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 (Fe0). Cadmium was efficiently removed by Fe0, although reactivity and reusability of Fe0 was significantly promoted by coupling with bismuth (Bi). At a reaction time of 20 min, 85% and 96% Cd2+ was removed by Fe0 and Bi/Fe0, respectively, at first cycle using [Cd2+]0 = 10 mg/L and [Fe0]0 = [Bi/Fe0]0 = 1.0 g/L. However, Cd2+ removal efficiency was reduced to 12% and 80% at sixth cycle by Fe0 and Bi/Fe0, respectively. The X-Ray diffraction and energy dispersive X-Ray spectroscopy analysis proved successful formation of Fe0 by the chemical reduction method and also confirmed coupling of Bi with Fe0 to form bimetallic Bi/Fe0. The oxidation of Fe0 and Bi/Fe0 yielded electron that played significant role in the conversion of toxic Cd2+ into non-toxic Cd0. The reactivity of electron with Cd2+ was calculated to be 4.3 × 109 M-1 s-1. The pH of solution showed pronounced effects on the reactivity of both Fe0 and Bi/Fe0. Removal of Cd2+ by both Fe0 and Bi/Fe0 followed pseudo-first-order kinetic model. The conversion of Cd2+ into non-toxic Cd0 proved Fe0 and Bi/Fe0 to be highly efficient and rewarding in detoxification of Cd2+ and other toxic metals in aqueous environments.