Capture effect of Pb, Zn, Cd and Cr by intercalation-exfoliation modified montmorillonite during coal combustion

Raw montmorillonite (MMT) was modified by intercalation-exfoliation method to improve the capture capacity of heavy metals (Pb, Zn, Cr and Cd) during coal combustion. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) Spectroscopy and Brunner-Emmett-Teller (BET) indicated that intercalation agents cetyltrimethylammonium bromide (CTAB) and sodium dodecyl benzene sulfonate (SDBS) could be successfully inserted into the interlayer of MMT during the intercalation step, additionally exfoliation process could peel off the MMT into fine flakes. The co-combustion of coal and MMTs was conducted in a tube furnace from 900 to 1300 degrees C. Results indicated that with the increase of temperature, the retention ratio of Pb, Zn and Cd gradually decreased, especially higher than 1200 degrees C with a great capture capacity reduction, whereas for Cr, it rose first and then decreased. The capture performance of modified MMT on Pb, Zn and Cr was obviously improved. However, for Cd, adverse effect was observed, of which the capacity was even worse than that of raw MMT in some cases. According to the mechanism analysis, the intercalation-exfoliation modification of MMT primarily enhances the chemisorption of heavy metals by exposing more active sites, which facilitates the fixation of heavy metals in the form of aluminosilicates.