Fate of adsorbed organic compounds during transformation of ferrihydrite: implications for biogenic origin of Precambrian iron formations

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Authors

Stanislav Jelavic , Andrew Mitchell, Karina Krarup Sand

Abstract

The absence of organic compounds from Precambrian iron formations (IF) challenges the hypothesis of their biogenic origin. Here we address the fate of adsorbed organic compounds during transformation from ferrihydrite to hematite. We determined the binding energy between hematite and common molecular terminations found in extracellular polymeric substances and biofilms: carboxylic, alcohol and phosphate functional groups. We found that the bond between hematite and alcohol group is approximately 2 times stronger than the bond between hematite-carboxyl and -phosphate groups. We then transformed synthetic ferrihydrite to hematite in presence of glycerol, which has a high density of alcohol groups and measured the amount of mineral associated glycerol before and after the transformation. We showed that the transformation releases glycerol highlighting that at least some organic compounds from initial IFs were desorbed very early during the process of sedimentation. Our results suggest that the absence of organic compounds in IF cannot be an evidence against their biogenic origin.

DOI

https://doi.org/10.31223/osf.io/pd73x

Subjects

Biogeochemistry, Chemistry, Earth Sciences, Physical Chemistry, Physical Sciences and Mathematics

Keywords

Dates

Published: 2020-01-30 13:40

Last Updated: 2020-03-20 15:31

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CC BY Attribution 4.0 International

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