Synergistic effects of bismuth coupling on the reactivity and reusability of zerovalent iron nanoparticles for the removal of cadmium from aqueous solution

Removal of cadmium (Cd2+), a highly toxic heavy metal, from aqueous solutions was investigated using nano zerovalent iron (Fe-0). Cadmium was efficiently removed by Fe-0, although reactivity and reusability of Fe-0 was significantly promoted by coupling with bismuth (Bi). At a reaction time of 20 min, 85% and 96% Cd2+ was removed by Fe-0 and Bi/Fe-0, respectively, at first cycle using [Cd2+](0) = 10 mg/L and [Fe-0](0) = [Bi/Fe-0](0) = 1.0 g/L. However, Cd2+ removal efficiency was reduced to 12% and 80% at sixth cycle by Fe-0 and Bi/Fe-0, respectively. The X-Ray diffraction and energy dispersive X-Ray spectroscopy analysis proved successful formation of Fe-0 by the chemical reduction method and also confirmed coupling of Bi with Fe-0 to form bimetallic Bi/Fe-0. The oxidation of Fe-0 and Bi/Fe-0 yielded electron that played significant role in the conversion of toxic Cd2+ into non-toxic Cd-0. The reactivity of electron with Cd2+ was calculated to be 4.3 x 109 M-1 s(-1). The pH of solution showed pronounced effects on the reactivity of both Fe-0 and Bi/Fe-0. Removal of Cd2+ by both Fe-0 and Bi/Fe-0 followed pseudo-first-order kinetic model. The conversion of Cd2+ into non-toxic Cd-0 proved Fe-0 and Bi/Fe-0 to be highly efficient and rewarding in detoxification of Cd2+ and other toxic metals in aqueous environments. (C) 2019 Elsevier B.V. All rights reserved.