A high-strength phosphogypsum-based aggregate and its preparation method

Abstract

This invention relates to the fields of solid waste resource utilization and building material production technology, and particularly to a high-strength phosphogypsum-based aggregate and its preparation method. A method for preparing a high-strength phosphogypsum-based aggregate includes the following steps: adding water to calcined phosphogypsum powder, stirring evenly to obtain moistened gypsum powder; pressing the moistened gypsum powder into shape, demolding, and obtaining the phosphogypsum-based aggregate. The raw material used in this invention is only calcined phosphogypsum powder, eliminating the need for the addition of inorganic cementing materials such as cement or slag. This reduces the cost of auxiliary raw materials and the mixing and processing steps between raw materials, thus helping to lower raw material and production costs.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and building material production technology, and particularly to a method for preparing high-strength phosphogypsum-based aggregate. Background Technology

[0002] Phosphogypsum is a major solid waste generated during the wet process of phosphoric acid production in phosphate chemical enterprises. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), consistent with the composition of natural gypsum, thus possessing the basic material conditions for resource utilization. On the other hand, engineering construction requires large quantities of sand and gravel aggregates. Using phosphogypsum as a raw material to produce phosphogypsum-based aggregates to replace traditional sand and gravel aggregates can both realize the resource utilization of phosphogypsum and reduce the mining and application of sand and gravel aggregates, thus contributing to environmental protection.

[0003] The production processes of phosphogypsum-based aggregates can be summarized into two categories. One category uses raw phosphogypsum as the main component, with the addition of inorganic cementing materials such as cement, slag powder, and metakaolin. The raw materials are mixed with water and then granulated into aggregates. The cementing effect of the inorganic cementing materials forms a high-strength aggregate, as described in invention 202310591896.4, "A High-Density Phosphogypsum-Based Aggregate and Its Preparation Method and Application." The other category uses calcined phosphogypsum (also known as calcined phosphogypsum, fired phosphogypsum, or β-hemihydrate phosphogypsum) as the main raw material, with the addition of auxiliary materials such as cement and slag. The mixture is then mixed with water and pressed into aggregates. The cementing effect of calcined phosphogypsum, the compaction effect of pressure, and the cementing effect of auxiliary cementing materials combine to form high-strength aggregates, as described in invention 202310129486.8, "A Phosphogypsum-Based Recycled Aggregate and Its Preparation Method and Application."

[0004] Clearly, the existing production process for high-strength phosphogypsum-based aggregates, which uses phosphogypsum as the main component and mixes various raw materials, increases both raw material costs and the costs of the raw material mixing process and its corresponding production costs. Furthermore, the incorporation of inorganic cementing materials such as cement and slag typically requires curing of the product. For example, the preferred curing time in Invention 202310591896.4 is 28 days, and the natural curing time in Invention 202310129486.8 is 1–7 days, to allow the inorganic cementing materials to exert their binding capacity, thus increasing the curing production process and its corresponding production costs. Summary of the Invention

[0005] To reduce the number of raw materials, simplify the preparation and mixing process, shorten the production cycle, lower production costs, and improve product strength, this invention provides a method for preparing high-strength phosphogypsum-based aggregate. Using phosphogypsum as the sole raw material, only 15% water (by weight of the phosphogypsum) needs to be added, without any other auxiliary materials or reagents. A compression molding process is employed to produce high-strength phosphogypsum-based aggregate with high mechanical strength that requires no curing. This reduces the difficulty of raw material preparation and mixing, shortens the production cycle, lowers raw material and production costs, and improves the mechanical strength of the product.

[0006] A method for preparing high-strength phosphogypsum-based aggregate includes the following steps: adding water to calcined phosphogypsum powder, stirring evenly to obtain moist gypsum powder; pressing the moist gypsum powder into shape, demolding, and obtaining phosphogypsum-based aggregate.

[0007] Furthermore, based on parts by weight, the ratio of calcined gypsum powder to water is 100:15.

[0008] Furthermore, the calcined phosphogypsum powder is raw phosphogypsum with a calcium sulfate dihydrate content of more than 80 wt%.

[0009] Furthermore, it includes the following steps:

[0010] S1. Add 100 parts by weight of calcined phosphogypsum powder to the mixer, start the mixer, then add 15 parts by weight of water and continue mixing until the material and water are evenly mixed to obtain moist gypsum powder.

[0011] S2. Moist gypsum powder is filled into the mold and pressed into shape. After demolding, phosphogypsum-based aggregate is obtained.

[0012] Furthermore, the processing interval between S1 and S2 is less than 15 minutes.

[0013] Furthermore, the pressure condition in S2 is 20 MPa.

[0014] The phosphogypsum-based aggregate obtained by the above-mentioned method for preparing high-strength phosphogypsum-based aggregate.

[0015] The beneficial effects of the preparation method provided by this invention are:

[0016] (1) Compared with inventions 202310591896.4 and 202310129486.8, the raw material of this invention is only calcined phosphogypsum powder, without the need to add inorganic cementitious materials such as cement and slag. This reduces the cost of auxiliary raw materials and the mixing and processing steps between raw materials, which is conducive to reducing raw material costs and production costs. This is because experiments have shown that calcined phosphogypsum can be directly obtained by mixing with water. As long as the amount of water added is reasonably controlled and the time from adding water to pressing into aggregate is well controlled, the pressure compaction effect and the hydration cementing effect of calcined phosphogypsum (i.e., hemihydrate phosphogypsum) can be fully utilized, and a high-strength compacted body can be obtained directly without the need for the cementing and strengthening effect of inorganic cementitious materials such as cement, activated slag, metakaolin, and fly ash.

[0017] (2) Compared with inventions 202310591896.4 and 202310129486.8, this invention does not use cement or other cementitious materials with long hydration reaction times, but only uses calcined phosphogypsum with a very short hydration and cementing time. After being pressed into aggregate, the calcined phosphogypsum can complete the hydration reaction within 15 to 20 minutes. Therefore, the pressed aggregate can complete hydration and cementing during loading and transportation, and generate its final strength, so no special curing treatment is required. In addition, the freshly pressed aggregate can achieve a compressive strength of 10 MPa through the compaction effect of pressure and the interlocking effect of the material particles, and the aggregate will not be crushed during loading and transportation.

[0018] (3) The present invention has a low water content and high molding pressure, which is beneficial to improving the strength of aggregate. The water content of the present invention is low, that is, the water content is 15% of the mass of calcined phosphogypsum powder. The less free water when it is pressed into aggregate means that there is less porosity left after the free water evaporates after the aggregate dries, and the density of the aggregate is high, which is beneficial to increasing the strength of the aggregate. In addition, the use of a higher pressure of 20MPa to press the aggregate is beneficial to compact the hemihydrate phosphogypsum material, which is beneficial to the contact, interlocking and overlapping of the dihydrate gypsum crystals generated by the hydration reaction of the pressed hemihydrate phosphogypsum, forming a high-strength dihydrate gypsum crystal microstructure, producing a high-strength macroscopic bulk structure, that is, obtaining a high-strength phosphogypsum-based aggregate. Detailed Implementation

[0019] 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.

[0020] 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.

[0021] <Example>

[0022] A method for preparing high-strength phosphogypsum-based aggregate includes the following steps:

[0023] S1. Add 100 parts by weight of calcined phosphogypsum powder to the mixer, start the mixer, then add 15 parts by weight of water and continue mixing until the material and water are evenly mixed to obtain moist gypsum powder.

[0024] S2. Moist gypsum powder is filled into the mold of a conventional hydraulic press. The hydraulic press is started and pressed into shape under a pressure of 20MPa. After demolding, phosphogypsum-based aggregate is obtained.

[0025] Furthermore, when producing tangible phosphogypsum-based aggregates, such as round, oval, square, and rectangular shapes, molds of corresponding shapes are required in step S2. After demolding, the aggregate product is obtained. When producing intangible, crushed, high-strength phosphogypsum-based aggregates, a square mold is required in step S2 to press out plate-shaped blanks, which are then crushed and screened to obtain the aggregate product.

[0026] The compressive strength of the wet aggregate prepared in this embodiment is about 10 MPa. In addition, the solidification time of calcined gypsum is usually 30 minutes. Therefore, the wet aggregate produced by S2 can be directly shipped out of the factory or stored in the warehouse. The curing process is completed naturally during product transportation or storage, and there is no need to set up a curing treatment process in production.

[0027] The calcined phosphogypsum powder of this invention is a building phosphogypsum powder product with calcium sulfate hemihydrate as the main component, obtained by calcining raw phosphogypsum containing more than 80 wt% dihydrate calcium sulfate discharged by phosphate chemical enterprises through gypsum calcination equipment. It is also known as β-hemihydrate phosphogypsum powder product.

[0028] In the application of this invention, it should be noted that S1 and S2 should operate continuously. That is, the moist gypsum powder prepared by S1 should be supplied to S2 in a timely manner and immediately pressed into shape. The total time from the start of adding water to the calcined phosphogypsum to the pressing of the moist gypsum powder into aggregate should not exceed 15 minutes. This is because, on the one hand, calcined phosphogypsum, i.e., hemihydrate phosphogypsum, can only produce a gelling effect and give the product bonding strength after undergoing a hydration reaction after pressing and molding. Hemihydrate phosphogypsum that has undergone a hydration reaction before pressing and molding has already been converted into dihydrate gypsum and no longer has a gelling effect. On the other hand, hemihydrate phosphogypsum begins to undergo a hydration reaction after adding water, and the time for the hydration reaction to be fully completed is usually about 30 minutes. Therefore, the longer the time from adding water to pressing into aggregate, the higher the degree of hydration reaction of hemihydrate phosphogypsum. After pressing, the amount of unhydrated hemihydrate phosphogypsum remaining is less, which means the overall cementing effect of hemihydrate phosphogypsum is weaker, resulting in a decrease in aggregate strength. Conversely, if the operation is done properly and the time from adding water to pressing into aggregate is shortened as much as possible, the proportion of unhydrated hemihydrate phosphogypsum remaining after pressing can be increased, which is conducive to giving full play to the cementing effect of hemihydrate phosphogypsum and thus improving the strength of aggregate.

[0029] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0030] 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 preparing high-strength phosphogypsum-based aggregate, characterized in that, Includes the following steps: S1. Add 100 parts by weight of calcined phosphogypsum powder to a mixer, start the mixer, add 15 parts by weight of water, and continue mixing until the material and water are evenly mixed to obtain moist gypsum powder; 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 dihydrate calcium sulfate content higher than 80 wt% discharged by phosphate chemical enterprises after being fryed by gypsum frying equipment, that is, β-hemihydrate phosphogypsum powder product. S2. Moist gypsum powder is filled into the mold and pressed into shape. After demolding, phosphogypsum-based aggregate is obtained. The pressure condition in S2 is 20 MPa. The interval between S1 and S2 is less than 15 min.

2. The phosphogypsum-based aggregate obtained by the preparation method of high-strength phosphogypsum-based aggregate according to claim 1.