A method for preparing gypsum-based lightweight hollow aggregate

Abstract

The present invention discloses a method for preparing gypsum-based lightweight hollow aggregate, which belongs to the technical field of building materials. Specifically, phosphogypsum is burned into a gypsum-based cementitious material with a β-type hemihydrate gypsum content of more than 90%, a retarder, a thickener, a water reducer, and chopped fibers are added and mixed evenly to form a gypsum mixture A, a mixed reactant is added into molten paraffin, and granulation is performed before the paraffin is completely dried and hardened to obtain a mixture ball C; the gypsum mixture A with a thickness of not less than 3mm is coated on the surface of the mixture ball C to form a new material ball D; the material ball D is placed in a microwave oven for irradiation, and after the material expansion is completed, it is cooled to room temperature, and the resulting material is a gypsum-based lightweight hollow aggregate. The gypsum-based lightweight hollow aggregate of the present invention can be used for the preparation of lightweight cement concrete and gypsum-based concrete, can effectively reduce the apparent density of the cementitious material, and has the advantages of good fire resistance, low apparent density, fireproofing and heat preservation, sound insulation and heat insulation, high specific strength, and green and low carbon.

Description

Technical Field

[0001] The invention relates to a preparation method of gypsum-based lightweight hollow aggregate, belonging to the technical field of building materials. Background Art

[0002] Phosphogypsum is a solid waste residue generated during the wet-process phosphoric acid production process. Producing one ton of phosphoric acid requires approximately two tons of sulfuric acid and produces four to five tons of phosphogypsum. Its primary component is CaSO₄·2H₂O, but it contains organic impurities, including phosphorus, fluorine, and alkali metal salts, making it difficult to directly utilize.

[0003] Currently, phosphogypsum has been used as a casting material for applications in construction projects, such as masonry, wall casting, and slope management. However, the lightweight aggregates used in these casting materials are mostly ceramsite and expanded vermiculite. These materials have the disadvantages of high water absorption, weak interfaces with gypsum-based cementitious materials, high costs, and insufficient strength. Furthermore, there are currently no known uses of phosphogypsum as a hollow lightweight aggregate. Summary of the Invention

[0004] The present invention aims to provide a method for preparing gypsum-based lightweight hollow aggregate, which prepares phosphogypsum into hollow, lightweight, high-strength aggregate, so that it can be better combined with gypsum-based cementitious materials, reduce usage costs, and improve aggregate strength. The method specifically comprises the following steps:

[0005] (1) The phosphogypsum is burned into a gypsum-based cementitious material having a β-hemihydrate gypsum content of more than 90% for later use.

[0006] (2) Add retarder, thickener, water reducer and chopped fiber to the gypsum-based cementitious material and mix them evenly to form gypsum mixture A; the retarder dosage is 0.1-0.3% of the gypsum-based cementitious material; the water reducer dosage is 0.1-0.5% of the gypsum-based cementitious material; the thickener dosage is 0.05-0.3% of the gypsum-based cementitious material; and the chopped fiber dosage is 1-2% of the gypsum-based cementitious material.

[0007] (3) Add a mixed reactant into the molten paraffin and stir evenly. The mixed reactant is carbon powder, ammonium bicarbonate, and sodium bicarbonate. The amount of carbon powder is 20-35% of the mass of the paraffin, the amount of ammonium bicarbonate is 40-60% of the mass of the paraffin, and the amount of sodium bicarbonate is 15-30% of the mass of the paraffin.

[0008] (4) Granulation is carried out before the paraffin wax is completely dried and hardened, and the surface of the pellets is fully coated with β-gypsum powder to form a mixed material ball C for later use; β-gypsum powder can be prepared by conventional methods or purchased from the market, and the β-hemihydrate gypsum content in the β-gypsum powder is greater than 90%; during the coating process, the particle size does not increase significantly, and the thickness is about 1-3 mm.

[0009] (5) Gypsum mixture A is evenly spread in the granulator, and then atomized tap water is sprayed on it; at the same time, mixture balls C are added into the granulator so that the surface is covered with gypsum mixture A with a thickness of not less than 3 mm, forming new balls recorded as balls D.

[0010] (6) Place the ball D in a microwave oven for irradiation. After the material has expanded, cool it to room temperature to obtain gypsum-based lightweight hollow aggregate.

[0011] Preferably, the sintering temperature in step (1) of the present invention is 200-350°C.

[0012] Preferably, the retarder in step (2) of the present invention is a protein retarder or a tribasic acid retarder; its purpose is to provide sufficient operation time to enable subsequent expansion.

[0013] The water reducer is a polycarboxylic acid water reducer; its purpose is to improve the overall strength of the ball.

[0014] The thickener is polyvinyl alcohol; its purpose is to increase the viscosity of the ball after it meets water, forming a colloid-like property, so that the material will not expand when heated and cracks will not occur.

[0015] The added short-cut fibers are not polypropylene fibers and have a length of 3-6 mm. The purpose is to improve the overall strength of the ball and the toughness of the surface material and to inhibit the generation of cracks during expansion.

[0016] Preferably, the paraffin wax used in step (3) of the present invention is a low-grade paraffin wax with a grade between 25 and 40.

[0017] Preferably, the total amount sprayed in step (4) of the present invention is 20-30% of the total mass of the gypsum mixture A, and the spraying time needs to be controlled within 30 minutes to ensure that all the gypsum mixture has been fully contacted with the atomized water within 30 minutes.

[0018] Preferably, the coating time in step (4) of the present invention is controlled to be 5-10 minutes.

[0019] Preferably, the microwave used in step (6) of the present invention has a frequency of not less than 2450 MHz, a power of 3-9 kW, and a duration of 20-45 s.

[0020] The principle of the present invention is to utilize various additives and chopped fibers to enhance the strength and viscosity of the outer coating cementitious material, forming a high-viscosity gelatinous outer skin. The carbon powder in the inner lining then absorbs large amounts of microwave radiation, releasing heat, thereby indirectly heating the non-absorbent materials, ammonium bicarbonate and sodium bicarbonate. This heat decomposes the materials and releases gases such as carbon dioxide, thereby causing the pellets to expand. The addition of paraffin wax serves two purposes: first, to prevent the ammonium bicarbonate and sodium bicarbonate from dissolving in the outer coating gypsum-based cementitious material; second, to control the uniform transfer of heat from the microwave-absorbing carbon powder to the ammonium bicarbonate and sodium bicarbonate; and third, to suppress the escape rate of generated gases, preventing them from rapidly breaking through the outer coating gypsum-based cementitious material.

[0021] The beneficial effects of the present invention are:

[0022] Broaden the comprehensive utilization of phosphogypsum, and the prepared hollow lightweight aggregate can be used in the fields of construction engineering, municipal engineering, soilless cultivation and breeding, etc.

[0023] The hollow lightweight aggregate prepared has the advantages of being lightweight, soundproof, heat-insulating, sound-absorbing, and recyclable. It can partially replace ceramsite and expanded vermiculite.

[0024] The main raw material of the prepared hollow lightweight aggregate is phosphogypsum, which is a waste-recycling product with low production cost.

[0025] Compared with the production of traditional lightweight aggregates, the present invention does not require high-temperature sintering of 700 to 800 degrees Celsius. The entire process is fast, simple and has no secondary pollution.

[0026] The gypsum-based lightweight hollow aggregate prepared by the method of the present invention is a gelling material with relatively high mechanical properties; the core lining has wave-absorbing capability; and after granulation, the material is subjected to microwave irradiation to expand due to heat to form a hollow sphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to the contents described above. Example

[0029] A method for preparing gypsum-based lightweight hollow aggregate specifically comprises the following steps:

[0030] (1) Place the phosphogypsum in a rotary kiln or other similar calcining equipment, and burn the phosphogypsum at 300°C to produce a gypsum-based cementitious material with a β-hemihydrate gypsum content of more than 90%, which is then stored for future use.

[0031] (2) Add retarder, thickener, water reducer and chopped fibers to the gypsum-based cementitious material and mix them evenly.

[0032] The added retarder is a tribasic acid retarder, and the added amount is 0.1% of the gypsum-based cementitious material.

[0033] The added water reducer is a polycarboxylic acid water reducer, and the addition amount is 0.1% of the gypsum-based cementitious material.

[0034] The added thickener is polyvinyl alcohol, and the amount is 0.05% of the gypsum-based cementitious material.

[0035] The added short-cut fibers are not polypropylene fibers, with a length of 3 mm and a dosage of 1% of the gypsum-based cementitious material.

[0036] The above materials are mixed evenly using a mixer to form gypsum mixture A.

[0037] Select paraffin wax No. 25, melt it, and then add 20% carbon powder by mass of gypsum mixture A, 40% ammonium bicarbonate by mass of gypsum mixture A, and 15% sodium bicarbonate by mass of gypsum mixture A into it and stir evenly.

[0038] The paraffin mixture is granulated before it is completely dried and hardened, and the surface of the granules is fully coated with β-type gypsum powder to form mixture balls C which are retained for later use.

[0039] The gypsum mixture A obtained in step (3) is evenly distributed in the granulator, and then atomized tap water is sprayed on it. The total amount of spraying is about 20% of the total mass of the gypsum mixture A, and the spraying time should be controlled within 30 minutes. Ensure that all gypsum mixtures have been fully contacted with the atomized water within 30 minutes.

[0040] At the same time, the mixed material balls are added into the granulator so that the surface of the balls is covered with gypsum mixture A with a thickness of not less than 3 mm, and the formed new balls are recorded as balls D. The whole process takes 5 minutes.

[0041] The pellet D was placed in a microwave oven for irradiation. The microwave used had a frequency of 2450 MHz, a power of 3 kW, and a time of 20 s.

[0042] After the material has expanded, it is cooled to room temperature to obtain gypsum-based lightweight hollow aggregate. Example

[0043] A method for preparing gypsum-based lightweight hollow aggregate specifically comprises the following steps:

[0044] (1) Place the phosphogypsum in a rotary kiln or other similar calcining equipment, and burn the phosphogypsum at 300°C to produce a gypsum-based cementitious material with a β-hemihydrate gypsum content of more than 90%, which is then stored for future use.

[0045] (2) Add retarder, thickener, water reducer and chopped fibers to the gypsum-based cementitious material and mix them evenly.

[0046] The added retarder is a tribasic acid retarder, and the added amount is 0.3% of the gypsum-based cementitious material.

[0047] The added water reducer is a polycarboxylic acid water reducer, and the addition amount is 0.5% of the gypsum-based cementitious material.

[0048] The added thickener is polyvinyl alcohol, and the amount is 0.3% of the gypsum-based cementitious material.

[0049] The added short-cut fibers are not polypropylene fibers, have a length of 6 mm, and are added in an amount of 2% of the gypsum-based cementitious material.

[0050] The above materials are mixed evenly using a mixer to form gypsum mixture A.

[0051] Select paraffin wax with label number 40, melt it, and then add 35% carbon powder, 60% ammonium bicarbonate and 30% sodium bicarbonate of the mass of gypsum mixture A into it and stir evenly.

[0052] The paraffin mixture is granulated before it is completely dried and hardened, and the surface of the granules is fully coated with β-type gypsum powder to form mixture balls C which are retained for later use.

[0053] The gypsum mixture A obtained in step (3) is evenly distributed in the granulator, and then atomized tap water is sprayed thereon; the total amount of spraying is about 30% of the total mass of the gypsum mixture A, and the spraying time needs to be controlled within 30 minutes; it is ensured that all the gypsum mixture has been fully contacted with the atomized water within 30 minutes.

[0054] At the same time, the mixed material balls are added into the granulator so that the surface of the balls is covered with gypsum mixture A with a thickness of not less than 3 mm, forming new balls which are recorded as balls D. The time is controlled within 10 minutes.

[0055] The pellet D was placed in a microwave oven for irradiation. The microwave used had a frequency of 2450 MHz, a power of 9 kW, and a time of 45 seconds.

[0056] After the material has expanded, it is cooled to room temperature to obtain gypsum-based lightweight hollow aggregate. Example

[0057] A method for preparing gypsum-based lightweight hollow aggregate specifically comprises the following steps:

[0058] (1) Place the phosphogypsum in a rotary kiln or other similar calcining equipment, and burn the phosphogypsum at 300°C to produce a gypsum-based cementitious material with a β-hemihydrate gypsum content of more than 90%, which is then stored for future use.

[0059] (2) Add retarder, thickener, water reducer and chopped fibers to the gypsum-based cementitious material and mix them evenly.

[0060] The added retarder is a tribasic acid retarder, and the added amount is 0.2% of the gypsum-based cementitious material.

[0061] The added water reducer is a polycarboxylic acid water reducer, and the addition amount is 0.3% of the gypsum-based cementitious material.

[0062] The added thickener is polyvinyl alcohol, and the amount is 0.2% of the gypsum-based cementitious material.

[0063] The added short-cut fibers are not polypropylene fibers, have a length of 6 mm, and are added in an amount of 2% of the gypsum-based cementitious material.

[0064] The above materials are mixed evenly using a mixer to form gypsum mixture A.

[0065] Select paraffin wax with label number 40, melt it, and then add 30% carbon powder, 50% ammonium bicarbonate and 20% sodium bicarbonate by mass of gypsum mixture A into it and stir evenly.

[0066] The paraffin mixture is granulated before it is completely dried and hardened, and the surface of the granules is fully coated with β-type gypsum powder to form mixture balls C which are retained for later use.

[0067] The gypsum mixture A obtained in step (3) is evenly distributed in the granulator, and then atomized tap water is sprayed thereon; the total amount of spraying is about 25% of the total mass of the gypsum mixture A, and the spraying time needs to be controlled within 30 minutes; it is ensured that all the gypsum mixture has been fully contacted with the atomized water within 30 minutes.

[0068] At the same time, the mixed material balls are added into the granulator so that the surface of the balls is covered with gypsum mixture A with a thickness of not less than 3 mm, forming new balls which are recorded as balls D. The time is controlled within 8 minutes.

[0069] The pellet D was placed in a microwave oven for irradiation. The microwave used had a frequency of 2450 MHz, a power of 9 kW, and a time of 30 seconds.

[0070] After the material has expanded, it is cooled to room temperature to obtain gypsum-based lightweight hollow aggregate.

[0071] Comparative Example 1: The same as Example 1, except that the tribasic acid retarder in step (2) is omitted.

[0072] Comparative Example 2: Same as Example 1, except that the water reducing agent in step (2) is omitted.

[0073] Comparative Example 3: Same as Example 1, except that the thickener in step (2) is omitted.

[0074] Comparative Example 4: The same as Example 1, except that the chopped fibers in step (2) are omitted.

[0075] Comparative Example 5: Same as Example 1, except that the carbon powder in step (4) is omitted.

[0076] Comparative Example 6: The same as Example 1, except that the ammonium bicarbonate and sodium bicarbonate in step (4) are omitted.

[0077] Comparative Example 7: Same as Example 1, except that step (8) is omitted.

[0078] The properties of the gypsum-based lightweight hollow aggregates prepared in various embodiments are shown in Table 1.

[0079] Table 1

[0080]

[0081] Note: For bulk density and cylinder pressure strength, refer to the test methods in "Lightweight Aggregates and Their Test Methods" GBT17431.1-1998. 3. Final ball volume expansion rate = (volume after expansion - volume before expansion) / volume before expansion; 4. After expansion and cooling, the surface cracks are calculated based on the 100mm with the most cracks. 2 Σ(crack length*number of cracks) within the range.

[0082] Table 1 shows that water reducers and retarders significantly affect strength and expansion rate. The absence of a retarder causes the outer coating to set and harden prematurely, preventing expansion. Thickeners and fibers provide sufficient consistency and toughness during expansion, preventing cracking after expansion. Carbon powder is the primary microwave absorber, releasing significant heat by absorbing microwaves. Paraffin wax is the primary heat transfer medium, evenly transferring the heat absorbed by the carbon powder to readily decomposable materials such as ammonium bicarbonate and sodium bicarbonate, promoting their decomposition and releasing carbon dioxide, which in turn causes the material to expand. The amount of these two agents determines the rate and amount of gas release. If they are absent, the sphere will barely expand.

[0083] The above describes in detail the specific implementation method of the present invention, but the present invention is not limited to the above implementation method. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for preparing gypsum-based lightweight hollow aggregate, characterized in that: The specific steps include: (1) sintering the phosphogypsum into a gypsum-based cementitious material having a β-hemihydrate gypsum content of >90% for standby use; (2) Add retarder, thickener, water reducer and chopped fiber to the gypsum-based cementitious material and mix them evenly to form gypsum mixture A; the retarder dosage is 0.1-0.3% of the gypsum-based cementitious material; the water reducer dosage is 0.1-0.5% of the gypsum-based cementitious material; the thickener dosage is 0.05-0.3% of the gypsum-based cementitious material; the chopped fiber dosage is 1-2% of the gypsum-based cementitious material; (3) Adding mixed reactants into the molten paraffin and stirring evenly, the mixed reactants are carbon powder, ammonium bicarbonate, and sodium bicarbonate; the amount of carbon powder is 20-35% of the mass of the paraffin, the amount of ammonium bicarbonate is 40-60% of the mass of the paraffin, and the amount of sodium bicarbonate is 15-30% of the mass of the paraffin; (4) Granulation is carried out before the paraffin wax is completely dried and hardened, and the surface of the pellets is covered with β-type gypsum powder to form mixed material balls C for later use; (5) Gypsum mixture A is evenly spread in the granulator, and then atomized tap water is sprayed on it; at the same time, mixture balls C are added into the granulator so that the surface is covered with gypsum mixture A with a thickness of not less than 3 mm, forming new balls recorded as balls D; (6) Place the ball D in a microwave oven for irradiation. After the material has expanded, cool it to room temperature to obtain gypsum-based lightweight hollow aggregate.

2. The method for preparing gypsum-based lightweight hollow aggregate according to claim 1, characterized in that: The sintering temperature in step (1) is 200-350°C.

3. The method for preparing gypsum-based lightweight hollow aggregate according to claim 2, characterized in that: In step (2), the retarder is a protein retarder or a tribasic acid retarder; the water reducer is a polycarboxylic acid water reducer; the thickener is polyvinyl alcohol; and the chopped fibers are polypropylene fibers with a length of 3-6 mm.

4. The method for preparing gypsum-based lightweight hollow aggregate according to claim 3, characterized in that: The paraffin wax used in step (3) is a low-grade paraffin wax with a grade between 25 and 40.

5. The method for preparing gypsum-based lightweight hollow aggregate according to claim 4, characterized in that: The coating time in step (4) is controlled to be 5-10 minutes.

6. The method for preparing gypsum-based lightweight hollow aggregate according to claim 5, characterized in that: The total amount of spraying in step (5) is 20-30% of the total mass of gypsum mixture A, and the spraying time needs to be controlled within 30 minutes.

7. The method for preparing gypsum-based lightweight hollow aggregate according to claim 6, characterized in that: The microwave used in step (6) has a frequency of not less than 2450 MHz, a power of 3-9 kW, and a duration of 20-45 s.

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