Recovery of gallium and vanadium from gasification fly ash
Abstract
The Puertollano Integrated Coal Gasification Combined Cycle (IGCC) Power Plant (Spain) fly ash is characterized by a relatively high content of Ga and V, which occurs mainly as Ga 2O 3 and as Ga 3+ and V 3+substituting for Al 3+ in the Al–Si fly ash glass matrix. Investigations focused on evaluating the potential recovery of Ga and V from these fly ashes. Several NaOH based extraction tests were performed on the IGCC fly ash, at different temperatures, NaOH/fly ash (NaOH/FA) ratios, NaOH concentrations and extraction times. The optimal Ga extraction conditions was determined as 25 °C, NaOH 0.7–1 M, NaOH/FA ratio of 5 L/kg and 6 h, attaining Ga extraction yields of 60–86%, equivalent to 197–275 mg of Ga/kg of fly ash. Re-circulation of leachates increased initial Ga concentrations (25–38 mg/L) to 188–215 mg/L, while reducing both content of impurities and NaOH consumption. Carbonation of concentrated Ga leachate demonstrated that 99% of the bulk Ga content in the leachate precipitates at pH 7.4. At pH 10.5 significant proportions of impurities, mainly Al (91%), co-precipitate while >98% of the bulk Ga remains in solution. A second carbonation of the remaining solution (at pH 7.5) recovers the 98.8% of the bulk Ga. Re-dissolution (at pH 0) of the precipitate increases Ga purity from 7 to 30%, this being a suitable Ga end product for further purification by electrolysis. This method produces higher recovery efficiency than currently applied for Ga on an industrial scale. In contrast, low V extraction yields (<64%) were obtained even when using extreme alkaline extraction conditions, which given the current marked price of this element, limits considerably the feasibility of V recovery from IGCC fly ash.
- Publication:
-
Journal of Hazardous Materials
- Pub Date:
- January 2007
- DOI:
- 10.1016/j.jhazmat.2006.02.041
- Bibcode:
- 2007JHzM..139..413F
- Keywords:
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- Gallium;
- Vanadium;
- Gasification