PRECIPITATION OF FE OXYHYDROXIDES AND JAROSITE FROM ACIDIC GROUNDWATER

The ferric minerals goethite, lepidocrocite, and jarosite precipitate from groundwater contaminated by mine waste leachate in Dalarna, Sweden. Goethite and lepidocrocite occur as massive precipitates at the water table, cementing together mineral grains and smaller rock fragments. Analysis of the precipitates by SEM indicates that they are primarily microcrystalline, but other crystal habits are also observed. Although jarosite is not thermodynamically stable at the pH-Eh conditions measured in the groundwater, it is postulated that jarosite can form at the capillary fringe where very acidic and high sulfate conditions can develop in micropores. In terms of the ferric oxyhydroxides, the substitution of Al-for-Fe in goethite, the rate of Fe2+ oxidation, and the presence of carbonate species are probably the major factors influencing the formation of goethite relative to lepidocrocite.