Synthesis of novel ion exchange/coordination resins and the mechanistic study of ion exchange/redox dual mechanism bifunctional polymers with their application in metal ion recovery

Selective separation of metal ions is important for many purposes, including treatment of waste water and recovery of precious metals. Polymer supported ion exchange ligands have good kinetics but lack selectivity. Ion selective polymers, however, have slow extraction kinetics and are difficult to regenerate. Several dual mechanism bifunctional polymers have been synthesized wherein ion exchange ligands with rapid kinetics were combined with ion selective ligands. The polymers are classified as ion exchange/redox resins (Class I) and ion exchange/coordination resins (Class II).; Class I polymers support covalently bound monoaryl- and diarylphosphinic acid ligands as the ion exchange functionality. The monoarylphosphinic acid ligand plays a dual role as the redox functionality. The ligands are bonded to a polystyrene support through an electrophilic aromatic substitution reaction. Phosphorus trichloride is used as the electrophile and aluminum chloride as the catalyst. Through a mechanistic study, three types of resins were defined. Type I resins supported monoarylphosphinic acid ligands; and Type II resins supported monoaryl- and diarylphosphinic acid ligands; and Type III resins supported both acid ligands with some amount of disubstitution on the aromatic rings. Class II polymers contain carboxylic acid or phosphonic acid ligands as the ion exchange functionality and penta(ethylene glycol) as the coordinating functionality covalently bonded on a poly(vinylbenzyl chloride) support. The carboxylic acid is formed by partially substituting the chloride with ethoxide, hydrolyzing the ethoxide and oxidizing the hydrolyzed resin to form the benzoic acid ligand. The phosphonic acid is formed through insertion of phosphorus trichloride into approximately one fourth of the benzyl chloride ligands. The penta(ethylene glycol) ligand is supported on both ion exchange resins through a Williamson reaction on the benzyl chloride ligands still remaining on the resins.; All Class II polymers extract potassium, rubidium, cesium, zinc, europium, and cadmium to the same extent as the monofunctional resins. The carboxylic acid/penta-(ethylene glycol) resins extracted calcium, strontium, barium, and mercury better or equal to monofunctional resins. The phosphonic acid/penta(ethylene glycol) prefers iron(III) and shows an increased extraction ability towards mercury and silver relative to the monofunctional resins.