Development of Multiphase Flows in a Microfluidic Device and its Application for Solvent Extraction

Abstract

We constructed two-phase (water/n-heptane) and three-phase (water/n-heptane/water) flows in a microchannel (0.1 mm width, 0.025 mm depth) on a glass microchip (3 cm × 7 cm). Then solvent extraction of metal ions was investigated employing the multiphase flows in the microchannel. Prior to the solvent extraction, we examined two ways to separate and collect each phase from another in the microchannel. One was chemical modification of the microchannel surface by octadecylsilane groups and another was flow-guiding walls in the microchannel. Both of them achieved the spontaneous phase separation of the multiphase flows in the microchannel, allowing control of interfacial contact time and off-chip analysis using conventional analytical apparatus. The forward and backward extraction of yttrium (Y³⁺) and zinc (Zn²⁺) ions was investigated in a two-phase flow on a microfluidic device using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester as an extractant. The extraction conditions (contact time of the two phases, pH and extractant concentration) in the microfluidic device were examined. These investigations demonstrate that the conventional methodology on solvent extraction of metal ions is applicable to the solvent extraction in the microchannel. The introduction of the flow-guiding walls interestingly improved the extraction efficiency in the microchannel. Finally, we employed a three-phase flow in the microchannel as a liquid membrane system and observed the rational and selective transport of Y³+ through the liquid membrane. In this study, we succeeded in the selective separation of a targeted metal ion from a feed aqueous solution within a few second employing multiphase flows in the microfluidic device.