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.

Abstract: A process for removing a carbon dioxide, HF or sulfur dioxide contaminant from an exhaust gas stream containing that contaminant comprising providing a gas stream to a reaction zone, the gas stream entering the reaction zone from underneath and being caused to flow through the reaction zone with components of velocity in substantially upwards and circumferential directions; contacting the gas stream in the reaction zone with particulate material to adsorb the contaminant on the particulate material, wherein the flow of gas in the reaction zone causes a dispersed toroidal bed of particulate material to be formed in the reaction zone; the slip velocity of the gas stream relative to the particulate material in the toroidal bed is greater than 1 m/s; and entraining a fine fraction of the particulate material in the gas stream whereby the fine fraction is removed from the toroidal bed by the gas stream exiting the bed; and separately recovering a coarse fraction of the particulate material from the reaction zone.