Porous alginate aerogel beads for effective and rapid heavy metal sorption from aqueous solutions: Effect of porosity in Cu2+ and Cd2+ ion sorption

Calcium alginate porous aerogel beads were prepared by sc-CO2 drying, characterized and for the first time evaluated for their performance on metal ion sorption in comparison with their non-porous xerogel analogues. The aerogels were mainly mesoporous, also containing micropores and macropores with BET surface area of 419 m(2) g(-1). The material exhibited enhanced sorption capacity with 20% higher degree of active site saturation after sorption compared to the xerogel beads and sorption values reaching 126.82 mg g(-1) for Cu2+ and 244.55 mg g(-1) for Cd2+. The sorption kinetics exhibited a significant decrease in sorption time, with 99% removal achieved 600-800 min earlier than for xerogel beads. This behaviour indicates increased functional groups accessibility combined with increased flexibility due to the effect of porosity, facilitating chain rearrangement during ion exchange. A multistage mechanism for heavy metal sorption kinetics was suggested by the results of both Weber-Morris and film diffusion models. (C) 2012 Elsevier B.V. All rights reserved.