Simple height determination models
Liquid-liquid extraction - Column modeling

A more realistic approach than that of the ideal stage, which assumes chemical equilibrium has always been reached, is to take into account the rate of material transfer within the stage. As this transfer rate is not infinite, the phases do not exit at equilibrium, and the stage is no longer ideal. The main application of this special case is the dimensioning of mixer-settlers, but it can be generalized to the calculation of columns whose packing elements introduce segmentation (tray columns).

The extraction profile in such a countercurrent extractor can be determined from a material balance around the n ^th stage: $F_x\left(c_{x\text{,}n-1}-c_{x,n}\right)=k_{ox}$