阅读说明：本技术 一种废旧磷酸铁锂正极材料中回收锂铁磷的方法 (Method for recovering lithium iron phosphorus from waste lithium iron phosphate positive electrode material ) 是由 张琦 曹玉欣 戴群英 华东 于 2020-12-07 设计创作，主要内容包括：本发明提供了一种废旧磷酸铁锂正极材料中回收锂铁磷的方法,包括：(1)用碱将废旧磷酸铁锂正极材料的铝溶解,收集固体；(2)用硫酸溶解步骤(1)的固体,固液分离得到的溶液进行第一次蒸发浓缩,降温结晶得到液体和结晶,纯化结晶；(3)对步骤(2)得到的液体进行第二次蒸发浓缩,固液分离得到液体和固体,对固体进行除杂和碳化；(4)对步骤(3)得到的液体进行第三次蒸发浓缩。通过该方法,实现了废旧磷酸铁锂材料中锂、铁、磷三种元素的分离,分别制备成了工业级碳酸锂、绿矾和磷酸,以及副产品芒硝。此外,本发明的方法消耗的辅料较少,可有效降低磷酸铁锂材料回收成本。(The invention provides a method for recovering lithium iron phosphorus from waste lithium iron phosphate anode materials, which comprises the following steps: (1) dissolving aluminum of the waste lithium iron phosphate anode material by using alkali, and collecting solid; (2) dissolving the solid in the step (1) by using sulfuric acid, carrying out first evaporation concentration on the solution obtained by solid-liquid separation, cooling and crystallizing to obtain liquid and crystals, and purifying the crystals; (3) carrying out second evaporation concentration on the liquid obtained in the step (2), carrying out solid-liquid separation to obtain liquid and solid, and carrying out impurity removal and carbonization on the solid; (4) and (4) carrying out third evaporation concentration on the liquid obtained in the step (3). By the method, the separation of three elements of lithium, iron and phosphorus in the waste lithium iron phosphate material is realized, and industrial-grade lithium carbonate, green vitriol and phosphoric acid and a byproduct mirabilite are respectively prepared. In addition, the method of the invention consumes less auxiliary materials, and can effectively reduce the recovery cost of the lithium iron phosphate material.)

1. A method for recovering waste lithium iron phosphate anode materials is characterized by comprising the following steps:

(1) dissolving aluminum of the waste lithium iron phosphate anode material by using alkali, and collecting solid;

(2) dissolving the solid in the step (1) by using sulfuric acid, carrying out first evaporation concentration on the solution obtained by solid-liquid separation, cooling and crystallizing to obtain liquid and crystals, and purifying the crystals;

(3) carrying out second evaporation concentration on the liquid obtained in the step (2), carrying out solid-liquid separation to obtain liquid and solid, and carrying out impurity removal and carbonization on the solid;

(4) and (4) carrying out third evaporation concentration on the liquid obtained in the step (3).

2. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (1), the alkali is a sodium hydroxide solution with a concentration of 4.5mol/L to 5.5 mol/L.

3. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (2), the sulfuric acid is a sulfuric acid solution with a concentration of 2.0mol/L to 2.5mol/L, and the weight ratio of the solid to the sulfuric acid solution is 1:4 to 1: 5.

4. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (2), the solid in the step (1) is dissolved by sulfuric acid at 50-70 ℃, and the density of the solution after dissolution is 1.30-1.35 g/mL.

5. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (2), the first evaporation and concentration is carried out at 80-95 ℃, the evaporation rate of the liquid is controlled to be 30-40%, and the density of the solution after evaporation is more than 1.50 g/mL; cooling and crystallizing at 0-5 deg.c for 0.5-1 hr.

6. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (3), the second evaporation and concentration is carried out at 80-95 ℃, the evaporation rate of the liquid is controlled to be 35-50%, and the density of the evaporated solution is above 1.55 g/mL.

7. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (3), the step of removing impurities is to dissolve the solid in water to obtain a solution with a concentration of 2.0mol/L to 3.0mol/L, adjust the pH value to 8.0 to 10.0 by using a 1.0mol/L to 2.0mol/L sodium hydroxide solution, and then perform solid-liquid separation to obtain the lithium carbonate solution.

8. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 7, wherein in the step (3), the carbonization step is to add the lithium sulfate solution into a sodium carbonate solution with a concentration of 1.5mol/L to 2.0mol/L, wherein the sodium carbonate is 1.0 to 1.1 times of the molar weight of the lithium sulfate, the carbonization temperature is maintained at 90 to 95 ℃, and the reaction is carried out for 2 to 3 hours.

9. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (3), the solid is subjected to impurity removal and carbonization and then is crystallized at 0-5 ℃.

10. The method for recycling the waste lithium iron phosphate cathode material as claimed in claim 1, wherein in the step (4), the third evaporation and concentration is performed at 80-95 ℃.

Technical Field

The invention relates to the technical field of comprehensive recycling of waste lithium batteries, in particular to a method for recycling lithium iron phosphorus from a waste lithium iron phosphate positive electrode material.

Background

The lithium battery taking the lithium iron phosphate as the anode material is generally applied to the field of new energy automobiles due to good safety performance and cycle performance. With the rapid development of the new energy automobile industry, the usage amount of the power lithium battery is rapidly increased continuously, and the scrappage amount of the lithium battery is also rapidly increased in recent years. Compared with elements such as cobalt, nickel, manganese and lithium with higher recovery value in the ternary battery, the lithium iron phosphate battery has lower recovery value of phosphorus and iron besides lithium element, and if only lithium element is recovered, a large amount of phosphorus and iron slag is generated to pollute soil environment and water environment. The recycling of various lithium battery materials is realized, the healthy development of the new energy automobile industry can be promoted, and the problem of environmental pollution caused by waste lithium battery materials can be solved. The recovery of cobalt, nickel and manganese elements in the waste ternary lithium battery materials is mainly realized by separating the cobalt, nickel and manganese elements through relatively mature extraction and back-extraction processes to prepare corresponding metal salts, and then preparing ternary precursors of various types according to requirements so as to prepare anode materials and lithium batteries, so that the lithium battery materials are recycled. The nickel, cobalt, manganese and lithium has higher value and better economic benefit for recycling. The waste lithium iron phosphate material has relatively low values of iron and phosphorus, so that the economic benefit is poor, and a good recycling process is not developed for a while.

The Chinese patent application with the application number of 202010138675.8 discloses a method for recovering waste lithium iron phosphate positive plates, which comprises the following steps: s1, mechanically crushing the positive plate obtained by disassembling the waste lithium iron phosphate battery to obtain positive fragments; s2, mixing the positive fragments with solid strong base uniformly, roasting to enable the molten strong base to react with aluminum to generate meta-aluminate, and collecting mixed powder obtained after roasting; s3, mixing the mixed powder obtained in the step S2 with water, carrying out solid-liquid separation, collecting a solid phase part, and recovering lithium, iron and/or phosphorus elements from the solid phase part. Although the method realizes the synchronous recovery of the three elements of the lithium iron and the phosphorus and directly obtains two products of the iron phosphate and the lithium carbonate, the process for preparing the iron phosphate in the sulfuric acid-lithium iron phosphate mixed solution is greatly different from the traditional iron phosphate preparation process, and the performance of the iron phosphate prepared by the method needs to be further verified.

Disclosure of Invention

In order to solve all or part of the problems, the invention aims to provide a method for recovering lithium iron phosphorus from waste lithium iron phosphate positive electrode materials.

The invention realizes the above purposes by the following technical scheme:

a method for recovering waste lithium iron phosphate anode materials comprises the following steps:

(1) dissolving aluminum of the waste lithium iron phosphate anode material by using alkali, and collecting solid;

(2) dissolving the solid in the step (1) by using sulfuric acid, carrying out first evaporation concentration on the solution obtained by solid-liquid separation, cooling and crystallizing to obtain liquid and crystals, and purifying the crystals;

(3) carrying out second evaporation concentration on the liquid obtained in the step (2), carrying out solid-liquid separation to obtain liquid and solid, and carrying out impurity removal and carbonization on the solid;

(4) and (4) carrying out third evaporation concentration on the liquid obtained in the step (3).

Alternatively, in step (1), the base is a sodium hydroxide solution having a concentration of 4.5mol/L to 5.5 mol/L.

Optionally, in the step (2), the sulfuric acid is a sulfuric acid solution with a concentration of 2.0mol/L to 2.5mol/L, and the weight ratio of the solid to the sulfuric acid solution is 1:4 to 1: 5.

Alternatively, in step (2), the solid of step (1) is dissolved with sulfuric acid at 50 ℃ to 70 ℃ and the density of the solution after dissolution is 1.30g/mL to 1.35 g/mL.

Optionally, in the step (2), the first evaporation concentration is carried out at 80-95 ℃, the evaporation rate of the liquid is controlled to be 30-40%, and the density of the solution after evaporation is more than 1.50 g/mL; cooling and crystallizing at 0-5 deg.c for 0.5-1 hr.

Optionally, in step (3), the second evaporation concentration is carried out at 80-95 ℃, the evaporation rate of the liquid is controlled to be 35-50%, and the density of the solution after evaporation is above 1.55 g/mL.

Optionally, in the step (3), the impurity removal is to dissolve the solid in water to obtain a solution with a concentration of 2.0mol/L to 3.0mol/L, adjust the pH value to 8.0 to 10.0 by using 1.0mol/L to 2.0mol/L sodium hydroxide solution, and then perform solid-liquid separation to obtain the lithium sulfate solution.

Optionally, in the step (3), the carbonization is performed by adding the lithium sulfate solution into a sodium carbonate solution with the concentration of 1.5-2.0 mol/L, wherein the sodium carbonate is 1.0-1.1 times of the molar weight of the lithium sulfate, the carbonization temperature is maintained at 90-95 ℃, and the reaction lasts for 2-3 h.

Optionally, in step (3), the solid is subjected to impurity removal and carbonization, followed by crystallization at 0 ℃ to 5 ℃.

Alternatively, in step (4), the third evaporative concentration is carried out at 80 ℃ to 95 ℃.

Compared with the prior art, the method for recovering lithium iron phosphorus from the waste lithium iron phosphate anode material has the following beneficial effects:

the separation of three elements of lithium, iron and phosphorus in the waste lithium iron phosphate material is realized, and industrial-grade lithium carbonate, green vitriol and phosphoric acid and a byproduct mirabilite are respectively prepared. The method firstly utilizes the solubility difference between ferrous sulfate and lithium sulfate, realizes the separation of iron, lithium and phosphorus by cooling crystallization after evaporation concentration, and realizes the separation of lithium and phosphorus by secondary evaporation concentration. The method of the invention consumes less auxiliary materials and can effectively reduce the recovery cost of the lithium iron phosphate material.

Drawings

Fig. 1 is a process flow chart of the method for recovering lithium iron phosphorus from the waste lithium iron phosphate positive electrode material.

Detailed Description

The present invention will be described in detail with reference to the following embodiments in order to fully understand the objects, features and effects of the invention. The process of the present invention employs conventional methods or apparatus in the art, except as described below. The following noun terms have meanings commonly understood by those skilled in the art unless otherwise specified.

In order to synchronously recover three elements of lithium, iron and phosphorus in the waste lithium iron phosphate battery, the inventor of the invention provides the following concepts through research: firstly, utilizing the solubility difference of ferrous sulfate and lithium sulfate, evaporating, concentrating, cooling and crystallizing to obtain ferrous sulfate, implementing separation of iron from lithium and phosphorus, then evaporating and concentrating again to implement separation of lithium and phosphorus.

Based on this, the inventor of the present invention provides a method for recovering lithium iron phosphorus from a waste lithium iron phosphate positive electrode material, which comprises: (1) dissolving aluminum of the waste lithium iron phosphate anode material by using alkali, and collecting solid; (2) dissolving the solid in the step (1) by using sulfuric acid, carrying out first evaporation concentration on the solution obtained by solid-liquid separation, cooling and crystallizing to obtain liquid and crystals, and purifying the crystals; (3) carrying out second evaporation concentration on the liquid obtained in the step (2), carrying out solid-liquid separation to obtain liquid and solid, and carrying out impurity removal and carbonization on the solid; (4) and (4) carrying out third evaporation concentration on the liquid obtained in the step (3).

By the method, the separation of three elements of lithium, iron and phosphorus in the waste lithium iron phosphate material is realized, and industrial-grade lithium carbonate, copperas (namely ferrous sulfate heptahydrate) and phosphoric acid and a byproduct mirabilite (namely sodium sulfate decahydrate) are respectively prepared. In addition, the method of the invention consumes less auxiliary materials, and can effectively reduce the recovery cost of the lithium iron phosphate material.

Fig. 1 is a process flow chart of the method for recovering lithium iron phosphorus from the waste lithium iron phosphate cathode material, and a preferred embodiment of the invention is described in detail below with reference to fig. 1:

(1) removing aluminum in waste lithium iron phosphate anode material

Dissolving the disassembled waste lithium iron phosphate material by using alkali, such as sodium hydroxide solution with the concentration of 4.5-5.5 mol/L so as to dissolve aluminum, carrying out solid-liquid separation after the reaction is completed, and collecting the solid. Subsequently, the solid is washed, for example, with a sodium hydroxide solution having a concentration of 0.05mol/L to 0.15 mol/L. The solid obtained in the step mainly comprises lithium iron phosphate with low aluminum content, a diaphragm, carbon black and the like.

In this step, the following chemical reactions mainly take place:

2Al+2NaOH+2H₂O＝2NaAlO₂+3H₂↑

(2) separation of iron from lithium and phosphorus

Dissolving the solid washed in the step (1) by using sulfuric acid, for example, a sulfuric acid solution with a concentration of 2.0 mol/L-2.5 mol/L, wherein the weight ratio of the solid to the sulfuric acid solution is 1: 4-1: 5. The pH value of the dissolution end point is controlled to be less than 1.0 by adjusting the adding amount of the sulfuric acid. In the dissolving process, the temperature of the solution is maintained between 50 ℃ and 70 ℃, the solubility of the ferrous sulfate is higher in the temperature range, and the density of the dissolved solution is between 1.30g/mL and 1.35g/mL, so that the solution is close to saturation.

After completion of the dissolution reaction, solid-liquid separation is performed to remove acid-insoluble substances such as a separator and carbon black. The obtained solution is heated to 80-95 ℃ for the first evaporation and concentration, and the pressure can be properly reduced in the process to improve the evaporation speed. The evaporation amount of the liquid is controlled between 30 percent and 40 percent, and the density of the solution after evaporation is more than 1.50 g/mL. Cooling the solution to 0-5 deg.c for 0.5-1 hr for cooling and crystallization. And then, carrying out solid-liquid separation, and leaching the solid on line by adopting a small amount of pure water at 0-5 ℃ to obtain the solid, namely the crude ferrous sulfate crystal. And (4) feeding the liquid obtained by solid-liquid separation into the step (3).

Subsequently, the crude ferrous sulfate crystals are purified. The crude ferrous sulfate crystals can be purified by the following method: adding pure water accounting for 50 percent of the weight of the crude ferrous sulfate crystal, dissolving at 50-70 ℃, cooling the solution to 0-5 ℃, maintaining for 0.5-1 h, and carrying out solid-liquid separation to obtain the copperas.

In this step, the following chemical reactions mainly take place:

2LiFePO₄+3H₂SO₄＝2Li⁺+2Fe²⁺+3SO₄ ^2-+6H⁺+2PO₄ ^3-2Li⁺+2Fe²⁺+3SO₄ ^2-+6H⁺+2PO₄ ^3-+14H₂O＝2FeSO₄·7H₂O↓+2Li⁺+SO₄ ^2-+6H⁺+2PO₄ ^3-

(3) separation of lithium and phosphorus

And (3) carrying out second evaporation concentration on the liquid separated and removed from the crude ferrous sulfate crystals in the step (2). The temperature of evaporation concentration is controlled between 80 ℃ and 95 ℃, the evaporation capacity of the solution is controlled between 35 percent and 50 percent, and the density of the solution after evaporation is over 1.55 g/mL. Then, the solution is subjected to solid-liquid separation, and the resulting liquid (i.e., crude phosphoric acid) is subjected to step (4).

And leaching the obtained solid on line by using a small amount of pure water with the temperature of 90-95 ℃ to obtain crude lithium sulfate crystals (lithium sulfate monohydrate). Then, removing impurities from the crude lithium sulfate crystal, specifically: dissolving lithium sulfate crystals by using pure water, controlling the concentration of the dissolved lithium sulfate to be 2.0-3.0 mol/L, adjusting the pH value to be 8.0-10.0 by using 1.0-2.0 mol/L sodium hydroxide solution, and then carrying out solid-liquid separation. And carbonizing the obtained lithium sulfate solution, specifically: adding the lithium sulfate solution into a sodium carbonate solution with the concentration of 1.5-2.0 mol/L, wherein the sodium carbonate is 1.0-1.1 times of the molar weight of the lithium sulfate, the carbonization temperature is maintained at 90-95 ℃, and the reaction is carried out for 2-3 h.

And (3) carrying out solid-liquid separation after carbonization treatment, washing the obtained solid lithium carbonate with pure water at 90-95 ℃, for example, pulping twice according to the solid-liquid weight ratio of 1: 3-1: 4, and thus obtaining the industrial-grade lithium carbonate. And cooling and crystallizing the solution after the lithium carbonate is separated, controlling the crystallization temperature to be 0-5 ℃, and obtaining crystallized solid which is mirabilite.

In this step, the following chemical reactions mainly take place:

2Li⁺+SO₄ ^2-+6H⁺+2PO₄ ^3-+H₂o (crystalline) ═ Li₂SO₄·H₂O↓+6H⁺+2PO₄ ^3-

Fe²⁺+2NaOH＝Fe(OH)₂↓+2Na⁺

Na₂CO₃+Li₂SO₄(high temperature) ═ Na₂SO₄+Li₂CO₃↓

(4) Recovery of phosphorus

And (4) carrying out third evaporation concentration on the crude phosphoric acid separated in the step (3), controlling the evaporation concentration temperature to be 80-95 ℃, evaporating the water in the solution, separating out a small amount of ferrous sulfate and lithium sulfate solids, and carrying out solid-liquid separation to obtain liquid, namely phosphoric acid.

Examples

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions. The starting materials referred to in the following examples are all conventionally commercially available. The equipment involved in the following examples is conventional in the art.

Example 1

(1) Weighing about 550g of waste lithium iron phosphate positive plate, crushing by using a small crusher, slowly adding into a 3L beaker containing 2.5L of NaOH solution with the concentration of 5.0mol/L, and stirring until no gas is generated. After filtration, pulping and washing twice by using 0.1mol/L NaOH solution according to the solid-to-liquid ratio of 1: 3. After filtration, the solid is pulped and washed twice by 0.1mol/L NaOH solution according to the solid-to-liquid ratio of 1: 3.

(2) And (3) adding 506g of powder obtained after solid washing and drying into 2.25L of sulfuric acid solution with the concentration of 2.0mol/L, maintaining the temperature between 50 and 70 ℃ in a water bath, reacting for 4 hours, and then performing suction filtration, wherein the pH value is 0.63. The total amount of the solution after suction filtration is about 1.975L, the density is 1.31g/mL, the weight of a filter cake is about 277g, the solid is dried by about 26g after pulping and washing according to the solid-to-liquid ratio of 1:3, and the washing liquid is not combined with the obtained 1.975L solution. About 2579g of 1.975L solution was evaporated in a water bath at 90 ℃ to 1692g, 34.39% weight loss and 1.58g/mL solution density. Cooling the solution in ice bath until a large amount of crystals are separated out at 3-5 ℃, maintaining for 0.5h, then carrying out suction filtration, leaching the solid crystals by adopting about 100mL of 5 ℃ cold water to obtain about 718g of crude ferrous sulfate crystals, adding about 360g of pure water into the crystals to dissolve in 60 ℃ water bath, cooling to 3-5 ℃ again after complete dissolution, maintaining for 0.5h, and carrying out suction filtration to obtain about 493g of copperas. The detection quality of the copperas is as follows:

table 1: copperas assay results

(3) The solution after the primary evaporation concentration, cooling and crystallization and solid separation is about 705mL, the weight is about 966g, the density is about 1.37g/mL, and the secondary evaporation concentration is carried out in a water bath at 90 ℃, the weight is reduced to 592g, the weight reduction rate is 38.72 percent, and the density is 1.55 g/mL. After the solution was cooled to room temperature, the solid obtained by suction filtration was washed with about 50mL of hot water having a temperature of 90 ℃ to obtain about 123g of white lithium sulfate crystals. Dissolving the obtained lithium sulfate crystal with 750mL of water, adjusting the pH value of the solution to 9.87 by using about 76mL of 2.0mol/L sodium hydroxide solution, carrying out solid-liquid separation, adding the lithium sulfate solution into 570mL of 1.98mol/L sodium carbonate solution for carbonization, maintaining the temperature at 95 ℃ for about 1h, carrying out suction filtration, pulping and washing the solid with 95 ℃ pure water according to the solid-liquid ratio of 1:2 twice, and finally obtaining about 56g of industrial-grade lithium carbonate. Evaporating about 1.3L of the carbonized solution to concentrate to 600mL, cooling and crystallizing to obtain about 319g of mirabilite. The detection results of the industrial grade lithium carbonate and the mirabilite are as follows:

table 2: lithium carbonate detection result

Table 3: detection result of mirabilite

(4) The filtrate obtained after the secondary evaporation concentration and separation of lithium sulfate crystals is about 243mL, the weight is about 378g, and the density is about 1.55 g/mL. And (3) carrying out evaporation concentration for three times, controlling the temperature of the evaporation concentration to be between 80 and 95 ℃, evaporating the water in the solution, separating out a small amount of solid, and separating to obtain 135mL of phosphoric acid with the density of about 1.63 g/mL.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other substitutions, modifications, combinations, changes, simplifications, etc., which are made without departing from the spirit and principle of the present invention, should be construed as equivalents and included in the protection scope of the present invention.