Facile recovery of lithium as Li2CO3 or Li2O from α-hydroxy-carboxylic acid chelates through pyrolysis and the decomposition mechanism

Chelation of lithium with readily available α-hydroxy carboxylic acids is a sustainable recovery method from spent Li-ion battery wastes as well as a possible lithium extraction method. In this work pyrolytic decomposition of a series of selected lithium chelates of glycolic, lactic, malic and tartaric acid were studied and compared with lithium acetate as a potential lithium recovery method from chelates. In thermogravimetric analysis, the four α-hydroxy carboxylic acid chelates studied showed lower initial decomposition temperatures in the 313–356 °C range, in comparison to the lithium acetate with an initial decomposition temperature of 444 °C. The ease of decomposition of α-hydroxy carboxylic acid chelates may be due to their favorable decomposition pathways through dimerization and tetramerization of α-hydroxy acids via esterification and free radical coupling mechanisms leading to a complex mixtures of products; including alkenes, dienes and enones. The lithium α-hydroxy carboxylic acid chelate pyrolysis residue formed above 300 °C was identified as lithium carbonate and further heating above 700 °C, lithium carbonate decomposes to lithium oxide, allowing the recovery of lithium as Li2CO3 or Li2O.