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Distribution of persistent free radicals in different molecular weight fractions from peat humic acids and their impact in reducing goethite.

Authors
  • Shi, Yafang1
  • Zhang, Chi1
  • Liu, Jinbo1
  • Dai, Qingyang1
  • Jiang, Yuanren1
  • Xi, Mengning1
  • Jia, Hanzhong2
  • 1 College of Natural Resources and Environment, Northwest A & F University, Yangling 712100, China. , (China)
  • 2 College of Natural Resources and Environment, Northwest A & F University, Yangling 712100, China; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Northwest A & F University, Yangling 712100, China. Electronic address: [email protected] , (China)
Type
Published Article
Journal
The Science of the total environment
Publication Date
Nov 25, 2021
Volume
797
Pages
149173–149173
Identifiers
DOI: 10.1016/j.scitotenv.2021.149173
PMID: 34303988
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Humic substances, the most abundant component of soil organic matter, play vital roles in the biogeochemical cycles and pollutant redox reactions. However, the knowledge regarding the distribution of persistent free radicals (PFRs) and redox capacity in different molecular weight fractions (MWF) of humic acid (HA) and their impact on the transformation of iron oxide minerals remains unknown. In this study, we separated bulk HA into various MWF using dialysis methods and systematically investigated their PFRs properties, redox capacity, and the impact in reducing goethite. The results showed that the PFRs in the low MWF (<3500, <7000, and <14,000 Da) can be assigned to oxygen-centered organic radicals while those in the bulk and high MWF (14000-retentate) were assigned to carbon-centered organic radicals. The PFRs concentrations of low MWF were 0.20-0.45 × 1016 spins/g, far less than those of bulk HA (3.04 × 1016 spins/g) and 14000-retentate (1.30 × 1016 spins/g). The total concentrations of reactive oxygen species (ROS) induced by PFRs in HA fractions ranged from 8.04 × 1016 (in 14000-retentate) to 32.35 × 1016 spins/g (in bulk HA). Compared with the low MWF, the 14000-retentate fractions had the higher reducing capacity, which was positively related to the content of PFRs and phenolic hydroxyl in HA. The results obtained provide valuable insight into the geochemistry processes of Fe-containing minerals during their interaction with HA in the natural environment. Overall, the results obtained provide valuable insight into the geochemical behaviors of HA-associated PFRs under natural conditions. Copyright © 2021 Elsevier B.V. All rights reserved.

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