THE SUBSTITUTION OF FE2+ IONS BY NI2+ IONS IN GREEN RUST ONE COMPOUNDS

The oxidation of Fe(OH)(2) in the presence of Cl- or CO32- ions leads, in the first stage of the reaction, to chloride-containing green rust one (GR1), 3Fe(OH)(2) . Fe(OH)(2)Cl . nH(2)O, or carbonate-containing GR1, 4Fe(OH)(2) Fe-2(OH)(4)CO3 . nH(2)O, respectively. These GR1 compounds give the ferric oxyhydroxides by further oxidation. If a hydroxide NixFe1-x(OH)(2) is initially precipitated, the reaction leads to a nickelous-ferric compound isomorphous to the ferrous-ferric GR1, but stable with respect to the oxidizing action of air. Similarly, the oxidation of a nickelous-ferrous hydroxide, in the presence of excess OH- ions, leads to a nickelous-ferric GR1, a layered hydroxide with anionic interlayers made of OH- ions and water molecules. The Mossbauer spectra of these nickelous-ferric GR1 display two ferric doublers, D-0 with IS = 0.34 mm/s and eS = 0.45 mm/s and D-1 with IS = 0.36 mm/s and eS = 0.86 mm/s. The existence of a ferrous-ferric GR1 incorporating OH- ions, a compound never observed so far, is strongly suspected.