Modeling kinetics and thermodynamics of Cs+ and Eu3+ removal from waste solutions using modified cellulose acetate membranes

Removal of Cs+ and Eu3+ ions using cellulose acetate (CA) and modified CA was studied. Cellulose acetate was modified using acrylamide (AAm) and polyethylene glycol (PEG). Specifically, CA, CA/AAm, and CA/PEG were used to remove Cs+ and Eu3+ from aqueous waste solutions. The CA-metal and modified CA-metal interactions were studied under different conditions such as concentration of metal ions and temperature in the range 298 K-333 +/- 1 K. Experimental equilibrium sorption data were analyzed using Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. These data were better fitted to both Langmuir and D-R isotherms compared to Freundlich model. On the other hand the sorption processes were better represented by pseudo-second order kinetic model. The sorption processes were endothermic with Delta H-o values 16.20, 23.55, and 21.70 (kJ/mol) for sorbed Cs+ ions onto CA, CA/AAm, CA/PEG, whereas that for sorbed Eu3+ are 21.79, 23.87 and 75.34 (kJ/mol), respectively. The entropy values Delta S-o for Cs+ ion sorbed onto CA, CA/AAm, and CA/PEG are 50.72, 80.15, and 77.10 (J/mol K), whereas that for the sorbed Eu3+ ion are 75.0, 87.30 and 256.10 (J/mol K) respectively. The activation energy, Ea, for Cs+ and Eu3+ ions sorbed onto all studied sorbent materials lies in the range 8.73-26.32 (kJ/mol) and 24.27-78.11 (kJ/mol), respectively. The negative values of Gibbs free energy, Delta G(o), confirm the feasibility and the spontaneous nature of both Cs+ and Eu3+ ions sorption removal using CA and AAm and PEG modified CA and indicating that the sorption processes are chemi-sorption mechanisms. The sorption removal capacities of both Cs+ and Eu3+ were in the order CA/PEG > CA/AAm > CA. The batch and dynamic sorption results show that the modified CA/PEG, CA/AAm, and CA membranes can be used to remove Cs+ and Eu3+ ions from wastewater. (C) 2012 Published by Elsevier B.V.