Abstract

Microfluidic Extraction of Metal Ions from a Complex Mineral Leach Solution

Craig Priest, Deputy Director, University of South Australia

Microfluidic solvent extraction (microSX) has demonstrated advantages over conventional mixer-settler methods based on the high surface to volume ratios and precise control over flow rates, ratios, and stability. While small-volume microSX is well-established, the major target of industrial-scale throughputs will require much greater interfacial control and stability over long time-scales. Furthermore, the vast majority of real-world industrial systems consist of fluid phases that are impure or complex, presenting major challenges for microfluidic process intensification. We have studied microSX from industrial-grade mineral processing solutions, with a particular focus on flow stability and phase disengagement. The behaviour of silica nanoparticles in parallel, stream-based flow and the role of adsorbing molecular species (extractant) will be discussed. The results show that silica nanoparticles have a much smaller impact on the flow stability than expected, despite the limitations observed for conventional (bulk-scale) extractions from particle-laden systems. This finding can be explained, in part, by considering the slow rate of particle diffusion, compared to the rapid transport of ions. In contrast, extractant molecules are shown to readily adsorb at microchannel walls over long time-scales (hours) changing the surface wettability and, therefore, the flow stability. In this case, adsorption is desirable and increases the stability of the two-phase flow. These effects and their potential impact on future "numbering-up" of microfluidic systems for industry will be discussed.