BACKGROUND Manganese-oxides are one of the most important minerals in soil due to their widespread distribution and high reactivity. Despite their invaluable role in cycling many redox sensitive elements, numerous unknowns remain about the reactivity of different manganese-oxide minerals under varying conditions in natural systems. By altering temperature, pH, and concentration of arsenite we were able to determine how manganese-oxide reactivity changes with simulated environmental conditions. The interaction between manganese-oxides and arsenic is particularly important because manganese can oxidize mobile and toxic arsenite into more easily sorbed and less toxic arsenate. This redox reaction is essential in understanding how to address the global issue of arsenic contamination in drinking water. RESULTS The reactivity of manganese-oxides in ascending order is random stacked birnessite, hexagonal birnessite, biogenic manganese-oxide, acid birnessite, and δ-MnO2. Increasing temperature raised the rate of oxidation. pH had a variable effect on the production of arsenate and mainly impacted the sorption of arsenate on δ-MnO2, which decreased with increasing pH. Acid birnessite oxidized the most arsenic at alkaline and acidic pHs, with decreased reactivity towards neutral pH. The δ-MnO2 showed a decline in reactivity with increasing arsenite concentration, while the acid birnessite had greater oxidation capacity under higher concentrations of arsenite. The batch reactions used in this study quantify the impact of environmental variances on different manganese-oxides' reactivity and provide insight to their roles in governing chemical cycles in the Critical Zone. CONCLUSIONS The reactivity of manganese-oxides investigated was closely linked to each mineral's crystallinity, surface area, and presence of vacancy sites. δ-MnO2 and acid birnessite are thought to be synthetic representatives of naturally occurring biogenic manganese-oxides; however, the biogenic manganese-oxide exhibited a lag time in oxidation compared to these two minerals. Reactivity was clearly linked to temperature, which provides important information on how these minerals react in the subsurface environment. The pH affected oxidation rate, which is essential in understanding how manganese-oxides react differently in the environment and their potential role in remediating contaminated areas. Moreover, the contrasting oxidative capacity of seemingly similar manganese-oxides under varying arsenite concentrations reinforces the importance of each manganese-oxide mineral's unique properties.

中文翻译：

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环境条件对锰氧化物被氧化锰氧化动力学的影响。

背景技术由于锰氧化物的广泛分布和高反应性，其是土壤中最重要的矿物质之一。尽管它们在循环许多氧化还原敏感元素方面起着不可估量的作用，但对于不同的锰氧化物矿物质在自然系统中的各种条件下的反应性，仍有许多未知数。通过改变温度，pH值和亚砷酸盐的浓度，我们能够确定锰氧化物反应性在模拟环境条件下如何变化。锰氧化物与砷之间的相互作用尤为重要，因为锰可以将可移动的有毒砷氧化为更易吸附且毒性较低的砷酸盐。这种氧化还原反应对于理解如何解决饮用水中砷污染这一全球性问题至关重要。结果锰氧化物的反应性从小到大依次为无规叠层水钠锰矿，六角型水钠锰矿，生物型锰氧化物，酸性水钠锰矿和δ-MnO2。温度升高提高了氧化速率。pH对砷酸盐的产生具有可变的影响，并且主要影响砷酸盐在δ-MnO2上的吸附，其随pH的升高而降低。酸性水钠锰矿在碱性和酸性pH值下氧化的砷最多，对中性pH的反应性降低。δ-MnO2随着亚砷酸盐浓度的增加而反应性下降，而酸性水钠锰矿在较高浓度的亚砷酸盐下具有更大的氧化能力。本研究中使用的分批反应量化了环境变化对不同锰氧化物的影响。反应性，并深入了解它们在控制关键区化学循环中的作用。结论所研究的锰氧化物的反应性与每种矿物的结晶度，表面积和空位的存在密切相关。δ-MnO2和酸水钠锰矿被认为是天然存在的生物成锰氧化物的合成代表。然而，与这两种矿物质相比，生物成因的锰氧化物在氧化方面表现出滞后时间。反应性显然与温度有关，这提供了有关这些矿物质在地下环境中如何反应的重要信息。pH值会影响氧化速率，这对于了解锰氧化物在环境中的反应方式及其在修复污染区域中的潜在作用至关重要。而且，