Mining from wastewater: Perspectives and current practices of non-dispersive solvent extraction for metallic compounds valorization

Abstract

Wastewater derived from mining sectors is presented as an alternative source for by-products recovery. For that, membrane contactors (MCs) could be employed in a non-dispersive solvent extraction (NDSX), which have shown selectivity for the compound of interest and recoveries up to 99%. The positive outcomes were favored by the advancements in hydrophobic membranes, module configurations and set-up, that still contributed for processes of lower specific energy consumption, lower waste generation, greater reliability, and units of smaller area requirement. Nevertheless, it is indispensable to comprehend how the different operating variables contribute for a greater recovery efficiency and selectivity, a research topic still worth of investigation. For that, aspects related to the aqueous and organic flowrate, organic phase composition and striping agents were critically discussed. Complementarily, mass transfer correlations for the lumen and shell side in hollow fiber MCs were described, along theoretic considerations, for a better extrapolation of recovery efficiency in hollow fiber contactors. The results reported for bench scale investigations have recently encouraged the NDSX scale-up for pilot studies. Novel modular systems have also been proposed, combining extraction and back-extraction processes in a single equipment, attaining the principles of process intensification. In fact, the modularity characteristic represents one of the greatest advantages of a membrane-based system, which also favors its scale-up and maintenance. In a broader context, a NDSX seems to be an interesting technology to suppress a future scenario of mineral goods scarcity.