Closing the loop in conventional rare Earth extraction: Treatment of acid crack leach residue using organic acids

Global decarbonisation and uptake of electronic devices have dramatically increased the demand for rare earth elements (REE). To aid supply expansion of these elements, it is beneficial to extract them from secondary sources. This study applied technospheric mining to extract REE from acid crack and leach (ACL) residue, an industrial byproduct from the conventional rare earth extraction process. A two-stage leaching process involving oxalic acid and ethylenediaminetetraacetic acid (EDTA) was utilised to recover REEs from the material. The ACL residue behaved significantly differently from primary ores. Rapid dissolution of P, Fe, and REE occurred, and the REE remained in the solution, necessitating the flowsheet modifications, such as additional oxalate to recrystallise the REEs. A secondary oxalate leach resulted in a significant improvement in overall REE recovery of approximately 65 %. This manuscript demonstrates the applicability of recyclable reagents to increase REE production from an existing waste stream, thereby contributing to sustainability.