Green Rust: a review on its crystallographic structure, redox flexibility and role in reducing soil pollutants.

Abstract

Green Rusts (GRs) are mixed hydroxysalts of Fe(II) and Fe(III) that belong to the Layered Double Hydroxide (LDH) group. Their crystallographic structure can be summarised as a stacking sequence of Fe(OH)2 layers with some Fe(III) cations substituting that provides a positive charge, and interlayers composed of anions and water molecules. Different types of GRs, depending on the anions in the interlayer, have been described and synthetised, and a mineral counterpart, fougerite, is found in hydromorphic soils. One of the most important features of GRs is their redox flexibility. On one hand, it implies that are very unstable compounds that easily oxidise, so special procedures must be followed to avoid it when working with natural or synthetic samples. On the other hand, its redox flexibility provides them an important role in reducing pollutants in hydromorphic soils, particularly the chlorinated ethenes