Countercurrent extraction

The counter current extraction is a physical-chemical process in order in solution to separate from each other substances contained.

The method is based on the different distribution of the various components of the starting solution between an aqueous and an organic phase that is immiscible with it . If one wishes to separate off a substance in the aqueous solution, the aqueous solution is brought into close contact with a suitable organic solution in which the substance is considerably more soluble. This is done, for example, by shaking the two phases or allowing them to flow against each other. The component that prefers the organic environment passes into the organic phase. After calming down, the two phases separate again. The organic phase is usually lighter than the aqueous solution and therefore floats on top so that it can be easily separated from the aqueous phase.

As a rule, the separation cannot be completely achieved in one step, so that the process has to be repeated several times. Suitable chemical additives can influence the behavior of the components within certain limits.

In nuclear technology , the process is used in the reprocessing of spent fuel elements . The fuel is dissolved in nitric acid . A solution of tributyl phosphate (TBP) in kerosene serves as the organic phase .