Characterization of Different Solid Particles Transformed from Green Rust in Aqueous Solution — Using XRD, Mössbauer Spectroscopy, and XANES

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The X-ray diffraction method and Mössbauer spectroscopy were used for characterizing solid particles transformed from hydroxysulfate GR2(SO₄²⁻) by oxidation in aqueous solution. The results revealed that different ferric oxyhydroxides (α-FeOOH and γ-FeOOH) and magnetite (Fe₃O₄) were formed through the precipitation of ferrous and ferric ions dissolved from GR2(SO₄²⁻) in aqueous solution. The X-ray absorption spectroscopy along with Mössbauer spectroscopy was also used for analyzing the chemical state of iron in GR2(SO₄²⁻). The molar ratio of ferrous to ferric ions [Fe(II)]/[Fe(III)] in GR2(SO₄²⁻) was shown to be nearly two during the transformation from GR2(SO₄²⁻). Moreover, the oxidation-reduction potential (ORP) and pH of the GR suspension were measured to examine formation conditions of the different ferric oxyhydroxides and magnetite. The results showed that formation conditions of magnetite in the aqueous solution were different from those of the ferric oxyhydroxides, indicating that reaction conditions in aqueous solution strongly influence the formation of different ferric oxyhydroxides and magnetite.