Heavy metal enrichment characteristics in ash of municipal solid waste combustion in CO_2/O_2 atmosphere

摘要

This paper investigated the behavior of six heavy metals (Cd, Pb, Cu, Cr, Ni and Zn) in the bottom ashes of recycled polyvinyl chloride pellets (PVC), wood sawdust (WS) and paper mixture (PM), representing the common components of municipal solid waste (MSW), obtained during combustion in CO_2/O_2 atmosphere in a lab-scale electrically heated tube furnace. Replacement of N_2 by CO_2 did not obviously change the shape of relative enrichment factor (RE) curves and subsequent order of heavy metals, but increased enrichment of these heavy metals in bottom ashes of WS, PM and PVC. The increment of O_2 concentration in CO_2/O_2 atmosphere further increased RE values. It was only when the temperature was higher than or equal to 700 ℃ that the increment of the combustion temperature reduced the RE values of heavy metals. The effect of temperature on heavy metals evaporation was the most pronounced for the medium volatile metal Pb, and the least for the low volatiles Cr and Ni. The effect of temperature was more pronounced for PVC ash than for WS and PM ashes. This paper contributes to the control of heavy metals during MSW incineration and management of MSW oxy-fuel residues.