Abstract: Bauxite that is to be used in the Bayer process for the recovery of alumina is washed with aqueous wash liquor having a caustic content of at least 50 g/l and which comprises aqueous caustic from the alumina recovery circuit of the Bayer process and, after removing organic material from the wash liquor, the wash liquor is included in the digestion stage, the separation stage or the alumina recovery circuit of the Bayer process.

Abstract: Water soluble polymer flocculants are formed from monomers derived from ethylenically unsaturated dibasic carboxylic acids of formula (I) where R.sup.1 =H and R.sup.2 =COOH or R.sup.1 =COOH and R.sup.2 =H. Flocculants are provided for use in Bayer process liquors which are copolymers of acids of formula (I) with ethylenically unsaturated copolymerisable monomer and which have molecular weight above 300,000. Preferably the polymer is a terpolymer of dibasic acid, monobasic and polymerisable termonomer. A particularly preferred flocculant is formed from at least 10 mol % maleic acid with acrylic acid and acrylamide as comonomers and is used preferably for flocculation of red mud in the primary settler and/or the various red mud washing stages.

Abstract: A Bayer alumina recovery process is described in which lime is added at an intermediate or final wash stage of the red mud recovery circuit to improve flocculation, especially with flocculants having lower anionic content. The process is particularly useful with liquors containing high amounts of sodium carbonate and for process where the mud is settled by mud stacking.

Abstract: In a Bayer process for production of aluminum, alumina trihydrate crystals are formed in the pregnant liquor and are flocculated using a combination of dextran and synthetic polymer, usually a homo- or copolymer of acrylic acid. The process is particularly advantageous where the liquor contains organic components such as humate and/or oxalate.

Abstract: Red mud in Bayer process liquors are flocculated using dextran and synthetic anionic polymer in the same stage, usually added separately to the liquor. The liquor may be the primary settler slurry, the secondary clarification liquor or one or more of the red mud washing stages. The process is of particular advantage where the liquors are high in carbonate content and/or total alkalinity.

Abstract: The clarification of a sodium aluminate liquor in the Bayer Process, especially the liquor obtained by Kelly filter filtration of the supernatant from the primary settling stage, is improved by flocculation with a polymer of the formula CH.sub.2 .dbd.C(R.sup.1)CONHR.sup.2 NR.sup.3 R.sup.4 wherein R.sup.1 is hydrogen or methyl, R.sup.2 is straight or branched chain C.sub.2-8 alkylene having at least 2 carbon atoms in the backbone and R.sup.3 and R.sup.4 are independently selected from C.sub.1-4 alkyl.