Compositions and methods for selectively binding metal ions from a source solution comprise using a polyhydroxypyridinone-containing ligand covalently bonded to a membrane support having the formula M-A-L(HOPO)n. M is a membrane having a hydrophilic surface, A is a covalent linkage mechanism, L is a ligand carrier, HOPO is a hydroxypyridinone appropriately spaced on the ligand carrier to provide a minimum of six functional coordination metal binding sites, and n is an integer of 3 to 6. The separation is accomplished by passing a source solution containing the ions to be separated through a cartridge containing the membrane-ligand composition, causing the selected ions to be complexed to the HOPO ligands and subsequently removing the selected ions from the cartridge by passing an aqueous receiving solution through the cartridge and quantitatively stripping the selected ions from the HOPO ligand.