Acid-extracting residue of circulating uidized bed (CFB) y ash is still underutilized leaving disposal problems. In fact, high silica content inside this material opens a possibility to become a potential zeolites precursor. In this study, ne particles of acid residues have been reused to prepare zeolite Na-X and Na-P with high purity and intensity. Acid residue was used to synthesize zeolite Na-X and Na-P using a single-step hydrothermal process. The effects of crystallization time, temperature and sodium hydroxide concentration on the end products were investigated. The results revealed that crystallization time and temperature determined whether or not zeolite Na-X or Na-P was formed. The zeolites were characterized in terms of their mineralogical composition, morphology, and fourier-transform infrared spectroscopy.
Alumina was extracted from mixtures of circulating fluidized-bed fly ash (CFBFA)/pulverized-coal fly ash (PCFA) and sodium pyrosulfate (Na 2 S 2 O 7 ) 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 Na 2 S 2 O 7 to CFBFA and PCFA released alumina in the form of Na 3 Al(SO 4 ) 3 . Up to 93.3% of the alumina was extracted from the PCFA calcined at 420 °C for 2 h when n(Al 2 O 3 )/n(Na 2 S 2 O 7 ) = 1:3; however, 92.8% of the alumina was extracted from the CFBFA calcined under the same conditions when n(Al 2 O 3 )/n(Na 2 S 2 O 7 ) = 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, Na 2 Ca(SO 2 ) 2 and CaAl 2 O 4 formed at the beginning of the reaction, which prevented the alumina from dissolving and provided resistance against mass transfer.
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