Rapid synthesis of magnetic zeolite materials from fly ash and iron-containing wastes using supercritical water for elemental mercury removal from flue gas

A novel one-step supercritical hydrothermal synthesis method was developed in this study to prepare magnetic zeolites from fly ash (FA) and iron-containing wastes (red mud (RM) and steel slag (SS)) for removing elemental mercury (Hg-0) from flue gas. The efficiency of these magnetic zeolites for Hg-0 removal and their regeneration and recyclability were evaluated using a fixed-bed reactor. The crystal structure, chemical compositions, surface chemistry, and Brunauer-Emmett-Teller specific surface area of the prepared magnetic zeolites were investigated by X-ray diffraction, inductively coupled plasma optical emission spectrometry, X-ray photoelectron spectroscopy, and nitrogen adsorption experiments. The main crystalline phase of the synthetic magnetic zeolite is cancrinite. SS is rich in iron oxide; therefore, the mixture of FA and SS containing 11-15% iron oxide was found to be a better precursor for preparing magnetic zeolite with better performance for Hg removal. The efficiency of Hg-0 removal over magnetic zeolites was above 80% in the presence of hydrochloric acid (HCl, 10-100 ppm). This study indicates that the mechanism of Hg-0 removal over magnetic zeolite in simulated atmosphere containing HCl follows the Eley-Rideal mechanism. Moreover, pre-adsorption of HCl leads to the generation of the active Cl*, which is the main reason that the Hg-0 removal efficiency of the HCl-modified zeolite within the temperature range of 50-300 degrees C was above 80%.