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Corrosion of anthropogenic uranium in natural environments is not well understood, but is important for determining potential health risks and mobility in the environment. A site in the southwestern United States contains depleted uranium that has been weathering for approximately 22 years. Soil-geomorphic, SEM/EDS, XRD, and electron microprobe analyses were conducted to determine the processes controlling the uranium corrosion. Schoepite and metaschoepite are the primary products of corrosion, and occur as silica-cemented, mixed schoepite-metaschoepite/clay/silt aggregates, as schoepite/metaschoepite-only aggregates, or rarely as coatings upon soil grains. Current extraction procedures do not adequately explain the behavior of uranium in alkaline soils when amorphous silica and clay coatings are present. Soil geomorphology and chemistry at this site limit uranium mobility and decreases potential health risks. However, if land-use and/or regional climate changes occur, uranium mobility could increase.

Thousands of hectares of forests are burned annually in wildfires and prescribed burns nationwide. Our objective was to determine the effects of such fires on soil phyllosilicates. At five sites throughout California representing Inceptisols, Andisols, and Mollisols, surface soil samples from similar depths were collected in burned and nearby unburned areas. Fires produced no visible soil alterations except in 1 to 2% of the land area where concentrated fuel such as logs or stumps burned slowly and at higher temperatures, effectively baking the underlying soil. Within the upper 1 to 8 cm at these severely burned areas, kaolin was completely destroyed or substantially depleted and d001 spacings of clay‐sized vermiculite, chlorite, chlorite‐vermiculite, and hydroxy‐interlayered vermiculite collapsed toward 1.0 nm or were decomposed as shown by x‐ray diffraction. Dehydroxylation of severely burned Fe‐bearing phyllosilicates was indicated by Mössbauer spectroscopy. The decomposition of virtually all phyllosilicates in the upper 2 cm of the soil was observed at one site after burning. The effects of severe burning on the soil phyllosilicates remained clearly expressed at least 3 yr after a fire.