Method for determining the parameters of an acidic functional chelating resin

Abstract

This invention provides a method for determining the property parameters of acidic functional group chelating resins based on potentiometric titration, comprising the following steps: preparing a potentiometric titration system including an acidic functional group chelating resin and an acidic titration medium; performing potentiometric titration using a titrant to obtain the electrode potential at titration equilibrium; and obtaining the property parameters of the acidic functional group chelating resin based on the electrode potential. The measurement method of this invention has high accuracy.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry, and more specifically to a method for determining the property parameters of acidic functional group chelating resins. Background Technology

[0002] Acidic functional group chelating resins have strong chelating ability for metal ions, such as rare earth metal ions, good stability, are readily available and inexpensive, and have wide applications in enrichment, concentration, separation and purification of metal ions.

[0003] In these types of resins, functional groups containing metal ion-chelating functional groups (i.e., acidic functional groups) are grafted onto the resin backbone. The higher the grafting rate of the functional groups in the resin, the greater the amount of metal ions bound, and the better the chelation and adsorption performance. The grafting rate is one of the most important parameters for evaluating resin performance.

[0004] Currently, methods for determining the grafting rate of functional groups in acidic functional group chelating resins include gravimetric methods, acid-base titration methods, and determination of saturated adsorption capacity for metal ions. Gravimetric methods calculate the grafting content by measuring the weight difference before and after chemical grafting, but are easily affected by byproducts and residual chemical reagents from the preparation process, leading to significant measurement errors. In acid-base titration methods, for some acidic functional groups, such as ethylenediaminetriacetic acid, whose tertiary proton dissociation constant is greater than 8, it is difficult to determine the titration endpoint. Furthermore, the saturated adsorption capacity method is affected by factors such as adsorption temperature and pH, and the measured results are often lower than the functional group grafting rate. These methods are insufficient to obtain accurate functional group grafting rates in resins.

[0005] Therefore, a method is needed to accurately determine performance parameters such as the functional group grafting rate in acidic functional group chelating resins. Summary of the Invention

[0006] In view of this, the main objective of the present invention is to provide a method for accurately determining performance parameters such as the functional group grafting rate in acidic functional group chelating resins.

[0007] Therefore, the present invention provides a method for determining the property parameters of acidic functional group chelating resins based on potentiometric titration, comprising the following steps:

[0008] Prepare an initial potentiometric titration system comprising an acidic functional group chelating resin and an acidic titration medium;

[0009] Potentiometric titration was performed using a titrant to obtain the electrode potential at equilibrium of the titration reaction; and

[0010] Based on the electrode potential, the property parameters of the acidic functional group chelating resin are obtained.

[0011] In some embodiments, the step of using a titrant to perform potentiometric titration to obtain the electrode potential at reaction equilibrium includes: performing potentiometric titration with the titrant at a set titration interval and titration step size to obtain the electrode potential at equilibrium of a set number of titration reactions.

[0012] In some embodiments, the set titration interval is greater than or equal to the titration reaction equilibrium time t0; preferably, the set titration interval is greater than 1.25t0.

[0013] In some embodiments, the titration step size is 0.02-0.05 ml.

[0014] In some embodiments, obtaining the property parameters of the acidic functional group chelating resin based on the electrode potential includes:

[0015] Based on the electrode potential, the concentrations of each species in the titration system at titration equilibrium are obtained; and

[0016] Based on the concentration of each species, the property parameters of the acidic functional group chelating resin were obtained.

[0017] In some embodiments, the property parameters include at least one of the grafting rate of the acidic functional group chelating resin and the protonation constant of the acidic functional groups in the acidic functional group chelating resin.

[0018] In some embodiments, obtaining the electrode potential at titration equilibrium includes collecting at least 10 electrode potentials at titration equilibrium.

[0019] In some embodiments, the equilibrium time t0 of the titration reaction is achieved through pre-titration; the pre-titration includes titrating with the same initial titration system and titrant as the potentiometric titration, and testing the time required for the titration reaction to reach equilibrium.

[0020] In some embodiments, the acidic titration medium comprises a mixed solution of a first perchlorate and perchloric acid of known concentration; the titrant comprises a mixed solution of a base and a second perchlorate of known concentration.

[0021] In some embodiments, the acidic functional group chelating resin is selected from resins containing carboxyl functional groups; preferably selected from ethylenediamine triacetic acid chelating resin, hyponitrotriacetic acid chelating resin, iminodiacetic acid chelating resin, and polyglycidyl methacrylate resin.

[0022] The method of this invention utilizes potentiometric titration to obtain electrode potential data during the titration process. By processing the data, the concentration and distribution of each species in the titration system are obtained. Based on this species and concentration data, performance parameters such as the grafting rate and protonation constant of the acidic functional group chelating resin are derived. Potentiometric titration provides accurate electrode potentials, rather than relying on pH jumps to determine the titration endpoint as in existing techniques. This improves the accuracy of data measurement and consequently enhances the accuracy of the measured resin performance parameters. Attached Figure Description

[0023] Figure 1 The potentiometric titration pH change curve and the distribution map of H3A protonated species at various levels obtained in Example 1 of this invention are shown.

[0024] Figure 2 The potentiometric titration pH change curve and the distribution diagram of H3A protonated species at various levels obtained in Example 2 of this invention are shown.

[0025] Figure 3 The potentiometric titration pH change curve and the distribution map of protonated species of H2A at various levels obtained in Example 3 of this invention are shown. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0028] It should be noted that, in the embodiments of the present invention, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a method or apparatus that includes a list of elements includes not only the elements expressly stated, but also other elements not expressly listed, or elements inherent to implementing the method or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other related elements in the method or apparatus that includes that element.

[0029] definition

[0030] The term "potential titration" in this document refers to a titration method that uses the measurement of changes in solution potential to indicate the endpoint. During titration, two electrodes connected to a potentiometer are inserted into the titrant; one is a reference electrode, and the other is an index electrode. Based on different titration reaction principles, potentiometric titration can be classified into, for example, pH potentiometric titration, redox titration, precipitation titration, and complexometric titration. In this invention, potentiometric titration can be performed using instruments or devices known to those skilled in the art, such as a pH potentiometric titrator.

[0031] The term "initial titration system" as used herein refers to the mixed solution comprising the titrant and the acidic functional group chelating resin contained in the titration apparatus before the titration reaction begins. "Titration system" refers to the mixed system formed after the addition of a titrant to the initial titration system and the reaching of titration equilibrium. In this invention, the titrant comprises the acidic functional group chelating resin and the titration medium. The term "titting medium" as used herein refers to the solution that provides the titration reaction environment for the functional groups on the acidic functional group chelating resin.

[0032] The term "electrode potential" in this article refers to the potential value of the titration system measured by the index electrode of the potentiometric titrator.

[0033] The term "titration equilibrium" in this article refers to the equilibrium state reached when the functional groups in the titrant and the titrant in the titrant reach a stable state, meaning that the types and contents of each substance in the titration system are stable and no longer change.

[0034] The term "titration equilibrium time" in this article refers to the time interval, denoted as t0, during which the electrode potential of the titration system reaches a stable state again after a certain amount of titrant has been added. In this article, "titration equilibrium time" and "time for the titration reaction to reach equilibrium" can be used interchangeably.

[0035] The term "electrode potential at titration equilibrium" in this paper refers to the electrode potential measured when the titration system reaches equilibrium. In this invention, the equilibrium state of the titration reaction is determined by the change in electrode potential measured by a potentiometric titrator; a stable electrode potential indicates that the titration reaction has reached equilibrium. In this invention, the equilibrium state of the electrode potential is defined as an electrode potential deviation of less than 0.1 mV and a stability of at least 30 s.

[0036] The term "titration interval" in this article refers to the time interval between two consecutive additions of titrant.

[0037] The term "titration step size" in this article refers to the amount of titrant added each time.

[0038] In existing technologies, the determination of the grafting rate of functional groups in chelating resins using acid-base titration usually relies on a pH jump to determine the titration endpoint. However, for acidic functional groups with a dissociation constant (pKa) less than 8, the reaction endpoint is easily affected by factors such as impurities, temperature, and pH, making it difficult to determine the titration endpoint and resulting in inaccurate measurements of the grafting rate.

[0039] Furthermore, existing technologies typically employ batch experiments using solutions with varying pH gradients to investigate the effect of pH on the adsorption of metal ions by aminocarboxylic acid chelating resins and to determine the optimal adsorption or separation pH. However, when the application scenario changes, for example: changes in the type and concentration of metal ions; interference from organic ligands such as lactic acid, glycolic acid, and citric acid; Cl... - NO3 - Changes in the concentrations of inorganic and organic ligands often necessitate readjusting batch experimental conditions to obtain the optimal pH.

[0040] In view of this, the present invention provides a method for determining the property parameters of acidic functional group chelating resins based on potentiometric titration. The method includes the following steps:

[0041] Prepare an initial titration system comprising an acidic functional group chelating resin and an acidic titration medium;

[0042] Potentiometric titration was performed using a titrant, and the electrode potentials at equilibrium of the titration reaction were collected; and

[0043] Based on the electrode potential, the property parameters of the acidic functional group chelating resin are obtained.

[0044] The method of this invention utilizes potentiometric titration to acquire electrode potential data of the titration system during the titration process, and obtains the performance parameters of acidic functional group chelating resins based on the obtained electrode potential data. The analytical method of this invention is applicable to aminocarboxylic acid functional group chelating resins and other acidic chelating resins, and can provide fundamental thermodynamic data and theoretical support for constructing chelating resin adsorption models and designing novel chelating resins.

[0045] The method for determining the properties of acidic functional group chelating resins in this invention has at least the following advantages when applied to constructing chelating resin adsorption models: 1) Potentiometric titration measures the effect of pH on adsorption by gradually increasing pH, enabling measurements under higher pH conditions while avoiding interference from hydrolysis; 2) When constructing chelating resin adsorption models, the resin can achieve solid-liquid separation after adsorbing metal ions through centrifugation, facilitating the setting of specific adsorption conditions for batch experiments. This allows for the measurement of changes in the concentration of free target metal ions and hydrogen ions (pH) in the solution after adsorption, which can then be compared with the results obtained through simulation calculations using Hyss software combined with speciation models and stability constants, ensuring the accuracy of the coordination model; 3) The speciation model, validated through batch experiments, combined with Hyss software simulation calculations, is applicable to multiple application scenarios, such as the treatment of uranium-contaminated wastewater and the separation and purification of uranium ore. Studying the coordination model between acidic functional groups on the resin surface and target metal ions using potentiometric titration not only overcomes the limitations of traditional methods but also provides a theoretical foundation and technical support for a deeper understanding of the interaction mechanism between aminocarboxylic acid chelating resins and metal ions, and for expanding its applications in fields such as the nuclear industry.

[0046] In this invention, the potentiometric titration is performed using pH potentiometric titration. The pH of the titration system changes due to an acid-base reaction, and the electrode potential of the titration system is collected using a pH electrode. The pH electrode potential in the titration system is... With H + The concentration relationship is shown in Equation 1.

[0047]

[0048] In the formula: R is the standard electrode potential; F is the standard gas constant; T is the Faraday constant; and T is the temperature in K.

[0049] Potentiometric titration provides accurate electrode potentials, rather than relying on pH jumps as in traditional techniques to determine the titration endpoint. This improves the accuracy of data measurement and consequently enhances the accuracy of the measured resin performance parameters. For example, ethylenediaminetriacetic acid (EDTA) is a weak acid; when its solution pH reaches 10, its carboxyl protons are not completely dissociated, making it impossible to accurately determine the titration endpoint using pH jumps as in traditional techniques. The method of this invention utilizes the relationship between electrode potential, pH value, and protonation constant, combined with multiple electrode potential data points collected during multiple titration reactions reaching chemical equilibrium. Software analysis is then used to obtain the amount of EDTA n0 and H in the initial solution. + The amount of n1 and the protonation constant of surface-functionalized ethylenediamine triacetic acid are obtained, thus eliminating the need to rely on other parameters to determine whether the reaction has reached equilibrium, and the larger sample size of the data further improves the accuracy of the calculation results.

[0050] In some embodiments, the acidic titration medium comprises a mixed solution of a first perchlorate and perchloric acid of known concentration. Perchloric acid is an inorganic compound with the chemical formula HClO4, possessing extremely strong acidity. It is almost completely ionized in aqueous solution, existing as hydrogen ions and perchlorate ions, which undergo almost no hydrolysis in aqueous solution. Furthermore, both perchloric acid and perchlorate exhibit good stability, are not easily decomposed or deteriorated, and do not readily react with metal ions adsorbed on the acidic functional group chelating resin. Using a mixed solution of perchloric acid and perchlorate as the titration medium reduces the influence of the titration medium on the pH titration reaction, ensuring that changes in hydrogen ion concentration in the titration system are almost solely due to acid-base reactions occurring on the acidic functional groups chelated on the chelating resin during the titration process, thereby improving the accuracy of the measurement.

[0051] In some embodiments, the concentration of the first perchlorate in the acidic titration medium is 1.00-1.20 mol / L; the concentration of the perchloric acid is 0.005-0.010 mol / L.

[0052] In some embodiments, the titrant comprises a mixture of a base and a second perchlorate at a known concentration. The base in the titrant reacts with the acidic functional groups on the chelating resin, thereby allowing performance data of the chelating resin to be obtained based on the acid-base reaction and the changes in electrode potential collected in the titration system.

[0053] In some embodiments, the concentration of the alkali in the titrant is 0.100-0.200 mol / L; and the concentration of the second perchlorate is 0.80-0.90 mol / L.

[0054] In some embodiments, the first perchlorate and the second perchlorate are each independently selected from alkali metal salts and alkaline earth metal salts. Since alkali metals undergo almost no hydrolysis, their effect on the hydrogen ion concentration in the titration system is negligible, thereby improving measurement accuracy. In some embodiments, the first perchlorate and the second perchlorate are each independently selected from lithium salts, sodium salts, and potassium salts; preferably, sodium salts.

[0055] In some embodiments, the base is selected from hydroxides of alkali metals and alkaline earth metals. Using these bases avoids the influence of metal cations on the titration system, thereby improving measurement accuracy. In some embodiments, the base is selected from sodium hydroxide, lithium hydroxide, and hydroxide agents; preferably, sodium hydroxide.

[0056] In some embodiments, the cation concentration in the acidic titration medium and / or titrant is 0.900-1.005 mol / L. Those skilled in the art can adjust the concentration of each component in the acidic titration medium and / or titrant as needed, and this invention does not impose specific limitations in this regard.

[0057] In some preferred embodiments, the acidic titration medium is a mixed solution of 0.005 mol / L HClO4 and 1 mol / L NaClO4.

[0058] In some preferred embodiments, the titrant is a 0.1 mol / L NaOH-0.9 mol / L NaClO4 solution.

[0059] In some embodiments, the acidic functional group chelating resin is swollen using an acidic titration medium before use. This swelling treatment with a titration medium stabilizes the resin volume in solution, reducing changes in the titration system, such as solution volume changes, during titration. It also fully exposes the functional groups within the resin, allowing for a more complete reaction with the titrant during titration, thus improving measurement accuracy. The swelling treatment involves mixing the chelating resin and the acidic titration medium at a volume ratio of 1:1.5 to 1:4 and allowing it to swell at room temperature for 20-30 hours.

[0060] In some embodiments, the acidic functional group chelating resin is selected from ethylenediamine triacetic acid chelating resin, hyponitrotriacetic acid chelating resin, iminodiacetic acid chelating resin, and polyglycidyl methacrylate resin.

[0061] In some embodiments, the potentiometric titration using a titrant to collect the electrode potential at reaction equilibrium includes:

[0062] Using a predetermined titration interval and titration step size, potentiometric titration is performed with the titrant to obtain the electrode potentials at equilibrium for a predetermined number of titration reactions. The predetermined titration interval is greater than or equal to the titration reaction equilibrium time t0. Through continuous potentiometric titration, the electrode potentials of multiple titration systems after reaching equilibrium are obtained. Based on the obtained multiple accurate electrode potential data, the concentration changes of each species during the titration process can be obtained, which is beneficial for more accurate analysis of the performance parameters of the chelating resin and improves the accuracy of the measurement results.

[0063] In some implementations, the equilibrium time t0 of the titration reaction is obtained by pre-titering with a titrant. The titration test is performed using the same initial potentiometric titration system and titrant as in potentiometric titration, and the time required for the titration reaction to reach equilibrium is recorded as t0. To obtain a more accurate equilibrium time, the titration can be repeated multiple times, and the average value is taken.

[0064] In some embodiments, the potentiometric titration is performed in a temperature range of 10-35°C. Preferably, the potentiometric titration is performed at 25.0 ± 0.1°C.

[0065] In some embodiments, the set titration interval is greater than 1.25t0, preferably 1.25t0-1.50t0. By setting the titration interval within the above range, the titration reaction is fully balanced after each titration, thereby acquiring more accurate electrode potential data at titration reaction equilibrium, which further helps to improve the accuracy of the measurement.

[0066] In some embodiments, the set titration step size is 0.02 mL to 0.05 mL. Using this titration step size allows for a measurable change in the electrode potential of the titration system after titration. Furthermore, adding only a small amount of titrant allows the titration reaction to reach equilibrium more quickly, which is beneficial for improving measurement efficiency.

[0067] In some embodiments, collecting a set number of electrode potentials at titration equilibrium includes collecting at least 10 electrode potentials at titration equilibrium. The number of electrode potentials collected at titration equilibrium in this invention is determined based on the number of acidic functional groups, such as carboxyl groups, on the acidic functional group chelating resin being measured. For example, if the acidic functional group on the acidic functional group chelating resin is an n-basic acid, then the number of electrode potential data collected is (10-15)n, where n = 1, 2, 3... In a preferred embodiment, 20-60 electrode potentials at titration equilibrium are collected. Collecting a sufficient number of electrode potentials helps reduce measurement errors and improves the accuracy of the measured performance parameters. Furthermore, it reduces the total volume of the solution in the titration system, saving costs.

[0068] In some embodiments, obtaining the property parameters of the acidic functional group chelating resin based on the electrode potential includes:

[0069] Based on the electrode potential, the concentrations of each species in the titration system at titration equilibrium are obtained; and

[0070] Based on the concentration of each species, the property parameters of the acidic functional group chelating resin were obtained.

[0071] In one example, the determination of species concentrations at titration equilibrium based on the electrode potential is achieved using Hyperquad software, but this is not the only method. The collected electrode potential data is imported into Hyperquad software, which solves the nonlinear simultaneous mass balance equations using the Newton-Raphson method, thereby calculating the concentrations of each species in the titration system. Based on the calculated concentrations of the titrant species, the property parameters of the acidic functional group chelating resin can be obtained.

[0072] In some embodiments, the property parameters include the grafting rate of the acidic functional group chelating resin and the protonation constant of the acidic functional groups in the acidic functional group chelating resin.

[0073] In one example, the grafting functional group is ethylenediaminetriacetic acid (EDTA), which illustrates the calculation method for the grafting rate and protonation constant. It should be understood that different software can be used to obtain the corresponding parameters through different calculation methods. The grafting rate of the acidic functional group chelating resin can be calculated using formula (2):

[0074] Grafting rate = (n0*M / m)*100% (2)

[0075] In the formula, n0 is the amount (mol) of ethylenediaminetriacetic acid in the initial potentiometric titration system calculated by Hyperquad software, M is the molar mass (g / mol) of ethylenediaminetriacetic acid which is 234.21 g / mol, and m is the mass (g) of the resin in the potentiometric titration.

[0076] Taking ethylenediaminetriacetic acid (H3A) as the grafted functional group as an example, its protonation reaction is shown in formula (3):

[0077] A 3- + rH + = H r A (r-3) (r=1,2,3) (3)

[0078] The protonation constants of its acidic functional groups can be calculated using formula (4):

[0079] Protonization constant

[0080] In the formula, [H r A (r-3) [H] is the H that is produced when the reaction reaches equilibrium. r A (r-3) Species concentration, [A 3- ] is A 3- Species concentration, [H + ] is H + Species concentration.

[0081] The present invention will be described in detail below through specific embodiments. It should be understood that the following embodiments are merely illustrative and should not be construed as limiting the scope of the present invention.

[0082] Example

[0083] The instruments used in the following examples are as follows: Automatic pH potentiometric titrator: 907-1 Titrando automatic pH potentiometric titrator, Metrohm, Switzerland; Analytical balance: BT125D analytical balance with an accuracy of 0.00001g, Sartorius, Germany.

[0084] Example 1

[0085] Pretreatment of resin: Ethylenediamine triacetic acid chelating resin (resin is polyglycidyl methacrylate resin) was washed sequentially with deionized water, ethanol and acetone, dried under vacuum at 50℃ for 24h, washed with an appropriate volume of 2mol / L HCl solution, and then washed with deionized water until the effluent was neutral, and dried under vacuum at 50℃ for 24h.

[0086] Preparation of acidic titration medium: Accurately weigh 122 g of anhydrous NaClO4, dissolve it in 1.4 L of deionized water, add 0.5 mL of concentrated HClO4 solution, boil until the remaining solution volume is 1 L, transfer the prepared solution to a blue-capped bottle, seal, and cool before use. To determine the accurate concentration of the prepared acidic titration medium, the H2O in the acidic titration medium... + The concentration was titrated with a 0.1005 mol / L NaOH standard solution. The concentration was calibrated in triplicate, and the average value was taken as 0.0056 mol / L. The acidic titration medium prepared was 0.0056 mol / L HClO4-1 mol / L NaClO4 solution.

[0087] Preparation of the titrant: Accurately weigh 122 g of anhydrous NaClO4, dissolve it in 1.4 L of deionized water, boil until the remaining solution volume is 1 L, transfer to a blue-capped bottle, cool, and then transfer to a glove box. Add 5 mL of saturated sodium hydroxide solution to prepare the titrant. To determine the accurate concentration of the titrant, attach a potentiometric titrator to the prepared titrant in a glove bag under argon protection. Accurately weigh 0.010 g of potassium hydrogen phthalate, dissolve it in deionized water, and titrate it with the prepared titrant solution. Calculate the NaOH concentration. Repeat the titration three times and take the average value as 0.1305 mol / L. The prepared titrant is a 0.1305 mol / L NaOH-0.9 mol / L NaClO4 solution.

[0088] To determine the time t0 required for the reaction to reach equilibrium during potentiometric titration: 0.2 g of resin was added to 5.00 mL of acidic titration medium and allowed to swell for 24 h. The solution was then transferred to a titration vessel, and 15.00 mL of acidic titration medium was added. A pH electrode was inserted, and the potentiometric titration was performed under argon protection. The titration vessel was placed in a constant-temperature water bath at 25.0 ± 0.1 °C. When the potential data deviation was less than 0.1 mV and exceeded 30 s, 0.50 mL of titrant solution was added for titration, and the time it took for the potential reading to stabilize again was measured. This measurement was repeated three times, and the average of the measured intervals was taken. The time t0 required for the reaction to reach equilibrium was determined to be 900 s.

[0089] Potentiometric titration: Accurately weigh 0.10271 g of resin and add it to 5.00 mL of acidic titration medium (0.0056 mol / L HClO4 - 1 mol / L NaClO4 solution). After swelling for 24 h, transfer the solution to a titration vessel, add another 15.00 mL of acidic titration medium, and perform potentiometric titration using 0.1305 mol / L NaOH - 0.9 mol / L NaClO4 solution as the titrant while stirring. Set the titration step size to 0.02 mL, the titration interval to 1200 s, and the total titration volume to 2.00 mL. Measure the potential change and collect 100 data points.

[0090] Data analysis: The potentiometric titration data were processed using Hyperquad 2014 software, and the total amount of ethylenediaminetriacetic acid in the initial titration system was calculated to be n0 = 0.0175 mmol, H... + The total amount n1 = 0.1654 mmol; the protonation constants of the surface functionalized ethylenediaminetriacetic acid of the chelating resin: logβ1 = 9.19, logβ2 = 14.72, logβ3 = 17.87, and H3A and H2A during titration. - HA 2- A 3- Species distribution map as follows Figure 1 As shown.

[0091] The grafting rate was calculated to be (n0 × M / m) × 100% = 3.99%.

[0092] In the formula, n0 is the amount (mol) of ethylenediaminetriacetic acid in the initial solution calculated by Hyperquad software, M is the molar mass (g / mol) of ethylenediaminetriacetic acid which is 234.21 g / mol, and m is the mass (g) of the resin in the potentiometric titration.

[0093] To verify the accuracy of the test results obtained by the method of the present invention, the grafting rate of the ethylenediaminetriacetic acid chelating resin was determined by back titration. 0.100 g of ethylenediaminetriacetic acid chelating resin was dispersed in 100.00 mL of 0.01 mol / L NaHCO3 standard solution (V1 = 100.00 mL) and stirred for 2 h under an Ar atmosphere. After filtration of the suspension, three aliquots of the filtrate (V2 = 20.00 mL each) were taken and titrated with 0.01 mol / L HCl standard solution. The average titration volume (V) was recorded. HCl =19.07mL.

[0094] Total amount of ethylenediaminetriacetic acid

[0095] in and c HCl V1 represents the concentrations (mol / L) of the NaHCO3 solution and the HCl solution, respectively; V2 represents the total volume (mL) of the NaHCO3 solution; V3 represents the volume (mL) of the NaHCO3 solution used for titration. HCl The average volume of titration of a 0.01 mol / L HCl standard solution.

[0096] Grafting rate = (n0 × M / m) × 100% = 3.65%

[0097] The grafting rate tested by this invention is basically consistent with the grafting rate data tested by the back titration method. It is understandable that the back titration method is a relatively common method for determining the grafting rate of ethylenediaminetriacetic acid chelating resin [1]. The problem with this method is that 0.01 mol / L NaHCO3 is not enough to completely dissociate ethylenediaminetriacetic acid, which will lead to a smaller measurement result. However, if the NaHCO3 solution is replaced with concentrated sodium hydroxide, the resin will cause a very small change in the sodium hydroxide concentration, which will lead to a larger error in the measurement result.

[0098] Example 2

[0099] Pretreatment of resin: The hyponitrotriacetic acid chelating resin (the resin is polyglycidyl methacrylate resin) was washed sequentially with deionized water, ethanol and acetone, dried under vacuum at 50°C for 24 h, washed with an appropriate volume of 2 mol / L HCl solution, and then washed with deionized water until the effluent was neutral, and then dried under vacuum at 50°C for 24 h.

[0100] To determine the time t0 required for the reaction to reach equilibrium during potentiometric titration: 0.2 g of resin was added to 5.00 mL of acidic titration medium and allowed to swell for 24 h. The solution was then transferred to a titration vessel, and 15.00 mL of acidic titration medium was added. A pH electrode was inserted, and the potentiometric titration was performed under argon protection. The titration vessel was placed in a constant-temperature water bath at 25.0 ± 0.1 °C. When the potential data deviation was less than 0.1 mV and exceeded 30 s, 0.50 mL of titrant solution was added for titration, and the time it took for the potential reading to stabilize again was measured. This measurement was repeated three times, and the average of the measured intervals was taken. The time t0 required for the reaction to reach equilibrium was determined to be 950 s.

[0101] Potentiometric titration: Accurately weigh 0.10131 g of resin and add it to 5.00 mL of 0.0056 mol / L HClO4-1 mol / L NaClO4 solution. After swelling for 24 h, transfer the solution to a titration vessel. Then add 15.00 mL of 0.0056 mol / L HClO4-1 mol / L NaClO4 solution. While stirring, perform potentiometric titration using 0.1305 mol / L NaOH-0.9 mol / L NaClO4 solution as the titrant. Set the titration step size to 0.02 mL, the titration interval to 1300 s, and the total titration volume to 2.50 mL. Measure the potential change and collect 125 data points.

[0102] Data Analysis: The potentiometric titration data were processed using Hyperquad 2014 software. The total amount of hypozinotriacetic acid in the initial potentiometric titration system was calculated to be n0 = 0.0242 mmol, and H... + The total amount n1 = 0.1844 mmol and the protonation constants of surface-functionalized hyponitrotriacetic acid: logβ1 = 9.47, logβ2 = 12.80, logβ3 = 14.98, as well as H3A and H2A during the titration process. - HA 2- A 3- Species distribution map as follows Figure 2 As shown.

[0103] The grafting rate was calculated to be (n0*M / m)*100% = 4.55%.

[0104] In the formula, n0 is the amount (mol) of hypotriacetic acid in the initial potentiometric titration system calculated by Hyperquad software, M is the molar mass (g / mol) of hypotriacetic acid (191.13 g / mol), and m is the mass (g) of the resin in the potentiometric titration.

[0105] To verify the accuracy of the test results obtained by the method of the present invention, the grafting rate of hypotriacetic acid chelating resin was determined by back titration. 0.101 g of hypotriacetic acid chelating resin was dispersed in 100.00 mL of 0.01 mol / L NaHCO3 standard solution (V1 = 100.00 mL) and stirred for 2 h under an Ar atmosphere. After filtration of the suspension, three aliquots of the filtrate (V2 = 20.00 mL each) were taken and titrated with 0.01 mol / L HCl standard solution. The average titration volume (V) was recorded. HCl =18.65mL.

[0106] Total amount of hypotriacetic acid

[0107] in and c HCl V1 represents the concentrations (mol / L) of the NaHCO3 solution and the HCl solution, respectively; V2 represents the total volume (mL) of the NaHCO3 solution; V3 represents the volume (mL) of the NaHCO3 solution used for titration. HCl The average volume of titration of a 0.01 mol / L HCl standard solution.

[0108] Grafting rate = (n0 × M / m) × 100% = 4.25%

[0109] Example 3

[0110] Pretreatment of resin: The iminodiacetic acid chelating resin (the resin is polyglycidyl methacrylate resin) was washed sequentially with deionized water, ethanol and acetone, dried under vacuum at 50°C for 24 h, washed with an appropriate volume of 2 mol / L HCl solution, and then washed with deionized water until the effluent was neutral, and then dried under vacuum at 50°C for 24 h.

[0111] To determine the time t0 required for the reaction to reach equilibrium during potentiometric titration: 0.2 g of resin was swollen in 5.00 mL of acidic titration medium for 24 h, then transferred to a titration vessel. 15.00 mL of acidic titration medium was added to the vessel, and a pH electrode was inserted. The potentiometric titration was performed under argon protection, with the titration vessel placed in a constant-temperature water bath at 25.0 ± 0.1 °C. When the potential data deviation was less than 0.1 mV and exceeded 30 s, 0.50 mL of titrant solution was added for titration, and the time it took for the potential reading to stabilize again was measured. This measurement was repeated three times, and the average of the measured intervals was taken. The time t0 required for the reaction to reach equilibrium was determined to be 700 s.

[0112] Potentiometric titration: Accurately weigh 0.10228 g of resin and add it to 5.00 mL of 0.0056 mol / L HClO4-1 mol / L NaClO4 solution. After swelling for 24 h, transfer the solution to a titration vessel. Then add 15.00 mL of 0.0056 mol / L HClO4-1 mol / L NaClO4 solution. While stirring, perform potentiometric titration using 0.1305 mol / L NaOH-0.9 mol / L NaClO4 solution as the titrant. Set the titration step size to 0.02 mL, the titration interval to 1000 s, and the total titration volume to 2.50 mL. Measure the potential change and collect 125 data points.

[0113] Data analysis: Potentiometric titration data were processed using Hyperquad 2014 software. The total amount of iminodiacetic acid in the initial potentiometric titration system was calculated to be n0 = 0.0308 mmol, and H... + The total amount n1 = 0.1737 mmol and the protonation constants of surface-functionalized iminodiacetic acid: logβ1 = 8.59, logβ2 = 10.83, as well as H2A and HA during titration. - A 2- Species distribution map as follows Figure 3 As shown.

[0114] The grafting rate was calculated to be (n0*M / m)*100% = 3.98%.

[0115] In the formula, n0 is the amount (mol) of iminodiacetic acid in the initial potentiometric titration system calculated by Hyperquad software, M is the molar mass (g / mol) of iminodiacetic acid (132.1 g / mol), and m is the mass (g) of the resin in the potentiometric titration.

[0116] To verify the accuracy of the test results obtained by the method of the present invention, the grafting rate of iminodiacetic acid chelating resin was determined by back titration. 0.105 g of iminodiacetic acid chelating resin was dispersed in 100.00 mL of 0.01 mol / L NaHCO3 standard solution (V1 = 100.00 mL) and stirred for 2 h under an Ar atmosphere. After filtration of the suspension, three aliquots of the filtrate (V2 = 20.00 mL each) were taken and titrated with 0.01 mol / L HCl standard solution. The average titration volume (V) was recorded. HCl =18.86mL.

[0117] Total amount of iminodiacetic acid

[0118] in and c HClV1 represents the concentrations (mol / L) of the NaHCO3 solution and the HCl solution, respectively; V2 represents the total volume (mL) of the NaHCO3 solution; V3 represents the volume (mL) of the NaHCO3 solution used for titration. HCl The average volume of titration of a 0.01 mol / L HCl standard solution.

[0119] Grafting rate = (n0 × M / m) × 100% = 3.59%

[0120] [References]

[0121] [1]Huang J,Ye M,Qu Y,et al.Pb(II)removal from aqueous media by EDTA-modified mesoporous silica SBA-15[J].Journal of Colloid And InterfaceScience,2012,385(1):137-146.

[0122] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for determining the property parameters of acidic functional group chelating resins based on potentiometric titration, comprising the following steps: Prepare an initial potentiometric titration system comprising an acidic functional group chelating resin and an acidic titration medium, wherein the acidic functional group chelating resin has a tertiary proton dissociation constant greater than 8, and the acidic functional group chelating resin is selected from resins containing carboxyl functional groups; the acidic titration medium comprises a mixed solution of sodium perchlorate and perchloric acid of known concentration. Potentiometric titration was performed using a titrant comprising a mixed solution of sodium hydroxide and sodium perchlorate of known concentrations to obtain the electrode potential at equilibrium of the titration reaction; and Based on the electrode potential, the property parameters of the acidic functional group chelating resin are obtained, wherein the property parameters include at least one of the grafting rate of the acidic functional group chelating resin and the protonation constant of the acidic functional group in the acidic functional group chelating resin.

2. The method according to claim 1, wherein, The step of using a titrant for potentiometric titration to obtain the electrode potential at reaction equilibrium includes: Potentiometric titration is performed using the titrant at set titration intervals and titration steps to obtain the electrode potential at equilibrium of a set number of titration reactions.

3. The method according to claim 2, wherein, The set titration interval is greater than or equal to the titration reaction equilibrium time t0.

4. The method according to claim 3, wherein, The set titration time interval is greater than 1.25t0.

5. The method according to any one of claims 2 to 4, wherein, The titration step size is 0.02-0.05 ml.

6. The method according to claim 1, wherein, The property parameters of the acidic functional group chelating resin obtained based on the electrode potential include: Based on the electrode potential, the concentrations of each species in the titration system at titration equilibrium are obtained; and Based on the concentration of each species, the property parameters of the acidic functional group chelating resin were obtained.

7. The method according to claim 1, wherein, The process of obtaining the electrode potential at titration equilibrium includes collecting the electrode potential at at least 10 titration equilibrium reactions.

8. The method according to claim 3, wherein, The equilibrium time t0 of the titration reaction is determined by pre-titration; the pre-titration includes titrating with the same initial titration system and titrant as the potentiometric titration, and testing the time required for the titration reaction to reach equilibrium.

9. The method according to claim 1, wherein, The acidic functional group chelating resin is selected from ethylenediamine triacetic acid chelating resin, hyponitrotriacetic acid chelating resin, iminodiacetic acid chelating resin, and polyglycidyl methacrylate resin.

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