The substitution of Fe2+ ions by Ni2+ ions in green rust one compounds

Abstract

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)2Cl·nH2O, or carbonate-containing GR1, 4Fe(OH)2·Fe2(OH)4CO3·nH2O, 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 nickelousferric GR1 display two ferric doublets, D0 withIS=0.34 mm/s andQS=0.45 mm/s and D1 withIS=0.36 mm/s andQS=0.86 mm/s. The existence of a ferrous-ferric GR1 incorporating OH− ions, a compound never observed so far, is strongly suspected.