State Key Laboratory of Coal Combustion, Huazhong University of Science & Technology, Wuhan 430074, People's Republic of China.
Environ Sci Technol. 2012 Mar 20;46(6):3567-73. doi: 10.1021/es204255h. Epub 2012 Mar 7.
Through the use of synchrotron XANES and Cr-doped brown coal, extensive efforts have been made to clarify the volatility of organically bound Cr during oxy-fuel combustion and the mode of occurrence and leachability of Cr in resulting fly ashes. As the continuation of our previous study using raw coal, the Cr-doped coal has been tested in this study to improve the signal-to-noise ratio for Cr K-edge XANES spectra, and hence the accuracy for Cr(VI) quantification. As has been confirmed, the abundant CO(2) as a balance gas for oxy-firing has the potential to inhibit the decomposition of organically bound Cr, thereby favoring its retention in solid ash. It also has the potential to promote the oxidation of Cr(III) to Cr(VI) to a minor extent. Increasing the oxygen partial pressure, particularly in the coexistence of HCl in flue gas, favored the oxidation of Cr(III) into gaseous Cr(VI)-bearing species such as CrO(2)Cl(2). Regarding the solid impurities including Na(2)SO(4) and CaO, Na(2)SO(4) has proven to preferentially capture the Cr(III)-bearing species at a low furnace temperature such as 600 °C. Its promoting effect on the oxidation of Cr(III) to Cr(VI), although thermodynamically available at the temperatures examined here, is negligible in a lab-scale drop tube furnace (DTF), where the particle residence time is extremely short. In contrast, CaO has proven facilitating the capture of Cr(VI)-bearing species particularly oxychloride vapors at 1000 °C, forming Ca chromate with the formulas of CaCrO(4) and Ca(3)(CrO(4))(2) via a direction stabilization of Cr(VI) oxychloride vapor by CaO particle or an indirect oxidation of Cr(III) via the initial formation of Ca chromite. The fly ash collected from the combustion of Cr-doped coal alone has a lower water solubility (i.e., 58.7%) for its Cr(VI) species, due to the formation of Ba/Pb chromate and/or the incorporation of Cr(VI) vapor into a slagging phase which is water-insoluble. Adding CaO to coal increased the water-solubility of both Cr(VI) and Cr(III) by forming Ca chromite and chromate, respectively.
通过使用同步加速器 XANES 和掺铬褐煤，我们进行了广泛的研究，以阐明含氧燃料燃烧过程中有机结合的铬的挥发性，以及在飞灰中铬的存在形式和浸出性。作为我们之前使用原煤进行研究的延续，本研究中测试了掺铬煤，以提高 Cr K 边 XANES 光谱的信噪比，从而提高 Cr(VI)定量的准确性。正如已经证实的那样，作为富氧燃烧的平衡气体的大量 CO2 有可能抑制有机结合的铬的分解，从而有利于其在固体灰分中的保留。它还有可能在较小程度上促进 Cr(III)氧化为 Cr(VI)。增加氧分压，特别是在存在烟气中的 HCl 时，有利于 Cr(III)氧化为气态含 Cr(VI)物种，如 CrO2Cl2。至于包括 Na2SO4 和 CaO 在内的固体杂质，Na2SO4 已被证明在 600°C 等较低的炉温下优先捕获含 Cr(III)的物种。尽管在研究的温度下从热力学上看它可以促进 Cr(III)氧化为 Cr(VI)，但在实验室规模的下降管炉 (DTF) 中，由于颗粒停留时间极短，其影响可以忽略不计。相比之下，CaO 已被证明有利于在 1000°C 下捕获含 Cr(VI)的物种，特别是氧氯化物蒸气，通过 CaO 颗粒对 Cr(VI)氧氯化物蒸气的定向稳定化或通过初始形成铬铁矿间接氧化 Cr(III)，形成 Ca 铬酸盐，其化学式为 CaCrO4 和 Ca3(CrO4)2。仅用掺铬煤燃烧收集的飞灰中 Cr(VI)物种的水溶性较低（即 58.7%），这是由于 Ba/Pb 铬酸盐的形成和/或 Cr(VI)蒸气掺入不溶于水的渣相中。向煤中添加 CaO 分别通过形成铬铁矿和铬酸盐来增加 Cr(VI)和 Cr(III)的水溶性。
