Aluminum Company of America

Bennett L McCormick

Nancy M Fitzgerald

Richard B Phillips

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.

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Cheswick, PA, United States of America

Bennett L McCormick