Supporting material
Scientific Basis for Efficient Extraction of Uranium from Seawater, I: Understanding the Chemical
Speciation of Uranium under Seawater Conditions
Francesco Endrizzi, # Christina J. Leggett, ± Linfeng Rao *
Chemical Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road,
Berkeley, California 94720, U.S.A.
KEYWORDS. Uranium, chemical speciation, seawater, extraction.
Re-calculation of the solubility products of Liebigite, Swarzite, Bayleyite and Andersonite from the original data by Alwan and Williams
In order to calculate a better estimate for the solubility products of Liebigite, Swarzite, Bayleyite and Andersonite from the original data by Alwan and Williams, 1 we used the following procedure:
1) The original Arrhenius’s plot in the paper by Alwan1 was re-plotted by using a dedicated computer software ‡ (Error! Reference source not found. in the present
(‡) https://www.quintessa.org/software/downloads-and-demos/graph-grabber-1.5.5.html 0 review) and the values of log K s at 298 K were extrapolated by linear regression as in the original paper. Error! Reference source not found. summarizes the parameters we calculated and used to fit the data. 2) The values of the solubility products calculated as described in (1) are reasonably a better estimate of the original results by Alwan 1 with respect to corresponding values further recalculated by Gorman-Lewis et al. 2 in their review paper. Nonetheless, further corrections were made in the present review, to account for the formation of 2+ 2+ 2+ 2- the ternary aqueous complexes of (Ca /Mg )-UO 2 -CO 3 . In fact, the original speciation model used by Alwan and Williams to determine the solubility products of the different mineral species from the solubility data did not include the formation of such ternary species, since their existence in solution was not known at that time. Generally, the solubility product of a species is expressed as a product of the
activities of the dissociated ions in solution and the activity of water, aw (aw = 1 when
I = 0 M, aw < 1 in electrolyte solutions) as in the equations (1a), (1b)
2+ 2+ 2+ 2- Ca jMg m(UO 2)(CO 3)3(H 2O) x = jCa + mMg + UO 2 + 3CO 3 + xH2O(l) (1a)
0 2+ j 2+ m 2+ 2- 3 x K sp = {Ca } {Mg } { UO 2 }{CO 3 } ⋅ (aw) (1b)
Indeed, the solubilities of Liebigite, Swarzite, Bayleyite and Andersonite are greatly 2+ 2- enhanced by the formation of both the binary aqueous complexes UO 2 –CO 3 and more 2+ 2+ 2+ 2- importantly by the ternary (Ca /Mg )-UO 2 -CO 3 species, as shown by Endrizzi and Rao. 3 Therefore, the contributions of all of these aqueous complex species must be 0 carefully considered when calculating K sp . In the present review, we used the simulation and speciation software HySS 2009 4 to calculate the solubility of the different aforementioned U(VI) minerals according to the speciation model originally used by Alwan. 1 The species included in the calculation, and the related values of the stability constants are summarized in Error! Reference source not found. . The molar solubilities of the different minerals calculated by means of this procedure are: 1.35 ×10 -3 M, 1.42 ×10 -3 M, 1.82 ×10 -3 M for Liebigite, Swartzite and Bayleyite, respectively ( I = 0 M, T = 298 K). The solubility of Andersonite was not determined, because according to our calculation the formation of Liebigite is predicted to be favored over Andersonite at lower calcium concentrations. 3) We then recalculated the solubility products of the U(VI) minerals using their molar solubilities and a speciation model accounting for all the relevant aqueous species known to date ( Error! Reference source not found. ). The solubility products of the different minerals at infinite dilution calculated according to this procedure are summarized in Error! Reference source not found. and represent the recommended values in the present review (Error! Reference source not found. ). 4) In order to evaluate the molar solubilities of the different minerals in seawater conditions ( T = 298 K, I = 0.5 M NaCl), the solubility products at infinite dilution determined as in (3), should be corrected to account for the effect of the ionic strength and the specific-ion
interactions in this medium. In the present review, we calculated the different log Ks in 0.5 M NaCl by means of the empirical equations by means of the Specific-ion Interaction Theory (S.I.T.).5 Values are summarized in Error! Reference source not found. .
Table S 1 Calculated parameters used to fit the data points in Figure 1.