Characteristics of hollow micron zero valent iron and its transport properties in groundwater: Effect of key engineering parameters and retention mechanism

In this study, a hollow micron zero-valent iron (H-mZVI) was synthesized, and its transport and retention property in saturated porous media was determined via a series of column experiments. Furthermore, the maximum migration distance (Lmax) and sedimentation rate coefficient (Kdep) models of H-mZVI in saturated porous media were established using statistical methods. The results revealed a distinct hollow structure in H-mZVI, with a density of 1.03±0.03 g/cm3, significantly lower than solid micron zero-valent iron (4.57±0.15 g/cm3). FTIR and XRD analyses indicated no formation of new functional groups on H-mZVI's surface, with iron being the main component. The column experiment demonstrated that the Lmax of H-mZVI in saturated porous media was 4.15 times that of solid micron zero-valent iron (mZVI) under the same conditions. The prediction model of Lmax aligned with the linear model, where Lmax correlated positively with particle size, injection velocity, and H-mZVI concentration, but inversely with ionic strength. Medium particle size and injection velocity were the main engineering parameters to control H-mZVI. The prediction model of Kdep accorded with the quadratic model, and an interaction was observed between medium particle size and injection velocity, which jointly affected the deposition rate of H-mZVI. Moreover, the single particle capture coefficient (η0) was hereby calculated and analyzed using the T-E theory. Interception primarily governed the precipitation of H-mZVI in saturated porous media, with gravity sedimentation contributing minimally to η0.