Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing, Jiangsu 210096, China.
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing, Jiangsu 210096, China.
Sci Total Environ. 2023 Sep 10;890:164381. doi: 10.1016/j.scitotenv.2023.164381. Epub 2023 May 20.
In this study, we utilized low-cost halloysite (Hal) for the first time to enhance the solid-phase enrichment and stability of heavy metals (HMs) during solid waste pyrolysis through experimental and theoretical methods, and compared with kaolinite (Kao). Experimental results demonstrated that Hal was superior to Kao in improving the solid-phase enrichment of HMs. Specifically, the solid-phase enrichment of Cd increased by 32.6 % (500 °C) and 25.94 % (600 °C), while that of Pb and Zn increased by 17.37 %/16.83 % and 19.82 %/22.37 % (700/800 °C), respectively. Adding Hal reduced the proportion of HMs in the unstable fraction (F1 + F2), consequently lowering the environmental risk of biochar and the extractable state of HMs. Through Grand canonical Monte Carlo and Density Functional Theory (DFT) simulations, we analyzed the adsorption amounts, adsorption sites, and adsorption mechanisms of Cd/Pb compound on Hal/Kao surfaces, revealing that the primary factor influencing the adsorption performance of Hal and Kao was the difference in specific surface area. The adsorption amounts of HMs by Hal were significantly higher than Kao and decreased with increasing temperature, while the difference in adsorption performance caused by structural bending was negligible. The DFT results indicated that Cd and Pb monomers were stabilized by establishing covalent bonds with OH or reactive O atoms on the Al-(001) surface, whereas the covalent bonds with ionic bonding properties formed between Cl atoms and unsaturated Al atoms played a crucial role in stabilizing HM chlorides. Furthermore, the adsorption energy of Hal on HMs increased with the removal rate of OH. Our study highlights the potential of Hal in stabilizing HMs during pyrolysis without requiring any modifications, thereby avoiding the generation of modified waste solutions and unnecessary cost loss.
在这项研究中，我们首次利用廉价的埃洛石（Hal）通过实验和理论方法来增强固废热解过程中重金属（HMs）的固相富集和稳定性，并与高岭石（Kao）进行了比较。实验结果表明，Hal 在提高 HMs 的固相富集方面优于 Kao。具体而言，Cd 的固相富集增加了 32.6%（500°C）和 25.94%（600°C），而 Pb 和 Zn 的固相富集分别增加了 17.37%/16.83%和 19.82%/22.37%（700/800°C）。添加 Hal 降低了 HMs 在不稳定部分（F1+F2）中的比例，从而降低了生物炭的环境风险和 HMs 的可提取性。通过巨正则蒙特卡罗和密度泛函理论（DFT）模拟，我们分析了 Cd/Pb 化合物在 Hal/Kao 表面的吸附量、吸附位置和吸附机制，揭示了影响 Hal 和 Kao 吸附性能的主要因素是比表面积的差异。Hal 对 HMs 的吸附量明显高于 Kao，且随温度升高而降低，而结构弯曲引起的吸附性能差异可忽略不计。DFT 结果表明，Cd 和 Pb 单体通过与 Al-(001)表面上的 OH 或反应性 O 原子建立共价键而稳定，而 Cl 原子与不饱和 Al 原子之间形成的具有离子键特性的共价键在稳定 HM 氯化物方面起着关键作用。此外，Hal 对 HMs 的吸附能随 OH 去除率的增加而增加。我们的研究强调了 Hal 在热解过程中稳定 HMs 的潜力，而无需进行任何修饰，从而避免了改性废溶液的产生和不必要的成本损失。
