Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China; Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-sen University, Zhuhai, 519082, China; CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
J Hazard Mater. 2014 Jul 15;276:422-32. doi: 10.1016/j.jhazmat.2014.05.066. Epub 2014 Jun 2.
The interaction of Se(IV) with natural pyrrhotite was investigated at pH conditions ranging from acidic to nearly neutral. The results indicate that the reduction rate can be described in terms of a pseudo-first order reaction. At pH ∼4.0 to ∼5.0, the rate decreased with increasing pH. Unexpectedly, at pH ∼5.0, the rate increased with increasing reaction time. This response was also observed at pH ∼6.0. Two different reaction mechanisms were proposed to explain pyrrhotite oxidation by Se(IV). Because pyrrhotite is acid-soluble and can be attacked by both Fe(3+) and protons, direct reduction by the released aqueous sulfide dominates the reaction at low pH, whereas the cyclic oxidation of aqueous Fe(2+) adsorbed on pyrrhotite surfaces becomes predominant at high pH. Phosphate, which can be irreversibly bound to Fe(3+) intermediates even under acidic conditions, can significantly decrease the reaction rate by an order of magnitude at pH ∼4.5. In contrast to the thermodynamic calculations and the predicted prevalence of FeSe based on previous reports of aqueous Se(IV) reduction by synthetic mackinawite or troilite, only Se(0) was observed as the reaction product in this study. This observation confirmed that a slow reaction favors the formation of Se(0) rather than iron selenides.
研究了硒（IV）与天然磁黄铁矿在从酸性到近中性的 pH 条件下的相互作用。结果表明，还原速率可以用准一级反应来描述。在 pH 值约为 4.0 到 5.0 时，速率随 pH 值的增加而降低。出乎意料的是，在 pH 值约为 5.0 时，速率随反应时间的增加而增加。在 pH 值约为 6.0 时也观察到了这种反应。提出了两种不同的反应机制来解释硒（IV）对磁黄铁矿的氧化作用。由于磁黄铁矿是酸溶性的，并且可以被 Fe(3+)和质子同时攻击，因此在低 pH 值下，释放出的水合硫化物的直接还原主导了反应，而在高 pH 值下，吸附在磁黄铁矿表面的水合 Fe(2+)的循环氧化则占主导地位。即使在酸性条件下，磷酸盐也可以不可逆地与 Fe(3+)中间体结合，在 pH 值约为 4.5 时，可以使反应速率降低一个数量级。与热力学计算以及先前关于合成铁镍矿或陨铁石还原水相硒（IV）的报道中预测的基于 FeSe 的优势相反，在这项研究中仅观察到硒（0）作为反应产物。这一观察结果证实，缓慢的反应有利于形成硒（0）而不是铁硒化物。
