Investigation of nitric acid for removal of noxious radionuclides from uranium ore or mill tailings

A conceptual process using nitric acid, rather than the currently used sulfuric acid, to extract 226Ra and 230Th in addition to the uranium from ore is proposed in order to decrease the potential hazard from discharge of mill tailing to the environment. Nitric acid leaching of representative uranium ores and tailings from the principal mining districts of the United States removes up to 98% of the 226Ra and 230Th, yielding a residue containing as low as 10 pCi of radium per gram. Leaching of uranium from ores is consistently greater than 99.5%. The residue after multistage leaching with nitric acid is resistant to further radium leaching with water. Radon emanation from nitric-acid-leached residues generally is low due to the low radium content. Heating to 8000C causes further reduction of radon emanation. Greater than 99% recovery of radium from nitric-acid-leach solutions is obtained by carrying on barium sulfate. Good adsorption of radium is also obtained on barite and Celite. Recovery of thorium and uranium by solvent extraction using tri-n-butyl phosphate (TBP) appears promising. Recycle of nitric acid may be accomplished by solvent extraction combined with evaporation and calcination