Extraction of Uranium From Alkali Residue With Supercritical Carbon Dioxide Fluid

Alkali residue was dissolved by the ammonium hydrogen fluoride method, in which the uranium content is determined to be (16.7±0.3)%(n=6) by inductively coupled plasma optical emission spectrometry(ICP-AES). By means of XRD and SEM-EDS, the main uranium occurrence form of alkali residue was determined. It includes UO₃, fluoride(CaF₂, NaF, MgF₂, UF₄, etc), SiO₂-P₂O₅-UO₃, Cr₂O₃-Fe₂O₃ and other solid melts, and the forms of UO₃ being wrapped by the above solid melts. Using TBP-HNO₃ as complexing agent, the effects of various parameters were investigated on the lab-scale supercritical CO₂ fluid extraction facility. The extraction parameters are optimized: the particle size is 0.250-0.420 mm, saturated Al(NO₃)₃ solution of w=25% alkali residue is used as salting agent, the mole ratio of TBP-HNO₃/U is ≥50, the extraction temperature is 50 ℃ and the pressure is 20 MPa. Under these conditions, the extraction rate of uranium in the alkali residue reaches as high as 98.5% within 2 h. This work provides a new method for the recovery of uranium in alkali residue.