| 摘要 |
<p>Conversion of the Al contained in clays to alpha-alumina of sufficient purify to allow its direct reduction to Al metal in an electrolytic cell comprises calcining the clay to transform the alumino silicate structure in the clay to an amorphous alumina, leaching the calcined clay with aq. HNO3 to reduce the SiO2 content of the final alumina to 0.05 wt.%, flocculating the insoluble impurities to aid in their separation by settling and filtration and contacting the leach liquor filtrate with an ion-exchange liquid dissolved in a carrier e g. di(2-ethylhexyl)hydrogen phosphate and tributyl phosphate dissolved in kerosene to remove the soluble ferric iron along with the other metallic impurities, introducing the substantially pure aluminium nitrate soln into a fluidised bed of alpha-alumina at 200 degrees -210 degrees C and having a fluidising gas contg. a controlled amt of water vapour to hydrolyse the aluminium nitrate, thus making it possible to remove 90-95% of the nitrate as nitric acid vapour, and heating the hydrolysed dry product from the fluidised bed to drive off the remaining nitrate as oxides of N2, and converting these solids to alpha-alumina.</p> |
