A method for resource utilization of phosphorus iron slag

Abstract

The application discloses a method for recycling phosphorus-iron slag, which comprises the following steps: subjecting LFP positive electrode black powder to lithium extraction treatment, and then grinding and sieving to obtain phosphorus-iron slag powder; mixing the phosphorus-iron slag powder, waste negative electrode graphite carbon powder and sodium carbonate to obtain a mixture; subjecting the mixture to calcination treatment in a nitrogen-containing atmosphere to obtain gray-black calcined clinker; dispersing the black calcined clinker in water, stirring and leaching, and then filtering and separating to obtain a leaching solution containing sodium phosphate and a solid residue containing elemental iron; subjecting the solid residue to magnetic separation to obtain metallic iron powder; and using the leaching solution to prepare battery-grade sodium phosphate. The method for recycling phosphorus-iron slag directly uses negative electrode graphite carbon obtained by disassembling waste batteries as a reducing agent, and one-time carbon thermal reduction and sodium transformation are completed through high-temperature collaborative calcination by component compounding, and then phosphorus is leached by water and iron is separated by magnetic separation to realize efficient separation of phosphorus and iron elements and realize resource closed-loop circulation.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for the resource utilization of phosphorus-iron slag. Background Technology

[0002] After lithium extraction from retired lithium iron phosphate batteries, a large amount of lithium extraction slag (phosphorus-iron slag) rich in phosphorus and iron is generated. In this slag, phosphorus mainly exists in insoluble forms such as apatite, and iron mainly exists in the form of ferric iron. Without proper resource utilization, this not only wastes phosphorus and iron resources but also leads to solid waste accumulation and environmental burden. How to efficiently separate and recycle phosphorus and iron from the slag into high-value-added products is an urgent problem to be solved in the field of retired lithium iron phosphate battery resource utilization.

[0003] In related technologies, the treatment of phosphorus iron slag often requires the purchase of reducing agents and the use of costly sodium-based / alkalizing reagents such as potassium carbonate, and the process is lengthy and energy-intensive; at the same time, there are limited ways to reuse graphite from waste lithium-ion battery anodes.

[0004] Therefore, it is of great significance to develop a resource utilization method for phosphorus-iron slag that utilizes raw materials locally, has low cost, short process, and thorough separation. Summary of the Invention

[0005] In view of this, the present invention provides a method for the resource utilization of phosphorus iron slag, which solves the problem of how to utilize the raw materials on-site to realize the resource utilization of phosphorus iron slag.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for the resource utilization of phosphorus-iron slag, comprising the following steps: The LFP cathode black powder is subjected to lithium extraction treatment, then ground and sieved to obtain phosphorus iron slag powder. The phosphorus iron slag powder, waste negative electrode graphite carbon powder, and sodium carbonate are mixed to obtain a mixture. The mixture is roasted under a nitrogen-containing atmosphere to obtain a gray-black roasted clinker. The black roasted clinker was dispersed in water, stirred and leached, and then filtered to obtain a leachate containing sodium phosphate and a solid residue containing elemental iron. The solid slag is subjected to magnetic separation to obtain metallic iron powder; the leachate is used to prepare battery-grade sodium phosphate.

[0007] Preferably, the mass ratio of the phosphorus iron slag powder, waste negative electrode graphite carbon powder, and sodium carbonate is 100:15-25:30-50.

[0008] Preferably, the final calcination temperature is 950-1050℃, and the holding time is 2-3 hours.

[0009] Preferably, the final temperature of the roasting is increased at a rate of 10-15℃ / min.

[0010] Preferably, the liquid-solid ratio of the black roasted clinker to water is 3-5:1.

[0011] Preferably, the particle size of the phosphorus iron slag powder and the waste negative electrode graphite carbon powder is ≤200 mesh.

[0012] Preferably, the intensity of the magnetic separation is 800-1200 GS.

[0013] Preferably, the waste negative electrode graphite carbon powder is prepared by mechanically crushing, washing and removing copper from waste lithium-ion battery negative electrode sheets, and drying them to obtain waste negative electrode graphite carbon powder.

[0014] Preferably, the stirring leaching temperature is 20-30℃ and the time is 1-5h.

[0015] The advantages of the present invention compared to the prior art are as follows: 1. This invention directly uses negative electrode graphite carbon obtained from the dismantling of waste batteries as a reducing agent, without the need to purchase additional carbon sources, and replaces the more expensive potassium carbonate with industrial-grade sodium carbonate. 2. This invention completes carbothermal reduction and sodium transformation in one step through high-temperature synergistic roasting at around 1000℃. The subsequent efficient separation of phosphorus and iron can be achieved in just two steps: water leaching for phosphorus extraction and magnetic separation for iron. 3. The iron powder obtained by this invention has high purity (≥98%) and strong magnetic properties, and can be directly used as a metallurgical raw material or battery-grade iron source for recycling; the sodium phosphate leachate can be directly used to prepare lithium iron phosphate precursors; 4. This invention does not use strong acids, strong alkalis or toxic reagents throughout the process, and there is no risk of secondary pollution; waste negative electrode graphite is reused, the tailings yield is low, and the amount of solid waste is significantly reduced. Detailed Implementation

[0016] The embodiments of the technical solution of the present invention will be described in detail below. These embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore merely examples and should not be used to limit the scope of protection of the present invention.

[0017] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0018] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0019] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0020] Unless otherwise explicitly defined and specified herein, all technical and scientific terms used in this invention have the generally accepted meanings understood by one of ordinary skill in the field of chemical and chemical materials technology (including but not limited to polymer chemistry, inorganic chemistry, organic synthesis, catalysis chemistry, materials processing, and chemical unit operations) based on their professional knowledge and conventional practice. The use of any terminology herein is intended to describe specific embodiments of the invention in the clearest and most accurate manner, so as to fully disclose the technical solutions. Such use should in no way be construed as limiting the scope of the claims, nor does it imply the exclusion of equivalent technical solutions that could be reasonably known by one of ordinary skill in the art based on the inventive concept.

[0021] The terms "comprising," "including," "having," "containing," and any grammatical variations or similar expressions used in the specification and claims of this invention are all open-ended and non-exhaustive descriptive terms. Their purpose is to explicitly describe the existence of the stated technical features, components, steps, or parts, while explicitly allowing and covering the possibility that other features, components, steps, parts, or any combinations thereof not explicitly listed may exist or be added to the technical solution, as long as such additions do not destroy the integrity and inventiveness of the original technical solution.

[0022] When the terms "embodiments," "some embodiments," or "specific embodiments" are mentioned in the specification, they refer to one or a group of examples that, in conjunction with the specific parameters, materials, steps, and results described in that section, constitute an implementation of the technical solution of the present invention. These embodiments are used for full disclosure and illustrative purposes, not for exhaustive enumeration. Those skilled in the art should understand that, without departing from the overall inventive concept of the present invention, the various technical features disclosed in different embodiments can be combined, substituted, modified, or deleted to form other implementation methods that are not listed one by one in the specification but also fall within the protection scope of the present invention.

[0023] Unless otherwise expressly specified and limited, all terms related to chemical process operations, material preparation, treatment, and analysis and testing involved in this invention should be understood in the broadest sense based on the conventional understanding of those skilled in the art.

[0024] Regarding performance testing and structural characterization, all testing and characterization methods involved in this invention, unless otherwise specified, refer to conventional methods known in the art. Specific testing conditions can be selected and adjusted according to the sample properties and relevant national standards, international standards, or industry-standard methods. Test items may include mechanical properties (such as tensile, bending, and impact strength), thermal properties (such as DSC and TGA analysis), and chemical stability (such as solvent resistance and acid / alkali corrosion resistance). Structural characterization methods may include FT-IR, NMR, XRD, SEM, TEM, and BET. All test results should be understood to be within the allowable range of conventional experimental errors.

[0025] Regarding numerical values ​​and ranges, all parameter ranges expressed in the form of "from a certain value to a certain value" in this invention should be understood as explicitly disclosing the endpoint values ​​of the range, each specific numerical point between the endpoints, and all sub-ranges formed by any two numerical points within the range. For example, "30℃ to 80℃" discloses 30, 31, ..., 80℃, as well as sub-ranges such as 30-50℃, 45-70℃, etc. When a numerical value is preceded by "about," "approximately," or similar words, it indicates that the numerical value is allowed to have reasonable errors recognized in the art under the measurement or control conditions, which can generally be understood as the deviation allowed by relevant standards or a normal fluctuation range of ±5% or ±10%.

[0026] This invention provides a method for the resource utilization of phosphate slag, comprising the following steps: The LFP cathode black powder is subjected to lithium extraction treatment, then ground and sieved to obtain phosphorus iron slag powder. The phosphorus iron slag powder, waste negative electrode graphite carbon powder, and sodium carbonate are mixed to obtain a mixture. The mixture is roasted under a nitrogen-containing atmosphere to obtain a gray-black roasted clinker. The black roasted clinker was dispersed in water, stirred and leached, and then filtered to obtain a leachate containing sodium phosphate and a solid residue containing elemental iron. The solid slag is subjected to magnetic separation to obtain metallic iron powder; the leachate is used to prepare battery-grade sodium phosphate.

[0027] By adopting the above technical solution, the negative electrode graphite carbon obtained from the dismantling of waste batteries is directly used as a reducing agent, eliminating the need for additional carbon source purchases. Industrial-grade sodium carbonate is selected to replace the more expensive potassium carbonate, reducing reagent costs. Carbothermic reduction and sodium conversion are completed in one step through high-temperature synergistic roasting, followed by two steps of water leaching for phosphorus extraction and magnetic separation for iron separation, achieving efficient separation of phosphorus and iron elements. The process is short, the equipment is simple, and it is easy to scale up. Iron is converted into high-purity metallic iron powder, and phosphorus is converted into soluble sodium phosphate, which can be directly used to prepare lithium iron phosphate precursors, realizing a closed-loop resource cycle. No strong acids, strong alkalis, or toxic reagents are used throughout the process, resulting in no secondary pollution. Waste negative electrode graphite is reused, and solid waste is significantly reduced. In particular, during the high-temperature roasting process, the waste negative electrode graphite acts as a reducing agent to reduce Fe(III) in the mixture to metallic iron, and also acts as a carbon source to synergistically promote the conversion of apatite into soluble sodium phosphate with sodium carbonate.

[0028] In some embodiments, the mass ratio of the phosphorus iron slag powder, waste negative electrode graphite carbon powder, and sodium carbonate is 100:15-25:30-50.

[0029] In some embodiments, the final calcination temperature is 950-1050℃, and the holding time is 2-3 hours.

[0030] In this embodiment, the mixture is calcined at 950-1050°C for 2-3 hours to complete the carbothermic reduction and sodium conversion reaction, and then naturally cooled to room temperature after calcination.

[0031] In some embodiments, the final temperature of the calcination is increased at a rate of 10-15 °C / min.

[0032] In some embodiments, the liquid-to-solid ratio of the black roasted clinker to water is 3-5:1.

[0033] In some embodiments, the particle size of the phosphorus iron slag powder and the waste negative electrode graphite carbon powder is ≤200 mesh.

[0034] In some embodiments, the intensity of the magnetic separation is 800-1200 GS.

[0035] In this embodiment, a permanent magnet magnetic separator is used to perform magnetic separation under a magnetic field strength of 800~1200Gs to separate high-purity metallic iron powder and a small amount of impurity tailings; the obtained metallic iron has strong magnetism and can be directly used as a metallurgical raw material or battery-grade iron source for recycling.

[0036] In some embodiments, the waste negative electrode graphite carbon powder is prepared by mechanically crushing, washing and removing copper from waste lithium-ion battery negative electrode sheets, and drying them to obtain waste negative electrode graphite carbon powder.

[0037] In some embodiments, the temperature of the stirring leaching is 20-30°C, and the time is 1-5 hours.

[0038] In this embodiment, a sodium phosphate-containing leachate and an iron-containing solid residue are obtained by leaching at room temperature and filtering. The leachate is then used directly to prepare battery-grade sodium phosphate.

[0039] The following specific embodiments further illustrate this solution.

[0040] Source of raw materials The experimental materials used in the various embodiments of this invention are as follows: the dry basis composition of the phosphorus iron slag is Fe 33.2%, P 17.8%, Li 0.3%, Al 0.1%, and moisture 4.2%; the waste negative electrode graphite is from the negative electrode sheets of retired lithium iron phosphate batteries of the same batch, and after crushing and screening to separate copper, the carbon content is 92.6%, Cu 0.38%, and the particle size is ≤200 mesh; the sodium carbonate is industrial grade with a purity of 98.2%.

[0041] Example 1 A method for resource utilization of phosphate slag includes the following steps: Waste lithium-ion battery negative electrode sheets are mechanically crushed, washed with water to remove copper, and dried to obtain waste negative electrode graphite carbon powder; lithium iron phosphate (LFP) positive electrode black powder is placed in sulfuric acid solution, hydrogen peroxide is added to oxidize it, and the pH is adjusted to 2. After filtration, lithium sulfate solution and iron phosphate slag are obtained.

[0042] The lithium-extracted ferrophosphate slag was further ground and passed through a 200-mesh sieve to obtain uniform ferrophosphate slag powder. Phosphorus iron slag, waste negative electrode graphite, and sodium carbonate are mixed evenly in a mass ratio of 100:20:40 and placed in a corundum crucible for later use to obtain a mixture. The mixture was placed in a high-temperature muffle furnace and heated to 1000°C at a rate of 10-15°C / min under an air atmosphere. It was held for 2 hours to complete the carbothermic reduction and sodium conversion reaction. After roasting, it was naturally cooled to room temperature to obtain a gray-black roasted clinker. The roasted clinker was added to deionized water at a liquid-to-solid ratio of 5:1, stirred and leached at 25°C for 5 hours, and filtered to separate the leachate containing sodium phosphate and the solid residue containing elemental iron; the leachate was directly used to prepare battery-grade sodium phosphate. The solid slag after water immersion is dried and then subjected to magnetic separation using a permanent magnet separator under a magnetic field strength of 1000 Gs to obtain high-purity metallic iron powder and a small amount of impurity tailings. The obtained metallic iron has strong magnetic properties and can be directly used as a metallurgical raw material or battery-grade iron source for recycling.

[0043] Example 2 A method for the resource utilization of phosphorus-iron slag is described, with other contents being the same as in Example 1, except that the roasting heating rate is 10℃ / min, the final temperature is 1000℃, and the holding time is 2h; the water leaching liquid-solid ratio is 5:1, and the stirring is carried out at room temperature for 2h; the magnetic separation magnetic field strength is 1000Gs. The sodium carbonate content is fixed at 40 parts, and the content of waste negative electrode graphite is varied. The parameters and results are shown in Table 1.

[0044] Table 1. Effect of waste negative electrode graphite content on resource utilization efficiency

[0045] As shown in Table 1, the optimal range for the content of waste negative electrode graphite is 15-25 parts: when the content is 10 parts, the reduction is incomplete, the phosphorus leaching rate is only 92.3%, and the purity of metallic iron is only 95.1%; when the content is 15-25 parts, the phosphorus leaching rate reaches 97.1%-97.8%, and the purity of metallic iron reaches 98.2%-98.9%; when the content is increased to 30 parts, due to the residual excess carbon impurities, the purity of metallic iron drops to 97.3%, and the tailings yield increases to 10.1%.

[0046] Example 3 A method for the resource utilization of phosphorus-iron slag is described, with other contents being the same as in Example 1, except that the roasting heating rate is 10℃ / min, the final temperature is 1000℃, and the holding time is 2h; the water leaching liquid-solid ratio is 5:1, and the stirring is carried out at room temperature for 2h; the magnetic separation magnetic field strength is 1000Gs. The amount of waste negative electrode graphite is fixed at 20 parts, and the amount of sodium carbonate is varied. The parameters and results are shown in Table 2.

[0047] Table 2. Effect of sodium carbonate dosage on resource utilization efficiency

[0048] Table 2 shows that the optimal sodium carbonate content is 30-50 parts: when the sodium carbonate content is 20 parts, the sodiumization of phosphorus is incomplete, and the phosphorus leaching rate is only 89.5%; when the sodium carbonate content is 30-50 parts, the phosphorus leaching rate reaches 97.0%-97.8% and the purity of metallic iron reaches 98.4%-98.9%; when the sodium carbonate content is increased to 60 parts, due to the introduction of sodium salt impurities, the tailings yield increases to 10.3% and the purity of metallic iron decreases to 97.1%.

[0049] Example 4 A method for the resource utilization of phosphorus iron slag is the same as that in Example 1, except that the material ratio is fixed at 100:20:40; the roasting heating rate is 10℃ / min, the roasting temperature is changed and the temperature is held for 2 hours; the water leaching liquid-solid ratio is 5:1, and the mixture is stirred at room temperature for 2 hours; the magnetic separation magnetic field strength is 1000Gs. The parameters and results are shown in Table 3.

[0050] Table 3. Effect of calcination temperature on resource utilization efficiency

[0051] Table 3 shows that the optimal roasting temperature range is 950~1050℃: at 900℃, the reaction is incomplete, with a phosphorus leaching rate of only 91.2% and a metallic iron recovery rate of only 87.5%; at 950~1050℃, the phosphorus leaching rate reaches 97.2%~97.8% and the metallic iron purity reaches 98.4%~98.9%; when the temperature rises to 1100℃, the material exhibits slight sintering and agglomeration, the phosphorus leaching rate drops to 95.8%, and the tailings yield increases to 9.8%.

[0052] Example 5 A method for the resource utilization of phosphorus iron slag is the same as that in Example 1, except that the material ratio is fixed at 100:20:40; the roasting heating rate is 10℃ / min, the roasting temperature is 1000℃, and the holding time is changed; the water immersion liquid-solid ratio is 5:1, and the stirring is carried out at room temperature for 2 hours; the magnetic separation magnetic field strength is 1000Gs. The parameters and results are shown in Table 4.

[0053] Table 4. Effect of roasting and holding time on resource utilization efficiency

[0054] As shown in Table 4, the optimal range for heat preservation is 2-3 hours: when heat preservation is 1 hour, the reaction is insufficient, with a phosphorus leaching rate of only 93.5% and a metallic iron recovery rate of only 90.2%; when heat preservation is 2-3 hours, the phosphorus leaching rate reaches 97.6%-97.8% and the metallic iron purity reaches 98.7%-98.9%; when heat preservation is extended to 4 hours, there is no obvious quality improvement effect, but rather an increase in production energy consumption.

[0055] Example 6 A method for the resource utilization of phosphorus iron slag is the same as that in Example 1, except that the material ratio is fixed at 100:20:40; the roasting heating rate is 10℃ / min, the roasting temperature is 1000℃, and the holding time is 2h; the water leaching liquid-solid ratio is changed, and the mixture is stirred at room temperature for 2h; the magnetic separation magnetic field strength is 1000Gs. The parameters and results are shown in Table 5.

[0056] Table 5. Effect of liquid-to-solid ratio in water immersion on resource utilization efficiency

[0057] As shown in Table 5, the optimal liquid-to-solid ratio is 3 to 5:1. When the liquid-to-solid ratio is 3:1, the liquid volume is too small, and a small amount of phosphorus is not completely leached out. The phosphorus leaching rate is 97.0%, and the concentration of sodium phosphate leachate is too high, reaching 142 g / L. When the liquid-to-solid ratio is 4:1 to 5:1, the phosphorus leaching rate reaches 97.5% to 97.8%. If the liquid-to-solid ratio is too large, it will dilute the sodium phosphate solution and increase the energy consumption for subsequent concentration.

[0058] Based on the above embodiments, it can be seen that under the conditions of phosphorus-iron slag: waste negative electrode graphite: sodium carbonate = 100:20:40, calcination temperature 1000℃, holding time 2h, water leaching liquid-solid ratio 5:1, and magnetic separation magnetic field strength 1000Gs, the phosphorus leaching rate reaches 97.8%, the metallic iron recovery rate reaches 98.5%, the metallic iron purity reaches 98.9%, the tailings yield is 8.3%, and the sodium phosphate leachate concentration reaches 128g / L, thus achieving efficient separation and resource recovery of phosphorus and iron in phosphorus-iron slag.

[0059] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for the resource utilization of phosphorus-iron slag, characterized in that, Includes the following steps: The LFP cathode black powder is subjected to lithium extraction treatment, then ground and sieved to obtain phosphorus iron slag powder. The phosphorus iron slag powder, waste negative electrode graphite carbon powder, and sodium carbonate are mixed to obtain a mixture. The mixture is roasted under a nitrogen-containing atmosphere to obtain a gray-black roasted clinker. The black roasted clinker was dispersed in water, stirred and leached, and then filtered to obtain a leachate containing sodium phosphate and a solid residue containing elemental iron. The solid slag is subjected to magnetic separation to obtain metallic iron powder; The leachate was used to prepare battery-grade sodium phosphate.

2. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The mass ratio of the phosphorus iron slag powder, waste negative electrode graphite carbon powder, and sodium carbonate is 100:15-25:30-50.

3. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The final roasting temperature is 950-1050℃, and the holding time is 2-3 hours.

4. The method for resource utilization of phosphorus-iron slag according to claim 4, characterized in that, The final temperature of the roasting is increased at a rate of 10-15℃ / min.

5. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The liquid-solid ratio of the black roasted clinker to water is 3-5:

1.

6. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The particle size of the phosphorus iron slag powder and the waste negative electrode graphite carbon powder is ≤200 mesh.

7. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The intensity of the magnetic separation is 800-1200 GS.

8. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The method for preparing the waste negative electrode graphite carbon powder is as follows: the waste lithium-ion battery negative electrode sheet is mechanically crushed, washed with water to remove copper, and dried to obtain the waste negative electrode graphite carbon powder.

9. The method for resource utilization of phosphorus-iron slag according to claim 1, characterized in that, The stirring leaching temperature is 20-30℃, and the time is 1-5 hours.

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