Application Foundation Research On The Selective Recovery Of Lithium From Spent Iron Phosphate Batteries

In order to alleviate the current supply of fossil fuels and effectively deal with the greenhouse effect,new energy vehicles with rechargeable lithium-ion batteries as power sources have begun to flourish.Currently,lithium iron phosphate(LFP)batteries are widely used in new energy vehicles due to their low cost of preparation,higher energy density,good stability,and good cycle performance.At the same time,a large number of spent lithium iron phosphate batteries are also produced.It is of great significance to effective recycle the spent lithium iron phosphate batteries.On one hand,in order to effectively solve the adverse effects of spent lithium iron phosphate batteries on the natural environment and human health.On the other hand,recycling the lithium from spent lithium iron phosphate batteries can effectively alleviate the shortage of lithium supply in China and ensure the sustainable and healthy development of the lithium-ion battery industry.Since the lithium iron phosphate battery does not contain other high-value metals except lithium,a selective recovery method for lithium,while retaining iron in the leaching residue was developed in this work.In the hydrochloric acid-sodium hypochlorite system.The experimental results showed that the leaching efficiency of lithium and iron were 95.59%and 0.047%within 20 min under the optimal operating conditions the optimal operating conditions:0.6 mol/L hydrochloric acid,Li:H:ClO(mol/mol/mol)=1:1.3:0.6,and 25℃.After leaching,lithium was recovered from the filtrate.The primary precipitation efficiency of lithium was 80.1%,and the purity of the obtained lithium carbonate product reached up to 99.7%.In order to solve the impurity problem in the process and further improve the selective leaching performance of lithium,ozone was used for selective leaching research.In the hydrochloric acid-ozone system.The experimental results showed that the leaching efficiencies of lithium and iron were 99.81%and 0.07%within 60 min under the optimal operating conditions 0.4mol/L hydrochloric acid solution,Li:H(mol/mol)=1:1,the ozone concentration of 10±1 mg/L,the penetration rate of 1.5 L/min,and 20℃.After leaching,lithium was recovered from the filtrate.The primary precipitation efficiency of lithium was 89%,and the purity of the obtained lithium carbonate product reached up to 99.9%.The leaching process of the hydrochloric acid-sodium hypochlorite system and the hydrochloric acid-ozone system were studied.In the hydrochloric acid-sodium hypochlorite system,the oxidant was added in excess at one time,and only the rapid leaching of the crystal lattice.The hydrochloric acid-ozone system continued to pass ozone,and the leaching process was mainly divided into two parts:the first part was the rapid leaching of the crystal lattice within 0-20 min;the second part was the slow oxdation of the solution in 30-60 min.Finally,the selective leaching mechanism of lithium from spent lithium iron phosphate was studied.The XRD and XPS characterization showed that the lithium iron phosphate was oxidized to iron phosphate,but the crystal structure has not changed.According to the experimental and characterization results,the selective leaching mechanism of lithium from spent lithium iron phosphate was proposed:under acidic environment and high redox potential condition,the lithium iron phosphate was oxidized to iron phosphate,and the lithium was leached into the solution.