Abstract: The mobility of nano zero-valent iron (nZVI) will greatly affect its potential application as a remediation material for polluted groundwater. One-dimensional (1D) column tests are commonly used in previous works to study the transport behavior of nZVI. However, the reports about the two-dimensional (2D) transport behavior of nZVI are still very limited. In this study, model test systems were developed to simulate the transport and retention of nanoparticles in porous media. Glass beads of different sizes (fine, medium and coarse) were used to simulate the porous media. The motion behavior of phosphate-sorbed nZVI (PS-nZVI) in porous media was obtained by sampling and image analysis. Results of 1D column tests show that PS-nZVI has certain mobility in medium and coarse glass beads with liquid-phase recoveries equal to 50.3% and 41.0%, but has poor mobility in fine glass beads. Results of 2D model tests show that the retention of PS-nZVI in medium glass beads decreases with the distance, while the retention in coarse glass beads increases first and then decreases with the distance. Results show that the transport and retention process of PS-nZVI is affected by both the particle size of porous media and the flow velocity. The combined influence of clogging and surface deposition leads to the different transport and retention behaviors of PS-nZVI in glass beads of different sizes. The results of this study can be used to evaluate the mobility of PS-nZVI and analyze its retention mechanism in porous media, and provide a reference for engineering application and environmental risk assessment of nZVI technology.

Key words: phosphate-sorbed nano zero-valent iron (PS-nZVI), porous media, transport, retention, model test