| 摘要 |
Fluorine values are recovered as cryolite from waste solids and gases obtained in the electrolytic production of aluminium by adding hydrofluoric acid obtained by the pyrohydrolysis of the solid residues to either (a) an acid solution obtained by washing the gases with water after removal of solid matter or (b) an alkaline solution obtained by washing the gases with sodium carbonate after removal of solid matter, and in both cases precipitating cryolite from the resulting mixture, in the case of method (a) by the addition of sodium aluminate and in the case of method (b) by the addition of aluminium sulphate. The waste solids include particles removed from the waste gases by e.g. electrofilters, and scraping and cathodic residues from the cells. Pyrohydrolysis is defined as attack by water at high temperature, e.g. about 1000 DEG C., and is exemplified in Specification 925,119. Specification 900,790 also is referred to. |
