Gel-coated ion-exchange resin: A new kinetic model

Abstract

Regenerable ‘gel-coated’ cationic resins with fast sorption kinetics and high sorption capacity have application potential for removal of trace metal ions even in large-scale operations. Poly(acrylic acid) has been gel-coated on high-surface area silica (pre-coated with ethylene–vinyl acetate copolymer providing a thin barrier layer) and insolubilized by crosslinking with a low-molecular-weight diepoxide (epoxy equivalent 180 g) in the presence of benzyl dimethylamine catalyst at 70°C. In experiments performed for Ca 2+ sorption from dilute aqueous solutions of Ca(NO 3) 2, the gel-coated acrylic resin is found to have nearly 40% higher sorption capacity than the bead-form commercial methacrylic resin Amberlite IRC-50 and also several times higher rate of sorption. The sorption on the gel-coated sorbent under vigorous agitation has the characteristics of particle diffusion control with homogeneous (gel) diffusion in resin phase. A new mathematical model is proposed for such sorption on gel-coated ion-exchange resin in finite bath and solved by applying operator-theoretic methods. The analytical solution so obtained shows good agreement with experimental sorption kinetics at relatively low levels (<70%) of resin conversion.