(565g) Role of Oxalate in Metal Separation and Recovery

Metal separation and recovery is an essential component in terms of sustainability for any process which involves precious, valuable metals. These metals need to be extracted efficiently using a clean and green process with minimal environmental impact. Oxalic acid is an organic acid and does not emit any harmful pollutants like SO_x and NO_X which are common in similar metal extraction processes done using sulufric acid or nitric acid. Oxalate is a conjugate base of oxalic acid and a ligand that can donate two pairs of electrons to a metal atom to form stable complexes. The solubility of these oxalate complexes is metal and oxidation state dependent, which permits the exploitation of solubility differences for metal separation. For example, separation of metals from the cathode of spent lithium-ion batteries can be efficiently performed using oxalic acid where lithium forms a soluble oxalate complex and other transition metal ions can form insoluble complexes. Possibility of soluble oxalate complexes also expands it’s use as a leaching reagent in the application such as iron removal from silica-based materials (clay and quartz) and metal recovery from spent catalysts. In this work, unique properties of oxalate along with the reaction conditions required to separate and recover metals such as lithium and cobalt will be discussed. In addition a thorough literature search of oxalate metal dissolution and separation processes has been conducted and the results will be summarized with experimental measurements.