Recent Developments in the Application of <i>Gallus domesticus</i> Eggshells for the Biosorption of Dyes and Heavy Metals

Global efforts to develop low-cost solutions for the treatment of contaminants in wastewater continue unabated. The conversion of eggshells, a waste material, into a high-value product can be economical and environmentally sustainable. The recent developments in applying eggshells towards the biosorption of contaminants are presented. Eggshells effectively remove pollutants such as metal cations, metal anions, and reactive, basic, and direct dyes. Promising advances in modifying eggshells, elucidating the critical operational parameters, and optimizing the biosorption process have been reported. To this end, the modeling of biosorption kinetics, equilibrium, thermodynamics, and mechanisms are discussed. Also, a 3-stage category is proposed to better classify the biosorbent preparation efforts. The pseudo-second-order model was reported to represent biosorption kinetics best, implying that chemisorption may be a key attachment mechanism in most instances. The Langmuir model best represented the equilibrium data, inferring monolayer sorption on homogenous surfaces. Most studies reported that the uptake mechanism was physisorption or chemisorption. Despite these strides, the application of eggshell biosorption remains mostly at the laboratory testing stage. Thus, key points from recent developments and recommendations for future inquiry are presented.