Effect of Urea on the Synthesis of Hydroxyapatite from Blood Cockle Shells: Kinetics and Adsorption Isotherms Study of Cd 2+ Metal Ion

Abstract Hydroxyapatite (HAp) was synthesized from blood cockle shells as an adsorbent for heavy metal ions in solution, specifically Cd 2+ . HAp was synthesized using the sol‐gel method with urea as an additive at various concentrations of 0, 0.01, 0.1, 0.25, 0.5, and 1 M. HAp with the addition of 0.1 M urea (HAp 3) showed an optimal adsorption capacity of 96.12%. FTIR characterization confirmed characteristic absorption bands of HAp, OH − , and PO 4 3− . XRD analysis confirmed a crystal size of 24.07 nm with low crystallinity. SEM‐EDS analysis showed irregular particle shapes with an average particle size of 1.34 µm and a Ca/P ratio of 1.23 for HAp 3. SAA analysis showed that HAp 3 had a surface area of 125.93 m 2 /g, a pore size of 16.08 nm, and a pore volume of 0.51 cm 2 /g. The adsorption of Cd 2+ by HAp 3 follows the Langmuir isotherm model and pseudo‐second‐order kinetics and can be reused for up to three cycles.