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 ΔHo 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 ΔSo 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, ΔGo, 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.