Volatilization of Solid-Phase Polycyclic Aromatic Hydrocarbons from Model Mixtures and Lampblack-Contaminated Soils

This work summarizes the results from batch experiments investigating the vapor pressure of solid-phase polycyclic aromatic hydrocarbon (PAH) mixtures. Literature regarding the vapor-phase behavior of such systems is sparse because of the relative difficulty in measuring these low volatility compounds. Emerging thermal technologies for remediating soils impacted by such mixtures would greatly benefit from a better understanding of their vapor pressures. An environmentally relevant example of a multicomponent, solid-phase organic contaminant may be associated with lampblack, a sooty byproduct of the oil gasification process employed at former manufactured gas plants (MGPs). PAHs persist at high concentrations in an unspecified state on lampblack and are typically the contaminants of greatest regulatory concern at lampblack-impacted sites. In the first part of this study, three mass ratios for two binary PAH solid combinations were fabricated and studied to determine equilibrium PAH partial pressures. Binary naphthalene−fluorene and naphthalene−anthracene solid samples were fabricated by melt- and solvent-growth crystallization methods to represent dissimilarly and similarly structured pairs, respectively. Results from the model systems demonstrated that the pure-phase vapor pressure was achieved for each component, suggesting that the fabricated multicomponent PAH solids did not behave as a continuous solid solution. Next, partial pressures of several PAHs were measured in the headspace above lampblack-impacted soils from two former MGP sites. Partial pressures ranging from 1% to 60% of the PAH vapor pressures were observed despite the low solid-phase concentrations present in the soils. This result corroborates the results for the fabricated PAH mixtures and implies that continuous solid solutions are unlikely to occur in the field. Thus, vapor pressure−temperature dependency for PAHs in such soils can be estimated using correlations developed for pure PAHs.