Combined use of CaCl2 roasting and nitric acid leaching for the removal of uranium and radioactivity from uranium tailings

Enhancement of Uranium Recycling from Tailings Caused by the Microwave Irradiation-Induced Composite Oxidation of the Fe–Mn Binary System

“…The average concentration of U in the crust of Earth is 2–4 ppm (i.e., parts per million), ranking the 51st element in order of abundance. The utilization of uranium has been closely linked to human society since the industrial age, such as to fuel nuclear power plants in the civilian sector and to make high-density penetrators in the military counterpart. − U is normally extracted from the U-bearing ores by grinding and leaching (e.g., biotic and abiotic) techniques in combination after the mining activities. − U tailings are produced after U-related minerals and separated from raw ore sands via leaching. − The U tailings are commonly stored or stacked in huge impoundments, which retains up to 85% of the radioactivity of original U ores emitting to surroundings due to the residual existences of some contained radioactive nuclides such as uranium-238 ( 238 U), uranium-235 ( 235 U), thorium-230 ( 230 Th), and radium-226 ( 226 Ra). − In China, most of the U tailings are stored in the open air at present. Although the environmental hazards posed by the U tailings have attracted more attention, the old reservoir way is still maintained in some stockpiling regions due to the blurred responsibilities and the shortage of funds. − Therefore, the radionuclides and some coexisting heavy metals (HMs) contained in the tailings can be potentially migrated into groundwater from the surface by heavy rains and carried great distances by strong winds, finally entering the biological terminals through the food chain and threatening the ecosystem operations. − The residents can be exposed to uranium and its radioactive daughters by ingesting contaminated food and water and even by inhaling sand dust in the air.…”