Hydrothermal synthesis and Mössbauer studies of ferrous phosphates of the homologous series Fe32+(PO4)2(H2O)n

Products of abiotic U(VI) reduction by biogenic magnetite and vivianite

“…The spectra do not show the typical asymmetry of vivianite spectra (Forsyth et al, 1970;Mattievich and Danon, 1977; McCammon and Burns, 1980 (Mattievich and Danon, 1977). The large quadrupole splitting of >3 mm/s of one of the doublets, however, is inferred to be a strong indication of vivianite (Table SC-3).…”

“…The incomplete splitting of the doublet at 5 K suggests nano-particulate vivianite, but electron microscopy indicated vivianite particles in the sub-micron to micron range. The presence of trace phosphoferrite could be due to the transformation of vivianite to phosphoferrite upon drying (Mattievich and Danon, 1977).…”

Mössbauer spectroscopy of iron phosphate Fe3(PO4)2(H2O)npigments

“…The Mössbauer parameters at room temperature, from and Fe 2+ ions are in an octahedral or distorted octahedral coordination, also not having an internal magnetic field, vivianite is considered paramagnetic. In opinion of Mattievich [3] a precise structure determination revels an extraordinarily complex atomic arrangement and the spectra differ notably from those of all the other ferrous phosphates an indicate the presence of Fe 2+ occupying three non equivalent sites in the crystal, the environment of two sites are distorted octahedral and the one is a figure 4.…”

“…Some changes in vivianite are due to the partial oxidation of Fe 2+ to Fe 3+ by being exposed to air and light but with the thermal treatment total oxidation occurs. Previous studies report that the laboratory synthesis of vivianite is complicated by the large number of Fe 2+ hydrates phosphates phases: ludlamite (n = 4), phosphoferrite (n = 3), two anhydrous forms, sarcopside and graphtonite; one acidic ferrous trihydrate and two basic ferrous species [1,3] with the tendency of solutions and powdered products to be promptly oxidize in air [2][3][4][5][6]. According to Mathevich, it is relatively easy to prepare vivianite by various methods, particularly by the Evans [8] method, in which preparation usually avoids any contact with air.…”

“…The blue coloration of partially oxidized vivianite is attributed to the Fe 2+ Fe 3+ electron transition [1][2][3]. The vivianite blue pigment has been used by dipping it in to oil or sealing it with a thin coat of lacquer.…”