Classifications

• • 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
  • C22B26/00—Obtaining alkali, alkaline earth metals or magnesium
  • C22B26/10—Obtaining alkali metals
  • C22B26/12—Obtaining lithium
• • 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
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/005—Preliminary treatment of scrap
• • 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
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
  • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
• • 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
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
  • C22B3/16—Extraction of metal compounds from ores or concentrates by wet processes by leaching in organic solutions
  • C22B3/1608—Leaching with acyclic or carbocyclic agents
  • C22B3/1616—Leaching with acyclic or carbocyclic agents of a single type
  • C22B3/165—Leaching with acyclic or carbocyclic agents of a single type with organic acids
• • 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
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/006—Wet processes
  • C22B7/007—Wet processes by acid leaching
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/54—Reclaiming serviceable parts of waste accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/84—Recycling of batteries or fuel cells

Definitions

• Lithium Iron Phosphate (LFP) battery recycling Related Application
• This application claims the benefit under 35 U.S.C. ⁇ 119(e) of U.S. provisional application number 63/228,331 filed August 2, 2021, having the title, “Lithium Iron Phosphate (LFP) battery recycling” by inventors, Eric Gratz and Kee-Chan Kim, which is hereby incorporated by reference herein in its entirety.
• Background Recycling of battery materials has garnished substantial attention as an increasing number of electric vehicles (EVs) approach their end of useful lifespan.
• EVs and a multitude of appliances and equipment that are more commonly reliant on rechargeable batteries rather than internal combustion engines, contribute to the generation of a recycling stream of exhausted (spent) batteries.
• An aspect of the invention described herein provides a method for recycling lithium iron phosphate batteries, the method including: adding an oxidizing agent to a recycling stream of lithium iron phosphate (LiFePO 4 ) batteries to form a leach solution; filtering the leach solution to remove a residue and obtain a lithium rich solution; modifying pH of the lithium rich solution for filtering impurities and obtaining a purified Li solution; and adding a precipitant to the purified Li solution thereby precipitating a lithium compound.
• An embodiment of the method prior to adding the oxidizing agent further includes shredding the recycling stream of lithium iron phosphate batteries to obtain granular powder of batteries.
• An embodiment of the method, prior to filtering further includes heating the leach solution.
• the leach solution is heated to a temperature in a range between 20 oC to 100 oC.
• the residue includes at least one of: graphite, and FePO 4 .
• modifying the pH of the lithium rich solution further includes adding a basic solution.
• the lithium rich solution is modified to attain the pH in a range between 5 to 13.
• An embodiment of the method further includes achieving a concentration of 0.3-3.0 M of the oxidizing agent to LiFePO4.
• An embodiment of the method further includes achieving a concentration of 0.5-2.2M of the oxidizing agent to the LiFePO 4 .
• An embodiment of the method further includes prior to adding an oxidizing agent, adding an acid solution.
• the acid solution is selected from an inorganic acid or an organic acid.
• the inorganic acid is at least one selected from: sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.
• the organic acid is at least one selected from: acetic acid, formic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, and adipic acid.
• the precipitant is at least one selected from: sodium carbonate, sodium phosphate, phosphoric acid, oxalic acid, and sodium oxalate.
• the lithium compound is at least one selected from lithium carbonate (Li 2 CO 3 ), lithium phosphate (Li 3 PO 4 ), and lithium oxalate (Li 2 C 2 O 4 ).
• An embodiment of the method further includes maintaining pH of the leach solution in a range between 1-6 or 2-6.
• the oxidizing agent or the oxidant is at least one selected from: a peroxide (O 2 2- ), a persulfate (S 2 O 8 2- ), a sulfate (SO 4 2 -), a hypoclorite (ClO-), a chlorite (ClO2-), a chlorate (ClO3-), a perchlorate (ClO4-), a nitrate (NO 3 -), a nitrous oxide (N 2 O), a nitrogen dioxide (NO 2 ), and a halogen.
• the oxidant is at least one selected from: hydrogen peroxide, sodium persulfate, and ammonium persulfate.
• An aspect of the invention described herein provides a method for recycling lithium iron phosphate batteries, the method including: adding at least one of: an oxidizing agent, and an acid, to a recycling stream of powdered lithium iron phosphate (LiFePO4) batteries to form a leach solution; maintaining the temperature of the leach solution from 20 oC to 100 oC; filtering the leach solution to remove graphite and FePO4 to obtain a lithium rich solution; modifying pH of the lithium rich solution from 11 to 13 for filtering impurities and obtaining a purified Li solution; and adding a precipitant to the purified Li solution thereby precipitating a lithium compound.
• LiFePO4 powdered lithium iron phosphate
• An embodiment of the method further includes after filtering, obtaining purified graphite by at least one process selected from: acid leaching, and froth flotation.
• An aspect of the invention described herein provides a method for recycling lithium iron phosphate batteries, the method including: adding an acid to a recycling stream of powdered lithium iron phosphate (LiFePO 4 ) batteries to form a leach solution; maintaining the temperature of the leach solution from 20 oC to 100 oC; filtering the leach solution to remove graphite and FePO 4 to obtain a lithium rich solution; modifying pH of the lithium rich solution from 11 to 13 for filtering impurities and obtaining a purified Li solution; and adding a precipitant to the purified Li solution thereby precipitating a lithium compound.
• LiFePO 4 powdered lithium iron phosphate
• FIG 1 is a schematic drawing of a method for recycling lithium iron phosphate batteries which includes adding an oxidizing agent to the recycling stream of lithium iron phosphate (LiFePO4) batteries to form a leach solution and heating to leach lithium into the solution by oxidizing iron phosphate.
• the leach solution is then filtered to remove solid FePO4 and graphite and obtain a lithium rich solution.
• the remaining impurities in the lithium rich solution are precipitated and filtered to obtain a pure lithium solution.
• the lithium in the solution is precipitated using a precipitant.
• the aspects of inventions described herein provide recycling processes for end-of-life lithium iron phosphate batteries which focuses on recovery of lithium compounds from cathode materials of these batteries.
• Lithium Iron Phosphate (LFP) batteries do not have a reliance on relatively rare nickel and cobalt. While NMC batteries may enjoy a slightly greater charge density, LFP batteries are fabricated from relatively inexpensive materials, of which lithium is the most sought after. The current methods for lithium iron phosphate recycling are not economically favorable. Therefore, a recycling stream directed to Lithium recovery is important and enhancements to recover graphite increase the overall efficiency of the method.
• NMC Nickel Manganese Cobalt
• a method for recycling lithium iron phosphate batteries described herein includes adding an oxidizing agent to a granular powder from a recycling stream of lithium iron phosphate (LiFePO4) batteries to form a leach solution and maintaining the leach solution at between 20 o C – 100 o C to leach lithium.
• LiFePO4 lithium iron phosphate
• a number of oxidizing agents may be employed, and these may be complemented by an organic or inorganic acid as discussed further below.
• Oxidizing agents may include peroxides (O 2 2- ), persulfates (S 2 O 8 2- ), sulfates (SO 4 2- ), hypoclorites (ClO-), chlorites (ClO2-), chlorates (ClO3-), perchlorates (ClO4-), nitrates (NO3-), nitrous oxides (N 2 O), nitrogen dioxide (NO 2 ), halogens (Cl 2 , Br 2 , I 2 ), etc.
• the oxidizing agents may be combined with an inorganic acid (such as sulfuric, hydrochloric, nitric or phosphoric acid) or an organic acid (including mono-carboxylic or dicarboxylic acids).
• FIG. 1 shows a recycling process 100 which commences with the gathering of a recycling stream 110 of spent batteries 105, such as from retired EVs, or retired batteries from EVs, which is processed to be in granular powder form 110.
• An oxidizing agent 112 and optional acid 114 combine with the granulated materials from the recycling stream in a leach solution 120.
• the oxidizing agent 112 may achieve a concentration of 0.3-3.0 M of the oxidizing agent to the concentration of LiFePO4 (molar ratio), and preferably will achieve a concentration of 0.5-2.2M of the oxidizing agent to the concentration of LiFePO 4 .
• the optional acid 114 may be an organic or inorganic acid added prior to heating to leach lithium into the solution, such that the acid is generally selected based on removal of iron from the leach solution.
• the leach solution is filtered at 130 to separate graphite and FePO 4 135 (such as in the form of a filter cake) from a lithium rich solution 132.
• the solution contains a substantial amount of the lithium contained in the recycling stream, attempting to strike a balance between leaching useful lithium without allowing excessive iron to dissolve into the leach solution.
• a strong base 134 is added to the lithium rich solution to increase the pH to between 5-13 for filtering impurities to form a purified Li solution 140, and preferably to attain a pH in a range between 11-13.
• Remaining impurities precipitate and are filtered out at 136, and a further precipitant 138 is added to the purified Li solution to precipitate a charge material including a lithium compound, suitable for use in a recycled battery.
• the recovered lithium compound is directed based on the precipitant added to the pure Li solution. For example, lithium is recovered as lithium carbonate (Li 2 CO 3 ) 142 by adding sodium carbonate to the purified Li solution.
• lithium may be recovered as lithium phosphate (Li 3 PO 4 ) 144 by adding sodium phosphate or phosphoric acid to the purified Li solution.
• Li lithium oxalate 146 (Li2C2O4)
• Other suitable charge material compounds may be precipitated based on the added materials to combine with the solution 140.
• Graphite may be recovered from the graphite and FePO 4 filter cake 135 by removing the FePO4138 by dissolving FePO4 in strong acid and washing or by froth flotation to selectively separate graphite 152 from FePO 4 precipitate 154 as shown at 150 Lithium recovery in industrial processes including battery recycling is accomplished by precipitation from solutions.
• lithium is selectively leached from lithium iron phosphate batteries, the resulting processes are capable of recovering lithium at high efficiencies with high purity technical or battery grade lithium products.
• lithium ion is leached by an oxidizing agent with or without an acid from a mixture of cathode and anode powder of spent LiFePO 4 batteries.
• the oxidizing agent is added at a concentration of 0.3 – 3 molar ratio to LiFePO4.
• the preferable concentration is 0.5 – 2.2 molar ratios.
• the acid is selected from an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, or from an organic acid.
• the organic acid is preferably a mono-carboxylic acid having the formula RCOOH; R: H, or alkyl (C n H 2n+1 ; n: 1 – 6) or a dicarboxylic acid having the formula HO 2 C- (CH2)n-CO2H; n: 0 – 8.
• monocarboxylic acid are acetic acid, formic acid, propionic acid, or butyric acid.
• dicarboxylic acid are oxalic acid, malonic acid, succinic acid, or adipic acid.
• the acid concentration in the leaching solution is from 0M to 5M.
• the preferred concentration is 0.5 -1 molar ratio of acid to lithium ion.
• the preferred concentration is 3- 5 molar ratio of acid to lithium ion.
• a base such as NaOH may be added to adjust the pH of the leaching solution pH at 2 - 6.
• the ratio for amount of solid LiFeSO 4 to the amount of acid solution is 100 g – 1000 g per liter; preferably 200 g – 500 g per liter.
• the leaching temperature is maintained from 20 °C to 100 °C depending on the selected oxidant, or the acid.
• the processed mixture is filtered, and the residue is washed with deionized water.
• the residue is black solid containing graphite and FePO 4 .
• the impurities in the filtrate are removed by adjusting the pH from 5 to 13, preferably from 11 to 13.
• the pH is adjusted by adding a strong base such as sodium hydroxide solution or potassium hydroxide solution at a concentration of 0 – 5 M.
• the precipitates from impurities are removed by filtration to obtain a lithium-ion enriched filtrate.
• the lithium-ion enriched filtrate can be concentrated by evaporating the water from the filtrate.
• the lithium is recovered as lithium carbonate (Li2CO3) by adding sodium carbonate as lithium phosphate (Li 3 PO 4 ) by adding sodium phosphate or phosphoric acid, or as lithium oxalate (Li2C2O4) by adding oxalic acid or sodium oxalate to the concentrated solution.
• Lithium hydroxide or carbonate can be obtained from lithium oxalate by heating, for example by thermal conversion at 350 °C to 500 °C.
• graphite may also be recovered. The graphite is recycled from the black solid by leaching the FePO4 or by froth floatation.
• the black solid is added to a diluted (2- 9 M) or concentrated inorganic acid, such as sulfuric acid, hydrochloric acid or nitric acid, preferably 4 – 6 M acid solutions.
• a diluted (2- 9 M) or concentrated inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid, preferably 4 – 6 M acid solutions.
• the mixture is heated and stirred at 25 °C – 80 °C.
• Purified graphite is collected by filtration and rinsed with 1 – 5 M inorganic acid.
• the purified graphite is then washed with deionized water until the filtrate becomes neutral pH.
• the graphite is floated, and the iron phosphate precipitates or sediments.
• the methods include acid only leaching, oxidant only leaching, acid and oxidant leaching with various acids such as inorganic and organic acids. Strong inorganic acid dissolves LFP and lithium ions leach with iron and phosphate ions. The coprecipitation of lithium ions with iron hydroxide precipitate results in reduced efficiency of lithium recovery and requires removal of iron impurities.
• dilute acid solutions lithium ions do not leach from LFP solid without assistance of an oxidant. However, lithium ions in LFP are selectively leached in a dilute acid solution ([H 2 SO 4 ]/[LFP]: ⁇ 0.6) with hydrogen peroxide as an oxidant.
• dilute acid solution system hydrogen peroxide oxidizes ferrous ions in LFP and liberates Li ions from LFP. Further acid helps dissolve the liberated lithium ions from LFP into the solution thereby balancing the charges. Sulfuric acid is a favorable choice among the inorganic acids. However, high concentrations of sulfate ions interfere the recovery of Li2CO3 because sodium sulfate in the lithium recovery solutions is often coprecipitated due to the moderate solubility of Na 2 SO 4 . Therefore, dilute sulfuric acid solutions are preferrable for selective Li leaching and Li2CO3 recovery.
• Sodium persulfate (Na 2 S 2 O 8 ) is a strong oxidant and is able to quantitatively and completely leach out the lithium in LFP by oxidative liberation of Li ions from LiFePO4 in aqueous solution without any acid. However, because the byproduct of the reaction is sulfate ions, Li2CO3 recovery is observed to be reduced. In some embodiments, ammonium persulfate (NH4)2S2O8 is used to reduce the interference.
• Environmentally friendly organic acid is an alternative acid for selective lithium ion leaching from LFP instead of strong inorganic acids.
• organic acids such as formic acid and acetic acid are weak acids in aqueous solutions and have carboxylic functional group for metal ion chelating, these acids were observed to selectivity leach lithium ion from the LFP via oxidative liberation of lithium ion from LiFe(II)PO4 to Fe(III)PO4. Hydrogen peroxide was observed to be a good oxidant for these reactions.
• Acetate is a stronger chelating agent than formate. Therefore, the required molar ratio of acetate to LFP was lesser compared to the required molar ratio of formate to LFP, thereby resulting in lower costs.
• the inventions described herein are the most practical methods.
• Example 1 Sulfuric Acid with Hydrogen Peroxide Selective lithium ion leaching from LFP was examined in various concentration of sulfuric acid solution with or without hydrogen peroxide (molar ratio of sulfuric acid to LFP [H2SO4]/[LFP] from 0.6 to 4.9; molar ration of H2O2 to LFP [H2O2]/[LFP]: 2.2 or 0; LFP (g) : Water (mL): 1 : 5; temperature: not controlled from ambient temp, 30 – 50 C; reaction / stirring time: 3 – 4 hours after completion of adding hydrogen peroxide).
• the impurity removal was performed at pH: 7 – 8, and Li2CO3 recovery was observed to have improved (56 % vs. 30 %).
• the improvement of Li ions is because of reduced loss of Li ion by impurity removal; low impurity concentration, and lower pH adjustment thereby introducing less sodium ions. Hydrogen peroxide is necessary to selectively leach lithium ion in dilute sulfuric acid solution.
• the presence of iron and phosphate ions impacts lithium recovery as lithium carbonate.
• Some lithium ions are precipitated as Li 3 PO 4 with ready-existing phosphate ions upon raising the solution pH to remove ferric ions as Fe(OH) 3 causing the loss of Li for Li 2 CO 3 recovery.
• the impurities (Cu, Al, Fe, Ni, Co, Mn, etc.) in the Li rich solution were removed by precipitating the impurities as metal hydroxides at pH: 7 – 12.
• the solution pH was adjusted depending on the nature of impurities present in the solution. If the impurities include Cu, Al and Fe, then pH was adjusted to 7 – 8. If the impurities contained Ni, Co and Mn, the pH was adjusted to 11 – 13.
• Lithium ions in the leaching solution are precipitated by adding sodium carbonate (1.25 times of the stoichiometric amount).
• the sodium carbonate is added as a solid or as a saturated solution to high concentration Li solution. It was observed that adding sodium carbonate as saturated solution resulted in better yield and purity of lithium.
• Table 1 The results of multiple tests using different recycling streams, and including the purity and yield of lithium are tabulated in Table 1.
• Example 2 Using Sodium Persulfate (Na 2 S 2 O 8 ) as oxidant Selective leaching of lithium ions from LFP was achieved by oxidation of Fe 2+ in the LFP to Fe 3+ in aqueous solutions.
• Sodium persulfate was used as the oxidant for Fe 2+ in the LFP in an aqueous solution. In this example, acid was not required, and water was used as the solvent. Sodium persulfate was slowly added to the LFP disperse solution mixture.
• the conditions for the reaction were: LFP (g) to water (mL) ratio: 1 : 2; molar ratio of Na 2 S 2 O 8 to LFP, [Na 2 S 2 O 8 ] / [LFP]: 1.00 – 1.37; temperature: ambient; stirring time: 1 – 4 hours.
• the molar ratio of [Na2S2O8]/[LFP] was calculated and observed to be about 1.37 to achieve 100 % Li leaching.
• the Li leaching percentage dropped to 75 % if plant shredded spent LFP battery material was used which is a mixture of cathode and anode with some contamination of Ni, Mn and Co from NMC spent batteries. If sodium persulfate is contacted with water, it is converted to acid and hydrogen peroxide as shown in the following equation. Therefore, the solution acidity increases and Fe is leached from LFP. The sodium sulfate from sodium persulfate hinders the ability to recover the leached Li from the solution as Li2CO3. Therefore, the recovery yield of Li2CO3 was low ( ⁇ 50 %) with purity below 99 %, even though the leaching efficiency is 100 %. The results of multiple tests including the purity and yield of lithium are tabulated in Table 2.
• Example 3 Formic Acid with Hydrogen Peroxide Formic acid (HCOOH) was used as an alternative acid for selective Li leaching from LFP because of the suitable pKa (3.75), which makes leaching solution less acidic thereby reducing the chance of Fe leaching.
• HCOOH Hydrogen Peroxide Formic acid
• the leached solution pH increases about 1 unit or more. Because the leaching solution is less acidic compared to strong inorganic acids (e.g, H 2 SO 4 , HCl or HNO 3 ), LiFeSO 4 or FeSO 4 dissolution was significantly suppressed.
• strong inorganic acids e.g, H 2 SO 4 , HCl or HNO 3
• LiFeSO 4 or FeSO 4 dissolution was significantly suppressed.
• 4.5 – 6 molar ratio of formic acid to LFP was used with 2.2 molar ratio of hydrogen peroxide.1 : 4 of LFP (g) to H2O (mL) ratio was sufficient to complete the leaching. The ratio can be further optimized.
• the Li ions in LFP are liberated from the LFP solid, and byproduct FePO 4 remains as a solid in the leaching process.
• Formic acid in the aqueous solution is favorable for the oxidative reaction by hydrogen peroxide and provides pH buffering effect during the leaching process.
• the results of multiple tests including the purity and yield of lithium are tabulated in Table 3.
• the conditions for the reactions are as follows: LFP (g) to Water (mL) ratio: 1 : 2 (4 for commercial samples); molar ratio of AcOH to LFP, [AcOH]/[LFP]: 1 – 3; [NaOH]/[AcOH]: 0 - 0.5 (molar ratio); [H2O2]/[LFP]: 2.2 – 2.5 (molar ratio); Stirring time: 3 hours – overnight. Temperature: 30 – 50 °C. Acetic acid / sodium acetate buffer solutions were prepared for the leaching experiments by adding 1/3 molar ratio of sodium hydroxide to acetic acid. Complete lithium leaching was observed even for one-to-one molar ratio of AcOH to LFP.
• Acetic acid is a good ligand and required one-to-one molar ratio for completing the leaching process. Acetic acid is less expensive than formic acid thereby has a cost benefit.
• Table 4 Results using Acetic Acid with Hydrogen Peroxide * The deviation could be due to possible experimental error.

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