Kinetic, Equilibrium and Thermodynamic Assessment of the Adsorption of Cadmium Using Water Lilly (Nymphaea ampla) Root Biomass

Abstract

biomass was investigated under batch mode. The effects of initial cadmium concentration, solution pH, sorbent dose, contact time and temperature on the adsorption were studied. A biosorbent dose of 50mg showed optimum adsorption capacity of 2.256mg/g (70%) for an initial metal concentration of 2mg/L at 150C and pH 6.5. Optimum sorption equilibrium time was observed in 30minutes. Four isotherms; Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherm models were used to model the equilibrium sorption experimental data. Temkin isotherm yielded best fit to the experimental equilibrium adsorption data with correlation coefficient (R2) of 0.980 followed by Langmuir isotherm (0.946), D-R isotherm (0.926) and Freundlich isotherm (0.537). The adsorption kinetics was determined by fitting pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models to the experimental data with the pseudo-second order model providing the best description for cadmium (II) ion adsorption onto Nymphaea ampla root biomass. Thermodynamic parameters such as Gibbs free energy (ΔG0), the enthalpy (ΔH0), the entropy (ΔS0) changes and the sticking probability (S*) were evaluated and it was found that the adsorption process was spontaneous, feasible, and exothermic and follows physisorption mechanism. Therefore, the experiments showed that Nymphaea ampla root biomass can be effectively used as a low cost adsorbent for the removal of cadmium (II) ions from aqueous solutions.