Heavy metals volatilization characteristics and risk evaluation of co-combusted municipal solid wastes and sewage sludge without and with calcium-based sorbents

Heavy metals, especially gaseous heavy metals, have high toxicity and do harm to human. Heavy metal volatilization characteristics of co-combusted municipal solid wastes (MSW) and sewage sludge (SS) from different mass fraction of MSW and SS, different temperature and different O-2 concentration atmosphere was investigated. Performance of calcium-based sorbents was also studied. Volatilization efficiency of As, Cr, Cu, Ni, Pb and Zn in MSW was 100%, 45.89%-66.58%, 75.62%-92.45%, 42.33%-65.70%, 39.25%-68.76% and 53.57%-84.62%, and that in SS was 28.37%-40.75%, 33.78%-43.42%, 46.08%-56.69%, 35.04%-51.52%, 18.54%-44.99% and 14.72%-48.88%. Volatilization efficiency of heavy metals increased as mass fraction of SS in a blend decreased and as temperature increased. Volatilization efficiency of all heavy metals examined decreased as O-2 concentration increased at high temperature and that of Cu, Pb and Zn increased as O-2 concentration increased at low temperature. CaO, Ca(OH)(2) and CaCO3 declined the volatilization of As, Cr, Cu, Ni, and Zn, while enhanced that of Pb. With calcium-based sorbents, volatilization efficiency of As, Cr, Cu, Ni, and Zn decreased from 70.06%, 39.91%, 75.52%, 44.08% and 40.10% to 54.24%, 33.73%, 39.98%, 20.56% and 32.06%, while that of Pb increased from 47.23% to 100%. Fitting formula was set to predict the heavy metals volatilization, and risk evaluation of gaseous heavy metals was exhibited.