What is the principle of “scrubbing” in liquid extraction or solvent extraction? There are many steps in solvent extraction:


Extraction
Scrubbing
Back extraction 


I understand the 1st and the 3rd. 
What is the principle of scrubbing?
Is it just washing the organic phase?
How undesirable species get removed from organic phase?
&quot;Scrubbing&quot; in this context is the treatment of the organic phase to remove impurity metals. This is as opposed to &quot;back extraction&quot; which is to remove the metal of interest from the organic phase.