Abstract
Ferrihydrite often precipitates with humic acid in natural ways, affecting the fate of lead ions, the stabilization of humic acid, and the aging process of ferrihydrite. A series of 2-line ferrihydrite-humic (Fh-HA) acid with varying C loadings has been prepared, the morphology and surface properties of Fh-HA organo-minerals have been characterized, and the adsorption property of Pb ions onto Fh-HA has been studied. The results indicated that a strong interference of HA to ferrihydrite 2-line Fh dominated mineral phase in all samples, but with increasing C/Fe molar ratios, the crystallinity gradually weakened, particles became smaller, and SSA decreased significantly. The data of Mössbauer spectra confirmed C loadings changed the unit structure of ferrihydrite. Fh-HA performed good adsorption properties to Pb (II): high efficiency and big capacity, especially Fh-HA_2.0. pH had great effect on Pb (II) sorption, the pH change affects not only the amounts of competitive ions in solutions, but also the dissociation and protonation of functional groups on the surface of Fh-HA. Sorption kinetics can be well modeled by a pseudo-second-order model, and the process was controlled by film and intraparticle adsorption simultaneously. The adsorption isotherms can be well described by Freundlich isotherm model. The detailed determination results of Fe 2p, O 1s, and Pb 4f spectra before and after lead adsorption showed mononuclear bidentate or binuclear bidentate ligands occurring on Fh-HA surface, forming stable inner-sphere complex. By comparison of Mössbauer spectra and TEM images, with aging time, a slower evolution of iron oxide/oxyhydroxide phases in Fh-HA-Pb system happened compared to pure ferrihydrite. Ferrihydrite has transformed to a combination of ferrihydrite, goethite, and hematite phases. In this study, the determination of C-Fe interaction, Pb fate influenced by Fh-HA, and transformation of ferrihydrite would have a great implication to application of Fh-HA precipitates in remediation for surface water or groundwater polluted by heavy metals.
Highlights
Lead (Pb) is present at elevated concentrations in air, soils and aquatic environment, its emission from a variety of anthropogenic sources, including municipal and industrial waste, metal mining and processing and agricultural activities (Pan et al.,2012)
C loadings can change surface and structure properties of ironoxides, for ferrihydrite, a new negative charge surface and more available sites formed by coprecipitation with humic acid, thereby affects the adsorption properties of Pb(II) onto ferrihydrite (Tiberg et al.,2016)
All reagents and chemicals were of analytical grade, all solutions were prepared using deionized water (DIW) (≥18 MΩ cm), CO2 was rigorously excluded to prevent the formation of Pb
Summary
Lead (Pb) is present at elevated concentrations in air, soils and aquatic environment, its emission from a variety of anthropogenic sources, including municipal and industrial waste, metal mining and processing and agricultural activities (Pan et al.,2012). Formed ferrihydrite is mostly efficient adsorbent known for Pb, As, Cu, Zn sequestration (Zhu et al.,2010), affecting their fate and mobility in the aqueous phase. It plays an important role in wastewater treatment and remediation activities (Kragovic et al.,2017; Chen et al.,2019). C loadings can change surface and structure properties of iron (hydr)oxides, for ferrihydrite, a new negative charge surface and more available sites formed by coprecipitation with humic acid, thereby affects the adsorption properties of Pb(II) onto ferrihydrite (Tiberg et al.,2016). The findings of this work could provide a better understanding of the Pb mobility and fate affected by Fh-HA in contaminated environment, facilitate our knowledge about the way ferrihydrite transformed when humic acid introduced and Pb adsorbed
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