Method for purifying and removing impurities from lithium iron phosphate positive electrode waste leaching solution

Abstract

The application discloses a method for purifying and removing impurities from a lithium iron phosphate anode waste leaching solution, and realizes effective removal of copper and aluminum impurities in the lithium iron phosphate waste leaching solution through the processes of acid leaching, copper-aluminum co-precipitation, regeneration of iron phosphate and lithium phosphate, eliminates the influence of the impurities on the regeneration and preparation of iron phosphate products, and improves the iron recovery rate, so that battery-grade iron phosphate with ultra-low aluminum content is finally obtained, and meanwhile, efficient recovery of iron and lithium is realized, the process flow is simple, the reagent cost is low, good economic benefits can be created, and the method is suitable for industrialized production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling waste lithium iron phosphate batteries, and particularly relates to a method for purifying and removing impurities from lithium iron phosphate positive electrode waste leaching solution. BACKGROUND

[0002] With the rapid growth of new energy vehicle sales, the scrap and replacement amount of power batteries also grows rapidly. According to the service life of 4 to 6 years of power batteries, it is estimated that the domestic power batteries have entered the peak of scrap, and the market scale is rapidly released. It is estimated that the recycling scale of lithium batteries in 2030 will reach 108.9 billion yuan, of which the recycling proportion of power batteries will reach 84%, and the recycling scale will reach 91.6 billion yuan. The scrap and disassembly scale of lithium iron phosphate batteries is expected to reach 44 billion yuan. Previously, enterprises mainly recycled LiCoO2, LiNi x Co y Mn 1-x-y O2, etc. However, there is no much enthusiasm for the recycling of LiFePO4. The reason is that the recycling value of LiFePO4 battery is low. However, due to the sharp rise in lithium prices, researchers have begun to invest more effort in the recycling of LiFePO4 batteries. If the effective recycling of Li, Fe and P in lithium iron phosphate can be realized, it will also have great economic benefits.

[0003] As patent CN201710857448.9 "A method for recycling battery-grade lithium carbonate from waste lithium iron phosphate battery positive electrode powder", its main scheme includes high temperature and high pressure alkali cooking of waste lithium iron phosphate battery positive electrode powder, and filtering to obtain alkali leaching solution containing aluminum and lithium; adding inorganic acid to the alkali leaching solution to adjust the pH value to 4.5-6, then adding flocculating agent, and filtering to remove aluminum to obtain lithium-containing liquid; adding ammonium carbonate to the lithium-containing liquid, and charging carbon dioxide to carry out high temperature and high pressure reaction, and filtering to obtain lithium carbonate. The patent realizes effective recovery of lithium in the form of battery-grade lithium carbonate, but does not mention how to recover Fe and P. Regenerated battery-grade iron phosphate is considered an effective way to recover Fe and P, but because the copper foil and aluminum foil in the battery cannot be completely separated from the positive electrode waste material during pretreatment, this will cause some copper and aluminum ions to exist in the lithium iron phosphate leaching solution, and then enter the product during the regeneration of iron phosphate, affecting the quality of iron phosphate. Therefore, in order to ensure that the regenerated iron phosphate can be used to prepare high-performance lithium iron phosphate, it is necessary to remove copper and aluminum preferentially before leaching or in the acid leaching solution. Patent 202210400945.7 reports "A method for selectively and deeply removing aluminum and copper in the recycling process of waste lithium iron phosphate", the recovered waste lithium iron phosphate positive electrode material is subjected to acid dissolution to obtain a mixed solution containing iron, lithium and phosphorus; insoluble iron powder, ferrous oxide, ferrous hydroxide and the like are added to adjust the pH of the mixed solution to 2.5-6.0, and aluminum phosphate and copper phosphate are precipitated and separated to obtain a mixed solution of phosphorus, iron and lithium with non-excessive impurities of aluminum and copper. This method effectively removes aluminum and copper from the solution, but the iron powder and other substances used in the process of adjusting the pH react slowly and have low utilization rate. Patent 201910704052.X mentions "A separation method for aluminum elements in waste lithium iron phosphate material", which realizes the precipitation separation of aluminum by adding a fluoride complexing agent to the waste lithium iron phosphate acid leaching solution containing aluminum elements and carrying out complexing reaction, with a precipitation rate of more than 99wt%, and the aluminum in the solution can be removed to less than 10ppm. This method realizes effective separation of aluminum by adding external fluorine, but the introduction of fluorine will cause corrosion of the equipment, and a small amount of fluorine will also remain in the product and aqueous solution, which is difficult to handle. SUMMARY

[0004] The purpose of the present application is to provide a method for purifying and removing impurities from lithium iron phosphate positive electrode waste leaching solution, which uses retired lithium iron phosphate battery positive electrode waste as the treatment object, and realizes effective removal of copper and aluminum impurities in lithium iron phosphate waste leaching solution through acid leaching-copper and aluminum co-precipitation-iron phosphate and lithium phosphate regeneration processes, eliminates the influence of impurities on the preparation of regenerated iron phosphate products and improves the recovery rate of iron, and finally obtains battery-grade iron phosphate with ultra-low aluminum content. The present application also realizes efficient recovery of iron and lithium; the process is simple, easy to operate, and suitable for industrial production.

[0005] The present application realizes the above-mentioned purposes through the following technical solutions:

[0006] A method for purifying and removing impurities from a lithium iron phosphate anode waste leaching solution, comprising the following steps:

[0007] Step 1: Dissolve the lithium iron phosphate anode waste powder with an acidic leaching agent and filter to obtain a first acidic solution containing lithium, iron, phosphorus, aluminum and copper, and carbon residue;

[0008] Step 2: Adjust the pH value of the first acidic solution containing lithium, iron, phosphorus, aluminum and copper obtained in step 1 to 0.5-2, preferably 1-2, by using a high-concentration hydroxide solution, and then further adjust the pH value to 2-6, preferably 2-5, by using a low-concentration carbonate solution, to selectively precipitate copper-aluminum residue; filter to obtain copper-aluminum residue and a second acidic solution containing lithium, iron and phosphorus; the concentration of the high-concentration hydroxide solution is 20-40 wt%, and the concentration of the low-concentration carbonate solution is 5-20 wt%; the hydroxide is at least one selected from sodium hydroxide, potassium hydroxide and lithium hydroxide; the carbonate is at least one selected from sodium carbonate, ammonium carbonate and lithium carbonate;

[0009] Step 3: Recrystallize the copper-aluminum residue obtained in step 2 to obtain secondary copper-aluminum residue and a third acidic solution;

[0010] The recrystallization is to adjust the slurry of the obtained copper-aluminum residue, the slurry concentration is 20-75%, adjust the pH of the slurry to 1-2.5, preferably 1-2, to dissolve the copper-aluminum residue, and then adjust the pH of the solution to 2-5 to generate a precipitate, and filter to obtain secondary copper-aluminum residue and a third acidic solution;

[0011] Step 4: Combine the second and third acidic solutions obtained in steps 3 and 4, add an oxidizing agent and adjust the pH value of the system to 1-3, and then wash and filter to obtain dihydrate iron phosphate and a fourth acidic solution.

[0012] Step 5: Adjust the pH of the fourth acidic solution obtained in step 4 to 6.5-12 by adding alkali, and then remove calcium and magnesium using a resin to obtain a purified solution; heat the purified solution to 50-95℃, slowly add Na3PO4 solution, and then react to obtain crude lithium phosphate; wash with pure water and dilute phosphoric acid solution to obtain battery-grade lithium phosphate.

[0013] In further embodiments, in step 1, the acidic leaching agent is one or more of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, and the concentration of the acidic leaching agent is 1.5-3.5 mol / L; during leaching, the liquid-solid ratio is controlled to be 2-6:1, the temperature is 25-85℃, and the leaching time is 0.5-6 h.

[0014] Further, in step 1, the leaching agent is sulfuric acid, and the concentration of sulfuric acid is 1.5-3 mol / L; during leaching, the liquid-solid ratio is controlled to be 2-4:1, the temperature is 25-50℃, and the leaching time is 0.5-3 h.

[0015] Further, in step 2, a hydroxide solution with a concentration of 20-40 wt% is added to adjust the solution pH to A, and then a carbonate solution with a concentration of 10-20% is added to adjust the pH to B, under the condition of stirring for 10-60 min, the local precipitation is dissolved, and then a carbonate solution with a concentration of 5-10% is slowly added to adjust the pH to C, so as to make copper-aluminum precipitate, and the temperature is controlled to be 25-60℃ during the precipitation of copper-aluminum, and the reaction time is 10-180 min; wherein the value of A is 1-2, the value of B is 2-5, and the value of C is 2-5; and A, B and C are not equal to each other.

[0016] Further, in step 3, the recrystallization is to adjust the slurry of the obtained copper-aluminum residue, the slurry concentration is 20-50%, an acid is added to adjust the slurry pH to 1-2 to dissolve the copper-aluminum residue, and then the pH of the solution is adjusted to 2-5 to generate a precipitate, and the secondary copper-aluminum residue and the third acidic solution are obtained by filtration.

[0017] Further, the slurry pH is adjusted to 1-2, and the copper-aluminum residue is dissolved by stirring for 30-120 min.

[0018] Further, in step 4, the oxidizing agent is hydrogen peroxide, which is used to oxidize the divalent iron ions, and the excess ratio is 1-2 times, and then the pH value of the system is adjusted to 1-3, and the crude iron phosphate and the fourth acidic solution are precipitated by heating to 30-90℃, the pH is controlled to be 1.5-2.5 during the precipitation of iron phosphate, and the product of dihydrate iron phosphate is obtained after washing at 30-60℃.

[0019] Further, the fourth acidic solution obtained in step 4 is adjusted to a pH of 6.5-12 by adding an alkali, and after removing calcium and magnesium using a resin, a impurity-removed solution is obtained; the impurity-removed solution is heated to 50-95℃, and then a Na3PO4 solution is slowly added, and the crude lithium phosphate is obtained after reaction; and the battery-grade lithium phosphate is obtained after washing with pure water and dilute phosphoric acid solution.

[0020] Further, the alkali is selected from one of sodium hydroxide, potassium hydroxide, calcium hydroxide and calcium oxide; the resin is one of D402 ion exchange resin and Further, the excess of the Na3PO4 solution is 1.05-1.3 times of the theoretical amount, and preferably 1.05-1.2 times of the theoretical amount.

[0021] The existing patent uses iron powder to replace copper during the recovery of lithium iron phosphate, however, under acidic conditions, the consumption of iron powder is large, and the utilization efficiency is low; aluminum is generally removed by alkali leaching before acid leaching or in the form of aluminum phosphate in the solution, the alkali consumption required for removing aluminum by alkali leaching is large, and the removal is not complete, and when aluminum phosphate is precipitated, iron and aluminum are easily co-precipitated, and the loss of iron is large. The present technology can remove copper and aluminum together through copper and aluminum co-precipitation, and the two-step impurity removal is changed into one-step impurity removal, and the process is simple. In addition, in view of the problem of large loss of iron during impurity removal, first, the pH value of the solution is adjusted by different alkali solutions, and during the process of copper and aluminum precipitation, the local over-alkaline phenomenon is avoided as much as possible, so that the loss of iron is small during the precipitation of copper and aluminum, and further, through the method of recrystallization, the copper and aluminum slag is refined, so that the iron in the slag is further reduced, the loss of iron in the recovery process is reduced, and the recovery rate of the target element is improved.

[0022] The present application adopts the above technical scheme, and has the following beneficial effects:

[0023] The present application realizes the method for purifying and removing impurities in lithium iron phosphate positive electrode waste leaching solution, regenerates battery-grade phosphoric acid iron and lithium phosphate with ultra-low aluminum content by effectively removing copper and aluminum, and has high iron recovery rate, simple process flow, low reagent cost, and can create good economic benefits, and is suitable for industrialized production. DETAILED DESCRIPTION

[0024] To make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0025] Embodiment 1

[0026] A method for purifying and removing impurities from lithium iron phosphate positive electrode waste leaching solution includes:

[0027] 500g material is leached at liquid-solid ratio 4ml:1g, sulfuric acid concentration 2mol / L, room temperature for 1h, filtration, to obtain the first acidic solution containing lithium, iron, phosphorus, aluminum and copper and carbon residue. The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to system pH value 2 with 30wt% NaOH solution, further adjusted to system pH value 3 with 15wt% Na2CO3 solution, stirring for 0.5h, then adjusted to system pH value 3.5 with 5wt% Na2CO3 solution, filtration to obtain the second acidic solution and copper aluminum residue, the copper aluminum residue is slurried with water, slurry concentration 50wt%, sulfuric acid is used to adjust pH value to 1.5, stirring for 0.5h to dissolve, and 15wt% Na2CO3 is used to adjust pH of the solution obtained after dissolution of the copper aluminum residue to 3.5 to precipitate copper aluminum, filtration to obtain secondary copper aluminum residue and the third acidic solution, the second acidic solution and the third acidic solution are combined to obtain the purified solution, first 1.2 times the amount of hydrogen peroxide is used to oxidize Fe 2+ , the system pH value is reduced to 1.1, then 15% Na2CO3 solution is used to adjust the system pH to 1.9, filtration to obtain crude iron phosphate and the fourth acidic solution, the crude iron phosphate is washed three times and dried to obtain dihydrate iron phosphate product, the product contains 89ppm aluminum and 5ppm copper, the iron recovery rate is 93.43%. The fourth acidic solution is adjusted to pH 11 with sodium hydroxide, and the calcium and magnesium are removed by D402 ion exchange resin, then 1.1 times the theoretical amount of sodium phosphate solution is added to obtain crude lithium phosphate, which is washed with pure water and dilute phosphoric acid to obtain battery grade lithium phosphate, the lithium recovery rate is 93.25%.

[0028] Example 2

[0029] A method for purifying and removing impurities from a lithium iron phosphate positive electrode waste leaching solution comprises:

[0030] 500g material is leached at liquid-solid ratio 4ml:1g, sulfuric acid concentration 2mol / L, room temperature for 1h, filtration, to obtain the first acidic solution containing lithium, iron, phosphorus, aluminum and copper and carbon residue. The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to system pH value 2 with 30wt% NaOH solution, further adjusted to system pH value 3 with 15wt% Na2CO3 solution, stirring for 0.5h, then adjusted to system pH value 3.5 with 5wt% Na2CO3 solution, filtration to obtain the second acidic solution and copper aluminum residue, the copper aluminum residue is slurried with water, slurry concentration 50wt%, sulfuric acid is used to adjust pH value to 1.5, stirring for 0.5h to dissolve, and 15wt% Na2CO3 is used to adjust pH of the solution obtained after dissolution of the copper aluminum residue to 3.5 to precipitate copper aluminum, filtration to obtain secondary copper aluminum residue and the third acidic solution, the second acidic solution and the third acidic solution are combined to obtain the purified solution, first 1.2 times the amount of hydrogen peroxide is used to oxidize Fe 2+, the pH of the system is reduced to 1.05, and then the pH of the system is adjusted to 2.0 by using 15% Na2CO3 solution, and the crude iron phosphate is obtained by filtering the precipitate, and the crude iron phosphate is washed three times to obtain the dried iron phosphate dihydrate product, the aluminum content in the product is 94 ppm, the copper content is 6 ppm, and the iron recovery rate is 94.15%. The fourth acidic solution is adjusted to pH 11 by adding potassium hydroxide, and the calcium and magnesium are removed by D402 ion exchange resin, and then 1.15 times the theoretical amount of sodium phosphate solution is added to obtain crude lithium phosphate, and then the battery-grade lithium phosphate is obtained by washing with pure water and dilute phosphoric acid, and the lithium recovery rate is 93.78%.

[0031] Example 3

[0032] A method for purifying and removing impurities from a lithium iron phosphate cathode waste leaching solution comprises:

[0033] 500g of material is leached at a liquid-solid ratio of 4mL:1g, a sulfuric acid concentration of 3mol / L, and a temperature of 40℃ for 1h, filtered, and a first acidic solution containing lithium, iron, phosphorus, aluminum, and copper and carbon residue is obtained. The first acidic solution containing lithium, iron, phosphorus, aluminum, and copper is adjusted to a system pH of 1.5 with a 30wt% NaOH solution, and then the system pH is adjusted to 3 with a 15wt% Na2CO3 solution, stirred for 0.5h, and then the system pH is adjusted to 3.8 with a 5wt% Na2CO3 solution, filtered to obtain a second acidic solution and a copper-aluminum residue, the copper-aluminum residue is slurried with water, the slurry concentration is 50wt%, the pH is adjusted to 1.8 with sulfuric acid, stirred for 0.5h, and then the pH of the solution obtained after the copper-aluminum residue is dissolved is adjusted to 3.8 with 15wt% K2CO3 to precipitate copper and aluminum, and the second acidic solution and the third acidic solution are combined to obtain a purified solution, which is first treated with 1.1 times the amount of hydrogen peroxide to oxidize Fe 2+ , the pH of the system is reduced to 0.95, and then the pH of the system is adjusted to 2.0 by using 15% K2CO3 solution, and the crude iron phosphate is obtained by filtering the precipitate, and the crude iron phosphate is washed three times to obtain the dried iron phosphate dihydrate product, the aluminum content in the product is 96 ppm, the copper content is 5.5 ppm, and the iron recovery rate is 92.77%. The fourth acidic solution is adjusted to pH 10 by adding calcium oxide, and the calcium and magnesium are removed by D402 ion exchange resin, and then 1.05 times the theoretical amount of sodium phosphate solution is added to obtain crude lithium phosphate, and then the battery-grade lithium phosphate is obtained by washing with pure water and dilute phosphoric acid, and the lithium recovery rate is 92.65%.

[0034] Example 4

[0035] A method for purifying and removing impurities from a lithium iron phosphate cathode waste leaching solution comprises:

[0036] 500g material was leached at 4ml:1g of liquid-solid ratio, 2.5mol / L of sulfuric acid concentration, 60℃ for 1h, filtered, to obtain a first acidic solution containing lithium, iron, phosphorus, aluminum and copper and carbon residue. The first acidic solution containing lithium, iron, phosphorus, aluminum and copper was adjusted to a system pH of 2 with a 30wt% NaOH solution, further adjusted to a system pH of 2.4 with a 15wt% Na2CO3 solution, stirred for 1h, then adjusted to a system pH of 3.2 with a 5wt% Na2CO3 solution, filtered to obtain a second acidic solution and copper-aluminum residue, the copper-aluminum residue was slurried with water, the slurry concentration was 50wt%, the pH was adjusted to 1.5 with sulfuric acid, stirred for 0.5h to dissolve, and the pH of the solution obtained after the dissolution of the copper-aluminum residue was adjusted to 3.2 with 10wt% Na2CO3 to precipitate copper-aluminum, filtered to obtain secondary copper-aluminum residue and a third acidic solution, the second acidic solution and the third acidic solution were combined to obtain a purified solution, which was first subjected to hydrogen peroxide oxidation Fe 2+ , the system pH was reduced to 0.98, then adjusted to a system pH of 2.2 with a 10% Na2CO3 solution, filtered to obtain crude iron phosphate and a fourth acidic solution, the crude iron phosphate was washed three times and then dried to obtain iron phosphate dihydrate product, the product contained 126ppm of aluminum and 7ppm of copper, and the iron recovery rate was 94.84%. The fourth acidic solution was adjusted to a pH of 11 with calcium oxide, and After the resin removed calcium and magnesium, 1.05 times the theoretical amount of sodium phosphate solution was added to obtain crude lithium phosphate, which was washed with pure water and dilute phosphoric acid to obtain battery-grade lithium phosphate, and the lithium recovery rate was 92.44%.

[0037] Example 5

[0038] A method for purifying and removing impurities from a lithium iron phosphate positive electrode waste leaching solution comprises:

[0039] 500g material was leached at 4ml:1g of liquid-solid ratio, 2.5mol / L of sulfuric acid concentration, 60℃ for 1h, filtered, to obtain a first acidic solution containing lithium, iron, phosphorus, aluminum and copper and carbon residue. The first acidic solution containing lithium, iron, phosphorus, aluminum and copper was adjusted to a system pH of 2 with a 30wt% NaOH solution, further adjusted to a system pH of 2.4 with a 15wt% Na2CO3 solution, stirred for 1h, then adjusted to a system pH of 3.2 with a 5wt% Na2CO3 solution, filtered to obtain a second acidic solution and copper-aluminum residue, the copper-aluminum residue was slurried with water, the slurry concentration was 50wt%, the pH was adjusted to 1.5 with sulfuric acid, stirred for 0.5h to dissolve, and the pH of the solution obtained after the dissolution of the copper-aluminum residue was adjusted to 3.2 with 10wt% Na2CO3 to precipitate copper-aluminum, filtered to obtain secondary copper-aluminum residue and a third acidic solution, the second acidic solution and the third acidic solution were combined to obtain a purified solution, which was first subjected to hydrogen peroxide oxidation Fe 2+, the pH of the system is reduced to 0.93, then the pH of the system is adjusted to 1.95 by using 15% Na2CO3 solution, the crude iron phosphate is obtained by filtering the precipitate, the crude iron phosphate is washed for three times, then dried to obtain the iron phosphate dihydrate product, the aluminum content in the product is 126 ppm, the copper content is 16 ppm, and the iron recovery rate is 90.62%. The fourth acidic solution is added with calcium oxide to adjust the pH to 12, and is treated by After the calcium and magnesium in the resin are removed, 1.1 times of the theoretical amount of sodium phosphate solution is added to obtain the crude lithium phosphate, and then the battery-grade lithium phosphate is obtained by washing with pure water and dilute phosphoric acid, and the lithium recovery rate is 93.94%.

[0040] Example 6

[0041] A method for purifying and removing impurities from a lithium iron phosphate anode waste leaching solution comprises the following steps:

[0042] 500g of material is leached at a liquid-solid ratio of 4mL:1g, a sulfuric acid concentration of 2mol / L, and a room temperature for 1h, filtered, to obtain a first acidic solution containing lithium, iron, phosphorus, aluminum and copper, and carbon residue. The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to a system pH of 1.2 with a 30wt% NaOH solution, and further adjusted to a system pH of 3 with a 15wt% Na2CO3 solution, stirred for 1h, then adjusted to a system pH of 3.6 with a 5wt% Na2CO3 solution, filtered to obtain a second acidic solution and a copper-aluminum residue, the copper-aluminum residue is slurried with water, the slurry concentration is 50wt%, the pH is adjusted to 1.1 with sulfuric acid, stirred for 0.5h to dissolve, and the pH of the solution obtained after the slurry is dissolved with 5wt% Na2CO3 is adjusted to 3.6, to precipitate copper and aluminum, and filtered to obtain secondary copper-aluminum residue and a third acidic solution. The second acidic solution and the second acidic solution are combined to obtain a purified solution, which is first treated with 1.5 times the amount of hydrogen peroxide to oxidize Fe 2+ , the pH of the system is reduced to 0.89, then the pH of the system is adjusted to 2.1 by using 15wt% Na2CO3 solution, the crude iron phosphate is obtained by filtering the precipitate, the crude iron phosphate is washed for three times, then dried to obtain the iron phosphate dihydrate product, the aluminum content in the product is 86 ppm, the copper content is 4 ppm, and the iron recovery rate is 91.56%. The fourth acidic solution is added with calcium oxide to adjust the pH to 11, and is treated by After the calcium and magnesium in the resin are removed, 1.2 times of the theoretical amount of sodium phosphate solution is added to obtain the crude lithium phosphate, and then the battery-grade lithium phosphate is obtained by washing with pure water and dilute phosphoric acid, and the lithium recovery rate is 93.86%.

[0043] Comparative Example 1

[0044] The difference between the example 1 and the comparative example 1 is that the 30% NaOH solution is used to adjust the pH.

[0045] The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to a system pH of 3.5 with a 30wt% NaOH solution, and a second acidic solution and copper-aluminum residue are filtered. The copper-aluminum residue is slurried with water to a slurry concentration of 50wt%, adjusted to a pH of 1.5 with sulfuric acid, stirred for 0.5h, and the pH of the solution obtained after the slurry is dissolved is adjusted to 3.5 with a 30wt% NaOH solution to precipitate the copper-aluminum, and a second copper-aluminum residue and a third acidic solution are filtered. The second acidic solution and the third acidic solution are combined to obtain a purified solution, which is first subjected to oxidation of Fe 2+ with 1.3 times the amount of hydrogen peroxide, the system pH is then reduced to 0.95, and the system pH is adjusted to 2.1 with a 15wt% Na2CO3 solution, and crude iron phosphate and a fourth acidic solution are filtered from the precipitate. The crude iron phosphate is washed three times and dried to obtain dihydrate iron phosphate product, which has an aluminum content of 86ppm, a copper content of 13ppm, and an iron recovery rate of 73.49%. The fourth acidic solution is adjusted to a pH of 11 with sodium hydroxide, and calcium and magnesium are removed with a D402 ion exchange resin, and 1.1 times the theoretical amount of sodium phosphate solution is added to obtain crude lithium phosphate, which is washed with pure water and dilute phosphoric acid to obtain battery-grade lithium phosphate, and the lithium recovery rate is 86.25%.

[0046] Comparative Example 2

[0047] The difference from Example 1 is that the copper-aluminum residue is not subjected to recrystallization treatment.

[0048] The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to a system pH of 2 with a 30wt% NaOH solution, and the system pH is further adjusted to 3 with a 15wt% Na2CO3 solution, stirred for 0.5h, and then the system pH is adjusted to 3.5 with a 5wt% Na2CO3 solution, and a second acidic solution and copper-aluminum residue are filtered. The second acidic solution is a purified solution, which is first subjected to oxidation of Fe 2+ with 1.25 times the amount of hydrogen peroxide, the system pH is then reduced to 0.98, and the system pH is adjusted to 2.1 with a 15wt% Na2CO3 solution, and crude iron phosphate and a fourth acidic solution are filtered from the precipitate. The crude iron phosphate is washed three times and dried to obtain dihydrate iron phosphate. The product has an aluminum content of 81ppm, a copper content of 6ppm, and an iron recovery rate of 81.25%. The fourth acidic solution is adjusted to a pH of 11 with sodium hydroxide, and calcium and magnesium are removed with a D402 ion exchange resin, and 1.1 times the theoretical amount of sodium phosphate solution is added to obtain crude lithium phosphate, which is washed with pure water and dilute phosphoric acid to obtain battery-grade lithium phosphate, and the lithium recovery rate is 87.11%.

[0049] Comparative Example 3

[0050] The difference from Example 1 is that the pH is adjusted to 5.0 during the recrystallization of the copper-aluminum and the copper-aluminum residue.

[0051] A method for purifying and removing impurities from a lithium iron phosphate anode waste leaching solution comprises:

[0052] The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to a system pH of 2 with a 30 wt% NaOH solution, further adjusted to a system pH of 3 with a 15 wt% Na2CO3 solution, stirred for 0.5 h, then adjusted to a system pH of 5.0 with a 5 wt% Na2CO3 solution, filtered to obtain a second acidic solution and a copper-aluminum residue, the copper-aluminum residue is slurried with water, the slurry concentration is 50 wt%, the pH is adjusted to 1.5 with sulfuric acid, stirred for 0.5 h to dissolve, and the pH of the solution obtained after the slurry is dissolved is adjusted to 5.0 with a 10 wt% Na2CO3 solution to precipitate copper and aluminum, filtered to obtain secondary copper-aluminum residue and a third acidic solution, the second acidic solution and the third acidic solution are combined to obtain a purified solution, and the purified solution is first subjected to oxidation Fe 2+ The system pH is then reduced to 0.98, the system pH is adjusted to 2.1 with a 15 wt% Na2CO3 solution, and the precipitate is filtered to obtain crude iron phosphate and a fourth acidic solution, the crude iron phosphate is washed three times and then dried to obtain dihydrate iron phosphate. The aluminum content in the product is 37 ppm, the copper content is 3 ppm, and the iron recovery rate is 51.56%. The fourth acidic solution is adjusted to a pH of 11 with sodium hydroxide, and the calcium and magnesium are removed by D402 ion exchange resin, then a 1.1 times theoretical amount of sodium phosphate solution is added to obtain crude lithium phosphate, which is washed with pure water and dilute phosphoric acid to obtain battery-grade lithium phosphate, and the lithium recovery rate is 60.54%.

[0053] Comparative Example 4

[0054] The difference from Example 1 is that the pH is adjusted to 2.5 during the removal of copper and aluminum and the recrystallization of the copper-aluminum residue.

[0055] A method for purifying and removing impurities from a lithium iron phosphate anode waste leaching solution comprises:

[0056] The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to a system pH of 2 with a 30 wt% NaOH solution, further adjusted to a system pH of 2.5 with a 15 wt% Na2CO3 solution, stirred for 0.5 h, filtered to obtain a second acidic solution and a copper-aluminum residue, the copper-aluminum residue is slurried with water, the slurry concentration is 50 wt%, the pH is adjusted to 1.5 with sulfuric acid, stirred for 0.5 h to dissolve, and the pH of the solution obtained after the copper-aluminum residue is dissolved is adjusted to 2.5 with a 15 wt% Na2CO3 solution to precipitate copper and aluminum, filtered to obtain secondary copper-aluminum residue and a third acidic solution, the second acidic solution and the third acidic solution are combined to obtain a purified solution, and the purified solution is first subjected to oxidation Fe 2+The pH of the system is then reduced to 0.98, and then the pH of the system is adjusted to 2.1 by using 15wt% Na2CO3 solution. The crude iron phosphate is obtained by filtering and precipitating, and the crude iron phosphate is dried after being washed for three times to obtain iron phosphate. The aluminum content in the product is 582ppm, the copper content is 36ppm, and the iron recovery rate is 96.97%. The fourth acidic solution is adjusted to pH 11 by adding sodium hydroxide, and then the calcium and magnesium are removed by using D402 ion exchange resin. Then, the crude lithium phosphate is obtained by adding 1.1 times of the theoretical amount of sodium phosphate solution. The battery-grade lithium phosphate is obtained after being washed with pure water and dilute phosphoric acid, and the lithium recovery rate is 93.67%.

[0057] Comparative Example 5

[0058] The difference from Example 1 is that the pH of the fourth acidic solution is adjusted to 5.5.

[0059] A method for purifying and removing impurities from a lithium iron phosphate cathode waste leaching solution comprises the following steps:

[0060] The first acidic solution containing lithium, iron, phosphorus, aluminum and copper is adjusted to a system pH of 2 by using 30wt% NaOH solution, and then the system pH is adjusted to 2.5 by using 15wt% Na2CO3 solution. After stirring for 0.5h, the second acidic solution and copper-aluminum residue are obtained by filtering. The copper-aluminum residue is slurried by adding water, and the slurry concentration is 50wt%. The pH is adjusted to 1.5 by using sulfuric acid, and the copper-aluminum residue is dissolved by stirring for 0.5h. Then, the pH of the solution obtained after the copper-aluminum residue is dissolved is adjusted to 2.5 by using 15wt% Na2CO3, so that the copper-aluminum is precipitated. The secondary copper-aluminum residue and the third acidic solution are obtained by filtering. The second acidic solution and the third acidic solution are combined to obtain the purified solution. The purified solution is first subjected to oxidation Fe 2+ The pH of the system is then reduced to 0.98, and then the pH of the system is adjusted to 2.1 by using 15wt% Na2CO3 solution. The crude iron phosphate is obtained by filtering and precipitating, and the crude iron phosphate is dried after being washed for three times to obtain iron phosphate. The aluminum content in the product is 582ppm, the copper content is 36ppm, and the iron recovery rate is 96.97%. The fourth acidic solution is adjusted to pH 11 by adding sodium hydroxide, and then the calcium and magnesium are removed by using D402 ion exchange resin. Then, the crude lithium phosphate is obtained by adding 1.1 times of the theoretical amount of sodium phosphate solution. The battery-grade lithium phosphate is obtained after being washed with pure water and dilute phosphoric acid, and the lithium recovery rate is 93.67%.

[0061] The copper, aluminum and iron contents in the obtained purified solution are tested by using inductively coupled plasma atomic emission spectrometry, and the iron recovery rate is calculated. The test results are shown in Table 1:

[0062] Table 1 Main element contents in the purified solution and iron recovery rate

[0063]

[0064] Table 2 Lithium and iron comprehensive recovery rate in the process flow

[0065]

[0066] As can be seen from Table 1, the copper concentration in the purified solution in Examples 1-6 can be reduced to below 0.02 mg / L, because at pH 2 or higher, copper ions can form copper phosphate precipitates with phosphate ions, and the same is true for aluminum concentration, which can be reduced to below 0.1 mg / L, because aluminum ions form aluminum phosphate with phosphate ions, and the iron ion has weak binding ability with phosphate, and the recovery rate can reach more than 90%.

[0067] As can be seen from Table 1, the iron recovery rate in Comparative Example 1 is low, because adjusting the pH value with a high concentration of sodium hydroxide solution can cause more ferrous phosphate to precipitate locally in the solution, and the increased iron loss is caused by the difficulty in dissolving the precipitate. Comparative Example 2 is because the copper-aluminum residue is not recrystallized, and the residue contains more iron elements. Comparative Example 3 is because the pH value of the solution is too high, and ferrous phosphate also precipitates. Comparative Example 4 is because the pH value of the system is too low, and it is difficult to remove copper and aluminum completely.

[0068] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction, in order to avoid unnecessary repetition, the present application will not further describe various possible combinations. Furthermore, 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, it should also be considered as disclosed by the present application.

Claims

1. A method for purifying and removing impurities from the leachate of lithium iron phosphate cathode waste, characterized in that, Includes the following steps: Step 1: Dissolve the lithium iron phosphate cathode waste powder with an acidic leaching agent and then filter it to obtain a first acidic solution containing lithium, iron, phosphorus, aluminum and copper and carbon slag. Step 2: The first acidic solution containing lithium, iron, phosphorus, aluminum, and copper obtained in Step 1 is adjusted to pH A by adding 20–40 wt% hydroxide solution. The pH is further adjusted to pH B by adding 10–20% carbonate solution. Under these conditions, the mixture is stirred for 10–60 min to dissolve the local precipitate. Then, 5–10% carbonate solution is slowly added to adjust the pH to pH C to precipitate copper and aluminum. The temperature during copper and aluminum precipitation is controlled at 25–60℃, and the reaction time is 10–180 min. The values ​​of A, B, and C are 1–2, 2.4–3, and 3.2–3.8, and A, B, and C are all unequal. The mixture is then filtered to obtain copper-aluminum slag and a second acidic solution containing lithium, iron, and phosphorus. Step 3: Recrystallize the copper-aluminum slag obtained in Step 2 to obtain secondary copper-aluminum slag and a third acidic solution; The recrystallization process involves preparing the obtained copper-aluminum slag into a slurry with a concentration of 20-50%, adding acid to adjust the pH of the slurry to 1-2 to dissolve the copper-aluminum slag, and then adjusting the pH of the solution to 3.2-3.8 to generate a precipitate. The precipitate is then filtered to obtain secondary copper-aluminum slag and a third acidic solution. After combining the second and third acidic solutions obtained in steps 4, 3, and 4, an oxidant was added and the pH of the system was adjusted to 1-3. After washing and filtration, ferric phosphate dihydrate and a fourth acidic solution were obtained. In steps 5 and 4, the fourth acidic solution is adjusted to pH 6.5-12 with alkali. After removing calcium and magnesium with resin, a purified solution is obtained. The purified solution is heated to 50-95°C, and Na3PO4 solution is slowly added. After the reaction, crude lithium phosphate is obtained. After washing with pure water and dilute phosphoric acid solution, battery-grade lithium phosphate is obtained.

2. The method as described in claim 1, characterized in that: In step 1, the acidic leaching agent is one or more of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and the concentration of the acidic leaching agent is 1.5 to 3.5 mol / L; during leaching, the liquid-solid ratio is controlled at 2 to 6:1, the temperature is 25 to 85°C, and the leaching time is 0.5 to 6 hours.

3. The method as described in claim 2, characterized in that: In step 1, the leaching agent is sulfuric acid, and the concentration of sulfuric acid is 1.5-3 mol / L; during leaching, the liquid-solid ratio is controlled at 2-4:1, the temperature is 25-50℃, and the leaching time is 0.5-3h.

4. The method as described in claim 1, characterized in that: In step 2, the hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the carbonate is selected from at least one of sodium carbonate, ammonium carbonate, and lithium carbonate.

5. The method as described in claim 1, characterized in that: Add acid to adjust the pH of the slurry to 1-2, and stir for 30-120 minutes to dissolve the copper-aluminum slag.

6. The method as described in claim 1, characterized in that: In step 4, the oxidant is hydrogen peroxide, which is used to oxidize ferrous ions. The excess ratio is 1 to 2 times. Then, the pH of the system is adjusted to 1 to 3, and the temperature is heated to 30 to 90°C to precipitate crude ferric phosphate and a fourth acidic solution. When precipitating ferric phosphate, the pH is controlled to 1.5 to 2.5, and the temperature is heated to 30 to 60°C. After washing, ferric phosphate dihydrate product is obtained.

7. The method as described in claim 1, characterized in that: The alkali is selected from sodium hydroxide, potassium hydroxide, and calcium hydroxide; the resin is D402 ion exchange resin and... One of CH-93; the Na3PO4 solution is in excess at 1.05 to 1.3 times the theoretical amount.

Images