MECHANISMS OF HF BONDING IN DRY SCRUBBER IN ALUMINIUM ELECTROLYSIS

摘要

Modern dry scrubbers in electrolytic winning of aluminium operate with very high efficiency, typically above 99 percent, and all but the fugitive fluoride losses are returned into electrolytic cell. The principle of purification of exhaust gases from electrolytic cells is adsorption of HF onto primary alumina in dry scrubber reactors, where gases from cells and flow of active (primary) alumina run into each other and react. It is very important how the reaction between gases and primary alumina takes place and which chemical mechanisms are taking part. Nevertheless, also industrial conditions are playing an important role in efficiency of the scrubbing reaction. In references on dealing with related systems there can be found that most research was made to improve dry scrubbing systems and their efficiency, but not much was done to explain chemical mechanisms of fluoride bonding on active alumina that is essential for the cleaning process of exhaust gases. Chemical and micro-chemical analyses enabled to determine the fraction of bonded fluoride on the surface and in the interior of the fluorinated alumina grains. Also the correlation between the most efficient fluoride bonding on active alumina and real industrial conditions was determined.