Use of Phosphate Compounds to Extract Thorium-230 and Radium-226 from Uranium Ore and Tailings

摘要

Orthophosphate and condensed phosphates (pyrophosphate, tripolyphosphate and hexametaphosphate) were tested to determine whether they were capable of forming soluble complexes with thorium-230 and radium-226 in a sulfuric acid or neutral medium. The tests were carried out to determine whether these compounds would be useful for removing thorium and radium from solid uranium mill tailings prior to disposal. Results showed that orthophosphate, pyrophosphate, and tripolyphosphate at concentrations up to 0.1 molar in a sulfuric acid medium showed no tendency to complex thorium or radium. Hexametaphosphate at a concentration of 0.1 molar in a sulfuric acid medium did solubilize approximately 40 percent of the radium present in the ore. Tests also showed that the hexametaphosphate interferes with uranium extraction from the ore and solubilizes thorium-230 and radium-226 from neutral residues left after acid leaching. This approach was tested further, and 70-80% removal of thorium and radium from the slimes (-200 mesh) fraction of the tailings was achieved. A final series of tests included an acid kill stage, followed by wet screening to separate the sands from the slimes. This produced a sands fraction that was relatively free of radium and thorium. The slimes from the acid kill leach were enriched in radium-226.