| With the vigorous development of the new energy vehicle industry,power batteries represented by lithium-ion batteries have begun to be widely used.Lithium iron phosphate battery(LFP)has gradually replaced lithium cobalt oxide battery(LCO)and ternary lithium battery(NCM)and become the most widely used power battery due to the advantages of low cost,good stability,and high cycle life.With the wide applications of lithium-ion batteries,a large number of spent lithium-ion batteries were produced.The effective recycling of these spent lithium-ion batteries is not only conducive to the protection of the environment,but also cyclically utilizes the high-value metals,which is of great significant to the green and sustainable development of the lithium-ion battery industry.Since there is only lithium as valuable metal in lithium iron phosphate,the selective recovery method was used to recover lithium.The formic acid-hydrogen peroxide system was used for selective leaching of lithium ions.Through single-factor condition optimation,the optimal leaching conditions with the concentration of formic acid as 0.8 mol/L,solid-liquid ratio as 50 g/L,initial volume fraction of hydrogen peroxide as 8%,leaching temperature as 60℃ and reaction time as 1 h were obtianed.Under these optimal conditions,the leaching efficiencies of lithium and iron reached 99.9%and 0.05%,respectively.Then through the multi-factor response surface experiment,the optimal leaching conditions with the concentration of formic acid as 0.87 mol/L,the solid-liquid ratio as 49.46 g/L,the initial volume fraction of hydrogen peroxide as 5.22%,and the reaction temperature as 67.2℃ were obtained.It can be seen that both the optimal leaching conditions obtained by these two optimized methods were very similar.Lithium was recovered from the filtrate after leaching by sodium carbonate precipitation method,and the primary precipitation efficiency and purity reached up to 85.05%and 99.9%,respectively.In order to decrease the dosage of oxidants,even no addition of oxidants and simultaneously realize the recovery of valuable metals from lithium cobalt oxide battery,the novel combined recovery process of lithium cobalt oxide and lithium iron phosphate were proposed based on the requirements of oxidation of ferrous ions in lithium iron phosphate and reduction of trivalent cobalt ions in lithium cobalt oxide.In the conbined recovery system,the experiments were designed based on stoichiometry.The optimal leaching conditions with the concentration of sulfuric acid as 0.75 mol/L,the total sulfuric acid as 120%of the theoretical value,the addition time of lithium cobaltate as 15 min,and the molar ratio of lithium iron phosphate to lithium cobalt oxide as 1:1 and the temperature as 60℃were obtained.Under these conditions,the leaching efficiencies of lithium and cobalt ions reached up to 99.92%and 81.11%,respectively.The recovery efficiencies of cobalt and lithium ions from the filtrate were 97.71%and 78.54%,respectively,while the purity of these two ions were up to 99.94%and 99.95%,respectively.Finally,a preliminary studies on the recovery reaction route of lithium iron phosphate-formic acid-hydrogen peroxide system and the combined recovery reaction route of lithium iron phosphate-lithium cobalt oxide were carried out.In the lithium iron phosphate-formic acid-hydrogen peroxide system,the ferrous ions in lithium iron phosphate lattice were selectively and in-situ oxidated to ferric ions in acidic and high redox potential environments,realizing the leaching of lithium ions into the solution.However,in the lithium iron phosphate-sulfuric acid-lithium cobalt oxide combined recovery system,the structure of lithium iron phosphate was first completely destroies by sulfuric acid to release ferrous ions.Then lithium cobalt oxide was added to realize the ex-situ oxidation reaction between cobalt ions in the lithium cobalt oxide and ferrous ions in an acidic environment. |
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