Biosorption of Cd(II) Ions from Aqueous Solution Onto Eggshell Waste Kinetic and equilibrium isotherm studies

Eggshell waste as adsorbent was successfully used for the removal of Cd(II) ions from model synthetic aqueous solutions. Batch biosorption studies were conducted in order to evaluate the effect of various parameters, such as: contact time and initial metal ion concentration. The changes in the morphological structure were evaluated by TEM and SEM analysis. The experimental isotherm data were analysed using Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherm equations, using regression analysis linear and non-linear form. Langmuir model was found to be in better correlation with experimental data (R2=0.99). Biosorption kinetics data were tested using pseudo-first-order, pseudo-second-order, intra-particle and liquid film diffusion models. Kinetics studies showed that the biosorption followed a pseudo-second-order reaction. Removal efficiencies up to 92 % and a maximum adsorption capacity of 8.2 mg/g Cd(II) were obtained experimentally and 7.14 mg/g Cd(II) were obtained from Langmuir isotherm model. The percentage of metal sorption (Ci=11 mg/L, E,(%)=92.42), EDS analyses, and bioconcentration factor were also calculated. The investigation findings suggested that the physical adsorption is controlling the adsorption rate. Results of this study indicate that eggshell waste can be effectively used for the removal of Cd(II) ions from aquatic environments. The process is feasible, reliable and eco-friendly.