β-cyclodextrin (βCD) can significantly improve the reactivity and long-term remediation performance of nano-zero-valent iron (nZVI), but the stability of composite and the migration performance in porous media have been less studied. In this study, a kind of βCD interface-modified iron-carbon composite (BC-nZVI@βCD) was synthesized, the Zeta potential measurements and sedimentation experiments were conducted to study the stability of materials. Afterwards, the migration behavior of BC-nZVI@βCD in porous media was explored by one-dimensional (1D) sand column experiments and a novel two-dimensional (2D) sand tank simulating the groundwater state. Specifically, in 1D sand column experiments, the primary focus was on investigating the relative effluent concentration ( C/C 0 ) and its distribution patterns within the sand column. In 2D sand tank experiment, the ERT technique was utilized to precisely and real-time monitor the migration behavior of the composite through changes in resistivity. The results showed that the suspensions of BC-nZVI@βCD had the best stability and slowest settling rate. 1D sand column migration experiments showed that the mobility of BC-nZVI@βCD was greatly enhanced, and C/C 0 was increased to 0.60. Moreover, the concentrations of Ca 2 + and SO 4 2- had little effect on migration performance. Humic acid (HA) promoted BC-nZVI@βCD migration at low concentrations (10 mM), while inhibited the migration at high concentrations (20 and 40 mM). In 2D sand tank, BC-nZVI@βCD also showed more excellent migration ability, with the migration distance of BC-nZVI@βCD clearly exceeded 0.40 m. Generally, this study provides a new approach for the study of stability and migration performance of iron-based materials.
DNAPLs are volatile, hardly degradable, highly toxic, and low solubility, which seriously threatens the ecological environment system and human health. While the fine characterization of DNAPLs migration process in porous media is crucial for remediating the contaminated sites. In order to finely characterize the migration process of DNAPLs in porous media, trichloroethylene (TCE) was selected as a typical DNAPLs pollutant in this paper. Then, based on the laboratory sand box model, image method and electrical resistivity tomography (ERT) technology were used to monitor the migration process of DNAPLs in saturated heterogeneous and homogeneous porous media, and the migration rules of TCE in different porous media were discussed and verified to achieve fine characterization of pollutant. The results of the sand box experiment indicated that when the particle size of heterogeneous quartz sand was small, TCE mainly migrated horizontally, and with the increase of quartz sand particle size, the vertical migration gradually dominated. For the homogeneous quartz sand media, TCE was also mainly horizontally migrated, supplemented by vertical migration. With the increase of pollutant injection time, TCE was mainly vertically migrated. When approaching the bottom of the sand box, the vertical migration speed of TCE in both heterogeneous and homogeneous quartz sand media slowed down, and the DNAPLs contamination pool could be formed at the bottom of the sand box. Generally, this paper uses the image method to visually reflect the migration of DNAPLs, and indirectly characterizes the distribution characteristics of DNAPLs by ERT technology, which is of great significance for studying the migration rule of DNAPLs and determining the pollution scope and degree, and can provide certain guiding value for fine characterization and low-cost remediation of DNAPLs pollutants in actual contaminated sites.
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