Reduction and removal of aqueous Hg(II) using indium-modified zero-valent iron particles

The zero-valent iron (ZVI) was impregnated with Ni, Cu and In, in order to maximize the reactivity and durability for Hg(II) reduction and removal. When the Hg removal efficiency was tested with 0.1 mM Hg(II) at pH 7, the In-doped ZVI (In-ZVI) showed the highest removal efficiency (99.3%) while the Hg(II) removal efficiency was only 15 and 3.6% with Ni and Cu, respectively. In the durability test of In-ZVI, no significant decrease in the Hg(II) removal efficiency was observed after seven successive spiking of Hg(II), with 99.9% removal at the first spiking and 99.4% at the seventh spiking. Diverse control tests confirmed that the coupling of In(0) oxidation and Fe(III) reduction on the surface of In-ZVI apparently caused the generation of reactive atomic hydrogen (center dot H), leading to the enhanced ZVI reactivity and durability toward the reduction and removal of Hg(II).