Magnetically retrievable nanocomposite of magnesium ferrite and bentonite clay for sequestration of Pb(II) and Ni(II) ions: a comparative study

Abstract

In the present work, nanocomposite of bentonite clay with $$\hbox {MgFe}_{2}\hbox {O}_{4}$$ nanoparticles (NPs) was synthesized by sol–gel route. It was studied for the sequestration of Pb(II) and Ni(II) ions from the aqueous solution. The nanocomposite was analysed using X-ray diffraction, vibrating sample magnetometry, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and Brunauer–Emmett–Teller (BET) as analytical tools. The lower value of saturation magnetization ( $$M_{\mathrm{s}}$$ ) of nanocomposite (5.70 emu $$\hbox {g}^{-1}$$ ) as compared with pristine $$\hbox {MgFe}_{2}\hbox {O}_{4}$$ NPs (12.32 emu $$\hbox {g}^{-1}$$ ) is due to the presence of non-magnetic bentonite clay. BET studies further revealed higher surface area for nanocomposite ( $$75.43~\hbox {m}^{2}$$ $$\hbox {g}^{-1}$$ ) than $$\hbox {MgFe}_{2}\hbox {O}_{4}$$ NPs ( $$62.51~\hbox {m}^{2}~\hbox {g}^{-1}$$ ). The presence of bentonite clay during sol–gel synthesis of $$\hbox {MgFe}_{2}\hbox {O}_{4}$$ NPs prevented particle growth. The adsorption data were modelled using Temkin, Freundlich, Dubinin–Radushkevitch and Langmuir adsorption isotherms. Comparative evaluation of adsorption potential of nanocomposite for Pb(II) and Ni(II) ions confirmed higher affinity of Pb(II) ions ( $$q_{\mathrm{max}} = 90.90~\hbox {mg g}^{-1}$$ ) towards the nanocomposite as compared with Ni(II) ions ( $$q_{\mathrm{max}} = 76.92~\hbox {mg g}^{-1}$$ ). The results were explained on the basis of their hydration enthalpy. Thermodynamic analysis confirmed endothermic and spontaneous nature of adsorption process with $$\Delta H^\mathrm{o}$$ values of 48.67 and $$21.54~\hbox {kJ}~\hbox {mol}^{-1}$$ for Pb(II) and Ni(II) ions, respectively. Kinetic studies confirmed that a pseudo-second-order kinetic model was followed. The obtained results suggested that adsorption capacity of nanofabricated composite for Pb(II) and Ni(II) ions was higher than that of pristine $$\hbox {MgFe}_{2}\hbox {O}_{4}$$ NPs and bentonite clay. The saturated adsorbent was magnetically retrievable and easily regenerated with 0.1 M HCl solutions. It can serve as a potential composite adsorbent for the remediation of heavy metal ions.