Inertial migration of fine mineral particles in a curved microfluidic channel: Demystifying the role of non-neutrally buoyant particles

Abstract

Fine mineral particles (FMPs) are ubiquitous in hazardous waste derived from metal mining, processing, and smelting. Inertial microfluidics has sparked tremendous attention due to its potential applications in separating neutral buoyant particles. However, it often fails when applied into non-neutral buoyant FMPs. The inertial migration and focusing tendencies of FMPs were still unknown. Herein, we present a modified microfluidic experiment platform to ensure the steady flow of FMPs in microfluidic systems. This platform avoids the deposition issue of FMPs by combined sample input and suspension system along with design of effective flow rate. FMPs of various particle diameter (2.2 μm, 6.8 μm and 10.2 μm, density of 6.29 g/cm3 or 3.2 g/cm3) were classified and compared to neutral buoyant particles (1.1 μm, 7 μm and 9.9 μm, density of 1.05 g/cm3) to investigate their differences in migration and focusing behaviors within a curved microfluidic channel (CR = 0.07). The migration dynamics of particles with multiple scale sizes may be divided into focusing, rough focusing, and non-focusing modes. Results revealed that a high density of FMPs had less effect on FMP migration and focusing behaviors in three modes. Nonetheless, the variability of FMP size and shape must be considered, as it will induce a shift in particle focusing position and, ultimately, might inhibit FMP separation in microfluidic channels. This work provides an experimental basis for the microfluidic behaviors of FMPs and might give advanced support for the possible application of microfluidic technology in mineral particle separation and sorting.