Determination method for organic additive in ammonia chloride process electrolytic zinc solution

Abstract

The invention discloses a method for determining an organic additive in an ammonia chloride method electrolytic zinc solution, and relates to the technical field of ammonia chloride method electrolytic zinc solution determination, and the method comprises the following steps: preparing an organic additive standard solution A with a concentration of a; the method comprises the following steps: diluting a to-be-detected sample of an ammonia chloride process electrolytic zinc solution with water to n times of volume to obtain a diluted sample; respectively measuring the permanganate indexes of the standard solution A and the diluted sample by adopting a potassium permanganate oxidation-sodium oxalate reduction titration method; calculating a conversion coefficient; and calculating the concentration of the organic additive in the to-be-detected sample according to a formula. According to the method, the unknown additive can be measured, and the measurement precision and reliability are improved, so that accurate data support is provided for the production process.

Description

Technical Field

[0001] This invention relates to the field of chloramine electrolytic zinc solution determination technology, and more particularly to a method for determining organic additives in chloramine electrolytic zinc solution. Background Technology

[0002] The ammonium chloride electrolytic zinc process is a commonly used method for extracting zinc concentrate in the metallurgical industry. Its main characteristic is the use of an ammonium chloride solution for electrolysis to obtain zinc with high purity. To improve the efficiency of the electrolysis process and product quality, a certain amount of organic additives is usually added to the electrolyte to adjust its redox state, thereby reducing the formation of zinc particles and dendrites. However, the amount of additives added must be strictly controlled; too much will lead to resource waste and affect product quality, while too little will not achieve the desired optimization effect.

[0003] In actual production processes, the organic additives used may be specific compounds whose exact components may not be publicly available or readily identifiable, making concentration determination a technical challenge. Existing methods rely on the direct analysis of known organic additives, but their applicability is poor for determining the concentration of unknown additives, especially in complex zinc electrolysis solutions using the ammonium chloride method. Current methods cannot effectively address this problem, particularly in the case of unknown additives, often making direct concentration measurement impossible and leading to uncertainties in the production process.

[0004] Therefore, how to accurately measure the concentration of additives without knowing their specific components has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for determining organic additives in zinc electrolytic solutions using the chloramine method. The specific technical solution is as follows: A method for determining organic additives in zinc electrolytic solution using the chloramine method, comprising the following steps: S1. Prepare a standard solution A of organic additive with a known concentration; S2. Take the zinc solution sample to be tested by the chloramine electrolytic method, dilute it with water to n times the volume to obtain a diluted sample, wherein the chloride ion concentration in the diluted sample does not exceed 3000 mg / L; S2. The permanganate index of the standard solution A and the diluted sample was determined by potassium permanganate oxidation-sodium oxalate reduction titration. and ; S3. Calculate the conversion factor In the formula, a is the concentration of organic additive in standard solution A (mg / L). The permanganate index (O2 mg / L) of standard solution A; S4. Calculate the concentration of organic additives in the sample to be tested using the following formula: In the formula, c is the concentration (mg / L) of the organic additive in the sample to be tested, and k is the conversion factor. denoted as permanganate index (O2 mg / L) for standard solution A, and n is the dilution volume factor.

[0006] Preferably, a soluble chloride salt is added to the standard solution A so that the absolute value of the difference in chloride ion concentration between the standard solution A and the diluted sample is less than 10 mg / L.

[0007] Preferably, in step S2, the potassium permanganate oxidation-sodium oxalate reduction titration method includes the following steps: S21. Transfer V0 volume of the test liquid into a container, wherein the test liquid is standard solution A or a diluted sample; S22. Add the first treatment solution, then add an excess of potassium permanganate standard solution, and heat to 95~100℃ and maintain for 10~35 min; S23. Add the second treatment solution, followed by an excess of sodium oxalate standard solution, and mix well; S24. Back-titrate excess sodium oxalate to the endpoint using potassium permanganate standard solution; S25. Record the amount of potassium permanganate standard solution consumed, V1, during the back titration process; S26. Transfer V0 volume of pure water into a container to conduct a blank experiment, and record the amount of potassium permanganate standard solution consumed, V2, during the back titration process; S27. Calculate the permanganate index using the net consumption of potassium permanganate standard solution. ; Among them, one of the first treatment solution and the second treatment solution is a sodium hydroxide solution and the other is a sulfuric acid (1+3) solution.

[0008] Preferably, in step S27, the permanganate index Calculated using the following formula: In the formula, V1 is the permanganate index (O2 mg / L), V2 is the volume of potassium permanganate standard solution consumed during the back titration of the blank experiment (mL), V1 is the volume of potassium permanganate standard solution consumed during the back titration of the test liquid (mL), c0 is the concentration of potassium permanganate standard solution, and V0 is the volume of the test liquid (mL).

[0009] Preferably: When the chloride ion concentration in the diluted sample is <300 mg / L, the first treatment solution is a sulfuric acid (1+3) solution, and the heating holding time is 10~20 min; When the chloride ion concentration in the diluted sample is ≥300 mg / L, the first treatment solution is a sodium hydroxide solution, and the heating holding time is 20~25 min.

[0010] Preferably: The concentration of the potassium permanganate standard solution is 0.0090~0.0110 mol / L; The concentration of the sodium oxalate standard solution is 0.0090~0.0110 mol / L; The concentration of the sodium hydroxide solution is 450~550 g / L, and the amount added is 0.4~0.8 mL; The sulfuric acid (1+3) solution is a mixture of concentrated sulfuric acid and water with a volume ratio of 1:3, and the amount added is 8~12 mL; V0 is 50.0~100.0 mL; In step S22, the amount of potassium permanganate standard solution added is 8.00~12.00 mL; In step S23, the amount of sodium oxalate standard solution added is 9.00~12.00 mL.

[0011] Preferably, in step S24, the endpoint is determined by one of the following methods: a) Visual inspection method: The solution appears pink and does not fade within 30 seconds; b) Optical inflection point method: The position of the laser beam projection spot passing through the solution is monitored in real time during the back-dropping process. When the displacement of the spot reaches an inflection point, it is determined as the titration endpoint.

[0012] Preferably, the optical inflection point method specifically includes the following steps: Add an inflection point enhancer to the liquid or pure water to be tested; A red laser beam with a wavelength of 600~700 nm is passed parallel to a transparent container at a fixed angle. A graduated ruler or marking paper is placed at a distance of ≥10 cm from the transparent container so that the light spot is projected onto the ruler or marking paper. During the droplet return process in step S24, the position of the projected light spot is continuously observed. When the ratio of the displacement caused by any single drop to the displacement of the previous drop is ≥5 for the first time, it is determined to be the titration endpoint.

[0013] Preferably, the inflection point enhancer is selected from at least one of β-cyclodextrin-benzyl benzoate inclusion complex, octadecyl isothiourea hydrochloride, and sodium 2-phenylbenzimidazole-5-sulfonate.

[0014] Preferably, the concentration of the inflection point enhancer in the test liquid or pure water is 0.01~0.1 g / L.

[0015] The method for determining organic additives in zinc electrolytic solution using the chloramine method provided by this invention has the following beneficial effects: 1. To achieve the determination of unknown additives: This invention enables the efficient determination of the concentration of unknown organic additives in zinc solutions obtained by the potassium permanganate oxidation-sodium oxalate reduction titration method. Because it is independent of known additive components, it is widely applicable to different types of additives, overcoming the limitation of traditional methods that can only measure known additives.

[0016] 2. Improve measurement accuracy and reliability: This method effectively reduces the interference of chloride ions and improves the accuracy and reliability of the measurement results by precisely controlling the chloride ion concentration and employing back titration and conversion factor calculations. This method ensures accurate determination of additive concentrations even in complex zinc electrolysis systems using the ammonium chloride method.

[0017] 3. Cost savings: Compared to traditional chemical analysis methods, this invention provides a simplified operating procedure and reduces complex equipment requirements. Through the preparation of standard solutions and the processing of diluted samples, the entire determination process is more efficient and saves experimental costs.

[0018] 4. Provide accurate data support for the production process: This method provides precise data support for additive control in electrolytic zinc production, thereby avoiding production instability or resource waste caused by inaccurate additive concentrations. Precise control of additive dosage helps optimize the production process and improve zinc yield and product quality. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0020] This embodiment provides a method for determining organic additives in zinc electrolytic solution using the chloramine method, comprising the following steps: S1. Prepare a standard solution A of organic additives with a known concentration.

[0021] S2. Take the zinc solution sample to be tested by the chloramine electrolytic method, dilute it with water to n times the volume to obtain the diluted sample. The chloride ion concentration in the diluted sample shall not exceed 3000 mg / L.

[0022] S2. The permanganate index of standard solution A and diluted samples was determined by potassium permanganate oxidation-sodium oxalate reduction titration. and .

[0023] S3. Calculate the conversion factor In the formula, a is the concentration of organic additive in standard solution A (mg / L). The permanganate index (O2 mg / L) of standard solution A.

[0024] S4. Calculate the concentration of organic additives in the sample to be tested using the following formula: In the formula, c is the concentration (mg / L) of the organic additive in the sample to be tested, and k is the conversion factor. denoted as permanganate index (O2 mg / L) for standard solution A, and n is the dilution volume factor.

[0025] This method first prepares a standard solution A of organic additive with a known concentration, and then takes a sample of the zinc electrolytic solution to be tested using the chloramine method. Before the determination, the chloride ion concentration in the sample is controlled below 3000 mg / L through dilution to reduce the interference of chloride ions on the titration reaction. Since chloride ions may affect the redox reaction, the dilution step ensures that the chloride ion concentration does not affect the accuracy of the final measurement result.

[0026] In a diluted sample, potassium permanganate solution is added to initiate an oxidation reaction. Potassium permanganate reacts with the organic additives in the sample to produce oxidation products. Subsequently, sodium oxalate solution is added to reduce excess potassium permanganate to a colorless state. During this process, the amount of potassium permanganate consumed is precisely measured using a back-titration method, and the concentration of the organic additives in the sample is ultimately calculated.

[0027] The permanganate index, derived experimentally, combined with the conversion factor k, allows for precise correlation between titration results and the concentration of organic additives in the sample. This method is independent of the specific chemical composition of the additives; therefore, even if the additives are unknown, their concentrations can still be indirectly estimated through redox reactions and the titration process.

[0028] This scheme, through innovative titration methods and the introduction of conversion factors, enables the accurate determination of unknown organic additives in zinc electrolytic solutions using the chloramine method, effectively solving the problem that traditional methods cannot measure the concentration of unknown additives.

[0029] The method for determining organic additives in zinc electrolytic solution using the chloramine method provided in this embodiment has the following advantages: 1. To achieve the determination of unknown additives: This invention enables the efficient determination of the concentration of unknown organic additives in zinc solutions obtained by the potassium permanganate oxidation-sodium oxalate reduction titration method. Because it is independent of known additive components, it is widely applicable to different types of additives, overcoming the limitation of traditional methods that can only measure known additives.

[0030] 2. Improve measurement accuracy and reliability: This method effectively reduces the interference of chloride ions and improves the accuracy and reliability of the measurement results by precisely controlling the chloride ion concentration and employing back titration and conversion factor calculations. This method ensures accurate determination of additive concentrations even in complex zinc electrolysis systems using the ammonium chloride method.

[0031] 3. Cost savings: Compared to traditional chemical analysis methods, this invention provides a simplified operating procedure and reduces complex equipment requirements. Through the preparation of standard solutions and the processing of diluted samples, the entire determination process is more efficient and saves experimental costs.

[0032] 4. Provide accurate data support for the production process: This method provides precise data support for additive control in electrolytic zinc production, thereby avoiding production instability or resource waste caused by inaccurate additive concentrations. Precise control of additive dosage helps optimize the production process and improve zinc yield and product quality.

[0033] Furthermore, a soluble chloride salt is added to standard solution A so that the absolute value of the difference in chloride ion concentration between standard solution A and the diluted sample is less than 10 mg / L.

[0034] The addition of soluble chloride salts can mitigate the potential impact of differences in chloride ion concentrations between standard solution A and the test sample. Since chloride ions can interfere with the potassium permanganate oxidation reaction, adding an appropriate amount of soluble chloride salt (such as sodium chloride or potassium chloride) to standard solution A ensures that the chloride ion concentration in standard solution A is similar to that in the test sample, thereby reducing the concentration difference and minimizing the influence of chloride ions on the titration reaction, thus guaranteeing the accuracy of the measurement results.

[0035] Commonly used soluble chloride salts include sodium chloride, potassium chloride, and calcium chloride, with sodium chloride (NaCl) and potassium chloride (KCl) being particularly widely applicable. These chloride salts are readily soluble in water and provide an appropriate amount of chloride ions, ensuring that the concentration of chloride ions in standard solution A is close to that in the sample to be tested, thereby guaranteeing the stability of the titration reaction.

[0036] Furthermore, in step S2, the potassium permanganate oxidation-sodium oxalate reduction titration method includes the following steps: S21. Transfer V0 volume of the test liquid into a container. The test liquid is standard solution A or diluted sample.

[0037] S22. Add the first treatment solution, followed by an excess of potassium permanganate standard solution, and heat to 95~100℃ and maintain for 10~35 min.

[0038] S23. Add the second treatment solution, followed by an excess of sodium oxalate standard solution, and mix well.

[0039] S24. Back-titrate the excess sodium oxalate to the endpoint using potassium permanganate standard solution.

[0040] S25. Record the amount of potassium permanganate standard solution consumed, V1, during the back titration process.

[0041] S26. Transfer V0 volume of pure water into a container to conduct a blank experiment, and record the amount of potassium permanganate standard solution consumed, V2, during the back titration process.

[0042] S27. Calculate the permanganate index using the net consumption of potassium permanganate standard solution. .

[0043] Among them, one of the first treatment solution and the second treatment solution is a sodium hydroxide solution and the other is a sulfuric acid (1+3) solution.

[0044] Specifically, this method uses potassium permanganate oxidation-sodium oxalate reduction titration to determine the concentration of organic additives. The specific calculation formula follows international standard methods. Potassium permanganate oxidizes the organic additive (organic matter), releasing oxygen molecules. In the reduction reaction, sodium oxalate reduces unreacted potassium permanganate to a colorless state. By measuring the consumption of potassium permanganate standard solution, combined with the known potassium permanganate concentration and sample volume, the permanganate index can be calculated, and thus the concentration of the organic additive can be deduced.

[0045] Furthermore, in step S27, the permanganate index Calculated using the following formula: In the formula, V1 is the permanganate index (O2 mg / L), V2 is the volume of potassium permanganate standard solution consumed during the back titration of the blank experiment (mL), V1 is the volume of potassium permanganate standard solution consumed during the back titration of the test liquid (mL), c0 is the concentration of potassium permanganate standard solution, and V0 is the volume of the test liquid (mL).

[0046] Specifically, this method uses the calculation formula of potassium permanganate oxidation-sodium oxalate reduction titration in the international standard, which ensures the reliability and accuracy of the measurement results and facilitates comparison with other laboratories or national standards.

[0047] By accurately measuring the consumption of potassium permanganate and combining it with a precise conversion formula, this method can accurately calculate the concentration of organic additives, reducing errors in the experimental process and improving the accuracy of measurement.

[0048] Furthermore: When the chloride ion concentration in the diluted sample is <300 mg / L, the first treatment solution is a sulfuric acid (1+3) solution, and the heating time is 10~20 min.

[0049] When the chloride ion concentration in the diluted sample is ≥300 mg / L, the first treatment solution is sodium hydroxide solution, and the heating time is 20~25 min.

[0050] Furthermore: The concentration of the potassium permanganate standard solution is 0.0090~0.0110 mol / L.

[0051] The concentration of the sodium oxalate standard solution is 0.0090~0.0110 mol / L.

[0052] The concentration of the sodium hydroxide solution is 450~550 g / L, and the amount added is 0.4~0.8 mL.

[0053] The sulfuric acid (1+3) solution is a mixture of concentrated sulfuric acid and water in a volume ratio of 1:3, and the amount added is 8~12 mL.

[0054] V0 is 50.0~100.0 mL.

[0055] In step S22, the amount of potassium permanganate standard solution added is 8.00~12.00 mL.

[0056] In step S23, the amount of sodium oxalate standard solution added is 9.00~12.00 mL.

[0057] Furthermore, in step S24, the endpoint is determined by one of the following methods: a) Visual judgment method: The solution appears pink and does not fade within 30 seconds.

[0058] b) Optical inflection point method: The position of the laser beam projection spot passing through the solution is monitored in real time during the back-dropping process. When the displacement of the spot reaches an inflection point, it is determined as the titration endpoint.

[0059] Method b is an innovative optical inflection point method that uses changes in the refractive index of the solution to determine the titration endpoint. During the back titration process, changes in the composition of the solution lead to changes in the refractive index. By monitoring the changes in refractive index in real time, when the rate of change of refractive index suddenly changes (i.e., the inflection point), it is determined that the titration is nearing its endpoint.

[0060] Furthermore, the optical inflection point method specifically includes the following steps: Add an inflection point enhancer to the liquid or pure water to be tested.

[0061] A red laser beam with a wavelength of 600~700 nm is passed parallel to a transparent container at a fixed angle. A graduated ruler or marking paper is placed at a distance of ≥10 cm from the transparent container so that the light spot is projected onto the ruler or marking paper.

[0062] During the droplet return process in step S24, the position of the projected light spot is continuously observed. When the ratio of the displacement caused by any single drop to the displacement of the previous drop is ≥5 for the first time, it is determined to be the titration endpoint.

[0063] Furthermore, the inflection point enhancer is selected from at least one of β-cyclodextrin-benzyl benzoate inclusion complex, octadecyl isothiourea hydrochloride, and sodium 2-phenylbenzimidazole-5-sulfonate.

[0064] Specifically, the three inflection point enhancers selected in this embodiment can significantly amplify the abrupt change in the refractive index / density of the solution near the endpoint of potassium permanganate back titration, since the essence of the endpoint of potassium permanganate back titration is the concentration of MnO4 in the solution. - The process of mutation from "almost zero" to "existing in trace amounts" is accompanied by Mn 7+ →Mn 2+ The change in charge and the tiny jump in ionic strength. Normally, this jump results in a refractive index change of only 10. -5 ~10 -4 The RI unit indicates a very small spot displacement, which is difficult to detect precisely with the naked eye. The inflection point enhancer added in this embodiment can amplify the abrupt change in refractive index / density by 5 to 20 times through the following three mechanisms, thereby producing a sharp jump in the laser spot: 1. Hydrophobic association / micelle mutation mechanism (β-cyclodextrin-benzyl benzoate inclusion complex, octadecyl isothiourea hydrochloride) Both substances are amphiphilic molecules with long-chain hydrophobic groups and hydrophilic / ionic heads. When MnO4 is in solution... - When the concentration is below a certain critical value, they exist in the form of unimolecular molecules or small associated molecules; once a trace excess of MnO4 appears... - (i.e., reaching the endpoint), strong oxidizing MnO4 - Immediately, electron transfer or oxidative cross-linking occurs with hydrophobic long chains, resulting in the instantaneous formation of large micelles or precipitated microparticles, and significant step changes in the local density and refractive index of the solution.

[0065] 2. Coordination-discoordination mutagenesis mechanism (sodium 2-phenylbenzimidazole-5-sulfonate and some cyclodextrin inclusion complexes) These compounds contain compounds that can react with Mn 2+(Present in large quantities after the endpoint) or MnO4 - Groups that form coordination compounds (benzimidazole ring, cyclodextrin cavity). Before the endpoint, the solution is in Mn... 2+ Mainly, the reinforcing agent is Mn 2+ Saturated coordination; the first drop of excess MnO4 after the endpoint - Its extremely strong oxidizing power instantly oxidizes Mn. 2+ - The oxidative destruction of the reinforcing agent ligands can release the reinforcing agent molecules, or it can directly form new dark / high refractive index complexes with the reinforcing agent, leading to abrupt changes in refractive index.

[0066] 3. Synergistic amplification effect of surface activity All three enhancers possess a certain degree of surface activity and can accumulate at the gas-liquid interface. When trace amounts of new phases (MnO2 particles, oxidation products, micelles) are generated near the endpoint, the surfactants rapidly adsorb onto them, further amplifying the local density gradient and refractive index gradient, resulting in more intense beam deflection.

[0067] The β-cyclodextrin-benzyl benzoate inclusion complex can be prepared by the following steps: Dissolve an appropriate amount of β-cyclodextrin in deionized water and stir until completely dissolved.

[0068] Slowly add benzyl benzoate and continue stirring to allow it to react fully, while maintaining the temperature at 50-60℃.

[0069] After the reaction is complete, filter to remove unreacted benzyl benzoate.

[0070] The obtained inclusion complex was freeze-dried or vacuum-dried to obtain a dried β-cyclodextrin-benzyl benzoate inclusion complex.

[0071] Octadecyl isothiourea hydrochloride can be prepared by the following steps: Dissolve octadecyl isothiourea in an appropriate amount of solvent (such as ethanol or dichloromethane).

[0072] Slowly add hydrochloric acid solution to adjust the pH to acidic, and allow the reaction to proceed at room temperature for 1 hour.

[0073] Unreacted solids are removed by filtration, resulting in a solution.

[0074] The final octadecyl isothiourea hydrochloride is obtained by evaporating the solvent or by crystallization.

[0075] Sodium 2-phenylbenzimidazole-5-sulfonate can be prepared by the following steps: 2-Phenylenimidazole is reacted with a sulfonating agent to produce a product with a sulfonic acid group.

[0076] Add sodium salt to neutralize the reaction solution and adjust the pH to neutral.

[0077] Sodium 2-phenylbenzimidazole-5-sulfonate was obtained by filtration and washing.

[0078] The product was dried to obtain purified sodium 2-phenylbenzimidazole-5-sulfonate.

[0079] Furthermore, the concentration of the inflection point enhancer in the test liquid or pure water is 0.01~0.1 g / L.

[0080] Specific embodiments are provided below. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0081] Example 1 The accuracy of the method described in this embodiment for determining known organic additives (using commonly used industrial animal glue as an organic additive) in zinc electrolytic solution via the chloramine method was verified, and compared with traditional chemical analysis methods (high performance liquid chromatography, HPLC).

[0082] Accurately weigh 0.5000 g of animal glue, dissolve it in deionized water containing 30.00 g / L NaCl, and make up to 1000 mL to obtain animal glue standard solution A with a concentration a = 500.0 mg / L.

[0083] Take 10.00 mL of actual electrolyte from the zinc electrolysis workshop of a certain factory using the chloramine process, accurately transfer it, and dilute it to 500 mL with deionized water. After dilution, Cl... - The concentration is approximately 1900 mg / L.

[0084] The concentration of Cl⁻ in the diluted sample is 1900 mg / L ≥ 300 mg / L, so the alkaline method is selected: the first treatment solution is NaOH, and the heating time is extended.

[0085] Accurately transfer 100.0 mL of the diluted sample into a 250 mL iodine flask.

[0086] Add 0.60 mL of 500 g / L NaOH solution and shake well.

[0087] Add 10.00 mL of 0.01000 mol / L KMnO4 standard solution.

[0088] Place in a 100℃ water bath and keep warm for 23 minutes.

[0089] Remove the container, add 10 mL of sulfuric acid (1+3), and shake well.

[0090] Add 10.50 mL of 0.01000 mol / L sodium oxalate standard solution, shake well, and the solution will be colorless.

[0091] Back-titrate with 0.01000 mol / L KMnO4 standard solution until the solution turns a distinct pink color that does not fade after 30 s, and record the volume consumed.

[0092] A blank experiment was conducted using 100.0 mL of pure water, and all other procedures were exactly the same.

[0093] Conversion factor k = a / I Mn1 =500.0 / 155.44=3.216mg / L The concentration of animal glue in the original solution of the sample to be tested is c = k × I Mn2 ×n=3.216×274.16×50=44.07mg / L Comparative verification (HPLC method): The same batch of electrolyte stock solution was sent to a third-party testing institution, and the concentration of animal glue was determined to be 43.8 mg / L using high performance liquid chromatography.

[0094] The method of this invention yielded a concentration of 44.07 mg / L, which, compared to 43.8 mg / L by the HPLC method, showed a relative error of +0.6%, meeting the requirements for industrial production control and proving that the method is accurate and reliable.

[0095] Example 2 Under the same samples and conditions as in Example 1, the titration endpoint was determined using the optical inflection point method, and its reproducibility and accuracy in determining the results were examined.

[0096] In addition to the endpoint determination method, an inflection point enhancer is added to all test solutions (including standard solution A, diluted samples, and blanks) to make the inflection point of the optical spot shift sharper and further improve the accuracy of endpoint determination.

[0097] All other conditions (dilution factor, reagent amount, heating time, temperature) were the same as in Example 1.

[0098] Add 250 mL of deionized water to a 500 mL three-necked flask, turn on magnetic stirring (400 r / min), and heat to 55 °C in an oil bath. Weigh 11.350 g of β-cyclodextrin and add it to the flask in three portions, 5 min apart, stirring until completely dissolved. Maintaining 55 °C, slowly add 2.230 g of benzyl benzoate dissolved in 15 mL of anhydrous ethanol dropwise over 15 min using a dropping funnel. A fine white precipitate gradually forms during the addition. After the addition is complete, raise the temperature to 58 °C and continue stirring vigorously for 3.5 h. Stop heating, allow to cool naturally to room temperature, and then refrigerate overnight (16 h) at 4 °C to allow the inclusion complex to fully precipitate. The next morning, filter under vacuum, wash the filter cake twice with 50 mL of ice water, then wash once with 20 mL of cold ethanol, and dry as much as possible. The filter cake was placed in a vacuum drying oven and dried at 40°C and -0.095 MPa for 22 h to obtain 8.67 g of off-white powder, which was then sealed and stored in a desiccator in a light-proof container.

[0099] Accurately weigh 0.050 g of the above inclusion complex, place it in a 1000 mL volumetric flask, add deionized water and sonicate for 5 min, make up to the mark, shake well, and obtain a stock solution of inflection point enhancer with a concentration of 50.00 mg / L.

[0100] Before the formal titration, 2.00 mL of the stock solution was accurately added to every 100.0 mL of the test solution (including standard solution A, diluted sample, and blank) to make the final concentration of the enhancer 0.010 g / L, which is within the specified range.

[0101] The laser beam passes horizontally through the side of the titration cup, and the projected spot falls clearly on the scale paper. During titration, the spot moves upward, and near the endpoint, a single drop causes a spot displacement of 2.5~4.8 mm. The inflection point is sharp, making endpoint determination very easy.

[0102] When the displacement of the light spot caused by a single drop is observed to be ≥ 5 times the displacement of the previous drop, the titration should be stopped immediately, and the volume of that drop should not be counted.

[0103] k = 500.0 / 155.12 = 3.222 c = 3.222 × 274.64 × 50 = 44.23 mg / L As can be seen from the above embodiments: 1. The results of the two endpoint determination methods of this invention are highly consistent with those of the HPLC method, with a relative error within ±1.1%, which meets the requirements of rapid analysis in industrial settings. 2. The optical inflection point method has better reproducibility than the traditional visual method; after adding 0.010 g / L of inflection point enhancer, the endpoint is sharper, making it suitable for the modification of automated or semi-automated instruments. 3. The entire method is simple to operate, low in cost, and does not require knowledge of the specific composition of the additives. It is suitable for real-time monitoring of organic additives in the entire process of zinc electrolysis using the chloramine process.

[0104] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for determining organic additives in zinc electrolytic solution using the chloramine method, characterized in that, Includes the following steps: S1. Prepare a standard solution A of organic additive with a known concentration; S2. Take the zinc solution sample to be tested by the chloramine electrolytic method, dilute it with water to n times the volume to obtain a diluted sample, wherein the chloride ion concentration in the diluted sample does not exceed 3000 mg / L; S2. The permanganate index of the standard solution A and the diluted sample was determined by potassium permanganate oxidation-sodium oxalate reduction titration. and ; S3. Calculate the conversion factor In the formula, a is the concentration of organic additive in standard solution A (mg / L). The permanganate index (O2 mg / L) of standard solution A; S4. Calculate the concentration of organic additives in the sample to be tested using the following formula: In the formula, c is the concentration (mg / L) of the organic additive in the sample to be tested, and k is the conversion factor. denoted as permanganate index (O2 mg / L) for standard solution A, and n is the dilution volume factor.

2. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 1, characterized in that, A soluble chloride salt is added to the standard solution A so that the absolute value of the difference in chloride ion concentration between the standard solution A and the diluted sample is less than 10 mg / L.

3. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 1 or 2, characterized in that, In step S2, the potassium permanganate oxidation-sodium oxalate reduction titration method includes the following steps: S21. Transfer V0 volume of the test liquid into a container, wherein the test liquid is standard solution A or a diluted sample; S22. Add the first treatment solution, then add an excess of potassium permanganate standard solution, and heat to 95~100℃ and maintain for 10~35 min; S23. Add the second treatment solution, followed by an excess of sodium oxalate standard solution, and mix well; S24. Back-titrate excess sodium oxalate to the endpoint using potassium permanganate standard solution; S25. Record the amount of potassium permanganate standard solution consumed, V1, during the back titration process; S26. Transfer V0 volume of pure water into a container to conduct a blank experiment, and record the amount of potassium permanganate standard solution consumed, V2, during the back titration process; S27. Calculate the permanganate index using the net consumption of potassium permanganate standard solution. ; Among them, one of the first treatment solution and the second treatment solution is a sodium hydroxide solution and the other is a sulfuric acid (1+3) solution.

4. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 3, characterized in that, In step S27, the permanganate index Calculated using the following formula: In the formula, V1 is the permanganate index (O2 mg / L), V2 is the volume of potassium permanganate standard solution consumed during the back titration of the blank experiment (mL), V1 is the volume of potassium permanganate standard solution consumed during the back titration of the test liquid (mL), c0 is the concentration of potassium permanganate standard solution, and V0 is the volume of the test liquid (mL).

5. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 3, characterized in that: When the chloride ion concentration in the diluted sample is <300 mg / L, the first treatment solution is a sulfuric acid (1+3) solution, and the heating holding time is 10~20 min; When the chloride ion concentration in the diluted sample is ≥300 mg / L, the first treatment solution is a sodium hydroxide solution, and the heating holding time is 20~25 min.

6. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 3, characterized in that: The concentration of the potassium permanganate standard solution is 0.0090~0.0110 mol / L; The concentration of the sodium oxalate standard solution is 0.0090~0.0110 mol / L; The concentration of the sodium hydroxide solution is 450~550 g / L, and the amount added is 0.4~0.8 mL; The sulfuric acid (1+3) solution is a mixture of concentrated sulfuric acid and water with a volume ratio of 1:3, and the amount added is 8~12 mL; V0 is 50.0~100.0 mL; In step S22, the amount of potassium permanganate standard solution added is 8.00~12.00 mL; In step S23, the amount of sodium oxalate standard solution added is 9.00~12.00 mL.

7. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 3, characterized in that, In step S24, the endpoint is determined by one of the following methods: a) Visual inspection method: The solution appears pink and does not fade within 30 seconds; b) Optical inflection point method: The position of the laser beam projection spot passing through the solution is monitored in real time during the back-dropping process. When the displacement of the spot reaches an inflection point, it is determined as the titration endpoint.

8. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 7, characterized in that, The optical inflection point method specifically includes the following steps: Add an inflection point enhancer to the liquid or pure water to be tested; A red laser beam with a wavelength of 600~700 nm is passed parallel to a transparent container at a fixed angle. A graduated ruler or marking paper is placed at a distance of ≥10cm from the transparent container so that the light spot is projected onto the ruler or marking paper. During the droplet return process in step S24, the position of the projected light spot is continuously observed. When the ratio of the displacement caused by any single drop to the displacement of the previous drop is ≥5 for the first time, it is determined to be the titration endpoint.

9. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 7, characterized in that, The inflection point enhancer is selected from at least one of β-cyclodextrin-benzyl benzoate inclusion complex, octadecyl isothiourea hydrochloride, and sodium 2-phenylbenzimidazole-5-sulfonate.

10. The method for determining organic additives in zinc electrolytic solution using the chloramine method according to claim 9, characterized in that, The concentration of the inflection point enhancer in the test liquid or pure water is 0.01~0.1 g / L.

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