Formation and transformation of schwertmannite through direct Fe3+ hydrolysis under various geochemical conditions,Environmental Science: Nano

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Formation and transformation of schwertmannite through direct Fe3+ hydrolysis under various geochemical conditions
Environmental Science: Nano ( IF 5.8 ) Pub Date : 2020-07-07 , DOI: 10.1039/d0en00252f
Hong Ying _{1,

2,

3,

4,

5} , Xionghan Feng _{1,

2,

3,

4,

5} , Mengqiang Zhu _{6,

7,

8,

9} , Bruno Lanson _{10,

11,

12,

13,

14} , Fan Liu _{1,

2,

3,

4,

5} , Xiaoming Wang _{1,

2,

3,

4,

5}

Affiliation

Schwertmannite formation and transformation, key processes that influence the speciation, mobility, and environmental fate of associated trace elements in acid mine drainage (AMD), were primarily studied through Fe²⁺ oxidation–hydrolysis. Direct Fe³⁺ hydrolysis is another important schwertmannite formation pathway, but the effects of geochemical conditions on the mineralogical properties of schwertmannite formed via such a pathway are poorly known. Here, the formation of schwertmannite through direct Fe³⁺ hydrolysis enforced by heating or adding OH⁻ and subsequent transformation were systematically examined under various geochemical conditions. Pure schwertmannite is obtained through Fe³⁺ hydrolysis at 25–60 °C for 12 min and subsequent dialysis for 1–15 days, while minor amounts of goethite appear at higher hydrolysis temperatures. A shorter dialysis time and the presence of K⁺ or NH₄⁺ both slightly increase schwertmannite crystallinity. During Fe³⁺ hydrolysis by adding OH⁻, sulfate-bearing ferrihydrite initially forms and then quickly transforms into schwertmannite. In contrast, pre-formed ferrihydrite does not transform into schwertmannite under the same solution conditions, despite sulfate adsorption. With decreasing Fe³⁺ hydrolysis rate, schwertmannite crystallinity slightly increases and its morphology of “network” structure becomes larger and less dense. As to schwertmannite transformation, high temperature, high pH, and the presence of Fe²⁺ favor its transformation to goethite, while a low Fe³⁺ hydrolysis rate and a high Cl⁻ concentration hinder the transformation. In contrast, the presence of K⁺ or high NH₄⁺ concentration favors schwertmannite transformation to jarosite with the former occurring more readily. These new insights into schwertmannite formation and transformation are essential for predicting the environmental fates of associated trace elements in AMD environments.

中文翻译：

在各种地球化学条件下通过直接Fe3 +水解形成Schwertmannite的过程

Schwertmannite的形成和转变是影响酸性矿山排水（AMD）中相关微量元素的形态，迁移率和环境命运的关键过程，主要通过Fe ²⁺氧化水解进行研究。直接的Fe ³⁺水解是另一个重要的schwertmannite形成途径，但人们尚不了解地球化学条件对通过这种途径形成的schwertmannite矿物学特性的影响。在这里，通过直接的Fe施威特曼石的形成³⁺水解强迫通过加热或添加OH ^-和随后的转化进行了系统的各种地球化学条件下观察。纯的Schwertmannite是通过Fe ³⁺获得的在25–60°C下水解12分钟，然后渗析1–15天，而较高的水解温度下出现少量针铁矿。较短的透析时间和K ⁺或NH ₄⁺的存在均会稍微增加Schwertmannite结晶度。期间的Fe ³⁺水解通过加入OH ^-，硫酸根轴承水铁矿最初形式，然后迅速变换成施威特曼石。相反，尽管有硫酸盐吸附，但在相同的溶液条件下，预先形成的亚铁水合物不会转变为schwertmannite。随着Fe ^3+的减少水解速率，schwertmannite结晶度略有增加，并且其“网状”结构的形态变得更大而密度更低。至于施威特曼石转化，高温，高pH值，和Fe的存在²⁺有利于其转变为针铁矿，而低的Fe ³⁺水解率和高氯^-浓度阻碍转化。相反，K ⁺或高NH ₄⁺浓度的存在有利于将Schwertmannite转变为黄钾铁矾，而前者更容易发生。这些关于schwertmannite形成和转变的新见解对于预测AMD环境中相关微量元素的环境命运至关重要。

更新日期：2020-08-14

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