Abstract
Red mud was treated with ammonium bisulfate at 400° to 450°C to form a double salt of ammonium aluminum sulfate soluble in water. Aluminum and iron were leached in sulfuric acid after sulfatizing roasting. Ammonium alum was crystallized out of the leaching solution containing iron. The optimum conditions for yielding ammonium alum in the leaching solution are: pH 1.7, the concentration degree 3/4 and the addition of ammonium sulfate 4.8 equivalent. The high purity ammonium alum is predominantly crystallized if the reducing agent is added into the leaching solution. The final recovery of aluminum from red mud can exceed about 77%. A flow sheet is also proposed for treating red mud by the use of ammonium sulfate as a solvent.
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