CN114976337A - Comprehensive recovery method of scrapped lithium iron phosphate - Google Patents
Comprehensive recovery method of scrapped lithium iron phosphate Download PDFInfo
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Abstract
The invention discloses a comprehensive recovery method of scrapped lithium iron phosphate, which relates to the technical field of internet, block chain, distributed data storage and image recognition, and comprises the following steps: s1, crushing and mixing; s2, calcining; s3, soaking in water; s4, adsorption and filtration. The method for comprehensively recycling the scrapped lithium iron phosphate adopts a method of calcining with calcium hydroxide to convert lithium in the scrapped lithium iron phosphate into water-soluble lithium hydroxide, iron and phosphorus generate insoluble oxides and salts and enter slag, the lithium hydroxide is prepared into industrial lithium carbonate, iron and phosphorus in the slag are dissolved by phosphoric acid and are supplemented with iron in a certain proportion to prepare iron phosphate, the crystal form of the iron phosphate is controlled by adjusting a precipitation process to meet the requirement of lithium iron phosphate production, an electrolyte and an adhesive of a battery are directly solidified in a treatment process, the treatment amount of waste gas is reduced, and the method has the advantages of simple treatment process, short flow and less waste slag generated in the process.
Description
Technical Field
The invention relates to the technical field of comprehensive recovery of lithium iron phosphate, in particular to a method for comprehensively recovering scrapped lithium iron phosphate.
Background
Lithium iron phosphate is a positive electrode material of a lithium ion battery, is generally formed by firing iron phosphate and lithium salt through a pyrogenic process, has a chemical formula of LiFePO4 (LFP for short), and has a similar crystal structure to that of the iron phosphate, and the iron phosphate is a main raw material for synthesizing the lithium iron phosphate and is called a lithium iron phosphate precursor.
The traditional method for recovering lithium iron phosphate can only effectively recover lithium in the lithium iron phosphate, a large amount of waste residues are generated after treatment, and the iron with the content of about 35 percent and the phosphorus with the content of about 18 percent are difficult to recover.
At present, iron phosphate in the iron phosphate can be recovered by a method, but the recovered iron phosphate is only a crude product, and the physical performance index of the iron phosphate cannot meet the requirement of lithium iron phosphate. It is mainly affected by several reasons: 1) the adhesive in the waste lithium iron phosphate battery or the positive plate is not removed during treatment; 2) when the scrapped battery is disassembled, the negative electrode powder can be mixed together, and the negative electrode contains graphite powder and organic matters; 3) when the traditional method is used for recycling the iron phosphate, only the chemical impurity indexes in the iron phosphate can meet the requirements of the indexes of the lithium iron phosphate, but the physical indexes of the lithium iron phosphate are influenced and hardly meet the requirements.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a comprehensive recovery method of scrapped lithium iron phosphate, and solves the problems in the background art.
In order to achieve the purpose, the invention provides a method for comprehensively recycling scrapped lithium iron phosphate, which is realized by the following technical scheme and comprises the following steps:
s1 crushing and mixing
Sieving calcium hydroxide through a 200-mesh sieve, taking only the sieved part and grinding the sieved part together with lithium iron phosphate scrap, wherein the dosage of the calcium hydroxide is 0.85-1.05 times of the theoretical dosage, sieving the calcium hydroxide through a 425-mesh sieve after mixing is finished, and then reserving sieved materials for later use;
s2, calcining
The sieved material which is sieved by a 425-mesh sieve in S1 enters a calcining furnace to be calcined for 180-mesh 240 minutes at the temperature of 630-750 ℃, and compressed air is introduced in the calcining process, the pressure of the compressed air is controlled to be 0.5-0.8MPa, and the flow is controlled to be 18-30m 3/hour;
s3, soaking in water
Cooling the calcined material, carrying out wet grinding, wherein the granularity of the wet grinding is 95%, and the wet grinding is sieved by a 100-mesh sieve, the granularity is controlled to be beneficial to water leaching of lithium, the wet grinding is carried out and then enters a water leaching tank for leaching, the leaching is carried out under the normal temperature condition, the leaching time is 60-120 minutes, the adding amount of water is 1.5-2.5 times of that of the calcined material before the wet grinding, the filtrate obtained after the water leaching and the filtration is a mixture of iron oxide and calcium phosphate;
s4, adsorption filtration
Adding activated carbon into the lithium hydroxide solution to remove organic impurities and suspended fine particles in the lithium hydroxide solution so as to purify the lithium hydroxide solution, controlling the temperature of filtrate to be 35-55 ℃, adding 0.1-0.5kg of activated carbon into each cubic meter, reacting for 30-60 minutes, filtering after the reaction is finished, and finely filtering by adopting a 0.05-0.1 micron pore size filter to remove fine activated carbon particles;
s5, concentrating and precipitating
Heating and evaporating the lithium hydroxide solution after fine filtration in a reactor filled with carbon dioxide to obtain the precipitate of lithium carbonate, wherein the pressure of the carbon dioxide is 0.2-0.5MPa, the filling amount is 10-30m 3/h, the reaction time is 180 minutes, filtering to obtain lithium carbonate, and returning the mother solution to the adsorption filtration process.
S6, washing slag
And (3) putting the slag subjected to water immersion in the step S3, which mainly comprises graphite, iron oxide, calcium phosphate, copper, aluminum and the like, into a slag washing tank, adding pure water for size mixing, controlling the temperature to be 55-70 ℃, controlling the pH value to be 3.0-4.5 by using sulfuric acid, and reacting for 60-90 minutes, wherein the residual lithium is mainly removed.
S7, leaching
Putting the slag washed in the step S6 into a leaching tank, adding phosphoric acid, wherein the adding amount of the phosphoric acid is 0.9-1.1 times of the theoretical amount of dissolved iron oxide, the reaction temperature is 65-95 ℃, the reaction time is 60-90 minutes, adding iron powder, adjusting the pH value to be less than 1, reacting for 60-90 minutes, supplementing the content of iron in the solution with the iron powder, and filtering to obtain a complex solution of phosphorus and iron, wherein the slag mainly comprises graphite, calcium phosphate, copper, aluminum and the like.
S8, oxidation
Heating the leached and filtered solution to 85-95 ℃, adding iron powder, wherein the dosage of the iron powder is 0.01-0.2kg per cubic meter, and the reaction time is 30-60 minutes, so as to continuously supplement iron ions in the solution and promote redundant iron and phosphorus to generate precipitates so as to reach a balanced phosphorus-iron ratio.
S9, precipitation
Adding the liquid after fine filtration and sodium hydroxide into a precipitation reaction tank in a cocurrent flow mode, controlling the crystal form and the growth speed of the iron phosphate by controlling the flow rate of the liquid and the sodium hydroxide, and calculating to obtain the flow of the fine filtration and the flow of the sodium hydroxide by staying in a reactor for 2-4 hours, namely when the effective volume of the reactor is 1 cubic meter, the sum of the flow of the fine filtration and the flow of the sodium hydroxide is 0.5-0.25 cubic meter per hour.
S10, curing
And after the reaction is finished, transferring the slurry into another reactor, reducing the stirring speed to 1/2-1/3 of the original reactor, mainly aiming at modifying the crystal form appearance of the iron phosphate under the condition of low stirring strength, dissolving fine particles generated before the curing process, correcting the particle size distribution of the iron phosphate, controlling the curing temperature to be 50-60 ℃ for 30-60 minutes, and filtering after the curing is finished.
S11, washing
And (3) washing the filtered solid namely iron phosphate by adopting pure water at the water temperature of 45-60 ℃ for three times, washing the iron phosphate for the next time after water is removed after each time of washing, wherein the total amount of washing water is 8-12 cubic meters per ton of iron phosphate, and finally drying the iron phosphate to obtain an iron phosphate finished product.
Further, the purpose of the crushing and mixing in the crushing and mixing process of step S1 is to crush the lithium iron phosphate to a certain extent and sufficiently mix the crushed lithium iron phosphate with the calcium hydroxide;
further, the calcination reaction process in the calcination process of step S2 is as follows:
2LiFePO 4 +3Ca(OH) 2 +1/2O 2 ＝2LiOH+Fe 2 O 3 +Ca 3 (PO 4 ) 2 +2H 2 O。
further, the reaction of the lithium hydroxide solution and the carbon dioxide during the concentration and precipitation in step S5 is as follows: 2LiOH + CO 2 ＝Li 2 CO 3 ↓+H 2 O。
Further, the reaction in the leaching process of step S7 is specifically as follows:
Fe+2H 3 PO 4 ＝Fe(H 2 PO 4 ) 2 +H 2 ↑
Fe 2 O 3 +4H 3 PO 4 ＝2HFe(HPO 4 ) 2 +3H 2 O
Fe 2 O 3 +4H 3 PO 4 ＝2H 3 Fe(PO 4 ) 2 +3H 2 O。
further, in the precipitation process in step S9, the precipitation principle is that iron phosphate precipitates at a PH of 1.8 to 2.0, and the flow ratio of iron phosphate to sodium hydroxide is controlled by controlling the end point PH value to 1.8 to 2.0.
The invention provides a comprehensive recovery method of scrapped lithium iron phosphate, which has the following beneficial effects: the method for comprehensively recovering the scrapped lithium iron phosphate comprises the steps of adding impurities as little as possible in the recovery process, recovering lithium into crude lithium carbonate, preparing iron phosphate into an iron phosphate precursor meeting the requirement of producing the lithium iron phosphate by controlling the synthesis process, adopting a method of calcining with calcium hydroxide to convert lithium in the iron phosphate into water-soluble lithium hydroxide, enabling iron phosphorus to generate insoluble oxides and salts to enter slag, preparing industrial lithium carbonate from the lithium hydroxide, dissolving iron and phosphorus in the slag by adopting phosphoric acid and supplementing iron in a certain proportion, preparing the iron phosphate, controlling the crystal form of the iron phosphate by adjusting the precipitation process to meet the requirement of producing the lithium iron phosphate, preparing the lithium into the industrial lithium carbonate by the method, directly firing the lithium carbonate serving as a positive electrode material, preparing the phosphorus and the iron into an iron phosphate product directly used for firing the lithium iron phosphate, and simultaneously directly curing electrolyte and an adhesive of a battery in the treatment process, the method reduces the treatment capacity of waste gas, and has the advantages of simple treatment process, short flow and less waste slag generated in the process.
Drawings
FIG. 1 is a schematic process flow diagram of the comprehensive recovery method of scrapped lithium iron phosphate.
Detailed Description
A method for comprehensively recovering scrapped lithium iron phosphate comprises the following steps:
s1 crushing and mixing
Sieving calcium hydroxide with a 200-mesh sieve, grinding only the sieved part together with the lithium iron phosphate scrap, wherein the dosage of the calcium hydroxide is 0.85-1.05 times of the theoretical dosage, crushing and mixing the lithium iron phosphate to a certain degree, fully mixing the crushed lithium iron phosphate with the calcium hydroxide, sieving with a 425-mesh sieve after mixing, and mainly removing impurities such as metal and the like, wherein the sieved material enters the next process;
s2, calcining
Introducing 425-mesh screen underflow into a calcining furnace for calcining for 180-750 ℃ for 240 minutes at the temperature of 630-750 ℃, introducing compressed air in the calcining process, controlling the pressure of the compressed air to be 0.5-0.8MPa, controlling the flow to be 18-30m 3/hour, wherein the reaction in the calcining process is as follows:
2LiFePO 4 +3Ca(OH) 2 +1/2O 2 ＝2LiOH+Fe 2 O 3 +Ca 3 (PO 4 ) 2 +2H 2 O；
s3, soaking in water
Cooling the calcined material, carrying out wet grinding, wherein the granularity of the wet grinding is 95%, and the wet grinding is sieved by a 100-mesh sieve, the granularity is controlled to be beneficial to water leaching of lithium, the wet grinding is carried out and then enters a water leaching tank for leaching, the leaching is carried out under the normal temperature condition, the leaching time is 60-120 minutes, the adding amount of water is 1.5-2.5 times of that of the calcined material before the wet grinding, the filtrate obtained after the water leaching and the filtration is a mixture of iron oxide and calcium phosphate;
s4, adsorption filtration
Adding activated carbon into the lithium hydroxide solution to remove organic impurities and suspended fine particles in the lithium hydroxide solution so as to purify the lithium hydroxide solution, controlling the temperature of filtrate to be 35-55 ℃, adding 0.1-0.5kg of activated carbon into each cubic meter, reacting for 30-60 minutes, filtering after the reaction is finished, and finely filtering by adopting a 0.05-0.1 micron pore size filter to remove fine activated carbon particles;
s5, concentrating and precipitating
And heating and evaporating the lithium hydroxide solution after fine filtration in a reactor filled with carbon dioxide to obtain the precipitate of lithium carbonate. The pressure of the carbon dioxide is 0.2-0.5MPa, the input amount is 10-30m 3/h, the reaction time is 120-180 minutes, lithium carbonate is obtained after filtration, and the mother liquor returns to the adsorption filtration process. The reaction is as follows: 2LiOH + CO 2 ＝Li 2 CO 3 ↓+H 2 O。
S6, washing slag
And (3) putting the slag subjected to water immersion in the step S3, which mainly comprises graphite, iron oxide, calcium phosphate, copper, aluminum and the like, into a slag washing tank, adding pure water for size mixing, controlling the temperature to be 55-70 ℃, controlling the pH value to be 3.0-4.5 by using sulfuric acid, and reacting for 60-90 minutes, wherein the residual lithium is mainly removed.
S7, leaching
Putting the slag washed in the step S6 into a leaching tank, adding phosphoric acid, wherein the adding amount of the phosphoric acid is 0.9-1.1 times of the theoretical amount of dissolved iron oxide, the reaction temperature is 65-95 ℃, the reaction time is 60-90 minutes, adding iron powder, adjusting the pH value to be less than 1, reacting for 60-90 minutes, supplementing the content of iron in the solution with the iron powder, filtering after the reaction is finished to obtain a complex solution of phosphorus and iron, wherein the slag mainly comprises graphite, calcium phosphate, copper, aluminum and the like, and the reaction is as follows:
Fe+2H 3 PO 4 ＝Fe(H 2 PO 4 ) 2 +H 2 ↑
Fe 2 O 3 +4H 3 PO 4 ＝2HFe(HPO 4 ) 2 +3H 2 O
Fe 2 O 3 +4H 3 PO 4 ＝2H 3 Fe(PO 4 ) 2 +3H 2 O。
s8, oxidation
Heating the leached and filtered solution to 85-95 ℃, adding iron powder, wherein the dosage of the iron powder is 0.01-0.2kg per cubic meter, and the reaction time is 30-60 minutes, so as to continuously supplement iron ions in the solution and promote the excessive iron and phosphorus to generate precipitates so as to reach the balance phosphorus-iron ratio, adding hydrogen peroxide after the iron powder is added for reaction, and oxidizing bivalent iron ions in the solution into trivalent iron ions, wherein the reaction is as follows:
2Fe(H 2 PO 4 ) 2 +H 2 O 2 ＝2FePO 4 +H 2 O+2H 3 PO 4
HFe(HPO 4 ) 2 +H 2 O 2 ＝FePO 4 +H 2 O+H 3 PO 4 +1/2O 2 ↑
H 3 Fe(PO 4 ) 2 +H 2 O 2 ＝FePO 4 +H 2 O+H 3 PO 4 +1/2O 2 ↑
a small amount of precipitate is generated in the oxidation process, precise filtration is needed to remove the precipitate, and the solution after the precise filtration enters the next working procedure.
S9, precipitation
The principle of precipitation is that iron phosphate can generate precipitation when the PH value is 1.8-2.0, and the invention adds the liquid after fine filtration and sodium hydroxide into a precipitation reaction tank in a parallel flow mode, and controls the crystal form and the growth speed of the iron phosphate by controlling the flow rate of the liquid and the sodium hydroxide. The flow rates of the fine filtrate and sodium hydroxide are calculated by staying in the reactor for 2-4 hours, namely when the effective volume of the reactor is 1 cubic meter, the sum of the flow rates of the fine filtrate and the sodium hydroxide is 0.5-0.25 cubic meter per hour. The flow ratio of ferric phosphate to sodium hydroxide was controlled at a final pH of 1.8-2.0.
S10, curing
And after the reaction is finished, transferring the slurry into another reactor, reducing the stirring speed to 1/2-1/3 of the original reactor, mainly aiming at modifying the crystal form appearance of the iron phosphate under the condition of low stirring strength, dissolving fine particles generated before the curing process, correcting the particle size distribution of the iron phosphate, controlling the curing temperature to be 50-60 ℃ for 30-60 minutes, and filtering after the curing is finished.
S11, washing
And (3) washing the filtered solid iron phosphate by adopting pure water at the water temperature of 45-60 ℃, washing the iron phosphate by three times, washing the iron phosphate for the next time after water is removed after each time of washing, wherein the total amount of washing water is 8-12 cubic meters per ton of iron phosphate, and finally drying the iron phosphate to obtain an iron phosphate finished product.
In summary, the method for comprehensively recycling scrapped lithium iron phosphate includes the following steps:
s1 crushing and mixing
Sieving calcium hydroxide with a 200-mesh sieve, grinding only the sieved part together with the lithium iron phosphate scrap, wherein the dosage of the calcium hydroxide is 0.85-1.05 times of the theoretical dosage, crushing and mixing the lithium iron phosphate to a certain degree, fully mixing the crushed lithium iron phosphate with the calcium hydroxide, sieving with a 425-mesh sieve after mixing, and mainly removing impurities such as metal and the like, wherein the sieved material enters the next process;
s2, calcining
Putting the 425-mesh screen underflow into a calcining furnace for calcining for 180-750 minutes at the temperature of 630-750 ℃, introducing compressed air in the calcining process, controlling the pressure of the compressed air to be 0.5-0.8MPa and controlling the flow to be 18-30m 3/hour;
s3, soaking in water
Cooling the calcined material, carrying out wet grinding, wherein the granularity of the wet grinding is 95%, and the wet grinding is sieved by a 100-mesh sieve, the granularity is controlled to be beneficial to water leaching of lithium, the wet grinding is carried out and then enters a water leaching tank for leaching, the leaching is carried out under the normal temperature condition, the leaching time is 60-120 minutes, the adding amount of water is 1.5-2.5 times of that of the calcined material before the wet grinding, the filtrate obtained after the water leaching and the filtration is a mixture of iron oxide and calcium phosphate;
s4, adsorption filtration
Adding activated carbon into the lithium hydroxide solution to remove organic impurities and suspended fine particles in the lithium hydroxide solution so as to purify the lithium hydroxide solution, controlling the temperature of filtrate to be 35-55 ℃, adding 0.1-0.5kg of activated carbon into each cubic meter, reacting for 30-60 minutes, filtering after the reaction is finished, and finely filtering by adopting a 0.05-0.1 micron pore size filter to remove fine activated carbon particles;
s5, concentrating and precipitating
And heating and evaporating the lithium hydroxide solution after fine filtration in a reactor filled with carbon dioxide to obtain the precipitate of lithium carbonate. The pressure of the carbon dioxide is 0.2-0.5MPa, the input amount is 10-30m 3/h, the reaction time is 120-180 minutes, lithium carbonate is obtained after filtration, and the mother liquor returns to the adsorption filtration process.
S6, washing slag
And (3) putting the slag subjected to water immersion in the step S3, which mainly comprises graphite, iron oxide, calcium phosphate, copper, aluminum and the like, into a slag washing tank, adding pure water for size mixing, controlling the temperature to be 55-70 ℃, controlling the pH value to be 3.0-4.5 by using sulfuric acid, and reacting for 60-90 minutes, wherein the residual lithium is mainly removed.
S7, leaching
Putting the slag washed in the step S6 into a leaching tank, adding phosphoric acid, wherein the adding amount of the phosphoric acid is 0.9-1.1 times of the theoretical amount of dissolved iron oxide, the reaction temperature is 65-95 ℃, the reaction time is 60-90 minutes, adding iron powder, adjusting the pH value to be less than 1, reacting for 60-90 minutes, supplementing the content of iron in the solution with the iron powder, and filtering to obtain a complex solution of phosphorus and iron, wherein the slag mainly comprises graphite, calcium phosphate, copper, aluminum and the like.
S8, oxidation
Heating the leached and filtered solution to 85-95 ℃, adding iron powder, wherein the dosage of the iron powder is 0.01-0.2kg per cubic meter, and the reaction time is 30-60 minutes, so as to continuously supplement iron ions in the solution and promote redundant iron and phosphorus to generate precipitates so as to reach a balanced phosphorus-iron ratio.
S9, precipitation
The principle of precipitation is that iron phosphate can generate precipitation when the PH value is 1.8-2.0, the invention adds the liquid after fine filtration and sodium hydroxide into a precipitation reaction tank in a cocurrent mode, and controls the crystal form and the growth speed of the iron phosphate by controlling the flow rate of the liquid and the sodium hydroxide. The flow rates of the fine filter liquid and the sodium hydroxide are calculated by staying in the reactor for 2-4 hours, namely when the effective volume of the reactor is 1 cubic meter, the sum of the flow rates of the fine filter liquid and the sodium hydroxide is 0.5-0.25 cubic meter per hour. The flow ratio of ferric phosphate to sodium hydroxide was controlled at a final pH of 1.8-2.0.
S10, curing
And after the reaction is finished, transferring the slurry into another reactor, reducing the stirring speed to 1/2-1/3 of the original reactor, mainly aiming at modifying the crystal form appearance of the iron phosphate under the condition of low stirring strength, dissolving fine particles generated before the curing process, correcting the particle size distribution of the iron phosphate, controlling the curing temperature to be 50-60 ℃ for 30-60 minutes, and filtering after the curing is finished.
S11, washing
And (3) washing the filtered solid namely iron phosphate by adopting pure water at the water temperature of 45-60 ℃ for three times, washing the iron phosphate for the next time after water is removed after each time of washing, wherein the total amount of washing water is 8-12 cubic meters per ton of iron phosphate, and finally drying the iron phosphate to obtain an iron phosphate finished product.
Claims (6)
1. The comprehensive recovery method of scrapped lithium iron phosphate is characterized by comprising the following steps of:
s1 crushing and mixing
Sieving calcium hydroxide through a 200-mesh sieve, taking only the sieved part and grinding the sieved part together with lithium iron phosphate scrap, wherein the dosage of the calcium hydroxide is 0.85-1.05 times of the theoretical dosage, sieving the calcium hydroxide through a 425-mesh sieve after mixing is finished, and then reserving sieved materials for later use;
s2, calcining
The sieved material which is sieved by a 425-mesh sieve in S1 enters a calcining furnace to be calcined for 180-mesh 240 minutes at the temperature of 630-750 ℃, and compressed air is introduced in the calcining process, the pressure of the compressed air is controlled to be 0.5-0.8MPa, and the flow is controlled to be 18-30m 3/hour;
s3, soaking in water
Cooling the calcined material, carrying out wet grinding, wherein the granularity of the wet grinding is 95%, and the wet grinding is sieved by a 100-mesh sieve, the granularity is controlled to be beneficial to water leaching of lithium, the wet grinding is carried out and then enters a water leaching tank for leaching, the leaching is carried out under the normal temperature condition, the leaching time is 60-120 minutes, the adding amount of water is 1.5-2.5 times of that of the calcined material before the wet grinding, the filtrate obtained after the water leaching and the filtration is a mixture of iron oxide and calcium phosphate;
s4, adsorption filtration
Adding activated carbon into the lithium hydroxide solution to remove organic impurities and suspended fine particles in the lithium hydroxide solution so as to purify the lithium hydroxide solution, controlling the temperature of filtrate to be 35-55 ℃, adding 0.1-0.5kg of activated carbon into each cubic meter, reacting for 30-60 minutes, filtering after the reaction is finished, and finely filtering by adopting a 0.05-0.1 micron pore size filter to remove fine activated carbon particles;
s5, concentrating and precipitating
Heating and evaporating the lithium hydroxide solution after fine filtration in a reactor filled with carbon dioxide to obtain the precipitate of lithium carbonate, wherein the pressure of the carbon dioxide is 0.2-0.5MPa, the filling amount is 10-30m 3/h, the reaction time is 180 minutes, filtering to obtain lithium carbonate, and returning the mother solution to the adsorption filtration process.
S6, washing slag
And (3) putting the slag subjected to water immersion in the step S3, which mainly comprises graphite, iron oxide, calcium phosphate, copper, aluminum and the like, into a slag washing tank, adding pure water for size mixing, controlling the temperature to be 55-70 ℃, controlling the pH value to be 3.0-4.5 by using sulfuric acid, and reacting for 60-90 minutes, wherein the residual lithium is mainly removed.
S7, leaching
Putting the slag washed in the step S6 into a leaching tank, adding phosphoric acid, wherein the adding amount of the phosphoric acid is 0.9-1.1 times of the theoretical amount of dissolved iron oxide, the reaction temperature is 65-95 ℃, the reaction time is 60-90 minutes, adding iron powder, adjusting the pH value to be less than 1, reacting for 60-90 minutes, supplementing the content of iron in the solution with the iron powder, and filtering to obtain a complex solution of phosphorus and iron, wherein the slag mainly comprises graphite, calcium phosphate, copper, aluminum and the like.
S8, oxidation
Heating the leached and filtered solution to 85-95 ℃, adding iron powder, wherein the dosage of the iron powder is 0.01-0.2kg per cubic meter, and the reaction time is 30-60 minutes, so as to continuously supplement iron ions in the solution and promote redundant iron and phosphorus to generate precipitates so as to reach a balanced phosphorus-iron ratio.
S9, precipitation
Adding the liquid after fine filtration and sodium hydroxide into a precipitation reaction tank in a cocurrent flow mode, controlling the crystal form and the growth speed of the iron phosphate by controlling the flow rate of the liquid and the sodium hydroxide, and calculating to obtain the flow of the fine filtration and the flow of the sodium hydroxide by staying in a reactor for 2-4 hours, namely when the effective volume of the reactor is 1 cubic meter, the sum of the flow of the fine filtration and the flow of the sodium hydroxide is 0.5-0.25 cubic meter per hour.
S10, curing
And after the reaction is finished, transferring the slurry into another reactor, reducing the stirring speed to 1/2-1/3 of the original reactor, mainly aiming at modifying the crystal form appearance of the iron phosphate under the condition of low stirring strength, dissolving fine particles generated before the curing process, correcting the particle size distribution of the iron phosphate, controlling the curing temperature to be 50-60 ℃ for 30-60 minutes, and filtering after the curing is finished.
S11, washing
And (3) washing the filtered solid namely iron phosphate by adopting pure water at the water temperature of 45-60 ℃ for three times, washing the iron phosphate for the next time after water is removed after each time of washing, wherein the total amount of washing water is 8-12 cubic meters per ton of iron phosphate, and finally drying the iron phosphate to obtain an iron phosphate finished product.
2. The method for comprehensively recycling scrapped lithium iron phosphate according to claim 1, characterized by comprising the following steps: the purpose of the crushing and mixing in the crushing and mixing process of step S1 is to crush the lithium iron phosphate to a certain extent and to mix it well with the calcium hydroxide.
3. The method for comprehensively recycling scrapped lithium iron phosphate according to claim 1, characterized by comprising the following steps: the calcination reaction process in the calcination process of step S2 is as follows:
2LiFePO 4 +3Ca(OH) 2 +1/2O 2 ＝2LiOH+Fe 2 O 3 +Ca 3 (PO 4 ) 2 +2H 2 O。
4. the method for comprehensively recycling scrapped lithium iron phosphate according to claim 1, characterized by comprising the following steps: the reaction of the lithium hydroxide solution with carbon dioxide during the concentration and precipitation in step S5 is as follows:
2LiOH+CO 2 ＝Li 2 CO 3 ↓+H 2 O。
5. the method for comprehensively recycling scrapped lithium iron phosphate according to claim 1, characterized by comprising the following steps: the reaction in the leaching process of the step S7 is specifically as follows: fe +2H 3 PO 4 ＝Fe(H 2 PO 4 ) 2 +H 2 ↑
Fe 2 O 3 +4H 3 PO 4 ＝2HFe(HPO 4 ) 2 +3H 2 O
Fe 2 O 3 +4H 3 PO 4 ＝2H 3 Fe(PO 4 ) 2 +3H 2 O。
6. The method for comprehensively recycling scrapped lithium iron phosphate according to claim 1, characterized by comprising the following steps: in the precipitation process of step S9, the precipitation principle is that iron phosphate will precipitate when the PH is 1.8-2.0, and the flow ratio of iron phosphate to sodium hydroxide is controlled by controlling the end point PH value to 1.8-2.0.
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