Transport behavior of nano zero-valent iron (nZVI) in porous media

The nano zero-valent iron (nZVI) has been seen as a promising material in the field of groundwater remediation. Researchers have studied the application of nZVI in in-situ remediation of groundwater. However, most of the existing studies focus on the transport of nZVI before reaching the polluted area. The transport behavior of contaminant-sorbed nZVI has not been fully studied. This study aims to illustrate the differences in the colloidal stability and motion ability of nZVI before and after phosphate adsorption is studied by sedimentation tests and one-dimensional column tests. The influences of environmental factors such as flow rate, ionic strength and porous medium characteristics on the motion ability of phosphate-sorbed nZVI (PS-nZVI) are analyzed. The results show that PS-nZVI has higher stability and mobility than nZVI, which is due to the increase of negative surface potential after phosphate adsorption. Geo-environmental conditions have great impact on the transport of PS-nZVI. Low ionic strength and high velocity are favorable for transport. The transport capacity of PS-nZVI in medium size glass beads is higher than that in fine and coarse size glass beads. PS-nZVI has higher mobility in glass beads than those in natural sand. The above experimental phenomena can be explained by the DLVO theory and various retention mechanisms of colloids in porous media, such as bridging, size exclusion and surface deposition. In the natural sand mixed with kaolinite, the mobility of PS-nZVI is very weak, and the settlement tests show that kaolinite can promote the agglomeration settlement process of PS-nZVI, which indicates that the soil layer containing kaolinite may collect PS-nZVI. The influences of contaminants and environmental factors on the mobility of nZVI should be considered in its filed application.