Stabilization of heavy metals in MSWI fly ash through sintering with montmorillonitic clay

Thermal treatments can stabilize the heavy metals in MSWI fly ash to some extent, and effectively decompose the toxic substance like dioxin and furans (PCDD/Fs). Sintering MSWI fly ash with montmorillonitic clay works for the stabilization of the heavy metals in MSWI fly ash. To explore the effect of sintering temperature, sintering time, and additional materials on the stabilization behavior of heavy metals, the instruments such as XRD, XRF; SEM and EDS are applied to analyze the stabilization mechanism of heavy metals in MSWI fly ash. The following conclusions below are drawn: (1) In sintered MSWI fly ash-montmorillonite specimen, temperature is a significant factor which affects fixation property of heavy metal in MSWI fly ash. The fixation effect of heavy metal in MSWI fly ash distinctly varies from temperature. (2) At various sintering temperatures, the tendencies of fixation rates of heavy metals are similar For high-content heavy metals Pb and Zn, the maximum of fixation rates appear at 1.0h, but fixation rates at 1000 degrees C are much higher than that at 800 degrees C and 1200 degrees C. (3) The addition of CaO does not help increase fixation rates of the heavy metals in fly ash. (4) By sintering MSWI fly ash-montmorillonite specimen, Ca(Mg,Fe,Al)(Si,Al)(2)O-5 and (Ca,Na)(Si,Al)(4)O-8 become the main compositions and new crystal solid solutions. Generated by replacement or filling effect, these compositions have a similar skeleton structure to albite (NaAlSi3O8) and gehlenite(NaAlSi3O8) which promote the heavy metals in MSWI fly ash to have an effective stabilization efficiency by encapsulation, solid state reaction and solid solution.