Some thermodynamic relations among the vanadium oxides, and their relation to the oxidation state of the uranium ores of the Colorado Plateaus^*

Fields of stability of several vanadium oxides in water solution at 25° C. have been calculated as functions of pH and oxidation potential. The bivalent oxide V₂O₂ is not expected under natural conditions; it should occur only at oxidation potentials below the breakdown potential of water. The oxide corresponding to the mineral montroseite, V₂O₃·H₂O or VOOH, is predicted to coexist with common metal sulfides and to oxidize to V₂O₄ atabout the same potential at which sulfide ion oxidizes to sulfate. Owing to difficulties entailed by the complex chemistry of vanadium, V⁺⁵, no attempt was made to calculate a boundary between V₂O₄ and a higher oxide. Diagrams showing the fields of stability of the various oxides have been constructed, and contours showing the activities of the various vanadium ions have been superimposed. The stability fields of the vanadium oxides should be useful in deducing the environment of formation of the carnotite ores and the “blue-black” ores of the Colorado Plateaus.