Speciation Controls the Kinetics of Iron Hydroxide Precipitation and Transformation at Alkaline pH
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2024-11-05
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Journal Article
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yes
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Abstract
The formation of energetically favorable and metastable mineral phases within the Fe-H2O system controls the long-term mobility of iron complexes in natural aquifers and other environmentally and industrially relevant systems. The fundamental mechanism controlling the formation of these phases has remained enigmatic. We develop a general partial equilibrium model, leveraging recent synchrotron-based data on the time evolution of solid Fe(III) hydroxides along with aqueous complexes. We combine thermodynamic considerations and particle-morphology-dependent kinetic rate equations under full consideration of the aqueous phase in disequilibrium with one or more of the forming minerals. The new model predicts the rate of amorphous 2-line ferrihydrite precipitation, dissolution, and overall transformation to crystalline goethite. It is found that the precipitation of goethite (i) occurs from solution and (ii) is limited by the comparatively slow dissolution of the first forming amorphous phase 2-line ferrihydrite. A generalized transformation mechanism further illustrates that differences in the kinetics of Fe(III) precipitation are controlled by the coordination environment of the predominant Fe(III) hydrolysis product. The framework allows modeling of other iron(bearing) phases across a broad range of aqueous phase compositions.
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published
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Journal / series
Volume
58 (44)
Pages / Article No.
19851 - 19860
Publisher
American Chemical Society
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Date collected
Date created
Subject
Dissolution; Iron; Kinetics; PH; Precipitation; Partial Equilibrium
Organisational unit
09593 - Angst, Ueli / Angst, Ueli
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Funding
848794 - Towards mastering the long-standing challenge of ageing infrastructures in corrosive environments (EC)