This work examines the largely unexplored role of illite spatial distribution patterns in dictating the sorption of Cr(VI), a ubiquitously occurring contaminant. Flow-through experiments were carried out at 0.6, 3.0, and 15.0 m/day using columns packed with the same illite and quartz mass however with different spatial patterns and permeability contrasts. Column-scale sorption macrocapacity and macrorates were found to decrease with transport connectivity, a quantitative measure of heterogeneity characteristics. At 0.6 and 3.0 m/day, well-connected low permeability illite zones oriented in the flow-parallel direction lead to diffusion-controlled mass transport limitation for accessing sorption sites. This results in up to 1.4 order of magnitude lower macrocapacity and macrorates compared to those in minimally connected columns with well-mixed illite and quartz. At 15.0 m/day, effects of spatial heterogeneities are less significant (up to a factor of 2.8) owing to the close to chemical kinetics-controlled condition. Although the column-scale macrocapacity can reach full sorption capacity under low flow conditions, the macrorates are 10-1 to 10-3 of the microrates measured in well-mixed reactors. Insights gained here bridge gaps between laboratory observations and field applications and advance predictive understanding of reactive transport processes in the naturally heterogeneous subsurface.
|Original language||English (US)|
|Number of pages||10|
|Journal||Environmental Science and Technology|
|State||Published - Feb 3 2015|
All Science Journal Classification (ASJC) codes
- Environmental Chemistry