Recovery method of ferrophosphorus solution

Abstract

The invention provides a recovery method of a ferrophosphorus solution, and relates to the technical field of battery-grade iron phosphate recovery. The method comprises the following steps: firstly, adjusting the molar ratio of Fe to P in a ferrophosphorus solution, adjusting the concentration of Fe < 3 + >, adjusting the acid, then carrying out precipitation separation, and treating the precipitate to obtain the battery-grade iron phosphate. And after separation and precipitation, the residual solution is subjected to two times of iron supplement and acid adjustment, so that an iron phosphate solution with relatively high purity can be obtained, and the iron phosphate solution can be added into an iron phosphate solution to be treated for continuous recovery treatment. The method provided by the invention can effectively recover iron phosphate in the ferrophosphorus solution.

Description

Technical Field

[0001] The invention belongs to the technical field of battery-grade ferric phosphate recovery and relates to a method for recovering ferrophosphorus solution. Background Art

[0002] Battery-grade iron phosphate (FePO4) is a precursor for preparing lithium iron phosphate, a positive electrode material for lithium-ion batteries. At present, the preparation methods of battery-grade iron phosphate are mainly divided into "liquid phase precipitation method", "hydrothermal method", "sol-gel method", "controlled crystallization method" and the like. Among them, the "liquid phase precipitation method" is to first add an oxidant to a mixed solution containing a phosphorus source and an iron source to obtain an intermediate product, a dihydrated iron phosphate precipitate, which is then filtered, washed, dried, and calcined to obtain battery-grade iron phosphate. With the continuous development of lithium iron phosphate, iron phosphate as its raw material has also developed rapidly, and a lot of iron phosphate solutions have also been produced. In addition to phosphorus and iron, these iron phosphate solutions also contain other impurities, such as Al 3+ 、Cu 2+ Mg 2+ , Ca 2+ 、Ni 2+ 、Co 2+ 、Mn 2+ 、Zn 2+ 、Ti 4+ 、Na + NH4 + One or more cations, and SO4 2- 、Cl - 、NO3 - If the ferrophosphorus waste liquid is not effectively treated or directly discharged, it will cause environmental pollution and waste of resources.

[0003] Chinese patent CN117585653A discloses a method for preparing low-cost battery-grade iron phosphate by multiple precipitation. For a mixed solution containing Fe, P and metal ion impurities, surfactants need to be added and multiple precipitations are required to obtain battery-grade iron phosphate, and the steps are relatively complicated.

[0004] Therefore, it is necessary to further study the recovery method of ferrophosphorus solution to achieve effective recycling of resources. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for recovering ferrophosphorus solution.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for recovering ferrophosphorus solution, comprising the steps of:

[0008] S1. Adding an iron source and / or a phosphorus source to a ferrophosphorus solution to obtain a first solution, wherein the molar ratio of Fe to P in the first solution is 1:0.95-1.1; adjusting the pH of the first solution to 0.8-1.5, and obtaining a second solution and a first solid after solid-liquid separation;

[0009] S2, the first solid in step S1 is processed to obtain battery-grade iron phosphate;

[0010] In step S1, the first iron salt is added to the second solution, the pH is adjusted to 1-2, and the second solid is collected;

[0011] After the second solid is slurried, a second iron salt is added to adjust the pH to 1-2, and the third solid is aged and collected.

[0012] Preferably, the total concentration of cationic impurities in the ferrophosphorus solution in step S1 does not exceed 6% of the sum of the concentrations of ferric ions and ferrous ions, and the pH of the ferrophosphorus solution does not exceed 5;

[0013] The anion impurities in the ferrophosphorus solution are selected from one or a combination of two or more of nitrate, sulfate, chloride, bromide and iodide.

[0014] Preferably, the iron source in step S1 is selected from one or a combination of two or more of water-soluble iron salts and water-soluble ferrous salts; the phosphorus source is selected from one or a combination of two or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate.

[0015] Preferably, the concentration of iron ions in the first solution in step S1 is 1-2 mol / L;

[0016] When the first solution contains ferrous ions, an oxidant is added to the first solution until the ferrous ions are completely converted into ferric ions;

[0017] The oxidant is selected from one or a combination of two or more of hydrogen peroxide, oxygen, air, sodium persulfate, sodium perchlorate and sodium hypochlorite.

[0018] Preferably, the treatment process of the first solid in step S2 at least includes washing, aging and calcining.

[0019] Preferably, in step S2, the first iron salt and the second iron salt are independently selected from water-soluble iron salts.

[0020] Preferably, in step S2, the ratio of the weight of iron in the second solution to the weight of iron in the first iron salt is 1:0.5-2.

[0021] Preferably, the concentration of the slurry obtained by slurry adjustment in step S2 is 10-25 wt%.

[0022] Preferably, in step S2, the ratio of the weight of iron in the second solid to the weight of iron in the second iron salt is 1:0.1-0.25.

[0023] Preferably, the steps further include:

[0024] S3, the third solid in step S2 is dissolved with acid to prepare a third solution, and the third solution is returned to the ferrophosphorus solution to be treated;

[0025] The concentration of iron ions in the third solution is 0.1-3 mol / L.

[0026] The beneficial effects of the present invention are:

[0027] (1) The present invention uses a step-by-step method for recovering ferric phosphate to recycle the ferric phosphate solution: first, the ferric phosphate solution is synthesized into battery-grade ferric phosphate at a higher iron and phosphorus concentration and a higher acidity, and part of the ferric phosphate is recovered. Then, iron salt is added to increase the molar ratio of iron ions to cationic impurities, and crude amorphous ferric phosphate (i.e., the second solid) is synthesized at a lower acidity. Iron salt is added to the obtained crude amorphous ferric phosphate to continue to increase the molar ratio of iron ions to cationic impurities, and the phosphate is aged at a suitable acidity. The ferric phosphate is removed by the process of recrystallization to obtain crystalline ferric phosphate with a lower impurity content (i.e., the third solid). The recovery rate of the ferric phosphate solution by the recovery method of the present invention can reach 80-95%, of which the recovery rate of battery-grade ferric phosphate can reach 50-80%.

[0028] (2) The crystalline ferric phosphate obtained by the present invention can be further purified to obtain battery-grade ferric phosphate, or can be returned to the ferrophosphorus solution for reuse after acid dissolution, thereby gradually reducing the impurities in the ferrophosphorus solution. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further illustrated and described below through specific implementation methods.

[0030] The present invention provides a method for recovering ferrophosphorus solution, comprising the following steps:

[0031] S1. Adding an iron source and / or a phosphorus source to a ferrophosphorus solution to obtain a first solution, wherein the molar ratio of Fe to P in the first solution is 1:0.95-1.1; adjusting the pH of the first solution to 0.8-1.5, and obtaining a second solution and a first solid after solid-liquid separation;

[0032] S2, the first solid in step S1 is processed to obtain battery-grade iron phosphate;

[0033] Add the first iron salt to the second solution in step S1, adjust the pH to 1-2, and collect the second solid;

[0034] After the second solid is slurried, a second iron salt is added to adjust the pH to 1-2, and the third solid is aged and collected.

[0035] For containing cationic impurities and anionic impurities in ferrophosphorus solution, the present invention adds iron source and / or phosphorus source in ferrophosphorus solution, adjusts the molar ratio of Fe and P and solution pH to stronger acidity, while improving iron phosphate and cationic solubility, the iron phosphate in the first solution is supersaturated, and the iron phosphate precipitation (i.e., the first solid) with higher purity can be directly isolated. The remaining second solution also contains a certain amount of iron phosphate in the dissolved state and the original impurity ions in the ferrophosphorus solution, continues to add the first iron salt, continues to precipitate phosphate radical in the form of iron phosphate in an excessive manner of iron ions, obtains crude amorphous iron phosphate (i.e., the second solid), and the second solid can carry a small amount of impurity ions secretly. The second solid is slurried into a slurry by adding water, then adds the second iron salt and adjusts pH so that phosphate radical is precipitated out (i.e., the third solid) in the form of iron phosphate again, and the impurity ion content in the third solid is lower than that in the second solid. Using the recovery method of the present invention, the overall recovery rate of phosphate in the ferrophosphorus solution (in the present invention, unless otherwise specified, the recovery rate is calculated based on the phosphate in the ferrophosphate solution) (including battery-grade ferric phosphate and the actual ferric phosphate in the third solid) can reach 80-95%, of which the recovery rate recovered in the form of battery-grade ferric phosphate can reach 50-80%. The recovery rate of phosphate will vary depending on the impurity content in the ferrophosphorus solution. The higher the impurity content, the lower the overall recovery rate of phosphate, especially the recovery rate of battery-grade ferric phosphate.

[0036] For example, the molar ratio of Fe to P in the first solution can be any value among 1:0.95, 1:0.97, 1:0.98, 1:1, 1:1.02, 1:1.05, 1:1.07, 1:1.1, etc., or any value in between. For the first solution after pH adjustment, the pH can be preferably 0.8-1.4. When the pH of the first solution is lower than 0.8, an appropriate amount of alkali (such as sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water, etc.) can be added for adjustment; when the pH of the first solution is higher than 1.5, an appropriate amount of acid (such as sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, etc.) can be added for adjustment.

[0037] In some embodiments, the total concentration of cationic impurities in the ferrophosphorus solution in step S1 does not exceed 6% of the sum of the concentrations of ferric ions and ferrous ions, and the pH of the ferrophosphorus solution does not exceed 5. The cationic impurities in the ferrophosphorus solution include Al 3+ 、Cu 2+ Mg 2+ , Ca 2+ 、Ni 2+ 、Co 2+ 、Mn 2+ 、Zn 2+、Ti 4+ 、Na + NH4 + If the total concentration of cationic impurities in the ferrophosphorus solution is too high, such as more than 6% of the sum of the concentrations of ferric ions and ferrous ions, the recovery method of the present invention can also be used for recovery, but the recovery rate and overall recovery rate of battery-grade ferric phosphate will be low. For example, the total concentration of cationic impurities in the ferrophosphorus solution can be any value of 6%, 5.5%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1% or any value in between of the sum of the concentrations of ferric ions and ferrous ions. The pH of the ferrophosphorus solution can be any value of -1, -0.5, 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any value in between.

[0038] The anionic impurities in the ferrophosphorus solution may be selected from one or a combination of two or more of nitrate, sulfate, chloride, bromide and iodide.

[0039] In some embodiments, the iron source in step S1 is selected from one or a combination of two or more of water-soluble iron salts and water-soluble ferrous salts; there are no particular limitations on the water-soluble iron salts, and examples thereof include ferric sulfate, ferric chloride, and ferric nitrate; there are no particular limitations on the water-soluble ferrous salts, and examples thereof include ferrous sulfate, ferrous chloride, and ferrous nitrate. The phosphorus source is selected from one or a combination of two or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0040] In some embodiments, the concentration of iron ions in the first solution in step S1 is 1-2 mol / L; if the concentration of iron ions in the first solution is not high enough, the recovery rate of battery-grade iron phosphate is not significant; if the concentration of iron ions in the first solution is too high, the first solid will carry too many impurity ions, and battery-grade iron phosphate cannot be recovered. For example, the concentration of iron ions in the first solution can be any value among 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, 2 mol / L, etc., or any value in between;

[0041] When the first solution contains ferrous ions, an oxidant is added to the first solution until all the ferrous ions are converted into ferric ions;

[0042] The oxidant is selected from one or a combination of two or more of hydrogen peroxide, oxygen, air, sodium persulfate, sodium perchlorate and sodium hypochlorite. The oxidant is used to convert ferrous ions into ferric ions, thereby avoiding the formation of ferrous phosphate.

[0043] In some embodiments, the treatment process of the first solid in step S2 includes at least washing, aging, and calcining. The first solid can be washed with water to remove some adsorbed impurities and / or soluble salts (the conductivity of the washing liquid after washing should not exceed 0.3 ms / cm); aging can convert amorphous ferric phosphate into crystalline ferric phosphate. Calcination can remove water of crystallization and obtain anhydrous ferric phosphate. The calcination temperature can be 500-550°C.

[0044] In some embodiments, the first iron salt and the second iron salt in step S2 are independently selected from water-soluble iron salts, for example, ferric sulfate, ferric chloride, ferric nitrate, etc.

[0045] In certain embodiments, in step S2, the ratio of iron weight in the second solution and iron weight in the first iron salt is 1:0.5-2. The second solution is compared to the first solution, and the concentration change of foreign ions is little, but the iron ion and / or phosphate radical concentration in the second solution are significantly lower than the first solution, and after adding the first iron salt, it is possible to continue to form iron phosphate precipitation (i.e., the second solid) to reclaim phosphate radical, and suppress the formation of other phosphates. The addition of the first iron salt is not enough, and the recovery rate of phosphate radical is on the low side, and the addition of the first iron salt is too high, and the foreign ions of phosphate radical recovery are high but adsorbed can be more. For example, the ratio of iron weight in the second solution and iron weight in the first iron salt can be 1:0.5, 1:0.6, 1:0.8, 1:0.1, 1:1.2, 1:1.3, 1:1.5, 1:1.8, 1:2 etc. in any value or between any value.

[0046] In some embodiments, the concentration of the slurry obtained by slurry adjustment in step S2 is 10-25wt%. For example, the concentration of the slurry can be any value among 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, etc. or any value in between.

[0047] In some embodiments, in step S2, the ratio of the weight of iron in the second solid to the weight of iron in the second iron salt is 1:0.1-0.25. After the second solid is slurried and then the second iron salt is added for precipitation, the impurities in the recovered ferric phosphate precipitate can be further reduced, so that the content of impurity ions in the third solid is lower than that in the second solid. For example, the ratio of the weight of iron in the second solid to the weight of iron in the second iron salt can be any value in the range of 1:0.1, 1:0.12, 1:0.15, 1:0.18, 1:0.2, 1:0.22, 1:0.25, etc., or any value in between.

[0048] In some embodiments, the method for recovering the ferrophosphorus solution further comprises:

[0049] S3, the third solid is dissolved with acid to prepare a third solution, and the third solution is returned to the ferrophosphorus solution to be treated;

[0050] The concentration of iron ions in the third solution is 0.1-3 mol / L, or preferably 0.5-2 mol / L.

[0051] If the purity of the recovered third solid does not meet the requirements for battery-grade ferric phosphate, it can be returned to the ferrophosphorus solution to increase the Fe and P contents in the ferrophosphorus solution and relatively reduce the impurity content therein, which is conducive to further recovery of ferrophosphate from the ferrophosphorus solution. Therefore, the recovery method of the present invention can achieve effective recovery of Fe and P in the ferrophosphorus solution.

[0052] The technical solution of the present invention is further described and illustrated below based on various embodiments.

[0053] Example 1

[0054] The pH of the ferrophosphorus solution in this embodiment is 0. 3+ and PO4 3- , anionic impurities include SO4 2- , cationic impurities include Na + NH4 + 、Al 3+ 、Cu 2+ Mg 2+ , and the total concentration of cationic impurities is Fe 3+ 0.03 times the concentration.

[0055] Add ferric sulfate to the above ferrophosphorus solution to make the molar ratio of iron to phosphorus in the solution be 1:0.95, and control the Fe 3+ The concentration is 1.2 mol / L, and then ammonia water is added to slowly adjust the pH to 1.4 to produce precipitation. After solid-liquid separation, a second solution and a first solid are obtained.

[0056] The obtained first solid was washed, aged, and calcined (500°C × 2h, air atmosphere) to obtain anhydrous iron phosphate, which was tested and found to meet the HG / T 4701-2021 "Iron Phosphate for Batteries" standard.

[0057] Ferric sulfate (the weight of iron in the ferric sulfate is 0.5 times the weight of iron in the second solution) is added to the resulting second solution, and then aqueous ammonia is slowly added until the pH reaches 1.8, producing a precipitate. The second solid obtained after solid-liquid separation is crude amorphous ferric phosphate.

[0058] The obtained crude amorphous ferric phosphate was slurried with water to a concentration of 25 wt%, and then ferric sulfate was added thereto (the weight of iron in the ferric sulfate was 0.1 times the weight of iron in the crude amorphous ferric phosphate), and then sulfuric acid was added to a pH of 1.8. An aging reaction was carried out at 100° C. After the solution turned white, the reaction was continued for 0.5 h. After solid-liquid separation, crystalline ferric phosphate was obtained; the obtained crystalline ferric phosphate was dissolved in sulfuric acid to prepare a third solution with a concentration of 0.5 mol / L, which was then added to the ferrophosphorus solution to be treated.

[0059] In this embodiment, the recovery rate of anhydrous ferric phosphate (ie, battery-grade ferric phosphate) is 65%, and the overall recovery rate of ferric phosphate reaches 86%.

[0060] Example 2

[0061] The third solution obtained in Example 1 was added to the ferrophosphorus solution in Example 1, with the weight ratio of the third solution to the ferrophosphorus solution being 1:1. The treatment was performed according to the recovery method in Example 1.

[0062] In this embodiment, the recovery rate of anhydrous ferric phosphate (i.e., battery-grade ferric phosphate) is 73%, and the overall recovery rate of ferric phosphate reaches 90%. Compared with the recovery rate of the ferrophosphorus solution in Example 1, this embodiment has a significant improvement.

[0063] Example 3

[0064] The pH of the ferrophosphorus solution in this embodiment is -1. 3+ and PO4 3- , anionic impurities include SO4 2- and Cl - , cationic impurities include Na + NH4 + 、Co 2+ 、Cu 2+ Mg 2+ , Ca 2+ 、Mn 2+ , and the total concentration of cationic impurities is Fe 3+ 0.06 times the concentration.

[0065] Add ferric sulfate to the above ferrophosphorus solution to make the molar ratio of iron to phosphorus in the solution be 1:1.05, and control the Fe 3+ The concentration is 1.8 mol / L, and then ammonia water is added to slowly adjust the pH to 1.2 to produce precipitation. After solid-liquid separation, a second solution and a first solid are obtained.

[0066] The obtained first solid is washed, aged, and calcined to obtain anhydrous iron phosphate, which is tested and meets the HG / T 4701-2021 "Iron Phosphate for Batteries" standard.

[0067] Ferric sulfate (the weight of iron in the ferric sulfate is 1 times the weight of iron in the second solution) is added to the resulting second solution, and then aqueous ammonia is slowly added until the pH reaches 1.6, producing a precipitate. The second solid obtained after solid-liquid separation is crude amorphous ferric phosphate.

[0068] The obtained crude amorphous ferric phosphate was slurried with water to a concentration of 17 wt%, and then ferric nitrate was added thereto (the weight of iron in the ferric nitrate was 0.25 times the weight of iron in the crude amorphous ferric phosphate), and then ammonia water was added to a pH of 1.5. The aging reaction was carried out at 95° C. After the solution turned white, the reaction was continued for 1 hour, and crystalline ferric phosphate was obtained after solid-liquid separation. The obtained crystalline ferric phosphate was dissolved with nitric acid to prepare a third solution with a concentration of 1 mol / L, which was then added to the ferrophosphorus solution to be treated.

[0069] In this embodiment, the recovery rate of anhydrous ferric phosphate (ie, battery-grade ferric phosphate) is 58%, and the overall recovery rate of ferric phosphate reaches 83%.

[0070] Example 4

[0071] The third solution obtained in Example 3 was added to the ferrophosphorus solution in Example 3, with the weight ratio of the third solution to the ferrophosphorus solution being 0.6:1. The treatment was performed according to the recovery method in Example 3.

[0072] In this embodiment, the recovery rate of anhydrous ferric phosphate (i.e., battery-grade ferric phosphate) is 66%, and the overall recovery rate of ferric phosphate reaches 89%. Compared with the recovery rate of the ferrophosphorus solution in Example 3, this embodiment has a significant improvement.

[0073] Example 5

[0074] The pH of the ferrophosphorus solution in this embodiment is 3.5. 3+ 、Fe 2+ and PO4 3- , anionic impurities include NO3 - and Cl - , cationic impurities include Na + 、Co 2+ NH4 + Mg 2+ , Ca 2+ 、Ti 4+ , and the total concentration of cationic impurities is Fe 3+ and Fe 2+ 0.04 times the sum of the concentrations.

[0075] Add ferric sulfate to the above ferrophosphorus solution to make the molar ratio of iron to phosphorus in the solution be 1:1, and control the Fe 3+The concentration is 1.0 mol / L, hydrogen peroxide is added to oxidize all ferrous ions to ferric ions, and then sulfuric acid solution is added to slowly adjust the pH to 1.0 to produce precipitation. After solid-liquid separation, a second solution and a first solid are obtained.

[0076] The obtained first solid is washed, aged, and calcined to obtain anhydrous iron phosphate, which is tested and meets the HG / T 4701-2021 "Iron Phosphate for Batteries" standard.

[0077] Ferric sulfate (the weight of iron in the ferric sulfate is 0.8 times the weight of iron in the second solution) is added to the resulting second solution, and then aqueous ammonia is slowly added until the pH reaches 1.6, producing a precipitate. The second solid obtained after solid-liquid separation is crude amorphous ferric phosphate.

[0078] The obtained crude amorphous ferric phosphate was slurried with water to a concentration of 12 wt%, and then ferric sulfate was added thereto (the weight of iron in the ferric sulfate was 0.2 times the weight of iron in the crude amorphous ferric phosphate), and then ammonia water was added to a pH of 1.5. The aging reaction was carried out at 95° C. After the solution turned white, the reaction was continued for 1 hour, and crystalline ferric phosphate was obtained after solid-liquid separation. The obtained crystalline ferric phosphate was dissolved with nitric acid to prepare a third solution with a concentration of 2 mol / L, which was then added to the ferrophosphorus solution to be treated.

[0079] In this embodiment, the recovery rate of anhydrous ferric phosphate (ie, battery-grade ferric phosphate) is 61%, and the overall recovery rate of ferric phosphate reaches 85%.

[0080] Example 6

[0081] The difference between this embodiment and embodiment 5 is that in embodiment 5, when ferric sulfate is added to the second solution, the weight of iron in the ferric sulfate is adjusted from 0.8 times the weight of iron in the second solution to 1.1 times. The remaining steps remain unchanged.

[0082] In this embodiment, the recovery rate of anhydrous ferric phosphate (ie, battery-grade ferric phosphate) is 61%, and the overall recovery rate of ferric phosphate reaches 90%.

[0083] Example 7

[0084] The difference between this embodiment and embodiment 5 is that in embodiment 5, after adding ferric sulfate to the ferrophosphorus solution, the Fe 3+ The concentration was adjusted from 1.0 mol / L to 0.8 mol / L. The remaining steps remained unchanged.

[0085] In this embodiment, the recovery rate of anhydrous ferric phosphate (ie, battery-grade ferric phosphate) is 37%, and the overall recovery rate of ferric phosphate reaches 84%.

[0086] Therefore, by comparing this embodiment with embodiment 5, it can be seen that after adding ferric sulfate to the ferrophosphorus solution, the Fe 3+When the concentration is not high enough, the recovery rate of battery-grade iron phosphate will be greatly reduced. Although the overall recovery rate is similar, the recovery rate of battery-grade iron phosphate is greatly reduced, resulting in a significant decrease in production efficiency.

[0087] Example 8

[0088] The pH of the ferrophosphorus solution in this embodiment is 0.5. 3+ and PO4 3- , anionic impurities include SO4 2- 、NO3 - and Cl - , cationic impurities include Na + 、Al 3+ NH4 + 、Ni 2+ 、Cu 2+ 、Co 2+ 、Mn 2+ , and the total concentration of cationic impurities is Fe 3+ 0.05 times the concentration.

[0089] Phosphoric acid was added to the above ferrophosphorus solution to make the molar ratio of iron to phosphorus in the solution 1:1, and the Fe 3+ The concentration is 2.0 mol / L, and ammonia water is added to slowly adjust the pH to 1.1 to produce precipitation. After solid-liquid separation, a second solution and a first solid are obtained.

[0090] The obtained first solid is washed, aged, and calcined to obtain anhydrous iron phosphate, which is tested and meets the HG / T 4701-2021 "Iron Phosphate for Batteries" standard.

[0091] Ferric nitrate (the weight of iron in the ferric nitrate is 1 times the weight of iron in the second solution) is added to the resulting second solution, and then aqueous ammonia is slowly added until the pH reaches 1.5, producing a precipitate. The second solid obtained after solid-liquid separation is crude amorphous ferric phosphate.

[0092] The obtained crude amorphous ferric phosphate was slurried with water to a concentration of 15 wt%, and then ferric chloride was added thereto (the weight of iron in the ferric chloride was 0.18 times the weight of iron in the crude amorphous ferric phosphate), and then ammonia water was added to a pH of 1.7. The aging reaction was carried out at 90° C. After the solution turned white, the reaction was continued for 1.5 hours, and crystalline ferric phosphate was obtained after solid-liquid separation. The obtained crystalline ferric phosphate was dissolved with hydrochloric acid to prepare a third solution with a concentration of 1.5 mol / L, which was then added to the ferrophosphorus solution to be treated.

[0093] In this embodiment, the recovery rate of anhydrous ferric phosphate (ie, battery-grade ferric phosphate) is 71%, and the overall recovery rate of ferric phosphate reaches 94%.

[0094] As described above, the basic principles, main features, and advantages of the present invention are shown and described. Those skilled in the art should understand that the present invention is not limited to the above-described embodiments. The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for recovering ferrophosphorus solution, characterized in that the steps include: S1. Adding an iron source and / or a phosphorus source to a ferrophosphorus solution to obtain a first solution, wherein the molar ratio of Fe to P in the first solution is 1:0.95-1.1; adjusting the pH of the first solution to 0.8-1.5, and obtaining a second solution and a first solid after solid-liquid separation; S2, the first solid in step S1 is processed to obtain battery-grade iron phosphate; In step S1, the first iron salt is added to the second solution, the pH is adjusted to 1-2, and the second solid is collected; After the second solid is slurried, a second iron salt is added to adjust the pH to 1-2, and the third solid is aged and collected.

2. The recovery method of ferrophosphorus solution according to claim 1, wherein The total concentration of cationic impurities in the ferrophosphorus solution in step S1 does not exceed 6% of the sum of the concentrations of ferric ions and ferrous ions, and the pH of the ferrophosphorus solution does not exceed 5; The anion impurities in the ferrophosphorus solution are selected from one or a combination of two or more of nitrate, sulfate, chloride, bromide and iodide.

3. The recovery method of ferrophosphorus solution according to claim 1, wherein In step S1, the iron source is selected from one or a combination of two or more of water-soluble iron salts and water-soluble ferrous salts; the phosphorus source is selected from one or a combination of two or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate.

4. The recovery method of ferrophosphorus solution according to claim 1, wherein In step S1, the concentration of iron ions in the first solution is 1-2 mol / L; When the first solution contains ferrous ions, an oxidant is added to the first solution until the ferrous ions are completely converted into ferric ions; The oxidant is selected from one or a combination of two or more of hydrogen peroxide, oxygen, air, sodium persulfate, sodium perchlorate and sodium hypochlorite.

5. The recovery method of ferrophosphorus solution according to claim 1, wherein The treatment process of the first solid in step S2 at least includes washing, aging and calcining.

6. The method for recovering ferrophosphorus solution according to claim 1, wherein In step S2, the first iron salt and the second iron salt are independently selected from water-soluble iron salts.

7. The method for recovering ferrophosphorus solution according to claim 1, wherein In step S2, the ratio of the weight of iron in the second solution to the weight of iron in the first iron salt is 1:0.5-2.

8. The method for recovering ferrophosphorus solution according to claim 1, wherein The concentration of the slurry obtained by slurry adjustment in step S2 is 10-25wt%.

9. The method for recovering ferrophosphorus solution according to claim 1, wherein In step S2, the ratio of the weight of iron in the second solid to the weight of iron in the second iron salt is 1:0.1-0.

25.

10. The method for recovering ferrophosphorus solution according to claim 1, wherein The steps also include: S3, the third solid in step S2 is dissolved with acid to prepare a third solution, and the third solution is returned to the ferrophosphorus solution to be treated; The concentration of iron ions in the third solution is 0.1-3 mol / L.