Method for preparing iron oxide black pigment by recycling waste lithium iron phosphate batteries

Abstract

The invention discloses a method for preparing iron oxide black pigment by recycling waste lithium iron phosphate batteries, and relates to the field of resource recycling of waste lithium batteries. The method comprises the following steps: recycling waste lithium iron phosphate powder from the waste lithium battery, leaching the waste lithium iron phosphate powder by utilizing phosphoric acid, and recycling iron-containing precipitate from leachate; mixing the obtained iron-containing precipitate with a powder peroxide, and carrying out a mechanochemical reaction to obtain an oxidized precursor; and carrying out electric heating shock on the oxidized precursor at 1900-2100 DEG C to obtain the iron oxide black pigment, the invention aims to realize resource recycling of the waste lithium iron phosphate power lithium battery and solve the problems of low purity and more impurities of the recycled iron oxide black caused by excessive impurities and disordered valence states of an iron source recycled from the waste lithium iron phosphate power lithium battery.

Description

Technical Field

[0001] The invention relates to the field of recycling waste lithium batteries, and in particular to a method for preparing iron oxide black pigment by recycling waste lithium iron phosphate batteries. Background Art

[0002] Lithium iron phosphate, LiFePO4, is one of the electrode materials for commercial lithium-ion batteries and is widely used in mainstream lithium battery products such as BYD's blade battery. Lithium iron phosphate batteries do not contain key metals such as nickel, cobalt and manganese, and their recycling value is low after the end of their cycle life. Existing recycling technologies focus on recovering the lithium element, while the phosphorus and iron elements left in the smelting slag are usually used as fertilizers.

[0003] Iron oxide black pigment, the main component is Fe3O4, it is light gray-black, and its density is between 4.9-5.9g / cm 3 The Mohs hardness is between 5.5-6.5, the oil absorption is 10-15g / 100g, and the refractive index is 2.44. These characteristics make the iron oxide black pigment have good light resistance and thermal stability, can withstand temperatures up to 150°C, and no color bleeding. The application field of iron oxide black pigment is very wide, including but not limited to building materials, coatings and paint industries, ceramics, rubber, plastics, leather polishing paste, etc. In the building materials industry, it is mainly used for colored cement, colored cement floor tiles, colored cement tiles, imitation glazed tiles, concrete floor tiles, colored mortar, colored asphalt, terrazzo, mosaic tiles, artificial marble and wall painting, etc. In the coating and paint industry, it is mainly used to manufacture various paints, coatings, and inks. In addition, it is also used in the production of primers and topcoats, pigments, polishing agents, and special electrodes, and also plays an important role in the production of welding rods and welding wires.

[0004] The existing patent "An iron oxide black pigment and its preparation method, CN 106084896 A" proposes to use ferrous sulfate solution as raw material, add alkaline solution to control the pH in a weak alkaline environment of 10-11, then heat and precipitate to obtain ferrous hydroxide, and finally high-temperature roasting to obtain iron oxide black pigment. This alkaline neutralization method and oxidation precipitation method will consume a large amount of strong alkaline reagents, and the amount of wastewater generated is extremely large, the production cost is high, and the impurity content is high.

[0005] The existing patent "Method for preparing black iron oxide, CN 111573740 A" proposes to dehydrate ferrous chloride tetrahydrate at a high temperature of about 110°C under the protection of an inert atmosphere to generate ferrous chloride monohydrate, and then perform high-temperature oxidation roasting at 800°C to directly obtain black iron oxide pigment. This dry method for preparing black iron oxide pigment involves high-temperature oxidation, and the heating rate is only about 5°C / min. The high-temperature reaction process takes 4-5 hours, has high power consumption and energy consumption, and is very likely to produce hydrogen chloride gas to corrode the high-temperature cavity, resulting in high equipment maintenance costs.

[0006] The above method proves that iron oxide black pigment can be prepared after fully oxidizing, precipitating and calcining ferrous ions. However, the raw materials of the existing methods are all ferrous ion reagents, which require long-term high-temperature oxidation treatment and are very likely to produce peroxidation reactions to generate Fe2O3 impurities. Recycling waste lithium iron phosphate batteries into iron oxide black pigment products can not only alleviate the potential environmental safety issues of waste lithium batteries, but also prepare high-value pigments with high economic benefits. Summary of the invention

[0007] One of the purposes of the present invention is to provide a method for preparing iron oxide black pigment to overcome the problem of Fe2O3 impurity contamination caused by the disorder of valence state of iron source.

[0008] In order to solve the above problems, the present invention adopts the following technical means: A method for preparing iron oxide black pigment comprises: S100. mixing the obtained iron-containing precipitate with powdered peroxide to perform a mechanochemical reaction to obtain an oxidative precursor; S200. The oxidation precursor is subjected to electric thermal shock at 1900-2100°C to obtain iron oxide black pigment.

[0009] Among them, during the mechanochemical reaction, the iron-containing precipitate is oxidized in a mechanical state using powdered peroxide to form a slurry-like oxidation precursor. During the mechanochemical reaction, the iron source with chaotic valence is oxidized into a uniformly flocculent slurry-like Fe2O3 oxidation precursor. The oxidation precursor is subjected to electrothermal shock, and the instantaneous high temperature environment generated by the electrothermal shock can break the Fe-O bond of Fe2O3, deoxidize and reduce to form Fe3O4 and O2. When the electrothermal shock is carried out at 1900~2100℃, the metal impurities introduced by the added powdered peroxide can volatilize during the electrothermal shock process, thereby using the electrothermal shock to convert the oxidation precursor into high-purity Fe3O4.

[0010] In some embodiments, the iron-containing precipitate includes a mixture of one or more of ferric oxyhydroxide, ferrous hydroxide, and ferric hydroxide.

[0011] When the iron-containing precipitate contains iron hydroxide, even if it is difficult to form a uniform Fe2O3 oxidation precursor during the mechanochemical reaction, in the subsequent electrothermal shock environment, the electrothermal shock can induce the dehydration condensation of the iron hydroxide and destroy the Fe-O bond, so that the iron hydroxide forms Fe3O4 and H20.

[0012] In some embodiments, the powdered potassium peroxide is one of sodium peroxide, iodine peroxide, and magnesium peroxide.

[0013] Among them, the use of powdered peroxide can effectively avoid the situation in which the viscosity of the oxidation precursor slurry is too low and the electrothermal shock is affected due to the generation of water during the mechanochemical reaction.

[0014] In some embodiments, the duration of the electrothermal shock is 5 to 60 seconds.

[0015] When controlling the duration of the electric thermal shock, within 60s, the sp 3 The hybrid orbital is only moderately reduced to the sp 2 and sp 3 hybrid orbital without completely converting to the sp 2 When the duration exceeds 60s, not only will a large amount of FeO be produced to reduce the purity of Fe3O4, but also a large amount of Fe will be volatilized and lost due to the long duration, thus reducing the content of Fe3O4.

[0016] In some embodiments, the mechanochemical reaction is applied at a rotation speed of 700-900 rpm.

[0017] The second purpose of the present invention is to provide a method for recycling waste lithium iron phosphate batteries to prepare black iron oxide pigment, so as to realize the resource reuse of waste lithium iron phosphate power lithium batteries and solve the problem that the iron source impurities recovered from waste lithium iron phosphate power lithium batteries are too many and the valence state is chaotic, resulting in the recycled iron oxide black having low purity and many impurities.

[0018] In order to solve the above problems, the present invention adopts the following technical means: A method for recycling waste lithium iron phosphate batteries to prepare iron oxide black pigments, comprising: recycling waste lithium iron phosphate powder from waste lithium batteries, leaching the waste lithium iron phosphate powder with phosphoric acid, and recovering iron-containing precipitates from the leaching solution; The iron-containing precipitate is treated by the aforementioned method for preparing black iron oxide pigment to prepare black iron oxide pigment.

[0019] The main purpose of using phosphoric acid to enter and exit the waste lithium iron phosphate powder is to reduce the introduction of new impurities into the system during the entry and exit process. At the same time, the iron-containing precipitate recovered from the waste lithium iron phosphate battery has a chaotic valence state and is in a mixed state. It contains iron-containing mixtures such as ferric hydroxide, ferrous hydroxide and ferric hydroxide. If the conventional direct high-temperature treatment is used, the problem of preferred orientation of the crystal plane is prone to occur, and it is difficult to control the degree of oxidation, resulting in Fe2O3 impurity pollution, reducing the oil absorption and coloring strength of the iron oxide black pigment. Therefore, the iron-containing precipitate is oxidized to a high-valent state of iron in the process of mechanochemical reaction using powdered peroxide, which is composed of a mixture of iron oxide and iron hydroxide to form a flocculent Fe2O3 precursor with uniform particle size, and then the instantaneous ultra-high temperature generated by the electrothermal shock is used to reduce the high-valent state of iron mixtures such as Fe2O3 and iron hydroxide into Fe3O4. Moreover, in the previous step, in order to reduce the introduction of impurities, when phosphoric acid is used for inlet and outlet, lithium and iron will be leached out simultaneously, so there will be a large amount of lithium and peroxide cations and other impurities in the flocculent Fe2O3 precursor. However, under the electrothermal shock of 1900~2100℃, other metal impurities except Fe can be volatilized, thereby completely removing the lithium ion impurities rich in waste lithium batteries, peroxide cations in mechanochemical reactions and conventional soluble impurity ions in industrial and domestic water, which will further improve the purity quality of iron oxide black pigment.

[0020] In some embodiments, the waste lithium iron phosphate powder is recycled by: soaking the waste lithium iron phosphate power lithium battery in a nitrate solution for discharge, and taking out the positive electrode strip after drying; The positive electrode strip was calcined at 400°C, and the lithium iron phosphate powder was obtained after peeling off the aluminum foil.

[0021] The positive electrode bar contains lithium iron phosphate. Baking the positive electrode bar at 400°C can not only effectively remove the binder and electrolyte, but also properly destroy the olivine structure of the lithium iron phosphate, so that iron can be leached better than lithium during subsequent leaching with phosphoric acid, thereby reducing the lithium impurity in the iron-containing precipitate. If the temperature is too high, the lithium iron phosphate will be greatly destroyed. Although the iron can be better leached, there will be a large amount of lithium impurities in the iron-containing precipitate, which is not conducive to improving the purity of black iron oxide. Baking at too low a temperature will affect the subsequent leaching of iron, which is not conducive to the content of black iron oxide in the product.

[0022] In some embodiments, the phosphoric acid concentration used to leaching waste lithium iron phosphate powder is 2 mol / L, the solid-liquid ratio is 200 g / L, and the leaching temperature is 35-45°C.

[0023] Similarly, when phosphoric acid is used to leach waste lithium iron phosphate powder, iron and lithium will be leached simultaneously. In order to allow iron to be leached with lithium first and reduce lithium impurities, a higher solid-liquid ratio can appropriately increase the pH of the reaction system, allowing iron to be leached before lithium.

[0024] In some embodiments, when recovering the iron-containing precipitate in the leachate, ammonia water is used to adjust the pH and sodium hydroxide is used as a precipitant. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0026] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0028] A method for recycling waste lithium iron phosphate batteries to prepare iron oxide black pigments, comprising: recycling waste lithium iron phosphate powder from waste lithium batteries, leaching the waste lithium iron phosphate powder with phosphoric acid, and recovering iron-containing precipitates from the leaching solution; The slurry formed by the mechanochemical reaction of the iron-containing precipitate and the powdered peroxide is subjected to an electrothermal shock in the range of 1900-2100°C to produce a high-quality iron oxide black pigment.

[0029] The iron-containing precipitate recovered from waste lithium iron phosphate power lithium batteries contains FeO(OH), Fe(OH)2 and Fe(OH)3 and other iron-related mixed phases. Direct high-temperature treatment is prone to problems of preferred crystal orientation, and it is difficult to control the degree of oxidation, resulting in Fe2O3 impurity pollution, reducing the oil absorption and tinting strength of iron oxide black pigments. In this application, the iron-containing precipitate is induced to react with powdered peroxide by mechanochemical method, and the prepared oxidation precursor has a good degree of oxidation, and its impurities can be removed in subsequent steps. It is uniformly and completely oxidized in a strong oxidizing environment to form a flocculent Fe2O3 precursor with uniform particle size. The chemical reaction mechanism is as follows:

[0030] The slurry formed contains a large amount of Fe2O3 and some Fe(OH)3 mixture. When the electrothermal shock is applied later, the instantaneous ultra-high temperature environment generated by the electrothermal shock will break the Fe-O bond of Fe2O3 and deoxidize and reduce it to form Fe3O4 and O2; it will also induce Fe(OH)3 to undergo dehydration condensation to form Fe3O4 and H2O. Since the thermal shock is only a short-term effect, the ultra-high temperature environment will only last for a short time, so the sp 3 The hybrid orbital is only moderately reduced to the sp 2 and sp 3 hybrid orbital, and will not be completely converted to the sp 2 Hybrid orbital. Therefore, electrothermal shock can induce the moderate reduction of Fe2O3 into Fe3O4, and its chemical reaction mechanism is as follows:

[0031] Moreover, impurities in the systems of metallic lithium, sodium, potassium, calcium, magnesium, etc. can volatilize in the state of electrothermal shock. Therefore, the electrothermal shock treatment proposed by this patented technology will not cause the volatilization loss of iron elements. It can also completely remove lithium ion impurities rich in waste lithium batteries, peroxidant cations in mechanochemical reactions, and conventional soluble impurity ions in industrial and domestic water, which will further improve the purity quality of iron oxide black pigment.

[0032] The following is a detailed description through different specific implementation methods. Example

[0033] To ensure the safety of the experimental process, 100 18650 waste lithium iron phosphate power lithium batteries weighing about 2 kg were fully discharged in a 5% nitrate solution for 48 hours, and then dried in a fume hood for 48 hours; The discharged cylindrical waste lithium iron phosphate batteries were manually disassembled to remove the complete positive electrode strips; The waste lithium iron phosphate battery positive electrode strips are calcined at 400°C to remove the binder and electrolyte, and the aluminum foil is peeled off to obtain lithium iron phosphate powder; Waste lithium iron phosphate powder was leached with H3PO4, H3PO4 was 2 mol / L, solid-liquid ratio was 200 g / L, reaction temperature was 40°C; H2O2 additive dosage was 6% volume fraction, and battery leachate was obtained; Add 1 mol / L ammonia water and 2 mol / L NaOH to the battery leaching solution to adjust the pH to a weakly alkaline environment of 10-12, and filter to obtain an iron-containing precipitate; The iron-containing precipitate obtained above is dried and then subjected to a mechanochemical reaction with sodium peroxide powder at 700-900 rpm for 2 hours to allow the iron-containing precipitate to fully react with sodium peroxide, magnesium peroxide or potassium peroxide powder to obtain an oxidative precursor; The oxidized precursor is then subjected to ultra-high temperature electrothermal shock reduction treatment at 1900-2100°C, with the voltage set to 30V, the current to 200A, and the reaction time to 5s to produce high-quality iron oxide black pigment. Example

[0034] On the basis of Example 1, the electrothermal shock reduction treatment time was adjusted to 60 s, and other conditions and steps remained unchanged. Example

[0035] On the basis of Example 1, the electrothermal shock reduction treatment time was adjusted to 70 s, and other conditions and steps remained unchanged.

[0036] The samples finally obtained from Examples 1 to 3 were tested using Fourier infrared spectroscopy, and it was found that an obvious ferrous peak appeared in Example 3, indicating that in Example 3, due to the long electrothermal shock reduction time, the iron oxide was over-reduced, resulting in the formation of ferrous oxide in the finished black iron oxide raw material. Moreover, after measuring the content of black iron oxide, it was found that it was reduced compared to Examples 1 and 2. Moreover, for the content of black iron oxide, the content of black iron oxide in Example 1 was higher than that in Example 2. This is because the duration of the electrothermal shock in Example 2 was longer, resulting in the volatilization of iron, and the content of black iron oxide in the finished product was reduced. Example

[0037] On the basis of Example 1, the peroxide for the mechanochemical reaction with the iron-containing precipitate was replaced by hydrogen peroxide, and the other conditions and steps remained unchanged.

[0038] After the powdered peroxide is replaced with liquid peroxide, since the mechanochemical reaction of the present application itself will produce water, and after the liquid peroxide is added, the viscosity of the oxidation precursor obtained by the mechanochemical reaction is too low. When the electrothermal shock is performed, the raw material contains a large number of OH bonds, which will compete with the Fe-O bonds of the iron oxide. When the electrothermal shock is performed, a longer time is required for treatment at the same temperature, which will cause the volatilization of iron. Therefore, after the mechanochemical reaction using hydrogen peroxide, the black iron oxide content of the final product is reduced. Example

[0039] On the basis of Example 1, the acid solution for leaching the waste lithium iron phosphate powder is replaced with sulfuric acid or nitric acid. Other conditions and steps remain unchanged.

[0040] In this embodiment, after the acid solution is replaced and the finished black iron oxide is tested for its components, the content of black iron oxide increases, so when treated with sulfuric acid or nitric acid, the iron in the lithium iron phosphate can be better leached. However, after the sample is tested using infrared spectroscopy, it is found that the peaks correspond to the sulfur and nitrogen impurities. Therefore, although the use of phosphoric acid for leaching will reduce the leaching rate of iron, it can better avoid the introduction of new non-metallic impurities into the system, resulting in the low purity of the black iron oxide pigment. Example

[0041] On the basis of Example 1, the solid-liquid ratio in the phosphoric acid system for leaching waste lithium iron phosphate powder was adjusted to 100 g / L (10 ml / g), and other conditions and steps remained unchanged. Example

[0042] Based on Example 1, the solid-liquid ratio in the phosphoric acid system for leaching waste lithium iron phosphate powder was adjusted to 500 g / L (2 ml / g), and other conditions and steps remained unchanged.

[0043] The iron-containing precipitates obtained in Example 1, Example 6 and Example 7 were tested. The iron-containing precipitate obtained in Example 7 had the most lithium impurities among the three. Although the lithium impurities in Example 6 were less, the content of black iron oxide prepared at the same time was lower. Therefore, too low solid-liquid ratio would not only affect the leaching of lithium, but also affect the leaching of iron. Example

[0044] On the basis of Example 1, the calcination temperature of the positive electrode strip was adjusted to 500° C., and other conditions and steps remained unchanged. Example

[0045] On the basis of Example 1, the calcination temperature of the positive electrode strip was adjusted to 300° C., and other conditions and steps remained unchanged.

[0046] The iron-containing precipitates obtained in Example 1, Example 8 and Example 9 were tested. The iron-containing precipitate obtained in Example 8 has the most lithium impurities among the three, indicating that under calcination at 500°C, the olivine structure of lithium iron phosphate collapsed in large quantities, causing lithium and iron to be leached simultaneously, and thus causing more lithium impurities to be present in the iron-containing precipitate. Although there are fewer lithium impurities in Example 9, the prepared black iron oxide has a lower content and contains a large amount of electrolyte impurities. Therefore, too low a calcination temperature will not only affect the leaching of lithium, but also the leaching of iron, and will also affect the removal of the electrolyte during the pre-treatment process.

[0047] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing iron oxide black pigment, characterized in that: include: S100. mixing the obtained iron-containing precipitate with powdered peroxide to perform a mechanochemical reaction to obtain an oxidative precursor; S200. The oxidation precursor is subjected to electric thermal shock at 1900-2100° C. to obtain iron oxide black pigment.

2. A method for preparing black iron oxide pigment according to claim 1, characterized in that: The iron-containing precipitate includes a mixture of one or more of ferric oxyhydroxide, ferrous hydroxide and ferric hydroxide.

3. A method for preparing black iron oxide pigment according to claim 1, characterized in that: The powdered peroxide is one of sodium peroxide, potassium peroxide and magnesium peroxide.

4. A method for preparing black iron oxide pigment according to claim 1, characterized in that: The duration of the electrothermal shock is 5 to 60 seconds.

5. The method for preparing an iron oxide black pigment according to claim 1, characterized in that: The rotation speed applied for the mechanochemical reaction is 700-900 rpm.

6. A method for recycling waste lithium iron phosphate batteries to prepare iron oxide black pigment, characterized in that: include: Recovering waste lithium iron phosphate powder from waste lithium batteries, leaching the waste lithium iron phosphate powder with phosphoric acid, and recovering iron-containing precipitates from the leaching solution; The iron-containing precipitate is treated by the method for preparing an iron oxide black pigment according to any one of claims 1 to 5 to prepare an iron oxide black pigment.

7. The method for recycling waste lithium iron phosphate batteries to prepare iron oxide black pigment according to claim 6, characterized in that: The waste lithium iron phosphate powder is recovered by: immersing the waste lithium iron phosphate power lithium battery in a nitrate solution for discharge, and taking out the positive electrode strip after drying; The positive electrode strip was calcined at 400°C, and the lithium iron phosphate powder was obtained after peeling off the aluminum foil.

8. The method for recycling waste lithium iron phosphate batteries to prepare iron oxide black pigment according to claim 6, characterized in that: The phosphoric acid concentration used for leaching waste lithium iron phosphate powder is 2 mol / L, the solid-liquid ratio is 200 g / L, and the leaching temperature is 35~45°C.

9. The method for recycling waste lithium iron phosphate batteries to prepare iron oxide black pigment according to claim 6 or 8, characterized in that: When recovering the iron-containing precipitate in the leachate, ammonia water is used to adjust the pH and sodium hydroxide is used as a precipitant.

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