In this work, the solid waste residue derived from the production of alumina, red mud, is modified by potassium halides impregnation, and is used to capture elemental mercury (Hg-0) from flue gas. The chemical and physical properties of materials are studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET). A series of experiments are conducted in a fixed-bed reactor to study the effects of some key parameters such as loading value, reaction temperature and main flue gas components on Hg-0 removal. The reaction mechanism and kinetics model analysis of Hg-0 removal are also studied. The results indicate that the modification of potassium halides significantly improve the Hg-0 removal performance of red mud, and the KI modified red mud exhibits the highest Hg-0 removal efficiency. Increasing reaction temperature, loading value, O-2 concentration and NO concentration enhances Hg-0 removal. Increasing SO2 concentration greatly reduces Hg-0 capture. Water vapor has a dual effect on Hg-0 removal, which has an optimal concentration of 4%. The process of Hg-0 adsorption on modified red mud conforms to the pseudo-second order kinetic model.