Comparative Study on Extracting Alumina from Circulating Fluidized-Bed and Pulverized-Coal Fly Ashes through Salt Activation
2013
Guo, Chunbin | Zou, Jingjing | Wei, Cundi | Jiang, Yinshan
Alumina was extracted from mixtures of circulating fluidized-bed fly ash (CFBFA)/pulverized-coal fly ash (PCFA) and sodium pyrosulfate (Na₂S₂O₇) through salt-roasting activation. The effects of the sodium pyrosulfate amount, calcining temperature, and calcining time on the efficiency of extracting alumina from CFBFA and PCFA were analyzed and compared. The results showed that adding Na₂S₂O₇ to CFBFA and PCFA released alumina in the form of Na₃Al(SO₄)₃. Up to 93.3% of the alumina was extracted from the PCFA calcined at 420 °C for 2 h when n(Al₂O₃)/n(Na₂S₂O₇) = 1:3; however, 92.8% of the alumina was extracted from the CFBFA calcined under the same conditions when n(Al₂O₃)/n(Na₂S₂O₇) = 1:5, meaning that the CFBFA consumed more sodium pyrosulfate than the PCFA because the Al–O–Si bonds in the CFBFA were more active than those in the PCFA. A new amorphous aluminosilicate phase formed while the CFBFA was calcining with sodium pyrosulfate. Meanwhile, Na₂Ca(SO₂)₂ and CaAl₂O₄ formed at the beginning of the reaction, which prevented the alumina from dissolving and provided resistance against mass transfer.
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