Preparation method of static pressure brick with high titanium gypsum mixing amount

Abstract

The invention provides a preparation method of a static pressure brick with high titanium gypsum mixing amount, and relates to the technical field of resource utilization of industrial solid wastes. The preparation method of the static pressure brick comprises the following steps: pretreating wet titanium gypsum until the moisture content is 16-20%, and then adding quicklime powder according to the mass ratio of 100: (2-3) for activating and aging to obtain an activated mixture; and then 68-72% of the activated mixture, 18-22% of limestone powder, 5-9% of cement and 1-3% of a curing agent are subjected to two-stage stirring, two-way static pressure forming and temperature-controlled and humidity-controlled curing. According to the method, acidity is effectively neutralized and gelation activity is excited through quick lime activation pretreatment, the contradiction between the high doping amount of the titanium gypsum and the high performance of the product is successfully solved by combining the synergistic effect of a quaternary system, and under the condition that the dry basis doping amount of the titanium gypsum is larger than 70%, the compressive strength of the product is larger than or equal to 33 MPa, the softening coefficient is larger than or equal to 0.85, and the heavy metal leaching concentration is far lower than the national standard limit value; the titanium gypsum has excellent mechanical properties, durability and environmental safety, and high-efficiency and high-value resource utilization of titanium gypsum is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial solid waste resource utilization, and particularly relates to a preparation method of high-titanium gypsum content static pressure brick. BACKGROUND

[0002] Titanium gypsum is a large industrial solid waste produced in the process of producing titanium dioxide by the sulfuric acid method. The main chemical component of the titanium gypsum is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains a certain amount of metal oxides such as iron, titanium and aluminum, and residual sulfuric acid and other acidic substances. The pH value of the titanium gypsum is usually acidic (3-6). With the continuous expansion of the titanium dioxide industry in China, the annual discharge of titanium gypsum has exceeded ten million tons, but the comprehensive utilization rate has been less than 20% for a long time. The large amount of stacking not only occupies land resources, but also contains soluble heavy metal ions (such as Pb, Cr and Cd) and acidic substances which are extremely easy to migrate under the leaching of rainwater, and pose a serious and lasting threat to the surrounding soil, groundwater and ecological environment.

[0003] Therefore, promoting the bulk and high-value resource utilization of titanium gypsum has become an urgent need for the sustainable development of the industry. Using it to prepare building material bricks is recognized as an effective way to achieve large-scale consumption. At present, the related researches mainly focus on the preparation of non-fired bricks (or static pressure bricks) to avoid the high energy consumption problem caused by the sintering process.

[0004] However, those skilled in the art know that there are several insurmountable technical bottlenecks to realize the high-content resource utilization of titanium gypsum, among which the strength bottleneck is particularly prominent. The cementing property of titanium gypsum is far weaker than that of cement, and the strength provided by its needle-shaped crystal structure is limited. The existing technologies generally show that when the titanium gypsum content (dry basis mass) is increased to more than 50%, the compressive strength of the brick will decrease significantly. In order to ensure that the strength of the brick meets the national standard (usually ≥15-20MPa), most of the published technical solutions have to strictly control the titanium gypsum content at a relatively low level.

[0005] For example, the invention patent (Hefei Guangneng New Material Technology Co., Ltd.) disclosed in the patent with the publication number CN106630883A discloses a titanium gypsum block, the dosage of titanium gypsum is 40-50 parts by weight, and various reinforcing components such as graphene oxide (1-4 parts), slag powder (5-10 parts), cement, acrylic emulsion and expensive composite activator (2-5 parts) need to be added. Although the technical scheme uses titanium gypsum as one of the main raw materials, the dosage is relatively limited (the dry basis is estimated to be less than 50%), and it depends on various additives and complex pretreatment (crushing, high-temperature dehydration and drying), and finally the compressive strength is only at the level of 12-15 MPa. In addition, the invention patent disclosed in the patent with the publication number CN106946537A shows a titanium gypsum high-performance concrete building material, the dosage of the original titanium gypsum slag is 20-60 parts by weight, but the water content is ≥40%, and the actual dry basis ratio after conversion is also not high.

[0006] These existing technologies clearly demonstrate the contradiction between dosage and strength: in order to achieve high mechanical properties, the dosage of titanium gypsum often has to be sacrificed, which seriously limits the large-scale consumption of titanium gypsum. If the dosage is blindly increased, the strength of the product will decrease sharply, which cannot meet the basic requirements of building applications.

[0007] In addition, high-dosage titanium gypsum bricks also face a series of problems such as water resistance bottleneck (low softening coefficient), environmental safety bottleneck (poor long-term stability of heavy metals) and process adaptability bottleneck (difficulty in forming the mixture), making it difficult to achieve the three goals of "high dosage, high performance and high safety" at the same time. SUMMARY

[0008] The purpose of the present application is to provide a preparation method of high-titanium gypsum dosage static pressure brick, which successfully converts large-scale industrial solid waste titanium gypsum into high-performance, high-value green building material products, and perfectly realizes the goal of "waste treatment and waste utilization".

[0009] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows: A preparation method of high-titanium gypsum dosage static pressure brick, comprising the following steps: S1. Raw material activation pretreatment: the wet titanium gypsum is naturally aired or dried to a water content of 16-20%, then lime powder is added at a mass ratio of 100: (2-3), mixed uniformly and aged for 24-48 hours to obtain an activated titanium gypsum mixture; S2. Collaborative batching: each raw material is weighed according to the following mass percentage: the S1 activated titanium gypsum mixture 68-72%, limestone powder 18-22%, cement 5-9%, and sulfur-based curing agent 1-3%; S3. Two-stage stirring mixing: all the raw materials weighed in S2 are put into a stirring machine, dry mixing for 3-5 minutes until uniform; then 10-12% of the total dry basis mass of the raw materials is added to wet mix for 5-8 minutes, to obtain a mixed material with consistent fluidity; S4. Two-way static pressure forming: the mixed material in S3 is sent into a two-way pressurized static pressure brick machine mold, and is pressed under a pressure of 20-25 MPa for 2-3 seconds to obtain dense green bricks; S5. Temperature and humidity controlled curing: after the formed green bricks are cured in a curing room with a temperature of 15-25 DEG C and a relative humidity of greater than or equal to 80% for 48 hours, they are cured under natural conditions for 24-48 hours to obtain finished static pressure bricks.

[0010] In the application, further, the water content of the wet titanium gypsum in step S1 is greater than 30%.

[0011] In the application, further, in step S1, the aging is carried out in a closed environment, and the aging time is 48 hours.

[0012] In the application, further, in step S2, the mass percentage of each raw material is: the activated titanium gypsum mixture 70%, limestone powder 20%, cement 7%, and sulfur-based curing agent 3%.

[0013] In the application, further, in step S4, the static pressure forming adopts a two-way pressurizing mode, a pre-pressure of 10-15 MPa is first applied to the upper surface of the green brick, and then a main pressure of 20-25 MPa is simultaneously applied to the upper and lower surfaces and is kept.

[0014] In the application, further, in step S5, the carbon dioxide concentration in the curing room is controlled to be 1000-1500 ppm to promote surface carbonation and enhance.

[0015] The application also provides a high-titanium gypsum content static pressure brick prepared by the preparation method described above, the dry basis mass of the titanium gypsum in the static pressure brick accounts for more than 70%, the 28-day compressive strength is not less than 33 MPa, the softening coefficient is not less than 0.85, and the leaching concentration of heavy metals Pb, Cr and Cd is lower than 50% of the limit value of the hazardous waste identification standard in GB 5085.3-2007.

[0016] In the application, further, the static pressure brick can be used for municipal sidewalks, square paving or garden slope protection structures.

[0017] Compared with the prior art, the technical scheme provided by the application produces extremely significant and unexpected beneficial effects, which are far from the simple superposition of the functions of various components. The core lies in the unique "pre-treatment activation-quaternary system synergy-fine process control" mechanism, which comprehensively solves the multiple contradictions of strength, durability and environmental safety under high titanium gypsum content. Specifically, it is shown that: 1. The synergy of high titanium gypsum content and high performance of the product is achieved, and the effect is much better than expected: it is generally known in the art that there is a negative correlation between titanium gypsum content and product performance, and the performance will be significantly degraded when the content is increased to more than 50%. The application overturns this traditional cognition by the key step of lime pretreatment activation. The principle is that the addition of lime (CaO) not only neutralizes the residual acidic substances (such as H2SO4) in titanium gypsum, eliminating its inhibition on cement hydration, but also undergoes a series of complex physical and chemical reactions (such as the generation of ettringite and other intermediate products) with titanium gypsum during the aging process, significantly improving the physicochemical properties of the titanium gypsum particle surface and stimulating its potential cementitious activity. On this basis, a quaternary synergistic system is formed with specific proportions of limestone powder, cement, and sulfur-based curing agent: the micro-aggregate effect and sustained release of weak alkali of limestone powder further optimizes the system structure; cement provides the core cementitious strength; and the sulfur-based curing agent generates extremely difficultly soluble sulfide precipitates with heavy metal ions, achieving permanent fixation. This multi-component, multi-level synergistic effect produces a "1+1>2" superposition enhancement effect. The experimental results are surprising: under the harsh conditions of a titanium gypsum dry basis content of up to 74.5% (Example 1), the 28-day compressive strength of the product of the application reaches 35.8 MPa, far exceeding that of the traditional formula with a content of only 50% (Comparative Example 4, 29.7 MPa). This fully proves that the application is not simply increasing the content, but through a new technical path, it not only realizes the large-scale consumption of solid waste, but also greatly improves the core mechanical properties of the material, which is completely unexpected.

[0018] 2. Excellent durability and environmental safety, breaking through the application scenario limitation of unfired bricks: The product of the present application exhibits excellent durability, with a softening coefficient as high as 0.89 or above (even reaching 0.93 through carbonization curing in Example 1), far exceeding the excellent line of 0.85. This indicates that the brick structure is extremely dense and has extremely strong resistance to water erosion, completely overcoming the fatal defect of traditional titanium gypsum bricks that are easily water-softened and powdered. The fundamental reason lies in the fact that the lime pretreatment and the synergistic formula fundamentally improve the morphology and structure of the hydration products, forming a more stable and durable whole. This makes the product application no longer limited to indoor or non-load-bearing structures, but can be widely used in harsh outdoor environments such as municipal sidewalks, squares, and garden slopes, greatly expanding the market prospects. In terms of environmental safety, the chemical reaction of the sulfur-based curing agent with heavy metal ions achieves in-situ and permanent stabilization, rather than physical encapsulation. The leaching toxicity test data show that the leaching concentration of key heavy metals such as Pb, Cr, and Cd is only 2-3% of the standard limit, leaving a large safety margin, ensuring that the product has no environmental risk throughout its life cycle and providing solid data support for project approval through environmental impact assessment.

[0019] In summary, the present application successfully converts large amounts of industrial solid waste titanium gypsum into high-performance, high-value green building material products through creative technical means, perfectly achieving the goal of "waste control and waste to treasure". DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in conjunction with examples and comparative examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0021] The source of the raw materials used in the examples is described as follows: Wet titanium gypsum: The wet titanium gypsum used in the examples is an industrial byproduct produced during the production of titanium dioxide by the sulfuric acid method, with an original moisture content of about 35% and a pH value of about 4.2, and may contain a small amount of metal oxides such as iron (Fe), titanium (Ti), and chromium (Cr).

[0022] Quicklime powder: commercially available, with an effective CaO content of ≥92% and a fineness of 200 mesh.

[0023] Limestone powder: commercially available, with a CaCO3 content of ≥98% and a fineness of 150 mesh.

[0024] Cement: P.O 42.5 grade ordinary Portland cement.

[0025] Sulfur-based curing agent: commercially available sodium sulfide (Na2S·9H2O) solid.

[0026] Sand: standard sand, used in the comparative examples.

[0027] Performance test method: Compressive strength: tested according to GB / T 2542-2012, test piece is standard brick (240mm x 115mm x 53mm), and the test is conducted after 28 days of curing.

[0028] Softening coefficient: tested according to GB / T 2542-2012. 5 samples are saturated to constant weight to determine the saturated strength, and another 5 samples are dried to determine the dry strength, and the softening coefficient = average saturated strength / average dry strength.

[0029] Heavy metal leaching concentration: sample preparation is conducted according to HJ / T 300-2007, and the concentration of Pb, Cr and Cd in the leaching solution is determined by ICP-MS. Example 1

[0030] In this example, high-titanium gypsum content static pressure bricks are prepared according to the method of claim 1, and the steps are as follows: (1) Raw material activation pretreatment: 1000 kg of original wet titanium gypsum (water content 35%) is naturally aired to a water content of 18%. Then, based on the mass of the treated titanium gypsum, 20 kg of lime powder (mass ratio 100:2) is added, and a double-shaft mixer is used to mix for 5 minutes until uniform. The mixture is transferred to a sealed warehouse for aging for 48 hours to obtain an activated titanium gypsum mixture.

[0031] (2) Synergistic batching: 700 kg of the activated titanium gypsum mixture obtained in step 1 (calculated on a dry basis, equivalent to about 574 kg of pure titanium gypsum), 200 kg of limestone powder, 70 kg of cement, and 30 kg of sulfur-based curing agent are weighed.

[0032] (3) Two-stage mixing: all the dry materials are put into a forced mixer, and dry mixing is carried out for 4 minutes until the color is uniform. Then, 11% of the total dry basis of the raw materials (about 110 kg) is added, and wet mixing is continued for 7 minutes to obtain a well-proportioned mixture with good workability and consistent fluidity.

[0033] (4) Two-way static pressure forming: the mixture is sent to the hydraulic two-way pressure brick machine mold, a pre-pressure of 12 MPa is applied to the upper pressure head, and then a main pressure of 22 MPa is applied to the upper and lower pressure heads at the same time, and the pressure is maintained for 2.5 seconds, and after demolding, standard brick blanks with complete appearance and compactness are obtained.

[0034] (5) Temperature and humidity control curing: the brick blanks are sent to the curing room (temperature control at 20±2℃, relative humidity control at 85%), and cured for 48 hours. Then, it is moved to a cool place in the factory area for natural curing for 72 hours to obtain the finished product static pressure brick.

[0035] Performance test results: The performance of the static pressure brick prepared in this example was tested, and the results are as follows: Titanium gypsum dry basis content: 74.5% (574 kg / (574+200+70+30) kg); 28-day compressive strength: 35.8 MPa; Softening coefficient: 0.89; Heavy metal leaching concentration: Pb: 0.15 mg / L (standard limit 5 mg / L); Cr: 0.32 mg / L (standard limit 15 mg / L); Cd: 0.02 mg / L (standard limit 1 mg / L); All indicators are lower than 50% of the limit value of "GB 5085.3-2007", and the environmental safety is excellent. Example 2

[0036] This example is used for partial parameter adjustment. Except for the emphasized parameter adjustment, other ways are the same as example 1.

[0037] (1) Pretreatment: wet titanium gypsum is dried to a moisture content of 16%. Add lime powder at a mass ratio of 100:3, and age for 24 hours.

[0038] (2) Proportioning: activated titanium gypsum mixture 680 kg, limestone powder 220 kg, cement 80 kg, sulfur-based curing agent 20 kg.

[0039] (3) Stirring: dry mixing for 3 minutes, water amount is 10% of dry basis mass, wet mixing for 5 minutes.

[0040] (4) Forming: pressure maintaining for 3 seconds under 20 MPa pressure.

[0041] (5) Curing: curing room temperature 25℃, humidity 80%, curing for 48 hours, then natural curing for 48 hours.

[0042] Performance test results: Titanium gypsum dry basis content: 71.2%; 28-day compressive strength: 33.5 MPa; Softening coefficient: 0.86; Heavy metal leaching concentration: far lower than 50% of the standard limit. Example 3

[0043] This example is used for partial parameter adjustment. Except for the emphasized parameter adjustment, other ways are the same as example 1, mainly controlling CO2 concentration.

[0044] (1) Pretreatment: wet titanium gypsum is aired to 20% moisture content. Add lime powder at a mass ratio of 100:2.5, and age for 36 hours.

[0045] (2) Proportioning: mix 720 kg of activated titanium gypsum, 180 kg of limestone powder, 50 kg of cement, and 30 kg of sulfur-based curing agent.

[0046] (3) Stirring: dry mix for 5 minutes, and wet mix for 8 minutes with 12% water based on dry mass.

[0047] (4) Molding: maintain pressure for 2 seconds at 25 MPa.

[0048] (5) Curing: the curing room temperature is 15°C, and the humidity is 90%. After curing for 48 hours, natural curing is performed for 24 hours. During the curing process, CO2 gas is introduced to maintain a concentration of about 1200 ppm.

[0049] Performance test results: Titanium gypsum dry content: 76.1%; 28-day compressive strength: 34.2 MPa; Softening coefficient: 0.91, indicating that surface carbonation effectively improves water resistance; Heavy metal leaching concentration: far below 50% of the standard limit.

[0050] Comparative Example 1 (omit the lime activation step) To prove the necessity of the "lime activation pretreatment" step, this comparative example omits the step.

[0051] Wet titanium gypsum is directly aired to 18% moisture content without adding lime powder and aging.

[0052] Directly weigh 574 kg of this dry titanium gypsum (same as the dry mass of titanium gypsum in Example 1), 200 kg of limestone powder, 70 kg of cement, and 30 kg of sulfur-based curing agent.

[0053] The subsequent steps are exactly the same as in Example 1.

[0054] Performance test results: 28-day compressive strength: 18.5 MPa (far lower than 35.8 MPa in Example 1); Softening coefficient: 0.62 (poor water resistance, structure has been damaged); Phenomenon analysis: the brick surface appears obvious whitening (acidic substances precipitate), and the internal structure is loose.

[0055] Comparative Example 2 (low lime ratio) In this comparative example, the amount of lime added in the pretreatment is changed to 10 kg (mass ratio of 100:1), and the aging time is 48 hours.

[0056] The remaining steps are exactly the same as Example 1.

[0057] Performance test results: 28-day compressive strength: 25.1 MPa (failed to reach the high-strength standard of 33 MPa); Softening coefficient: 0.78 (still lower than the excellent level of 0.85).

[0058] This comparative example verifies the importance of the lower limit of the addition ratio of quicklime. The amount of quicklime is insufficient, and the complete neutralization of the system acidity is failed, resulting in that the cement hydration is still partially inhibited, and the performance is significantly reduced.

[0059] Comparative Example 3 (high addition ratio of quicklime) In this comparative example, the addition amount of quicklime in the pretreatment is changed to 50 kg (mass ratio 100:5), and the aging time is 48 hours.

[0060] The remaining steps are exactly the same as Example 1.

[0061] Performance test results: 28-day compressive strength: 28.4 MPa; Softening coefficient: 0.81; Phenomenon analysis: The brick appears slight expansion in the early stage of curing, and there are fine cracks on the surface.

[0062] This comparative example verifies the importance of the upper limit of the addition ratio of quicklime.

[0063] Comparative Example 4 (low dosage of titanium gypsum comparison) In this comparative example, the ingredients are changed to: dry titanium gypsum 385 kg (dry basis 50%), limestone powder 250 kg, cement 100 kg, sulfur-based curing agent 20 kg, and sand 255 kg.

[0064] The same pretreatment, stirring, molding and curing process as Example 1 is adopted.

[0065] Performance test results: 28-day compressive strength: 29.7 MPa; Softening coefficient: 0.83.

[0066] This comparative example proves the difficulty of achieving high performance at a high dosage and the remarkable effect of the present application.

[0067] Technical effect summary: The above data shows that, through specific "quicklime activation pretreatment" and "synergistic batching" system, the application successfully realizes the excellent performance of compressive strength ≥ 33MPa, softening coefficient ≥ 0.85 under the condition of titanium gypsum dry base content > 70%, and is environmentally friendly and safe, far exceeding the national standard and the existing technology level. The application realizes the resource utilization goal of "high content, high performance and high safety" of titanium gypsum solid waste, and the technical effect is remarkable.

[0068] Although the present application has been described in detail with general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of protection required by the present application.

Claims

1. A method for preparing a high-titanium gypsum-content statically pressed brick, characterized in that, Includes the following steps: S1. Raw material activation pretreatment: The wet titanium gypsum is naturally sun-dried or dried until the moisture content is 16-20%, and then quicklime powder is added at a mass ratio of 100:(2-3). After mixing evenly, it is aged for 24-48 hours to obtain activated titanium gypsum mixture. S2. Co-ingredients: Weigh the raw materials according to the following mass percentages: 68-72% of the S1 activated titanium gypsum mixture, 18-22% of limestone powder, 5-9% of cement, and 1-3% of sulfur-based curing agent; S3. Two-stage mixing: Put all the raw materials weighed in S2 into the mixer and dry mix for 3-5 minutes until uniform; then add water at 10-12% of the total dry weight of the raw materials and wet mix for 5-8 minutes to obtain a mixture with uniform flowability; S4. Bidirectional static pressure molding: The mixture described in S3 is fed into the mold of a bidirectional static pressure brick machine, and pressed under a pressure of 20-25MPa for 2-3 seconds to obtain a dense brick blank. S5. Temperature and humidity controlled curing: After the shaped brick blanks are cured in a curing room with a temperature of 15-25℃ and a relative humidity of ≥80% for 48 hours, they are then cured in the shade under natural conditions for 24-48 hours to obtain the finished static pressure bricks.

2. The method according to claim 1, characterized in that, In step S1, the moisture content of the wet titanium gypsum is greater than 30%.

3. The method according to claim 1, characterized in that, In step S1, the aging process is carried out in a closed environment for 48 hours.

4. The method according to claim 1, characterized in that, In step S2, the mass percentage of each raw material is as follows: 70% of the activated titanium gypsum mixture, 20% of the limestone powder, 7% of the cement, and 3% of the sulfur-based curing agent.

5. The method according to claim 1, characterized in that, In step S4, the static pressure molding adopts a bidirectional pressure method, first applying a pre-pressure of 10-15MPa to the upper surface of the brick blank, and then simultaneously applying a main pressure of 20-25MPa to the upper and lower surfaces and maintaining the pressure.

6. The method according to claim 1, characterized in that, In step S5, the carbon dioxide concentration in the curing chamber is controlled at 1000-1500 ppm to promote enhanced surface carbonization.

7. A high-titanium gypsum-content static-pressed brick prepared by the preparation method according to any one of claims 1-6, characterized in that, The dry basis weight of the titanium gypsum in the static pressure brick is greater than 70%, its 28-day compressive strength is not less than 33 MPa, and its softening coefficient is not less than 0.

85.

8. The high-titanium gypsum-content static-pressed brick according to claim 7, characterized in that, The static pressure bricks can be used for municipal sidewalks, plaza paving, or garden slope protection structures.