Method for preparing lithium iron phosphate from phosphated residues

Abstract

The invention discloses a method for preparing lithium iron phosphate from phosphated residues. The method comprises the following steps: pre-treating the phosphated residues; alkaline leaching is conducted on the phosphated residues, wherein the phosphated residues are placed in a sodium hydroxide solution and filtered; decoloring is performed; adding a lithium source: adding the lithium source into the filtrate, then adding hydrochloric acid to adjust the pH value to 6-6.5, then adding a solution composed of urotropine, thiourea, tetraethylammonium oxalate, hydrogen peroxide and polydodecyl acrylamide acrylic acid, and stirring for a certain time; adding alkali to adjust the pH value to 8.5-9.5, and filtering, washing and drying the precipitate; and adding carbon and calcining: carrying out ball milling on the solid, uniformly mixing with graphene oxide particles, mixing with hydrazine hydrate, stirring, and calcining in an inert environment. The phosphated residues are fully utilized to prepare the lithium iron phosphate meeting battery requirements, so that the problem of phosphated residue discharge is effectively controlled, and the prepared lithium iron phosphate has good electrochemical performance as a battery positive electrode material.

Description

Technical Field

[0001] The invention relates to a method for preparing lithium iron phosphate from phosphating slag, and belongs to the technical field of phosphating slag treatment. Background Art

[0002] During the production of steel and metal products, the phosphating treatment of the steel surface will produce solid waste phosphating slag. In addition to a certain amount of water, the main components of phosphating slag are iron phosphate and zinc phosphate. Analysis shows that the mass content of each component in the phosphating slag is approximately: water accounts for 15-20%, TFe (Fe 3+ and Fe 2+ ) accounts for 15-25%, Zn 2+ 2-5%, PO4 3- In addition, the phosphating slag also contains a small amount of Ca 2+ Mg 2+ , Mn 2+ 、Ni 2+ , Cu 2+ The total mass content of impurity elements such as phosphating elements is about 0.5-2.0%. At present, the amount of phosphating slag produced in my country accounts for about 0.5-1.0% of the phosphating treatment of steel products, and the amount of phosphating slag solid waste produced each year is as high as more than 500,000 tons. In recent years, with the continuous expansion of the deep processing capacity of steel products in my country's steel enterprises, the treatment / disposal of phosphating slag produced in the metal product process has seriously affected the normal production of enterprises and the quality of phosphating products. At the same time, since phosphating slag solid waste has been included in the "National Hazardous Waste List", if it is discharged at will without treatment, it will also cause environmental pollution problems and waste recyclable valuable resources. And with the rapid development of new energy, lithium iron phosphate used in batteries has become an important raw material. Lithium iron phosphate is a new type of lithium-ion positive electrode material and a battery material with great development potential. It has the characteristics of being cheap and easy to obtain, environmentally friendly, high theoretical capacity, long service life, good cycle performance, excellent thermal stability and large current charge and discharge. How to design a treatment process for phosphating slag to prepare it into lithium iron phosphate has become a problem to be solved. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing lithium iron phosphate from phosphating slag, which can prepare lithium iron phosphate that meets battery requirements.

[0004] To solve the above technical problems, the purpose of the present invention is achieved as follows:

[0005] The present invention relates to a method for preparing lithium iron phosphate from phosphating slag, comprising the following steps:

[0006] S1. Pretreatment of phosphating slag: crush the phosphating slag into particles with a particle size of 100-500 microns, then place the particles in a phosphoric acid aqueous solution, heat in a water bath and stir; remove the upper foam after precipitation, and pass through a 250-mesh sieve in water, retain the sieve, filter, dry and set aside;

[0007] S2, phosphating slag alkaline leaching: the phosphating slag after pretreatment is placed in a 30% by mass sodium hydroxide solution for a certain period of time, and then water is added to adjust the pH value to 10-11, and the reaction is continued for a certain period of time, and then passed through a 500 mesh sieve, and the filtrate is collected;

[0008] S3, decolorization: adding activated carbon to the filtrate obtained in the previous step, stirring for adsorption, filtering, and collecting the filtrate;

[0009] S4, adding a lithium source: adding a lithium source to the filtrate obtained in the previous step, and then adding hydrochloric acid to adjust the pH value to 6-6.5, and then adding a solution composed of hexamethylenetetramine, thiourea, tetraethylammonium oxalate, hydrogen peroxide, and polydodecyl acrylamide acrylic acid and stirring for a certain period of time; then adding alkali to adjust the pH to 8.5-9.5, and filtering, washing, and drying the precipitate;

[0010] S5, calcination with carbon: ball-mill the solid prepared in the previous step to an average particle size of 100-200, then evenly mix it with a certain proportion of graphene oxide particles to form a solid mixture, then mix it with hydrazine hydrate, stir it for a certain period of time, and then calcine it in an inert environment to obtain lithium iron phosphate.

[0011] On the basis of the above scheme and as a preferred scheme of the above scheme: in step S1, the phosphoric acid aqueous solution includes 20-30% by mass of analytically pure phosphoric acid, and the mass ratio of phosphating slag particles to phosphoric acid aqueous solution is 1:2-5.

[0012] On the basis of the above scheme and as a preferred scheme of the above scheme: in step S2, the mass ratio of the phosphating slag to the sodium hydroxide solution is 1:5-10.

[0013] On the basis of the above scheme and as a preferred scheme of the above scheme: the lithium source is lithium oxalate, lithium chloride or lithium nitrate.

[0014] On the basis of the above scheme and as a preferred scheme of the above scheme: in step S4, the amount of urotropine used is 0.1-0.2% of the mass of the filtrate, the amount of thiourea used is 0.05-0.1% of the mass of the filtrate, the amount of tetraethylammonium oxalate used is 0.1-0.2% of the mass of the filtrate, the amount of hydrogen peroxide used is 0.2-0.3% of the mass of the filtrate; the amount of the polydodecyl acrylamide acrylic acid group used is 0.05-0.08% of the mass of the filtrate.

[0015] On the basis of the above scheme and as a preferred scheme of the above scheme: in step S5, the weight of the added hydrazine hydrate is 1.1-1.5 times the mass of the solid mixture.

[0016] The beneficial effects of the present invention are as follows: the method for preparing lithium iron phosphate from phosphating slag involved in the present invention makes full use of the phosphating slag to make it into lithium iron phosphate that meets the requirements of the battery, so that the problem of phosphating slag emission is effectively controlled, and the prepared lithium iron phosphate has good electrochemical properties as a battery positive electrode material. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with specific embodiments.

[0018] Example

[0019] A method for preparing lithium iron phosphate from phosphating slag involved in this embodiment comprises the following steps:

[0020] S1. Pretreatment of phosphating slag: crush the phosphating slag into particles with a particle size of 100-500 microns, and then place the particles in a phosphoric acid aqueous solution, heat in a water bath and stir; remove the upper foam after precipitation, and pass it through a 250-mesh sieve in water, retain the sieve, filter it with suction, dry it and set it aside; specifically in this embodiment, the particles are crushed to an average particle size of about 300 microns.

[0021] Further, in step S1, the phosphoric acid aqueous solution includes 20-30% by mass of analytically pure phosphoric acid, and the mass ratio of the phosphating slag particles to the phosphoric acid aqueous solution is 1:2-5. Specifically, in this embodiment, the phosphoric acid aqueous solution includes 25% by mass of analytically pure phosphoric acid, and the mass ratio of the phosphating slag particles to the phosphoric acid aqueous solution is 1:4.

[0022] S2. Alkaline leaching of phosphating slag: the phosphating slag after pretreatment is placed in a 30% by mass sodium hydroxide solution for reaction for 30 minutes, then water is added to adjust the pH value to 10, the reaction is continued for 20 minutes, and the slag is passed through a 500 mesh sieve to collect the filtrate.

[0023] Furthermore, in step S2, the mass ratio of the phosphating slag to the sodium hydroxide solution is 1:5-10, and specifically 1:8 in this embodiment.

[0024] S3, decolorization: add activated carbon to the filtrate obtained in the previous step, stir and adsorb, filter, and collect the filtrate. Further, in step S3, the amount of activated carbon is 2-3% of the mass of the filtrate, the adsorption time is 30-45 minutes, and the adsorption temperature is room temperature. In this embodiment, the amount of activated carbon is 3% of the mass of the filtrate, and the adsorption time is 30 minutes.

[0025] S4, adding lithium source: adding lithium source to the filtrate obtained in the previous step, adding hydrochloric acid to adjust the pH value to 6-6.5, then adding a solution consisting of hexamethylenetetramine, thiourea, tetraethylammonium oxalate, hydrogen peroxide, and polydodecyl acrylamide acrylic acid and stirring for 15 minutes; then adding alkali to adjust the pH to 8.5-9.5, filtering, washing, and drying the precipitate.

[0026] Furthermore, the lithium source is lithium oxalate, lithium chloride or lithium nitrate. In this embodiment, lithium chloride is selected. The amount of the lithium source is 10-20% of the filtrate, specifically 15%.

[0027] Further, in step S4, the amount of urotropine used is 0.1-0.2% of the mass of the filtrate, the amount of thiourea is 0.0.5-0.1% of the mass of the filtrate, the amount of tetraethylammonium oxalate is 0.1-0.2% of the mass of the filtrate, and the amount of hydrogen peroxide is 0.2-0.3% of the mass of the filtrate; the amount of the polydodecyl acrylamide acrylic acid group is 0.05-0.08% of the mass of the filtrate. In this embodiment, the amount of urotropine used is 0.1% of the mass of the filtrate, the amount of thiourea is 0.1% of the mass of the filtrate, the amount of tetraethylammonium oxalate is 0.1% of the mass of the filtrate, and the amount of hydrogen peroxide is 0.3% of the mass of the filtrate; the amount of the polydodecyl acrylamide acrylic acid group is 0.08% of the mass of the filtrate.

[0028] S5, calcination with carbon: ball-mill the solid prepared in the previous step to an average particle size of 100-200, then evenly mix with a certain proportion of graphene oxide particles to form a solid mixture, then mix with hydrazine hydrate, stir for a certain period of time, and then calcine under an inert environment to obtain lithium iron phosphate. The mass ratio of the solid to the graphene oxide particles is 2:1.

[0029] Furthermore, in step S5, the weight of the added hydrazine hydrate is 1.1-1.5 times the weight of the solid mixture. Specifically, in this embodiment, it is 1.2 times. The average particle size of the graphene oxide particles is 50 microns.

[0030] The obtained lithium iron phosphate positive electrode material was made into an electrode sheet according to the conventional method, assembled into a button battery in a glove box, and the relevant electrochemical performance tests were carried out. At a rate of 0.1C, the first charge and discharge specific capacity of the electrode was 156.2mAh / g, and at a rate of 1C, the first charge and discharge specific capacity of the electrode was 131.8mAh / g. After 100 cycles at 0.1C and 1C rates, the retention rate of the lithium iron phosphate positive electrode sheet was 95.4% and 93.4%.

[0031] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing lithium iron phosphate from phosphating slag, characterized in that: The steps include: S1. Pretreatment of phosphating slag: crush the phosphating slag into particles with a particle size of 100-500 microns, then place the particles in a phosphoric acid aqueous solution, heat in a water bath and stir; remove the upper foam after precipitation, and pass through a 250-mesh sieve in water, retain the sieve, filter, dry and set aside; S2, phosphating slag alkaline leaching: the phosphating slag after pretreatment is placed in a 30% by mass sodium hydroxide solution for a certain period of time, and then water is added to adjust the pH value to 10-11, and the reaction is continued for a certain period of time, and then passed through a 500 mesh sieve, and the filtrate is collected; S3, decolorization: add activated carbon to the filtrate obtained in the previous step, stir for adsorption, filter, and collect the filtrate; S4, adding a lithium source: adding a lithium source to the filtrate obtained in the previous step, and then adding hydrochloric acid to adjust the pH value to 6-6.5, and then adding a solution composed of hexamethylenetetramine, thiourea, tetraethylammonium oxalate, hydrogen peroxide, and polydodecyl acrylamide acrylic acid and stirring for a certain period of time; then adding alkali to adjust the pH to 8.5-9.5, and filtering, washing, and drying the precipitate; S5, calcination with carbon: ball-mill the solid prepared in the previous step to an average particle size of 100-200, then evenly mix it with a certain proportion of graphene oxide particles to form a solid mixture, then mix it with hydrazine hydrate, stir it for a certain period of time, and then calcine it in an inert environment to obtain lithium iron phosphate.

2. The method for preparing lithium iron phosphate from phosphating slag according to claim 1, characterized in that: In step S1, the phosphoric acid aqueous solution includes 20-30% by mass of analytically pure phosphoric acid, and the mass ratio of the phosphating slag particles to the phosphoric acid aqueous solution is 1:2-5.

3. The method for preparing lithium iron phosphate from phosphating slag according to claim 1, characterized in that: In step S2, the mass ratio of the phosphating slag to the sodium hydroxide solution is 1:5-10.

4. The method for preparing lithium iron phosphate from phosphating slag according to claim 1, characterized in that: The lithium source is lithium oxalate, lithium chloride or lithium nitrate.

5. The method for preparing lithium iron phosphate from phosphating slag according to claim 1, characterized in that: In step S4, the amount of urotropine used is 0.1-0.2% of the mass of the filtrate, the amount of thiourea used is 0.05-0.1% of the mass of the filtrate, the amount of tetraethylammonium oxalate used is 0.1-0.2% of the mass of the filtrate, the amount of hydrogen peroxide used is 0.2-0.3% of the mass of the filtrate; the amount of polydodecyl acrylamide acrylic acid group used is 0.05-0.08% of the mass of the filtrate.

6. The method for preparing lithium iron phosphate from phosphating slag according to claim 1, characterized in that: In step S5, the weight of the added hydrazine hydrate is 1.1-1.5 times the mass of the solid mixture.