Fluorine recycling method in waste battery recycling process

Abstract

The invention provides a method for recycling fluorine in a waste battery recycling process, which comprises the following steps: S1, discharging a waste lithium ion battery, crushing, and pyrolyzing the obtained positive plate material to obtain a metal material to be recycled and fluorine-containing flue gas; s2, the fluorine-containing flue gas in the step S1 is sequentially introduced into fluorine-containing sludge and alkali liquor for absorption; s3, after the fluorine-containing sludge in the step S2 is absorbed to be saturated, spraying the alkali liquor which absorbs the fluorine-containing flue gas in the step S2 to the surface layer of the fluorine-containing sludge which is absorbed to be saturated, then carrying out ball milling on the sprayed fluorine-containing sludge, and roasting the obtained ball-milled material to obtain a roasted solid; and S4, the roasted solid in the step S3 is smashed and then leached, leached solid is obtained after solid-liquid separation, and the leached solid is washed and dried to obtain a calcium fluoride product. According to the method, the fluorine-containing sludge and the alkali liquor are used for absorbing the fluorine-containing flue gas, so that recycling of the fluorine element in the recycling process of the waste lithium ion battery is effectively realized.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste treatment, and specifically relates to a method for fluorine resource recovery in the process of recycling waste batteries. Background Art

[0002] At present, the main treatment method for high-concentration fluoride-containing wastewater generated during the wet recycling of waste batteries is the chemical precipitation-coagulation treatment method. This method generally adds calcium hydroxide to form a precipitate, and the resulting sludge often contains calcium fluoride, calcium hydroxide, calcium sulfate, and certain metal hydroxides. Calcium fluoride accounts for a large proportion of fluorine-containing sludge. Fluorite (calcium fluoride) is a non-renewable resource. If the fluorine-containing sludge is directly scrapped and disposed of, it is easy to cause a waste of fluorine resources. However, the content of other impurities in the fluorine-containing sludge is not low. It is difficult to meet the requirements of the metallurgical industry for calcium fluoride content by directly using the fluorine-containing sludge. Therefore, the fluorine-containing sludge needs to be purified. At present, the industrial method of purifying calcium fluoride is mostly wet purification based on flotation and acid leaching. Wet purification often needs to consider the secondary leaching of fluorine during the purification process. Some technicians choose NaF and other fluoride salts as mineral phase regulators and fluorine-containing sludge mixed with roasting to purify. Although this method can effectively improve the purity of calcium fluoride, the price of the fluoride salts such as NaF used is relatively high, which also increases the cost of purifying fluorine-containing sludge. Some other technicians only recycle the fluorine in the fluorine-containing sludge itself. The amount of fluorine resources recovered is limited, and the fluorine-containing sludge needs to be converted into sulfate by adding carbonate before calcination, so the treatment process is relatively cumbersome.

[0003] For economic reasons, the current recycling of waste batteries in industry is mainly focused on high-value metal elements, while the electrolyte is burned and decomposed in the pyrolysis process, and then the tail gas is treated. The lithium salt in the electrolyte mainly uses lithium hexafluorophosphate. The F in the electrolyte enters the tail gas after gasification and combustion and is absorbed by alkaline solution, which also makes the F in the electrolyte not effectively utilized.

[0004] In summary, seeking a process that can effectively utilize fluorine resources in the process of recycling used batteries, reduce fluorine pollution and waste of fluorine resources, and has low treatment costs is an urgent problem that needs to be solved in the current industrial solid waste treatment. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for fluorine resource utilization in the process of waste battery recycling, which can effectively utilize the fluorine resources in the process of waste lithium-ion battery recycling, reduce fluorine pollution and fluorine resource waste, and has low processing cost.

[0006] According to a first aspect of the present invention, a method for fluorine resource recovery in a waste battery recycling process is proposed, comprising the following steps: S1: Discharging and crushing the waste lithium-ion batteries, and pyrolyzing the obtained positive electrode sheets to obtain metal materials and fluorine-containing flue gas to be recycled; S2: passing the fluorine-containing flue gas in step S1 into fluorine-containing sludge and alkali solution in sequence for absorption; S3: When the fluorine-containing sludge in step S2 is saturated with absorption, the alkali solution after absorbing the fluorine-containing flue gas in step S2 is sprayed onto the surface of the saturated fluorine-containing sludge, and then the sprayed fluorine-containing sludge is ball-milled, and the obtained ball-milled material is roasted to obtain a roasted solid; S4: crushing the roasted solid in step S3 and leaching it, obtaining a leached solid after solid-liquid separation, washing and drying the leached solid to obtain a calcium fluoride product; In step S2, the pH of the fluorine-containing sludge is ≥12, the dry basis ratio of CaF2 in the fluorine-containing sludge is 45%~65%, and the water content is 30%~50%.

[0007] The fluorine-containing sludge used in the present invention is derived from the sludge formed by adding calcium hydroxide to high-concentration fluorine-containing wastewater generated in the process of wet recovery and treatment of waste lithium-ion batteries. In addition to calcium fluoride, the sludge also contains components such as calcium hydroxide, calcium sulfate, calcium carbonate, sodium sulfate, a small amount of silicon and magnesium impurities, and hydroxides of some metals.

[0008] In some embodiments, in step S1, the crushing is performed under vacuum conditions.

[0009] In some embodiments, in step S1, the pyrolysis temperature is 200-1000° C. and the time is 1-5 h.

[0010] In some embodiments, in step S2, the fluorine-containing flue gas is discharged after passing through the alkali solution, and the heat from the combustion can be supplied to the subsequent roasting process.

[0011] In some embodiments, in step S2, the flow rate of the fluorine-containing flue gas passing into the fluorine-containing sludge is 20-40 L / h; and / or, the alkali solution is a 0.1-1 mol / L NaOH solution. The main purpose of using alkali solution for absorption after the fluorine-containing sludge absorption stage in the present invention is to prevent the residual fluorine in the flue gas from entering the air. Therefore, the amount of alkali solution can be selected according to the fluorine absorption situation, for example, it can be 1 L, 2 L, etc., and the present invention does not specifically limit this.

[0012] In some embodiments, in step S3, after the fluorine-containing sludge is saturated with absorption, the moisture content is reduced to 1%~5%; and / or, the spraying amount of the alkali solution after absorbing the fluorine-containing flue gas is 3%~8% of the mass of the fluorine-containing sludge that is saturated with absorption; and / or, the ball milling time is 0.5~2h.

[0013] In some embodiments, the fluorine content in the alkali solution after absorbing the fluorine-containing flue gas is greater than or equal to 50 mg / L. When the fluorine content in the alkali solution reaches 50 mg / L, it can be considered that the fluorine-containing sludge has absorbed saturated fluorine-containing flue gas. The fluorine-containing flue gas obtained by pyrolysis is acidic, and the alkalinity of the fluorine-containing sludge weakens after fully absorbing the fluorine-containing flue gas. A small amount of alkali solution that absorbs the residual fluorine in the fluorine-containing flue gas is sprayed on the surface of the fluorine-containing sludge after fully absorbing the fluorine-containing flue gas, and then ball milled. This can make the fluorine-containing sludge maintain a uniform alkaline state during roasting while the moisture content does not increase significantly, reduce the fluorine in the sludge during roasting. Escape in the form of hydrogen fluoride or silicon tetrafluoride, ensure the safety of the operation process, and further effectively utilize the residual fluorine absorbed by the alkali solution.

[0014] If the fluorine-containing sludge does not absorb fluorine sufficiently, the fluorine content in the fluorine-containing sludge will be low, and the calcium will not be fully utilized and converted into calcium fluoride. The calcium exists in the sludge in the form of impurities, which increases the pressure of subsequent acid removal, and easily causes an increase in the secondary leaching amount of F in the acid or a decrease in the dry basis CaF2 content.

[0015] In some embodiments, in step S2, the fluorine-containing sludge includes a first-stage sludge and a second-stage sludge, and the fluorine-containing flue gas is absorbed in the first-stage sludge, the second-stage sludge and the alkali solution in sequence; when the first-stage sludge is saturated with absorption, the step S2 includes: passing the fluorine-containing flue gas in step S1 into the second-stage sludge, the spare sludge and the alkali solution in sequence for absorption. At this time, the second-stage sludge serves as a new first-stage sludge to absorb the fluorine-containing flue gas, and the spare sludge serves as a new second-stage sludge to absorb the fluorine-containing flue gas, and the source of the spare sludge is the same as that of the first-stage sludge and the second-stage sludge. To ensure the absorption effect, when the first-stage sludge is replaced after absorption is saturated, the alkali solution is also replaced with an equal concentration (0.1~1mol / L) of NaOH solution.

[0016] The present invention preferably utilizes two-stage fluorine-containing sludge and alkaline solution to absorb the fluorine-containing flue gas generated by the pyrolysis of the positive electrode sheet, which has the following effects: (1) the three-stage absorption (two-stage alkaline fluorine-containing sludge absorption + alkaline solution absorption) can fully absorb the fluorine in the pyrolysis flue gas, and the fluorine-containing sludge also contains unreacted calcium hydroxide and generated calcium sulfate. The fluorine in the fluorine-containing flue gas can further react with the calcium hydroxide and calcium sulfate in the fluorine-containing sludge to generate calcium fluoride; (2) the two-stage fluorine-containing sludge absorption can absorb most of the fluorine in the fluorine-containing flue gas, and the alkaline solution absorption is to absorb the residual fluorine in the fluorine-containing flue gas when the fluorine-containing sludge is about to absorb saturation, so the alkaline solution concentration does not need to be too high to avoid alkali waste; (3) the two-stage fluorine-containing sludge absorption produced by pyrolysis When the fluorine-containing flue gas is absorbed, the residual heat of the fluorine-containing flue gas can be absorbed to reduce the moisture content of the fluorine-containing sludge, and reduce the consumption of heat energy required for subsequent sludge roasting; and the fluorine-containing sludge can also absorb and intercept part of the carbon dioxide in the fluorine-containing flue gas and the hydrocarbon organic matter produced by incomplete combustion. The carbon dioxide can react with the calcium hydroxide of the fluorine-containing sludge to form calcium carbonate, and the organic matter can be burned during the sludge roasting to release heat energy, further reducing the consumption of heat energy required for subsequent sludge roasting; (4) After the initial one-stage sludge absorption is saturated, the original two-stage sludge absorption is used as a new one-stage sludge absorption, and the spare sludge absorption is used as a new two-stage sludge absorption to continue to absorb the fluorine-containing flue gas, thereby ensuring that the one-stage fluorine-containing sludge can fully absorb the fluorine-containing flue gas. The present invention preferably uses two-stage fluorine-containing sludge and alkali solution to perform multi-stage absorption of fluorine-containing flue gas, which ensures the continuity of the process and facilitates the rapid replacement of one-stage sludge after the absorption is saturated, while reducing the loss of fluorine and the consumption of alkali solution, so that fluorine is enriched in the fluorine-containing sludge as much as possible. It is understandable that the fluorine-containing sludge can be set to only one section, but this will increase the amount of alkali solution used, and the alkali solution that absorbs a large amount of fluorine-containing flue gas also needs further defluorination treatment; of course, the fluorine-containing sludge can also be set to 3, 4 or 5 sections, which is beneficial to further reduce the loss of fluorine and the consumption of alkali solution, but too many sludge absorption sections will make the treatment process of fluorine-containing flue gas complicated.

[0017] In some embodiments, in step S3, the calcination temperature is 650-1000°C and the time is 1-4 hours. The calcination process can utilize the waste heat generated by the combustion of the flue gas after absorption by the alkali solution to maintain high temperature conditions. The calcium sulfate and calcium hydroxide in the fluorine-containing sludge that fully absorbs the fluorine-containing flue gas will react with fluorine to be converted into calcium fluoride, and the remaining unreacted calcium sulfate, calcium carbonate, and calcium hydroxide will decompose under high temperature conditions to generate calcium oxide. Under high temperature conditions, calcium fluoride crystals grow. During their growth process, due to the impurity exclusion phenomenon of crystal growth, calcium carbonate and calcium oxide particles cannot enter the interior of the calcium fluoride crystals, thereby achieving the purification of calcium fluoride. That is, the fluorine enriched in the fluorine-containing sludge can be used as a regulator of the growth of calcium fluoride crystals to induce crystal phase transition.

[0018] In some embodiments, in step S4, the particle size of the calcined solid after crushing is ≤0.15mm; and / or, the leaching agent used in the leaching is hydrochloric acid, and the liquid-to-solid ratio of the leaching is 4-5L / kg; and / or, the pH of the solution during the leaching process is maintained at 5-8; and / or, the leaching time is 0.5-2h. The solid after calcining the fluorine-containing sludge is hard in texture, and the calcined solid needs to be ground and crushed to a certain degree so that the impurities such as calcium oxide, sulfate, silicon and magnesium in the calcined solid can be fully dissolved in the acid solution to achieve impurity removal of the calcined solid; controlling the pH of the leachate during the leaching process can reduce the secondary leaching of fluorine in the calcined solid.

[0019] In some embodiments, in step S4, the washing method is pulp washing, and the pulp washing process is: the leached solid is mixed with water at a liquid-solid ratio of 4-5 L / kg and stirred for 0.5-2 hours. The calcined solid after leaching is pulp washed with pure water to further wash away impurities and achieve further purification of calcium fluoride.

[0020] According to the second aspect of the present invention, the application of the method described in the first aspect of the present invention in the recycling of waste lithium batteries is proposed. The purity of the calcium fluoride product obtained by the method is above 90%, realizing the effective utilization of fluorine resources in the recycling process of waste lithium batteries.

[0021] According to one embodiment of the present invention, there are at least the following beneficial effects: 1. The treatment method of the present invention can effectively absorb the fluorine-containing flue gas generated in the pyrolysis stage during the recycling of waste batteries, while effectively utilizing the fluorine and heat in the fluorine-containing flue gas, thereby reducing the waste of fluorine resources and thermal energy.

[0022] 2. The treatment method of the present invention can reduce the dissolution of fluorine in the sludge and reduce the secondary pollution of fluorine while using the fluorine-containing sludge to produce high-purity calcium fluoride.

[0023] 3. The treatment method of the present invention has a wide range of treatment conditions, uses commonly available reagents, does not require expensive equipment investment, is low-cost, and is easy to promote.

[0024] 4. The treatment method of the present invention can effectively recycle fluorine-containing sludge, reduce the output of fluorine-containing sludge, and reduce the treatment cost of solid waste in the process of fluorine-containing wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a process flow chart of Example 1 of the present invention; Figure 2 is the XRD pattern of untreated fluorine-containing sludge; Figure 3This is the XRD diagram of the fluorine-containing sludge after calcination and acid leaching in Comparative Example 1 of the present invention; Figure 4 This is the XRD diagram of the fluorine-containing sludge that fully absorbs the fluorine-containing flue gas after roasting and acid leaching in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The concept and technical effects of the present invention will be clearly and completely described below in conjunction with embodiments to fully understand the purpose, features and effects of the present invention.

[0027] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0028] Example 1 This embodiment provides a method for recycling fluorine in the process of recycling waste batteries. Figure 1 As shown, the specific steps include: S1: Take a number of fully discharged waste lithium-ion batteries, dismantle and crush them to obtain positive electrode sheets.

[0029] S2: Pyrolyze the positive electrode sheet obtained in step S1 at 650°C for 3 hours to obtain the metal material to be recovered, and collect the fluorine-containing flue gas generated by the pyrolysis.

[0030] S3: The fluorine-containing flue gas collected in step S2 is absorbed by 1kg of the first-stage fluorine-containing sludge and the second-stage fluorine-containing sludge with a water content of 42% at a flow rate of 25L / h. The residual fluorine-containing flue gas after passing through the second-stage fluorine-containing sludge is passed into a 1L NaOH solution with a concentration of 0.5mol / L. The absorption process lasts for 3 hours. The tail gas absorbed by the alkali solution is collected and passed into the tail gas treatment system for combustion and discharge. The residual heat of combustion can be used for heat preservation in the subsequent roasting process. When the fluorine content in the NaOH solution reaches 50mg / L, the first-stage fluorine-containing sludge that is saturated with absorption is replaced, the second-stage fluorine-containing sludge is used as the new first-stage fluorine-containing sludge, the spare fluorine-containing sludge is used as the new second-stage fluorine-containing sludge, and the alkali solution after absorbing the fluorine-containing flue gas is replaced with an equal concentration of NaOH solution, and the absorption of the fluorine-containing flue gas is continued. The source of the spare sludge is the same as that of the first-stage fluorine-containing sludge and the second-stage fluorine-containing sludge.

[0031] S4: Spray the 0.5 mol / L NaOH solution that has absorbed the fluorine-containing flue gas in step S3 onto the surface of the fluorine-containing sludge that has absorbed the fluorine-containing flue gas and whose moisture content has dropped to about 3%. The mass of the sprayed alkali solution is 4% of the mass of the saturated fluorine-containing sludge. Then, the sprayed fluorine-containing sludge is ball-milled for 1 hour to mix evenly.

[0032] S5: calcining the fluorine-containing sludge obtained by ball milling in step S4 at 850° C. for 3 h to obtain a calcined solid.

[0033] S6: After cooling the roasted solid obtained in step S5 to room temperature, the roasted solid is crushed to ≤0.15 mm (below 100 mesh) using a crusher, and the crushed roasted solid is placed in 0.5 mol / L dilute hydrochloric acid at a liquid-to-solid ratio of 4 (L / kg) and leached and stirred for 1 hour. During the leaching and stirring process, hydrochloric acid is added to maintain the solution pH at about 7. After leaching, solid-liquid separation is performed to obtain a leached solid.

[0034] S7: The leached solid obtained in step S6 is placed in pure water at a liquid-to-solid ratio of 4 (L / kg) for stirring and slurry washing for 1 hour, and then the solid-liquid separation is performed. The obtained solid is then dried to remove moisture to obtain a high-purity calcium fluoride product.

[0035] The fluorine-containing sludge used in step S3 of this embodiment is derived from the sludge formed by adding calcium hydroxide to the high-concentration fluorine-containing wastewater generated in the process of wet recovery treatment of waste lithium-ion batteries. In addition to calcium fluoride, the sludge also contains calcium hydroxide, calcium sulfate, calcium carbonate, sodium sulfate, a small amount of silicon and magnesium impurities, and some metal hydroxides, etc., and the pH value is ≥12.

[0036] Example 2 The only difference from Example 1 is that the flow rate of the fluorine-containing flue gas in step S3 is 35 L / h.

[0037] Example 3 The only difference from Example 1 is that the calcination temperature of the fluorine-containing sludge in step S5 is 750°C.

[0038] Comparative Example 1 The only difference from Example 1 is that steps S1-S3 are not performed, and in step S4, the fluorine-containing sludge is heated and dried to a moisture content of about 3%, and then sprayed with NaOH solution that has not absorbed flue gas, and the fluorine-containing sludge is ball-milled and mixed, and then directly calcined and the subsequent steps are performed.

[0039] Comparative Example 2 The only difference from Example 1 is that the flow rate of the fluorine-containing flue gas in step S3 is 60 L / h.

[0040] Comparative Example 3 The only difference from Example 1 is that the calcination temperature of the fluorine-containing sludge in step S5 is 550°C.

[0041] Test example The dry basis CaF2 content of the fluorine-containing sludge before and after treatment in each embodiment is shown in Table 1: Table 1 CaF2 content on dry basis before and after treatment of fluorine-containing sludge

[0042] The dry CaF2 content of the calcium fluoride products in Examples 1 to 3 is above 90%, which reflects that fluorine is effectively utilized in the waste battery recycling process. The XRD pattern of the fluorine-containing sludge after roasting and acid leaching that fully absorbs the fluorine-containing flue gas in Example 1 is as follows: Figure 4 As shown, it can be seen that the product has a high purity. The XRD pattern of the untreated fluorine-containing sludge is as follows Figure 2 As shown, it can be seen that it contains more calcium sulfate and calcium carbonate impurities. In Comparative Example 1, the fluorine-containing sludge was not subjected to flue gas absorption and was directly roasted. The removal effect of impurities such as calcium sulfate and calcium carbonate was not obvious. There were more calcium impurities other than calcium fluoride, and the purity of calcium fluoride in the product was low. Its XRD diagram is shown in Figure 3 As shown. In Comparative Example 2, the flow rate of fluorine-containing flue gas absorbed by the fluorine-containing sludge was too large, and more fluorine in the fluorine-containing flue gas entered the alkali solution. When the sludge was replaced, the fluorine-containing sludge did not fully absorb the fluorine-containing flue gas, and the removal effect of impurities such as calcium sulfate and calcium carbonate was not obvious. There were many calcium impurities other than calcium fluoride, and the purity of calcium fluoride in the product was relatively low. In Comparative Example 3, the roasting temperature was low, the phase change of calcium fluoride crystal was insufficient, the impurity removal effect of the product was not obvious, and the purity of calcium fluoride in the product was relatively low.

[0043] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for fluorine resource recovery in the process of waste battery recycling, characterized in that: The following steps are involved: S1: Discharging and crushing the waste lithium-ion batteries, and pyrolyzing the obtained positive electrode sheets to obtain metal materials and fluorine-containing flue gas to be recycled; S2: passing the fluorine-containing flue gas in step S1 into fluorine-containing sludge and alkali solution in sequence for absorption; S3: When the fluorine-containing sludge in step S2 is saturated with absorption, the alkali solution after absorbing the fluorine-containing flue gas in step S2 is sprayed onto the surface of the saturated fluorine-containing sludge, and then the sprayed fluorine-containing sludge is ball-milled, and the obtained ball-milled material is roasted to obtain a roasted solid; S4: crushing the roasted solid in step S3 and leaching it, obtaining a leached solid after solid-liquid separation, washing and drying the leached solid to obtain a calcium fluoride product; In step S2, the pH of the fluorine-containing sludge is ≥12, the dry basis ratio of CaF2 in the fluorine-containing sludge is 45%~65%, and the water content is 30%~50%.

2. The method according to claim 1, characterized in that: In step S1, the pyrolysis temperature is 200-1000°C and the time is 1-5h.

3. The method according to claim 1, characterized in that In step S2, the fluorine-containing sludge includes a first-stage sludge and a second-stage sludge, and the fluorine-containing flue gas is absorbed by the first-stage sludge, the second-stage sludge and the alkaline solution in sequence; when the first-stage sludge is saturated with absorption, step S2 also includes: passing the fluorine-containing flue gas in step S1 into the second-stage sludge, the spare sludge and the alkaline solution in sequence for absorption.

4. The method according to claim 1, characterized in that: In step S2, the flow rate of the fluorine-containing flue gas into the fluorine-containing sludge is 20-40 L / h; and / or the alkali solution is 0.1-1 mol / L NaOH solution.

5. The method according to claim 1, characterized in that In step S3, after the fluorine-containing sludge is saturated with absorption, the moisture content is reduced to 1%~5%; and / or, the spraying amount of the alkali solution after absorbing the fluorine-containing flue gas is 3%~8% of the mass of the fluorine-containing sludge that is saturated with absorption; and / or, the ball milling time is 0.5~2h.

6. The method according to claim 5, characterized in that The fluorine content in the alkaline solution after absorbing the fluorine-containing flue gas is greater than or equal to 50 mg / L.

7. The method according to claim 1, characterized in that In step S3, the calcination temperature is 650-1000° C. and the calcination time is 1-4 hours.

8. The method according to claim 1, characterized in that In step S4, the particle size of the calcined solid after crushing is ≤0.15mm; and / or the leaching reagent used in the leaching is hydrochloric acid, and the liquid-to-solid ratio of the leaching is 4~5L / kg; and / or the pH of the solution is maintained at 5~8 during the leaching process; and / or the leaching time is 0.5~2h.

9. The method according to claim 1, characterized in that: In step S4, the washing method is pulp washing, and the pulp washing process is: mixing and stirring the leached solid with water at a liquid-solid ratio of 4-5 L / kg, and the stirring time is 0.5-2 h.

10. Use of the method according to any one of claims 1 to 9 in the recycling of waste lithium batteries.

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