元素硒的无机氧化动力学研究Ⅱ：硝酸与二氧化锰的氧化

The Kinetic Study on the Abiotic Oxidation of Elemental Selenium Ⅱ:Nitric Acid and Manganese Dioxide

地球表生环境中还原态硒的氧化释放是生物可利用态硒的重要来源,为了解元素Se氧化至硒氧离子过程的反应动力学机制和规律,使用^(74)Se-^(77)Se同位素双稀释剂硒浓度测定技术,开展了HNO_3、MnO_2氧化元素Se的实验研究。结果表明,两者均可将元素Se氧化为Se^(4+),且产物较为单一。HNO_3和MnO_2氧化元素Se的过程可分别用拟一级和零级动力学方程描述,其反应速率常数分别为0.0045h^(-1)和0.033μg·m L^(-1)·h^(-1)。从实验数据和动力学模拟推测,NO_3^-离子向固体元素Se内部扩散是NO_3^-氧化元素Se反应的控制步骤,固体MnO_2与元素Se的反应则主要与Se表层原子活化的量密切相关。

The release of reduced Se by oxidation is an important source of bioavailable selenium in the Earth surface environment. However, kinetic on the redox reactions of elemental Se is limited and specific rate constants are generally un-known. By using the technology of ^74Se-^77Se double spike, we carried out the experimental study on the kinetic mechanism of elemental Se oxidization by HNO3 and MnO2. The results showed that elemental Se could only be oxidized to Se（Ⅳ）by HNO3 and MnO2 , and the reaction process of elemental Se oxidation by nitric acid and manganese dioxide can be fitted by the pseudo first-order and zero order rate law, in which the rate constants are 0. 0045 h^-1 and 0. 033μg·mL^-1·h^-1, respectively. Furthermore, the obtained data and kinetic simulation suggest that diffusion of NO3 anion to elemental Se surface is the rate-controlling step during HNO3 oxidation process, and the reaction of solid MnO2 with elemental Se is closely related to the amount of the activated Se atoms.