Talc powder is the most commonly used filler in the paper industry. It is made from natural ore talc and becomes talc. Its main chemical composition is 3MgO·4SiO2·H2O. It is insoluble in water and stable in weak acid-alkaline solution. Widely used as a filler for paper to improve paper performance and reduce costs. The talc powder commonly used in the paper industry has a composition of 30.6% MgO and 62% SiO2, a specific gravity of 2.7, a particle size of 0.25-5.0 um (equivalent to 325 mesh), a refractive index of 1.57, and a fine sheet shape under a microscope.
1. Influence of different calcium content and different whiteness talc powder on paper production
A papermaking enterprise in Shandong conducted a comparative study on talc powder with low calcium, low whiteness, low calcium, high whiteness and high calcium and high whiteness, so as to analyze the application effect of talc powder with different calcium content and different whiteness in actual production.
The characteristics of talc powder are shown in Table 1.
Through experimental experiments and production applications, the following conclusions are drawn: talc powders with different calcium contents and different whiteness have their own advantages and disadvantages. Production tests were carried out on a 1760 mm long wire machine. The paper machine speed was 240 m/min, and an 80-mesh polyester net was used to produce 60 g/m2 writing paper. The amount of talc powder was 30%, the amount of PAM was 250 mg/l, the amount of AKD was 0.225%, and the concentration of surface sizing solution was 0.8%. The test results are shown in Table 2.
Test and production applications show that:
(1) Using high calcium and high whiteness talcum powder, the paper has good whiteness, crack length, folding resistance, opacity, etc., but the retention rate, smoothness and other indicators are not as good as low calcium talc powder. Good, and the use of high calcium and high whiteness talc has an adverse effect on acidic sizing.
(2) using low calcium and low whiteness talcum powder, the paper has good smoothness, opacity, surface strength, etc., and the use of low calcium low whiteness talcum powder has the best retention rate, but paper The length of the break and the folding resistance are the worst.
(3) Using low calcium and high whiteness talcum powder, the paper has good retention rate, crack length and folding resistance, and the paper smoothness is better than the paper, and it has a favorable side for sizing. However, the unfavorable aspect is that the paper is tight and the surface strength is much lower.
Therefore, according to the actual situation, it is necessary to rationally use talc powder with different calcium content and different whiteness.
2. Method for determining CaCO3 content in talc powder
The CaCO3 content in talc is too high, and it will react with free sulfuric acid (H2SO4) in aluminum sulfate to produce a large amount of carbon dioxide (CO2), which causes a lot of foam in the slurry, which brings certain difficulties to production, so it is in production. The quality of the talc filler used should not only control its particle size and whiteness, but also the content of calcium carbonate.
At present, the determination of CaCO3 content in talc powder is generally adopted by the national standard method. The analysis results are prepared reliably and reproducible. However, the method is cumbersome and has a long analysis time, often contradicting the rapid and accurate analysis requirements of the production process. Unable to guide production in time. Here, we introduce a rapid determination method - complexometric titration method, which has the advantages of high accuracy, simple and fast operation, good reproducibility, etc. The method is described as follows:
(1) Measurement principle:
In the pH>12 alkaline medium, a small amount of AL3+, Fe3+, Mn2+ plasma was masked with triethanolamine, calcium indicator was used as an indicator, Ca2+ was titrated with EDTA standard solution, and excess EDTA captured Ca2+ which had been complexed with the indicator. The indicator is released, and the reaction end point is judged based on the change in color.
(2) Reagents:
a. Calcium indicator: Weigh 10g of NaCI which is dried at 105°C for 3 hours at room temperature, place it in the study and grind it, add 0.1g of indicator to finely mix and store it in brown grinding bottle.
b. 0.02mol / L EDTA standard solution: according to GB601--77 "standard solution preparation method" preparation and calibration.
(3) Analysis steps:
Weigh about 0.5g (accurate to 0.0001g) to a constant weight sample at 105 ° 3 ° C, placed in a 250mL beaker, add 6mol / l HCI 20mL, stir and cover the surface dish, wait for no bubbles After the production, transfer the sample to a 250 mL volumetric flask, rinse the watch glass and the beaker several times with distilled water, and wash the liquid into a volumetric flask. Finally, dilute to the mark with distilled water and shake well. Pipette 25 mL of the diluted solution into a 250 mL flask, add 25 mL of distilled water, 5 mL of 30% triethanolamine solution, 15 mL of 10% NaHH solution, add appropriate amount of calcium indicator, and titrate with 0.02 mol/L EDTA standard solution. The solution is changed from burgundy to pure blue.
Result calculation:
The percentage of calcium carbonate is calculated as follows: Where: the molar concentration of C-EDTA standard solution, mol / L;
V one-time timing consumes the volume of EDTA standard solution, mL;
M-sample quality, g;
0.10009 - The mass of calcium carbonate expressed in grams equivalent to the 1.00 ml EDTA standard solution [C(EDTA) = 1.00 mol/L].
(4) The following points should be noted in the operation of complexometric titration:
a. Calcium and magnesium often coexist. When adding NaOH solution, the pH should be controlled at 12-13, at which time magnesium is masked as Mg(OH)2 precipitate.
b. When using triethanolamine solution as a masking agent, it should be added to the acidic solution and then adjusted to alkaline, otherwise the hydrolyzed high-valent metal ions are not easily masked by it.
c. Through comparative tests, the relative error measured by the two methods of the method and the national standard method is less than the allowable difference of two parallel determinations specified by the national standard law, indicating that the method is equally applicable to the national standard method.
1. Influence of different calcium content and different whiteness talc powder on paper production
A papermaking enterprise in Shandong conducted a comparative study on talc powder with low calcium, low whiteness, low calcium, high whiteness and high calcium and high whiteness, so as to analyze the application effect of talc powder with different calcium content and different whiteness in actual production.
The characteristics of talc powder are shown in Table 1.
Table 1 Comparison of characteristics of different talc powders
Through experimental experiments and production applications, the following conclusions are drawn: talc powders with different calcium contents and different whiteness have their own advantages and disadvantages. Production tests were carried out on a 1760 mm long wire machine. The paper machine speed was 240 m/min, and an 80-mesh polyester net was used to produce 60 g/m2 writing paper. The amount of talc powder was 30%, the amount of PAM was 250 mg/l, the amount of AKD was 0.225%, and the concentration of surface sizing solution was 0.8%. The test results are shown in Table 2.
Table 2 Production test results
Test and production applications show that:
(1) Using high calcium and high whiteness talcum powder, the paper has good whiteness, crack length, folding resistance, opacity, etc., but the retention rate, smoothness and other indicators are not as good as low calcium talc powder. Good, and the use of high calcium and high whiteness talc has an adverse effect on acidic sizing.
(2) using low calcium and low whiteness talcum powder, the paper has good smoothness, opacity, surface strength, etc., and the use of low calcium low whiteness talcum powder has the best retention rate, but paper The length of the break and the folding resistance are the worst.
(3) Using low calcium and high whiteness talcum powder, the paper has good retention rate, crack length and folding resistance, and the paper smoothness is better than the paper, and it has a favorable side for sizing. However, the unfavorable aspect is that the paper is tight and the surface strength is much lower.
Therefore, according to the actual situation, it is necessary to rationally use talc powder with different calcium content and different whiteness.
2. Method for determining CaCO3 content in talc powder
The CaCO3 content in talc is too high, and it will react with free sulfuric acid (H2SO4) in aluminum sulfate to produce a large amount of carbon dioxide (CO2), which causes a lot of foam in the slurry, which brings certain difficulties to production, so it is in production. The quality of the talc filler used should not only control its particle size and whiteness, but also the content of calcium carbonate.
At present, the determination of CaCO3 content in talc powder is generally adopted by the national standard method. The analysis results are prepared reliably and reproducible. However, the method is cumbersome and has a long analysis time, often contradicting the rapid and accurate analysis requirements of the production process. Unable to guide production in time. Here, we introduce a rapid determination method - complexometric titration method, which has the advantages of high accuracy, simple and fast operation, good reproducibility, etc. The method is described as follows:
(1) Measurement principle:
In the pH>12 alkaline medium, a small amount of AL3+, Fe3+, Mn2+ plasma was masked with triethanolamine, calcium indicator was used as an indicator, Ca2+ was titrated with EDTA standard solution, and excess EDTA captured Ca2+ which had been complexed with the indicator. The indicator is released, and the reaction end point is judged based on the change in color.
(2) Reagents:
a. Calcium indicator: Weigh 10g of NaCI which is dried at 105°C for 3 hours at room temperature, place it in the study and grind it, add 0.1g of indicator to finely mix and store it in brown grinding bottle.
b. 0.02mol / L EDTA standard solution: according to GB601--77 "standard solution preparation method" preparation and calibration.
(3) Analysis steps:
Weigh about 0.5g (accurate to 0.0001g) to a constant weight sample at 105 ° 3 ° C, placed in a 250mL beaker, add 6mol / l HCI 20mL, stir and cover the surface dish, wait for no bubbles After the production, transfer the sample to a 250 mL volumetric flask, rinse the watch glass and the beaker several times with distilled water, and wash the liquid into a volumetric flask. Finally, dilute to the mark with distilled water and shake well. Pipette 25 mL of the diluted solution into a 250 mL flask, add 25 mL of distilled water, 5 mL of 30% triethanolamine solution, 15 mL of 10% NaHH solution, add appropriate amount of calcium indicator, and titrate with 0.02 mol/L EDTA standard solution. The solution is changed from burgundy to pure blue.
Result calculation:
The percentage of calcium carbonate is calculated as follows:
V one-time timing consumes the volume of EDTA standard solution, mL;
M-sample quality, g;
0.10009 - The mass of calcium carbonate expressed in grams equivalent to the 1.00 ml EDTA standard solution [C(EDTA) = 1.00 mol/L].
(4) The following points should be noted in the operation of complexometric titration:
a. Calcium and magnesium often coexist. When adding NaOH solution, the pH should be controlled at 12-13, at which time magnesium is masked as Mg(OH)2 precipitate.
b. When using triethanolamine solution as a masking agent, it should be added to the acidic solution and then adjusted to alkaline, otherwise the hydrolyzed high-valent metal ions are not easily masked by it.
c. Through comparative tests, the relative error measured by the two methods of the method and the national standard method is less than the allowable difference of two parallel determinations specified by the national standard law, indicating that the method is equally applicable to the national standard method.
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