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Oxidation of Fe(II) in rainwater

机译：雨水中Fe（II）的氧化

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Photochemically produced Fe(II) is oxidized within hours under environmentally realistic conditions in rainwater. The diurnal variation between photochemical production and reoxidation of Fe(II) observed in our laboratory accurately mimics the behavior of ferrous iron observed in field studies where the highest concentrations of dissolved Fe(II) occur in afternoon rain during the period of maximum sunlight intensity followed by gradually decreasing concentrations eventually returning to early morning pre-light values. The experimental work presented here, along with the results of kinetics studies done by others, suggests that the primary process responsible for the decline in photochemically produced Fe(II) concentrations is oxidation by hydrogen peroxide. This reaction is first order with respect to both the concentrations of Fe(II) and H2O2. The second-order rate constant determined for six different authentic rain samples varied over an order of magnitude and was always less than or equal to the rate constant determined for this reaction in simple acidic solutions. Oxidation of photochemically produced ferrous iron by other oxidants including molecular oxygen, ozone, hydroxyl radical, hydroperoxyl/superoxide radical, and hexavalent chromium were found to be insignificant under the conditions present in rainwater. This study shows that Fe(II) occurs as at least two different chemical species in rain; photochemically produced Fe(II) that is oxidized over time periods of hours, and a background Fe(II) that is protected against oxidation, perhaps by organic complexation, and is stable against oxidation for days. Because the rate of oxidation of photochemically produced Fe (II) does not increase with increasing rainwater pH, the speciation of this more labile form of Fe(II) is also not controlled by simple hydrolysis reactions.
机译：光化学生产的Fe（II）在环境条件下在雨水中几小时内就会被氧化。在我们的实验室中观察到的光化学生成和Fe（II）的再氧化之间的日变化准确地模拟了实地研究中观察到的亚铁的行为，其中最大浓度的Fe（II）发生在午后的雨中，随后是最大的阳光强度。通过逐渐降低浓度最终返回到清晨的预发光值。这里介绍的实验工作以及其他人进行的动力学研究的结果表明，造成光化学产生的Fe（II）浓度下降的主要过程是过氧化氢的氧化。就Fe（II）和H 2 O 2的浓度而言，该反应是一级反应。为六个不同的真实降雨样品确定的二阶速率常数变化一个数量级，并且始终小于或等于在简单的酸性溶液中为此反应确定的速率常数。在雨水中存在的条件下，发现由其他氧化剂（包括分子氧，臭氧，羟基自由基，氢过氧/超氧化物自由基和六价铬）对光化学生成的亚铁的氧化作用微不足道。这项研究表明，Fe（II）在雨中至少以两种不同的化学物质形式存在。光化学生成的Fe（II）会在数小时的时间内被氧化，而本底Fe（II）可能会受到有机配位保护而免受氧化，并在几天内稳定地被氧化。由于光化学方法生成的Fe（II）的氧化速率不会随雨水pH值的增加而增加，因此这种较不稳定形式的Fe（II）的形态也不受简单的水解反应控制。

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