Abstract: A process for heat treating spent pot linings from Hall-Heroult electrolytic cells which comprise carbon and silico-aluminous materials impregnated with fluorides. The pot linings are ground to a particle size less than 5 mm, and formed into an intimate mixture with calcium sulfate or calcium sulfate dihydrate having a particle size less than 1 mm. The mixture is injected into the center of a vortex formed by a flow of circulating hot gas at the top part of a reactor at a temperature between 700.degree. and 1100.degree. C., and extracted from the bottom part of the reaction at a temperature between 400.degree. and 750.degree. C. after a contact time of less than 2 seconds.

Abstract: The invention relates to a thermal shock treatment in a reactor of ground spent pot linings, constituted both by carbon-containing products and silico-aluminous products impregnated with fluorine-containing mineral compounds, mixed with a pulverulent mineral additive able to combine hot, with or without melting or fusion, with the fluorine-containing impregnating compounds in order to form new stable and insoluble compounds such as CaF.sub.2, binary, ternary or quaternary compounds of NaF, CaF.sub.2, SiO.sub.2, Al.sub.2 O.sub.3, CaSO.sub.4, Na.sub.2 SO.sub.4, of the nephelite, hauynite or similar type.

Abstract: A process for the treatment of spent pot linings impregnated with alkali metal cyanide and fluoric products by grinding previously crushed pot linings in the presence of lime, suspending the ground pot linings in an aqueous medium in order to precipitate a flux in the form of CaF.sub.2 accompanied by the release of soda, followed by the heating of the suspension at a temperature T>140.degree. C. in the presence of clay to form, after fixing the free soda, insoluble synthetic silicate compounds of the feldspathoid or zeolite type and finally the separation by filtration of the resulting solid phase from the liquid phase, which liquid phase is recycled to form a new ground pot lining suspension.