An intercalation-exfoliation method is applied to modify the natural kaolin mineral, so that to improve the enrichment effects on heavy metals (Zn, Pb, Cr & Cd) during coal combustion. The modified kaolin is scanned by electron microscope (SEM), X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and Brunner-Emmett-Teller (BET), which indicate that the natural kaolin is peeled off to form fine flakes and the interlayer spacing is significantly increased. The coal-kaolin combustion tests were performed in a tube furnace from 900°C to 1300°C. It is found that the enrichment of heavy metals is enhanced obviously during the coal combustion, especially when the raw kaolin has high activity. Besides, the adsorption effects on the above four heavy metals are different. To be specific, the kaolin modified by potassium acetate has a better performance for Zn and Pb, but that intercalated by dimethyl sulfoxide shows better influences on Cd and Cr. The modified kaolin can provide more active sites for the adsorption of heavy metals, enhance chemical adsorption, and fix heavy metals in the form of aluminosilicates, silicates and aluminates. These founding could reduce the pollutant emissions of coal combustion in industrial applications.
Keywords: Coal; enrichment; heavy metal; intercalation-exfoliation; kaolin.