Researchers from China’s Tsinghua University have developed a mechano-chemical method for extracting lithium from used lithium iron phosphate (LiFePo) batteries.
The process offers an alternative to pyrometallurgy and hydrometellurgy methods, while generating three chemical products and easily recyclable waste water within five minutes.
The method involves discharging the batteries in a saturated sodium-chloride solution to prevent them combusting and manually separating the cathode, anode and plastic separator.
The cathode was crushed to separate aluminium foil using a mesh screen. The team then used mechanochemistry to treat the remaining cathode material powder (C/LiFePO4) with the solid-phase oxidant co-grinding agent, sodium persulfate (Na2S2O8).
Further steps involved water leaching and vacuum filtration to remove iron phosphate. This was followed by chemical precipitation, using sodium phosphate to remove the lithium ions in solution, in the form of lithium phosphate (Li3PO4).
Finally the remaining sodium-sulphate in the solution was precipitated and removed via evaporation and crystallisation.
By recovering each chemical product, the resulting wastewater can be recycled.
The method provides an alternative to pyrometallurgy— which requires high energy consumption and flue gas release, and hydrometallurgy—which requires acid–base reagents and may produce wastewater containing heavy metals.
Research into biometallurgy is still in the scientific research stage.
Researcher Kang Lui said: “I think dissembling the lithium-ion batteries was the most difficult part of the project, because the electrolyte and organic solvent will volatilise during the recycling process under laboratory conditions. If this is not carried out in a fume hood, it may cause harm to the operator.”
An abstract on the process read: “The results show that by using solid-phase oxidant sodium persulfate (Na2S2O8) as a mechanochemical co-grinding agent, and by carrying out the mechanochemical reaction under optimal conditions (rotary speed of 600 rpm, reaction time of 5.0 min, and Na2S2O8: LiFePO4 mass ratio of 2:1), 99.7 wt% of the lithium in LiFePO4 can be selectively released and converted to lithium sulphate (Li2SO4), while the iron phosphate maintains an olivine frame structure. Lithium can then be recovered as a lithium phosphate (Li3PO4) product by integrated water leaching and chemical precipitation.”