Kinetic Modeling on the Adsorption of Vapor-Phase Mercury Chloride on Activated Carbon by Thermogravimetric Analysis

Abstract

This study applied thermogravimetric analysis (TGA) technique to investigate the adsorption kinetics of vapor-phase mercury chloride (HgCl2) on activated carbon. HgCl2 is mainly emitted from the incineration of municipal solid waste (MSW) and causes severe adverse effects on human health and environment. Activated carbon injection (ACI) is the best available control technology for mercury removal from the flue gas of MSW incinerators. To investigate the adsorption of HgCl2 on activated carbons, TGA was used to determine the adsorptive capacity and adsorption isotherm of vapor-phase HgCl2 on spherical activated carbons (SACs) with the adsorption temperatures of 30–150 °C and the influent HgCl2 concentrations of 50–1000 μg/m3. Experimental results indicated that the Freundlich adsorption coefficient, n, was determined as 0.40 and 1.2 for the adsorption temperatures of 30 and 150 °C, respectively. The adsorption of HgCl2 on SACs was at a favorable equilibrium at 30 °C and an unfavorable equilibrium at 150 °C. The Freundlich isotherm simulated the adsorptive experimental data better than the Langmuir isotherm. Furthermore, a new approach was proposed to modify the adsorption kinetic model based on pore diffusion scheme describing the transport of HgCl2 molecules within the inner pores of carbon grains for high-temperature adsorption. Model simulation successfully fitted the adsorptive experimental data by varying effective diffusivity and the Freundlich adsorption coefficient, n.