Uranium speciation in two Freital mine tailing samples: EXAFS, micro-XRD, and micro-XRF results

We investigated the uranium speciation in a former WISMUT mine tailing, which was buried for 30 years under mine and construction debris.
Chemical extractions, EXAFS, -XRD, and -XRF reveal two major U pools. The first with a relatively high potential mobility was identified as U(VI) sorbed to layer silicates by inner-sphere complexation; the second pool is represented by the relatively insoluble U(IV) minerals pitchblende and coffinite, and by the U(VI) solids uranyl hydroxide and vanuralite.
Distribution between the two pools seems to be con-trolled by pH. Evidence for reductive precipitation of uraninite was found.