Supporting material

Scientific Basis for Efficient Extraction of 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 , Swarzite, 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 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.

Equation used: log = + ⋅ (1000 /), where T is in K. mineral: a ± σ b ± σ Adj. R2 fit

Andersonite – 11.0 ± 2.1 – 5.75 ± 0.59 0.959 Bayleyite – 22.16 ± 1.01 – 2.08 ± 0.29 0.928 Liebigite – 25.01 ± 0.67 – 1.36 ± 0.19 0.945 Swar tzite – 24.7 ± 1.4 – 1.59 ± 0.38 0.801 The points in the diagram have been digitized from the original Arrhenius plot by Alwan et al. 1 0 From these linear regressions, more reliable log K s at 298 K were estimated (see Table 2 in the 0 article). The new estimates of the solubility products were then used to recalculate the fG of the minerals.

Table S 2 List of the most relevant reaction equilibria and the related stability constants or solubility products considered in the speciation model used to calculate the distribution of the U(VI) species (Table 2 in the article) as a function of pH and T = 25.0 ºC. Third column: values of the constants at infinite dilution; fourth column: corresponding values in 0.5 mol dm -3 NaCl (resembling the ionic medium in seawater environment).

log β ± 3σ, Aqueous species log β0 ± 3σ 0.5 M NaCl Used by Alwan and Used in the current Williams 1 review U(VI) hydrolysis 2+ + 6 7 UO 2 + H 2O = (UO 2)(OH) + H – 5.87 – 5.25 ± 0.08 – 5.6 ± 0.3 (p.w.) 2+ + 7 UO 2 + 2H 2O = (UO 2)(OH) 2 (aq) + 2H not considered – 12.15 ± 0.07 – 12.5 ± 0.1 (p.w.) 2+ – + 7 UO 2 + 3H 2O = (UO 2)(OH) 3 + 3H not considered – 20.25 ± 0.42 – 20.3 ± 0.4 (p.w.) 2+ 2– + 7 UO 2 + 4H2O = (UO 2)(OH) 4 + 3H not considered – 32.40 ± 0.68 – 31.8 ± 0.8 (p.w.) 2+ 2+ + 6 7 2UO 2 + 2H 2O = (UO 2)2(OH) 2 + 2H – 5.54 – 5.62 ± 0.04 – 6.1 ± 0.1 (p.w.) 2+ 2+ + 7 7 3UO 2 + 4H 2O = (UO 2)3(OH) 4 + 4H – 11.9 ± 0.3 (a) – 11.9 ± 0.3 – 12.7 ± 0.4 (p.w.) 2+ + + 6 7 3UO 2 + 5H 2O = (UO 2)3(OH) 5 + 5H – 15.98 – 15.55 ± 0.12 – 16.4 ± 0.3 (p.w.) Uranyl-carbonato and ternary complexes 2+ 2- 9 7 3 UO 2 + CO 3 = UO 2(CO 3) (aq) 10.1 9.94 ± 0.03 8.61 ± 0.04 2+ 2- 2- 9 7 3 UO 2 + 2CO 3 = UO 2(CO 3)2 17.1 16.61 ± 0.09 15.26 ± 0.10 2+ 2- 4- 9 7 3 UO 2 + 3CO 3 = UO 2(CO 3)3 21.4 21.84 ± 0.03 21.85 ± 0.07 2+ 2+ 2- 2- 3 3 Ca + UO 2 + 3CO 3 = CaUO 2(CO 3)3 not considered (b) 27.00 ± 0.12 24.28 ± 0.21 2+ 2+ 2- 3 3 2Ca + UO 2 + 3CO 3 = Ca 2UO 2(CO 3)3 (aq) not considered (b) 30.84 ± 0.12 26.81 ± 0.21 2+ 2+ 2- 2- 3 3 Mg + UO 2 + 3CO 3 = MgUO 2(CO 3)3 not considered (b) 26.25 ± 0.12 23.62 ± 0.21 Additional relevant aqueous species included in the model + – 10 H + OH = H 2O 13.99 ± 0.01 13.99 ± 0.01 13.70 ± 0.01 + 2– – 7 H + CO 3 = HCO 3 9.9 ± 0.1 (c) 10.33 ± 0.02 9.2 ± 0.3 + 2– 7 2H + CO 3 = H 2CO 3 (aq) 16.0 ± 0.1 (c) 16.7 ± 0.1 (15) 2+ 2– Ca + CO 3 = CaCO 3 (aq) 3.2 ± 0.1 (c) 3.2 ± 0.1 (1.8) 2+ 2– Mg + CO 3 = MgCO 3 (aq) (2.98) (1.6) 0 Solubility products log K s ± 3σ log Ks ± 3σ, 0.5 M NaCl Determined by Alwan Evaluated and Calculated in this review by

and Williams 1 recommended in the means of the S.I.T. current review approach 5,7 2+ Liebigite: Ca 2(UO 2)(CO 3)3·10H 2O(s) = 2Ca + (– 29.6 ± 2.7) (– 33.9 ± 3.0) (– 29.7 ± 3.0) 2+ 2- UO 2 + 3CO 3 + 10H 2O 2+ Swartzite: CaMg(UO 2)(CO 3)3·12H 2O(s) = Ca + (– 30.1 ± 5.7) (– 33.4 ± 6.0) (– 29.2 ± 6.0) 2+ 2+ 2- Mg + UO 2 + 3CO 3 + 12H 2O 2+ Bayleyite: Mg 2(UO 2)(CO 3)3·18H 2O(s) = 2Mg + (– 29.1 ± 4.2) (– 31.7 ± 4.5) (– 27.5 ± 4.5) 2+ 2- UO 2 + 3CO 3 + 18H 2O + Andersonite: Na 2Ca(UO 2)(CO 3)3·6H 2O(s) = 2Na (– 37.5 ± 6.3) -- -- 2+ 2+ 2- + Ca + UO 2 + 3CO 3 + 6H 2O Additional relevant solid species included in the model 2+ 2- Calcite: CaCO 3(cr) = Ca + CO 3 -8.48 (-5.7)

2+ 2- Magnesite: MgCO 3(cr) = Mg + CO 3 -8.91 (-3.3)

(p.w.) : calculated in this review by means of the S.I.T. approach. 5,7 (a) Value originally taken from ref. 6 The authors of this review could not retrieve the original value of this hydrolysis constant, we therefore used a value updated more recently. (b) The formation of this aqueous species was not ascertained at the time of the publication. (c) Value originally taken by Alwan and Williams from ref. 6, although not reported in their original publication. Note: values reported in brackets are estimation or values suggested in this review. Further experimental work is possibly needed to obtain more reliable values.

Additional information

0 Table S 3 fG and related standard formation enthalpies used in this review.

0 0 – fG ± σ, kJ/mol – fH ± σ, kJ/mol Ref. + 11 Na (aq) 261.9 ± n.d. 239.7 ± n.d. 261.953 ± 0.096 240.34 ± 0.06 7 2+ 11 Ca (aq) 553.5 ± n.d. 542.7 ± n.d. 552.81 ± 1.05 543.00 ± 1.00 7 Mg 2+ (aq) 454.8 ± n.d. 466.9 ± n.d. 11 455.38 ± 1.34 467.0 ± 0.6 7 2+ 11 UO 2 (aq) 994.1 ± n.d. 1036.0 ± n.d. 952.55 ± 1.75 1019.00 ± 1.50 7 2- 11 CO 3 (aq) 528.0 ± n.d. 677.4 ± n.d. 527.90 ± 0.39 675.23 ± 0.25 7 11 H2O (l) 237.2 ± n.d. 286.8 ± n.d. 237.14 ± 0.04 285.83 ± 0.04 7

Table S 4 Specific-ion interaction parameters used to apply the S.I.T. corrections.

Interacting ions Interaction parameter, Ref. ε ± 3σ (mol -1kg -1) 2+ - 7 UO 2 , Cl 0.21 ± 0.02 + - 12 UO 2(OH) , Cl 0.46 ± 0.03 + - 12 (UO 2)3(OH) 5 , Cl 0.81 ± 0.17 2+ - 12 (UO 2)2(OH) 2 , Cl 0.69 ± 0.07 2+ - 12 (UO 2)3(OH) 4 , Cl 0.50 ± 0.18 + - 12 Na , UO 2(OH) 3 –0.09 ± 0.05 + 2- Na , UO 2(OH) 4 –0.15 ± 0.05 p.w. Na +, OH - 0.04 ± 0.01 5 H+, Cl - 0.21 ± 0.01 7 Na+, Cl - 0.03 ± 0.01 5 Ca 2+ , Cl - 0.14 ± 0.01 7 Mg 2+ , Cl - 0.19 ± 0.02 7 + 2- 7 Na , CO 3 –0.08 ± 0.03 + 2- 7 Na , UO 2(CO 3)2 –0.02 ± 0.09 + 4- 7 Na , UO 2(CO 3)3 –0.01 ± 0.11 + 2- 13 Na , CaUO 2(CO 3)3 –0.02 ± 0.09 (a) + 2- 13 Na , MgUO 2(CO 3)3 –0.02 ± 0.09 (a) p.w.: Estimated in the p.w. 13 + 2- (a) assumed by the Lee et al. to be equal to ε(Na , UO 2(CO 3)2 ), since the two anions are bearing the same charge and a similar structure.

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