Exploring the chemistry of waste eggshells and its diverse applications

The large-scale production of chicken eggs results in a substantial amount of eggshell (ES) residue, often considered as waste. These discarded shells naturally decompose in soil approximately within a year. Eggshells (ES), comparatively contribute lesser towards environmental pollution, contain a remarkable amount of calcium, which can be converted into various valuable products that finds applications in industries, pharmaceuticals, and medicine. Among the diverse applications of ES, most effective and promising applications are removal of heavy metals (Cd, Cr, Pb, Zn, and Cu) ∼93-99 % metal adsorption capacity and capturing of flue gases (CO₂ and SO₂) from the environment. With ES having a maximum CO₂ sorption capacity of 92 % as compared to other sources, and SO₂ adsorption capacity of Calcined ES∼11.68 mg/g. The abundance, low cost and easy availability of CaO from ES makes them sustainable and eco-friendly. Additionally, its versatility extends beyond environmental prospects, as it is widely used in various industries as a catalyst, sorbent, fertilizer, and calcium supplement in food for individuals, plants and animals, among other diverse fields of study. Owing to its versatile applications, current review focuses on structure, chemical composition, treatment methods, and valorization pathways for diverse applications, aiming to reduce the eggshells waste and mitigate environmental pollution.