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 NH4Cl in the first step, followed by vanadium leaching with Na2CO3 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 Na2S, 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 NH4Cl. 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 NH4VO3 crystals.