ADSORPTION EQUILIBRIA OF SILVER(I) AND COPPER(II) IONS ON N-(2-HYDROXYLBENZYL)CHITOSAN DERIVATIVE

N-(2-Hydroxybenzyl)chitosan (=HR) of an insoluble chitosan derivative was synthesized by reducing N-(2-hydroxy-benzylidene)chitosan obtained from chitosan and 2-hydroxybenzaldehyde. We examined its adsorption selectivities for various metal ions in terms of the pH dependence of the distribution ratio of metal ions at 303 K. The chelating ability of N-(2-hydroxybenzyl)chitosan for various metal ions was measured by a batchwise operation from 1 mol dm-3 of ammonium nitrate solution. The separations of gallium and iron(III) from zinc, and nickel from cobalt were possible because of the high selectivity of the present derivative. Since N-(2-hydroxybenzyl)chitosan showed the high adsorption abilities for silver(I) and copper(II), the adsorption equilibria of both silver(I) and copper(II) were investigated in order to elucidate the adsorbed species by examining the concentration dependencies of hydrogen ion and ammonium nitrate. Silver(I) was adsorbed according to this adsorption reaction, accompanied by an ammonia molecule: AgNH3+ + HRBAR half arrow right over half arrow left RAgNH3BAR + H+ while, copper(II) was adsorbed according to the following reactions: Cu2+ + 2HRBAR half arrow right over half arrow left R2CuBAR + 2H+ and CuNH32+ + 2HRBAR half arrow right over half arrow left R2CuNH3BAR + 2H+.