Process for manufacturing sodium-metal oxide by burning a mixture comprising as a first constituent compounds containing sodium (1) and, as a second constituent, compounds containing the metals aluminium, titanium or vanadium (2). The burning is accomplished by spraying the mutually mixed compounds in the aqueous phase and in dropshape into a burning chamber (6) where the combustion takes place at a temperature between 970 and 1870° K (700 and 1600° C).
Advantageously, the compounds containing sodium are combustible sodium lignosulfonates or other sodium derivatives of lignin contained in the spent digestion liquors from the production of cellulose. Preferably, an aluminium compound is used, which is subsequently converted into sodium aluminate.