A method for calculating the reversibility of radionuclide adsorption

Abstract

The present invention relates to a method for calculating the reversibility of radionuclide adsorption, which defines the area between the adsorption isotherm and the desorption isotherm of the nuclide in the soil and groundwater rock medium as "adsorption hysteresis area S", and uses the "adsorption hysteresis area S" to quantify the reversibility of the adsorption of the nuclide in the soil and groundwater rock medium, and is used to judge the magnitude of the reversibility of the adsorption of the nuclide. In addition, the adsorption amount of the nuclide is the sum of the reversible adsorption amount and the irreversible adsorption amount. The method can be used to solve the reversible adsorption amount and the irreversible adsorption amount respectively, laying a foundation for accurately and scientifically evaluating the fate behavior of the nuclide in the soil and groundwater environment, and has great significance for the treatment and remediation of radioactive contaminated sites.

Description

Technical Field

[0001] The invention belongs to the field of radiation protection, and in particular relates to a method for calculating the reversibility of radionuclide adsorption. Background Art

[0002] Adsorption is the main interfacial process of radionuclides in soil and groundwater environments, and is the sum of reversible adsorption and irreversible adsorption. The reversible adsorption in solid media can be desorbed and released under certain conditions, which is very important for evaluating the migration range, concentration distribution and bioavailability of nuclides. The irreversible adsorption is the part that remains in the solid media for a long time, and is the key to breaking through the deep elution and separation technology for the remediation of contaminated sites. At present, thermodynamics and kinetics are still the main means to study the environmental fate behavior of nuclides. One or several representative key migration parameters are used to comprehensively reflect the adsorption process of nuclides. The traditional concept is that under thermodynamic conditions, the equilibrium parameters have the properties of thermodynamic constants. With the deepening of research, it is found that the adsorption density on the surface of solid media is not a thermodynamic state function corresponding to a unique adsorption equilibrium constant, but is affected by reaction processes such as reversibility and kinetics.

[0003] Therefore, in order to accurately and reasonably evaluate the fate behavior of radionuclides in soil and groundwater environments, it is necessary to consider the reversibility of adsorption during the migration of radionuclides, that is, the interaction between the reversible and irreversible adsorption amounts of radionuclides. Summary of the Invention

[0004] In response to the defects existing in the prior art, the purpose of the present invention is to provide a method for calculating the reversibility of radionuclide adsorption. By defining the area between the adsorption isotherm and the desorption isotherm of the nuclide in soil and groundwater rock media as the "adsorption hysteresis area S", the reversibility of the adsorption system is quantitatively calculated based on the size of this area.

[0005] To achieve the above objectives, the present invention adopts a technical solution: a method for calculating the reversibility of radionuclide adsorption, the method comprising the following steps:

[0006] S1. Treating prepared radionuclide-groundwater-rock medium system samples with different initial concentrations C0 to an adsorption equilibrium state, performing solid-liquid separation on the radionuclide-groundwater-rock medium system samples in the adsorption equilibrium state, recording the equilibrium concentration of the sample solution obtained after solid-liquid separation as Ce1, obtaining unit adsorption amount qe1 data of the rock medium sample based on the equilibrium concentration Ce1 of the sample solution and the initial concentration C0 data, and then performing data fitting based on the obtained equilibrium concentration Ce1 of multiple groups of sample solutions with different initial concentrations and the unit adsorption amount qe1 data of the rock medium sample to obtain the adsorption isotherm of the radionuclide-groundwater-rock medium system;

[0007] S2. Adding the rock and soil medium obtained after solid-liquid separation back into groundwater and treating it until it reaches a desorption equilibrium state, performing solid-liquid separation on the radionuclide-groundwater-rock and soil medium system sample in the desorption equilibrium state, repeating this step several times, recording the equilibrium concentration of the last desorption sample solution as Ce2, and recording the remaining unit adsorption amount of the rock and soil medium as qe2. Performing data fitting to obtain the desorption isotherm of the radionuclide-groundwater-rock and soil medium system;

[0008] S3. According to the adsorption isotherm and desorption isotherm of the radionuclide-groundwater-rock medium system, the "adsorption hysteresis area S" is solved by a graphical method, and the reversible adsorption amount and the irreversible adsorption amount are calculated accordingly.

[0009] Furthermore, before preparing the radionuclide-groundwater-rock medium system samples with different initial concentrations C0 in step S1, the test container is subjected to acid treatment to reduce the adsorption of the nuclides by the container wall.

[0010] Furthermore, before preparing radionuclide-groundwater-rock medium system samples with different initial concentrations of C0 in step S1, the particle size distribution of the on-site rock medium is measured. The rock medium used in the test is formulated using a particle size spectrum to maintain consistency with the on-site conditions and increase the representativeness of the calculation results.

[0011] Furthermore, the radionuclide-groundwater-rock medium system adopts a constant temperature oscillation method to achieve adsorption equilibrium and desorption equilibrium.

[0012] Furthermore, when the difference between two consecutive nuclide concentration measurement results is less than a preset threshold, it is determined that the adsorption equilibrium state and the desorption equilibrium state are reached.

[0013] Furthermore, when performing solid-liquid separation on a radionuclide-groundwater-rock medium system sample that has reached adsorption equilibrium and desorption equilibrium, the centrifuge speed is determined according to the minimum particle size of the rock medium sample.

[0014] Furthermore, the pH value of the radionuclide-groundwater-rock medium system with different initial concentrations of C0 is adjusted using a specific acid solution and / or alkaline solution.

[0015] Furthermore, the weight of the geotechnical medium sample of the radionuclide-groundwater-geotechnical medium system with different initial concentrations C0 in step S1 is recorded as g1. The method for calculating the reversible adsorption amount and the irreversible adsorption amount in step S3 is that the intersection of the line connecting the two points in the adsorption stage (Ce1, qe1) and the desorption stage (Ce2, qe2) and the vertical coordinate is recorded as (Ce3, qe3), the irreversible adsorption amount is qe3×g1, and the reversible adsorption amount is (qe1-qe3)×g1.

[0016] The present invention provides the following advantages: The disclosed method for calculating the reversibility of radionuclide adsorption defines the area between the adsorption and desorption isotherms of the nuclide in soil and groundwater geotechnical media as the "adsorption hysteresis area S." This area is used to quantify the reversibility of nuclide adsorption in soil and groundwater geotechnical media and to assess the magnitude of the reversibility. Furthermore, the adsorption capacity of a nuclide is the sum of the reversible and irreversible adsorption capacities. This method can be used to separately determine the reversible and irreversible adsorption capacities, laying the foundation for accurate and scientific assessment of the fate of nuclides in soil and groundwater environments, and is of great significance for the remediation and remediation of radioactively contaminated sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of adsorption hysteresis area used in the method for calculating the reversibility of radionuclide adsorption according to the present invention;

[0018] Figure 2-1 and Figure 2-2 The present invention is a method for calculating the reversibility of radionuclide adsorption according to the nuclide 90 Sr. 137 Freundlich adsorption isotherm fitted from the adsorption data of Cs in strongly weathered biotite granodiorite;

[0019] Figure 3-1 and Figure 3-2 The present invention is a method for calculating the reversibility of radionuclide adsorption according to the nuclide 90 Sr. 137 Freundlich desorption isotherm fitted from the desorption data of Cs in strongly weathered biotite granodiorite;

[0020] Figure 4-1 and Figure 4-2 The method for calculating the reversibility of radionuclide adsorption according to the present invention is based on Figure 2-1 and Figure 2-2 The adsorption isotherms and Figure 3-1 and Figure 3-2 The desorption isotherm obtained in the calculation of nuclides 90 Sr. 137 Hysteresis area of ​​Cs adsorption in strongly weathered biotite granodiorite. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1

[0023] The present invention discloses a method for calculating the reversibility of radionuclide adsorption, comprising the following steps:

[0024] S1. Prepare radionuclide-groundwater-rock medium system samples with different initial concentrations C0 and oscillate them at a constant temperature until they reach an adsorption equilibrium state. Then, perform solid-liquid separation on the radionuclide-groundwater-rock medium system samples in the adsorption equilibrium state. The equilibrium concentration of the sample solution obtained after solid-liquid separation is recorded as Ce1. Based on the equilibrium concentration Ce1 of the sample solution and the initial concentration C0 data, the unit adsorption amount qe1 data of the rock medium sample is obtained. Then, based on the obtained equilibrium concentration Ce1 of multiple sets of sample solutions with different initial concentrations and the unit adsorption amount qe1 data of the rock medium sample, data fitting is performed to obtain the Freundlich adsorption isotherm of the radionuclide-groundwater-rock medium system.

[0025] S2. Re-add the rock and soil medium obtained after solid-liquid separation to groundwater and oscillate at a constant temperature until desorption equilibrium is reached. Solid-liquid separation is then performed on the radionuclide-groundwater-rock and soil medium system sample at desorption equilibrium. Repeat this step three times. The equilibrium concentration of the desorbed sample solution from the final desorption is recorded as Ce2, and the remaining unit adsorption capacity of the rock and soil medium is recorded as qe2. Data fitting is performed to obtain the Freundlich desorption isotherm of the radionuclide-groundwater-rock and soil medium system.

[0026] S3. According to the adsorption isotherm and desorption isotherm of the radionuclide-groundwater-rock medium system, the "adsorption hysteresis area S" is solved by a graphical method, and the reversible adsorption amount and the irreversible adsorption amount are calculated accordingly.

[0027] In this embodiment, the preparation of radionuclide-groundwater-rock medium system samples with different initial concentrations of C0 in step S1 includes the following sub-steps:

[0028] Soak a 15mL polypropylene centrifuge tube in 0.1mol / L HCl for 7 days, then pour out, rinse, and set aside. Acid treatment of the centrifuge tube reduces radionuclide adsorption by the tube wall and improves the accuracy of calculations of the reversibility of radionuclide adsorption.

[0029] According to the measured particle size spectrum, a soil or groundwater rock medium sample with a weight of g1 (in this embodiment, g1 is 1 g for illustration) is prepared and added to a 15 mL polypropylene centrifuge tube. Then, 9.0 mL of groundwater is added, shaken, and allowed to stand for seven days.

[0030] Since the particle size distribution of soil or groundwater rock media will affect the adsorption characteristics of radioactive nuclides in soil or groundwater rock media, the rock media used in the test are prepared according to the on-site rock media particle size spectrum to keep it consistent with the on-site conditions and increase the representativeness of the calculation results.

[0031] Add volume V1 (in this example, V1 is 1 mL) of radioactive nuclide source liquid to a 15 mL polypropylene centrifuge tube to make the volume 10 mL. -1 of NaOH and 0.1 mol·L -1 The pH value of the source solution was adjusted by adding HCl to keep it consistent with the measured groundwater. At least five samples of the radionuclide-groundwater-rock medium system with different initial concentrations (denoted as C0) were prepared.

[0032] Step S1 includes the following sub-steps:

[0033] S101. Place the centrifuge tube in an oscillation box and oscillate the radionuclide-groundwater-rock medium system sample at a temperature of T = 25°C until adsorption equilibrium is reached.

[0034] When the difference between two consecutive nuclide concentration measurement results of the sample solution is less than 10%, the system can be considered to have reached an adsorption equilibrium state. Of course, other means can be used to make the sample solution reach an adsorption equilibrium state, which is not limited to this.

[0035] S102. Place the centrifuge tube in a centrifuge at a speed of 5000 r / min and centrifuge for 40 min to separate the solid and liquid of the sample, and take a volume V2 (in this embodiment, V2 is 10 mL as an example for illustration) of the supernatant.

[0036] The centrifuge speed is determined according to the minimum particle size of the rock and soil medium sample.

[0037] S103. Filter 10 mL of the separated supernatant through a 0.45 μm microporous filter membrane and determine the equilibrium concentration Ce1 of the nuclide in the filtrate.

[0038] The particle size of suspended matter is generally larger than 0.45 μm, so the suspended matter in the supernatant can be filtered out by filtering the supernatant with a microporous filter membrane with a pore size of 0.45 μm.

[0039] After determining the equilibrium concentration Ce1 of the nuclide in the filtrate, the unit adsorption amount qe1 of the geotechnical medium is calculated based on the difference between the initial concentration C0 and the equilibrium concentration Ce1, qe1 = (C0×V1-Ce1×V2) / g 1。

[0040] Then, based on the obtained data of the equilibrium concentration Ce1 of the sample solution with different initial concentrations and the unit adsorption amount qe1 of the rock and soil medium, data fitting is performed to obtain the adsorption isotherm of the system;

[0041] In step S2, the process of treating the rock and soil medium obtained by solid-liquid separation of the system in the adsorption equilibrium state to obtain a desorption isotherm includes the following sub-steps:

[0042] S201. A volume of V3 of groundwater (10 mL in this embodiment) is added to the rock and soil medium obtained after solid-liquid separation. The system is then oscillated at a constant temperature until desorption equilibrium is reached. Solid-liquid separation is then performed on the radionuclide-groundwater-rock and soil medium system at desorption equilibrium. This step is repeated three times for illustrative purposes only, but this is not intended to be limiting.

[0043] S202, the equilibrium concentration of the last desorption sample solution is recorded as Ce2, the remaining unit adsorption capacity of the rock and soil medium is recorded as qe2, and the data are fitted to obtain the desorption isotherm of the system;

[0044] The equilibrium concentration Ce2 of the desorbed sample solution and the residual unit adsorption capacity qe2 of the rock and soil medium can both be measured by instruments.

[0045] In step S3, the "adsorption hysteresis area S" is solved by a graphical method according to the adsorption isotherm and the desorption isotherm, and the adsorption reversibility, the reversible adsorption amount, and the irreversible adsorption amount are calculated accordingly.

[0046] like Figure 1 As mentioned above, the area between the adsorption and desorption isotherms of a nuclide in soil and groundwater geotechnical media is defined as the "adsorption hysteresis area S." The size of this area quantifies the reversibility of the adsorption system. When S is zero, the adsorption and desorption isotherms coincide, indicating reversible adsorption of the nuclide in the soil and groundwater geotechnical media. When S is not zero, the nuclide is irreversibly adsorbed in the soil and groundwater geotechnical media. A larger S indicates a higher degree of irreversibility.

[0047] The total adsorption capacity of the rock and soil medium is qe1×g1. The intersection of the line connecting the two points in the adsorption stage (Ce1, qe1) and the desorption stage (Ce2, qe2) and the vertical coordinate is recorded as (Ce3, qe3). The irreversible adsorption capacity is qe3×g1, and the reversible adsorption capacity is (qe1-qe3)×g1.

[0048] In this embodiment, the nuclide 90 Sr. 137 The calculation of the reversibility of Cs adsorption in strongly weathered biotite granodiorite is used as an example to illustrate the problem.

[0049] The step of obtaining the adsorption isotherm in step S1 includes obtaining 5 different initial concentrations according to the above steps. 90 Sr. 137 The adsorption characteristics of Cs in the strongly weathered biotite granodiorite-groundwater system are shown in Table 1.

[0050] Table 1 Nuclides in strongly weathered biotite granodiorite 90 Sr. 137 Cs adsorption characteristics data

[0051]

[0052]

[0053] like Figure 2-1 and Figure 2-2 As shown, the data in Table 1 were fitted with the Freundlich adsorption isotherm to obtain the corresponding adsorption isotherm and the fitting parameter K in Table 2 were obtained. F and β, and the linear correlation coefficient R 2 .

[0054] Table 2 Strongly weathered biotite granodiorite 90 Sr. 137 Cs adsorption fitting parameters

[0055] Nuclide β <![CDATA[K F (mL·g -1 )]]> <![CDATA[R 2 <!-- 4 -->]]> <![CDATA[ 90 Sr]]> 0.98 47.42 1.00 <![CDATA[ 137 Cs]]> 1.00 6872.21 0.96

[0056] At 5 different initial concentrations, 90 Sr. 137 The desorption characteristics of Cs in the strongly weathered biotite granodiorite-groundwater system are shown in Table 3.

[0057] Table 3 Strongly weathered biotite granodiorite 90 Sr. 137 Cs desorption characteristic data

[0058]

[0059] like Figure 3-1 and Figure 3-2 As shown, the data in Table 3 were fitted with the Freundlich desorption isotherm to obtain the corresponding desorption isotherm, and the fitting parameters K in Table 4 were obtained. F and β, and the linear correlation coefficient R 2 .

[0060] Table 4 Strongly weathered biotite granodiorite 90 Sr. 137 Cs desorption fitting parameters

[0061] Nuclide β <![CDATA[K F (mL·g -1 )]]> <![CDATA[R 2 ]]> <![CDATA[ 90 Sr]]> 1.06 37.66 0.99 <![CDATA[ 137 Cs]]> 1.00 9469.11 1.00

[0062] The step of calculating adsorption reversibility according to the adsorption isotherm and the desorption isotherm in step S3 includes:

[0063] like Figure 4-1 and Figure 4-2 As shown, according to Figure 2-1 and Figure 2-2 The adsorption isotherms and Figure 3-1 and Figure 3-2The desorption isotherms in 90 Sr. 137 The adsorption hysteresis area S of Cs in strongly weathered biotite granodiorite. After calculation, 90 The adsorption hysteresis area of ​​Sr is 0. 137 The adsorption hysteresis area of ​​Cs is 0.3980. In terms of the irreversibility of adsorption, 90 Sr< 137 Cs, 90 Sr is adsorbed almost reversibly in strongly weathered biotite granodiorite.

[0064] Table 5 90 Sr. 137 Calculation of hysteresis area of ​​Cs adsorption in strongly weathered biotite granodiorite

[0065]

[0066] As can be seen from the above examples, the present invention discloses a method for calculating the reversibility of radionuclide adsorption. By defining the area between the adsorption and desorption isotherms of a nuclide in soil and groundwater geotechnical media as the "adsorption hysteresis area S," this area is used to quantify the reversibility of radionuclide adsorption in soil and groundwater geotechnical media and to determine the magnitude of radionuclide adsorption reversibility. The adsorption capacity of a nuclide is the sum of the reversible and irreversible adsorption capacities. This method can be used to separately determine the reversible and irreversible adsorption capacities, laying the foundation for accurate and scientific assessment of the fate of radionuclides in soil and groundwater environments, and is of great significance for the remediation and remediation of radioactively contaminated sites.

[0067] The method described in the present invention is not limited to the embodiments described in the specific implementation manner. Those skilled in the art may derive other implementation manners based on the technical solution of the present invention, which also fall within the scope of the technical innovation of the present invention.

Claims

1. A method for calculating the reversibility of radionuclide adsorption, the method comprising the following steps: S1, by preparing different initial concentrations C 0 The radionuclide-groundwater-rock medium system sample is treated to an adsorption equilibrium state, and the radionuclide-groundwater-rock medium system sample in the adsorption equilibrium state is subjected to solid-liquid separation. The equilibrium concentration of the sample solution obtained after solid-liquid separation is recorded as Ce 1 , according to the equilibrium concentration Ce of the sample solution 1 With the initial concentration C 0 The unit adsorption capacity qe of the rock medium sample is obtained by using the data 1 Data, and then according to the obtained multiple groups of different initial concentrations of the sample solution equilibrium concentration Ce 1 The unit adsorption amount qe of the rock medium sample 1 Data, performing data fitting to obtain the adsorption isotherm of the radionuclide-groundwater-rock medium system; S2. Add the rock and soil medium obtained after solid-liquid separation back into groundwater and treat it to a desorption equilibrium state. Perform solid-liquid separation on the radionuclide-groundwater-rock and soil medium system sample in the desorption equilibrium state. Repeat this step several times. The equilibrium concentration of the last desorption sample solution is recorded as Ce. 2 The remaining unit adsorption capacity of the rock and soil medium is recorded as qe 2 , performing data fitting to obtain the desorption isotherm of the radionuclide-groundwater-rock medium system; S3, according to the adsorption isotherm and desorption isotherm of the radionuclide-groundwater-rock medium system, the "adsorption hysteresis area S" is solved by a graphical method, and the reversible adsorption amount and the irreversible adsorption amount are calculated accordingly; The different initial concentrations C in step S1 0 The weight of the rock medium sample of the radionuclide-groundwater-rock medium system is recorded as g. 1 In step S3, the method for calculating the reversible adsorption amount and the irreversible adsorption amount is as follows: 1 ,qe 1 ) and desorption stage (Ce 2 ,qe 2 The intersection of the line connecting the two points and the ordinate is denoted as (Ce 3 ,qe 3 ), irreversible suction capacity qe 3 ×g 1 , the reversible adsorption capacity is (qe 1 -qe 3 )×g 1 .

2. A method for calculating the reversibility of radionuclide adsorption as claimed in claim 1, Features: In step S1, different initial concentrations C 0 Before testing the radionuclide-groundwater-rock medium system samples, the test containers were treated with acid to reduce the adsorption of nuclides on the container wall.

3. A method for calculating the reversibility of radionuclide adsorption as claimed in claim 1, Features: In step S1, different initial concentrations C are prepared 0 Before sampling the radionuclide-groundwater-rock medium system, the particle size distribution of the on-site rock medium is determined. The rock medium used in the test is prepared using a particle size spectrum to keep it consistent with the on-site conditions and increase the representativeness of the calculation results.

4. A method for calculating the reversibility of radionuclide adsorption as claimed in claim 1, Features: The radioactive nuclide-groundwater-rock medium system achieves adsorption equilibrium and desorption equilibrium by means of constant temperature oscillation.

5. A method for calculating the reversibility of radionuclide adsorption as claimed in claim 4, Features: When the difference between two consecutive nuclide concentration measurement results is less than a preset threshold, it is determined that the adsorption equilibrium state and the desorption equilibrium state are reached.

6. A method for calculating the reversibility of radionuclide adsorption as claimed in claim 1, Features: When performing solid-liquid separation on a radionuclide-groundwater-rock medium system sample that has reached adsorption equilibrium and desorption equilibrium, the centrifuge speed is determined according to the minimum particle size of the rock medium sample.

7. A method for calculating the reversibility of radionuclide adsorption as claimed in claim 1, Features: For the different initial concentrations C 0 The radionuclide-groundwater-rock medium system is adjusted with specific acid solution and / or alkaline solution.

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