SORPTION OF MANGANESE, URANIUM, AND RADIUM BY HIGHLY WEATHERED SOILS

Large concentrations of Mn, U-238, and Ra-226 are present in U mine wa ste waters in comparison with those in surrounding natural waters. Exc ess mine waste water is being disposed by irrigation of bushland near Ranger Uranium Mine, Northern Territory, Australia. We report the sorp tion properties of highly weathered and sandy soils (Utric Acruustox, Grossameric Kandiustalf, and Typic Fragiumbrept), near the mine for Mn , U, and Ra-226 as determined by batch sorption experiments, and compe titive sorption between U and Mn. Manganese sorption was small in comp arison with loads expected to be applied to the soils, and Mn was expe cted to be mobile within the soils. In contrast with Mn, U sorption by the soils was very much greater than the amount that may be applied. Simultaneous additions of U and Mn reduced sorption of both, but the e ffect of U on Mn sorption was far greater than that of Mn on U. Uraniu m also caused the displacement of Mn from the soil in the absence of a dded Mn. The U additions favored the mobility of Mn. Radium-226 at tra ce levels was strongly sorbed by the soil and <1% of the sorbed Ra-226 was displaced during the desorption step. Uranium and Ra-226 applied as mine waste water will be retained in surface soil, but Mn was expec ted to be relatively mobile, particularly in the sandiest soils and wh en applied in waters that also contain U.