Abstract: A process for the removal of reactive silica from a feedstock to the digestion step of the Bayer process for the manufacture of alumina, in which (a) the feedstock is contacted with a caustic liquor under process conditions which result in dissolving and stabilizing at least 50% of the silica into solution at a level of at least 3 gpL and without significant precipitation from solution of dissolved silica, (b) the silica bearing liquor is separated from solid residue of step (a) under conditions which do not promote significant precipitation of the silica; and (c) aluminosilicates are precipitated from the separated silica bearing liquor from step (b), to form a solid aluminosilicate product which is free of a majority of all other components of the feedstock.

Abstract: A process for treatment of a solid material containing fluoride and sodium, such as spent potlining from aluminum reduction cells, comprising the following steps: 1) contacting the solid material with recycled caustic liquor and source of calcium in a digestor; 2) passing the mixture to a separating device to separate into liquid and solid fraction; 3) recycling part of the liquid fraction containing caustic concentration of 75-200 g/l, calculated as Na.sub.2 CO.sub.3 to step (1); and 4) recovering concentrated caustic liquor from liquid fraction. The product of the process is a solid residue having low levels of leachable fluoride and a concentrated caustic liquor.