A method for preparing alpha-type high-strength gypsum from desulfurized gypsum

Abstract

This invention belongs to the field of material preparation technology, specifically relating to a method for preparing desulfurized gypsum into α-type high-strength gypsum. This method improves the utilization rate and value of desulfurized gypsum, alleviating resource waste and environmental pollution caused by the landfilling of desulfurized gypsum. The method involves pre-treating the desulfurized gypsum with three water washes, followed by drying. During the third pre-treatment, 1% lime (by weight of the desulfurized gypsum) is added. A solution containing a crystallizing agent is added to the pre-treated desulfurized gypsum and mixed thoroughly. The crystallizing agent, aluminum sulfate, and water are present at 0.08-0.12 wt% and 10-15 wt% of the dry weight of the desulfurized gypsum, respectively. The resulting mixture is then double-pressed at 20 MPa using a press, and then placed in an autoclave for 8-10 hours at 150℃ and 1.4 MPa. Immediately afterward, it is dried at 100℃, and then ground to obtain high-quality α-type high-strength gypsum with a whiteness of 70% and a strength of α30.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to a method for preparing desulfurized gypsum into α-type high-strength gypsum. Background Technology

[0002] With rapid industrial development, the emissions of desulfurized gypsum have surged. Currently, my country's accumulated stockpile of desulfurized gypsum exceeds 360 Mt, with an annual increase of 120 Mt, and this trend continues to rise year by year. This massive accumulation and landfilling of desulfurized gypsum leads to resource waste and environmental pollution.

[0003] Currently, the utilization rate of desulfurized gypsum in my country is only 70%, and it is usually used as an auxiliary building material, such as cement retarder and filler, resulting in low utilization efficiency.

[0004] Desulfurized gypsum typically contains impurities such as K, Na, P, and F. To reduce the harm of these impurities to the product, pretreatment methods such as calcination, water washing, and acid treatment are commonly used. However, calcination is generally energy-intensive and has low processing efficiency, water washing consumes a large amount of water, and acid treatment can reduce product quality and pose a risk of equipment corrosion due to the addition of acidic substances.

[0005] Currently, there are several methods for preparing α-type high-strength gypsum, including the traditional autoclaving method, pressurized aqueous solution method, atmospheric pressure salt solution method, atmospheric pressure acidification method, and atmospheric pressure alcohol-water method. However, the shortcomings of each technology limit its application and promotion: the traditional autoclaving method is only suitable for natural gypsum and not for powdered industrial by-product gypsum, and it cannot change the crystal morphology by adding crystal-changing agents, resulting in poor quality α-type high-strength gypsum; the pressurized aqueous solution method, atmospheric pressure salt solution method, atmospheric pressure acidification method, and atmospheric pressure alcohol-water method are complex processes that can only be implemented in the laboratory at present, making it difficult to achieve industrial production, and they also generate a large amount of chlorine- and acid-containing wastewater, the treatment of which remains a problem to be solved.

[0006] In existing technologies, the utilization rate of desulfurized gypsum is low and the added value is low. The current preparation methods of α-type high-strength gypsum make it difficult to realize the resource utilization of desulfurized gypsum. How to industrially prepare desulfurized gypsum into α-type high-strength gypsum is a technical problem that needs to be solved. Summary of the Invention

[0007] To address the aforementioned problems, this invention aims to provide a method for preparing desulfurized gypsum into α-type high-strength gypsum. This method is simple, has low operating and investment costs, can be industrialized, is environmentally friendly, and offers significant economic benefits.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing desulfurized gypsum into α-type high-strength gypsum involves pretreating the desulfurized gypsum, adding a solution containing a crystallizing agent and mixing it evenly, then pressing the mixture into blocks using a press, steaming it in an autoclave and drying it immediately, and then grinding it to obtain α-type high-strength gypsum with a strength of α30.

[0010] Furthermore, the above-mentioned desulfurized gypsum pretreatment method involves soaking the desulfurized gypsum in tap water, wherein the mass ratio of gypsum to water is 1:3, stirring once every 20 minutes, filtering and changing the water every 60 minutes, and repeating 3 times. In the third pretreatment, an additional 1% of the mass of desulfurized gypsum lime is added.

[0011] Furthermore, the above-mentioned solution containing the crystallization agent is an aqueous solution of aluminum sulfate, wherein the amount of aluminum sulfate and water added is 0.08-0.12 wt% and 10-15 wt% of the dry weight of the pretreated desulfurized gypsum, respectively.

[0012] Furthermore, the pressing method of the above-mentioned press is as follows: the mixture is placed in the static press mold and pressed in a double-sided two-stage manner. The first stage pressing pressure is 20 MPa, and the load is stopped after 30 seconds. After waiting for 1 minute, the second stage pressing is carried out. The second stage pressing pressure is 20 MPa, and the load is held for 30 seconds, and the mixture is pressed into a block shape of 240mm×115mm×(30-50)mm.

[0013] Furthermore, the autoclave conditions described above are 150℃, 1.4 MPa, and autoclaving for 8-10 hours.

[0014] Furthermore, the above drying conditions are drying at 100°C;

[0015] Furthermore, the above grinding conditions are as follows: grinding until the residue on a 0.125 mm square hole sieve is no more than 5%.

[0016] A type α high-strength gypsum prepared by the above method has a whiteness of 70% and a strength that meets α30.

[0017] Advantages of this invention

[0018] (1) The process of this invention is simple and can be industrialized using equipment that has already been industrialized.

[0019] (2) my country’s cumulative stockpile of desulfurized gypsum exceeds 360 Mt, with an annual increase of 120 Mt, and the trend is still rising year by year. This invention can turn the cheap industrial by-product desulfurized gypsum into high-value α-type high-strength gypsum, which has huge potential economic benefits and can also alleviate environmental pollution.

[0020] (3) Pretreatment of desulfurized gypsum by combining water washing and lime neutralization not only reduces the amount of water used, but also effectively improves the purity and whiteness of the gypsum. The addition of lime can further reduce the impurity content and appropriately reduce the acidity of the gypsum.

[0021] (4) Compared with the traditional autoclaving method, the present invention can be applied to powdered desulfurized gypsum and can also change the crystal morphology by adding a crystallizing agent to obtain higher quality α-type high-strength gypsum. Compared with the pressurized aqueous solution method, atmospheric pressure salt solution method, atmospheric pressure acidification method and atmospheric pressure alcohol water method, the present invention has a simple process, can realize industrial production, and will not generate a large amount of chlorine-containing and acid-containing wastewater.

[0022] (5) The present invention adopts a double-sided two-stage pressing method to improve the density uniformity of desulfurized gypsum blocks. Under pressure, the powder particles undergo condensation movement, which is more conducive to the dehydration of desulfurized gypsum to form α-type gypsum crystals, thereby obtaining higher strength α-type high-strength gypsum. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0025] Comparative Example 1

[0026] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 2500 g of clean desulfurized gypsum was weighed, and 0 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 40 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of the type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0027] Comparative Example 2

[0028] Desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3, stirred every 20 minutes, and filtered and the water changed every 60 minutes. This process was repeated three times, followed by drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 2500 g of clean desulfurized gypsum was weighed, and 2 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed directly into an autoclave and autoclaved at 150℃ and 1.4 MPa for 9 hours. Immediately after autoclaving, it was dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, yielding α-type high-strength gypsum. The whiteness and setting time of the α-type high-strength gypsum were tested according to specifications. 40 mm × 40 mm × 150 mm specimens were prepared and cured according to the compressive and flexural strength test block preparation and curing methods, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0029] Comparative Example 3

[0030] The desulfurized gypsum was directly dried. 2500 g of desulfurized gypsum was weighed, and 2.0 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the desulfurized gypsum and stirred evenly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, pressing the mixture into blocks of 240 mm × 115 mm × 40 mm. The resulting desulfurized gypsum blocks were then placed in an autoclave and pressurized at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, the blocks were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, yielding α-type high-strength gypsum. The whiteness and setting time of α-type high-strength gypsum were tested according to the specifications. In accordance with the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0031] Example 1

[0032] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 2500 g of clean desulfurized gypsum was weighed, and 2.0 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 40 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0033] Example 2

[0034] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3, stirred every 20 minutes, and filtered and the water changed every 60 minutes. This process was repeated three times, followed by drying. During the third pretreatment, 1% lime was added to the desulfurized gypsum. 2500 g of clean desulfurized gypsum was weighed, and 2.5 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 40 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of the type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0035] Example 3

[0036] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 2500 g of clean desulfurized gypsum was weighed, and 3.0 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 40 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 10 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0037] Example 4

[0038] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 2500 g of clean desulfurized gypsum was weighed, and 2.5 g of aluminum sulfate was dissolved in 250 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 40 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0039] Example 5

[0040] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 1875 g of clean desulfurized gypsum was weighed, and 1.88 g of aluminum sulfate was dissolved in 225 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 30 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 9 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0041] Example 6

[0042] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 3125 g of clean desulfurized gypsum was weighed, and 3.16 g of aluminum sulfate was dissolved in 375 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 50 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of the type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0043] Example 7

[0044] The desulfurized gypsum was soaked in tap water at a gypsum-to-water mass ratio of 1:3. The solution was stirred every 20 minutes and filtered and the water changed every 60 minutes, repeated three times before drying. During the third pretreatment, 1% lime (by weight of the desulfurized gypsum) was added. 2500 g of clean desulfurized gypsum was weighed, and 3.13 g of aluminum sulfate was dissolved in 375 g of water. The resulting solution was poured into the clean desulfurized gypsum and stirred thoroughly. The mixture was then placed in a static press mold and pressed using a double-sided, two-stage pressing method. The first stage pressing pressure was 20 MPa, held for 30 seconds, and then the loading was stopped. After waiting 1 minute, the second stage pressing was performed at a pressure of 20 MPa for 30 seconds, resulting in blocks measuring 240 mm × 115 mm × 50 mm. The obtained desulfurized gypsum blocks were then placed in an autoclave and autoclaved at 150℃ and 1.4 MPa for 8 hours. Immediately after autoclaving, they were dried at 100℃ and then ground until the residue on a 0.125 mm square-hole sieve was no more than 5%, thus obtaining type α high-strength gypsum. The whiteness and setting time of type α high-strength gypsum were tested according to specifications. Following the preparation and curing methods for compressive and flexural strength test blocks, 40 mm × 40 mm × 150 mm test blocks were made, and their 2-hour flexural strength and oven-dry compressive strength were tested.

[0045] The α-type high-strength gypsum specimens prepared by Comparative Examples 1-3 and Examples 1-7 were tested according to the setting time, 2-hour flexural strength and oven-dry compressive strength of (JC / T2038-2010 "α-type high-strength gypsum") standard. The results are shown in Table 1.

[0046] Table 1 Performance testing of type α high-strength gypsum

[0047]

[0048] As shown in Table 1, the test results indicate that the α-type high-strength gypsum prepared using the method of this invention all meet the α30 requirement in the standard JC / T2038-2010 "α-type High-Strength Gypsum". When the amount of crystal-changing agent added is in the range of 0.08-0.12 wt%, the strength of the α-type high-strength gypsum increases with the increase of the crystal-changing agent. The strength of the α-type high-strength gypsum prepared by pressing gypsum into blocks and then steam-pressing is significantly higher than that prepared by direct steam pressing. Water washing and lime pretreatment can effectively improve the strength and whiteness of the product. Therefore, the method for preparing α-type high-strength gypsum according to this invention is feasible and represents a significant improvement over existing technologies.

[0049] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing desulfurized gypsum into α-type high-strength gypsum, characterized in that: After pretreatment of desulfurized gypsum, a solution containing crystallizing agent is added and mixed evenly. The mixture is then pressed into blocks using a press, placed in an autoclave for autoclaving, dried immediately, and then ground to obtain α-type high-strength gypsum. The pretreatment is as follows: the desulfurized gypsum is soaked in tap water, wherein the mass ratio of desulfurized gypsum to tap water is 1:3, the mixture is stirred once every 20 minutes, the water is filtered and changed every 60 minutes, and the process is repeated 3 times before drying. In the third pretreatment, 1% lime by mass of the desulfurized gypsum is added. The solution containing the crystallization agent is an aqueous solution of aluminum sulfate, wherein the amount of aluminum sulfate and water added is 0.08-0.12 wt% and 10-15 wt% of the dry weight of the pretreated desulfurized gypsum, respectively. The pressing method of the press is as follows: the mixture is placed into the static press mold and pressed in a double-sided two-stage manner. The first stage pressing pressure is 20MPa, and the load is stopped after 30s. After waiting for 1 minute, the second stage pressing is carried out. The second stage pressing pressure is 20MPa and the load is held for 30s. The autoclave conditions are as follows: desulfurized gypsum blocks are placed in the autoclave and autoclaved at 150℃ and 1.4MPa for 8-10 hours. The drying conditions are as follows: the desulfurized gypsum blocks after autoclaving are dried immediately at 100°C; The grinding conditions are as follows: grinding until the residue on a 0.125mm square hole sieve is no more than 5%.

2. The α-type high-strength gypsum prepared by the method described in claim 1.

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