A method for recovering valuable resources from waste lithium iron phosphate materials

Abstract

The present invention relates to a method for recovering valuable resources from waste lithium iron phosphate materials, belonging to the technical field of recycling and utilizing waste lithium iron phosphate batteries. After dispersing waste lithium iron phosphate materials in water, a mixture I is obtained; an acid solution and an oxidant solution are added simultaneously to the mixture I for leaching reaction, and after solid-liquid separation, a leachate A and an active ferrophosphorus slag are obtained; iron powder is subjected to a replacement reaction with the leachate A to recover copper in the leachate A, thereby obtaining sponge copper and a lithium-rich leachate; and the active ferrophosphorus slag is calcined and crystallized to obtain decarbonized ferrophosphorus slag; the decarbonized ferrophosphorus slag is mixed with an alkali solution and placed in a mill for ball milling and leaching to obtain a leachate B and ferric hydroxide; the pH of the leachate B is adjusted to be alkaline to obtain aluminum hydroxide and a phosphate solution. The method provided by the present invention is simple to operate, low in cost, has good economic benefits, and is easy to industrialize.

Description

Technical Field

[0001] The invention relates to a method for recovering valuable resources from waste lithium iron phosphate materials, belonging to the technical field of recycling waste lithium iron phosphate batteries. Background Art

[0002] Patent application (publication number CN117821752A) discloses a method for leaching metal elements from lithium iron phosphate waste, comprising the following steps: (a1) adding water to the lithium iron phosphate waste after separating the aluminum foil, mixing uniformly, and forming a lithium iron phosphate slurry; (a2) immersing a carbon electrode in the lithium iron phosphate slurry, removing it, and drying it to obtain a working electrode; (a3) ​​forming an electrolytic cell with the working electrode as the anode, the counter electrode as the cathode, and a phosphoric acid solution as the electrolyte; immersing the working electrode in the electrolyte for a period of time, and then performing electrolysis; filtering the electrolyte to obtain a filtrate; and leaching the metal elements into the filtrate. However, this method is costly due to the expensive electrolysis equipment and high energy consumption, and does not separate and recover valuable elements such as lithium, iron, and phosphorus in the leaching solution.

[0003] Patent application (publication number CN116404284A) discloses a method for selectively recovering lithium iron phosphate waste and its application. The method involves reacting pretreated lithium iron phosphate cathode material with an acid and an oxidant to produce a solid residue and a liquid solution containing lithium ions; precipitating the lithium ions in the solution to produce a lithium salt product; and directly calcining the residue to produce an iron phosphate product. This method allows for the simultaneous recovery of lithium, iron, and phosphorus. However, because the ferrophosphorus residue contains not only carbon impurities but also small amounts of copper and aluminum metallic impurities, it is difficult to ensure the purity of the iron phosphate product.

[0004] In short, achieving the comprehensive utilization of multiple valuable resources such as lithium, iron, and phosphorus in waste lithium iron phosphate materials is the key to effectively recovering phosphorus and iron from lithium iron phosphate waste. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, one of the objects of the present invention is to provide a method for recovering valuable resources from waste lithium iron phosphate materials. The present invention takes waste lithium iron phosphate battery materials as the processing object, and realizes the classified recovery and utilization of lithium, iron, phosphorus, aluminum and copper resources in the raw materials by diluting the acid in advance and performing acid leaching, calcination, alkaline leaching and ball milling. The present invention achieves the purpose of recovering valuable resources in waste lithium iron phosphate materials, is simple to operate, low in cost, has good economic benefits, and is easy to industrially apply.

[0006] In order to achieve the above object, a first aspect of the present invention is to provide a method for recovering valuable resources from waste lithium iron phosphate materials, the method comprising:

[0007] (1) Dispersing waste lithium iron phosphate material in water to obtain a mixture I;

[0008] (2) adding the acid solution and the oxidant solution to the mixture I simultaneously for leaching reaction, and obtaining leachate A and active ferrophosphorus slag after solid-liquid separation; the oxidant solution is added at a rate of 2-10 mL / min;

[0009] (3) performing a replacement reaction between the iron powder and the leachate A to recover the copper in the leachate A, and obtaining sponge copper and lithium-rich leachate through solid-liquid separation;

[0010] and calcining the active ferrophosphorus slag to transform the crystals and remove the impurity carbon to obtain decarbonized ferrophosphorus slag;

[0011] (4) mixing the decarburized ferrophosphorus slag with an alkaline solution, and placing the mixture in a mill for ball milling and leaching, and obtaining a leachate B and ferric hydroxide through solid-liquid separation;

[0012] (5) The pH of the leachate B is adjusted to alkaline, aluminum and phosphorus in the solution are separated, and aluminum hydroxide and phosphate solution are obtained by solid-liquid separation.

[0013] The present invention firstly performs a leaching reaction by simultaneously adding an acid solution and an oxidant solution, wherein the acid solution is used to adjust the pH value of the leachate, and the oxidant solution is used to adjust the potential value of the leaching reaction. By controlling the dripping rate of the oxidant solution, highly reactive ferrophosphorus slag and leachate A can be obtained. Iron powder is then added to the leachate A to recover copper. The active ferrophosphorus slag is calcined to remove carbon impurities and then used for ball milling and alkaline leaching to obtain leachate B and ferric hydroxide. The separation and recovery of phosphorus and aluminum resources are achieved by adjusting the pH value of the leachate B.

[0014] In the prior art, when processing ferrophosphorus slag, generally adopt first acid dissolving and then make the mode of ferric phosphate precipitation be able to reclaim iron, phosphorus resources in ferrophosphorus slag, but the method is except facing the dilemma that phosphorus, iron resource leaching rate are low in ferrophosphorus slag, due to also containing a small amount of aluminum metal in ferrophosphorus slag, cause obtained iron phosphate purity to be low, economic added value is poor. The present invention adopts dual channel by oxidant solution and acid solution respectively and two kinds of solution are added simultaneously in mixture I, obtain active ferrophosphorus slag, after calcining and decarburizing of the ferrophosphorus slag obtained, by adopting ball milling alkali leaching process, break chemical bond in ferric phosphate, reduce reaction activation energy, further enhance the reactive activity of ferrophosphorus slag, realize the efficient separation of iron and phosphorus, make phosphorus, aluminum resource in ferrophosphorus slag enter into leachate synchronously under alkali action, leaching residue is then directly ferric hydroxide product, further realizes the separation and recovery of aluminium hydroxide and phosphate solution by regulating the pH value of leachate.

[0015] When processing waste lithium iron phosphate material in prior art, concentrated acid is usually used first to dissolve raw material in leaching process, and then oxidant is added to oxidize divalent iron to ferric iron, and reaction temperature is higher under concentrated acid and oxidant co-action, resulting in the main component of the ferrophosphorus slag obtained being dihydrated iron phosphate and carbon of monoclinic structure. The dihydrated iron phosphate of monoclinic structure has a large water content, causes slag amount to increase, is difficult to store, and has poor reactivity, and iron and phosphorus resources therein are difficult to be dissolved by acid or alkali. The present invention is when leaching, by diluting acid in advance, and by controlling the addition rate of oxidant solution to be 2~10mL / min, oxidant solution is slowly added, and then control reaction system pH value, potential value, temperature, realize the selectivity in waste lithium iron phosphate material and deviate from, the ferrophosphorus slag obtained is mainly the iron phosphate of isophosphorus manganese iron ore structure, and its water content is few, and reactivity is high, and iron and phosphorus resources are easily leached, are more conducive to subsequent further processing recovery.

[0016] The present invention effectively realizes the classified recovery and utilization of lithium, iron, phosphorus, aluminum and copper resources in raw materials through the coordinated cooperation of the above technical features.

[0017] As a preferred solution, in step (1), the liquid-to-solid ratio of water to waste lithium iron phosphate material is 1-5 mL / g, more preferably 2-4 mL / g.

[0018] As a preferred solution, the acid solution is added at a rate of 2 to 10 mL / min. Adding the acid solution too quickly will cause the leaching reaction to proceed violently, resulting in severe heat release. At high temperatures, the ferrophosphate in the ferrophosphorus slag is likely to transform into a monoclinic structure, affecting the subsequent ferrophosphorus leaching efficiency.

[0019] As a more preferred solution, the acid solution is added at a rate of 2-5 mL / min.

[0020] As a preferred solution, the oxidant solution is added at a rate of 2-5 mL / min. Adding the oxidant too quickly will result in a vigorous reaction, severe heat release, and the high temperature will easily cause the ferric phosphate in the ferrophosphorus slag to convert to a monoclinic structure, affecting the subsequent ferrophosphorus leaching efficiency. Adding the oxidant too slowly will result in a prolonged reaction time, which is not conducive to production.

[0021] As a preferred solution, in step (2), the conditions of the leaching reaction include: pH value of 0.5-3, potential value of 300-700 mV, temperature of 50-90°C, and time of 1-4 hours.

[0022] As a more preferred solution, the leaching reaction conditions include: pH 1-2, potential 500-700 mV, temperature 50-75°C, and time 1-3 hours. Experiments have found that appropriate pH and potential values ​​can increase the recovery rate of Fe and P.

[0023] As a preferred solution, the acid solution is selected from at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution and phosphoric acid solution;

[0024] The concentration of the acid solution is 1.5-8 mol / L.

[0025] As a preferred solution, the oxidant solution is selected from at least one of hydrogen peroxide solution, sodium persulfate solution and sodium chlorate solution.

[0026] As a preferred solution, the molar ratio of iron powder to copper in the leachate A is 1-3:1, and the pH of the replacement reaction is 1.5-4.

[0027] As a preferred solution, the concentration of the oxidant solution is 5-10 mol / L.

[0028] As a preferred solution, in step (3), the method further comprises: adjusting the pH value of the lithium-rich leachate to 9-12 for impurity removal, obtaining a lithium-rich purified liquid and impurity-removed slag through solid-liquid separation, and subjecting the lithium-rich purified liquid to a precipitation reaction with a lithium precipitant to obtain a lithium salt product.

[0029] As a preferred solution, the lithium precipitant is sodium carbonate and / or sodium phosphate; and the lithium salt product is lithium carbonate and / or lithium phosphate.

[0030] As a preferred solution, the calcination and crystallization temperature is 400-800°C for 1-6 hours. If the calcination temperature is too low or the calcination time is too short, the ferrophosphorus slag cannot undergo crystallization, and a small amount of monoclinic ferric phosphate will be present in the ferrophosphorus slag, reducing the leaching rate of Fe and P and making it difficult to remove graphite from the ferrophosphorus slag. If the calcination temperature is too high or the calcination time is too long, energy consumption will increase and phosphorus will be easily lost through volatilization.

[0031] As a more preferred solution, the calcination temperature is 500-700° C. and the time is 1-3 hours.

[0032] As a preferred solution, the alkali solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, potassium carbonate solution and ammonia water.

[0033] As a preferred embodiment, the ball milling speed for ball milling and leaching is 150 to 700 r / min. More preferably, it is 200 to 500 r / min. The purpose of ball milling is to disrupt the crystal structure of the ferrophosphorus slag, reduce the binding energy of the ferrophosphate structural groups, and make the ferrophosphorus slag easier to crystallize and leach. Too low a ball milling speed makes it difficult to disrupt the crystal structure of the ferrophosphorus slag; too high a speed increases energy consumption.

[0034] As a preferred solution, in step (4), the concentration of the alkali solution is 1-10 wt%, and the liquid-to-solid ratio is 1-10 mL / g.

[0035] As a more preferred solution, in step (4), the concentration of the alkali solution is 1-5 wt%, and the liquid-to-solid ratio is 1-5 mL / g. The iron in the ferrophosphorus slag reacts with hydroxide to form ferric hydroxide precipitate, and the phosphate dissolves in the solution, thereby achieving separation of iron and phosphorus.

[0036] As a preferred solution, in step (4), the ball-to-material ratio of the ball milling leaching is 5 to 20:1.

[0037] As a preferred solution, the pH of the leachate B is adjusted to 8-11. Aluminum and phosphorus in the solution are separated, and aluminum hydroxide and phosphate solution are obtained by solid-liquid separation.

[0038] Compared with the prior art, the present invention has at least the following advantages:

[0039] The present invention achieves the purpose of recycling valuable resources in waste lithium iron phosphate materials, and obtains lithium salt, iron hydroxide, phosphate, sponge copper and aluminum hydroxide products in steps. The operation is simple, the cost is low, the economic benefit is good, and the industrial application is easy. DETAILED DESCRIPTION

[0040] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0041] The present invention is further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without making creative efforts are still within the scope of protection of the present invention.

[0042] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0043] Example 1

[0044] First, 100g of waste lithium iron phosphate material was placed in 300mL of water and thoroughly stirred and dispersed. Then, diluted sulfuric acid with a concentration of 5mol / L and 8mol / L hydrogen peroxide were simultaneously injected through peristaltic pumps (the addition rate of sulfuric acid was 5mL / min, and the addition rate of hydrogen peroxide was 5mL / min). The amount of sulfuric acid and hydrogen peroxide was controlled to make the pH value of the leaching reaction 1.7 and the potential value 620mV. At the same time, the leaching reaction temperature was controlled at 70℃ and the reaction time was 2h to obtain lithium solution and ferrophosphorus slag. At a pH value of 2.0, an excess of 1.3 iron powder was added (i.e., the ratio of iron powder content to copper molar amount in the solution was 1.3:1) to obtain sponge copper and lithium-rich leachate. The pH value of the lithium-rich leachate was further adjusted to 11. After solid-liquid separation, lithium-rich purified solution and impurity-removed slag were obtained. Sodium carbonate solution was added to the lithium-rich purified solution to obtain lithium carbonate (purity of 99.3%). The ferrophosphorus slag was calcined at 600°C for 3 hours and then ball-milled in a 3 wt% NaOH solution for 2 hours (at a milling speed of 500 r / min, a liquid-to-solid ratio of 4 mL / g, and a ball-to-material ratio of 5:1). The resulting product was filtered to obtain ferric hydroxide and an alkaline leachate. The pH of the leachate was adjusted to 8 to produce aluminum hydroxide and a sodium phosphate solution. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the product were 95%, 98%, 97%, 61%, and 95%, respectively.

[0045] Example 2

[0046] First, 100g of waste lithium iron phosphate material was placed in 400mL of water and stirred thoroughly to disperse. Then, diluted sulfuric acid with a concentration of 4mol / L and 6mol / L hydrogen peroxide were simultaneously injected through peristaltic pumps (the addition rate of sulfuric acid was 4mL / min and the addition rate of hydrogen peroxide was 2mL / min). The amount of sulfuric acid and hydrogen peroxide was controlled so that the pH value of the leaching reaction was 2.0 and the potential value was 650mV. At the same time, the leaching reaction temperature was controlled at 75℃ and the reaction time was 1.5h to obtain lithium solution and ferrophosphorus slag. At a pH value of 2.5, an excess of 1.2% iron powder was added (i.e., the ratio of iron powder content to copper molar amount in the solution was 1.2:1) to obtain sponge copper and lithium-rich leachate. The pH value of the lithium-rich leachate was further adjusted to 10. After solid-liquid separation, lithium-rich purified solution and impurity-removed slag were obtained. Sodium carbonate solution was added to the lithium-rich purified solution to obtain lithium carbonate (purity of 99.3%). The ferrophosphorus slag was calcined at 550°C for 3 hours and then ball-milled in a 4 wt% NaOH solution for 2 hours (at a milling speed of 400 r / min, a liquid-to-solid ratio of 5 mL / g, and a ball-to-material ratio of 10:1). The mixture was filtered to obtain ferric hydroxide and an alkaline leachate. The pH of the leachate was adjusted to 9 to produce aluminum hydroxide and a sodium phosphate solution. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the product were 94%, 98%, 98%, 63%, and 97%, respectively.

[0047] Example 3

[0048] First, 100g of waste lithium iron phosphate material was placed in 300mL of water and thoroughly stirred and dispersed. Then, diluted hydrochloric acid with a concentration of 4mol / L and 5mol / L hydrogen peroxide were simultaneously injected through peristaltic pumps (the addition rate of hydrochloric acid was 4mL / min and the addition rate of hydrogen peroxide was 3mL / min). The amount of hydrochloric acid and hydrogen peroxide was controlled so that the pH value of the leaching reaction was 1.5 and the potential value was 620mV. At the same time, the leaching reaction temperature was controlled at 70℃ and the reaction time was 3h to obtain lithium solution and ferrophosphorus slag. At a pH value of 1.5, an excess of 1.1 iron powder was added (i.e., the ratio of iron powder content to copper molar amount in the solution was 1.1:1) to obtain sponge copper and lithium-rich leachate. The solution pH was further adjusted to 11. After solid-liquid separation, lithium-rich purified solution and impurity-removed slag were obtained. Sodium carbonate solution was added to the lithium-rich purified solution to obtain lithium carbonate (purity of 99.4%). Ferrophosphorus slag was calcined at 650°C for 2 hours and then ball-milled in a 3wt% NaOH solution for 2 hours (at a milling speed of 450 r / min, a liquid-to-solid ratio of 4 mL / g, and a ball-to-material ratio of 8:1). The product was filtered to obtain ferric hydroxide and an alkaline leachate. The pH of the leachate was adjusted to 8 to produce aluminum hydroxide and a sodium phosphate solution. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the product were 96%, 99%, 98%, 58%, and 97%, respectively.

[0049] Example 4

[0050] First, 100g of waste lithium iron phosphate material was placed in 300mL of water and thoroughly stirred and dispersed. Then, diluted phosphoric acid with a concentration of 4mol / L and 2mol / L sodium persulfate solution were simultaneously pumped in via peristaltic pumps (the phosphoric acid was added at a rate of 5mL / min and the sodium persulfate solution was added at a rate of 2mL / min). The amount of phosphoric acid and sodium persulfate was controlled to achieve a pH of 1.4 and a potential of 590mV for the leaching reaction. The leaching reaction temperature was also controlled at 70°C for a reaction time of 2h, resulting in a lithium solution and ferrophosphorus slag. At a pH of 1.8, an excess of 1.2% iron powder was added (i.e., the ratio of iron powder content to copper molar mass in the solution was 1.2:1) to obtain sponge copper and lithium-rich leachate. The solution pH was further adjusted to 11. After solid-liquid separation, a lithium-rich purified solution and impurity-removed slag were obtained. Sodium carbonate solution was added to the lithium-rich purified solution to obtain lithium carbonate (purity of 99.2%). The ferrophosphorus slag was calcined at 600°C for 3 hours and then ball-milled in a 3 wt% NaOH solution for 2 hours (at a milling speed of 500 r / min, a liquid-to-solid ratio of 5 mL / g, and a ball-to-material ratio of 5:1). The resulting product was filtered to obtain ferric hydroxide and an alkaline leachate. The pH of the leachate was adjusted to 8 to produce aluminum hydroxide and a sodium phosphate solution. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the product were 95%, 96%, 98%, 63%, and 98%, respectively.

[0051] Example 5

[0052] First, 100g of waste lithium iron phosphate material was placed in 200mL of water and stirred thoroughly to disperse. Then, diluted sulfuric acid with a concentration of 5mol / L and 3mol / L hydrogen peroxide were simultaneously injected through peristaltic pumps (the addition rate of sulfuric acid was 2mL / min and the addition rate of hydrogen peroxide was 4mL / min). The amount of sulfuric acid and hydrogen peroxide was controlled so that the pH value of the leaching reaction was 2.0 and the potential value was 600mV. At the same time, the leaching reaction temperature was controlled at 75℃ and the reaction time was 3h to obtain lithium solution and ferrophosphorus slag. At a pH value of 2.0, an excess of 1.1 iron powder was added (i.e., the ratio of iron powder content to copper molar amount in the solution was 1.1:1) to obtain sponge copper and lithium-rich leachate. The solution pH was further adjusted to 10. After solid-liquid separation, lithium-rich purified solution and impurity-removed slag were obtained. Sodium carbonate solution was added to the lithium-rich purified solution to obtain lithium carbonate (purity of 99.4%). The ferrophosphorus slag was calcined at 700°C for 2 hours and then ball-milled in a 5wt% sodium carbonate solution for 2 hours (at a milling speed of 300 r / min, a liquid-to-solid ratio of 3 mL / g, and a ball-to-material ratio of 15:1). The product was filtered to obtain ferric hydroxide and an alkaline leachate. The pH of the leachate was adjusted to 8 to produce aluminum hydroxide and a sodium phosphate solution. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the product were 98%, 96%, 98%, 63%, and 97%, respectively.

[0053] Example 6

[0054] First, 100g of waste lithium iron phosphate material was placed in 300mL of water and thoroughly stirred and dispersed. Then, diluted sulfuric acid and 3mol / L sodium chlorate solutions were simultaneously pumped in via peristaltic pumps (the sulfuric acid was added at a rate of 4mL / min and the sodium chlorate solution was added at a rate of 3mL / min). The amount of sulfuric acid and sodium chlorate solution was controlled to achieve a pH of 2.0 and a potential of 620mV for the leaching reaction. The leaching reaction temperature was also controlled at 75°C and the reaction time was 2h, resulting in a lithium solution and ferrophosphorus slag. At a pH of 2.0, an excess of 1.2% iron powder was added (i.e., the ratio of iron powder content to copper molar mass in the solution was 1.2:1) to obtain sponge copper and lithium-rich leachate. The solution pH was further adjusted to 11. After solid-liquid separation, a lithium-rich purified solution and impurity-free slag were obtained. Sodium carbonate solution was added to the lithium-rich purified solution to obtain lithium carbonate (purity of 99.2%). The ferrophosphorus slag was calcined at 600°C for 3 hours and then ball-milled in a 3 wt% KOH solution for 2 hours (stirring speed 500 r / min, liquid-to-solid ratio 3 mL / g, ball-to-material ratio 12:1). The mixture was filtered to obtain ferric hydroxide and an alkaline leachate. The pH of the alkaline leachate was adjusted to 8 to obtain aluminum hydroxide and potassium phosphate solution. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the obtained product were 95%, 98%, 98%, 62%, and 97%, respectively.

[0055] Example 7

[0056] This example was carried out using a method similar to that of Example 1, except that the ball milling speed was adjusted to 100 r / min. The recoveries of lithium, iron, phosphorus, aluminum, and copper in the obtained product were 96%, 82%, 84%, 57%, and 96%, respectively. The purity of the lithium carbonate was 99.3%.

[0057] Comparative Example 1

[0058] This comparative example was carried out with reference to a method similar to Example 1, except that sulfuric acid and hydrogen peroxide were added simultaneously, with sulfuric acid added first and hydrogen peroxide added later (hydrogen peroxide was added after sulfuric acid was added dropwise, and the amounts and addition rates of sulfuric acid and hydrogen peroxide were the same as in Example 1). The lithium, iron, phosphorus, aluminum, and copper recoveries in the obtained product were 95%, 61%, 62%, 65%, and 97%, respectively. The purity of lithium carbonate was 99.2%. In this comparative example, sulfuric acid was first added to easily leach the Li, Fe, and P elements in the lithium iron phosphate. At this time, the iron in the solution was mainly ferrous iron. After adding hydrogen peroxide, the ferrous iron was oxidized to ferric iron, and Fe and P formed monoclinic iron phosphate. This iron phosphate structure is stable and subsequent leaching is difficult, which reduces the Fe and P recoveries.

[0059] Comparative Example 2

[0060] This comparative example was conducted using a method similar to Example 1, except that the calcined ferrophosphorus slag was subjected to agitated alkali leaching (at the same agitation speed as in Example 1) rather than ball-milled alkali leaching. The resulting product had lithium, iron, phosphorus, aluminum, and copper recoveries of 96%, 75%, 79%, 51%, and 96%, respectively. The purity of the lithium carbonate was 99.3%. In this comparative example, the ferrophosphorus slag partially agglomerated after calcination, resulting in a weaker alkali leaching rate due to the lack of a ball-milling step.

[0061] Comparative Example 3

[0062] This comparative example was carried out in a manner similar to that of Example 1, except that concentrated sulfuric acid was used to adjust the pH (at a constant addition rate). The resulting product had recoveries of 97%, 82%, 84%, 58%, and 95% for lithium, iron, phosphorus, aluminum, and copper, respectively. The purity of the lithium carbonate was 99.4%.

[0063] In this comparative example, since concentrated sulfuric acid was used to adjust the pH value of the system, the reaction was violent and the system temperature was too high, and Fe and P formed monoclinic iron phosphate, which was difficult to be leached subsequently.

[0064] Comparative Example 4

[0065] This comparative example was conducted using a method similar to Example 1, except that the hydrogen peroxide addition rate was adjusted to 20 mL / min (the volume and concentration of hydrogen peroxide remained unchanged; only the addition rate was changed). The resulting product had recoveries of 95%, 64%, 68%, 55%, and 94% for lithium, iron, phosphorus, aluminum, and copper, respectively. The purity of the lithium carbonate was 99.2%.

[0066] In this comparative example, the hydrogen peroxide was added too quickly, resulting in a violent reaction and an excessively high system temperature. Fe and P formed monoclinic iron phosphate, which made it difficult to subsequently leach Fe and P.

[0067] Comparative Example 5

[0068] This comparative example was conducted using a method similar to Example 1, except that the resulting ferrophosphorus slag was directly ball-milled in an alkaline solution without calcination and crystallization. The resulting product had lithium, iron, phosphorus, aluminum, and copper recoveries of 96%, 88%, 84%, 58%, and 93%, respectively. The purity of lithium carbonate was 99.3%. In this comparative example, due to the lack of crystallization treatment, a small amount of monoclinic iron phosphate was present in the ferrophosphorus slag, which reduced the leaching rates of Fe and P.

[0069] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for recovering valuable resources from waste lithium iron phosphate materials, characterized by: The method includes: (1) Dispersing waste lithium iron phosphate material in water to obtain a mixture I; (2) adding an acid solution and an oxidant solution to the mixture I simultaneously to carry out a leaching reaction, and obtaining a leachate A and an active ferrophosphorus slag after solid-liquid separation; the oxidant solution is added at a rate of 2 to 10 mL / min; the acid solution is added at a rate of 2 to 10 mL / min; and the concentration of the acid solution is 1.5 to 8 mol / L; The leaching reaction conditions include: pH value of 0.5-3, potential value of 300-700 mV, temperature of 50-90° C., and time of 1-4 hours; (3) performing a replacement reaction between the iron powder and the leachate A to recover the copper in the leachate A, and obtaining sponge copper and lithium-rich leachate through solid-liquid separation; and calcining the active ferrophosphorus slag to transform the crystals and remove the impurity carbon to obtain decarbonized ferrophosphorus slag; (4) mixing the decarburized ferrophosphorus slag with an alkaline solution, and placing the mixture in a mill for ball milling and leaching, and obtaining a leachate B and ferric hydroxide through solid-liquid separation; (5) The pH of the leachate B is adjusted to alkaline, aluminum and phosphorus in the solution are separated, and aluminum hydroxide and phosphate solution are obtained by solid-liquid separation.

2. The method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1, characterized in that: The acid solution is selected from at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution and phosphoric acid solution.

3. A method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1 or 2, characterized in that: The oxidant solution is selected from at least one of a hydrogen peroxide solution, a sodium persulfate solution and a sodium chlorate solution.

4. The method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1 or 2, characterized in that: The molar ratio of the iron powder to the copper in the leachate A is 1-3:1, and the pH of the replacement reaction is 1.5-4.

5. The method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1 or 2, characterized in that: In step (3), the method further comprises: The pH value of the lithium-rich leachate is adjusted to 9-12 for impurity removal, and solid-liquid separation is performed to obtain a lithium-rich purified liquid and impurity-removed residue. The lithium-rich purified liquid is subjected to a precipitation reaction with a lithium precipitant to obtain a lithium salt product.

6. The method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1 or 2, characterized in that: The calcination and crystallization temperature is 400-800° C. and the time is 1-6 hours.

7. A method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1 or 2, characterized in that: The alkali solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution and potassium carbonate solution.

8. The method for recovering valuable resources from waste lithium iron phosphate materials according to claim 1 or 2, characterized in that: The ball milling speed of the ball milling leaching is 150-700 r / min.