Because GR minerals are commonly found in iron-rich sediments and anoxic waters metal sorption by GR particles can play a significant role in contaminant sequestration and trace nutrient cycling. The crystal edges contain reactive octahedral sites that are involved in metal binding and divalent metal ions such as Ni 2+ and Zn 2+ are known to integrate into these flexibly charged surface sites. The GR crystal structure is composed of brucite-like octahedral sheets that envelop an interlayer of interchangeable anions (e.g. Green rust (GR) minerals are a group of Fe 2+/Fe 3+layered double hydroxides (LDH) that are known to remove metal cations from solution. The implications for using diagenetic magnetite from green rust precursors as paleo-proxies of Precambrian ocean chemistry are discussed. The results indicate that the transformation of green rust to magnetite is accelerated by metal impurities, and that magnetite is a highly effective scavenger of trace metals during mineral transformation. Dissolution ratio curves showed that Ni 2+, Zn 2+, and Co 2+ cations were incorporated into the mineral structure during magnetite crystal growth. The conversion of green rust to magnetite was concurrent to significant increases in metal uptake, demonstrating a strong affinity for metal sorption/co-precipitation by magnetite. The addition of Ni 2+, Zn 2+, and Co 2+ resulted in faster rates of mineral transformation. Transmission electron microscopy and powder X-ray diffraction showed the conversion of hexagonal green rust platelets to fine grained cubic magnetite crystals. Mineral transformation experiments were conducted by heating green rust suspensions at 85 ☌ in the presence of Ni 2+, Zn 2+, or Co 2+ under strict anoxic conditions.

In this study, we investigated Ni 2+, Zn 2+, and Co 2+ mineralogical incorporation and its effect on green rust transformation to magnetite.

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