Method for determining chloride ions in cobalt hydroxide
After reacting with aqueous nitric acid solution and pure water in cobalt hydroxide, the silver ion concentration is measured with excessive silver nitrate, and the chloride ion content is indirectly calculated, which solves the problem of chloride ion determination error in the prior art, and achieves simple and accurate Determination of chloride ions in cobalt hydroxide.
Patent Information
- Application Number
- CN202411262976.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-10
- Publication Date
- 2024-12-31
AI Technical Summary
The existing methods for measuring chloride ions in cobalt hydroxide have problems such as water extraction that cannot completely dissolve chloride ions, divalent cobalt ions in the solution interfere with the end point of titration, titration speed and uneven stirring, resulting in measurement errors.
After heating and dissolving the cobalt hydroxide sample with aqueous nitric acid solution, it is added to pure water and reacts with excess silver nitrate. After standing, it is determined the silver ion concentration. The chloride ion content is indirectly calculated using the formula, which avoids direct observation of the titration end point and divalent cobalt ions. The effect of color.
Accurate determination of chloride ions is achieved, operating difficulty and measurement errors are reduced, and the accuracy and reliability of measurement results are improved.
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Abstract
Description
Technical Field
[0001] The invention relates to the field of measurement technology, in particular to a method for determining chloride ions in cobalt hydroxide. Background Art
[0002] In the cobalt industry, it is critical to measure the chloride ion content in cobalt hydroxide because the presence of chloride ions may affect the purity of cobalt hydroxide and the quality of the final product. Chloride ions may come from raw materials, contamination during the production process, or by-products in the reaction system. If the chloride ion content in cobalt hydroxide is too high, it may introduce impurities in subsequent chemical reactions and affect the electrochemical properties of cobalt, especially in applications such as battery manufacturing, which may lead to decreased battery performance. In addition, chloride ions may react with cobalt ions in cobalt hydroxide under certain conditions to form unstable compounds, which may cause problems during storage or handling. Therefore, by accurately measuring the chloride ion content, it can be ensured that the cobalt hydroxide product meets the strict standards of specific applications and avoid product performance problems caused by excessive chloride ions.
[0003] At present, the determination of chloride ions in cobalt hydroxide is mainly carried out by silver nitrate titration and colorimetry. For the silver nitrate titration method, the following steps are mainly included: (1) Sample preparation: Accurately weigh a certain amount of cobalt hydroxide sample and dissolve it in distilled water to prepare the test solution; (2) Indicator addition: Add a few drops of potassium chromate indicator to the test solution to make the solution light yellow; (3) Titration operation: Use a calibrated silver nitrate standard solution for titration, shake the solution while titrating to ensure that silver nitrate and chloride ions react fully, and the end point is when the solution changes from light yellow to light red; (4) Result calculation: Record the volume of silver nitrate standard solution consumed, and calculate the chloride ion content in the sample based on the concentration and volume of silver nitrate. The titration should be carried out in a neutral or slightly alkaline solution to avoid interference from the indicator under acidic or alkaline conditions. At the same time, ensure that the silver nitrate titrant used is stored away from light and the titration operation is carried out in a brown bottle. For the colorimetric method, the following steps are mainly included: (1) Sample preparation: First, a certain amount of cobalt hydroxide sample needs to be accurately weighed and dissolved in an appropriate solvent, usually deionized water or distilled water; (2) Color reaction: Add a color developer (such as silver nitrate solution) to the sample solution, and chloride ions react with silver nitrate to form a white silver chloride precipitate. In some cases, other reagents may need to be added to promote the color reaction or eliminate the influence of interfering substances; (3) Colorimetric determination: Transfer the color-developed sample solution to a cuvette and use a spectrophotometer to measure the absorbance at a specific wavelength. Usually, the silver chloride precipitate will produce absorption in the visible light region. The concentration of chloride ions in the sample can be determined by comparing the absorbance of the sample with the absorbance of a standard solution of known chloride ion concentration; (4) Result calculation: Calculate the actual concentration of chloride ions in the sample based on the standard curve and the absorbance value of the sample.
[0004] The above method has the following main problems in the determination of chloride ions. The first is that the use of water to extract chloride ions cannot completely dissolve the chloride ions in the pores of cobalt hydroxide in water, resulting in serious deviations in the test. If acid is used for digestion first, the solution after digestion contains divalent cobalt ions, causing the solution to be brick red, and this color is consistent with the color of the titration endpoint, so the solution after digestion cannot be used for this method. In addition, the titration endpoint is judged based on color changes, which may be affected by the judgment and introduce errors; and too fast a titration speed or uneven stirring may cause an inaccurate titration endpoint because the precipitate may be formed incompletely or unevenly. All of the above problems will affect the accurate determination of chloride ions.
[0005] In summary, a method for determining chloride ions in cobalt hydroxide with simple steps, accuracy and low cost is provided to solve the problems existing in the existing measurement methods, which has positive significance for improving the quality of cobalt hydroxide products. Summary of the invention
[0006] In view of the above-mentioned defects of the prior art, in a first aspect of the present invention, a method for determining chloride ions in cobalt hydroxide with a simple method and accurate results is provided, comprising the following steps: (1) Take a cobalt hydroxide sample, whose mass is recorded as m1 in g; take a nitric acid aqueous solution, whose volume is recorded as L1 in mL; add the cobalt hydroxide sample to the nitric acid aqueous solution, heat it to completely dissolve it, and obtain a sample digestion solution; (2) Take a portion of the sample digestion solution as the test solution, and record its volume as L2 in mL; add the test solution to pure water and mix to obtain a titration solution; add an excess of silver nitrate aqueous solution to the titration solution until the precipitation is complete and no solid is precipitated, thereby obtaining a titration solution; wherein the concentration of the silver nitrate aqueous solution is recorded as C1 in g / L; the amount of the silver nitrate aqueous solution is recorded as V1 in L; and the volume of the titration solution is V2 in L; (3) After the titration solution is allowed to stand, the supernatant is aspirated and the silver ion concentration in the supernatant is measured, which is recorded as C2 in g / L. (4) The chloride ion content is calculated based on the following formula: ; Wherein, C is the chloride ion content, in mg / g; is the molar mass of silver nitrate; is the molar mass of silver ion; is the molar mass of chloride ion.
[0007] Nitric acid digestion is applicable to a variety of samples, including water quality testing, soil heavy metal content analysis, etc., and can handle complex samples including organic matter and various inorganic substances. Generally, the operation of using nitric acid (1+1) for sample digestion is relatively simple and can be performed under normal pressure, which can ensure the analysis effect while controlling the cost.
[0008] Preferably, in step (1), the nitric acid aqueous solution is prepared by mixing nitric acid and water in a volume ratio of 1:1.
[0009] The temperature of nitric acid digestion is usually controlled at 95±5℃. Within this temperature range, nitric acid can ensure sufficient digestion capacity while avoiding sample volatilization or incomplete decomposition due to excessively high temperature. In addition, controlling within this temperature range can ensure the safety of the digestion process, reduce the generation of harmful gases, and improve digestion efficiency.
[0010] Preferably, in step (1), the heating temperature is 90-100°C.
[0011] Adding pure water is helpful to dilute the test solution so that the chloride ions can fully react with the excess silver nitrate. The amount of pure water can be added according to the actual situation. From the perspective of test convenience, the final volume of the solution to be titrated is suitable to be fixed to the volume of the nitric acid aqueous solution, which is also helpful for recording the test process and reducing human errors caused by different amounts of each indicator.
[0012] Preferably, in step (2), the volume of the solution to be titrated obtained after adding the test solution to pure water and mixing is the same as L1.
[0013] After using excess silver nitrate to react with chloride ions, the solution needs to be left to stand for a while. This is because the silver chloride precipitate generated by the reaction may be suspended in the solution due to Brownian motion and other reasons. If the measurement is performed immediately, some of the precipitate may not settle, resulting in inaccurate results. Standing allows the precipitate to settle fully, thereby improving the accuracy of the test. In addition, standing can also help observe the formation of the precipitate to ensure that the reaction has been completed.
[0014] Preferably, in step (3), the step is performed at room temperature for 2-3 hours.
[0015] 3,5-Br2-PADAP spectrophotometry and flame atomic absorption spectrophotometry are two commonly used analytical methods for determining the content of silver ions. The 3,5-Br2-PADAP spectrophotometry uses silver ions and 3,5-Br2-PADAP (3,5-dibromo-2-pyridylazo-5-diethylaminophenol) to form a stable purple-red complex under alkaline conditions, and quantitatively analyzes the content of silver ions by measuring the absorbance. This method has high sensitivity and selectivity and is suitable for the determination of silver in water samples. Flame atomic absorption spectrophotometry is based on the absorption characteristics of silver atoms at a specific wavelength of light (328.1 nm) to quantitatively analyze the content of silver ions. This method is suitable for samples with high silver content and has high accuracy and a wide dynamic range. The advantages of flame atomic absorption are simple operation, fast analysis speed, and good anti-interference ability for multiple coexisting elements. Those skilled in the art can choose a suitable method according to actual conditions.
[0016] Preferably, in step (3), the silver ion concentration is determined by 3,5-Br2-PADAP spectrophotometry or flame atomic absorption spectrophotometry.
[0017] In the measurement of samples, choosing decimal integer sampling helps to simplify the measurement process, reduce the difficulty of statistics and calculations, and improve the efficiency of data processing.
[0018] Preferably, the sampling mass of the cobalt hydroxide sample is 1.0 g, the volume of the nitric acid aqueous solution is 100 mL, the sampling volume of the test solution is 10 mL, and the concentration of the silver nitrate aqueous solution is 0.01 g / L.
[0019] Further preferably, the calculation of chloride ion content is simplified to the following formula: .
[0020] Based on the above technical scheme, the inventive concept of the present invention is to indirectly determine the reaction amount of chloride ions by measuring the consumption of silver ions, thereby replacing the method of directly measuring the chloride ion content. In the formula, C1V1 can determine the total amount of silver nitrate used, and its molar amount can be determined by dividing it by the molar mass of silver nitrate; similarly, the silver ion concentrations in the supernatant and the titration solution are consistent, so the content of remaining silver ions in the titration solution can be determined by C2V2, and the molar content of silver ions can be obtained by dividing it by its molar mass. The actual silver ion consumption involved in the titration reaction can be obtained by subtracting the remaining molar content of silver ions from the total molar amount of silver nitrate. According to the titration reaction formula (Cl - + Ag + = AgCl↓), from which the molar amount of chloride ions in the test solution can be determined, and the amount of chloride ions can be obtained by multiplying it by the molar mass of chloride ions. Since the test solution is taken from the sample digestion solution, the total amount of chloride ions in the sample digestion solution needs to be further multiplied by L1 / L2, and finally divided by the sample mass m1 to obtain the content of chloride ions per unit mass of cobalt hydroxide, in g / g. Usually, the chloride ion content in the sample is low and is suitable to be expressed in mg / g, so its value needs to be multiplied by 1000 in the end.
[0021] The advantage of the present invention is that there is no need to strictly control the operation (such as observing color changes, etc.) to determine the endpoint of the titration. The determination can be completed by adding an excess of silver nitrate solution, and the difficulty of operation is significantly reduced. The core of the present invention is that the accurate determination of the titration endpoint in the traditional method can be omitted, so there is no need to consider the influence of the color of the divalent cobalt ions. All chloride ions in the cobalt hydroxide can be leached out by acid digestion, making the test results more accurate. In addition, the determination of chloride ions is converted into the form of determining silver ions, and only excess silver nitrate needs to be added to determine the dosage by difference, which is simpler than the traditional test method.
[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: The invention provides a method for determining chloride ions in cobalt hydroxide, which can fully leach chloride ions in the cobalt hydroxide, and converts the determination of chloride ions into the determination of silver ions, and does not require precise control of the titration end point, and has the advantages of simple method and accurate result. DETAILED DESCRIPTION
[0023] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.
[0024] In the following embodiments: Aqueous nitric acid solution (1+1), prepared by mixing nitric acid and water in a volume ratio of 1:1; Cobalt hydroxide sample 1, washed conductivity is about 100 us / cm; Cobalt hydroxide sample 2, washed conductivity is about 500 us / cm.
[0025] Example 1 The method for determining chloride ions in cobalt hydroxide is as follows: (1) Take 1.0 g of cobalt hydroxide sample 1 and place it in 100 mL of nitric acid aqueous solution (1+1), and heat it on a low-temperature heating plate until it is completely dissolved to obtain a sample digestion solution; (2) Take 10 mL of the sample digestion solution as the test solution, add the test solution to a beaker containing 90 mL of pure water, and mix to obtain the titration solution; slowly add an excess of 0.01 g / L of silver nitrate aqueous solution to the beaker until no solid precipitates to obtain the titration solution; record the amount of silver nitrate aqueous solution used, recorded as V1, in L; record the total volume of the titration solution, recorded as V2, in L; (3) The titration solution was allowed to stand at room temperature for 2 h, 10 mL of the supernatant was taken for later use, and the concentration of silver ions in the supernatant was determined by 3,5-Br2-PADAP spectrophotometry, which was recorded as C2 in g / L. (4) The chloride ion content is calculated based on the following formula: ; The chloride ion content was measured to be 0.432 mg / g.
[0026] The cobalt hydroxide sample 1 was tested repeatedly 5 times, and the chloride ion contents were measured to be 0.435 mg / g, 0.437 mg / g, 0.428 mg / g, 0.407 mg / g, and 0.461 mg / g, respectively.
[0027] Example 2 The method for determining chloride ions in cobalt hydroxide is as follows: (1) Take 1.0 g of cobalt hydroxide sample 2 and place it in 100 mL of nitric acid aqueous solution (1+1), and heat it on a low-temperature heating plate until it is completely dissolved to obtain a sample digestion solution; (2) Take 10 mL of the sample digestion solution as the test solution, add the test solution to a beaker containing 90 mL of pure water, and mix to obtain the titration solution; slowly add an excess of 0.01 g / L of silver nitrate aqueous solution to the beaker until no solid precipitates to obtain the titration solution; record the amount of silver nitrate aqueous solution used, recorded as V1, in L; record the total volume of the titration solution, recorded as V2, in L; (3) The titration solution was allowed to stand at room temperature for 2 h, 10 mL of the supernatant was taken for later use, and the concentration of silver ions in the supernatant was determined by 3,5-Br2-PADAP spectrophotometry, which was recorded as C2 in g / L. (4) The chloride ion content is calculated based on the following formula: ; The chloride ion content was measured to be 1.534 mg / g.
[0028] The test of cobalt hydroxide sample 2 was repeated 5 times, and the chloride ion contents were measured to be 1.551 mg / g, 1.548 mg / g, 1.578 mg / g, 1.564 mg / g, and 1.547 mg / g, respectively.
[0029] Example 3 The method for determining chloride ions in cobalt hydroxide is as follows: (1) Take 1.0 g of cobalt hydroxide sample 1 and place it in 100 mL of nitric acid aqueous solution (1+1), and heat it on a low-temperature heating plate until it is completely dissolved to obtain a sample digestion solution; (2) Take 10 mL of the sample digestion solution as the test solution, add the test solution to a beaker containing 90 mL of pure water, and mix to obtain the titration solution; slowly add an excess of 0.01 g / L of silver nitrate aqueous solution to the beaker until no solid precipitates to obtain the titration solution; record the amount of silver nitrate aqueous solution used, recorded as V1, in L; record the total volume of the titration solution, recorded as V2, in L; (3) The titration solution was allowed to stand at room temperature for 2 h, 10 mL of the supernatant was taken for later use, and the concentration of silver ions in the supernatant was determined by flame atomic absorption spectrophotometry, which was recorded as C2 in g / L. (4) The chloride ion content is calculated based on the following formula: .
[0030] Example 4 This example calculates the relative standard deviation (RSD) of multiple measurement results in Examples 1 and 2 in the application, which is used to represent the degree of dispersion of the data set relative to its average value, so as to study the accuracy of the test of this method. The statistical results are shown in Table 1.
[0031] Table 1: Chloride ion content test results and relative standard deviation
[0032] Cobalt hydroxide sample 1 has a relatively low chloride content with an RSD of 4.004%. A relative standard deviation of less than 5% indicates a low degree of dispersion in the results. Although it is not as tight as when it is less than 2%, it still indicates that the data has good stability and reliability. In general application scenarios, relative standard deviations below 5% are considered acceptable, especially when extreme precision is not required. Cobalt hydroxide sample 2 has a relatively higher chloride content with an RSD of 0.984%. A relative standard deviation of less than 2% generally means that the results are very tight, and the data points are very close to the mean, indicating extremely high measurement accuracy and data stability. This low dispersion indicates that the results are highly reliable and repeatable.
[0033] In summary, the present invention has the advantages of being easy to operate and accurate. The present invention does not need to strictly control the operation, such as observing the color change to determine the endpoint of the titration, and the determination can be completed by adding an excess of silver nitrate solution, and the difficulty of operation is significantly reduced. This method solves the adverse effects of the color of divalent cobalt ions, and can leach all chloride ions in cobalt hydroxide by acid digestion, making the test results more accurate. In addition, the determination of chloride ions is converted into the form of determining silver ions, and it is only necessary to add excess silver nitrate to determine the dosage by difference, which is simpler than the traditional test method and has good applicability in the cobalt industry.
[0034] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.
Claims
1. A method for determining chloride ions in cobalt hydroxide, characterized in that: The steps include: (1) Take a cobalt hydroxide sample, record its mass as m1, in g; take a nitric acid aqueous solution, record its volume as L1, in mL; The cobalt hydroxide sample is added to the nitric acid aqueous solution and heated to completely dissolve it to obtain a sample digestion solution; (2) Take a portion of the sample digestion solution as the test solution, and record its volume as L2 in mL; add the test solution to pure water and mix to obtain a titration solution; add an excess of silver nitrate aqueous solution to the titration solution until the precipitation is complete and no solid is precipitated, thereby obtaining a titration solution; wherein the concentration of the silver nitrate aqueous solution is recorded as C1 in g / L; the amount of the silver nitrate aqueous solution is recorded as V1 in L; and the volume of the titration solution is V2 in L; (3) After the titration solution is allowed to stand, the supernatant is aspirated and the silver ion concentration in the supernatant is measured, which is recorded as C2 in g / L. (4) The chloride ion content is calculated based on the following formula: ； Wherein, C is the chloride ion content, in mg / g; is the molar mass of silver nitrate; is the molar mass of silver ion; is the molar mass of chloride ion.
2. The method for determining chloride ions in cobalt hydroxide according to claim 1, wherein: In the step (1), the nitric acid aqueous solution is prepared by mixing nitric acid and water in a volume ratio of 1:
1.
3. The method for determining chloride ions in cobalt hydroxide according to claim 1, wherein: In the step (1), the heating temperature is 90-100°C.
4. The method for determining chloride ions in cobalt hydroxide according to claim 1, wherein: In the step (2), the volume of the solution to be titrated obtained after adding the test solution into pure water and mixing is L1.
5. The method for determining chloride ions in cobalt hydroxide according to claim 1, wherein: In the step (3), the mixture is allowed to stand at room temperature for 2-3 hours.
6. The method for determining chloride ions in cobalt hydroxide according to claim 1, wherein: In the step (3), the silver ion concentration is determined by 3,5-Br2-PADAP spectrophotometry or flame atomic absorption spectrophotometry.
7. The method for determining chloride ions in cobalt hydroxide according to claim 1, wherein: The sampling mass of the cobalt hydroxide sample is 1.0 g, the volume of the nitric acid aqueous solution is 100 mL, the sampling volume of the test solution is 10 mL, and the concentration of the silver nitrate aqueous solution is 0.01 g / L.
8. The method for determining chloride ions in cobalt hydroxide according to claim 7, wherein The calculation of chloride ion content is simplified to the following formula: 。