Efficient lanthanides adsorption using magnetic hydroxyapatite incorporated cobalt

Magnetic hydroxyapatite incorporated cobalt (Co/HAp@Fe3O4) was fabricated by introducing both Co2+ and Fe3O4 into the hydroxyapatite (HAp) matrix. HAp@Fe3O4 and Co/HAp@Fe3O4 were characterised by IR, XRD, EDX, SEM and TG/DTA. The adsorption efficiency of La(III) and Sm(III) was compared on both HAp@Fe3O4 and Co/HAp@Fe3O4 using several factors, such as solution pH, contact time, initial metal concentrations and reaction temperature. It was found that the appropriate factors for the highest adsorption were at pH 5 and the equilibrium time was 60 min. The Co/HAp@Fe3O4 exhibited enhanced adsorption efficiency compared to HAp@Fe3O4 due to the existence of additional adsorption sites. The equilibrium adsorption isotherms for both Sm(III) and La(III) were fitted well with Langmuir model.The adsorption capacity was found to be 259.06 and 200.80 for La(III) and 413.22 and 476.19 mg/g for Sm(III) on Co/HAp@Fe3O4 and HAp@Fe3O4respectively. Thermodynamic parameters (∆G°, ∆S°, ∆H°) of La(III) and Sm(III) equilibrium with Co/HAp@Fe3O4 indicated a non-spontaneity and endothermic nature. The positive ΔSo suggested an entropy un-favoured or disorder at the solid/liquid interface.