Method for recycling multi-impurity waste lithium iron phosphate black powder
Technical Field
The invention belongs to the field of recycling of waste lithium iron phosphate batteries, and particularly relates to a method for recycling multi-impurity waste lithium iron phosphate black powder.
Background
In recent years, the problems of traditional energy crisis and environmental pollution are more and more emphasized by many people, and the new energy industry is developed more and more vigorously under the condition. The new energy automobile is a scientific product which is closest to the life of people and is bound to be widely used in the future. Among various types of energy storage batteries for electric vehicles, lithium iron phosphate batteries account for half of the electric vehicle market due to their excellent stability and excellent safety. A large number of energy storage batteries are inevitably scrapped in the production of a large number of electric vehicles, and from the perspective of resource recycling, the waste lithium ion batteries have remarkable resource performance, wherein the equivalent value of metal elements such as Li is high, and the consumption of mineral resources can be greatly relieved by efficient recovery. From the viewpoint of environmental protection, the components are complex, and the random discarding brings harm to the ecological environment and human health. Therefore, the recycling of the waste lithium iron phosphate batteries occupying a large market share is imperative.
At present, the recovery method of the waste lithium iron phosphate anode material generally comprises pyrogenic process regeneration and wet process recovery. For the pyrogenic process regeneration process, although the process is simple, the energy consumption is large, the product consistency is poor, and the product performance is poor due to the existence of impurities, such as CN102280673A. For the wet method, if the recovered raw materials are cleaner, the recovery process is short, and the performance of the obtained product is excellent; if the components in the raw materials are complex, high-value lithium is often selectively extracted firstly, and then Fe and P are recycled, for example, in CN113896211A, most of the existing researches on the phosphorous iron slag obtained after selective lithium extraction firstly dissolve the phosphorous iron slag, then remove impurities from the solution to obtain pure Fe and P solution, and synthesize an iron phosphate product.
In summary, for a raw material with complex components, the existing lithium iron phosphate recovery process is often complicated, and the problems of repeated change of valence state of Fe element, large acid and alkali consumption, high cost and the like exist in the process.
Disclosure of Invention
Aiming at the problem of recycling waste lithium iron phosphate raw materials with complex components in the prior art, the invention aims to provide a method for recycling waste lithium iron phosphate black powder with multiple impurities. Selectively extracting high-value lithium from the waste lithium iron phosphate black powder under an inorganic acid and hydrogen peroxide system, placing the high-value lithium in a solution, and obtaining a corresponding lithium product through subsequent operation; pre-removing impurities from leaching residues obtained after lithium is selectively leached by the waste lithium iron phosphate black powder dilute acid, so that a multi-step impurity removing procedure in a solution is avoided, the flow is shortened, the acid and alkali consumption is reduced, and the obtained recovered product has low impurity content; the solution after impurity removal is returned to the oxidation leaching process, so that the loss of lithium, iron and phosphorus is reduced.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention relates to a method for recycling waste lithium iron phosphate black powder with multiple impurities, which comprises the following steps:
step (1): carrying out primary oxidation leaching on waste lithium iron phosphate black powder in a leaching solution containing inorganic acid and hydrogen peroxide, and carrying out solid-liquid separation to obtain a primary lithium-containing leaching solution and a primary iron phosphate leaching residue;
step (2): performing secondary pre-impurity removal leaching on the primary ferric phosphate leaching residue obtained in the step (1) in an acid solution A, and performing solid-liquid separation to obtain secondary impurity removal liquid and secondary ferric phosphate leaching residue; returning the second-stage impurity-removed liquid as a recovery leaching liquid to the step (1) for first-stage oxidation leaching, wherein in the acid solution A, H + The concentration of (b) is less than or equal to 0.6mol/L;
and (3): leaching the second-stage ferric phosphate leaching residue obtained in the step (2) in an acid solution B for three stages, and performing solidification separation to obtain three stages of leaching solution containing Fe and P and three stages of leaching residue, wherein in the acid solution B, H + Concentration of (2)Not less than 0.8mol/L; and adjusting the phosphorus-iron ratio of the leaching solution containing Fe and P, and carrying out chemical precipitation reaction to obtain the iron phosphate.
The method takes waste lithium iron phosphate black powder with multiple impurities as a recovery raw material, the waste lithium iron phosphate black powder contains multiple impurities such as aluminum, copper, nickel, cobalt, manganese and the like, the recovery mode of the method firstly obtains a section of lithium-containing leaching solution and a section of ferric phosphate leaching residue through a section of oxidation leaching, and the main component in the section of ferric phosphate leaching residue is FePO 4 C, including a small amount of impurities such as Al, cu and the like; one-stage Li-containing leaching solution mainly contains Li + 、Al 3+ 、Cu 2+ (ii) a Based on the ferric phosphate leaching slag, the invention controls the leaching conditions of the two-stage pre-impurity-removal leaching to leach a small amount of impurities such as Al, cu and the like into the two-stage impurity-removal liquid and simultaneously leach FePO 4 C still remains in the slag, and the obtained second-stage impurity removal liquid is returned to the leaching liquid in the step (1), so that the Fe leached into the second-stage impurity removal liquid is replaced by FePO 4 And finally, leaching the second-stage iron phosphate leaching slag almost containing no other metal impurities to obtain a leaching solution containing Fe and P, and finally realizing the regeneration of the iron phosphate.
In the invention, the waste lithium iron phosphate black powder is the anode powder of the lithium iron phosphate battery or the mixture of the anode powder and the cathode powder of the lithium iron phosphate battery.
Preferably, in the step (1), in the leachate containing inorganic acid and hydrogen peroxide, the inorganic acid is at least one selected from sulfuric acid, nitric acid and phosphoric acid, and the concentration of the inorganic acid is 0.1-0.3 mol/L.
In the preferable scheme, in the step (1), the molar ratio of the waste lithium iron phosphate black powder to the hydrogen peroxide is 1:1 to 1:2.
in the preferable scheme, in the step (1), the solid-liquid mass volume ratio of the waste lithium iron phosphate black powder to the leachate containing inorganic acid and hydrogen peroxide is 1g:5 to 10mL.
Preferably, in the step (1), the temperature of the first-stage oxidation leaching is 25-70 ℃, and the time of the first-stage oxidation leaching is 1-2 hours.
Preferably, in the step (1), the pH value of the first-stage lithium-containing leaching solution is 1.5-4.
In the first stage of oxidation leaching, the acid liquor with lower concentration is combined with the hydrogen peroxide with stronger oxidizability to serve as the steeping liquor, so that although partial metal impurities enter the first stage of iron phosphate leaching slag, on one hand, the acid liquor with lower concentration can reduce the leaching rate of Fe and P in the first stage of leaching, thereby avoiding the loss of Fe and P and improving the recovery rate, and on the other hand, the final second stage of iron phosphate leaching slag is easier in the third stage of leaching.
Preferably, in the step (2), the acid solution a is at least one selected from sulfuric acid, nitric acid and phosphoric acid, and the concentration of the acid solution a is 0.05 to 0.3mol/L.
Preferably, in the step (2), the solid-liquid mass-volume ratio of the first-stage iron phosphate leaching residue to the acid solution A is 1g: 8-10 mL.
In the preferable scheme, in the step (2), the temperature of the second-stage pre-impurity-removal leaching is 65-90 ℃, preferably 80-90 ℃, and the time of the second-stage pre-impurity-removal leaching is 0.5-2 h.
The inventor unexpectedly finds that the impurity activity of aluminum and copper is higher and the reaction is more complete when the temperature is high, and FePO simultaneously 4 The solubility is lower at high temperatures, so better temperatures are used for two-stage pre-impurity leaching, while for three-stage leaching we need to let FePO 4 Since the leaching is relatively complete, a low temperature is selected when the solubility is high.
Preferably, in the step (2), the pH value of the second-stage impurity removal liquid is 0.6-1.5. The temperature of the second-stage impurity removal liquid is controlled within the range, so that the loss of Fe and P can be effectively avoided, the impurities can be fully leached, and if the pH is too low, fePO is used 4 Most of the Fe and P are leached out along with the Fe and P, and more Fe and P are lost; if the pH is too high, the reaction of the impurities and the acid is weak, and the impurity removal effect is not obvious.
Preferably, in the step (3), the acid solution B is at least one selected from sulfuric acid, nitric acid and phosphoric acid, and the concentration of the acid solution B is 0.8 to 1.5mol/L.
Preferably, in the step (3), the solid-liquid mass volume ratio of the first-stage ferric phosphate leaching residue to the acid solution B is 1g: 5-8 mL.
In a preferable scheme, in the step (3), the temperature of the three-stage leaching is 25-60 ℃, preferably 25-40 ℃, and the time of the three-stage leaching is 1-3 hours.
Preferably, in the step (3), the pH of the leaching solution containing Fe and P in three sections is-0.5.
Preferably, in the step (3), the phosphorus-iron ratio of the leaching solution containing Fe and P is adjusted to be 1-1.05: 1, adjusting the pH value by adopting ammonia water, and controlling the end point pH value of the chemical precipitation reaction to be 1.6-2.2 to obtain the iron phosphate.
Preferably, at least one of potassium hydroxide and sodium hydroxide is used as a pH regulator, the pH value of the first-stage lithium-containing leaching solution is regulated to 11-13, solid-liquid separation is carried out, sodium carbonate is added into the obtained liquid phase, and the liquid phase reacts at 80-100 ℃ for 1-2 h to obtain lithium carbonate, wherein the addition amount of the sodium carbonate is 1.2-1.5 times of the molar amount of lithium in the liquid phase.
Preferably, at least one of potassium hydroxide and sodium hydroxide is used as a pH regulator, the pH value of the first-stage lithium-containing leachate is regulated to 11-13, solid-liquid separation is carried out, sodium phosphate is added into the obtained liquid phase, and the liquid phase reacts at 80-100 ℃ for 1-2 h to obtain lithium phosphate, wherein the addition amount of the sodium phosphate is 1.1-1.3 times of the molar amount of lithium in the liquid phase.
In a preferable scheme, at least one of potassium hydroxide and sodium hydroxide is used as a pH regulator, the pH value of the first-stage lithium-containing leachate is regulated to 12-14, solid-liquid separation is carried out, sodium hydroxide is added into the obtained liquid phase, reaction is carried out for 1-2 h at 90-100 ℃, hydrogen hydroxide is obtained, and the addition amount of the sodium hydroxide is 1.3-1.5 times of the molar amount of lithium in the liquid phase.
Principles and advantages
The method takes waste lithium iron phosphate black powder with multiple impurities as a recovery raw material, the waste lithium iron phosphate black powder contains multiple impurities such as aluminum, copper, nickel, cobalt, manganese and the like, the recovery mode of the method firstly obtains a section of lithium-containing leaching solution and a section of ferric phosphate leaching residue through a section of oxidation leaching, and the main component in the section of ferric phosphate leaching residue is FePO 4 C, including a small amount of impurities such as Al, cu and the like; one-stage Li-containing leaching solution mainly contains Li + 、Al 3+ 、Cu 2+ (ii) a Based on the ferric phosphate leaching slag, the invention controls the leaching conditions of the two-stage pre-impurity-removal leaching to leach a small amount of impurities such as Al, cu and the like into the two-stage impurity-removal liquid and simultaneously leach FePO 4 C still remains in the slag, and the obtained second-stage impurity removal liquid is returned to the leaching liquid in the step (1), so that the Fe leached into the second-stage impurity removal liquid is replaced by FePO 4 And finally, leaching the second-stage iron phosphate leaching slag almost containing no other metal impurities to obtain a leaching solution containing Fe and P, and finally realizing the regeneration of the iron phosphate.
In the invention, for the treatment of the iron phosphate slag, the conventional idea of dissolving iron phosphate slag acid in a solution and then removing impurities is changed, namely, pre-removing impurities is carried out before acid dissolution, and after acid dissolution, phosphorus and iron are directly supplemented to precipitate the iron phosphate. It brings the following benefits:
(1) In the first oxidation leaching process, the impurity elements are expected to enter lithium solution mostly, and Fe and P are remained in slag, so that the subsequent recovery process of Fe and P is beneficial. Therefore, in the prior art, an acid solution with a high concentration is often used, so that impurities enter the solution, but the leaching of Fe and P becomes high after the acid concentration is high, and the recovery rate of Fe and P is reduced. After the pre-impurity removal step, the impurities do not need to be considered to enter the solution in the first oxidation leaching process; after the acid liquor with lower concentration is used, the leaching rate of Fe and P is low, and the recovery rate is increased.
(2) The phosphorus-iron slag after lithium extraction is subjected to one-step solid-phase pre-impurity removal instead of multi-step liquid-phase post-impurity removal, so that the recovery process of black powder of the waste lithium iron phosphate battery is greatly simplified, the process flow is reduced, the equipment investment is reduced, the occupied area is reduced, and the like;
(3) Returning the pre-impurity-removing liquid to the process of oxidizing and leaching lithium by inorganic acid, so that the entrainment loss of element lithium in the phosphorus iron slag can be reduced, and the recovery rate of lithium is improved;
(4) Repeated transformation of Fe valence state in the impurity removal process after liquid phase is avoided, auxiliary material consumption is reduced, and recovery cost is reduced;
(5) After the pre-impurity-removed ferrophosphorus slag is leached by peracid, the ferric phosphate can be directly generated without adding an oxidant, and the oxidant is not consumed.
The method has the advantages that the process for selectively recycling the waste lithium iron phosphate is simpler, the treatment of the iron phosphate slag is simpler, and the cost is reduced.
Drawings
Fig. 1 is a schematic flow diagram of recycling of waste lithium iron phosphate black powder containing multiple impurities according to the present invention.
Detailed Description
In order to make the objects and methods of the present invention clearer, the present invention will be described in further detail with reference to embodiments. The examples described herein are intended to be illustrative of the invention and are not intended to be limiting thereof.
Example 1
Step (1): the waste lithium iron phosphate black powder comprises 15.7wt% of iron, 2.01wt% of lithium, 8.34wt% of phosphorus, 2.1wt% of aluminum, 1.69wt% of copper, 0.17wt% of nickel, 0.16wt% of cobalt and 0.19wt% of manganese, and the solid-to-liquid ratio of the waste lithium iron phosphate black powder is 1: performing primary oxidation leaching on 10g/mL under a 0.2mol/L dilute sulfuric acid and hydrogen peroxide system (the molar ratio of the waste lithium iron phosphate black powder to the hydrogen peroxide is 1: 2), wherein the leaching temperature is 50 ℃, the leaching time is 2h, and performing solid-liquid separation to obtain primary leaching residue and primary leaching liquid; the primary leaching residue mainly contains FePO 4 C, including a small amount of impurities such as Al, cu and the like; the primary leaching solution is mainly Li + 、Al 3+ 、Cu 2+ ;
Step (2): and (2) mixing the first-stage leaching residue obtained in the step (1) according to a solid-to-liquid ratio of 1: pre-removing impurities in 10g/mL low-concentration sulfuric acid, wherein the concentration of the sulfuric acid is 0.1mol/L, the impurity removal temperature is 90 ℃, the time is 1h, performing solid-liquid separation to obtain second-stage leaching residue and second-stage impurity removal liquid, the loss of Fe is 3%, the pH of the impurity removal liquid is 1.21, returning the second-stage impurity removal liquid to the first-stage oxidation leaching process in the step (1), and re-using FePO to remove Fe 4 The form is recovered in the first stage leaching residue of the next batch.
And (3): and (3) mixing the two-stage leaching residue obtained in the step (2) according to a solid-to-liquid ratio of 1: leaching 8g/mL in high-concentration sulfuric acid to obtain a solution containing Fe and P, wherein the concentration of the sulfuric acid is 1mol/L, the leaching temperature is 30 ℃, the leaching time is 1h, and the pH of the solution containing Fe and P is 0.40; through detection, al impurities in the pure Fe and P solutions are lower than 150ppm, cu impurities are lower than 50ppm, and Ni, co and Mn are lower than 20ppm; adjusting the iron-phosphorus ratio of the obtained Fe-containing solution and P solution according to the ratio of Fe in the solution: p =1:1.05, supplementing phosphorus and iron, regulating the final pH value of the solution to be 1.8 by using ammonia water, and filtering to obtain an iron phosphate product.
And (4): regulating the pH value of the first-stage leaching solution obtained in the step (1) to 11.5 by using sodium hydroxide, filtering, then carrying out lithium product precipitation on the filtrate, wherein a precipitator is sodium carbonate, the addition amount of the precipitator is 1.2 times of the molar amount of lithium in the solution, the reaction temperature is 95 ℃, the reaction time is 1h, and hot water is filtered to obtain lithium carbonate. The recovery rates of the respective elements are shown in Table 1.
Example 2
Step (1): the waste lithium iron phosphate black powder comprises 15.7wt% of iron, 2.01wt% of lithium, 8.34wt% of phosphorus, 2.1wt% of aluminum, 1.69wt% of copper, 0.17wt% of nickel, 0.16wt% of cobalt and 0.19wt% of manganese, and the solid-to-liquid ratio of the waste lithium iron phosphate black powder is 1: performing primary oxidation leaching on 10g/mL under a 0.2mol/L dilute sulfuric acid and hydrogen peroxide system (the molar ratio of the waste lithium iron phosphate black powder to the hydrogen peroxide is 1; the primary leaching residue mainly contains FePO 4 C, including a small amount of impurities such as Al, cu and the like; the primary leaching solution is mainly Li + 、Al 3+ 、Cu 2+ ;
Step (2): and (2) mixing the first-stage leaching residue obtained in the step (1) according to a solid-to-liquid ratio of 1: pre-removing impurities in 10g/mL low-concentration sulfuric acid, wherein the concentration of the sulfuric acid is 0.2mol/L, the impurity removal temperature is 90 ℃, the time is 1h, performing solid-liquid separation to obtain second-stage leaching residue and second-stage impurity removal liquid, the Fe loss is 10 percent, the pH of the impurity removal liquid is 1.02, returning the second-stage impurity removal liquid to the first-stage oxidation leaching process in the step (1), and re-using FePO for the Fe 4 The form is recovered in the next batch of first-stage leaching residue.
And (3): and (3) mixing the two-stage leaching residue obtained in the step (2) according to a solid-to-liquid ratio of 1: leaching 8g/mL in high-concentration sulfuric acid to obtain a solution containing Fe and P, wherein the concentration of the sulfuric acid is 1mol/L, the leaching temperature is 30 ℃, the leaching time is 1h, and the pH value of the solution containing Fe and P is 0.31; through detection, al impurities in pure Fe and P solutions are lower than 70ppm, cu impurities are lower than 30ppm, and Ni, co and Mn are lower than 10ppm; adjusting the iron-phosphorus ratio of the obtained solution containing Fe and P according to the ratio of Fe in the solution: p =1:1.05, supplementing phosphorus and iron, regulating the final pH value of the solution to be 2 by using ammonia water, and filtering to obtain an iron phosphate product.
And (4): regulating the pH value of the first-stage leaching solution obtained in the step (1) to 11.5 by using sodium hydroxide, filtering, then carrying out lithium product precipitation on the filtrate, wherein a precipitator is sodium carbonate, the addition amount of the precipitator is 1.2 times of the molar amount of lithium in the solution, the reaction temperature is 95 ℃, the reaction time is 1h, and hot water is filtered to obtain lithium carbonate. The recovery rates of the respective elements are shown in Table 1.
Example 3
Step (1): the waste lithium iron phosphate black powder comprises 15.7wt% of iron, 2.01wt% of lithium, 8.34wt% of phosphorus, 2.1wt% of aluminum, 1.69wt% of copper, 0.17wt% of nickel, 0.16wt% of cobalt and 0.19wt% of manganese, wherein the waste lithium iron phosphate black powder is prepared by mixing the following raw materials in a solid-to-liquid ratio of 1: performing primary oxidation leaching on 10g/mL under a 0.2mol/L dilute sulfuric acid and hydrogen peroxide system (the molar ratio of the waste lithium iron phosphate black powder to the hydrogen peroxide is 1; the primary leaching residue mainly contains FePO 4 C, including a small amount of impurities such as Al, cu and the like; the primary leaching solution is mainly Li + 、Al 3+ 、Cu 2+ ;
Step (2): and (2) mixing the first-stage leaching residue obtained in the step (1) according to a solid-to-liquid ratio of 1: pre-removing impurities in 10g/mL low-concentration sulfuric acid, wherein the concentration of the sulfuric acid is 0.25mol/L, the impurity removal temperature is 90 ℃, the time is 1h, performing solid-liquid separation to obtain second-stage leaching residue and second-stage impurity removal liquid, the Fe loss is 15%, the pH of the impurity removal liquid is 0.89, returning the second-stage impurity removal liquid to the first-stage oxidation leaching process in the step (1), and re-using FePO for Fe 4 The form is recovered in the next batch of first-stage leaching residue.
And (3): and (3) mixing the two-stage leaching residue obtained in the step (2) according to a solid-to-liquid ratio of 1: leaching 8g/mL in high-concentration sulfuric acid to obtain a solution containing Fe and P, wherein the concentration of the sulfuric acid is 1mol/L, the leaching temperature is 30 ℃, the leaching time is 1h, and the pH of the solution containing Fe and P is 0.2; detection shows that Al impurities in the pure Fe and P solutions are lower than 30ppm, cu impurities are lower than 20ppm, and Ni, co and Mn impurities are lower than 10ppm; adjusting the iron-phosphorus ratio of the obtained solution containing Fe and P according to the ratio of Fe in the solution: p =1:1.05, supplementing phosphorus and iron, regulating the final pH value of the solution to be 1.8 by using ammonia water, and filtering to obtain an iron phosphate product.
And (4): regulating the pH value of the first-stage leaching solution obtained in the step (1) to 11.5 by using sodium hydroxide, filtering, then carrying out lithium product precipitation on the filtrate, wherein a precipitator is sodium carbonate, the addition amount of the precipitator is 1.2 times of the molar amount of lithium in the solution, the reaction temperature is 95 ℃, the reaction time is 1h, and hot water is filtered to obtain lithium carbonate. The recovery rates of the respective elements are shown in Table 1.
Example 4
Step (1): the waste lithium iron phosphate black powder comprises 15.7wt% of iron, 2.01wt% of lithium, 8.34wt% of phosphorus, 2.1wt% of aluminum, 1.69wt% of copper, 0.17wt% of nickel, 0.16wt% of cobalt and 0.19wt% of manganese, wherein the waste lithium iron phosphate black powder is prepared by mixing the following raw materials in a solid-to-liquid ratio of 1: performing primary oxidation leaching on 10g/mL under a 0.2mol/L dilute sulfuric acid and hydrogen peroxide system (the molar ratio of the waste lithium iron phosphate black powder to the hydrogen peroxide is 1; the primary leaching residue mainly contains FePO 4 C, including a small amount of impurities such as Al, cu and the like; the primary leaching solution is mainly Li + 、Al 3+ 、Cu 2+ ;
Step (2): and (2) mixing the first-stage leaching residue obtained in the step (1) according to a solid-to-liquid ratio of 1: pre-removing impurities in 10g/mL low-concentration sulfuric acid, wherein the concentration of the sulfuric acid is 0.3mol/L, the impurity removal temperature is 90 ℃, the time is 1h, performing solid-liquid separation to obtain second-stage leaching residue and second-stage impurity removal liquid, the loss of Fe is 20%, the pH of the impurity removal liquid is 0.71, returning the second-stage impurity removal liquid to the first-stage oxidation leaching process in the step (1), and re-using FePO to remove Fe 4 The form is recovered in the first stage leaching residue of the next batch.
And (3): and (3) mixing the two-stage leaching residue obtained in the step (2) according to a solid-to-liquid ratio of 1: leaching 8g/mL in high-concentration sulfuric acid to obtain a solution containing Fe and P, wherein the concentration of the sulfuric acid is 1mol/L, the leaching temperature is 30 ℃, the leaching time is 1h, and the pH of the solution containing Fe and P is 0.40; through detection, al impurities in the pure Fe and P solutions are lower than 20ppm, cu impurities are lower than 10ppm, and Ni, co and Mn are lower than 10ppm; adjusting the iron-phosphorus ratio of the obtained solution containing Fe and P according to the ratio of Fe in the solution: p =1:1.05, supplementing phosphorus and iron, regulating the final pH value of the solution to be 2 by using ammonia water, and filtering to obtain an iron phosphate product.
And (4): and (2) regulating the pH value of the first-stage leaching solution obtained in the step (1) to 11.5 by using a calcium hydroxide emulsion, filtering, then carrying out lithium product precipitation on the filtrate, wherein a precipitator is sodium carbonate to obtain lithium carbonate, the addition amount of the precipitator is 1.2 times of the molar amount of lithium in the solution, the reaction temperature is 95 ℃, the reaction time is 1 hour, and hot water is filtered to obtain the lithium carbonate. The recovery rates of the respective elements are shown in Table 1.
Comparative example 1
Step (1): the waste lithium iron phosphate black powder comprises 15.7wt% of iron, 2.01wt% of lithium, 8.34wt% of phosphorus, 2.1wt% of aluminum, 1.69wt% of copper, 0.17wt% of nickel, 0.16wt% of cobalt and 0.19wt% of manganese, wherein the waste lithium iron phosphate black powder is prepared by mixing the following raw materials in a solid-to-liquid ratio of 1: performing primary oxidation leaching on 10g/mL in a 0.20mol/L dilute sulfuric acid and hydrogen peroxide system (the molar ratio of the waste lithium iron phosphate black powder to the hydrogen peroxide is 1: 2), wherein the leaching temperature is 60 ℃, the leaching time is 2h, and performing solid-liquid separation to obtain a primary leaching residue and a primary leaching solution; the primary leaching residue mainly contains FePO 4 C, including a small amount of impurities such as Al, cu and the like; the primary leaching solution is mainly Li + 、Al 3+ 、Cu 2+ ;
Step (2): and (2) mixing the first-stage leaching residue obtained in the step (1) according to a solid-to-liquid ratio of 1:8g/mL of the solution is directly leached in high-concentration sulfuric acid, the concentration of the sulfuric acid is 1.0mol/L, the leaching temperature is 30 ℃, the leaching time is 1h, and the pH value of the leaching solution is 0.56; detection shows that Al impurities in the obtained Fe and P solution are as high as 1100ppm, cu impurities are as high as 680ppm, ni, co and Mn are higher than 40ppm, the Fe and P solution needs further impurity removal, al, cu, ni, co and Mn are sequentially removed to obtain a solution containing Fe and P, the iron-phosphorus ratio of the solution containing Fe and P is adjusted, and the ratio of Fe to P is calculated according to the weight of Fe: p =1:1.05, supplementing phosphorus and iron, regulating the final pH value of the solution to be 2 by using ammonia water, and filtering to obtain an iron phosphate product;
and (3): and (2) regulating the pH value of the leachate obtained in the step (1) to 11.5 by using sodium hydroxide, filtering, and then performing lithium product precipitation on the filtrate to obtain lithium carbonate, wherein a precipitator is sodium carbonate, the addition amount of the precipitator is 1.2 times of the molar amount of lithium in the solution, the reaction temperature is 95 ℃, the reaction time is 1 hour, and hot water is filtered to obtain lithium carbonate. The recovery rates of the respective elements are shown in Table 1.
Comparative example 2
The other conditions were the same as in example 1 except that the acid concentration used in step (1) was 0.6mol/L. The recovery rates of the respective elements are shown in Table 1.
Comparative example 3
The other conditions were the same as in example 1 except that the low concentration sulfuric acid in step (2) was 0.04mol/L. The recovery rates of the respective elements are shown in Table 1.
TABLE 1