A method for recovering lithium from lithium iron phosphate black powder

Abstract

The invention belongs to the technical field of battery material recovery, and specifically relates to a method for recovering lithium from lithium iron phosphate black powder. The method comprises the following steps: mixing the lithium iron phosphate black powder with auxiliary materials, burning, and acid dissolving to obtain a lithium liquid; the auxiliary materials include an inorganic compound M that does not undergo redox reaction with lithium iron phosphate at normal temperature and pressure. a N b or a mixture thereof, M includes calcium, magnesium, aluminum, silicon, trivalent iron, titanium, zinc, N includes oxygen, hydroxide, carbonate, sulfate, silicate, aluminate, and a and b are positive integers > 0. The method can effectively improve the yield of lithium, and the addition of specific auxiliary materials can control the burning temperature, reduce the carbon emission in the tail gas, increase the ferrous oxidation rate during the burning process, thereby reducing the use of subsequent oxidants, and even achieve no use of oxidants.

Description

Technical Field

[0001] The invention belongs to the technical field of battery material recovery, and in particular relates to a method for recovering lithium from lithium iron phosphate black powder. Background Art

[0002] As the commercial secondary battery with the best comprehensive performance, lithium-ion batteries have made great progress in the 21st century, and the scale of production and use is expanding day by day, but it is inevitable that a large number of waste lithium-ion batteries will be produced. How to better recycle and treat these waste lithium-ion batteries and efficiently extract the recyclable resources, especially lithium, has become one of the problems that need to be solved urgently.

[0003] At present, lithium iron phosphate batteries are in great demand among lithium-ion batteries. In the existing technology, there are three main mainstream processes for recycling and extracting lithium from waste lithium iron phosphate batteries: First, waste lithium iron phosphate batteries are first subjected to high-temperature carbonization and cracking during the powdering process, and the black powder produced by the powdering is acid-dissolved to extract lithium. In this process, the equipment investment is large, the operating energy consumption is high, and the oxidant consumption in the acid-dissolving process is large; second, waste lithium iron phosphate batteries are powdered after low-temperature baking or directly powdered, and the black powder produced by the powdering is directly acid-dissolved to extract lithium. In this process, the acid-dissolving process is unstable, the oxidant consumption is large, and the wastewater treatment is difficult; third, waste lithium iron phosphate batteries are baked at low temperature or directly powdered, and the black powder produced by the powdering is oxidized and burned, and the burned material is acid-dissolved to extract lithium. In this process, the temperature of the oxidation and burning step is difficult to control. Temperature out of control will cause the material to be sintered and the iron oxidation rate is low, and the oxidant consumption is large. In addition, there are problems such as large carbon emissions, especially the generation of a large amount of toxic gas CO, low oxidation rate of the burned material, and low lithium yield. Moreover, ferrous complex salts are easily formed during the acid dissolution process in these three processes, which requires an increase in the acid solution-to-solid ratio during operation, thereby making the concentration of the lithium solution very low. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art in which the temperature of the oxidation and burning step is difficult to control, the amount of carbon emission during the oxidation and burning step is large, the oxidation rate of the burning material is low, the oxidant consumption is excessive, and the lithium yield is low when recycling lithium iron phosphate waste batteries to extract lithium, thereby providing a method for recovering lithium from lithium iron phosphate black powder.

[0005] To this end, the present invention provides the following technical solutions.

[0006] The present invention provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps: mixing the lithium iron phosphate black powder with auxiliary materials, burning, and acid dissolving to obtain a lithium liquid; the auxiliary materials include an inorganic compound M that does not undergo redox reaction with lithium iron phosphate at normal temperature and pressure. a N bor a mixture thereof, wherein M includes calcium, magnesium, aluminum, silicon, trivalent iron, titanium, zinc, and N includes oxygen, hydroxide, carbonate, sulfate, silicate, and aluminate, and a and b are positive integers greater than 0. Further, the auxiliary material may be a pure compound or a compound containing the compound M. a N b Or minerals of mixtures thereof, such as cement, clay, mica, etc.

[0007] Preferably, the compound M a N b Here, M includes calcium, magnesium, aluminum, silicon, trivalent iron, titanium, and zinc; N includes oxygen and hydroxide; a and b are positive integers greater than 0, which can neutralize the fluoride gas generated during the combustion process, significantly reduce the corrosion of the fluoride gas to the pipeline system of the combustion equipment, and help extend the service life of the equipment.

[0008] Optionally, the mass of the auxiliary material is greater than or equal to 0.5% of the mass of the lithium iron phosphate black powder; preferably, the mass of the auxiliary material is 0.5% to 25% of the mass of the lithium iron phosphate black powder.

[0009] Optionally, the burning temperature is 300-600° C., and the burning time is 0.5-6 hours.

[0010] Further preferably, the mass of the auxiliary material is 10% to 25% of the mass of the lithium iron phosphate black powder, the calcination temperature is 380 to 480° C., and the calcination time is 1 to 4 hours.

[0011] Optionally, the acid dissolution comprises the following steps: mixing the calcined mixture with deionized water at a solid-liquid mass ratio of 1:(1-3), adjusting the pH to 0.5-2.5 for the first time, aging, and adjusting the pH to 3-6 for the second time.

[0012] Optionally, the aging temperature is 60 to 90° C., and the time is 1 to 6 hours.

[0013] Optionally, the reagent used for the first pH adjustment is at least one of sulfuric acid and hydrochloric acid.

[0014] Optionally, the reagent used for the second pH adjustment is at least one of sodium hydroxide, calcium oxide, and sodium carbonate.

[0015] Optionally, a ferrous indicator is used to detect the acid-soluble acid-soluble liquid. If the presence of ferrous ions can be detected, an oxidant is also added to the acid-soluble step to completely oxidize the remaining ferrous ions.

[0016] Optionally, the oxidant includes at least one of sodium chlorate, hydrogen peroxide, and oxygen-containing gas.

[0017] Optionally, an oxidizing gas is introduced during the burning, and the oxygen volume fraction of the oxidizing gas is greater than or equal to 20%.

[0018] Optionally, during the burning process, the amount of oxidizing gas introduced per ton of black powder is ≥60m 3 / h; Preferably, during the burning process, the amount of oxidizing gas introduced per ton of black powder is 60 to 600m 3 / h.

[0019] In the method for recovering lithium from lithium iron phosphate black powder provided by the present invention, the method of introducing oxidizing gas into the black powder during burning includes positive pressure blowing and negative pressure suction.

[0020] Optionally, the lithium iron phosphate black powder is obtained by powdering waste lithium iron phosphate batteries; typically and non-limitingly, the specific powdering process includes: taking waste lithium iron phosphate batteries, discharging with salt water, draining, disassembling, selecting whether to separate the positive and negative electrodes according to needs, crushing, drying or high-temperature cracking, and obtaining black powder. The main component of the obtained black powder is positive electrode powder, or a mixed powder of positive and negative electrodes. In addition, the lithium iron phosphate black powder can also be directly purchased and recycled for use.

[0021] In the method for recovering lithium from lithium iron phosphate black powder provided by the present invention, the feeding state of the auxiliary material includes solid, slurry and solution.

[0022] In the method for recovering lithium from lithium iron phosphate black powder provided by the present invention, a mixer can be used to mix the lithium iron phosphate black powder and auxiliary materials, and a solid-solid mixer or a solid-liquid mixer can be selectively used according to the feeding state of the auxiliary materials, and a continuous mixing method or an intermittent mixing method can be adopted.

[0023] In the method for recovering lithium from lithium iron phosphate black powder provided by the present invention, a solid-liquid separation step is also included after acid dissolution, and solid-liquid separation can be achieved by filtration, such as vacuum filtration, mechanical filter press, centrifugal filtration, etc.

[0024] The beneficial effects of the present invention are:

[0025] The method for recovering lithium from lithium iron phosphate black powder provided by the present invention comprises the following steps: mixing lithium iron phosphate black powder and auxiliary materials, burning, acid dissolving, and obtaining lithium liquid; the auxiliary materials include an inorganic compound M that does not undergo redox reaction with lithium iron phosphate at normal temperature and pressure. a N b or a mixture thereof, M includes calcium, magnesium, aluminum, silicon, trivalent iron, titanium, zinc, N includes oxygen, hydroxide, carbonate, sulfate, silicate, aluminate, and a and b are positive integers > 0. The method can effectively improve the yield of lithium, and the addition of specific auxiliary materials can control the burning temperature, reduce the carbon emission in the tail gas, increase the ferrous oxidation rate during the burning process, thereby reducing the use of subsequent oxidants, and even achieve no use of oxidants.

[0026] The addition of specific auxiliary materials can disperse the high calorific value carbon powder in the lithium iron phosphate black powder, reduce the heat transfer between the carbon powders, improve heat dissipation, reduce the heat accumulation of the burning material layer, and prevent the temperature of the carbon powder from getting out of control during the burning process; this directly makes it possible to selectively increase the burning temperature during the burning process, thereby increasing the oxidation rate of ferrous ions, significantly increasing the output and improving the yield of lithium iron phosphate waste lithium, which is conducive to the controllable and stable large-scale production of lithium iron phosphate battery black powder. The dispersed high calorific value carbon powder can control the slow decomposition of the carbon powder in the whole burning process, and the oxygen consumption for carbon decomposition is greatly reduced, while the oxygen amount for lithium iron phosphate oxidation is greatly increased, so that the oxidation rate of ferrous iron in the burning material is significantly increased, thereby reducing the use of oxidants in the subsequent acid dissolution, and even achieving no use of oxidants, and can directly reduce the ferrous iron content in the acid-soluble liquid, which can reduce the formation of ferrous iron complex salts; at the same time, the greatly reduced oxygen consumption for carbon decomposition also means a reduction in carbon emissions, which is environmentally friendly; the oxidation rate of ferrous iron in the burning material is significantly improved, which can ensure that the burning material will not agglomerate due to insufficient oxidation rate, prevent the material from agglomerating during sintering, and also make the burning material directly acid-soluble without crushing.

[0027] In the method for recovering lithium from lithium iron phosphate black powder provided by the present invention, the mass of the auxiliary material is preferably 0.5% to 25% of the mass of the lithium iron phosphate black powder. Too little auxiliary material mass affects the burning effect, and too much auxiliary material mass has limited improvement on the burning effect, which is not economically cost-effective.

[0028] The method for recovering lithium from lithium iron phosphate black powder provided by the present invention is most preferably that the mass of the auxiliary material is 10% to 25% of the mass of the lithium iron phosphate black powder, the calcination temperature is 380 to 480° C., and the calcination time is 1 to 4 hours. Under these conditions, it is possible to achieve an acid dissolution process without using an oxidant, and the direct recovery rate of lithium is also very high, thereby achieving an ideal effect while saving raw materials and time.

[0029] The present invention provides a method for recovering lithium from lithium iron phosphate black powder, wherein the acid dissolution comprises the following steps: mixing the calcined mixture with deionized water at a solid-liquid mass ratio of 1:(1-3), adjusting the pH to 0.5-2.5 for the first time, aging, and adjusting the pH to 3-6 for the second time. The solid-liquid mass ratio is 1:(1-3). Since the ferrous content in the acid-dissolved feed liquid is relatively low in the method provided by the present invention, less ferrous complex salt is formed, and less deionized water can be added without causing the pot to stick. The amount of deionized water added is controlled to be relatively low, which directly leads to a reduction in the amount of acid and alkali required for the acid dissolution, and also makes the lithium concentration in the final lithium feed liquid higher and easier to recover. DETAILED DESCRIPTION

[0030] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0031] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0032] Experimental drugs:

[0033] Lithium iron phosphate black powder: purchased from Ganzhou Haopeng Technology Co., Ltd., the composition by mass percentage includes Fe: 20.77%, Fe 2+ : 15%, C: 42.28%, Li: 2.89%, F: 1.93%.

[0034] Example 1

[0035] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0036] (1) Clay is used as auxiliary material. Lithium iron phosphate black powder and clay are mixed in a mass ratio of 1:0.25, put into a planetary mixer for mixing, and then transported into a rotary kiln by a screw conveyor at a feeding rate of 0.5 t / h. The rotary kiln is set at a temperature of 480° C., the kiln rotation is 12.5 Hz, the burning time is 4 h, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas per ton of black powder is 360 m 3 / h, after 4h of continuous feeding, fluffy reddish brown powder began to be discharged, and after 48h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0037] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 500 ml of water, stir and heat to 90°C, add sulfuric acid to adjust the pH to 2.5; if no ferrous iron is detected by the ferrous indicator, no oxidant is needed, and keep aging at 90°C for 1 hour; adjust the pH to 3.5 with soda ash, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and drying, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the ferric phosphate residue.

[0038] Example 2

[0039] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0040] (1) Silicon oxide is used as auxiliary material. Lithium iron phosphate black powder and silicon oxide are mixed in a mass ratio of 1:0.1, put into a planetary mixer for mixing, and then transported into a rotary kiln by a screw conveyor at a feeding rate of 0.5 t / h. The rotary kiln is set at a temperature of 380°C, the kiln rotation is 22 Hz, the burning time is 1 hour, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas per ton of black powder is 360m 3 / h, after 4h of continuous feeding, fluffy reddish brown powder began to be discharged, and after 48h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0041] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 500 ml of water, stir and heat to 90°C, add sulfuric acid to adjust the pH to 2.5; if no ferrous iron is detected by the ferrous indicator, no oxidant is needed, and keep aging at 90°C for 1 hour; adjust the pH to 3.5 with soda ash, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and drying, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the ferric phosphate residue.

[0042] Example 3

[0043] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0044] (1) As auxiliary materials, lime and titanium oxide are used. Lithium iron phosphate black powder, lime and titanium oxide are mixed in a mass ratio of 1:0.05:0.025, put into a planetary mixer for mixing, and then transported into a rotary kiln by a screw conveyor at a feeding rate of 0.36 t / h. The rotary kiln is set at a temperature of 400° C., the kiln rotates at 20 Hz, the burning time is 2 h, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas passed per ton of black powder is 200 m 3 / h, after 4h of continuous feeding, fluffy, whitish, dark reddish-brown powder began to be discharged, and after 48h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0045] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 1000 ml of water, stir and heat to 60°C, add sulfuric acid to adjust the pH to 1.0; use a ferrous indicator to measure ferrous iron, add 10.34 g of sodium chlorate, and the ferrous indicator detects that it does not contain ferrous iron, keep 60°C for aging for 1 hour; use quicklime to adjust the pH to 4, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the iron phosphate residue.

[0046] Example 4

[0047] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0048] (1) As auxiliary materials, ferric hydroxide and aluminum hydroxide are used. Lithium iron phosphate black powder and ferric hydroxide and aluminum hydroxide are mixed in a mass ratio of 1:0.05:0.05, put into a planetary mixer for mixing, and then transported into a rotary kiln by a screw conveyor at a feeding rate of 0.36 t / h. The rotary kiln is set at a temperature of 350° C., the kiln rotation is 10 Hz, the burning time is 6 h, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas per ton of black powder is 60 m 3 / h, after 4h of continuous feeding, light brown powder began to be discharged, and after 36h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0049] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 1000 ml of water, stir and heat to 75°C, add hydrochloric acid to adjust the pH to 1.0; use a ferrous indicator to measure ferrous iron, add 9.28 g of sodium chlorate, and the ferrous indicator detects that it does not contain ferrous iron, keep aging at 75°C for 1 hour; use soda ash to adjust the pH to 3.5, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the ferric phosphate residue.

[0050] Example 5

[0051] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0052] (1) Magnesium carbonate and aluminum hydroxide are used as auxiliary materials. Lithium iron phosphate black powder, magnesium carbonate, aluminum hydroxide and water are mixed in a mass ratio of 1:0.075:0.075:0.2, and mixed in a planetary mixer. The mixture is then conveyed into a rotary kiln at a feed rate of 0.45 t / h by a screw conveyor. The rotary kiln is set at a temperature of 450° C., the kiln rotates at 10 Hz, the burning time is 6 h, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas passed per ton of black powder is 240 m 3 / h, after 4h of continuous feeding, light brown powder began to be discharged, and after 36h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0053] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 500 ml of water, stir and heat to 80° C., add sulfuric acid to adjust the pH to 1.5; use a ferrous acid indicator to measure ferrous acid, pass a mixed gas of oxygen and air with a volume ratio of 1.5:1 until the ferrous acid indicator detects that it does not contain ferrous acid, and keep aging at 80° C. for 1 hour; use liquid alkali to adjust the pH to 3.5, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the iron phosphate residue.

[0054] Example 6

[0055] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0056] (1) The auxiliary materials are cement, iron oxide, and aluminum hydroxide. Lithium iron phosphate black powder and cement, iron oxide, aluminum hydroxide, and water are mixed in a mass ratio of 1:0.1:0.05:0.05:0.2, and mixed in a planetary mixer. The mixture is then conveyed into a rotary kiln at a feed rate of 0.6 t / h through a screw conveyor. The rotary kiln is set at a temperature of 550° C., the kiln rotates at 25 Hz, the burning time is 0.5 h, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas passed per ton of black powder is 300 m 3 / h, after 4h of continuous feeding, reddish brown powder began to be discharged, and after 36h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0057] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 500 ml of water, stir and heat to 85°C, add hydrochloric acid to adjust the pH to 2.0; use a ferrous acid indicator to measure ferrous iron, add 7.68 g of sodium chlorate, and the ferrous acid indicator detects that it does not contain ferrous iron, keep aging at 85°C for 1 hour; use liquid alkali to adjust the pH to 3.5, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the iron phosphate residue.

[0058] Example 7

[0059] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0060] (1) Mica was used as auxiliary material. Lithium iron phosphate black powder and mica were mixed in a mass ratio of 1:0.005, put into a planetary mixer for mixing, and then transported into a rotary kiln at a feeding rate of 0.2 t / h by a screw conveyor. The rotary kiln was set at a temperature of 380°C, the kiln rotation was 20 Hz, the burning time was 2 h, and an oxidizing gas containing an oxygen volume fraction of 21% was introduced. The amount of oxidizing gas per ton of black powder was 180 m 3 / h, after 4h of continuous feeding, gray-brown powder began to be discharged, and after 48h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0061] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 500 ml of water, stir and heat to 60°C, add sulfuric acid to adjust the pH to 1.5; use a ferrous acid indicator to measure ferrous iron, add 16.7 g of sodium chlorate, and the ferrous acid indicator detects that it does not contain ferrous iron, keep 60°C for aging for 2 h; use liquid alkali to adjust the pH to 4, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the iron phosphate residue.

[0062] Example 8

[0063] This embodiment provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0064] (1) Calcium sulfate, silicon dioxide, and aluminum hydroxide are used as auxiliary materials. Lithium iron phosphate black powder and calcium sulfate, silicon dioxide, and aluminum hydroxide are mixed in a mass ratio of 1:0.15:0.15:0.1, put into a planetary mixer for mixing, and then transported into a rotary kiln by a screw conveyor at a feeding rate of 0.6 t / h. The rotary kiln is set at a temperature of 550° C., the kiln rotates at 25 Hz, the burning time is 0.5 h, and an oxidizing gas containing an oxygen volume fraction of 21% is introduced. The amount of oxidizing gas passed per ton of black powder is 300 m 3 / h, after 4h of continuous feeding, reddish brown powder began to be discharged, and after 36h of continuous operation, the discharge was stable, and the discharged material was calcined material;

[0065] (2) Take 500 g of the calcined material obtained in (1), put it into a beaker with 500 ml of water, stir and heat to 85° C., add hydrochloric acid to adjust the pH to 2.0; use a ferrous acid indicator to measure ferrous acid, add 26.4 g of hydrogen peroxide (27.5%), and use the ferrous acid indicator to detect that it does not contain ferrous acid, and keep aging at 85° C. for 1 hour; use liquid alkali to adjust the pH to 3.5, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the iron phosphate residue.

[0066] Comparative Example 1

[0067] This comparative example provides a method for recovering lithium from lithium iron phosphate black powder, comprising the following steps:

[0068] (1) Lithium iron phosphate black powder is conveyed into a rotary kiln via a screw conveyor at a feed rate of 0.3 t / h. The rotary kiln is set at a temperature of 400°C, the kiln rotation is 15 Hz, the burning time is 2 h, and an oxidizing gas containing 21% oxygen by volume is introduced. The amount of oxidizing gas per ton of black powder is 360 m 3 / h, continuous feeding for 6h, during which the temperature in the high temperature section was out of control, the discharge temperature at the kiln tail was very high, the temperature was >400℃ and it was in the form of black hard blocks, and the discharge material was burnt material;

[0069] (2) Take 500 g of the calcined material obtained in (1), crush it and put it into a beaker with 1500 ml of water, stir and heat it to 75°C, add sulfuric acid to adjust the pH to 0.5; use a ferrous acid indicator to measure ferrous iron, add 28.29 g of sodium chlorate, and the ferrous acid indicator detects that it does not contain ferrous iron, keep aging at 75°C for 1 hour; use liquid alkali to adjust the pH to 3.5, vacuum filter, and filter the mother liquor to obtain the lithium feed liquid. After filtering and draining, rinse the residue with water for 4 times, each time using 500 ml of water. After washing, the filter cake is the iron phosphate residue.

[0070] Test Example 1

[0071] The calcined materials obtained in the examples and comparative examples were used to detect the Fe content, Fe 2+ The infrared sulfur carbon method is used to detect the C content, and the ion electrode method is used to detect the F content; and the Fe content of the burning step is further calculated. 2+ Total oxidation rate, Fe 2+ The calculation formulas for the burning oxidation rate, C decomposition rate, and F volatilization rate are as follows (where clinker refers to the burning material, and the raw material refers to lithium iron phosphate black powder, the same below):

[0072] Fe 2+ Total oxidation rate = (clinker Fe content - clinker Fe 2+ Content) / clinker Fe content × 100%;

[0073] Fe 2+ Burning oxidation rate = (clinker Fe content - clinker Fe 2+ Fe content) / clinker Fe content × 100% - (Fe content of raw materials - Fe content of raw materials 2+ Content) / Fe content of raw materials × 100%;

[0074] C decomposition rate = 100% - raw material Fe content / clinker Fe content × clinker C content / raw material C content;

[0075] F volatilization rate = 100% - raw material Fe content / clinker Fe content × clinker F content / raw material F content.

[0076] The iron phosphate slag obtained in the embodiment and the comparative example was taken, dried, weighed, and its Li content was detected by inductively coupled plasma emission spectrometry, and the direct recovery of lithium was further calculated by the following formula: direct recovery of lithium = 100% - dry weight of iron phosphate slag × lithium content of dry iron phosphate slag / (mass of calcined material used × lithium content of raw material).

[0077] All the above test calculation results are shown in Table 1.

[0078] Table 1

[0079]

[0080] Continued

[0081]

[0082]

[0083] As can be seen from Table 1 and the foregoing, in the comparative example, the lithium in the lithium iron phosphate black powder is recovered by the prior art without adding auxiliary materials. The Li content in the obtained iron phosphate slag is as high as 1.12%, and the direct recovery rate of lithium is only 69.52%. 2+The oxidation rate is 18.15%, the decomposition rate of C is as high as 77.50% and the volatilization rate of F is as high as 61.03%. The temperature of the black powder in the kiln will be out of control, and the burned material will be a black hard lump when it comes out of the furnace. After dissolving 500g of the burned material in acid, 28.29g of sodium chlorate is required to oxidize the ferrous iron to the point where the ferrous iron indicator cannot be detected.

[0084] In the embodiment, the method provided by the present invention is used to recover lithium from lithium iron phosphate black powder. The highest Li content in the obtained iron phosphate slag is only 0.47%, and the direct recovery rate of lithium reaches more than 84%, and the highest can reach 97.35%. 2+ The lowest oxidation rate is 21.72% and the highest can reach 70.42%. The highest decomposition rate of C is 47.34%, and the highest volatilization rate of F is 35.91%. There will be no phenomenon of black powder temperature getting out of control. All the powders obtained out of the furnace are powders. After acid dissolving 500g of the calcined material, the maximum amount of sodium chlorate required to oxidize the ferrous iron to the point where the ferrous iron indicator cannot detect it is 16.7g.

[0085] By comparing the examples and comparative examples, it can be seen that the method for recovering lithium from lithium iron phosphate black powder provided by the present invention can effectively improve the yield of lithium and increase the Fe 2+ This reduces the addition of oxidants during the acid dissolution process, and can also control the temperature during combustion and reduce carbon emissions in the tail gas. 2+ The oxidation rate can directly reduce the ferrous content in the acid-soluble feed solution, which can reduce the formation of ferrous complex salts. When using this method, less deionized water can be used to mix with the burning material during acid dissolution without worrying about the occurrence of pot sticking. For example, the solid-liquid mass ratio of Examples 1, 2, 5, 6, 7, and 8 is 1:1, which makes the lithium concentration in the final lithium feed solution higher and easier to recover. In addition, the method used in the embodiment also reduces the volatility of F, which can significantly reduce the corrosion of fluoride gas to the pipeline system of the burning equipment and help extend the service life of the equipment.

[0086] By analyzing Examples 1 and 2 and other Examples, it can be found that the use of the most preferred auxiliary materials, lithium iron phosphate black powder mass ratio, calcination temperature and time can achieve the acid dissolution process without the use of oxidants, and the direct lithium recovery rate is also very high, while achieving the ideal effect and saving raw materials and time. By analyzing Example 8 and other Examples, it can be found that after exceeding a certain amount, continuing to increase the amount of auxiliary materials added has an effect on the Fe 2+ The oxidation rate has not been greatly improved, and considering the overall raw material cost, it is not economical.

[0087] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims

1. A method for recovering lithium from lithium iron phosphate black powder, characterized in that: The steps include: The lithium iron phosphate black powder is mixed with auxiliary materials, burned, and acid-dissolved to obtain a lithium liquid; The auxiliary material includes an inorganic compound M which does not undergo redox reaction with lithium iron phosphate at normal temperature and pressure. a N b or a mixture thereof, wherein M comprises calcium, magnesium, aluminum, silicon, trivalent iron, titanium, zinc, N comprises oxygen, hydroxide, carbonate, sulfate, silicate, aluminate, and a and b are positive integers > 0; The mass of auxiliary materials is greater than or equal to 0.5% of the mass of lithium iron phosphate black powder; The burning temperature is 300~600℃ and the burning time is 0.5~6h; The acid dissolution comprises the following steps: mixing the calcined mixture with deionized water at a solid-liquid mass ratio of 1:1-3, adjusting the pH to 0.5-2.5 for the first time, aging, and adjusting the pH to 3-6 for the second time.

2. The method for recovering lithium from lithium iron phosphate black powder according to claim 1, characterized in that: The compound M a N b In the formula, M includes calcium, magnesium, aluminum, silicon, trivalent iron, titanium, and zinc; N includes oxygen and hydroxide; and a and b are positive integers >0.

3. The method for recovering lithium from lithium iron phosphate black powder according to claim 1, characterized in that: The mass of the auxiliary materials is 0.5%~25% of the mass of the lithium iron phosphate black powder.

4. The method for recovering lithium from lithium iron phosphate black powder according to claim 3, characterized in that: The mass of the auxiliary material is 10%~25% of the mass of the lithium iron phosphate black powder, the burning temperature is 380~480℃, and the burning time is 1~4h.

5. The method for recovering lithium from lithium iron phosphate black powder according to claim 1, characterized in that: The aging temperature is 60-90° C. and the time is 1-6 hours.

6. The method for recovering lithium from lithium iron phosphate black powder according to claim 1, characterized in that: The reagent used for the first pH adjustment is at least one of sulfuric acid and hydrochloric acid; And / or, the reagent used for the second pH adjustment is at least one of sodium hydroxide, calcium oxide and sodium carbonate.

7. The method for recovering lithium from lithium iron phosphate black powder according to claim 1, characterized in that: An oxidizing agent is also added during the acid dissolution step.

8. The method for recovering lithium from lithium iron phosphate black powder according to claim 7, characterized in that: The oxidant includes at least one of sodium chlorate, hydrogen peroxide, and oxygen-containing gas.

9. The method for recovering lithium from lithium iron phosphate black powder according to claim 1, characterized in that: During the burning, an oxidizing gas is introduced, wherein the oxygen volume fraction of the oxidizing gas is greater than or equal to 20%.

10. The method for recovering lithium from lithium iron phosphate black powder according to claim 9, characterized in that: During the burning process, the amount of oxidizing gas introduced per ton of black powder is ≥60m 3 / h.

11. The method for recovering lithium from lithium iron phosphate black powder according to claim 10, characterized in that: During the burning process, the amount of oxidizing gas introduced per ton of black powder is 60~600 m 3 / h.

12. The method for recovering lithium from lithium iron phosphate black powder according to any one of claims 1 to 11, characterized in that: The lithium iron phosphate black powder is obtained by grinding waste lithium iron phosphate batteries into powder.

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