HEAVY METALS VOLATILITY STUDY DURING THERMAL PLASMA VITRIFICATION BY OPTICAL EMISSION SPECTROSCOPY

摘要

Fly ash issued of incineration of wastes content high proportion of heavy metals salts specially chlorides and sulfates. According to the volatility of these compounds observed during vitrification of fly ash, a predictive model has been used to simulate the elimination of Pb, Zn and S from the melt as a function of time and temperature for a system including chlorides, oxides and sulfates. The objective of this work was the experimental study of heavy metals volatility using optical emission spectroscopy. A twin torch plasma system, mounted above a cold crucible with Ar (or Ar + O_2) as plasma gas, has been used. The crucible was filled with synthetic glass in which known amounts of metallic salts were added to obtain the same chemical composition as used in the model. From spectral lines intensities of Ar, the plasma temperature profiles along the observation direction has been first established, before using ratios of spectral lines of Ar and metallic (Pb, Zn) or Cl vapors to reach the evolution of the elements concentrations above the melt. The influence of the atmosphere( Ar or Ar + O_2) above the crucible has been studied and differences in elements behaviors have been pointed out. The results of the spectroscopic measurements have been compared to the ones issued of modeling, in order to validate our model of vaporization.