Abstract
In order to investigate the fate of chromium during thermal treatment of municipal solid waste incineration (MSWI) fly ash, typical raw fly ashes sampled from five different incinerators in China were thermal treated under air or N2 atmosphere using an electrically heated horizontal furnace at the temperature of 1023–1323K. For understanding of the chromium behavior during thermal treatment, leaching tests of the raw and thermal treated fly ash were conducted in an agitation apparatus. The results showed that the fraction of Cr(VI) in the total Cr of raw fly ash was small and leaching concentration of Cr from all samples was low. During thermal process, CaO was confirmed to play a significant role in the oxidation of Cr2O3 in MSWI fly ash which led to a sharply increase of Cr concentration in leaching solution from one CaO-rich fly ash. In addition, it was found that the reaction between CaO and Cr2O3 occurred at a quite low temperature of 773K and became more rapid when the temperature was higher than 1173K. However, the reaction was effectively prevented under N2 atmosphere. Furthermore, most of CaO was found to transfer into aluminosilicate rather than react with Cr2O3 or β-CaCr2O4 to produce Cr(VI) at the case of fly ash with high content of silica and aluminum oxides. The adjustment of the ratio of CaO and total of silicon and aluminum oxides in the fly ash compositions could inhibit the leaching of Cr from thermal treated MSWI fly ash.
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