| 摘要 |
<p>Fluoride-containing wastes, arising in the aluminium industry, particularly spent cell linings from reduction cells, are digested with caustic soda for conversion of sodium cryolite to NaF.</p><p>By use of very strong caustic soda NaF may be left in the solid residues after removal of the residual liquor and recovered from such residues by water leaching.</p><p>As an alternative weaker caustic soda may be used in the digestion stage and subsequently be crystallised out from the residual liquor, after separation from the solid residues, by evaporating and/or cooling the liquor. The precipitated NaF is then conveniently redissolved in water.</p><p>The NaF solution prepared by either route is then preferably subjected to electrodialysis to recover a solution of HF from it. Such HF is conveniently converted to AIF3 by reaction with alumina.</p> |
