Absorption and desorption of chromium ions by poly(acrylic acid) gels

The ability of crosslinked poly(acrylic acid) gels to retain chromium speci es was studied as a function of pH. Chromium retention was found to increas e with pH according to two mechanisms. In the low pH range where chromium s pecies are soluble, retention occurs via ion-binding in the whole volume of the gel. At higher pH where insoluble chromium hydroxide particles are for med, retention comes from an adsorption process at the surface of the gel. The desorption of chromium species under acidic conditions was also investi gated and found to be very dependent on retention mechanism and aging time of the polymer-chromium complex. When retention occurs by ion-binding, only partial desorption was achieved at very short aging time. In contrast, a v ery fast desorption was observed when retention occurs via adsorption at th e surface of the polymer gel. (C) 1999 John Wiley & Sons, Inc.