Study On Spatial Variation Of Porous Media Inner Structure Caused By Colloidal Sediment Based On XDMT Approach

Contaminants in natural water body can be attached on colloidal particles, which leads to a speedup of contaminant migration. Moreover, the dynamics process of colloidal particles in porous media like soil, aquifers and river bed, will affect the inner structure and permeability of porous media. This phenomenon caused by particle deposition is termed of clogging. Clogging greatly affects the flow and mass transport in porous media, which is very important for a variety of applications including performance of water treatment filters, pathogen and contaminant transport in groundwater, oil extraction, in situ bioremediation of contaminant plumes, and degradation of streambed habitat by siltation, etc.However, the current research on migration of colloidal particles in porous media is mostly based on median scale (10-3～100m) studies like column experiments. Previous studies show that the porous media has great effects on dynamics process of colloidal particles. But the pore-scale (10-6m) studies on the inner structure variation caused by deposition are less investigated. In this dissertation, as a basic tool, X-ray difference micro-tomography was used to observe the variation of inner structure of porous media, without any destructions. And Lattice Boltzmann simulation was applied to quantitatively analyze the spatial variation of porous media, in order to evaluate the effects on local porosity and permeability caused by particle deposition. The main research work includes:(1) Non-destructive observation was applied on arsenic-rich fluvial sediments and lab-prepared arsenic samples by X-ray Difference Micro-tomography. And the inner structure of porous media and arsenic aggregates were three-dimensionally visualized by using Avizo6and Blob3D. These results show that difference micro-tomography can be used to observe the pre-and post-deposition structure of porous media, without any destructions to the samples, the morphology and size of particle aggregates were also analyzed.(2) Geostatistics and wavelet analysis were used to study the distribution of colloidal deposits in the media and the spatial correlation length that controls the deposition process. Study showed that the distribution of colloid deposits had great relation with the media’s inner structure and the spatial correlation length was closed to the medium grain diameter.(3) Flume experiments, X-ray micro-tomography and Lattice Boltzmann methods were combined to investigate the mixing of sand grains and glass beads in a streambed with active bed sediment transport, as well as the simulation of stream-subsurface exchange of colloid ZrO2particles in the recirculating laboratory flume. Quantitative analysis was applied to evaluate the affects of media’s local porosity and permeability caused by deposition. Results show that local permeability increased with increasing local porosity, following a power law with k∝(?(2.9.Overall, this dissertation combined the XDMT, image processing, column experiments, flume experiments with LB simulations to study the dynamics process of colloidal particles in porous media. Quantitative analysis was applied to study the spatial variation of media inner structure and permeability caused by colloid deposition. From the results, the combination of XDMT and LB methods has a great feasibility in the pore-scale study of particle migration and offers a brand new approach in this research field.