Migration experiment and numerical simulation of modified nanoscale zero-valent iron (nZVI) in porous media

Abstract

A packed column experiment was carried out to study the migration process of modified nano-zero-valent iron (nZVI) in porous media and the change process of hydraulic characteristics of porous media. In view of the complexity of the migration mechanism of modified nZVI in porous media, an unsteady variable parameter mathematical model considering the effects of interception, Brownian diffusion, gravity settling and the change of porous media properties was established. By fitting the model with the experimental data, the changes of various mechanisms in the experimental process were studied. The results show that the higher the injection flow rate, the higher the concentration at the outlet, and the lower the injection concentration, the higher the throughput. The distribution of iron particles in porous media is not uniform, the maximum at the entrance and the lowest at the exit. The model fits the test results well under various test conditions. The model analysis shows that in the process of particle injection, the particle size is small at the beginning, and the particles are mainly attached to the surface of the medium due to Brownian motion. As the experiment proceeds, the particle size increases, the Brownian motion effect decreases, but the interception and gravity settlement effect strengthens. In addition, during the whole process, the porosity of the medium decreases gradually, and the probability of collision between particles and porous media increases, which leads to the increase of the deposition rate coefficient.