&lt;strong&gt;Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization&lt;/strong&gt;

Chengshuai Liu,Jian Long,Jian Hua,Minghua Gu,Fangbai Li,Fei Wu,Ting Gao,Manjia Chen,Jing Lei

doi:10.3390/iecms2018-05460

<strong>Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization</strong>

Chengshuai Liu, Jian Long + Show 7 more

Open Access

https://doi.org/10.3390/iecms2018-05460

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Abstract

The interaction between aqueous Fe(II) (Fe(II)aq) and iron (hydr)oxides is an important reaction of iron cycle and plays a critical role in the environmental behavior of heavy metal in soils. The metal substitution has been reported to decrease the Fe atom exchange rates between the Fe(II)aq and metal-substituted iron (hydr)oxides as well as inhibiting the recrystallization of iron (hydr)oxides, whereas the environmental behaviors of the substituted metal during the processes remain unclear. In this study, Fe(II)aq-induced recrystallization of Cr-substituted goethite (Cr-goethite) and the sequentially release of substituted Cr were investigated under different conditions. The results of stable Fe isotopic tracer and Mössbauer characterization studies show that Fe atom exchange occurred between Fe(II)aq and structural Fe(III) in Cr-goethites, during which Cr-goethites were recrystallized. The Cr substitution inhibited the rates of Fe atom exchange and Cr-goethite recrystallization. During the processes, Cr were released from Cr-goethite and Cr-goethites with higher Cr-substituted contents released more. Highest Fe atom exchange rate and most amount of Cr release were observed at pH 7.5, while no change in mineral phase after reaction for 30 days. At a lower pH of 5.5 or a higher pH of 8.5, significantly less exchange and Cr release occurred. The releases of Cr were positively correlated with the Fe atom exchanges rates, suggesting the driving force of sorbed Fe(II) for the Fe atom exchange and Cr release. The release and re-incorporation of Cr simultaneously occurred during the Fe(II)aq-induced recrystallization of Cr-goethites, especially at the late stage of the reactions. Our findings indicate that dynamic changes of Cr forms relating to Fe(II)aq-induced recrystallization of iron (hydr)oxides should be considered when evaluating the soil Cr pollution in Fe-rich soils.

Highlights

Ironoxides such as lepidocrocite, goethite, and hematite are common secondary iron minerals in soils
The results showed that neither Cr(III)aq nor Cr(III)extr was detected, indicating that all of the Cr(III) was structurally incorporated into the goethites
The release of Cr(III) from Cr-goethites was investigated during the recrystallization recrystallization process induced by Fe(II)aq under various conditions

Summary

Introduction

Iron (hydr)oxides such as lepidocrocite, goethite, and hematite are common secondary iron minerals in soils. Iron (hydr)oxides rarely occur in a chemically pure form, and usually contain. A number of trace metals, including Al(III), Ti(II), Cr(III), Mn(III), Ni(II), As(III), and Cu(II), were observed to be substituted into the structures of iron (hydr)oxides upon replacing Fe(III). 33 mol%, respectively, of Fe(III) sites within iron (hydr)oxides [3,6]. Cr-substituted goethites are common in natural soil due to the similar ionic radii of Cr(III) (61.5 pm) and. Isomorphous substitution of metals in the structures of iron (hydr)oxides can lead to metal immobilization and, to the formation of stable metal-containing mineral phases, reducing the activities of iron (hydr)oxides and the bioavailability of metals [3,7,8]

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