A method for separating and recovering rare earth elements from uranium-containing materials

Abstract

The present invention provides a method for separating, recovering and determining rare earth elements in uranium-containing substances. The method for separating and recovering rare earth elements in uranium-containing substances comprises the following steps: step (1) preparing a uranium matrix sample solution; step (2) pre-balancing resin; step (3) column loading and elution. The method for determining rare earth elements in uranium-containing substances comprises the following steps: step (1) preparing a uranium matrix sample solution; step (2) pre-balancing resin; step (3) column loading and elution; step (4) measuring the content of rare earth elements. The prior art is unable to achieve the disadvantages of synchronous and efficient separation and recovery of 14 rare earth elements in uranium-containing substances, and the process is complicated and the organic solvent treatment is inconvenient.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth elements, and in particular relates to a method for separating and recovering rare earth elements in uranium-containing materials. Background Art

[0002] Rare earth elements are an important element in the nuclear industry. The separation and analysis of four rare earth elements, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lul, is one of the important contents of nuclear fuel cycle quality control and nuclear forensics origin tracing. The most widely used scenario is the detection of trace levels (10 - 6 gg-1) Analysis of rare earth elements. Although the elements and matrix compositions of different uranium materials are different, uranium is the main matrix element in the process of converting (digesting, dissolving) solid uranium materials into solution samples for rare earth element separation and analysis. Therefore, the separation of rare earth elements in uranium-containing materials is a key technology for rare earth element analysis of various uranium materials.

[0003] Since the measurement of rare earth elements is usually carried out using the external standard method. In order to achieve the purpose of accurate quantification of rare earth elements, it is necessary to ensure that the rare earth elements can be efficiently and stably recovered during the separation process to reduce the measurement deviation of the rare earth element content caused by the loss of the chemical process. At the same time, since uranium is a large element in uranium-containing substances and its content is much higher than the rare earth elements to be analyzed, it is necessary to achieve effective separation of rare earth elements and uranium matrix elements during the separation process to facilitate subsequent measurements.

[0004] At present, the most common method for analyzing rare earth elements in uranium-containing materials is liquid-liquid extraction chromatography. For example, after the uranium material is dissolved and converted into a 4mol / L HNO3 solution system, a TBP extractant dissolved in a CCl4 organic solvent is added for thorough mixing. TBP adsorbs uranium in the sample but does not adsorb rare earth elements. By standing, the organic phase (CCl4) and the solution phase are separated. The CCl4 organic phase containing TBP is discarded, and the uranium element is removed, while the rare earth elements remain in the solution phase. By repeatedly using TBP-CCl4 for extraction, the uranium element in the sample solution is removed, and the purpose of separating rare earth elements is achieved. In order to increase the removal effect of uranium matrix elements, after the TBP-CCl4 extraction is completed, a TOPO extractant dissolved in CCl4 can be added to the sample solution to continue the extraction, so that after the TOPO extraction adsorbs the uranium element, it is separated from the solution phase along with the CCl4 organic solution.

[0005] The disadvantage of the above rare earth element separation technology in uranium-containing materials is that it is impossible to achieve efficient (chemical recovery rate > 90%) separation and recovery of all rare earth elements (such as Sc) simultaneously. In addition, the above technical process is cumbersome and requires repeated extraction and stripping processes, which takes a long time (several hours). In addition, the TBP extractant is unstable in an acid solution system for a long time, and there is a lot of organic solvent waste liquid containing radioactive substances (uranium), which is inconvenient to handle. Summary of the invention

[0006] Aiming at the shortcomings of the prior art that the 14 rare earth elements in uranium-containing materials cannot be separated and recovered simultaneously and efficiently, and the process is complicated and the organic solvent treatment is inconvenient, the present invention proposes a method for separating and recovering rare earth elements in uranium-containing materials, which specifically adopts the following technical scheme:

[0007] A method for separating and recovering rare earth elements from uranium-containing materials, characterized in that the method comprises the following steps:

[0008] Step (1) preparing a uranium matrix sample solution;

[0009] Step (2) pre-equilibrate the resin;

[0010] Step (3) is column loading and elution to obtain an eluent containing rare earth elements, thereby completing the separation of rare earth elements in the uranium-containing material.

[0011] Furthermore, the step (1) of preparing a uranium matrix sample solution specifically comprises: completely dissolving the uranium-containing substance to be tested into a mixed solution system of ultrapure nitric acid and hydrofluoric acid to form a uranium matrix sample solution.

[0012] Further, the step (2) of pre-equilibrating the resin specifically comprises:

[0013] Step (2.1) connects a plurality of UTEVA resins in series and to a vacuum box, wherein a centrifuge tube A is placed at the lower end of the UTEVA resin in the vacuum box to collect the effluent;

[0014] Step (2.2) Add deionized water to the syringe, turn on the pump of the vacuum box, and the deionized water in the syringe flows through the UTEVA resin under the action of the pressure difference to infiltrate and clean the resin, and the effluent is collected in centrifuge tube A;

[0015] Step (2.3) Add a mixed solution of ultrapure nitric acid and hydrofluoric acid into the syringe, turn on the pump of the vacuum box, and the solution in the syringe flows through the UTEVA resin under the action of the pressure difference to pre-balance the resin, and the effluent is collected in centrifuge tube A.

[0016] Furthermore, the step (3) of column loading and elution specifically comprises:

[0017] In step (3.1), centrifuge tube A is taken out and discarded, and another centrifuge tube B is placed in the vacuum box at a position corresponding to the lower end of the UTEVA resin; the uranium matrix sample solution in step (1) is added to the syringe, and the pump of the vacuum box is turned on. The sample solution flows through the UTEVA resin under the action of the pressure difference and is collected in centrifuge tube B;

[0018] Step (3.2) Add a mixed solution of ultrapure nitric acid and hydrofluoric acid as an eluent into a syringe, take another new centrifuge tube C and place it at the lower end of the UTEVA resin, turn on the pump of the vacuum box, allow the eluent to flow through the UTEVA resin under the action of the pressure difference, and collect it in the centrifuge tube C;

[0019] Step (3.3) diluting the eluate collected in centrifuge tube C in step (3.2) with deionized water, and detecting rare earth elements in the diluted eluate;

[0020] Step (3.4) repeats steps (3.2) to (3.3) n times until the rare earth element concentration in the diluted eluent is detected to be within the instrument background range for the nth time.

[0021] Furthermore, in step (3.2), the concentration of the ultrapure nitric acid is 6-9 mol / L, and the concentration of the hydrofluoric acid is 0.1-0.2 mol / L.

[0022] A method for determining the content of rare earth elements in uranium-containing materials based on the above-mentioned method for separating and recovering rare earth elements in uranium-containing materials, characterized in that the determination method further comprises the following steps:

[0023] Step (4) measures the rare earth element content, specifically comprising: uniformly mixing the sample solution obtained in the centrifuge tube B in step (3.1) and the eluent in (n-1) centrifuge tubes C obtained by repeating steps (3.2) to (3.3) (n-1) times in step (3.4), and using the mixture as the recovered solution to be tested; diluting the recovered solution to be tested and measuring the rare earth element content, thereby obtaining the rare earth element content in the uranium-containing substance.

[0024] The present invention solves the technical difficulty of synchronously and efficiently separating and recovering 14 rare earth elements in uranium-containing materials. At the same time, the technology adopts a simple operation process, which greatly shortens the separation time compared with conventional methods. The solid waste generated by solid phase extraction is easier to recover and treat, thereby improving the practicability of the separation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the rare earth element separation and recovery method of the present invention;

[0026] Figure 2 This is a flow chart of the rare earth element determination method of the present invention;

[0027] Figure 3 The invention relates to a device used in the method for separating and recovering rare earth elements. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] like Figure 1 As shown, the method for separating and recovering rare earth elements from uranium-containing materials of the present invention comprises the following steps (the uranium-containing materials mentioned in the present invention specifically refer to uranium materials involved in the nuclear industry, such as yellow cake, uranium ore, uranium pellets, etc.):

[0030] Step (1) preparing a uranium matrix sample solution;

[0031] Step (2) pre-equilibrate the resin;

[0032] Step (3) is column loading and elution to obtain an eluent containing rare earth elements, thereby completing the separation of rare earth elements in the uranium-containing material.

[0033] Furthermore, the step (1) of preparing a uranium matrix sample solution is specifically: completely dissolving the uranium-containing substance to be tested into a mixed solution system of ultrapure nitric acid (HNO3) and hydrofluoric acid (HF), or transferring the substance after digestion (dissolution) into a mixed solution system of ultrapure nitric acid and hydrofluoric acid to form a uranium matrix sample solution.

[0034] Further, the step (2) of pre-equilibrating the resin specifically comprises:

[0035] Step (2.1) connects several UTEVA resins in series and to a vacuum box, as shown in the attached Figure 3 As shown, a centrifuge tube A is placed at the lower end of the UTEVA resin in the vacuum box to collect the effluent; the number of UTEVA solid phase extraction resins used is not limited to 2, and different numbers can be selected according to different requirements for the removal efficiency of uranium elements in actual detection;

[0036] Step (2.2) Add deionized water to the syringe, turn on the pump of the vacuum box, and the deionized water in the syringe flows through the UTEVA resin under the action of the pressure difference to infiltrate and clean the resin, and the effluent is collected in centrifuge tube A;

[0037] Step (2.3) Add a mixed solution of ultrapure nitric acid and hydrofluoric acid into the syringe, turn on the pump of the vacuum box, and the solution in the syringe flows through the UTEVA resin under the action of the pressure difference to pre-balance the resin, and the effluent is collected in centrifuge tube A.

[0038] Furthermore, the step (3) of column loading and elution specifically comprises:

[0039] In step (3.1), centrifuge tube A is taken out and discarded, and another centrifuge tube B is placed in a position corresponding to the lower end of the UTEVA resin in the vacuum box; the uranium matrix sample solution in step (1) is sucked with a pipette and added to a syringe, and the pump of the vacuum box is turned on. The sample solution flows through the UTEVA resin under the action of the pressure difference and is collected in the centrifuge tube B; in this process, the uranium in the sample solution is adsorbed on the UTEVA resin, and the rare earth elements are not adsorbed;

[0040] Step (3.2) Add a mixed solution of ultrapure nitric acid and hydrofluoric acid as an eluent into a syringe, take another new centrifuge tube C and place it at the lower end of the UTEVA resin, turn on the pump of the vacuum box, and allow the eluent to flow through the UTEVA resin under the action of the pressure difference to further elute the rare earth elements, and collect them in the centrifuge tube C;

[0041] Step (3.3) diluting the eluate collected in centrifuge tube C in step (3.2) with deionized water, and detecting rare earth elements in the diluted eluate using an inductively coupled plasma mass spectrometer;

[0042] Step (3.4) repeats steps (3.2) to (3.3) n times until the rare earth element concentration in the diluted eluent is detected to be within the instrument background range for the nth time. This indicates that the rare earth element is completely recovered when step (3.4) is repeated to the last (n-1) times.

[0043] The present invention comprises steps (1) to (3.4), and the method solves the problem in the prior art that 14 rare earth elements cannot be recovered simultaneously and efficiently, and greatly simplifies the rare earth element separation process in uranium-containing materials, thereby significantly improving the simplicity and practicality of the method.

[0044] Furthermore, in step (3.2), the concentration of the ultrapure nitric acid is 6-9 mol / L, and the concentration of the hydrofluoric acid is 0.1-0.2 mol / L.

[0045] The key technical points and intended protection points of the present invention are:

[0046] (1) Separation of rare earth elements from uranium matrix solution by several UTEVA solid phase extraction resins connected in series.

[0047] (2) The solution loading and elution conditions are a mixed solution system of 6-9 mol / L ultrapure nitric acid (HNO3) and 0.1-0.2 mol / L hydrofluoric acid (HF).

[0048] (3) The elution volume is 10 mL.

[0049] like Figure 2As shown, the present invention also provides a method for determining the content of rare earth elements in uranium-containing materials based on the above separation and recovery method, characterized in that the determination method further comprises the following steps:

[0050] Step (4) measures the rare earth element content, specifically: the sample solution obtained in the centrifuge tube B in step (3.1) and the eluent in the (n-1) centrifuge tube C obtained by repeating steps (3.2) to (3.3) (n-1) times in step (3.4) are mixed evenly to form a recovery solution to be tested, and the recovery solution to be tested is diluted and the rare earth element content is measured to obtain the rare earth element content in the uranium-containing substance. The determination method can be selected according to actual conditions, such as using an external standard method to measure the rare earth element content in the recovery solution to be tested.

[0051] Example 1

[0052] A standard sample of uranium ore containing 14 rare earth elements was selected for testing to verify the chemical recovery rate of the rare earth element separation process in the present invention. The operation was carried out according to the following steps:

[0053] Step (1) Preparation of uranium matrix sample solution

[0054] Step (1) 0.5 g of a uranium ore standard sample is completely digested using 30 mL of concentrated nitric acid and 15 mL of hydrofluoric acid. After the digestion is completed, the sample is evaporated to dryness and transferred to a mixed solution system of 8 mol / L ultrapure nitric acid and 0.2 mol / L hydrofluoric acid to form a uranium ore sample solution.

[0055] Step (2) Pre-equilibration of resin

[0056] Step (2.1) connects two UTEVA resins in series and to a vacuum box, wherein a 50 mL centrifuge tube A is placed at the lower end of the UTEVA resin in the vacuum box to collect the effluent;

[0057] Step (2.2) Add 10 mL of deionized water to the syringe, turn on the pump of the vacuum box, the vacuum degree in the vacuum box is 0.8 MPa, and the deionized water in the syringe flows through the UTEVA resin under the action of the pressure difference to infiltrate and clean the resin, and the effluent is collected in centrifuge tube A;

[0058] Step (2.3) Add 10 mL of a mixed solution of 8 mol / L ultrapure nitric acid and 0.2 mol / L hydrofluoric acid into the syringe, turn on the pump of the vacuum box, the vacuum degree in the vacuum box is 0.8 MPa, the solution in the syringe flows through the UTEVA resin under the action of the pressure difference to pre-balance the resin, and the effluent is collected in centrifuge tube A;

[0059] Step (3) Column loading and elution

[0060] In step (3.1), centrifuge tube A is taken out and discarded, and another 50 mL centrifuge tube B is placed in the vacuum box at a position corresponding to the lower end of the UTEVA resin; the uranium ore sample solution in step (1) is drawn with a pipette, added to a syringe, and the pump of the vacuum box is turned on. The sample solution flows through the UTEVA resin under the action of the pressure difference and is collected in centrifuge tube B;

[0061] Step (3.2) Add 10 mL of a mixed solution of 8 mol / L ultrapure nitric acid and 0.2 mol / L hydrofluoric acid as an eluent into a syringe, take another new 50 mL centrifuge tube C and place it at the lower end of the UTEVA resin, turn on the pump of the vacuum box, and allow the eluent to flow through the UTEVA resin under the action of the pressure difference and be collected in the centrifuge tube C;

[0062] Step (3.3) diluting the eluate collected in centrifuge tube C in step (3.2) with deionized water, and detecting rare earth elements in the diluted eluate using an inductively coupled plasma mass spectrometer;

[0063] Step (3.4) Repeat steps (3.2) to (3.3) twice, that is, the concentration of rare earth elements in the eluent after the second dilution is detected to be within the instrument background range, indicating that the rare earth elements have been completely eluted during the first repetition.

[0064] Step (4) measuring the rare earth element content. The sample solution obtained in the centrifuge tube B in step (3.1) and the eluate in a centrifuge tube C obtained by repeating step (3.4) for the first time are mixed evenly to form a recovery solution to be tested. The recovery solution to be tested is diluted and the rare earth element content is determined by an inductively coupled plasma mass spectrometer according to the external standard method.

[0065] The measurement results and reference values ​​of rare earth element contents in uranium ore standard samples are shown in Table 1.

[0066] Table 1 Measured values ​​and reference values ​​of 14 rare earth elements in uranium ore standard samples

[0067] Rare Earth Elements Measurement value (μg / g) Reference value (μg / g) Recovery rate La 8.38±0.015 8.81 95±1％ Ce 20.46±0.013 21.50 95±1％ Pr 3.21±0.014 3.11 103±1％ Nd 15.16±0.016 15.60 97±1％ Sm 4.12±0.017 4.27 96±1％ Eu 1.28±0.012 1.32 97±1％ G 4.48±0.012 4.67 96±1％ Tb 0.72±0.011 0.73 99±2％ Dy 4.50±0.022 4.54 99±1％ Ho 0.95±0.015 0.80 119±3％ Er 2.66±0.019 2.49 107±1％ Tm 0.41±0.012 0.42 98±3％ Yb 2.45±0.031 2.55 96±1％ Lu 0.38±0.002 0.39 97±1％

[0068] According to the data shown in Table 1, it can be seen that the chemical recovery rate of the rare earth element separation method provided by the present invention for all 14 rare earth elements is higher than 95%, achieving the simultaneous and efficient recovery of all rare earth elements; taking into account the evaluation error, the recovery rate for some rare earth elements Sc, Y, Sm, Dy, Er, and Yb is close to 100%, which is close to complete recovery.

Claims

1. A method for separating and recovering rare earth elements from uranium-containing materials, characterized in that: The method comprises the following steps: Step (1) preparing a uranium matrix sample solution; Step (2) pre-equilibrate the resin; In step (2.1), several UTEVA resins are connected in series and connected to a vacuum box, and a centrifuge tube A is placed at the lower end of the UTEVA resin in the vacuum box to collect the effluent; Step (2.2) adding deionized water to the syringe, turning on the pump of the vacuum box, the deionized water in the syringe flows through the UTEVA resin under the action of the pressure difference to wet and clean the resin, and the effluent is collected in centrifuge tube A; Step (2.3) adding a mixed solution of ultrapure nitric acid and hydrofluoric acid to the syringe, turning on the pump of the vacuum box, the solution in the syringe flows through the UTEVA resin under the action of the pressure difference to pre-balance the resin, and the effluent is collected in centrifuge tube A; Step (3) column loading and elution to obtain an eluent containing rare earth elements, thereby completing the separation of rare earth elements in the uranium-containing material; Wherein, in step (3.1), centrifuge tube A is taken out and discarded, and another centrifuge tube B is placed at a position corresponding to the lower end of the UTEVA resin in the vacuum box; the uranium matrix sample solution in step (1) is added to a syringe, and the pump of the vacuum box is turned on, and the sample solution flows through the UTEVA resin under the action of the pressure difference and is collected in centrifuge tube B; in step (3.2), a mixed solution of ultrapure nitric acid and hydrofluoric acid is added to the syringe as an eluent, and another new centrifuge tube C is taken and placed at the lower end of the UTEVA resin, and the pump of the vacuum box is turned on, so that the eluent flows through the UTEVA resin under the action of the pressure difference and is collected in centrifuge tube C; the concentration of the ultrapure nitric acid is 6-9 mol / L, and the concentration of the hydrofluoric acid is 0.1-0.2 mol / L; Step (3.3) diluting the eluate collected in centrifuge tube C in step (3.2) with deionized water, and detecting rare earth elements in the diluted eluate; Step (3.4) repeats steps (3.2) to (3.3) n times until the rare earth element concentration in the diluted eluent is detected to be within the instrument background range for the nth time.

2. The separation and recovery method according to claim 1, characterized in that: The step (1) of preparing a uranium matrix sample solution specifically comprises: completely dissolving the uranium-containing substance to be tested into a mixed solution system of ultrapure nitric acid and hydrofluoric acid to form a uranium matrix sample solution.

3. A method for determining the content of rare earth elements in uranium-containing materials based on the method for separating and recovering rare earth elements in uranium-containing materials according to claim 1 or 2, characterized in that: The determination method also includes the following steps: Step (4) measures the rare earth element content, specifically comprising: uniformly mixing the sample solution obtained in the centrifuge tube B in step (3.1) and the eluent in (n-1) centrifuge tubes C obtained by repeating steps (3.2) to (3.3) (n-1) times in step (3.4), and using the mixture as the recovered solution to be tested; diluting the recovered solution to be tested and measuring the rare earth element content, thereby obtaining the rare earth element content in the uranium-containing substance.

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