Department of Chemical Engineering, Monash University, Clayton, GPO Box 36, Victoria 3800, Australia; State Key Laboratory of Coal Combustion, Huazhong University of Science & Technology, Wuhan 430074, China.
J Hazard Mater. 2013 Oct 15;261:260-8. doi: 10.1016/j.jhazmat.2013.07.023. Epub 2013 Jul 22.
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 Ca(2+) 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°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.
研究了含铬物种与碱性金属氧化物（如 K2O、Fe2O3、MgO 和 CaO）在煤的空气和富氧燃烧过程中相互作用的热力学。基于同步加速器的 X 射线吸收近边光谱（XANES）用于研究 Cr 的形态。对于所测试的氧化物，Cr(VI)的形成主要取决于金属的还原电位。还原电位高的 Ca(2+)氧化物有利于 Cr(III)的氧化，K(+)也是如此。另外两种还原电位较低的碱性金属 Fe2O3 和 MgO 在 600°C 以上的温度下与 Cr(III)反应形成相应的铬铁矿。在滴落管式炉中的煤燃烧实验证实了 Cr 蒸汽（无论是三价还是六价）被 CaO 快速捕获到固体灰分中。烟道气中 HCl 的存在有利于 Cr 以 CrO2Cl2 的形式蒸发，而 CrO2Cl2 又被 CaO 捕获形成铬酸盐。Fe2O3 和 MgO 对捕获 Cr(VI)蒸汽的能力都较弱。特别是，MgO 单独对捕获蒸发的 Cr(III)蒸汽的能力较低。然而，它与 CaO 共存于炉中抑制了 Cr(VI)的形成。这有利于最大限度地减少煤燃烧飞灰中 Cr 的毒性。
