Separation and recovery method for phosphorus and iron in lithium extraction slag

Abstract

The invention discloses a method for separating and recycling phosphorus and iron in lithium extraction slag, and relates to the technical field of battery recycling. The method comprises the following steps: mixing and leaching the lithium extraction slag and sulfuric acid, and filtering to obtain iron-containing filtrate; reducing ferric iron in the iron-containing filtrate into ferrous iron, and filtering to obtain a first mixed solution; adding battery black powder into the first mixed solution, mixing and leaching, and filtering to obtain a second mixed solution; ferrous sulfate in the second mixed solution is separated out in a precipitation mode through the alcohol precipitation effect, and ferrous sulfate precipitate is obtained; removing impurities from the mother liquor, and extracting to obtain a phosphoric acid solution and a lithium-containing solution; after phosphoric acid is supplemented into the lithium-containing solution, the pH is adjusted to be 8-10, and battery-grade lithium phosphate precipitates are obtained. According to the method, the filtrate containing phosphorus and ferric iron is converted into the second mixed solution containing phosphorus, ferrous iron and lithium, then iron in the leachate is separated out, and the follow-up impurity removal difficulty is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of battery recycling technology, and in particular to a method for separating and recovering phosphorus and iron from lithium extraction slag. Background Technology

[0002] Lithium iron phosphate (LFP) batteries possess excellent cycle performance, high safety, and low cost, leading to their rapid growth in application in fields such as new energy vehicles. With the booming development of the new energy industry and the increasing number of new energy vehicles deployed annually, a large number of waste LFP batteries are generated each year. These waste LFP battery materials contain abundant lithium, iron, and phosphorus elements, making them important secondary energy sources.

[0003] Waste lithium iron phosphate batteries have low lithium content and high iron and phosphorus content, but lithium has high recycling value. In traditional recycling processes, only lithium is usually recovered as high-value lithium carbonate or lithium hydroxide, and the remaining material is treated as waste residue, collectively known as lithium extraction slag. Lithium extraction slag contains high levels of iron and phosphorus, but removing impurities during iron and phosphorus recovery is difficult, and significant amounts of phosphorus and iron are lost during the removal process. Therefore, lithium extraction slag is basically disposed of as waste, which not only fails to maximize the utilization of iron and phosphorus resources but also causes significant environmental pollution.

[0004] Therefore, in order to improve resource utilization and reduce environmental pollution, providing a method for separating and recovering phosphorus and iron from lithium extraction slag is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention discloses a method for separating and recovering phosphorus and iron from lithium extraction slag, in order to solve the technical problems of high difficulty in removing impurities during the recovery of iron and phosphorus from lithium extraction slag, and significant loss of phosphorus and iron during the impurity removal process.

[0006] To solve the above problems, the present invention adopts the following technical solution: The present invention provides a method for separating and recovering phosphorus and iron from lithium extraction slag, comprising the following steps: Step 100: The lithium extraction residue is mixed with sulfuric acid for leaching, and after solid-liquid separation, an iron-containing filtrate and the first filter residue are obtained; Step 200: Add a reducing agent to the iron-containing filtrate to reduce ferric iron to ferrous iron, and obtain the first mixed solution after solid-liquid separation; Step 300: Add battery black powder to the first mixed solution, and mix and leach the lithium-containing slag with the first mixed solution. After solid-liquid separation, a second mixed solution and a second filter residue are obtained. Step 400: Control the pH of the second mixed solution to 0.5 or below, add alcohol to the second mixed solution, and use alcohol precipitation to precipitate the ferrous sulfate in the second mixed solution. After solid-liquid separation, ferrous sulfate precipitate and mother liquor are obtained. Step 500: After evaporating and concentrating the mother liquor, add a purification agent to the mother liquor to remove impurities in the solution, and then obtain a phosphoric acid solution and a lithium-containing solution by extraction; Step 600: After adding phosphoric acid to the lithium-containing solution, adjust the pH to 8-10 and obtain battery-grade lithium phosphate precipitate.

[0007] The technical solution adopted in this invention can achieve the following beneficial effects: Firstly, the present invention provides a method for separating and recovering phosphorus and iron from lithium extraction slag. Through the steps of leaching lithium extraction slag, reducing trivalent iron with reducing agents, and adding battery black powder, the filtrate containing phosphorus and trivalent iron can be converted into a second mixed solution containing phosphorus, ferrous iron, and lithium. Then, ferrous iron in the leachate is separated first, and then phosphorus and lithium are recovered. This process not only breaks the conventional process of first extracting lithium and then separating phosphorus and iron, but also separates phosphorus and iron first, which greatly reduces the difficulty of subsequent impurity removal of ferrous sulfate, phosphoric acid, and lithium phosphate. This facilitates the recovery of phosphorus and iron from lithium extraction slag, which can not only increase the recycling value of waste lithium iron phosphate batteries, but also avoid the environmental problems caused by the stockpiling of lithium extraction slag.

[0008] Secondly, this invention provides a method for separating and recovering phosphorus and iron from lithium residue. An alcohol is added to a second mixed solution, and ferrous sulfate is precipitated out of the solution via alcohol precipitation, while phosphorus and lithium remain in the mother liquor. This achieves the separation of iron from phosphorus and lithium. This invention utilizes alcohol precipitation to precipitate ferrous sulfate from the second mixed solution, offering advantages such as high separation selectivity, high product purity and yield, and reduced loss of phosphorus and lithium. Specifically, using alcohol precipitation to separate ferrous sulfate, the iron recovery rate is greater than 96%, and the loss rate of phosphorus and lithium is less than 2%. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0010] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0011] Related technologies remove impurities from lithium extraction slag by adjusting pH. However, increasing pH leads to the loss of phosphorus and iron, resulting in low economic value. Specifically, ferric phosphate completely precipitates at pH=2, at which point titanium and aluminum also form phosphate precipitates mixed with the ferric phosphate. Even if ferric iron is reduced to ferrous iron, ferrous phosphate does not precipitate at pH=2. At this point, phosphate ions in the solution react with ferrous ions to form ferrous phosphate. To remove aluminum ions from the solution, the pH needs to be raised to 4.5-5.0. Since ferrous phosphate begins to precipitate at pH>2, when the pH reaches 4.5-5.0, the loss of phosphorus and iron reaches approximately 50%.

[0012] To address this, this application provides a method for separating and recovering phosphorus and iron from lithium extraction slag. This method converts the lithium extraction slag leachate containing phosphorus and ferric iron into a second mixed solution containing phosphorus, ferrous iron, and lithium. Then, the ferrous iron in the leachate is separated first, followed by the recovery of phosphorus and lithium. This process not only breaks with the conventional method of first extracting lithium and then separating phosphorus and iron, but also significantly reduces the difficulty of subsequent impurity removal from ferrous sulfate, phosphoric acid, and lithium phosphate by separating phosphorus and iron first. Furthermore, this process can not only treat currently stockpiled lithium extraction slag but also simultaneously treat battery black powder, achieving "waste-to-waste treatment."

[0013] This application discloses a method for separating and recovering phosphorus and iron from lithium extraction slag, comprising the steps of acid leaching, reduction, pre-neutralization, iron extraction by alcohol precipitation, phosphorus extraction by extraction, impurity removal, and lithium precipitation by phosphate. Each step is described in detail below.

[0014] Step 100: The lithium extraction residue is mixed with sulfuric acid for leaching. After solid-liquid separation, an iron-containing filtrate and the first filter residue are obtained. The lithium extraction residue is not limited to the waste residue after lithium extraction from lithium iron phosphate battery black powder, but can also be other lithium extraction waste residue.

[0015] Preferably, the mass concentration of sulfuric acid is 20-60%.

[0016] Preferably, the solid-liquid mass ratio of lithium extraction residue to sulfuric acid is 1:2~6.

[0017] Preferably, the temperature for leaching lithium residue in sulfuric acid is 20~90℃ and the time is 0.5~4h.

[0018] The acid leaching process described above is similar to that for battery black powder, and will not be described in detail here. After acid leaching, phosphorus and iron in the lithium extraction residue exist in the leachate in the form of phosphoric acid (H3PO4) and ferric sulfate (Fe2(SO4)3), respectively.

[0019] Step 200: Add a reducing agent to the iron-containing filtrate to reduce ferric iron to ferrous iron, and obtain the first mixed solution after solid-liquid separation.

[0020] Preferably, the reducing agent is iron powder. By adding iron powder, ferric iron in the solution can be reduced to ferrous iron, providing a basis for subsequent processes.

[0021] Preferably, the reducing agent is ferrophosphorus slag, which is one or more of FeP, Fe2P, and Fe3P. For example, the ferrophosphorus slag is a by-product waste residue from the production of yellow phosphorus.

[0022] More preferably, the solid-liquid mass ratio of the iron-containing filtrate to the ferrophosphate slag is 1:8~12. If the added ferrophosphate slag is in excess, the incompletely leached ferrophosphate slag can be recovered and added to the next batch of iron-containing filtrate to continue the reaction (a small amount of fresh ferrophosphate slag can be added to the recovered ferrophosphate slag).

[0023] More preferably, the temperature during the reaction of the iron-containing filtrate with the phosphorus-iron slag is 50~90℃ and the time is 1.5~3h.

[0024] After the lithium extraction slag is mixed with acid for leaching, the metal elements in the lithium extraction slag dissolve in the acid. The resulting iron-containing filtrate is still acidic. Adding ferrophosphate slag to this filtrate utilizes the acidity of the filtrate to leach the ferrophosphate slag. Simultaneously, the reducing properties of the ferrophosphate slag reduce the ferric iron in the filtrate to ferrous iron, providing a basis for subsequent processes. This method allows for the graded utilization of acid to treat both lithium extraction slag and ferrophosphate slag, achieving "waste treatment with waste." It also improves the utilization rate of acid, avoids the use of expensive iron powder as a reducing agent, reduces the treatment costs of lithium extraction slag and ferrophosphate slag, and improves the economic efficiency of lithium extraction slag treatment.

[0025] Step 300: Add battery black powder to the first mixed solution, and leach the lithium-containing slag with the first mixed solution. After solid-liquid separation, a second mixed solution and a second filter residue are obtained. For example, the battery black powder is recycled lithium iron phosphate battery material; or the battery black powder is a mixture of recycled lithium iron phosphate battery material and lithium extraction slag. It is not limited to this; the battery black powder can also be lithium extraction slag (eliminating the need for a subsequent lithium phosphate precipitation step). The battery black powder can also be other waste materials containing phosphorus, iron, and lithium.

[0026] Preferably, the solid-liquid mass ratio of battery black powder to the first mixed solution is 1:3~6.

[0027] Preferably, the temperature during the leaching of the battery black powder with the first mixed solution is room temperature, and the time is 1.5 to 3 hours.

[0028] After obtaining the first mixed solution, this application adds battery black powder to the first mixed solution and mixes and leaches the battery black powder with the first mixed solution. In this process, the acidity of the first mixed solution can be used to leach the battery black powder, so that this application can treat three types of waste: lithium extraction slag, phosphorus iron slag and battery black powder, and fully realize "waste treatment with waste".

[0029] Specifically, the pH of the iron-containing filtrate obtained in step 100 is around 0; in step 200, after adding phosphorus-iron slag for reduction, the pH of the first mixed solution is less than 0.5; in step 300, after adding battery black powder, the pH of the second mixed solution can be increased to around 1.0~1.5. This application, by adding phosphorus-iron slag and battery black powder in stages, not only achieves the reduction of ferric iron but also enables the gradient utilization of the acid solution.

[0030] Step 400: Control the pH of the second mixed solution to 0.5 or below, add an alcohol to the second mixed solution, and use alcohol precipitation to precipitate the ferrous sulfate in the second mixed solution. After solid-liquid separation, ferrous sulfate precipitate and mother liquor are obtained.

[0031] For example, the pH of the second mixed solution can be controlled by the amount of sulfuric acid added in step 100. At the same time, the amount of sulfuric acid added must also meet the sulfate ions required for the theoretical precipitation of ferrous ions.

[0032] Adding alcohols at this pH level reduces the solution polarity, decreasing the solubility of ferrous sulfate and promoting its precipitation. Since phosphoric acid has higher solubility, adding alcohols is insufficient to precipitate it. Maintaining the pH at 0.5 or below prevents impurities such as lithium phosphate and ferrous phosphate from precipitating along with ferrous sulfate, thus allowing lithium ions and phosphate ions to remain in the solution, thereby separating iron from phosphorus and lithium.

[0033] Preferably, the alcohol is one or more of ethanol, n-propanol, and isopropanol. More preferably, the alcohol is ethanol.

[0034] Preferably, the alcohol content is 1 to 2 times the mass of the second mixed solution.

[0035] Preferably, the second mixed solution is stirred and mixed with the alcohol for 10-60 minutes.

[0036] This application utilizes alcohol precipitation to precipitate ferrous sulfate from the second mixed solution, while phosphorus and lithium remain in the mother liquor, thus achieving the separation of iron from phosphorus and lithium. Furthermore, this method of precipitating ferrous sulfate from the second mixed solution via alcohol precipitation not only offers advantages such as high separation selectivity, high product purity and yield, but also reduces the loss of phosphorus and lithium. Specifically, using alcohol precipitation to separate ferrous sulfate, the iron yield is greater than 96%, while the loss rate of phosphorus and lithium is less than 2%.

[0037] In some embodiments, step 200 is followed by a step of removing impurities from ferrous sulfate.

[0038] Preferably, the ferrous sulfate precipitate is purified by the following steps: Ferrous sulfate precipitate is dissolved in water to obtain ferrous sulfate aqueous solution. The pH of the ferrous sulfate aqueous solution is adjusted to 5-7 under inert gas protection. After solid-liquid separation, ferrous sulfate solution and second filter residue are obtained.

[0039] Ferrous sulfate heptahydrate can be obtained by evaporating, concentrating, and crystallizing a ferrous sulfate solution; or by adding an alcohol to a ferrous sulfate solution and stirring to precipitate ferrous sulfate heptahydrate.

[0040] Ferrous sulfate heptahydrate is washed with an alcohol solution of 20-50% by mass, and then stirred, filtered, and vacuum dried to obtain battery-grade ferrous sulfate heptahydrate. The alcohol is one or more of ethanol solution, n-propanol solution, and isopropanol solution.

[0041] For example, the ethanol solution is a mixture of industrial ethanol and water, wherein the mass concentration of ethanol is 20%, 30%, 40%, or 50%. For example, the ethanol solution can be used to wash ferrous sulfate precipitate one or more times to obtain higher quality ferrous sulfate.

[0042] More preferably, when ferrous sulfate precipitate is dissolved in water, the solid-liquid mass ratio is 1:2 to 5, which allows the ferrous sulfate to dissolve completely.

[0043] More preferably, one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium carbonate, ammonium bicarbonate, and sodium acetate are added to the ferrous sulfate aqueous solution to adjust the pH of the ferrous sulfate aqueous solution. However, this is not limited to this method; other alkaline solutions can also be used to adjust the pH of the ferrous sulfate aqueous solution.

[0044] More preferably, the solution pH is adjusted at room temperature.

[0045] More preferably, the amount of alcohol solution added is 1 to 2 times the mass of the ferrous sulfate aqueous solution.

[0046] This application allows for the removal of Ti from ferrous sulfate obtained through alcohol precipitation simply by adjusting the pH.4+ Al 3+ V 3+ Cr 3+ Metallic elements such as titanium, chromium, vanadium, and aluminum are removed, causing metallic impurities to precipitate out. The removal rate of metallic elements such as titanium, chromium, vanadium, and aluminum is greater than 98%, resulting in high-purity ferrous sulfate with a low iron loss rate, specifically less than 5%. Furthermore, this application adjusts the pH of the ferrous sulfate aqueous solution under inert gas protection, preventing oxygen in the air from oxidizing ferrous iron to ferric iron, which would otherwise reduce the purity of the ferrous sulfate.

[0047] After adjusting the pH, this application further washes the ferrous sulfate with a 20-50% mass concentration alcohol solution to remove free sodium ions from the solid ferrous sulfate. After washing with the alcohol solution, ferrous sulfate with low sodium content can be obtained.

[0048] Specifically, ferrous sulfate heptahydrate obtained through alcohol precipitation and impurity removal can be used in the production of battery materials.

[0049] Step 500: After evaporating and concentrating the mother liquor, add a purification agent to the mother liquor to remove impurities in the solution, and then obtain a phosphoric acid solution and a lithium-containing solution by extraction.

[0050] The mother liquor after alcohol precipitation in step 400 mainly contains phosphoric acid and lithium sulfate. After evaporation and concentration, the alcohol solution can be recovered. The recovered alcohol solution can be used for further alcohol precipitation to extract iron. For example, the mother liquor is evaporated and concentrated until the phosphorus content is 5-7%. After removing impurities from the mother liquor, it is then extracted to obtain a phosphoric acid solution and a lithium-containing solution.

[0051] Preferably, the impurity remover is an alkaline solution. More preferably, the alkaline solution is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium carbonate, ammonium bicarbonate, and sodium acetate. After adding the alkaline solution, the pH of the solution is 5.5~6.5, which can remove most of the metal ions in the solution, such as Mg, Al, K, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Cd, Pb, etc., while lithium ions do not precipitate at this pH.

[0052] The above-mentioned impurity removal steps can improve the purity of subsequent phosphate and lithium salts.

[0053] Preferably, the phosphoric acid solution is obtained by multi-stage countercurrent extraction. For example, obtaining the phosphoric acid solution by multi-stage countercurrent extraction includes the following steps: Step 510: The extractant is introduced through one of the bottom and top of the extraction device, and the mother liquor is introduced through the other of the bottom and top of the extraction device, to perform three-stage countercurrent extraction on the mother liquor. More preferably, the extractant includes an extractant and a diluent, wherein the extractant is tributyl phosphate, the diluent is kerosene and / or sulfonated kerosene, and the volume ratio of the extractant to the diluent is 1:2 to 4.

[0054] Step 520: Add pure water to the extract and wash the extract. More preferably, the volume ratio of extract to pure water is 8~10:1. Washing with pure water can remove impurities from the extract.

[0055] Step 530: Add pure water to the washed extract for back-extraction to obtain a phosphoric acid solution. The phosphoric acid solution contains 2-5% phosphorus. More preferably, the volume ratio of the washed extract to pure water is 1-5:1, and the mixture is heated to 70°C for 30 minutes.

[0056] This application obtains a phosphoric acid solution through multi-stage countercurrent extraction. The extract can be recycled and reused, and the total phosphorus yield is >95%. Finally, the phosphoric acid solution obtained by back-extraction can be evaporated and concentrated to obtain battery-grade phosphoric acid.

[0057] Step 600: After adding phosphoric acid to the lithium-containing solution, adjust the pH to 8-10 and obtain battery-grade lithium phosphate precipitate.

[0058] Preferably, the amount of phosphoric acid added is sufficient to completely convert lithium sulfate in the lithium-containing solution into lithium phosphate. Since the phosphorus content in the system is much greater than the lithium content, the excess phosphorus can be separated by extraction. In step 500, approximately 20% phosphorus remains; adding phosphoric acid as needed will yield lithium phosphate. Furthermore, the preparation of lithium phosphate not only achieves a yield of up to 98%, but also, due to the low solubility of lithium phosphate, only 1 / 3 of the water needs to be evaporated to obtain solid lithium phosphate, thus reducing energy consumption.

[0059] Preferably, after adding phosphoric acid, the pH of the solution decreases. By adding one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium carbonate, ammonium bicarbonate, and sodium acetate to the solution, the pH of the solution can be adjusted to 8-10, which can cause lithium phosphate to precipitate.

[0060] Preferably, adjusting the pH of the solution to 8-10 and heating it to 60-100°C can improve the yield of lithium phosphate.

[0061] This invention discloses a method for separating and recovering phosphorus and iron from lithium extraction slag. Through steps such as leaching the lithium extraction slag, adding a reducing agent to reduce ferric iron, and adding battery black powder, the filtrate containing phosphorus and ferric iron can be converted into a second mixed solution containing phosphorus, ferrous iron, and lithium. Then, the ferrous iron in the leachate is separated first, followed by the recovery of phosphorus and lithium. This process not only breaks with the conventional method of first extracting lithium and then separating phosphorus and iron, but also separates phosphorus and iron first, greatly reducing the difficulty of subsequent impurity removal from ferrous sulfate, phosphoric acid, and lithium phosphate. This facilitates the recovery of phosphorus and iron from the lithium extraction slag, increasing the recycling value of waste lithium iron phosphate batteries and avoiding environmental problems caused by the stockpiling of lithium extraction slag.

[0062] The method for separating and recovering phosphorus, iron and lithium in battery black powder provided in this application will be described in detail below with reference to specific embodiments.

[0063] In subsequent examples, the content of phosphorus and iron was determined by chemical titration, and the content of other elements was determined by ICP-MS.

[0064] Lithium extraction slag: This is the waste residue from lithium iron phosphate plants after lithium extraction, and its main components are phosphorus and iron. Specifically, the iron content in lithium extraction slag is 30.54%, the phosphorus content is 16.54%, and it also contains a significant amount of other elements, including 1942 ppm residual lithium, 1420 ppm sodium, 73 ppm magnesium, 7504 ppm aluminum, 235 ppm potassium, 850 ppm calcium, 9 ppm titanium, 18 ppm vanadium, 19 ppm chromium, 295 ppm manganese, 113 ppm cobalt, 350 ppm nickel, 560 ppm copper, 12 ppm zinc, 6 ppm arsenic, 0.1 ppm cadmium, and 3 ppm lead.

[0065] Phosphorus-iron slag: a byproduct of yellow phosphorus production, its main components are phosphorus and iron. Specifically, the iron content in phosphorus-iron slag is 65.05%, and the phosphorus content is 21.54%. Lithium extraction slag also contains a significant amount of other elements, including 158 ppm sodium, 816 ppm magnesium, 757 ppm aluminum, 311 ppm potassium, 15072 ppm calcium, 6028 ppm titanium, 2139 ppm vanadium, 1451 ppm chromium, 24781 ppm manganese, 207 ppm cobalt, 1005 ppm nickel, 688 ppm copper, 72 ppm zinc, 5 ppm arsenic, and 152 ppm lead.

[0066] Battery black powder: sourced from battery recycling plants, its main components are lithium, phosphorus, and iron. Specifically, the iron content in battery black powder is 23.79%, the phosphorus content is 11.30%, and the lithium content is 33,132 ppm. Battery black powder also contains a significant amount of other elements, including 1,340 ppm sodium, 49 ppm magnesium, 16,495 ppm aluminum, 130 ppm potassium, 438 ppm calcium, 1,187 ppm titanium, 122 ppm vanadium, 30 ppm chromium, 4,532 ppm manganese, 3,864 ppm cobalt, 3,127 ppm nickel, 16,045 ppm copper, 31 ppm zinc, 8 ppm arsenic, 9 ppm cadmium, and 12 ppm lead.

[0067] Example 1 The method for separating and recovering phosphorus and iron from lithium extraction slag in this embodiment includes the following steps: Step 100: Take 100g of lithium extraction residue, add 300g of 50% sulfuric acid solution, stir at room temperature for 1 hour, the lithium extraction residue dissolves in the sulfuric acid solution, and after filtration, obtain iron-containing filtrate and first filter residue.

[0068] The pH of the iron-containing filtrate is 0.01.

[0069] Step 200: Add phosphorus iron slag to the iron-containing filtrate at a solid-liquid mass ratio of 1:12. After mixing the phosphorus iron slag with the iron-containing filtrate, heat the mixture to 80°C and react the mixture under stirring for 2 hours. After solid-liquid separation, the first mixed solution is obtained.

[0070] The pH of the first mixed solution is 0.34.

[0071] Step 300: Add battery black powder to the first mixed solution at a solid-liquid mass ratio of 1:5. At room temperature, the first mixed solution and battery black powder react under stirring for 2 hours. After solid-liquid separation, a second mixed solution and a second filter residue are obtained.

[0072] The pH of the second mixed solution is 1.24.

[0073] The second mixed solution weighs 428.1g, has a ferrous ion concentration of 9.64%, a phosphorus content of 4.325%, and a lithium content of 0.23%.

[0074] Step 400: Add sulfuric acid to the second mixed solution to adjust the pH of the second mixed solution to 0.5. At room temperature, slowly add industrial ethanol to the leachate. The amount of ethanol added is twice that of the leachate. After 5 minutes, ferrous sulfate begins to precipitate at the bottom of the container. Continue stirring for 30 minutes until the ethanol and leachate are completely mixed. After filtration, ferrous sulfate precipitate and mother liquor are obtained.

[0075] In the above steps, the contents of phosphorus, iron, and lithium are as follows: Ferrous sulfate precipitate: 199.3g of ferrous sulfate heptahydrate, with a phosphorus content of 0.39g and a lithium content of 0.01g.

[0076] Mother liquor: The mother liquor weighs 200.7g, contains 1.24g of iron, 19.31g of phosphorus, and 2.447g of lithium.

[0077] Based on solids, the iron yield is 97% (iron yield = (199.3 / 278*55.85) / (428.1*9.64%)). Phosphorus and lithium in the ferrous sulfate precipitate are considered as losses, with phosphorus loss rate of 2% (phosphorus loss rate = 0.39 / (428.1*4.325%)) and lithium loss rate of 1%.

[0078] The following steps are used to remove impurities from ferrous sulfate precipitation: Dissolve 100g of ferrous sulfate in 200g of water, add sodium carbonate under nitrogen protection, and adjust the pH of the solution to 6.0. This will allow Ti to... 4+ Al 3+ V 3+ Cr 3+ Metal element impurities precipitate out in the form of precipitates.

[0079] After filtration, 1.5 times the mass of ethanol was added to the solution to precipitate ferrous sulfate heptahydrate solid. Then, a 40% ethanol solution was added to the ferrous sulfate solid, with an ethanol solution of 200g. The mixture was stirred at room temperature for 30 minutes, filtered, and vacuum dried to obtain battery-grade ferrous sulfate.

[0080] The content of each element in the ferrous sulfate solution before and after impurity removal is shown in Table 1 below.

[0081] Table 1. Content of each element in ferrous sulfate solution before and after impurity removal (unit: ppm) sample Fe Na Mg Al K Ca Ti V Cr original solution 65439 524 543 43 21 45 425 76 35 pH=6.0 63254 1941 2 1.32 5.13 12.8 0.24 0.01 0.04 In the above steps, by adjusting the pH to 6.0, most of the metal ions in ferrous sulfate can be removed, and the loss of iron is minimal. The resulting ferrous sulfate product has high purity and can be used in the production of battery materials.

[0082] The purified ferrous sulfate solution was evaporated, concentrated, and crystallized to obtain ferrous sulfate heptahydrate. The impurity content of the ferrous sulfate heptahydrate was determined, and the results are shown in Table 2.

[0083] Table 2 Impurity Index of Sulfuric Acid Heptahydrate As can be seen from Table 2 above, the ferrous sulfate heptahydrate obtained in this embodiment is of high quality and can be used in the production of lithium iron phosphate battery material.

[0084] Step 500: Take 1 kg of mother liquor, heat the mother liquor to evaporate and recover ethanol, and concentrate it until the phosphorus content is 6%. Add sodium hydroxide to the concentrated mother liquor to adjust the pH to 5.5. The content of each element in the mother liquor before and after impurity removal is shown in Table 3.

[0085] Table 3. Content of each element in the mother liquor before and after impurity removal (unit: ppm) In the above steps, by adjusting the pH to 5.5, most of the metal ions in the mother liquor can be removed. This mother liquor can be used to prepare high-purity phosphoric acid and / or lithium products, which can be used in the production of battery materials.

[0086] Tributyl phosphate and kerosene were mixed evenly in a volume ratio of 1:3 to obtain an extract. The extract was introduced from the bottom of the extraction apparatus, while the mother liquor was introduced from the top, resulting in a three-stage extraction process.

[0087] Add pure water to the extract for washing; the volume ratio of extract to pure water is 10:1.

[0088] After separation, pure water was added to the extract for back-extraction to obtain a phosphoric acid solution. The volume ratio of extract to pure water was 1:1. The phosphoric acid solution had a phosphorus concentration of 1.24%.

[0089] Table 4 shows a comparison of the properties of the concentrated phosphoric acid solution with those of chemically pure phosphoric acid (GB / T1282-2013).

[0090] Table 4 Comparison of Phosphoric Acid Indicators As can be seen from Table 4 above, the quality of phosphoric acid obtained in this embodiment is higher than the requirements for chemically pure phosphoric acid in the national standard GB / T1282-2013. Some indicators can even meet the requirements for superior grade phosphoric acid in GB / T1282-2013, and it can be used in the production of lithium iron phosphate battery material.

[0091] Step 600: Add phosphate to the purified solution until lithium can be completely precipitated. Add sodium carbonate to adjust the pH of the solution to 10 to obtain lithium phosphate precipitate. Wash and dry the lithium phosphate precipitate to obtain the lithium phosphate product.

[0092] Table 6 shows a comparison between the obtained lithium phosphate and the indicators of the YS / T 637-2022 lithium phosphate industry standard.

[0093] Table 6 Comparison of Lithium Phosphate Indicators Indicator Name (Quality Score / %) <![CDATA[Li3PO4-1]]> Product in this embodiment <![CDATA[Li3PO4 content]]> ≥99.9 99.9 Ca ≤0.002 0.0005 Mg ≤0.001 0.0003 Fe ≤0.0005 0.0002 Cu ≤0.0001 0.00003 Pb ≤0.0001 0.00002 Ni ≤0.0001 0.00007 Cl ≤0.08 0.0005 Co ≤0.0001 0.00004 Mn ≤0.0001 0.00006 Al ≤0.0005 0.0001 Na ≤0.001 0.0008 Si ≤0.005 0.0001 Zn ≤0.0001 0.00005 <![CDATA[SO4 2- ]]> ≤0.02 0.007 Cr ≤0.0001 0.00002 Cd ≤0.0001 0.00003 As can be seen from Table 6 above, the quality of the lithium phosphate obtained in this embodiment meets the requirements of the lithium phosphate industry standard for Li3PO4-1, and can be used in the production of lithium iron phosphate battery material.

[0094] Example 2 The method for separating and recovering phosphorus and iron from lithium extraction slag in this embodiment differs from that in Example 1 in that: in step 200, iron powder is added to the iron-containing filtrate at a solid-liquid mass ratio of 1:20, and the iron powder is completely dissolved.

[0095] The remaining steps are the same as in Example 1, and will not be repeated here.

[0096] The pH of the first mixed solution is 0.01.

[0097] Example 3 The method for separating and recovering phosphorus and iron from lithium extraction slag in this embodiment differs from that in Embodiment 1 in that: in step 200, phosphorus-iron slag is added to the iron-containing filtrate at a solid-liquid mass ratio of 1:8.

[0098] The remaining steps are the same as in Example 1, and will not be repeated here.

[0099] The pH of the first mixed solution is 0.36.

[0100] Example 4 The method for separating and recovering phosphorus and iron from lithium extraction slag in this embodiment differs from that in Embodiment 1 in that: in step 300, battery black powder is added to the first mixed solution at a solid-liquid mass ratio of 1:3.

[0101] The remaining steps are the same as in Example 1, and will not be repeated here.

[0102] The second mixed solution has a pH of 1.42.

[0103] Example 5 The method for separating and recovering phosphorus and iron from lithium extraction slag in this embodiment differs from that in Example 1 in that: in step 400, the amount of ethanol added is 1 times that of the second mixed solution, and the stirring and mixing time is 60 minutes.

[0104] The remaining steps are the same as in Example 1, and will not be repeated here.

[0105] In the above steps, the contents of phosphorus, iron, and lithium are as follows: The second mixed solution weighs 428.1g, has a ferrous ion concentration of 9.64%, a phosphorus content of 4.325%, and a lithium content of 0.23%.

[0106] Ferrous sulfate precipitation: 198.54g of ferrous sulfate heptahydrate, with a phosphorus content of 0.23g and a lithium content of 0.023g; Mother liquor: The mother liquor weighs 110.5g, contains 1.53g of iron, 19.54g of phosphorus, and 2.533g of lithium; Based on solids, the iron yield is 97%. Phosphorus and lithium in the ferrous sulfate precipitate are considered as losses, with phosphorus loss of 1.2% and lithium loss of 2.3%.

[0107] Example 6 The method for separating and recovering phosphorus and iron from lithium extraction slag in this embodiment differs from that in Example 1 in that: during the precipitation and impurity removal of ferrous sulfate, sodium carbonate is added under nitrogen protection to adjust the solution pH to 6.5, which allows Ti to... 4+ Al 3+ V 3+ Cr 3+ Metal element impurities precipitate out in the form of precipitates.

[0108] The remaining steps are the same as in Example 1.

[0109] The content of each element in the ferrous sulfate solution before and after impurity removal is shown in Table 7 below.

[0110] Table 7. Content of each element in ferrous sulfate solution before and after impurity removal (unit: ppm) sample Fe Na Mg Al K Ca Ti V Cr original solution 65439 524 543 43 21 45 425 76 35 pH=6.5 62679 2056 1.5 0.3 6.1 10.5 0.8 0.4 0.3 In the above steps, by adjusting the pH to 6.5, most of the metal ions in ferrous sulfate can be removed with minimal iron loss, resulting in a high-purity ferrous sulfate product that can be used in the production of battery materials.

[0111] Example 7 The method for separating and recovering phosphorus, iron and lithium in battery black powder in this embodiment differs from that in Example 1 in that sodium hydroxide is added under nitrogen protection during the precipitation and impurity removal of ferrous sulfate to adjust the solution pH to 5.0.

[0112] The remaining steps are the same as in Example 1, and will not be repeated here.

[0113] The content of each element in the ferrous sulfate solution before and after impurity removal is shown in Table 8 below.

[0114] Table 8. Content of each element in ferrous sulfate solution before and after impurity removal (unit: ppm) sample Fe Na Mg Al K Ca Ti V Cr original solution 65439 524 543 43 21 45 425 76 35 pH=5.0 64295 1874 1.5 0.7 4.5 12 0.4 0.8 0.3 In the above steps, by adjusting the pH to 5.0, most of the metal ions in ferrous sulfate can be removed, and the loss of iron is small. The resulting ferrous sulfate product has high purity and can be used in the production of battery materials.

[0115] Example 9 The method for separating and recovering phosphorus, iron, and lithium in battery black powder in this embodiment differs from that in Example 1 in the following steps: Step 600: Phosphoric acid is added to the purified solution until lithium can be completely precipitated. Sodium carbonate is added to adjust the pH of the solution to 9, thereby obtaining lithium phosphate precipitate. The lithium phosphate precipitate is washed and dried to obtain the lithium phosphate product.

[0116] The comparison between the obtained lithium phosphate and the indicators of the YS / T 637-2022 lithium phosphate industry standard is shown in Table 9.

[0117] Table 9 Comparison of Lithium Phosphate Indicators Indicator Name (Quality Score / %) <![CDATA[Li3PO4-1]]> Product in this embodiment <![CDATA[Li3PO4 content]]> ≥99.9 99.9 Ca ≤0.002 0.0004 Mg ≤0.001 0.0007 Fe ≤0.0005 0.0003 Cu ≤0.0001 0.00006 Pb ≤0.0001 0.00008 Ni ≤0.0001 0.00006 Cl ≤0.08 0.0003 Co ≤0.0001 0.00002 Mn ≤0.0001 0.00007 Al ≤0.0005 0.0001 Na ≤0.001 0.0005 Si ≤0.005 0.0001 Zn ≤0.0001 0.00006 <![CDATA[SO4 2- ]]> ≤0.02 0.004 Cr ≤0.0001 0.00003 Cd ≤0.0001 0.00001 As can be seen from Table 9 above, the quality of the lithium phosphate obtained in this embodiment meets the requirements of the lithium phosphate industry standard for Li3PO4-1, and can be used in the production of lithium iron phosphate battery material.

[0118] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for separating and recovering phosphorus and iron from lithium extraction slag, characterized in that, Includes the following steps: Step 100: The lithium extraction residue is mixed with sulfuric acid for leaching, and after solid-liquid separation, an iron-containing filtrate and the first filter residue are obtained; Step 200: Add a reducing agent to the iron-containing filtrate to reduce ferric iron to ferrous iron, and obtain the first mixed solution after solid-liquid separation; Step 300: Add battery black powder to the first mixed solution, and mix and leach the lithium-containing slag with the first mixed solution. After solid-liquid separation, a second mixed solution and a second filter residue are obtained. Step 400: Control the pH of the second mixed solution to 0.5 or below, add alcohol to the second mixed solution, and use alcohol precipitation to precipitate the ferrous sulfate in the second mixed solution. After solid-liquid separation, ferrous sulfate precipitate and mother liquor are obtained. Step 500: After evaporating and concentrating the mother liquor, add a purification agent to the mother liquor to remove impurities in the solution, and then obtain a phosphoric acid solution and a lithium-containing solution by extraction; Step 600: After adding phosphoric acid to the lithium-containing solution, adjust the pH to 8-10 and obtain battery-grade lithium phosphate precipitate.

2. The method for separating and recovering phosphorus and iron from lithium extraction slag according to claim 1, characterized in that, The reducing substance is ferrophosphorus slag, which is one or more of FeP, Fe2P, and Fe3P. Alternatively, in step 200, the reducing agent is iron powder.

3. The method for separating and recovering phosphorus and iron from lithium extraction slag according to claim 2, characterized in that, In step 100, the mass concentration of sulfuric acid is 20-60%, the solid-liquid mass ratio of lithium extraction residue to sulfuric acid is 1:2-6, and the leaching temperature of lithium extraction residue in sulfuric acid is 20-90℃, and the time is 0.5-4h.

4. The method for separating and recovering phosphorus and iron from lithium extraction slag according to claim 2, characterized in that, In step 200, the solid-liquid mass ratio of the iron-containing filtrate to the phosphorus-iron slag is 1:8~12, and the reaction temperature of the iron-containing filtrate and the phosphorus-iron slag is 50~90℃, and the reaction time is 1.5~3h.

5. The method for separating and recovering phosphorus and iron from lithium extraction slag according to claim 2, characterized in that, In step 300, the solid-liquid mass ratio of battery black powder to the first mixed solution is 1:3~6, and the temperature during the leaching of battery black powder and the first mixed solution is room temperature, and the time is 1.5~3h.

6. The method for separating and recovering phosphorus and iron from lithium extraction slag according to any one of claims 1 to 5, characterized in that, In step 400, the alcohol is one or more of ethanol, n-propanol, and isopropanol; And / or, in step 400, the alcohol is 1 to 2 times the mass of the second mixed solution; And / or, in step 400, the second mixed solution is stirred and mixed with the alcohol for 10-60 minutes.

7. The method for separating and recovering phosphorus and iron from lithium extraction slag according to any one of claims 1 to 5, characterized in that, After step 400, the ferrous sulfate precipitate is purified by the following steps: Ferrous sulfate precipitate is dissolved in water at a solid-liquid mass ratio of 1:2 to 5 to obtain a ferrous sulfate aqueous solution. The pH of the ferrous sulfate aqueous solution is adjusted to 5 to 7 under inert gas protection. After solid-liquid separation, a ferrous sulfate solution and a second filter residue are obtained. Ferrous sulfate heptahydrate can be obtained by evaporating, concentrating, and crystallizing a ferrous sulfate solution, or by adding an alcohol to a ferrous sulfate solution and stirring to precipitate ferrous sulfate heptahydrate. Ferrous sulfate heptahydrate is washed with an alcohol solution of 20-50% by mass, and then stirred, filtered, and vacuum dried to obtain battery-grade ferrous sulfate heptahydrate. The alcohol is one or more of ethanol solution, n-propanol solution, and isopropanol solution, and the amount of alcohol solution added is 1-2 times the mass of the ferrous sulfate aqueous solution.

8. The method for separating and recovering phosphorus and iron from lithium extraction slag according to any one of claims 1 to 5, characterized in that, In step 500, the impurity removal agent is an alkaline solution; the alkaline solution is one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium carbonate, ammonium bicarbonate, and sodium acetate, and the pH of the solution is 5.5 to 6.5 after the alkaline solution is added.

9. The method for separating and recovering phosphorus and iron from lithium extraction slag according to claim 8, characterized in that, In step 500, a phosphoric acid solution is obtained through multi-stage countercurrent extraction, and the multi-stage countercurrent extraction for obtaining the phosphoric acid solution includes the following steps: Step 510: The extract is introduced from one of the bottom and top of the extraction device, and the mother liquor is introduced from the other of the bottom and top of the extraction device. The mother liquor is subjected to three-stage countercurrent extraction. The extract includes an extractant and a diluent. The extractant is tributyl phosphate, and the diluent is kerosene and / or sulfonated kerosene. The volume ratio of the extractant to the diluent is 1:2 to 4. Step 520: Add pure water to the extract to wash the extract, and the volume ratio of extract to pure water is 8~10:

1. Step 530: Add pure water to the washed extract for back-extraction to obtain a phosphoric acid solution. The volume ratio of the washed extract to pure water is 1~5:

1. Heat to 70℃ and react for 30 min.

10. The method for separating and recovering phosphorus and iron from lithium extraction slag according to any one of claims 1 to 5, characterized in that, In step 600, the amount of phosphoric acid added satisfies the following condition: at least enough to completely convert lithium sulfate in the lithium-containing solution into lithium phosphate; And / or, in step 600, one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, ammonium carbonate, ammonium bicarbonate, and sodium acetate are added to adjust the pH of the lithium-containing solution; And / or, in step 600, after adding phosphoric acid, heat to 60~100℃.

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