Colloid-borne uranium and other heavy metals in the water of a mine drainage gallery

The water of a mine drainage gallery was investigated for its contents of c olloid-borne heavy metals with emphasis on uranium. About 1 mg/L of colloid particles of 100 to 300nm were found. They consist of a matrix of Fe and A l oxyhydroxides and are formed when anoxic slightly acidic shaft waters mix with oxic near-neutral gallery water. The colloid particles bear toxic tra ce elements such as As, Pb, and Cu. Almost 100% of the As and Pb and about 70% of the Cu contained in the water are colloid-borne. Carbonate complexes prevent the uranyl from being adsorbed on the colloids in the unaltered ga llery water. Acidification destroys these complexes: up to 50% of the urani um is attached to the colloids in the slightly acidic pH region. Further ac idification converts the uranyl again to a 'non-colloidal' form.