Niloy Banik, Kamran Siddique, Safat Anam, Mohammad Nurur Rahman, Md. Masumul Haque
This study explores the potential of discarded eggshells as sustainable and cost-effective biosorbents for removing heavy metals and dyes from water. The influence of chemical and thermal activation on their adsorption properties was thoroughly examined. Raw eggshells, mainly composed of calcium, carbon, and oxygen forming carboxylic and carbonate functional groups, were chemically activated with 5% and 10% orthophosphoric acid and then heat-treated at 550 °C for 2 hours. The materials were characterized using FT-IR, SEM, UV–Vis spectroscopy, and AAS. FT-IR confirmed the retention of functional groups after activation, while SEM images showed that acid treatment produced a more porous and irregular surface, enhancing the material’s adsorption capacity. The modified eggshells showed remarkable improvement in removing contaminants. After 60 minutes of contact time, removal efficiencies reached 98.76% and 98.51% for Cr, 100% for Cd, and 96.23% and 96.17% for Pb using 5% and 10% activated samples, respectively. Methylene blue removal also increased from 27% for the raw powder to 89% for the 10% activated eggshell. Overall, phosphoric acid activation significantly enhanced the surface reactivity and porosity of eggshells, demonstrating their strong potential as eco-friendly biosorbents for wastewater purification.