Reduction of impurities in bayer process alumina trihydrate

A process for reducing alumina trihydrate impurity levels in the Bayer process by centrifugation, comprising contacting and efficiently mixing an alumina trihydrate suspension containing leachable soda with a water-soluble polymer containing pendant hydroxamic acid or salt groups in an amount effective to flocculate the suspended solids therein, said polymer having a molecular weight ranging from about 1.times.10.sup.4 to about 1.times.10.sup.8 and a degree of hydroxamation ranging from about 1 to about 90 mole percent, and centrifuging resultant flocculated solids to thereby separate centrifuged solids containing said alumina trihydrate from said suspension, and reduce said leachable soda in the separated alumina trihydrate.