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

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 kinet...

Full description

Saved in:
Bibliographic Details
Published in:Environmental science & technology 2014-05, Vol.48 (10), p.5477-5485
Main Authors: Boland, Daniel D, Collins, Richard N, Miller, Christopher J, Glover, Chris J, Waite, T. David
Format: Article
Language:eng
Subjects:
Aqueous chemistry
Crystallization
Crystals
Earth sciences
Earth, ocean, space
Electrons
Exact sciences and technology
Ferric Compounds - chemistry
Geochemistry
Iron - chemistry
Iron Compounds - chemistry
Kinetics
Marine and continental quaternary
Microscopy, Electron, Transmission
Mineralogy
Minerals
Minerals - chemistry
Models, Theoretical
Oxidation-Reduction
Silicates
Solutions
Surficial geology
Thermodynamics
Water - chemistry
Water geochemistry
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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 solution 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.
ISSN:0013-936X
1520-5851