A review of CANMET's acid chloride leaching of uranium ores

Conventional sulphuric acid leach processing of uranium ore is technically and economically viable but presents some environmental concerns because almost all of the radium and the sulphides, especially pyrite (an acid generating mineral), present in the ore report to the tailing disposal sites. In order to obtain leach tailings with a radium (226) content of 20-25 pCi/g solids and essentially free of pyrite, an alternative HCl leach process has been developed. Hydrochloric acid leaching of low-grade pyritic uranium ore (e.g. Elliot Lake U-ore) followed by flotation for pyrite removal from the final leach residue yielded tailings essentially free of pyrite and radionuclides, the radium level in the tailings being in the range of 25-30 pCi g-1 solids. Acid chloride leaching of Midwest Lake uranium ore, under various conditions (e.g., HCl, HCl-CaCl2-O2 pressure, HCL-FeCl3) provided high extraction of U, Ni, As and Ra and tailings with radium levels above 177 pCi g-1 solids. However HCl leaching of the radium preleached Midwest Lake uranium ore provided the best extraction of U(>99%), Ni(88%), As(90%) and Ra (98%) and the tailings with only 108 pCi g-1 solids radium. Of course, out of these 108 pCi/g solids, at least 66 pCi/g solids were tied up with the residual uranium (0.02%) in the tailings, and the remaining radium (42 pCi/g solids) present as sparingly soluble radium salt/salts (e.g., RaS04). The acid chloride leaching process for uranium ore has definite technological and environmental merits but presently compares unfavourably both in capital and operating costs with the conventional sulphuric acid leach process. However, the economics of the HCl leach process could become viable when the costs of removing the radium (226) and the sulphides (i.e., the acid generating minerals) from sulphuric acid leach tailings are taken into consideration