Kinetic analysis of an ionic liquid-based metal extraction process using a single droplet extraction column

In this study a liquid-liquid extraction (LLX) process has been investigated based on experimental analysis and kinetic modelling. The purpose of this investigation is (1) to understand the mass transfer behaviour, (2) to determine the rate limiting step via evaluating different mass transfer models, and (3) to estimate the mass transfer and kinetic parameters. This has been discussed in the context of the extraction of Co by the ionic liquid (IL) [P₈₈₈₈][Oleate] as an example of LLX with chemical reaction. Mass transfer models, with and without a chemical reaction, are evaluated based on a statistical cross-validation method. The following operational parameters are included in the analysis: column lengths, droplet diameter, droplet rising velocity and continuous and dispersed phase concentrations on Co uptake. This method reveals that a single parameter representing the external mass transfer resistance can describe the forward extraction of Co (i.e., into the IL) for the whole data set sufficiently accurate (error ±30%) regardless of the studied operational conditions. Back-extraction of Co from pre-loaded IL droplets shows a different transfer mechanism. Now the mass transfer in the dispersed IL phase dominates the process which is attributed to a change of the physical properties of the pre-loaded IL.