Comprehensive treatment method of lithium iron phosphate waste

Abstract

The invention relates to a comprehensive treatment method of a lithium iron phosphate waste material, which comprises the following steps: simultaneously or sequentially carrying out oxidation treatment and alkaline leaching treatment on the lithium iron phosphate waste material to be treated, and carrying out solid-liquid separation to obtain a slag phase 1 and a liquid phase 1; adjusting the pH value of the liquid phase 1 to 6.5-8 by using a first acid reagent, aging, and carrying out solid-liquid separation to obtain a liquid phase 2 and a slag phase 2; mixing the slag phase 1 with a second acid reagent, and leaching to obtain a liquid phase 3 and a slag phase 3; mixing the liquid phase 2 and the liquid phase 3 to obtain a mixed solution; carrying out chemical sedimentation impurity removal on the mixed solution, and carrying out solid-liquid separation to obtain a liquid phase 4; and carrying out iron precipitation treatment on the liquid phase 4, and carrying out solid-liquid separation to obtain an iron phosphate dehydrate product and a lithium-rich solution. According to the method, Li, Fe, P, Al and graphite in the waste lithium iron phosphate material can be effectively recycled, the comprehensive treatment benefit is high, finally, iron and phosphorus can be recycled and prepared into iron phosphate for batteries, Li can be converted into battery-grade lithium carbonate, and graphite is enriched in the slag phase 3 and can be sold as a byproduct.

Description

Technical Field

[0001] The present invention relates to a comprehensive treatment method for lithium iron phosphate waste, belonging to the field of solid waste resource treatment. Background Art

[0002] Aluminum is one of the main impurities in current waste lithium iron phosphate electrodes. Since aluminum is an amphoteric metal, the current treatment process for lithium iron phosphate waste generally adopts acid leaching or alkali leaching methods. Whether it is acid leaching or alkali leaching, it is difficult to achieve effective selective separation of aluminum in the leaching step, that is, aluminum inevitably coexists with lithium and / or iron and / or phosphorus in the leaching system. In battery-grade iron phosphate, battery-grade lithium carbonate, and lithium iron phosphate active materials, if the content of aluminum elements with non-specific crystal forms exceeds the standard, it will significantly reduce the electrochemical performance of the precursor material and battery material, such as significantly reducing the battery capacity. Moreover, materials with low aluminum content are the mainstream products currently circulating in the market. Therefore, in the process of recycling and recovery of waste lithium iron phosphate batteries, the efficient and low-consumption separation of impurity aluminum is one of the industry problems that currently restricts the effective recovery of waste lithium iron phosphate batteries.

[0003] In response to the above problems, some solutions have been provided in the prior art. For example:

[0004] Australian Patent Application AU2022388904A1 discloses a lithium iron phosphate battery recycling process, which uses a process of first alkali and then acid to recycle lithium iron phosphate waste. The alkali leaching step of this process mainly removes the doped aluminum foil in the waste first, but it will cause about 30% of Li and about 75% of PO4 3- to enter the impurity liquid phase of Al 3+ and F - , and the process method for separating and recovering the Li and P elements in this liquid phase is not clearly described in this patent application. The alkali leaching residue phase removes fluorine and copper through acid leaching and two ion exchanges respectively. Not only is the impurity removal process flow long, but also the cost of ion exchange for impurity removal is high and the waste water volume is large. In addition, due to the loss of a large amount of phosphorus elements in the alkali leaching step, it is necessary to supplement phosphoric acid in the step of obtaining iron phosphate products by controlling the pH, which increases the reagent cost, and the purity of the final product only reaches 99.5%, which does not meet the relevant standards of battery-grade iron phosphate and is industrial-grade iron phosphate with relatively low added value. It can be seen that its solution has deficiencies in aspects such as process industrialization operability, cost, environmental protection, and economic benefits, and is not suitable for large-scale industrial production implementation.

[0005] Chinese Invention Patent Application CN 113862475 A discloses a method for directional dissolution treatment of high-aluminum waste lithium battery cathode materials, which uses a process of mixing alkali and carbonate roasting and water leaching to transfer aluminum and phosphorus into the liquid phase. The carbonate roasting mainly converts lithium into lithium carbonate with lower solubility in alkaline solution. Although the solubility product constant of lithium carbonate is relatively low (Ksp = 2.5×10-2 (at 25 °C)), and it also has a certain solubility in liquid caustic soda. Therefore, lithium inevitably enters the sodium aluminate liquid phase and is lost during the water leaching step. This process does not propose a feasible solution for this. From the data of its examples, it can be seen that its lithium recovery rate is between 81% and 91%, which obviously cannot meet the requirements of resource recycling. Secondly, since the roasting step does not achieve the oxidation of the materials, oxidants need to be added to the water leached slag phase, increasing the complexity of the process operation. Moreover, this process does not further purify the leaching solution. It can be seen that it can only be recovered in the form of industrial-grade lithium phosphate, iron hydroxide, and aluminum hydroxide, with relatively low added value, large lithium loss, and low industrial economic feasibility.

[0006] Chinese Patent Application CN 113737018 A discloses a method for recycling the positive electrode raw materials of waste batteries. This process is a common process for recycling lithium from waste lithium iron phosphate waste in current industrialization. It uses acid leaching to completely dissolve and separate graphite and other insoluble impurities, uses iron powder replacement to remove a small amount of copper impurities, and uses oxidation and alkali adjustment to precipitate phosphorus and iron impurities. However, due to the lack of a core process for removing aluminum impurities, the final obtained iron phosphate has a high impurity content and low economic value. Moreover, this process uses excessive strong acid to completely dissolve and then uses alkali to reverse adjust and precipitate iron and phosphorus, resulting in a large consumption of acid and alkali, and the disposal cost of the high-salt wastewater containing phosphorus and sodium chloride is high.

[0007] Chinese Patent Application CN116768180A discloses a method for preparing lithium iron phosphate cathode material from waste lithium iron phosphate batteries. The method includes crushing the waste lithium iron phosphate batteries to obtain a positive and negative electrode mixed powder, performing a low-temperature alkali leaching reaction to obtain an alkali leaching filtrate and a filter residue; adding acid to the alkali leaching filtrate and the filter residue for reaction, and filtering to obtain a lithium-containing filtrate I and an acid leaching filtrate; adding urea to the acid leaching filtrate for impurity removal, adjusting the phosphorus-iron molar ratio, adjusting the pH, and filtering to obtain a lithium-containing filtrate II and a ferrous phosphate filter cake; mixing the lithium-containing filtrates I and II, adding sulfide and carbonate for impurity removal, mixing with the ferrous phosphate filter cake, adding water and phosphoric acid, and performing a hydrothermal reaction to obtain a mixed slurry; filtering and washing the mixed slurry, adding water and a carbon source for mixing, and performing grinding, drying, sintering, and crushing to obtain the lithium iron phosphate cathode material. The applicant's research found that it is actually difficult to completely separate aluminum and iron in this low-temperature alkali leaching process. Under the low-temperature weak alkali leaching conditions described in this patent, for the electrode powder with a high aluminum foil content, the aluminum content in its alkali leaching residue is difficult to be reduced to less than 1%; especially for materials with a low aluminum content or waste lithium iron phosphate battery powder or gutter materials with more complex impurity contents, the effect of selective separation is even worse, and even the lithium lost in the alkali leaching solution is much higher than the leached aluminum. Therefore, this patent cannot treat Al impurities to ppm-level concentration only through low-temperature alkali leaching treatment. And without appropriate aluminum removal means and processes in the subsequent steps, Al impurities will inevitably affect the purity of the final product and cause it to fail to reach the purity of the battery grade standard, and will also affect the electrochemical performance of the prepared material. Secondly, it removes impurities from the acid leaching filtrate and the lithium-containing filtrate independently, which requires a lot of impurity removal reagents, has a cumbersome operation, and has a high difficulty and cost in treating the settling mother liquor wastewater; thirdly, it controls the pH of the acid leaching filtrate at 2.5-4.5 for impurity removal with urea, and then adds an alkali solution to adjust the pH to 2.5-5.0 to obtain a ferrous phosphate filter cake. The precipitation pH value range is too close, and according to experimental experience, this process flow is extremely easy to oxidize and generate a co-precipitation phenomenon, thus inevitably resulting in the loss of phosphorus and iron in the impurity removal stage, resulting in a low comprehensive recovery rate of phosphorus and iron, thereby reducing the economic benefits of the process; in addition, the phosphorus and iron elements in the solution are precipitated in the form of ferrous phosphate by adding a ferrous salt regulator and an alkali, which requires additional consumption of ferrous salts and has a high process cost. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a comprehensive treatment method for lithium iron phosphate waste to better realize the separation and recovery of valuable elements such as Li, Fe, and P.

[0009] To solve the above technical problems, the technical solution of the present invention is as follows:

[0010] A comprehensive treatment method for lithium iron phosphate waste, comprising the following steps:

[0011] S1. Oxidize and leach the lithium iron phosphate waste to be treated simultaneously or sequentially with an alkaline solution, followed by solid-liquid separation to obtain a slag phase 1 and a liquid phase 1.

[0012] S2. Adjust the pH value of the liquid phase 1 to 6.5 - 8 with a first acid reagent, age, and then perform solid-liquid separation to obtain a phosphate-rich liquid phase 2 and an aluminum hydroxide-rich slag phase 2.

[0013] Mix the slag phase 1 with a second acid reagent, leach, and then obtain a liquid phase 3 and a graphite-rich slag phase 3.

[0014] S3. Mix the liquid phase 2 and the liquid phase 3 to obtain a mixed solution.

[0015] S4. After chemically depositing and removing impurities from the mixed solution, perform solid-liquid separation to obtain a liquid phase 4.

[0016] S5. After performing iron precipitation on the liquid phase 4, perform solid-liquid separation to obtain a ferric phosphate dihydrate product and a lithium-rich solution.

[0017] Optionally, in S1, the lithium iron phosphate waste to be treated is waste lithium iron phosphate electrode sheet powder, and its main impurities are aluminum foil, organic binder, solvent, and graphite powder.

[0018] The comprehensive treatment method of the present invention can treat lithium iron phosphate waste with an aluminum impurity content of 0.1 - 10 wt% and a relatively high graphite impurity content (not limited, generally the graphite content of normal sorted lithium iron phosphate waste is within 15 wt%). The present invention can also be used to treat lithium iron phosphate waste containing metal impurities such as calcium, magnesium, manganese, and copper, such as lithium iron phosphate waste with a Ca content ≤ 5%, a Mg content ≤ 5%, a Mn content ≤ 5%, and a Cu content ≤ 5%.

[0019] Optionally, in the lithium iron phosphate waste, the lithium content is 0.5 - 5%, the iron content is 15 - 35%, the phosphorus content is 5 - 25%, the aluminum content is 0.1 - 10%, and the total impurity content is 1 - 30%.

[0020] Further, in the lithium iron phosphate waste, the lithium content is 1.5 - 4.5%, the iron content is 18 - 32%, the phosphorus content is 8 - 22%, the aluminum content is 0.5 - 8%, and the total impurity content is 5 - 25%.

[0021] Furthermore, in the lithium iron phosphate waste, the lithium content is 2 - 4%, the iron content is 20 - 30%, the phosphorus content is 10 - 20%, the aluminum content is 1 - 7%, and the total impurity content is 8 - 22%.

[0022] Further, the impurities include one or more of Mn, Mg, Cu, Ca, and graphite. Preferably, they include Mn, Mg, Cu, Ca, and graphite.

[0023] Further, in S1, the oxidation treatment includes one or more of oxidative roasting and oxidative leaching;

[0024] Preferably, the temperature of oxidative roasting is 500 - 680 °C, more preferably 550 - 650 °C, still more preferably 580 - 620 °C, and the time is 0.5 - 7 h, more preferably 0.75 - 6 h, still more preferably 1 - 4 h; more preferably, oxidative roasting is carried out in an air atmosphere or an oxygen atmosphere; after oxidative roasting, the Fe content in the material is < 0.1 wt%; 2+ content < 0.1 wt%;

[0025] Preferably, the lithium iron phosphate waste to be treated is mixed with an oxidant in water for oxidative leaching; more preferably, the oxidant includes one or more of hydrogen peroxide, water-soluble chlorate, and oxygen; more preferably, the addition amount of the oxidant is 0.8 - 2.5 times, more preferably 0.85 - 2.1 times, still more preferably 0.9 - 2.0 times, and also preferably 1.0 - 1.5 times, and further optionally 1.1 times, 1.2 times, 1.3 times, or 1.4 times of the theoretical amount required to completely oxidize divalent iron in the lithium iron phosphate waste to trivalent iron; more preferably, the water-soluble chlorate is one or more of sodium chlorate, potassium chlorate, and ammonium chlorate;

[0026] Preferably, an alkali or its solution is mixed in for alkaline leaching treatment; more preferably, the alkali includes one or more of sodium hydroxide, potassium hydroxide, and ammonia water; more preferably, the total amount of OH in the added alkali is 1.0 - 1.5 times, preferably 1.1 - 1.4 times, and more preferably 1.2 - 1.35 times of the theoretical alkali consumption amount, and the theoretical alkali consumption amount is the theoretical total amount of OH required to completely convert iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 respectively, that is, 3n(Fe) + 4n(Al); more preferably, the alkali is sodium hydroxide flakes and / or potassium hydroxide flakes, and the reaction is exothermic by itself. Generally, no additional heating is required during the alkali leaching process at this time; - the total amount of OH in the added alkali is 1.0 - 1.5 times, preferably 1.1 - 1.4 times, and more preferably 1.2 - 1.35 times of the theoretical alkali consumption amount, and the theoretical alkali consumption amount is the theoretical total amount of OH required to completely convert iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 respectively, that is, 3n(Fe) + 4n(Al); more preferably, the alkali is sodium hydroxide flakes and / or potassium hydroxide flakes, and the reaction is exothermic by itself. Generally, no additional heating is required during the alkali leaching process at this time; - the theoretical total amount of OH required to completely convert iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 respectively, that is, 3n(Fe) + 4n(Al); more preferably, the alkali is sodium hydroxide flakes and / or potassium hydroxide flakes, and the reaction is exothermic by itself. Generally, no additional heating is required during the alkali leaching process at this time; - the theoretical total amount of OH required to completely convert iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 respectively, that is, 3n(Fe) + 4n(Al); more preferably, the alkali is sodium hydroxide flakes and / or potassium hydroxide flakes, and the reaction is exothermic by itself. Generally, no additional heating is required during the alkali leaching process at this time;

[0027] Preferably, when carrying out oxidative leaching and / or alkaline leaching treatment, the initial liquid-solid ratio of the reaction system is controlled to be 4 - 8 ml:1 g, preferably 5 - 6 ml:1 g; preferably, the initial liquid-solid ratio of the reaction system is controlled by adding water;

[0028] Preferably, the reaction time of oxidative leaching and / or alkaline leaching treatment is 1 - 5 h, more preferably 2 - 3 h;

[0029] Preferably, when performing solid-liquid separation, the temperature of the filtration system is controlled ≥ 50 °C, preferably 70 - 90 °C. In this way, phosphate crystallization can be better prevented.

[0030] Preferably, before solid-liquid separation, the alkaline leaching system is heated to 80-100 °C, preferably 85-95 °C, and kept warm for 10-60 min, preferably 20-30 min. This can convert ferric hydroxide in colloidal form into molecular form as much as possible, preventing the generation of ferric hydroxide colloid after alkali leaching, which may cause filtration difficulties and impurity adsorption problems.

[0031] Generally, the slag phase 1 contains lithium phosphate and ferric hydroxide. Generally, the liquid phase 1 contains aluminate and phosphate.

[0032] Preferably, before oxidative leaching, the lithium iron phosphate waste to be treated is mixed with water to form a slurry, and a slurry with a liquid-solid ratio of 1-2 ml: 1-2 g is obtained; preferably, the water is one or more of pure water, industrial water, purified wastewater, and wash water generated by washing.

[0033] Furthermore, to prevent the generation of ferric hydroxide colloid after alkali leaching, which may cause filtration difficulties and impurity adsorption problems, after the alkaline leaching is completed, the alkaline leaching system is heated to 80-100 °C (preferably 85-95 °C) and kept warm for 10-60 min (preferably 20-30 min) to convert ferric hydroxide in colloidal form into molecular form, and then solid-liquid separation is carried out.

[0034] Furthermore, in S1, after solid-liquid separation, the obtained solid phase is washed with dilute alkali solution and then further solid-liquid separated to obtain the slag phase 1;

[0035] Preferably, the pH value of the dilute alkali solution is > 11, more preferably 11.1-14, still more preferably 11.5-13.5, and even more preferably 12-13;

[0036] Preferably, the number of washing times is 2-5 times, preferably 3-4 times, the washing time is 5-60 min / time, preferably 20-30 min / time, and the washing temperature is 10-50 °C, preferably 15-45 °C, still more preferably 20-30 °C;

[0037] Preferably, the dilute alkali solution contains one or more of sodium hydroxide and potassium hydroxide.

[0038] In this way, by alkali-washing the solid phase, it can better ensure that the leached aluminum element can completely enter the liquid phase 1 to be separated from iron, further improving the Al impurity removal rate and reducing the risk of unqualified Al impurity content in the subsequent obtained product.

[0039] Furthermore, in S2, the pH value of the liquid phase 1 is adjusted to 6.8-7.5 with the first acid reagent;

[0040] Preferably, the first acid reagent includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid;

[0041] Preferably, the aging time is 1 - 6 h, more preferably 3 - 5 h.

[0042] The pH value of the liquid phase 1 is adjusted with the first acid reagent to convert the phosphate in the liquid phase 1 into monohydrogen phosphate and dihydrogen phosphate with higher solubility, preventing the crystallization of the phosphorus solution; meanwhile, the amphoteric metal elements leached in the alkali leaching step, such as aluminum, tin, lead, chromium, and zinc, can be hydrolyzed and transformed into M(OH) x (M is one or more of Al, Sn, Pb, Cr, Zn), and generally, the slag phase 2 is mainly Al(OH)3.

[0043] The aluminum concentration in the liquid phase 2 < 0.01 g / L.

[0044] Furthermore, in S2, the total amount of H + in the added second acid reagent is 1 - 1.2 times the theoretical acid consumption, preferably 1 - 1.15 times, more preferably 1.02 - 1.08 times; wherein, the theoretical acid consumption is the theoretical total amount of H + required to completely dissolve Li and Fe in the slag phase 1.

[0045] Preferably, the leaching temperature is controlled at 50 - 95 °C, preferably 55 - 90 °C, and the leaching time is 0.5 - 3.5 h, preferably 1.5 - 2 h.

[0046] Preferably, the second acid reagent includes one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0047] By treating the slag phase 1 with the second acid reagent, valuable elements such as lithium, phosphorus, and iron in the slag phase can be completely dissolved into the liquid phase 3, while impurities such as graphite still remain in the slag phase, obtaining a graphite-rich slag phase 3, which can be sold as a by-product.

[0048] Furthermore, in S3, the liquid phase 2 and the liquid phase 3 obtained in S2 are mixed.

[0049] Furthermore, in S4, the mixed solution is mixed with a precipitant for chemical sedimentation to remove impurities.

[0050] Among them, the precipitant is a water-soluble carbonate and its hydrate and / or a water-soluble bicarbonate and its hydrate; preferably, the water-soluble carbonate includes one or more of sodium carbonate, ammonium carbonate, and potassium carbonate, and the water-soluble bicarbonate includes one or more of sodium bicarbonate, ammonium bicarbonate, and potassium bicarbonate; more preferably, the addition amount of the precipitant is 1.1-1.5 times the theoretical amount of the precipitant, and further preferably 1.2-1.4 times, where the theoretical amount of the precipitant is the theoretical amount of the precipitant required to completely convert the metal impurity ions in the mixed solution into precipitates, and the metal impurity ions are one or more of Ca ions, Mg ions, Mn ions, and Cu ions;

[0051] Preferably, during the chemical sedimentation and impurity removal process, the reaction temperature is controlled at ≥50°C, preferably 55-95°C, and the reaction time is 1-2 h, preferably 1.3-1.8 h.

[0052] In the liquid phase 4, the concentrations of Ca, Mg, and Al are all <0.02 g / L.

[0053] Furthermore, in S5, after adjusting the pH value of the liquid phase 4 to 2-3 with an alkali solution having an OH - concentration <5 mol / L and stirring for 0.5-2 h, preferably for 0.6-1 h, solid-liquid separation is performed to obtain crude iron phosphate dihydrate and a lithium-rich solution; after washing the crude iron phosphate dihydrate, an iron phosphate dihydrate product is obtained;

[0054] Preferably, the OH - concentration in the alkali solution is 2-4 mol / L, and more preferably 2.5-3 mol / L; optionally, the alkali solution contains sodium hydroxide and / or potassium hydroxide;

[0055] Preferably, the pH value of the liquid phase 4 is adjusted to 2.1-2.5;

[0056] Preferably, during the pH value adjustment process, the change rate of the pH value is controlled <0.3 / min, and more preferably 0.1-0.2 / min;

[0057] Preferably, during the pH value adjustment process, the stirring rate is controlled ≥300 rpm, preferably 310-500 rpm;

[0058] Preferably, the crude iron phosphate dihydrate is washed with an acidic washing water having a pH value of 0.5-2;

[0059] Preferably, the pH value of the acidic washing water is 0.6-1, and more preferably 0.7-1; optionally, the acidic washing water is a phosphoric acid solution. In this way, a good washing effect can be obtained, and the iron hydroxide that may be mixed in the crude iron phosphate dihydrate can be converted into iron phosphate to regulate the iron-phosphorus balance;

[0060] Preferably, the temperature of the acid washing water is ≥ 75 °C, preferably 85 - 95 °C;

[0061] Preferably, the number of washing times is 3 - 8 times, preferably 5 - 7 times, and the washing time is 10 - 60 min / time, preferably 20 - 30 min / time;

[0062] Preferably, during washing, the liquid - solid ratio is controlled to be 3 - 5 ml:1 g, preferably 3.5 - 4 ml:1 g.

[0063] Furthermore, after S5, the iron phosphate dihydrate product is calcined at 550 - 650 °C for 1 - 6 h to obtain an iron phosphate product; preferably, it is calcined at 580 - 620 °C for 2 - 4 h; preferably, the purity of the iron phosphate product is ≥ 99.95 wt%.

[0064] Furthermore, after S5, the lithium - rich solution is subjected to impurity removal and lithium precipitation treatment to obtain a lithium salt product. Optionally, ion - exchange technology is used for impurity removal. Optionally, lithium precipitation treatment is carried out by adding a water - soluble carbonate or its solution to the lithium - rich solution. Optionally, the water - soluble carbonate includes one or more of sodium carbonate and potassium carbonate.

[0065] In the present invention, through oxidation treatment and alkaline leaching treatment simultaneously or sequentially, 95 - 99% of lithium elements enter the slag phase 1 in the form of lithium phosphate together with iron, most of the aluminum enters the liquid phase 1 in the form of meta - aluminate ions, and most of the phosphorus enters the liquid phase 1 in the form of phosphate ions, realizing good separation of aluminum and iron and solving the problem of aluminum - iron separation in traditional processes; then, acid leaching is carried out on the slag phase 1, so that iron, lithium, phosphorus, etc. in the slag phase are leached into the liquid phase 3, while insoluble impurities such as graphite enter the slag phase 3 and are separated; at the same time, the pH value of the liquid phase 1 is adjusted, so that amphoteric components such as aluminum in the liquid phase 1 precipitate and separate in the form of hydroxides, and then a liquid phase 2 rich in valuable elements such as phosphorus and lithium is obtained. Subsequently, the liquid phase 2 and the liquid phase 3 are mixed and iron is precipitated, so that iron and phosphorus can be recovered in the form of iron phosphate dihydrate, and a relatively pure lithium - rich solution can be obtained, which can be used for lithium precipitation to recover lithium to obtain battery - grade lithium salt products. Therefore, the present invention can fully recover phosphorus and lithium elements entering the alkali leaching solution (i.e., the liquid phase 1), realize simple wet - chemical aluminum removal, and effectively solve the problem of lithium and phosphorus entrainment loss caused thereby. The present invention not only has a high recovery rate of valuable metals, with the recovery rates of lithium, phosphorus, and iron reaching 99.0%, 97.4%, and 97.9% respectively, but also recovers relevant valuable elements as high - value products, has good economic benefits, and has broad prospects for large - scale industrialization.

[0066] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0067] (1) Through the comprehensive treatment method of the present invention, Li, Fe, P, Al and graphite in waste lithium iron phosphate materials can be effectively recycled and utilized. By improving the alkaline leaching process to optimize the aluminum removal effect, the aluminum removal rate reaches more than 98%, and the aluminum content of the alkaline leaching residue is reduced to 0.036%, which is significantly lower than the existing technical level. In addition, the impurity removal effect is good and phosphorus and iron can be fully recovered. Finally, the iron and phosphorus can be recycled and prepared into iron phosphate for batteries. The lithium-rich solution can be used for the preparation of battery-grade lithium carbonate after impurity removal and purification. Graphite is enriched in the slag phase 3 and can be sold as a by-product. The comprehensive treatment efficiency is high.

[0068] (2) Using weak alkali or a small amount of alkali leaching pretreatment to remove aluminum foil impurities in lithium iron phosphate materials is a common idea and method in lithium battery material recycling technology. Its main goal is to achieve selective leaching of Al under the premise of not leaching lithium iron phosphate as much as possible. However, this process technology is rarely used in actual industrial applications. This is because when alkali leaching is used to directly pretreat waste lithium iron phosphate powder with more impurities, there will inevitably be leaching losses of Li and P elements in the process. In order to avoid the loss of Li and P, dilute alkali is often used for pretreatment. Under this condition, on the one hand, the leached phosphate is easy to react with Al. 3+ On the other hand, aluminum may react with divalent iron or organic components in the waste to form a complex reaction or co-precipitation reaction and partially remain in the solid phase. Therefore, it is impossible to achieve high-selective separation of aluminum foil and lithium iron phosphate through alkaline leaching pretreatment. If the residual Al content in the solid phase is not further treated to remove impurities, the purity of the recovered product will inevitably fail to meet battery-grade standards.

[0069] The present invention adopts the method of oxidation alkaline leaching or high temperature oxidation pretreatment, first destroying the structure of lithium iron phosphate, converting divalent iron into trivalent iron through oxidation reaction, and effectively reducing the organic components in the system, so that Fe can better react with OH in the alkaline leaching step. - Combined with the separation of Al from the slag phase, the impact of organic impurities on the reaction is also reduced accordingly. In addition, the present invention uses an appropriate amount of alkali, under which the solubility of Al is maximized. At the same time, in conjunction with the alkali washing process, Al is fully leached into the liquid phase to achieve iron-aluminum separation. Due to the destruction of the lithium iron phosphate structure and the characteristic that iron preferentially combines with hydroxide, lithium is better combined with phosphate under strong alkaline conditions and remains in the solid phase. The loss of lithium in the leachate is relatively small, and because the liquid phase will eventually return and form a closed loop, the loss rate of lithium and phosphorus is very low, and the recovery rate can be stabilized to more than 99%. At the same time, the iron and phosphorus elements in the system are also balanced, which is significantly better than other recovery processes for the same type of raw materials. The aluminum hydroxide obtained by precipitation and aluminum removal and the crude graphite obtained by acid dissolution can also be sold as by-products.

[0070] (3) In the recycling process of the present invention, a process route of removing impurities from the leaching solution and then recycling it back to the main recycling system is adopted. On the one hand, it reduces the loss of lithium elements. On the other hand, it balances the iron and phosphorus in the system. At the same time, due to controlling the precipitation pH when precipitating iron phosphate, iron and phosphorus can be completely precipitated with almost no loss. Then, in the purification and washing steps, phosphoric acid washing water is used. While purifying iron phosphate, it directly improves the iron and phosphorus balance in iron phosphate and reduces the steps of synthesizing iron phosphate after conventionally supplementing iron sources and phosphorus sources.

[0071] (4) The iron phosphate product and lithium carbonate product obtained by the recycling of the present invention have high purity, can reach battery grade, have high recycling added value, and have high comprehensive recovery rates of lithium, iron, and phosphorus, and high economic feasibility;

[0072] (5) Most of the recycling processes of the comprehensive treatment method of the present invention are wet processes. The overall process operation is simple, easy to achieve industrial control, the types and dosages of reagents are few, the settling mother liquor is easy to treat, without complex operations, the overall process has high industrial feasibility, has no requirements for complex or precision equipment, and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 is a flow chart of a comprehensive treatment method for lithium iron phosphate waste materials of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] The present invention will be described in detail below with reference to the embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0075] Example 1

[0076] The comprehensive treatment method for waste lithium iron phosphate materials in this embodiment includes the following steps:

[0077] S1. Provide lithium iron phosphate waste powder;

[0078] Among them, in the lithium iron phosphate waste powder, the lithium content is 3.554%, the iron content is 30.013%, the phosphorus content is 17.692%, the aluminum content is 1.706%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 8.637%.

[0079] S2. Slurry 50 kg of the above-mentioned lithium iron phosphate waste powder with water at a liquid-solid ratio of 1:2 ml / g. Add sodium hydroxide flakes at an alkali dosage of 1.1 times the theoretical alkali consumption, and add the hydrogen peroxide at 1.5 times the theoretical amount of hydrogen peroxide with a concentration of 30% required for the complete oxidation of ferrous iron in the lithium iron phosphate waste. Add water to control the initial liquid-solid ratio of the system to 5:1 ml / g. The reaction is a self-exothermic leaching process without additional heating, and the temperature during the reaction can reach up to 90 °C. After reacting for 2 h, perform liquid-solid separation at 65 ± 10 °C to obtain liquid phase 1 and solid phase material;

[0080] After washing the above solid phase material 3 times with a sodium hydroxide solution with a pH value of 12.85 (each washing time is 20 min / time, and the temperature is 30 °C), perform solid-liquid separation to obtain residue phase 1 (Li content is 4.602%, Fe content is 38.859%, Al content is 0.0482%, P content is 5.329%).

[0081] S3. Adjust the pH value of liquid phase 1 to 7.2 with 5 mol / L sulfuric acid. After aging for 2.5 h, perform liquid-solid separation to obtain phosphate-rich liquid phase 2 and aluminum hydroxide-rich residue phase 2;

[0082] Mix the residue phase 1 with the second acid reagent. After leaching, obtain liquid phase 3 and graphite-rich residue phase 3;

[0083] Among them, the total amount of H + added in the second acid reagent is 1.05 times the theoretical acid consumption; control the leaching temperature to 80 °C and the leaching time to 1 h; the second acid reagent is 5 mol / L sulfuric acid.

[0084] S4. Mix the liquid phase 2 and liquid phase 3 obtained in S3 to obtain a mixed solution;

[0085] S5. Measure the contents of Ca, Mg, Mn, and Cu in the mixed solution, add a precipitant for chemical sedimentation and impurity removal, control the reaction temperature at 60 °C, the reaction time at 2 h, and perform liquid-solid separation to obtain the purified lithium iron phosphate solution;

[0086] Among them, the precipitant is sodium carbonate, the addition amount of the precipitant is 1.1 times the theoretical precipitant consumption, and the metal impurity ions are Ca ions, Mg ions, Mn ions, and Cu ions.

[0087] S6. Slowly adjust the pH value of the above purified lithium iron phosphate solution to 2.2 with a 3 mol / L sodium hydroxide solution. Control the stirring speed at 350 rpm during the pH adjustment process, control the pH value change rate <0.3 / min during the adjustment period. After adjusting to the target pH, continue stirring and stabilizing for 0.5 h, and then perform liquid-solid separation to obtain crude dihydrate ferric phosphate and lithium-rich solution.

[0088] After the lithium-rich solution is deeply purified by ion exchange technology, saturated sodium carbonate solution is added for lithium precipitation to obtain 5.08 kg of lithium carbonate product, and the mother liquor after lithium precipitation can still be recycled.

[0089] The crude iron phosphate dihydrate is washed 3 times with acidic wash water (phosphoric acid solution) with pH = 0.6 (the temperature of the acidic wash water is 95 °C, the liquid-solid ratio is controlled at 3:1 ml / g during washing, and the washing time for each time is 30 min) to obtain iron phosphate dihydrate. Then, the obtained iron phosphate dihydrate is placed in a muffle furnace and calcined at 600 °C for 3 h to obtain 38.89 kg of battery-grade anhydrous iron phosphate product.

[0090] In this example, the recovery rates of iron, phosphorus, and lithium elements are 97.027%, 96.823%, and 99.017% respectively.

[0091] Among them, the recovery rates of Fe and P elements are calculated according to the iron and phosphorus contents in liquid phase 2 and liquid phase 3; the recovery rate of Li is calculated according to the lithium content in the lithium-rich solution.

[0092] Example 2

[0093] The comprehensive treatment method of waste lithium iron phosphate materials in this example includes the following steps:

[0094] S1. Provide lithium iron phosphate waste powder;

[0095] Among them, in the lithium iron phosphate waste powder, the lithium content is 2.726%, the iron content is 21.96%, the phosphorus content is 13.45%, the aluminum content is 5.943%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 25.964%.

[0096] S2. Slurry 50 kg of the above lithium iron phosphate waste powder with water at a liquid-solid ratio of 1:1 ml / g, add 5 mol / L sodium hydroxide solution at an alkali dosage of 1.2 times the theoretical alkali consumption, and add NaClO3 at 1.2 times the theoretical amount required for complete oxidation of ferrous in the lithium iron phosphate waste. Add water to control the initial liquid-solid ratio of the system at 6:1 ml / g. The reaction is exothermic by itself, and the temperature during the reaction can reach up to 60 °C at most. After reacting for 3 h, heat to 90 °C and keep it stable for 30 min, and perform liquid-solid separation at 75 ± 10 °C to obtain liquid phase 1 and solid phase;

[0097] After washing the above solid phase 3 times with sodium hydroxide solution with a pH value of 12.03 (the washing time for each time is 30 min / time, and the temperature is 50 °C), perform solid-liquid separation to obtain slag phase 1 (the Li content is 3.375%, the Fe content is 27.192%, the Al content is 0.0361%, and the P content is 4.865%).

[0098] S3. Adjust the pH value of the liquid phase 1 to 6.85 with 3 mol / L hydrochloric acid. After aging for 3 h, perform solid-liquid separation to obtain the phosphate-rich liquid phase 2 and the aluminum hydroxide-rich residue phase 2;

[0099] Mix the residue phase 1 with the second acid reagent. After leaching, obtain the liquid phase 3 and the graphite-rich residue phase 3;

[0100] Among them, the total amount of H + in the added second acid reagent is 1.08 times the theoretical acid consumption; control the leaching temperature at 60 °C and the leaching time at 2 h; the second acid reagent is 6 mol / L hydrochloric acid.

[0101] S4. Mix the liquid phase 2 and the liquid phase 3 obtained in S3 to obtain a mixed solution;

[0102] S5. Measure the contents of Ca, Mg, Mn, and Cu in the mixed solution, add a precipitant for chemical sedimentation and impurity removal, control the reaction temperature at 70 °C and the reaction time at 1.5 h, and perform solid-liquid separation to obtain the purified lithium iron phosphate solution;

[0103] Among them, the precipitant is sodium carbonate, the addition amount of the precipitant is 1.3 times the theoretical precipitant consumption, and the metal impurity ions are Ca ions, Mg ions, Mn ions, and Cu ions.

[0104] S6. Slowly adjust the pH value of the above-mentioned purified lithium iron phosphate solution to 2.0 with a 2 mol / L sodium hydroxide solution. During the pH adjustment process, control the stirring speed at 400 rpm, control the pH value change rate <0.3 / min during the adjustment, and after adjusting to the target pH, continue to stir and stabilize for 1 h, then perform liquid-solid separation to obtain crude iron phosphate dihydrate and lithium-rich solution.

[0105] After the lithium-rich solution is deeply purified by ion exchange technology, add saturated sodium carbonate solution for lithium precipitation to obtain 4.03 kg of lithium carbonate product. The mother liquor after lithium precipitation can still be recycled.

[0106] Wash the crude iron phosphate dihydrate 4 times with acidic wash water (phosphoric acid solution) with pH = 0.8 (the temperature of the acidic wash water is 85 °C, control the liquid-solid ratio at 4:1 ml / g during washing, and the washing time for each time is 30 min) to obtain iron phosphate dihydrate. Then place the obtained iron phosphate dihydrate in a muffle furnace, heat it to 650 °C and calcine for 2 h to obtain 28.53 kg of battery-grade anhydrous iron phosphate product.

[0107] In this example, the recovery rates of iron, phosphorus, and lithium elements are 97.912%, 97.416%, and 98.823% respectively.

[0108] Among them, the recovery rates of Fe and P elements are calculated according to the iron and phosphorus contents in the liquid phase 2 and the liquid phase 3; the recovery rate of Li is calculated according to the lithium content in the lithium-rich solution.

[0109] Example 3

[0110] The comprehensive treatment method of the waste lithium iron phosphate material in this example includes the following steps:

[0111] S1. Provide lithium iron phosphate waste powder;

[0112] Among them, in the lithium iron phosphate waste powder, the lithium content is 3.473%, the iron content is 31.78%, the phosphorus content is 19.82%, the aluminum content is 0.93%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 2.744%.

[0113] S2. After roasting 50 kg of the above lithium iron phosphate waste powder in an air atmosphere at 600 °C for 3 h, add a 5 mol / L sodium hydroxide solution according to 1.2 times the theoretical alkali consumption, and add water to control the initial liquid-solid ratio of the system to 6:1 ml / g. The reaction is a self-exothermic leaching process without additional heating, and the reaction temperature can reach 60 °C. After reacting for 2.5 h, heat to 95 °C and keep it stable for 20 min, and then carry out liquid-solid separation at 80 ± 10 °C to obtain the liquid phase 1 and the solid phase;

[0114] After washing the above solid phase with a sodium hydroxide solution with a pH value of 13.65 four times (each washing time is 20 min / time, and the temperature is 35 °C), carry out solid-liquid separation to obtain the slag phase 1 (the lithium content is 4.259%, the iron content is 38.976%, the aluminum content is 0.055%, and the phosphorus content is 4.91%).

[0115] S3. Adjust the pH value of the liquid phase 1 to 7.5 with 5 mol / L nitric acid, age for 4 h, and then carry out liquid-solid separation to obtain the phosphate-rich liquid phase 2 and the aluminum hydroxide-rich slag phase 2;

[0116] Mix the slag phase 1 with the second acid reagent, and after leaching, obtain the liquid phase 3 and the graphite-rich slag phase 3;

[0117] Among them, the total amount of H + in the added second acid reagent is 1.06 times the theoretical acid consumption; control the leaching temperature to 95 °C and the leaching time to 1 h; the second acid reagent is 6 mol / L nitric acid.

[0118] S4. Mix the liquid phase 2 and the liquid phase 3 obtained in S3 to obtain a mixed solution;

[0119] S5. Determine the contents of Ca, Mg, Mn, and Cu in the mixed solution, add a precipitant for chemical sedimentation and impurity removal, control the reaction temperature at 70 °C, the reaction time at 2 h, and perform solid-liquid separation to obtain the purified solution of lithium iron phosphate.

[0120] Among them, the precipitant is sodium carbonate, the addition amount of the precipitant is 1.3 times the theoretical amount of the precipitant, and the metal impurity ions are Ca ions, Mg ions, Mn ions, and Cu ions.

[0121] S6. Slowly adjust the pH value of the above-mentioned purified solution of lithium iron phosphate to 2.5 with a sodium hydroxide solution with a concentration of 4 mol / L. During the pH adjustment process, control the stirring speed at 350 rpm, control the pH change rate < 0.3 / min during the adjustment, and after adjusting to the target pH, continue to stir and stabilize for 1.5 h, then perform solid-liquid separation to obtain crude iron phosphate dihydrate and a lithium-rich solution.

[0122] After the lithium-rich solution is deeply purified by ion exchange technology, add saturated sodium carbonate solution for lithium precipitation to obtain 5.33 kg of lithium carbonate product. The mother liquor after lithium precipitation can still be recycled.

[0123] Wash the crude iron phosphate dihydrate 4 times with acidic wash water (phosphoric acid solution) with pH = 0.5 (the temperature of the acidic wash water is 95 °C, control the liquid-solid ratio at 4:1 ml / g during washing, and the washing time for each time is 30 min) to obtain iron phosphate dihydrate. Then place the obtained iron phosphate dihydrate in a muffle furnace, heat it to 600 °C and calcine for 3 h to obtain 39.03 kg of battery-grade anhydrous iron phosphate product.

[0124] In this example, the recovery rates of iron, phosphorus, and lithium elements are 93.628%, 97.234%, and 98.932% respectively.

[0125] Among them, calculate the recovery rates of Fe and P elements according to the iron and phosphorus contents in liquid phase 2 and liquid phase 3; calculate the recovery rate of Li according to the lithium content in the lithium-rich solution.

[0126] Example 4

[0127] The comprehensive treatment method of the waste lithium iron phosphate material in this example includes the following steps:

[0128] S1. Provide waste lithium iron phosphate powder;

[0129] Among them, in the waste lithium iron phosphate powder, the lithium content is 2.922%, the iron content is 25.14%, the phosphorus content is 15.06%, the aluminum content is 4.701%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 20.979%.

[0130] S2. After oxidizing and roasting 50 kg of the above lithium iron phosphate waste powder in an air atmosphere at 620 °C for 5 h, add potassium hydroxide solid with an alkali dosage of 1.15 times the theoretical alkali consumption, and add water to control the initial liquid-solid ratio of the system to 5:1 ml / g. The reaction is a self-exothermic leaching process without additional heating, and the temperature during the reaction can reach up to 90 °C at most. After reacting for 2 h, heat to 95 °C and keep it stable for 10 min, and perform liquid-solid separation at 75 ± 10 °C to obtain liquid phase 1 and solid phase substances;

[0131] After washing the above solid phase substances 4 times with a potassium hydroxide solution with a pH value of 13.08 (each washing time is 30 min / time, and the temperature is 35 °C), perform solid-liquid separation to obtain residue phase 1 (Li content is 3.696%, Fe content is 31.798%, Al content is 0.056%, and P content is 5.85%).

[0132] S3. Adjust the pH value of liquid phase 1 to 7.05 with 5 mol / L sulfuric acid. After aging for 1.5 h, perform solid-liquid separation to obtain liquid phase 2 rich in phosphate and residue phase 2 rich in aluminum hydroxide;

[0133] Mix the residue phase 1 with the second acid reagent. After leaching, obtain liquid phase 3 and residue phase 3 rich in graphite;

[0134] Among them, the total amount of H + in the added second acid reagent is 1.05 times the theoretical acid consumption; control the leaching temperature to 95 °C and the leaching time to 1 h; the second acid reagent is 6 mol / L sulfuric acid.

[0135] S4. Mix the liquid phase 2 and liquid phase 3 obtained in S3 to obtain a mixed solution;

[0136] S5. Measure the contents of Ca, Mg, Mn, and Cu in the mixed solution, add a precipitant for chemical sedimentation and impurity removal, control the reaction temperature at 80 °C, the reaction time at 2 h, and perform solid-liquid separation to obtain the purified lithium iron phosphate solution;

[0137] Among them, the precipitant is sodium carbonate, the addition amount of the precipitant is 1.25 times the theoretical precipitant consumption, and the metal impurity ions are Ca ions, Mg ions, Mn ions, and Cu ions.

[0138] S6. Slowly adjust the pH value of the above purified lithium iron phosphate solution to 2.0 with a 1 mol / L sodium hydroxide solution. During the pH adjustment process, control the stirring speed to 450 rpm, control the pH value change rate < 0.3 / min during the adjustment, and after adjusting to the target pH, continue to stir and stabilize for 1 h, and then perform liquid-solid separation to obtain crude dihydrate iron phosphate and lithium-rich solution.

[0139] After the lithium-rich solution is deeply purified by ion exchange technology, saturated sodium carbonate solution is added for lithium precipitation, and 4.21 kg of lithium carbonate product is obtained. The mother liquor after lithium precipitation can still be recycled.

[0140] The crude iron phosphate dihydrate was washed 5 times with acidic wash water (phosphoric acid solution) with pH = 0.65 (the temperature of the acidic wash water was 75 °C, the liquid-solid ratio was controlled at 4:1 ml / g during washing, and the washing time for each time was 20 min) to obtain iron phosphate dihydrate. Then, the obtained iron phosphate dihydrate was placed in a muffle furnace and calcined at 580 °C for 6 h to obtain 30.66 kg of battery-grade anhydrous iron phosphate product.

[0141] In this example, the recovery rates of iron, phosphorus, and lithium elements were 92.947%, 96.721%, and 98.249% respectively.

[0142] Among them, the recovery rates of Fe and P elements were calculated according to the iron and phosphorus contents in liquid phase 2 and liquid phase 3; the recovery rate of Li was calculated according to the lithium content in the lithium-rich solution.

[0143] Detected according to HG / T 4701-2021, the component and purity analysis results of the anhydrous iron phosphate products obtained in Examples 1-4 are shown in Table 1. It can be seen from the table that the iron phosphate products recovered in the present invention meet the requirements of the industry standard HG / T 4701-2021 and reach the requirements of battery grade.

[0144] Table 1 Component and purity analysis results of anhydrous iron phosphate products

[0145] Group Fe P Fe:P Al Na S Ca K Mg Mn Purity Industry Standard 35.7～36.7 20.0～21.1 0.96～1.0 0.05 0.02 0.03 0.01 0.02 0.06 0.1 Example 1 36.62 20.57 0.9855 0.0129 0.0058 0.007 0.003 0.001 0.0012 0 99.969 Example 2 36.839 20.412 0.9991 0.0094 0.0049 0.003 0.003 0.001 0.0013 0 99.977 Example 3 36.639 20.587 0.9852 0.0181 0.0092 0.007 0.001 0.001 0.0015 0 99.962 Example 4 36.591 20.362 0.9948 0.00928 0.0073 0.003 0.002 0 0.0012 0.001 99.976

[0146] In Table 1, except that "Fe:P" represents the molar ratio of Fe and P, the units of other columns are all %.

[0147] The component and purity analysis results of the lithium carbonate products obtained in Examples 1-4 are shown in Table 1. It can be seen from the table that the lithium carbonate products recovered in the present invention all meet the requirements of the national standard GB / T 6678-2003 and reach the requirements of battery grade.

[0148] Table 2 Component and purity analysis results of lithium carbonate products (unit: %)

[0149] Group Na Ca Mg Fe Zn Pb Cu Al Mn Ni Cr P B Si <![CDATA[SO4 2- > Purity National Standard ≤0.025 ≤0.005 ≤0.008 ≤0.001 ≤0.0003 ≤0.0003 ≤0.0003 ≤0.001 ≤0.0002 ≤0.001 ≤0.003 ≤0.005 ≤0.005 ≤0.003 ≤0.008 ≥99.5 Example 1 0.0182 0.0015 0.0002 0.0005 0.0001 0.0001 0 0.0001 0 0 0 0.004 0.0022 0.0004 0.0065 99.5 Example 2 0.0142 0.0019 0.0002 0.0008 0.0001 0.0002 0 0.0001 0 0 0 0.002 0.0023 0.0004 0.0057 99.5 Example 3 0.0150 0.0021 0.0003 0.0003 0.0001 0.0001 0 0.0001 0 0 0 0.007 0.0018 0.0006 0.0076 99.6 Example 4 0.0182 0.0024 0.0007 0.0009 0.0002 0.0002 0 0.0001 0 0 0 0.005 0.0024 0.0003 0.0065 99.8

[0150] Comparative Example 1

[0151] The comprehensive treatment method of the waste lithium iron phosphate material in this comparative example includes the following steps:

[0152] S1. Provide lithium iron phosphate waste powder;

[0153] Among them, in the lithium iron phosphate waste powder, the lithium content is 3.91%, the iron content is 31.883%, the phosphorus content is 18.535%, the aluminum content is 2.5%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 4.253%.

[0154] S2. Slurry the above lithium iron phosphate waste powder with water at a liquid-solid ratio of 1:2 ml / g. Add sodium hydroxide flakes at an alkali dosage of 1.2 times the theoretical alkali consumption. Do not add an oxidant. Add water to control the initial liquid-solid ratio of the system to 5:1 ml / g. The reaction is a self-exothermic leaching process without additional heating. The highest temperature during the reaction process can reach 90°C. After reacting for 2 h, perform liquid-solid separation at 65 ± 10°C to obtain liquid phase 1 and solid phase substances.

[0155] Wash the above solid phase substances 3 times (each washing time is 20 min / time, and the temperature is 30°C) with a 0.1 mol / L sodium hydroxide solution with a pH value of 13.00, and then perform solid-liquid separation to obtain slag phase 1 (the lithium content is 4.808%, the iron content is 39.979%, the aluminum content is 0.18%, and the phosphorus content is 7.341%).

[0156] Example 5

[0157] Repeat Comparative Example 1, with the only difference being that the hydrogen peroxide is added at 0.9 times the theoretical amount of hydrogen peroxide with a concentration of 30% required to completely oxidize ferrous iron in the lithium iron phosphate waste.

[0158] After testing, in slag phase 1, the lithium content is 5.101%, the iron content is 41.141%, the aluminum content is 0.091%, and the phosphorus content is 7.295%.

[0159] Example 6

[0160] Repeat Comparative Example 1, with the only difference being that the hydrogen peroxide is added at 1 times the theoretical amount of hydrogen peroxide with a concentration of 30% required to completely oxidize ferrous iron in the lithium iron phosphate waste.

[0161] After testing, in slag phase 1, the lithium content is 5.001%, the iron content is 40.834%, the aluminum content is 0.118%, and the phosphorus content is 7.565%.

[0162] Example 7

[0163] Repeat Comparative Example 1, with the only difference being that the hydrogen peroxide is added at 2 times the theoretical amount of hydrogen peroxide with a concentration of 30% required to completely oxidize ferrous iron in the lithium iron phosphate waste.

[0164] After testing, in slag phase 1, the lithium content is 5.069%, the iron content is 40.976%, the aluminum content is 0.11%, and the phosphorus content is 7.438%.

[0165] Example 8

[0166] Repeat Comparative Example 1, except that: hydrogen peroxide is added in an amount 2.1 times the theoretical amount of hydrogen peroxide with a concentration of 30% required to completely oxidize ferrous iron in the lithium iron phosphate waste.

[0167] Upon detection, in the slag phase 1, the Li content is 5.071%, the Fe content is 41.013%, the Al content is 0.106%, and the P content is 7.477%.

[0168] By comparison, it can be seen that the addition of an oxidant can effectively reduce the aluminum content in the slag phase 1, improve the separation effect of aluminum from iron and lithium, and prepare for the subsequent preparation of high-purity iron phosphate products.

[0169] Example 9

[0170] The comprehensive treatment method of the waste lithium iron phosphate material in this example includes the following steps:

[0171] S1. Provide lithium iron phosphate waste powder;

[0172] Among them, in the lithium iron phosphate waste powder, the lithium content is 3.91%, the iron content is 31.883%, the phosphorus content is 18.535%, the aluminum content is 2.5%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 4.253%.

[0173] S2. After oxidizing and roasting the above-mentioned lithium iron phosphate waste powder in an air atmosphere at 600 °C for 3 h, adjust the slurry with water at a liquid-solid ratio of 1:2 ml / g, add sodium hydroxide flake alkali at an alkali dosage of 1.0 times the theoretical alkali consumption, add water to control the initial liquid-solid ratio of the system to 5:1 ml / g. The reaction is a self-exothermic leaching process without additional heating, and the temperature during the reaction can reach a maximum of 90 °C. After reacting for 2 h, perform liquid-solid separation at 65 ± 10 °C to obtain liquid phase 1 and solid phase substances;

[0174] Wash the above-mentioned solid phase substances 3 times with a 0.1 mol / L sodium hydroxide solution with a pH value of 13.00 (each washing time is 20 min / time, and the temperature is 30 °C), then perform solid-liquid separation to obtain slag phase 1 (Li content is 5.134%, Fe content is 37.462%, Al content is 0.074%, P content is 5.169%).

[0175] Among them, the theoretical alkali consumption is the theoretical total amount of OH required to completely convert iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 respectively. - -

[0176] Example 10

[0177] ​​Repeat Example 9, with the only difference being that in S2, sodium hydroxide flakes are added at an alkali dosage of 1.3 times the theoretical alkali consumption.

[0178] Upon detection, in the slag phase 1, the Li content is 5.148%, the Fe content is 37.583%, the Al content is 0.043%, and the P content is 4.942%.

[0179] Example 11

[0180] Repeat Example 9, with the only difference being that in S2, sodium hydroxide flakes are added at an alkali dosage of 1.4 times the theoretical alkali consumption.

[0181] Upon detection, in the slag phase 1, the Li content is 5.293%, the Fe content is 38.912%, the Al content is 0.057%, and the P content is 5.101%.

[0182] It can be seen that by pre - performing oxidative roasting and then alkaline leaching, compared with alkali leaching oxidation, the separation of aluminum and iron in the alkaline leaching step is further optimized, laying a foundation for subsequent steps. Although the prior art involves pre - roasting followed by alkaline leaching, its roasting is carried out in a non - oxidative atmosphere, and its roasting process requires avoiding the oxidation of elemental aluminum into aluminum oxide. Therefore, the roasting idea is significantly different from the above - mentioned treatment idea of the present invention.

[0183] Example 12

[0184] Repeat Example 9, with the only difference being that in S2, the oxidative roasting temperature is 500 °C, and sodium hydroxide flakes are added at an alkali dosage of 1.2 times the theoretical alkali consumption.

[0185] Upon detection, in the slag phase 1, the Li content is 5.222%, the Fe content is 38.257%, the Al content is 0.089%, and the P content is 5.96%.

[0186] Example 13

[0187] Repeat Example 9, with the only difference being that in S2, the oxidative roasting temperature is 550 °C, and sodium hydroxide flakes are added at an alkali dosage of 1.2 times the theoretical alkali consumption.

[0188] Upon detection, in the slag phase 1, the Li content is 5.253%, the Fe content is 38.533%, the Al content is 0.076%, and the P content is 5.39%.

[0189] Example 14

[0190] Repeat Example 9, with the only difference being that in S2, the oxidative roasting temperature is 650 °C, and sodium hydroxide flakes are added at an alkali dosage of 1.2 times the theoretical alkali consumption.

[0191] After detection, in slag phase 1, the Li content is 5.268%, the Fe content is 38.673%, the Al content is 0.065%, and the P content is 5.28%.

[0192] Comparative Example 2

[0193] Repeat Example 9, with the only difference being that in S2, the oxidation roasting temperature is 700 °C, and sodium hydroxide flake is added with an alkali dosage of 1.2 times the theoretical alkali consumption.

[0194] After detection, in slag phase 1, the Li content is 5.505%, the Fe content is 40.823%, the Al content is 0.328%, and the P content is 8.97%.

[0195] It can be seen that the increase in the oxidation roasting temperature helps to reduce the aluminum and phosphorus contents in slag phase 1 and increase the lithium content. However, it is different from the general rule that the higher the temperature, the more conducive to the progress of relevant reactions. But when the oxidation roasting temperature rises to 700 °C, it will instead lead to an increase in the aluminum and phosphorus contents in the slag, which is bound to be unfavorable to the smooth progress of subsequent steps. The possible reason is that after the temperature rises to a certain extent, the roasted materials melt, and the agglomeration phenomenon becomes more serious, which is not conducive to the full leaching of the materials during the alkaline leaching process.

[0196] Example 15

[0197] Repeat Example 9, with the only difference being that in S2, the oxidation roasting time is 1 h, and sodium hydroxide flake is added with an alkali dosage of 1.2 times the theoretical alkali consumption.

[0198] After detection, in slag phase 1, the Li content is 5.573%, the Fe content is 37.201%, the Al content is 0.039%, and the P content is 8.5%.

[0199] Example 16

[0200] Repeat Example 9, with the only difference being that in S2, the oxidation roasting time is 2 h, and sodium hydroxide flake is added with an alkali dosage of 1.2 times the theoretical alkali consumption.

[0201] After detection, in slag phase 1, the Li content is 5.262%, the Fe content is 36.774%, the Al content is 0.045%, and the P content is 7.518%.

[0202] Example 17

[0203] Repeat Example 9, with the only difference being that in S2, the oxidation roasting time is 6 h, and sodium hydroxide flake is added with an alkali dosage of 1.2 times the theoretical alkali consumption.

[0204] After detection, in slag phase 1, the Li content is 5.135%, the Fe content is 37.148%, the Al content is 0.049%, and the P content is 4.639%.

[0205] Example 18

[0206] Repeat Example 9, with the only difference being that in S2, the oxidative roasting time is 7 h, and sodium hydroxide flakes are added at an alkali dosage of 1.2 times the theoretical alkali consumption.

[0207] Upon detection, in slag phase 1, the Li content is 5.128%, the Fe content is 36.125%, the Al content is 0.051%, and the P content is 3.952%.

[0208] Comparative Example 3

[0209] The comprehensive treatment method for the waste lithium iron phosphate material in this comparative example includes the following steps:

[0210] S1. Provide lithium iron phosphate waste powder;

[0211] Among them, in the lithium iron phosphate waste powder, the lithium content is 3.18%, the iron content is 32.349%, the phosphorus content is 18.763%, the aluminum content is 0.157%, and the total content of impurities (Mn, Mg, Cu, Ca, graphite) is 23.182%.

[0212] S2. Slurry the above lithium iron phosphate waste powder with water at a liquid-solid ratio of 1:2 ml / g, add sodium hydroxide solution at an alkali dosage of 1.2 times the theoretical alkali consumption, add water to control the initial liquid-solid ratio of the system to 5:1 ml / g, react at room temperature for 2 h, and then perform liquid-solid separation at 65 ± 10 °C to obtain liquid phase 1 and solid phase material;

[0213] After washing the above solid phase material 3 times with a sodium hydroxide solution with a pH value of 12.85 (each washing time is 20 min / time, and the temperature is 30 °C), perform solid-liquid separation to obtain slag phase 1 (Li content is 2.27%, Fe content is 30.25%, Al content is 0.2%, and P content is 9.78%).

[0214] Among them, the theoretical alkali consumption is the theoretical total amount of OH - required for completely converting iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 - respectively.

[0215] It can be seen that without oxidation treatment, that is, alkaline leaching is carried out at room temperature, the aluminum content in slag phase 1 reaches 0.2%, the dissolution effect of aluminum is poor, and the separation effect of aluminum and iron is not ideal.

[0216] The content illustrated in the above embodiments should be understood that these embodiments are only used to more clearly illustrate the present invention, rather than to limit the scope of the present invention. After reading the present invention, various equivalent forms of modification made by those skilled in the art to the present invention all fall within the scope defined by the appended claims of this application.

Claims

1. A comprehensive treatment method for lithium iron phosphate waste, characterized in that, It includes the following steps: S1. Simultaneously or sequentially perform oxidation treatment and alkaline leaching treatment on the lithium iron phosphate waste to be treated, followed by solid-liquid separation to obtain a solid phase 1 and a liquid phase 1; S2. Adjust the pH value of the liquid phase 1 to 6.5 - 8 with a first acid reagent, and after aging, perform solid-liquid separation to obtain a phosphate-rich liquid phase 2 and an aluminum hydroxide-rich solid phase 2; Mix the solid phase 1 with a second acid reagent, and after leaching, obtain a liquid phase 3 and a solid phase 3; S3. Mix the liquid phase 2 and the liquid phase 3 to obtain a mixed solution; S4. After chemically settling and removing impurities from the mixed solution, perform solid-liquid separation to obtain a liquid phase 4; S5. After performing iron precipitation treatment on the liquid phase 4, perform solid-liquid separation to obtain a dihydrate iron phosphate product and a lithium-rich solution.

2. The comprehensive processing method according to claim 1, wherein In S1, the oxidation treatment includes one or more of oxidative roasting and oxidative leaching; Preferably, the temperature of oxidative roasting is 500 - 680 °C, more preferably 550 - 650 °C, still more preferably 580 - 620 °C, and the time is 0.5 - 7 h, more preferably 0.75 - 6 h, still more preferably 1 - 4 h; More preferably, oxidative roasting is carried out in an air atmosphere or an oxygen atmosphere; Preferably, mix the lithium iron phosphate waste to be treated with an oxidant in water for oxidative leaching; More preferably, the oxidant includes one or more of hydrogen peroxide, water-soluble chlorates, and oxygen; More preferably, the addition amount of the oxidant is 0.8 - 2.5 times, more preferably 0.85 - 2.1 times, still more preferably 0.9 - 2.0 times, and also preferably 1.0 - 1.5 times of the theoretical amount required to completely oxidize divalent iron in the lithium iron phosphate waste to trivalent iron; More preferably, the water-soluble chlorate is one or more of sodium chlorate, potassium chlorate, and ammonium chlorate; Preferably, an alkali or its solution is mixed in for alkaline leaching treatment; more preferably, the alkali includes one or more of sodium hydroxide, potassium hydroxide, and ammonia water; more preferably, the total amount of OH - in the added alkali is 1.0 - 1.5 times, preferably 1.1 - 1.4 times, more preferably 1.2 - 1.35 times the theoretical alkali consumption, and the theoretical alkali consumption is the theoretical total amount of OH - required to completely convert iron and Al in the lithium iron phosphate waste into iron hydroxide and AlO2 - respectively; Preferably, when performing oxidative leaching and / or alkaline leaching treatment, control the initial liquid-solid ratio of the reaction system to be 4 - 8 ml:1 g, preferably 5 - 6 ml:1 g; Preferably, control the initial liquid-solid ratio of the reaction system by adding water; Preferably, the reaction time of oxidative leaching and / or alkaline leaching treatment is 1 - 5 h, more preferably 2 - 3 h; Preferably, when performing solid-liquid separation, control the temperature of the filtration system ≥50 °C, preferably 70 - 90 °C.

3. The comprehensive processing method according to claim 1, wherein In S1, after solid-liquid separation, wash the obtained solid phase with a dilute alkali solution and then perform further solid-liquid separation to obtain a solid phase 1; Preferably, the pH value of the dilute alkali solution > 11, more preferably 11.1 - 14, still more preferably 11.5 - 13.5; Preferably, the number of washing times is 2 - 5 times, the washing time is 5 - 60 min / time, preferably 20 - 30 min / time, and the washing temperature is 10 - 50 °C, preferably 15 - 45 °C; Preferably, the dilute alkali solution contains one or more of sodium hydroxide and potassium hydroxide.

4. The integrated processing method according to claim 1, characterized in that In S2, adjust the pH value of the liquid phase 1 to 6.8 - 7.5 with a first acid reagent; Preferably, the first acid reagent includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; Preferably, the aging time is 1 - 5 h, more preferably 3 - 5 h.

5. The integrated processing method according to claim 1, characterized in that In S2, the total amount of H in the added second acid reagent is 1 - 1.2 times, preferably 1 - 1.15 times, more preferably 1.02 - 1.08 times the theoretical acid consumption; where the theoretical acid consumption is the theoretical total amount of H required to completely dissolve Li and Fe in slag phase 1. + + ​ Preferably, the leaching temperature is controlled at 50 - 95°C, preferably 55 - 90°C, and the leaching time is 0.5 - 3.5 h, preferably 1.5 - 2 h; Preferably, the second acid reagent includes one or more of hydrochloric acid, sulfuric acid, and nitric acid.

6. The integrated processing method according to any one of claims 1-5, characterized in that In S4, the mixed solution is mixed with a precipitant for chemical sedimentation and impurity removal; Among them, the precipitant is a water-soluble carbonate and its hydrate and / or a water-soluble bicarbonate and its hydrate; preferably, the water-soluble carbonate includes one or several of sodium carbonate, ammonium carbonate, and potassium carbonate, and the water-soluble bicarbonate includes one or several of sodium bicarbonate, ammonium bicarbonate, and potassium bicarbonate; more preferably, the addition amount of the precipitant is 1.1 - 1.5 times the theoretical amount of the precipitant, and further preferably 1.2 - 1.4 times, where the theoretical amount of the precipitant is the theoretical amount of the precipitant required to completely convert the metal impurity ions in the mixed solution into precipitates, and the metal impurity ions are one or several of Ca ions, Mg ions, Mn ions, and Cu ions; Preferably, during the chemical sedimentation and impurity removal process, the reaction temperature is controlled ≥50°C, preferably 55 - 95°C, and the reaction time is 1 - 2 h.

7. The integrated processing method according to any one of claims 1-5, characterized in that, In S5, OH is adopted - After adjusting the pH value of the liquid phase 4 to 2-3 with an alkali solution having a concentration of <5 mol / L and stirring for 0.5-2 h, preferably for 0.6-1 h, solid-liquid separation is carried out to obtain crude iron phosphate dihydrate and a lithium-rich solution; after washing the crude iron phosphate dihydrate, an iron phosphate dihydrate product is obtained. Preferably, the OH in the lye - has a concentration of 2 - 4 mol / L; Preferably, the pH value of the liquid phase 4 is adjusted to 2.1 - 2.5; Preferably, during the pH value adjustment process, the change rate of the pH value is controlled <0.3 / min, and more preferably 0.1 - 0.2 / min; Preferably, during the pH value adjustment process, the stirring rate is controlled ≥300 rpm, preferably 310 - 500 rpm; Preferably, the crude iron phosphate dihydrate is washed with acidic wash water having a pH value of 0.5 - 2; Preferably, the pH value of the acidic wash water is 0.7 - 1; Preferably, the temperature of the acidic wash water is ≥75°C, preferably 85 - 95°C; Preferably, the number of washing times is 3 - 8 times, preferably 5 - 7 times, and the washing time is 10 - 60 min / time, preferably 20 - 30 min / time; Preferably; during washing, the liquid-solid ratio is controlled at 3 - 5 ml:1 g, preferably 3.5 - 4 ml:1 g.

8. The integrated processing method according to any one of claims 1-5, characterized in that, After S5, the iron phosphate dihydrate product is calcined at 550 - 650°C for 1 - 6 h to obtain an iron phosphate product; preferably, it is calcined at 580 - 620°C for 2 - 4 h; preferably, the purity of the iron phosphate product is ≥99.95 wt%.

9. The integrated processing method according to any one of claims 1-5, characterized in that, After S5, the lithium-rich solution is subjected to impurity removal and lithium precipitation treatment to obtain a lithium salt product.

10. The integrated processing method according to any one of claims 1-5, characterized in that, In S1, in the lithium iron phosphate waste, the lithium content is 0.5 - 5%, the iron content is 15 - 35%, the phosphorus content is 5 - 25%, the aluminum content is 0.1 - 10%, and the total impurity content is 1 - 30%; Preferably, in the lithium iron phosphate waste, the lithium content is 1.5 - 4.5%, the iron content is 18 - 32%, the phosphorus content is 8 - 22%, the aluminum content is 0.5 - 8%, and the total impurity content is 5 - 25%; Preferably, in the lithium iron phosphate waste, the lithium content is 2 - 4%, the iron content is 20 - 30%, the phosphorus content is 10 - 20%, the aluminum content is 1 - 7%, and the total impurity content is 8 - 22%; Among them, the impurities include one or more of Mn, Mg, Cu, Ca, and graphite.

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