Method for preparing non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment

Abstract

The present application relates to a kind of pressure-ultrasonic-microwave processing preparation baking-free phosphogypsum building material method, comprising the following steps: 1) phosphogypsum is added with calcium sulfate supersaturated liquid, rubber powder, calcium stearate, liquid paraffin, aluminate, succinic acid, graphene oxide in high-speed mixer in turn, and mixed uniformly to obtain modified phosphogypsum;2) modified phosphogypsum is simultaneously treated with ultrasonic and pressing, and modified phosphogypsum block is obtained;3) modified phosphogypsum block is treated with microwave, and baking-free phosphogypsum building material is obtained.The present application has high waste rate, and low carbon emission, and the phosphogypsum ratio in the final baking-free phosphogypsum product of the present application can reach more than 90%, and compared with the traditional baking-free brick needing to be treated by autoclave curing, the present application uses normal temperature forming, low-temperature treatment, and the carbon emission generated in the product preparation process is lower, and the baking-free phosphogypsum building material prepared by the method of the present application has good economic benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of calcium sulfate cement containing composition, and particularly relates to a method for preparing baking-free phosphogypsum building material through pressure-ultrasound-microwave treatment. BACKGROUND

[0002] The phosphorus chemical industry will discharge a large amount of phosphogypsum every year, and the long-term accumulation of phosphogypsum will pollute the air, soil and groundwater resources, and even affect the safe production of surrounding crops, causing serious harm to the ecological environment and human health. From the chemical composition, since the phosphogypsum contains a certain amount of SiO2, P, F and impurities such as organic matter, the product usually has problems such as low mechanical strength, poor water resistance and the like, which is easy to cause secondary pollution. Therefore, to carry out research on new phosphogypsum treatment and further develop the building material utilization mode of phosphogypsum is a major technical problem in the current industry.

[0003] Baking-free phosphogypsum building material is a new direction of phosphogypsum building material utilization in recent years, and the existing baking-free phosphogypsum building material technology can be divided into two general directions according to the amount of phosphogypsum. One is to use cement, fly ash and the like as cementitious materials, and finally obtain products through the action of binding agents and autoclave curing. Although the product obtained by this technology has good mechanical properties, the volume stability is poor, the utilization rate of phosphogypsum is less than 60%, the raw material cost is high, and the preparation process is complex. The other is to directly press the wet phosphogypsum material, and to prepare the phosphogypsum building material by using the pressing forming method, which greatly reduces the complexity of the process, but the pressing process generally requires high pressure of more than 400 MPa, and the water resistance is poor, which has problems of high production cost and difficult to be used on a large scale. SUMMARY

[0004] The technical problem to be solved by the present application is to solve the above-mentioned deficiencies in the prior art, and to provide a method for preparing baking-free phosphogypsum building material through pressure-ultrasound-microwave treatment. The method is used for pretreating and modifying the phosphogypsum, ultrasonic treatment and molding under low pressure conditions, promoting the dissolution of calcium sulfate in the supersaturated calcium sulfate solution, and accelerating the internal densification of the phosphogypsum, so as to significantly improve the mechanical properties and water resistance of the baking-free phosphogypsum building material prepared under low pressure. Compared with the traditional baking-free building material, the method reduces the autoclave curing step, and has the advantages of good product performance, low energy consumption and short preparation period.

[0005] To solve the above technical problems, the technical scheme provided by the present application is as follows:

[0006] A method for preparing baking-free phosphogypsum building material through pressure-ultrasound-microwave treatment is provided, comprising the following steps:

[0007] 1) adding phosphogypsum, calcium sulfate supersaturated liquid, rubber powder, calcium stearate, liquid paraffin, aluminates, succinic acid, graphene oxide into a high-speed mixer in turn, and mixing uniformly to obtain modified phosphogypsum;

[0008] 2) simultaneously performing ultrasonic and pressing treatment on the modified phosphogypsum obtained in step 1) to obtain modified phosphogypsum blocks;

[0009] 3) performing microwave treatment on the modified phosphogypsum blocks obtained in step 2) to obtain unfired phosphogypsum building materials.

[0010] According to the above scheme, the weight ratio of each raw material in step 1) is as follows: 100 parts of dihydrate phosphogypsum, 1.5-5 parts of calcium sulfate supersaturated liquid, 0.1-0.5 parts of rubber powder, 0.05-0.1 parts of calcium stearate, 0.1-0.2 parts of liquid paraffin, 1.5 parts of aluminates, 0.2-0.5 parts of succinic acid, and 0.02-0.08 parts of graphene oxide.

[0011] According to the above scheme, the phosphogypsum in step 1) has a water content of ≤5wt%, a dihydrate calcium sulfate content of ≥80wt%, a water-soluble phosphorus pentoxide content of ≤0.3wt%, a water-soluble fluoride ion content of ≤0.2wt%, a water-soluble magnesium oxide content of ≤0.1wt%, a water-soluble sodium oxide content of ≤0.1wt%, and a water-soluble chloride ion content of ≤0.04wt%, meeting the secondary phosphogypsum standard in GB / T23456-2018.

[0012] According to the above scheme, the calcium sulfate supersaturated liquid in step 1) is prepared by the following method:

[0013] S1, drying the phosphogypsum (meeting the secondary phosphogypsum standard in GB / T23456-2018) at 40±5℃ to constant weight to obtain dihydrate phosphogypsum powder;

[0014] S2, placing the dihydrate phosphogypsum powder obtained in step S1 into a muffle furnace for calcination and dehydration to obtain hemihydrate phosphogypsum, and then grinding the hemihydrate phosphogypsum to pass through a 200-mesh sieve to obtain hemihydrate phosphogypsum powder;

[0015] S3, mixing the hemihydrate phosphogypsum powder obtained in step S2 with sodium polyphosphate, quicklime, and sodium chloride, stirring uniformly to obtain a mixed powder, and then adding the mixed powder into water and stirring uniformly to obtain a calcium sulfate supersaturated liquid.

[0016] According to the above scheme, the calcination and dehydration process conditions in step S2 are as follows: heating at a heating rate of 5℃ / min to 140℃ at room temperature, and maintaining for 2h.

[0017] According to the above scheme, the weight ratio of the hemihydrate phosphogypsum powder, sodium polyphosphate, quicklime, sodium chloride and water in step S3 is as follows: hemihydrate phosphogypsum powder 3 parts, sodium polyphosphate 0.1-0.2 parts, quicklime 0.2-0.5 parts, sodium chloride 10-15 parts, and water 100 parts.

[0018] According to the above scheme, the purity of the sodium polyphosphate, quicklime and sodium chloride is higher than 90wt%.

[0019] According to the above scheme, the rubber powder in step 1) has a mesh number of 100-200. The rubber powder is used as a wave absorber in the system of the present application to prevent the phase change of the phosphogypsum under the action of microwaves.

[0020] According to the above scheme, the aluminate in step 1) is DL-411 aluminate coupling agent. The aluminate is used as a surface modifier to improve the water resistance of the product.

[0021] According to the above scheme, the purity of the succinic acid in step 1) is ≥90wt%. The succinic acid is added in the system of the present application to improve the microwave absorption of the liquid phase in the system and accelerate the crystalline phase precipitation speed of the supersaturated phosphogypsum solution under the action of microwaves.

[0022] According to the above scheme, the graphene oxide in step 1) is D 90 Multilayer graphene oxide powder with a particle size of 10-15μm. The graphene oxide is used as an ultrasonic enhancer to further fill the pores during ultrasonic and pressing treatment and improve the density of the system.

[0023] According to the above scheme, the process condition of the high-speed stirring in step 1) is continuous stirring at a speed of 600-1000rpm for 5-10min.

[0024] According to the above scheme, the ultrasonic process condition in step 2) is that the ultrasonic direction is perpendicular to the stress direction of the modified phosphogypsum during the pressing treatment, and the power of the ultrasonic treatment is 500-600W.

[0025] According to the above scheme, the pressing process condition in step 2) is that the pressure during the pressing forming process is 15-30MPa.

[0026] According to the above scheme, the ultrasonic and pressing treatment time in step 2) is 5-15min.

[0027] According to the above scheme, the power of the microwave treatment in step 3) is 600-800W, the frequency of the microwaves is 2450MHz, and the microwave treatment time is 0.5-2.5min.

[0028] The present application also includes the sinter-free phosphogypsum building material prepared by the above method.

[0029] The application utilizes the characteristics that the solubility of calcium sulfate hemihydrate is significantly greater than that of calcium sulfate dihydrate, prepares a calcium sulfate supersaturated solution, and further improves the solubility of calcium sulfate in water by using sodium chloride, but the supersaturation of the calcium sulfate solution is too high to cause the rapid precipitation of calcium sulfate, which is difficult to preserve, therefore, the system of the application adds sodium polyphosphate and a small amount of quicklime to adjust the pH value of the solution to make the calcium sulfate hemihydrate partially hydrated, and utilizes the soluble phosphorus and impurities released in the hydration process of the calcium sulfate hemihydrate to couple with the retarder (sodium polyphosphate) in the alkaline environment to form a hardened layer to coat the gypsum particles and thus block the hydration process of the calcium sulfate hemihydrate. The method can greatly slow down the hydration speed of the calcium sulfate hemihydrate and thus prolong the ion saturation state duration of the calcium sulfate supersaturated solution.

[0030] The above-prepared calcium sulfate supersaturated solution with high supersaturation concentration and long saturation state duration is added into the phosphogypsum material system of the application, and in the process of ultrasonic and pressing treatment, under the synergistic crushing effect of ultrasonic and pressing, the hardened layer coated on the surface of the phosphogypsum particles in the calcium sulfate supersaturated solution is destroyed, and part of the unhydrated calcium sulfate hemihydrate is released into the pores of the pressed body to hydrate, which plays a binding effect and thus improves the strength of the product. In addition, the ultrasonic and pressing treatment can also make the crushed fine particles fill the pores to improve the pressing density of the product, and in the subsequent microwave treatment process, the calcium sulfate supersaturated solution is precipitated quickly in the pores before it has time to migrate, and the precipitated calcium sulfate dihydrate plays a secondary binding effect and thus further improves the strength of the product. In this process, the characteristics of the rubber powder of absorbing waves and slowing down the temperature rising speed of the phosphogypsum are utilized to prevent the conversion of the dihydrate phosphogypsum into the hemihydrate phosphogypsum, and the strong polar molecular structure and water-soluble characteristics of the succinic acid are also utilized to increase the temperature rising speed of the liquid phase, which reduces the microwave treatment time and ensures the volume stability of the sample, realizes the high-speed and stable solidification effect, and finally prepares the non-burned phosphogypsum building material with excellent performance under the modification effect of the external additive.

[0031] The application has the following beneficial effects: 1. The application has high waste utilization rate and low carbon emission. Compared with the traditional phosphogypsum-slag non-burned building material system in which the proportion of phosphogypsum is 10-20%, most of the chemical raw materials used in the application, such as a small amount of sodium chloride, rubber powder, calcium stearate, aluminate coupling agent, succinic acid and graphene oxide, are phosphogypsum waste discharged by the phosphorus chemical industry. According to the calculation, the proportion of phosphogypsum in the final non-burned phosphogypsum product can reach more than 90%, and compared with the traditional non-burned brick which needs to be treated by autoclave curing, the application adopts the method of normal temperature forming and low temperature treatment, and the carbon emission generated in the product preparation process is low. The preparation of non-burned phosphogypsum building material by using the method of the application has good economic benefits. 2. The non-burned phosphogypsum building material prepared by the application has excellent mechanical properties and good water resistance, and has good market application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A comparison chart of the concentration of calcium sulfate in different solution systems over time;

[0033] Figure 2 A comparison chart of the setting time of hemihydrate phosphogypsum in different solution systems;

[0034] Figure 3 A SEM image of the hydration product of hemihydrate phosphogypsum in different solution systems after 48 hours of hydration;

[0035] Figure 4 A microscopic image of the sample obtained by the present application example 9, example 4, example 10, example 11 under different ultrasonic treatment time;

[0036] Figure 5 A microscopic image of the sample obtained by example 2, example 3, example 4, example 1, example 5, example 6 under different microwave treatment time;

[0037] Figure 6 A microscopic image of the sample obtained by example 10, example 12, example 13, example 14 with different content of graphene oxide. DETAILED DESCRIPTION

[0038] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the accompanying drawings.

[0039] The "parts" in the embodiments of the present application refer to mass parts.

[0040] The phosphogypsum used in the embodiments of the present application has an attached water content of ≤5wt%, a calcium sulfate dihydrate content of ≥80wt%, a water-soluble phosphorus pentoxide content of ≤0.3wt%, a water-soluble fluoride ion content of ≤0.2wt%, a water-soluble magnesium oxide content of ≤

[0041] 0.1wt%, a water-soluble sodium oxide content of ≤0.1wt%, and a water-soluble chloride ion content of ≤0.04wt%, meeting the secondary phosphogypsum standard in GB / T23456-2018.

[0042] The rubber powder used in the embodiments of the present application has a mesh number of 100.

[0043] The succinic acid used in the embodiments of the present application has a purity of ≥90wt%.

[0044] The graphene oxide used in the embodiments of the present application is D 90 multilayer graphene oxide powder with a particle size of 10-15μm.

[0045] The calcium sulfate supersaturated solution used in the embodiments of the present application is prepared by the following method:

[0046] S1, the phosphogypsum is dried at 40℃ to constant weight to obtain dihydrate phosphogypsum powder;

[0047] S2, the dihydrate phosphogypsum powder obtained in step S1 is placed in a muffle furnace, heated to 140℃ at a rate of 5℃ / min, calcined for 2h and cooled to obtain hemihydrate phosphogypsum, which is then ground to fine powder and sieved through a 200 mesh screen to obtain hemihydrate phosphogypsum powder;

[0048] S3, 3 parts of hemihydrate phosphogypsum powder obtained in step S2, 0.2 parts of sodium polyphosphate, 0.3 parts of quicklime and 15 parts of sodium chloride are mixed to obtain a mixed powder, which is then added to 100 parts of water and stirred to obtain a calcium sulfate supersaturated solution (marked as sodium chloride + sodium polyphosphate + lime).

[0049] As a comparison, a solution containing only 3 parts of hemihydrate phosphogypsum powder in 100 parts of water (marked as no additive), a solution containing 3 parts of hemihydrate phosphogypsum powder and 15 parts of sodium chloride in 100 parts of water (marked as sodium chloride), and a solution containing 3 parts of hemihydrate phosphogypsum powder, 15 parts of sodium chloride and 0.2 parts of sodium polyphosphate in 100 parts of water (marked as sodium chloride + sodium polyphosphate) are prepared, and the changes of calcium sulfate concentration in these solutions and the above prepared calcium sulfate supersaturated solution with time are tested, and the comparison chart is shown in Figure 1 As can be seen from the chart, the calcium sulfate supersaturated solution can basically maintain the calcium sulfate concentration unchanged within 24h, while the calcium sulfate concentrations of the other solutions have been greatly reduced after 2h.

[0050] 158 parts of hemihydrate phosphogypsum powder is added to 100 parts of water (marked as blank), 100 parts of water containing 0.2 parts of sodium polyphosphate (marked as sodium polyphosphate), and 100 parts of water containing 0.3 parts of quicklime and 0.2 parts of sodium polyphosphate (marked as sodium polyphosphate + quicklime), and the setting time of the hemihydrate phosphogypsum in the above three solutions is tested according to the standard GB / T 17669.4-1999 "Determination of physical properties of building gypsum neat paste", and the comparison results are shown in Figure 2 As can be seen from the results in Figure 2 , the hemihydrate phosphogypsum without adding additive will set in half an hour, and it is difficult to maintain the supersaturation state of the solution. Although the system directly adding sodium polyphosphate retarder can prolong the time of hemihydrate gypsum starting to hydrate, once the effect of the retarder weakens with time, the hemihydrate gypsum will quickly hydrate into dihydrate gypsum, and the supersaturation state of the solution will quickly disappear. By adjusting the pH value of the solution system with quicklime, the time from initial setting to final setting of the hemihydrate gypsum can be greatly prolonged, which confirms that the sodium polyphosphate + quicklime system can delay the hydration speed of the hemihydrate phosphogypsum and block the hydration process of the hemihydrate phosphogypsum, thereby maintaining the supersaturation of the solution for a long time.

[0051] Figure 3The images on the left, middle, and right are SEM images of the hydration products of hemihydrate phosphogypsum after hydration for 48 hours in three solutions: blank, sodium polyphosphate, and sodium polyphosphate + quicklime. It can be seen that the hydration products of hemihydrate phosphogypsum in the blank and sodium polyphosphate solutions are formed by the stacking of short columnar dihydrate gypsum crystals. However, the hydration products of hemihydrate phosphogypsum in sodium polyphosphate + quicklime solution are composed of a bunch of intermediate phases of hemihydrate gypsum without obvious boundaries. Incompletely grown dihydrate gypsum crystals can be seen inside the intermediate phase, and a hardened layer can be clearly seen on the surface to wrap the gypsum crystals.

[0052] Combination Figures 1 to 3 The test results show that the calcium sulfate supersaturated solution prepared in this invention, by adjusting the pH value of the solution, guides the phosphorus impurities in phosphogypsum to precipitate during the hydration process of gypsum, and couples with the retarder to form a hardened layer on the surface of the gypsum hydration intermediate, hindering its continued reaction. Thus, while delaying the hydration of hemihydrate phosphogypsum, it can also block the process of hemihydrate gypsum turning into dihydrate gypsum after the hemihydrate gypsum begins to hydrate, greatly extending the time required for hemihydrate gypsum to turn into dihydrate gypsum, thereby maintaining the supersaturated state of the solution for a long time.

[0053] Example 1

[0054] A method for preparing non-fired phosphogypsum building materials by pressure-ultrasound-microwave treatment includes the following steps:

[0055] 1) Weigh the raw materials according to the following proportions: 100 parts phosphogypsum, 3 parts supersaturated calcium sulfate solution, 0.5 parts rubber powder, 0.1 parts calcium stearate, 0.2 parts liquid paraffin, 1.5 parts aluminate coupling agent DL-411, 0.5 parts succinic acid, and 0.02 parts graphene oxide.

[0056] 2) The phosphogypsum weighed in step 1) is mixed with supersaturated calcium sulfate solution, rubber powder, calcium stearate, liquid paraffin, aluminate coupling agent DL-411, succinic acid, and graphene oxide in a high-speed mixer and stirred at 600 rpm for 10 min to obtain a mixture.

[0057] 3) Place the mixture into a pressing mold and press it under a pressure of 15MPa. At the same time, apply an ultrasonic wave with a power of 600W and a frequency of 50kHz to the side of the pressing mold. The pressing and ultrasonic treatment time is 5min. After completion, remove the pressed phosphogypsum from the mold and heat it in a microwave oven with a power of 700W and a frequency of 2450MHz for 1.5min to obtain non-fired phosphogypsum building material.

[0058] Example 2

[0059] A method for preparing non-fired phosphogypsum building materials by pressure-ultrasound-microwave treatment differs from Example 1 in that the microwave heating time is 0 min.

[0060] Example 3

[0061] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 1 in that the microwave heating time is 0.5 min.

[0062] Example 4

[0063] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 1 in that the microwave heating time is 1 min.

[0064] Example 5

[0065] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 1 in that the microwave heating time is 2 min.

[0066] Example 6

[0067] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 1 in that the microwave heating time is 2.5 min.

[0068] Example 7

[0069] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 4 in that the added calcium sulfate supersaturated liquid is 1.5 parts.

[0070] Example 8

[0071] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 4 in that the added calcium sulfate supersaturated liquid is 5 parts.

[0072] Example 9

[0073] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 4 in that the pressing and ultrasonic treatment time is 0 min.

[0074] Example 10

[0075] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 4 in that the pressing and ultrasonic treatment time is 10 min.

[0076] Example 11

[0077] A pressure-ultrasound-microwave treatment method for preparing a non-burned phosphogypsum building material, which differs from Example 4 in that the pressing and ultrasonic treatment time is 15 min.

[0078] Example 12

[0079] A pressure-ultrasound-microwave treatment method for preparing the unfired phosphogypsum building material, which is different from example 10 in that the added graphene oxide is 0.04 parts.

[0080] Example 13

[0081] A pressure-ultrasound-microwave treatment method for preparing the unfired phosphogypsum building material, which is different from example 10 in that the added graphene oxide is 0.06 parts.

[0082] Example 14

[0083] A pressure-ultrasound-microwave treatment method for preparing the unfired phosphogypsum building material, which is different from example 10 in that the added graphene oxide is 0.08 parts.

[0084] Comparative example 1

[0085] A pressure-ultrasound-microwave treatment method for preparing the unfired phosphogypsum building material, which is different from example 1 in that water is used instead of the calcium sulfate supersaturated solution in this comparative example.

[0086] Comparative example 2

[0087] This comparative example is different from example 1 in that this comparative example does not use ultrasonic treatment, and the sample preparation process step 3) is as follows:

[0088] 3) Put the mixed material into the pressing mold, and press under the pressure of 15 MPa for 5 min, after completion, take out the pressed phosphogypsum from the mold, and put it into a microwave oven with the power of 700 W and the frequency of 2450 MHz for heating for 1 min, to obtain the unfired phosphogypsum building material.

[0089] Comparative example 3

[0090] This comparative example is different from example 1 in that this comparative example does not use microwave treatment after pressing, but puts the sample into an oven at 40±5℃ for 48 h, and the sample preparation process step 3) is as follows:

[0091] 3) Put the mixed material into the pressing mold, and press under the pressure of 15 MPa, while applying ultrasonic waves with the power of 600 W and the frequency of 50 kHz on the side of the pressing mold, wherein the pressing and ultrasonic treatment time are both 5 min, after completion, take out the pressed phosphogypsum from the mold, and put it into an oven at 40±5℃ for 48 h, to obtain the unfired phosphogypsum building material.

[0092] Example 9, example 4, example 10 and example 11 are different in that the pressing and ultrasonic treatment time is 0 min, 5 min, 10 min and 15 min respectively, and the microscopic images of the obtained samples are as follows: Figure 4As shown in the figure, it can be seen that when the pressing and ultrasonic treatment time is 5 min (corresponding to example 4), the average pore size of the sample is the smallest, but as the pressing and ultrasonic treatment time increases, the average pore size of the sample gradually increases.

[0093] Example 2, example 3, example 4, example 1, example 5 and example 6 are compared, the difference is that the microwave heating time is 0 min, 0.5 min, 1 min, 1.5 min, 2 min and 2.5 min respectively, and the microscopic images of the obtained samples are as shown in Figure 5 As shown in the figure, it can be seen that when the microwave treatment time is 1.5 min (corresponding to example 1), the average pore size of the sample is the smallest, and when the microwave treatment time is further increased to 2.5 min (corresponding to example 5), a large number of pores appear on the surface of the sample, and obvious loose phenomenon appears.

[0094] Example 10, example 12, example 13 and example 14 are compared, the difference is that the content of graphene oxide in the raw material is 0.02%, 0.04%, 0.06%, 0.08% respectively, and the microscopic images of the samples obtained in the four examples are as shown in Figure 6 As shown in the figure, it can be seen that when the content of graphene oxide is 0.02% (corresponding to example 10), the average pore size of the sample is the smallest, and as the content of graphene oxide further increases, the average pore size of the sample begins to increase.

[0095] The performances of the unfired phosphogypsum prepared in the present application and the comparative examples are detected according to the method of Chinese building materials industry standard “JC / T 239-2014 Autoclaved Fly Ash Brick”, and compared with the indexes, and the detection results are shown in Table 1.

[0096] Table 1 Comparison of performances of examples and comparative examples with standards

[0097]

[0098] In the examples of the present application, phosphogypsum raw material, calcium sulfate supersaturated liquid and a series of additives are used to prepare unfired phosphogypsum building materials under pressure-ultrasonic-microwave treatment. The compressive strength of the unfired phosphogypsum material is between 17.5-31.9 MPa, the flexural strength is between 3.1-5.1 MPa, the water absorption is between 6.2-8.1%, the softening coefficient is between 0.71-0.82, and the density is between 79-84%. Compared with the performances of comparative examples 1-3 which do not use calcium sulfate supersaturated liquid, ultrasonic treatment and microwave treatment, there is a significant improvement. The above detection results show that the mechanical properties, density and water resistance of the unfired phosphogypsum building materials obtained by using the technical scheme provided in the present application are excellent, which indicates that the material has good application prospect.

Claims

1. A method for preparing a non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment, characterized in that, The method comprises the following steps: 1) adding phosphogypsum, calcium sulfate supersaturated solution, rubber powder, calcium stearate, liquid paraffin, aluminate, succinic acid and graphene oxide into a high-speed mixer in sequence and mixing uniformly to obtain modified phosphogypsum; 2) simultaneously performing ultrasonic treatment and pressing treatment on the modified phosphogypsum obtained in step 1) to obtain modified phosphogypsum blocks; 3) performing microwave treatment on the modified phosphogypsum blocks obtained in step 2) to obtain the unfired phosphogypsum building material. The calcium sulfate supersaturated solution in step 1) is prepared by the following method: S1, drying the phosphogypsum at 40±5℃ to constant weight to obtain dihydrate phosphogypsum powder; S2, the dihydrate phosphogypsum powder obtained in step S1 is put into a muffle furnace for calcination and dehydration to obtain hemihydrate phosphogypsum, S2, calcining the dihydrate phosphogypsum powder to obtain hemihydrate phosphogypsum powder; After ball milling, the hemihydrate phosphogypsum powder is obtained by passing through a 200-mesh screen; S3, mixing the hemihydrate phosphogypsum powder obtained in step S2 with sodium polyphosphate, quicklime and sodium chloride, stirring uniformly to obtain a mixed powder, and then adding the mixed powder into water and stirring uniformly to obtain the calcium sulfate supersaturated solution.

2. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, The weight ratio of the raw materials in step 1) is as follows: dihydrate phosphogypsum 100 parts, calcium sulfate supersaturated solution 1.5-5 parts, rubber powder 0.1-0.5 parts, calcium stearate 0.05-0.1 parts, liquid paraffin 0.1-0.2 parts, aluminate 1.5 parts, succinic acid 0.2-0.5 parts and graphene oxide 0.02-0.08 parts.

3. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, The calcination and dehydration process conditions in step S2 are as follows: heating at a temperature increasing rate of 5℃ / min to 140℃ and keeping the temperature for 2h.

4. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, The weight ratio of the hemihydrate phosphogypsum powder, sodium polyphosphate, quicklime, sodium chloride and water in step S3 is as follows: hemihydrate phosphogypsum powder 3 parts, sodium polyphosphate 0.1-0.2 parts, quicklime 0.2-0.5 parts, sodium chloride 10-15 parts and water 100 parts.

5. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, The rubber powder in step 1) has a mesh number of 100-200; and the aluminate in step 1) is aluminate coupling agent DL-411.

6. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, Step 1) said graphene oxide is D 90 Multilayer graphene oxide powder with particle size = 10-15 pm.

7. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, The ultrasonic treatment process conditions in step 2) are as follows: the ultrasonic direction is perpendicular to the stress direction of the modified phosphogypsum pressing treatment, and the ultrasonic treatment power is 500-600W; the pressing process conditions in step 2) are as follows: the pressure during the pressing forming process is 15-30MPa; and the ultrasonic and pressing treatment time in step 2) is 5-15min.

8. The method for preparing the non-burned phosphogypsum building material by pressure-ultrasonic-microwave treatment according to claim 1, characterized in that, The microwave treatment power in step 3) is 600-800W, the microwave frequency is 2450MHz, and the microwave treatment time is 0.5-2.5min.

9. The unfired phosphogypsum building material prepared by the method according to any one of claims 1-8.

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