Microfluidic solvent extraction, stripping, and phase disengagement for high-value platinum chloride solutions Frederik H. Kriel a , Gregor Holzner a , Richard A. Grant b , Stephen Woollam c , John Ralston a , Craig Priest a,n a Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia b Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, United Kingdom c Anglo American’s Technical Solutions, Johannesburg, South Africa HIGHLIGHTS  Platinum extraction, scrubbing, and stripping in a microfluidic chip.  Extraction and stripping reached equilibrium between 2 and 13 s.  Online measurement of phase separation showed 98% efficiency. GRAPHICAL ABSTRACT article info Article history: Received 15 June 2015 Received in revised form 7 August 2015 Accepted 30 August 2015 Available online 16 September 2015 Keywords: Platinum Solvent extraction Refining Microfluidics Mineral processing abstract Extraction, scrubbing, and stripping of Pt(IV) in microfluidic solvent extraction (microSX) chips were studied using a secondary amine as the extractant. Real-time efficiency of phase disengagement was precisely determined. The time-dependant platinum concentration in the aqueous phase could be fitted with a pseudo-first order rate equation for three different organic/aqueous phase ratios (0.6, 2.2, and 5.7) that were achieved using dissimilar channel cross-sections. Extraction equilibrium was achieved within several seconds (2–6 s) in agreement with the fast extraction rate expected for a diffusion-limited ion exchange mechanism and the microscopic dimensions involved. Aqueous phase derived from a precious metals refinery was also extracted successfully, demonstrating that the process is relevant to refinery conditions. Scrubbing reported negligible loss of platinum from the organic phase. Stripping revealed that longer contact times were necessary to achieve equilibrium ( 12 s) compared with extraction. Phase disengagement efficiencies were precisely determined for the first time using an online and quantitative approach, revealing up to 2% inefficiency with a slight bias towards the organic phase being lost into the aqueous stream. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Microfluidic systems boast very high surface-to-volume ratios, which can be exploited in a wide variety of flow chemistry applications (Wang and Li, 2011; Al Lawati, 2013; Elvira et al., 2013; Ciceri et al., 2014; del Campo, 2014; Rodrigues et al., 2014). The attraction of these miniaturised systems has been driven, in part, by the desire to use rare or expensive samples in process Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science http://dx.doi.org/10.1016/j.ces.2015.08.055 0009-2509/& 2015 Elsevier Ltd. All rights reserved. Abbreviations: A, cross-sectional area; aq, aqueous; d, etch depth; D, hydraulic diameter; h, meniscus height; L, contact length; m, dynamic viscosity; MicroSX, micro-solvent extraction; org, organic; P, hydrodynamic pressure drop; Q, volu- metric flow rate; R, flow rate ratio; SX, solvent extraction; t, contact time n Corresponding author. E-mail address: craig.priest@unisa.edu.au (C. Priest). Chemical Engineering Science 138 (2015) 827–833