Identification and Formation of Complex Hydrated Sulfate Salts in Acid Sulfate Soils From Australia Using Advanced XRD Techniques.

Many complex hydrated sulfate salts (e.g. sideronatrite, metavoltine, tamarugite, alunogen etc.) have recently been discovered in drought affected wetlands across the Australian Murray-Darling Basin. Some of these salts represent the first recorded occurrences in Australia and little is known of their distribution and impact on the properties of soils and surrounding waters both during extreme dry weather, burning and re-wetting. These Fe/Al oxyhydroxides and oxyhydroxysulfates are important indicators of extreme soil environments (Fitzpatrick and Self 1997), which may seriously impact surrounding wetland ecosystems.

Investigations conducted on a wide range of salt efflorescences from several sites using laboratory XRD sources often result in incomplete phase identification due to extensive peak overlaps. Dehydration by relatively low temperature ex-situ heating experiments has greatly assisted in identification of these salts, however, lengthy data collection times and subsequent re-hydration during data collection has often further confounded the analysis. Consequently, in-situ dehydration experiments were performed on synthetic and naturally occurring salts at the Australian Synchrotron using the powder diffraction beam line.

These experiments have not only provided superior resolution to aid identification but also permit rapid simultaneous data collection during heating experiments to replicate mineral transformations in the environment. This information has enabled the construction of more robust soil-regolith toposequence models, which incorporates both seasonal wetting and drying cycles as well as high temperature burning from fire.

Fitzpatrick, R.W. and Self, P.G. (1997) Iron oxyhydroxides, sulfides and oxyhydroxysulfates as indicators of acid sulphate surface weathering environment. pp. 227–240. In K. Auerswald, Stanjek H. & Bigham J.M. (Eds.) Soils and Environment: Soil Processes from Mineral to Landscape Scale. Advances in GeoEcology 30. Catena Verlag, Reiskirchen, Germany.