METHOD FOR SEPARATING LUTETIUM AND YTTERBIUM USING CHROMATOGRAPHY

Abstract

The invention relates to the field of separating rare earth elements by chromatography. The claimed method for separating lutetium and ytterbium from acidic solutions resulting from the recycling of irradiated ytterbium-176 targets is carried out using ion exchange chromatography. Ion sorption is performed on a sulphonic cation resin in copper or nickel form, and lutetium and ytterbium are eluted using a solution of a chelator at elevated temperature with the aid of a system consisting of at least two series connected columns of decreasing diameter, filled with a sulphonic cation resin. The separation of ytterbium and lutetium is carried out in the presence of a bivalent ion of a stable intercalator element selected from the group consisting of cobalt, lead or zinc, in an amount in mEq that is equal to not less than 80% of the total capacity of the last column in the direction of travel of the solution. A solution of ethylenediaminetetraacetic acid or nitrilotriacetic acid is used as the eluent. The technical result is that of increasing the degree of chromatographic separation of lutetium and ytterbium from acidic solutions resulting from, the recycling of ytterbium-176 targets, including targets having a mass greater than 10 g, as well as expanding the range of methods available for separating the aforesaid components.

Claims

1. A method for separating lutetium and ytterbium from acidic solutions for processing irradiated ytterbium-176 targets by ion-exchange chromatography, comprising sorption on a cation exchange resin and elution of lutetium and ytterbium with a complexing agent solution at an elevated temperature using a system consisting of at least two serially connected columns with a decreasing diameter filled with sulfonic cation exchange resin in copper or nickel form, wherein ytterbium and lutetium are separated in the presence of a bivalent ion of a stable intercalator element selected from the group of cobalt, lead or zinc, taken in an amount in mEq equal to at least 80% of the total capacity of the last column, and a solution of ethylenediaminetetraacetic acid or nitrilotriacetic acid is used as the eluent.

2. The method of claim 1 wherein the intercalator element is added into the process either preliminarily at the stage of converting the sulfonic cation exchange resin to the copper or nickel form, or into the solution at the stage of sorption or elution.

3. The method of claim 1 wherein the used eluents comprise ethylenediaminetetraacetic or nitrilotriacetic acid solutions with a concentration of 0.04 to 0.08 mol/l at pH of 5 to 9.

4. The method of claim 1 wherein lutetium and ytterbium are eluated at a temperature of 70 to 80° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The feasibility of the proposed technical solution is supported by the following examples.

[0028] The achieved technical effect is confirmed by presented Figures and in the Table below.

[0029] FIG. 1 represents a chromatogram for separating Yb-Lu mixture without intercalator element on Tokem-308 sulfonic cation exchange resin. Eluent composition: 0.05 mol/l NTA, pH 7.7.

[0030] FIG. 2 represents a chromatogram for separating Yb-Lu mixture with intercalator element (Co) on Tokem-308 sulfonic cation exchange resin. Eluent composition: 0.04 mol/l EDTA, pH 5.0.

[0031] FIG. 3 represents a chromatogram for separating Yb-Lu mixture with intercalator element (Co) on Tokem-308 sulfonic cation exchange resin. Eluent composition: 0.04 mol/l NTA, pH 7.7.

[0032] FIG. 4 represents a chromatogram for separating Yb-Lu mixture with intercalator element (Zn) on a KU-2×8 sulfonic cation exchange resin. Eluent composition: 0.04 mol/l EDTA, pH 5.7.

[0033] FIG. 5 represents a chromatogram for separating Yb-Lu mixture with intercalator element (Pb) on Tokem-308 sulfonic cation exchange resin. Eluent composition: 0.08 mol/l EDTA, pH 7.7.

[0034] FIG. 6 represents a chromatogram for separating Yb-Lu mixture with intercalator element (Pb) on Cromalite CGC200×8 sulfonic cation exchange resin. Eluent composition: 0.08 mol/l NTA, pH 8.7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples

Example 1 (Prior Art)

[0035] The separation of 400 mg of ytterbium and trace amount (~1 MBq) of lutetium-177 was carried out on two serially connected columns having a diameter of 9 mm and 6 mm filled with Tokem-308 sulfonic cation exchange resin in nickel form with a grain size of 0.22 mm. The first column contained 50 ml and the second contained 20 ml of sulfonic cation exchange resin. The mixture to be separated was sorbed on the first column from a nitric acid solution containing 400 mg of Yb and ~1 MBq of Lu-177 at pH 2 and temperature of 20 to 25° C.

[0036] After sorption, the first column was washed with distilled water and the eluent solution of 0.05 mol/l HTA at pH 7.7 was passed through at a rate of 4 ml.Math.min/cm.sup.2 and temperature of 70° C. When the lutetium front approached the bottom of the column, the second column was connected. The solution at the outlet of the second column was collected by fractions and the concentration of ytterbium ions and the specific activity of lutetium-177 were analyzed therein.

Example 2

[0037] The separation of 54 mg of ytterbium and trace amount (~1 MBq) of lutetium-177 was carried out on two serially connected columns having a diameter of 8 mm and 6.5 mm, respectively, filled with Tokem-308 sulfonic cation exchange resin in a copper form with a grain size of 0.22 mm. The first column contained 42 ml of sulfonic cation exchange resin and the second column contained 13 ml of sulfonic cation exchange resin. The total capacity of the cation exchange resin in the second column was about 26 mEq. The mixture to be separated was sorbed on the first column from a nitric acid solution containing 54 mg of Yb and ~1 MBq of Lu-177, at pH 2 and temperature of 20 to 25° C. The intercalator element (cobalt) in the amount of 31 mEq (120% of the total capacity of the last column) was added at the stage of converting the first column to a copper form.

[0038] After sorption, the first column was washed with distilled water, the eluent solution (0.04 mol/l EDTA, pH 5.0) was passed through at a rate of 4 ml.Math.min/cm.sup.2 and temperature of 80° C. When the lutetium front approached the bottom of the column, the second column was connected. The solution at the outlet of the last column was collected by fractions and the concentration of ytterbium ions and the specific activity of lutetium-177 were analyzed therein.

Example 3

[0039] The separation of 250 mg of ytterbium and trace amount (~1 MBq) of lutetium-177 was carried out on three serially connected columns with a diameter of 10, 6 and 3.4 mm, respectively, filled with Tokem-308 sulfonic cation exchange resin in a nickel form with a grain size of 0.22 mm. The first column contained 72 ml, the second and third columns contained 40 and 10 ml of sulfonic cation exchange resin, respectively. The total capacity of the cation exchange resin in the third column was about 20 mEq. The mixture to be separated was sorbed on the first column from a nitric acid solution containing 250 mg of Yb and ~1 MBq of Lu-177 at pH 2 and temperature of 20 to 25° C. The intercalator element (cobalt) in the amount of 20 mEq (100% of the total capacity of the last column) was added to the starting solution at the stage of sorption.

[0040] After sorption, the first column was washed with distilled water, the eluent solution (0.04 mol/l NTA, pH 7.7) was passed through at a rate of 4 ml.Math.min/cm.sup.2 and temperature of 70° C. When the lutetium front approached the bottom of the column, each following column was connected. The solution at the outlet of the last column was collected by fractions and the concentration of ytterbium ions and the specific activity of lutetium-177 were analyzed therein.

Example 4

[0041] The separation of 400 mg of ytterbium and trace amount (~1 MBq) of lutetium-177 was carried out on two serially connected columns with a diameter of 8 mm and 6.5 mm, respectively, filled with KU-2×8 sulfonic cation exchange resin in a copper form with a grain size of 0.125 to 0.25 mm. The first column contained 42 ml and the second contained 3 ml of the sulfonic cation exchange resin. The total capacity of the cation exchange resin in the second column was about 26 mEq. The mixture to be separated was sorbed on the first column from a nitric acid solution containing 400 mg of Yb and ~1 MBq of Lu-177 at pH 2 and temperature of 20 to 25° C. Further, the intercalator element (Zn) was added to the eluent solution in the amount of 21 mEq (80% of the total capacity of the last column).

[0042] After sorption, the first column was washed with distilled water, the eluent solution (0.04 mol/l EDTA, pH 5.7) was passed through at a rate of 4 ml.Math.min/cm.sup.2 and temperature of 80° C. When the lutetium front approached the bottom of the column, the second column was connected. The solution at the outlet of the last column was collected by fractions and the concentration of ytterbium ions and the specific activity of lutetium-177 were analyzed therein.

Example 5

[0043] The separation of 400 mg of ytterbium and trace amount (~1 MBq) of lutetium-177 was carried out on three serially connected columns with a diameter of 10, 6 and 3.4 mm, respectively, filled with Tokem-308 sulfonic cation exchange resin in a nickel form with a grain size of 0.22 mm. The first column contained 72 ml, the second and third columns contained 40 and 12 ml of sulfonic cation exchange resin, respectively. The total capacity of the cation exchange resin in the third column was about 24 mEq. The mixture to be separated was sorbed on the first column from a nitric acid solution containing 400 mg of Yb and ~1 MBq of Lu-177 at pH 2 and temperature of 20 to 25° C.

[0044] After sorption, the first column was washed with distilled water, the eluent solution (0.08 mol/l NTA, pH 7.7) was passed through at a rate of 4 ml.Math.min/cm.sup.2 and temperature of 70° C. Further, the intercalator element (Pb) was added to the eluent solution in the amount of 21 mEq (88% of the total capacity of the last column). When the lutetium front approached the bottom of the column, each following column was connected. The solution at the outlet of the last column was collected by fractions and the concentration of ytterbium ions and the specific activity of lutetium-177 were analyzed therein.

Example 6

[0045] The separation of 5.4 g of ytterbium and trace amount (~1 MBq) of lutetium-177 was carried out on four serially connected columns with a diameter of 16, 10, 6 and 4.4 mm, respectively, filled with Cromalite CGC200×8 sulfonic cation exchange resin in a nickel form with a grain size of 0.15 to 0.30 mm. The first column contained 180 ml, the second, third and fourth columns contained 72, 40 and 12 ml of sulfonic cation exchange resin, respectively. The total capacity of the cation exchange resin in the fourth column is about 24 mEq. The mixture to be separated was sorbed on the first column from a nitric acid solution containing 5.4 mg of Yb and ~1 MBq of Lu-177 at pH 2 and temperature of 20 to 25° C.

[0046] After sorption, the first column was washed with distilled water, the eluent solution (0.08 mol/l NTA, pH 8.7) was passed through at a rate of 4 ml.Math.min/cm.sup.2 and temperature of 80° C. Further, the intercalator element (Pb) was added to the eluent solution in the amount of 21 mEq (88% of the total capacity of the last column). When the lutetium front approached the bottom of the column, each following column was connected. The solution at the outlet of the last column was collected by fractions and the concentration of ytterbium ions and the specific activity of lutetium-177 were analyzed therein.

[0047] The Yb-Lu mixture separation efficiency of the claimed method vs. the prior art is represented in the Table below.

TABLE-US-00001 Example No. Intercalator element Post-separation Yb content in Lu, % 1 (prior art) - 31,8 2 Co <3 3 Co <3 4 Zn 6,0 5 Pb 3,1 6 Pb 0,2

[0048] The data presented in FIGS. 1-6 and in the Table show that the chromatographic separation of a solution containing a macroquantity of Yb and a microquantity of Lu carried out in accordance with the claimed invention achieves higher separation efficiency of Yb/Lu pair as compared to the prior art. The Table shows the residual Yb percentage in Lu by weight of the original content. As follows from the data in the Table, the separation efficiency of the claimed pair of ions achieved in specific examples according to the proposed invention is 6-160 times higher than that of the prior art. It can be seen from the examples that the effective separation of ytterbium and lutetium is achieved regardless of the weight of the initial ytterbium-176 target, while the separation of ytterbium and lutetium under the prior art conditions yields unsatisfactory results due to the overlapping zones (bands) of these ions.

[0049] The proposed method can be implemented both in conventional displacement chromatography and in high-speed pressure chromatography, which expands the range of effective methods for separating lutetium and ytterbium ions.

INDUSTRIAL APPLICABILITY

[0050] The proposed invention can be used in nuclear medicine when processing an irradiated ytterbium-176 target to obtain pure carrier-free lutetium-177 compounds and in chemical technology to obtain purified ytterbium and lutetium compounds.