Vaporization characteristics of heavy metal compounds at elevated temperatures

Volatilities and conversions of heavy metal compounds under oxidation conditions at elevated temperatures up to 1,000°C are analyzed using a thermogravimetric furnace to evaluate their behaviors in an incinerator. Most pure metals and their oxides are relatively stable without releasing metal substances into the atmosphere, except for several metals such as As and Hg. However, some chlorides are vaporized in the combustion temperatures and for these volatile chlorides, vaporization fluxes are obtained based on the measurement of their weight losses with increasing temperatures in the furnace. Experimental vaporization fluxes are compared to maximum theoretical fluxes from Herz-Knudsen's kinetic theory of gas. Results of comparison show that evaporation coefficient, α, for each volatile heavy metal compound appears to be a characteristic value of the evaporating substance, not varying with increasing temperatures and the obtained coefficients are ranged in 10^-6 to 10⁸, which could be explained by a vaporization-condensation model of liquids. With some theoretical consideration on interfacial resistance, mass transfer coefficients, K_c for evaporation, are determined as a function of absolute temperatures, and ranged in 10 -6 to 10^-7.