Comprehensive recovery method of lithium iron phosphate black powder

Abstract

The invention relates to a comprehensive recovery method of lithium iron phosphate black powder, and belongs to the technical field of lithium iron phosphate battery recovery. The technical problem to be solved by the invention is to provide the lithium iron phosphate black powder comprehensive recovery method. The method comprises the following steps: mixing lithium iron phosphate black powder with acid, and adding an oxidizing agent for reaction to obtain iron phosphorus slag; the iron phosphorus slag is subjected to acid pickling and then acid leaching to obtain secondary acid leaching liquid; and dropwise adding the secondary acid leaching solution into bottom water to generate a precipitate, and adjusting the molar ratio of phosphorus to iron or the molar ratio of phosphorus to (iron and manganese) to obtain battery-grade iron phosphate or ferromanganese phosphate. According to the method, alkali is not adopted as a precipitator, iron powder is not introduced, iron phosphate or the ferromanganese phosphate precursor is obtained through a normal-pressure one-step method, the problems that mixing is not uniform when the ferromanganese phosphate precursor is prepared through a solid-phase method, and alkali is needed as the precipitator or organic matter is introduced in a liquid-phase method are solved, use of alkaline chemical reagents and generation treatment of by-products are reduced, and the method is suitable for industrial production. The method has the advantages of simple process, low equipment use requirements, battery grade and high purity of the prepared product, improves the utilization rate of the phosphorus source, and has high yield.

Description

Technical Field

[0001] The invention relates to a comprehensive recovery method for lithium iron phosphate black powder, and belongs to the technical field of lithium iron phosphate battery recovery. Background Art

[0002] Due to the fossil energy crisis and environmental pollution, the traditional automobile market is gradually being replaced by new energy vehicles driven by lithium batteries. From 2015 to 2024, the number of new energy vehicles has exceeded 20 million, and will continue to increase over time. Usually, the cycle life of lithium batteries is 5 to 8 years. The increase in new energy vehicles also brings a large number of scrapped batteries, which brings serious environmental risks. Lithium iron phosphate batteries account for a large proportion of existing new energy vehicles due to their high cycle performance and safety performance. Therefore, efficient recovery and reuse of valuable metals in lithium iron phosphate batteries and economical and environmentally friendly disposal of lithium iron phosphate batteries are the key to the sustainable development of the new energy power industry.

[0003] Compared with the high energy consumption, high emissions and low utilization rate of pyrometallurgical recovery, the complex process and poor universality of direct repair of lithium iron phosphate, the hydrometallurgical recovery process is still the main means of lithium iron phosphate recovery. At present, the wet recovery of lithium iron phosphate mainly includes non-selective lithium extraction and selective lithium extraction. The former directly uses acid to leach out various metal elements, and first recycles phosphorus and iron, and then recycles lithium after removing impurities. Due to the long process flow, the recovery rate of high-value metallic lithium is low. The latter uses oxidants and acids to selectively separate lithium and phosphorus iron slag. Iron and phosphorus recovery and lithium recovery can be carried out simultaneously, and the lithium yield is higher.

[0004] Patent CN114195112A adopts the method of alkaline leaching of iron-phosphorus slag after selective lithium extraction, calcining and recovering the secondary leaching slag to obtain iron red, evaporating and concentrating the leachate to obtain the sodium phosphate product, and recovering the mother liquor to prepare iron phosphate (FePO4). This method is simple in process, but has low output value, large alkali consumption, and cannot guarantee product purity. The mother liquor cannot be fully recycled. CN112410556 A, CN108899601A, CN115583640A and CN113896211A adopt the method of selective lithium extraction and then acid leaching of iron-phosphorus slag to separate carbon slag and iron-phosphorus. After removing impurities from the leaching solution, alkaline compounds such as ammonia water, liquid alkali or soda ash are used to adjust the pH to prepare battery-grade FePO4 products. The product value is high and the process is mature, but this method has more impurity removal processes and higher requirements for aluminum impurity removal. Secondly, in order to ensure a high precipitation rate, the pH of the iron precipitation process is close to 2-2.5. Due to the instantaneous addition of alkali, the local pH of the solution is high, and aluminum ions begin to precipitate and enrich, resulting in a high aluminum impurity in the FePO4 product. In order to remove aluminum, the subsequent use of dilute acid and water will increase, and the use of alkali will cause a large amount of by-product sodium sulfate (Na2SO4) to be produced in the subsequent mother liquor treatment. If ammonia water is used in the precipitation process, environmental protection issues in industrial production must also be considered, and the mother liquor circulation effect after iron precipitation is poor. In order to overcome the problems of by-products, product purity and water circulation, patent CN113912032A adopts the method of adding iron powder, phosphoric acid and sulfuric acid to the iron-phosphorus slag after lithium extraction to reduce and leach iron and phosphorus, and uses the reducing property of iron powder to remove copper impurities, and uses hydrogen peroxide (H2O2) to oxidize and precipitate battery-grade FePO4 products in the leachate. This method can remove impurities in one step, and the mother liquor can be returned to the primary and secondary leaching water without producing by-products. However, the leaching process reacts violently and produces a large amount of hydrogen instantly, which will bring serious safety hazards in industrial production.

[0005] Patents CN116924365A, CN116902946B, and CN106829906A propose a method for preparing FePO4 without alkali solution, that is, using water and high temperature and high pressure to decomplex the iron phosphate complex and precipitate FePO4, and the mother liquor is used as water for subsequent dilution. The method is simple in process and suitable for industrial production, but the phosphorus-iron ratio before iron precipitation is more than 3:1, the phosphorus source utilization rate is low, and the reaction process is to directly dilute the phosphorus-iron complex with water and then increase the temperature and pressurize, resulting in slow crystal growth after decomplexation, insufficient decomplexation leads to a low iron-phosphorus precipitation rate, high temperature and high pressure have high requirements on equipment, and the purity of the product obtained by using iron oxide and phosphoric acid as the iron source and phosphorus source respectively cannot be guaranteed, there are many impurity peaks, and the problem of impurity enrichment in the mother liquor is not considered, and the recycling rate is greatly reduced. CN118026222A uses hydrochloric acid to dissolve the iron-phosphorus slag after lithium extraction, and evaporates 70-75% of the hydrochloric acid in the acid leaching solution under negative pressure, and adjusts the solution pH to 0-0.2 to obtain an iron phosphate product. The product has high purity, but 25-30% of the acid solution remains in the mother liquor after negative pressure evaporation. The pH of the precipitation process is low, which easily leads to the dissolution of the precipitated iron phosphate. The precipitation rate of iron and phosphorus is low. The negative pressure evaporation has high requirements on the air tightness of the equipment, and the iron precipitation mother liquor and the acid recovered by evaporation are continuously used for the dissolution of the iron-phosphorus slag. In the subsequent circulation, the impurities in the mother liquor are easily enriched, which makes it difficult to remove impurities from the product.

[0006] In addition, due to the convenience of production and the need for high-value conversion of recycled products, the recovered iron phosphate and lithium carbonate can be used to prepare lithium iron phosphate and lithium iron manganese phosphate positive electrode materials, but in the process of doping lithium iron manganese phosphate precursor, the uniformity and consistency of manganese in the precursor cannot be well guaranteed. Patent CN110323434A adopts a high-temperature solid phase method, simply mixes and grinds the lithium source, iron source, manganese source, and phosphorus source, and sinters them to obtain the product. The process is simple and mature, and the cost is low, but the product has poor mixing uniformity and poor electrochemical performance. Patent CN110980682A first coprecipitates the manganese source, iron source, and phosphorus source, then mixes and spray-dries with a carbon source to obtain a manganese iron phosphate precursor, and then mixes and calcines with a lithium source to prepare lithium iron manganese phosphate. This method has a good improvement in the mixing uniformity and dissolution of the manganese source, thereby improving the capacitance and voltage of the product, but the coprecipitation process inevitably brings in impurity metal ions in the organic complexing agent and precipitant, resulting in product safety issues. Patent CN117023547A utilizes soluble lithium source, phosphorus source, manganese source and carbon source to be uniformly mixed under water-soluble conditions. The raw materials are dispersed in ionic form and the product is obtained after spray drying and sintering. This method makes the manganese iron mixed evenly, reduces the dissolution and segregation of manganese, and the product has high capacitance. However, since the raw materials are water-soluble raw materials, the spray drying process will volatilize with the steam, change the raw material ratio, and the product stability cannot be guaranteed. In addition, the raw material acquisition path is long, which is not conducive to environmental protection. Summary of the invention

[0007] In view of the problems of impurity ions, safety and non-normal pressure reaction in the acid leaching and precipitation of iron phosphate in the slag after selective lithium extraction from lithium iron phosphate black powder, the technical problem solved by the present invention is to provide a comprehensive recovery method for lithium iron phosphate black powder. The method does not use alkali as a precipitant to avoid the introduction of impurities, and obtains battery-grade iron phosphate or battery-grade manganese iron phosphate in one step at normal pressure, with high purity and good product consistency.

[0008] The comprehensive recovery method of lithium iron phosphate black powder of the present invention comprises the following steps:

[0009] 1) mixing lithium iron phosphate black powder with acid, adding an oxidant to react, and separating the solid and liquid to obtain iron phosphorus slag and a lithium-containing solution;

[0010] 2) mixing the iron-phosphorus slag obtained in step 1) with an acid for pickling, and then pickling by acid leaching to obtain a secondary acid leaching solution;

[0011] 3) adding the secondary acid leaching solution obtained in step 2 dropwise into the bottom water to produce precipitation, adjusting the phosphorus-iron molar ratio to obtain battery-grade iron phosphate, or adjusting the phosphorus: (iron + manganese) molar ratio to obtain ferromanganese phosphate.

[0012] The method of the present invention does not use alkali as a precipitant to avoid the introduction of impurities, does not introduce iron powder to avoid the generation of hydrogen, and only drips the secondary acid leaching liquid into the bottom water to precipitate iron phosphate or ferromanganese phosphate, reducing the use of alkaline chemical reagents and by-product generation treatment. The reaction process is carried out at normal pressure, which reduces the equipment use requirements. After the slag material after selective lithium extraction is acid-leached, electrodialysis wastewater or high-temperature evaporation condensed water or ordinary tap water is used as the bottom water, and the acid leaching liquid is dripped into the bottom water. The iron phosphate or ferromanganese phosphate precursor is obtained in a normal pressure step, avoiding the problem of uneven mixing of the solid phase method for preparing the ferromanganese phosphate precursor, and the liquid phase method requires alkali as a precipitant or the introduction of organic matter. In addition, the iron phosphate or ferromanganese phosphate prepared by the method of the present invention is battery grade, high purity, and improves the utilization rate of the phosphorus source, and the yield is high.

[0013] The present invention does not limit the source of the lithium iron phosphate black powder, which can be a recycled mixed material, positive electrode sheet material or positive electrode scraps, but all of them are powder materials with the electrode sheet peeled off.

[0014] The following is a detailed explanation of each step of the present invention.

[0015] Step 1) is for selective lithium extraction, where black lithium iron phosphate powder is mixed with acid, an oxidant is added to react, and the solid-liquid separation is performed. The obtained liquid is a lithium-containing solution, and the solid is a slag.

[0016] Acids commonly used in the art are suitable for the present invention. In some embodiments, the acid is at least one of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, citric acid, tartaric acid, acetic acid, malic acid, and oxalic acid.

[0017] The ratio of lithium iron phosphate black powder to acid can be a commonly used ratio in the art. In some embodiments of the present invention, lithium iron phosphate black powder and dilute acid are mixed at a solid-liquid mass ratio of 1:3 to 6. In some specific embodiments, the solid-liquid mass ratio of lithium iron phosphate black powder to dilute acid is selected from any value of 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6 or a range of values ​​therebetween. In a preferred embodiment, the solid-liquid mass ratio of lithium iron phosphate black powder to dilute acid is 1:3. If the amount of water used is higher than this value, the amount of water used is large. If the amount of water used is lower than this value, the slurry viscosity is large and it is difficult to disperse evenly.

[0018] In some embodiments of the present invention, in step 1), the acid concentration is 0.80-1.00 mol / L. Optionally, in step 1), the dilute acid concentration is selected from any value of 0.80 mol / L, 0.82 mol / L, 0.85 mol / L, 0.90 mol / L, 0.95 mol / L, 0.98 mol / L, 1.00 mol / L, or a range therebetween.

[0019] Commonly used oxidants in the art are suitable for the present invention. In some specific embodiments, the oxidant is at least one of hydrogen peroxide, sodium hypochlorite, potassium hypochlorite, sodium chlorate, potassium chlorate, sodium perchlorate, potassium perchlorate, sodium peroxide, potassium peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate.

[0020] In some embodiments of the present invention, in step 1), the concentration of the oxidant is 0.72-1.15 mol / L. In some specific embodiments, the concentration of the oxidant is 0.72 mol / L, 0.75 mol / L, 0.80 mol / L, 0.82 mol / L, 0.84 mol / L, 0.88 mol / L, 1.01 mol / L, 1.05 mol / L, 1.08 mol / L, 1.10 mol / L, 1.12 mol / L, 1.15 mol / L, or any value in between.

[0021] In some embodiments of the present invention, in step 1), the molar ratio of oxidant: Li is 2.50 to 4.00: 1. In some specific embodiments, the molar ratio of oxidant: Li is selected from any value of 2.50: 1, 2.60: 1, 2.80: 1, 3.00: 1, 3.20: 1, 3.50: 1, 3.60: 1, 3.80: 1, 4.00: 1 or a range value therebetween. In a preferred embodiment, in step 1), the molar ratio of oxidant: Li is 4.00: 1, so that the selective lithium extraction process can react fully and reduce the leaching of iron and phosphorus.

[0022] In some embodiments of the present invention, in step 1), the pH at the end of the reaction is 1.50 to 2.0. In some more specific embodiments, the pH at the end of the reaction is 1.80 to 2.0.

[0023] In some embodiments of the present invention, the comprehensive recovery method of lithium iron phosphate black powder of the present invention, after step 1), further comprises the following steps:

[0024] a. Purification and impurity removal: Step 1) Add iron powder to the obtained lithium-containing solution, separate the solid and liquid to obtain a copper removal solution, adjust the pH value of the copper removal solution to remove aluminum, nickel, cobalt, and manganese impurities, pass the obtained liquid through a resin to remove calcium and magnesium impurities, obtain a purified solution, and concentrate to obtain a concentrated purified solution;

[0025] b. Lithium precipitation: The concentrated purified liquid is heated to 90-100°C and added to a saturated sodium carbonate solution at the same temperature to obtain crude lithium carbonate. The lithium precipitation mother liquor is evaporated and crystallized to obtain sodium sulfate. The crude lithium carbonate is dispersed with water and continuously hydrogenated with CO2. The obtained hydrogenated solution is evaporated and crystallized to obtain battery-grade lithium carbonate.

[0026] In step a, the iron powder is added according to the copper content of the lithium-containing solution. In some embodiments of the present invention, the molar ratio of the iron powder added in step a to the copper is 1.1 to 1.5:1.

[0027] In some embodiments of the present invention, in step a, the specific operation of adjusting the pH value of the copper removal solution to remove aluminum, nickel, cobalt, and manganese impurities is: first adjusting the pH value to 2-3, solid-liquid separation to obtain liquid, then adjusting the pH value of the liquid to 5.5-6.5, solid-liquid separation, and then adjusting the pH value of the liquid to 11.5-12.5, solid-liquid separation to obtain liquid. In a specific embodiment, in step a, the specific operation of adjusting the pH value of the copper removal solution to remove aluminum, nickel, cobalt, and manganese impurities is: first adjusting the pH value to 2.5, solid-liquid separation to obtain liquid, then adjusting the pH value of the liquid to 6, solid-liquid separation, and then adjusting the pH value of the liquid to 12, solid-liquid separation to obtain liquid.

[0028] In some embodiments of the present invention, in step a, the lithium ion concentration in the concentrated purified solution is controlled to be 0.44-0.56 mol / L. In some specific embodiments, the lithium ion concentration in the concentrated purified solution is controlled to be any value among 0.44 mol / L, 0.46 mol / L, 0.48 mol / L, 0.50 mol / L, 0.52 mol / L, 0.54 mol / L, 0.56 mol / L, or a range between the two.

[0029] In a specific embodiment, in step b, the concentrated purified liquid is heated to 95°C.

[0030] In some embodiments of the present invention, the molar ratio of Li:Na2CO3 is controlled to be 2:1.1 to 1.4. In some specific embodiments, the molar ratio of Li:Na2CO3 is controlled to be any value of 2:1.1, 2:1.2, 2:1.3, 2:1.4 or a range thereof. In a preferred embodiment, the molar ratio of Li:Na2CO3 is controlled to be 2:1.1 to 1.2.

[0031] In some embodiments of the present invention, in step b, the liquid after evaporation and crystallization of the lithium precipitation mother liquor is returned to step b to prepare a saturated sodium carbonate solution.

[0032] The method of the present invention can recover copper, nickel, cobalt and manganese in steps while recovering and preparing lithium carbonate. The leached iron and phosphorus are precipitated and recycled to the acid leaching step. The resin and repeated hydrogenation and impurity removal ensure that a battery-grade lithium carbonate product is obtained. The mother liquor is returned to the lithium precipitation step after sodium precipitation. The whole step realizes the recycling of materials and liquids.

[0033] Step 2) is acid leaching after pickling the slag. The slag in step a is mixed with acid for pickling, and the solid and liquid are separated. The solid obtained is the slag after pickling. Aluminum and copper in the slag can be removed by pickling. After pickling, acid is used for pickling again to obtain a secondary pickling solution.

[0034] According to the method of the present invention, if secondary acid leaching is directly performed, it is difficult to remove copper and aluminum impurities under acidic conditions. However, a small amount of acid washing is used to remove copper and aluminum, so that the impurities in the iron-phosphorus slag are reduced to a controllable range. The liquid after acid washing (i.e., the pickling liquid) is returned to the lithium extraction acid step, and the lithium extraction acid leaching liquid is separated and impurities are removed. There is no need to specifically remove copper and aluminum impurities subsequently, and the prepared iron phosphate product can also reach battery grade.

[0035] Commonly used pickling acids are suitable for the present invention. In some specific embodiments, in step 2), the pickling acid is at least one of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, citric acid, tartaric acid, acetic acid, malic acid, and oxalic acid.

[0036] A conventional solid-liquid mass ratio can be used for pickling. In some specific embodiments, in step 2), the solid-liquid mass ratio of the slag material to the acid is 1:2 to 5. In some specific embodiments, the solid-liquid mass ratio of the slag material to the dilute acid is any value of 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or a range value therebetween. In a preferred embodiment, the solid-liquid mass ratio of the slag material to the dilute acid is 1:3.

[0037] The present invention can adopt the dilute acid concentration commonly used in the art. In one embodiment of the present invention, the dilute acid concentration is 0.10 to 0.25 mol / L. In some specific embodiments, the dilute acid concentration is 0.10 mol / L, 0.12 mol / L, 0.13 mol / L, 0.15 mol / L, 0.18 mol / L, 0.20 mol / L, 0.23 mol / L, 0.25 mol / L, or any value in the range therebetween.

[0038] The pickling temperatures commonly used in the art are applicable to the present invention. In some embodiments, in step 2), the pickling temperature is 60 to 90°C. In some specific embodiments, the pickling temperature is any value of 60°C, 62°C, 65°C, 70°C, 75°C, 78°C, 80°C, 82°C, 85°C, 90°C or a range therebetween.

[0039] For resource recycling, in some embodiments of the present invention, the liquid after pickling is returned to step 1).

[0040] After pickling, acid leaching is performed to separate the solid and liquid, and the obtained liquid is the secondary acid leaching liquid. The obtained solid is carbon slag.

[0041] The acid leaching temperature can be a conventional temperature. In some embodiments, the acid leaching temperature is 30 to 90°C. In some specific embodiments, the acid leaching temperature is 30°C, 32°C, 36°C, 38°C, 40°C, 45°C, 50°C, 55°C, 60°C, 62°C, 65°C, 68°C, 70°C, 74°C, 78°C, 80°C, 82°C, 85°C, 88°C, 90°C, or any range thereof. In a preferred embodiment, the acid leaching temperature is 70°C.

[0042] In some embodiments of the present invention, the pickling acid is at least one of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, citric acid, tartaric acid, acetic acid, malic acid, and oxalic acid.

[0043] In one embodiment of the present invention, during pickling, the acid concentration is 1.42 to 4.28 mol / L, and the molar ratio of acid for pickling:Fe is 1.5 to 4.5:1.

[0044] In one embodiment of the present invention, when the dilute acid is dilute sulfuric acid, the concentration of the dilute sulfuric acid is 1.42 to 2.14 mol / L, and the molar ratio of H2SO4:Fe is 1.5 to 2.25:1.

[0045] In some specific embodiments, the concentration of dilute sulfuric acid is any value among 1.42 mol / L, 1.45 mol / L, 1.50 mol / L, 1.60 mol / L, 1.70 mol / L, 1.74 mol / L, 1.80 mol / L, 1.85 mol / L, 1.90 mol / L, 2.01 mol / L, 2.08 mol / L, 2.14 mol / L, or a range therebetween.

[0046] In some specific embodiments, the molar ratio of H2SO4:Fe is any value of 1.50:1, 1.60:1, 1.75:1, 1.80:1, 1.85:1, 1.90:1, 2.0:1, 2.10:1, 2.15:1, 2.20:1, 2.25:1, or a range thereof. Preferably, the molar ratio of H2SO4:Fe is 1.75:1.

[0047] In another embodiment of the present invention, when the dilute acid is dilute phosphoric acid, the concentration of the dilute phosphoric acid is 1.72-2.30 mol / L, and the molar ratio of H3PO4:Fe is 1.60-2.20:1.

[0048] In some specific embodiments, the concentration of dilute phosphoric acid is any value among 1.72 mol / L, 1.74 mol / L, 1.80 mol / L, 1.84 mol / L, 1.88 mol / L, 1.95 mol / L, 2.00 mol / L, 2.10 mol / L, 2.15 mol / L, 2.20 mol / L, 2.25 mol / L, 2.28 mol / L, 2.30 mol / L or a range therebetween.

[0049] In some specific embodiments, the H3PO4:Fe molar ratio is 1.65:1, 1.70:1, 1.72:1, 1.75:1, 1.80:1, 1.90:1, 1.92:1, 1.98:1, 2.02:2.05:1, 2.08:1, 2.15:1, 2.20:1, or any range thereof. Preferably, the H3PO4:Fe molar ratio is 1.80:1.

[0050] In another embodiment of the present invention, when the dilute acid is dilute hydrochloric acid, the concentration of the dilute hydrochloric acid is 2.84-4.28 mol / L, and the molar ratio of HCl:Fe is 3.0-4.5:1.

[0051] In some specific embodiments, the concentration of dilute hydrochloric acid is any value among 2.84mol / L, 2.90mol / L, 3.00mol / L, 3.20mol / L, 3.40mol / L, 3.58mol / L, 3.60mol / L, 3.70mol / L, 3.85mol / L, 3.90mol / L, 4.02mol / L, 4.16mol / L, 4.28mol / L, or a range therebetween.

[0052] In some specific embodiments, the HCl:Fe molar ratio is any value of 3.00:1, 3.20:1, 3.50:1, 3.60:1, 3.70:1, 3.85:1, 4.0:1, 4.20:1, 4.3:1, 4.40:1, 4.50:1, or a range therebetween. Preferably, the HCl:Fe molar ratio is 3.50:1.

[0053] In another embodiment of the present invention, when the dilute acid is nitric acid, the concentration of the dilute nitric acid is 2.90-4.12 mol / L, and the molar ratio of HNO3:Fe is 3.1-4.4:1.

[0054] In some specific embodiments, the concentration of dilute nitric acid is any value among 2.90 mol / L, 2.95 mol / L, 3.00 mol / L, 3.20 mol / L, 3.40 mol / L, 3.58 mol / L, 3.60 mol / L, 3.70 mol / L, 3.85 mol / L, 3.90 mol / L, 4.02 mol / L, 4.12 mol / L or a range therebetween.

[0055] In some specific embodiments, the HNO3:Fe molar ratio is 2.90, 3.00:1, 3.20:1, 3.50:1, 3.60:1, 3.70:1, 3.85:1, 4.0:1, 4.20:1, 4.3:1, 4.40:1, or any value thereof, or a range thereof. Preferably, the HNO3:Fe molar ratio is 3.45:1.

[0056] Step 3) is to recover ferrophosphorus by adding the secondary acid leaching solution obtained in step 2) dropwise into the bottom water to produce precipitation, adjusting the phosphorus to iron molar ratio to obtain battery-grade ferric phosphate, or adjusting the phosphorus: (iron + manganese) molar ratio to obtain ferromanganese phosphate.

[0057] The dripping of the present invention is based on the precipitation in water. The secondary acid leaching solution is added to the bottom water to precipitate iron, the dilution effect is amplified, the decomplexation rate of the iron-phosphorus complex is increased, and the precipitation is rapid, and this is used as a crystal seed to increase the formation and growth of iron phosphate added to the acid leaching solution later.

[0058] In some specific embodiments, the secondary acid leaching solution is added for more than 20 minutes, and the bottom water volume is more than 3 times the volume of the secondary acid leaching solution. In some specific embodiments, the secondary acid leaching solution is added for 20 to 240 minutes, and the bottom water volume is 3 to 12 times the volume of the secondary acid leaching solution.

[0059] The adding time of the secondary acid leaching solution is 20 to 240 minutes.

[0060] In some specific embodiments, two methods can be used to recover battery-grade iron phosphate or battery-grade ferromanganese phosphate, respectively. Method A is used to recover ferrophosphorus to obtain battery-grade iron phosphate; or method B is used to recover ferrophosphorus to obtain battery-grade ferromanganese phosphate.

[0061] Both method A and method B use normal pressure iron precipitation and low phosphorus-iron ratio. The secondary acid leaching solution is slowly added to the bottom water to precipitate iron phosphate. The ferrophosphate acid leaching solution will produce turbid precipitation when it encounters a large amount of water, avoiding the direct addition of phosphorus-iron complexes into the water for iron precipitation. The required phosphorus-iron ratio is above 3.0 or high pressure reaction can guarantee a yield of more than 90%, and the utilization rate of phosphorus and iron sources is low. The process of adding the secondary acid leaching solution drop by drop into the bottom water dilutes the impurity ions in the iron phosphate leaching solution, avoiding Na, SO4 2- The impurity ions such as iodine enter the iron phosphate, which makes it difficult to clean and remove the impurities in the subsequent process. With the dripping of the acid leaching solution, the pH of the bottom water and the precipitation mixture gradually decreases to 1.00-1.25, which prevents the precipitation of Cu and Al impurities into the iron phosphate product. The reaction process is smooth and the product particle size is uniform. After electrodialysis or high-temperature evaporation of the iron precipitation mother liquor, the fresh water is used as the bottom water for iron precipitation, and the acid is used as lithium extraction or cleaning acid, which is recycled to avoid water waste and treatment problems, and will not introduce impurity ions. The product quality is guaranteed and it is environmentally friendly and clean.

[0062] Specifically, the steps of method A include:

[0063] A1: The secondary acid leaching liquid is added dropwise to the bottom water, aged to obtain dihydrated iron phosphate, and the solid-liquid separation is carried out. The solid is dried to obtain battery-grade iron phosphate, and the liquid is the iron precipitation mother liquor A;

[0064] A2: The iron precipitation mother liquor A is subjected to electrodialysis to separate acid and water, wherein the acid is used in step 1) and the water is used as the bottom water of step A1.

[0065] According to the method of the present invention, after iron precipitation in acid leaching solutions with different acid contents, iron precipitation mother liquors with different acid contents can be obtained. After electrodialysis concentration or evaporation concentration, sulfuric acid with a relatively high concentration can be obtained and used in the lithium extraction step. Electrodialysis uses sodium sulfate as an extreme liquid. Under the action of an electric field, sodium ions will not enter the dilute chamber but will remain in the concentrated chamber. In addition to the concentration of sulfuric acid, a selective permeable membrane allows copper ions to be basically retained in the concentrated chamber, and part of aluminum ions are retained in the concentrated chamber. The lithium extraction acid leaching solution is step-by-step impurity-removed and recycled. Due to the step of pickling aluminum and copper removal and membrane concentration, only a small amount of aluminum ions enter the dilute chamber. The pH of the iron precipitation reaction end point is 1.00-1.20, and aluminum ions will not be precipitated. The waste water in the electrodialysis dilute chamber is used as bottom water for iron precipitation, and impurity ions will not exceed the standard.

[0066] Step A1 is an iron precipitation step, wherein when the method is used for the first time, pure water can be used as the bottom water, and in the later circulation, water separated by electrodialysis or water recovered by high-temperature evaporation and condensation can be used as the bottom water.

[0067] In some embodiments of the present invention, in step A1, the volume of bottom water is 3 to 12 times the volume of the secondary acid leaching solution, the time for dripping the secondary acid leaching solution is 20 min to 240 min, the aging temperature is 90 to 95° C., the phosphorus-iron molar ratio is controlled to be 1.01 to 1.25:1, and the reaction endpoint pH is 1.00 to 1.25.

[0068] In some embodiments of the present invention, in step A1, the bottom water volume is 3 times, 3.2 times, 3.4 times, 4.0 times, 4.4 times, 5.0 times, 5.6 times, 6.2 times, 7.5 times, 8.2 times, 9.4 times, 9.8 times, 10.0 times, 10.3 times, 10.5 times, 10.7 times, 11.0 times, 11.2 times, 11.4 times, 11.5 times, 11.8 times, 12 times of the volume of the secondary acid leaching solution, or a range value therebetween. In a preferred embodiment, the bottom water volume is 4 times the volume of the secondary acid leaching solution.

[0069] When the volume of bottom water is too low, the decomplexation of the phosphorus-iron complex is insufficient, and the product precipitation rate is low. If the volume of bottom water is too high, it will cause excessive waste of water resources. Under the condition of 4 times the volume of bottom water and no pressure, the precipitation rate of iron-phosphorus can be guaranteed to be more than 90%. The aging temperature determines the growth of iron phosphate crystals. A lower aging temperature forms amorphous iron phosphate with smaller particle size and poor uniformity, which is difficult to collect and filter. At a higher temperature, water volatilizes and causes waste. In some embodiments of the present invention, in step A1, the aging temperature is any value of 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, or a range of values ​​therebetween.

[0070] In some embodiments of the present invention, the phosphorus-iron molar ratio is controlled to be any value among 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.12, 1.15, 1.18, 1.20, 1.23, 1.25 or a range value therebetween. The phosphorus-iron ratio can be controlled by adding a phosphorus source or an iron source. Wherein, the iron source is ferric sulfate and the phosphorus source is phosphoric acid.

[0071] After the reaction in step A1 is completed, the pH of the slurry is 1.00 to 1.25.

[0072] In some embodiments of the present invention, in step A2, the electrodialysis uses sodium sulfate as the polar liquid, the polar liquid concentration is 2.0-4.5wt.%, the acid concentration of the iron precipitation mother liquor is 0.125-0.18mol / L, and after the acid and water are separated, the acid concentration is 1.0-1.44mol / L.

[0073] In some embodiments of the present invention, the concentration of the polar liquid is 2.0wt.%, 2.2wt.%, 2.5wt.%, 2.6wt.%, 2.8wt.%, 3.0wt.%, 3.2wt.%, 3.3wt.%, 3.4wt.%, 3.5wt.%, 3.7wt.%, 3.9wt.%, 4.0wt.%, 4.5wt.% or any value thereof or a range thereof. Preferably, the polar liquid is a 3.0wt.% Na2SO4 solution. The solution is filled to half the volume of the polar chamber.

[0074] The dilute chamber contains the iron precipitating mother liquor, and half of its volume of the iron precipitating mother liquor is added to the concentrated chamber for circulation.

[0075] In some embodiments of the present invention, in step A2, the sulfuric acid concentration of the iron precipitation mother liquor is any value among 0.125mol / L, 0.130mol / L, 0.132mol / L, 0.135mol / L, 0.140mol / L, 0.150mol / L, 0.155mol / L, 0.160mol / L, 0.164mol / L, 0.168mol / L, 0.170mol / L, 0.172mol / L, 0.180mol / L, or a range value therebetween.

[0076] By electrodialysis, the concentration of the separated acid is any value among 1.00mol / L, 1.05mol / L, 1.12mol / L, 1.15mol / L, 1.18mol / L, 1.23mol / L, 1.24mol / L, 1.29mol / L, 1.33mol / L, 1.35mol / L, 1.37mol / L, 1.40mol / L, 1.44mol / L or a range between them.

[0077] In some embodiments of the present invention, the voltage is set to 2.2V and the current is set to 1.5A during the electrodialysis.

[0078] When high-temperature evaporation of the iron precipitation mother liquor is used to separate acid and water, the evaporation temperature is 100±10° C. Through evaporation, water in the iron precipitation mother liquor is volatilized, and the acid solution is retained in the concentrated mother liquor. The water in the iron precipitation mother liquor is condensed by evaporation and used as bottom water in step 2). After evaporation, the concentration of the separated acid is any value among 1.00mol / L, 1.05mol / L, 1.12mol / L, 1.15mol / L, 1.18mol / L, 1.23mol / L, 1.24mol / L, 1.29mol / L, 1.33mol / L, 1.35mol / L, 1.37mol / L, 1.40mol / L, and 1.44mol / L, or a range value therebetween.

[0079] The steps of method B include:

[0080] B1: The secondary acid leaching liquid is added dropwise to the bottom water, a manganese source is added to the bottom water as a crystal nucleus, and aged at high temperature to obtain ferromanganese phosphate, and the solid-liquid separation and the solid drying are battery-grade ferromanganese phosphate, and the liquid is the iron precipitation mother liquor B;

[0081] B2: The iron precipitation mother liquor B is mixed with the pickling water, and subjected to electrodialysis to separate the acid and water. The acid is used in step 1), and the water is used as the bottom water of step B1.

[0082] The difference between method B and method A is that method B prepares ferromanganese sulfate. On the basis of recycling and preparing ferrophosphate, phosphoric acid is used as acid for acid leaching, and manganese salt insoluble in phosphoric acid is added to the bottom water as a manganese source. The high-speed dispersed manganese source is dripped into the crystal nucleus and then coated with the decomplexed ferrophosphate to form a ferromanganese phosphate precursor. This solves the problem of uneven dispersion and uneven coating of manganese in the product when directly adding manganese source, iron source and lithium source in the solid phase method in the process of preparing manganese iron phosphate lithium precursor, resulting in poor electrochemical performance of the product. It avoids the use of alkali as a precipitant or organic matter when preparing ferromanganese phosphate precursor by liquid phase method, and directly adds manganese source when precipitating ferrophosphate, so as to prepare ferromanganese phosphate precursor in one step.

[0083] In step B1, the bottom water is 3 to 12 times the volume of the secondary acid leaching solution, the secondary acid leaching solution is added for 20 to 240 minutes, the phosphorus: (iron + manganese) molar ratio is controlled to be 1.01 to 1.25:1 and the iron-manganese molar ratio is controlled to be 1 to 5:1, the aging temperature is 90 to 95° C., and the reaction endpoint pH is 1.00 to 1.25.

[0084] Step B1 is the iron precipitation step, wherein when the method is used for the first time, pure water can be used as the bottom water, and in the later circulation, water separated by electrodialysis or water condensed by high-temperature evaporation can be used as the bottom water.

[0085] In some embodiments of the present invention, in step B1, the manganese source is at least one of manganous oxalate and manganese phosphate; the bottom water volume is 3 to 12 times the volume of the secondary acid leaching solution, the secondary acid leaching solution is added dropwise for 20 to 240 minutes, the aging temperature is 90 to 95° C., the phosphorus: (iron + manganese) molar ratio is controlled to be 1.01 to 1.25:1 and the iron-manganese molar ratio is controlled to be 1 to 5:1, and the reaction endpoint pH is 1.00 to 1.25.

[0086] In some embodiments of the present invention, in step B1, the bottom water volume is 3 times, 3.2 times, 3.4 times, 4.0 times, 4.4 times, 5.0 times, 5.6 times, 6.2 times, 7.5 times, 8.2 times, 9.4 times, 9.8 times, 10.0 times, 10.3 times, 10.5 times, 10.7 times, 11.0 times, 11.2 times, 11.4 times, 11.5 times, 11.8 times, 12 times of the volume of the secondary acid leaching solution, or a range value therebetween. In a preferred embodiment, the bottom water volume is 4 times the volume of the secondary acid leaching solution.

[0087] When the volume of bottom water is too low, the decomplexation of the ferrophosphorus complex is insufficient, and the product precipitation rate is low. If the volume is too high, it will cause excessive waste of water resources. Under the condition of 8 times the volume of bottom water and no pressure, the precipitation rate of iron-phosphorus can be guaranteed to be more than 90%. The aging temperature determines the growth of iron phosphate crystals. Amorphous iron phosphate is formed at a lower aging temperature, which has a smaller particle size, poorer uniformity, and is difficult to collect and filter. At a higher temperature, water evaporates and causes waste. When preparing ferromanganese phosphate, the acid used in the pickling liquid is phosphoric acid. Manganous oxalate and manganese phosphate are difficult to dissolve in phosphoric acid and will not be carried into the mother liquor. With manganese salt as the core, iron phosphate covers its growth to form a ferromanganese phosphate precursor without introducing impurity ions.

[0088] In some embodiments of the present invention, in step B1, the aging temperature is any value of 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, or a range therebetween. Preferably, the aging temperature is 92°C.

[0089] In some embodiments of the present invention, the phosphorus: (iron + manganese) molar ratio is controlled to be any value in 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.12, 1.15, 1.18, 1.20, 1.23, 1.25 or a range value therebetween. The proportioning can be controlled by adding a phosphorus source, an iron source or a manganese source. Wherein, the iron source is ferric sulfate, and the phosphorus source is phosphoric acid. The iron-manganese molar ratio is any value in 1:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.4:1, 3.6:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1 or a range value therebetween.

[0090] After the reaction in step B1 is completed, the pH of the slurry is 1.00-1.25.

[0091] In some embodiments of the present invention, in step B2, the electrodialysis uses sodium sulfate as the polar liquid, the polar liquid concentration is 2.0-4.5wt.%, the sulfuric acid concentration of the iron precipitation mother liquor is 0.125-0.18mol / L, and after the acid and water are separated, the acid concentration is 1.0-1.44mol / L.

[0092] In some embodiments of the present invention, the concentration of the polar liquid is 2.0wt.%, 2.2wt.%, 2.5wt.%, 2.6wt.%, 2.8wt.%, 3.0wt.%, 3.2wt.%, 3.3wt.%, 3.4wt.%, 3.5wt.%, 3.7wt.%, 3.9wt.%, 4.0wt.%, 4.5wt.% or any value thereof or a range thereof. Preferably, the polar liquid is a 3.0wt.% Na2SO4 solution. The solution is filled to half the volume of the polar chamber.

[0093] The dilute chamber contains the iron precipitating mother liquor, and half of its volume of the iron precipitating mother liquor is added to the concentrated chamber for circulation.

[0094] In some embodiments of the present invention, in step B2, the sulfuric acid concentration of the iron precipitation mother liquor is any value among 0.125mol / L, 0.130mol / L, 0.132mol / L, 0.135mol / L, 0.140mol / L, 0.150mol / L, 0.155mol / L, 0.160mol / L, 0.164mol / L, 0.168mol / L, 0.170mol / L, 0.172mol / L, 0.180mol / L, or a range value therebetween.

[0095] By electrodialysis, the concentration of the separated acid is any value among 1.00mol / L, 1.05mol / L, 1.12mol / L, 1.15mol / L, 1.18mol / L, 1.23mol / L, 1.24mol / L, 1.29mol / L, 1.33mol / L, 1.35mol / L, 1.37mol / L, 1.40mol / L, 1.44mol / L or a range between them.

[0096] When high-temperature evaporation of the iron precipitation mother liquor is used to separate acid and water, the evaporation temperature is 100±10° C. Through evaporation, water in the iron precipitation mother liquor is volatilized, and the acid solution is retained in the concentrated mother liquor. The water in the iron precipitation mother liquor is condensed by evaporation and used as bottom water in step 2). After evaporation, the concentration of the separated acid is any value among 1.00mol / L, 1.05mol / L, 1.12mol / L, 1.15mol / L, 1.18mol / L, 1.23mol / L, 1.24mol / L, 1.29mol / L, 1.33mol / L, 1.35mol / L, 1.37mol / L, 1.40mol / L, and 1.44mol / L, or a range value therebetween.

[0097] In some embodiments of the present invention, the voltage is set to 2.2V and the current is set to 1.5A during the electrodialysis.

[0098] In some embodiments of the present invention, the comprehensive recovery method of lithium iron phosphate black powder of the present invention further comprises the following steps:

[0099] 4) Preparation of products: The battery-grade lithium carbonate obtained in step b, the battery-grade iron phosphate / battery-grade ferromanganese phosphate obtained in step 3), a carbon source, a phosphorus source, an iron source, a conductive agent and water are uniformly dispersed, and the lithium iron phosphate / lithium ferromanganese phosphate product is obtained by grinding, spray drying, sintering and crushing.

[0100] In some embodiments of the present invention, the carbon source is one or more of sucrose, polyethylene glycol, polyvinyl alcohol, glucose, graphene, citric acid, and carbon nanotubes; the phosphorus source is one or more of phosphoric acid, manganese phosphate, and lithium phosphate; the iron source is iron oxide, and the lithium source is lithium carbonate and lithium phosphate; the conductive agent is one or more of titanium dioxide, zirconium oxide, vanadium pentoxide, aluminum oxide, and magnesium oxide.

[0101] In some embodiments of the present invention, in step 4), the median particle size of the mixture after grinding is 400-500 nm. In some specific embodiments, the median particle size of the mixture after grinding is any value among 400 nm, 410 nm, 420 nm, 430 nm, 440 nm, 450 nm, 460 nm, 470 nm, 480 nm, 490 nm, 500 nm, or a range value therebetween.

[0102] Preferably, the median particle size of the mixture after grinding is 400-420 nm.

[0103] In some embodiments of the present invention, in step 4), the temperature in the highest constant temperature zone of sintering is 740℃, 750℃, 760℃, 770℃, 780℃, 781℃, 783℃, 785℃, 786℃, 788℃, 790℃, 792℃, 794℃, 796℃, 798℃, 800℃, 802℃, 804℃, 806℃, 808℃, 810℃, 815℃, 818℃, 820℃, 825℃, 830℃, 832℃, 835℃, 838℃, 840℃, any value or a range between them.

[0104] Compared with the prior art, the present invention has the following beneficial effects:

[0105] 1. When using iron lithium black powder to recover and prepare iron phosphate, alkali solution is not used as a precipitant, and iron powder reduction is not introduced to produce a large amount of hydrogen to cause safety hazards. Only 3 to 12 times the volume of the acid leaching solution is used to precipitate iron phosphate at normal pressure. The bottom water is the wastewater after the mother liquor is electrodialyzed or the mother liquor is evaporated and condensed. The addition of the precipitant avoids the introduction of Cu and Al impurities due to excessively high local pH values, and avoids the use of the precipitant causing Na and SO4 in the iron precipitation process 2- The entry of ferric phosphate makes impurity removal difficult, while reducing the use of precipitants and subsequent by-product treatment.

[0106] 2. The iron phosphate precipitation process is carried out under normal pressure and the temperature is controlled below 100°C, which reduces energy consumption and equipment safety risks. The phosphorus-iron ratio is controlled below 1.25, and the utilization rate of the phosphorus source is increased. The wastewater after the mother liquor is subjected to electrodialysis or the evaporation and condensation wastewater is used as the bottom water. The iron phosphate leaching solution is dripped into the bottom water to precipitate iron. The dilution effect is amplified, the decomplexation rate of the iron-phosphorus complex is increased, and the precipitation is rapid. This is used as a crystal seed to increase the formation and growth efficiency of the subsequent iron phosphate. The iron-phosphorus precipitation rate is as high as 93%. The phosphorus precipitation rate is lower than 90% when the acid leaching solution is diluted and pressurized or a high phosphorus-iron ratio precipitation method is used.

[0107] 3. The process of slowly adding the iron phosphate leaching solution into the bottom water dilutes the impurity ions in the iron phosphate leaching solution, avoiding Na, SO4 2- Impurity ions such as Cu and Al enter the ferric phosphate, making it difficult to clean and remove impurities in the subsequent process. With the addition of the acid leaching solution, the pH value of the bottom water and precipitate mixture gradually decreases to 1.00-1.25, thus preventing the precipitation of Cu and Al impurities from entering the ferric phosphate product. The reaction process is gentle, and the product particle size is uniform, with a median particle size of 3-4 μm.

[0108] 4. The wastewater or condensed water of the mother liquor after electrodialysis is used as the bottom water for iron precipitation. The concentrated acid is used as lithium extraction or cleaning acid and is recycled to avoid water waste and treatment problems. Due to the electric field effect of the electrodialysis process, Na, K, Fe, Cu, Al, SO4 2-The iron phosphate products are separated into the acid solution, and the Cu and Al impurity content used as bottom water is below 0.01 g / L, so the impurities will not be enriched in the bottom water. The iron phosphate products obtained by iron precipitation using the circulating mother liquor meet the battery grade standards and are environmentally friendly and clean.

[0109] 5. Lithium iron phosphate is prepared using recycled iron phosphate and lithium carbonate to obtain a material with high charge and discharge efficiency. The charge and discharge capacity is about 158-154 mAh / g at 0.1C, and the first efficiency is 96-97%, which is comparable to the performance of lithium iron phosphate products prepared from commercially available raw materials.

[0110] 6. On the basis of recycling and preparing iron phosphate, manganese salts insoluble in phosphate are added to the bottom water as a manganese source. The manganese source is coated with iron phosphate as a crystal nucleus to form a manganese iron phosphate precursor. This solves the problem of poor electrochemical performance of the product caused by uneven dispersion and coating of manganese in the product when directly adding manganese source, iron source and lithium source and mixing them in the solid phase method in the process of preparing manganese iron phosphate lithium precursor. It avoids the use of alkali as a precipitant or organic matter when preparing manganese iron phosphate precursor by liquid phase method. Manganese source is directly added when precipitating iron phosphate. The manganese iron phosphate precursor is prepared by a one-step method, and its scanning electron microscope image shows that it is evenly distributed.

[0111] 7. Prepare lithium iron manganese phosphate with recycled iron manganese phosphate and lithium carbonate to obtain a high compaction density of -2.4g / cm 3 Above, high specific surface area -14m 2 / g and high charge and discharge efficiency - the charge and discharge capacity at 0.1C is about 162~156mAh / g, and the first efficiency is 97%. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Figure 1 This is a process flow chart for comprehensive recovery of lithium iron phosphate black powder in Examples 1-15 of the present invention.

[0113] Figure 2 This is the X-ray diffraction pattern of the iron phosphate recovered in Example 1 of the present invention.

[0114] Figure 3 This is the particle size distribution diagram of the prepared iron phosphate recovered in Example 1 of the present invention.

[0115] Figure 4 This is a scanning electron microscope image of the ferromanganese phosphate recovered in Example 9 of the present invention. DETAILED DESCRIPTION

[0116] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0117] Example 1

[0118] The main element composition of the lithium iron phosphate black powder used in this embodiment is shown in Table 1.

[0119] Table 1 Main element composition of lithium iron phosphate black powder

[0120] Black powder element composition <![CDATA[Li2O]]> Fe P Al Cu C Ni Co Mn Content (wt.%) 5.76 16.7 9.5 0.51 0.55 38.01 1.43 1.16 1.38

[0121] like Figure 1 As shown, the following method is used to comprehensively recover lithium iron phosphate black powder:

[0122] 1) Selective lithium extraction and lithium precipitation:

[0123] ① Lithium extraction: The obtained lithium iron phosphate black powder, as shown in Table 1, is added with 0.95 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:4, and the mixture is evenly mixed to form a slurry. The slurry is stirred continuously and an oxidant solution with a H2O2:Li molar ratio of 3.5 is slowly added from the bottom, and the H2O2 concentration is 1.10 mol / L. After the addition is completed, the reaction is continued for 2 hours. The pH value at the reaction end point is 1.78. The iron-phosphorus slag is filtered and dried for subsequent recovery of iron-phosphorus to obtain a primary leaching solution for lithium precipitation.

[0124] ②Impurity removal: Add iron powder to the primary leaching solution with a Fe:Cu molar ratio of 1.2:1. Disperse at room temperature and filter to recover copper. Add sodium phosphate to the filtrate to adjust the pH to 2.5 to remove iron. Filter and continue to add liquid alkali to the filtrate to adjust the pH to 6 to remove aluminum. Continue to filter and add liquid alkali to the filtrate to adjust the pH to 12 to remove nickel, cobalt and manganese. After filtration, pass the filtrate through a resin to remove calcium, and finally obtain a purified liquid with a lithium content of 12.4 g / L.

[0125] ③ Lithium precipitation: evaporate and concentrate the purified liquid to a lithium content of 26-30g / L concentrated solution, add it to the Na2CO3 solution, the Li:Na2CO3 molar ratio is 2:1.3, the reaction temperature is 95°C, keep warm for 1h after the addition is completed, separate the solid and liquid and wash with hot water, then prepare the obtained lithium carbonate into a 60g / L mixed solution, stir continuously, and continuously introduce CO2 gas during the period, continue for 6h, separate the solid and liquid, and evaporate and crystallize the liquid to obtain battery-grade Li2CO3.

[0126] ④ Mother liquor recovery: The lithium precipitation mother liquor is adjusted to neutral, evaporated and crystallized to obtain sodium sulfate, and the solution is evaporated and concentrated and then returned to the lithium precipitation liquid.

[0127] 2) Pickling and impurity removal of iron phosphorus slag:

[0128] The iron-phosphorus slag dried in step 1) is added to a 0.15 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:3 to form a slurry, and the temperature is gradually raised to 90°C, kept warm and dispersed for 2 hours, and the solid and liquid are separated, and the liquid is returned to the water for lithium extraction.

[0129] 3) Secondary acid leaching:

[0130] The solid was added to a 1.6 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:3, heated to 70 °C for 2 h, filtered, and the filtrate was used as the acid leaching solution for the subsequent preparation of FePO4. The main element composition of the acid leaching solution is shown in Table 2. It can be seen that the copper content in the acid leaching solution is reduced to 0.012 g / L, and the aluminum content is reduced to 0.026 g / L.

[0131] Table 2 Main element composition of acid leaching solution

[0132] Acid leaching liquid composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Content (g / L) ND 50.79 36.09 0.026 0.012 144.43

[0133] 4) Recycling and preparation of FePO4:

[0134] ① Iron and phosphorus precipitation: add bottom water 3 times the volume of the acid leaching solution into the reactor. The initial bottom water is pure water, and the subsequent bottom water is wastewater after electrodialysis or evaporation condensation water. Heat the bottom water to 90°C, calculate the phosphorus-iron ratio, add ferric sulfate or phosphoric acid to make the phosphorus-iron ratio 1.05:1, slowly drip the acid leaching solution into the bottom water within 240 minutes, and after the addition is completed, keep warm at 90°C for 5 hours. The solution pH is 1.1, and the solid-liquid separation is performed. The iron precipitation mother liquor is used for electrodialysis. The main components of the obtained iron precipitation mother liquor are shown in Table 3.

[0135] Table 3 Main component content of iron precipitation mother liquor

[0136] Mother liquor composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Content (g / L) ND 0.54 0.64 0.012 0.0098 40.35

[0137] ② Preparation of anhydrous FePO4: The solid after iron precipitation was calcined at 600℃ for 3h, taken out and crushed to obtain battery-grade anhydrous FePO4, whose X-ray diffraction spectrum is shown in Figure 2 , the particle size distribution of iron phosphate is shown in Figure 3 .

[0138] from Figure 2 It can be seen that the X-ray diffraction spectrum of iron phosphate prepared by recycling iron lithium black powder has obvious main characteristic peaks and no impurity peaks compared with the standard card, and the purity of the synthetic product is relatively high. Figure 3 It can be seen that the iron phosphate prepared by recycling iron-lithium black powder has a uniform particle size distribution, a median particle size of 3-4 μm, and a D100 of less than 10 μm.

[0139] ③ Electrodialysis of mother liquor: The sodium sulfate recovered from lithium precipitation is prepared into a 4.0wt.% solution and placed in the electrode chamber. The iron precipitation mother liquor is placed in fresh water and a small amount in the concentration chamber. The voltage is set to 15.00V, the current is 2.2A, and the temperature threshold is 40°C. When the material conductivity is lower than 12ms / cm, the concentration is terminated. The acid in the concentration chamber is used for lithium extraction and pickling and impurity removal, and the water in the fresh chamber is used as bottom water for precipitation of iron phosphate. The compositions of the obtained concentration chamber and fresh chamber are shown in Table 4.

[0140] Table 4 Mother liquor after electrodialysis water composition

[0141] Mother liquor composition (g / L) <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Concentrated Room ND 1.01 0.62 0.0024 0.0082 119.32 Tanshiro ND 0.051 0.19 0.0015 0.0001 2.79

[0142] 5) Preparation of lithium iron phosphate using recycled materials: Add the recovered Li2CO3 and FePO4 in a molar ratio of 1:1.98 into 8 times the volume of pure water and disperse evenly, and add 0.95wt.% of sucrose, 1.24wt.% of polyethylene glycol, 0.076wt.% of titanium dioxide, 0.01wt.% of iron oxide and lithium phosphate in sequence, continue to disperse evenly, and grind the mixture to a median particle size of 450nm, spray dry to obtain a precursor, and sinter the precursor to lithium iron phosphate at room temperature, 180°C, 240°C, 320°C, 340°C, 400°C, 500°C, 600°C, 680°C, 720°C, 780°C, and 802°C, and sinter in a nitrogen protective atmosphere, cool to room temperature, and pulverize to obtain the final lithium iron phosphate product.

[0143] Example 2

[0144] The main element composition of the lithium iron phosphate black powder used in this embodiment is shown in Table 5.

[0145] Table 5 Main element composition of lithium iron phosphate black powder

[0146] Black powder element composition <![CDATA[Li2O]]> Fe P Al Cu C Ni Co Mn Content (wt.%) 4.45 14.23 7.85 0.58 0.82 38.44 1.35 1.44 1.27

[0147] like Figure 1 As shown, the following method is used to comprehensively recover lithium iron phosphate black powder:

[0148] 1) Selective lithium extraction and lithium precipitation:

[0149] ① Lithium extraction: The obtained lithium iron phosphate black powder, as shown in Table 5, was added with 1.08 mol / L hydrochloric acid solution at a solid-liquid mass ratio of 1:3, and mixed evenly to form a slurry. The slurry was continued to be stirred and an oxidant solution with a H2O2:Li molar ratio of 2.5 was slowly added from the bottom. The H2O2 concentration was 0.72 mol / L. After the addition was completed, the reaction was continued for 2 hours. The pH at the reaction end point was 1.85. The solid was filtered and dried for subsequent recovery of iron and phosphorus, and a primary leachate was obtained for lithium precipitation.

[0150] ②Impurity removal: Add iron powder to the primary leaching solution with a Fe:Cu molar ratio of 1.5:1. Disperse at room temperature and filter to recover copper. Add sodium phosphate to the filtrate to adjust the pH to 2.5 to remove iron. Continue to add liquid caustic soda to adjust the pH to 6 to remove aluminum. Continue to filter and add liquid caustic soda to adjust the pH to 12 to remove nickel, cobalt and manganese. Pass the filtrate through resin to remove calcium, and finally obtain a purified liquid with a lithium content of 10.4 g / L.

[0151] ③ Lithium precipitation: evaporate and concentrate the purified liquid to a concentrated solution with a lithium content of 26-30g / L, add it to the Na2CO3 solution, the Li:Na2CO3 molar ratio is 2:1.1, the reaction temperature is 95°C, keep warm for 1h after the addition, separate the solid and liquid, and prepare the obtained lithium carbonate into a 60g / L mixed solution, stir continuously, and continuously introduce CO2 gas during the period, continue for 6h, separate the solid and liquid, and evaporate and crystallize the liquid to obtain battery-grade Li2CO3.

[0152] ④ Mother liquor recovery: adjust the lithium precipitation mother liquor to neutral, evaporate and crystallize to obtain sodium chloride, and evaporate and concentrate the solution to return it to the lithium precipitation solution.

[0153] 2) Pickling and impurity removal of iron phosphorus slag:

[0154] The iron-phosphorus slag dried in step 1) is added to a 0.25 mol / L hydrochloric acid solution at a solid-liquid mass ratio of 1:3 to form a slurry, and the temperature is gradually raised to 60°C, kept warm and dispersed for 2 hours, solid-liquid separation, and the liquid is returned to the lithium extraction water. The copper content of the acid leaching solution is reduced to 0.020 g / L, and the aluminum content is reduced to 0.011 g / L.

[0155] 3) Secondary acid leaching:

[0156] The solid was added to a 3.50 mol / L hydrochloric acid solution at a solid-liquid mass ratio of 1:3, heated to 90°C for reaction for 2 h, filtered, and the filtrate was used as the acid leaching solution for the subsequent preparation of FePO4. The main composition of the acid leaching solution is shown in Table 6.

[0157] Table 6 Main element composition of acid leaching solution

[0158] Acid leaching liquid composition <![CDATA[Li2O]]> Fe P Al Cu Cl Content (g / L) ND 47.87 30.10 0.020 0.011 97.53

[0159] 4) Recovery and preparation of FePO4: ① Iron and phosphorus precipitation: Add bottom water 4 times the volume of the acid leaching solution into the reactor. The initial bottom water is pure water, and the subsequent bottom water is waste water after electrodialysis or evaporation and condensation. Heat the bottom water to 92°C, calculate the iron-phosphorus ratio, add ferric sulfate or phosphoric acid to make the phosphorus-iron ratio of 1.25:1, slowly drip the acid leaching solution into the bottom water within 200 minutes, and keep warm for 5 hours after the addition is completed. The solution pH is 1.05, solid-liquid separation, and the iron precipitation mother liquor is evaporated. The main components of the obtained iron precipitation mother liquor are shown in Table 7.

[0160] Table 7 Main component content of iron precipitation mother liquor

[0161] Mother liquor composition <![CDATA[Li2O]]> Fe P Al Cu Cl Content (g / L) ND 0.48 0.54 0.0011 0.0098 39.01

[0162] ② Preparation of anhydrous FePO4: Calcine the solid after iron precipitation at 600℃ for 3h, take it out and crush it to obtain battery-grade anhydrous FePO4 recovery product.

[0163] ③ High-temperature evaporation of mother liquor: The iron precipitation mother liquor is evaporated at high temperature. The evaporated acid is used for lithium extraction and pickling and impurity removal. The evaporated water is condensed and used as bottom water for precipitation of iron phosphate. The composition of the obtained acid and water is shown in Table 8.

[0164] Table 8 Water composition after high temperature evaporation of mother liquor

[0165]

[0166]

[0167] 5) Preparation of lithium iron phosphate using recycled materials: Add the recovered Li2CO3 and FePO4 in a molar ratio of 1:2.01 into 8 times the volume of pure water and disperse evenly, and add 0.95wt.% of glucose, 1.24wt.% of polyethylene glycol, 0.076wt.% of titanium dioxide, 0.010wt.% of iron oxide and phosphoric acid in sequence, continue to disperse evenly, and grind the mixture to a median particle size of 480nm, spray dry to obtain a precursor, and sinter the precursor at room temperature, 180℃, 240℃, 320℃, 340℃, 400℃, 500℃, 600℃, 680℃, 720℃, 780℃, and 789℃ to obtain lithium iron phosphate, and sinter in a nitrogen protective atmosphere, cool to room temperature, and pulverize to obtain the final lithium iron phosphate product.

[0168] Example 3

[0169] The main element composition of the lithium iron phosphate black powder used in this embodiment is shown in Table 9.

[0170] Table 9 Main element composition of lithium iron phosphate black powder

[0171] Black powder element composition <![CDATA[Li2O]]> Fe P Al Cu C Ni Co Mn Content (wt.%) 5.48 16.8 9.6 0.45 0.42 37.78 1.443 1.22 1.33

[0172] like Figure 1 As shown, the following method is used to comprehensively recover lithium iron phosphate black powder:

[0173] 1) Selective lithium extraction and lithium precipitation:

[0174] ① Lithium extraction: The obtained lithium iron phosphate black powder, as shown in Table 9, was added with 1.00 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:6, and mixed evenly to form a slurry. The slurry was continued to be stirred and an oxidant solution with a H2O2:Li molar ratio of 4.0 was slowly added from the bottom. The H2O2 concentration was 1.15 mol / L. After the addition was completed, the reaction was continued for 2 hours. The pH at the reaction endpoint was 1.95. The solid was filtered and dried for subsequent recovery of iron and phosphorus to obtain a primary leachate for lithium precipitation.

[0175] ② Impurity removal: add iron powder to the primary leaching solution, Fe:Cu molar ratio 1.1:1, disperse at room temperature and filter to recover copper, add sodium phosphate to the filtrate to adjust the pH to 2.5 to remove iron, continue to add liquid caustic soda to adjust the pH to 6 to remove aluminum, and after separating the solid, add liquid caustic soda to adjust the pH to 12 to remove nickel, cobalt and manganese, and pass the filtrate through resin to remove calcium, and finally obtain a purified liquid with a lithium content of 12.6g / L;

[0176] ③ Lithium precipitation: evaporate and concentrate the purified liquid to a concentrated solution with a lithium content of 26-30g / L, add it to the Na2CO3 solution, the Li:Na2CO3 molar ratio is 2:1.2, the reaction temperature is 95°C, keep warm for 1h after the addition, separate the solid and liquid, and prepare the obtained lithium carbonate into a 60g / L mixed solution, stir continuously, and continuously introduce CO2 gas during the period, continue for 6h, separate the solid and liquid, and evaporate and crystallize the liquid to obtain battery-grade Li2CO3.

[0177] ④ Mother liquor recovery: adjust the lithium precipitation mother liquor to neutral, evaporate and crystallize to obtain sodium sulfate, and evaporate and concentrate the solution to return it to the lithium precipitation solution.

[0178] 2) Pickling and impurity removal of iron phosphorus slag:

[0179] The iron-phosphorus slag dried in step 1) is added to a 0.10 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:3 to form a slurry, and the temperature is gradually raised to 75°C, kept warm and dispersed for 2 hours, solid-liquid separation, and the liquid is returned to the lithium extraction water. The copper content of the acid leaching solution is reduced to 0.0095 g / L, and the aluminum content is reduced to 0.011 g / L.

[0180] 3) Secondary acid leaching:

[0181] The solid was added to a 2.14 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:3, the temperature was raised to 30°C for reaction for 2 h, and the solution was filtered. The filtrate was used as the acid leaching solution for the subsequent preparation of FePO4.

[0182] Table 10 Main element composition of acid leaching solution

[0183] Acid leaching liquid composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Content (g / L) ND 52.83 34.75 0.011 0.0095 161.33

[0184] 4) Recycling and preparation of FePO4:

[0185] ① Iron and phosphorus precipitation: add bottom water 12 times the volume of the acid leaching solution into the reactor. The bottom water is the electrodialysis wastewater. Heat the bottom water to 95°C, calculate the iron-phosphorus ratio, add ferric sulfate or phosphoric acid to make the phosphorus-iron ratio 1.08:1, slowly drip the acid leaching solution into the bottom water within 20 minutes, keep warm and age for 5 hours, the solution pH is 1.05, separate the solid and liquid, and use the iron precipitation mother liquor for electrodialysis. The main components of the obtained iron precipitation mother liquor are shown in Table 2.

[0186] Table 11 Main component content of iron precipitation mother liquor

[0187] Mother liquor composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Content (g / L) ND 0.2 0.23 0.0013 0.00088 17.42

[0188] ② Preparation of anhydrous FePO4: Calcine the solid after iron precipitation at 600℃ for 3h, take it out and crush it to obtain battery-grade anhydrous FePO4 recovery product.

[0189] ③ Electrodialysis of mother liquor: The sodium sulfate recovered from lithium precipitation is prepared into a 4.5wt.% solution and placed in the electrode chamber. The iron precipitation mother liquor is placed in fresh water and a small amount in the concentration chamber. The voltage is set to 15.00V, the current is 2.2A, and the temperature threshold is 40°C. When the material conductivity is lower than 12ms / cm, the concentration is terminated. The acid in the concentration chamber is used for lithium extraction and pickling and impurity removal, and the water in the fresh chamber is used as bottom water for precipitation of iron phosphate. The compositions of the obtained concentrated chamber and fresh chamber are shown in Table 12.

[0190] Table 12 Mother liquor after electrodialysis water composition

[0191] Mother liquor composition (g / L) <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Concentrated Room ND 1.05 0.70 0.0026 0.0089 122.45 Tanshiro ND 0.049 0.22 0.0017 0.00012 2.98

[0192] 5) Preparation of lithium iron phosphate using recycled materials: Add the recovered Li2CO3 and FePO4 in a molar ratio of 1:1.99 into 8 times the volume of pure water and disperse evenly, and add 0.95wt.% of sucrose, 1.24wt.% of polyethylene glycol, 0.076wt.% of zirconium oxide, 0.01wt.% of iron red and phosphoric acid in sequence, continue to disperse evenly, and grind the mixture to a median particle size of 500nm, spray dry to obtain a precursor, and sinter the precursor at room temperature, 180°C, 240°C, 320°C, 340°C, 400°C, 500°C, 600°C, 680°C, 720°C, 780°C, and 805°C to obtain lithium iron phosphate, and sinter in a nitrogen protective atmosphere, cool to room temperature, and pulverize to obtain a final lithium iron phosphate product.

[0193] Example 4

[0194] The main element composition of the lithium iron phosphate black powder used in this embodiment is shown in Table 13.

[0195] Table 13 Main element composition of lithium iron phosphate black powder

[0196] Black powder element composition <![CDATA[Li2O]]> Fe P Al Cu C Ni Co Mn Content (wt.%) 4.45 17.2 9.7 0.49 0.52 38.23 1.33 1.21 1.28

[0197] like Figure 1 As shown, the following method is used to comprehensively recover lithium iron phosphate black powder:

[0198] 1) Selective lithium extraction and lithium precipitation:

[0199] ① Lithium extraction: The obtained lithium iron phosphate black powder, as shown in Table 13, was added with 0.90 mol / L nitric acid solution at a solid-liquid mass ratio of 1:3, and mixed evenly to form a slurry. The slurry was continued to be stirred and an oxidant solution with a H2O2:Li molar ratio of 4.0 was slowly added from the bottom. The H2O2 concentration was 1.15 mol / L. After the addition was completed, the reaction was continued for 2 hours. The pH value at the reaction end point was 1.96. The solid was filtered and dried for subsequent recovery of iron and phosphorus, and a primary leachate was obtained for lithium precipitation.

[0200] ②Impurity removal: Add iron powder to the primary leaching solution with a Fe:Cu molar ratio of 1.4:1. Disperse at room temperature and filter to recover copper. Add sodium phosphate to the filtrate to adjust the pH to 2.5 to remove iron. Continue to add liquid alkali to the filtrate to adjust the pH to 6 to remove aluminum. Add liquid alkali to the aluminum removal solution to adjust the pH to 12 to remove nickel, cobalt and manganese. Pass the filtrate through a resin to remove calcium, and finally obtain a purified liquid with a lithium content of 13.5 g / L.

[0201] ③ Lithium precipitation: evaporate and concentrate the purified liquid to a lithium content of 26-30g / L concentrated solution, add it to Na2CO3 solution, the molar ratio of Li:Na2CO3 is 2:1.4, the reaction temperature is 95°C, keep warm for 1h after the addition, separate the solid and liquid, and prepare the obtained lithium carbonate into a 60g / L mixed solution, stir continuously, and continuously introduce CO2 gas during the period, continue for 6h, separate the solid and liquid, and evaporate and crystallize the liquid to obtain battery-grade Li2CO3.

[0202] ④ Mother liquor recovery: adjust the lithium precipitation mother liquor to neutral, evaporate and crystallize to obtain sodium nitrate, and evaporate and concentrate the solution to return it to the lithium precipitation solution.

[0203] 2) Pickling and impurity removal of iron phosphorus slag:

[0204] The iron-phosphorus slag dried in step 1) is added to a 0.20 mol / L nitric acid solution at a solid-liquid mass ratio of 1:3 to form a slurry, and the temperature is gradually raised to 80°C, kept warm and dispersed for 2 hours, solid-liquid separation, and the liquid is returned to the lithium extraction water. The copper content of the acid leaching solution is reduced to 0.023 g / L, / L, and the aluminum content is reduced to 0.019 g / L.

[0205] 3) Secondary acid leaching:

[0206] The solid was added to 3.60 mol / L nitric acid solution at a solid-liquid mass ratio of 1:3, heated to 70°C for reaction for 2 h, filtered, and the filtrate was used as the acid leaching solution for the subsequent preparation of FePO4 as shown in Table 14.

[0207] Table 14 Main element composition of acid leaching solution

[0208] Acid leaching liquid composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[NO3 - ]]> Content (g / L) ND 44.92 27.01 0.023 0.019 193.48

[0209] 4) Recovery and preparation of FePO4: ① Iron and phosphorus precipitation: Add bottom water 10 times the volume of the acid leaching solution into the reactor. The bottom water is the electrodialysis wastewater. Heat the bottom water to 95°C, calculate the iron-phosphorus ratio, add ferric sulfate or phosphoric acid to make the phosphorus-iron ratio of 1.07:1, and slowly drip the acid leaching solution into the bottom water within 40 minutes. After the addition is completed, keep warm and age for 5 hours. The solution pH is 1.15. The solid-liquid separation is performed, and the iron precipitation mother liquor is used for electrodialysis. The main components of the obtained iron precipitation mother liquor are shown in Table 15.

[0210] Table 15 Main component content of iron precipitation mother liquor

[0211] Mother liquor composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[NO3 - <!-- 15 -->]]> Content (g / L) ND 0.21 0.25 0.0021 0.0019 24.20

[0212] ② Preparation of anhydrous FePO4: Calcine the solid after iron precipitation at 600℃ for 3h, take it out and crush it to obtain battery-grade anhydrous FePO4 recovery product.

[0213] ③ Electrodialysis of mother liquor: The sodium sulfate recovered from lithium precipitation is prepared into a 3.5wt.% solution and placed in the electrode chamber. The iron precipitation mother liquor is placed in fresh water and a small amount in the concentration chamber. The voltage is set to 15.00V, the current is 2.2A, and the temperature threshold is 40°C. When the material conductivity is lower than 12ms / cm, the concentration is terminated. The acid in the concentration chamber is used for lithium extraction and pickling and impurity removal, and the water in the fresh chamber is used as bottom water for precipitation of iron phosphate. The compositions of the obtained concentrated chamber and fresh chamber are shown in Table 16.

[0214] Table 16 Mother liquor after electrodialysis water composition

[0215] Mother liquor composition (g / L) <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[NO3 - ]]> Concentrated Room ND 1.22 0.67 0.0025 0.0099 2.67 Tanshiro ND 0.056 0.22 0.0017 0.00016 180.44

[0216] 5) Preparation of lithium iron phosphate using recycled materials: Add the recovered Li2CO3 and FePO4 in a molar ratio of 1:1.99 to 8 times the volume of pure water and disperse evenly, and add 0.95wt.% of sucrose, 1.1wt.% of polyethylene glycol, 0.14wt.% of graphene, 0.076wt.% of titanium dioxide, 0.01wt.% of iron oxide and phosphoric acid in sequence, continue to disperse evenly, and grind the mixture to a median particle size of 450nm, spray dry to obtain a precursor, and sinter the precursor at room temperature, 180°C, 240°C, 320°C, 340°C, 400°C, 500°C, 600°C, 680°C, 720°C, 780°C, and 820°C to obtain lithium iron phosphate, and sinter in a nitrogen protective atmosphere, cool to room temperature, and pulverize to obtain the final lithium iron phosphate product.

[0217] Example 5

[0218] The main element composition of the lithium iron phosphate black powder used in this embodiment is shown in Table 17.

[0219] Table 17 Main element composition of lithium iron phosphate black powder

[0220] Black powder element composition <![CDATA[Li2O]]> Fe P Al Cu C Ni Co Mn Content (wt.%) 6.4 13.56 9.28 0.62 0.69 41.08 3.9 1.11 1.46

[0221] like Figure 1 As shown, the following method is used to comprehensively recover lithium iron phosphate black powder:

[0222] 1) Selective lithium extraction and lithium precipitation:

[0223] ① Lithium extraction: The obtained lithium iron phosphate black powder, as shown in Table 17, was added with 0.82 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:3, and mixed evenly to form a slurry. The slurry was continued to be stirred and an oxidant solution with a H2O2:Li molar ratio of 3.0 was slowly added from the bottom, and the H2O2 concentration was 0.95 mol / L. After the addition was completed, the reaction was continued for 2 hours. The pH value at the reaction end point was 1.95. The solid was filtered and dried for subsequent recovery of iron and phosphorus, and a primary leachate was obtained for lithium precipitation.

[0224] ②Impurity removal: Add iron powder to the primary leaching solution with a Fe:Cu molar ratio of 1.2:1. Disperse at room temperature and filter to recover copper. Add sodium phosphate to the filtrate to adjust the pH to 2.5 to remove iron. Continue to add liquid alkali to the filtrate to adjust the pH to 6 to remove aluminum. Continue to filter and add liquid alkali to the filtrate to adjust the pH to 12 to remove nickel, cobalt and manganese. Pass the filtrate through a resin to remove calcium, and finally obtain a purified liquid with a lithium content of 14.2 g / L.

[0225] ③ Lithium precipitation: evaporate and concentrate the purified liquid to a lithium content of 26-30g / L concentrated solution, add it to the Na2CO3 solution, the Li:Na2CO3 molar ratio is 2:1.15, the reaction temperature is 95°C, keep warm for 1h after the addition is completed, separate the solid and liquid and wash with hot water, then prepare the obtained lithium carbonate into a 60g / L mixed solution, stir continuously, and continuously introduce CO2 gas during the period, continue for 6h, separate the solid and liquid, and evaporate and crystallize the liquid to obtain battery-grade Li2CO3.

[0226] ④ Mother liquor recovery: The lithium precipitation mother liquor is adjusted to neutral, evaporated and crystallized to obtain sodium sulfate, and the solution is evaporated and concentrated and then returned to the lithium precipitation liquid.

[0227] 2) Pickling and impurity removal of iron phosphorus slag:

[0228] The iron-phosphorus slag dried in step 1) is added to a 0.20 mol / L sulfuric acid solution at a solid-liquid mass ratio of 1:3 to form a slurry, and the temperature is gradually raised to 90°C, kept warm and dispersed for 2 hours, solid-liquid separation, the liquid and the iron precipitate mother liquor are mixed and electrodialyzed, and the copper content of the acid leaching solution is reduced to 0.014 g / L, and the aluminum content is reduced to 0.030 g / L.

[0229] 3) Secondary acid leaching:

[0230] The solid was added to 2.30 mol / L phosphoric acid solution at a solid-liquid mass ratio of 1:3, heated to 70°C for reaction for 2 h, filtered, and the filtrate was used as the acid leaching solution for the subsequent preparation of FePO4. The main element composition of the obtained acid leaching solution is shown in Table 18.

[0231] Table 18 Main element composition of acid leaching solution

[0232] Acid leaching liquid composition <![CDATA[Li2O]]> Fe P Al Cu Content (g / L) ND 38.21 46.83 0.030 0.014

[0233] 4) Recycling and preparation of FePO4:

[0234] ① Iron and phosphorus precipitation: add bottom water 5 times the volume of the acid leaching solution into the reactor, heat the bottom water to 90℃, calculate the phosphorus-iron ratio, add ferric sulfate to make the phosphorus-iron ratio 1.01:1, slowly drip the acid leaching solution into the bottom water within 120min, and after the addition is completed, keep warm at 90℃ for 5h. The solution pH is 1.00, separate the solid and liquid, mix the iron precipitation mother liquor and pickling water, evaporate at high temperature to separate the acid and water, and the main components of the obtained mixed solution of iron precipitation mother liquor and pickling water are shown in Table 19.

[0235] Table 19 Main component content of iron precipitation mother liquor

[0236] Mother liquor composition <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Content (g / L) ND 0.78 1.25 0.024 0.011 4.90

[0237] ② Preparation of anhydrous FePO4: Calcine the solid after iron precipitation at 600℃ for 3h, take it out and crush it to obtain battery-grade anhydrous FePO4 recovery product.

[0238] ③ High-temperature evaporation of mother liquor: The iron precipitation mother liquor is evaporated at high temperature. The evaporated acid is used for lithium extraction and pickling and impurity removal. The evaporated water is condensed and used as bottom water for iron phosphate precipitation. The composition of the obtained acid and water is shown in Table 20.

[0239] Table 20 Main content composition of mother liquor and pickling water mixed solution after evaporation

[0240] Mother liquor composition (g / L) <![CDATA[Li2O]]> Fe P Al Cu <![CDATA[SO4 2- ]]> Acid ND 1.42 1.27 0.023 0.068 38.12 Evaporation of water ND 0.053 0.38 0.0088 0.0012 1.24

[0241] 5) Preparation of lithium iron phosphate using recycled materials: Add the recovered Li2CO3 and FePO4 in a molar ratio of 1:1.98 into 8 times the volume of pure water and disperse evenly, and add 0.95wt.% of sucrose, 1.24wt.% of polyethylene glycol, 0.076wt.% of titanium dioxide, 0.01wt.% of iron oxide and lithium phosphate in sequence, continue to disperse evenly, and grind the mixture to a median particle size of 400nm, spray dry to obtain a precursor, and sinter the precursor to lithium iron phosphate at room temperature, 180°C, 240°C, 320°C, 340°C, 400°C, 500°C, 600°C, 680°C, 720°C, 780°C, and 812°C, and sinter in a nitrogen protective atmosphere, cool to room temperature, and pulverize to obtain a final lithium iron phosphate product.

[0242] Example 6

[0243] The method of this embodiment is the same as that of Example 5, except that 1.72 mol / L phosphoric acid is used for the acid leaching of iron-phosphorus slag. When precipitating iron, the amount of bottom water is 6 times the volume of the acid leaching solution. Ferric sulfate is added to control the phosphorus-iron ratio to 1.10:1. The acid leaching solution is added for 100 min. The mother liquor is mixed with the pickling solution and subjected to electrodialysis. The dilute chamber is used for dilution with water, and the concentrated chamber is used for lithium acid extraction.

[0244] Example 7

[0245] The method of this embodiment is the same as that of Example 5, except that 1.80 mol / L phosphoric acid is used for the acid leaching of iron-phosphorus slag. When precipitating iron, the amount of bottom water is 8 times the volume of the acid leaching solution. Ferric sulfate is added to control the phosphorus-iron ratio to 1.08:1. The acid leaching solution is added for 60 min. The mother liquor is mixed with the pickling solution and subjected to electrodialysis. The dilute chamber is used for dilution with water, and the concentrated chamber is used for lithium acid extraction.

[0246] Example 8

[0247] The method of this embodiment is the same as that of Example 1, except that 1.80 mol / L phosphoric acid is used for the acid leaching of iron-phosphorus slag. When iron is precipitated, the amount of bottom water is 10 times the volume of the acid leaching solution. Ferric sulfate is added to control the phosphorus-iron ratio to 1.06:1. The mother liquor is mixed with the pickling solution and subjected to electrodialysis. The dilute chamber is used for dilution water, and the concentrated chamber is used for lithium acid extraction.

[0248] Example 9

[0249] The method of this embodiment is the same as that of embodiment 5, except that pure water of 9 times the volume of the acid leaching solution is added to the reactor, the bottom water is heated to 95°C, the iron-phosphorus ratio and the iron-manganese ratio are calculated, and ferrous sulfate and manganous oxalate are added to make the phosphorus: (iron + manganese) molar ratio 1.10:1, and the iron-manganese molar ratio 1.5:1. The acid leaching mixture is slowly dripped into the bottom water within 30 minutes, and after the addition is completed, the mixture is kept warm and aged for 5 hours. The solution pH is 1.2, and the solid-liquid separation is performed. The mother liquor and the pickling water are mixed and electrodialyzed, and the product is sintered at 600°C under nitrogen positive pressure protection for 3 hours to obtain manganese-doped iron phosphate, i.e., ferromanganese phosphate. The scanning electron microscope image of the ferromanganese phosphate is shown in Figure 4 .from Figure 4 It can be seen that the recovered and prepared ferromanganese phosphate has uniform particle distribution.

[0250] The recovered Li2CO3 and manganese-doped FePO4 are added into 8 times volume of pure water in a molar ratio of 1:1.98 and dispersed evenly, and 0.95wt.% of sucrose, 1.1wt.% of polyethylene glycol, 0.14wt.% of graphene, 0.076wt.% of titanium dioxide, 0.01wt.% of iron oxide and manganese phosphate are added in sequence, and the dispersion continues to be evenly distributed, and the mixture is ground to a median particle size of 400nm, and a precursor is obtained by spray drying. The precursor is sintered into lithium iron phosphate at room temperature, 180°C, 240°C, 320°C, 340°C, 400°C, 500°C, 600°C, 680°C, 720°C, 780°C, and 820°C, and sintered in a nitrogen positive pressure protective atmosphere, cooled to room temperature, and pulverized to obtain a final lithium manganese iron phosphate product.

[0251] Example 10

[0252] The method of this embodiment is the same as that of embodiment 9, except that ferrous sulfate and manganous oxalate are added, and the iron-manganese ratio is 5:1.

[0253] Embodiment 11

[0254] The method of this embodiment is the same as that of embodiment 9, except that ferrous sulfate and manganous oxalate are added, and the iron-manganese ratio is 1:1.

[0255] Example 12

[0256] The method of this embodiment is the same as that of embodiment 9, except that ferrous sulfate and manganous oxalate are added, and the iron-manganese ratio is 2:1.

[0257] Example 13

[0258] The method of this embodiment is the same as that of embodiment 9, except that ferrous sulfate and manganese phosphate are added, and the iron-manganese ratio is 1.5:1.

[0259] Embodiment 14

[0260] The method of this embodiment is the same as that of embodiment 9, except that ferrous sulfate and manganese phosphate are added, and the iron-manganese ratio is 3:1.

[0261] Embodiment 15

[0262] The method of this embodiment is the same as that of embodiment 9, except that ferrous sulfate and manganese phosphate are added, and the iron-manganese ratio is 2:1.

[0263] Comparative Example 1

[0264] The method of this embodiment is the same as that of embodiment 1, except that the bottom water during precipitation of iron and phosphorus is the iron precipitation mother liquor which has not been treated by electrodialysis.

[0265] Comparative Example 2

[0266] The method of this embodiment is the same as that of embodiment 1, except that when preparing ferric phosphate, the pH of the acid leaching solution is adjusted to 2.0 with ammonia water at 90° C., filtered, washed, and calcined to obtain the ferric phosphate product.

[0267] Comparative Example 3

[0268] The method of this embodiment is the same as that of embodiment 1, except that when preparing iron phosphate, the pH of the acid leaching solution is adjusted to 2.0 with liquid alkali at 90° C., and then filtered, washed, and calcined to obtain the iron phosphate product.

[0269] Comparative Example 4

[0270] The method of this embodiment is the same as that of embodiment 1, except that the bottom water used in preparing ferric phosphate is pure water.

[0271] Comparative Example 5

[0272] The method of this embodiment is the same as that of Example 1, except that when recovering and preparing iron phosphate, the acid leaching solution is added for 15 minutes, and the other conditions remain unchanged.

[0273] Comparative Example 6

[0274] The method of this embodiment is the same as that of embodiment 3, except that when recovering and preparing iron phosphate, the acid leaching solution is added for 10 minutes, and the other conditions remain unchanged.

[0275] Comparative Example 7

[0276] The method of this embodiment is the same as that of embodiment 1, except that when recovering and preparing iron phosphate, the bottom water is 1 times the amount of the acid leaching solution, and the other conditions remain unchanged. The pH of the mother liquor after iron precipitation is 0.42.

[0277] Comparative Example 8

[0278] The method of this embodiment is the same as that of embodiment 1, except that when recovering and preparing iron phosphate, the bottom water is 1.5 times the acid leaching solution, and the other conditions remain unchanged. The pH of the mother liquor after iron precipitation is 0.63.

[0279] Comparative Example 9

[0280] The method of this embodiment is the same as that of embodiment 1, except that when recovering and preparing iron phosphate, the bottom water is twice as much as the acid leaching solution, and the other conditions remain unchanged. The pH of the mother liquor after iron precipitation is 0.85.

[0281] Comparative Example 10

[0282] The method of this embodiment is the same as that of Example 1, except that when recovering and preparing iron phosphate, the bottom water is twice as much as the acid leaching solution, the bottom water and the acid leaching solution are mixed and then heated, and the acid leaching solution is not added dropwise to the bottom water. At the same time, a pressure of 0.5 MPa is applied to the reactor, and the other conditions remain unchanged.

[0283] Comparative Example 11

[0284] The method of this embodiment is the same as that of Example 1, except that when recovering and preparing iron phosphate, the bottom water is 4 times the acid leaching solution, the bottom water and the acid leaching solution are mixed and heated, and the acid leaching solution is not added dropwise to the bottom water. At the same time, a pressure of 0.6 MPa is applied to the reactor, and the other conditions remain unchanged.

[0285] Comparative Example 12

[0286] The method of this embodiment is the same as that of Example 1, except that when recovering and preparing iron phosphate, the bottom water is 4 times the acid leaching solution, the bottom water and the acid leaching solution are mixed and then heated, and the acid leaching solution is not added dropwise to the bottom water. The phosphorus-iron ratio is adjusted to 4:1, and a pressure of 0.6 MPa is applied to the reactor, while the other conditions remain unchanged.

[0287] Comparative Example 13

[0288] The method of this embodiment is the same as that of Example 1, except that when recovering and preparing iron phosphate, the bottom water is 4 times the acid leaching solution, the bottom water and the acid leaching solution are mixed and then heated, and the acid leaching solution is not added dropwise to the bottom water. The phosphorus-iron ratio is adjusted to 4:1, and the other conditions remain unchanged.

[0289] Comparative Example 14

[0290] The method of this embodiment is the same as that of Embodiment 9, but the difference from Embodiment 9 is that the manganese source is not added when the ferric phosphate is precipitated, but is added when it is subsequently mixed with the carbon source.

[0291] Comparative Example 15

[0292] In this embodiment, commercial battery-grade iron phosphate and lithium carbonate are used to prepare lithium iron phosphate. The preparation method is the same as that of Example 9.

[0293] Result analysis:

[0294] Table 21 shows the precipitation rates of iron and phosphorus when recovering and preparing iron phosphate (FePO4), where:

[0295] The precipitation rate calculation formula is as follows:

[0296] W Fe / P =(1-C 母 V 母 / C 酸 V 酸 )*100

[0297] Among them C 母 Represents the iron concentration or phosphorus concentration in the mother liquor after iron precipitation, V 母 represents the volume of mother liquor after iron precipitation, C acid represents the concentration of iron or phosphorus in the acid leaching solution, and V acid represents the volume of the acid leaching solution.

[0298] Table 21 Recovery and preparation of iron phosphate iron and phosphorus precipitation rate

[0299] serial number Iron precipitation rate (%) Phosphorus precipitation rate (%) serial number Iron precipitation rate (%) Phosphorus precipitation rate (%) Example 1 90.92 90.78 Comparative Example 6 85.28 84.88 Example 2 92.32 92.21 Comparative Example 7 56.42 54.98 Example 3 94.88 93.71 Comparative Example 8 70.72 69.93 Example 4 94.97 93.13 Comparative Example 9 75.48 74.33 Example 5 92.65 92.11 Comparative Example 10 89.87 88.65 Example 6 92.89 92.48 Comparative Example 11 92.01 91.97 Example 7 93.15 92.67 Comparative Example 12 94.01 76.97 Comparative Example 5 32.28 30.45 Comparative Example 13 77.44 68.08

[0300] By comparing Examples 1 to 7 with Comparative Examples 5 to 13, it can be seen that the precipitation rate of iron and phosphorus can reach more than 90% by dripping the acid leaching solution into the bottom water. This is because the iron phosphate leaching solution is added to the bottom water to precipitate iron, and the dilution effect is amplified, which increases the decomplexation rate of the iron-phosphorus complex and precipitates quickly. This is used as a seed to increase the formation and growth of iron phosphate that is subsequently added to the acid leaching solution. As can be seen from Examples 1, 3 and Comparative Examples 5, 6, when the bottom water is 3 times the volume of the acid leaching solution, iron precipitation is added dropwise quickly within 15min, and iron and phosphorus precipitation rates are only about 30%, this is because the rapid addition of the acid leaching solution causes the bottom water pH to decrease rapidly, and the precipitated iron phosphate is not grown up and is subsequently dripped into the acid leaching solution and re-dissolved, when the bottom water is 12 times the acid leaching solution, iron precipitation is added dropwise quickly within 10min, and iron and phosphorus precipitation rates are 85.28%, 84.88%, and the bottom water slows down the pH change more, but the precipitation rate still does not reach 90%, this is because too fast a drop rate causes the crystal nucleus formed to have no time to grow, and it is impossible to effectively serve the purpose of providing crystal seeds for subsequent dripping of liquid precipitation. Therefore, when iron phosphate is precipitated, when the bottom water multiple is low, it is necessary to slowly add the acid leaching solution to prevent the product from being dissolved, and when the bottom water multiple is high, the acid leaching solution can be added relatively quickly.

[0301] After determining the acid leaching solution dropping time, it can be seen from comparative examples 7 to 9 that the bottom water dosage is reduced to 1, 1.5, and 2 times, the iron precipitation rate is reduced to 56.42%, 70.72%, and 75.48%, and the phosphorus precipitation rate is reduced to 54.98%, 69.93%, and 74.33%. When the bottom water is low, even if the acid leaching solution time is extended, a higher precipitation rate cannot be achieved. The mother liquor pH after iron precipitation is 0.42, 0.63, and 0.85, and the precipitation process pH is too low to be conducive to product generation, and 4 times the volume of bottom water is the dosage of iron and phosphorus precipitation is relatively complete. Continue to increase the bottom water dosage, although it can also increase iron and phosphorus precipitation rates, water consumption is too large, which is not conducive to environmental protection. And comparative examples 10 and 11 can be seen that the acid leaching solution is used to mix with the bottom water first and then heat up to precipitate iron, and under pressurized conditions, the iron and phosphorus precipitation rates can reach more than 89%. It can be seen from Comparative Examples 12 and 13 that only by increasing the phosphorus-iron ratio, the iron precipitation rate can reach 94%, but the phosphorus precipitation rate is low, the utilization rate is low, and the iron-phosphorus precipitation rate is even more unsatisfactory without pressure. Compared with the low precipitation rate of iron precipitation in the mixed method of acid leaching solution and bottom water, the acid leaching solution is slowly added to the bottom water iron precipitation method, which has a higher yield. This is because the bottom water volume is much larger than the volume of the acid leaching solution, and the iron-phosphoric acid leaching solution is slowly added to the bottom water. The iron-phosphorus complex quickly decomplexes to form a precipitate, and as a seed crystal, the subsequent droplet decomplexation and precipitation are increased, and the precipitation rate of iron-phosphorus in the iron-phosphorus complex is increased.

[0302] The test indicators of iron phosphate or ferromanganese phosphate are shown in Table 22.

[0303] Table 22 Various testing indicators of iron phosphate

[0304]

[0305] Among them, ND means not detected.

[0306] It can be seen from Table 22 that compared with the examples, the comparative examples have a higher content of Al, Cu, SO4 2- Impurity elements are likely to exceed the standard. For liquid alkali precipitation, Na, SO4 2- The impurity ions exceed the standard. This is because the instantaneous addition of liquid alkali causes the local pH of the solution to be high, resulting in precipitation that quickly encapsulates the impurity ions into the iron phosphate. The subsequent cleaning process is difficult to separate the internal impurities. The mother liquor is not subjected to electrodialysis and is directly used for dilution water. SO4 2- The impurities are excessive, and the Cu and Al impurities do not meet the standards. The electric field effect in the electrodialysis process also has the effect of removing impurities and separating Na, K, Fe, Al, Cu, SO4 2- The mother liquor is electrodialyzed, and the wastewater in the dilute room is used as bottom water, which does not cause impurity enrichment problems. Therefore, the indicators of the iron phosphate prepared by recycling the electrodialysis wastewater are normal. Therefore, the dilution precipitation method has better control over impurity ions, does not introduce impurities, and the mother liquor is recycled.

[0307] The various testing indicators of lithium carbonate are shown in Table 22.

[0308] Table 23 Lithium carbonate testing indicators

[0309]

[0310] It can be seen from Table 23 that the recycled lithium carbonate meets battery grade standards.

[0311] The electrochemical properties of lithium iron phosphate and lithium manganese iron phosphate are shown in Table 23.

[0312] Table 23 Electrical properties of lithium iron phosphate and lithium manganese iron phosphate

[0313]

[0314]

[0315] It can be seen from Table 23 that the prepared lithium manganese iron phosphate has a higher specific surface area than lithium iron phosphate and the comparative example -13m 2 / g or more, compacted density -2.4g / cm 3The above, charging capacity -162mAh / g, discharge capacity -156mAh / g, first efficiency above 97%, lithium iron phosphate prepared from recycled materials and lithium iron phosphate prepared from commercial battery grade iron phosphate and lithium carbonate have the same compaction density -2.3g / cm 3 Above, specific surface area 1013m 2 / g and above, and the charging capacity is about -158mAh / g, and the discharging capacity is about -154mAh / g.

Claims

1. Comprehensive recovery method of lithium iron phosphate black powder, Features: The following steps are involved: 1) mixing lithium iron phosphate black powder with acid, adding an oxidant to react, and separating the solid and liquid to obtain iron phosphorus slag and a lithium-containing solution; 2) mixing the iron-phosphorus slag obtained in step 1) with an acid for pickling, and then pickling by acid leaching to obtain a secondary acid leaching solution; 3) adding the secondary acid leaching solution obtained in step 2) dropwise into the bottom water to produce precipitation, adjusting the phosphorus to iron molar ratio to obtain battery-grade iron phosphate, or adjusting the phosphorus: (iron + manganese) molar ratio to obtain ferromanganese phosphate.

2. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: In step 1), the acid is at least one of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, citric acid, tartaric acid, acetic acid, malic acid, and oxalic acid. The oxidant is at least one of hydrogen peroxide, sodium hypochlorite, potassium hypochlorite, sodium chlorate, potassium chlorate, sodium perchlorate, potassium perchlorate, sodium peroxide, potassium peroxide, sodium persulfate, potassium persulfate, and ammonium persulfate.

3. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: In step 1), lithium iron phosphate black powder and acid are mixed at a solid-liquid mass ratio of 1:3-6; the acid concentration is 0.80-1.00 mol / L, the oxidant concentration is 0.72-1.15 mol / L, the molar ratio of oxidant:Li is 2.50-4.00:1, and the reaction endpoint pH is 1.50-2.

0.

4. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: The following steps are also included: a. Purification and impurity removal: Step 1) Add iron powder to the obtained lithium-containing solution, separate the solid and liquid to obtain a copper removal solution, adjust the pH value of the copper removal solution to remove aluminum, nickel, cobalt, and manganese impurities, pass the obtained liquid through a resin to remove calcium and magnesium impurities, obtain a purified solution, and concentrate to obtain a concentrated purified solution; b. Lithium precipitation: The concentrated purified liquid is heated to 90-100°C and added to a saturated sodium carbonate solution at the same temperature to obtain crude lithium carbonate. The lithium precipitation mother liquor is evaporated and crystallized to obtain sodium salt. The crude lithium carbonate is dispersed with water and CO is continuously introduced. 2 Hydrogenation, the obtained hydrogenated solution is evaporated and crystallized to obtain battery-grade lithium carbonate; preferably, the concentrated purified solution is heated to 95°C.

5. The comprehensive recovery method of lithium iron phosphate black powder according to claim 4, Features: In step a, iron powder is added according to a molar ratio of iron powder to copper of 1.1 to 1.5:1; in step a, the lithium ion concentration in the concentrated purified solution is controlled to be 0.44 to 0.56 mol / L; in step b, the Li:Na 2 CO 3 The molar ratio is 2:1.1~1.

4.

6. The comprehensive recovery method of lithium iron phosphate black powder according to claim 4, Features: In step a, the specific operation of adjusting the pH value of the copper removal liquid to remove aluminum, nickel, cobalt, and manganese impurities is: first adjusting the pH value to 2-3, solid-liquid separation to obtain liquid, then adjusting the pH value of the liquid to 5.5-6.5, solid-liquid separation, and then adjusting the pH value of the liquid to 11.5-12.5, and solid-liquid separation to obtain liquid; preferably, the specific operation of adjusting the pH value of the copper removal liquid to remove aluminum, nickel, cobalt, and manganese impurities is: first adjusting the pH value to 2.5, solid-liquid separation to obtain liquid, then adjusting the pH value of the liquid to 6, solid-liquid separation, and then adjusting the pH value of the liquid to 12, and solid-liquid separation to obtain liquid.

7. The comprehensive recovery method of lithium iron phosphate black powder according to claim 4, Features: In step b, the liquid after evaporation and crystallization of the lithium precipitation mother liquor is returned to step b to prepare a saturated sodium carbonate solution.

8. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: In step 2), during pickling, the pickling acid is at least one of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, citric acid, tartaric acid, acetic acid, malic acid, and oxalic acid, and the solid-liquid mass ratio of the slag to the acid is 1:2 to 5; the concentration of the pickling acid is 0.10 to 0.25 mol / L, and the pickling temperature is 60 to 90° C.; preferably, the solid-liquid mass ratio of the slag to the acid is 1:

3.

9. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: In step 2), during acid leaching, the acid leaching temperature is 30-90° C.; the acid used for acid leaching is at least one of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, citric acid, tartaric acid, acetic acid, malic acid, and oxalic acid; the concentration of the acid used for acid leaching is 1.42-4.28 mol / L; and the molar ratio of acid used for acid leaching:Fe is 1.5-4.5:

1.

10. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: In step 3), the secondary acid leaching solution is added for more than 20 minutes, and the bottom water volume is more than 3 times the volume of the secondary acid leaching solution; preferably, the secondary acid leaching solution is added for 20 to 240 minutes, and the bottom water volume is 3 to 12 times the volume of the secondary acid leaching solution.

11. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, Features: In step 3), method A is used to obtain battery-grade iron phosphate, and method B is used to obtain battery-grade ferromanganese phosphate; The steps of method A include: A1: The secondary acid leaching liquid is added dropwise to the bottom water, aged to obtain dihydrated iron phosphate, and the solid-liquid separation is carried out. The solid is dried to obtain battery-grade iron phosphate, and the liquid is the iron precipitation mother liquor A; A2: The iron precipitation mother liquor A is separated into acid and water by electrodialysis or high temperature evaporation, the acid is used in step 1), and the water is used as the bottom water of step A1; The steps of method B include: B1: The secondary acid leaching liquid is added dropwise to the bottom water, a manganese source is added to the bottom water as a crystal nucleus, and aged at high temperature to obtain ferromanganese phosphate, and the solid-liquid separation and the solid drying are battery-grade ferromanganese phosphate, and the liquid is the iron precipitation mother liquor B; B2: The iron precipitation mother liquor B is separated into acid and water by electrodialysis or high-temperature evaporation. The acid is used in step 1) and the water is used as the bottom water of step B1.

12. The comprehensive recovery method of lithium iron phosphate black powder according to claim 11, Features: In step A1, the volume of bottom water is 4 times the volume of the secondary acid leaching solution, the molar ratio of phosphorus to iron is controlled to be 1.01-1.25:1, the aging temperature is 90-95°C, and the pH at the reaction endpoint is 1.00-1.25; In step A2, the electrodialysis uses sodium sulfate as the polar liquid, the polar liquid concentration is 2.0-4.5wt.%, the acid concentration of the iron precipitation mother liquor is 0.125-0.18mol / L, the temperature of high-temperature evaporation is 100±10°C, and after the acid and water are separated, the acid concentration is 1.0-1.44mol / L.

13. The comprehensive recovery method of lithium iron phosphate black powder according to claim 11, Features: In step B1, the manganese source is at least one of manganous oxalate and manganese phosphate; the bottom water volume is 4 times the volume of the secondary acid leaching solution, the phosphorus: (iron + manganese) molar ratio is controlled to be 1.01-1.25:1 and the iron-manganese molar ratio is controlled to be 1-5:1, the aging temperature is 90-95°C, and the reaction endpoint pH is 1.00-1.25; In step B2, the electrodialysis uses sodium sulfate as the polar liquid, the polar liquid concentration is 2.0-4.5wt.%, the acid concentration of the iron precipitation mother liquor is 0.125-0.18mol / L, the temperature of high-temperature evaporation is 100±10°C, and after the acid and water are separated, the acid concentration is 1.0-1.44mol / L.

14. The comprehensive recovery method of lithium iron phosphate black powder according to claim 1, It is characterized in that The following steps are also included: 4) Preparation of products: The battery-grade lithium carbonate obtained in step b, the battery-grade iron phosphate / battery-grade ferromanganese phosphate obtained in step 3), a carbon source, a phosphorus source, an iron source, a conductive agent and water are uniformly dispersed, and the lithium iron phosphate / lithium ferromanganese phosphate product is obtained by grinding, spray drying, sintering and crushing.

15. The comprehensive recovery method of lithium iron phosphate black powder according to claim 14, Features: The carbon source is one or more of sucrose, polyethylene glycol, polyvinyl alcohol, glucose, graphene, citric acid, and carbon nanotubes; the phosphorus source is one or more of phosphoric acid, manganese phosphate, and lithium phosphate; the iron source is iron oxide; and the conductive agent is one or more of titanium dioxide, zirconium oxide, vanadium pentoxide, aluminum oxide, and magnesium oxide.

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