Effect of additive and washing pre-treatment on heavy metal vaporization during sintering process of MSWI fly ash

An experimental work was carried out to investigate the effect of additives (clay and coal fly ash) and washing-pretreatment on the stabilization of critical heavy metals (Cd, Cu, Zn, Pb, Cr, Ni) during a sintering process of municipal solid waste incinerator(MSWI) fly ash. The proportions of the three constituents were varied to adjust the mixture compositions. The washing time were 8 h, 16 h and 24 h. The material was compacted in cylindrical specimens at 3 kN and treated at 11001 for 4 h. When the clay content was increased to 70%, the stabilized ratio was increased from 16.96% to 28.42% for Cd, from 10.58% to 37.02% for Pb. from 46.38% to 55.14% for Cu, from 42.14% to 64.47% for Zn, but the stabilized ratio of Ni and Cr was decreased. When coal fly ash was increased in the MSWI fly ash, the stabilized ratio was decreased from 16.96% to4.67% for Cd, increased from 46.86% to 81.43% for Cu, but the addition of coal fly ash did not increased the stabilized ratio of Zn, Pb, Ni and Cr. Washing pre-treatment increased the stabilized ratio of Cd, Cu and Pb significantly. The leaching behavior of the heavy metals in the sintered products was studied by the toxicity characteristic leaching procedure (TCLP), the results showed that the leaching concentration of the six heavy metals were very low.