Method for analyzing content of fe2o3 in coal ash

Abstract

The application discloses a method for analyzing the content of Fe2O3 in coal ash, which comprises the following steps: determining the total iron; determining the FeO; and calculating the Fe2O3: W(Fe2O3) / %=(W(TFe) / %-0.7773*W(FeO) / %)*1.43; wherein, 0.7773 is the coefficient for converting the FeO into the iron; and 1.43 is the coefficient for converting the iron into the Fe2O3. The application provides the method for analyzing the content of Fe2O3 in the coal ash, provides the accurate data for the content of Fe2O3 in the coal ash, and fills the blank of the component analysis of Fe2O3 in the coal ash.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical analysis technology, and in particular relates to an analytical method for the content of ferric oxide in coal ash. Background Technology

[0002] With the continuous development of iron and steel smelting technology, coal ash, as an important raw material, plays an increasingly important role in the iron and steel smelting process. Coal ash has wide applications in iron and steel smelting, mainly in the following aspects: 1. Blast furnace injection: Coal ash is injected into the blast furnace through injection equipment, reacting with iron ore to improve the output and quality of molten iron. The high reactivity and high calorific value of coal ash make it an important raw material in blast furnace injection. 2. Steel rolling: In the steel rolling process, coal ash acts as fuel and reducing agent, providing heat to the furnace and generating protective gas, ensuring good protection of the steel during rolling and improving steel quality and output. 3. Casting: In the casting process, coal ash acts as fuel and filler, providing sufficient heat to the mold and serving as a filling material to improve the quality and output of castings. Ferric oxide (Fe2O3) is one of the main components of coal ash, and accurately determining its content is of great significance. Therefore, we have invented an analytical method for the ferric oxide content in coal ash.

[0003] Patent CN 118258950 A discloses an analytical method for iron content in coal ash, comprising the following steps: weighing a certain amount of sample → dissolving the sample in hydrochloric acid-sodium fluoride → reducing a large amount of ferric iron with stannous chloride → using sodium tungstate as an indicator → reducing ferric iron to ferrous iron with titanium trichloride → oxidizing excess titanium trichloride with potassium dichromate until the "tungsten blue" color disappears → using sodium diphenylamine sulfonate as an indicator → titrating with potassium dichromate to determine the iron content. This invention offers a simple, rapid, and accurate determination process, making it an effective and practical method. However, its total iron (TFe) determination measures the total mass of all iron elements, including: Fe²⁺, Fe³⁺, metallic iron, FeO, Fe3O4, Fe2O3, and iron-containing impurities. It only reflects the total amount of iron, not its existing forms, valence states, or phases. Summary of the Invention

[0004] The purpose of this invention is to provide an analytical method for the ferric oxide content in coal ash, addressing the following problems:

[0005] 1. Methods for determining ferric oxide in coal ash often employ large-scale instrument analysis, which is costly. For small enterprises, chemical analysis methods offer greater advantages, being convenient and faster. 2. To control the slagging phenomenon of ferric oxide in coal ash on water-cooled walls, thereby improving steelmaking quality and service life. 3. To address the lack of a detection method for ferric oxide content in coal ash, an analytical method for ferric oxide content in coal ash was invented. This method has been applied in production practice; the determination process is simple, rapid, and accurate, making it an effective and practical method.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a method for analyzing the ferric oxide content in coal ash, comprising:

[0008] Determination of total iron: The sample is dissolved in a sulfuric acid-phosphoric acid mixture. In hydrochloric acid medium, a large amount of ferric iron is reduced with stannous chloride. Using sodium tungstate as an indicator, titanium trichloride is used to reduce ferric iron to ferrous iron. Excess titanium trichloride is oxidized with potassium dichromate until the "tungsten blue" color disappears. The total iron content is determined by titration with potassium dichromate using sodium diphenylamine sulfonate as an indicator.

[0009] Determination of ferrous oxide: The sample is placed in an air-free Erlenmeyer flask and decomposed with hydrochloric acid and sodium fluoride. In the presence of a mixed acid of sulfuric acid and phosphoric acid, sodium diphenylamine sulfonate is used as an indicator and the solution is titrated with potassium dichromate standard solution until a stable purple endpoint is reached. Ferrous oxide is determined by this titration.

[0010] Calculation of ferric oxide:

[0011] W(Fe2O3) / % = (W(TFe) / % - 0.7773×W(FeO) / %)×1.43;

[0012] In the formula: 0.7773: the coefficient for converting ferrous oxide to iron;

[0013] 1.43: The coefficient for converting iron to ferric oxide.

[0014] Further, the determination of total iron specifically includes: placing the weighed sample in a 300mL Erlenmeyer flask, adding 20mL of sulfuric acid-phosphoric acid mixture, dissolving it on a high-temperature electric furnace until the sulfuric acid fumes are halfway up the bottom of the flask, removing it and letting it cool slightly, adding 20mL of hydrochloric acid, reducing it with tin dichloride solution to a light yellow color, removing it and letting it cool slightly, adding 50mL of hot water; adding 8 drops of sodium tungstate solution, reducing it with titanium trichloride solution to a stable blue color, adding potassium dichromate solution until the blue color disappears, immediately adding four drops of sodium diphenylamine sulfonate solution, titrating with potassium dichromate standard solution until a stable purple color is reached as the endpoint, and recording the volume of this titration in mL;

[0015] Calculation of analysis results:

[0016] ;

[0017] In the formula: V0: is the volume of potassium dichromate standard titration solution consumed by the blank reagent, mL;

[0018] V: The volume of potassium dichromate standard titration solution consumed by the sample, in mL;

[0019] C: Concentration of potassium dichromate standard titration solution, mol / L;

[0020] m: Sample mass, g;

[0021] M: Molar mass of iron, 55.85 g / mol.

[0022] Furthermore, after reducing the solution to a light yellow color with tin dichloride, ensure that the solution does not turn white when boiled after reduction.

[0023] Furthermore, after heating 50 mL of water, the solution temperature is maintained at 40–50 °C.

[0024] Further, the determination of ferrous oxide specifically includes: placing the weighed sample in a dry 300 mL Erlenmeyer flask, adding 3 g sodium bicarbonate, 0.2 g sodium fluoride, and 50 mL hydrochloric acid, immediately covering the mouth of the flask with a porcelain crucible, heating it on a low-temperature electric furnace until the volume is reduced to 8-10 mL, removing it, immediately diluting it to 100 mL with distilled water, then covering it with the porcelain crucible again, and cooling it to room temperature with running water; adding 10 mL of sulfuric acid-phosphoric acid mixture and four drops of sodium diphenylamine sulfonate indicator, and immediately titrating with potassium dichromate standard solution until a stable purple endpoint is reached;

[0025] Analysis results settlement:

[0026] ;

[0027] In the formula: V0: is the volume of potassium dichromate standard titration solution consumed by the blank reagent, mL;

[0028] V: The volume of potassium dichromate standard titration solution consumed by the sample, in mL;

[0029] C: Concentration of potassium dichromate standard titration solution, mol / L;

[0030] m: Sample mass, g;

[0031] M: Molar mass of ferrous oxide, 71.85 g / mol.

[0032] Furthermore, for the determination of total iron, 0.2000 g of sample was weighed.

[0033] Further, for the determination of ferrous oxide, 0.4000 g of sample was weighed.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0035] Coal ash plays an increasingly important role in the steelmaking process as a crucial raw material. However, during smelting, some impurities are present, which can affect the quality and service life of steel. Ferric oxide (Fe2O3) can act as an oxidizing agent, reacting with these impurities to generate volatile substances, thereby removing them and improving the purity and quality of the steel. At high temperatures, ferric oxide can also react with steel to form an oxidation reaction, enhancing the steel's strength and hardness. Therefore, we have invented an analytical method for the ferric oxide content in coal ash. This invention provides accurate data on the ferric oxide content in coal ash, filling a gap in the analysis of ferric oxide components in coal ash. Detailed Implementation

[0036] An analytical method for the content of ferric oxide in coal ash, comprising:

[0037] 1. Scope

[0038] This method specifies the determination of ferric oxide by potassium dichromate titration.

[0039] This method is applicable to the determination of ferric oxide content in coal ash.

[0040] 2. Method Summary

[0041] Total iron: The sample was dissolved in a sulfuric acid-phosphoric acid mixture. In hydrochloric acid medium, a large amount of ferric iron was reduced with stannous chloride. Using sodium tungstate as an indicator, titanium trichloride was used to reduce the ferric iron to ferrous iron. Excess titanium trichloride was oxidized with potassium dichromate until the "tungsten blue" color disappeared. The total iron content was determined by titration with potassium dichromate using sodium diphenylamine sulfonate as an indicator.

[0042] Ferrous oxide: The sample is placed in an air-free Erlenmeyer flask (with a small amount of sodium bicarbonate added), and the sample is decomposed with hydrochloric acid and sodium fluoride. In the presence of a mixed acid of sulfuric acid and phosphoric acid, sodium diphenylamine sulfonate is used as an indicator, and the solution is titrated with potassium dichromate standard solution until a stable purple endpoint is reached, thereby determining ferrous oxide.

[0043] 3. Reagents and Materials

[0044] 3.1 Hydrochloric acid (ρ1.19) (1+1)

[0045] 3.2 Hydrochloric acid (2+1)

[0046] 3.3 Sodium fluoride (solid)

[0047] 3.4 Sodium bicarbonate (solid)

[0048] 3.5 Sulfuric acid-phosphoric acid mixture (2+3)

[0049] 3.6 Sulfuric acid (5+95)

[0050] 3.7 Titanium trichloride solution (1+9)

[0051] Take a portion of titanium trichloride solution (15%–20%), put it in an amber bottle, dilute it with hydrochloric acid (5+95), mix well, and then add a layer of liquid paraffin for protection.

[0052] 3.8 Sodium tungstate solution (250 g / L)

[0053] Dissolve 25 g of sodium tungstate in 90 mL of water, add 10 mL of phosphoric acid and mix well. If the mixture is cloudy, filter it.

[0054] 3.9 Sodium diphenylamine sulfonate indicator (4 g / L)

[0055] 3.10 Tin dichloride solution (60 g / L)

[0056] Weigh 6g of tin dichloride, dissolve it in 100mL of hydrochloric acid (1+1), and add a few tin granules.

[0057] 3.11 Potassium dichromate standard titration solution C (1 / 6 K2Cr2O7) = 0.05 mol / L

[0058] 3.12 Ferrous ammonium sulfate (approximately 0.05 mol / L)

[0059] Weigh 19.7g of ferrous ammonium sulfate, dissolve it in sulfuric acid (5+95), transfer it to a 100mL volumetric flask, and dilute it to the mark with sulfuric acid (5+95).

[0060] 4. Analysis Steps

[0061] 4.1 Sample Size

[0062] Weigh 0.2000 g of the sample for total iron.

[0063] Weigh 0.4000 g of ferrous oxide sample.

[0064] 4.2 Blank Test

[0065] Perform a blank test along with the sample.

[0066] 4.3 Measurement

[0067] Determination of total iron: The weighed sample[1] was placed in a 300 mL Erlenmeyer flask, 20 mL of sulfuric acid-phosphoric acid mixture was added, and dissolved on a high-temperature electric furnace until the sulfuric acid fumes were halfway up the bottom of the flask[2]. After cooling slightly, 20 mL of hydrochloric acid (1+1)[3] was added, and the solution was reduced to a light yellow color with tin dichloride solution (60 g / L) (it should not turn white after boiling)[4]. After cooling slightly, 50 mL of hot water was added (the solution temperature was kept at 40-50℃)[7]. 8 drops of sodium tungstate solution (250 g / L) were added, and the solution was reduced to a stable blue color with titanium trichloride solution (1+9). Potassium dichromate solution was added until the blue color disappeared. Four drops of sodium diphenylamine sulfonate solution (4 g / L) were added immediately, and the solution was titrated with potassium dichromate standard solution until a stable purple color was reached. The volume of this titration (mL) was recorded.

[0068] Note [1]: When the carbon, sulfur and organic matter content is high, it should be burned at high temperature before measurement.

[0069] [2]: When using a mixture of sulfuric acid and phosphoric acid to dissolve the sample, the temperature should not be too low and the time should not be too long, otherwise the result will be too low.

[0070] [3]: When the sample is difficult to dissolve, the residue should be treated by alkaline fusion or potassium pyrosulfate treatment. The treatment methods are as follows:

[0071] After filtering, washing, and igniting the residue, melt it in a platinum or porcelain crucible with potassium pyrosulfate or a mixed flux. Leach the molten material with the original filtrate, and then proceed with the original analytical steps.

[0072] [4]: When tin dichloride is added in excess, potassium permanganate (400g / L) can be added to oxidize it until it turns light yellow before continuing the operation.

[0073] [5]: When copper and vanadium (>1%) are high, they should be treated in accordance with national standards.

[0074] [6]: When the vanadium content of the sample is between 0.08% and 1%, it is reduced with tin dichloride solution (6 g / L) until the yellow color disappears. Then, potassium permanganate solution (400 g / L) is added dropwise to make the test solution yellow and 10 drops in excess. The original analytical steps are then continued.

[0075] [7]: The temperature of the hot water should not be too high, as high water temperature will damage the indicator and make it difficult to observe the titration endpoint.

[0076] Determination of ferrous oxide: Place the weighed sample in a dry 300 mL Erlenmeyer flask, add 3 g sodium bicarbonate, 0.2 g sodium fluoride, and 50 mL hydrochloric acid (2+1). Immediately cover the mouth of the flask with a porcelain crucible and heat it on a low-temperature electric furnace until the volume is reduced to 8-10 mL. Remove the flask and immediately dilute it with distilled water to about 100 mL. Cover the flask with the porcelain crucible again and cool it to room temperature with running water. Add 10 mL of sulfuric acid-phosphoric acid mixture and four drops of sodium diphenylamine sulfonate indicator. Immediately titrate with potassium dichromate standard solution until a stable purple endpoint is reached.

[0077] Note:

[0078] [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 be very different. In order to detect this phenomenon in time, a standard sample should be brought along for each inspection.

[0079] [2]: During the decomposition of the sample, heating should not be interrupted to prevent air from entering the bottle and oxidizing the ferrous ions, which would result in a lower result.

[0080] [3]: If the sample contains metallic iron, the metallic iron should be dissolved first using the metallic iron dissolution method. Then, the total amount of potassium dichromate consumed by ferrous oxide and metallic iron should be determined according to this method. The amount of metallic iron consumed for the same sample amount should be subtracted to calculate the content of ferrous oxide.

[0081] [4]: If the sample contains rare earth elements, add 1g of sodium sulfite (solid) before dissolving the sample.

[0082] 5. Calculation of analysis results:

[0083]

[0084] In the formula: V0: is the volume (mL) of potassium dichromate standard titration solution consumed by the blank reagent.

[0085] V: Volume (mL) of potassium dichromate standard titration solution consumed by the sample.

[0086] C: Concentration of potassium dichromate standard titration solution (mol / L)

[0087] m: Sample mass (g)

[0088] M: Molar mass of iron (55.85 g / mol)

[0089]

[0090] In the formula: V0: is the volume (mL) of potassium dichromate standard titration solution consumed by the blank reagent.

[0091] V: Volume (mL) of potassium dichromate standard titration solution consumed by the sample.

[0092] C: Concentration of potassium dichromate standard titration solution (mol / L)

[0093] m: Sample mass (g)

[0094] M: Molar mass of ferrous oxide (71.85 g / mol)

[0095] Calculation of ferric oxide:

[0096] W(Fe2O3) / % = (W(TFe) / % - 0.7773×W(FeO) / %)×1.43

[0097] In the formula: 0.7773: the coefficient for converting ferrous oxide to iron.

[0098] 1.43: Conversion factor for iron to ferric oxide

[0099] 6 Results and Discussion

[0100] 6.1 Precision Experiment

[0101] Eleven coal ash samples were weighed and precision tests were performed according to the experimental method. The test results are shown in Table 1.

[0102] Table 1 (%)

[0103]

[0104] The above data indicate that the precision of this analytical method is good.

[0105] 6.2 Accuracy Experiment

[0106] Two portions of coal ash sample were weighed and ferric oxide standard solution with different concentrations were added to conduct a spiked recovery experiment. The results are shown in Table 2.

[0107] Table 2 (%)

[0108]

[0109] The data in the table show that the recovery rate of the spiked experiment was between 95% and 110%, indicating that the accuracy of this analytical method is high.

[0110] 7 Conclusions

[0111] Extensive experimental data demonstrate that this invention provides a reliable and novel analytical method for determining ferric oxide in coal ash. This method is simple to operate, easy to master, produces minimal pollution, and has high detection efficiency, fully meeting the requirements for detection and analysis, and providing accurate data on the composition of coal ash for utilization.

[0112] The core differences between the technical solutions of this invention and the patent in the background art (comparison document 1) (item-by-item comparison):

[0113]

[0114] 1. At the conceptual level: The shift from "measuring total quantity" to "measuring price state + difference reduction" is a non-obvious combination invention.

[0115] (1) Common understanding in this field: only total iron is measured in coal ash, and there are no methods for measuring valence iron separately in national / industry standards;

[0116] (2) This application is not a simple superposition: the total iron method: open sample dissolution and reduction titration; the ferrous oxide method: air isolation, CO2 protection, and anti-oxidation full-process design;

[0117] (3) Those skilled in the art have not established a separate “ferrous isolation determination system” for coal ash, let alone thought of using total iron - ferrous iron to calculate ferric oxide.

[0118] In terms of results: the improvement in precision and accuracy is an unexpected technological leap.

[0119] (1) Example: Fe2O3 determination data of this application • 11 parallel tests: 8.26~8.32%, average value 8.29%, SD=0.0205, RSD=0.247% • Spiked recovery: 0.50→0.503 (100.6%); 10.00→9.95 (99.5%)

[0120] (2) Comparative example: Total iron determination data from the comparative document • 11 parallel studies: 4.26~4.34%, average 4.30%, SD=0.0276, RSD=0.642%

[0121] (3) Non-obvious conclusions: From total iron to valence iron, the RSD decreased from 0.642% to 0.247%, and the precision was significantly improved; the recovery rate remained stable at 99.5%~100.6%, meeting the requirements for precise control in front of the metallurgical furnace.

[0122] Comparative Example + Example:

[0123] Comparative example: Fe2O3 was determined using the all-iron method of the comparative document.

[0124] Technical solution: Use only total iron titration to directly convert Fe2O3, without measuring FeO.

[0125] Experimental data: Result deviation >1.2%, RSD >1.0%, unsuitable for slagging control.

[0126] Conclusion: Conventional methods in this field cannot accurately obtain Fe2O3.

[0127] Example: The method of this application (TFe + isolated FeO + differential calculation)

[0128] Technical solution: Independent measurement of two systems → Coupled calculation → Correction coefficient;

[0129] Experimental data: RSD = 0.247%, recovery rate 99.5%~100.6%

[0130] Conclusion: Only the method of this invention can stably and accurately determine Fe2O3 in coal ash.

[0131] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing the ferric oxide content in coal ash, characterized in that, include: Determination of total iron: The sample is dissolved in a sulfuric acid-phosphoric acid mixture. In hydrochloric acid medium, a large amount of ferric iron is reduced with stannous chloride. Using sodium tungstate as an indicator, titanium trichloride is used to reduce ferric iron to ferrous iron. Excess titanium trichloride is oxidized with potassium dichromate until the "tungsten blue" color disappears. The total iron content is determined by titration with potassium dichromate using sodium diphenylamine sulfonate as an indicator. Determination of ferrous oxide: The sample is placed in an air-free Erlenmeyer flask and decomposed with hydrochloric acid and sodium fluoride. In the presence of a mixed acid of sulfuric acid and phosphoric acid, sodium diphenylamine sulfonate is used as an indicator and the solution is titrated with potassium dichromate standard solution until a stable purple endpoint is reached. Ferrous oxide is determined by this titration. Calculation of ferric oxide: W(Fe2O3) / % = (W(TFe) / % - 0.7773×W(FeO) / %)×1.43; In the formula: 0.7773: the coefficient for converting ferrous oxide to iron; 1.43: the coefficient for converting iron to ferric oxide.

2. The method for analyzing the ferric oxide content in coal ash according to claim 1, characterized in that, The determination of total iron specifically includes: placing the weighed sample in a 300mL Erlenmeyer flask, adding 20mL of sulfuric acid-phosphoric acid mixture, dissolving it on a high-temperature electric furnace until the sulfuric acid fumes are halfway up the bottom of the flask, removing it and letting it cool slightly, adding 20mL of hydrochloric acid, reducing it with tin dichloride solution to a light yellow color, removing it and letting it cool slightly, adding 50mL of hot water; adding 8 drops of sodium tungstate solution, reducing it with titanium trichloride solution to a stable blue color, adding potassium dichromate solution until the blue color disappears, immediately adding four drops of sodium diphenylamine sulfonate solution, titrating with potassium dichromate standard solution until a stable purple color is reached as the endpoint, and recording the volume of this titration in mL; Calculation of analysis results: ； In the formula: V0: is the volume of potassium dichromate standard titration solution consumed by the blank reagent, mL; V: The volume of potassium dichromate standard titration solution consumed by the sample, in mL; C: Concentration of potassium dichromate standard titration solution, mol / L; m: Sample mass, g; M: Molar mass of iron, 55.85 g / mol.

3. The method for analyzing the ferric oxide content in coal ash according to claim 2, characterized in that, Reduce the solution of tin dichloride to a light yellow color, and ensure that it does not turn white after boiling.

4. The method for analyzing the ferric oxide content in coal ash according to claim 2, characterized in that, After adding 50 mL of hot water, maintain the solution temperature at 40–50 °C.

5. The method for analyzing the ferric oxide content in coal ash according to claim 1, characterized in that, The determination of ferrous oxide specifically includes: placing the weighed sample in a dry 300 mL Erlenmeyer flask, adding 3 g sodium bicarbonate, 0.2 g sodium fluoride, and 50 mL hydrochloric acid, immediately covering the mouth of the flask with a porcelain crucible, and heating it on a low-temperature electric furnace until the volume is reduced to 8-10 mL. Remove the flask and immediately dilute it to 100 mL with distilled water. Cover the flask with the porcelain crucible again and cool it to room temperature with running water. Add 10 mL of sulfuric acid-phosphoric acid mixture and four drops of sodium diphenylamine sulfonate indicator, and immediately titrate with potassium dichromate standard solution until a stable purple endpoint is reached. Analysis results settlement: ； In the formula: V0: is the volume of potassium dichromate standard titration solution consumed by the blank reagent, mL; V: The volume of potassium dichromate standard titration solution consumed by the sample, in mL; C: Concentration of potassium dichromate standard titration solution, mol / L; m: Sample mass, g; M: Molar mass of ferrous oxide, 71.85 g / mol.

6. The method for analyzing the ferric oxide content in coal ash according to claim 2, characterized in that, For the determination of total iron, weigh 0.2000 g of the sample.

7. The method for analyzing the ferric oxide content in coal ash according to claim 5, characterized in that, For the determination of ferrous oxide, weigh 0.4000 g of the sample.

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