Morphology of solvent-impregnated resins based on reactive supports

Hydrophobic metal-complexing extractants of the alkylphosphoric acid type (di-(2-ethylhexyl)dithiophosphoric acid, di-(2-ethylhexyl) monothiophosphoric acid and di-(2-ethylhexyl)phosphoric acid) are used as ligands for separation of metal ions from aqueous solutions. Upon immobilization on polymer carriers containing vinylpyridine and alkylamine basic groups they are held by chemisorption and absorbed into the polymer mass of the support. The capacity of the support for the organic ligand depends on the ability of its polymer mass to swell and also on the strength of the interaction between the basic functional groups of the polymer and the ligand. This is a newly observed phenomenon. Interaction of the supported ligand with metal ions results in expulsion of the ligand from the polymer mass. In macroreticular polymeric supports the metal-saturated ligand fills the macropores and escapes from the support when the macropore volume of the support is smaller than the volume of the organic ligand. Stripping of the metal from the ligand by washing with mineral acids causes the ligand to return from the macropores into the polymer mass of the support. Note: In this paper, the term ligand generally describes a hydrophobic metal extraction ligand.