Separation of Co(II)/Ni(II) with Cyanex 272 using a flat membrane microcontactor: Extraction kinetics study

In the present study, the extraction kinetics of cobalt with Cyanex 272 in a flat membrane microcontactor is studied. Pseudo-first order and non-first order models are proposed to describe the extraction kinetics with acidic Cyanex 272 and saponified Cyanex 272. The impact of the acetate buffer concentration, the Cyanex 272 concentration, the feed concentration, the channel depth and saponification of Cyanex 272 on the extraction kinetics was experimentally measured. From this, it was shown that for acidic Cyanex 272 pseudo-first order reaction kinetics could be assumed under at least following conditions: (1) when the feed was buffered; (2) the Cyanex 272 concentration was 4.4 times higher than the cobalt concentration; and (3) the cobalt concentration remained below 17 mmol/L. In that case a linear model could be derived that could be solved analytically. At higher cobalt concentrations, saturation of the interface had to be taken into account, resulting in a non-linear model that had to be solved numerically. When Cyanex 272 was saponified, the extraction kinetics dropped significantly indicating that pseudo-first order kinetics does not apply any longer. Consequently, faster extraction kinetics in membrane contactors with acidic Cyanex 272 is obtained by buffering the feed phase compared to the saponification approach of Cyanex 272. (C) 2015 Elsevier B.V. All rights reserved.