Fe-exchanged nano-bentonite outperforms Fe₃O₄ nanoparticles in removing nitrate and bicarbonate from wastewater

Nitrate (NO₃^-) and bicarbonate (HCO₃^-) are harmful for the water quality and can potentially create negative impacts to aquatic organisms, crops and humans. This study deals with the removal of NO₃^- and HCO₃^- from contaminated wastewater using Fe-exchanged nano-bentonite and Fe₃O₄ nanoparticles. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, surface area measurement and particle size analysis revealed that the adsorbents fall under the nano-scale size range with high specific surface area, and Fe was successfully exchanged in the nano-bentonite clay. The kinetics of adsorption was well defined by pseudo-first order and pseudo-second order kinetic models for both NO₃^- and HCO₃^-. The Fe-exchanged nano-bentonite was a better performing adsorbent of the oxyanions than Fe₃O₄ nanoparticles. According to the Sips isothermal model, the Fe-exchanged nano-bentonite exhibited the highest NO₃^- and HCO₃^- adsorption potential of 64.76 mg g^-1 and 9.73 meq g^-1, respectively, while the respective values for Fe₃O₄ nanoparticles were 49.90 mg g^-1 and 3.07 meq g^-1. Thus, inexpensiveness and easy preparation process of Fe-exchanged nano-bentonite make it attractive for NO₃^- and HCO₃^- removal from contaminated wastewater with significant environmental and economic benefits.