Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 902, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.scitotenv.2023.165820
Keywords
Evaporation; Gypsum; Bassanite; Anhydrite; EPS; Mars
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In laboratory precipitation experiments, it was found that anhydrite can form at 35 degrees Celsius from evaporated seawater through a microbially influenced mineralization process. This finding provides a possible explanation for the origin of certain natural occurrences of anhydrite and reveals a new precipitation pathway with potential industrial applications.
Calcium sulfate minerals are abundant in nature - on Earth and on Mars - and important in several fields of material sciences. With respect to gypsum and bassanite, anhydrite represents the anhydrous crystalline phase in the CaSO4-H2O system. Despite years of research, the formation of anhydrite in the laboratory at low temperature remains challenging and, in the geological record, this mineral is mostly interpreted as a secondary phase that form through metamorphic dehydration of gypsum. Here, we present the results of laboratory precipitation experiments showing that anhydrite can form at 35 degrees C from evaporated seawater through a microbially influenced mineralization process. The experiments were conducted in the presence of extracellular polymeric substances (EPS) produced by bacterial strains isolated from a modern evaporitic environment, the Dohat Faishakh sabkha in Qatar. Without organic molecules, only gypsum formed in parallel control experiments. This finding provides a possible explanation for the origin of several natural occurrences of anhydrite that cannot be satisfactorily explained by existing models and reveals a new precipitation pathway that may have industrial applications.
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