Distribution of elemental mercury in saturated porous media

Elemental mercury (Hg0) is often found in the vicinity of industrial facilities such as chlor alkali plants, thermometer manufacturing units, and pharmaceutical industries. During accidental land spills or improper disposals of used Hg0, it penetrates into the subsurface and gets entrapped in the available pore spaces. Once Hg0 is entrapped in the subsurface as residual blobs, it would be subjected to biochemical transformations and be converted to other toxic forms of mercury. A significant lacuna prevails in addressing Hg0 contamination and remediation which is dominated by pore scale processes in the subsurface. In this study, a series of experiments was performed to characterize the morphological distribution of Hg0 at its residual saturation as a function of capillary number (NC). An initially water-saturated micromodel was flooded with Hg0 at a prescribed rate to simulate the migration of Hg0 into the saturated zone. Then Hg0 was displaced by water flooding and finally residual Hg0 was established at different NC. Images taken during the experiment were processed to generate residual Hg0 saturation, size, shape, and interfacial area. Residual Hg0 ranged from small spherical blobs to large complex blobs and was found to have an inverse relationship with NC. The results obtained in this study would serve as fundamental parameters for evaluating relationship amongst residual mercury saturation, interfacial area, and ground water flow in mercury-contaminated sites.