Insoluble ferrocyanides:

The ion exchange properties of a large number of insoluble ferrocyanides of various metals e.g., Ag(I), Zn(II), Cd(II), Cu(II), Ni(II), Co(II), Pb(II), Mn(II), Fe(III), Ti(IV), Zr(IV), V(V), Mo(VI), W(VI), U(VI), have been studied. The ferrocyanides act as cation exchangers with a high affinity for heavy alkali metal ions, especially for Cs⁺. The ion exchange mechanism in ferrocyanide is rather complicated and not yet clear. In order to improve the mechanical properties of ferrocyanides for use in column operations, the exchanger has been prepared by precipitation on solid inert supports e.g., bentonite, silica gel, etc., freezing the gel or bonding the precipitate particles to insoluble polymers such as polyvinyl acetate.