Methods and applications for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate.

Abstract

This invention relates to the field of wastewater treatment technology, and more particularly to a method and application for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate. The method includes the steps of: removing impurity ions from the phosphogypsum leachate to obtain a first treated liquid; the impurity ions include fluoride ions, calcium ions, and magnesium ions; setting a cathode and iron as the anode in the first treated liquid, and mixing the resulting lapis lazuli precipitate with lithium phosphate and a carbon source, followed by calcination, to obtain lithium iron phosphate. By adjusting the pH to first remove impurity ions from the phosphogypsum leachate, and then using iron as a sacrificial electrode, a large amount of Fe is generated in situ using an electrochemical method. 2+ With PO4 in the first treatment solution 3‑ The reaction enables the recovery of phosphorus from phosphogypsum leachate in the form of vivianite, which is then used as a raw material to prepare lithium iron phosphate via the molten salt method.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method and application for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate. Background Technology

[0002] Phosphogypsum leachate is formed by the accumulation and leaching of phosphogypsum produced during the wet-process phosphoric acid production. For every ton of phosphoric acid produced, 4.5-5.5 tons of phosphogypsum are generated. Furthermore, the comprehensive utilization rate of phosphogypsum is very low, and the current stockpile exceeds 700 million tons, increasing at a rate of approximately 80 million tons annually. Due to the moisture inherent in phosphogypsum itself and natural rainfall, a large amount of phosphogypsum leachate is generated. The main characteristics of phosphogypsum leachate are its high phosphorus content, acidic environment, and potential environmental hazards. Because it contains a large amount of soluble phosphates, direct discharge into water bodies without effective treatment can lead to eutrophication, algal blooms, and disruption of the aquatic ecological balance, posing a serious threat to water quality and the ecological environment.

[0003] Currently, the main methods for treating phosphogypsum leachate are chemical precipitation, biological treatment, and physical treatment. Chemical precipitation involves adding metal ion salts to phosphorus-containing wastewater, causing a chemical reaction that produces phosphate precipitates. Phosphorus is then transferred from the solution to the solid through solid-liquid separation. This method is simple to operate and has good phosphorus removal efficiency, but it generates a large amount of solid waste, causing secondary pollution. Biological treatment relies on microorganisms and is more economical and practical than chemical methods. However, its phosphorus removal stability is poor, easily affected by wastewater composition and environmental factors, and it produces a large amount of sludge. Physical methods include adsorption, membrane separation, ion exchange, and electrodialysis, but they suffer from high adsorbent costs and regeneration issues, high membrane equipment and maintenance costs, high ion exchange resin costs, and high energy consumption. Furthermore, these methods have high requirements for water quality; the presence of other ions or particulate matter can affect their effectiveness.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method and application for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate, aiming to solve the problems of secondary pollution, poor stability and high cost of existing methods for removing phosphorus from phosphogypsum leachate.

[0006] The technical solution of the present invention is as follows:

[0007] A method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate includes the following steps:

[0008] The impurity ions in the phosphogypsum leachate are removed to obtain the first treated solution; the impurity ions include fluoride ions, calcium ions and magnesium ions.

[0009] In the first treatment solution, a cathode and iron are set as the anode, and an electric current is passed through to obtain lapis lazuli precipitate.

[0010] The lapis lazuli precipitate was mixed with lithium phosphate and a carbon source and then calcined to obtain lithium iron phosphate.

[0011] The method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate, wherein the step of removing impurity ions from the phosphogypsum leachate to obtain a first treated solution includes:

[0012] The phosphogypsum leachate was mixed with the first pH adjuster to adjust the pH to the first pH value. After the first reaction, the first solid-liquid separation was carried out to obtain the pretreated solution.

[0013] The pretreated solution is mixed with a second pH adjuster to adjust the pH to a second pH value. After a second reaction, a second solid-liquid separation is performed to obtain the first treated solution.

[0014] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the first pH adjuster and the second pH adjuster are both alkaline solutions, and the alkaline solutions are free of calcium, magnesium and aluminum.

[0015] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the first pH adjuster and the second pH adjuster are independently selected from one or more of ammonia water, sodium hydroxide solution, and potassium hydroxide solution.

[0016] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the first pH value is 3.5-4.5; and the second pH value is 6-7.5.

[0017] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the current is a constant current.

[0018] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate further includes, before applying an electric current, introducing an inert atmosphere into the first treatment solution.

[0019] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the carbon source includes one or more of citric acid, glucose, and sucrose.

[0020] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the molar ratio of the lapis lazuli precipitate, the lithium phosphate and the carbon source is (1-1.1):(1-1.1):(0.1-0.3).

[0021] The method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate, wherein the calcination temperature is 850-950℃, the heating rate of the calcination is 4-6℃ / min, and the calcination time is 5-7 hours.

[0022] Application of a method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate in the production of lithium batteries.

[0023] Beneficial Effects: This invention provides a method and application for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate. The method includes the following steps: removing impurity ions from the phosphogypsum leachate to obtain a first treated solution; the impurity ions include fluoride ions, calcium ions, and magnesium ions; setting a cathode and iron as the anode in the first treated solution, passing an electric current to obtain lapis lazuli precipitate; mixing the lapis lazuli precipitate with lithium phosphate and a carbon source, and then calcining the mixture to obtain lithium iron phosphate. This invention utilizes a first pH adjuster and a second pH adjuster to first remove impurity ions from the phosphogypsum leachate, and then uses iron as a sacrificial electrode to generate a large amount of Fe in situ using an electrochemical method. 2+ With PO4 in the first treatment solution 3- The reaction process recovers phosphorus from phosphogypsum leachate in the form of vivianite, which is then used as a raw material to produce lithium iron phosphate via the molten salt method. This process achieves a phosphorus recovery rate of over 99% in the phosphogypsum leachate, and yields over 7.4 kg of lithium iron phosphate per ton of phosphogypsum leachate. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of a method for recovering phosphorus from phosphogypsum leachate to prepare lithium iron phosphate according to the present invention.

[0025] Figure 2 The image shows the XRD characterization of the first solid in Example 1.

[0026] Figure 3 The image shows the XRD characterization of the second solid in Example 1.

[0027] Figure 4 The image shows the XRD characterization of the precipitate in Example 1.

[0028] Figure 5 The image shows the XRD characterization of the calcined product in Example 1. Detailed Implementation

[0029] This invention provides a method and application for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0031] Phosphorus (P) is an essential element for the growth and reproduction of organisms. With population growth and industrial technological development, global demand for phosphate rock has steadily increased, from approximately 4.8 billion tons in 2002 to approximately 6.4 billion tons in 2017. Unfortunately, phosphate rock is a non-renewable resource, and its consumption rate far exceeds its regeneration rate. Recovering phosphorus from phosphogypsum leachate can not only effectively reduce the demand for phosphate rock but also avoid environmental problems caused by excessive phosphate emissions.

[0032] However, existing methods for treating phosphogypsum leachate have problems such as secondary pollution, poor phosphorus removal stability, and high costs.

[0033] Based on this, such as Figure 1 As shown, the present invention provides a method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate, comprising the following steps:

[0034] Step S10: Remove impurity ions from the phosphogypsum leachate to obtain the first treated solution; the impurity ions include fluoride ions, calcium ions and magnesium ions;

[0035] Step S20: Set a cathode and iron as an anode in the first treatment solution, pass an electric current through it, and obtain blue iron ore precipitate;

[0036] Step S30: The blue iron ore precipitate is mixed with lithium phosphate and a carbon source and then calcined to obtain lithium iron phosphate.

[0037] In this embodiment, impurity ions in the phosphogypsum leachate are first removed, and then iron is used as a sacrificial electrode to generate a large amount of Fe in situ using an electrochemical method. 2+ With PO4 in the first treatment solution 3-The reaction process recovers phosphorus from the phosphogypsum leachate in the form of lapis lazuli [Fe3(PO4)2·8H2O]. Using lapis lazuli [Fe3(PO4)2·8H2O] as a raw material, lithium iron phosphate is prepared with lithium phosphate and a carbon source. This method has the advantages of short reaction time, high efficiency, and simple operation, making it suitable for large-scale application in wastewater treatment. After treatment by this process, the phosphorus recovery rate in the phosphogypsum leachate can reach over 99%, and more than 7.4 kg of lithium iron phosphate can be produced from each ton of phosphogypsum leachate.

[0038] Specifically, due to the very low solubility of Fe3(PO4)2 (K... sp =1.04×10 -24 Therefore, as the reaction proceeds, phosphorus is continuously transferred from the solution to the precipitate, thus being removed, and a removal rate of 99% can be achieved.

[0039] In some embodiments, step S10, the step of removing impurity ions from the phosphogypsum leachate to obtain a first treated solution, includes:

[0040] Step S11: Mix the phosphogypsum leachate with the first pH adjuster, adjust the pH to the first pH value, and after the first reaction, perform the first solid-liquid separation to obtain the pretreated solution;

[0041] Step S12: Mix the pretreatment solution with the second pH adjuster, adjust the pH to the second pH value, and after the second reaction, perform a second solid-liquid separation to obtain the first treatment solution.

[0042] In this embodiment, the pH value of the phosphogypsum leachate is adjusted by using a first pH adjuster and a second pH adjuster to remove impurity ions (including F) from the phosphogypsum leachate. - Ca 2+ Mg 2+ (etc.) can yield high-purity blue iron ore precipitate.

[0043] Specifically, the method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate utilizes a first pH adjuster and a second pH adjuster to adjust the pH of the phosphogypsum leachate to a second pH value. Then, using an iron sheet as an electrode, ferrous ions are generated in situ using an electrochemical method, avoiding the use of additional chemical reagents. Phosphorus is recovered in the form of high-value-added Fe3(PO4)2, which can be used as a material for the preparation of lithium iron phosphate. Simultaneously, because iron is used as a sacrificial anode, waste iron resources can be fully utilized.

[0044] In some embodiments, both the first pH adjuster and the second pH adjuster are alkaline solutions, which are free of calcium, magnesium, and aluminum. The alkaline solution is used to adjust the pH of the phosphogypsum leachate and the pretreatment solution to remove fluoride and calcium ions from the leachate. The avoidance of using alkaline solutions containing calcium, magnesium, and aluminum is primarily to prevent the introduction of new impurities into the phosphogypsum leachate.

[0045] In some embodiments, the first reaction takes 1-2 hours. During this reaction, the phosphogypsum leachate and the first pH adjuster form a precipitate, thereby removing fluoride ions and some calcium ions from the phosphogypsum leachate. The second reaction takes 1-2 hours to allow the pretreated solution to form a precipitate with the second pH adjuster, thus completely removing calcium ions from the pretreated solution.

[0046] In some embodiments, the first pH adjuster and the second pH adjuster are independently selected from, but not limited to, one or more of ammonia, sodium hydroxide solution, and potassium hydroxide solution. Using one or more of ammonia, sodium hydroxide, and potassium hydroxide as the first pH adjuster or the second pH adjuster can regulate the pH, causing fluoride ions and calcium ions to precipitate and be removed from the leachate.

[0047] In a preferred embodiment, both the first pH adjuster and the second pH adjuster are selected from ammonia.

[0048] In some embodiments, the first pH value is 3.5-4.5; the second pH value is 6-7.5; adjusting the pH of the phosphogypsum leachate to 3.5-4.5 using the first pH adjuster can make F - The removal rate reached 90%, Ca 2 + The removal rate reached 58%; then, by using a second pH adjuster to further adjust the pH value between 6 and 7, the Ca removal rate was reduced. 2+ The removal rate reached 98%.

[0049] In a preferred embodiment, the first pH value is 4; the second pH value is 6.5; when the pH is controlled at this value, F - Removal rate and Ca 2+ The removal rate reached its maximum, effectively removing impurity ions from the leachate.

[0050] In some implementations, the current is a constant current.

[0051] In some embodiments, the current is less than 0.5A; preferably, the current is between 0.05A and 0.1A.

[0052] In some embodiments, the cathode is selected from, but not limited to, commonly used electrode materials such as iron sheets, titanium sheets, and carbon cloth.

[0053] In some embodiments, before the current is applied, an inert atmosphere is introduced into the first treatment solution to control the dissolved oxygen in the first treatment solution to a low level to avoid affecting the electrochemical reaction.

[0054] In some embodiments, the inert atmosphere includes, but is not limited to, one or more of nitrogen, helium, neon, and argon.

[0055] Specifically, before powering on, an inert gas (argon or nitrogen, etc.) is passed through the first treatment liquid for 20 minutes to remove dissolved oxygen from the first treatment liquid.

[0056] In some embodiments, the carbon source includes one or more of citric acid, glucose, and sucrose. The carbon source is added during the preparation of lithium iron phosphate so that the final lithium iron phosphate exists in the form of LiFePO4 / C.

[0057] In some embodiments, the molar ratio of the lapis lazuli precipitate, the lithium phosphate, and the carbon source is (1-1.1):(1-1.1):(0.1-2). If the ratio of lapis lazuli to lithium phosphate exceeds this range, the purity of the synthesized lithium iron phosphate will decrease. The molar ratio range of the carbon source can be increased, but this will affect the thickness of the carbon layer coating on the lithium iron phosphate surface, thus impacting the performance of lithium iron phosphate as an electrode material.

[0058] In a preferred embodiment, the molar ratio of the lapis lazuli precipitate, the lithium phosphate, and the carbon source is 1:1:0.3.

[0059] In some embodiments, the calcination temperature is 850-950°C, the heating rate is 4-6°C / min, and the calcination time is 5-7 hours. Calcination under these parameters yields lithium iron phosphate with high purity; excessively low or high temperatures may generate impurity phases, affecting the formation of lithium iron phosphate.

[0060] In a preferred embodiment, the calcination temperature is 900°C, the heating rate of the calcination is 5°C / min, and the calcination time is 6 hours, under which lithium iron phosphate with excellent electrochemical performance is obtained.

[0061] In some embodiments, the calcination process is carried out under an inert atmosphere, which includes, but is not limited to, one or more of nitrogen, helium, neon, and argon.

[0062] In some embodiments, in step S10, after adjusting the pH to a first pH value, a sufficient reaction is required before solid-liquid separation; in step S20, after adjusting the pH to a second pH value, a sufficient reaction is required before solid-liquid separation. In both steps S10 and S20, after adjusting the pH value, the reaction is carried out for 1 hour before solid-liquid separation. This sufficient reaction can improve the removal rate of impurity ions.

[0063] In some embodiments, in step S30, after the current is applied, i.e. during the electrochemical reaction, the pH change of the solution is detected, and the pH of the solution is adjusted to below 9 by acid control.

[0064] In addition, the present invention also provides an application of a method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate in the preparation of lithium batteries.

[0065] In this embodiment, phosphorus is recovered from phosphogypsum leachate in the form of lapis lazuli [Fe3(PO4)2·8H2O] using the method described above. Then, lithium iron phosphate is prepared using this lapis lazuli as a raw material, which can be used as a positive electrode material for lithium batteries to prepare lithium batteries.

[0066] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0067] Example 1

[0068] The pH of the 1:1 leached phosphogypsum leachate was adjusted to 4 using ammonia water. After reacting for 1 hour, solid-liquid separation was performed to obtain a first solid and a pretreated liquid. The 1:1 leached phosphogypsum leachate means that it was obtained by percolation of water and phosphogypsum in a mass ratio of 1:1. In this embodiment, the phosphogypsum leachate was obtained by percolation of 1 ton of water and 1 ton of phosphogypsum.

[0069] The first solid obtained by separation was characterized by XRD, and its XRD pattern is shown below. Figure 2 As shown in the figure, the first solid obtained is Ca5(PO4)3F. The results, as shown in Table 1, are as follows: F... - The removal rate reached 90%, Ca 2+ The removal rate reached 58%.

[0070] The pH of the pretreated solution was adjusted to 6.5 using ammonia. After reacting for 1 hour, solid-liquid separation was performed to obtain a second solid and the first treated solution. The second solid was characterized by XRD, and its XRD pattern is shown below. Figure 3As shown in the figure, the second solid obtained is CaPO3(OH)·2H2O. The results, as shown in Table 1, indicate that Ca... 2+ The removal rate reached 98%.

[0071]

[0072] Using 2*2cm iron sheets as the anode and cathode, 40mL of pretreated fluid was processed to remove F. - and Ca 2+ Mg 2+ The 1:1 leachate of phosphogypsum (first treatment solution) was reacted for 190 minutes under a constant current of 0.1 A. A precipitate and a dephosphorized solution were obtained. The precipitate was characterized by XRD, as shown below. Figure 4 As shown, the formation of vivianite was demonstrated, and the phosphorus concentration in the solution decreased to 6.97 ppm after the reaction, with a phosphorus removal rate of 99.77%.

[0073] The obtained precipitate (0.5016 g) was mixed with 0.1158 g Li3PO4 and 0.0576 g anhydrous citric acid and ground for 30 minutes. The mixture was then calcined at 900 °C for 6 hours under an argon atmosphere in a tube furnace with a heating rate of 5 °C / min. The calcined product was characterized by XRD. Figure 5 As shown, the synthesis of LiFePO4(LFP) is demonstrated.

[0074] Example 2

[0075] Using a 2*2cm iron sheet as the anode and a 2*2cm titanium plate as the cathode, 40mL of pretreated material (F-removal process described in Example 1) was processed. - and Ca 2+ Mg 2+ The 1:1 leachate of phosphogypsum was reacted at a constant current of 0.1 A for 190 minutes. A precipitate and a dephosphorized solution were obtained. XRD characterization of the precipitate confirmed the formation of vivianite. After the reaction, the phosphorus concentration in the solution decreased to 2.85 ppm, achieving a phosphorus removal rate of 99.91%. 0.5016 g of the obtained precipitate was mixed with 0.1158 g of Li3PO4 and 0.0576 g of anhydrous citric acid and ground for 30 minutes. The mixture was then calcined at 900 °C for 6 hours under an argon atmosphere in a tube furnace with a heating rate of 5 °C / min. XRD characterization of the calcined product confirmed the synthesis of LiFePO4.

[0076] Example 3

[0077] Using a 2*2cm iron sheet as the anode and a 2*2cm carbon cloth as the cathode, 40mL of pretreated material (F-removal) from Example 1 was processed. - and Ca2+ Mg 2+ The 1:1 leachate of phosphogypsum was reacted under a constant current of 0.1 A for 190 minutes. A precipitate and a dephosphorized solution were obtained. XRD characterization of the precipitate confirmed the formation of vivianite. After the reaction, the phosphorus concentration in the solution decreased to 1.43 ppm, achieving a phosphorus removal rate of 99.95%. 0.5016 g of the obtained precipitate was mixed with 0.1158 g of Li3PO4 and 0.0576 g of anhydrous citric acid and ground for 30 minutes. The mixture was then calcined at 900 °C for 6 hours under an argon atmosphere in a tube furnace with a heating rate of 5 °C / min. XRD characterization of the calcined product confirmed the synthesis of LiFePO4.

[0078] In summary, this invention provides a method and application for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate. The method includes the following steps: removing impurity ions from the phosphogypsum leachate to obtain a first treated solution; the impurity ions include fluoride ions, calcium ions, and magnesium ions; setting a cathode and iron as the anode in the first treated solution, passing an electric current to obtain a blue iron precipitate; mixing the blue iron precipitate with lithium phosphate and a carbon source, and then calcining the mixture to obtain lithium iron phosphate. This invention utilizes a first pH adjuster and a second pH adjuster to first remove impurity ions from the phosphogypsum leachate, and then uses iron as a sacrificial electrode to generate a large amount of Fe in situ using an electrochemical method. 2+ With PO4 in the first treatment solution 3- The reaction process recovers phosphorus from phosphogypsum leachate in the form of lapis lazuli, which is then used as a raw material to produce lithium iron phosphate. This process achieves a phosphorus recovery rate of over 99% in the phosphogypsum leachate, and can ultimately produce over 7.4 kg of lithium iron phosphate per ton of phosphogypsum leachate.

[0079] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate, characterized in that, Including the following steps: The impurity ions in the phosphogypsum leachate are removed to obtain the first treated solution; the impurity ions include fluoride ions, calcium ions and magnesium ions. In the first treatment solution, a cathode and iron are set as the anode, and a constant current of 0.05A-0.1A is passed through to carry out an electrochemical reaction to obtain lapis lazuli precipitate; During the electrochemical reaction, the pH change of the solution is detected, and the pH of the solution is adjusted to be below 9 by acid control; The lapis lazuli precipitate was mixed with lithium phosphate and a carbon source and then calcined to obtain lithium iron phosphate. The step of removing impurity ions from the phosphogypsum leachate to obtain the first treated solution includes: The phosphogypsum leachate was mixed with the first pH adjuster to adjust the pH to the first pH value. After the first reaction for 1-2 hours, the first solid-liquid separation was carried out to obtain the pretreated solution. The pretreated solution is mixed with a second pH adjuster to adjust the pH to a second pH value. After a second reaction of 1-2 hours, a second solid-liquid separation is performed to obtain the first treated solution. The first pH adjuster and the second pH adjuster are independently selected from one or more of ammonia water, sodium hydroxide solution, and potassium hydroxide solution; the first pH value is 3.5-4.5; the second pH value is 6-7.5; Before the current is applied, the process also includes: introducing an inert atmosphere into the first processing liquid; The carbon source includes one or more of citric acid, glucose, and sucrose; The calcination treatment temperature is 850-950℃, the heating rate of the calcination treatment is 4-6℃ / min, and the calcination treatment time is 5-7 hours.

2. The method for recovering phosphorus from phosphogypsum leachate for the preparation of lithium iron phosphate according to claim 1, characterized in that, The molar ratio of the lapis lazuli precipitate, the lithium phosphate, and the carbon source is (1-1.1):(1-1.1):(0.1-2).

3. The application of the method for recovering phosphorus from phosphogypsum leachate as described in any one of claims 1-2 for the preparation of lithium iron phosphate in the preparation of lithium batteries.

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