| abstract |
A process for treating spent potliner material from aluminum reduction cells and recovering useful products. In the process, spent potliner material is introduced into an acid digester (24) containing, for example, sulfuric acid. A gas component is produced which includes hydrogen fluoride and hydrogen cyanide. A slurry component is produced which includes carbon, silica, alumina, sodium compounds such as sodium sulfate, aluminum compounds such as aluminum sulfate, iron compounds such as iron sulfate, magnesium and calcium compounds such as magnesium and calcium sulfate. The slurry component remains in the digester after the gas component is removed. The gas component is recovered and heated an effective amount to convert or decompose the hydrogen cyanide to a remaining gas component including carbon dioxide, water, and nitrogen oxides as well as HF gas. The remaining gas component is directed through a water scrubber (44) in which the HF gas is converted to liiquid hydrofluoric acid. The hydrofluoric acid is then admixed with alumina trihydrate to form aluminum fluoride and water. |