In situ immobilization of lead species in combustion environments by injection of gas phase silica sorbent precursors

A mechanistic study of the in situ immobilization of a toxic metal species in a high-temperature environment using gas phase sorbent precursors is described. Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained to study the interaction of lead with silicon species in high-temperature oxidizing environments. The application of laser-induced fluorescence, the spectroscopy of PbO(g), and the techniques of measurement of gas phase precursors to particle formation are discussed. The silicon precursor is oxidized to form silica particles in the high temperatures, followed by a reactive scavenging of PbO(g). The result is that the lead oxide gas phase concentration is reduced, and homogenous nucleation of lead species is suppressed. The resultant particles are not only larger than a lead only case but also have morphologies in which lead is effectively immobilized and vitrified within a silica matrix. Trace quantities of silicon species have been shown to be effective in conversion of lead oxide to lead silicate. The measured conversion efficiencies of lead oxide to lead silicate agree well with equilibrium calculations, and no rate limitations were observed.