Reductive dissolution of natural jarosite in a tidally inundated acid sulfate soil: geochemical implications

Jarositic pedofeatures are a significant mineralogical indicator of the weathering conditions in ASS wetland environments. The geochemical processes in the reductive dissolution of natural jarosite are presented for a tidally inundated acid sulfate soil (ASS) of northeastern Australia. The extent of reductive dissolution of jarosite was determined from mineral micromorphology and by identifying differences in geochemical weathering along a toposequence. With increasing pH and decreasing Eh under tidal inundation, reduction of Fe(III) minerals occurred and jarosite became increasingly unstable. Direct evidence from scanning electron microscopy (SEM) and x;ray diffractometry (XRD) identified mineral structure and composition consistent with jarosite. Natural jarosite from the intertidal zone exhibited features associated with dissolution. Molar ratios of Fe to K indicated increasing depletion of K in natural jarosite downslope. Results provide important insights to the observed and predicted variability and stability of jarosite with tidal inundation.