Synchronous graphite flotation and separation coupling method for oxidizing and extracting lithium from used lithium iron phosphate

Abstract

The invention discloses a graphite coupling method for oxidation lithium extraction and synchronous flotation separation of used lithium iron phosphate, and belongs to the related technical field of waste battery recycling. Water is added into the black powder after the surface binder is removed through pyrolysis for size mixing, flotation is carried out after a flotation reagent is added, an acid reagent is added for adjusting the pH of a solution, O2-containing gas is introduced during flotation, lithium iron phosphate is oxidized and converted into iron phosphate in the flotation process, lithium ions are selectively leached and enter the solution, and a negative electrode material becomes concentrate foam; and iron phosphate enters flotation tailings. Foam of the negative electrode graphite material separated through flotation is defoamed, residual gas is circularly returned for flotation inflation, flotation concentrate and flotation tailing pulp are filtered respectively, filtrate is mixed for lithium precipitation and evaporative crystallization, and a lithium carbonate product is obtained. The steps are simple, lithium extraction and negative electrode separation are synchronously completed, the process steps are reduced, the battery recovery efficiency is improved, the use of chemicals is reduced, the generation of leaching residues is avoided, and the method has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field related to the recycling of waste batteries, and particularly relates to a coupling method for extracting lithium by oxidizing old lithium iron phosphate and separating graphite by synchronous flotation. Background Art

[0002] The traditional waste lithium iron phosphate battery processing process is to subject the crushed and screened materials to an oxidation-reduction reaction. After the reaction, the black powder is leached with water to extract lithium, and the remaining lithium extraction residue is iron phosphate. The remaining graphite residue after leaching is difficult to handle and difficult to recycle. When the electrode material is flotated and separated, the leaching of lithium is not fully considered. The floated negative electrode material contains lithium, resulting in lithium loss.

[0003] The prior art with publication number CN113991204A is a short-process recycling method for waste lithium iron phosphate positive electrode materials. The waste lithium iron phosphate battery positive electrode sheet material is placed in deionized water at 25°C and 90°C and repeatedly soaked three times to obtain waste lithium iron phosphate material in pieces; the waste lithium iron phosphate material in pieces is dried and placed in a ball mill for grinding for 1 to 3 hours to obtain waste lithium iron phosphate material powder; the waste lithium iron phosphate material powder is placed in N-methyl-2-pyrrolidone and magnetically stirred for 10 to 14 hours. After the stirring is completed, it is filtered to obtain a black precipitate, which is centrifuged with an organic solvent, washed, and dried to obtain waste lithium iron phosphate positive electrode materials. The recovery of this method relies on the use of a large amount of reagents and requires a large amount of ionized water for soaking, and the reduction efficiency is low. Summary of the invention

[0004] In view of the shortcomings of the prior art, a method for simultaneously flotation separation of graphite and oxidation of old lithium iron phosphate is provided, which can simultaneously realize the oxidation of positive electrode materials and the leaching of lithium elements in the process of separating positive and negative electrode materials by flotation, and use micro-nano oxygen bubble water for flotation and oxidation extraction of lithium, thereby improving the flotation efficiency and oxidizing the lithium iron phosphate into iron phosphate.

[0005] In order to achieve the above technical purpose, the present invention provides a coupling method for extracting lithium from old lithium iron phosphate by oxidation and separating graphite by simultaneous flotation, and the steps are as follows:

[0006] The waste lithium iron phosphate batteries are crushed, pyrolyzed and classified to obtain black powder mixed with positive and negative electrode materials, the black powder is mixed with deionized water at a ratio of 30-60g / L, and a flotation agent of the negative electrode material is added, and stirred to form a black powder slurry;

[0007] Feed the black powder ore pulp into a flotation device in a sealed environment for flotation. At the same time, introduce an acidic gas or acidic substance into the black powder ore pulp in the flotation device to adjust the pH value of the black powder ore pulp to between 4 and 6. Then, introduce micro-nano bubble water containing oxygen, and use the bubble water as the supplementary water in the flotation process; the bubble size of the micro-nano bubble water is between 100 and 200 nm, so as to oxidize lithium iron phosphate by oxygen during the flotation process; separate the cathode material and the anode material in the ore pulp by flotation. During this process, the oxygen introduced into the black powder ore pulp reacts with lithium iron phosphate in the black powder.

[0008] After the flotation separation of the anode material in the black powder ore pulp is completed, the anode material is discharged through the concentrate foam, lithium iron phosphate is oxidized and converted into iron phosphate and discharged through the tailings, and lithium ions are selectively leached into the solution.

[0009] Filter the concentrate foam and the tailings pulp respectively. The filtered concentrate and tailings are further purified to form graphite products and iron phosphate products; mix the filtrates together for lithium precipitation and evaporation crystallization to obtain lithium carbonate products.

[0010] Furthermore, when adjusting the slurry of the black powder of waste lithium iron phosphate batteries and water, add flotation reagents; the flotation reagents include collectors: n-dodecane, kerosene, diesel; the foaming agents are selected from one or a mixture of no. 2 oil, sec-octanol, terpineol, and methyl isobutyl carbinol.

[0011] Furthermore, the acidic gas introduced into the black powder ore pulp during flotation is carbon dioxide or a mixed gas containing carbon dioxide, and this process adjusts the pH value of the black powder ore pulp to between 4 and 6.

[0012] Furthermore, the remaining gas released after defoaming the concentrate foam of the anode material obtained by flotation is recycled and returned to the flotation aeration.

[0013] According to the method for synchronous flotation separation of graphite coupled with oxidative lithium extraction from waste lithium iron phosphate as described in claim 1, it is characterized in that: the flotation device in the sealed environment is obtained by sealing the existing flotation device to prevent internal gas leakage.

[0014] The above technical solution has the following advantages or beneficial effects:

[0015] This method simultaneously realizes the water leaching of lithium elements and the flotation separation of the anode and cathode materials for the electrode materials of waste lithium iron phosphate batteries after pyrolyzing to remove the surface binder. This method realizes the synchronous implementation of selective lithium extraction by oxidation and flotation separation of the anode graphite material from the black powder of waste lithium iron phosphate batteries, and realizes the green and short-process high-efficiency recovery of lithium, graphite, and iron phosphate in waste lithium iron phosphate. This process improves the extraction efficiency of lithium in waste lithium iron phosphate batteries, preferentially separates the anode material, is conducive to the reuse of iron phosphate, avoids the generation of leaching residues, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic flow chart of the method for coupling the oxidation of lithium from spent lithium iron phosphate to extract lithium and the synchronous flotation separation of graphite in an embodiment of the present invention;

[0017] Figure 2 is a graph of the flotation separation rate of graphite obtained by micro-nano bubbles in an embodiment of the present invention;

[0018] Figure 3 is an energy spectrum diagram EDS obtained in an embodiment of the present invention, (A) is the energy spectrum diagram EDS of the concentrate, and (B) is the energy spectrum diagram EDS of the tailings;

[0019] Figure 4 is a schematic diagram showing the change of the pH of micro-nano CO2 bubble water with the preparation conditions in an embodiment of the present invention;

[0020] Figure 5 is a schematic diagram of the test results of the surface wettability characterization of graphite, lithium iron phosphate, and iron phosphate. In the figure, (a) is graphite; (b) is lithium iron phosphate; (c) is iron phosphate. SPECIFIC IMPLEMENTATION METHOD

[0022] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0023] As Figure 1 shown, the present invention discloses a method for coupling the oxidation of lithium from spent lithium iron phosphate to extract lithium and the synchronous flotation separation of graphite, and the steps are as follows:

[0024] After the waste lithium iron phosphate battery electrode material mixture (black powder) is pyrolyzed to remove the surface binder, the black powder is stirred and slurried, and at the same time, a flotation reagent for flotation of the negative electrode material is added. The black powder pulp enters the flotation equipment for flotation. An acid reagent or acidic gas is added to adjust the pH of the solution to between 4 and 6, and then a gas containing O2 or other oxidizing gases is introduced to float and separate the negative electrode graphite material in the black powder. During the flotation process, lithium iron phosphate is oxidized and converted into iron phosphate, and lithium ions are selectively leached into the solution. The negative electrode material becomes concentrated ore foam, and iron phosphate enters the flotation tailings. The foam of the negative electrode graphite material separated by flotation is defoamed, and the remaining gas is recycled and returned to the flotation aeration. The flotation concentrate (negative electrode graphite material) and the flotation tailings (iron phosphate) pulp are filtered respectively, and the filtrates are mixed together for lithium precipitation and evaporation crystallization to obtain lithium carbonate products, and the evaporated liquid is returned to the mixing tank for recycling. The filtered concentrate (negative electrode graphite) is further repaired and regenerated into graphite products for reuse, and the iron phosphate products obtained after filtering the tailings are purified and then reused. This process simultaneously realizes the selective lithium extraction by oxidation of the waste lithium iron phosphate battery black powder and the flotation separation of the negative electrode graphite material, and realizes the green and short-process high-efficiency recovery of lithium, graphite, and iron phosphate in the waste lithium iron phosphate. This process improves the extraction efficiency of lithium in the waste lithium iron phosphate battery, preferentially separates the negative electrode material, is beneficial to the reuse of iron phosphate, avoids the generation of leaching residues, and has broad application prospects.

[0025] Example 1:

[0026] The black powder after pyrolysis treatment of the waste lithium iron phosphate battery and deionized water enter the stirring and slurrying equipment at a ratio of 40 g / L for strong stirring. Kerosene with a dosage of 200 g / t of flotation reagent and methyl isobutyl carbinol with a dosage of 150 g / t are added. To ensure that the flotation process can be carried out in a suitable acidic environment, carbon dioxide or a mixed gas containing carbon dioxide is introduced into the slurry formed by stirring. This process adjusts the pH value of the black powder pulp to 5, as specifically shown in Figure 4 shown; then the pulp enters the XFD-0.5L flotation device for flotation, and the gas filled during flotation is oxygen or an oxidizing gas-containing gas. During the flotation process, the negative electrode graphite is separated as concentrate, and iron phosphate is used as tailings. The lithium element in lithium iron phosphate dissolves in deionized water, and lithium ions are enriched by evaporation crystallization to obtain lithium carbonate precipitation. The rate of graphite separation by micro-nano bubble flotation is as shown in Figure 2 shown.

[0027] Example 2:

[0028] Prepare micro-nano oxygen bubble water with a micro-nano bubble generator of product model XZCP-K. Mix the oxidized iron phosphate of the positive electrode of the waste lithium iron phosphate battery with the pyrolysis material of the negative electrode at a mass ratio of 1:1. The mixed black powder and the micro-nano oxygen bubble water enter the flotation cell at a ratio of 40 g / L, and add kerosene with a flotation reagent dosage of 200 g / t and methyl isobutyl carbinol with a dosage of 150 g / t to carry out the flotation rate experiment. The flotation results are as Figure 1 shown. As time increases, the grade of graphite decreases, and the recovery rate of graphite increases significantly. As time continues to increase, the increase rate of the recovery rate slows down, and the decrease rate of the grade becomes larger. Considering comprehensively, the flotation time is selected as 4 minutes. Through the EDS analysis of the concentrate and tailings at 1 minute, it can be seen that there is only a small amount of iron phosphate mixed in the graphite in the 1-minute flotation concentrate, while the iron phosphate content in the tailings increases significantly, and the graphite grade shows a change from high to low, which is the same as the flotation rate experiment result. Specifically, as Figure 3 shown, Figure 3 in (A) is the EDS of the concentrate energy spectrum diagram, and (B) is the EDS of the tailings energy spectrum diagram.

[0029] Example 3:

[0030] First, calibrate the pH meter with a standard buffer solution. After calibration, rinse the pH electrode with deionized water and dry it with lint-free paper. Then, immerse the pH electrode in a standard solution with a known pH value to verify whether the reading of the pH meter is accurate. After the calibration is confirmed to be correct, use the pH meter to measure the pH value of the micro-nano carbon dioxide bubble water prepared under different aeration times and aeration flows. The test results are as Figure 4 shown. Under normal temperature conditions, when the aeration flow is set to 600 ml / min, the pH value of the micro-nano carbon dioxide bubble water shows a trend of first decreasing and then increasing with the extension of the aeration time. When the aeration time increases from 2 min to 4 min, the pH value of the solution decreases from 4.58 to 4.35. However, as the aeration time further increases, the pH value does not continue to decrease. It may be because during the preparation process, due to the long generation time of bubbles, the heat generated by the nano-bubble generator causes the solution temperature to rise. Since the solubility of carbon dioxide in aqueous solution decreases with the increase of temperature, too long aeration time instead makes the solubility of carbon dioxide decrease, resulting in the rise of the pH value of the solution. Another curve shows the influence of the aeration flow on the pH value of the micro-nano carbon dioxide bubble water. The general trend is that as the aeration flow increases, the pH value decreases. When the aeration flow increases from 400 ml / min to 600 ml / min, the pH value of the solution decreases from 5.0 to 4.35. However, when the aeration flow exceeds 600 ml / min, the change of the pH value tends to be stable, which may be because there is an upper limit to the solubility of carbon dioxide in the solution.

[0031] Example 4:

[0032] The surface wettability of graphite, lithium iron phosphate and iron phosphate was characterized using a JC2000D1 type contact angle measuring instrument. The test results are as Figure 5 shown. The contact angle of graphite reaches 82°, showing obvious hydrophobic characteristics, indicating its good floatability. The contact angle of lithium iron phosphate is 49°, showing weak hydrophilicity, but the difference in contact angle with graphite is small, which is 33°. The contact angle of the oxidation product iron phosphate is reduced to 12°, showing extremely strong hydrophilicity, and the difference in contact angle with graphite is as high as 70°. Through the measurement and observation of the contact angle, it is found that after the oxidation of lithium iron phosphate to iron phosphate, the surface wettability of the material is enhanced, laying a foundation for improving the flotation separation of the positive and negative electrode materials.

[0033] The above are only individual embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for coupling the oxidation of lithium from spent lithium iron phosphate to synchronously flotation and separate graphite, characterized in that, The steps are as follows: The waste lithium iron phosphate battery is crushed, pyrolyzed, and classified to obtain black powder mixed with positive and negative electrode materials. The black powder is mixed with deionized water at a ratio of 30-60 g / L and the flotation reagent for the negative electrode material is added, and then stirred to form a black powder pulp; The black powder pulp is fed into a flotation device in a sealed environment for flotation. At the same time, an acidic gas or acidic substance is introduced into the black powder pulp in the flotation device to adjust the pH value of the black powder pulp to between 4 and 6. Then, micro-nano bubble water containing oxygen is introduced, and the bubble water is used as supplementary water in the flotation process; the bubble size of the micro-nano bubble water is between 100 and 200 nm, so as to oxidize lithium iron phosphate with oxygen during the flotation process; the positive and negative electrode materials in the pulp are separated by flotation, and the oxygen introduced into the black powder pulp reacts with lithium iron phosphate in the black powder during this process; When the flotation separation of the negative electrode material in the black powder pulp is completed, the negative electrode material is discharged through the concentrate foam, lithium iron phosphate is oxidized and converted into iron phosphate and discharged through the tailings, and lithium ions are selectively leached into the solution; The concentrate foam and the tailings pulp are filtered respectively, and the filtered concentrate and tailings are further purified to form graphite products and iron phosphate products; the filtrates are mixed together for lithium precipitation and evaporation crystallization to obtain lithium carbonate products.

2. The method for coupling the oxidation of lithium extraction from spent lithium iron phosphate and synchronous flotation separation of graphite according to claim 1, wherein: When the waste lithium iron phosphate battery black powder is slurried with water, the added flotation reagent; the flotation reagent includes collectors: n-dodecane, kerosene, diesel; the foaming agent is selected from one or a mixture of no. 2 oil, sec-octanol, terpineol, and methyl isobutyl carbinol.

3. The method for coupling the oxidation of lithium extraction from used lithium iron phosphate and synchronous flotation separation of graphite according to claim 1, wherein: The acidic gas introduced into the black powder pulp during flotation is carbon dioxide or a mixed gas containing carbon dioxide, and this process adjusts the pH value of the black powder pulp to between 4 and 6.

4. The method for coupling lithium extraction from spent lithium iron phosphate by oxidation and synchronous flotation separation of graphite according to claim 1, wherein: The remaining gas released after defoaming the concentrate foam of the flotation negative electrode material is recycled and returned to the flotation aeration.

5. The method for coupling lithium extraction from spent lithium iron phosphate by oxidation and synchronous flotation separation of graphite according to claim 1, characterized in that: The flotation device in the sealed environment is obtained by sealing the existing flotation device to prevent internal gas leakage.

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