Carbon sequestration during Fe(III)-Fulvic acid coprecipitation and kinetics of hydrated Cu(II)

Abstract

The dynamic interactions among iron (Fe) oxides and organic matter (OM) play vital roles in controlling the geochemical cycling of carbon (C) and toxic trace metals. Although the effects of OM on the Fe oxides transformation, and dynamic with toxic trace metals have been studied previously, it is still poor to understand the mechanistic and quantitative on the C sequestration during the Fe(III) mineralization process, and kinetics with hydrated Cu(II) in the acid drainage. In this study, Mössbauer spectroscopy, X-ray absorption spectroscopy (XAS), high resolution transmission electron microscopy (HRTEM), and density functional theory (DFT) were used to elucidate the underlying mechanism for the fine structure of iron minerals, fulvic acid (FA) sequestration and hydrated Cu(II) coordination on Fe oxides. FA dosages played an essential role in the formation of Fe oxides, which can inhibit the formation of Fe-O octahedrons and benefit to the Fe-O tetrahedron. FA molecules were mainly sequestrated on the surfaces of Fe oxides and van der Waals forces were the main interaction between FA and Fe oxides. The hydrated Cu(II) oxides mainly distributed on the surface of iron oxides as divalent oxidation states, and feasible coordinated with phenolic hydroxyl group of FA and Fe oxides. The knowledge of the dynamic coupling between Fe oxide transformation under the effect of FA and the fate of hydrated Cu(II) on Fe oxides provided the basis for predicting the geochemical process of Fe, C and toxic trace metals.