Thallium adsorption onto polyacryamide-aluminosilicate composites: A Tl isotope tracer study
Adsorptive features of the composites of polyacrylamide (PAAm) and bentonite (B), and zeolite (Z) were investigated for Tl+ and TP3+. Langmuir monolayer adsorption capacities for the corresponding ions were 1.85 and 0.97 mol kg(-1) for PAAm-Z and 0.36 and 0.16 mol kg(-1) for PAAm-B. The values of enthalpy and entropy changes were positive for both composites and ions. The compatibility of the second order adsorption kinetics implied that the rate-controlling step was concentration dependent; the sorption process was ion exchange. High adsorption rate was found for both composites; the time required for adsorption of half of Tl+ concentrations was 7 min. In the presence of both ions, PAAm-B was more selective for Tl3+ than PAAm-Z. The reusability tests for Tl+ for five uses proved that the composites were reusable after complete recovery of the loaded ion. The values of Tl+ adsorption onto PAAm-Z from solutions containing Fe3+, Pb2+, Zn2+ confirmed that the effect of the presence of these ions on Tl+ extraction was not significant. Although Tl+ sorption decreased with increasing ionic strength (CaCl2) of the medium, the results of adsorption from sea water containing 5 x 10(-6) mol L-1 (1 mg L-1) of Tl+ ascertained that the composites still adsorbed about 10% of Tl. (C) 2010 Elsevier B.V. All rights reserved.