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, Swede n. Goethite and lepidocrocite occur as massive precipitates at the wat er table, cementing together mineral grains and smaller rock fragments . Analysis of the precipitates by SEM indicates that they are primaril y microcrystalline, but other crystal habits are also observed. Althou gh jarosite is not thermodynamically stable at the pH-Eh conditions me asured 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 subs titution of Al-for-Fe in goethite, the rate of Fe2+ oxidation, and the presence of carbonate species are probably the major factors influenc ing the formation of goethite relative to lepidocrocite.