Formation and crystallographical structure of hydroxysulphate and hydroxycarbonate green rusts synthetised by coprecipitation

Hydroxycarbonate {GR(CO32−)} and hydroxysulphate {GR(SO42−)} green rusts are synthesised by coprecipitation. Mössbauer spectroscopy shows that for both compounds the FeII: FeIII ratio is 2:1. A Rietveld refinement of a high resolution X-ray powder diffractogram of GR(CO32−) that uses a disordered pyroaurite like structure is performed. It leads to the cell parameters a=3.17588(2) Å and c=22.7123(3) Å and to a refined chemical formula [FeII4FeIII2(OH)12]2+[CO3, 3H2O]2− with Z=1/2. By comparing the structural properties of GR(SO42−) and GR(CO32−), the preferential formation of GR(SO42−) in aqueous solution is explained.