Method for measuring calcium content of seamless pure calcium line

Abstract

The invention discloses a method for measuring the calcium content of a seamless pure calcium line, and aims to solve the problem of inaccurate detection of a sample containing an oxide layer. According to the method disclosed by the invention, a two-step acidolysis strategy of diluted hydrochloric acid-hexamethylenetetramine and glacial acetic acid warming is adopted, so that comprehensive and rapid dissolution of metal calcium and calcium oxide and super-strong protection of iron sheets are realized; a gradient alkalization masking strategy of triethanolamine-ammonia water-potassium hydroxide is adopted, so that deep masking of interference ions and an acute titration end point are realized. The method has the advantages of good selectivity, strong anti-interference capability, high accuracy and simple operation, and is especially suitable for accurate quality evaluation of seamless pure calcium line products in iron and steel enterprises.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis technology for metallurgical materials, and in particular to a method for determining the calcium content of a seamless pure calcium wire. Background Technology

[0002] During storage or production, a dense calcium oxide (CaO) layer may form on the surface of the seamless pure calcium wire's metallic calcium core. Existing detection methods have limitations when dealing with such samples: for example, patent CN108663476A uses dilute hydrochloric acid for direct dissolution, which can dissolve metallic calcium, but has low dissolution efficiency for the calcium oxide layer and insufficient protection of the iron oxide layer, leading to iron ion interference in titration; patent CN112858570A uses glacial acetic acid for selective dissolution, which has a good protection effect on the iron oxide layer, but the dissolution rate of the dense calcium oxide layer is slow, and a single acidic system cannot simultaneously achieve rapid dissolution of metallic calcium and complete dissolution of calcium oxide.

[0003] Therefore, there is an urgent need for an integrated detection method that can simultaneously achieve rapid dissolution of metallic calcium, efficient treatment of the calcium oxide layer, maximum protection of the iron sheet to reduce interference, and ensure a highly purified titration environment, in order to accurately assess the true quality of seamless pure calcium wire. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for determining the calcium content of seamless pure calcium wire. The core concept lies in combining a pretreatment strategy of "stepwise acidolysis-synergistic protection" with a titration pretreatment strategy of "composite masking-gradient alkalization," which is simple to operate, yields accurate results, and has strong anti-interference capabilities.

[0005] To achieve this technical objective, the present invention adopts the following solution: A method for determining the calcium content of seamless pure calcium thread includes the following steps: S1. Selective Dissolution and Oxide Layer Treatment: The seamless pure calcium wire sample is placed in a first acidic dissolving solution, which is a dilute hydrochloric acid solution containing a corrosion inhibitor, to selectively dissolve the metallic calcium core and form a protective film on the iron sheet surface. After the violent reaction subsides, a second acidic dissolving solution, which is glacial acetic acid, is added to the reaction system, and the system is then heat-treated at 60~80℃ to fully dissolve any calcium oxide layer that may exist on the surface of the calcium core and enhance the protective effect of the iron sheet. S2. Weighing the sheet metal: After the reaction is complete, take out the complete core sheet metal, clean and dry it, and weigh it to obtain the sheet metal mass M2. The original mass of the sample is M1, and the calcium mass is (M1-M2). S3. Composite masking and gradient alkalization: After the completely dissolved solution obtained in step S1 is brought to a final volume and separated, triethanolamine masking agent and concentrated ammonia are added sequentially to adjust the pH of the solution to 9-11, forming the first masking alkalization environment; then potassium hydroxide solution is added to adjust the pH of the solution to above 12, forming the second strong base titration environment. The gradient alkalization process avoids local precipitation or masking failure caused by the direct addition of strong base. S4. Complexometric titration: Add calcium indicator to the solution obtained in step S3, titrate with EDTA standard solution to the endpoint, and record the volume V consumed. S5. Result Calculation: Based on the sample mass M1, the sheet metal mass M2, the EDTA titration volume V, and the concentration C, calculate the calcium content X of the seamless pure calcium wire. The calculation formula is as follows: F represents the total dilution factor from the original solution to the titrant.

[0006] Further, in step S1, the volume concentration of dilute hydrochloric acid in the first acidic solution is 3%~10%, and the corrosion inhibitor is hexamethylenetetramine with a mass concentration of 2%~5%; the volume ratio of dilute hydrochloric acid solution to corrosion inhibitor solution is (15:1)~(25:1).

[0007] Furthermore, the volume concentration of the dilute hydrochloric acid is 5%, the corrosion inhibitor is a 3.5% hexamethylenetetramine solution, and the volume ratio of the dilute hydrochloric acid solution to the corrosion inhibitor solution is 20:1.

[0008] Further, in step S1, the amount of glacial acetic acid added to the second acidic solution is: 1~5ml of glacial acetic acid is added to every 100ml of the first acidic solution reaction system, and the heat treatment time is 5~15 minutes.

[0009] Further, in step S3, the gradient alkalization is specifically as follows: first, add 5-10 ml of triethanolamine solution with a volume ratio of 1:1, stir evenly, then add concentrated ammonia dropwise until the solution pH is 9-11, and finally add 20-40 ml of potassium hydroxide solution with a mass concentration of 20%-30%.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Comprehensive and efficient dissolution: The "dilute hydrochloric acid-corrosion inhibitor" system ensures the rapid dissolution of metallic calcium (can be started at room temperature), while the "glacial acetic acid warming" stage is specifically designed to efficiently dissolve the dense calcium oxide layer, solving the problem that a single acid cannot take into account both dissolution speed and comprehensiveness.

[0011] (2) Extreme protection of iron sheet and interference control: Hexamethylenetetramine forms a primary protective film in hydrochloric acid, and the glacial acetic acid environment further stabilizes the film, achieving dual protection. The iron sheet dissolution rate is extremely low, and the interference of iron ions is reduced to the minimum from the source.

[0012] (3) Optimization of masking effect depth: The gradient alkalization strategy of "triethanolamine-ammonia-potassium hydroxide" provides the best weak base masking environment for triethanolamine, realizing deep and stable masking of trace interference ions, and the color change at the titration endpoint is extremely sensitive, thus improving the accuracy of analysis.

[0013] (4) The results are accurate and reliable: The method combines the advantages of gravimetric method and titration method. For pure calcium lines without oxide layer, the results of the two methods can be mutually verified. For calcium lines with oxide layer, this method can more accurately measure its "total calcium content" and has more practical guiding value.

[0014] (5) Easy to operate: No special equipment is required throughout the process, reagents are common, and conditions are mild and controllable, making it very suitable for daily batch testing in enterprise laboratories. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Reagent preparation:

[0016] First acidic solution (5% HCl + 3.5% hexamethylenetetramine): Measure 950 ml of the prepared 5% (v / v) dilute hydrochloric acid, add 50 ml of 3.5% (m / v) hexamethylenetetramine solution, and mix well.

[0017] Second acidic dissolving solution (glacial acetic acid): Use analytical grade glacial acetic acid directly.

[0018] Masking agent (triethanolamine): Triethanolamine is mixed with an equal volume of water.

[0019] First alkalizing agent (concentrated ammonia): analytical grade reagent.

[0020] Second alkalizing agent (20% KOH): Weigh 200g KOH, dissolve it in water, and make up to 1000ml.

[0021] Calcium indicator (0.5% sodium calcium carboxylate): Dissolve 0.5g sodium calcium carboxylate in 100ml of water.

[0022] Titrant (0.01784 mol / L EDTA): Weigh 66.5 g of disodium EDTA, dissolve it in water, and dilute to approximately 9 L. Standardize. Example 1

[0023] S1. Weigh approximately 20 mm of seamless pure calcium wire sample, and record the weight as M1. Place the sample in a 400 ml beaker, add 100 ml of the first acidic dissolving solution (5% HCl + 3.5% hexamethylenetetramine), and react at room temperature until no vigorous bubbling occurs. Add 2ml of glacial acetic acid, place the beaker in an 80℃ water bath for 10 minutes, then remove and cool.

[0024] S2. Remove the sheet metal, wash it, dry it at 105℃, cool it and weigh it to obtain M2.

[0025] S3. Transfer all the solution from the beaker in step S1 to a 500ml volumetric flask and make up to volume (mother liquor I). Transfer 25.00ml of mother liquor I to a 250ml volumetric flask and make up to volume (mother liquor II). Then transfer 50.00ml of mother liquor II to a 300ml conical flask for titration. Add 5 ml of triethanolamine masking agent to the conical flask and shake well. Add concentrated ammonia dropwise and control the pH of the solution to around 10 using pH paper; then add 30 ml of the second alkalizing agent (20% KOH).

[0026] S4. Add 3-5 drops of calcium indicator; the solution will turn wine-red. Titrate with EDTA standard solution to a pure blue endpoint and record the volume V.

[0027] S5. Calculation of calcium content:

[0028] In the formula, C is the concentration of DETA standard solution, which is 0.01784 mol / L, and the total dilution factor F is 100. Examples 2-6

[0029] Seamless pure calcium wire samples from different batches were extracted and measured by inductively coupled plasma atomic emission spectrometry according to the method in Example 1. The results of ICP-OES were used as a reference. The results are shown in Table 1.

[0030] Table 1

[0031] As shown in Table 1, the chemical titration method provided by this invention has an accuracy comparable to that of analytical methods (ICP-OES), and can completely replace the latter for routine quality inspection of seamless pure calcium wire. Furthermore, the method of this invention has the advantages of low cost, simple operation, and rapid analysis, making it more suitable for routine batch testing in production sites and laboratories. Comparative Example 1

[0032] Take a 20mm seamless pure calcium wire sample (from the same batch as in Example 1) and measure it according to the specific implementation method of patent CN108663476A. Comparative Example 2

[0033] Take a 20mm seamless pure calcium wire sample (from the same batch as in Example 1) and measure it according to the specific implementation method of patent CN112858570A. Example 7

[0034] Take a 20mm calcium wire with slight surface oxidation and measure it according to the method in Example 1. Comparative Example 3

[0035] Take a 20mm sample of calcium wire with slight surface oxidation (from the same batch as in Example 7) and measure it according to the method of Comparative Example 1. Comparative Example 4

[0036] Take a 20mm sample of calcium wire with slight surface oxidation (from the same batch as in Example 7) and measure it according to the method of Comparative Example 2. Example 8

[0037] Take a 20mm calcium wire with a distinct dense oxide layer on its surface and measure it according to the method in Example 1. Comparative Example 5

[0038] Take a 20mm calcium wire with a distinct dense oxide layer on the surface (from the same batch as in Example 8) and measure it according to the method of Comparative Example 1. Comparative Example 6

[0039] Take a 20mm calcium wire with a distinct dense oxide layer on the surface (from the same batch as in Example 8) and measure it according to the method of Comparative Example 2.

[0040] The results of Examples 1, 7, 8 and Comparative Examples 1-6 are shown in Table 2. The dissolution time in the table is the time required from the start of the reaction until the solution is completely clear and no bubbles are visible within 1 minute.

[0041] Table 2

[0042] As shown in Table 2, the method of the present invention is superior to the two existing methods in terms of the dissolution rate and completeness of samples containing oxide layers, the sensitivity of the titration endpoint, and the accuracy of the final results. The advantages are particularly significant for samples containing oxide layers that are common in actual production.

[0043] To further verify the protective effect of the method of the present invention on cored iron sheets, the following experiments were conducted: Example 9

[0044] Sample preparation: Cut blank sheet metal into 20mm long segments, clean with acetone, dry and weigh accurately (M0).

[0045] The blank sheet metal fragment was dissolved according to step S1 in Example 1. After the treatment was completed, the sheet metal was removed, washed, dried, cooled, and then weighed accurately again (M2').

[0046] Calculate the weight loss rate using the following formula. Perform three parallel measurements and take the average value.

[0047] Comparative Example 7

[0048] The blank iron sheet processed in Example 9 was dissolved according to the method of Comparative Example 1. Comparative Example 8

[0049] The blank iron sheet processed in Example 9 was dissolved according to the method of Comparative Example 2.

[0050] The experimental results of Example 9 and Comparative Examples 7 and 8 are shown in Table 3.

[0051] Table 3

[0052] The data in Table 3 show that the method of the present invention has the lowest corrosion weight loss rate of iron sheet, demonstrating the best iron sheet protection performance and selective dissolution ability, effectively reducing the interference of the iron matrix on the measurement results from the source.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should all be considered to be within the protection scope of the present invention.

Claims

1. A method for determining the calcium content of seamless pure calcium thread, characterized in that, Includes the following steps: S1. Selective dissolution and oxide layer treatment: The seamless pure calcium wire sample is placed in the first acidic dissolution solution for reaction. The first acidic dissolution solution is a dilute hydrochloric acid solution containing corrosion inhibitor, which is used to selectively dissolve the metallic calcium core and form a protective film on the iron sheet surface. After the violent reaction subsides, a second acidic dissolving solution, namely glacial acetic acid, is added to the reaction system, and the system is then heated at 60-80°C to fully dissolve any calcium oxide layer that may exist on the surface of the calcium core and to enhance the protective effect of the iron sheet. S2. Weighing the sheet metal: After the reaction is complete, take out the complete core sheet metal, clean and dry it, and weigh it to obtain the sheet metal mass M2. The original mass of the sample is M1. S3. Composite masking and gradient alkalization: After making up the volume of the completely dissolved solution obtained in step S1 and separating it, triethanolamine masking agent and concentrated ammonia water are added in sequence to adjust the pH of the solution to 9-11 to form the first masking alkalization environment; then potassium hydroxide solution is added to adjust the pH of the solution to above 12 to form the second strong base titration environment. S4. Complexometric titration: Add calcium indicator to the solution obtained in step S3, titrate with EDTA standard solution to the endpoint, and record the volume V consumed. S5. Result Calculation: Based on the sample mass M1, the sheet metal mass M2, the EDTA titration volume V, and the concentration C, calculate the calcium content X of the seamless pure calcium wire. The calculation formula is as follows: F represents the total dilution factor from the original solution to the titrant.

2. The method for determining the calcium content of seamless pure calcium thread according to claim 1, characterized in that, In step S1, the volume concentration of dilute hydrochloric acid in the first acidic solution is 3%~10%, and the corrosion inhibitor is hexamethylenetetramine with a mass concentration of 2%~5%; the volume ratio of dilute hydrochloric acid solution to corrosion inhibitor solution is (15:1)~(25:1).

3. The method for determining the calcium content of seamless pure calcium thread according to claim 2, characterized in that, The volume concentration of the dilute hydrochloric acid is 5%, and the corrosion inhibitor is a 3.5% hexamethylenetetramine solution. The volume ratio of the dilute hydrochloric acid solution to the corrosion inhibitor solution is 20:

1.

4. The method for determining the calcium content of seamless pure calcium thread according to claim 1, characterized in that, In step S1, the amount of glacial acetic acid added as the second acidic dissolving solution is 1-5 ml of glacial acetic acid per 100 ml of the first acidic dissolving solution reaction system, and the heating treatment time is 5-15 minutes.

5. The method for determining the calcium content of seamless pure calcium thread according to claim 1, characterized in that, In step S3, the gradient alkalization is specifically as follows: first, add 5-10 ml of triethanolamine solution with a volume ratio of 1:1, stir evenly, then add concentrated ammonia dropwise until the solution pH is 9-11, and finally add 20-40 ml of potassium hydroxide solution with a mass concentration of 20%-30%.

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