Mineralogical and process controls on the pxidative acid-leaching of radioactive phases in Elliot Lake, Ontario, uranium ores: I - uraninite, uranothorite and monazite

CIM Bulletin, Vol. 82, No. 925, 1989

Roy O. If ill, Department of Metallurgical Engineering, Alan H. Clark, Department of Geological Sciences, and W. Charles Cooper, Department of Metallurgical Engineering, Queen's University, Kingston, Ontario

A detailed study of the compositional relationships of the U-and Th-bearing minerals in Elliot Lake uranium ores has been conducted, particularly with regard to uranothorite, which clearly plays a critical role in hydrometallurgical processing. Application of the rotating disc progressive-leaching technique to individual mineral grains and intergrowths of known compositions has defined for the first time the solubilization behaviour of the minerals in question. In descending order of teachability, regardless of leaching conditions, the phases are: uranothorite, uraninite, and monazite. Inclusions of secondary uranothorite enhance the dissolution kinetics of uraninite, which exhibits a complex dissolution mode. U-rich uranothorite dissolves more readily than Th-rich. Monazite is soluble in H2SO4 and HCl solutions only at temperatures exceeding 85 °C. Consequently, it is deduced that the 15% to 20% of thorium not leached from the ore is lost both as monazite and as uranothorite inclusions locked in monazite which persists to the tailings.

Keywords: Elliot Lake uranium ores, Monazite, Oxidative leaching, Radioactive phases, Thorium extraction, Uraninite, Extraction, Uranium mineralogy, Uranothorite, Leaching, Mineral processing