Description
Green rust (GR) is the generic name, which refers to a family of compounds consisting of brucite-like layers of Fe(II),Fe(III)-hydroxide. GR is a layered double hydroxide (LDH), also known as hydrotalcite-like materials (HLM). They have been identified in nature in soil taken from the redox boundary where groundwater is oxidised and they are important first solids during corrosion of iron in remediation barriers. The presence of Fe(II) in the brucite-like layer, makes GR very reactive towards redox sensitive elements, such as Cr, Se, Np and chlorinated solvents and pesticides. Understanding the GR system is thus interesting with regards to remediation techniques. It will also aid to better understand the redox processes taking place in the groundwater zone and to improve prediction of contaminant transport.
Previous studies have reported structurally bound water and anions in the interlayers, the thickness of which is assumed to be defined by the anion. Compounds with spherical or planar anions, such as Cl- or CO32-, produce similar X-ray diffraction (XRD) patterns and are known as Group 1 GR. Group 2 compounds incorporate three dimensional anions, such as tetrahedral SO42-, and produce larger basal-plane spacings.
If we want to predict redox reactions and contaminant transport, it is important to know the structural parameters of the various GR types. GRSO4, which is used in many studies, has not been characterised correctly in the past. We used several high resolution techniques including XRD, Mössbauer spectroscopy, ICP-AES and atomic force microscopy to investigate the GRSO4 compounds. We observed a difference in X-ray diffraction patterns depending on which monovalent cation was dominant during formation.
Within the last decade, two observations of naturally occurring sodium and sulphate-containing hydrotalcites have been described: nikischerite, NaFe2+6Al3(SO4)2(OH)18•12H2O and shigaite NaAl3Mn2+6(SO4)2(OH)18•12H2O. We refined the structure for green rust sodium sulfate and potassium sulfate using the nikischerite structure as a basis. The calculations, as well as careful chemical analyses, clearly indicated presence of Na or K in the structure. Thus we present new chemical formulae and new crystal structures for GRNa,SO4 and GRK,SO4: NaFe2+6Fe3+3(SO4)2(OH)18•XH2O, P-3, a-axis = 9.520 Å, c-axis = 10.932 Å and KFe2+12Fe3+6(SO4)3.5(OH)36•XH2O a-axis = 9.530 Å, c-axis = 11.183 Å| Period | 20 Aug 2007 |
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| Event title | Goldschmidt 2007 - "atoms to planets" |
| Event type | Conference |
| Location | Köln, GermanyShow on map |