Experimental and theoretical-based study of heavy metal capture by modified silica-alumina-based materials during thermal conversion of coal at high temperature combustion

Abstract

Heavy metals emitted from coal combustion can easily pose many threats. In this study, five modified additives based on kaolin were prepared for reducing the emission of heavy metals from high temperature coal combustion and characterized by XRD, FT-IR, XRF, BET, SEM and zeta potential. The heavy metal retention characteristics of the additives under high temperature (900–1300 °C) coal combustion were investigated by static and dynamic experiments, and the results showed that pseudo-boehmite-metakaolin (BMK) was the most effective additive, and the ability of heavy metal capture was Cr > Zn > Pb > Cd, and the dynamic experiments were better than the static experiments. The quantum chemical models of heavy metals (monomers, oxides and chlorides), kaolin and adsorbent-active substances were developed and optimized, and the adsorption energy was calculated. The morphological changes of the active substances were taken into account in the simulation, and new mathematical models for adsorption energy calculation were proposed, which effectively solved the extreme results of adsorption energy calculation and made a comprehensive evaluation of heavy metal adsorption for the whole studied temperature range system. The mechanism of heavy metal adsorption on the active substance was further investigated by the simulations. Heavy metal atoms can form covalent or ionic bonds with O atoms of the active substance, Cl atoms of heavy metal chlorides can be covalently bonded or non-bonded with Al atoms of the active substance, and O atoms of heavy metal oxides can combine with Al atoms of the active substance to form ionic bonds. This study sheds new light on the control of heavy metals in high-temperature coal combustion, the methods for the optimization of simulation and the adsorption mechanism of heavy metals on relevant reactive substances. The method has a promising potential for large-scale application due to its simple preparation, low cost and significant effect.