Soil minerals recover after they are damaged by bushfires

We studied the impact of bushfires on soil minerals and the recovery of minerals under wet conditions. Samples were taken shortly after a bushfire from under and adjacent to burnt logs. Kaolinite, goethite and gibbsite were dehydroxylated by the bushfire. Pure minerals were also investigated to determine how heating affects soil minerals and their recovery by rehydroxylation at 55 and 95 o C. Rehydroxylation of heated gibbsite was extensive during hydrothermal treatment at 95 o C and after 14 days had formed boehmite, bayerite and gibbsite. The process was much slower at lower temperatures. On heating metakaolinite formed from kaolinite and hematite formed from goethite. These minerals showed no change in XRD patterns after hydrothermal treatment but TGA weight loss did increase substantially for metakaolinite. SSA for all three dehydroxylated minerals increased substantially with period of hydrothermal treatment. These results suggest that dehydroxylated minerals and their partly rehydroxylated forms will exist in heated soils and may affect the chemical behaviour of soils