron phosphate filter cake, and then the crude filter cake is washed with a small amount of pure water to obtain pure iron phosphate. The obtained pure iron phosphate can be used as a precursor for lithium iron phosphate batteries.

[0040] Step 7): The sodium hydroxide obtained by the three-compartment bipolar membrane system can be used to recover waste lithium iron phosphate batteries. During the process, it can be used to adjust pH and precipitate iron hydroxide and other different process stages to obtain a mixed salt solution of disodium hydrogen phosphate and sodium phosphate. The obtained product can be used as a raw material for the process of the present invention and continue to participate in resource recycling.

[0041] In order to more intuitively understand the above-mentioned purposes, features and advantages of the present invention, the implementation methods of the system are described in detail below in combination with specific examples. The following content is only a description of the use of the system. The technicians in this technical field can make various modifications or purification process supplements to the specific implementation cases described, as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0042] Example 1

[0043] This embodiment uses sodium phosphate dodecahydrate obtained from lithium sulfate precipitation mother liquor to prepare acid and alkali by three-compartment bipolar membrane electrodialysis. After dissolving sodium phosphate dodecahydrate to a concentration of 13%, it passes through a hollow fiber membrane with a retention pore size of 0.1μm, and the resulting ultrafiltration clear liquid NTU <1. The ultrafiltration clear liquid enters the manganese sand filter and chelating resin to remove iron and calcium and magnesium. After treatment, the total amount of calcium and magnesium in the solution is 0.3ppm by ICP detection, and the iron content is 0.1ppm, which meets the conditions for entering the three-compartment bipolar membrane electrodialysis system.

[0044] In a three-compartment bipolar membrane system, the current density was controlled to be 750 A / m 2 , the concentration of hydrogen ion and hydroxide ion in the acid-base chamber is controlled to be 2mol / L. At this time, the sodium ion content in phosphoric acid is 338ppm, and the phosphorus content in sodium hydroxide is 517ppm. Both meet the requirements of entering the production section of iron phosphate and waste lithium iron phosphate batteries.

[0045] The phosphoric acid product obtained from the three-compartment bipolar membrane system is reacted with ferrous sulfate to generate crude phosphoric acid, which is then filtered to obtain iron phosphate cake, which is then washed with pure water to obtain pure iron phosphate.

[0046] Example 2

[0047] This embodiment uses sodium phosphate dodecahydrate recovered from waste lithium iron phosphate to prepare acid and alkali through three-compartment bipolar membrane electrodialysis. After dissolving the mixed sodium phosphate solution produced in the recovery section to prepare a sodium phosphate dodecahydrate aqueous solution with a concentration of 18%, it passes through a hollow fiber membrane with a retention pore size of 0.1μm, and the resulting ultrafiltration clear liquid NTU <1. The ultrafiltration clear liquid enters the manganese sand filter and chelating resin to remove iron and calcium and magnesium. After treatment, the total ICP content of calcium and magnesium in the solution is 0.8ppm, and the iron content is 0.1ppm, which meets the conditions for entering the three-compartment bipolar membrane electrodialysis system.

[0048] In a three-compartment bipolar membrane system, the current density is controlled to be 800A / m 2, the acid chamber controls the hydrogen ion concentration to 1.5mol / L, and the alkali chamber controls the hydroxide ion concentration to 2mol / L. At this time, the sodium ion content in the phosphoric acid is 257ppm, and the phosphorus content in the sodium hydroxide is 423ppm. Both meet the requirements for entering the production section of iron phosphate and waste lithium iron phosphate batteries.

[0049] The phosphoric acid obtained by the three-compartment bipolar membrane system is reacted with ferrous sulfate to generate crude phosphoric acid, which is then filtered to obtain iron phosphate cake, which is then washed with pure water to obtain pure iron phosphate. At the same time, the sodium hydroxide obtained by the three-compartment bipolar membrane system is recycled to the waste lithium iron phosphate battery recovery section. In the recovery section, it reacts with iron phosphate to generate iron hydroxide, disodium hydrogen phosphate and sodium phosphate. The obtained mixed salt solution of disodium hydrogen phosphate and sodium phosphate can be further used in the three-compartment bipolar membrane system to prepare phosphoric acid and sodium hydroxide.

[0050] The present invention utilizes a three-compartment bipolar membrane electrodialysis system and related supporting pretreatment (filtration system and ion exchange system) to recycle the sodium phosphate in the original lithium precipitation section mother liquor, replacing the original treatment and entering the sewage treatment section and solid waste treatment section, thus realizing resource utilization to the greatest extent. At the same time, the phosphoric acid obtained by the bipolar membrane can replace sodium phosphate to synthesize iron phosphate, greatly reducing the amount of pure water used for washing. A green circulation process is achieved at low operating costs.

[0051] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, characterized in that: The details are as follows: Sodium phosphate dodecahydrate is dissolved in water to obtain a sodium phosphate solution; the sodium phosphate solution is subjected to ultrafiltration to remove impurities, and then iron removal and hardness removal are performed in sequence through a manganese sand filter material and a chelating resin; the treated solution is passed into a three-compartment bipolar membrane system to generate phosphoric acid and sodium hydroxide products by electrolysis reaction; the phosphoric acid is reacted with ferrous sulfate to obtain a crude iron phosphate filter cake, which is washed with water to obtain pure iron phosphate; the sodium hydroxide is used for recycling waste lithium iron phosphate batteries to obtain a mixed salt solution of disodium hydrogen phosphate and sodium phosphate.

2. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The sodium phosphate dodecahydrate comes from lithium precipitation mother liquor or waste lithium iron phosphate batteries.

3. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The mass fraction of sodium phosphate dodecahydrate in the sodium phosphate solution is 13%-40%.

4. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The ultrafiltration impurity removal treatment is carried out through a hollow fiber membrane.

5. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The contents of calcium ions and magnesium ions in the solution obtained after the hardness removal treatment are both reduced to below 1 ppm.

6. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The setting parameters of the three-compartment bipolar membrane system are as follows: Current density is 600A / m 2 -800A / m 2 The acid chamber uses potentiometric titration to control the hydrogen ion concentration between 0.8mol / L and 2mol / L, the alkali chamber uses acid-base neutralization titration to control the hydroxide ion concentration between 0.8mol / L and 2mol / L, the sodium ion content in the acid chamber is between 200-1000ppm, and the phosphorus content in the alkali chamber is between 200-1000ppm.

7. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The pure iron phosphate is used as a precursor for lithium iron phosphate batteries, and the mixed salt solution of disodium hydrogen phosphate and sodium phosphate is used as a raw material in the production process of preparing iron phosphate from sodium phosphate, a byproduct of lithium extraction.

8. The production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 1, characterized in that: The three-compartment bipolar membrane system comprises an anode plate and a cathode plate connected to a direct current power supply, and a membrane stack sandwiched between the anode plate and the cathode plate, wherein the membrane stack is composed of at least one electrodialysis unit and both ends of the membrane stack are bipolar membranes; the electrodialysis unit is a three-compartment structure composed of a bipolar membrane, an anion exchange membrane, a cation exchange membrane and a bipolar membrane arranged in sequence, and the three compartments are respectively an acid chamber composed of a bipolar membrane and an anion exchange membrane, a salt chamber composed of an anion exchange membrane and a cation exchange membrane, and an alkali chamber composed of a cation exchange membrane and a bipolar membrane.

9. A production process for preparing ferric phosphate from sodium phosphate, a byproduct of lithium extraction, according to claim 8, characterized in that: Pure water, solution after iron removal and hardness removal and pure water are introduced into the acid chamber, salt chamber and alkali chamber respectively. Under the action of electric field force, phosphoric acid solution and sodium hydroxide solution are obtained in the acid chamber and alkali chamber respectively.

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