Green rust (GR) minerals are mixed-valent iron (Fe) hydroxide minerals that are composed of brucitic Fe<sup>II</sup>(OH)<sub>2</sub> sheets in which part of the ferrous (divalent) Fe cations have been replaced with ferric (trivalent) Fe. These Fe(II)-Fe(III) phases are believed to be widespread in redox transition zones, although identification in natural systems is hindered by the rapid oxidation of GR into Fe(III)-oxides when exposed to air. Because of their layered structure and high Fe(II) content, GR minerals are effective reductants of a broad range compounds, and their redox reactivity has been studied in considerable detail. Much less is known about the reactivity of GR minerals towards redox-inactive trace metals such as Ni(II) and Zn(II). The aim of the research presented here was to assess the affinity and mechanisms of Ni(II) and Zn(II) sorption onto GR in circumneutral anoxic solutes. The work combined macroscopic batch experiments to characterize sorption trends with X-ray absorption spectroscopic analyses to determine prevailing sorption mechanisms as a function of time and metal concentration. The results demonstrate that Ni(II) and Zn(II) have a high affinity for GR  and compete effectively with Fe(II) for coordination at the mineral surface. Sorption reactions with GR may therefore represent a significant control on the mobility and solubility of trace metals in suboxic environments.

Sorption of Ni(II) and Zn(II) onto green rust

2019 Fall National Meeting

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