Abstract: The specification describes a process for recovering alkali metal hydroxides from an organic liquor such as black liquors derived from pulping wood chips. The organic liquor is burned in a fluidised bed combustion furnace containing fluidised particles of an iron rich mixed oxide of an alkali metal and iron. Particles of alkali metal ferrite are extracted from the furnace and dissolved in a solution of alkali metal hydroxide to form a more concentrated solution of alkali metal hydroxide and a precipitate of the iron rich mixed oxides of alkali metal and iron. A mixed oxide disclosed in the specification generally has the following formula: NaFe.sub.5 O.sub.8.4H.sub.2 O.