Synthesis of Highly Porous Chitosan Derivative with Phosphinic Acid and Its Adsorption Properties for Rare Metals

Abstract

The crosslinked and highly porous chitosan microspheres PHAC that introduce phosphinic acid as a ligand were synthesized to apply to perfusion chromatography for the recovery of indium(III) and gallium(III). The formation of pores of PHAC was performed through dehydration caused by the difference of the water osmotic pressure for dehydration from the oil-in-water-in-oil (O/W/O) emulsion containing chitosan in the water phase and the W/O emulsion containing 15 wt% sodium chloride in the aqueous phase. Introduction of phosphinic acid moiety was carried out after crosslinking with glutaric aldehyde by using phosphinic acid and paraformaldehyde according to the Mannich reaction. The microspheres were an average diameter of 100 µm and average pore size of 3.75 nm. The adsorption of metal ions on PHAC was examined from a 1 M aqueous ammonium nitrate solution by a batchwise method. PHAC exhibited high selectivity for In(III) and Ga(III) in the aqueous ammonium nitrate solution. PHAC selectively adsorbed In(III) and Ga(III) over other metals such as copper(II), zinc(II), cobalt(II), nickel(II) and cadmium(II) below pH 2, suggesting that PHAC can perform the selective adsorption of In(III) and Ga(III) only by adjusting pH in the aqueous solution.