Short review of oxalic acid-based hydrometallurgical systems for processing lithium-ion batteries, electronic wastes, spent catalysts, and red mud

Oxalic acid-based hydrometallurgical processes have attracted attention due to the unique combination of acidity, complexation, redox activity, and precipitation behaviour of oxalic acid. However, the advantages of oxalate systems cannot be evaluated solely by metal extraction, as separation efficiency, product quality, reagent consumption, and process integration are also critical. This short review summarizes the applications of oxalic acid in spent lithium-ion batteries, electronic wastes, spent catalysts, and red mud processing. The roles of oxalic acid in metal dissolution, complex formation, selective precipitation, and precursor preparation are discussed, with emphasis on metal recovery, impurity behaviour, and reagent recycling. Oxalate chemistry shows potential for selective recovery and intermediate production in various secondary resources, but its performance strongly depends on feed composition and downstream processing requirements. Current limitations include insufficient information on impurity accumulation, oxalate balance, product quality, and long-term recycling performance. Further studies should focus on realistic feedstocks, complete material balances, and practical evaluation of oxalate recovery and reuse.