| 摘要 |
<p>Fluorine values are recovered from waste gases deriving from the electrolytic production of aluminium in a fluoride-containing fused salt bath, which gases also contain sulfur dioxide, by washing the gases with water until a 3% to 10% hydrofluoric acid solution is obtained, and then reacting this solution with aluminium-and sodium-containing materials to precipitate a double fluoride of sodium and aluminium. The aluminium- and sodium-containing materials are selected from the group consisting of sodium compounds, aluminium compounds, and their solutions, which are soluble in the hydrofluoric acid solution, and also metallic aluminium, for example in the form of dross or skimmings. Thus, a solution of sodium aluminate may be added to the hydrofluoric acid solution, or aluminium hydroxide or dross or skimmings may be added to form aluminium fluoride, to which is then added a sodium fluoride solution to precipitate the double fluoride. If the aluminium fluoride contains excess HF, the sodium fluoride may be formed in situ by adding for example sodium hydroxide or carbonate. The sodium fluoride solution may be obtained by leaching wastes from the electrolytic furnace and reacting the liquor obtained with HF, or the liquor may be added directly with the HF-AlF3 solution. Alternatively, the sodium fluoride solution may be obtained by washing part of the waste gases with a solution of sodium carbonate or hydroxide or with the furnace waste leach liquor previously referred to.</p> |
