A low-cost adsorbent deriving from eggshell modified with Mg(II)-doped hydroxyapatite for removal of Cd2+ from water

作者：Gong, Xiangyi^*; Meng, Dekang; Peng, Zhang; Wang, Zeya; Ren, Dajun; Wu, Fengying

来源：Desalination and Water Treatment, 2022, 273: 149-161.

DOI：10.5004/dwt.2022.28870

• Eggshell
• Low-cost adsorbent
• Hydroxyapatite
• Cadmium

The industrial by-product cadmium can pollute the environment and be harmful to humans after being discharged from wastewater. In this study, a low-cost adsorbent deriving from kitchen waste eggshells (BC), was modified by magnesium-doped hydroxyapatite in order to form a new adsorbent (MHBC) capable of removing Cd2+ from water. When compared to BC, the adsorption capacity of MHBC was found to be greatly improved, while their equilibrium adsorption capacities were 4.82 and 49.41 mg center dot g(-1), respectively. Kinetic, isothermal, and environmental factors' analyses suggested that chemisorption played a major role in the Cd2+ adsorption process delivered by MHBC. Particularly, chemical complexation, ion exchange, and electrostatic interaction could be the main mechanisms involved. Both the pseudo-second-order kinetics equation and the Sips isotherm model were found to fit the adsorption process well. Sips model revealed that the maximum adsorption capacity of MHBC at 25 degrees C was 68.898 mg center dot g(-1). Acidic conditions and the presence of Mg2+, Pb2+, Cu2+, and Zn2+ were found to reduce the adsorption capacity of MHBC for Cd2+. After three cycles, the removal percentage of Cd2+ by MHBC was still able to reach 78.75%. Therefore, our study suggests that MHBC is a highly efficient, green, and sustainable Cd2+-removing adsorbent.