The separation of compounds of Rh, Pd, Ir and Pt by multistage batch liquid-liquid extraction with tributyl phosphate (TBP)
from hydrochloric acid solution has been studied. The existence of complexes of the same platinum group metal, which are capable
of being extracted to different degrees, has been concluded from the variation of the distribution coefficient of the respective
platinum group metals with the stage number. In addition to monomeric chlorocomplexes, metastable inert species (presumably
polymeric chloroaquo or aquo/oxo complexes) were found, which were not formed during the extraction, but had been present
already in the initial solutions. Because the solvent TBP does not enter the internal coordination sphere, the separation
effect attainable is determined by the extraction behaviour and the content of these complex types in the initial solutions.
This fact explains the strong influence of solution preparation on the separation effect.