Microfluidic solvent extraction (microSX) of metal ions from industrial grade mineral leach solutions was studied. In conventional bulk-scale SX, partially hydrophobic nanoparticles that are present in the leach solution readily adsorb at the liquid-liquid interface of the dispersed droplets, causing delayed or incomplete phase separation and reduce efficiency. In contrast, microSX employs continuous microscopic streams of aqueous and organic phases (without mixing the phases) and, in this way, bypasses the need for a conventional phase separation stage. This makes the technique promising for handling complex leach solutions. The stability of the two-phase flow is considered in terms of the surface wettability and guiding geometry of the microchannel, which determines the Laplace pressure window that stabilizes the liquid-liquid interface. We show that careful characterization of the microchannel wettability, including contact angle hysteresis, is essential to predict long-term flow stability.