Method for determining property parameters of acidic functional group chelate resin

Abstract

The invention provides a potentiometric titration-based method for measuring property parameters of acidic functional group chelating resin. The method comprises the following steps: preparing a potentiometric titration system comprising the acidic functional group chelating resin and an acidic titration medium; carrying out potentiometric titration by adopting a titrant to obtain an electrode potential when a titration reaction is balanced; and obtaining property parameters of the acidic functional group chelate resin based on the electrode potential. The measurement method is high in accuracy.

Description

Technical Field

[0001] The invention relates to the field of analytical chemistry, in particular to a method for measuring property parameters of an acidic functional group chelating resin. Background Art

[0002] Acidic functional group chelating resins have strong chelating ability for metal ions, such as rare earth metal ions, good stability, easy availability and low price, and are widely used in enrichment, concentration, separation and purification of metal ions.

[0003] In this type of resin, 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 of the resin, the greater the amount of bound metal ions and the better the chelating adsorption performance. The grafting rate is one of the most important parameters for evaluating resin performance.

[0004] At present, the methods for determining the grafting rate of functional groups in acidic functional group chelating resins include weight method, acid-base titration method, and determination of saturated adsorption capacity for metal ions. The weight method calculates the grafting content by measuring the weight difference before and after chemical grafting, which is easily affected by by-products and chemical reagent residues in the preparation process, resulting in large measurement errors. In the acid-base titration method, for some acidic functional groups, such as ethylenediaminetriacetic acid functional groups, the tertiary proton dissociation constant is greater than 8, and it is difficult to determine the titration end point by acid-base titration. The saturated adsorption capacity method is affected by factors such as adsorption temperature and pH, and the results of the measurement are often lower than the functional group grafting rate. These methods are difficult to obtain accurate functional group grafting rates in resins.

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

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

[0007] To this end, the present invention provides a method for measuring the property parameters of an acidic functional group chelating resin based on potentiometric titration, comprising the following steps:

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

[0009] Perform potentiometric titration 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, performing potentiometric titration with a titrant to obtain the electrode potential at reaction equilibrium includes: performing potentiometric titration with the titrant at a set titration interval and titration step to obtain the electrode potential at a set number of titration reactions at equilibrium.

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

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

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

[0015] Based on the electrode potential, the concentration of each species in the titration system when the titration reaction is in equilibrium is obtained; and

[0016] Based on the concentrations of the various species, the property parameters of the acidic functional group chelating resin are obtained.

[0017] In some embodiments, the property parameter includes at least one of a grafting rate of the acidic functional group chelating resin and a protonation constant of an acidic functional group in the acidic functional group chelating resin.

[0018] In some embodiments, obtaining the electrode potential at the equilibrium of the titration reaction comprises collecting the electrode potentials at the equilibrium of at least 10 titration reactions.

[0019] In some embodiments, the titration reaction equilibrium time t0 is performed by pre-titration; the pre-titration includes: using the same initial titration system and titrant as the potentiometric titration to perform 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 with known concentrations and perchloric acid; and the titrant comprises a mixed solution of a base with known concentrations and a second perchlorate.

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

[0022] The method of the present invention uses potentiometric titration to obtain electrode potential data of the titration process, and obtains the concentration and species distribution diagram of each species in the titration system during the titration process by processing the data, and obtains performance parameters such as the grafting rate and protonation constant of the acidic functional group chelating resin based on the data such as the species and concentration. The accurate electrode potential can be obtained by potentiometric titration, instead of judging the titration end point by pH jump in the prior art, which is conducive to improving the accuracy of data measurement, and thus improving the accuracy of the measured resin performance parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The potentiometric titration pH change curve and the distribution diagram of protonated species at various levels of H3A obtained by testing in Example 1 of the present invention;

[0024] Figure 2 The potentiometric titration pH change curve and the distribution diagram of protonated species at various levels of H3A obtained by testing in Example 2 of the present invention;

[0025] Figure 3 The potentiometric titration pH change curve and the distribution diagram of protonated species of H2A at various levels obtained by testing in Example 3 of the present invention are shown. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0028] It should be noted that, in the embodiments of the present invention, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a method or device including a series of elements includes not only the elements explicitly stated, but also other elements not explicitly listed, or also includes elements inherent to the implementation of the method or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other related elements in the method or device including the element.

[0029] definition

[0030] The term "potentiometric titration" herein refers to a titration method that uses the change in the potential of a measuring solution to indicate the endpoint. During the titration process, two electrodes connected to a potentiometer are inserted into the titrated solution, one being a reference electrode and the other being an indicator electrode. Based on different principles of titration reactions, potentiometric titration can be divided into, for example, pH potentiometric titration, redox titration, precipitation titration, complexometric titration, etc. In the present invention, potentiometric titration can be performed using instruments or devices known to those skilled in the art, such as a pH potentiometric titrator, etc.

[0031] The term "initial titration system" herein refers to a mixed solution of the titrated liquid and the acidic functional group chelating resin contained in the titration apparatus before the titration reaction begins." titration system" refers to a mixed system formed by the titration reaction equilibrium after the titration agent has been added to the initial titration system after the titration begins. In the present invention, the titrated liquid comprises the acidic functional group chelating resin and a titration medium. Herein, the term "titration medium" refers to a solution that provides a titration reaction environment for the functional group on the acidic functional group chelating resin.

[0032] The term "electrode potential" herein refers to the potential value of a titration system measured by an index electrode of a potentiometric titrator.

[0033] The term "titration reaction equilibrium" in this article refers to the equilibrium state reached between the functional group reaction of the titrant and the titrant in the titration system, that is, the type and content of each substance in the titration system are stable and no longer change, that is, the titration reaction equilibrium is reached.

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

[0035] The term "electrode potential at titration reaction equilibrium" herein refers to the electrode potential measured when the titration system reaches titration reaction equilibrium. In the present invention, the equilibrium state of the titration reaction is determined by the change in the electrode potential measured by the potentiometric titrator, and the electrode potential reaching a stable state indicates that the titration reaction has reached an equilibrium state. In the present invention, the equilibrium state of the electrode potential is that the electrode potential offset value is less than 0.1 mV and is stable for at least 30 seconds.

[0036] The term "titration interval" herein refers to the time interval between two adjacent additions of titrant.

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

[0038] In the prior art, the grafting rate of chelating resin functional groups is determined by acid-base titration, usually by determining the titration endpoint through pH jump. However, for acidic functional groups with a dissociation constant (pKa) less than 8, the reaction endpoint is easily disturbed by factors such as impurities, temperature, and pH, making it difficult to determine the titration endpoint, resulting in inaccurate grafting rate measurement.

[0039] In addition, the existing technology usually conducts batch experiments by configuring different gradient pH solutions to explore the effect of pH on the adsorption of metal ions by aminocarboxylic acid chelating resins and determine the optimal adsorption or separation pH. However, when the application scenario changes, for example: the type and concentration of metal ions change; the interference of organic ligands such as lactic acid, glycolic acid, and citric acid is added; Cl - , NO3 - Changes in the concentrations of inorganic and organic ligands, etc., often require readjustment of 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 an acidic functional group chelating resin based on potentiometric titration. The method comprises the following steps:

[0041] preparing an initial titration system including an acidic functional group chelating resin and an acidic titration medium;

[0042] Perform potentiometric titration using a titrant and collect the electrode potential at equilibrium of the titration reaction; and

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

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

[0045] When the method of the property parameter of the acidic functional group chelating resin of the present invention is applied to the construction of the chelating resin adsorption model and the like, it has at least the following advantages: 1) the potentiometric titration method determines the effect of pH on adsorption by gradually increasing pH, which can realize the determination under higher pH conditions and avoid the interference of hydrolysis on the results; 2) when constructing the chelating resin adsorption model, the resin can achieve solid-liquid separation by centrifugation after adsorbing metal ions, which is convenient for setting specific adsorption conditions for batch experiments, and determining the free target metal ion concentration and hydrogen ion concentration (pH) changes in the solution after adsorption, and then comparing with the results obtained by combining the species formation model and the stability constant simulation calculation by Hyss software to ensure the accuracy of the coordination model. 3) The species formation model verified by batch experiments combined with the simulation calculation of Hyss software can be applied to multiple application scenarios, such as the treatment of uranium-contaminated wastewater, the separation and purification of uranium ore, etc. The coordination model between the acidic functional groups on the resin surface and the target metal ions is studied by potentiometric titration, which can not only overcome the limitations of traditional methods, but also provide a theoretical basis and technical support for in-depth understanding of the interaction mechanism between aminocarboxylic acid chelating resin and metal ions, and expanding its application in the fields of nuclear industry and the like.

[0046] In the present invention, the potentiometric titration is performed by pH potentiometric titration. The pH in the titration system changes through the acid-base reaction in the titration system, and the electrode potential of the titration system is collected through the pH electrode, wherein the pH electrode potential in the titration system With H + The relationship of concentration is shown in Formula 1.

[0047]

[0048] Where: is the standard electrode potential; R is the standard gas constant; F is the Faraday constant; T is the temperature, the unit is K.

[0049] The accurate electrode potential can be obtained by potentiometric titration, instead of judging the titration endpoint by pH jump in traditional technology, which is conducive to improving the accuracy of data measurement, and thus improving the accuracy of the measured resin performance parameters. For example, ethylenediaminetriacetic acid is a weak acid. When the pH value of its solution reaches 10, its carboxyl protons have not yet completely dissociated, so it is impossible to accurately judge the titration endpoint by pH jump in traditional technology. The method of the present invention is to obtain the amount of ethylenediaminetriacetic acid in the initial solution n0, H by combining the relationship between electrode potential, pH value, protonation constant, etc., and multiple electrode potential data points collected when multiple titration reactions reach a chemical reaction equilibrium state, and the data is analyzed by software. + The amount n1 and the protonation constant of surface functionalized EDTA are calculated, so there is no need to use other parameters to determine whether the reaction has reached equilibrium, and more data sample solutions further improve the accuracy of the calculation results.

[0050] In some embodiments, the acidic titration medium includes a mixed solution of a first perchlorate of known concentration and perchloric acid. Perchloric acid is an inorganic compound with a chemical formula of HClO4, which is extremely acidic and almost completely ionized in an aqueous solution, existing in the form of hydrogen ions and perchlorate ions, and perchlorate ions hardly undergo hydrolysis reaction in an aqueous solution. In addition, perchloric acid and perchlorate have good stability, are not easy to decompose and deteriorate, and are not easy to react with metal ions adsorbed on an acidic functional group chelating resin. Using a mixed solution of perchloric acid and perchlorate as a titration medium can reduce the effect of the titration medium on the pH titration reaction, so that the change in hydrogen ion concentration in the titration system is almost only caused by the acid-base reaction of the acidic functional groups chelated on the chelating resin during the titration process, thereby improving the accuracy of the measurement.

[0051] In some embodiments, in the acidic titration medium, the concentration of the first perchlorate 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 includes a base of known concentration and a second perchlorate mixed solution. The base in the titrant reacts with the acidic functional groups on the chelating resin to produce an acid-base reaction, thereby obtaining performance data of the chelating resin based on the acid-base reaction and the changes in electrode potential in the titration system collected.

[0053] In some embodiments, in the titrant, the concentration of the base 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 hardly undergo hydrolysis reaction, the influence on the hydrogen ion concentration of the titration system can be ignored, which is conducive to improving the accuracy of measurement. In some embodiments, the first perchlorate and the second perchlorate are each independently selected from lithium salts, sodium salts, potassium salts; preferably sodium salts.

[0055] In some embodiments, the base is selected from hydroxides of alkali metals and alkaline earth metals. The selection of the above bases can avoid the influence of metal cations on the titration system, thereby facilitating the improvement of the measurement accuracy. In some embodiments, the base is selected from sodium hydroxide, lithium hydroxide, and a hydroxyl radical; 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 the present invention is not specifically limited to this.

[0057] In some preferred embodiments, the acidic titration medium is a 0.005 mol / L HClO4-1 mol / LNaClO4 mixed solution.

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

[0059] In some embodiments, the acidic functional group chelating resin is swollen with an acidic titration medium before use. The acidic functional group chelating resin is swollen with a titration medium. On the one hand, the volume of the resin in the solution is stabilized, thereby reducing the change of the titration system during the titration process, such as the change of the solution volume; on the other hand, the functional groups inside the resin are fully exposed, so that they fully react with the titrant during the titration process, thereby improving the accuracy of the measurement. The swelling treatment includes mixing the chelating resin and the acidic titration medium in a volume ratio of 1:1.5-1:4, and swelling at room temperature for 20-30 hours.

[0060] In some embodiments, the acidic functional group chelating resin is selected from ethylenediaminetriacetic acid chelating resin, nitrilotriacetic 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 comprises:

[0062] The electrode potential when a set number of titration reactions are balanced is obtained by using the titrant for potentiometric titration with a set titration interval and titration step length, wherein the set titration interval is greater than or equal to the titration reaction equilibrium time t0. Through continuous potentiometric titration, the electrode potential after a plurality of titration systems reach equilibrium is obtained, and based on the obtained plurality of accurate electrode potential data, the concentration change of each species in the titration process can be obtained, thereby facilitating more accurate analysis of the performance parameters of the chelating resin and improving the accuracy of the measurement result.

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

[0064] In some embodiments, the potentiometric titration is performed at 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, the set titration interval is 1.25t0-1.50t0. By setting the titration interval within the above range, the titration reaction fully reaches equilibrium after each titration, thereby collecting more accurate electrode potential data when the titration reaction is in equilibrium, which is further conducive to improving the accuracy of the measurement.

[0066] In some embodiments, the titration step size is set to 0.02 mL-0.05 mL. The above titration step size can make the electrode potential in the titration system produce a measurable change after titration. On the other hand, adding only a small amount of titrant allows the titration reaction to reach equilibrium faster, which is conducive to improving measurement efficiency.

[0067] In some embodiments, the electrode potentials at the equilibrium of the set number of titration reactions are collected, including collecting the electrode potentials at the equilibrium of at least 10 titration reactions. The number of electrode potentials at the equilibrium of the titration reactions collected in the present invention is determined according to the number of acidic functional groups, such as carboxyl groups, on the measured acidic functional group chelating resin. For example, if the acidic functional groups on the acidic functional group chelating resin are n-acids, the number of electrode potential data collected is (10-15)n, where n=1, 2, 3... In a preferred embodiment, the electrode potentials at the equilibrium of 20 to 60 titration reactions are collected. By collecting a sufficient number of electrode potentials, it is beneficial to reduce the error of the measurement process and improve the accuracy of the performance parameters measured. On the other hand, it can also reduce the total volume of the solution in the titration system and save costs.

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

[0069] Based on the electrode potential, the concentration of each species in the titration system when the titration reaction is in equilibrium is obtained; and

[0070] Based on the concentrations of the various species, the property parameters of the acidic functional group chelating resin are obtained.

[0071] In one example, the species concentration at the time of titration reaction equilibrium obtained based on the electrode potential is implemented by Hyperquad software, but is not limited thereto. The collected electrode potential data is imported into Hyperquad software, and the software solves the nonlinear simultaneous mass balance equation by the Newton-Raphson method, thereby calculating the concentration of each species in the titration system, and based on the calculated concentration of the titration species, the property parameters of the acidic functional group chelating resin can be obtained.

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

[0073] In one example, the calculation method of the grafting rate and the protonation constant is illustrated by taking the grafted functional group as ethylenediaminetriacetic acid as an example. It should be understood that the corresponding parameters can be obtained by different calculation methods using different software. The grafting rate of the acidic functional group chelating resin can be calculated by formula (2):

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

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

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

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

[0078] The protonation constant of its acidic functional group can be calculated by formula (4):

[0079] Protonation constant

[0080] In the formula, [H r A (r-3) ] is 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 is described in detail below by means of specific examples. It should be understood that the following examples are only exemplary 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: precision: 0.00001 g, BT125D analytical balance, Sartorius, Germany.

[0084] Example 1

[0085] Resin pretreatment: EDTA chelating resin (resin is poly(glycidyl methacrylate) resin) was washed with deionized water, ethanol and acetone in turn, vacuum dried at 50°C for 24 h, washed with an appropriate volume of 2 mol / L HCl solution, then washed with deionized water until the effluent was neutral, and vacuum dried at 50°C for 24 h.

[0086] Preparation of acidic titration medium: accurately weigh 122g of anhydrous NaClO4, dissolve it in 1.4L of deionized water, add 0.5mL of concentrated HClO4 solution, boil until the remaining solution volume is 1L, transfer the prepared solution into a blue-capped bottle, seal it, and cool it for later use. In order to determine the exact concentration of the acidic titration medium prepared above, the H + The concentration was titrated with 0.1005mol / L NaOH standard solution. The concentration was calibrated three times in parallel and the average value was 0.0056mol / L. The acidic titration medium was 0.0056mol / L HClO4-1mol / L NaClO4 solution.

[0087] Preparation of titrant: Accurately weigh 122g of anhydrous NaClO4, dissolve it in 1.4L of deionized water, boil until the remaining solution volume is 1L, transfer it to a blue-capped bottle, transfer it to a glove box after cooling, add 5mL of saturated sodium hydroxide solution, and prepare the titrant. In order to determine the exact concentration of the titrant, the above-prepared titrant is installed in a potentiometric titrator in a glove bag under argon protection. Accurately weigh 0.010g 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 0.1305mol / L. The prepared titrant is 0.1305mol / LNaOH-0.9mol / L NaClO4 solution.

[0088] Determine the time t0 required for the reaction to reach equilibrium during potentiometric titration: Take 0.2g of resin, add 5.00mL of acidic titration medium, swell for 24h, and then transfer to the titration cup. Add 15.00mL of acidic titration medium to the titration cup, insert the pH electrode, and conduct the potentiometric titration experiment under argon protection. The titration cup is placed in a constant temperature water bath, and the temperature is controlled at 25.0±0.1℃. After the potential data offset value is less than 0.1mV and exceeds 30s, add 0.50mL of titrant solution for titration, and determine the time for the potential reading to stabilize again. Repeat the measurement three times, take the average of the measured interval time, and obtain the time t0 required for the reaction to reach equilibrium as 900s.

[0089] Potentiometric titration: Accurately weigh 0.10271g of resin, add 5.00mL of acidic titration medium (0.0056mol / LHClO4-1mol / L NaClO4 solution), swell for 24h, transfer to the titration cup, add 15.00ml of acidic titration medium, stir and use 0.1305mol / L NaOH-0.9mol / L NaClO4 solution as titrant for potentiometric titration, set the titration step length to 0.02ml, the titration interval time to 1200s, and the total titration volume to 2.00mL. Measure the potential change and collect 100 data points.

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

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

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

[0093] In order to verify the accuracy of the test results of the method of the present invention, the grafting rate of ethylenediaminetriacetic acid chelating resin was determined by back titration. 0.100g of ethylenediaminetriacetic acid chelating resin was dispersed in V1=100.00mL 0.01mol / L NaHCO3 standard solution and stirred for 2h under Ar atmosphere. After the suspension was filtered, three volumes of V2=20.00mL of the obtained filtrate were taken respectively, and titrated with 0.01mol / L HCl standard solution, and the titration volume was taken as the average value V HCl =19.07mL.

[0094] Total amount of EDTA

[0095] in and c HCl are the concentrations of NaHCO3 solution and HCl solution (mol / L), respectively; V1 is the total volume of NaHCO3 solution (mL); V2 is the volume of the NaHCO3 solution taken out for titration (mL); V HCl It is the average titration volume of 0.01mol / L HCl standard solution.

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

[0097] The grafting rate tested by the present invention is basically consistent with the grafting rate data tested by the back titration method. It is understandable that the back titration method [1] is a more common determination method for the grafting rate of ethylenediaminetriacetic acid chelating resin. 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 result of the determination. However, if the NaHCO3 solution is replaced with concentrated sodium hydroxide, the resin will cause a small change in the sodium hydroxide concentration, which will lead to a larger error in the determination result.

[0098] Example 2

[0099] Resin pretreatment: Nitrilotriacetic acid chelating resin (resin is poly(glycidyl methacrylate) resin) is washed with deionized water, ethanol and acetone in sequence, vacuum dried at 50°C for 24 h, washed with an appropriate volume of 2 mol / L HCl solution, then washed with deionized water until the effluent is neutral, and vacuum dried at 50°C for 24 h.

[0100] Determine the time t0 required for the reaction to reach equilibrium during potentiometric titration: Take 0.2g of resin, add 5.00mL of acidic titration medium, swell for 24h, and then transfer to the titration cup. Add 15.00mL of acidic titration medium to the titration cup, insert the pH electrode, and conduct the potentiometric titration experiment under argon protection. The titration cup is placed in a constant temperature water bath, and the temperature is controlled at 25.0±0.1℃. After the potential data offset value is less than 0.1mV and exceeds 30s, add 0.50mL of titrant solution for titration, and determine the time for the potential reading to stabilize again. Repeat the measurement three times, take the average of the measured interval time, and obtain the time t0 required for the reaction to reach equilibrium as 950s.

[0101] Potentiometric titration: Accurately weigh 0.10131g of resin, add 5.00mL 0.0056mol / LHClO4-1mol / L NaClO4 solution, swell for 24h, transfer to a titration cup, add 15.00ml 0.0056mol / L HClO4-1mol / L NaClO4 solution, and use 0.1305mol / L NaOH-0.9mol / LNaClO4 solution as titrant for potentiometric titration under stirring, set the titration step length to 0.02ml, the titration interval to 1300s, and the total titration volume to 2.50mL. Measure the potential change and collect 125 data points.

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

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

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

[0105] In order to verify the accuracy of the test results of the method of the present invention, the grafting rate of nitrilotriacetic acid chelate resin was determined by back titration. 0.101g of nitrilotriacetic acid chelate resin was dispersed in V1=100.00mL 0.01mol / L NaHCO3 standard solution and stirred for 2h under Ar atmosphere. After the suspension was filtered, three volumes of V2=20.00mL of the obtained filtrate were taken respectively, and titrated with 0.01mol / L HCl standard solution, and the titration volume was taken as the average value V HCl =18.65mL.

[0106] The total amount of nitrilotriacetic acid

[0107] in and c HCl are the concentrations of NaHCO3 solution and HCl solution (mol / L), respectively; V1 is the total volume of NaHCO3 solution (mL); V2 is the volume of the NaHCO3 solution taken out for titration (mL); V HCl It is the average titration volume of 0.01mol / L HCl standard solution.

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

[0109] Example 3

[0110] Resin pretreatment: The iminodiacetic acid chelating resin (resin is poly(glycidyl methacrylate) resin) was washed with deionized water, ethanol and acetone in sequence, vacuum dried 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 vacuum dried at 50°C for 24 h.

[0111] Determine the time t0 required for the reaction to reach equilibrium during potentiometric titration: Take 0.2g of resin, add 5.00mL of acidic titration medium, swell for 24h, and then transfer to the titration cup. Add 15.00mL of acidic titration medium to the titration cup, insert the pH electrode, and conduct the potentiometric titration experiment under argon protection. The titration cup is placed in a constant temperature water bath, and the temperature is controlled at 25.0±0.1℃. After the potential data offset value is less than 0.1mV and exceeds 30s, add 0.50mL of titrant solution for titration, and determine the time for the potential reading to stabilize again. Repeat the measurement three times, take the average of the measured interval time, and obtain the time t0 required for the reaction to reach equilibrium as 700s.

[0112] Potentiometric titration: Accurately weigh 0.10228g of resin, add 5.00mL 0.0056mol / LHClO4-1mol / L NaClO4 solution, swell for 24h, transfer to a titration cup, add 15.00ml 0.0056mol / L HClO4-1mol / L NaClO4 solution, and use 0.1305mol / L NaOH-0.9mol / LNaClO4 solution as titrant for potentiometric titration under stirring, set the titration step length to 0.02ml, the titration interval to 1000s, and the total titration volume to 2.50mL. Measure the potential change and collect 125 data points.

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

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

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

[0116] In order to verify the accuracy of the test results of the method of the present invention, the grafting rate of the iminodiacetic acid chelating resin was determined by back titration. 0.105g of iminodiacetic acid chelating resin was dispersed in V1=100.00mL 0.01mol / L NaHCO3 standard solution and stirred for 2h under Ar atmosphere. After the suspension was filtered, three volumes of V2=20.00mL of the obtained filtrate were taken respectively, and titrated with 0.01mol / L HCl standard solution, and the titration volume was taken as the average value V HCl =18.86mL.

[0117] The total amount of iminodiacetic acid

[0118] in and c HClare the concentrations of NaHCO3 solution and HCl solution (mol / L), respectively; V1 is the total volume of NaHCO3 solution (mL); V2 is the volume of the NaHCO3 solution taken out for titration (mL); V HCl It is the average titration volume of 0.01mol / 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 changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for determining the property parameters of an acidic functional group chelating resin based on potentiometric titration, comprising the following steps: preparing an initial potentiometric titration system including an acidic functional group chelating resin and an acidic titration medium; Use titrant to perform potentiometric titration to obtain the electrode potential when the titration reaction is in equilibrium; and Based on the electrode potential, the property parameters of the acidic functional group chelating resin are obtained.

2. The method according to claim 1, wherein: The electrode potential when the titrant is used for potentiometric titration to obtain the reaction equilibrium includes: The titrant is used to perform potentiometric titration at a set titration interval and titration step length to obtain the electrode potential when a set number of titration reactions are in equilibrium.

3. The method according to claim 2, wherein: The set titration interval is greater than or equal to the titration reaction equilibrium time t0; preferably, the set titration time interval is greater than 1.25t0.

4. The method according to claim 2 or 3, wherein: The titration step length is 0.02-0.05 ml.

5. 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 concentration of each species in the titration system when the titration reaction is in equilibrium is obtained; and Based on the concentrations of the various species, the property parameters of the acidic functional group chelating resin are obtained.

6. The method according to claim 1 or 5, wherein: The property parameter includes at least one of a grafting rate of the acidic functional group chelating resin and a protonation constant of an acidic functional group in the acidic functional group chelating resin.

7. The method according to claim 1, wherein: The obtaining of the electrode potential at the time of titration reaction equilibrium comprises collecting at least 10 electrode potentials at the time of titration reaction equilibrium.

8. The method according to claim 3, wherein: The titration reaction equilibrium time t0 is carried out by pre-titration; the pre-titration includes: using the same initial titration system and titrant as the potentiometric titration to perform titration, and testing the time required for the titration reaction to reach equilibrium.

9. The method according to claim 1, wherein: The acidic titration medium includes a mixed solution of a first perchlorate and perchloric acid of known concentration; The titrant includes a base of known concentration and a second perchlorate solution mixture.

10. The method according to claim 1, wherein: The acidic functional group chelating resin is selected from resins containing carboxyl functional groups; preferably selected from ethylenediaminetriacetic acid chelating resin, nitrilotriacetic acid chelating resin, iminodiacetic acid chelating resin, and polyglycidyl methacrylate resin.

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