Aluminum Company of America

Nancy M Fitzgerald

C Norman Cochran

Richard B Phillips

Bennett L McCormick

There is disclosed a method for improving the brightness level of aluminum hydroxide removed from a caustic solution. The method comprises:(a) pre-filtering the solution to remove contaminants therefrom; and (b) contacting the filtered solution with an adsorbent consisting essentially of a calcined compound having the formula: A.sub.w B.sub.x (OH).sub.y C.sub.z.nH.sub.2 O wherein A represents a divalent metal cation selected from the group consisting of: Mg.sup.2+, Ni.sup.2+, Fe.sup.2+, Ca.sub.2+ and Zn.sup.2+ ; B represents a trivalent metal cation selected from the group consisting of: Al.sup.3+, Fe.sup.3+ and Cu.sup.3+ ; C represents a mono- to tetravalent anion selected from the group consisting of: OH.sup.-, Cl.sup.-, Br.sup.-, NO.sub.3.sup.- CH.sub.3 COO.sup.-, C.sub.2 O.sub.4.sup.2-, CO.sub.3.sup.2-, SO.sub.4.sup.2-, PO.sub.4.sup.3-, Fe(CN).sub.6.sup.3- and Fe(CN).sub.6.sup.4- ; and w, x, y, z and n satisfy the following: 0&lt;z.ltoreq.x.ltoreq.4.ltoreq.w.ltoreq. 1/2 y and 12.gtoreq.n.gtoreq. 1/2 (w-x); and (c) adsorbing additional contaminants onto the calcined compound. On a preferred basis, this method also includes: (d) filtering or sepiating contacted compound and additional contaminants from the solution. Still further preferred method steps include: adding to the filtered solution as seed material an aluminum hydroxide of high brightness, preferably with a whiteness level of about 85% or higher based on a 100% TiO.sub.2 reference standard. Preferably, the method further includes: (i) separating calcined compound from the solution; (ii) recalcining the separated compound; and (iii) contacting recalcined compound with additional solution. A preferred adsorbent for step (b) consists essentially of calcined hydrotalcite. There is also provided an improved aluminum hydroxide product having a whiteness level of 85% or higher based on a 100% TiO.sub.2 reference standard, said compound having been removed from a caustic solution and decolorized by the foregoing method.

Method for improving the brightness of aluminum hydroxide

A method for production of aluminum by carbothermic reduction of Al.sub.2 O.sub.3 in a stack-type reactor. A charge of Al.sub.2 O.sub.3 and C is inserted into an upper reaction zone of the reactor and reacted at an elevated temperature to form CO and a first liquid comprising Al.sub.2 O.sub.3 and Al.sub.4 C.sub.3. The first liquid is transferred to a lower reaction zone beneath the upper reaction zone and heated to form CO and a second liquid of Al and C. A portion of the second liquid is removed, and liquid Al is extracted therefrom. In a preferred method, Al.sub.2 O.sub.3 and C in the upper zone are heated by partial combustion of the C, and the lower zone is heated electrically. Gaseous Al and Al.sub.2 O formed in the lower zone are reclaimed in the upper zone. Gaseous CO produced in both zones heats the Al.sub.2 O.sub.3 and C in the upper zone. Excess CO is removed from the upper zone and used for generation of electricity or chemical process use. Liquid Al.sub.4 C.sub.3 separated from the second liquid is returned to the upper zone. Production of 1.00 kg Al requires an expenditure of 32.7 megajoules (MJ) of electrical energy, and 3.45 kg C. Total consumption of electrical energy and carbon energy equivalent is 121 MJ/kg Al, compared with 186 MJ/kg Al using the best Bayer-Hall technology.

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Wilkins Township, PA, United States of America

Nancy M Fitzgerald