Gum Arabic modified nano-hydroxyapatite for cobalt(II) removal from water: Adsorption performance and molecular-level mechanism
Souhayla Latifi, Khalil Azzaoui, Rachid Sabbahi, Ghadir Hanbali, B. Hammouti, Mohammed Merzouki, Mohammed M. Alanazi, Solhe F. Alshahateet, Shehdeh Jodeh, Sanaâ Saoiabi
Abstract
Cobalt(II) contamination in industrial wastewater poses serious environmental and public health concerns due to its toxicity and persistence. In this study, a novel eco-friendly composite based on nano-hydroxyapatite and gum arabic was synthesized via a green dissolution–precipitation method and evaluated for the removal of cobalt(II) ions from aqueous solutions. Characterization techniques including FTIR, XRD, SEM, TGA, and XPS confirmed the successful integration and structural stability of the composite. Batch adsorption experiments revealed a maximum adsorption capacity of 124.2 mg/g at pH 7, with equilibrium reached within 180 minutes. The process followed the Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer chemisorption. Thermodynamic analysis showed a spontaneous and endothermic process (ΔG° = –22.9 kJ/mol, ΔH° = +16.0 kJ/mol). Monte Carlo simulations provided molecular-level insight, revealing preferential Co(II) binding to phosphate and carboxyl-rich regions of the composite surface, with a calculated adsorption energy of –104.38 kcal/mol. Additionally, the composite maintained over 88% efficiency after five regeneration cycles. These findings support the potential of this green material as a robust and reusable adsorbent for cobalt removal in wastewater treatment applications.