| 摘要 |
1371777 Reaction of fluorides with alumina BAYER AG 30 Dec 1971 [31 Dec 1970] 60711/71 Heading C1A HF, NH4F and/or an alkali metal fluoride, which may be present in a waste gas stream, is contacted with Al2O3 having a surface area of at least 250 m.<2>/g., a residual water content of 2-15% by wt. and a water absorption capacity at 50% R.H. of more than 10% and prepared by flash heating Bayer Al(OH)3 (hydrar gillite), the contact being carried out at 20-700‹ C. when AlF3 and/or cryolite is being prepared and at 20-100‹ C. when ammonium cryolite is being prepared. Fluorides may be separated from gases by passing the stream upwardly into the U-shaped tube 1 whilst Al2O3 particles are introduced via side tube 3. The solids are separated in cyclone 4 and the purified stream vented via 5 and wet-scrubbed to remove SiF4. Ammonium cryolite may be prepared from an aqueous solution of NH4F obtained by ammoniating H2SiF6 solution to a pH of 8-9. |
