[Effect of Nano-TiO₂ on Release and Speciation Changes of Heavy Metals in Soil]

The effects of nano-TiO₂ on migration and transformation of heavy metals in soil were investigated by outdoor flooding simulation experiments. Cr, Pb, Zn, Cd and Cu contents of different forms were determined in soil of typical fluctuating zone of Three Gorges Reservoir. The results showed that, after flooding months, both addition of 4 g · kg⁻¹ of rutile and anatase particles resulted in the release of about 30% Cr into the water. Nano-TiO₂ particles mainly promoted the dissolution of oxidizable residual Cr, and elevated its ecological risk. Thus nano-TiO₂promoted the activation of chromium and improved the mobility of chromium in soil. 4 g · kg⁻¹ of rutile particles caused the decrease of acid exchangeable lead by 25.92% and oxidizable lead by 33.09%, and enhanced the mobility of Pb. However, anatase particles caused the increase of oxidizable zinc by 30% in soil, which facilitated fixing of zinc. In addition, two types of nano-TiO₂particles had no significant effect on the speciation changes of Cu and Cd. Therefore, the effect of nano-TiO₂ on release and transformation of Cr in soil was the largest, followed by Pb and Zn. This needs special attention when using nano-TiO₂ to remediate heavy metals contaminated soil and assessing its environmental risk.