CN114369720A - Treatment method and application of leachate recovered from lithium iron phosphate positive electrode material - Google Patents

Treatment method and application of leachate recovered from lithium iron phosphate positive electrode material Download PDF

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CN114369720A
CN114369720A CN202111394680.6A CN202111394680A CN114369720A CN 114369720 A CN114369720 A CN 114369720A CN 202111394680 A CN202111394680 A CN 202111394680A CN 114369720 A CN114369720 A CN 114369720A
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leaching solution
aluminum
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copper
iron phosphate
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杜进桥
田杰
李艳
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Shenzhen Power Supply Bureau Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
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    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
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Abstract

The invention provides a treatment method and application of a leachate recovered from a lithium iron phosphate positive electrode material. The processing method comprises the following steps: adjusting the pH value of the leaching solution to 0.8-1.6, then adding iron powder, and filtering to obtain a copper-removed leaching solution; under the protection of protective gas, continuously adding iron powder into the copper-removing leaching solution until the pH value of the copper-removing leaching solution is 3.3-3.6, and filtering to obtain a first aluminum-removing leaching solution; under the protection of protective gas, adjusting the pH value of the first aluminum-removing leaching solution to 2.5-3.0, adding a di (2-ethylhexyl) phosphonic acid extractant to extract aluminum ions, and taking a water phase to obtain a second aluminum-removing leaching solution; and adjusting the pH value of the second aluminum-removal leaching solution to 2.0-4.0, adding La-Al-Ca ternary carbonate for reaction, and filtering to obtain an impurity-removal leaching solution. The treatment method comprises the steps of replacing copper impurities with iron powder, removing aluminum impurities by combining chemical precipitation and an extraction method, removing fluorine impurities by adopting La-Al-Ca ternary carbonate, and adjusting the pH range of each stage to achieve higher impurity removal rate.

Description

Treatment method and application of leachate recovered from lithium iron phosphate positive electrode material
Technical Field
The invention relates to the technical field of waste battery recovery treatment, in particular to a treatment method and application of a leachate obtained by recovering a lithium iron phosphate positive electrode material.
Background
In recent years, with the rapid development of new energy automobile industry, the demand of lithium ion batteries is increasing year by year. The lithium iron phosphate battery has the advantages of high energy density, good safety, long cycle life and the like, and is widely applied to new energy automobiles and energy storage markets. However, the lithium resources are low in reserves on the earth and unevenly distributed, which raises extensive concerns even though lithium ion batteries perform perfectly in many respects. With the surge of the number of electric vehicles and the accelerated development of energy storage devices, lithium resources tend to be in a short supply and short demand state gradually. Therefore, recycling of the waste lithium ion battery is particularly important.
Wherein the lithium iron phosphate battery is a lithium iron phosphate (LiFePO)4) As the anode material, carbon is used as the lithium ion battery of the cathode material, and the charge and discharge reaction of the lithium iron phosphate battery is in LiFePO4And FePO4Between the two phases. During charging, LiFePO4Gradually separated out lithium ions to form FePO4During discharge, lithium ions are intercalated into FePO4Formation of LiFePO4. The lithium iron phosphate battery has the advantages of high working voltage, high energy density, long cycle life, good safety performance, small self-discharge rate, no memory effect and the like. With the high-speed development of new energy automobiles, lithium iron phosphate batteries are more and more widely applied. Because the lithium iron phosphate battery contains a large amount of metal lithium, the discarded lithium iron phosphate battery is recycled, so that the pollution of the waste battery to the environment can be reduced, and certain economic benefit can be brought. In the traditional method for recovering the waste lithium iron phosphate batteries, the waste lithium iron phosphate batteries are generally discharged, disassembled and crushed, and then the crushed materials of the positive plate are incinerated at high temperature to remove the organic binder, so that the positive active material is separated from the aluminum foil, and the positive active powder is obtained after separation. And dissolving the positive active powder by adopting sulfuric acid, and respectively obtaining iron salt, lithium salt and the like after impurity removal and sorting to complete the recovery of elements such as iron, lithium and the like.
The positive active powder obtained from the crushed positive plates is usually inevitably mixed with impurities such as copper, aluminum and the like, and in the traditional impurity removal process, the removal rate of the copper and aluminum impurities is low, and iron elements in the leachate are lost. Meanwhile, the fluorine removal effect in the curing-water leaching process is unstable, so that the removal rate is low. Impurities such as copper, aluminum, fluorine and the like in the leaching solution have great influence on the purity of the subsequent recovered iron, phosphorus and lithium elements.
Disclosure of Invention
Therefore, a treatment method for recovering leachate of the lithium iron phosphate positive electrode material with high impurity removal rate is needed.
In one aspect of the invention, a treatment method for recovering leachate of a lithium iron phosphate positive electrode material is provided, and the treatment method comprises the following steps:
adjusting the pH value of the leaching solution to 0.8-1.6, then adding iron powder for replacement reaction, and filtering to obtain a copper-removed leaching solution;
under the protection of protective gas, continuously adding iron powder into the copper-removing leaching solution until the pH value of the copper-removing leaching solution is 3.3-3.6, and filtering to obtain a first aluminum-removing leaching solution;
under the protection of protective gas, adjusting the pH value of the first aluminum-removal leaching solution to 2.5-3.0, adding a di (2-ethylhexyl) phosphonic acid extractant to extract aluminum ions in the first aluminum-removal leaching solution, and taking a water phase to obtain a second aluminum-removal leaching solution;
and adjusting the pH value of the second aluminum-removal leaching solution to 2.0-4.0, adding La-Al-Ca ternary carbonate for reaction, and filtering to obtain an impurity-removal leaching solution.
In some embodiments, in the step of adding iron powder to perform a displacement reaction, a ratio of a sum of molar amounts of copper ions and iron ions in the leachate to a molar amount of the iron powder is 1: (1.1-1.4).
In some of these embodiments, the reaction time for the metathesis reaction is from 15min to 90 min.
In some of these embodiments, the bis (2-ethylhexyl) phosphonic acid extraction agent comprises 30% by weight of bis (2-ethylhexyl) phosphonic acid, and the solvent of the bis (2-ethylhexyl) phosphonic acid extraction agent is sulfonated kerosene.
In some of these embodiments, the volume ratio of the bis (2-ethylhexyl) phosphonic acid extractant to the first aluminum-removal leachate is from 1: (1-2).
In some embodiments, the La-Al-Ca ternary carbonate is added in an amount of 3g/L to 6 g/L.
In some embodiments, in the step of adding the La-Al-Ca ternary carbonate for reaction, the reaction temperature is 20-70 ℃.
In some embodiments, in the step of adding the La-Al-Ca ternary carbonate for reaction, the reaction time is 50min to 120 min.
In some embodiments, in the step of adding the La-Al-Ca ternary carbonate for reaction, the reaction time is 60min to 90 min.
On the other hand, the invention also provides the application of the treatment method for recovering the leachate of the lithium iron phosphate positive material in the recovery of the waste lithium iron phosphate batteries.
The treatment method for the leachate recovered from the lithium iron phosphate anode material comprises the following steps: and adjusting the pH value of the leaching solution to 0.8-1.6, then adding iron powder for replacement reaction, replacing copper ions in the leaching solution, and filtering to obtain the copper-removed leaching solution. Under the protection of protective gas, continuously adding iron powder into the copper removal leaching solution until the pH value of the copper removal leaching solution is 3.3-3.6, wherein the iron powder can perform a displacement reaction with hydrogen ions in the copper removal leaching solution to consume the hydrogen ions in the copper removal leaching solution, so that the pH value of the copper removal leaching solution is increased, and aluminum ions in the copper removal leaching solution are replaced by AlPO4Precipitating in form, and filtering to obtain a first aluminum-removing leaching solution. Under the protection of protective gas, adjusting the pH value of the first aluminum-removing leaching solution to 2.5-3.0, adding a di (2-ethylhexyl) phosphonic acid extractant to extract aluminum ions in the first aluminum-removing leaching solution, and taking a water phase to obtain a second aluminum-removing leaching solution; under the protection of protective gas, Fe in the leaching solution can be avoided2+React with oxygen to produce Fe3+Avoiding the extraction of Fe by the extractant of di (2-ethylhexyl) phosphonic acid3+Meanwhile, the leaching efficiency of the extracting agent to aluminum ions can be improved by adjusting the first aluminum removal leaching solution. And adjusting the pH value of the second aluminum-removal leaching solution to 2.0-4.0, adding La-Al-Ca ternary carbonate for reaction, and filtering to obtain an impurity-removal leaching solution. The fluoride ions can be further removed by La-Al-Ca ternary carbonateThe fluoride ions in the leaching solution are removed, and the removal rate can reach 96 percent at most. The treatment method is used for treating the recovered leachate of the lithium iron phosphate positive electrode material, removing impurity aluminum by replacing impurity copper with iron powder and combining chemical precipitation and extraction, removing impurity fluorine by adopting La-Al-Ca ternary carbonate, and simultaneously adjusting the pH range of each stage in the treatment process, so that higher impurity removal rate can be achieved. The concentration of copper ions in the leachate treated by the treatment method is within 4.9mg/L, the concentration of aluminum ions is within 10mg/L, and the removal rate of fluorine ions can reach 96%.
Drawings
Fig. 1 is a schematic flow chart of a treatment method for recovering leachate from a lithium iron phosphate positive electrode material according to an embodiment of the present invention;
FIG. 2 is a graph showing the variation of the copper ion content of the leachate solution with the amount of iron powder used according to an embodiment of the present invention;
FIG. 3 is a graph showing the variation of pH of the leachate solution with the amount of iron powder used according to an embodiment of the present invention;
FIG. 4 is a graph of the relationship between the initial pH of the leachate and the copper ion concentration of the solution after the reaction, according to one embodiment of the present invention;
FIG. 5 is a graph showing the variation of the aluminum ion content and the aluminum slag content of the solution with pH after the chemical precipitation reaction according to one embodiment of the present invention;
FIG. 6 is a graph showing the change of the fluorine removal amount of the fluorine-containing zinc sulfate solution and the fluorine ion content of the reacted solution in the La-Al-Ca ternary carbonate pair under different pH conditions according to one embodiment of the present invention;
FIG. 7 is a graph showing the relationship between the La-Al-Ca ternary carbonate in accordance with one embodiment of the present invention and the amount of fluorine removed and the content of fluorine ions in the solution after the reaction, as a function of the reaction time;
FIG. 8 is a graph showing the effect of the amount of La-Al-Ca ternary carbonate used on the fluorine removal rate according to one embodiment of the present invention;
FIG. 9 shows the effect of different temperature conditions on the fluorine removal rate of La-Al-Ca ternary carbonate according to one embodiment of the present invention.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
Referring to fig. 1, an embodiment of the present invention provides a processing method for a leachate recovered from a lithium iron phosphate positive electrode material, including steps S100 to S400.
Step S100: and adjusting the pH value of the leaching solution to 0.8-1.6, then adding iron powder for replacement reaction, and filtering to obtain the copper-removed leaching solution.
Due to Fe2+Fe is much higher than Cu in standard potential (-0.141V)2+The standard potential (0.330V) of Cu is low, Fe powder has strong reducibility, copper ions in the acid leaching solution can be completely replaced by copper powder, and no new impurity is introduced. Therefore, the invention adopts iron powder to replace and remove copper. The reaction of adding iron powder into the leaching solution is as follows:
Fe+2Fe3+＝3Fe2+；
Fe+Cu2+＝Fe2++Cu；
the addition of the iron powder replaces copper ions and simultaneously leads Fe in the leaching solution3+Reduction to Fe2+. The reaction of replacing copper ions by iron powder is influenced by the pH value of the solution, and researches find that the pH value of the leaching solution is controlled to be 0.8-1.6, so that the good effect can be achieved by replacing and removing copper by the iron powder once.
In some embodiments, in step S100, the ratio of the sum of the molar amounts of the copper ions and the iron ions to the molar amount of the iron powder in the leaching solution is 1: (1.1-1.4). Research shows that when the adding amount of the iron powder is 1.1 times of the theoretical content, the content of copper ions in the leaching solution is less than 4.9mg/L, and the removal rate is high. And when the addition amount of the iron powder is continuously increased, the removal rate of copper ions is basically unchanged, and the pH value of the leaching solution is increased. Further, the ratio of the sum of the molar amounts of the copper ions and the iron ions to the molar amount of the iron powder in the leaching solution is 1: (1.1-1.2).
In some of these embodiments, the reaction time for the shift reaction in step S100 is 15min to 90 min.
In the embodiment of the present invention, the reaction temperature of the displacement reaction in step S100 is 60 ℃, which is the same as the temperature of the aging-water leaching process, i.e., the leachate obtained by the aging-water leaching process may be directly subjected to step S100.
Step S200: under the protection of protective gas, continuously adding iron powder into the copper-removing leaching solution until the pH value of the copper-removing leaching solution is 3.3-3.6, and filtering to obtain a first aluminum-removing leaching solution.
From Ksp(AlPO4)＝9.84×10-21、Ksp(FePO4·2H2O)＝9.91×10-16Known as AlPO4Prior to FePO4·2H2And (4) precipitating O. Therefore, the invention adjusts the leaching solution to make the aluminum ion impurity be AlPO4Removing in the form of precipitate, wherein the iron powder can perform a replacement reaction with hydrogen ions in the copper removal leaching solution to consume the hydrogen ions in the copper removal leaching solution so as to increase the pH value of the copper removal leaching solution, and simultaneously, the iron powder can be used as a neutralizer to reduce Fe3+And preventing iron phosphate precipitation.
In some of these embodiments, the protective gas is selected from one of nitrogen and argon. Under the protection of protective gas, Fe in the leaching solution can be avoided2+Contact reaction with oxygen to further reduce Fe in the leaching solution3+。
Step S300: under the protection of protective gas, adjusting the pH value of the first aluminum-removing leaching solution to 2.5-3.0, adding a di (2-ethylhexyl) phosphonic acid extracting agent to extract aluminum ions in the first aluminum-removing leaching solution, and taking a water phase to obtain a second aluminum-removing leaching solution.
The bis (2-ethylhexyl) phosphonic acid extractant will generally preferentially extract Fe3+Ion(s)Therefore, in step S300, the protection of the protective gas prevents Fe in the leaching solution2+Is oxidized into Fe by oxygen3+Reducing Fe in leaching solution3+The concentration of (c). Meanwhile, the pH value of the leachate is adjusted to 2.5-3.0, and in the pH range, the extraction rate of the bis (2-ethylhexyl) phosphonic acid extractant on aluminum ions is high, so that the aluminum ions in the leachate can be effectively removed.
In some of these embodiments, the bis (2-ethylhexyl) phosphonic acid extractant has a mass percentage of bis (2-ethylhexyl) phosphonic acid of 30% and the solvent of the bis (2-ethylhexyl) phosphonic acid extractant is sulfonated kerosene.
In some of these embodiments, the volume ratio of the bis (2-ethylhexyl) phosphonic acid extractant to the first dealumination leachate is 1: (1-2). Preferably, the volume ratio of the bis (2-ethylhexyl) phosphonic acid extractant to the first aluminium-removal leach solution is 1: 1. Under the proportion, the extracting agent has better extracting effect.
Step S400: and adjusting the pH value of the second aluminum-removal leaching solution to 2.0-4.0, adding La-Al-Ca ternary carbonate for reaction, and filtering to obtain an impurity-removal leaching solution.
Fluoride ions are removed through the La-Al-Ca ternary carbonate, the fluoride ions in the leachate can be further removed, and the removal rate can reach 96 percent at most.
Further, adjusting the pH value of the second aluminum-removing leaching solution to 2.5-3.5. In the pH range, the La-Al-Ca ternary carbonate has higher removal rate of fluoride ions. Preferably, the pH value of the second aluminum-removing leaching solution is adjusted to 3.0, and the removal rate of fluoride ions by the La-Al-Ca ternary carbonate can reach 96%.
In some embodiments, the La-Al-Ca ternary carbonate is added in an amount of 3g/L to 6 g/L. When the dosage of the La-Al-Ca ternary carbonate is lower than 3g/L, the fluorine removal rate increases faster along with the increase of the dosage of the La-Al-Ca ternary carbonate; when the dosage of the La-Al-Ca ternary carbonate reaches 3g/L, the increase trend of the fluorine removal rate is higher than 90 percent and tends to be flat.
In some of these embodiments, the temperature of the reaction is 20 ℃ to 70 ℃ in step S400. In this reaction temperature range, the fluorine removal rate was about 95%. It was found that the fluorine removal rate of the La-Al-Ca ternary carbonate decreased with the increase of the reaction temperature, probably because the fluoride precipitate formed in the aqueous solution increased in solubility with the increase of the temperature, and fluorine ions re-dissolved in the solution to decrease the fluorine removal rate. Therefore, the reaction temperature is preferably 20 ℃ to 40 ℃.
In some embodiments, in step S400, the reaction time is 50min to 120 min. Further, in step S400, the reaction time is 60 to 90 min.
The treatment method is used for treating the recovered leachate of the lithium iron phosphate positive electrode material, removing impurity aluminum by replacing impurity copper with iron powder and combining chemical precipitation and extraction, removing impurity fluorine by adopting La-Al-Ca ternary carbonate, and simultaneously adjusting the pH range of each stage in the treatment process, so that higher impurity removal rate can be achieved. The concentration of copper ions in the leachate treated by the treatment method is within 4.9mg/L, the concentration of aluminum ions is within 10mg/L, and the removal rate of fluorine ions can reach 96%.
The invention further provides application of the treatment method for recovering the leachate of the lithium iron phosphate positive material in recovering waste lithium iron phosphate batteries.
A method for recovering waste lithium iron phosphate batteries is characterized in that a recovery leachate of a lithium iron phosphate positive electrode material is treated by adopting the treatment method for the recovery leachate of the lithium iron phosphate positive electrode material.
The treatment method of the leachate recovered from the lithium iron phosphate positive electrode material according to the present invention is further described below with reference to specific examples.
Example 1:
in this example, leachate obtained by a slaking-water leaching process is used as a raw material, and the contents of main impurity elements, namely copper and aluminum, in the leachate are detected as shown in table 1.
TABLE 1
Figure BDA0003369604120000081
Figure BDA0003369604120000091
In this example, the influence of the amount of iron powder on the copper ion removal rate was examined. Reacting for 1 hour at the reaction temperature of 60 ℃ and the stirring speed of 300r/min, and investigating the influence of different iron powder addition amounts on the copper ion removal rate, wherein the specific iron powder addition amounts are shown in Table 2.
TABLE 2
Figure BDA0003369604120000092
Referring to fig. 2, the content of copper ions in the leachate solution varies according to the amount of iron powder used. It can be seen that the concentration of the copper ions in the leaching solution gradually decreases with the increase of the addition amount of the iron powder, and when the amount of the iron powder is more than 1.1 times of the theoretical amount, the concentration of the copper ions in the leaching solution is kept below 4.9mg/L, so that the technical target requirement can be met when the amount of the iron powder is more than 1.1 times of the theoretical amount.
Further, referring to FIG. 3, the pH of examples 1-1 to 1-5 was also measured. It can be seen that the pH of the leachate gradually increases as the amount of iron powder used increases, because the iron powder also undergoes a displacement reaction with hydrogen ions in the leachate to generate hydrogen gas as the amount of iron powder used increases, thereby increasing the pH of the leachate.
Example 2:
in this example, leachate obtained by a slaking-water leaching process is used as a raw material, and the contents of main impurity elements, namely copper and aluminum, in the leachate are detected as shown in table 1. In this example, the influence of the initial pH of the leachate on the copper ion removal rate was investigated. Reacting for 15 minutes at the reaction temperature of 60 ℃, the use amount of iron powder is 1.2 times of the theoretical amount, and the stirring speed is 300r/min, and investigating the influence of the initial pH of different leachates on the removal rate of copper ions, wherein the specific initial pH of the leachates is shown in Table 3.
TABLE 3
Examples of the invention Example 2-1 Examples 2 to 2 Examples 2 to 3 Examples 2 to 4 Examples 2 to 5
Initial pH of leachate 0.4 0.8 1.2 1.6 2.0
Referring to FIG. 4, the relationship between the initial pH of the leachate and the copper ion concentration of the reacted solution is shown. As can be seen, in the range of pH 0.4-2.0, as the initial pH of the leaching solution becomes higher, the copper ion content of the solution after reaction is reduced from 1116mg/L to 1.6mg/L and then is increased to 722.2 mg/L. The copper removal effect is better within the range of pH 0.8-1.6.
Example 3:
this example used the copper removal leachate of examples 2-3 as a starting material for chemical precipitation to remove aluminum. In this example, the influence of the pH of the copper removal leach solution on the aluminum removal rate was investigated. At the reaction temperature of 70 ℃ and the stirring speed of 400r/min, iron powder is respectively added into the copper-removing leaching solution to adjust the pH value to be shown in table 4. And respectively measuring the content of aluminum ions and the content of aluminum slag in the solution after the reaction. FIG. 5 is a graph showing the change of the aluminum ion content and the aluminum slag content in the solution after the reaction according to pH. As can be seen from the figure, the chlorine content in the leachate gradually decreases with the increase of the pH, and when the pH is increased from 2.96 to 3.62, the Al content gradually decreases from 1380mg/L to 30mg/L, however, as the pH value of the reaction solution is kept at about 3.6 without changing with the continuous addition of the iron powder and the extension of the reaction time, the solution begins to generate grey floccules, so that the aluminum ions in the leachate cannot be further removed by increasing the dosage of the iron powder.
TABLE 4
Examples of the invention Example 3-1 Examples 3 to 2 Examples 3 to 3 Examples 3 to 4 Examples 3 to 5
pH 2.96 3.08 3.28 3.56 3.62
Example 4:
this example investigates the effect of system pH on the defluorination effect of La-Al-Ca ternary carbonate. 6 parts of fluorine-containing zinc sulfate solution with different pH conditions are selected to test the fluorine removal effect, and the dosage of the La-Al-Ca ternary carbonate is 6 g/L. The pH of 6 parts of the zinc sulfate fluoride-containing solution is shown in Table 5.
TABLE 5
Figure BDA0003369604120000112
Referring to FIG. 6, it is a curve showing the fluorine removal amount of the fluorine-containing zinc sulfate solution by La-Al-Ca ternary carbonate pair and the fluorine ion content of the reacted solution under different pH conditions. It can be seen that the defluorination efficiency increases with increasing pH when the pH of the solution is 1 to 3, reaching a maximum of 96% at pH 3. Further increase in pH resulted in a decrease in the fluorine removal rate. At pH < 3, the lower the pH, the higher the acid concentration, the more easily the precipitate is dissociated, and the fluorine ions are re-dissolved in the solution, so that the fluorine removal rate is greatly reduced. When the pH is greater than 3, the pH is changed to OH-And F-Extremely similar in electronegativity and ionic radius, OH increases with pH-Gradually occupy the active sites on the surface of the fluorine removing agent, thereby reacting with F-Generates competitive adsorption to reduce the fluorine removal rate.
Example 5:
in this example, the fluorine-containing zinc sulfate solution of examples 4 to 3 was selected to further study the influence of the reaction time on the fluorine removal rate of the La-Al-Ca ternary carbonate, and the dosage of the La-Al-Ca ternary carbonate was 6 g/L. See table 6 for each set of reaction times.
TABLE 6
Figure BDA0003369604120000111
FIG. 7 is a graph showing the fluorine removal amount of La-Al-Ca tribasic carbonate with respect to fluorine-containing zinc sulfate solution and the fluorine ion content in the solution after the reaction as a function of the reaction time. It can be seen that when the reaction time is less than 60min, the fluorine removal rate rapidly increases as the reaction time is prolonged. The reaction time is further prolonged and the slow rise of the fluorine removal rate is likely to be the reason for the lower concentration of fluorine ions in the solution. When the reaction time reaches 90min, the concentration of the fluorine ions in the solution is not changed any more, and the reaction tends to saturate and the fluorine removal rate reaches the maximum value (96%).
Example 6:
this example further investigated the effect of the amount of La-Al-Ca ternary carbonate on the fluorine removal rate. The fluorine-containing zinc sulfate solution of the embodiment 4-3 is selected and added with La-Al-Ca ternary carbonate with different addition amounts for reaction for 90min, and then the fluorine removal rate and the fluorine ion content in the solution after the reaction are tested. The amount of La-Al-Ca tribasic carbonate used in this example is shown in Table 7.
TABLE 7
Figure BDA0003369604120000121
The effect of example 6-1 to example 6-6 on the fluorine removal rate can be seen in FIG. 8. It can be seen that when the dosage of the fluorine removing agent is less than 3g/L, the fluorine removing efficiency is increased rapidly along with the increase of the dosage of the fluorine removing agent, and finally the fluorine concentration is reduced from 287mg/L to 30 mg/L. After the dosage of the fluorine removing agent is more than 3g/L, the fluorine removing rate is higher than 90 percent. The dosage of the fluorine removal agent is increased, and the increase trend of fluorine removal efficiency tends to be smooth; the dosage of the fluorine removing agent is increased from 3g/L to 6g/L, and the final fluorine concentration is gradually reduced from 30mg/L to 12 mg/L.
Example 7:
this example further investigated the effect of reaction temperature on the fluorine removal rate. The fluorine-containing zinc sulfate solution of the embodiment 4-3 is selected, added with 3g/L of La-Al-Ca ternary carbonate, reacted for 90min under different temperature conditions, and then tested for the fluorine removal rate. The reaction temperatures for the various groups of this example are shown in Table 8.
TABLE 8
Figure BDA0003369604120000131
Referring to FIG. 9, the effect of different temperature conditions on the fluoride removal rate of La-Al-Ca ternary carbonate is shown. It can be seen that the fluorine removal rate of the La-Al-Ca ternary carbonate decreases with the increase of the temperature, which is probably because in the aqueous solution, the fluoride precipitate generated after the fluorine removal of the fluorine removal agent increases with the increase of the temperature, and the fluorine ions are re-dissolved in the solution to decrease the fluorine removal rate. In the temperature range of 20-70 ℃, the La-Al-Ca ternary carbonate has high fluorine removal rate which is about 95 percent, and can effectively remove fluorine ions in the leaching solution.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, so as to understand the technical solutions of the present invention specifically and in detail, but not to be understood as the limitation of the protection scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. It should be understood that the technical solutions provided by the present invention, which are obtained by logical analysis, reasoning or limited experiments, are within the scope of the present invention as set forth in the appended claims. Therefore, the protection scope of the present invention should be subject to the content of the appended claims, and the description and the drawings can be used for explaining the content of the claims.

Claims (10)

1. The treatment method for the leachate recovered from the lithium iron phosphate positive material is characterized by comprising the following steps of:
adjusting the pH value of the leaching solution to 0.8-1.6, then adding iron powder for replacement reaction, and filtering to obtain a copper-removed leaching solution;
under the protection of protective gas, continuously adding iron powder into the copper-removing leaching solution until the pH value of the copper-removing leaching solution is 3.3-3.6, and filtering to obtain a first aluminum-removing leaching solution;
under the protection of protective gas, adjusting the pH value of the first aluminum-removal leaching solution to 2.5-3.0, adding a di (2-ethylhexyl) phosphonic acid extractant to extract aluminum ions in the first aluminum-removal leaching solution, and taking a water phase to obtain a second aluminum-removal leaching solution;
and adjusting the pH value of the second aluminum-removal leaching solution to 2.0-4.0, adding La-Al-Ca ternary carbonate for reaction, and filtering to obtain an impurity-removal leaching solution.
2. The method according to claim 1, wherein in the step of adding iron powder to perform a displacement reaction, a ratio of a sum of molar amounts of copper ions and iron ions in the leachate to a molar amount of the iron powder is 1: (1.1-1.4).
3. The method for treating leachate caused by recycling lithium iron phosphate positive electrode material according to claim 1, wherein the reaction time of the replacement reaction is 15 to 90 min.
4. The method for treating leachate recovered from the lithium iron phosphate positive electrode material according to claim 1, wherein the mass percentage of di (2-ethylhexyl) phosphonic acid in the di (2-ethylhexyl) phosphonic acid extractant is 30%, and the solvent of the di (2-ethylhexyl) phosphonic acid extractant is sulfonated kerosene.
5. The method for treating leachate recovered from the lithium iron phosphate positive electrode material according to claim 1, wherein the volume ratio of the bis (2-ethylhexyl) phosphonic acid extractant to the first aluminum-removal leachate is 1: (1-2).
6. The method for treating leachate recovered from the lithium iron phosphate positive electrode material according to claim 1, wherein the amount of the La-Al-Ca ternary carbonate added is 3g/L to 6 g/L.
7. The method for treating leachate recovered from the lithium iron phosphate positive electrode material according to claim 1, wherein in the step of adding the La-Al-Ca ternary carbonate for reaction, the reaction temperature is 20 ℃ to 70 ℃.
8. The method for treating leachate recovered from the lithium iron phosphate positive electrode material according to claim 1, wherein in the step of adding La-Al-Ca ternary carbonate for reaction, the reaction time is 50min to 120 min.
9. The method for treating leachate recovered from the lithium iron phosphate positive electrode material according to claim 8, wherein in the step of adding La-Al-Ca ternary carbonate for reaction, the reaction time is 60 to 90 min.
10. The application of the treatment method for recovering leachate of lithium iron phosphate positive electrode material according to any one of claims 1 to 9 in recovering waste lithium iron phosphate batteries.
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