Abstract:

In the process of extracting lithium from salt lake brines by the extraction method，the extraction capacity of the tributylphosphate-FeCl₃-kerosene co⁃extraction system will decrease or fail after multiple cycles of use.The recovery of Fe（Ⅲ） in the spent extractant is of great significance to the sustainable development of recovery of lithium from salt lake brines.In this paper，a high concentration of hydrochloric acid system was used to simulate the spent lithium extractant.Fe（Ⅲ） in the spent lithium extractant was used as iron source and NH₄H₂PO₄ solution as phosphorus source to prepare iron phosphate in the heterogeneous system.The effects of reaction time，amount of ammonia，concentration of NH₄H₂PO₄ solution，reaction temperature and stirring speed on product yield，particle size（D₅₀） and Fe/P molar ratio were studied.The research showed that high⁃purity monoclinic iron phosphate dihydrate were obtained under optimized process conditions.The product′s yield was 89.43%，Fe/P molar ratio was 0.98，D₅₀ was 1.81 μm，the specific surface area was 37.38 m²/g，and the water content was 19.64%，which met the industry standard for battery⁃grade iron phosphate.The electrochemical performance of the LiFePO₄/C prepared from self⁃made iron phosphate as the precursor was excellent.The initial discharge specific capacity was 146.58 mA·h/g，the initial charge-discharge efficiency was 94.90%，and the capacity retention rate after 80 cycles of constant current charge and discharge was 91.72% at 0.1C.The research showed that the use of NH₄H₂PO₄ solution for reverse extraction and precipitation could effectively recover Fe（Ⅲ） from spent lithium extractants and prepare battery⁃grade iron phosphate.

Key words: lithium extractant, iron phosphate, lithium iron phosphate