Adsorptive separation of Ginsenoside from aqueous solution by polymeric resins: Equilibrium, kinetic and thermodynamic studies

The adsorption behaviour of Ginsenoside from aqueous solution onto polymeric resins such as XAD-4, XAD-7, XAD-16 and XAD-1180 was studied. Adsorption isotherms were interpreted from various isotherm models like Langmuir, Freundlich, Redlich–Peterson, Dubinin–Radushkevich and Temkin and their parameters were evaluated and compared. The adsorption kinetics was analyzed using series of rate equations like first-order rate equation, second-order rate equation, Bangham's model, Intra-particle diffusion model, Boyd's diffusivity model and Elovich kinetic equation. The adsorption performance was investigated thermodynamically under batch equilibrium conditions at 293, 298, 303 and 308 K. The optimum temperature of adsorption was observed to be 298 K. Studies of external mass transfer and pore diffusion effects revealed that both film and pore diffusion play significant role in different extent and stages of contact in the sorption process. The adsorption efficiency and uptake rates of Ginsenoside were compared and the highest adsorption efficiency was observed with XAD-7 (>90%). The removal effectiveness is in order of XAD-7 > XAD-16 > XAD-1180 > XAD-4. The rate of Ginsenoside removal better follows pseudo-second-order rate kinetic model, corroborating high correlation coefficients for calculated parameters with the experimental data.