Evaporation of Heavy Metals during the Heat Treatment of Municipal Solid Waste Incinerator Fly Ash

Abstract

Thermal treatment is a promising way for the decontamination and inertization of residues from waste incineration. The evaporation of heavy metals thereby is of great significance. It is the goal of this work to investigate the fundamental aspects of the evaporation of heavy metals in the heat treatment process and to determine the process parameters leading to complete evaporation of the relevant heavy metals. Evaporation experiments in different atmospheres were carried out with filter ash from municipal solid waste incineration. The quantities of the heavy metals Zn, Pb, Cd, and Cu evaporated as a function of time were measured at temperatures between 670 and 1300 °C; evaporation turned out to be most effective at temperatures just below the melting range of the residue (i.e., at 1000–1100 °C) and decreased drastically above this temperature range. The amounts of evaporation (relative to the contents in untreated filter ash) at about 1100 °C were 98–100% of Pb, Cd, and Cu and 50% of Zn in air and 98–100% of Pb, Cd, and Zn and 10% of Cu in argon atmosphere, respectively. Results of experiments using model systems indicate that the decrease in the Zn evaporation at high temperatures is caused by the formation of compounds like Zn2SiO4 and ZnAl2O4 The results of the experiments in argon atmosphere are explained thermodynamically by the reductive potential of the carbon, contained in the residue.