Water of crystallization and its hydrogen-bonded crosslinking in vivianite Fe3(PO4)2 · 8H2O; a neutron diffraction investigation

Early diagenetic vivianite [Fe3(PO4)2·8H2O] in a contaminated freshwater sediment and insights into zinc uptake: A μ-EXAFS, μ-XANES and Raman study

“…The tetrahedral coordination fit for our vivianites also matches the second shell of these previous studies, suggesting that either our data are not of sufficient quality to fit the additional shell of 2 O around the Fe, or that the Fe is more disordered within the normally octahedral site. The identification of a shell of two P atoms at a distance of 3.23 Å in grains 2 to 4 is typical of the vivianite structure (Mori and Ito, 1950;Fejdi et al, 1980;Bartl, 1989; Table 1). …”

“…2σ 2 is the Debye-Waller type factor, and the R factor indicates quality of fit (lower R factor indicates a better fit). Structural data of vivianite (averages) from Mori and Ito (1950), Fejdi et al (1980) and Bartl (1989) are shown for comparison purposes. Errors in this table are as follows: Number of atoms ± 1; r ± 0.02Å; DW ± 0.002Å2.…”

“…The parameters derived from the EXAFS fitting for Fe are shown in Table 1, together with Fe-O and Fe-P co-ordination numbers and bond lengths for vivianite from Mori and Ito (1950), Fejdi et al (1980) and Bartl (1989). EXAFS Fe K-edge spectra and Fourier transforms for vivianites 1 and 4 are shown in Figure 6 (the spectra for vivianites 2 and 3 are virtually identical to that of vivianite 4 and so are not shown Mori and Ito, 1950;Fejdi et al, 1980;Bartl, 1989; Table 1).…”

“…EXAFS Fe K-edge spectra and Fourier transforms for vivianites 1 and 4 are shown in Figure 6 (the spectra for vivianites 2 and 3 are virtually identical to that of vivianite 4 and so are not shown Mori and Ito, 1950;Fejdi et al, 1980;Bartl, 1989; Table 1). Because it is an averaging technique, the EXAFS analysis is unable to resolve these differences in our vivianites, but the bond distance of 2.03-2.05 Å is similar to the average first shell Fe-O distances calculated for the data of Fejdi et al (1980) and Bartl (1989 ; Table 1) and the average second shell distance of 2.02 Å calculated for the data of Mori and Ito (1950). The tetrahedral coordination fit for our vivianites also matches the second shell of these previous studies, suggesting that either our data are not of sufficient quality to fit the additional shell of 2 O around the Fe, or that the Fe is more disordered within the normally octahedral site.…”

Babánekite, Cu3(AsO4)2 ∙ 8H2O, from Jáchymov, Czech Republic - a new member of the vivianite group

“…The refined structure of babánekite shows characteristic features of the vivianite-type minerals and synthetic compounds, characterized by the general formula Me 2+ 3 (XO 4 ) 2 •8H 2 O (Me = Mg, Fe, Co, Ni, Zn; X = P, As) (Mori and Ito 1950;Cesbron et al 1977;Hill 1979;Fejdi et al 1980;Giuseppetti and Tadini 1982;Dormann et al 1982;Takagi et al 1986;Riou et al 1989;Bartl 1989;Wildner et al 1996;Yakubovich et al 2001;Capitelli et al 2007Capitelli et al , 2012Assani et al 2010;Yoshiasa et al 2016;Antao and Dhaliwal 2017). Vivianite-type structures consist of MelO 2 (H 2 O) 4 octahedra and dimers of Me2 2 O 6 (H 2 O) 4 octahedra that are linked via XO 4 tetrahedra (where X = P, As and probably can be also V) and hydrogen bonds to form complex layers parallel to (010).…”