1. H.E. Gardner, Recovery of vanadium and nickel from petroleum residues, US Patent 4,816,236 (1989).
2. Analisi di un processo di estrazione di vanadio e nichel da fuliggine;Giorgini;Inquinamento,1978
3. Extraction of vanadium from Athabasca tar sands fly ash;Gomez-Bueno;Metall. Trans. B,1981
4. Haehn, R., Hess, H., Sattelberger, S., (1985). Recovery of vanadium compounds from vanadium-containing residues. Ger. Offen. DE 3,402,357.
5. Recovery of vanadium from combustion ashes of Egyptian crudes;Manieh;Trans. Egypt. Soc. Chem. Eng.,1987