Preparation Of LiFePO₄from Pyrite Cinder Using Hydrometallurgical And Hydrothermal Process

China has produced large amount of pyrite cinder due to the production of sulfuricacid, which accordingly brings serious environmental pollution problems. Thus, more andmore researchers focused on recycling the pyrite cinder containing60%iron into allkinds of iron compounds in recent years. Especially, LiFePO4as a key cathode materialof Li-ion energy storage has attracted a lot of attention. In this project, we synthesized thehigh performance LiFePO4using the cheap pyrite cinder as raw materials, which isexpected to reduce the production cost of LiFePO4and promote its mass applications inenergy storage.First, pure FeSO4solution is produced by a hydrometallurgical process from pyritecinder. The hydrometallurgical process was designed as follows: pyrite cinderâ†'reduction calcinationâ†'vitriol lixiviationâ†'dissolutionâ†'reaction with NH4OHâ†'precipitation. We systematically studied the effects of reducer dosage, calcinationtemperature, acid leaching temperature, leaching time and acid concentration on the ironleaching ratio. The optimized leaching parameters can be expressed as10%reducerdosage, calcination at800℃for20min in N2,30%sulfuric acid with an excesscoefficient of1.2, and leaching at70℃~80℃for20min. The ruthner method was usedto remove the impurity in the leaching solution and we investigated the parametersaffecting the purity of FeSO4solution. The optimized ruthner process can be expressed asfollows: NH4OH as precipitant at80℃,0.1%neutral polyacrylamide as flocculants.Under the above conditions, FeSO4solution with a high purity was successivelyproduced.Secondly, the obtained pure FeSO4solution was used as the iron precursor tohydrothermally synthesize the nano-sized LiFePO4. Especially, we design thehydrothermal process based on FeSO4, Li2CO3and H3PO4, in which the excessive Li inthe reacted solution can be recycled to lower the production cost of LiFePO4. H2SO4was added into the precursor solution to improve the composition homogeneity. It wasobserved that H2SO4addition can greatly increase the particle size of LiFePO4. Thenano-sized LiFePO4demonstrates good electrochemical performances of154.1mAh/gunder0.1C, retaining capacity of142.5mAh/g after50cycles, and coulombic efficiencyover98%.