Method for measuring zinc content by using precipitation separation EDTA (Ethylene Diamine Tetraacetic Acid) dropping method

Abstract

The invention belongs to the technical field of zinc content determination, and particularly relates to a method for determining zinc content by using a precipitation separation EDTA (Ethylene Diamine Tetraacetic Acid) dropping method, which comprises the following steps: S1, putting a sample into a beaker, and adding sodium fluoride, concentrated hydrochloric acid and concentrated nitric acid for dissolving; s2, purging a watch glass and a beaker, and adding water for dilution; s3, adding ammonium chloride, and neutralizing with ammonia water to precipitate; s4, adding anhydrous sodium sulfite, heating to slightly boil, and filtering with filter paper; s5, washing the beaker and the precipitate with an ammonium chloride washing solution, adding p-nitrophenol, and adjusting to be colorless; s6, adding an acetic acid-sodium acetate buffer solution, adding sodium fluoride and ascorbic acid, and uniformly mixing; s7, dropwise adding an indicator, and titrating with an EDTA standard solution; and S8, calculating. According to the method, one-step efficient separation of lead, iron and aluminum can be achieved, interference of lead residues on zinc determination is reduced, interference of coexisting ions is eliminated, and errors are obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc content determination, and particularly relates to a method for determining zinc content by utilizing a precipitation separation EDTA drop method. Background Art

[0002] As an important nonferrous metal resource, zinc has extremely high economic value in lead-zinc mining, smelting, and downstream processing. Accurate zinc content determination is crucial for ore grade assessment, beneficiation process optimization, and product quality control. Currently, zinc content determination technologies mainly include EDTA titration, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), etc. Among them, EDTA titration is widely used in mine sites and industrial testing due to its simple equipment and low cost. However, in complex lead-zinc ore samples (especially ores containing high levels of interfering metals such as lead, iron, and aluminum), the existing EDTA titration technology still has significant defects, which are specifically manifested in the following aspects:

[0003] (1) Low separation efficiency of interfering metals leads to measurement deviation

[0004] Lead-zinc ores are often accompanied by metal elements such as iron, aluminum, and copper. Traditional EDTA titration requires multiple steps of precipitation or masking to eliminate interference, but the existing technology has the following problems:

[0005] a. Lead (Pb²⁺) interferes significantly: The complexation constant of lead with EDTA (logK=18.0) is similar to that of zinc (logK=16.5), and lead-zinc paragenetic ores are typically high in lead. Existing methods often use sulfate precipitation for lead, but these conditions are not optimized for high-lead samples, resulting in incomplete lead precipitation. Residual lead ions compete with EDTA for zinc complexation, leading to higher results.

[0006] b. Insufficient masking of iron (Fe³⁺) and aluminum (Al³⁺): Traditional methods rely on a single masking agent (such as sodium fluoride). However, when the iron and aluminum content is high, their hydroxide precipitates easily adsorb zinc ions, and the Fe³⁺ is not fully reduced. The residual Fe³⁺ combines with the indicator, resulting in a delayed endpoint.

[0007] c. Copper (Cu²⁺) interference was not effectively addressed: Copper has a stronger complexing ability with EDTA (logK=18.8) than zinc. Existing technologies lack a targeted masking step, which causes copper ions to consume EDTA and inflated measurement results.

[0008] (2) Sample pretreatment steps are cumbersome and inefficient

[0009] The existing EDTA titration method usually adopts the following process: acid dissolution of sample → step-by-step precipitation of interfering metals → filtration and washing → pH adjustment and titration. However, this process has obvious defects:

[0010] a. Imprecise precipitation conditions: When ammonia is used to neutralize and precipitate iron and aluminum, pH control relies on empirical judgment, which can easily lead to zinc co-precipitation loss due to excess or insufficient ammonia, or introduce interference from ammonium salts due to excess.

[0011] b. Zinc loss during the washing process: The concentration and temperature of traditional ammonium chloride washing solution are not optimized, and the residual zinc ions in the filter residue are difficult to completely recover. Especially for high-silicate ores, the zinc adsorption loss rate can reach 2%~5%.

[0012] c. The process is too time-consuming: Steps such as sedimentation, aging, and multiple filtrations result in single-sample analysis taking more than two hours, making it difficult to meet the large-scale testing needs of mining sites.

[0013] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0014] The object of the present invention is to provide a method for determining zinc content by using the precipitation separation EDTA drop method, so as to solve the problems existing in the prior art in the background technology.

[0015] To achieve the above object, the present invention provides the following technical solutions:

[0016] A method for determining zinc content using a precipitation separation EDTA drop method comprises the following steps:

[0017] S1. Place the sample in a beaker, add sodium fluoride, dissolve in concentrated hydrochloric acid at low temperature, and dissolve in concentrated nitric acid.

[0018] S2. Rinse the watch glass and beaker and dilute to 50 mL with water.

[0019] S3. Add 3-5g of ammonium chloride and neutralize with ammonia until the precipitation is completely in excess of 10mL;

[0020] S4. Add 2-3g of anhydrous sodium sulfite, heat to a slight boil for 5min, and filter with a quick qualitative filter paper while hot;

[0021] S5. Wash the beaker and precipitate with ammonium chloride washing solution, add 1-2 drops of p-nitrophenol, and adjust to colorless with sulfuric acid;

[0022] S6. Add 30 mL of acetic acid-sodium acetate buffer solution, sodium fluoride and ascorbic acid, and mix well;

[0023] S7. Add 2 drops of indicator and EDTA standard solution until the solution changes from purple to bright yellow;

[0024] S8. Calculate the zinc content in the sample according to the following formula:

[0025] ;

[0026] Where, T is the titration coefficient of EDTA standard solution to zinc, unit: g / mL;

[0027] V is the volume of EDTA standard solution consumed by the test solution, unit: mL;

[0028] m is the mass of the sample, unit: g.

[0029] Furthermore, in step S1, the mass-to-volume ratio of the sample to concentrated hydrochloric acid is 0.3 g:15 mL, and the mass-to-volume ratio of the sample to concentrated nitric acid is 0.3 g:5 mL.

[0030] Furthermore, in step S1, concentrated hydrochloric acid is added and dissolved at low temperature for 5 minutes, and concentrated nitric acid is added and dissolved until the volume of the solution in the beaker is 1 / 10 of the total volume of concentrated hydrochloric acid and concentrated nitric acid.

[0031] Furthermore, in step S5, the ammonium chloride washing solution is prepared by dissolving 20 g of ammonium chloride in 1000 mL of water, adding 1-2 mL of ammonia water, and mixing.

[0032] Furthermore, in step S5, the concentration of p-nitrophenol is 10 g / L.

[0033] Furthermore, in step S6, the acetic acid-sodium acetate buffer solution is prepared by dissolving 150 g of sodium acetate in water, adding 18 mL of glacial acetic acid, and diluting with water to 1000 mL.

[0034] Furthermore, in step S7, the indicator is xylenol orange with a concentration of 5 g / L.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention adopts the "ammonia-ammonium chloride-sodium sulfite" synergistic precipitation strategy to achieve one-step efficient separation of lead, iron and aluminum.

[0037] (2) The present invention uses sodium fluoride (complexing Al³⁺), ascorbic acid (reducing Fe³⁺) and sodium thiosulfate (masking Cu²⁺) in combination to construct a multi-level masking network to completely eliminate the interference of coexisting ions.

[0038] (3) The present invention adopts a xylenol orange-sodium acetate buffer system to enhance the stability of the zinc-indicator complex under weakly acidic conditions. The endpoint color changes significantly from purple-red to bright yellow, which can significantly reduce the error. DETAILED DESCRIPTION

[0039] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts are within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for determining zinc content using a precipitation separation EDTA drop method comprises the following steps:

[0042] S1. Place 0.30g of sample in a 250mL beaker, add 0.5g of sodium fluoride, and 15mL of concentrated hydrochloric acid (38.0%). Heat to 90°C to dissolve for 5 minutes. Add 5mL of concentrated nitric acid (68.0%) and boil until 2mL remains.

[0043] S2. Rinse the watch glass and beaker with water and dilute to 50 mL with water.

[0044] S3. Add 5g of ammonium chloride and 28% aqueous ammonia until precipitation occurs, then add 10mL of excess 28% aqueous ammonia.

[0045] S4. Add 3g of anhydrous sodium sulfite and heat to a gentle boil on an induction cooker for 5 minutes (if the sample is high in lead, add a small amount of potassium sulfate). Filter while hot using a rapid qualitative filter paper.

[0046] S5. Wash the beaker and precipitate five times each with 70°C hot ammonium chloride solution. Add 1-2 drops of 10g / L p-nitrophenol and adjust the colorless solution with 50% sulfuric acid. The ammonium chloride solution is prepared by dissolving 20g of ammonium chloride in 1000mL of water, adding 1-2mL of aqueous ammonia, and mixing.

[0047] S6. Add 30 mL of acetic acid - sodium acetate buffer solution, add 0.2 g of sodium fluoride and 0.2 g of ascorbic acid, and mix; wherein the acetic acid - sodium acetate buffer solution is prepared by: dissolving 150 g of sodium acetate in water, adding 18 mL of acetic acid (99.5%), and diluting with water to 1000 mL;

[0048] S7. Add 2 drops of 5g / L xylenol orange indicator and EDTA standard solution until the solution changes from purple to bright yellow;

[0049] S8. Calculate the zinc content in the sample according to the following formula:

[0050] ;

[0051] Where, T is the titration coefficient of EDTA standard solution to zinc, unit: g / mL;

[0052] V is the volume of EDTA standard solution consumed by the test solution, unit: mL;

[0053] m is the mass of the sample, unit: g.

[0054] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many modifications and variations are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to make and utilize a variety of exemplary embodiments of the invention and various options and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for determining zinc content using the precipitation separation EDTA drop method, characterized in that: The following steps are involved: S1. Place the sample in a beaker, add sodium fluoride, dissolve in concentrated hydrochloric acid at low temperature, and dissolve in concentrated nitric acid. S2. Rinse the watch glass and beaker and dilute to 50 mL with water. S3. Add 3-5g of ammonium chloride and neutralize with ammonia until the precipitation is completely in excess of 10mL; S4. Add 2-3g of anhydrous sodium sulfite, heat to a slight boil for 5min, and filter with a quick qualitative filter paper while hot; S5. Wash the beaker and precipitate with ammonium chloride washing solution, add 1-2 drops of p-nitrophenol, and adjust to colorless with sulfuric acid; S6. Add 30 mL of acetic acid-sodium acetate buffer solution, sodium fluoride and ascorbic acid, and mix well; S7. Add 2 drops of indicator and EDTA standard solution until the solution changes from purple to bright yellow; S8. Calculate the zinc content in the sample according to the following formula: ； Where, T is the titration coefficient of EDTA standard solution to zinc, unit: g / mL; V is the volume of EDTA standard solution consumed by the test solution, unit: mL; m is the mass of the sample, unit: g.

2. The method for measuring zinc content by the precipitation separation EDTA drop method according to claim 1, wherein In step S1, the mass volume ratio of the sample to concentrated hydrochloric acid is 0.3 g:15 mL, and the mass volume ratio of the sample to concentrated nitric acid is 0.3 g:5 mL.

3. The method for measuring zinc content by precipitation separation EDTA drop method according to claim 1, wherein In step S1, concentrated hydrochloric acid is added and dissolved at low temperature for 5 minutes, and concentrated nitric acid is added and dissolved until the volume of the solution in the beaker is 1 / 10 of the total volume of concentrated hydrochloric acid and concentrated nitric acid.

4. The method for measuring zinc content by precipitation separation EDTA drop method according to claim 1, wherein In step S5, the ammonium chloride washing solution is prepared by dissolving 20 g of ammonium chloride in 1000 mL of water, adding 1-2 mL of ammonia water, and mixing.

5. The method for measuring zinc content by precipitation separation EDTA drop method according to claim 1, wherein In step S5, the concentration of p-nitrophenol is 10 g / L.

6. The method for measuring zinc content by precipitation separation EDTA drop method according to claim 1, wherein In step S6, the acetic acid-sodium acetate buffer solution is prepared by dissolving 150 g of sodium acetate in water, adding 18 mL of glacial acetic acid, and diluting with water to 1000 mL.

7. The method for measuring zinc content by precipitation separation EDTA drop method according to claim 1, wherein In step S7, the indicator is xylenol orange with a concentration of 5 g / L.

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