The effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. X-ray absorption spectroscopy (XAS) was used to determine the nature of the adsorbed product on the surface of the birnessite. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5. At pH 7 and 9, As(V) production was significantly less than at pH 5 and the amount of As(V) production for a given reaction time was the same under dark and light conditions. The first order rate constant (kobs) for As(III) oxidation in the presence of light and in the dark at pH 5 were determined to be 0.07 and 0.04 h-1, respectively. The As(V) product was released into solution along with Mn(II), with the latter product resulting from the reduction of Mn(IV) and/or Mn(III) during the As(III) oxidation process. Post-reaction XAS analysis of As(III) exposed birnessite showed that arsenic was present on the surface as As(V). Experimental results also showed no evidence that reactive oxygen species played a role in the As(III) oxidation process.

中文翻译：

---

在有光的情况下将亚砷酸盐氧化成水钠锰矿上的砷。

研究了模拟的太阳辐射对层状氧化锰水钠锰矿上的亚砷酸盐[As（III）]氧化为砷酸盐[As（V）]的影响。进行了实验，在有氧（As）（III），pH 5、7和9的条件下，在缺氧和有氧条件下，水钠锰矿悬浮液用模拟太阳辐射进行辐照。在水钠锰矿表面上的吸附产物的性质。在模拟的日光照射下，在有水钠锰矿存在下，As（III）的氧化速率要快于在pH 5下不存在光的情况下的氧化速率。在pH 7和9下，As（V）的产生显着低于在pH 5时。在黑暗和明亮的条件下，pH 5和给定反应时间的As（V）生成量相同。在有光和在黑暗中，pH为5时，As（III）氧化的一级速率常数（kobs）分别确定为0.07和0.04 h-1。As（V）产物与Mn（II）一起释放到溶液中，后者产物是由于As（III）氧化过程中Mn（IV）和/或Mn（III）的还原而产生的。暴露于As（III）的水钠锰矿的反应后XAS分析表明，砷以As（V）的形式存在于表面。实验结果也没有证据表明活性氧在As（III）氧化过程中起作用。后者的产物是由于在As（III）氧化过程中还原了Mn（IV）和/或Mn（III）而产生的。暴露于As（III）的水钠锰矿的反应后XAS分析表明，砷以As（V）的形式存在于表面。实验结果也没有证据表明活性氧在As（III）氧化过程中起作用。后者的产物是由于在As（III）氧化过程中还原了Mn（IV）和/或Mn（III）而产生的。暴露于As（III）的水钠锰矿的反应后XAS分析表明，砷以As（V）的形式存在于表面。实验结果也没有证据表明活性氧在As（III）氧化过程中起作用。