Interaction of metals and phosphate with ferrihydrite and environmental implications

Description

The Fe(III) hydroxide ferrihydrite (Fh) is highly reactive towards dissolved metals and other aqueous compounds. This reactivity suggests a possible role for Fh in environmental remediation and in controlling ambient concentrations of metals and nutrients in both modern and ancient aqueous environments. Though the reactivity of Fh towards a variety of aqueous compounds has been determined in previous studies, its reactivity under seawater-like conditions has not been systematically explored. Furthermore, the fate of the aqueous compounds upon aging of the Fh has been examined in only a few studies. To bridge these gaps, we conducted a series of adsorption and co-precipitation experiments of various metals and phosphate with Fh, in seawater-analog solutions, at circumneutral pH (pH 7.5 and 8.0) and 25˚C. We quantified the effect of interaction with Fh on the aqueous concentrations of Cd(II), Co(II), Cr(II), Cu(II), Mn(II), Mo(VI), N(II), V(V), U(VI), Zn(II), and phosphate. The experimental results are provided as uptake percentages at different metal:Fe ratios and as a series of partition coefficients of the studied metals and phosphate between aqueous solution and Fh. Additionally, aging experiments of up to ~4 years in duration were used to determine the potential effects of mineral transformation on the uptake of the metals and phosphate. We discuss the mechanisms of metal and phosphate uptake by Fh, the effects of solution composition on uptake, and the implications of our findings for modern and ancient natural environments and for environmental remediation.

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