Equilibrium, Kinetic and Thermodynamic Assessment of the Adsorption of Cadmium Using Water Lily (Nymphaea Ampla) Leaf Biomass

The adsorption of cadmium (II) ions from aqueous solution by Nymphaea ampla leaf biomass was carried out with effects of initial cadmium concentration, solution pH, contact time, adsorbent dose and temperature of the process investigated. An adsorbent dosage of 120 mg showed maximum metal uptake capacity (qe) of 2.75 mg/g (82.6%) for an initial metal ion concentration of 2.0 mg/L and pH 7. Sorption equilibrium time was observed in 30 minutes. The equilibrium adsorption data were analyzed by the Langmuir, Freundlich, Temkin and DubininRadushkevich (D-R) adsorption isotherm models. Freundlich isotherm yielded the best fit to the experimental equilibrium adsorption data with a correlation coefficient (R2) of 0.990. The kinetics of cadmium (II) ions adsorption was discussed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. It was discovered that the adsorption of cadmium (II) ions could be described by the pseudo-second-order kinetic model. Thermodynamic parameters such as Gibbs free energy (ΔG0), enthalpy (ΔH0) and entropy change of the sorption (ΔS0) evaluated showed that the process was spontaneous, feasible and exothermic in nature. The results indicated that Nymphaea ampla leaf biomass can be used as an effective and low-cost adsorbent to remove cadmium (II) ions from aqueous solutions.