Recovery of vanadium and nickel in fly ash from heavy oil

Recovery of vanadium and nickel from an oil fly ash is studied in a two‐step leaching process, carried out under ambient pressure without calcination. In the leaching, nickel is dissolved with NH 4 Cl in the first step, followed by vanadium leaching with Na 2 CO 3 in the second step. Both leachants depress the dissolution of iron and aluminium from the ash and hence the selective leachings are feasible. Nickel was recovered in 87% yield from the leach liquor by precipitation with Na 2 S, the purity of NiS being over 99% on the basis of the target metals (V, Ni, Fe, Al and Mg). For the recovery of vanadium, which has a relatively low concentration in the leach liquor, solvent extraction with TOA is preferable to concentration, prior to crystallization with NH 4 Cl. The experimental data showed that the vanadium concentration of the stripping solution is increased by about 15 times that of the leach liquor, which results in 78% yield as NH 4 VO 3 crystals.