Life cycle analysis of the ionic liquid leaching process of valuable metals from electronic wastes

In recent years, ionic liquids have generated a high interest as an ecological alternative in various processes as a replacement for traditional volatile organic solvents, one of these processes is the leaching of valuable metals from electronic waste or waste from electrical and electronic equipment (WEEE), a very relevant topic these days in the circular economy framework. Therefore, the present work's objective is to perform a life cycle analysis of the leaching process of valuable metals extracted from these wastes for the ionic liquids 1-butyl-3-methyl-imidazolium hydrogen sulfate (Bmim HSO₄), 1-methylimidazolinium hydrogen sulfate (Hmim HSO₄), 1-butyl-3-methylimidazolium bromide (Bmim Br), 1-butyl-3-methylimidazolium chloride (Bmim Cl), using a “cradle-to-gate” life cycle analysis approach. For the leaching inventory, a 60% ionic liquid concentration at 60 °C was considered, based on previous studies where high copper and cobalt extractions are achieved by using Bmim HSO₄ and Hmim HSO₄, on the other hand, high silver and gold extractions are achieved with Bmim Br and Bmim Cl. When performing the impact analysis, it was observed that ionic liquids have a high impact which is attributed to glyoxal, 1-methylimidazole, and finally sulfuric acid. As this impact was considerable, a sensitivity analysis with two options was considered, decreasing the ionic liquid concentration from 60% to 20% at the same temperature of 60 °C. The other option is an assumption of recovering 90% of the ionic liquid from the leaching solution. In both options, the decrease in impact related to the main analysis is very considerable. This opens research possibilities on the IL recovery, which is a very tentative option, it is emphasized that the recovery effect can increase or decrease the impact depending on the type of separation process that is used.