HIGHLY SELECTIVE ADSORPTION RESINS .1. PREPARATION OF CHITOSAN DERIVATIVES CONTAINING 2-PYRIDYLMETHYL, 2-THIENYLMETHYL, AND 3-(METHYLTHIO)PROPYL GROUPS AND THEIR SELECTIVE ADSORPTION OF PRECIOUS METALS

Crosslinked N-(2-pyridylmethyl)chitosan, N-(2-thienylmethyl)chitosan, and N-[3-(methylthio)propyl]chitosan were newly synthesized. The amino group of the active adsorption site of chitosan was protected by Schi ff's base formation prior to being crosslinked by 2-(chloromethyl)oxir ane. The final chitosan derivatives were obtained by reducing the imin e moiety of the Schiff's bases with sodium borohydride. The adsorption behavior of metal ions on the chitosan derivatives was examined from a solution containing hydrochloric acid using a batchwise method. Thes e chitosan derivatives exhibited high selectivities and excellent load ing capacities for gold(III), palladium(II), and platinum(IV) over bas e metals in hydrochloric acid. In order to elucidate the adsorption sp ecies of palladium(II) on the chitosan derivatives, the effect of the chloride ion concentration on the distribution ratio in the adsorption of palladium(II) was examined. The adsorption capacities of these chi tosan derivatives for palladium(TI) were found to be about 2.5-3 times greater than that of the cross-linked original chitosan. The desorpti on of palladium(II) was performed to an extent of 70% by a single batc hwise treatment with aqueous thiourea solution.