This work examines the largely unexplored role of clay distribution patterns in determining reactive transport and natural attenuation of Marcellus Shale waters accidentally released into natural water systems (e.g., aquifers). Two heterogeneous flow cells (40 cm by 12 cm by 1 cm) were built with the same amount of clay (vermiculite) but different spatial patterns embedded in quartz. The "1/4-zone" and "1/2-zone" cells have rectangular vermiculite clusters at a quarter and a half lengths of the cells, respectively. Effluent chemistrycoming out of these cells with the same influent water compostions were compared to those in a "Uniform" column with evenly distributed vermiculite and quartz with the same vermiculite-to-quartz mass ratio. Effluent chemistry data show that spatial patterns regulate the types of dominant reactions: barium mostly precipitates as barite in the heterogeneous cells whereas primarilyexchanges onto vermiculite in the Uniform column. Spatial patterns also control the extent of reactions: the retention of trace metals (Mn, Pb, Zn, Cu, and Cd) through mineral precipitation is lowered by 1-2 orders of magnitude and presorbed Mg and K are exchanged less from the clay by 1 order of magnitude in the heterogeneous cells compared to the Uniform column. Two-dimensional reactive transport modeling reveals >90% of injected Marcellus waters flow through the higher-permeability sand zones without interacting with the clay. When ion exchange does occur, > 90% reactions occur at the quartz-clay interfaces. These findings reveals that spatial patterns can not only determine reaction rates as has been previously documented, but also regulate reaction types. This underscores the significance of spatial patterns and have important implications for predicting natural attenuation and assessing risks in naturally heterogeneous aquifer systems.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology