Development of nano-hydroxyapatite/chitosan composite for cadmium ions removal in wastewater treatment

• Nano-sized hydroxyapatite and hydroxyapatite/chitosan composite sorbents were synthesized using the sol–gel method.
• The sorbents were employed in the Cd2+ ions removal in wastewater treatment.
• Batch experiments were pursued to evaluate the sorbent's capacity and efficiency.
• The Cd2+ uptake was addressed in view of the Pseudo second order, Freundlich and Langmuir kinetics.
• The sorbent's regeneration was promising.

Hydroxyapatite nanorods (nHAp) and nano-hydroxyapatite chitosan composites (nHApCs) were proposed for the removal of Cd2+ ions in water treatment. The high resolution transmission electron microscopy, energy dispersive X-ray analysis, X-ray diffraction spectrophotometer, Fourier transform infrared spectrophotometer and Zeta potential measurements were all employed to reveal the morphology, composition, crystal structure, functionality and stability of the prepared sorbents (nHAp and nHApCs). The potential of these synthesized sorbents to remove Cd2+ ions from aqueous solutions was investigated in batch experiments, where several parameters such as the sorbate/sorbent's contact time, initial Cd2+ ions concentration, pH and sorbent dosage were investigated. The equilibrium concentration of Cd2+ ions was identified by the atomic absorption spectrophotometry. The Cd2+ uptake was quantitatively evaluated using the Pseudo second order kinetic equation, Freundlich and Langmuir models. It is remarkable that with these sorbents (nHAp, nHApCs), up to 92% of Cd2+ could be removed “100 ppm initial cadmium concentration in 200 mL, 0.4 g nHAp and pH = 5.6″. The sorption capacity of nHAp and nHApCs to Cd2+ was 92 and 122 mg/g respectively, which appears excellent when compared to other previously reported materials. This capacity could be enhanced by increasing initial Cd2+ concentration and the nHAp/Cd2+ mass ratio. Furthermore, the sorbents’ regeneration was addressed and found promising.