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With dramatically increasing emission of heavy metals and chlorinated compounds from thermal treatments of fuels and wastes, kaolin, one of the widely used materials in the industry, was researched to control these pollutants in recent years. To investigate the retention of lead chloride (PbCl2) by kaolin and metakaolin obtained from thermal activation of kaolin, the PbCl2 adsorption experiment in a two-stage furnace was conducted from 600 to 900 °C under N2, H2O, and O2. Furthermore, the toxicity leaching procedure was also utilized to evaluate the leachability of Pb from used sorbents. The results showed that the capture efficiency of PbCl2 by the sorbents and leachability of Pb from the used sorbents were closely related to the increase of the experimental temperature. The retention of Pb by raw kaolin was superior to that by metakaolin; however, the leachability of Pb from the used metakaolin was totally lower. Adding H2O in the adsorption experiment can obviously increase the retention of Pb by the sorbents and decrease the leachability of Pb from the used sorbents. Besides, the effects of adding O2 on promoting the retention of Pb by kaolin and reducing the leachability of Pb from used kaolin were also noticeable due to the influence of adding O2 on enhancing chemical adsorption and melting behavior of kaolin. The maximum capture efficiency of Pb by kaolin and the minimum ratio of leachability from the used kaolin can reach 74.01% and 1.60%, respectively, with the addtion of O2 in the adsorption experiment at 900 °C.

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With the spread of phytoremediation, research on the behavior of heavy metals (HMs), such as Cd, during the heat treatment of contaminated biomass is necessary. The thermodynamic equilibrium calculation was used to forecast the form of Cd during the combustion of ryegrass. When co-existing with Pb and Zn, Cd mainly existed as CdO for the prior combination between trace Cl and numerous K/Mg. The combustion experiment with mineral additives was conducted in the horizontal tube furnace, and the sub-step leaching procedure was also used to evaluate the leaching toxicity of products. During combustion at 900 °C without additives, about 93.7% Cd transferred to the atmosphere. Kaolin, montmorillonite, and γ-Al2O3 provide active Si or Al to restrain the volatilization of Cd and reduce the concentration of Cd in the leaching solution via similar mechanisms, while montmorillonite is more efficient on Cd retention than kaolin over 900 °C. According to the X-ray diffraction analysis, reactions between the K and Si/Al components may form K–Si–Al compounds, such as KAlSiO4, and restrain the retention of Cd directly. Although the addition of CaO promotes the volatilization of Cd and other HMs, it can restrain the complexation of cadmium cations and reduce the leaching toxicity greatly by raising the pH value.