Formation and stabilization of elemental sulfur through organomineralization

Elemental sulfur (S(0)) is an important intermediate in the biogeochemical cycle of sulfur that is formed by chemical or biological oxidation of more reduced sulfur species. Given the restricted geochemical conditions under which S(0) should persist, the mechanisms whereby S(0) can be stabilized in the environment are not fully understood. Here we identify a process called S(0) organomineralization, by which S(0) minerals are produced and stabilized following the oxidation of hydrogen sulfide in the presence of numerous types of dissolved organics, including simple sugars and amino acids. The S(0) particles formed through this mechanism are closely associated with organics, which often form an envelope around the mineral. The organic envelopes are formed by self-assembly of the dissolved organic molecules in the presence of hydrogen sulfide and oxygen, and play in a role in the stabilization of S(0). Organic compound sulfurization probably plays an important role in the self-assembly mechanism, by causing the polymerization of relatively small dissolved organic molecules into solid, macromolecular, polymeric organics. The organomineralized S(0) particles present unique and complex morphologies, which are controlled by the type of dissolved organic compound present in the experimental media. Depending on the organics present, organomineralized S(0) can exist as different combinations of several crystal structures, including the non-thermodynamically stable beta- and gamma-S-8 allotropes, which are most likely stabilized by their close association with the organic phase. We propose that complex particle morphology combined with the presence of metastable S(0) allotropes could be used as a signature of S(0) organomineralization in natural settings. S(0) organomineralization was obtained in the laboratory under a wide range of experimental conditions that span across geochemical conditions which can be encountered in many sulfidic environments. It is possible that the reaction between reduced sulfur species and organics may significantly affect the production and preservation of S(0) in numerous natural systems. (C) 2018 Elsevier Ltd. All rights reserved.