UV spectroscopy of metal volatilization during thermal plasma processing of waste glass melts

Atomic emission spectroscopy (AES) is used to monitor volatilization during waste vitrification with thermal plasmas. Model waste specimens consist of an alumino-silicate clay spiked with 10 wt. % Fe, Ni, or Cr. Specimens are vitrified in processing atmospheres with 0, 8.5, and 17 vol. % oxygen/argon concentrations. Particulate generated from condensation of the volatilized materials is collected following each specimen run and analyzed by energy dispersive X-ray analysis to determine composition. Spectra are collected from the ultraviolet range 240-380 nm where the presence of metal vapor is readily detected. Correlation between line emission intensities and volatilization rates allows the establishment of provisional detection limits for the volatilization of Ni, Cr, Si, and Fe, of 1 × 10^-3 g/s, 4 × 10^-4 g/s, 2 × 10^-4 g/s, and 5 × 10^-5 g/s, respectively. The results of this investigation support the concept of using AES as an in-situ process monitor for feedback to optimize plasma processing of hazardous metal-containing waste.