Kinetics modeling of the volatilization of mercury compounds involved in spent mercury-containing catalyst under microwave irradiation

The industrial design and development of microwave-induced volatilization of hazardous substances in waste greatly depend on their dielectric properties. The dielectric properties of different mercury compounds in spent mercury-containing catalyst (SAC) were investigated by the cavity perturbation method at different temperatures. The decomposition absorption mechanisms for HgS and HgCl2 show the same trend according to thermogravimetric analysis results over the temperature range of interest. The SAC composite exhibits sufficient microwave absorption from 20 degrees C to approximately 600 degrees C owing to the superior dielectric properties of non-volatile mercury-containing compounds (HgCl2 and HgS). At temperatures above 600 degrees C, the dielectric properties of the SAC are determined by the residual mercury and carbon matrix. Phase analyses indicate that the entire process of microwave heating could be divided into three stages: (1) The volatilization temperature of unbound water and some impurities are between 20 degrees C and 100 degrees C; (2) The main thermal disintegration region of mercury species is between 100 degrees C and 600 degrees C; (3) HgCl2 and HgS volatilize completely to gas at 600 degrees C. Meanwhile, HgCl2 decomposing more readily than HgS. (C) 2021 Published by Elsevier B.V. on behalf of King Saud University.

Automated summary

The industrial design and development of microwave-induced volatilization of hazardous substances in waste heavily relies on their dielectric properties. The study found that the dielectric properties of SAC composite allow for sufficient microwave absorption within a specific temperature range. Additionally, phase analyses revealed that the microwave heating process can be divided into three stages with different volatilization behaviors of mercury compounds.