Exploring the adsorption behavior of cationic and anionic dyes on industrial waste shells of egg

The objective of this work is to investigate the feasibility of using the whole eggshell matrix (eggshell + membrane) as a potential and low-cost bio-sorbent for color removal from dyes. The two tested dyes (Methylene blue, MB & Congo red, CR) revealed different adsorption behaviors reflecting the complex nature of the interaction between the adsorbent surface and these molecules. The functional groups and surface morphologies of untreated eggshell powder and adsorbed Eggshell were analyzed by Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM). The electrical double layer mechanism explained the adsorption behavior of MB cations onto the eggshell surface, whilst that of the CR anions favored the electrostatic attraction on the positively charged surface of eggshell at lower pH. The adsorption of dyes on the surface of eggshell follows a second order kinetics, while the adsorption isotherm obeys the Freundlich model and exhibits multilayer adsorption. The maximum adsorption capacity was estimated to be 94.9 mg/g and 49.5 mg/g for MB and CR respectively for a concentration of 1000 mg/l at room temperature. The heterogeneity of the eggshell surface may cause rearrangement of dye molecules once they are primarily adsorbed. The free energy of adsorption showed an increase with temperature, indicating the occurrence of physical adsorption. The present results indicate the suitability of bio-composite eggshell wastes to be used as adsorbent for the removal of dyes.