Effect of Solution and Solid-Phase Conditions on the Fe(II)-Accelerated Transformation of Ferrihydrite to Lepidocrocite and Goethite
Effect of Solution and Solid-Phase Conditions on the Fe(II)-Accelerated Transformation of Ferrihydrite to Lepidocrocite and Goethite
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DOI：
10.1021/es4043275
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发表时间：
2014-05-20
影响因子：
11.4
通讯作者：
Waite, T. David
中科院分区：
文献类型：
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作者：
Boland, Daniel D.;Collins, Richard N.;Waite, T. David
含水亚铁（Fe（II））加速水铁矿转化为次生的、更结晶的矿物，然而控制速率的因素以及该转化过程的基本机制仍不清楚。在这里，我们提出了第一个详细的动力学研究的Fe（II）-加速转化为针铁矿，通过lepidocrotite，为一系列的pH值和Fe（II）的浓度，并从所获得的结果，提供洞察到的因素控制的转化率和负责转化的过程。Fe（II）-加速的二次矿化的水铁矿的反应计划的开发，其中Fe（II）原子连接到水铁矿表面，在那里它立即被氧化为Fe（III）与所得的电子转移，顺序地，其他铁羟基氧化物Fe（III）原子之前释放到溶液中的Fe（II）。这种新鲜沉淀的Fe（III）形成了形成次生矿物的核，并且还通过创建新鲜的表面位点促进了Fe（II）的持续吸收。固体相关的Fe（II）的浓度和Fe（II）向羟基氧化物表面的运输速率似乎决定了哪些特定的次生矿物形成及其形成速率。在较低的固体相关的Fe（II）的浓度，而条件导致更快速的吸收Fe（II）从溶液中导致更高的针铁矿生长速率增强鳞铁矿的增长。
Aqueous ferrous iron (Fe(II) accelerates the transformation of ferrihydrite into secondary, more crystalline minerals however the factors controlling the rate and, indeed, the underlying mechanism of this transformation process remain unclear. Here, we present the first detailed study of the kinetics of the Fe(II)-accelerated transformation of ferrihydrite to goethite, via lepidocrocite, for a range of pH and Fe(II) concentrations and, from the results obtained, provide insight into the factors controlling the transformation rate and the processes responsible for transformation. A reaction scheme for the Fe(II)-accelerated secondary mineralization of ferrihydrite is developed in which an Fe(II) atom attaches to the ferrihydrite surface where it is immediately oxidized to Fe(III) with the resultant electron transferred, sequentially, to other iron oxyhydroxide Fe(III) atoms before release to solution as Fe(II). This freshly precipitated Fe(III) forms the nuclei for the formation of secondary minerals and also facilitates the ongoing uptake of Fe(II) from by creation of fresh surface sites. The concentration of solid-associated Fe(II) and the rate of transport of Fe(II) to the oxyhydroxide surface appear to determine which particular secondary minerals form and their rates of formation. Lepidocrocite growth is enhanced at lower solid-associated Fe(II) concentrations while conditions leading to more rapid uptake of Fe(II) from solution lead to higher goethite growth rates.