Method for measuring manganese content in manganese source
By using an automatic potentiometric titrator and EDTA automatic potentiometric titration method, the problems of multiple interfering factors and safety risks in manganese content determination methods have been solved, achieving high precision and high efficiency in manganese content detection, which is suitable for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-29
- Publication Date
- 2026-03-13
AI Technical Summary
Existing methods for determining manganese content are subject to numerous interfering factors, and the use of strong oxidants poses safety risks and environmental pollution, while also yielding inaccurate results.
EDTA automatic potentiometric titration was performed using an automatic potentiometric titrator. The sample was dissolved in a weakly acidic solution, and an automated pretreatment process of reduction-masking-precomplexation was combined. The equal volume titration mode and endpoint determination were adopted to reduce manual operation and subjective judgment errors.
It improves the repeatability and accuracy of analytical results, reduces safety risks and environmental pollution, and is suitable for rapid, batch testing in industrial production.
Smart Images
Figure CN121656359A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of elemental determination technology, and in particular relates to a method for determining the manganese content in a manganese source. Background Technology
[0002] In recent years, with the rapid development of new energy vehicles, the demand for high-performance cathode materials for lithium batteries has increased significantly. Lithium manganese iron phosphate (LFP), as one of the materials used in lithium battery production, is considered a promising cathode material due to its high voltage platform and energy density, high cycle performance and safety, and good low-temperature performance. The accuracy of manganese content testing in the manganese source directly affects product performance. Manganese dihydrogen phosphate, as one of the manganese source materials for LFP, is a key material for preparing LFP precursors. Currently, monitoring manganese content in industrial production mainly relies on chemical manual titration. Manual titration primarily depends on the color change of the indicator to identify the test endpoint. If the sample is turbid or the color is difficult to observe, it will cause testing errors, leading to inaccurate results.
[0003] Currently, the common method for testing manganese is the traditional ferrous ammonium sulfate method, which involves using perchloric acid or ammonium nitrate to react manganese with sulfuric acid. 2+ Oxidation to Mn 3+ Then, titration with a reducing agent is a complicated and time-consuming process with many interfering factors. Furthermore, the use of strong oxidizing agents poses safety risks and causes environmental pollution. Summary of the Invention
[0004] The purpose of this application is to provide a method for determining the manganese content in a manganese source, which aims to solve to some extent the problems of existing methods for determining manganese content, such as numerous interfering factors and safety risks and environmental pollution caused by the use of strong oxidants.
[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a method for determining the manganese content in a manganese source, comprising the following steps: Obtain a manganese source and dissolve the manganese source in a weakly acidic solution with a mass fraction of 4% to 8% to prepare a sample solution; The sample solution was placed on the test stage of an automatic potentiometric titrator, and a reducing agent solution was added under acidic conditions to stabilize Mn. 2+ Then, the pH value was adjusted to a weakly acidic condition, and a complexing agent solution and a masking agent solution were added to mix and react to obtain a pretreated sample solution; The test was conducted using an equal volume titration mode. After mixing the pretreated sample solution with ethylenediaminetetraacetic acid standard titration solution, a buffer solution was added to adjust the pH to 9.5-10.5. An indicator was added, and the solution was titrated to the endpoint with the ethylenediaminetetraacetic acid standard titration solution. The volume V1 of the ethylenediaminetetraacetic acid standard titration solution consumed was recorded. Calculate the manganese content using the formula: ; Wherein, C is the concentration of the ethylenediaminetetraacetic acid standard titration solution, in mol / L; V1 is the volume of the ethylenediaminetetraacetic acid standard titration solution consumed, in mL; m is the mass of the manganese source, in grams; M is the molar mass of manganese, which is 54.94 g / mol.
[0006] In some possible implementations, the manganese source includes at least one of manganese dihydrogen phosphate, manganese nitrate, and manganese phosphate.
[0007] In some possible implementations, the preparation of the sample solution includes the steps of: wetting the manganese source with water, adding the weakly acidic solution, performing cavitation effect treatment by ultrasound, and heating at a temperature of 30℃~40℃ to obtain the sample solution.
[0008] In some possible implementations, the weakly acidic solution is prepared by mixing (3~10) mL of nitric acid and (90~97) mL of water to form dilute nitric acid.
[0009] In some possible implementations, the ratio of the manganese source to the weakly acidic solution is 0.5 g : (4~6) mL.
[0010] In some possible implementations, the preparation of the pretreated sample includes the following steps: placing the sample solution in the test stage container of an automatic potentiometric titrator, placing the photometric electrode, stirrer and titration head into the test stage container, and automatically adding preset amounts of the reducing agent solution, pH adjuster, complexing agent solution and masking agent solution in sequence according to a set program to mix and obtain the pretreated sample solution.
[0011] In some possible implementations, the pH value of the acidic conditions is 0.55 to 1.
[0012] In some possible implementations, the reducing agent in the reducing agent solution includes at least one of hydroxylamine hydrochloride and ascorbic acid.
[0013] In some possible implementations, the volume ratio of the reducing agent solution to the sample solution is 1 mL: (5~6) mL.
[0014] In some possible implementations, the concentration of the reducing agent solution is 80 g / L to 120 g / L.
[0015] In some possible implementations, the pH of the weakly acidic conditions is adjusted by adding water as a pH adjuster.
[0016] In some possible implementations, the pH value of the weakly acidic condition satisfies: 3 ≤ pH < 7.
[0017] In some possible implementations, the complexing agent solution includes at least one of trisodium citrate and potassium sodium tartrate.
[0018] In some possible implementations, the amount of the complexing agent solution used is 5 mL to 10 mL, and the concentration is 3% to 8%.
[0019] In some possible implementations, the masking agent in the masking agent solution includes at least one of aminotrimethylphosphonic acid and ammonium fluoride.
[0020] In some possible implementations, the amount of the masking agent solution used is 1 mL to 5 mL, and the concentration is 1% to 3%.
[0021] In some possible implementations, the pH of the pretreated sample solution is adjusted to 5-6 by pH gradient control before testing using the equal volume titration mode.
[0022] In some possible implementations, the amount of the pre-added ethylenediaminetetraacetic acid standard titration solution is 15 mL to 20 mL.
[0023] In some possible implementations, the concentration C of the ethylenediaminetetraacetic acid standard titration solution is 0.08 mol / L to 0.12 mol / L, preferably 0.10 mol / L.
[0024] In some possible implementations, the buffer solution includes an ammonia-ammonium chloride buffer solution.
[0025] In some possible implementations, the volume of the buffer solution used is 8 mL to 12 mL.
[0026] In some possible implementations, the indicator includes Chrome Black T.
[0027] In some possible implementations, the amount of the indicator used is 0.2 mL to 0.7 mL, and the concentration is 0.3% to 0.8%.
[0028] In some possible implementations, the titration to the endpoint is in blue.
[0029] In some possible implementations, during the determination of manganese content in the manganese source, the signal drift value of the automatic potentiometric titrator is 25 mv / min to 35 mv / min, and the stirring speed is 6 r / s to 10 r / s.
[0030] The method for determining the manganese content in a manganese source provided in the first aspect of this application employs an automated potentiometric titrator for EDTA potentiometric titration to test the manganese content in the manganese source. The sample is dissolved in a weakly acidic solution with a specific mass fraction (4%~8%), avoiding the safety risks and environmental pollution associated with traditional methods that use strong oxidizing acids (perchloric acid, phosphoric acid, etc.). Subsequently, through an automated pretreatment step of "reduction-masking-pre-complexation," combined with the equal-volume titration mode and endpoint determination of the automated potentiometric titrator, the complex analytical process is integrated into a coherent and controlled workflow. This significantly reduces manual operation and subjective judgment errors, and significantly improves the repeatability, accuracy (high precision, RSD not exceeding 0.20%), and overall detection efficiency (short testing time for a single sample) of the analytical results. It is particularly suitable for the rapid, batch detection needs of manganese source quality in industrial production. Attached Figure Description
[0031] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0032] Figure 1 This is a schematic flowchart of the method for determining the manganese content in a manganese source provided in the embodiments of this application. Detailed Implementation
[0033] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0034] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.
[0035] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.
[0036] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.
[0037] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.
[0038] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as µg, mg, g, or kg.
[0039] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.
[0040] The first aspect of this application provides a method for determining the manganese content in a manganese source, as shown in the attached figure. Figure 1 As shown, it includes the following steps: S10. Obtain a manganese source and dissolve the manganese source in a weakly acidic solution with a mass fraction of 4% to 8% to prepare a sample solution; S20. Place the sample solution on the test stage of the automatic potentiometric titrator, and add a reducing agent solution to stabilize Mn under acidic conditions. 2+Then, the pH value was adjusted to a weakly acidic condition, and a complexing agent solution and a masking agent solution were added to mix and react to obtain a pretreated sample solution; S30. The test was conducted using the equal volume titration mode. After mixing the pretreated sample solution with ethylenediaminetetraacetic acid standard titration solution, a buffer solution was added to adjust the pH to 9.5~10.5. An indicator was added, and the solution was titrated to the endpoint with ethylenediaminetetraacetic acid standard titration solution. The volume of ethylenediaminetetraacetic acid standard titration solution consumed, V1, was recorded. S40. Calculate the manganese content using the formula: Wherein, C is the concentration of the ethylenediaminetetraacetic acid standard titration solution, in mol / L; V1 is the volume of the ethylenediaminetetraacetic acid standard titration solution consumed, in mL; m is the mass of the manganese source, in g; and M is the molar mass of manganese, which is 54.94 g / mol.
[0041] The method for determining the manganese content in a manganese source provided in the first aspect of this application employs an automatic potentiometric titrator to perform EDTA automatic potentiometric titration to test the manganese content in the manganese source. The sample is dissolved in a weakly acidic solution with a specific mass fraction (4%~8%), avoiding the safety risks and environmental pollution associated with traditional methods that use strong oxidizing acids (perchloric acid, phosphoric acid, etc.). Subsequently, through an automated pretreatment step of "reduction-masking-pre-complexation," combined with the equal-volume titration mode and endpoint determination of the automatic potentiometric titrator, the complex analytical process is integrated into a coherent and controlled workflow. This greatly reduces manual operation and subjective judgment errors, significantly improving the repeatability, accuracy (high precision), and overall detection efficiency (short testing time for a single sample) of the analytical results. It is particularly suitable for the rapid, batch detection needs of manganese source quality in industrial production.
[0042] In this embodiment of the automatic potentiometric titrator, the electrodes convert the solution color into an electrical signal during testing. When the solution color changes abruptly, the electrical signal also changes accordingly. The point of abrupt change in potential is the titration endpoint. The content of the analyte is calculated by the amount of titrant consumed. Therefore, the automatic potentiometric titration method used in this embodiment can completely avoid interference from the inherent color of the solution being titrated, and it can automate the titration process, resulting in high efficiency and reduced human titration errors. Compared to traditional manual titration testing, this embodiment uses an automatic potentiometric titration instrument, which simplifies sample pretreatment, allows for simultaneous testing of large batches of samples, improves testing efficiency, avoids errors in endpoint determination and human error during manual titration operations, and enhances the stability of the method. It also involves fewer steps, simpler operation, and shorter testing time for a single sample.
[0043] In step S10 above: In some possible implementations, the manganese source includes at least one of manganese dihydrogen phosphate, manganese nitrate, and manganese phosphate. The determination method of this application establishes a highly universal and stable standardized detection system. Through a unified "weak acid dissolution-reduction masking-automatic potentiometric titration" process, it can accurately address the differences in chemical properties of different manganese sources, thus broadening the application scope of the technology.
[0044] In some possible implementations, the preparation of the sample solution includes the following steps: wetting the manganese source with water, adding the weakly acidic solution, performing cavitation treatment by ultrasound, and then heating at a temperature of 30°C to 40°C to obtain the sample solution. In this case, wetting the manganese source with water first allows the water to fill the gaps between the solid particles of the manganese source and expel air. This process greatly slows down the subsequent reaction rate with the acidic solution, making the reaction stable and gentle, thereby avoiding splashing. Then, the weakly acidic solution is added, and cavitation treatment by ultrasound is performed. Ultrasound treatment increases the activity of manganese ions and enhances the frequency of molecular collisions through cavitation, aiding in dissolution and shortening the dissolution time to 30 seconds. Then, heating is performed at a temperature of 30°C to 40°C, which provides optimal complexation kinetics and better promotes the dissolution of the manganese source.
[0045] In some embodiments, 0.5 g of manganese source is moistened with 0.5 mL to 1 mL of water, and then placed in an ultrasonic instrument for 30 s. The cavitation effect enhances the activity of manganese ions and increases the frequency of molecular collisions, thus aiding dissolution and shortening the dissolution time to 30 s. The sample is then heated to 30°C to 40°C in an electric furnace to provide optimal complexation kinetics.
[0046] In some embodiments, the mass fraction of the weakly acidic solution can be any point value or an interval between any two point values, such as 4%, 5%, 6%, 7%, 8%, etc.
[0047] In some possible implementations, dilute nitric acid is prepared using a weakly acidic solution of (3-10) mL nitric acid and (90-97) mL water. In this case, the dilute nitric acid in this ratio provides a suitable acidic environment, which can efficiently dissolve manganese source samples, effectively inhibit the precipitation of anions such as phosphate, and ensure that manganese ions completely enter the solution. Furthermore, because its concentration is much lower than that of concentrated nitric acid or mixed strong acids used in traditional methods, it significantly reduces the volatilization of acid mist, the corrosiveness to equipment, and the environmental pressure of waste liquid treatment. Thus, while ensuring the sample pretreatment effect and the accuracy of the measurement, it greatly improves the safety and environmental friendliness of the experimental operation.
[0048] For example, in dilute nitric acid, the amount of nitric acid is 3 mL and the amount of water is 97 mL; or, the amount of nitric acid is 4 mL and the amount of water is 96 mL; or, the amount of nitric acid is 5 mL and the amount of water is 95 mL; or, the amount of nitric acid is 6 mL and the amount of water is 94 mL; or, the amount of nitric acid is 7 mL and the amount of water is 93 mL; or, the amount of nitric acid is 8 mL and the amount of water is 92 mL; or, the amount of nitric acid is 9 mL and the amount of water is 91 mL; or, the amount of nitric acid is 10 mL and the amount of water is 90 mL.
[0049] In some possible implementations, the ratio of manganese source to weakly acidic solution is 0.5 g : (4~6) mL. This specific liquid-solid ratio is optimized to ensure that a unit mass of manganese source powder receives the optimal proportion of acid wetting and reaction space.
[0050] For example, the ratio of manganese source to weakly acidic solution can be any typical but non-limiting point value or a range between any two point values, such as 0.5g:4mL, 0.5g:5mL, 0.5g:6mL.
[0051] In step S20 above: In some possible implementations, the preparation of pretreated samples includes the following steps: placing the sample solution in the test stage container of an automated potentiometric titrator; placing the photometric electrode, stirrer, and titration head into the test stage container; and automatically adding preset amounts of reducing agent solution, pH adjuster, complexing agent solution, and masking agent solution sequentially according to a set program for mixing to obtain a pretreated sample solution. In this case, by pre-positioning the photometric electrode, stirrer, and titration head in the container and automatically and accurately adding various reagents sequentially according to a set program, a closed, controlled, and automated pretreatment reaction environment is constructed. This not only completely eliminates the operational errors, cross-contamination, and time inconsistencies that may result from manual step-by-step reagent addition, but also ensures that each sample can undergo reduction, pH adjustment, and ion masking under identical conditions, thereby greatly improving the consistency and reproducibility of pretreatment for different batches of samples.
[0052] In some possible implementations, the acidic conditions have a pH of 0.55–1; this specific strongly acidic environment provides optimal reactivity for reducing agents such as hydroxylamine hydrochloride, enabling them to rapidly and thoroughly remove any Mn that may be present in the solution. 3+ Mn 4+ High-valence manganese ions are reduced to the target valence state of Mn. 2+ At the same time, it effectively inhibited Mn 2+ Hydrolysis or oxidation by air occurs during this stage.
[0053] For example, the pH value of acidic conditions can be any typical but non-limiting point value or a range between any two point values, such as 0.55, 0.6, 0.7, 0.8, 0.9, 1.0.
[0054] In some possible implementations, the reducing agent in the reducing agent solution includes at least one of hydroxylamine hydrochloride and ascorbic acid. Both of these reducing agents maintain excellent reactivity in the aforementioned strongly acidic environment, and can rapidly and selectively remove all high-valence manganese ions (such as Mn) from the solution. 3+ Efficiently and thoroughly reduce it to the target valence state Mn being measured. 2+ At the same time, it effectively prevents Mn 2+ Re-oxidation by air ensures that Mn is in a single and stable valence state. Among them, hydroxylamine hydrochloride has strong reducing properties and good stability, while ascorbic acid provides a more environmentally friendly alternative. The choice between the two gives the method good adaptability and operational flexibility under different laboratory conditions and environmental protection requirements.
[0055] In some possible implementations, the volume ratio of reducing agent solution to sample solution is 1 mL : (5~6) mL. This optimized ratio ensures that a unit volume of sample solution yields a sufficient but not excessive amount of reducing agent, guaranteeing that all high-valence manganese ions are completely and rapidly reduced to Mn under strongly acidic conditions. 2+ This also avoids the potential interference that excessive reducing agent residue may cause to subsequent pH adjustment, complexation reaction or endpoint determination.
[0056] For example, the volume ratio of the reducing agent solution to the sample solution can be any typical but non-limiting point value or an interval between any two point values, such as 1 mL: 5 mL, 1 mL: 5.5 mL, 1 mL: 6 mL.
[0057] In some possible implementations, the concentration of the reducing agent solution is 80 g / L to 120 g / L. In this case, it ensures that the reducing agent added to the sample solution has a sufficient effective concentration, avoiding two problems that may arise from excessive reducing agent: first, excess reducing agent itself is slowly oxidized by dissolved oxygen under subsequent alkaline titration conditions, potentially consuming the titrant EDTA and introducing errors; second, excessively high ionic strength may slightly interfere with the determination of the titration endpoint. Thus, while ensuring complete reaction, it provides optimal assurance for the accuracy and precision of subsequent titration steps, achieving a highly efficient balance between reduction effect and measurement accuracy.
[0058] For example, the concentration of the reducing agent solution can be any typical but non-limiting point value or an interval between any two point values, such as 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L.
[0059] In some possible implementations, the pH of the weakly acidic conditions is adjusted by adding water as a pH adjuster. This avoids the risks of introducing additional alkaline reagents (such as ammonia or sodium hydroxide) that could lead to excessively high local pH levels, hydrolysis and precipitation of manganese or other metal ions.
[0060] In some possible implementations, the pH of the weakly acidic conditions satisfies: 3 ≤ pH < 7. In this case, subsequently added masking agents (such as trisodium citrate and ATMP) can be sufficiently activated, efficiently complexing Fe in the solution. 3+ Ca 2+ Mg 2+ Interfering ions form stable, soluble complexes, preemptively complexing metal ions and preventing precipitation with phosphate ions during subsequent alkali adjustment. Simultaneously, it ensures that Mn... 2+ The ions remain stable without undergoing hydrolysis or premature complexation by EDTA.
[0061] For example, the pH value of a weakly acidic condition can be any typical but non-limiting point value such as 3, 4, 5, 6, 6.5, 6.8, or a range between any two point values.
[0062] In some possible implementations, the complexing agent solution includes at least one of trisodium citrate and potassium sodium tartrate. These complexing agents, under acidic or weakly acidic conditions, react with Fe in the solution. 3+ Ca 2+ Mg 2+ Once the metal ions form stable, soluble complexes, they preemptively complex with the metal ions to prevent precipitation with phosphate ions during subsequent alkali adjustment.
[0063] In some possible implementations, the amount of complexing agent solution used is 5 mL to 10 mL, and the concentration is 3% to 8%. In this case, it is ensured that the complexing agent in the solution is sufficient to completely complex all metal ions.
[0064] For example, the volume of the complexing agent solution can be any typical but non-limiting point value or a range between any two points, such as 5 mL, 6 mL, 7 mL, 8 mL, 9 mL, 10 mL, and the concentration can be any typical but non-limiting point value or a range between any two points, such as 3%, 4%, 5%, 6%, 7%, 8%.
[0065] In some possible implementations, the masking agent solution includes at least one of aminotrimethylphosphonic acid and ammonium fluoride. These masking agents "steal" the Ca complexation by the complexing agent. 2+ and Mg 2+ Ions form more stable complexes, achieving selective interference with ion masking.
[0066] In some possible implementations, the masking agent solution is used in volumes of 1 mL to 5 mL, with a concentration of 1% to 3%. In this case, it ensures complete masking of all Ca. 2+ and Mg 2+ Metal ions, etc.
[0067] For example, the volume of the masking agent solution can be any typical but non-limiting point value or a range between any two points, such as 1 mL, 2 mL, 3 mL, 4 mL, 5 mL, etc., and the concentration can be any typical but non-limiting point value or a range between any two points, such as 1%, 2%, 3%.
[0068] In some embodiments, under weakly acidic conditions (pH 3 ≤ pH < 7), 5 mL to 10 mL of a 5% trisodium citrate solution and 1 mL to 5 mL of a 2% aminotrimethylphosphonic acid (ATMP) solution are added in combination to mask Fe. 3+ Ca 2+ Mg 2 + Interference from plasma. When added under conditions of 3 ≤ pH < 7, citrate ions will react with Fe in the solution. 3+ Ca 2+ Mg 2+ ATMP preemptively complexes metal ions to form stable, soluble complexes, preventing precipitation with phosphate ions during subsequent alkali adjustment. ATMP will "preempt" the Ca complex formed by citric acid. 2+ and Mg 2+ This forms a more stable complex, achieving selective masking of interfering ions. Citrate ions and Fe... 2+ It has a strong complexing ability and can also complex Ca. 2+ / Mg 2+ When the calcium and magnesium content is high, the masking of metal ions may be incomplete. It is used in combination with ATMP to avoid incomplete masking when the calcium and magnesium content is too high, which may lead to precipitation after the addition of buffer solution.
[0069] In step S30 above: In some possible implementations, before testing using the equal volume titration mode (i.e., MET-U titration mode), the pH of the pretreated sample solution is adjusted to 5-6 via pH gradient control. Titration then begins from pH ≈ 5-6 using pH gradient control technology. This precise pH pre-control creates extremely smooth transition conditions for the subsequent rapid addition of buffer solution and instantaneous transition to the optimal titration pH (9.5-10.5), thus avoiding the drastic pH changes and side reactions that might be caused by direct alkali adjustment.
[0070] In some possible implementations, the amount of ethylenediaminetetraacetic acid (EDTA) standard titration solution pre-added is 15 mL to 20 mL. This operation cleverly utilizes the advantages of the equal volume titration mode, avoiding the problems of insufficient pre-addition leading to an excessively long precision titration stage and signal drift affecting endpoint judgment, while also preventing measurement failure caused by excessive pre-addition directly skipping the endpoint. Ultimately, with the assistance of an automatic potentiometric titrator, it achieves efficient detection with rapid titration, accurate endpoint judgment, and high result reproducibility.
[0071] For example, the amount of EDTA standard titration solution added can be any typical but non-limiting point value or an interval between any two points, such as 15 mL, 16 mL, 17 mL, 18 mL, 19 mL, 20 mL.
[0072] In some possible implementations, the concentration C of the ethylenediaminetetraacetic acid standard titration solution is 0.08 mol / L to 0.12 mol / L, preferably 0.10 mol / L. This concentration is the optimal choice after rigorous trade-offs, ensuring that for a typical sample weight (approximately 0.5 g) of manganese source sample, the titration volume consumed (usually in the range of 15-20 mL) falls within the high-precision measurement range of the automatic potentiometric titrator, thereby minimizing calculation errors caused by volume reading errors.
[0073] For example, the concentration C of the ethylenediaminetetraacetic acid standard titration solution can be any typical but non-limiting point value or an interval between any two point values, such as 0.08 mol / L, 0.09 mol / L, 0.10 mol / L, 0.11 mol / L, 0.12 mol / L.
[0074] In some possible implementations, the buffer solution includes an ammonia-ammonium chloride buffer solution. This buffer solution can rapidly and smoothly raise the pH of the reaction system and stabilize it within the optimal titration range of 9.5-10.5. This pH environment not only ensures the preservation of manganese ions (Mn) 2+ ) and EDTA can form a stable complex in a 1:1 stoichiometric ratio, and its stability constant is much higher than that of other coexisting metal ions (such as masked Ca). 2+ Mg 2+ This allows for highly selective titration of manganese ions.
[0075] In some possible implementations, the volume of buffer solution used is 8 mL to 12 mL. This optimized volume ensures that in a sample system containing pre-added EDTA, the pH of the reaction environment can be rapidly and stably increased in one step and precisely maintained within the optimal titration range of 9.5 to 10.5.
[0076] For example, the volume of buffer solution used can be any typical but non-limiting point value or an interval between any two point values, such as 8 mL, 9 mL, 10 mL, 11 mL, 12 mL.
[0077] In some embodiments, the pH is raised to 9.5-10.5 by adding 10 mL of ammonia-ammonium chloride buffer solution through an automated buffer solution system. At this point, the complexation constant of manganese ions with EDTA is significantly higher than that of other metal ions.
[0078] In some possible implementations, the indicator includes Eriochrome Black T (EBT). Eriochrome Black T reacts with Mn in the specific environment of an ammoniacal buffer solution (pH 9.5–10.5). 2+ It forms a sufficiently stable wine-red complex, but its stability is significantly lower than that of Mn. 2+ The colorless complex formed with EDTA; this just-right difference in stability allows EDTA to rapidly abstract Mn bound to Eriochrome Black T at the titration endpoint. 2+ This causes a sharp, reversible abrupt change in the solution color from wine red to pure blue. This color signal is not only easy to observe manually, but can also be accurately and stably captured and identified by the photometric electrodes of an automatic potentiometric titrator. This provides a crucial guarantee for achieving automated endpoint determination with no human subjective bias and high reproducibility.
[0079] In some possible implementations, the indicator is used in quantities of 0.2 mL to 0.7 mL at a concentration of 0.3% to 0.8%. This combination of quantity and concentration provides a moderately strong and clearly distinguishable color signal for the reaction solution in an ammoniacal buffer system, ensuring both the indicator itself and the presence of a small amount of Mn. 2+ This method generates a sufficiently deep wine-red color, ensuring the solution color before the endpoint is easily detectable by the instrument. It also strictly avoids problems such as an excessively dark background color due to excessive indicator dosage or concentration, the consumption of trace amounts of EDTA, or interference with the main complexation reaction due to steric hindrance. In practice, 4 to 6 drops of indicator can be added to achieve the desired effect.
[0080] For example, the amount of indicator can be any typical but non-limiting point value or any range between two points, such as 0.2 mL, 0.3 mL, 0.4 mL, 0.5 mL, 0.6 mL, 0.7 mL, etc., and the concentration can be any typical but non-limiting point value or any range between two points, such as 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%.
[0081] In some possible implementations, the titration endpoint is marked with blue. This blue color is the intrinsic color of the Chrome Black T (EBT) indicator in its free state, serving as a clear, stable, and easily identifiable signal indicating all Mn in the solution. 2+The ions are completely complexed by EDTA, and the EBT indicator is completely released, thus accurately indicating the arrival of the stoichiometric endpoint.
[0082] In some possible implementations, during the determination of manganese content in the manganese source, the signal drift value of the automatic potentiometric titrator is 25 mV / min to 35 mV / min, and the stirring speed is 6 r / s to 10 r / s. In this case, the appropriate stirring speed (6 to 10 r / s) ensures that the reactants and titrant are thoroughly mixed instantaneously, avoiding local concentration unevenness, while accelerating the complexation reaction rate and providing a continuously updated liquid flow to the electrode surface to obtain a stable potential signal. The matched signal drift value (25 to 35 mV / min) serves as a precise endpoint determination threshold, effectively filtering baseline noise caused by stirring or slight temperature fluctuations to avoid premature endpoint misjudgment, and also keenly capturing the true potential jump caused by the addition of trace amounts of EDTA near the endpoint.
[0083] For example, the signal drift value of the automatic potentiometric titrator can be any typical but non-limiting point value or an interval between any two points, such as 25 mv / min, 26 mv / min, 27 mv / min, 28 mv / min, 29 mv / min, 30 mv / min, 31 mv / min, 32 mv / min, 33 mv / min, 34 mv / min, 35 mv / min, etc., and the stirring speed can be any typical but non-limiting point value or an interval between any two points, such as 6 r / s, 7 r / s, 8 r / s, 9 r / s, 10 r / s, etc.
[0084] In step S40 above: based on the concentration C of the ethylenediaminetetraacetic acid standard titration solution, the volume V1 consumed, the mass m of the manganese source, and the molar mass M of manganese, the manganese content is calculated using the following formula: Where C is in mol / L, V1 is in mL, m is in g, and M is the molar mass of manganese, 54.94 g / mol.
[0085] To enable those skilled in the art to clearly understand the above-described implementation details and operations, and to demonstrate the significant advancements in the method for determining the manganese content in the manganese source in the embodiments of this application, the following examples illustrate the above technical solutions.
[0086] Example 1 A method for determining the manganese content in manganese dihydrogen phosphate includes the following steps: 1. Weigh 0.47-0.50g of dried manganese dihydrogen phosphate sample into a 250mL beaker, moisten the sample with a small amount of water, add 5mL of dilute nitric acid (5mL water + 95mL nitric acid), and place the sample in an ultrasonic instrument for 30s to enhance the activity of manganese ions and increase the frequency of molecular collisions through cavitation effect, thus aiding in dissolution. Place the sample on an electric furnace and heat it to 30℃ to provide optimal complexation kinetics conditions, thus obtaining the sample solution.
[0087] 2. Place the sample solution obtained in step 1 into a beaker on the test stage of the automatic potentiometric titrator. Place the photometric electrode, stirrer, and titration head into the beaker. Click the start test button. The reagents will be added automatically according to the set program. Under acidic conditions (pH 0.55~1), add 1 mL of 100 g / L hydroxylamine hydrochloride solution as a reducing agent to stabilize Mn. 2+ Add approximately 150 mL of water to adjust the pH of the solution to a weakly acidic condition of 5-6. Add 10 mL of 5% trisodium citrate solution and 5 mL of 2% ATMP aminotrimethylphosphonic acid solution, and stir thoroughly for 1-2 minutes. Perform the test using MET-U titration mode. Pre-add 15 mL of EDTA standard titration solution (concentration C: 0.1 mol / L) using an automatic dispenser, stir thoroughly for 20 seconds, add 10 mL of ammonia-ammonium chloride buffer solution to adjust the pH to 9.5-10.5, and add 5 drops of 0.5% EBT Chrome Black T indicator. Continue titrating with EDTA standard titration solution (concentration C) in conjunction with a photometric electrode until a pure blue endpoint is reached. The automatic potentiometric titrator will automatically stop and record the EDTA consumption volume V1. The manganese content in manganese dihydrogen phosphate will be automatically calculated according to the following formula: ; Where C is in mol / L, V1 is in mL, m is in g, and M is the molar mass of manganese, 54.94, in g / mol.
[0088] The test results of manganese content for different sample masses are shown in Table 1 below (where RSD is the relative standard deviation):
[0089] Example 2 A method for determining the manganese content in manganese dihydrogen phosphate includes the following steps: 1. Weigh 0.47-0.50g of dried manganese dihydrogen phosphate sample into a 250mL beaker, moisten the sample with a small amount of water, add 5mL of dilute nitric acid (5mL water + 95mL nitric acid), and treat the sample in an ultrasonic instrument for 30s. The cavitation effect will increase the activity of manganese ions and enhance the frequency of molecular collisions, thus aiding in their dissolution. Place the sample on an electric furnace and heat it to 40℃ to provide optimal complexation kinetics conditions, thus obtaining the sample solution.
[0090] 2. Place the sample solution obtained in step 1 into a beaker on the test stage of the automatic potentiometric titrator. Place the photometric electrode, stirrer, and titration head into the beaker. Click the start test button. The reagents will be added automatically according to the set program. Under acidic conditions (pH 0.55~1), add 1 mL of 100 g / L hydroxylamine hydrochloride solution as a reducing agent to stabilize Mn. 2+ Add approximately 150 mL of water to adjust the pH of the solution to a weakly acidic condition of 5-6. Add 5 mL of 5% trisodium citrate solution and 5 mL of 2% ATMP aminotrimethylphosphonic acid solution, and stir well for 1-2 minutes. Perform the test using MET-U titration mode. Pre-add 15 mL of EDTA standard titration solution (concentration C: 0.1 mol / L) using an automatic dispenser, stir well for 20 seconds, add 10 mL of ammonia-ammonium chloride buffer solution to adjust the pH to 9.5-10.5, and add 5 drops of 0.5% EBT Chrome Black T indicator. Continue titrating with EDTA standard titration solution (concentration C) in conjunction with a photometric electrode until a pure blue endpoint is reached. The automatic potentiometric titrator will automatically stop and record the EDTA consumption volume V1. The manganese content in manganese dihydrogen phosphate will be automatically calculated according to the following formula: ; Where C is in mol / L, V1 is in mL, m is in g, and M is the molar mass of manganese, 54.94, in g / mol.
[0091] The test results of manganese content for different sample masses are shown in Table 2 below (where RSD is the relative standard deviation):
[0092] Example 3 A method for determining the manganese content in manganese dihydrogen phosphate includes the following steps: 1. Weigh 0.47-0.50g of dried manganese dihydrogen phosphate sample into a 250mL beaker, moisten the sample with a small amount of water, add 5mL of dilute nitric acid (5mL water + 95mL nitric acid), and treat the sample in an ultrasonic instrument for 30s. The cavitation effect will increase the activity of manganese ions and enhance the frequency of molecular collisions, thus aiding in their dissolution. Place the sample on an electric furnace and heat it to 40℃ to provide optimal complexation kinetics conditions, thus obtaining the sample solution.
[0093] 2. Place the sample solution obtained in step 1 into a beaker on the test stage of the automatic potentiometric titrator. Place the photometric electrode, stirrer, and titration head into the beaker. Click the start test button. The reagents will be added automatically according to the set program. Under acidic conditions (pH 0.55~1), add 1 mL of 110 g / L hydroxylamine hydrochloride solution as a reducing agent to stabilize Mn. 2+ Add approximately 150 mL of water to adjust the pH of the solution to a weakly acidic condition of 5-6. Add 8 mL of 5% trisodium citrate solution and 5 mL of 2% ATMP aminotrimethylphosphonic acid solution, and stir thoroughly for 2 min. Perform the test using MET-U titration mode. Pre-add 16 mL of EDTA standard titration solution (concentration C: 0.1 mol / L) using an automatic dispenser, stir thoroughly for 20 s, add 10 mL of ammonia-ammonium chloride buffer solution to adjust the pH to 9.5-10.5, and add 5 drops of 0.5% EBT Chrome Black T indicator. Continue titrating with EDTA standard titration solution (concentration C) in conjunction with a photometric electrode until a pure blue endpoint is reached. The automatic potentiometric titrator will automatically stop and record the EDTA consumption volume V1. It will also automatically calculate the manganese content in manganese dihydrogen phosphate according to the following formula: ; Where C is in mol / L, V1 is in mL, m is in g, and M is the molar mass of manganese, 54.94, in g / mol.
[0094] The test results of manganese content for different sample masses are shown in Table 3 below (where RSD is the relative standard deviation):
[0095] Example 4 A method for determining the manganese content in manganese dihydrogen phosphate includes the following steps: 1. Weigh 0.47-0.50g of dried manganese dihydrogen phosphate sample into a 250mL beaker, moisten the sample with a small amount of water, add 5mL of dilute nitric acid (5mL water + 95mL nitric acid), and treat the sample in an ultrasonic instrument for 30s. The cavitation effect will increase the activity of manganese ions and enhance the frequency of molecular collisions, thus aiding in their dissolution. Place the sample on an electric furnace and heat it to 40℃ to provide optimal complexation kinetics conditions, thus obtaining the sample solution.
[0096] 2. Place the sample solution obtained in step 1 into a beaker on the test stage of the automatic potentiometric titrator. Place the photometric electrode, stirrer, and titration head into the beaker. Click the start test button. The reagents will be added automatically according to the set program. Under acidic conditions (pH 0.55~1), add 1 mL of 120 g / L hydroxylamine hydrochloride solution as a reducing agent to stabilize Mn. 2+ Add approximately 150 mL of water to adjust the pH of the solution to a weakly acidic condition of 5-6. Add 5 mL of 5% trisodium citrate solution and 5 mL of 2% ATMP aminotrimethylphosphonic acid solution, and stir thoroughly for 1-2 minutes. Perform the test using MET-U titration mode. Pre-add 17 mL of EDTA standard titration solution (concentration C: 0.1 mol / L) using an automatic dispenser, stir thoroughly for 20 seconds, add 10 mL of ammonia-ammonium chloride buffer solution to adjust the pH to 9.5-10.5, and add 5 drops of 0.5% EBT Chrome Black T indicator. Continue titrating with EDTA standard titration solution (concentration C) in conjunction with a photometric electrode until a pure blue endpoint is reached. The automatic potentiometric titrator will automatically stop and record the EDTA consumption volume V1. The manganese content in manganese dihydrogen phosphate will be automatically calculated according to the following formula: ; Where C is in mol / L, V1 is in mL, m is in g, and M is the molar mass of manganese, 54.94, in g / mol.
[0097] The test results of manganese content for different sample masses are shown in Table 4 below (where RSD is the relative standard deviation):
[0098] Comparative Example 1 A method for determining the manganese content in manganese dihydrogen phosphate by artificial titration, comprising the following steps: Weigh the sample into a 250 mL Erlenmeyer flask, accurate to 0.0001 g, dissolve in nitric acid, add 1 mL of hydroxylamine hydrochloride solution, 100 mL of water, 10 mL of ammonia-ammonium chloride buffer solution to adjust the pH to ≈10, and add 5 drops of Eriochrome Black T indicator. Titrate with 0.10 mol / L EDTA standard titration solution in a 50 mL burette until the solution turns pure blue, which is the endpoint.
[0099] The formula for calculating the manganese content is: Mn%=(C*V*M) / (m*1000)*100%; where: C is the concentration of EDTA standard solution, mol / L, V is the volume of EDTA standard solution consumed, mL, M is the relative atomic mass of manganese, 54.94 g / mol, and m is the sample weight, g.
[0100] This Comparative Example 1 is compared with the same sample tested by the EDTA automatic potentiometric titration method in Example 3 of this application. The test results are shown in Table 5 below (where RSD is the relative standard deviation):
[0101] As shown in Table 3 above, the EDTA automatic potentiometric titration method used in Example 3 of this application provides better accuracy in sample detection than the manual titration method used in Comparative Example 1. This application uses an automatic potentiometric titration instrument, avoiding testing errors caused by manual titration and improving the stability of the method. Furthermore, it is simple to operate, with a single sample detection time ≤15 minutes, while manual titration is much more time-consuming.
[0102] Comparative Example 2 A national standard method for determining the manganese content in manganese dihydrogen phosphate by perchloric acid redox titration, comprising the following steps: Weigh the sample into a 250 mL Erlenmeyer flask, accurate to 0.0001 g. Add 15 mL of phosphoric acid, 5 mL of nitric acid, and 5 mL of perchloric acid. Heat until the sample is completely dissolved. Continue heating to evaporate the perchloric acid until no more fumes are emitted, no small bubbles are produced at the bottom of the flask, and the liquid surface is calm. Remove the flask and cool it. Add 60 mL of distilled water, shake well, and cool to room temperature. Titrate with ferrous ammonium sulfate until the solution changes from red to bright yellow, indicating the endpoint.
[0103] The formula for calculating the manganese content is: Mn%=(C*V*M) / (m*1000)*100%; where: C is the concentration of EDTA standard solution, mol / L, V is the volume of EDTA standard solution consumed, mL, M is the relative atomic mass of manganese, 54.94 g / mol, and m is the sample weight, g.
[0104] This Comparative Example 2 is compared with the same sample tested by the EDTA automatic potentiometric titration method in Example 4 of this application. The test results are shown in Table 4 below (where RSD is the relative standard deviation):
[0105] As can be seen from the test results in Table 4 above, the EDTA automatic potentiometric titration method used in Example 4 of this application has a higher accuracy in detecting the sample than the detection results of the perchloric acid redox titration method used in Comparative Example 2.
[0106] The EDTA automatic potentiometric titration method of this application is used to measure manganese content. Its RSD (relative standard deviation) does not exceed 0.20%, which greatly reduces the manual operation and subjective judgment error, and significantly improves the repeatability, accuracy (high precision) and overall detection efficiency (short test time for a single sample) of the analysis results. It is particularly suitable for the rapid and batch detection needs of manganese source quality in industrial production.
[0107] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A method for determining the manganese content in a manganese source, characterized in that, Includes the following steps: Obtain a manganese source and dissolve the manganese source in an acidic solution with a mass fraction of 4% to 8% to prepare a sample solution; The sample solution was placed on the test stage of an automatic potentiometric titrator, and a reducing agent solution was added under acidic conditions to stabilize Mn. 2+ Then, the pH value was adjusted to a weakly acidic condition, and a complexing agent solution and a masking agent solution were added to mix and react to obtain a pretreated sample solution; The test was conducted using an equal volume titration mode. After mixing the pretreated sample solution with ethylenediaminetetraacetic acid standard titration solution, a buffer solution was added to adjust the pH to 9.5-10.
5. An indicator was added, and the solution was titrated to the endpoint with the ethylenediaminetetraacetic acid standard titration solution. The volume V1 of the ethylenediaminetetraacetic acid standard titration solution consumed was recorded. Calculate the manganese content using the formula: ; Wherein, C is the concentration of the ethylenediaminetetraacetic acid standard titration solution, in mol / L; V1 is the volume of the ethylenediaminetetraacetic acid standard titration solution consumed, in mL; m is the mass of the manganese source, in grams; M is the molar mass of manganese, which is 54.94 g / mol.
2. The method for determining the manganese content in a manganese source as described in claim 1, characterized in that, The manganese source includes at least one of manganese dihydrogen phosphate, manganese nitrate, and manganese phosphate.
3. The method for determining the manganese content in a manganese source as described in claim 1 or 2, characterized in that, The preparation of the sample solution includes the following steps: wetting the manganese source with water, adding the weak acidic solution, performing cavitation effect treatment by ultrasound, and heating at a temperature of 30℃~40℃ to obtain the sample solution.
4. The method for determining the manganese content in a manganese source as described in claim 3, characterized in that, The weakly acidic solution comprises (3~10) mL of nitric acid and (90~97) mL of water to make dilute nitric acid; And / or, the ratio of the manganese source to the weakly acidic solution is 0.5 g: (4~6) mL.
5. The method for determining the manganese content in a manganese source as described in claim 1, 2, or 4, characterized in that, The preparation of the pretreated sample includes the following steps: placing the sample solution in the test stage container of an automatic potentiometric titrator, placing the photometric electrode, stirrer and titration head into the test stage container, and automatically adding preset amounts of the reducing agent solution, pH adjuster, complexing agent solution and masking agent solution in sequence according to the set program to mix and obtain the pretreated sample solution.
6. The method for determining the manganese content in a manganese source as described in claim 5, characterized in that, The pH value of the acidic conditions is 0.55~1; And / or, in the reducing agent solution, the reducing agent includes at least one of hydroxylamine hydrochloride and ascorbic acid; And / or, the volume ratio of the reducing agent solution to the sample solution is 1 mL: (5~6) mL; And / or, the concentration of the reducing agent solution is 80 g / L to 120 g / L; And / or, the pH value of the weakly acidic conditions is adjusted by adding water as the pH adjuster; And / or, the pH value of the weakly acidic condition satisfies: 3 ≤ pH < 7; And / or, in the complexing agent solution, the complexing agent includes at least one of trisodium citrate and potassium sodium tartrate; And / or, the amount of the complexing agent solution used is 5 mL to 10 mL, and the concentration is 3% to 8%; And / or, in the masking agent solution, the masking agent includes at least one of aminotrimethylphosphonic acid and ammonium fluoride; And / or, the amount of the masking agent solution used is 1 mL to 5 mL, and the concentration is 1% to 3%.
7. The method for determining the manganese content in a manganese source as described in claims 1, 2, 4, or 6, characterized in that, Before conducting the test using the aforementioned equal-volume titration mode, the pH of the pretreated sample solution is adjusted to 5-6 using pH gradient control.
8. The method for determining the manganese content in a manganese source as described in claim 7, characterized in that, The amount of the ethylenediaminetetraacetic acid standard titration solution added beforehand is 15 mL to 20 mL; And / or, the concentration C of the ethylenediaminetetraacetic acid standard titration solution is 0.08 mol / L to 0.12 mol / L, preferably 0.10 mol / L; And / or, the buffer solution comprises an ammonia-ammonium chloride buffer solution; And / or, the amount of the buffer solution used is 8 mL to 12 mL.
9. The method for determining the manganese content in a manganese source as described in claim 8, characterized in that, The indicator includes Chrome Black T; And / or, the amount of the indicator used is 0.2 mL to 0.7 mL, and the concentration is 0.3% to 0.8%; And / or, the color of the titration to the endpoint is blue.
10. The method for determining the manganese content in a manganese source as described in claims 1, 2, 4, 6, 8, or 9, characterized in that, During the determination of manganese content in the manganese source, the signal drift value of the automatic potentiometric titrator is 25mv / min~35mv / min, and the stirring speed is 6r / s~10r / s.