GB1123184A - Improved method for recovering alumina from aluminate liquor - Google Patents

Abstract

<PICT:1123184/C1/1> A method of recovering alumina from aluminate liquor, comprises passing aluminate liquor down a column, passing a vapour mixture containing steam and methanol and/or ethanol through said column in countercurrent to the aluminate liquor, whereby alumina hydrate is precipitated and separating solid hydrate from the methanol and/or ethanolcontaining liquor thus formed. In a preferred embodiment the methanol and/or ethanol is driven off from the methanol and/or ethanolcontaining liquor in a distilling column, at least part of the vapour from the first column being introduced into the lower part of the distilling column and at least part of the vapour from the distilling column being introduced into the lower part of said first column. In the drawing, liquor 10 which has been separated from red mud is introduced into the top of column 3 and flows downwards, its methanol content increasing and its water content becoming less. Liquid methanol 15 containing about 20 mol% water is added to the emerging liquor 14 which flows into the precipitation agitators 9. When the hydrate has been stirred out and separated from the liquor, the liquor 11 is pumped into column 2 in which it loses the main proportion of its methanol content. The remaining methanol is driven off in column 4 and the liquor 12 which leaves column 4 contains only traces of methanol. The liquor 12 from which methanol has been expelled is concentrated by evaporating a portion of its water content. The concentration of the liquor may be carried out in a multi-stage evaporator, the first stage of which is heated with steam. Vapour 16 from column 2 may be condensed in a water-cooled condenser and part may be used to heat evaporator 8 which operates at less than atmospheric pressure and is used for concentrating liquor 12. The major part of the vapour 16 is taken into column 1. The vapour 17 leaving column 1 may be introduced into column 2, the remainder into column 3 from which vapour 19 with a very small methanol content can be withdrawn. Vapour 19 is taken into the bottom part of column 4.