阅读说明：本技术 一种从提锂渣酸浸液中选择性回收电池级磷酸铁的方法 (Method for selectively recovering battery-grade iron phosphate from acid leaching solution of lithium extraction slag ) 是由 杨利明 冯裕发 罗旭彪 邵鹏辉 石慧 吴稚骅 宋亮 王超强 章小明 谢绍忠 彭爱 于 2020-12-04 设计创作，主要内容包括：一种从提锂渣酸浸液中选择性回收电池级磷酸铁的方法,涉及一种处理废弃提锂渣的方法。本发明是要解决现有的湿法冶金回收退役磷酸铁锂电池产生的提锂渣中杂质金属且含量较高,并且成分复杂,很难再次利用的技术问题。本发明将废弃提锂渣用无机酸浸出,基于溶度积原理,分析多金属沉淀体系的平衡热力学,选择性沉淀磷酸铁,再进行煅烧使其变成结晶程度高的电池级磷酸铁,用来重新制备磷酸铁锂正极材料。本发明探索适合的沉淀剂、煅烧温度等沉淀条件和煅烧条件,回收电化学性能优异的电池级磷酸铁,实现废弃提锂渣的资源化回收,使得整个废旧磷酸铁锂正极材料能够再生回用,这对于动力锂电池退役高峰期的到来具有重要意义。(A method for selectively recovering battery-grade iron phosphate from an acid leaching solution of a lithium extraction residue relates to a method for treating waste lithium extraction residue. The invention aims to solve the technical problems that the impurity metal content in the lithium extraction slag generated by the existing hydrometallurgy recovery of the retired lithium iron phosphate battery is high, the components are complex, and the reutilization is difficult. According to the invention, the waste lithium extraction slag is leached by using inorganic acid, the equilibrium thermodynamics of a multi-metal precipitation system is analyzed based on the solubility product principle, the iron phosphate is selectively precipitated, and then the iron phosphate is calcined to be changed into battery-grade iron phosphate with high crystallization degree, so that the lithium iron phosphate cathode material is prepared again. The method explores suitable precipitating conditions and calcining conditions such as a precipitator and calcining temperature, recovers the battery-grade iron phosphate with excellent electrochemical performance, realizes resource recovery of the waste lithium extraction slag, enables the whole waste lithium iron phosphate anode material to be regenerated and reused, and has important significance for the arrival of the retired peak period of the power lithium battery.)

1. A method for selectively recovering battery-grade iron phosphate from acid leaching solution of lithium extraction residue is characterized in that the method for selectively recovering the battery-grade iron phosphate from the acid leaching solution of the lithium extraction residue is carried out according to the following steps:

dissolving lithium extraction slag in an inorganic acid solution, heating to 60-70 ℃, preserving heat and dissolving for 1-1.5 h to dissolve metals in the lithium extraction slag into the solution, and obtaining an acid leaching solution of the lithium extraction slag;

the lithium extraction slag is the solid remained after extracting lithium from the waste lithium iron phosphate by using inorganic acid;

taking out the supernatant in the acid leaching solution of the lithium extraction residue, dripping a precipitator into the supernatant until the pH value is 1-4, heating and stirring the solution at the temperature of 40-180 ℃ for 0.5-10 h, naturally cooling the solution to room temperature, performing solid-liquid separation, and drying residues;

the precipitator is one or a mixture of more of sodium hydroxide, ammonia water and ammonium acetate;

and thirdly, placing the residues obtained in the second step into a quartz crucible, heating the quartz crucible for 1 to 10 hours in a tubular furnace at the temperature of between 200 and 1200 ℃, and naturally cooling the quartz crucible to room temperature to obtain the battery-grade iron phosphate.

2. The method for selectively recovering battery-grade iron phosphate from the acid leaching solution of the lithium extraction residue according to claim 1, wherein the inorganic acid solution in the first step is one or a mixture of more of a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution, a nitric acid aqueous solution and a phosphoric acid aqueous solution.

3. The method for selectively recovering the battery-grade iron phosphate from the acid leaching solution of the lithium extraction slag according to claim 1, wherein the first step is heating to 60 ℃ and dissolving for 1 hour under the condition of heat preservation.

4. The method for selectively recovering battery-grade iron phosphate from the acid leaching solution of the lithium extraction slag according to claim 1, characterized in that the solid-liquid separation method in the second step is as follows: and pouring the solution into a cloth type funnel on a filter flask, and performing suction filtration by using a circulating water type multipurpose vacuum pump to obtain a solid in the cloth type funnel.

5. The method for selectively recovering battery-grade iron phosphate from the acid leaching solution of the lithium extraction slag according to claim 1, wherein a precipitant is added dropwise to the solution in the second step until the pH value is 2.

6. The method for selectively recovering battery-grade iron phosphate from the acid leaching solution of the lithium extraction slag according to claim 1, wherein the residue obtained in the second step is placed in a quartz crucible in the third step, heated for 4 hours at 600 ℃ in a tubular furnace, and naturally cooled to room temperature to obtain the battery-grade iron phosphate.

7. The method for selectively recovering battery-grade iron phosphate from the acid leaching solution of the lithium extraction slag according to claim 1, wherein the model of the tubular furnace in the third step is OTF-1200X.

Technical Field

The invention relates to a method for treating waste lithium extraction slag.

Background

Lithium ion batteries have high energy density and reliability, and thus are widely used in portable electronic devices and new energy electric vehicles. The lithium iron phosphate battery is praised as the most potential lithium ion power battery due to rich raw material sources, low price, longer cycle life, good high-temperature performance and good safety performance. In 4 months in 2020, the Ministry of industry and communications issued 331 th batch of road motor vehicle manufacturing enterprises and product bulletins, and the new energy vehicles reported in the Ministry of industry and communications had 306 types, and 78% of vehicles adopting lithium iron phosphate batteries. The lithium iron phosphate battery has to be out of service after being used for a certain period of time. If the retired lithium iron phosphate battery cannot be properly treated, heavy metals leaked from the positive electrode material can continuously migrate along with the atmosphere, water and soil or be converted into compounds with stronger toxicity, so that the pollution to water and soil is caused. Decomposition of the electrolyte solvent and the binder and hydrolysis products may cause contamination of organic substances such as aldehyde, ketone, methanol, etc. Heavy metals and organic matters entering the ecological system are enriched in high-grade organisms through a food chain, and great harm is generated to the ecological system and human health. The lithium content in the lithium iron phosphate battery reaches 1.1 percent, which is obviously higher than that of lithium ores developed and utilized in China, and meanwhile, the price of lithium carbonate reaches 50000 yuan/ton. If can recycle the used battery, not only can make the enterprise profit, can also protect the environment simultaneously.

Among a plurality of lithium battery anode materials, the lithium iron phosphate battery is always popular due to the outstanding high-temperature performance and stability, the excellent cycle life and the use experience of the lithium iron phosphate battery, the market share of the lithium iron phosphate battery is continuously improved, and the retirement amount is also increased rapidly. The conventional ex-service lithium iron phosphate battery recycling method comprises pyrometallurgy and hydrometallurgy, wherein the pyrometallurgy is to uniformly calcine various recycled batteries at high temperature, products of the batteries are sold as secondary alloys, and the method is simple but difficult to purposefully recycle. The hydrometallurgical method can extract more than 90% of Li, but a large amount of Li-extracting slag remains. The typical process of hydrometallurgy is to selectively extract expensive lithium and to obtain the residual lithium extraction slag. The lithium extraction slag contains impurity metals such as Mg, Ca, Cu, Ni and the like, has high content and complex components, and is difficult to reuse.

Disclosure of Invention

The invention provides a method for selectively recovering battery-grade iron phosphate from an acid leaching solution of lithium extraction residues, aiming at solving the technical problems that the lithium extraction residues generated by the existing hydrometallurgical recovery of retired lithium iron phosphate batteries are high in impurity metal content, complex in components and difficult to reuse.

The method for selectively recovering battery-grade iron phosphate from the acid leaching solution of the lithium extraction residue is carried out according to the following steps:

dissolving lithium extraction slag in an inorganic acid solution, heating to 60-70 ℃, preserving heat and dissolving for 1-1.5 h to dissolve metals in the lithium extraction slag into the solution, and obtaining an acid leaching solution of the lithium extraction slag;

the lithium extraction slag is a solid remained after lithium is extracted from waste lithium iron phosphate by using inorganic acid, wherein impurity metal elements comprise Mg, Ca, Cu, Ni and the like;

taking out the supernatant in the acid leaching solution of the lithium extraction residue, dripping a precipitator into the supernatant until the pH value is 1-4, heating and stirring the solution at the temperature of 40-180 ℃ for 0.5-10 h, naturally cooling the solution to room temperature, performing solid-liquid separation, and drying residues;

the precipitator is one or a mixture of more of sodium hydroxide, ammonia water and ammonium acetate;

based on the types and concentrations of metal elements in the acid leaching solution of the lithium extraction slag, performing electrochemical balance analysis on a solution system, analyzing the forms of metal ions in a coordination-precipitation system so as to screen a precipitator, and preferably selecting proper precipitation temperature and time to realize selective precipitation separation, wherein trace other metals can be doped with modified iron phosphate;

and thirdly, placing the residues obtained in the second step into a quartz crucible, heating the quartz crucible for 1 to 10 hours in a tubular furnace at the temperature of between 200 and 1200 ℃, and naturally cooling the quartz crucible to room temperature to obtain the battery-grade iron phosphate.

The residue obtained in the step two is coarse ferric phosphate which has no obvious crystal lattice, is disordered in arrangement, has a loose structure and is large in volume, amorphous coarse ferric phosphate can be subjected to secondary crystallization through moderate-temperature calcination treatment in the step three and is converted into an alpha-quartz type, and trace other metals in the crystallization process are beneficial to increasing the crystal interplanar spacing of the ferric phosphate and are beneficial to Li⁺De-intercalation; and secondly, the shape of the iron phosphate is regular by calcination, and the particle size is uniform.

According to the invention, the waste lithium extraction slag is leached by using inorganic acid, the equilibrium thermodynamics of a multi-metal precipitation system is analyzed based on the solubility product principle, the iron phosphate is selectively precipitated, and then the iron phosphate is calcined to be changed into battery-grade iron phosphate with high crystallization degree, so that the lithium iron phosphate cathode material is prepared again. The method explores suitable precipitating conditions and calcining conditions such as a precipitator and calcining temperature, recovers the battery-grade iron phosphate with excellent electrochemical performance, realizes resource recovery of the waste lithium extraction slag, enables the whole waste lithium iron phosphate anode material to be regenerated and reused, and has important significance for the arrival of the retired peak period of the power lithium battery.

The invention has the following advantages and positive significance:

1. the wet treatment process adopted by the invention is simple and can be applied to industry in a large scale;

2. the invention can close the waste lithium iron phosphate recovery ring, and has great significance for protecting environment and saving resources;

3. the selective precipitation recovery of the invention provides a new idea and solution for solid waste treatment;

4. the contents of heavy metals, such as Mg, Zn, Cu and Ni, in the recovered battery-grade iron phosphate are far lower than the index requirements (HG/T4701-.

Drawings

FIG. 1 is a graph representing the content of impurity metals in battery grade iron phosphate;

fig. 2 is a graph of the first charge and discharge performance of the lithium iron phosphate battery at a rate of 0.1C.

Detailed Description

The first embodiment is as follows: the embodiment is a method for selectively recovering battery-grade iron phosphate from acid leaching solution of lithium extraction slag, which is specifically carried out according to the following steps:

dissolving lithium extraction slag in an inorganic acid solution, heating to 60-70 ℃, preserving heat and dissolving for 1-1.5 h to dissolve metals in the lithium extraction slag into the solution, and obtaining an acid leaching solution of the lithium extraction slag;

the lithium extraction slag is the solid remained after extracting lithium from the waste lithium iron phosphate by using inorganic acid;

taking out the supernatant in the acid leaching solution of the lithium extraction residue, dripping a precipitator into the supernatant until the pH value is 1-4, heating and stirring the solution at the temperature of 40-180 ℃ for 0.5-10 h, naturally cooling the solution to room temperature, performing solid-liquid separation, and drying residues;

the precipitator is one or a mixture of more of sodium hydroxide, ammonia water and ammonium acetate;

and thirdly, placing the residues obtained in the second step into a quartz crucible, heating the quartz crucible for 1 to 10 hours in a tubular furnace at the temperature of between 200 and 1200 ℃, and naturally cooling the quartz crucible to room temperature to obtain the battery-grade iron phosphate.

The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the inorganic acid solution in the first step is one or a mixture of more of a sulfuric acid aqueous solution, a hydrochloric acid aqueous solution, a nitric acid aqueous solution and a phosphoric acid aqueous solution. The rest is the same as the first embodiment.

The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: heating to 60 ℃ in the first step, and keeping the temperature to dissolve for 1 h. The others are the same as in the first or second embodiment.

The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: the solid-liquid separation method in the step two comprises the following steps: and pouring the solution into a cloth type funnel on a filter flask, and performing suction filtration by using a circulating water type multipurpose vacuum pump to obtain a solid in the cloth type funnel. The rest is the same as one of the first to third embodiments.

The fifth concrete implementation mode: the fourth difference between this embodiment and the specific embodiment is that: in step two, a precipitant is added dropwise thereto to a pH of 2. The rest is the same as the fourth embodiment.

The sixth specific implementation mode: the fifth embodiment is different from the fifth embodiment in that: and step three, placing the residues obtained in the step two in a quartz crucible, heating for 4 hours in a tube furnace at the temperature of 600 ℃, and naturally cooling to room temperature to obtain the battery-grade iron phosphate. The rest is the same as the fifth embodiment.

The invention was verified with the following tests:

test one: the test is a method for selectively recovering battery-grade iron phosphate from acid leaching solution of lithium extraction slag, and is specifically carried out according to the following steps:

dissolving 1g of lithium extraction slag in 30mL of inorganic acid solution, heating to 60 ℃, preserving heat and dissolving for 1h to dissolve metals in the lithium extraction slag into the solution, and obtaining acid leaching solution of the lithium extraction slag;

the lithium extraction slag is a solid remained after lithium is extracted from waste lithium iron phosphate by using inorganic acid, wherein impurity metal elements comprise Mg, Ca, Cu, Ni and the like;

the inorganic acid solution is 2mol/L hydrochloric acid aqueous solution;

taking out the supernatant in the acid leaching solution of the lithium extraction residue, dropwise adding a precipitator into the supernatant until the pH is 2, heating and stirring the solution at 60 ℃ for 3 hours, naturally cooling the solution to room temperature, performing solid-liquid separation, and drying residues;

the precipitator is ammonia water;

the solid-liquid separation method comprises the following steps: pouring the solution into a distributed funnel on a filter flask, and performing suction filtration by using a circulating water type multipurpose vacuum pump to obtain a solid in the distributed funnel;

and thirdly, placing the residues obtained in the second step into a quartz crucible, heating for 4 hours at the temperature of 600 ℃ in a tube furnace, naturally cooling to room temperature to obtain battery-grade iron phosphate, weighing part of the obtained iron phosphate, dissolving the part in aqua regia, and measuring the content of impurity metals by using ICP-OES.

Fig. 1 is a representation diagram of the content of impurity metals in battery-grade iron phosphate, a dotted line 1 is the content standard of battery iron phosphate for Mg, Ca, Cu, Ni, and Zn (HG/T4701-2014), a dotted line 2 is the content standard of battery iron phosphate for Na and K (HG/T4701-2014), the left column corresponding to each metal element is commercial battery-grade iron phosphate, and the right column is test-recovered battery-grade iron phosphate. For elements such as Ca, Na, K and the like which have little influence on the performance of the lithium battery, the difference between the iron phosphate recovered in the first test and the commercial battery grade iron phosphate is not great.

Fig. 2 is a diagram of the first charge-discharge performance of a lithium iron phosphate battery at a rate of 0.1C, where a curve 1 is a lithium iron phosphate battery prepared from commercial battery-grade iron phosphate, a curve 2 is a lithium iron phosphate battery prepared from a test-recovered battery-grade iron phosphate, the preparation processes of the two batteries are completely the same, and it can be seen that the test-recovered FePO₄The first discharge specific capacity of the prepared lithium iron phosphate battery reaches 151mAh/g, which is higher than commercial battery grade FePO₄140mAh/g of the prepared lithium iron phosphate battery.