Removal of Cadmium from water using magnetic Fe3O4 coated non-stochiometric hydroxyapatite nanocomposite powder

A novel magnetic nanocomposite, consisting of Fe3O4 embedded within non-stoichiometric hydroxyapatite (nST-HAP), was synthesized for the removal of Cd from water. The material was characterized using FTIR, PXRD, and SEM-EDX and BET–analyzer. A series of batch sorption experiments were conducted to evaluate its efficacy in terms of sorption kinetics, isotherms, and the effect of various water quality parameters. The study demonstrates that embedding Fe3O4 induces magnetism in the composite. The Cd sorption followed the Langmuir isotherm (R² = 0.964), with a maximum monolayer capacity of 27.85 ± 2.81 mg g− 1 and a low separation factor (RL = 0.012), indicating homogeneous adsorption. This finding is further supported by EDX elemental mapping, which showed a uniform distribution of Ca, P, O, and Fe on the composite, as well as Cd after treatment. The RL factor from the Langmuir isotherm indicates favourable sorption. The effects of ionic strength (0.5–15 mM CaCl2) and pH (4–10) were minimal, demonstrating the material’s stability across different water conditions. Sorption data revealed that Cd binds to the nanocomposite through complexation, occupying vacant crystal lattice sites, binding to PO43− of non-stoichiometric hydroxyapatite, the “O” of FeO, and ion exchange at exchangeable active sites (PO43−, Ca2+) of hydroxyapatite. These results suggest that Fe3O4 embedded in non-stoichiometric hydroxyapatite is a promising adsorbent for Cd removal, with potential for environmental remediation applications. Fe3O4 embedded non-stoichiometric hydroxyapatite was synthesized for treatment of Cd in water. Fe3O4 inclusion imparts magnetism to the composite easing separation after treatment. The material exhibits stable efficiency across varying pH levels and ionic strengths. Sorption follows pseudo-2nd order kinetics and the Langmuir adsorption isotherm.