Kinetics, product properties, and migration of heavy metals during co-pyrolysis of textile dyeing sludge and litchi shells

Abstract

In this study, the co-pyrolysis behavior, products, and the migration of heavy metals (HMs) during the co-pyrolysis of textile dyeing sludge (DS) and litchi shells (LS) were investigated. Thermogravimetric (TG) analysis was used to identify the pyrolysis stages of mixtures, and the activation energy (Ea) of the main pyrolysis stages was calculated by Kissinger Akahira Sunose (KAS) method. The average of Ea decreased from 326.1 to 232.5 kJ/mol with increasing the proportion of LS. The bio-oil compositions indicated that the interaction effect between DS and LS mainly promoted the generation of phenols and acid compounds and inhibited the production of nitrogenated compounds, ketones, and ethers. The emission characteristics of gases from the co-pyrolysis of three samples were analyzed by TG-FTIR. The results found that the addition of LS could inhibit the generation of NOx precursors. Finally, LS in co-pyrolysis was beneficial to the increase of Cu, Zn, Cr, and Ni stable fractions (F3 +F4) to 96%, 69%, 99% and 80%, and the potential Ecological Risk Index (RI) of biochar was reduced to 7.26. This study provided a cleaner and more efficient idea for co-pyrolysis strategy and resource utilization of solid waste.