Influence of silica-aluminum materials on heavy metals release during paper sludge pyrolysis: Experimental and theoretical studies

Qian Li; Zhaoping Zhong; Haoran Du; Yuxuan Yang; Xiang Zheng; Bo Zhang; Baosheng Jin

doi:10.1016/j.wasman.2023.08.013

Influence of silica-aluminum materials on heavy metals release during paper sludge pyrolysis: Experimental and theoretical studies

Waste Manag. 2023 Oct 1:170:177-192. doi: 10.1016/j.wasman.2023.08.013. Epub 2023 Aug 16.

Authors

Qian Li¹, Zhaoping Zhong², Haoran Du¹, Yuxuan Yang¹, Xiang Zheng¹, Bo Zhang¹, Baosheng Jin¹

Affiliations

¹ Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing 210096, China.
² Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing 210096, China. Electronic address: zzhong@seu.edu.cn.

PMID: 37595503
DOI: 10.1016/j.wasman.2023.08.013

Abstract

It is of great significance to reduce the secondary risk of heavy metals during the pyrolysis of paper sludge. This study used kaolin and alumina-silica-based xerogels to control heavy metals released during sludge pyrolysis. Pyrolyzing a mixture of sludge and 7% kaolin at 400 °C achieved high retention rates for Cu (95.85%), Zn (95.97%), Pb (97.15%), Cd (84.23%), and Cr (84.05%) when the pyrolysis tail gas was treated with 9 g of xerogel. The addition of kaolin facilitated the transformation of Cu, Zn, Pb, and Cr from the unstable fraction to the stable fraction in pyrolysis biochar, reducing their leachability. The xerogels also played a crucial role in adsorbing and stabilizing the heavy metals. The results of thermodynamic equilibrium calculations showed that Pb(g), PbS(g), PbCl₂(g), PbCl(g), Zn(g), ZnCl₂(g), and Cd(g) were the main gaseous products of Zn, Pb, and Cd during paper sludge pyrolysis. The Pb atoms in PbCl₂ and PbS, and the Zn atoms in ZnCl₂ bond with the oxygen atoms on the kaolin surface by covalent bonds, while the Cl atoms in PbCl and the Pb atoms of elemental lead form ionic bonds with H and O atoms on the kaolinite surface, respectively. These experimental and simulation results offer new ideas for controlling heavy metals during sludge pyrolysis.

Keywords: Adsorption mechanism; Heavy metals; Paper sludge; Pyrolysis; Quantum chemistry.