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The role and fate of organic carbon during aging of ferrihydrite

DOI: 10.1016/j.gca.2022.07.003 DOI Help

Authors: Yao Zhao (University of Leeds) , Oliver W. Moore (University of Leeds) , Ke-Qing Xiao (University of Leeds) , Lisa Curti (University of Leeds) , Alba Otero-Farina (University of Leeds) , Steven A. Banwart (University of Leeds) , Caroline L. Peacock (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Geochimica Et Cosmochimica Acta , VOL 212

State: Published (Approved)
Published: July 2022
Diamond Proposal Number(s): 23049

Open Access Open Access

Abstract: The persistence of organic carbon (OC) in natural environments is widely attributed to mineral protection, especially by iron (Fe) (oxyhydr)oxides. The effect of OC binding strength on the aging of Fe (oxyhydr)oxides and the mobility and fate of OC during aging however, is unknown. Here we investigate how OC binding strength controls the aging of ferrihydrite (Fh) and subsequent retention or release of the associated OC. We focus on carboxyl-rich OC coprecipitated with Fh and track the physiochemical properties and OC stability as a function of carboxyl-richness over time. In agreement with previous work we find that during carboxyl-rich OC coprecipitation with Fh, OC is adsorbed to the Fh particle surfaces and that increasing carboxyl-richness results in an increasing number of carboxylate-Fe bonds between the OC and the mineral particles and thus increasing OC binding strength. We show that OC substantially retards the aging of Fe (oxyhydr)oxide from Fh to more crystalline Fe minerals and that this retardation increases with increasing OC binding strength. We also show that the total amount of OC decreases during aging and that the proportion of the remaining OC that is non-desorbable with 0.1 M NaOH decreases during aging for OC with relatively low binding strength but increases during aging for OC with relatively high binding strength. Our results therefore indicate that OC with higher binding strength coprecipitated with Fh becomes proportionally more stable with the solid phase and thus less mobile during aging in natural environments. We suggest that our work might offer a deeper mechanistic insight into the processes responsible for OC persistence with minerals and thus the long-term preservation of OC in natural environments.

Journal Keywords: iron (oxyhydr)oxidesiron; (hydr)oxides; iron oxides; organic matter; organic carbon; carboxyl; binding strength; aging; dissolution recrystallisation; mobility

Subject Areas: Earth Science

Instruments: I08-Scanning X-ray Microscopy beamline (SXM)

Added On: 13/07/2022 08:54


Discipline Tags:

Earth Sciences & Environment Mineralogy Geology Geochemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Near Edge X-ray Absorption Fine Structures (NEXAFS)