Method for determining sulfate radicals in ammonia chloride process electrolytic zinc solution

Abstract

The invention discloses a method for determining sulfate radicals in an ammonia chloride process electrolytic zinc solution, and relates to the technical field of solution ion content determination, and the method comprises the following steps: adding a precipitator into a sample solution to generate a barium sulfate precipitate; adding a magnesium source and a chelating agent, titrating by using a standard chelating agent solution under the condition that the pH value is 9-11 and the end point is indicated by an indicator, and measuring the volume V2 of the consumed chelating agent; taking the same amount of sample solution, indicating the end point by using the indicator under the same pH value, titrating by using the standard chelating agent solution, and measuring the volume V3 of the consumed chelating agent; carrying out a blank experiment, and measuring the volume V1 of the consumed chelating agent; and calculating the content of sulfate radicals in the electrolytic zinc sample solution according to V1, V2, V3, the volume V of the sample solution and the concentration of the standard chelating agent solution. According to the method, the influence of a zinc matrix, calcium and magnesium is quantitatively eliminated, so that the determination result is highly matched with the actual content, and the color change of a titration end point is sharper by adding a magnesium source.

Description

Technical Field

[0001] The invention relates to the technical field of solution ion content determination, in particular to a method for determining sulfate in a chloramine process electrolytic zinc solution. Background Art

[0002] Traditional electrolytic zinc smelting methods usually adopt the acid method, that is, using sulfuric acid to dissolve ore powder, resulting in the presence of a large amount of sulfate in the solution. However, since sulfate in this method does not affect production, it does not need to be determined. However, the presence of too much sulfate in the chloramine electrolytic zinc method will seriously affect production, so a reasonable analytical method must be found. Spectrophotometry and gravimetric methods are not suitable due to the presence of a large amount of ammonium chloride in the solution, and the traditional titration method will seriously interfere with the determination due to the presence of a large amount of zinc matrix. Therefore, a suitable titration method is urgently needed. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a method for determining sulfate in a zinc electrolytic solution by a chloramine process, and the specific technical solution is as follows:

[0004] A method for determining sulfate in a zinc electrolytic solution produced by a chloramine process comprises the following steps:

[0005] Step a: adding a precipitant containing barium ions to the electrolytic zinc sample solution to generate barium sulfate precipitate and then adding a small amount of precipitant to make the barium ions remain;

[0006] Step b: adding a magnesium source and a chelating agent to a solution containing residual barium ions and interfering ions, titrating with a standard chelating agent solution under a buffer condition of pH 9 to 11 with an indicator indicating the endpoint, and measuring the volume V2 of the chelating agent consumed by the residual barium ions and interfering ions;

[0007] Step c: taking another equal amount of electrolytic zinc sample solution, titrating with the standard chelating agent solution under the same pH buffer conditions using the indicator to indicate the endpoint, and determining the volume V3 of the chelating agent consumed by the interfering ions;

[0008] Step d: performing a blank experiment to determine the volume V1 of the chelating agent consumed by the precipitant;

[0009] Step e: calculating the sulfate content in the electrolytic zinc sample solution based on V1, V2, V3, the volume V of the electrolytic zinc sample solution, and the concentration of the standard chelating agent solution;

[0010] Wherein, the interfering ions include zinc ions, calcium ions and magnesium ions.

[0011] Preferably, the precipitant is selected from a barium chloride solution or a barium sulfate seed crystal combined with a barium chloride solution, wherein:

[0012] The concentration of the barium chloride solution is 0.01 to 0.02 mol / L;

[0013] The barium sulfate seed crystals are high-purity barium sulfate nanoparticles with a particle size of 50 to 100 nm, which are added to the barium chloride solution in an amount of 0.05 to 0.1 mg / L. During the preparation process, 0.005 to 0.02% (w / v) polyethylene glycol is added as a dispersant.

[0014] Preferably, the chelating agent is selected from EDTA or CyDTA, wherein:

[0015] The concentration of the EDTA solution is 0.01 to 0.04 mol / L;

[0016] The concentration of the CyDTA solution is 0.015-0.03 mol / L.

[0017] Preferably, the preparation process of the barium sulfate seed crystals specifically includes the following steps:

[0018] Mix equal volumes of barium chloride solution and sodium sulfate solution of equal concentration, add polyethylene glycol while stirring, and react for 30 to 50 minutes;

[0019] The precipitate was collected by centrifugation, washed 2 to 3 times with deionized water, and then dispersed in deionized water.

[0020] Preferably, the CyDTA is carboxymethyl-modified CyDTA, and its preparation process specifically includes the following steps:

[0021] Dissolve 1,2-cyclohexanediaminetetraacetic acid in 0.1-0.2 mol / L sodium hydroxide solution, add 1.2-1.5 times the molar equivalent of chloroacetic acid, and react at 60-80°C for 4 hours;

[0022] After the reaction is completed, the solution is neutralized with 1 mol / L hydrochloric acid to a pH of 6 to 7 to precipitate CyDTA-COOH solid, which is filtered, washed, dried, and then dissolved in deionized water.

[0023] Preferably:

[0024] The magnesium source is selected from magnesium disodium ethylenediaminetetraacetate or CyDTA magnesium salt solution, and its concentration is 0.015-0.04 mol / L;

[0025] The indicator is chrome black T;

[0026] The buffer condition is an ammonia buffer solution.

[0027] Preferably, the standard chelating agent solution is calibrated by the following steps:

[0028] Take 20.00 mL of 1 g / L zinc standard solution, add 5 mL of ammonia buffer solution and 4 drops of chrome black T indicator;

[0029] Titrate with standard chelating agent solution until bright blue, and record the amount of chelating agent V0;

[0030] Calculate T 螯合剂 / Zn =1×20 / (1000×V0);

[0031] Calculate T 螯合剂 / SO4 2- =T 螯合剂 / Zn ×96.06 / 65.39.

[0032] Preferably, the calculation formula for the sulfate content in the electrolytic zinc sample solution is:

[0033] [SO4 2- ](g / L)=T 螯合剂 / SO4 2- ×(V1-V2+V3)×1000 / V;

[0034] Wherein, V1 is the amount of chelating agent used in step d) (mL), V2 is the amount of chelating agent used in step b) (mL), V3 is the amount of chelating agent used in step c) (mL), and V is the sampling volume of the electrolytic zinc sample solution (mL).

[0035] Preferably:

[0036] Step a specifically includes the following sub-steps:

[0037] Take 5-10 mL of electrolytic zinc sample solution and add 1 drop of 1 mol / L hydrochloric acid;

[0038] Add 5 mL of 0.02 mol / L barium chloride solution or 0.5 mL of barium sulfate seed suspension combined with 5 mL of 0.01 mol / L barium chloride solution, stir for 2 minutes, let stand for 10 minutes, and filter or centrifuge to separate the precipitate;

[0039] Step b specifically includes the following sub-steps:

[0040] Add 5 mL of ammonia buffer solution, 4 drops of chrome black T indicator, and 5 mL of 0.04 mol / L ethylenediaminetetraacetic acid disodium magnesium or CyDTA magnesium salt solution to the filtrate, and titrate with EDTA or CyDTA solution until bright blue appears. Record the amount V2.

[0041] Preferably, step d specifically includes the following sub-steps:

[0042] Take an equal volume of deionized water to the electrolytic zinc sample solution in step a and add 1 drop of 1 mol / L hydrochloric acid;

[0043] Add 5 mL of the same precipitant as in step a, stir for 2 minutes, let stand for 10 minutes, and filter or centrifuge to separate the precipitate;

[0044] Add 5 mL of ammonia buffer solution, 4 drops of chrome black T indicator, and 5 mL of the same magnesium source as in step b to the filtrate, and titrate with the same standard chelating agent solution as in step b to bright blue. Record the amount of standard chelating agent solution V1.

[0045] The method for determining sulfate in a zinc electrolytic solution using the chloramine method provided by the present invention quantitatively eliminates the influence of the zinc matrix and calcium and magnesium, so that the determination result is highly consistent with the actual content, and the addition of a magnesium source makes the color change at the titration endpoint sharper. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0047] This embodiment provides a method for determining sulfate in a zinc solution electrolyzed by ammonia chloride method, comprising the following steps:

[0048] Step a: adding a precipitant containing barium ions to the electrolytic zinc sample solution, generating barium sulfate precipitate, and then continuing to add a small amount of precipitant to make the barium ions remain.

[0049] Step b: adding a magnesium source and a chelating agent to a solution containing residual barium ions and interfering ions, and titrating with a standard chelating agent solution under a buffer condition of pH 9 to 11 with an indicator indicating the end point, to determine the volume V2 of the chelating agent consumed by the residual barium ions and interfering ions.

[0050] Step c: taking another equal amount of electrolytic zinc sample solution, titrating with the standard chelating agent solution under the same pH buffer condition using the indicator to indicate the end point, and determining the chelating agent volume V3 consumed by the interfering ions.

[0051] Step d: Perform a blank experiment to determine the volume V1 of the chelating agent consumed by the precipitant.

[0052] Step e: Calculate the sulfate content in the electrolytic zinc sample solution based on V1, V2, V3, the volume V of the electrolytic zinc sample solution, and the concentration of the standard chelating agent solution.

[0053] Among them, interfering ions include zinc ions, calcium ions and magnesium ions.

[0054] Wherein, hydrochloric acid can be added in step a to adjust the solution system to slightly acidic, the precipitant can be barium chloride, the chelating agent solution can be selected from disodium ethylenediaminetetraacetic acid solution, and the indicator can be chrome black T, chrome black T and Mg 2+ Or Ba 2+ A red / purple complex is formed. When EDTA titration completely chelates all metal ions, Eriochrome Black T returns to a free state and the solution turns bright blue, marking the titration end point. In order to make the titration end point clear, a magnesium source can be added to allow a certain amount of magnesium ions to exist in the test solution. The magnesium source can be disodium magnesium ethylenediaminetetraacetate. Disodium magnesium ethylenediaminetetraacetate releases Mg during the titration process. 2+ , forming a red complex with chrome black T, enhancing the sharpness of the end point color change.

[0055] Specifically, in a slightly acidic solution, an excess of barium chloride is added to allow sulfate to quantitatively react with barium ions to form insoluble barium sulfate precipitates. The remaining barium ions are titrated with disodium EDTA at a pH of 10. Not only are the excess barium ions titrated with disodium EDTA, but the zinc and calcium and magnesium ions in the original test solution are also titrated at the same time. Therefore, the zinc and total hardness in the test solution should be included in the calculation.

[0056] Among them, V1 is the amount of EDTA consumed by barium chloride and magnesium source in the blank test, and V2 is the amount of Ba remaining in the sample. 2+ , the amount of EDTA consumed by magnesium source and interfering ions, V3 is the amount of EDTA consumed by interfering ions in the sample, so V1-V2 can reflect the amount of EDTA consumed by SO4 2- and Ba consumed by interfering ions 2+ The corresponding EDTA amount, V1-V2+V3, can be expressed as SO4 after correcting the interfering ions. 2- The corresponding amount of EDTA, since the chelating agent and barium ion are paired in a 1:1 ratio during the chelation process, it can be removed by SO4 2- Calculate SO4 based on the amount of EDTA consumed 2- The amount of sulfate in the sample can be calculated by the volume V of the electrolytic zinc sample solution.

[0057] The method for determining sulfate in a zinc electrolytic solution using the chloramine method provided in this embodiment quantitatively eliminates the influence of the zinc matrix and calcium and magnesium, so that the determination result is highly consistent with the actual content, and by adding a magnesium source, the color change at the titration endpoint is sharper.

[0058] Furthermore, the precipitant is selected from a barium chloride solution or a barium sulfate seed crystal combined with a barium chloride solution, wherein:

[0059] The concentration of the barium chloride solution is 0.01-0.02 mol / L.

[0060] The barium sulfate seed crystals are high-purity barium sulfate nanoparticles with a particle size of 50 to 100 nm, which are added to the barium chloride solution in an amount of 0.05 to 0.1 mg / L. During the preparation process, 0.005 to 0.02% (w / v) polyethylene glycol is added as a dispersant.

[0061] Among them, high-purity barium sulfate nanoparticles can be added to the sample solution as crystal nuclei to induce sulfate to preferentially react with barium ions to form uniform and pure BaSO4 precipitation. Low concentration of BaCl2 can reduce the entrainment of Ca in BaSO4. 2+ 、Zn 2+ Mg 2+ During the preparation of BaSO4 seed crystals, adding a small amount of polyethylene glycol as a dispersant can improve the dispersion of the seed crystals and reduce crystal agglomeration and impurity adsorption.

[0062] Further, the chelating agent is selected from EDTA or CyDTA, wherein:

[0063] The concentration of EDTA solution is 0.01~0.04mol / L.

[0064] The concentration of the CyDTA solution is 0.015-0.03 mol / L.

[0065] Furthermore, the preparation process of barium sulfate seed crystals specifically includes the following steps:

[0066] Mix equal volumes of barium chloride solution and sodium sulfate solution of equal concentration, add polyethylene glycol under stirring, and react for 30 to 50 minutes.

[0067] The precipitate was collected by centrifugation, washed 2 to 3 times with deionized water, and then dispersed in deionized water.

[0068] Furthermore, CyDTA is carboxymethyl-modified CyDTA, and its preparation process specifically includes the following steps:

[0069] Dissolve 1,2-cyclohexanediaminetetraacetic acid in 0.1-0.2 mol / L sodium hydroxide solution, add 1.2-1.5 times the molar equivalent of chloroacetic acid, and react at 60-80°C for 4 hours.

[0070] After the reaction is completed, the solution is neutralized with 1 mol / L hydrochloric acid to a pH of 6 to 7 to precipitate CyDTA-COOH solid, which is filtered, washed, dried, and then dissolved in deionized water.

[0071] Further:

[0072] The magnesium source is selected from magnesium disodium ethylenediaminetetraacetate or CyDTA magnesium salt solution, and its concentration is 0.015-0.04 mol / L.

[0073] The indicator is chrome black T.

[0074] The buffer condition is an ammonia buffer solution.

[0075] Furthermore, the standard chelating agent solution is calibrated by the following steps:

[0076] Take 20.00 mL of 1 g / L zinc standard solution, add 5 mL of ammonia buffer solution and 4 drops of chrome black T indicator.

[0077] Titrate with standard chelating agent solution until bright blue, and record the amount of chelating agent V0.

[0078] Calculate T 螯合剂 / Zn =1×20 / (1000×V0).

[0079] Calculate T 螯合剂 / SO4 2- =T 螯合剂 / Zn ×96.06 / 65.39.

[0080] Furthermore, the calculation formula for the sulfate content in the electrolytic zinc sample solution is:

[0081] [SO4 2- ](g / L)=T 螯合剂 / SO4 2- ×(V1-V2+V3)×1000 / V.

[0082] Wherein, V1 is the amount of chelating agent used in step d) (mL), V2 is the amount of chelating agent used in step b) (mL), V3 is the amount of chelating agent used in step c) (mL), and V is the sampling volume of the electrolytic zinc sample solution (mL).

[0083] Further:

[0084] Step a specifically includes the following sub-steps:

[0085] Take 5-10 mL of electrolytic zinc sample solution and add 1 drop of 1 mol / L hydrochloric acid.

[0086] Add 5 mL of 0.02 mol / L barium chloride solution or 0.5 mL of barium sulfate seed suspension combined with 5 mL of 0.01 mol / L barium chloride solution, stir for 2 minutes, let stand for 10 minutes, and filter or centrifuge to separate the precipitate.

[0087] Step b specifically includes the following sub-steps:

[0088] Add 5 mL of ammonia buffer solution, 4 drops of chrome black T indicator, and 5 mL of 0.04 mol / L ethylenediaminetetraacetic acid disodium magnesium or CyDTA magnesium salt solution to the filtrate, and titrate with EDTA or CyDTA solution until bright blue appears. Record the amount V2.

[0089] Furthermore, step d specifically includes the following sub-steps:

[0090] Take deionized water of equal volume to the electrolytic zinc sample solution in step a and add 1 drop of 1 mol / L hydrochloric acid.

[0091] Add 5 mL of the same precipitant as in step a, stir for 2 minutes, let stand for 10 minutes, and filter or centrifuge to separate the precipitate.

[0092] Add 5 mL of ammonia buffer solution, 4 drops of chrome black T indicator, and 5 mL of the same magnesium source as in step b to the filtrate, and titrate with the same standard chelating agent solution as in step b to bright blue. Record the amount of standard chelating agent solution V1.

[0093] Specific examples are provided below. The provided examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0094] Example 1

[0095] Weigh 67.5g of ammonium chloride and dissolve it in CO2-free distilled water. Add 570ml of 25% aqueous ammonia and dilute to 1000ml with CO2-free distilled water to prepare an ammoniacal buffer solution. Weigh 0.2g of Eriochrome Black T and 2g of hydroxylamine hydrochloride and dissolve them in anhydrous ethanol. Dilute to 100ml with anhydrous ethanol and store in a brown bottle to prepare an indicator solution. Weigh 17.2g of magnesium disodium ethylenediaminetetraacetate and dissolve it in CO2-free distilled water to prepare a magnesium source solution.

[0096] Weigh 40g of EDTA and dissolve it in CO2-free distilled water. Dilute to 5000ml to prepare a standard chelating agent solution. Pipette 20.00mL of zinc standard solution (1g / L) into a 150mL conical flask. Add 5mL of ammoniacal buffer solution and 4 drops of chrome black T indicator. Titrate with EDTA standard solution until the solution turns bright blue. Record the volume of EDTA consumed (V0 = 14.23mL). Calculate T. EDTA / Zn =1×20 / (1000×V0)=0.001405. Calculate T EDTA / SO4 2- =T EDTA / Zn ×96.06 / 65.39=0.002064.

[0097] Place 10 mL of deionized water in a 150 mL conical flask and add 1 drop of 1 mol / L hydrochloric acid. Use a pipette to add 5.00 mL of 0.02 mol / L barium chloride solution. Add 5 mL of 0.04 mol / L disodium magnesium ethylenediaminetetraacetic acid solution. Add 10 mL of anhydrous ethanol. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with EDTA standard solution until the solution turns bright blue. Record the volume of EDTA consumed (V1 = 15.12 mL).

[0098] Take 10.00mL of electrolytic zinc sample solution in a 150mL conical flask and add 1 drop of 1mol / L hydrochloric acid. Use a pipette to add 5.00mL of 0.02mol / L barium chloride solution. Stir on a magnetic stirrer for 2 minutes (300rpm) and let it stand for 5 minutes to allow the barium sulfate to precipitate completely. Add 5mL of 0.04mol / L disodium magnesium ethylenediaminetetraacetic acid solution. Add 10mL of anhydrous ethanol. Add 5mL of ammoniacal buffer solution and confirm the pH is 10.0 with a pH meter. Add 4 drops of chrome black T indicator; the solution turns purple-red. Titrate with EDTA standard solution until the solution turns bright blue and record the volume of EDTA consumed (V2 = 15.57mL).

[0099] Place 10.00 mL of the electrolytic zinc sample solution in a 150 mL conical flask and add one drop of 1 mol / L hydrochloric acid. Add 5.50 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add four drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with EDTA standard solution until the solution turns bright blue. Record the volume of EDTA consumed (V3 = 0.50 mL).

[0100] Calculate the sulfate content in the electrolytic zinc sample solution: [SO4 2- ](g / L)=T EDTA / SO4 2- ×(V1-V2+V3)×1000 / V=0.01032.

[0101] Example 2

[0102] Weigh 2.5g of barium chloride, dissolve it in deionized water, and dilute to 1000mL. Weigh 1.5g of sodium sulfate, dissolve it in deionized water, and dilute to 1000mL. Take 50mL of barium chloride solution and 50mL of sodium sulfate solution, mix them in equal volumes, and stir them at 500rpm on a magnetic stirrer. Add 0.01g of polyethylene glycol and continue stirring for 40 minutes, controlling the temperature at 25°C. Centrifuge at 10,000rpm for 10 minutes to collect the barium sulfate precipitate. Wash the precipitate with deionized water three times, each time using 10mL of deionized water, and disperse it with the aid of an ultrasonic cleaner for 5 minutes. The washed barium sulfate precipitate is dispersed in 100mL of deionized water to obtain a barium sulfate seed suspension (particle size 50-100nm). Take 100mL of barium chloride solution, add 0.1mL of the barium sulfate seed suspension, and ultrasonically disperse it for 5 minutes before use.

[0103] Place 10 mL of deionized water in a 150 mL conical flask and add 1 drop of 1 mol / L hydrochloric acid. Use a pipette to add 5.00 mL of barium sulfate seed crystals combined with the barium chloride solution. Add 5 mL of 0.04 mol / L magnesium disodium ethylenediaminetetraacetic acid solution. Add 10 mL of anhydrous ethanol. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with EDTA standard solution until the solution turns bright blue. Record the volume of EDTA consumed (V1 = 15.13 mL).

[0104] Take 10.00mL of electrolytic zinc sample solution in a 150mL conical flask and add 1 drop of 1mol / L hydrochloric acid. Use a pipette to add 5.00mL of barium sulfate seeds combined with barium chloride solution. Stir on a magnetic stirrer for 2 minutes (300rpm) and let it stand for 5 minutes to allow the barium sulfate to precipitate completely. Add 5mL of 0.04mol / L disodium magnesium ethylenediaminetetraacetic acid solution. Add 10mL of anhydrous ethanol. Add 5mL of ammoniacal buffer solution and confirm that the pH is 10.0 with a pH meter. Add 4 drops of chrome black T indicator and the solution turns purple-red. Titrate with EDTA standard solution until the solution turns bright blue and record the volume of EDTA consumed, V2 = 15.57mL.

[0105] Place 10.00 mL of the electrolytic zinc sample solution in a 150 mL conical flask and add 1 drop of 1 mol / L hydrochloric acid. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with EDTA standard solution until the solution turns bright blue. Record the volume of EDTA consumed (V3 = 0.50 mL).

[0106] Calculate the sulfate content in the electrolytic zinc sample solution: [SO4 2- ](g / L)=T EDTA / SO4 2-×(V1-V2+V3)×1000 / V=0.01238.

[0107] Example 3

[0108] Weigh 18.5 g of CyDTA magnesium salt and dissolve it in CO2-free distilled water. Dilute to 1000 mL. Store in a sealed plastic bottle at room temperature.

[0109] Weigh 40g of CyDTA disodium salt and dissolve it in CO2-free distilled water. Dilute to 5000ml to prepare a standard chelating agent solution. Pipette 20.00mL of zinc standard solution (1g / L) into a 150mL conical flask. Add 5mL of ammoniacal buffer solution and 4 drops of Eriochrome Black T indicator. Titrate with the CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V0 = 16.38mL). Calculate T CyDTA =1×20 / (1000×V0)=0.001221. Calculate T CyDTA / SO4 2- =T CyDTA ×96.06 / 65.39=0.001794.

[0110] Place 10 mL of deionized water in a 150 mL Erlenmeyer flask and add 1 drop of 1 mol / L hydrochloric acid. Use a pipette to add 5.00 mL of 0.02 mol / L barium chloride solution. Add 5 mL of 0.04 mol / L CyDTA magnesium salt solution. Add 10 mL of anhydrous ethanol. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V1 = 15.14 mL).

[0111] Place 10.00 mL of electrolytic zinc sample solution in a 150 mL conical flask and add 1 drop of 1 mol / L hydrochloric acid. Use a pipette to add 5.00 mL of 0.02 mol / L barium chloride solution. Stir on a magnetic stirrer for 2 minutes (300 rpm) and let stand for 5 minutes to allow the barium sulfate to precipitate completely. Add 5 mL of 0.04 mol / L CyDTA magnesium salt solution. Add 10 mL of anhydrous ethanol. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of chrome black T indicator; the solution turns purple-red. Titrate with CyDTA standard solution until the solution turns bright blue and record the volume of CyDTA consumed (V2 = 15.60 mL).

[0112] Separately, place 10.00 mL of the electrolytic zinc sample solution in a 150 mL conical flask and add one drop of 1 mol / L hydrochloric acid. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add four drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V3 = 0.52 mL).

[0113] Calculate the sulfate content in the electrolytic zinc sample solution: [SO4 2- ](g / L)=T CyDTA / SO4 2- ×(V1-V2+V3)×1000 / V=0.001794×(15.00-12.45+10.20)×1000 / 10=0.01076.

[0114] Example 4

[0115] Weigh 34.6 g of 1,2-cyclohexanediaminetetraacetic acid and dissolve it in 500 mL of 0.15 mol / L sodium hydroxide solution. Add 14.2 g of chloroacetic acid. Incubate the mixture in a thermostatic reactor at 70°C for 4 hours with stirring at 300 rpm. After the reaction, slowly neutralize the mixture with 1 mol / L hydrochloric acid to a pH of 6.5 (approximately 50 mL of hydrochloric acid) to precipitate CyDTA-COOH solid. Collect the solid by filtration and wash it three times with 50 mL of deionized water. Dry it in a vacuum oven at 60°C for 12 hours to obtain a white CyDTA-COOH solid. Transfer 20.00 mL of a 1 g / L zinc standard solution to a 150 mL conical flask. Add 5 mL of ammoniacal buffer solution and add 4 drops of Eriochrome Black T indicator. Titrate with the carboxymethylated CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V0 = 16.40 mL). Calculate T CyDTA =1×20 / (1000×V0)=0.001220. Calculate T CyDTA / SO4 2- =T CyDTA ×96.06 / 65.39=0.001792.

[0116] Place 10 mL of deionized water in a 150 mL conical flask and add 1 drop of 1 mol / L hydrochloric acid. Use a pipette to add 5.00 mL of 0.02 mol / L barium chloride solution. Add 5 mL of 0.04 mol / L CyDTA magnesium salt solution. Add 10 mL of anhydrous ethanol. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with carboxymethylated CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V1 = 15.13 mL).

[0117] Place 10.00 mL of electrolytic zinc sample solution in a 150 mL conical flask and add 1 drop of 1 mol / L hydrochloric acid. Use a pipette to add 5.00 mL of 0.02 mol / L barium chloride solution. Stir on a magnetic stirrer for 2 minutes (300 rpm) and let stand for 5 minutes to allow the barium sulfate to precipitate completely. Add 5 mL of 0.04 mol / L CyDTA magnesium salt solution. Add 10 mL of anhydrous ethanol. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add 4 drops of chrome black T indicator; the solution turns purple-red. Titrate with carboxymethyl-modified CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V2 = 15.59 mL).

[0118] Separately, place 10.00 mL of the electrolytic zinc sample solution in a 150 mL Erlenmeyer flask and add one drop of 1 mol / L hydrochloric acid. Add 5 mL of ammoniacal buffer solution and confirm the pH is 10.0 using a pH meter. Add four drops of Eriochrome Black T indicator; the solution will turn purple-red. Titrate with carboxymethylated CyDTA standard solution until the solution turns bright blue. Record the volume of CyDTA consumed (V3 = 0.52 mL).

[0119] Calculate the sulfate content in the electrolytic zinc sample solution: [SO4 2- ](g / L)=T CyDTA / SO4 2- ×(V1-V2+V3)×1000 / V=0.01075.

[0120] Comparative Example

[0121] Take 10.00 mL of electrolytic zinc sample solution and measure the sulfate content using ion chromatography.

[0122] The sulfate ion content data in the electrolytic zinc sample solutions obtained by Examples 1 to 4 and the comparative example are shown in the following table:

[0123]

[0124] It can be seen that the determination method provided in this embodiment can better determine the content of sulfate ions in the sample solution by eliminating the interference of the zinc matrix, calcium and magnesium ions, and adding a magnesium source and titrating with a standard chelating agent solution.

[0125] The principles and implementation methods of the present invention are described herein using specific examples. The description of the above embodiments is only intended to help understand the method and core ideas of the present invention. The above are only preferred implementation methods of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art, within the technical scope disclosed by the present invention, can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, and all of these should fall within the scope of protection of the present invention.

Claims

1. A method for determining sulfate in a chlorine-ammonia electrolytic zinc solution, characterized in that: The steps include: a) adding a precipitant containing barium ions to an electrolytic zinc sample solution, and then adding a small amount of precipitant to form a barium sulfate precipitate so that the barium ions remain; b) adding a magnesium source and a chelating agent to a solution containing residual barium ions and interfering ions, titrating with a standard chelating agent solution under a buffer condition of pH 9 to 11 with an indicator indicating the endpoint, and determining the volume V2 of the chelating agent consumed by the residual barium ions and interfering ions; c) taking another equal amount of electrolytic zinc sample solution, titrating with the standard chelating agent solution under the same pH buffer conditions using the indicator to indicate the endpoint, and determining the volume V3 of the chelating agent consumed by the interfering ions; d) performing a blank experiment to determine the volume V1 of the chelating agent consumed by the precipitant; e) calculating the sulfate content in the electrolytic zinc sample solution based on V1, V2, V3, the volume V of the electrolytic zinc sample solution, and the concentration of the standard chelating agent solution; Wherein, the interfering ions include zinc ions, calcium ions and magnesium ions.

2. The measuring method according to claim 1, wherein The precipitant is selected from a barium chloride solution or a barium sulfate seed crystal combined with a barium chloride solution, wherein: The concentration of the barium chloride solution is 0.01 to 0.02 mol / L; The barium sulfate seed crystals are high-purity barium sulfate nanoparticles with a particle size of 50 to 100 nm, which are added to the barium chloride solution in an amount of 0.05 to 0.1 mg / L. During the preparation process, 0.005 to 0.02% (w / v) polyethylene glycol is added as a dispersant.

3. The measuring method according to claim 1, wherein The chelating agent is selected from EDTA or CyDTA, wherein: The concentration of the EDTA solution is 0.01 to 0.04 mol / L; The concentration of the CyDTA solution is 0.015-0.03 mol / L.

4. The measuring method according to claim 2, wherein The preparation process of the barium sulfate seed crystals specifically includes the following steps: Mix equal volumes of barium chloride solution and sodium sulfate solution of equal concentration, add polyethylene glycol while stirring, and react for 30 to 50 minutes; The precipitate was collected by centrifugation, washed 2 to 3 times with deionized water, and then dispersed in deionized water.

5. The measuring method according to claim 3, wherein The CyDTA is carboxymethyl-modified CyDTA, and its preparation process specifically includes the following steps: Dissolve 1,2-cyclohexanediaminetetraacetic acid in 0.1-0.2 mol / L sodium hydroxide solution, add 1.2-1.5 times the molar equivalent of chloroacetic acid, and react at 60-80°C for 4 hours; After the reaction is completed, the solution is neutralized with 1 mol / L hydrochloric acid to a pH of 6 to 7 to precipitate CyDTA-COOH solid, which is filtered, washed, dried, and then dissolved in deionized water.

6. The assay method according to any one of claims 1 to 5, wherein: The magnesium source is selected from magnesium disodium ethylenediaminetetraacetate or CyDTA magnesium salt solution, and its concentration is 0.015-0.04 mol / L; The indicator is chrome black T; The buffer condition is an ammonia buffer solution.

7. The measuring method according to any one of claims 1 to 5, characterized in that The standard chelating agent solution is calibrated by the following steps: Take 20.00 mL of 1 g / L zinc standard solution, add 5 mL of ammonia buffer solution and 4 drops of chrome black T indicator; Titrate with standard chelating agent solution until bright blue, and record the amount of chelating agent V0; Calculate T 螯合剂 / Zn =1×20 / (1000×V0); Calculate T 螯合剂 / SO4 2- =T 螯合剂 / Zn ×96.06 / 65.

39.

8. The measuring method according to claim 7, wherein The calculation formula for the sulfate content in the electrolytic zinc sample solution is: [SO4 2- ](g / L)=T 螯合剂 / SO4 2- ×(V1-V2+V3)×1000 / V; Wherein, V1 is the amount of chelating agent used in step d) (mL), V2 is the amount of chelating agent used in step b) (mL), V3 is the amount of chelating agent used in step c) (mL), and V is the sampling volume of the electrolytic zinc sample solution (mL).

9. The assay method according to claim 6, wherein: Step a) specifically includes the following sub-steps: Take 5-10 mL of electrolytic zinc sample solution and add 1 drop of 1 mol / L hydrochloric acid; Add 5 mL of 0.02 mol / L barium chloride solution or 0.5 mL of barium sulfate seed suspension combined with 5 mL of 0.01 mol / L barium chloride solution, stir for 2 minutes, let stand for 10 minutes, and filter or centrifuge to separate the precipitate; Step b) specifically includes the following sub-steps: Add 5 mL of ammonia buffer solution, 4 drops of chrome black T indicator, and 5 mL of 0.04 mol / L ethylenediaminetetraacetic acid disodium magnesium or CyDTA magnesium salt solution to the filtrate, and titrate with EDTA or CyDTA solution until bright blue appears. Record the amount V2.

10. The measuring method according to claim 9, characterized in that Step d) specifically includes the following sub-steps: Take deionized water of equal volume to the electrolytic zinc sample solution in step a) and add 1 drop of 1 mol / L hydrochloric acid; Add 5 mL of the same precipitant as in step a), stir for 2 minutes, let stand for 10 minutes, and filter or centrifuge to separate the precipitate; Add 5 mL of ammonia buffer solution, 4 drops of chrome black T indicator, and 5 mL of the same magnesium source as in step b) to the filtrate, and titrate with the same standard chelating agent solution as in step b) to bright blue, and record the amount of standard chelating agent solution V1.

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