China Nonferrous Metallurgy

At present, alumina is widely used to absorb hydrogen fluoride escaping during the aluminum electrolysis process, but the adsorption mechanism and process are not clear. This paper introduces the current research status of the adsorption process of hydrogen fluoride on alumina and the structure of the adsorption products. The research methods adopted by the researchers include two types. One is the experimental methods, including measuring the volume and pressure of hydrogen fluoride before and after the adsorption, drawing adsorption isotherms, analyzing the thermal stability of the adsorption products, and studying Nuclear Magnetic Resonance(NMR) and Infrared Radiation(IR) of the adsorption products to obtain the adsorption structure indirectly. The other is to simulate the adsorption structure by computer based on density functional theory. There are two different models of hydrogen fluoride adsorption on alumina suggested by the researchers. One is Lamb model in which F atom is directly adsorbed on Al atom of alumina. The other is a bimolecular layer model in which F atoms are adsorbed on hydroxyl or water molecules on the surface of alumina. The simulated adsorption structure is also based on these two models with focusing on the adsorption sites of hydrogen fluoride on alumina surface and the formation process of Al—F bond and O—H…F bond. Finally, the similarities and differences between the two adsorption models are summarized, and the future research direction of the adsorption process and structure of adsorbed products is prospected.