Stabilization of Fe-0 nanoparticles with silica fume for enhanced transport and remediation of hexavalent chromium in water and soil

Effective in situ remediation of Cr(VI) in groundwater requires the successful delivery of reactive iron particles to the subsurface. Fe-0 nanoparticles (20-110 nm diameter) supported on silica fume were synthesized by borohydride reduction of an aqueous iron salt in the presence of a support material. The experimental result showed that attachment of Fe-0 nanoparticles on the commercial available sub-micrometer silica fume prevented them from aggregation while maintaining the particle reactivity. When the Fe-0 concentration was 0.4 g/L, 88.00% of 40 mg/L Cr(VI) was removed by silica fume-supported Fe-0 nanoparticles (SF-Fe-0) in 120 min, 22.55% higher than unsupported Fe-0. Furthermore, transport experiments confirmed that almost all unsupported Fe-0 was retained, whereas 51.50% and 38.29% of SF-Fe-0 were eluted from the vertical and horizontal sand column, respectively. Additionally, the effect of solution ionic strength on the transport ability of SF-Fe-0 was evaluated. The result showed that increase in the salt concentration led to a decrease in the mobility and also the divalent ion Ca2+ had a greater effect than that of monovalent ion Na+.