Method for high and low temperature crystal phase precipitation to remove impurities from graphite

Abstract

The present application relates to a method for removing impurities from graphite by high and low temperature crystalline phase precipitation, high temperature calcination of graphite residue; placing a dilute acid solution, ethanol and the obtained graphite residue in a reaction kettle, sealing, and starting the hydrothermal reaction; cooling the reaction kettle after the reaction is completed, forming a temperature difference between the upper and lower layers of the reaction liquid in the reaction kettle, and the temperature of the lower layer being lower than that of the upper layer; filtering the obtained reaction liquid, and filtering out the crystalline substance; using sand core to filter the obtained graphite reaction liquid, and washing with water to obtain graphite filter cake; drying the graphite filter cake to obtain high-purity graphite. The beneficial effects are that the reaction kettle is cooled by high and low temperature methods, a temperature difference is formed between the upper and lower layers of the reaction liquid, the temperature of the lower layer is lower than that of the upper layer, the lower layer reaction liquid first reaches saturation and precipitates metal salt crystalline substance, and because the water proportion is relatively reduced, the metal salt solution is more easily saturated, the crystallized particles are larger, are more easily screened out, the number of acid immersion is reduced, and the purpose of efficient removal of impurities from graphite is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of graphite recovery, in particular to a method for removing impurities from graphite by high and low temperature crystalline phase precipitation. BACKGROUND

[0002] In recent years, electric vehicles have developed rapidly at home and abroad. In 2017, the global sales of electric vehicles exceeded one million for the first time. By 2030, the sales of electric vehicles will reach 44 million. At that time, the waste power batteries will reach 100GWh-120GWh. Lithium-ion batteries contain Ni, Co, Mn, Li, Fe and phosphide, etc. high-risk substances. If simple garbage disposal methods are adopted, environmental pollution and waste of rare metal elements will inevitably occur. Therefore, battery recycling has high environmental and economic value.

[0003] The negative graphite in waste lithium-ion batteries contains 12%-21%. For countries that do not produce graphite or have low graphite reserves, flaky graphite is used as a key material. In lithium-ion batteries, the toxicity of electrolyte and solvent, the lithium content in the graphite negative electrode which is much higher than the environment, and the increasing demand for graphite make the recovery of graphite negative material an important part of lithium-ion battery recycling.

[0004] At present, the recovery of graphite negative material includes pyrometallurgy, hydrometallurgy and combination of pyrometallurgy and hydrometallurgy. Waste graphite negative material can be divided into battery electrode pieces prepared but not assembled into batteries, assembled but not cycled, assembled and cycled for a small number of times, and black powder (including positive and negative materials, separators, etc.) after waste battery crushing. Compared with the black powder to be recovered (assembled but not cycled, assembled and cycled for a small number of times, and black powder after waste battery crushing), the metal elements need to be extracted, and the remaining graphite residue is more difficult to recover. Because it contains a large number of metal ions, and the structure of lithium-ion battery is seriously damaged after cycling, combined with the formation of SEI film during the electrolyte and graphite cycling process, a large number of metal ions will be adsorbed on the surface or interlayer of the graphite. It is difficult to remove completely by using single hydrometallurgy. At present, many researchers have found that the combination of hydrometallurgy and pyrometallurgy can greatly increase the efficiency of impurity removal. Although this method can effectively change the valence state and reaction activity of metal elements in graphite residue, graphite has a two-dimensional layered structure, and the graphite structure is damaged during battery cycling, which leads to an increase in the interlayer spacing of graphite. With the continuous leaching of metal elements by pyrometallurgy and hydrometallurgy, the graphite layers re-aggregate under the action of van der Waals force, and a part of the un-leached metal compounds are coated in the graphite. In the acid leaching process, this part is difficult to combine with the acid solution. In addition, the graphite structure is damaged, and the number of graphite layers is further reduced. In the same mass of graphite, the number of graphite layers of the damaged graphite is more. These will bind metal ions or metal compounds in the form of ions into the solution, reducing the efficiency of hydrometallurgical impurity removal. SUMMARY

[0005] The technical problem to be solved by the present invention is to provide a method for removing impurities from graphite by high and low temperature crystalline phase precipitation, which aims to solve the technical problem of high metal content in waste graphite and low efficiency of ordinary acid leaching (multi-stage acid leaching).

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for removing impurities from graphite by high and low temperature crystalline phase precipitation, comprising the following steps:

[0007] S100, High-temperature calcination of graphite residue after wet extraction of cathode material;

[0008] S200: Place dilute acid solution, ethanol and graphite residue obtained from S100 into a reaction vessel, seal it, and begin the hydrothermal reaction.

[0009] S300: Cool the reactor after the reaction is completed. A temperature difference is formed between the upper and lower layers of the reaction liquid in the reactor, with the lower layer temperature being lower than the upper layer temperature.

[0010] S400: Filter the reaction solution obtained from S300 to remove crystals;

[0011] S500: The graphite reaction solution obtained from S400 is filtered by sand core filtration and washed with water to obtain graphite filter cake.

[0012] S600, dry the graphite filter cake to obtain high-purity graphite.

[0013] Based on the above technical solution, the present invention can be further improved as follows.

[0014] Furthermore, the wet-process extracted cathode material is one or a mixture of several of the following: ternary cathode material, lithium iron phosphate cathode material, and lithium cobalt oxide cathode material, with a metal impurity content of 10% to 30%.

[0015] Furthermore, the high-temperature calcination temperature is 400℃~500℃, the heating rate is 10℃ / min~20℃ / min, and the calcination time is 1h~2h.

[0016] Furthermore, the ratio of graphite residue to dilute acid solution is 1:2 to 1:5, the acid concentration is 3 mol / L to 6 mol / L, and the ethanol content is 5% to 70%.

[0017] Furthermore, the acid used in the dilute acid solution is one or a mixture of several of the following: hydrochloric acid, sulfuric acid, nitric acid, citric acid, malic acid, and acetic acid.

[0018] Furthermore, the temperature of the hydrothermal reaction is 110℃~140℃.

[0019] Furthermore, in the S300, cooling water is used to cool the reactor, with the cooling water level being 1 / 2 to 2 / 3 of the reactor height, and the cooling water temperature being controlled at room temperature.

[0020] Furthermore, the cooling time is 8 to 12 hours.

[0021] Furthermore, the S400 uses sieve filtration with a mesh size of 50 to 500 mesh.

[0022] Furthermore, the graphite residue is washed in the S500 until the pH of the washing solution is 6-7.

[0023] The beneficial effects of this invention are as follows:

[0024] 1) The micro-high pressure state of the hydrothermal reactor is used to remove metal impurities from the graphite residue. Compared with ordinary acid leaching, the boiling temperature of the reaction acid solution is higher and the pressure is greater, which makes the reaction more vigorous and complete, and increases the acid leaching efficiency.

[0025] 2) Add ethanol to the dilute acid solution to adjust the pressure of the reaction system, increase the reaction rate and the probability of contact between the acid solution and the metal impurity particles. In addition, the concentration of ethanol can be adjusted according to the metal content of the residue to adapt to the removal of metal impurities from different graphite residues.

[0026] 3) The reactor is cooled using both high and low temperatures, creating a temperature difference between the upper and lower layers of the reaction solution. The lower layer is cooler than the upper layer, so the lower layer of the reaction solution reaches saturation first and precipitates metal salt crystals (the principle is that metal salts are poorly soluble in ethanol). Furthermore, due to the relatively reduced water content, the metal salt solution is more easily saturated, resulting in larger crystals that are easier to sieve, reducing the number of acid leaching cycles and lowering the cost of graphite acid leaching. This achieves the goal of efficient impurity removal from graphite. The graphite obtained using the method described in this invention has a total metal ion content of less than or equal to 4.0% as determined by ICP testing. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for removing impurities from graphite by high and low temperature crystalline phase precipitation as described in this invention. Detailed Implementation

[0028] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] Example 1

[0030] like Figure 1 As shown, a method for removing impurities from graphite by high and low temperature crystalline phase precipitation includes the following steps:

[0031] The graphite residue after wet extraction of ternary cathode material was placed in a corundum crucible and then placed in a tube furnace. The temperature was increased to 500℃ at a rate of 15℃ / min and held for 1 hour to calcine the metallic elements in the graphite oxide residue.

[0032] Weigh 30g of the calcined graphite residue and place it in a 500ml polytetrafluoroethylene-lined container. Then weigh 24.3g of concentrated sulfuric acid, 12.6g of anhydrous ethanol, and 53.1g of deionized water. Slowly add the concentrated sulfuric acid to the deionized water to prepare a 5mol / L dilute sulfuric acid solution. Pour the solution into the container containing the graphite residue. Tighten the steel lid of the reactor. Then place the reactor in an oven at 120℃ for 8 hours and remove it from the oven.

[0033] Place it in cold water, with the cold water level reaching 2 / 3 of the height of the reactor, until the reactor system reaches room temperature, and the cooling water temperature is controlled at room temperature;

[0034] Remove the metal salt crystals formed in the reaction solution by filtering through a 100-mesh nylon sieve;

[0035] The obtained graphite reaction solution was filtered using a sand core filter and washed with water until the pH reached 7 to obtain a graphite filter cake.

[0036] The graphite filter cake was dried in an oven at 100℃ for 12 hours to obtain high-purity graphite. ICP analysis showed that the total metal ion content was 2.0%.

[0037] Example 2

[0038] A method for removing impurities from graphite by high and low temperature crystalline phase precipitation includes the following steps:

[0039] The graphite residue after wet extraction of lithium iron phosphate cathode material was placed in a corundum crucible and then placed in a tube furnace. The temperature was increased to 450°C at a rate of 10°C / min and held for 1 hour to calcine the metallic elements in the graphite oxide residue.

[0040] Weigh 30g of the calcined graphite residue and place it in a 500ml polytetrafluoroethylene-lined container. Then weigh 24.3g of concentrated hydrochloric acid, 12.6g of anhydrous ethanol, and 53.1g of deionized water. Slowly add the concentrated hydrochloric acid to the deionized water to prepare a 6mol / L hydrochloric acid solution. Pour the solution into the container containing the graphite residue. Tighten the steel lid of the reactor. Then place the reactor in an oven at 120℃ for 8 hours and remove it from the oven.

[0041] Place it in cold water, with the cold water level reaching 2 / 3 of the height of the reactor, until the reactor system reaches room temperature, and the cooling water temperature is controlled at room temperature;

[0042] Remove the metal salt crystals formed in the reaction solution by filtering through a 300-mesh nylon sieve;

[0043] The obtained graphite reaction solution was filtered using a sand core filter and washed with water until the pH reached 7 to obtain a graphite filter cake.

[0044] The graphite filter cake was dried in an oven at 100℃ for 12 hours to obtain high-purity graphite. ICP analysis showed that the total metal ion content was 4.0%.

[0045] Example 3

[0046] A method for removing impurities from graphite by high and low temperature crystalline phase precipitation includes the following steps:

[0047] The graphite residue after the wet extraction of lithium cobalt oxide cathode material was placed in a corundum crucible and then placed in a tube furnace. The temperature was increased to 450°C at a rate of 10°C / min and held for 1 hour to calcine the metallic elements in the graphite oxide residue at high temperature.

[0048] Weigh 40g of the calcined graphite residue and place it in a 500ml polytetrafluoroethylene-lined container. Then weigh 32.4g of concentrated sulfuric acid, 12.6g of anhydrous ethanol, and 75g of deionized water. Slowly add the concentrated sulfuric acid to the deionized water to prepare a 5mol / L sulfuric acid solution. Pour the solution into the container containing the graphite residue. Tighten the steel lid of the reactor. Then place the reactor in an oven at 120℃ for 8 hours and remove it from the oven.

[0049] Place it in cold water, with the cold water level reaching 2 / 3 of the height of the reactor, until the reactor system reaches room temperature, and the cooling water temperature is controlled at room temperature;

[0050] Remove the metal salt crystals formed in the reaction solution by filtering through a 300-mesh nylon sieve;

[0051] The obtained graphite reaction solution was filtered using a sand core filter and washed with water until the pH reached 7 to obtain a graphite filter cake.

[0052] The graphite filter cake was dried in an oven at 100℃ for 12 hours to obtain high-purity graphite. ICP analysis showed that the total metal ion content was 2.4%.

[0053] Example 4

[0054] A method for removing impurities from graphite by high and low temperature crystalline phase precipitation includes the following steps:

[0055] The graphite residue after wet extraction of ternary cathode material was placed in a corundum crucible and then placed in a tube furnace. The temperature was increased to 450°C at a rate of 15°C / min and held for 1 hour to calcine the metallic elements in the graphite oxide residue.

[0056] Weigh 40g of the calcined graphite residue and place it in a 500ml polytetrafluoroethylene-lined container. Then weigh 32.4g of concentrated sulfuric acid, 19.2g of anhydrous ethanol, and 68.4g of deionized water. Slowly add the concentrated sulfuric acid to the deionized water to prepare a 6mol / L dilute sulfuric acid solution. Pour the solution into the container containing the graphite residue. Tighten the steel lid of the reactor. Then place the reactor in an oven at 120℃ for 8 hours and remove it from the oven.

[0057] Place it in cold water, with the cold water level reaching 1 / 2 of the height of the reactor, until the reactor system reaches room temperature, and the cooling water temperature is controlled at room temperature;

[0058] Remove the metal salt crystals formed in the reaction solution after filtering through a 50-mesh nylon sieve;

[0059] The obtained graphite reaction solution was filtered using a sand core filter and washed with water until the pH reached 7 to obtain a graphite filter cake.

[0060] The graphite filter cake was dried in an oven at 100℃ for 12 hours to obtain high-purity graphite. ICP analysis showed that the total metal ion content was 2.0%.

[0061] Example 5

[0062] A method for removing impurities from graphite by high and low temperature crystalline phase precipitation includes the following steps:

[0063] The graphite residue after wet extraction of ternary cathode material and lithium iron phosphate cathode material was placed in a corundum crucible and then placed in a tube furnace. The temperature was increased to 500℃ at a rate of 15℃ / min and held for 1 hour to calcine the metallic elements in the graphite oxide residue.

[0064] Weigh 40g of the calcined graphite residue and place it in a 500ml polytetrafluoroethylene-lined container. Then weigh 32.4g of concentrated sulfuric acid, 24g of anhydrous ethanol, and 63.6g of deionized water. Slowly add the concentrated sulfuric acid to the deionized water to prepare a 5mol / L dilute sulfuric acid solution. Pour the solution into the container containing the graphite residue. Tighten the steel lid of the reactor. Then place the reactor in an oven at 130℃ for 8 hours and remove it from the oven.

[0065] Place it in cold water, with the cold water level reaching 1 / 2 of the height of the reactor, until the reactor system reaches room temperature, and the cooling water temperature is controlled at room temperature;

[0066] Remove the metal salt crystals formed in the reaction solution after filtering through a 50-mesh nylon sieve;

[0067] The obtained graphite reaction solution was filtered using a sand core filter and washed with water until the pH reached 7 to obtain a graphite filter cake.

[0068] The graphite filter cake was dried in an oven at 100℃ for 12 hours to obtain high-purity graphite. ICP analysis showed that the total metal ion content was 3.3%.

[0069] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of high and low temperature crystalline phase precipitation for impurity removal of graphite, characterized by, The method comprises the following steps: S100, high-temperature calcination of the graphite residue after wet extraction of the positive electrode material to oxidize the metal elements in the graphite residue, the high-temperature calcination temperature is 400-500 DEG C, the temperature rising rate is 10-20 DEG C / min, and the calcination time is 1-2 h; S200, the dilute acid solution, ethanol and the graphite residue obtained in S100 are placed in a reaction kettle, sealed, and the hydrothermal reaction is started, the ratio of the graphite residue to the dilute acid solution is 1:2-1:5, the acid concentration is 3-6 mol / L, the ethanol content is 5-70%, the hydrothermal reaction temperature is 110-140 DEG C, the dilute acid solution is added with ethanol to adjust the reaction system pressure, increase the reaction rate and the contact probability of the acid solution and the metal impurity particles; S300, the reaction kettle after the reaction is cooled by high and low temperature methods, the reaction kettle is cooled by cooling water, the cooling water liquid level is 1 / 2-2 / 3 of the height of the reaction kettle, and the cooling water temperature is controlled at room temperature, so that the upper and lower layers of the reaction liquid in the reaction kettle form a temperature difference, the lower layer temperature is lower than the upper layer temperature, and the lower layer reaction liquid first reaches saturation and precipitates metal salt crystals; S400, the reaction liquid obtained in S300 is filtered to remove the crystals; S500, the graphite reaction liquid obtained in S400 is filtered by a sand core, and washed with water to obtain a graphite filter cake; S600, the graphite filter cake is dried to obtain high-purity graphite.

2. The method of claim 1, wherein the graphite is purified by high and low temperature crystalline phase precipitation. The wet extraction positive electrode material is one or a mixture of several of the following: ternary positive electrode material, lithium iron phosphate positive electrode material and lithium cobaltate positive electrode material, and the metal impurity content is 10-30%.

3. The method of claim 1, wherein the graphite is purified by high and low temperature crystalline phase precipitation. The acid used in the dilute acid solution is one or a mixture of several of the following: hydrochloric acid, sulfuric acid, nitric acid, citric acid, malic acid and acetic acid.

4. The method of claim 1, wherein the graphite is purified by high and low temperature crystalline phase precipitation. The cooling time is 8-12 h.

5. The method of claim 1, wherein the method is characterized by: The filter screen used in S400 is a screen filter, and the mesh number of the screen is 50-500.

6. The method of claim 1, wherein the graphite is purified by high and low temperature crystalline phase precipitation. In S500, the graphite residue is washed until the pH value of the washing liquid is 6-7.

Images