Extractability:
It is possible to make certain generalizations regarding the extraction of metals as a function of the properties of the metal ion. As the charge on the metal ion increases, then so does its extractability. For metals having the same charge, extraction varies inversely as the ionic radius. This means small ions extract better than large ions having the same charge. Thus, in general, at a fixed pH, the monovalent alkali metal exhibits the lowest extractability and ions like Ce4+ and Th4+ exhibit much higher extractability. This is the reason that sodium or ammonium salt of DEHPA (di-2-ethylhexyl phosphoric acid) can be used for the extraction of metal ions having charges greater than +1. The type of anionic species present in the aqueous phase also affects the extraction.