DISTRIBUTION OF ELEMENTAL MERCURY IN SATURATED POROUS MEDIA

Elemental mercury (Hg-0) 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 Hg-0, it penetrates into the subsurface and gets entrapped in the available pore spaces. Once Hg-0 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 Hg-0 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 Hg-0 at its residual saturation as a function of capillary number (N-C). An initially water-saturated micromodel was flooded with Hg-0 at a prescribed rate to simulate the migration of Hg-0 into the saturated zone. Then Hg-0 was displaced by water flooding and finally residual Hg-0 was established at different N-C. Images taken during the experiment were processed to generate residual Hg-0 saturation, size, shape, and interfacial area. Residual Hg-0 ranged from small spherical blobs to large complex blobs and was found to have an inverse relationship with N-C. 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.