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Metal Recovery Processes
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2017
The production of sodium diuranate, Na2U2O7, as a uranium concentrate is practiced for processing the carbonate leach liquor. Addition of a slight excess of caustic soda to the leach liquor results in precipitation of Na2U2O7 according to the following reaction: () 2UO2(CO3)34−+2Na++6OH−→Na2U2O7+6CO32−+3H2O
Leaching with Acids
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2019
Over the years specifications for uranium concentrates (yellow cake) have gradually become stricter, and most mills have found it necessary to modify their precipitation procedures. Impurities that have passed through the leaching and extraction steps may require separation during the final processing operations. Of particular significance are Mo, V, and Fe derived from the leaching of the ore, and components such as Na ions introduced subsequent to leaching with the eluting or stripping solutions. A variety of precipitation procedures have been used, including single-stage precipitation with ammonia, magnesium oxide, or sodium hydroxide, two-stage ammonia precipitation with redissolution between stages; two-stage precipitation with magnesium oxide and ammonia; and precipitation with hydrogen peroxide. In precipitation with H2O2, the pH of the solution is adjusted to 3.5 prior to addition of H2O2. This procedure is often more costly than other techniques, but material having U3Og grades of 98% or higher has been produced. The procedure is a good method for the production of yellow cake that contains very little of molybdenum and vanadium. In alkaline-leaching circuits, the uranium is generally precipitated as sodium diuranate by the addition of sodium hydroxide to the clarified pregnant liquors. The sodium content of the product is high but can be reduced if the cake is washed with an ammonium sulfate solution or if the cake is redissolved and a second precipitation is made with ammonia. The yellow cake is usually dried and calcined at 300 to 500°C. The temperature must be controlled because temperatures above 600°C can produce refractory compounds that will not dissolve in the subsequent refinery operations. Yellow cake dried at low temperatures tends to be relatively light and fluffy and requires considerably more packing and shipping space. The multiple-hearth furnace is probably the most common type of drying and calcining unit.
Uranium thermochemical cycle: hydrogen production demonstration
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Aimei Chen, Xiaobei Zheng, Chunxia Liu, Yuxia Liu, Lan Zhang
A commercially available Raman instrument termed as LabRAM HR from HORIBA Jobin Yvon was also used for the analyses of products in this study, with a laser wavelength of 532nm. The Raman spectrum (Figure 5) of the reaction product is collected from 100 to 4000 cm−1, and the small figure at the top-right corner is the partially enlarged view. It can be seen that there is a single observable Raman band at 772 cm−1, which is assigned to the symmetric stretching mode of uranyl ion (Lin et al. 2014), and an envelope band from 3000 to 3700 cm−1 which is assigned to H–O vibration in the water molecule (Walrafen 1964, 1967). No observable bands corresponding to U3O8 and Na2CO3 (1066 cm−1) exists in the spectrum. The denoted peaks for the product are briefly described and compared to Table 5 (based on literature values). The bands are comparable for sodium diuranate, which confirms the XRD results. Water molecule peak around from 3500 to 3800 cm−1 disappeared after the product was annealed in far infrared rapid drying apparatus for 0.5 h.