Fe-Ni bimetallic adsorbent for efficient As2O3 removal from coal-fired flue gas under a wide temperature range: Experimental and DFT study

Abstract

Adding metal oxides in the furnace can effectively control the emission of heavy metal arsenic in the coal-fired flue gas, and α-Fe2O3 has excellent adsorption performance. However, single metal oxides still have defects such as easy sintering or weak oxidation ability during use, which significantly impact the adsorption effect of arsenic. In this work, a new Fe-Ni bimetallic adsorbent was prepared by hydrothermal calcination, and its mechanism of As2O3 adsorption was investigated in depth through the combination of experiment and theory. The experimental results show that the FN8 (Ni-doped molar percentage is 8%) adsorbent exhibits excellent performance, and its arsenic adsorption capacity reaches 405.60 mg/kg, which is more than twice the adsorption capacity of α-Fe2O3. Ni doping can not only regulate the electron transfer between the α-Fe2O3 interface and As, but also promote the conversion of lattice oxygen to chemisorbed oxygen in the system. In the temperature range of 500 °C–900 °C, the prepared FN8 adsorbent can maintain a good microsphere structure, avoid sintering and provide more adsorption sites, and its arsenic capture capacity is stronger than α-Fe2O3. The density functional theory further reveals the microscopic mechanism of improving the oxidation performance of Fe-Ni adsorbent. The results show that Fe-Ni adsorbent has lower adsorption energy than α-Fe2O3. This is due to the synergism of Ni and O, which leads to the redistribution of electrons on the α-Fe2O3 (001) surface, and the Ni atom provides more free electrons for O atoms, which ultimately promotes the oxidation ability of Fe-Ni adsorbent and forms an As-O covalent bond. The Fe-Ni bimetallic composite adsorbent proposed in this work provides a new idea of bimetallic adsorbent for the effective adsorption of arsenic in the flue gas.