PROCEDIMENTO PER LA BONIFICA TER MICA DI SOSTANZE SOLIDE IMPIEGATE PER LA DEPURAZIONE A SECCO DI GAS DI SCARICO

摘要

1375623 HF removal; aluminium fluoride VEREINIGTE ALUMINIUM-WERKE AG 2 June 1972 [4 June 1971] 25957/72 Heading C1A [Also in Division C7] Exhaust gases comprising hydrogen fluoride and carbon dust produced by electrolysis of a melt comprising Al 2 O 3 , AlF 3 , CaF 2 and NaF are dry cleaned by contact with a solid material which binds the hydrogen fluoride by adsorption and/or chemical reaction and on which carbon dust is adsorbed wherein the solid material-is subjected to a thermal treatment (e.g. heating to 500-1000‹ C. in the presence of air or oxygen) to remove adsorbed carbon by combustion and to convert the adsorbed hydrogen fluoride to a stable fluid and is then charged to the electrolysis step. The thermal treatment may be carried out using a fluidized solids chamber or rotary furnace employing indirect or direct heating (e.g. electrical heating) and may be carried out either within the gas cleaning plant or in plant separate therefrom. The solids material used in the gas cleaning may be aluminium oxide which may be present in an amount of 9% of the total quantity of oxide required in the electrolytic production of aluminium.