Preparation and Thermodynamic Equilibria of Green

Authors: JMR GÉnin G BourriÉ PH Refait F Trolard M Abdelmoula B Humbert A Herbillon

Publish Date: 1999

Volume: , Issue: , Pages: 25-36

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Abstract

Many natural minerals are made by stacking positively and negatively charged layers Among them the pyroauritesjögrenite group Allmann et Lohse 1966 Allmann 1968 corresponds to the stacking of brucitelike layers carrying a positive charge and layers constituted of anions and water molecules In this paper we deal with the FeIIFeIII compounds generally known by the generic name of Green Rusts GRs since the original classification by Bernai et al 1959 and the major anions which are found in natural waters ie Cl − SO42− and CO32− are concerned From Xray diffraction XRD two types of GRs are distinguished Green Rust one GR1 incorporating “planar anions” eg Cl− and CO32su− and Green Rust two GR2 incorporating “three dimensional anions” The preparation of these compounds in the laboratory by controlled oxidation of a ferrous hydroxide precipitate in anion containing aqueous solutions allows us by monitoring the E h and pH versus time curves to elaborate them at stoichiometry with the appropriate Fe++ / OH− concentration ratio The Xray diffraction characterization of these “Green Rusts” and the corresponding Mössbauer spectra allow us to determine structural information and chemical formulae

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