Recovery of gallium and vanadium from gasification fly ash.
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 Ga2O3 and as Ga3+ and V3+ substituting for Al3+ 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 degrees 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.
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Oriol
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Institute of Earth Sciences Jaume Almera, CSIC, Lluis Solé i Sabarís, s/n, 08028 Barcelona, Spain. ofont@ija.csic.es
Querol
Xavier
X
Juan
Roberto
R
Casado
Raquel
R
Ruiz
Carmen R
CR
López-Soler
Angel
A
Coca
Pilar
P
García Peña
Francisco
F
D002244:Carbon / Q000737:chemistry*; D011232:Chemical Precipitation; D060729:Coal Ash; D005708:Gallium / Q000302:isolation & purification*; D007220:Industrial Waste; D052638:Particulate Matter / Q000737:chemistry*; D011210:Power Plants; D012972:Sodium Hydroxide; D013696:Temperature; D013997:Time Factors; D014639:Vanadium / Q000302:isolation & purification*
D060729:Coal Ash; D007220:Industrial Waste; D052638:Particulate Matter; D014639:Vanadium; D012972:Sodium Hydroxide; D002244:Carbon; D005708:Gallium