Capture of Airborne Particulate Using Surface Applied Emulsions: Potential for Postdetonation Dirty Bomb Cleanup

Recent research has proposed the use of asphalt and tall-oil-pitch emulsions for stabilizing radioactive contamination deposited on surfaces in urban areas. The objective of this project was to investigate whether surface applied emulsions could capture airborne radioactive particulate. Laboratory experiments included wind-blown particulate capture studies using an acrylic column and particulate retainment experiments using a wind box capable of producing wind speeds of $96\mathrm{km}∕\mathrm{h}$ . A probe methodology was developed to relate particulate retainment to a tack force on the emulsion surface. Experiments were also performed to determine the potential for such emulsions to absorb particulate matter into their emulsion matrix. Tall-oil-pitch emulsions outperformed asphalt emulsions in terms of particulate retention, tack force, and the ability to absorb magnesium silicate. Both tall-oil-pitch and asphalt emulsions were capable of extracting $22–24\mathrm{g}{\mathrm{m}}^{-2}$ of powder from particulate-laden airflow. Tall-oil-pitch emulsions were capable of retaining as much as 5–10% of magnesium silicate powder applied (i.e., retainment densities of $10–20\mathrm{g}{\mathrm{m}}^{-2}$ ) even after $\text{seven}\text{days}$ of curing and after applying $96.5\mathrm{km}∕\mathrm{h}$ $\left(60\mathrm{mph}\right)$ wind. Tall-oil-pitch emulsions were able to absorb surface-applied magnesium silicate (approximately $0.1–0.2\mathrm{g}$ of magnesium silicate per $1.0\mathrm{g}$ of emulsion within $\text{three}\text{days}$ ) into their emulsion matrix, preventing the magnesium silicate from being exposed to the external environment. Initial results with these five different emulsion formulations suggested particulate capture was feasible. Future emulsion formulations (i.e., longer curing times with greater acid concentrations) should be tested to optimize this postdetonation response strategy.