Process for producing fluoride-free columbium or tantalum pentoxide

Claim 1

A PROCESS FOR PRODUCING A SUBSTANTIALLY FLUORIDE-FREE PENTOXIDE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF COLUMBIUM AND TANTALUM FROM AN AQUEOUS HYDROFLUORIC ACID SOLUTION CONTAINING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF H2CBF7, H2CBOF5 AND H2TAF7 WHICH PROCESS COMPRISES ADDING AT LEAST 2 1/2 MOLES OF SULFURIC ACID TO SAID SOLUTION FOR EVERY MOLE OF H2CBF7 AND H2TAF7 CONTAINED THEREIN AND AT LEAST 1 1/2 MOLES OF SULFURIC ACID FOR EVERY MOLE OF H2CBOF5 CONTAINED THEREIN; DIGESTING THE SO-ACIDIFIED SOLUTION BY BOILING IT WHEREBY THE COMBINED FLUORINE IS DISSOCIATED FROM THE METAL COMPOUNDS AND VOLATILIZED DURING SAID DIGESTION AS GASEOUS HYDROGEN FLUORIDE; CONTINUING SAID DIGESTION UNTIL THE EVOLUTION OF GASEOUS HYDROGEN FLUORIDE FROM SAID SOLUTION HAS SUBSTANTIALLY SUBSIDED; AND PRECIPITATING SAID SELECTED METAL FROM THE SOLUTION AS A HYDRATED PENTOXIDE OF SAID METAL.