Method for measuring coordination number of organic acid and RE < 3 + > by using molar ratio method

Abstract

The invention relates to the technical field of analytical chemistry and hydrometallurgy, in particular to a method for measuring coordination number of organic acid and RE < 3 + > by using a molar ratio method. The method comprises the following steps: S1, preparing a plurality of organic acid solutions of CY with different concentrations, preparing a RE3 + solution of CM, mixing the organic acid solutions and the RE3 + solution in an isovolumetric manner, adjusting the pH value, and carrying out a complexation reaction; s2, carrying out ultraviolet spectrophotometric measurement, determining the maximum absorption wavelength, and determining the absorbance A of the solutions after the complexation reaction under the maximum absorption wavelength; s3, drawing by taking the molar ratio n = [CY] / [CM] as a horizontal coordinate and the absorbance A as a vertical coordinate, and finding out an interval in which the absorbance linearly rises along with the increase of n and an interval in which the absorbance reaches a platform or the slope is obviously changed; linear fitting is conducted on the data points of the two intervals, two straight lines are obtained, and the value of an abscissa n corresponding to the intersection point of the two straight lines is the coordination ratio of the complex. The method is reliable in result, low in cost, easy to popularize, convenient and fast.

Description

Technical Field

[0001] This invention relates to the fields of analytical chemistry and hydrometallurgy, and particularly to a method for determining organic acids and REs using the molar ratio method. 3+ Methods for determining coordination numbers. Background Technology

[0002] Weathering crust leaching rare earth deposits are an important new type of mineral resource, often hailed as the "heart of modern industry" due to their superior performance in high-end fields such as military, aerospace, electronics, and new materials. However, the grade of rare earth oxides in these deposits is typically only 0.05%–0.2%, and rare earth elements are mainly adsorbed in ionic form on the surface of clay minerals such as kaolinite, halloysite, and illite, which can be considered natural ion exchangers, requiring the assistance of electrolyte cations (such as Na+). + K + NH4 + H + (etc.) substitution extraction is performed. Rare earth elements have a unique electron orbital filling situation; the ground state 5d orbital is empty. Under certain ligands (such as CO and CN) or high-energy excitation conditions, electrons can jump from the 4f or 6s orbital to the 5d orbital, forming an excited state d-electron configuration and participating in covalent bonding. Furthermore, the d orbital has high energy, large spatial expansion, and strong coordination ability. Organic oxygen-containing groups in organic acids, such as C-O, P-O, and S-O, can react with REs... 3+ Coordination occurs, forming coordination compounds.

[0003] In the green leaching process of ion-adsorption rare earth ores, organic acids are often used as additives in combination with leaching agents such as magnesium salts to enhance leaching or improve selectivity. The core of their mechanism of action is the interaction between organic acid anions and reticulum (RE). 3+ The formation of coordination compounds with different coordination ratios directly affects leaching efficiency and impurity suppression. Currently, the main method for determining the coordination ratio is potentiometric titration, but this method is cumbersome, has limited applicability to specific systems, and involves solvent selection, electrode treatment, humidity control, etc., making it cumbersome and with poor reproducibility. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by proposing a simple, accurate, and widely applicable method for determining the coordination number of organic acids and RE3+ using the molar ratio method.

[0005] The present invention provides a method for determining organic acids and REs using a molar ratio method. 3+ The method for determining coordination number includes the following steps: S1. Prepare several C solutions of different concentrations. Y An organic acid solution is prepared to a concentration of C. M RE 3+Rare earth ion solution: Mix equal volumes of organic acid solution and rare earth ion solution, adjust the pH value, and carry out a complexation reaction; S2. After the complexation reaction is completed, ultraviolet spectrophotometry is performed to determine the maximum absorption wavelength of the complex and the absorbance A of the solution after each complexation reaction at the maximum absorption wavelength. S3, with a molar ratio n=[C Y ] / [C M Plot the absorbance A on the x-axis and the measured absorbance A on the y-axis. Find the interval where the absorbance increases linearly with increasing n and the interval where the absorbance reaches a plateau or the slope changes significantly. Perform linear fitting on the data points of the two intervals to obtain two straight lines. The x-axis value n corresponding to the intersection of the two straight lines is the coordination ratio of the complex.

[0006] Furthermore, C M =0.01mol / L, C Y The concentrations were 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L, respectively.

[0007] Furthermore, in step S2, a full wavelength scan of 400-800nm ​​is performed, or 200-400nm is selected for organic acids that have ultraviolet absorption.

[0008] Furthermore, RE 3+ It can be one or more of La, Ce, Y, and Nd.

[0009] Furthermore, the organic acid is an organic soluble compound having a carboxyl group, a phenolic hydroxyl group, and an organophosphorus functional group.

[0010] Furthermore, the organic acid is one or more of citric acid, malic acid, acetic acid, and phthalic acid.

[0011] Furthermore, if n = 1-2, and n = 1, a 1:1 coordination compound is formed; if the intersection point n = 2, a 1:2 coordination compound complex is formed; if n is greater than 1 and less than 2, both 1:1 and 1:2 coordination compound complexes are formed.

[0012] Furthermore, the pH value is 4-5.

[0013] Further, the pH value was adjusted using 0.01M sodium hydroxide.

[0014] Furthermore, the maximum absorption wavelength is 210-297 nm.

[0015] This invention employs a molar ratio method to determine the coordination strength between organic acids and rare earth ions. It only requires preparing a series of solutions with constant total metal and ligand concentrations but different ratios, measuring their absorbance, and plotting the results. This method offers advantages such as simple operation, reliable results, wide applicability, low cost, and ease of promotion, providing a new approach for the screening, design, and performance evaluation of rare earth green organic leaching aids. This invention can be directly used to evaluate the interaction between different organic acids and target REs under simulated leaching conditions. 3+ The strength of the coordination ability and the composition of the complex provide key experimental data support for optimizing the formulation of "magnesium salt-organic acid" composite leaching agent (such as selecting the best type of organic acid and determining its addition ratio with magnesium salt). Attached Figure Description

[0016] Figure 1 The following are the UV-Vis absorption spectra of a series of rare earth chloride solutions; Figure 2 The curves show the absorbance versus concentration ratio of the La-PA complex; Figure 3 The curves show the absorbance versus concentration ratio of the Ce-PA complex. Figure 4 The absorbance curve of the Nd-H3cit complex versus its concentration ratio; Figure 5 The curves show the absorbance versus concentration ratio of the γ-H2Mal complex. Detailed Implementation

[0017] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0018] Multiple measurements were performed on rare earth chloride solutions with different concentration gradients, and their spectral data were recorded. Through comprehensive analysis and comparison of the data, it was ultimately determined that a rare earth chloride concentration of 0.01 mol / L was most suitable. At this concentration, the absorption peak intensity was significant and clearly presented in the spectrum, while effectively reducing experimental errors and laying the foundation for the accuracy of subsequent experimental results. A series of UV-Vis absorption spectra of rare earth chloride solutions are shown below. Figure 1 .

[0019] As shown in the figure, all four rare earth chlorides exhibit partial absorption between 200 nm and 900 nm. The absorption of a single rare earth chloride is usually caused by the ff electron transition of rare earth elements in the rare earth hydrate ions, and is related to the number of unpaired electrons. 3+ and Y 3+ Because the outer 4f electrons are zero and have no unpaired electrons, Ce is relatively stable and therefore exhibits almost no absorption between 200nm and 900nm. 3+(4f 1 The absorption peak of Nd is around 300 nm in the ultraviolet region. 3+ (4f 3 The absorption peaks of f orbitals are located in the ultraviolet and visible light regions. Furthermore, because the f orbitals are shielded by the outer orbitals, they are minimally affected by solvent properties or ligands, resulting in a narrower spectral band.

[0020] Example 1: Determination of La 3+ Coordination number with phthalic acid (PA) Reagent preparation: La 3+ Standard stock solution: Accurately weigh and prepare a solution with a concentration of 1.00 × 10⁻⁶. -2 Lanthanum chloride solution at concentrations of 0.005 mol / L. Phthalic acid stock solution: Accurately weigh phthalic acid (analytical grade), dissolve and dilute with deionized water to prepare PA ligand solutions with concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L.

[0021] Determine the characteristic absorption wavelength: An equal volume of 0.01 mol / L NdCl3 solution was mixed with H3cit ligand solutions of concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L, respectively. The pH was adjusted to 4-5 using 0.01 M sodium hydroxide solution, and the mixture was allowed to react completely. At 25°C, using deionized water as a reference, wavelength scans (200 nm-400 nm) were performed on the lanthanum chloride solution and the resulting complexation mixture.

[0022] Comparing the spectra, the absorbance of the PA ligand solution (0.01 mol / L) and the solution after the La ion complexation reaction was significantly greater than that of the lanthanum chloride solution, and the wavelength with the stable absorption peak shape was determined to be the maximum absorption wavelength λmax, which was 297 nm.

[0023] Measure absorbance: After determining the maximum absorption wavelength λmax, the absorbance A of the solution after each complexation reaction was measured, and the ratio C of absorbance A to the concentration of the component added to the solution was used. Y / C M Drawing, such as Figure 2 As shown.

[0024] In the LaCl3-PA solution, n = 1.90; this indicates that under these conditions, both 1:1 and 1:2 type La-PA complexes are generated simultaneously in the LaCl3-PA aqueous solution.

[0025] Example 2: Determination of Ce3+ Coordination ratio with phthalic acid Reagent preparation: Ce 3+ Standard stock solution: Accurately weigh and prepare a solution with a concentration of 1.00 × 10⁻⁶. -2 Cerium chloride solution at concentrations of 0.005 mol / L. Phthalic acid stock solution: Accurately weigh phthalic acid (analytical grade), dissolve and dilute with deionized water to prepare PA ligand solutions with concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L.

[0026] Determine the characteristic absorption wavelength: An equal volume of 0.01 mol / L CeCl3 solution was mixed with H3cit ligand solutions of concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L, respectively. The pH was adjusted to a constant 4-5 using 0.01 M sodium hydroxide solution, and the mixture was allowed to react completely. At 25°C, using deionized water as a reference, wavelength scans (200 nm-400 nm) were performed on the cerium chloride solution and the resulting complexed mixture.

[0027] Comparing the spectra, the absorbance of the PA ligand solution (0.01 mol / L) and the solution after the Ce ion complexation reaction was significantly greater than that of the cerium chloride solution, and the wavelength with the stable absorption peak shape was determined to be the maximum absorption wavelength λmax, which was 297 nm.

[0028] Measure absorbance: After determining the maximum absorption wavelength λmax, the absorbance A of the solution after each complexation reaction was measured, and the ratio C of absorbance A to the concentration of the component added to the solution was used. Y / C M Drawing, such as Figure 3 As shown.

[0029] In CeCl3-PA solution, n = 1.22; this indicates that under these conditions, both 1:1 and 1:2 Ce-PA complexes are generated simultaneously in the CeCl3-PA aqueous solution.

[0030] Example 3: Determination of Nd 3+ Coordination ratio with citric acid (H3cit) Reagent preparation: Nd 3+ Standard stock solution: Accurately weigh and prepare a solution with a concentration of 1.00 × 10⁻⁶. -2Neodymium chloride solution (mol / L). Citric acid stock solution: Accurately weigh citric acid (analytical grade), dissolve and dilute to volume with ultrapure water to prepare H3cit ligand solutions with concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L.

[0031] Determine the characteristic absorption wavelength: An equal volume of 0.01 mol / L NdCl3 solution was mixed with H3cit ligand solutions of concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L, respectively. The pH was adjusted to a constant 4-5 using 0.01 M sodium hydroxide solution, and the mixture was allowed to react completely. At 25°C, using deionized water as a reference, wavelength scans (200 nm-400 nm) were performed on the neodymium chloride solution and the resulting complexation mixture.

[0032] Comparing the spectra, the absorbance of the PA ligand solution after the complexation reaction at 0.01 mol / L was significantly greater than that of the neodymium chloride solution, and the wavelength with a stable absorption peak shape was determined to be the maximum absorption wavelength λmax, which was 214 nm.

[0033] Measure absorbance: After determining the maximum absorption wavelength λmax, the absorbance A of different solutions after the complexation reaction was measured, and the ratio C of absorbance A to the concentration of the component added to the solution was used. Y / C M Drawing, such as Figure 4 As shown.

[0034] In the NdCl3-H3cit solution, n = 1.92; this indicates that under these conditions, both 1:1 and 1:2 Nd-H3cit complexes are generated simultaneously in the RECl3-PA aqueous solution.

[0035] Example 4: Measurement of Y 3+ Coordination ratio with malic acid (H2Mal) Reagent preparation: Y 3+ Standard stock solution: Accurately weigh and prepare a solution with a concentration of 1.00 × 10⁻⁶. -2 Yttrium chloride solution at concentrations of 0.005 mol / L. Malic acid stock solution: Accurately weigh malic acid (analytical grade), dissolve and dilute to volume with ultrapure water to prepare H2Mal ligand solutions with concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L.

[0036] Determine the characteristic absorption wavelength: Equal volumes of 0.01 mol / L YCl3 solution and H3cit ligand solutions with concentrations of 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L were mixed, and the pH was adjusted to a constant 4-5 using 0.01 M sodium hydroxide solution to ensure complete reaction. At 25°C, using deionized water as a reference, wavelength scans (200 nm-400 nm) were performed on the yttrium chloride solution and the resulting complexation mixture.

[0037] Comparing the spectra, the absorbance of the PA ligand solution after the complexation reaction at 0.01 mol / L was significantly greater than that of the yttrium chloride solution, and the wavelength with the stable absorption peak shape was determined to be the maximum absorption wavelength λmax, which was 210 nm.

[0038] Measure absorbance: After determining the maximum absorption wavelength λmax, the absorbance A of the solution after each complexation reaction was measured, and the ratio C of absorbance A to the concentration of the component added to the solution was used. Y / C M Drawing, such as Figure 5 As shown.

[0039] In the YCl3-H2Mal solution, n = 1.57; this indicates that under these conditions, both 1:1 and 1:2 type Y-H2Mal complexes are generated simultaneously in the RECl3-PA aqueous solution.

[0040] For any points not covered above, existing technologies shall apply.

[0041] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining organic acids and REs using the molar ratio method 3+ The method of coordination number is characterized by, Includes the following steps: S1. Prepare several C solutions of different concentrations. Y An organic acid solution is prepared to a concentration of C. M RE 3+ Rare earth ion solution: Mix equal volumes of organic acid solution and rare earth ion solution, adjust the pH value, and carry out a complexation reaction; S2. After the complexation reaction is completed, ultraviolet spectrophotometry is performed to determine the maximum absorption wavelength of the complex and the absorbance A of the solution after each complexation reaction at the maximum absorption wavelength. S3, with a molar ratio n=[C Y ] / [C M Plot the absorbance A on the x-axis and the measured absorbance A on the y-axis. Find the interval where the absorbance increases linearly with increasing n and the interval where the absorbance reaches a plateau or the slope changes significantly. Perform linear fitting on the data points of the two intervals to obtain two straight lines. The x-axis value n corresponding to the intersection of the two straight lines is the coordination ratio of the complex.

2. The method for determining organic acids and REs using the molar ratio method as described in claim 1 3+ The method of coordination number is characterized by, C M =0.01mol / L, C Y The concentrations were 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, and 0.05 mol / L, respectively.

3. A method for determining organic acids and REs using the molar ratio method as described in claim 1. 3+ The method of coordination number is characterized by, In step S2, a full wavelength scan of 400-800nm ​​is performed. If the organic acid has ultraviolet absorption, 200-400nm is selected.

4. A method for determining organic acids and REs using the molar ratio method as described in claim 1. 3+ The method of coordination number is characterized by, RE 3+ It can be one or more of La, Ce, Y, and Nd.

5. The method for determining organic acids and REs using the molar ratio method as described in claim 1 3+ The method of coordination number is characterized by, The organic acid is an organic soluble compound having a carboxyl group, a phenolic hydroxyl group, and an organophosphorus functional group.

6. The method for determining organic acids and REs using the molar ratio method as described in claim 1 3+ The method of coordination number is characterized by, The organic acid is one or more of citric acid, malic acid, acetic acid, and phthalic acid.

7. A method for determining organic acids and REs using the molar ratio method as described in claim 1. 3+ The method of coordination number is characterized by, If n = 1-2, and n = 1, then a 1:1 coordination compound is formed; if the intersection point n = 2, then a 1:2 coordination compound complex is formed; if n is greater than 1 and less than 2, then both 1:1 and 1:2 coordination compound complexes are formed.

8. The method for determining organic acids and REs using the molar ratio method as described in claim 1 3+ The method of coordination number is characterized by, The pH value is 4-5.

9. The method for determining organic acids and REs using the molar ratio method as described in claim 1 3+ The method of coordination number is characterized by, Adjust the pH value using 0.01M sodium hydroxide.

10. A method for determining organic acids and REs using the molar ratio method as described in claim 1. 3+ The method of coordination number is characterized by, The maximum absorption wavelength is 210-297nm.

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