CN115745443B - Method for preparing alpha-hemihydrate gypsum from undisturbed phosphogypsum with low reaction medium dosage - Google Patents

Abstract

The invention relates to a method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum at a low dosage of reaction medium. The specific steps are as follows: 1) Mix water and plasticizer evenly, add it to the undisturbed phosphogypsum, and then add a passivating agent; Stir evenly and age to obtain a high-fluid phosphogypsum slurry; 2) Add salt medium to the high-fluid phosphogypsum slurry, stir evenly, and heat to perform a crystallization reaction to obtain a high-solid content α-type high-strength gypsum slurry. ; 3) The α-type high-strength gypsum slurry with high solid content is spray-dried to obtain α-type semi-hydrated gypsum. The present invention releases water in the pores of phosphogypsum by adding a plasticizer, improves water utilization, and realizes the reaction to prepare α-type semi-hydrated gypsum under the condition of a lower water-to-gypsum ratio, which consumes less water, is easy to post-process, and is fast drying. , which solves the problem that the existing atmospheric pressure hydrothermal method consumes a large amount of reaction medium and requires high energy consumption for post-processing.

Description

A method of preparing α-type hemihydrate gypsum with undisturbed phosphogypsum under low reaction medium dosage method

Technical field

The invention belongs to the technical field of building materials using phosphorus-containing gypsum as raw material, and specifically relates to a method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum at a low dosage of reaction medium.

Background technique

Phosphogypsum is a solid by-product produced when phosphate rock is treated with sulfuric acid during the wet production of phosphoric acid. Depending on the production process, phosphogypsum contains impurities such as soluble phosphorus, eutectic phosphorus, fluorine, organic matter, and alkali metals. For every ton of phosphoric acid produced, about 4 to 5 tons of phosphogypsum will be emitted. The stockpiles of phosphogypsum in my country are huge, and with the increase in phosphate fertilizer production, the stockpiles of phosphogypsum are increasing day by day, causing serious environmental pollution and ecological hazards. The use of phosphogypsum to produce α-type high-strength gypsum is an important way and research direction for the resource utilization of phosphogypsum, and has broad commercial prospects and social significance.

The existing method of preparing α-high-strength gypsum usually uses an atmospheric pressure hydrothermal process to perform a crystal phase transformation reaction, which requires the addition of a large amount of relatively high-concentration electrolyte solution as the reaction medium. On average, 2.4 to 5.9 tons of reaction medium are needed to produce 1 ton of α-high-strength gypsum. , the reaction process does not consume the reaction medium, so after the crystal phase transformation, the product α high-strength gypsum is obtained by filtration, washing, and drying. After the reaction is completed, most of these reaction media face exhaust pressure, and the entire production process has a heavy impact on the reaction medium and The energy consumption is too high. For every ton of high-strength gypsum produced, 2.2 to 5.3 tons of electrolyte waste liquid are discharged. Since it is a high-concentration electrolyte solution and contains complex impurities, the waste liquid treatment is difficult, increases production costs, and is not green and environmentally friendly.

Based on this, it is necessary to study a method for preparing α-type hemihydrate gypsum with a low dosage of reaction medium.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing α-type hemihydrate gypsum in undisturbed phosphogypsum at a low dosage of reaction medium in view of the above-mentioned deficiencies in the prior art. It adopts an extremely low dosage of reaction medium and has simple post-processing. , low energy consumption, and the prepared α-type semi-hydrated gypsum has high purity, excellent performance, and high added value advantages.

In order to solve the above technical problems, the technical solution provided by the present invention is:

Provided is a method for preparing α-type hemihydrate gypsum with undisturbed phosphogypsum at a low dosage of reaction medium. The specific steps are as follows:

1) Mix water and plasticizer evenly, add it to the original phosphogypsum, then add passivation agent, stir evenly and age to obtain a high-fluid phosphogypsum slurry;

2) Add salt medium to the high-fluid phosphogypsum slurry obtained in step 1), stir evenly, and heat to perform a crystallization reaction to obtain an α-type high-strength gypsum slurry with high solid content;

3) The α-type high-strength gypsum slurry with high solid content obtained in step 2) is spray-dried to obtain α-type semi-hydrated gypsum.

According to the above scheme, the moisture content of the original phosphogypsum in step 1) is 10-40wt%, in which calcium sulfate dihydrate accounts for more than 95% of the solid content of phosphogypsum.

According to the above scheme, the plasticizer in step 1) is a polycarboxylic acid water-reducing agent containing a phosphate group, a silane coupling modified polycarboxylic acid water-reducing agent (such as γ-methacryloyloxypropyltrimethyl Oxysilane-modified polycarboxylate water-reducing agent), one or more of the naphthalene-based water-reducing agents, the dosage is 0.1 to 1% of the mass of the original phosphogypsum. The plasticizer acts in the gypsum and can be adsorbed on the surface of the gypsum particles, making the surface of the gypsum particles negatively charged to form electrostatic repulsion, promote the mutual dispersion of the gypsum particles, destroy the flocculation structure, and release the wrapped water molecules to participate in the flow. Polycarboxylate water-reducing agents containing phosphate ester groups and silane coupling modified polycarboxylic acid water-reducing agents are more effective than naphthalene-based water-reducing agents.

According to the above solution, the passivating agent in step 1) is one or more of quicklime, carbide slag, and steel slag. Passivating agents are used to adjust the pH value and stabilize impurities in phosphogypsum. Steel slag is alkaline, with a calcium oxide content of 40 to 60 wt%.

According to the above scheme, the mass ratio of step 1) water, plasticizer, passivator and original phosphogypsum is 20~50:0.3~1:1~5:100.

According to the above plan, the aging time of step 1) is 1 to 8 hours.

According to the above scheme, the fluidity of the high-fluid phosphogypsum slurry described in step 1) is 150-250mm, and the pH value is 5-7.

According to the above scheme, the salt medium in step 2) is one or more of calcium chloride, sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, potassium sulfate, sodium sulfate, and the salt medium is the same as the salt medium in step 1). The mass ratio of water is 1:3~5. Salt medium can increase the solubility of calcium sulfate dihydrate in phosphogypsum.

According to the above scheme, the crystallization reaction conditions in step 2) are: reaction at 95-100°C for 30-240 minutes.

The present invention also includes α-type hemihydrate gypsum prepared according to the above method, with a purity of more than 95wt% and an average particle size of 2 to 50 μm.

The present invention uses undisturbed phosphogypsum as raw material, and realizes in-situ transcrystallization of phosphogypsum with high solid content through plasticizing modification. Since the plasticizer contains functional groups with strong adsorption properties, the functional groups can be complexed with calcium ions in phosphogypsum. Thus, it is effectively adsorbed on the surface of gypsum particles, making the surface of gypsum particles negatively charged to form electrostatic repulsion, promoting mutual dispersion between gypsum particles, destroying the flocculation structure, and releasing the water molecules wrapped in phosphogypsum to participate in the flow. In the presence of a small amount of reaction medium (salt solution), the fluidity of phosphogypsum can be improved, which facilitates the complete mixing of calcium sulfate dihydrate in phosphogypsum and the salt solution, and provides a good liquid for the crystallization of calcium sulfate dihydrate in phosphogypsum. phase environment. When the salt solution meets certain thermodynamic conditions, the solubility of calcium sulfate dihydrate is greater than that of α-type hemihydrate gypsum. Calcium sulfate dihydrate gradually dissolves in the salt solution to release Ca ²⁺ and SO ₄ ²⁺ , reaching the level of sulfuric acid dihydrate. After the dissolution balance of calcium, these Ca ²⁺ and SO ₄ ²⁺ are supersaturated for α-type hemihydrate gypsum, which combines with 0.5 times more water molecules to form α-type hemihydrate gypsum with lower solubility, while α-type hemihydrate gypsum The precipitation will reduce the concentration of Ca ²⁺ and SO ₄ ²⁺ , promote the continued dissolution of calcium sulfate dihydrate, and finally achieve the complete conversion of calcium sulfate dihydrate into α-type hemihydrate gypsum, preparing a product with easy post-processing and excellent performance. α-type hemihydrate gypsum provides a new way to prepare high-strength α-hemihydrate gypsum with high efficiency and low cost from phosphogypsum.

The beneficial effects of the present invention are: 1. The present invention provides a method for preparing α-type hemihydrate gypsum with undisturbed phosphogypsum at a low dosage of reaction medium. The water in the pores of the phosphogypsum is released by adding a plasticizer to improve water utilization. It can efficiently prepare α-type semi-hydrated gypsum under the condition of low water-to-gypsum ratio, which consumes less water, easy post-processing, and fast drying. It solves the problem of existing atmospheric pressure hydrothermal method that consumes a large amount of reaction medium and requires post-processing. The problem of high energy consumption is required. 2. The α-type hemihydrate gypsum provided by the present invention has high purity, excellent performance in terms of strength, hardness, biocompatibility, etc., and high economic added value.

Description of drawings

Figure 1 is a photo of the process of preparing α-type hemihydrate gypsum using undisturbed phosphogypsum as raw material in Example 1 of the present invention;

Figure 2 is an optical microscope photograph of α-type hemihydrate gypsum prepared in Example 1;

Figure 3 is an optical microscope photograph of α-type hemihydrate gypsum prepared in Example 2;

Figure 4 is an optical microscope photo of α-type hemihydrate gypsum prepared in Example 3;

Figure 5 is an optical microscope photo of the α-type hemihydrate gypsum prepared in Comparative Example 1;

Figure 6 is a 3D compressive strength comparison chart of α-type hemihydrate gypsum prepared in Examples 1-3 and Comparative Example 1.

Detailed ways

In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in further detail below in conjunction with the accompanying drawings.

For the preparation method of the polycarboxylate superplasticizer containing phosphate groups used in the embodiments of the present invention, see: J. Huang, etl. Dispersing silica fume in cementitious materials by silanecopolymerizedpolycarboxylate Superplasticizer: On the role of dispersioneffectiveness as a function of silane concentration [ J].Construction andBuilding Materials,326(2022)126832.

The silane coupling modified polycarboxylic acid water reducing agent used in the embodiment of the present invention is γ-methacryloyloxypropyltrimethoxysilane modified polycarboxylic acid water reducing agent. For its preparation method, please refer to: H.Qi, etl .Polycarboxylatesuperplasticizer modified by phosphate ester in side chain and itsbasicproperties in gypsum plaster[J]. Construction and Building Materials, 271(2021)121566.

Example 1

A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum at a low dosage of reaction medium. The specific steps are as follows:

1) Mix water and the polycarboxylate water-reducing agent containing phosphate ester groups evenly, add it to the original phosphogypsum (moisture content is 37%, calcium sulfate dihydrate accounts for 95.18wt% solid content), and then add quicklime, where The mass of the polycarboxylate water-reducing agent containing phosphate groups is 0.8% of the mass of the original phosphogypsum, the mass of quicklime is 2% of the mass of the original phosphogypsum, the mass ratio of water to the original phosphogypsum is 1:5, stir evenly and After aging for 5 hours, a high-fluid phosphogypsum slurry with a fluidity of 180mm and a pH value of 6.7 was obtained;

2) Add calcium chloride to the high-fluid phosphogypsum slurry obtained in step 1). The mass ratio of calcium chloride to the water in step 1) is 1:4. Stir evenly and heat to 95°C to perform a crystallization reaction for 3 hours. After 3 hours of reaction, an α-type hemihydrate gypsum slurry with high solid content was obtained;

3) The high solid content phosphorus-based high-strength gypsum slurry obtained in step 2) is pressure spray dried through an atomizing spray gun to obtain α-type hemihydrate gypsum with an average particle size of 19.8 μm and a purity of 97wt%.

Figure 1 is a photo of the reaction process of preparing α-type hemihydrate gypsum using original phosphogypsum as raw material in this embodiment, where a is a photo of the original phosphogypsum, b is a photo of high-fluid phosphogypsum slurry, and c is a high-fluid phosphogypsum slurry. Optical micrograph of phosphogypsum in the body, d is the optical micrograph of α-type hemihydrate gypsum slurry. From the comparison, it can be found that in this example, a polycarboxylate water-reducing agent containing a phosphoric acid group is used, and only a small amount of water is added to obtain a liquid high-fluid phosphogypsum slurry. Comparing c and d, it can be seen that the crystallization reaction Finally, the parallelogram plate-shaped calcium sulfate dihydrate in the gypsum slurry is completely converted into pin-rod-shaped α-type hemihydrate gypsum.

Figure 2 is an optical micrograph of the α-type hemihydrate gypsum prepared in this embodiment. It can be seen that the particle size of the obtained product is uniform, and it is a pin-rod crystal. The product is α-type hemihydrate gypsum.

Example 2

The difference between this embodiment and Example 1 is that the polycarboxylate water-reducing agent containing phosphate ester groups in step 1) is replaced by an equal mass of silane coupling-modified polycarboxylic acid water-reducing agent. The remaining steps are the same as in Example 1.

The optical micrograph of the α-type hemihydrate gypsum prepared in this example is shown in Figure 3. It can be seen that the particle size of the obtained product is uniform, and it is a pin-rod crystal. The product is α-type hemihydrate gypsum.

Example 3

The difference between this example and Example 1 is that the polycarboxylate water-reducing agent containing phosphate ester groups in step 1) is replaced with an equal mass of naphthalene-based water-reducing agent. The mass ratio of the required added water to the original phosphogypsum is: 1:4. The remaining steps are the same as in Example 1.

The optical micrograph of the α-type hemihydrate gypsum prepared in this example is shown in Figure 4. It can be seen that the particle size of the obtained product is uniform, and it is a pin-rod crystal. The product is α-type hemihydrate gypsum.

Comparative example 1

The difference between this comparative example and Example 1 is that the polycarboxylate water-reducing agent with phosphate ester group is not added in step 1), and the mass ratio of added water to original phosphogypsum is 1:1. The remaining steps are the same as in Example 1.

The optical micrograph of the α-type hemihydrate gypsum prepared in this comparative example is shown in Figure 5. It can be seen that the particle size of the obtained product is uniform, and it is a pin-rod crystal. The product is α-type hemihydrate gypsum.

The high fluidity phosphogypsum slurry obtained in step 1) of the above Examples 1-3 and Comparative Example 1 was subjected to a fluidity test. The test results are shown in Table 1.

Table 1

It can be seen from the comparison that compared with the prior art, the present invention uses a plasticizer to modify the original phosphogypsum, which can effectively reduce the amount of water in the system and basically maintain the fluidity of the prepared phosphogypsum slurry.

Figure 6 is a comparison chart of the 3D compressive strength of α-type hemihydrate gypsum prepared in Examples 1-3 and Comparative Example 1. It can be seen that the 3D compressive strength of several α-type hemihydrate gypsum is basically close, indicating that by using plasticizers It is possible to significantly reduce the amount of water while maintaining comparable mechanical properties of the prepared samples. In comparison, the 3d compressive strength of the α-type hemihydrate gypsum prepared in Example 1 is the highest.

Claims (7)

1. A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum at a low dosage of reaction medium, which is characterized in that the specific steps are as follows: 1) Mix water and plasticizer evenly, add it to the original phosphogypsum, and then add the passivator. The mass ratio of water, plasticizer, passivator and original phosphogypsum is 20~50:0.3~1:1~ 5:100, stir evenly and age to obtain a high-fluid phosphogypsum slurry. The aging time is 1 to 8 hours. The plasticizer is a polycarboxylate water-reducing agent containing a phosphate group, modified by silane coupling Polycarboxylate water-reducing agent, one or more of the naphthalene-based water-reducing agents; 2) Add salt medium to the high-fluid phosphogypsum slurry obtained in step 1), stir evenly, and heat to perform a crystallization reaction. The crystallization reaction conditions are: react at 95~100°C for 30~240 minutes to obtain high solid content α-type high-strength gypsum slurry; 3) The α-type high-strength gypsum slurry with high solid content obtained in step 2) is spray-dried to obtain α-type semi-hydrated gypsum. 2. A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum under low reaction medium dosage according to claim 1, characterized in that the moisture content of the undisturbed phosphogypsum in step 1) is 10~40wt%, wherein dihydrate Calcium sulfate accounts for more than 95% of the solid content of phosphogypsum. 3. A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum under low reaction medium dosage according to claim 1, characterized in that the plasticizer dosage in step 1) is 0.1 to 1% of the mass of undisturbed phosphogypsum. . 4. A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum under low reaction medium dosage according to claim 1, characterized in that the passivating agent in step 1) is one of quicklime, carbide slag and steel slag. or more. 5. A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum under low reaction medium dosage according to claim 1, characterized in that the fluidity of the high-fluid phosphogypsum slurry in step 1) is 150~250mm, The pH value is 5~7. 6. A method for preparing α-type hemihydrate gypsum from undisturbed phosphogypsum under low reaction medium dosage according to claim 1, characterized in that the salt medium in step 2) is calcium chloride, sodium chloride, potassium chloride , one or more of magnesium chloride, magnesium sulfate, potassium sulfate, and sodium sulfate, and the mass ratio of the salt medium to the water described in step 1) is 1:3~5. 7. The α-type hemihydrate gypsum prepared according to the method of any one of claims 1 to 6 is characterized in that its purity is more than 95wt% and the average particle size is 2 to 50 μm.