A STUDY OF THE EXTRACTION OF VANADIUM AND NICKEL IN OIL-FIRED FLY-ASH

Annual production of oil-fired fly ash in Taiwan is approximately 4300 0 tons, of this approximately 13000 tons is electrostatically precipit ated, the rest is cyclonically collected. Structurewise, both consist of porous unburned carbon, vanadium and nickel oxide, and water-solubl e sulfate. Electrostatically precipitated fly ash contains large amoun ts of ammonium sulfate. If these ashes are not properly disposed of th ey become environmental problems, such as dusting, leakage of acid liq uids, and pollution with heavy metals. This paper discusses the experi mental extraction of vanadium and nickel from oil-fired fly ash. The r esults indicated that leaching of oil-fired fly ash in 0.5 N of sulfur ic acid led to an extraction of 65%, vanadium, 60% nickel, and 42% iro n, along with an increase in the concentration of sulfuric acid. When leached in 2 N sodium hydroxide solution, the extraction of vanadium w as 80%, and the extraction of nickel was negligible. If leached in an ammonia water, the extraction of nickel increased, along with an incre ase in the concentration of ammonia in water. When leached with 4 N am monia water, the extraction of nickel was 60%,, the extraction of vana dium was less than that obtainable from leaching in sulfuric acid solu tion or in sodium hydroxide solution. If electrostatically precipitate d fly ash was leached in a solution of 0.25 N ammonia water and 2 N am monium sulfate, it would yield an extraction of 60% nickel and 8% vana dium-leading to a selective extraction of nickel. This study has estab lished an extraction flowsheet in which fly ash was first leached in a n ammoniacal solution containing ammonium sulfate to recover nickel. T he leached residues were then leached in an alkaline solution to recov er vanadium. (C) 1998 Elsevier Science B.V. All rights reserved.