Method for enhancing calcined desulfurized gypsum

Abstract

The invention relates to a method for enhancing calcined flue gas desulfurization gypsum, which specifically comprises the following steps: (1) adding anhydrous calcium chloride, a defoaming agent and redispersible latex powder into water, stirring, adding calcined flue gas desulfurization gypsum, slag powder, steel slag powder and calcium aluminate cement, and uniformly mixing and stirring; then, adding sodium methyl silicate, and uniformly mixing and stirring to obtain mixed slurry; and (2) pouring and molding the mixed slurry obtained in the step (1), and curing to obtain the enhanced desulfurized gypsum product. Calcium chloride, sodium methyl silicate, mineral slag, steel slag and calcium aluminate cement are utilized to reinforce the calcined desulfurized gypsum, so that the mechanical strength and water resistance of the gypsum material can be remarkably improved; the hydration reaction product can solidify Cl <-> and Na < + > introduced after calcium chloride and sodium methyl silicate are added, the problems of frosting and yellowing of gypsum products caused by Cl <-> and Na < + > can be effectively inhibited, and the product quality is improved.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a method for reinforcing calcined desulfurized gypsum. Background Art

[0002] The wet desulfurization process of coal-fired power plants produces a large amount of flue gas desulfurization gypsum. If it is not used properly, it will cause a large amount of accumulation, which will not only occupy a large amount of land but also cause resource waste and environmental pollution. The current utilization rate of desulfurization gypsum in my country is about 80%, and a large amount of desulfurization gypsum is still accumulated every year. Gypsum products are one of the preferred modern building materials because of their environmental protection, light weight, comfort, high construction efficiency, good fireproof and sound insulation performance, easy maintenance, and economy. However, due to the fact that calcium sulfate dihydrate is slightly soluble in water, gypsum building materials have poor water resistance and are subject to many restrictions on their use.

[0003] The main indicator reflecting the water resistance of gypsum building materials is the softening coefficient, which is the ratio of the saturated strength of the gypsum specimen to the absolute dry strength of the gypsum specimen. Although some people believe that sodium methyl silicate can improve the water resistance of gypsum, this is at the expense of the absolute strength of the gypsum, which greatly reduces the mechanical properties of the gypsum. Han Qingqing explored the effect of sodium methyl silicate on desulfurized building gypsum and believed that sodium methyl silicate forms a siloxane hydrophobic film in the gypsum slurry that adheres to the surface of the gypsum crystals and affects the hydration process of the gypsum. When the dosage of sodium methyl silicate is 5%, the compressive strength of the desulfurized building gypsum decreases by 62% (Han Qingqing. Research on the Water Resistance of Desulfurized Building Gypsum [D]. Henan Polytechnic University, 2023.000191. Page 22). Zhang Mingtao et al. modified phosphogypsum blocks with sodium methyl silicate and believed that sodium methyl silicate would form a hydrophobic film on the surface of gypsum crystals, affecting the bonding force between gypsum crystals. When the sodium methyl silicate content was 1.5%, the compressive strength of phosphogypsum blocks decreased by 68% (Zhang Mingtao et al. Effect of methyl silicate waterproofing agents on the water resistance of phosphogypsum building blocks [J]. Journal of Chongqing University of Science and Technology (Natural Science Edition), 2024, 26(04): 61-67). It can be seen that sodium methyl silicate will affect the hydration process of gypsum and the morphology of gypsum crystals, causing its mechanical strength to be greatly reduced.

[0004] In view of the above technical problems, the present invention provides a gypsum reinforcement method, wherein adding sodium methyl silicate to desulfurized gypsum can significantly improve the water resistance and mechanical strength of the gypsum. Summary of the invention

[0005] In order to solve the problem that sodium methyl silicate significantly reduces the mechanical strength of gypsum, the present invention provides a method for strengthening calcined desulfurized gypsum, comprising the following steps.

[0006] Step (1): adding anhydrous calcium chloride, a defoamer and a redispersible latex powder into water and stirring, then adding calcined desulfurized gypsum, slag powder, steel slag powder and calcium aluminate cement and mixing and stirring uniformly; then, adding sodium methyl silicate, mixing and stirring uniformly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a shape, and after curing, an enhanced desulfurized gypsum product can be obtained.

[0007] In the above method, the weight proportions of each material are: 100 parts of calcined desulfurized gypsum, 1 to 2 parts of anhydrous calcium chloride, 3 to 8 parts of sodium methyl silicate, 10 to 20 parts of slag powder, 10 to 20 parts of steel slag powder, 4 to 6 parts of calcium aluminate cement, 0.05 to 0.06 parts of defoaming agent, 2 to 4 parts of redispersible latex powder and mixing water.

[0008] In the above method, the calcined desulfurized gypsum is semi-hydrated desulfurized gypsum obtained by calcining desulfurized gypsum at 180° C. for 2 hours.

[0009] In the above method, the sodium methyl silicate is commercially available and has an effective content of 25%.

[0010] In the above method, the calcium aluminate cement is CA80 high alumina cement.

[0011] In the above method, the slag powder is S95 slag powder, and its specific surface area is 400-450m 2 / kg.

[0012] In the above method, the specific surface area of ​​the steel slag powder is 400-450m 2 / kg.

[0013] In the above method, the redispersible latex powder is commercially available Wacker 5044N model latex powder.

[0014] In the above method, the defoaming agent is a commercially available silicon-based defoaming agent.

[0015] In the above method, the mixing water is sufficient for mixing, stirring and casting the mixture, and 74 to 78 parts is preferred.

[0016] In the above method, the mixed slurry in step (2) is cast and molded, demoulded after 12 hours, and cured for 7 to 15 days at a temperature of 30° C. and a humidity of 60% to obtain an enhanced desulfurized gypsum product.

[0017] The positive and beneficial effects of the present invention: The present invention solves the problem that sodium methyl silicate can significantly reduce the mechanical strength of gypsum materials, and provides a method for strengthening calcined desulfurized gypsum, that is, using calcium chloride, sodium methyl silicate, slag, steel slag and calcium aluminate cement to strengthen calcined desulfurized gypsum, which can significantly improve the mechanical strength and water resistance of gypsum materials. (1) The anhydrous calcium chloride-sodium methyl silicate component and the slag powder-steel slag powder-calcium aluminate cement component can both improve the mechanical strength and softening coefficient of gypsum, and the slag powder-steel slag powder-calcium aluminate cement component can significantly improve the 24-hour saturated compressive strength of the gypsum test block (which is the key to improving the softening coefficient), and significantly reduce the Cl - (2) The technical solution of the present application can significantly enhance the performance of calcined desulfurized gypsum and reduce the Cl content in the product. - Content, also applies to its own Cl - High content of phosphogypsum.

[0018] At the same time, the hydration reaction product can solidify the Cl introduced by adding calcium chloride and sodium methyl silicate. - and Na + , which can effectively inhibit the - and Na + It can eliminate the frosting and yellowing problems of gypsum products and improve product quality.

[0019] The technical solution of the present invention can consume a large amount of industrial solid waste and reduce carbon emissions. The method of the present invention can be applied to phosphogypsum with high chlorine content to solve the problem of easy frosting and yellowing of phosphogypsum products. DETAILED DESCRIPTION

[0020] In the following examples, the mixed slurry was cast into a 40mm×40mm×160mm test piece for curing and then the performance test was performed; the absolute dry strength is the strength measured after the test piece was dried at 45°C in a blast drying oven for 3 days after curing, the 24-hour saturated strength is the strength measured after the dried test piece was completely immersed in water for 24 hours, and the softening coefficient is the ratio of the 24-hour saturated compressive strength of the test piece to the absolute dry compressive strength. The specific surface area of ​​the slag powder used is 433m 2 / kg, the specific surface area of ​​the steel slag powder used is 417m 2 / kg.

[0021] The method for measuring the chloride ion content in the following embodiments refers to "Method for Determining Chloride Ion Concentration in Concrete" (Zhuang Qichang et al., "Fly Ash" 2010 No. 1: 25-26, 33), specifically: the test block after strength testing is dried in a forced air drying oven at 45°C for 1 day, and then crushed and ground to pass through a 0.106 mm sieve; 5 g of the sample is weighed and placed in 100 mL of deionized water and allowed to stand for 1 day, and then filtered to obtain a filtrate; 0.05 mol / L silver nitrate solution is added dropwise to the filtrate to measure the chloride ion content. Blank example

[0022] 100 parts of calcined desulfurized gypsum and 58 parts of mixing water were evenly mixed to form a slurry, which was cast and molded. The slurry was demoulded after curing at room temperature for 12 hours. The test block was cured at a temperature of 30°C and a humidity of 60% for 7 days to obtain a gypsum test block.

[0023] After testing, the absolute dry flexural strength of the test block was 8.1MPa, and the absolute dry compressive strength was 13.4MPa; the 24-hour saturated compressive strength was 5.2MPa, and the softening coefficient was 0.39. Example 1

[0024] Step (1): add 2 parts of anhydrous calcium chloride, 0.055 parts of defoaming agent and 3 parts of redispersible latex powder to 74 parts of mixing water and stir, then add 100 parts of calcined desulfurized gypsum, 10 parts of slag powder, 20 parts of steel slag powder and 4 parts of calcium aluminate cement and mix and stir evenly; then, add 3 parts of sodium methyl silicate, mix and stir evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0025] After testing, the absolute dry flexural strength of the test block was 9.3MPa, and the absolute dry compressive strength was 16.9MPa; the 24-hour saturated compressive strength was 11.7MPa, the softening coefficient was 0.69, and the measured free chloride ion content was 480mg / kg. Example 2

[0026] Step (1): add 1.5 parts of anhydrous calcium chloride, 0.050 parts of defoaming agent and 2 parts of redispersible latex powder to 78 parts of mixing water and stir, then add 100 parts of calcined desulfurized gypsum, 15 parts of slag powder, 15 parts of steel slag powder and 5 parts of calcium aluminate cement and mix and stir evenly; then, add 6 parts of sodium methyl silicate, mix and stir evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0027] After testing, the absolute dry flexural strength of the test block was 9.5MPa, and the absolute dry compressive strength was 17.5MPa; the 24-hour saturated compressive strength was 12.6MPa, the softening coefficient was 0.72, and the measured free chloride ion content was 230mg / kg. Example 3

[0028] Step (1): add 2 parts of anhydrous calcium chloride, 0.06 parts of defoamer and 4 parts of redispersible latex powder to 78 parts of mixing water and stir, then add 100 parts of calcined desulfurized gypsum, 20 parts of slag powder, 10 parts of steel slag powder and 6 parts of calcium aluminate cement and mix and stir evenly; then, add 8 parts of sodium methyl silicate, mix and stir evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0029] After testing, the absolute dry flexural strength of the test block was 9.9MPa, the absolute dry compressive strength was 19.0MPa; the 24-hour saturated compressive strength was 15.2MPa, the softening coefficient was 0.80, and the measured free chloride ion content was 220mg / kg. Example 4

[0030] Step (1): add 1 part of anhydrous calcium chloride, 0.05 parts of defoaming agent and 2 parts of redispersible latex powder to 78 parts of mixing water and stir, then add 100 parts of calcined desulfurized gypsum, 17 parts of slag powder, 13 parts of steel slag powder and 5 parts of calcium aluminate cement and mix and stir evenly; then, add 6 parts of sodium methyl silicate, mix and stir evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0031] After testing, the absolute dry flexural strength of the test block was 9.1MPa, the absolute dry compressive strength was 16.2MPa; the 24-hour saturated compressive strength was 12.2MPa, the softening coefficient was 0.75, and the measured free chloride ion content was 190mg / kg. Comparative Example 1

[0032] Compared with the blank example, comparative example 1 added anhydrous calcium chloride and sodium methyl silicate.

[0033] Step (1): add 2 parts of anhydrous calcium chloride to 58 parts of mixing water and stir, then add 100 parts of calcined desulfurized gypsum and mix and stir evenly; then, add 3 parts of sodium methyl silicate, mix and stir evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0034] After testing, the absolute dry flexural strength of the test block was 8.8MPa, and the absolute dry compressive strength was 15.6MPa; the 24-hour saturated compressive strength was 7.0MPa, the softening coefficient was 0.45, and the measured free chloride ion content was 800mg / kg. Comparative Example 2

[0035] Compared with Comparative Example 1, the order of adding sodium methyl silicate in Comparative Example 2 is different.

[0036] Step (1): add 2 parts of anhydrous calcium chloride and 3 parts of sodium methyl silicate to 58 parts of mixing water and stir, then add 100 parts of calcined desulfurized gypsum and mix and stir evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0037] After testing, the absolute dry flexural strength of the test block was 6.5MPa, and the absolute dry compressive strength was 9.8MPa; the 24-hour saturated compressive strength was 4.2MPa, the softening coefficient was 0.43, and the measured free chloride ion content was 810mg / kg. Comparative Example 3

[0038] Compared with Example 3, Comparative Example 3 did not add anhydrous calcium chloride and sodium methyl silicate.

[0039] Step (1): adding 0.06 parts of defoamer and 4 parts of redispersible latex powder to 78 parts of mixing water and stirring, and then adding 100 parts of calcined desulfurized gypsum, 20 parts of slag powder, 10 parts of steel slag powder and 6 parts of calcium aluminate cement and stirring to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0040] After testing, the absolute dry flexural strength of the test block was 7.1 MPa, and the absolute dry compressive strength was 16.1 MPa, which was 15% lower than that of Example 3; the 24-hour saturated compressive strength was 10.3 MPa, and the softening coefficient was 0.64. Comparative Example 4

[0041] Compared with Example 3, Comparative Example 4 did not add sodium methyl silicate.

[0042] Step (1): adding 2 parts of anhydrous calcium chloride, 0.06 parts of defoaming agent and 4 parts of redispersible latex powder to 78 parts of mixing water and stirring, and then adding 100 parts of calcined desulfurized gypsum, 20 parts of slag powder, 10 parts of steel slag powder and 6 parts of calcium aluminate cement and stirring to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0043] After testing, the absolute dry flexural strength of the test block was 7.1 MPa, and the absolute dry compressive strength was 16.0 MPa (the compressive strength was reduced by 15.8% compared with Example 3); the 24-hour saturated compressive strength was 9.9 MPa, the softening coefficient was 0.62, and the free chloride ion content was measured to be 240 mg / kg. Comparative Example 5

[0044] Compared with Example 3, in Comparative Example 5, no anhydrous calcium chloride is added, and the dosage of sodium methyl silicate is 4 parts.

[0045] Step (1): adding 0.06 parts of defoamer and 4 parts of redispersible latex powder to 78 parts of mixing water and stirring, then adding 100 parts of calcined desulfurized gypsum, 20 parts of slag powder, 10 parts of steel slag powder and 6 parts of calcium aluminate cement and mixing and stirring evenly; then, adding 4 parts of sodium methyl silicate, mixing and stirring evenly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0046] After testing, the absolute dry flexural strength of the test block was 6.7 MPa, and the absolute dry compressive strength was 12.8 MPa (the compressive strength was reduced by 32.6% compared with Example 3); the 24-hour saturated compressive strength was 8.7 MPa, and the softening coefficient was 0.68. Comparative Example 6

[0047] Compared with Example 3, in Comparative Example 6, no anhydrous calcium chloride was added, and the dosage of sodium methyl silicate was 8 parts.

[0048] Step (1): adding 0.06 parts of defoamer and 4 parts of redispersible latex powder to 78 parts of mixing water and stirring, then adding 100 parts of calcined desulfurized gypsum, 20 parts of slag powder, 10 parts of steel slag powder and 6 parts of calcium aluminate cement and mixing and stirring uniformly; then, adding 8 parts of sodium methyl silicate, mixing and stirring uniformly to obtain a mixed slurry; Step (2): The mixed slurry obtained in step (1) is cast into a mold, and the mold is removed after curing at room temperature for 12 hours. The test block is cured at a temperature of 30° C. and a humidity of 60% for 7 days to obtain an enhanced desulfurized gypsum test block.

[0049] After testing, the absolute dry flexural strength of the test block was 5.1 MPa, and the absolute dry compressive strength was 9.3 MPa (compressive strength was reduced by 51.1% compared with Example 3); the 24-hour saturated compressive strength was 6.5 MPa, and the softening coefficient was 0.70.

[0050] Table 1 Comparison of test results Absolute dry compressive strength (MPa) 24h saturated compressive strength (MPa) Softening coefficient <![CDATA[Free Cl - Content (mg / kg)]]> Blank example 13.4 5.2 0.39 Example 1 16.9 11.7 0.69 480 Example 2 17.5 12.6 0.72 230 Example 3 19.0 15.2 0.80 220 Example 4 16.2 12.2 0.75 190 Comparative Example 1 15.6 7.0 0.45 800 Comparative Example 2 9.8 4.2 0.43 810 Comparative Example 3 16.1 10.3 0.64 Comparative Example 4 16.0 9.9 0.62 240 Comparative Example 5 12.8 8.7 0.68 Comparative Example 6 9.3 6.5 0.70 From the results of the above-mentioned Examples, Comparative Examples and Table 1, the following findings were made.

[0051] 1. Compared with the blank example, the anhydrous calcium chloride and sodium methyl silicate in comparative example 1 can significantly improve the mechanical strength and softening coefficient of the gypsum material; however, a large amount of Cl - , which will cause frost on the surface of gypsum products and affect the appearance quality.

[0052] 2. In Comparative Example 1, anhydrous calcium chloride is added first and sodium methyl silicate is added last (i.e., anhydrous calcium chloride is first added into water to dissolve, then calcined desulfurized gypsum is added and mixed evenly, and then sodium methyl silicate is added and mixed evenly before casting), in Comparative Example 2, anhydrous calcium chloride and sodium methyl silicate are added first at the same time (i.e., anhydrous calcium chloride and sodium methyl silicate are first added into water to dissolve, then calcined desulfurized gypsum is added and mixed evenly before casting), and the strength of the test block of Comparative Example 2 is significantly lower than that of the test block of the blank example and Comparative Example 1, which indicates that the order of adding sodium methyl silicate has a great influence on the strength of the gypsum material, that is, when sodium methyl silicate is added last, the strength of the gypsum material is improved, but when it is added first, it has the opposite effect.

[0053] 3. In Comparative Examples 1 and 2, anhydrous calcium chloride and sodium methyl silicate were added (without slag powder, steel slag powder and calcium aluminate cement). - , the Cl in the test block was measured - The contents were 800 mg / kg and 810 mg / kg respectively. In addition to anhydrous calcium chloride and sodium methyl silicate, slag powder, steel slag powder and calcium aluminate cement were added in Examples 1 to 3, which not only further improved the mechanical strength (especially the 24-hour saturated compressive strength increased by 54% to 117%) and the softening coefficient, but also significantly reduced the Cl - content.

[0054] 4. Comparison between Comparative Examples 3 and 4 shows that adding only anhydrous calcium chloride has little effect on the mechanical strength and softening coefficient of the test block.

[0055] V. Comparison of Comparative Examples 5 and 6 with Example 3 shows that when only sodium methyl silicate is added without adding anhydrous calcium chloride, the mechanical strength of the test block will be greatly reduced, and the greater the amount of sodium methyl silicate added, the greater the reduction in strength.

[0056] From the above analysis, the following conclusions can be drawn: (1) Both the anhydrous calcium chloride-sodium methyl silicate component and the slag powder-steel slag powder-calcium aluminate cement component can improve the mechanical strength and softening coefficient of gypsum, while the slag powder, steel slag powder, and calcium aluminate cement components can significantly improve the 24-hour saturated compressive strength of the gypsum specimen (which is the key to improving the softening coefficient) and significantly reduce the Cl - (2) The technical solution of the present application can significantly enhance the performance of calcined desulfurized gypsum and reduce the Cl content in the product. - Content, also applies to its own Cl - High content of phosphogypsum.

Claims

1. A method for enhancing calcined desulfurized gypsum, characterized in that: It includes the following steps: Step (1): adding anhydrous calcium chloride, a defoamer and a redispersible latex powder into water and stirring, then adding calcined desulfurized gypsum, slag powder, steel slag powder and calcium aluminate cement and mixing and stirring uniformly; then, adding sodium methyl silicate, mixing and stirring uniformly to obtain a mixed slurry; Step (2): casting the mixed slurry obtained in step (1) into a mold, and after curing, an enhanced desulfurized gypsum product can be obtained; The calcined desulfurized gypsum is semi-hydrated desulfurized gypsum obtained by calcining desulfurized gypsum at 180° C. for 2 hours.

2. A method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The weight proportions of each material are 100 parts of calcined desulfurized gypsum, 1 to 2 parts of anhydrous calcium chloride, 3 to 8 parts of sodium methyl silicate, 10 to 20 parts of slag powder, 10 to 20 parts of steel slag powder, 4 to 6 parts of calcium aluminate cement, 0.05 to 0.06 parts of defoaming agent, 2 to 4 parts of redispersible latex powder and mixing water.

3. The method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The slag powder is S95 ore powder, and its specific surface area is 400-450m 2 / kg; the specific surface area of ​​the steel slag powder is 400-450m 2 / kg.

4. The method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The calcium aluminate cement is CA80 high alumina cement.

5. The method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The sodium methyl silicate is commercially available and has an effective content of 25%.

6. A method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The redispersible latex powder is commercially available Wacker 5044N model latex powder.

7. The method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The defoamer is a commercially available silicon-based defoamer.

8. The method for enhancing calcined desulfurized gypsum according to claim 1, characterized in that: The mixed slurry in step (2) is cast and molded, demoulded after 12 hours, and cured at a temperature of 30° C. and a humidity of 60% for 7 to 15 days.