Method for recovering lithium and iron in lithium iron phosphate-containing material

Abstract

The invention relates to a method for recycling lithium and iron in a lithium iron phosphate-containing material, in particular to the field of resource utilization, and the recycling method comprises the following steps: mixing the lithium iron phosphate-containing material with sulfate, and then roasting under the atmosphere that the oxygen volume fraction phi is more than or equal to 5% and less than 15% to obtain a roasted material; and leaching the roasted material, and carrying out solid-liquid separation to obtain a lithium-containing leachate and an iron phosphate-containing material. According to the recovery method provided by the invention, by controlling the content of oxygen in the atmosphere during roasting, the iron element in the lithium iron phosphate-containing material can be prevented from being converted into an active component to be dissolved out in the leaching process, so that the recovery effect of iron is ensured, and the leaching rate of iron in the recovery process is less than 1%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of resource utilization, and particularly relates to a method for recovering lithium and iron in lithium iron phosphate material. BACKGROUND

[0002] At present, lithium in lithium iron phosphate material is mainly recovered through two ways:

[0003] 1. Dissolving lithium iron phosphate (LFP) material with sulfuric acid solution to make iron, lithium and phosphate into ionic state At the same time, hydrogen peroxide solution is used to oxidize Fe 2+ to Fe 3+ , and sodium hydroxide is used to adjust the pH of the solution, in the process, Li + remains in ionic state, while iron and phosphorus form iron phosphate (FePO4) in the form of precipitate and are insoluble in the system, and lithium sulfate solution and solid slag containing iron phosphate are obtained by filtration separation, the lithium sulfate solution can be obtained after a series of impurity removal, and the pure lithium sulfate solution can be used to prepare lithium carbonate;

[0004] 2. Mixing LFP material with sulfate salt uniformly, and roasting at high temperature provided by a furnace equipment, lithium is converted into lithium sulfate, and iron and phosphorus are converted into iron phosphorus compounds which are difficult to dissolve in water, mixing and stirring the roasted material with water to leach out, and filtering to obtain a solution and a solid slag, the main component of the solution is lithium sulfate, and the main components of the solid slag are iron phosphate and graphite, the lithium sulfate solution is subjected to impurity removal to obtain a pure lithium sulfate solution which can be used to prepare lithium carbonate.

[0005] For example, the prior art CN117185319A discloses a method for recovering lithium iron phosphate battery by sulfate air roasting, sodium sulfate is mixed with LFP, and roasting is performed under air atmosphere at 400-800℃ for 5h, then the roasted material is soaked in water to obtain lithium ion solution and sodium iron phosphate, carbonate is added to the lithium ion solution to obtain precipitated lithium carbonate, and finally, the sodium iron phosphate is mixed with a reducing agent to prepare battery-grade sodium iron phosphate; the roasting temperature of this scheme is 400-800℃, and in this scheme, LFP is oxidized to Li3Fe2(PO4)3 under air atmosphere, which is insoluble in water and is also difficult to be dissolved by hydrochloric acid, nitric acid or sulfuric acid, and belongs to difficult-to-handle waste slag.

[0006] CN113562717A discloses a method for recovering and regenerating waste lithium iron phosphate battery at low temperature, ammonium sulfate is mixed with LFP, and after being uniformly ground, the mixture is placed in a roasting furnace, heated at a rate of 5℃ / min to 300℃, and then roasting is performed at 300℃ for 2h, and then the temperature is decreased to room temperature at a rate of 10℃ / min to obtain solid powder; the solid powder is placed in water, the water temperature is adjusted to 80℃, and stirring is performed for 1h, and then filtration is performed to obtain lithium-containing solution and phosphorus-iron-containing solid slag.

[0007] However, in existing technical solutions, if wet leaching is used to extract lithium, acid is used to dissolve the LFP material, converting Li, Fe, and P into ionic Li. + Fe 2+ , Graphite powder was separated by filtration, and Fe was oxidized by hydrogen peroxide. 2+ For Fe 3+ Next, sodium hydroxide is used to adjust the pH of the solution so that only lithium is retained in the solution, while iron and phosphorus are converted into precipitates in the form of ferric phosphate, thus achieving the separation of lithium from iron and phosphorus. This method requires a large amount of acid and alkali. Due to the presence of graphite, organic matter, and aluminum powder, the leaching process causes serious overflow of the leaching material. The addition rate of acid and hydrogen peroxide needs to be strictly controlled during leaching. The actual leaching process takes a lot of time.

[0008] In existing pyrometallurgical processes, CN113562717A, CN118908167A, and others use air roasting to extract lithium, resulting in leachates containing a large amount of Fe. 3+ The selectivity of lithium is unstable. In order to separate iron and lithium in subsequent processes, additional alkali is needed to change the pH of the leachate to remove impurities.

[0009] In summary, while pyrometallurgical recovery of valuable elements in lithium iron phosphate materials has achieved good lithium recovery results, iron in the material tends to enter the leachate during the recovery process, which is not conducive to efficient iron recovery. Summary of the Invention

[0010] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for recovering lithium and iron from lithium iron phosphate materials, so as to solve the defect that although pyrometallurgical recovery of valuable elements in lithium iron phosphate materials has a good recovery effect on lithium, a large amount of iron in the material will enter the leachate during the recovery process, which is not conducive to the efficient recovery of iron.

[0011] To achieve this objective, the present invention adopts the following technical solution:

[0012] This invention provides a method for recovering lithium and iron from lithium iron phosphate materials, the recovery method comprising:

[0013] The lithium iron phosphate-containing material and sulfate were mixed, and then the oxygen volume fraction was... for The material is roasted under a certain atmosphere to obtain roasted material;

[0014] The roasted material is leached, and the solid-liquid separation yields a lithium-containing leachate and a material containing iron phosphate.

[0015] The recovery method provided by the present application can avoid the conversion of iron elements in the lithium-iron-phosphate-containing material into active components and the dissolution of the active components in the leaching process by controlling the oxygen content in the atmosphere during roasting, thereby ensuring the recovery effect of iron, and the leaching rate of iron during recovery is less than 1%.

[0016] As a preferred technical solution of the present application, the molar ratio of lithium in the lithium-iron-phosphate-containing material to sulfate in the sulfate is 2:(1-1.2).

[0017] As a preferred technical solution of the present application, the sulfate includes one or a combination of at least two of sodium sulfate, ammonium sulfate, or iron sulfate.

[0018] As a preferred technical solution of the present application, the mixing method includes ball milling.

[0019] Preferably, the rotation speed of the mixing is 300-400 r / min.

[0020] As a preferred technical solution of the present application, the mixing time is 10-30 min.

[0021] As a preferred technical solution of the present application, the heating rate of the roasting is 5-15 ℃ / min.

[0022] Preferably, the temperature of the roasting is 300-350 ℃.

[0023] As a preferred technical solution of the present application, the holding time of the roasting is greater than or equal to 4 h.

[0024] As a preferred technical solution of the present application, the leaching method includes water leaching and / or acid leaching.

[0025] Preferably, the solid-liquid ratio g / mL in the leaching is 1:(3-5).

[0026] As a preferred technical solution of the present application, the leaching time is greater than or equal to 0.5 h.

[0027] As a preferred technical solution of the present application, the solid-liquid separation method includes one or a combination of at least two of sedimentation, filtration, or centrifugation.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) For the method of separating lithium and phosphorus iron by dissolving, filtering, and precipitating LFP material with sulfuric acid, the present application volatilizes the organic matter in the LFP powder by roasting, while introducing sulfate ions, Fe 2+ in LFP is oxidized to Fe 3+ , and Forming a solid insoluble in water, not entering the liquid when leaching, thereby avoiding the use of acid, hydrogen peroxide, and the occurrence of tank.

[0030] (2) In order to solve the problem of oxidation of the material after high-temperature roasting, the present application controls the oxygen partial pressure range during the reaction and strictly controls the temperature range to avoid the reaction 12LiFePO4+3O2=4Li3Fe2(PO4)3+2Fe2O3 from occurring, and the oxygen volume fraction is controlled The Fe leaching rate is controlled below 1%, the subsequent process alkali consumption is reduced, the loss of iron phosphate is avoided, the impurity removal time is shortened, and the cost investment is reduced.

[0031] The present application will be further described in detail below. However, the following examples are only simple examples of the present application and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims. DETAILED DESCRIPTION

[0032] In order to better illustrate the present application and facilitate understanding of the technical solutions of the present application, the typical but non-limiting embodiments of the present application are as follows:

[0033] At present, when the iron and lithium in the lithium iron phosphate material are recovered by fire method, the lithium can be well recovered, however, during the roasting in the recovery process, part of the iron elements in the material will also be activated, resulting in that the iron and lithium will enter the leaching liquid at the same time in the leaching process, resulting in that the subsequent separation and impurity removal of the iron in the leaching liquid as impurities is needed, and at the same time, the recovery effect of the iron is also poor, which is not conducive to the efficient utilization of the lithium iron phosphate material. Based on this, the present application optimizes and adjusts the roasting process, so that the material is roasted in a specific oxygen-containing atmosphere, so as to significantly reduce the dissolution of iron in the leaching process, thereby improving the recovery effect of the iron, which is as follows:

[0034] I. The present embodiment provides a recovery method of lithium and iron in a lithium iron phosphate-containing material, which comprises:

[0035] Mixing the lithium iron phosphate-containing material and the sulfate, and then roasting in an oxygen-containing atmosphere with an oxygen volume fraction For to obtain a roasted material.

[0036] Leaching the roasted material to obtain a lithium-containing leaching liquid and a phosphoric acid iron-containing material through solid-liquid separation.

[0037] In the present application, the oxygen-containing atmosphere has an oxygen volume fraction For The oxygen volume fraction For example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 14.5%, etc., but is not limited to the listed values, and other unlisted values within the range are also acceptable.

[0038] The molar ratio of lithium in the lithium-containing iron phosphate material to sulfate radical in the sulfate is 2:(1-1.2), for example, it can be 2:1, 2:1.02, 2:1.04, 2:1.06, 2:1.08, 2:1.1, 2:1.12, 2:1.14, 2:1.16, 2:1.18, or 2:1.2, etc., but is not limited to the listed values, and other unlisted values within the range are also acceptable.

[0039] The sulfate includes one or a combination of at least two of sodium sulfate, ammonium sulfate, or iron sulfate.

[0040] For example, the combination of the sulfate can be selected as a combination of sodium sulfate and ammonium sulfate, a combination of ammonium sulfate and iron sulfate, a combination of sodium sulfate, ammonium sulfate, and iron sulfate, etc.

[0041] The mixing method includes ball milling.

[0042] It should be noted that the present application does not specifically require and particularly limit the rotation speed and the mixing time, and the common rotation speed and time in the art are applicable to the present application, as long as the raw materials can be uniformly mixed.

[0043] For example, the rotation speed of the mixing is 300-400 r / min, for example, it can be 300 r / min, 310 r / min, 320 r / min, 330 r / min, 340 r / min, 350 r / min, 360 r / min, 370 r / min, 380 r / min, 390 r / min, or 400 r / min, etc., but is not limited to the listed values, and other unlisted values within the range are also acceptable.

[0044] For example, the mixing time is 10-30 min, for example, it can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, or 30 min, etc., but is not limited to the listed values, and other unlisted values within the range are also acceptable.

[0045] In the present application, the holding time of the roasting is not specifically required and particularly limited, and the common time in the art is applicable to the present application, as long as the lithium leaching rate can reach more than 90%.

[0046] The temperature of the roasting is 300-350℃, for example, it can be 300℃, 302℃, 304℃, 306℃, 308℃, 310℃, 312℃, 314℃, 316℃, 318℃, 320℃, 322℃, 324℃, 326℃, 328℃, 330℃, 340℃ or 350℃, etc., but is not limited to the listed values, and other values not listed in the range are also required.

[0047] The temperature of the roasting is 300-350℃, for example, it can be 300℃, 302℃, 304℃, 306℃, 308℃, 310℃, 312℃, 314℃, 316℃, 318℃, 320℃, 322℃, 324℃, 326℃, 328℃, 330℃, 340℃ or 350℃, etc., but is not limited to the listed values, and other values not listed in the range are also required.

[0048] In the present application, the holding time of the roasting is not specifically required and specially limited, and the common time in the field is applicable to the present application, as long as the lithium leaching rate reaches more than 90%.

[0049] Exemplarily, the holding time of the roasting is ≥4h, for example, it can be 4h, 4.5h, 5h, 5.5h or 6h, etc., but is not limited to the listed values, and other values not listed in the range are also required.

[0050] It is explained that the leaching mode, liquid-solid ratio in leaching, and leaching time in the present application are not specifically required and specially limited, and the common leaching mode, liquid-solid ratio in leaching, and leaching time in the field are applicable to the present application, as long as the lithium sulfate in the roasting product is fully dissolved in water.

[0051] Exemplarily, the leaching mode includes water leaching and / or acid leaching.

[0052] Exemplarily, the solid-liquid ratio g / mL in the leaching is 1:(3-5), for example, it can be 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4, 1:4.2, 1:4.4, 1:4.6, 1:4.8 or 1:5, etc., but is not limited to the listed values, and other values not listed in the range are also required.

[0053] Exemplarily, the leaching time is ≥0.5h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc., but is not limited to the listed values, and other values not listed in the range are also required.

[0054] The solid-liquid separation method includes one or a combination of at least two of the following: sedimentation, filtration or centrifugation.

[0055] II. In order to illustrate the recovery effect achieved by the provided recovery method, the following actual examples are used for illustration, as follows:

[0056] Example 1

[0057] The existing LFP battery powder has a lithium mass fraction of 4.2%; the analyzed pure ammonium sulfate has a purity of 99%.

[0058] The Li + : The molar ratio is 2:1, 2:1.1, 2:1.2, 2:1.3, 2:1.4 and 2:1.5, respectively. 10g of lithium iron phosphate battery powder and ammonium sulfate are mixed in a ball mill, the rotation speed is set to 300r / min, and the mixing time is 20min. The mixed material is filled into an alumina crucible;

[0059] The crucible is placed in a tube furnace with an oxygen volume fraction of 10%, and the temperature is raised to 300℃ at a rate of 10℃ / min, and then the material is calcined for 4h. After cooling, the calcined material is taken out;

[0060] Water is added at a liquid-solid ratio of 4:1 mL / g, and a magnetic stirrer is used for stirring for 30min. The stirred solid-liquid mixture is filtered and separated using a Buchner funnel to obtain iron phosphate filter residue and lithium sulfate solution;

[0061] The iron lithium phosphorus concentration of the lithium sulfate solution is detected by ICP, and the leaching rate of iron lithium phosphorus is calculated as shown in Table 1.

[0062] Table 1

[0063]

[0064] From the above data, it can be seen that the increase in the amount of ammonium sulfate has little effect on the lithium extraction, but the leaching rate of iron and phosphorus increases significantly. In order to ensure the selectivity of lithium, the amount of ammonium sulfate should be controlled at Li + : At this time, the leaching rate of iron is within 1%.

[0065] Example 2

[0066] The existing LFP battery powder has a lithium mass fraction of 4.2%; the analyzed pure ammonium sulfate has a purity of 99%.

[0067] The Li + : With a molar ratio of 2:1.1, weigh 34.6g of lithium iron phosphate battery powder and 15.4g of ammonium sulfate, place them in a ball mill and mix them. Set the speed to 300r / min and the time to 20min. The mixed material is then evenly filled into an alumina crucible.

[0068] The crucible was placed in a tube atmosphere furnace, and different volume fractions (volume fractions of oxygen) were introduced. A nitrogen-oxygen mixture of 5%, 10%, and 15% was prepared at a flow rate of 1 L / min and heated to 300°C at a rate of 10°C / min. The mixture was then roasted at 300°C for 4 hours. After roasting, the gas was turned off and the roasted material was removed after cooling in the furnace.

[0069] Add the solid to water at a liquid-to-solid ratio of 4:1 mL / g, stir with a magnetic stirrer for 30 min, and then filter the solid-liquid mixture using a Buchner funnel to obtain ferric phosphate residue and lithium sulfate solution.

[0070] The lithium and iron concentrations of the lithium sulfate solution were obtained by ICP detection, and the extraction efficiency of lithium and iron was calculated as shown in Table 2 below.

[0071] Table 2

[0072] O 2 % 5％ 10％ 15％ Li leaching rate 92.7％ 96.1％ 95.0％ Fe leaching rate 0.39％ 0.70％ 1.02％

[0073] Comparative Example 1

[0074] The only difference from Example 2 is that the volume fraction of the nitrogen-oxygen mixture during roasting is controlled to be 0% (pure nitrogen), 3%, 21% (i.e., air), 30%, 40%, and 100% (pure oxygen). As a comparative example, the results are detailed in Table 3.

[0075] Table 3

[0076] O2% 0％ 3％ 21％ 30％ 40％ 100％ Li leaching rate 32.9％ 69.4％ 95.7％ 94.8％ 92.7％ 28.5％ Fe leaching rate 0.04％ 0.05％ 2.32％ 2.72％ 2.39％ 0.002％

[0077] Combining Tables 2 and 3, it can be seen that, at the oxygen volume fraction Lithium extraction was effective under different atmospheric conditions, and the oxygen volume fraction was [not specified]. Lithium extraction is poor at concentrations of 0-3%, and oxygen volume fraction is also low. for The lithium extraction efficiency reached over 90%, with an Fe leaching rate of less than 1% and an oxygen volume fraction of [missing information]. At 15%, the iron leaching rate is >1%, lithium selectivity deteriorates, and some Fe is converted to Fe2(SO4)3 and enters the leachate. Further increasing the oxygen volume fraction... The lithium leaching rate decreased, with some LFP oxidized to Li3Fe2(PO4)3, and the lithium extraction efficiency was only 28.5% under pure oxygen conditions. Therefore, a suitable oxygen volume fraction is crucial. more than 5%, and because the oxygen concentration is too high, Fe can enter the leaching solution or the LFP material can be oxidized to Li3Fe2(P04)3, resulting in poor lithium extraction, so the oxygen volume fraction is less than 15%, and the appropriate oxygen volume fraction is

[0078] Example 3

[0079] The difference from Example 2 is only that the oxygen volume fraction of the nitrogen-oxygen mixed gas in roasting is controlled to be 10%, and roasting is performed at 300-500°C, and the results are as shown in Table 4.

[0080] Table 4

[0081] Temperature 300℃ 330℃ 350℃ 450℃ 550℃ Li leaching rate 95.10％ 96.70％ 90.54％ 61.00％ 4.80％ Fe leaching rate 0.70％ 0.83％ 0.81％ 0.009％ 0.001％

[0082] As can be seen from the results in Table 4, under the conditions of 300°C, 330°C, and 350°C, the lithium leaching rate is more than 90% and the iron leaching rate is less than 1%, achieving good iron-lithium separation effect, and under the condition of 450°C, because the temperature is too high, although the iron leaching rate can be ensured to be less than 1%, most of the LFP is oxidized to Li3Fe2(P04)3 which is difficult to dissolve in water, and a small part of Li is converted to Li2S04 and then dissolved into water, and under the condition of 550°C, the material is more completely oxidized, and only a very small part of Li can be smoothly leached out.

[0083] Comparative Example 2

[0084] The difference from Example 3 is only that the nitrogen-oxygen mixed gas in roasting is air.

[0085] The lithium concentration of the lithium sulfate solution is detected by ICP, and the iron and lithium extraction effects are calculated as shown in Table 5.

[0086] Table 5

[0087] Temperature 300℃ 330℃ 380℃ 450℃ 550℃ Li leaching rate 88.9％ 96.0％ 80.12％ 58.40％ 9.5％ Fe leaching rate 0.76％ 3.6％ 1.98％ 0.03％ 0.01％

[0088] From the experimental data, it can be seen that the iron leaching rate significantly increases at 330°C, and the lithium selectivity decreases, and after the temperature continues to rise, the lithium leaching rate decreases, most of the LFP material is oxidized to Li3Fe2(P04)3 at 550°C, which cannot be recovered by ordinary process, and under the air atmosphere, the lithium leaching rate and the iron leaching rate are positively correlated, which is not conducive to the separation of lithium and iron.

[0089] From the above examples and comparative examples, it can be seen that when the molar ratio of Li+: to Fe3+ is 2:(1.0-1.2), and the oxygen volume fraction of the roasting atmosphere is The roasting temperature is 300-350 DEG C, at which the lithium leaching rate is greater than 90% and the Fe leaching rate is less than 1%, realizing efficient lithium extraction and lithium-iron separation.

[0090] The above describes the preferred embodiments of the present application, but the present application is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0091] In addition, it should be noted that each specific technical feature described in the above-described specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0092] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A method for recovering lithium and iron from lithium iron phosphate materials, characterized in that, The recycling method includes: The lithium iron phosphate material and sulfate were mixed and then calcined in an atmosphere with an oxygen volume fraction φ of 5% ≤ φ < 15% to obtain the calcined material. The roasted material is leached, and the solid-liquid separation yields a lithium-containing leachate and a material containing iron phosphate.

2. The recycling method as described in claim 1, characterized in that, The molar ratio of lithium in the lithium iron phosphate material to sulfate in the sulfate is 2:(1-1.2).

3. The recycling method as described in claim 1, characterized in that, The sulfate includes one or a combination of at least two of sodium sulfate, ammonium sulfate, or ferric sulfate.

4. The recycling method as described in claim 1, characterized in that, The mixing method includes: ball milling; Preferably, the mixing speed is 300-400 r / min.

5. The recycling method as described in claim 1, characterized in that, The mixing time is 10-30 minutes.

6. The recycling method as described in claim 1, characterized in that, The heating rate for the roasting is 5-15℃ / min; Preferably, the roasting temperature is 300-350℃.

7. The recycling method as described in claim 1, characterized in that, The roasting time is ≥4h.

8. The recycling method as described in claim 1, characterized in that, The leaching methods include: water immersion and / or acid immersion; Preferably, the solid-liquid ratio in the leaching is 1:(3-5) g / mL.

9. The recycling method as described in claim 1, characterized in that, The leaching time is ≥0.5h.

10. The recycling method as described in claim 1, characterized in that, The solid-liquid separation method includes one or a combination of at least two of sedimentation, filtration, or centrifugation.

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