Experiments were conducted in a bench-scale fixed bed reactor with alpha-Fe2O3 and gamma-Fe2O3 samples to investigate the mechanism of Hg-0 oxidation in the presence of HCl at 80-680 degrees C respectively. HCl is one of the main impurities in coal-derived fuel gas and its contribution to Hg-0 removal is complex and necessary to research. The experimental results showed that the Hg-0 removal mechanism with HCl could probably be divided into three stages based on the reaction temperature. At low temperature, the Eley-Rideal mechanism with HCl pre-adsorption was the most probable Hg-0 oxidation pathway. As the temperature increased more than 280 degrees C, Hg-0 removal efficiency differs significantly on alpha-Fe2O3 and delta-Fe2O3, and the most suitable mechanism was Langmuir-Hinshelwood. With the increasing temperature to 680 degrees C, the homogeneous reaction between HCl and Hg-0 as well as Langmuir-Hinshelwood are responsible for the transformation of Hg-0. We also discovered that the reaction time played a significant impact on the Hg-0 removal at low temperature, and caused the secondary mercury removal efficiency owing to the probable product of FeCl3. Additionally, HBr was adopted to compare with HCl, which obviously enhanced the Hg-0 oxidation on alpha-Fe2O3. (C) 2016 Elsevier Ltd. All rights reserved.