Co-transport of Pb(2+) and TiO2 nanoparticles in repacked homogeneous soil columns under saturation condition: Effect of ionic strength and fulvic acid

This study investigated the effects of suspended TiO2 nanoparticles (nTiO2) on the transport of Pb(2+) in saturated repacked soil columns under different ionic strengths (IS) and in the presence of fulvic acid (FA). Also, the contribution of soil colloids to the mobility of Pb(2+) was discussed. In the absence of nTiO2, little amount of Pb(2+) was detected in the effluent even in the presence of FA. However, the presence of nTiO2 significantly enhanced the mobility of Pb(2+) in soil columns under all tested conditions and nTiO2-associated Pb(2+) was the major migration species of Pb(2+). Increasing the solution IS decreased the nTiO2-associated Pb(2+) migration due to the significant decrease in the mobility of nTiO2 in soil. FA remarkably increased the nTiO2-associated Pb(2+) mobility in soil column, which was mainly to increase the mobility of nTiO2 in soil and decrease desorption rate of Pb(2+) from nTiO2 during transport. Moreover, nTiO2 significantly enhanced the release of Fe-Al soil colloids, which in turn was also responsible for the enhancement of Pb(2+) mobility in soil.