A team from the Beijing University of Chemical Technology has used a formic acid-hydrogen peroxide system for selective leaching of lithium ions from spent lithium iron phosphate batteries. A paper on their process was published in the Journal of Power Sources.

The team achieved optimal leaching conditions by single-factor optimization: formic acid concentration of 0.8 mol/L, solid–liquid ratio of 50 g/L, initial hydrogen peroxide volume fraction of 8%, temperature of 60° C, and a reaction time of 1 hour. Under these conditions, the extent of lithium leaching reaches 99.9%, while iron leaching is only 0.05%. 

The optimal leaching conditions were verified by multi-factor response surface experiments and the results obtained by the two methods were similar. The primary precipitation extent and purity of the lithium product achieved 85.05% and 99.9%, respectively, using sodium carbonate precipitation to recover lithium ions from the leach filtrate.

“In this study, formic acid, an organic acid that is less acidic, green, easily decomposed and less polluting than inorganic acids, was used as the leaching agent and hydrogen peroxide was used as the oxidizing agent. The proposed recovery technology has the advantages of simple, short process, good performance, high lithium concentration in leaching solution with almost no iron ion and high purity of lithium carbonate,” the authors wrote.

Source: Green Car Congress