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For the first time, widespread aqueous biphasic polymer-salt extraction system was applied for selective separation of Pd(II) and Pt(IV) from chloride technological solutions by countercurrent chromatography using a rotating coiled column (an analog of centrifugal extractor). The principle novelty of the proposed approach is the possibility of multistage extraction process and the needlessness to add any specific reagents for targeted metal binding. The results showed that the use of poly(ethylene glycol)-1500 (PEG-1500) as a stationary phase allows 96–100% of both Pd(II) and Pt(IV) to be recovered from chloride solutions containing copper and nickel. To obtain individual solutions of targeted metals it is enough to change the composition of the salt-rich phase for stripping stage, in particular the salt concentration and pH value. The final purity of the targeted metal fractions obtained after their extraction from model technological solutions is ≥ 99.9%. The components of the aqueous biphasic system are recyclable, non-toxic, available, and widespread in laboratory and technology practice. A scheme of the multistage separation of platinum metals using a rotating coiled column is proposed.

In countercurrent chromatography (CCC) both stationary and mobile liquids undergo intense mixing in the variable force field of a coil planet centrifuge and the separation process, like the separation in conventional solvent extraction column, is influenced by longitudinal mixing in the phases and mass transfer between them. This paper describes how the residence time distribution (or the elution profile) of a solute in CCC devices and the interpretation of experimental peaks, can be described by a recently developed cell model of longitudinal mixing. The model considers a CCC column as a cascade of perfectly mixed equal-size cells, the number of which is determined by the rates of longitudinal mixing in the stationary and mobile phases. Experiments were carried out to demonstrate the validation of the model and the possibility of predicting the partitioning behaviour of the solutes. The methods for estimating model parameters are discussed. Longitudinal mixing rates in stationary and mobile phases have been experimentally determined and experimental elution profiles are compared with simulated peaks. It is shown that using the cell model the peak shape for a solute with a given distribution constant can be predicted from experimental data on other solutes.