Chemical distribution of hazardous natural radionuclides during monazite mineral processing

摘要

It is very important to calculate the radioactivity concentration for low-grade monazite ore (50%) and different other materials produced as results of chemical processing stages to avoid the risk to workers. Chemical processing of low-grade monazite pass through different stages, washing by hydrochloric acid and digested with sulfuric acid and influence of pH on the precipitation of rare earth elements has been studied. The radioactivity concentrations Of U-238(Ra-226) and Th-232 as well as K-40 were calculated in crude low-grade ore and found to be 54,435 +/- 3138, 442,105 +/- 29,200 and 5841 +/- 345 Bq/kg, respectively. These values are greatly higher than the exempt levels 25 Bq/kg. After chemical digestion of the ore, the results demonstrated that un-reacted material contains significant radioactivity reached to approximately 8,13 and 23% for U-238, Th-232 and K-40, respectively. The results show that 60% of Th-232 are located in the digested white slurry with small portions of U-238 and K-40. Most of U-238 radioactivity is extracted in the green phosphoric acid which produced from conversion of P2O5 by H2SO4 into phosphoric acid. The average values of the Ra-eq for monazite ore, un-reacted black precipitate, white precipitate, brown precipitate and crystalline material samples were calculated and found to be 687,095 +/- 44,921, 85,068 +/- 5339, 388,381 +/- 22,088, 313,046 +/- 17,923 and 4531 +/- 338 Bq/kg, respectively. The calculated values of Ra-eq are higher than the average world value (it must be less than 370 Bq/kg). Finally the external hazardous, internal hazardous and I-gamma r must be less than unity. This means that specific radiation protection program must be applied and implemented during monazite processing. (C) 2016 Elsevier Ltd. All rights reserved.