Method for recycling iron phosphate synthesis mother liquor in iron phosphate synthesis reaction

Abstract

The invention discloses a method for recycling iron phosphate synthesis mother liquor in iron phosphate synthesis reaction. The method comprises the steps of primary acid dissolution, acid solution value adjustment, iron phosphate synthesis, washing and roasting, mother liquor purification, mother liquor concentration and secondary acid dissolution which are carried out in sequence. Metal ions such as copper and aluminum are removed through resin adsorption before the iron phosphate synthesis mother liquor is reused in the iron phosphate synthesis reaction, the mother liquor is purified while pH regulators such as liquid caustic soda are prevented from being added, and energy consumption is reduced; and meanwhile, a countercurrent acid dissolution mode is adopted, so that the acid dissolution rate of the lithium-phosphorus-iron slag is improved, and the yield of iron and phosphorus is further improved.

Description

Technical Field

[0001] The present application relates to the technical field of ferric phosphate synthesis, and in particular to a method for reusing ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction. Background Art

[0002] As lithium-ion battery technology continues to mature and improve, its role as a core power component in new energy vehicles has become increasingly prominent. It has been widely used in various sectors of society and has become an indispensable component of modern life. However, with the large-scale production and application of lithium batteries, global lithium resource consumption continues to rise. Given the limited nature of lithium resources, establishing a comprehensive lithium battery recycling and reuse system has become a critical issue that needs to be addressed.

[0003] In the field of lithium battery recycling, ternary lithium batteries, due to their high-value-added metal elements such as nickel, cobalt, and manganese, have developed a relatively mature recycling system and technical route. In contrast, the recycling of lithium iron phosphate batteries still faces many challenges. Currently, the mainstream domestic recycling process focuses on the extraction of high-value-added metallic lithium. However, the ferrophosphorus slag produced after lithium extraction is mostly stored or treated as general solid waste, resulting in a large amount of ferrophosphorus resources not being effectively utilized, making it difficult to maximize economic benefits.

[0004] From a production process perspective, domestic iron phosphate manufacturers generally use ferrous sulfate as the iron source and phosphoric acid, monoammonium phosphate, and diammonium phosphate as the phosphorus source for synthesis. However, for lithium battery recycling companies, recovering iron phosphate from lithium-iron phosphate slag faces numerous technical challenges: the high cost of handling large amounts of mother liquor and wash water, and the huge consumption of auxiliary materials. These factors severely restrict the economic benefits of iron phosphate production and dampen companies' enthusiasm for production.

[0005] Furthermore, during the disassembly of lithium iron phosphate batteries, the complete separation of metals such as copper and aluminum presents technical difficulties, resulting in a certain amount of copper and aluminum impurities remaining in the black powder. After the sulfuric acid and hydrogen peroxide leaching process for lithium extraction, these impurities are difficult to completely leach out and enter the acid solution during the acid dissolution of the ferrophosphorus slag for lithium extraction. Although iron phosphate can be synthesized in a strongly acidic metal solution through seed-induced precipitation, the precipitation rate of the copper and aluminum impurities is difficult to precisely control, ultimately leading to excessive impurity enrichment in the iron phosphate synthesis mother liquor. This not only affects product quality, but also significantly increases production costs due to the need for neutralization of the mother liquor, further restricting the company's normal production.

[0006] In summary, the recycling of lithium iron phosphate batteries still faces many technical bottlenecks, and there is an urgent need for technological innovation and process optimization to improve resource utilization efficiency, reduce production costs, and promote sustainable development of the industry. In view of this, this application is hereby filed. Summary of the Invention

[0007] The purpose of this application is to provide a method for recycling ferric phosphate synthesis mother liquor in ferric phosphate synthesis reaction to improve resource utilization efficiency.

[0008] This application is implemented as follows:

[0009] In a first aspect, the present application provides a method for reusing a ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction, comprising:

[0010] Primary acid dissolution, adding acid solution to the lithium-phosphorus-iron slag to make pulp and then sequentially perform acid dissolution reaction and solid-liquid separation to obtain a primary acid solution and primary acid-dissolved slag;

[0011] Adjusting the acid solution value, adjusting the Fe / P molar ratio and iron concentration of the primary acid solution to obtain ferrophosphorus liquid metal;

[0012] Ferric phosphate synthesis, adding ferric phosphate seeds to the ferrophosphorus metal liquid to induce seed growth, followed by solid-liquid separation to obtain crude ferric phosphate dihydrate solid and ferric phosphate synthesis mother liquor;

[0013] Washing and roasting: washing the crude ferric phosphate dihydrate solid to obtain wash water and ferric phosphate dihydrate solid, and roasting the ferric phosphate dihydrate solid to obtain anhydrous ferric phosphate;

[0014] Mother liquor purification: the mother liquor of ferric phosphate synthesis is passed through a resin column to remove impurity ions and obtain a purified mother liquor;

[0015] Concentrating the mother liquor, concentrating the purified mother liquor to obtain a concentrated mother liquor;

[0016] Secondary acid dissolution, slurrying the primary acid-dissolved residue and the concentrated mother liquor and sequentially performing acid dissolution reaction and solid-liquid separation to obtain a secondary acid solution and secondary acid-dissolved residue;

[0017] Wherein, the acid solution added in the primary acid dissolution step is the secondary acid solution.

[0018] In an optional embodiment, in the primary acid dissolution step, the secondary acid solution and the lithium-extracted ferrophosphorus slag are slurried according to an S / Fe molar ratio of 0.9-1.1;

[0019] and / or, the acid dissolution reaction temperature is 40°C-80°C, and the reaction time is 4h-10h;

[0020] And / or, the lithium-extracting ferrophosphorus slag comprises Fe 20wt%-25wt%, Al≤0.15wt%, Cu≤0.001wt%, and the moisture content of the lithium-extracting ferrophosphorus slag is 25wt%-40wt%.

[0021] In an optional embodiment, phosphoric acid is added to adjust the Fe / P molar ratio and iron concentration of the primary acid solution;

[0022] And / or, the Fe / P molar ratio in the ferrophosphorus metal liquid is 0.85-1.0, the iron concentration is 55-65 g / L, Cu≤0.03 g / L, and Al≤0.3 g / L.

[0023] In an optional embodiment, ferric phosphate seeds are added when the temperature of the ferrophosphorus metal liquid is 50° C.-60° C.;

[0024] and / or, adding ferric phosphate seed crystals to the ferrophosphorus metal liquid, heating the temperature to 90° C.-95° C. and maintaining the temperature for 6 h-20 h, and obtaining crude ferric phosphate dihydrate solid and ferric phosphate synthesis mother liquor after solid-liquid separation;

[0025] and / or, the ferric phosphate synthesis mother liquor is returned to the acid dissolution step once;

[0026] And / or, the heating rate of the heating step is 10°C / h-30°C / h.

[0027] In an optional embodiment, the mass of the added ferric phosphate seed crystals is 5%-30% of the mass of iron in the ferrophosphorus metal liquid;

[0028] And / or, the particle size D50 of the seed crystal is 1 μm-2 μm.

[0029] In an optional embodiment, the calcination temperature is 500°C-750°C, and the calcination time is 5h-8h;

[0030] And / or, air is introduced into the roasting environment during the roasting process, and the air flow rate is 0.05L / h-0.15L / h.

[0031] In an optional embodiment, the conductivity of the wash water is ≤2000 μS / m;

[0032] And / or, the method for preparing the seed crystal comprises: mixing solid ferric phosphate dihydrate with water to prepare a slurry, and then sand milling or ball milling at a rotation speed of 500 r / min-1000 r / min.

[0033] In an optional embodiment, the flow rate of the ferric phosphate synthesis mother liquor through the resin column is 2BV / h-10BV / h;

[0034] In an optional embodiment, the resin column is an aluminum ion adsorption resin.

[0035] In an optional embodiment, Al≤0.02 g / L and Cu≤0.001 g / L in the purified mother liquor.

[0036] In an optional embodiment, in the mother liquor concentration step, sulfuric acid is first added to the purified mother liquor, and the ratio of the mass of the added sulfuric acid to the mass of sulfur in the purified mother liquor is 10%-30%;

[0037] and / or, a concentration ratio of 1-2;

[0038] And / or, the concentration of sulfuric acid in the concentrated mother liquor is 1 mol / L-1.5 mol / L.

[0039] In an optional embodiment, the primary acid slag and the concentrated mother liquor are slurried according to a solid-liquid ratio of 1 g: 3-5 mL.

[0040] This application has the following beneficial effects:

[0041] In the present application, the mother liquor of ferric phosphate synthesis is subjected to resin adsorption to remove metal ions such as copper and Al before being reused in the ferric phosphate synthesis reaction, thereby avoiding the addition of pH regulators such as liquid alkali while achieving purification of the mother liquor, which is beneficial to saving energy consumption; at the same time, the countercurrent acid dissolution method is adopted, which is beneficial to improving the acid solubility rate of lithium-ferrophosphorus slag, thereby improving the yield of iron and phosphorus. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 This is a flow chart of the method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction in Example 1 of the present application;

[0044] Figure 2 This is a comparison between the iron phosphate synthesized in Example 1 of the present application and the standard card. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0046] The present application provides a method for reusing a ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction, comprising:

[0047] Primary acid dissolution, adding acid solution to the lithium-phosphorus-iron slag to make pulp and then sequentially perform acid dissolution reaction and solid-liquid separation to obtain a primary acid solution and primary acid-dissolved slag;

[0048] Adjusting the acid solution value, adjusting the Fe / P molar ratio and iron concentration of the primary acid solution to obtain ferrophosphorus liquid metal;

[0049] Ferric phosphate synthesis, adding ferric phosphate seeds to the ferrophosphorus metal liquid to induce seed growth, followed by solid-liquid separation to obtain crude ferric phosphate dihydrate solid and ferric phosphate synthesis mother liquor;

[0050] Washing and roasting: washing the crude ferric phosphate dihydrate solid to obtain wash water and ferric phosphate dihydrate solid, and roasting the ferric phosphate dihydrate solid to obtain anhydrous ferric phosphate;

[0051] Mother liquor purification: the mother liquor of ferric phosphate synthesis is passed through a resin column to remove impurity ions and obtain a purified mother liquor;

[0052] Concentrating the mother liquor, concentrating the purified mother liquor to obtain a concentrated mother liquor;

[0053] Secondary acid dissolution, slurrying the primary acid-dissolved residue and the concentrated mother liquor and sequentially performing acid dissolution reaction and solid-liquid separation to obtain a secondary acid solution and secondary acid-dissolved residue;

[0054] Wherein, the acid solution added in the primary acid dissolution step is the secondary acid solution.

[0055] In the present application, the mother liquor of ferric phosphate synthesis is subjected to resin adsorption to remove metal ions such as copper and Al before being reused in the ferric phosphate synthesis reaction, thereby avoiding the addition of pH regulators such as liquid alkali while achieving purification of the mother liquor, which is beneficial to saving energy consumption; at the same time, the countercurrent acid dissolution method is adopted, which is beneficial to improving the acid solubility rate of lithium-ferrophosphorus slag, thereby improving the yield of iron and phosphorus.

[0056] The present application adopts a seed crystal induced precipitation method to synthesize iron phosphate, adjusts the supersaturation of the system synthesis process, reduces the use of pH regulators compared to traditional ammonium method, sodium method, etc., avoids local over-alkalinity, and makes it easier to control the morphology of iron phosphate. The particle size and specific surface area of iron phosphate can be controlled by the particle size and specific surface area of the seed crystal, and different series of iron phosphate can be prepared by adjusting the particle size and specific surface area of the seed crystal.

[0057] In an optional embodiment, in the primary acid dissolution step, the secondary acid solution and the lithium-extracted ferrophosphorus slag are slurried according to an S / Fe molar ratio of 0.9-1.1. For example, the S / Fe molar ratio can be 0.9, 1.0, or 1.1.

[0058] In an optional embodiment, the acid dissolution reaction temperature is 40°C-80°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C; the reaction time is 4h-10h, for example, 4h, 6h, 8h, 10h.

[0059] In an optional embodiment, the lithium-extracting ferrophosphorus slag includes Fe 20wt%-25wt%, Al≤0.15wt%, Cu≤0.001wt%, and the moisture content of the lithium-extracting ferrophosphorus slag is 25wt%-40wt%.

[0060] In the primary acid dissolution step, iron and other elements in the lithium-phosphorus iron slag are dissolved under the action of acid. Theoretically, S and Fe react in a molar ratio of 1:1, so the S / Fe molar ratio is 0.9-1.1, which is conducive to ensuring the dissolution rate. Appropriately increasing the temperature is conducive to increasing the dissolution rate and dissolution rate.

[0061] In an alternative embodiment, phosphoric acid is added to adjust the Fe / P molar ratio and the iron concentration of the primary acid solution.

[0062] In an optional embodiment, the Fe / P molar ratio in the ferrophosphorus metal liquid is 0.85-1.0, the iron concentration is 55-65 g / L, Cu≤0.03 g / L, and Al≤0.3 g / L.

[0063] In the ferrophosphorus metal liquid, Fe / P=0.85-1.0, for example, 0.85, 0.90, 0.95, 1.0; S / Fe=0.9-1.3, for example, 0.9, 1.0, 1.1, 1.2, 1.3; Cu≤0.03g / L, Al≤0.3g / L, which is beneficial to reducing the impurity content and improving the utilization of phosphorus and iron in the subsequent ferric phosphate synthesis.

[0064] In an alternative embodiment, ferric phosphate seeds are added when the ferrophosphorus metal temperature is 50°C-60°C. Adding seeds at this time can effectively lower the nucleation barrier and avoid competition between homogeneous nucleation (heterogeneous nucleation) and heterogeneous nucleation (seed-induced nucleation). For example, the ferrophosphorus metal temperature can be 50°C, 52°C, 54°C, 56°C, 58°C, or 60°C.

[0065] In an optional embodiment, after adding ferric phosphate seeds to the ferrophosphorus metal liquid, the temperature is raised to 90° C.-95° C., such as 90° C., 91° C., 92° C., 93° C., 94° C., and 95° C., and maintained for 6 h-20 h, such as 6 h, 10 h, 15 h, and 20 h. After solid-liquid separation, crude ferric phosphate dihydrate solid and ferric phosphate synthesis mother liquor are obtained; under this temperature condition, atomic mobility is improved, which can promote the repair of crystal defects and obtain high-crystallinity pure phase FePO.

[0066] In an optional embodiment, the ferric phosphate synthesis mother liquor is returned to the acid dissolution step once, which is beneficial to improving utilization and reducing costs.

[0067] In an optional embodiment, the heating rate of the heating step is 10°C / h-30°C / h, such as 10°C / h, 15°C / h, 20°C / h, 25°C / h, 30°C / h. Rapid heating is beneficial to accelerate ion diffusion, promote particle coarsening, and easily form a porous or agglomerated structure.

[0068] In an optional embodiment, the mass of the added ferric phosphate seed crystals is 5%-30% of the mass of iron in the ferrophosphorus metal liquid, such as 5%, 10%, 15%, 20%, 25%, or 30%.

[0069] In an optional embodiment, the particle size D50 of the seed crystal is 1 μm-2 μm, such as 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, or 2 μm.

[0070] The particle size of the synthesized ferric phosphate can be adjusted by adjusting the amount and particle size of the added seed crystals. Generally, the smaller the seed crystal particle size and the more seed crystals added, the smaller the particle size of the synthesized ferric phosphate.

[0071] In an optional embodiment, the calcination temperature is 500°C-750°C, such as 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, and the calcination time is 5h-8h, such as 5h, 6h, 7h, 8h.

[0072] In an optional embodiment, air is introduced into the roasting environment during the roasting process, and the air flow rate is 0.05 L / h-0.15 L / h, such as 0.05 L / h, 0.10 L / h, and 0.15 L / h.

[0073] Calcination of ferric phosphate dihydrate under the above conditions is beneficial to obtaining anhydrous ferric phosphate with both high tap density and high specific surface area, and is beneficial to improving the electrical performance of the subsequently prepared lithium iron phosphate for use in lithium-ion batteries.

[0074] In an optional embodiment, the conductivity of the wash water is ≤2000 μS / m, thereby reducing the inclusion of impurities in the ferric phosphate product. In some embodiments, the ferric phosphate dihydrate solid can be pulped and solid-liquid separated to improve the impurity removal effect, but the efficiency is low. In other embodiments, the ferric phosphate dihydrate solid can be rinsed to improve efficiency.

[0075] In an optional embodiment, the method for preparing the seed crystals includes: mixing solid ferric phosphate dihydrate with water to form a slurry, and then sand milling or ball milling at a rotation speed of 500r / min-1000r / min, such as 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, to obtain seed crystals with a particle size that meets the requirements.

[0076] In an optional embodiment, the flow rate of the ferric phosphate synthesis mother liquor through the resin column is 2BV / h-10BV / h, such as 2BV / h, 4BV / h, 5BV / h, 6BV / h, 8BV / h, 10BV / h.

[0077] In an optional embodiment, the resin column is an aluminum ion adsorption resin, which is a polymer material with an exchange effect. It has a certain pore structure and has some positively charged groups on the surface, such as amino groups or hydrochloric acid groups. When the solution contains aluminum ions, these positively charged groups will have a charge attraction effect with the aluminum ions and adsorb them on the resin surface. At the same time, the positively charged groups on the resin will also exchange with other cations in the solution, so that they are adsorbed on the resin. It should be noted that the aluminum ion adsorption resin needs to be activated and loaded before use. The specific steps can be: measure 500mL of resin and add it to a 3mol / L dilute sulfuric acid solution and soak it for 5h and filter it. Repeatedly rinse with 5L deionized water until the pH value of the wash water is 1-2; load the activated resin into the resin column, immerse the resin column with dilute sulfuric acid with a pH value of 1.5, and shake it back and forth until there are no obvious pores on the resin column wall; install the peristaltic pump, resin column feed pipe and discharge pipe; pass the mother liquor into the resin column according to the set flow rate to adsorb and remove aluminum.

[0078] Purifying the mother liquor using aluminum ion adsorption resin at an appropriate flow rate can improve purification efficiency and reduce residual impurities. In some embodiments, after resin purification, the purified mother liquor contains Al ≤ 0.02 g / L and Cu ≤ 0.001 g / L.

[0079] In an optional embodiment, sulfuric acid is first added to the purified mother liquor in the mother liquor concentration step, and the ratio of the mass of the added sulfuric acid to the mass of sulfur in the purified mother liquor is 10-30%, such as 10%, 15%, 20%, 25%, or 30%. After the mother liquor is purified, the S lost during the ferric phosphate synthesis process is supplemented, which can save 70-90% of the sulfuric acid usage and reduce production costs.

[0080] In an optional embodiment, the concentration ratio is 1-2, such as 1, 1.5, or 2.

[0081] In an optional embodiment, the concentration of sulfuric acid in the concentrated mother liquor is 1 mol / L-1.5 mol / L, such as 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, and 1.5 mol / L.

[0082] Concentration after adding sulfuric acid is beneficial to ensuring the dissolution effect of the subsequent concentrated mother liquor on the primary acid-soluble slag and lithium-phosphorus-iron slag.

[0083] In an optional embodiment, the primary acid soluble residue and the concentrated mother liquor are slurried according to a solid-liquid ratio of 1g:3-5mL. The solid-liquid ratio of 1:3-5 can be 1g:3ml, 1g:4ml, 1g:5ml, which is beneficial to improve the utilization rate of the lithium-ferrophosphorus slag.

[0084] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0085] Example 1:

[0086] This embodiment provides a method for reusing ferric phosphate synthesis mother liquor in ferric phosphate synthesis reaction, the flow chart is as follows: Figure 1 Shown, including:

[0087] Step 1, primary acid dissolution: Weigh 1000 g of lithium-extracted ferrophosphorus slag with a composition as shown in Table 1, add a secondary acid solution calculated according to the total S / Fe ratio of 1, mix and slurry, then heat in a water bath to 50° C. and keep in a water bath for 6 hours for acid dissolution reaction. After solid-liquid separation, obtain a primary acid solution and a primary acid-dissolved slag. The specific composition of the primary acid dissolution is shown in Table 2;

[0088] Step 2, phosphorus supplementation and adjustment: sample and test the acid-soluble Fe / P ratio, add phosphoric acid to adjust the Fe / P ratio to 0.85 to obtain phosphorus-iron metal liquid. The specific composition is shown in Table 2;

[0089] Step 3, ferrophosphorus synthesis: the ferrophosphorus metal liquid is transferred to a synthesis reactor, the temperature is raised to 55°C, iron phosphate seed crystals are added, and the temperature is continued to be raised to 95°C. The reaction is kept warm for aging for 6 hours, and then solid-liquid separation is performed to obtain crude ferric phosphate dihydrate and a synthetic mother liquor. The composition of the synthetic mother liquor is shown in Table 3, wherein the heating rate is 25°C / h, the mass ratio of the added iron phosphate seed crystals to the mass of the iron in the metal liquid is 8%, and the particle size D50 of the iron phosphate seed crystals is 1.4 μm;

[0090] Step 4, washing and roasting: add pure water twice the theoretical ferrophosphorus yield to the ferrophosphorus liquid twice for elution until the conductivity of the elution water reaches 2000μS / m, mix the elution water and the synthetic mother liquor, place the eluted dihydrate ferric phosphate in a crucible and transfer it to a muffle furnace for roasting at 600℃, turn off the heating for 5h, and introduce air into the roasting environment during the roasting process at an air flow rate of 0.1L / h. After cooling, take out and obtain anhydrous ferric phosphate, the XRD pattern is as follows Figure 2 shown.

[0091] Step 5, mother liquor purification and mother liquor concentration: the mixed mother liquor is passed through aluminum removal resin T62-MP at a flow rate of 6 BV / h to obtain a purified mother liquor, the composition of which is shown in Table 3; sulfuric acid is added to the purified mother liquor at a ratio of 10% by mass of sulfuric acid to the mass of sulfur in the purified mother liquor to replenish the lost sulfuric acid, to obtain a sulfur-replenishing mother liquor, the composition of which is shown in Table 3; the sulfur-replenishing mother liquor is transferred to a negative pressure evaporator for reduced pressure concentration, and the concentration ratio is controlled at 1.5 to obtain a concentrated mother liquor, the sulfuric acid concentration in the concentrated mother liquor being 1.2 mol / L, and the specific composition is shown in Table 3;

[0092] Step 6, secondary acid dissolution: The concentrated mother liquor and the primary acid-dissolved residue are mixed and slurried at a solid-liquid ratio of 1g:4ml, heated in a water bath to 50°C, and kept in a water bath for 6 hours for acid dissolution reaction. After solid-liquid separation, a secondary acid solution and secondary acid-dissolved residue are obtained, and the secondary acid solution is returned to step 1 for primary acid dissolution.

[0093] Step 7, seed crystal preparation: take about 20% of the iron phosphate dihydrate washed in step 4 and perform cyclic ball milling as seed crystals. The ball milling speed is 550 r / min, and the seed crystal particle size D50 is controlled to be 1.4 μm.

[0094] The liquid compositions involved in each step of this embodiment are shown in Tables 1-3.

[0095] Table 1 Lithium-phosphorus iron slag composition

[0096]

[0097] Table 2 Composition of pre-adjustment liquid and post-adjustment liquid

[0098]

[0099] Table 3 Composition of synthetic mother liquor and purified mother liquor

[0100]

[0101] “ / ” in the table means not calculated.

[0102] Example 2:

[0103] This embodiment provides a method for reusing ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction, comprising:

[0104] Step 1, primary acid dissolution: Weigh 1000 g of lithium-ferrophosphorus slag with a composition as shown in Table 1, add a secondary acid solution according to the total S / Fe ratio of 1, mix and slurry, then heat in a water bath to 70° C. and keep in a water bath for 6 hours for acid dissolution reaction, and after solid-liquid separation, obtain a primary acid solution and a primary acid-dissolved slag;

[0105] Step 2, phosphorus supplementation and adjustment: sampling and testing the acid-soluble Fe / P ratio, adding phosphoric acid to adjust the Fe / P ratio to 0.85 to obtain phosphorus-iron metal liquid;

[0106] Step 3, ferrophosphorus synthesis: the ferrophosphorus metal liquid is transferred to a synthesis reactor, the temperature is raised to 55°C, iron phosphate seed crystals are added, and the temperature is further raised to 95°C. The reaction is kept warm for aging for 6 hours, and then solid-liquid separation is performed to obtain crude ferric phosphate dihydrate and a synthetic mother liquor, wherein the heating rate is 30°C / h, the mass ratio of iron in the added iron phosphate seed crystals to the mass ratio of iron in the metal liquid is 15%, and the particle size D50 of the iron phosphate seed crystals is 2 μm;

[0107] Step 4, washing and roasting: adding pure water twice the theoretical ferrophosphorus yield in the ferrophosphorus metal liquid twice for elution until the conductivity of the elution water reaches 2000 μS / m, mixing the elution water and the synthetic mother liquor, placing the eluted ferric phosphate dihydrate in a crucible and transferring it to a muffle furnace for roasting at 600°C, turning off the heating for 5 hours, and introducing air into the roasting environment during the roasting process at an air flow rate of 0.05 L / h. After cooling, the anhydrous ferric phosphate is obtained.

[0108] Step 5, mother liquor purification and mother liquor concentration: the mixed mother liquor is passed through an aluminum removal resin at a controlled flow rate of 2 BV / h, sulfuric acid is added to the purified mother liquor, and the ratio of the mass of sulfuric acid to the mass of sulfur in the purified mother liquor is 10% to replenish the lost sulfuric acid. The sulfur-replenished mother liquor is transferred to a negative pressure evaporator for reduced pressure concentration, and the concentration ratio is controlled to be 1. The S concentration of the concentrated mother liquor is 1 mol / L;

[0109] Step 6, secondary acid dissolution: The concentrated mother liquor and the primary acid-dissolved residue are mixed and slurried at a solid-liquid ratio of 1g:3ml, heated in a water bath to 50°C, and kept in a water bath for 6 hours for acid dissolution reaction. After solid-liquid separation, a secondary acid solution and secondary acid-dissolved residue are obtained, and the secondary acid solution is returned to step 1 for primary acid dissolution.

[0110] Step 7, seed crystal preparation: take about 20% of the iron phosphate dihydrate washed in step 4 and perform cyclic ball milling as seed crystals. The ball milling speed is 500 r / min, and the seed crystal particle size Dv50 is controlled to be 2 μm.

[0111] Example 3:

[0112] This embodiment provides a method for reusing ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction, comprising:

[0113] Step 1, primary acid dissolution: Weigh 1000 g of lithium-ferrophosphorus slag with a composition as shown in Table 1, add a secondary acid solution according to the total S / Fe ratio of 1, mix and slurry, then heat in a water bath to 60° C. and keep in a water bath for 6 hours for acid dissolution reaction, and after solid-liquid separation, obtain a primary acid solution and a primary acid-dissolved slag;

[0114] Step 2, phosphorus supplementation and adjustment: sampling and testing the acid-soluble Fe / P ratio, adding phosphoric acid to adjust the Fe / P ratio to 0.85 to obtain phosphorus-iron metal liquid;

[0115] Step 3, ferrophosphorus synthesis: the ferrophosphorus metal liquid is transferred to a synthesis reactor, the temperature is raised to 55°C, iron phosphate seed crystals are added, and the temperature is further raised to 95°C. The mixture is kept at this temperature for reaction and aging for 6 hours, and then solid-liquid separation is performed to obtain crude ferric phosphate dihydrate and a synthetic mother liquor, wherein the heating rate is 10°C / h, the mass ratio of iron in the added iron phosphate seed crystals to the mass ratio of iron in the metal liquid is 5%, and the particle size D50 of the iron phosphate seed crystals is 1 μm;

[0116] Step 4, washing and roasting: adding pure water twice the theoretical ferrophosphorus yield in the ferrophosphorus metal liquid for elution twice until the conductivity of the elution water reaches 2000 μS / m, mixing the elution water and the synthetic mother liquor, placing the eluted ferric phosphate dihydrate in a crucible and transferring it to a muffle furnace for roasting at 600°C, turning off the heating for 5 hours, and introducing air into the roasting environment during the roasting process at an air flow rate of 0.15 L / h. After cooling, take out and obtain anhydrous ferric phosphate.

[0117] Step 5, mother liquor purification and mother liquor concentration: the mixed mother liquor is passed through an aluminum removal resin at a controlled flow rate of 10 BV / h, sulfuric acid is added to the purified mother liquor at a ratio of 10% by mass of sulfuric acid to the mass of sulfur in the purified mother liquor to replenish the lost sulfuric acid, and the mother liquor is transferred to a negative pressure evaporator for reduced pressure concentration at a controlled concentration ratio of 1.5, and the S concentration of the concentrated mother liquor is 1.2 mol / L;

[0118] Step 6, secondary acid dissolution: The concentrated mother liquor and the primary acid-dissolved residue are mixed and slurried at a solid-liquid ratio of 1g:5ml, heated in a water bath to 50°C, and kept in a water bath for 6 hours for acid dissolution reaction. After solid-liquid separation, a secondary acid solution and secondary acid-dissolved residue are obtained, and the secondary acid solution is returned to step 1 for primary acid dissolution.

[0119] Step 7, seed crystal preparation: take about 20% of the iron phosphate dihydrate washed in step 4 and perform cyclic ball milling as seed crystals. The ball milling speed is 600 r / min, and the seed crystal particle size Dv50 is controlled to be 1 μm.

[0120] Comparative Example 1:

[0121] This embodiment provides a method for reusing ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction. The main difference from Example 1 is that in step 5, the mixed mother liquor is not passed through an aluminum removal resin, but is directly concentrated after sulfuric acid is added.

[0122] Comparative Example 2:

[0123] This embodiment provides a method for reusing ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction. The main difference from Example 1 is that in step 5, the ratio of the mass of sulfuric acid added to the purified mother liquor to the mass of sulfur in the purified mother liquor is 20%, and then a secondary acid dissolution is performed without concentration.

[0124] Comparative Example 3:

[0125] This embodiment provides a method for reusing ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction. The main difference from Example 1 is that in step 5, the mother liquor is directly concentrated without adding sulfuric acid after being impurities removed by aluminum removal resin T62-MP.

[0126] Comparative Example 4:

[0127] This embodiment provides a method for reusing a ferric phosphate synthesis mother liquor in a ferric phosphate synthesis reaction. The method differs from Example 1 mainly in that, in step 5, the mixed mother liquor is not passed through the aluminum removal resin T62-MP but through the resin HP-4020, and the ratio of the mass of the added sulfuric acid to the mass of the sulfur in the purified mother liquor is 30%.

[0128] Comparative Example 5:

[0129] This embodiment provides a method for reusing the mother liquor of ferric phosphate synthesis in the ferric phosphate synthesis reaction. The main difference from Example 1 is that the mother liquor is not supplemented with sulfuric acid, is not subjected to resin impurity removal and concentration, and is directly mixed with lithium-extracted ferrophosphorus slag for pulping.

[0130] The compositions of the iron phosphates prepared in the above examples and comparative examples are shown in Table 4.

[0131] Table 4 Anhydrous ferric phosphate components

[0132]

[0133] Note: The amount of sulfuric acid used is t / ferric phosphate. Only the amount added to the purified mother liquor is calculated, and the consumption of sulfuric acid in the first and second acid dissolutions is not considered.

[0134] According to Table 4, it can be seen from the comparison of Example 1 and Comparative Example 1 that the mother liquor did not pass through the aluminum removal resin, and the contents of aluminum and copper in the obtained ferric phosphate were significantly increased; in Comparative Example 2, the mother liquor was not concentrated, resulting in a significant increase in sulfuric acid consumption compared to Example 1; in Comparative Example 3, due to the lack of additional sulfuric acid, the utilization rate of iron in the lithium ferrophosphorus slag was significantly reduced compared to Example 1; in Comparative Example 4, resin HP-4020 was selected, which had a reduced aluminum removal effect compared to the aluminum removal resin T62-MP, and the contents of aluminum and copper in the obtained ferric phosphate were significantly increased; at the same time, the amount of sulfuric acid was increased, but the yield of iron was not significantly improved; in Comparative Example 5, due to the lack of additional sulfuric acid, the mother liquor was not impurity-removed and concentrated, which significantly increased the contents of aluminum and copper in the ferric phosphate, and the utilization rate of iron in the lithium ferrophosphorus slag was significantly reduced compared to Example 1.

[0135] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for reusing ferric phosphate synthesis mother liquor in ferric phosphate synthesis reaction, characterized in that: include: Primary acid dissolution, adding acid solution to the lithium-phosphorus-iron slag to make pulp and then sequentially perform acid dissolution reaction and solid-liquid separation to obtain a primary acid solution and primary acid-dissolved slag; Adjusting the acid solution value to adjust the Fe / P molar ratio and iron concentration of the primary acid solution to obtain ferrophosphorus liquid metal; Ferric phosphate synthesis, adding ferric phosphate seeds to the ferrophosphorus metal liquid to induce seed growth, followed by solid-liquid separation to obtain crude ferric phosphate dihydrate solid and ferric phosphate synthesis mother liquor; Washing and roasting: washing the crude ferric phosphate dihydrate solid to obtain wash water and ferric phosphate dihydrate solid, and roasting the ferric phosphate dihydrate solid to obtain anhydrous ferric phosphate; Purifying the mother liquor, passing the ferric phosphate synthesis mother liquor through a resin column to remove impurity ions and obtain a purified mother liquor; Concentrating the mother liquor, concentrating the purified mother liquor to obtain a concentrated mother liquor; Secondary acid dissolution, slurrying the primary acid-dissolved residue and the concentrated mother liquor and sequentially performing acid dissolution reaction and solid-liquid separation to obtain a secondary acid solution and secondary acid-dissolved residue; Wherein, the acid solution added in the primary acid dissolution step is the secondary acid solution.

2. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: In the primary acid dissolution step, the secondary acid solution and the lithium-extracted ferrophosphorus slag are slurried according to an S / Fe molar ratio of 0.9-1.1; And / or, the acid dissolution reaction temperature is 40°C-80°C, and the reaction time is 4h-10h; And / or, the lithium-extracting ferrophosphorus slag comprises Fe 20wt%-25wt%, Al≤0.15wt%, Cu≤0.001wt%, and the moisture content of the lithium-extracting ferrophosphorus slag is 25wt%-40wt%.

3. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: Phosphoric acid is added in the acid solution adjustment step to adjust the Fe / P molar ratio and iron concentration of the primary acid solution; And / or, the Fe / P molar ratio in the ferrophosphorus metal liquid is 0.85-1.0, the iron concentration is 55-65 g / L, Cu≤0.03 g / L, and Al≤0.3 g / L.

4. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: When the temperature of the ferrophosphorus metal liquid is 50°C-60°C, ferrophosphate seed crystals are added; and / or, adding the ferric phosphate seed crystals to the ferrophosphorus metal liquid, heating the temperature to 90° C.-95° C. and maintaining the temperature for 6 h-20 h, and obtaining the crude ferric phosphate dihydrate solid and the ferric phosphate synthesis mother liquor after solid-liquid separation; Preferably, the heating rate of the heating step is 10°C / h-30°C / h; And / or, the ferric phosphate synthesis mother liquor is returned to the acid dissolution step once.

5. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: The mass of the ferric phosphate seed crystals added is 5%-30% of the mass of iron in the ferrophosphorus metal liquid; And / or, the particle size D50 of the iron phosphate seed crystals is 1 μm-2 μm.

6. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: The calcination temperature is 500-750°C and the calcination time is 5-8 hours; And / or, air is introduced into the roasting environment during the roasting process, with an air flow rate of 0.05L / h-0.15L / h.

7. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: The conductivity of the wash water is ≤2000 μS / m; And / or, the method for preparing the iron phosphate seed crystals comprises: mixing solid iron phosphate dihydrate with water to prepare a slurry, and then sand milling or ball milling at a rotation speed of 500 r / min-1000 r / min.

8. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: The flow rate of the ferric phosphate synthesis mother liquor through the resin column is 2BV / h-10BV / h; And / or, the resin column is an aluminum ion adsorption resin; And / or, Al≤0.02 g / L and Cu≤0.001 g / L in the purified mother liquor.

9. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: In the mother liquor concentration step, sulfuric acid is first added to the purified mother liquor, and the ratio of the mass of the added sulfuric acid to the mass of the sulfur in the purified mother liquor is 10%-30%; and / or, a concentration ratio of 1-2; And / or, the concentration of sulfuric acid in the concentrated mother liquor is 1 mol / L-1.5 mol / L.

10. The method for reusing the ferric phosphate synthesis mother liquor in the ferric phosphate synthesis reaction according to claim 1, characterized in that: The primary acid slag and the concentrated mother liquor are slurried according to a solid-liquid ratio of 1 g:3-5 mL.

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