Removal of elemental mercury from coal combustion flue gas by sodium halides impregnated red mud

Abstract

Mercury removal from coal combustion flue gas remains a significant challenge for environmental protection due to the lack of cost-effective sorbents. In this study, a series of red mud (RM)-based sorbents impregnated with sodium halides (NaBr and NaI) are presented to capture elemental mercury (Hg⁰) from flue gas. The modified RM underwent comprehensive characterization, including analysis of its textural qualities, crystal structure, chemical composition, and thermal properties. The results indicate that the halide impregnation substantially impacts the surface area and pore size of the RM. Hg⁰ removal performance was evaluated on a fixed-bed reactor in simulated flue gas (consisting of N₂, O₂, CO₂, NO and SO₂, etc.) on a modified RM. At an optimal adsorption temperature of 160 °C, NaI-modified sorbent (RMI5) offers a removal efficiency of 98% in a mixture of gas, including O₂, NO and HCl. Furthermore, pseudo-second-order model fitting results demonstrate the chemisorption mechanism for the adsorption of Hg⁰ in kinetic investigations.