METHOD FOR SEPARATING URANIUM AND/OR THORIUM

Abstract

The invention pertains to a method for separating uranium and/or thorium from an aqueous suspension, said method comprising: a) Contacting said suspension with at least a polymer having formula (I), wherein n is an integer which is not 0 and is no more than 50, R1 is H or CH.sub.3, R2 is H or a C1-C20-alkyl, R3 and R4 arc independently H or a C1-C20-alkyl, X, Y arc O or NH, said polymer being soluble in said aqueous suspension, and wherein when R3 and R4 are H, p is an integer which is 1 or more and 10 at the most, and said polymer is a flocculating polymer, and when at least one of R3 and R4 is not H, p is an integer which is 3 or more and 10 at the most, and said polymer is a thermosensitive polymer and has a LCST in said suspension, b) Carrying out at least one of the following steps b1) and b2) b1) If said suspension contains uranium, separating the aggregates resulting from flocculation of said polymer, from said mixture, b2) If said suspension contains thorium, modifying the mixture until the LCST of the polymer in the mixture is reached or exceeded and separating the resulting aggregates from said mixture; and c) Recovering at least one of uranium and/or thorium-free mixture, aggregates bearing uranium and aggregates bearing thorium.

##STR00001##

Claims

1. A method for separating uranium and/or thorium from an aqueous suspension, said method comprising: a) Contacting said suspension with at least a polymer having formula (I) ##STR00003## wherein n is an integer which is not 0 and is no more than 50 R1 is H or CH.sub.3, R2 is H or a C1-C20-alkyl, R3 and R4 are independently H or a C1-C20-alkyl, X is O or NH, Y is O or NH, said polymer being soluble in said aqueous suspension, and wherein when R3 and R4 are H, p is an integer which is 1 or more and 10 at the most, and said polymer is a flocculating polymer, and when at least one of R3 and R4 is not H, p is an integer which is 3 or more and 10 at the most, and said polymer is a thermosensitive polymer and has a LCST in said suspension, b) Carrying out at least one of the following steps b1) and b2) b1) If said suspension contains uranium, separating the aggregates resulting from flocculation of said polymer, from said mixture, b2) If said suspension contains thorium, modifying the mixture until the LCST of the polymer in the mixture is reached or exceeded and separating the resulting aggregates from said mixture; and c) Recovering at least one of uranium and/or thorium-free mixture, aggregates bearing uranium and aggregates bearing thorium.

2. The method for separating uranium and thorium from an aqueous suspension according to claim 1, comprising a) Contacting said suspension with at least two polymers having formula (I), one polymer having formula (I) wherein R3 and R4 are H and p is an integer which is 1 or more and 10 at the most, said polymer being a flocculating polymer, and one polymer having formula (I) wherein at least one of R3 and R4 is not H and p is an integer which is 3 or more and 10 at the most, said polymer being a thermosensitive polymer and having a LCST in said suspension, b 1) Allowing flocculation to occur and separating the aggregates resulting from flocculation of said polymer, from said mixture, b2) Modifying the mixture until the LCST of the polymer in the mixture is reached or exceeded and separating the resulting aggregates from said mixture; and c) Recovering the uranium- and thorium-free mixture and/or aggregates bearing uranium and aggregates bearing thorium.

3. The method according to claim 1, wherein said polymer(s) is(are) selected from the group consisting of polymers of formula (I), wherein R2 is H or a C1-C6-alkyl, and R3 and R4 are independently H or a C1-C20-alkyl.

4. The method according to claim 1, wherein said polymer(s) is(are) selected from the group consisting of polymers of formula (I), wherein R1 is H, R2 is H, R3 and R4 are independently H or CH.sub.2-CH.sub.3, X and Y are NH, respectively, and p is 3.

5. The method according to claim 1, wherein in step b2), the LCST of the polymer (I) in said suspension is reached or exceeded by modifying at least one of temperature, pH and ionic strength of said suspension.

6. The method according to claim 1, further comprising separating uranium from aggregates of step b1) and/or separating thorium from aggregates of step b2).

Description

DESCRIPTION AND EXAMPLES

[0045] Methods That May Be Used to Measure Parameters are Below Described.

[0046] Metal analysis: The concentrations of metals were determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) with a SPECTRO ARCOS ICP spectrometer. The spectrometer was calibrated with 0; 0.5; 1; 5; 10 and 15 mg.L.sup.−1 standard solutions (prepared by dilution of 1000 commercial standards of Gd, Th and U) and all samples were diluted to be within this reference range.

[0047] pH-metric titration of hP(CPAAm6C): hP(CPAAm6C) (500 mg) was dissolved in water (50 mL). Titration of the resulting solution was achieved using a 0.1 N NaOH solution. pH values were plotted as a function of the volume of NaOH and pK.sub.a values were determined at the half equivalence point for each titration.

[0048] Cloud point (CP) measurements: Thermosensitivity of the polymers was estimated by a change in the transmittance through the polymer solution with temperature. The measurement of the transmittance was carried out on different concentrations of polymer aqueous solutions with a Perkin Elmer Lambda 35 UV-Visible spectrometer equipped with a Peltier temperature programmer PTP-1+1. A wavelength of 500 nm was selected. The temperature ramp was 0.1° C. per minute between 15° C. and 50° C. The thermosensitivity was characterized by a sudden slope change in the transmittance curve. The CP values of the copolymers thus corresponded to the minimum of the derivative curves.

Example 1

Synthesis of hydrolyzed poly(diethyl-6-(acrylamido)hexylcarbamoylmethylphosphonate [hP(CPAAm6C)]

[0049] The reaction is carried out starting from poly(diethyl-6-(acrylamido)hexylcarbamoyl-methylphosphonate) P(CPAAm6C) which was prepared as described in D. Gomes Rodrigues et al., Polym. Chem., 2015, 6, 5264-5272.

[0050] It was achieved in two steps.

[0051] First, the formation of the silyl derivative was carried out with addition of bromotrimethylsilane (TMSBr) to poly(diethyl-6-(acrylamido)hexylcarbamoyl-methylphosphonate) P(CPAAm6C): TMSBr (5.47 mL, 37 mmol) was added to a solution of P(CPAAm6C) (3 g, 8.61 mmol, 34600 g.mol.sup.−1, ÐD=3.7) in anhydrous dichloromethane (40 mL). After stirring for 3 hours at room temperature, the mixture was concentrated under reduced pressure. The second step consisted in hydrolyzing the silyl derivative by the addition of a large excess of methanol: methanol (100 mL) was added and the mixture was stirred for 4 hours at room temperature. The solvent was evaporated and the product was dried to a constant weight under vacuum.

[0052] Resulting hP(CPAAm6C) containing phosphonic diacid moieties, was characterized by .sup.1H NMR and IR spectroscopy.

[0053] .sup.1H NMR (D.sub.2O, 300 MHz) δ (ppm): 1.16-1.57 (m, 4H, —CH.sub.2—), 2.72-2.89 (m, 2H CO—CH.sub.2—PO), 3.00-3.24 (m,4H, NH—CH.sub.25—).

Example 2

Separating Uranium From an Aqueous Suspension Containing Gadolinium and Thorium

[0054] Sorption experiments were performed with solution containing targeted cations modeling the mineral dissolution processes (0.82 mol. % Gd, 0.10 mol. % Th, 0.04 mol. % U). All solutions were prepared with pH equal to 1. Experiments were carried out with dialysis method using 10 mL of hP(CPAAm6C) (5 g.L.sup.−1) and 100 mL of cationic solution with various total amount of cations.

[0055] Gd/Th/U mixture: The distribution of Gd, Th and U loaded on the hP(CPAAm6C) is a function of Σ.sub.initalC/cmp where C represents all cations present in the suspension and cmp represents the carbamoylmethylphosphonate complexing functions. The increasing Σ.sub.initalC/cmp causes a modification of the distribution. The uranyl ion (UO.sub.2.sup.2+) was preferentially sorbed on the hcmp functionalized polymer. The molar fraction of sorbed uranium reached 15% for Σ.sub.initalC/cmp=0.06, 27% for Σ.sub.initalC/cmp=0.28, 37% for Σ.sub.initalC/cmp=0.86 and 97% for Σ.sub.initalC/cmp=8.34. At the same time, a modification of the distribution of gadolinium and thorium was observed when increasing the Σ.sub.initalC/cmp ratio from 77% to 2% for Gd and 8 to 1% for Th. This tendency towards the molar percentage of uranium trapped on the sorbent, with a mixture initially containing only 4% of U, clearly shows that the carbamoylmethylphosphonic acid is very selective for U. hP(CPAAm6C) precipitated with the complexation of U.

Example 3

Separating Thorium From an Aqueous Suspension Containing Gadolinium and Uranium

[0056] Gd/Th/U mixture: the molar distribution of the Gd(III), Th(IV) and U(VI) sorbed on the P(CPAAm6C) at equilibrium, shows an increasing Σ.sub.initalC/cmp. As Σ.sub.initalC/cmp increased, the distribution was modified to preferentially sorb the thorium on the cmp functionalized polymer: the mole fraction of loaded thorium reached 72% at Σ.sub.initalC/cmp of 0.1, 85% at Σ.sub.initalC/cmp of 0.4 and 100% at Σ.sub.initalC/cmp of 10.3. Simultaneously, a complementary decrease of sorbed gadolinium (from 3% to 0%) and uranium (24% to 0%) was observed with the increase of the Σ.sub.initalC/cmp ratio. The mixture initially contained 86 mol. % of gadolinium, 10 mol. % of thorium and 4 mol. % of uranium. Despite this initial distribution, the fraction of loaded thorium was the highest for all Σ.sub.initalC/cmp. These results clearly showed that the P(CPAAm6C) was selective for Th(IV) in the presence of U(VI) and Gd(III).