Microfluidic Solvent Extraction of Metal Ions from Industrial Grade Leach Solutions: Extraction Performance and Channel Aging

Abstract

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.

Microfluidic solvent extraction of rare earth elements from a mixed oxide concentrate leach solution using Cyanex® 572

“…Furthermore, the presence of fine particles (e.g. silica) and surfactants in a mineral leach solution can slow down the extraction by limiting the availability of the interface for extraction and/or by forming an emulsion stabilized by fine particles (known as crud) [9]. Crud formation is a major issue as it retards phase disengagement by protecting droplets against coalescence, often for very long periods, leading to unrecoverable losses of REEs or uneconomic throughput [9].…”

Chromatography as an inspiration for microreactors

“…Omitting a membrane significantly reduces the mass transfer resistance from minutes of needed residence time to tens of seconds . However, by operating without a membrane the operating range where the parallel flow is stable, expressed through the breakthrough pressure, reduces from a few bar to only ∼1000 Pa, constituting a large disadvantage.…”

Solvent extraction of Nd(III) in a Y type microchannel with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester

“…In particular, they have the following advantages [11][12][13][14][15]: (1) an effective extraction in a short time due to high surface area to volume ratio; (2) simple operation and an environment friendly system; and (3) fast and direct amplification via "numbering-up" parallel processing without scale-up effect. Many literatures indicate that solvent extraction can be carried out very efficiently in a microfluidic chip, due to the high surface-to-volume ratio [16][17][18][19].…”