Method for measuring content of total iron, ferrous iron and ferric oxide in covering agent

Abstract

The invention discloses a method for determining the content of total iron, ferrous iron and ferric oxide in a covering agent. The method comprises the following steps: determining total iron by using a titanium trichloride-potassium dichromate titration method, determining ferrous iron by using a potassium dichromate titration method, and calculating ferric oxide according to the content of total iron and ferrous iron. The method provided by the invention can provide accurate data for the content of total iron, ferrous iron and ferric oxide in the covering agent.

Description

Technical Field

[0001] The invention belongs to the technical field of raw material analysis, and specifically relates to a method for determining the contents of total iron, ferrous iron and ferric oxide in a covering agent, and in particular to a determination and analysis technology for determining total iron according to a titanium trichloride-potassium dichromate titration method, determining ferrous iron according to a potassium dichromate titration method, and calculating ferric oxide according to the contents of total iron and ferrous iron. Background Art

[0002] During the continuous casting process, the molten steel is transferred to the tundish. Due to the large exposed surface of the molten steel, the heat loss increases, resulting in excessive temperature drop of the molten steel. The covering agent covers the surface of the molten steel, which plays a role in heat insulation and heat preservation and reduces the heat loss of the molten steel surface. With the continuous development of steel production technology, the cleanliness requirements of steel are constantly increasing. The covering agent is not only required to have the function of heat insulation, but also to prevent the secondary oxidation of the molten steel, adsorb the floating inclusions in the molten steel, participate in the refining of the molten steel to reduce or remove harmful elements in the molten steel, and other metallurgical functions. Therefore, it is of great significance to accurately determine the content of total iron, ferrous iron and ferric oxide in the covering agent. Summary of the invention

[0003] Purpose: This method was invented to solve the problem of no detection method for total iron, ferrous iron, and ferric oxide in the covering agent. Since there is basically no standard sample for the detection of the content of total iron, ferrous iron, and ferric oxide in the covering agent, the method of spike recovery is used to determine its accuracy. This method has been used in production practice for many years and is an effective and practical method.

[0004] The present invention provides a method for determining the contents of total iron, ferrous iron and ferric oxide in a covering agent, which comprises the following operations:

[0005] 1) Determination of total iron in covering agent

[0006] The sample is dissolved in sulfuric acid-phosphoric acid mixed acid, and a large amount of trivalent iron is reduced with stannous chloride in hydrochloric acid medium. Sodium tungstate is used as an indicator, and trivalent iron is reduced to divalent iron with titanium trichloride. Excess titanium trichloride is oxidized with potassium dichromate until the blue color of "tungsten blue" disappears. Sodium diphenylamine sulfonate is used as an indicator, and potassium dichromate is used to titrate to determine the iron content.

[0007] 2) Determination of ferrous iron in covering agent

[0008] The sample is placed in an air-tight conical flask, decomposed with hydrochloric acid and sodium fluoride, and titrated with potassium dichromate standard solution in the presence of sulfuric acid and phosphoric acid mixed acid, with sodium diphenylamine sulfonate as an indicator until a stable purple color is reached, thereby determining ferrous oxide;

[0009] 3) Calculation of ferric oxide in covering agent

[0010] The content of ferric oxide is calculated based on the content of total iron and ferrous iron.

[0011] In some embodiments, the method comprises the following operations:

[0012] 1) Determination of total iron in covering agent

[0013] Weigh 0.2000g of the sample and place it in a conical flask, add 20mL of sulfuric acid-phosphoric acid mixed acid, dissolve it on a high-temperature electric furnace until the sulfuric acid smoke leaves the bottom of the bottle at half the height of the bottle, take it off and cool it slightly, add 20mL of hydrochloric acid (1+1), reduce it to light yellow with tin dichloride solution (60g / L), take it off and cool it slightly, add 50mL of hot water (the solution temperature is kept at 40-50℃), add 8 drops of sodium tungstate solution (250g / L), reduce it to stable blue with titanium trichloride solution (1+9), add potassium dichromate standard solution until the blue disappears, immediately add four drops of sodium diphenylamine sulfonate solution (4g / L), titrate with potassium dichromate standard titration solution until stable purple is the end point, record the volume of this titration (mL), and calculate the iron content;

[0014] 2) Determination of ferrous iron in covering agent

[0015] Weigh 0.4000g of the sample and place it in a dry 300mL conical flask, add 3g of sodium bicarbonate, 0.2g of sodium fluoride, and 50mL of hydrochloric acid (2+1), immediately cover the bottle mouth with a porcelain crucible, place it on a low-temperature electric furnace for heating and decomposition, remove it when the volume is left to 8-10mL, immediately dilute it with distilled water to about 100mL, cover the porcelain crucible again, cool it to room temperature with running water, add 10mL of sulfuric acid-phosphoric acid mixed acid and four drops of sodium diphenylamine sulfonate solution (4g / L), and immediately titrate it with potassium dichromate standard titration solution until a stable purple color is the end point, record the volume (mL) of this titration, and use this to determine the ferrous oxide content;

[0016] 3) Calculation of ferric oxide in covering agent

[0017] The content of ferric oxide is calculated based on the content of total iron and ferrous iron.

[0018] In some embodiments, the total iron in the covering agent is calculated as follows:

[0019]

[0020] Where: V0: the volume of potassium dichromate standard titration solution consumed by the blank reagent (mL)

[0021] V: Volume of potassium dichromate standard titration solution consumed by the sample (mL)

[0022] C: Concentration of potassium dichromate standard titration solution (mol / L)

[0023] M: molar mass of iron (55.85 g / mol)

[0024] m: sample mass (g).

[0025] In some embodiments, the calculation formula of ferrous iron in the covering agent is:

[0026]

[0027] Where: V0: the volume of potassium dichromate standard titration solution consumed by the blank reagent (mL)

[0028] V: Volume of potassium dichromate standard titration solution consumed by the sample (mL)

[0029] C: Concentration of potassium dichromate standard titration solution (mol / L)

[0030] M: molar mass of ferrous oxide (71.85 g / mol)

[0031] m: sample mass (g).

[0032] In some embodiments, the calculation formula of ferric oxide in the covering agent is:

[0033] W(Fe2O3)(%)=(W(TFe)(%)-0.7773×W(FeO)(%))×1.43.

[0034] During the continuous casting process, the molten steel is transferred to the tundish. Due to the large exposed surface of the molten steel, the heat loss increases, resulting in excessive temperature drop of the molten steel. The covering agent covers the surface of the molten steel, which plays a role in heat insulation and heat preservation and reduces the heat loss of the molten steel surface. With the continuous development of steel production technology, the cleanliness requirements of steel are constantly increasing. The covering agent is not only required to have the function of heat insulation, but also to prevent the secondary oxidation of molten steel, adsorb the floating inclusions of molten steel, participate in the refining of molten steel to reduce or remove harmful elements in the molten steel and other metallurgical functions. Therefore, it is of great significance to accurately determine the content of total iron, ferrous iron and ferric oxide in the covering agent. However, there is currently a lack of relevant detection methods. This method provides accurate data for the content of total iron, ferrous iron and ferric oxide in the covering agent. DETAILED DESCRIPTION

[0035] The invention aims to provide a method for determining the contents of total iron, ferrous iron and ferric oxide in a covering agent.

[0036] The present invention is described in more detail below with examples. These examples are merely descriptions of the best mode for carrying out the present invention and do not impose any limitation on the content of the present invention.

[0037] 1. Reagents and materials:

[0038] 1. Sulfuric acid-phosphoric acid mixed acid (2+3)

[0039] 2. Sulfuric acid (5+95)

[0040] 3. Hydrochloric acid (ρ1.19)(1+1)(2+1)(5+95)

[0041] 4. Sodium fluoride (solid)

[0042] 5. Sodium bicarbonate (solid)

[0043] 6. Titanium trichloride solution (1+9)

[0044] Take a portion of titanium trichloride solution (15%-20%), put it into a brown bottle and dilute it with hydrochloric acid (5+95), mix it well and add a layer of liquid paraffin for protection.

[0045] 7. Sodium tungstate solution (250g / L)

[0046] Take 25g of sodium tungstate and dissolve it in 90mL of water. Add 10mL of phosphoric acid and mix well. If it is turbid, filter it.

[0047] 8. Sodium diphenylamine sulfonate indicator (4g / L)

[0048] 9. Tin dichloride solution (60g / L)

[0049] Weigh 6g of tin dichloride, dissolve it in 100mL of hydrochloric acid (1+1), and add a few tin particles.

[0050] 10. Potassium dichromate standard titration solution C (1 / 6K2Cr2O7) = 0.05 mol / L

[0051] 11. Ammonium ferrous sulfate (0.05 mol / L)

[0052] Weigh 19.7 g of ammonium ferrous sulfate, dissolve it in sulfuric acid (5+95), transfer it into a 100 mL volumetric flask, and dilute it to the mark with sulfuric acid (5+95).

[0053] 2 Experimental methods

[0054] 2.1 Determination of total iron in covering agent

[0055] 2.1.1 Blank test

[0056] The blank analysis is carried out according to the determination (2.1.2). Before titration, 6.00 mL of ammonium ferrous sulfate solution (0.05 mol / L) is added. After titration, the volume A (mL) of the consumed potassium dichromate standard solution is recorded. Then 6.00 mL of ammonium ferrous sulfate (0.05 mol / L) is added to the solution. Then, the solution is titrated with potassium dichromate standard solution until a stable purple color is formed. The titrated volume B (mL) is recorded. The reagent blank V0 = AB.

[0057] 2.1.2 Determination

[0058] Weigh 0.2000g of the sample [1] and place it in a 300mL conical flask. Add 20mL of sulfuric acid-phosphoric acid mixture and dissolve it on a high-temperature electric furnace until the sulfuric acid smoke leaves the bottom of the flask at half the height of the flask [2]. Remove and cool slightly. Add 20mL of hydrochloric acid (1+1). Reduce to light yellow with tin dichloride solution (60g / L) (it cannot turn white after reduction when boiled) [3]. Remove and cool slightly. Add 50mL of hot water (the solution temperature is kept at 40-50℃) [4]. Add 8 drops of sodium tungstate solution (250g / L). Reduce to a stable blue with titanium trichloride solution (1+9). Add potassium dichromate standard solution until the blue disappears. Immediately add 4 drops of sodium diphenylamine sulfonate solution (4g / L). Titrate with potassium dichromate standard titration solution until a stable purple color is reached. Record the volume of the titration (mL).

[0059] Note [1]: When the carbon, sulfur and organic matter content is high, the sample should be burned at high temperature before measurement.

[0060] [2]: When dissolving samples with sulfuric acid and phosphoric acid mixed acid, the temperature should not be too low and the time should not be too long, otherwise the result will be too low.

[0061] [3]: When an excess of tin dichloride is added, potassium permanganate (400 g / L) can be added to oxidize it to a light yellow color before continuing the operation.

[0062] [4]: When heating water, the temperature should not be too high. If the water temperature is too high, it will destroy the indicator and make it difficult to observe the titration endpoint.

[0063] 2.2 Determination of ferrous iron in covering agent

[0064] 2.2.1 Blank test

[0065] Blank analysis is performed according to the determination (2.2.2). Before titration, add 6.00 mL of ammonium ferrous sulfate solution (0.05 mol / L). After titration, record the volume A (mL) of the consumed potassium dichromate standard solution. Then add 6.00 mL of ammonium ferrous sulfate (0.05 mol / L) to the solution, and titrate with potassium dichromate standard solution until it turns stable purple. Record the titrated volume B (mL). The reagent blank V0 = AB.

[0066] 2.2.2 Determination

[0067] Weigh 0.4000g of the sample and place it in a dry 300mL conical flask, add 3g of sodium bicarbonate, 0.2g of sodium fluoride, and 50mL of hydrochloric acid (2+1), immediately cover the mouth of the flask with a porcelain crucible, place it on a low-temperature electric furnace for heating and decomposition, remove it when the volume is left to 8-10mL, immediately dilute it with distilled water to about 100mL, cover the porcelain crucible, and cool it to room temperature with running water. Add 10mL of sulfuric acid-phosphoric acid mixed acid and four drops of sodium diphenylamine sulfonate solution (4g / L), and immediately titrate it with potassium dichromate standard titration solution until the end point is stable purple, and record the volume of this titration (mL).

[0068] Note [1]: The hydrochloric acid and other reagents used to decompose the sample must not be mixed with nitric acid or other redox substances, otherwise the results will vary greatly. In order to detect this phenomenon in time, a standard sample should be brought in for inspection each time.

[0069] [2]: During the decomposition process of the sample, heating should not be interrupted to prevent air from entering the bottle and oxidizing the ferrous ions, causing the result to be low.

[0070] [3]: If the sample contains rare earth, add 1g of sodium sulfite (solid) before dissolving the sample.

[0071] 2.3 Calculation of analysis results

[0072] 2.3.1 Calculation of total iron in the covering agent

[0073]

[0074] Where: V0: the volume of potassium dichromate standard titration solution consumed by the blank reagent (mL)

[0075] V: Volume of potassium dichromate standard titration solution consumed by the sample (mL)

[0076] C: Concentration of potassium dichromate standard titration solution (mol / L)

[0077] M: molar mass of iron (55.85 g / mol)

[0078] m: sample mass (g)

[0079] 2.3.2 Calculation of ferrous iron in covering agent

[0080]

[0081] Where: V0: the volume of potassium dichromate standard titration solution consumed by the blank reagent (mL)

[0082] V: Volume of potassium dichromate standard titration solution consumed by the sample (mL)

[0083] C: Concentration of potassium dichromate standard titration solution (mol / L)

[0084] M: molar mass of ferrous oxide (71.85 g / mol)

[0085] m: sample mass (g)

[0086] 2.3.3 Calculation of ferric oxide in covering agent

[0087] W(Fe2O3)(%)=(W(TFe)(%)-0.7773×W(FeO)(%))×1.43

[0088] 3 Results and discussion

[0089] 3.1 Precision of the method

[0090] The TFe measurements were performed 10 times on the same sample to verify the precision of the method, as shown in Table 1.

[0091] Table 1: TFe method precision experiment

[0092]

[0093] As can be seen from the above table, the RSDs are all less than 1%, so they have good precision.

[0094] FeO was measured 10 times on the same sample to verify the precision of the method, as shown in Table 2.

[0095] Table 2: FeO method precision experiment

[0096]

[0097] As can be seen from the above table, the RSDs are all less than 1%, so they have good precision.

[0098] Fe2O3 calculations were performed 10 times on the same sample to verify the precision of the method, as shown in Table 3.

[0099] Table 3: Fe2O3 method precision experiment

[0100]

[0101] As can be seen from the above table, the RSDs are all less than 1%, so they have good precision.

[0102] 3.2 Accuracy of the method

[0103] The present invention adopts the accuracy of the standard addition recovery determination method when there is no suitable standard sample. The corresponding addition amount and recovery rate of total iron and ferrous iron are shown in Table 4 and Table 5.

[0104] Table 4: TFe method accuracy experiment

[0105]

[0106] Table 5: FeO method accuracy experiment

[0107]

[0108] It can be seen from Table 4 and Table 5 that the invention can ensure the accuracy of the test results.

[0109] 4. Conclusion

[0110] A large amount of experimental data shows that the present invention provides a reliable analytical method for determining the total iron, ferrous iron, and ferric oxide in the covering agent. The method has the advantages of simple operation, easy mastery, high accuracy and precision of the measurement results, and can fully meet the requirements of detection and analysis, and provide accurate data of its composition for the use of the covering agent.

[0111] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining the content of total iron, ferrous iron and ferric oxide in a covering agent, comprising the following operations: 1) Determination of total iron in covering agent The sample is dissolved in sulfuric acid-phosphoric acid mixed acid, and a large amount of trivalent iron is reduced with stannous chloride in hydrochloric acid medium. Sodium tungstate is used as an indicator, and trivalent iron is reduced to divalent iron with titanium trichloride. Excess titanium trichloride is oxidized with potassium dichromate until the blue color of "tungsten blue" disappears. Sodium diphenylamine sulfonate is used as an indicator, and potassium dichromate is used to titrate to determine the iron content. 2) Determination of ferrous iron in covering agent The sample is placed in an air-tight conical flask, decomposed with hydrochloric acid and sodium fluoride, and titrated with potassium dichromate standard solution in the presence of sulfuric acid and phosphoric acid mixed acid, with sodium diphenylamine sulfonate as an indicator until a stable purple color is reached, thereby determining ferrous oxide; 3) Calculation of ferric oxide in covering agent The content of ferric oxide is calculated based on the content of total iron and ferrous iron.

2. The method according to claim 1, comprising the following operations: 1) Determination of total iron in covering agent Weigh 0.2000g of the sample and place it in a conical flask, add 20mL of sulfuric acid-phosphoric acid mixed acid, dissolve it on a high-temperature electric furnace until the sulfuric acid smoke leaves the bottom of the bottle at half the height of the bottle, take it off and cool it slightly, add 20mL of hydrochloric acid (1+1), reduce it to light yellow with tin dichloride solution (60g / L), take it off and cool it slightly, add 50mL of hot water (the solution temperature is kept at 40-50℃), add 8 drops of sodium tungstate solution (250g / L), reduce it to stable blue with titanium trichloride solution (1+9), add potassium dichromate standard solution until the blue disappears, immediately add four drops of sodium diphenylamine sulfonate solution (4g / L), titrate with potassium dichromate standard titration solution until stable purple is the end point, record the volume of this titration (mL), and calculate the iron content; 2) Determination of ferrous iron in covering agent Weigh 0.4000g of the sample and place it in a dry 300mL conical flask, add 3g of sodium bicarbonate, 0.2g of sodium fluoride, and 50mL of hydrochloric acid (2+1), immediately cover the bottle mouth with a porcelain crucible, place it on a low-temperature electric furnace for heating and decomposition, remove it when the volume is left to 8-10mL, immediately dilute it with distilled water to about 100mL, cover the porcelain crucible again, cool it to room temperature with running water, add 10mL of sulfuric acid-phosphoric acid mixed acid and four drops of sodium diphenylamine sulfonate solution (4g / L), and immediately titrate it with potassium dichromate standard titration solution until a stable purple color is the end point, record the volume (mL) of this titration, and use this to determine the ferrous oxide content; 3) Calculation of ferric oxide in covering agent The content of ferric oxide is calculated based on the content of total iron and ferrous iron.

3. The method according to claim 2, wherein the calculation formula of total iron in the covering agent is: Where: V0: the volume of potassium dichromate standard titration solution consumed by the blank reagent (mL) V: Volume of potassium dichromate standard titration solution consumed by the sample (mL) C: Concentration of potassium dichromate standard titration solution (mol / L) M: molar mass of iron (55.85 g / mol) m: sample mass (g).

4. The method according to claim 2, wherein the calculation formula of ferrous iron in the covering agent is: Where: V0: the volume of potassium dichromate standard titration solution consumed by the blank reagent (mL) V: Volume of potassium dichromate standard titration solution consumed by the sample (mL) C: Concentration of potassium dichromate standard titration solution (mol / L) M: molar mass of ferrous oxide (71.85 g / mol) m: sample mass (g).

5. The method according to claim 2, wherein the calculation formula of ferric oxide in the covering agent is: W(Fe2O3)(%)=(W(TFe)(%)-0.7773×W(FeO)(%))×1.43.

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