ProcESS, Process Engineering for Sustainable Systems, Department of Chemical Engineering, KU Leuven, W. De Croylaan 46, B-3001 Leuven, Belgium.
Environ Sci Technol. 2013 Jun 4;47(11):5858-63. doi: 10.1021/es4001455. Epub 2013 May 14.
In this paper, the temperature dependence of Cr(III) oxidation in high temperature processes and the subsequent Cr(VI) leaching was studied using synthetic mixtures. It was experimentally shown that in the presence of alkali and alkaline earth salts, oxidation of Cr(III) takes place, consistent with thermodynamic calculations. Heating of synthetic mixtures of Cr2O3 and Na, K, or Ca salts led to elevated leaching of Cr(VI); in the presence of Na, more than 80% of the initial Cr(III) amount was converted to Cr(VI) at 600-800 °C. Kinetic experiments allowed explanation of the increase in Cr(VI) leaching for increasing temperatures up to 600-800 °C. After reaching a maximum in Cr(VI) leaching at temperatures around 600-800 °C, the leaching decreased again, which could be explained by the formation of a glassy phase that prevents leaching of the formed Cr(VI). By way of illustration, Cr(VI) formation and leaching was evaluated for a case study, the fabrication of ceramic material from contaminated sludge. Based on the proposed reaction mechanisms, countermeasures to prevent Cr oxidation (addition of NH4H2PO4, heating under inert atmosphere) were proposed and successfully tested for synthetic mixtures and for the case study.
本文研究了高温过程中 Cr(III)氧化和随后 Cr(VI)浸出的温度依赖性，使用合成混合物进行了实验。实验表明，在碱和碱土金属盐存在的情况下，Cr(III)发生氧化，与热力学计算一致。加热 Cr2O3和 Na、K 或 Ca 盐的合成混合物导致 Cr(VI)的浸出增加；在 Na 的存在下，超过 80%的初始 Cr(III)量在 600-800°C 下转化为 Cr(VI)。动力学实验可以解释 Cr(VI)浸出随温度升高至 600-800°C 而增加的原因。在 600-800°C 左右的温度下，Cr(VI)浸出达到最大值后，浸出再次下降，这可以通过形成阻止形成的 Cr(VI)浸出的玻璃相来解释。作为说明，对受污染污泥制造陶瓷材料的案例研究进行了 Cr(VI)形成和浸出的评估。基于提出的反应机制，提出了防止 Cr 氧化的对策（添加 NH4H2PO4，在惰性气氛下加热），并在合成混合物和案例研究中成功进行了测试。
