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

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 (