PREPARATION AND E-H-PH DIAGRAMS OF FE(II)-FE(III) GREEN RUST COMPOUNDS - HYPERFINE INTERACTION CHARACTERISTICS AND STOICHIOMETRY OF HYDROXY-CHLORIDE, HYDROXY-SULFATE AND HYDROXY-CARBONATE

Fe(II)-Fe(III) hydroxy-chloride, -sulphate and -carbonate were prepare d by oxidation of a ferrous hydroxide precipitate in anion-containing aqueous solutions. The compounds are characterized by monitoring the r edox potential E-h and the pH of stoichiometric suspension vs time wit h the appropriate concentration ratios. X-ray diffraction allows us to characterize the crystal structure by distinguishing ''green rust one '' (GR1) from ''green rust two'' (GR2). Since green rusts (GRs) are of a pyroaurite-sjogrenite-like structure, i.e., consisting of intercala ted foreign anions and water molecules in the interlayers between the brucite-like layers of Fe(OH)(2), their chemical formulae can be deter mined from the Mossbauer spectra. Three quadrupole doublets are observ ed: D-1 and D-2 correspond to a ferrous state with isomershift IS of a bout 1.27 mm s(-1) and quadrupole splittings QS of about 2.85 and 2.60 mm s(-1), respectively, whereas D-3 corresponds to a ferric state wit h IS and QS of about 0.4 mm s(-1). The hyperfine parameters of these d oublets are similar from one green rust to another but their intensity ratios vary considerably. Finally, E-h and pH equilibrium diagrams of the Fe species in the presence of chloride, sulphate and carbonate an ions contained within the water solution are drawn and the thermodynam ic conditions of existence and degrees of oxidation of green rusts are discussed.