A method for producing gypsum blocks from phosphogypsum

Abstract

This invention relates to the fields of solid waste resource utilization and building material production technology, and particularly to a method for producing gypsum blocks using phosphogypsum. The method comprises the following steps: preparing moist gypsum powder from calcined phosphogypsum powder, pressing it to obtain a gypsum block blank, and then naturally curing the gypsum block blank to obtain the gypsum block. The method of this invention uses phosphogypsum as the sole raw material, without adding other auxiliary raw materials or agents, requiring only 15-20% water by weight of the phosphogypsum. The pressing and molding process produces high-strength gypsum blocks that do not require drying, thereby reducing the difficulty of raw material preparation and mixing, eliminating the product drying process, shortening the product production cycle, and improving the mechanical strength of the product.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid waste resource utilization and the field of building material production, and particularly relates to a method for producing gypsum blocks by using phosphogypsum. BACKGROUND

[0002] Phosphogypsum is a large amount of industrial solid waste discharged in the production process of wet-process phosphoric acid. Generally, about 4.5-5.5 tons of phosphogypsum are generated per ton of phosphoric acid produced. The main component of phosphogypsum is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains soluble phosphorus, soluble fluorine, organic pollutants, residual acid and other pollutants. When disposed by open-air storage, it will pollute water bodies, soil and the like, and therefore needs to be harmlessly treated to eliminate its environmental hazards. On the other hand, since the main component of phosphogypsum is calcium sulfate dihydrate, which is consistent with the main component of natural gypsum, it is a potential gypsum resource and has the basic material conditions for development and utilization. When natural gypsum is replaced by phosphogypsum to produce gypsum building materials, the environmental hazards of phosphogypsum can be effectively eliminated, and the resource utilization of phosphogypsum solid waste can be realized.

[0003] Gypsum blocks belong to wall building materials and can replace traditional autoclaved aerated concrete blocks (commonly known as "aerated blocks") for masonry walls.

[0004] There are mainly two types of production processes for gypsum blocks. One type is to use casting molding technology, that is, first mix half-hydrated gypsum powder with 60%-80% water, stir and prepare gypsum slurry, then pour it into a mold, remove it after solidification, and then transport it to a drying yard for natural drying, to obtain gypsum block products. The main disadvantage of this technology is that the gypsum blocks contain a large amount of free water, which needs to be dried for a long time (20-40 days) before being delivered, resulting in a long production cycle and a large factory area. The other type is to use pressing molding technology, such as patent No. 201510041740.4 "Gypsum hollow block and semi-dry production method thereof", 201811338559.X "Semi-dry high-strength gypsum product and production method thereof", 201810886428.9 "Semi-dry phosphogypsum block and processing technology thereof", 202110104322.0 "Semi-dry production method for mechanical and continuous preparation of phosphogypsum blocks", and 202110548212.3 "Semi-dry production method for mechanical and continuous preparation of phosphogypsum blocks and phosphogypsum blocks". The feature of this type of technology is to first add about 30% water to half-hydrated gypsum powder, then use a stirring device to stir the water and half-hydrated gypsum powder uniformly to form wet half-hydrated gypsum material, fill it into a mold, start a hydraulic machine to press and form it, and finally remove it and stack it to obtain gypsum block products. The biggest advantage of this technology is that the formed gypsum blocks do not need to be dried and can be directly delivered for use, thus reducing the factory area and shortening the production cycle of the products.

[0005] Regarding the second type of compression molding technology, existing technologies generally require the addition of auxiliary raw materials and agents. For example, patent number 201510041740.4, "Gypsum Hollow Blocks and Their Semi-Dry Production Method," requires the addition of fly ash, water-reducing agents, retarders, methylcellulose, activators, etc.; patent number 201811338559.X, "A Semi-Dry High-Strength Gypsum Product and Its Production Method," proposes the addition of a mixing agent (SK additive); and patent number 201810886428.9, "A Semi-Dry Phosphogypsum Block and Its Processing Technology," proposes the addition of hydrogen fluoride and water-reducing agents. Dispersants, retarders, and reinforcing agents; 202110104322.0 "A semi-dry production method for mechanized continuous preparation of phosphogypsum blocks" proposes the addition of auxiliary agents including water-reducing agents, dispersants, retarders, and reinforcing agents; 202110548212.3 "A semi-dry production method for mechanized continuous preparation of phosphogypsum blocks and phosphogypsum blocks" proposes the addition of auxiliary agents (including polymeric water-retaining agents, water-reducing agents, dispersants, retarders, and reinforcing agents). It is well known that the more types of materials or agents included in the raw material composition, the more difficult the raw material preparation becomes, and the more difficult it is to ensure the uniformity of mixing between the various raw material components. This increases production difficulty and cost, and also affects the stability of product quality.

[0006] High-strength gypsum blocks are a type of gypsum block with higher mechanical strength than ordinary gypsum blocks, with a compressive strength reaching 40 MPa. For example, the paper 201811338559.X, "A Semi-Dry High-Strength Gypsum Product and Its Production Method," reports that its gypsum blocks can reach a strength of 40 MPa. Due to their high mechanical strength and strong resistance to damage, high-strength gypsum blocks help reduce breakage rates during product stacking, loading and unloading, transportation, and construction. Simultaneously, they effectively increase the strength and stability of walls. Summary of the Invention

[0007] The purpose of this invention is to provide a method for producing high-strength gypsum blocks that does not require drying, using phosphogypsum as the sole raw material without adding other auxiliary materials or agents. This method only requires adding 15-20% water by weight of the phosphogypsum and employing a pressing molding process. This reduces the difficulty of raw material preparation and mixing, eliminates the product drying process, shortens the product production cycle, and improves the mechanical strength of the product.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for producing gypsum blocks using phosphogypsum, comprising the following steps: preparing hydrated phosphogypsum powder into moist gypsum powder, pressing it to obtain a gypsum block blank, and naturally curing the gypsum block blank to obtain gypsum blocks.

[0009] Preferably, it specifically includes the following steps:

[0010] S1. Preparation of moist gypsum powder: Add water to calcined phosphogypsum powder and stir evenly to obtain moist gypsum powder;

[0011] S2, Pressing and molding: The moist gypsum powder prepared in S1 is filled into the mold, pressed and molded, and then demolded to obtain the gypsum block blank.

[0012] S3. Natural curing: Place the gypsum block blank on a horizontal roller conveyor and run for 30 minutes to obtain gypsum blocks.

[0013] Preferably, in S1, the ratio of calcined phosphogypsum powder to water is 100:15-20 by mass.

[0014] Preferably, in S1, the calcined phosphogypsum powder is prepared from raw phosphogypsum containing more than 80 wt% calcium sulfate dihydrate.

[0015] Preferably, in S2, the pressure condition for compression molding is 15-25 MPa.

[0016] Preferably, in S2, the moist gypsum powder obtained in S1 is filled into the mold and pressed into shape within 10 minutes.

[0017] The above-mentioned method for producing gypsum blocks using phosphogypsum produces gypsum blocks.

[0018] The beneficial effects of the technical solution provided by this invention are as follows: The method for producing high-strength gypsum blocks using phosphogypsum described in this invention has the following beneficial effects:

[0019] (1) Compared with patents such as 201510041740.4, 201811338559.X, 201810886428.9, 202110104322.0, and 202110548212.3, the raw material is only calcined phosphogypsum powder. There is no need to add auxiliary raw materials or agents such as water-reducing agents, dispersants, retarders, and reinforcing agents. The raw material composition is greatly simplified and simplified, saving the mixing process between raw materials. The reason is that although hydrated phosphogypsum powder begins to hydrate upon contact with water, this process takes time, typically around 30 minutes. Therefore, within a short period, such as 10 minutes, a large amount of water remains in a free state, effectively wetting the phosphogypsum powder and transforming it into a moist powder, making it suitable for pressing into blocks. Subsequent rapid molding and pressing operations allow for the formation of block structures, thus completing the pressing process. As long as the three operations—mixing with water, filling the mold, and pressing—are completed within 10 minutes, the added water ensures the gypsum powder remains moist, facilitating successful pressing and producing block blanks with good mechanical strength. Therefore, water-reducing agents, retarders, and water-retaining agents are unnecessary, reducing the raw material composition, optimizing raw material mixing, and ensuring successful molding.

[0020] (2) Compared with patents such as 201510041740.4, 201811338559.X, 201810886428.9, 202110104322.0, and 202110548212.3, the amount of water added is greatly reduced, that is, the amount of water added is 15-20% of the mass of calcined phosphogypsum powder. The reason is that, as mentioned in (1), the three operations of adding water and stirring, filling the mold, and pressing are performed continuously. Within 10 minutes, the water consumed by the hydration reaction of calcined phosphogypsum is only about 5%, which means that 10-15% of the water is still in a free state. It can play the role of moistening the calcined phosphogypsum powder that has not yet undergone hydration reaction, that is, forming moist calcined phosphogypsum powder, which can meet the moisture conditions of conventional pressing and molding, and can realize the processing operation of pressing and molding into block materials.

[0021] (3) The water content of this invention is low, that is, the water content is 15-20% of the mass of calcined phosphogypsum powder. Compared with the traditional casting method of producing gypsum blocks with a water content of 60%-80%, the gypsum blocks produced by this invention contain less free water, which means that the porosity remaining in the final gypsum block product after the free water dries and loses water will be greatly reduced. At the same time, because the molding is carried out by pressure of 15-25MPa, it is conducive to close contact between materials. That is, the dihydrate gypsum crystals in the gypsum block product will be in close contact and overlap each other. The gypsum block structure is dense and the porosity is low, thereby generating high mechanical strength. Its compressive strength can reach 45MPa, making it a high-strength gypsum block product.

[0022] Of course, due to the reasons mentioned in (3) above, the product density is high and does not meet the requirements of lightweight wall materials. However, through holes can be pressed in the center of the vertical direction of the gypsum block to form a hollow gypsum block, similar to the patent number 201510041740.4 "Gypsum Hollow Block and Semi-Dry Production Method Thereof". This can greatly reduce the volume density of the gypsum block and meet the specific gravity requirements of lightweight wall materials. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0024] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0025] The present invention provides a method for producing gypsum blocks using phosphogypsum, specifically comprising the following steps:

[0026] S1. Preparation of moist gypsum powder: Add 100 parts by weight of calcined phosphogypsum powder to a mixer and start the mixer. Then add 15-20 parts by weight of water and continue stirring until the water and material are evenly mixed to obtain moist gypsum powder. The calcined phosphogypsum powder is a building phosphogypsum powder product with calcium sulfate hemihydrate as the main component, obtained by frying raw phosphogypsum with a content of more than 80 wt% dihydrate calcium sulfate discharged by phosphate chemical enterprises through gypsum frying equipment.

[0027] S2, Pressing and Molding: Immediately fill the mold of the conventional hydraulic press with the moist gypsum powder prepared in S1, start the hydraulic press, and press and mold it under a pressure of 15-25 MPa. After demolding, the gypsum block blank is obtained. It should be noted that S1 and S2 should be run continuously. That is, the moist gypsum powder prepared in step S1 should be supplied to the hydraulic press in step S2 in a timely manner and pressed and molded immediately. The material residence time between the two steps should not exceed 10 minutes to avoid the problem of calcined phosphogypsum powder and water agglomerating into lumps after a long period of stagnation.

[0028] S3. Natural curing: Place the gypsum block blanks on a horizontal roller conveyor and run for 30 minutes to complete the natural curing process. Then stack and store them in the warehouse to obtain high-strength gypsum blocks.

[0029] <Example 1>

[0030] A method for producing gypsum blocks using phosphogypsum specifically includes the following steps:

[0031] S1. Preparation of moist gypsum powder: Add 100 parts by weight of calcined phosphogypsum powder to a mixer and start the mixer. Then add 20 parts by weight of water and continue mixing until the water and material are evenly mixed to obtain moist gypsum powder.

[0032] S2, Pressing and Molding: The moist gypsum powder prepared in S1 is promptly filled into the mold of a conventional hydraulic press. The hydraulic press is started and pressed and shaped under a pressure of 15MPa. After demolding, a gypsum block blank is obtained.

[0033] S3. Natural curing: Place the gypsum block blanks on a horizontal roller conveyor and run for 30 minutes to complete the natural curing process. Then stack and store them in the warehouse to obtain high-strength gypsum blocks.

[0034] The compressive strength of the gypsum block prepared in this embodiment is 42 MPa.

[0035] <Example 2>

[0036] A method for producing gypsum blocks using phosphogypsum specifically includes the following steps:

[0037] S1. Preparation of moist gypsum powder: Add 100 parts by weight of calcined phosphogypsum powder to the mixer and start the mixer. Then add 18 parts by weight of water and continue mixing until the water and material are evenly mixed to obtain moist gypsum powder.

[0038] S2, Pressing and Molding: The moist gypsum powder prepared in S1 is promptly filled into the mold of a conventional hydraulic press. The hydraulic press is started and pressed and shaped under a pressure of 25MPa. After demolding, a gypsum block blank is obtained.

[0039] S3. Natural curing: Place the gypsum block blanks on a horizontal roller conveyor and run for 30 minutes to complete the natural curing process. Then stack and store them in the warehouse to obtain high-strength gypsum blocks.

[0040] The compressive strength of the gypsum block prepared in this embodiment is 48 MPa.

[0041] <Example 3>

[0042] A method for producing gypsum blocks using phosphogypsum specifically includes the following steps:

[0043] S1. Preparation of moist gypsum powder: Add 100 parts by weight of calcined phosphogypsum powder to the mixer and start the mixer. Then add 15 parts by weight of water and continue mixing until the water and material are evenly mixed to obtain moist gypsum powder.

[0044] S2, Pressing and Molding: The moist gypsum powder prepared in S1 is promptly filled into the mold of a conventional hydraulic press. The hydraulic press is started and pressed and shaped under a pressure of 20MPa. After demolding, a gypsum block blank is obtained.

[0045] S3. Natural curing: Place the gypsum block blanks on a horizontal roller conveyor and run for 30 minutes to complete the natural curing process. Then stack and store them in the warehouse to obtain high-strength gypsum blocks.

[0046] The compressive strength of the gypsum block prepared in this embodiment is 45 MPa.

[0047] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing gypsum blocks using phosphogypsum, characterized in that, Specifically, it includes the following steps: S1. Preparation of moist gypsum powder: Water is added to calcined phosphogypsum powder and stirred evenly to obtain moist gypsum powder; by weight, calcined phosphogypsum powder:water = 100:15~20; wherein, the calcined phosphogypsum powder is a building phosphogypsum powder product with calcium sulfate hemihydrate as the main component obtained by frying raw phosphogypsum with a content of more than 80 wt% dihydrate calcium sulfate discharged by phosphate chemical enterprises after being frying with gypsum frying equipment; S2, Pressing and Molding: The moist gypsum powder prepared in S1 is filled into the mold, pressed and shaped, and then demolded to obtain a gypsum block blank; the moist gypsum powder prepared in S1 is filled into the mold and pressed within 10 min; the pressure conditions for pressing and molding are 15~25MPa. S3. Natural curing: Place the gypsum block blank on a horizontal roller conveyor and run for 30 minutes to obtain gypsum blocks.

2. The gypsum block produced by the method of producing gypsum blocks using phosphogypsum according to claim 1.