Elucidating the mechanism of Cr(VI) formation upon the interaction with metal oxides during coal oxy-fuel combustion

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• 作者：Juan Chen ; Facun Jiao ; Lian Zhang ; Hong Yao ; Yoshihiko Ninomiya
• 关键词：Cr(VI) ; XANES ; Oxy-fuel combustion ; Cr capture
• 刊名：Journal of Hazardous Materials
• 出版年：15 October, 2013
• 年：2013
• 卷：261
• 期：Complete
• 页码：260-268
• 全文大小：1395 K

文摘

The thermodynamics underpinning the interaction of Cr-bearing species with basic metal oxides, i.e. K₂O, Fe₂O₃, MgO and CaO, during the air and oxy-fuel combustion of coal have been examined. The synchrotron-based X-ray adsorption near-edge spectroscopy (XANES) was used for Cr speciation. For the oxides tested, Cr(VI) formation is dominated by the reduction potential of the metals. The oxides of Ca²⁺ with high reduction potential favored the oxidation of Cr(III), same for K⁺. The other two basic metals, Fe₂O₃ and MgO with lower reduction potentials reacted with Cr(III) to form the corresponding chromites at the temperatures above 600 掳C. Coal combustion experiments in drop-tube furnace have confirmed the rapid capture of Cr vapors, either trivalent or hexavalent, by CaO into solid ash. The existence of HCl in flue gas favored the vaporization of Cr as CrO₂Cl₂, which was in turn captured by CaO into chromate. Both Fe₂O₃ and MgO exhibited less capability on scavenging the Cr(VI) vapor. Particularly, MgO alone exhibited a low capability for capturing the vaporized Cr(III) vapors. However, its co-existence with CaO in the furnace inhibited the Cr(VI) formation. This is beneficial for minimizing the toxicity of Cr in the coal combustion-derived fly ash.