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AssigneeKaiser Aluminum & Chemical Corporation
InventorsMorris L. Roberson, John W. Beck, Jack S. Maples, Anthony Savariste, Donald J. Donaldson, David L. Stein, Allan C. Kelly
Estimating the term…
A process is provided which allows control of the impurity level of Bayer process streams with simultaneous generation of an environmentally acceptable effluent and recovery of valuable dissolved aluminum and sodium values. The process involves carbonation of a blow-down stream at 40.degree.-100.degree. C to produce sodium dawsonite [NaAl(OH).sub.2 CO.sub.2 ] and an effluent essentially free of dissolved alumina and significantly depleted in dissolved sodium. The sodium dawsonite can be used as such or returned to the Bayer process after thermal decomposition to sodium aluminate. The effluent can be directly discharged into natural receiving bodies without further treatment.
In the Bayer process production of alumina from bauxite by digestion of the bauxite with a caustic solution to produce a sodium aluminate solution and a caustic-insoluble spent bauxite residue, the improvement which comprises selecting for blow-down a Bayer process stream having a pH in excess of about 12, caustic concentration expressed as Na.sub.2 CO.sub.3, in excess of about 50 g/l and a dissolved alumina content, expressed as Al.sub.2 O.sub.3, in excess of about 20 g/l, treating the stream with CO.sub.2 within the temperature range of about 40.degree.-100.degree. C until substantially all of the dissolved alumina content of the stream is precipitated as sodium dawsonite;
Dependencies are inferred from the claim text.