Recovery of uranium from carbonate solutions using strongly basic anion exchanger 4. Column operation and quantitative analysis

A process scheme for effectively recovering uranium from dilute solutions, particularly from alkaline carbonate solutions, is developed. The uranyl qu adrivalent complex anions [UO2(CO3)(3)](4-) are made unstable at pH 6.5-8.5 so that they are partly converted into U2O72- anions in resin phase and mo stly exist in the form of [UO2(CO3)(2)](2-) in solution, except for a certa in amount of H-n[UO2(CO3)(3)]((n-4)) (n = 0-3). The conversion causes (1) g reater than 2-fold of uranium loading capacity at pH 6.5-7.5 referred to th at obtained from conventional ion-exchange mechanism, and (2) the minimum r atio between the moles of CO2 released from the reaction of hydrochloric ac id with uranium loading resin and that of uranium loaded by the same amount of resin. The optimum pH range is sensitive to the composition of the solu tion, such as Cl- and HCO3- concentrations, although the SO42-, CO32-, HCO3 - and Cl- cannot make a great deal of difference in uranium loading capacit y because the selectivity sequence of some anions for the resin used is [UO 2(CO3)(3)](4-) much greater than NO3- much greater than SO42- approximate t o CO32- > HCO3- > Cl-. The major amount of uranium which cannot be eluted w ith 1 mol/l NaCl can be easily removed with 1 mol/l NaNO3, suggesting the s electivity of anions for the resin used should be considered as the main fa ctor during distinguishing uranium in resin phase. (C) 1999 Elsevier Scienc e B.V. All rights reserved.