Comprehensive utilization and treatment process of phosphogypsum

Abstract

The invention provides an ardealite comprehensive utilization treatment process, and belongs to the field of ardealite waste utilization. According to the comprehensive utilization and treatment process of phosphogypsum, water and a curing agent are added into a mixture of phosphogypsum, bentonite and carbide slag, after uniform mixing, the mixture is subjected to granulation and balling, autoclaved reaction and natural hardening, and dihydrate gypsum is obtained. The obtained dihydrate gypsum contains relatively low water-soluble P2O5 and water-soluble fluorine, the content of sulfur trioxide is 38% or above, the retarding effect is stable, and the dihydrate gypsum is a high-quality cement retarder. The method disclosed by the invention is simple in process, efficient and free of generation of redundant waste residues, the problem of environmental pollution caused by excessive stockpiling of the phosphogypsum is solved, and recycling of the phosphogypsum is realized.

Description

Technical Field

[0001] The invention relates to the field of comprehensive utilization of phosphogypsum, and in particular to a comprehensive utilization treatment process of phosphogypsum. Background Art

[0002] Phosphogypsum is a solid waste residue produced during the production of wet phosphoric acid. Its main component is calcium sulfate dihydrate. At present, the common bulk utilization is mainly in the production of cement retarders, gypsum building materials, etc. When phosphogypsum is used as a cement retarder, due to the presence of harmful impurities such as soluble phosphorus and fluorine, phosphogypsum is acidic, which will seriously delay the setting time of cement and reduce its early strength, thus limiting the application of phosphogypsum in cement. Therefore, when phosphogypsum is used as a cement retarder, it must be treated to remove harmful impurities.

[0003] Patent CN109734344B discloses a method for preparing a cement retarder using hemihydrate phosphogypsum, wherein the hemihydrate phosphogypsum is adjusted to be alkaline using an alkaline calcium-containing modifier, and then the hemihydrate phosphogypsum is modified through processes such as aging and composting, so that the hemihydrate phosphogypsum is naturally crystallized into dihydrate gypsum under alkaline conditions for use as a cement retarder. Because its raw material is hemihydrate gypsum, the dihydrate method and hemihydrate-dihydrate method currently used on a large scale cannot directly produce hemihydrate gypsum. If it is first crystallized into hemihydrate gypsum, the cost is relatively high.

[0004] Application publication number CN110395929A discloses a phosphogypsum modified cement retarder, which is prepared by dry-mixing dihydrate gypsum and a modifier to adjust the mixture to alkaline, and then granulating the mixture in a granulator; the granulated material is then placed in an autoclave for autoclave reaction until the phosphogypsum is converted into hemihydrate gypsum, and during the cooling process after exiting the autoclave, the hemihydrate gypsum is converted into dihydrate gypsum to become a cement retarder. After pelletizing, the mixture is steam-cured to crystallize into hemihydrate gypsum, and then absorbs water to crystallize into dihydrate gypsum, which has a long process and high energy consumption.

[0005] Application publication number CN113072318A discloses a spherical phosphogypsum and its preparation method and application. The phosphogypsum powder, cement and modifier are mixed to form balls, and the balls are then naturally stacked or autoclaved. Finally, the balls are slurried in cement slurry to obtain a high-strength phosphogypsum spherical retarder.

[0006] Based on this, the present invention provides a new method for comprehensive utilization of phosphogypsum. By adding bentonite to phosphogypsum, excess water and other impurities in phosphogypsum can be effectively absorbed. Carbide slag reacts with phosphogypsum to effectively adjust the pH value, thereby reducing the water-soluble fluorine and phosphorus content in phosphogypsum. The use of a curing agent can adjust the setting time and hardening process of cement, solve the frequency of using process water in actual production, and reduce the powder ball rate. The method has low cost, short process, and stable quality of the prepared product, and is a high-quality cement retarder. Summary of the invention

[0007] The main purpose of the present invention is to provide a comprehensive utilization and treatment process of phosphogypsum, which solves the environmental pollution caused by excessive storage of phosphogypsum and realizes the recovery and reuse of phosphogypsum; at the same time, the obtained dihydrate phosphogypsum is used as a cement retarder with a stable retarding effect, which greatly improves the economic benefits of cement production enterprises.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: A comprehensive utilization and treatment process of phosphogypsum comprises the following steps: (1) After phosphogypsum, carbide slag and bentonite are fully mixed, process water and a curing agent are added, and the mixture is further mixed to obtain a mixture; (2) granulating the mixed material I into balls, autoclaving, cooling and hardening, thereby obtaining dihydrate gypsum; In the step (1), the mass ratio of phosphogypsum to bentonite is (92-95):(5-8).

[0009] In the step (1), carbide slag is added to control the pH value to be ≥7.

[0010] In the step (1), the mass fraction of water-soluble phosphorus pentoxide in the phosphogypsum is less than 5%, the mass fraction of water-soluble fluorine is less than 1%, the sum of the mass fraction of attached water and the mass fraction of crystallization water is less than 40%, and the pH value is less than 2.5.

[0011] In the step (1), the curing agent is curing agent DST-812, and the mass of the curing agent is 0.3% of the mass of the phosphogypsum.

[0012] In the step (1), the process water controls the attached water content of the granulator during granulation into balls to be 18-24%.

[0013] In the step (2), the mixed material is granulated into balls by a granulator, and the particle size of the balls is controlled to be above 20 mm.

[0014] In the step (2), the pressure of the autoclave reaction is 0.3-1.0 MPa, the temperature is 140-160° C., and the time is 150-180 min.

[0015] In the step (2), the hardening time is 18-22 days.

[0016] In the step (2), the mass fraction of water-soluble phosphorus pentoxide in the dihydrate gypsum is less than 0.1%, the water-soluble fluorine is less than 0.03%, the attached water is less than 12%, the crystal water is less than 15%, and the pH value is greater than 7.

[0017] The present invention also provides the use of dihydrate gypsum prepared by the phosphogypsum comprehensive utilization and treatment process as a cement retarder.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. In the comprehensive utilization and treatment process of phosphogypsum of the present invention, carbide slag can neutralize acidic water-soluble impurities such as phosphorus and fluorine in phosphogypsum, converting them into inert and sparingly soluble calcium phosphate and calcium fluoride, thereby reducing the influence on the setting time of cement; bentonite can absorb moisture and other impurities in phosphogypsum, reduce the content of attached water of phosphogypsum, and improve the performance of dihydrate gypsum; curing agent is used to adjust the setting time and hardening process of cement, and improve the performance of dihydrate gypsum as a cement retarder.

[0019] 2. The comprehensive utilization and treatment method of phosphogypsum of the present invention solves the environmental pollution caused by excessive storage of phosphogypsum and realizes the recycling and reuse of phosphogypsum. At the same time, the sulfur trioxide content in the dihydrate phosphogypsum obtained thereby is above 38%. As a cement retarder, the retarding effect is stable, which greatly improves the economic benefits of cement production enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0021] Figure 1 The present invention is a process flow chart of the comprehensive utilization and treatment of phosphogypsum. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with embodiments.

[0023] The phosphogypsum in the following examples is obtained from a phosphorus chemical enterprise.

[0024] Embodiment 1: A comprehensive utilization and treatment process of phosphogypsum comprises the following steps: (1) adding phosphogypsum and bentonite in a mass ratio of 92:8 into a mixer, adding carbide slag to adjust the pH to 7, and mixing uniformly to obtain a mixture I; adding a curing agent of 0.3% by mass of the phosphogypsum and process water to the mixture I, and mixing uniformly to obtain a mixture II, wherein the process water is added to ensure that the attachment water content of the granulating balls of the granulator is 21%; (2) feeding the mixed material II into a granulator for granulation to obtain phosphogypsum balls with an attached water content of 21%; (3) placing the phosphogypsum balls into an autoclave at a steam pressure of 0.6 MPa, an autoclave temperature of 160° C., and an autoclave time of 180 min to obtain hemihydrate gypsum; (4) After the hemihydrate gypsum is naturally cooled and hardened for 20 days, dihydrate gypsum is obtained.

[0025] Embodiment 2: A comprehensive utilization and treatment process of phosphogypsum comprises the following steps: (1) adding phosphogypsum and bentonite in a mass ratio of 95:5 into a mixer, adding carbide slag to adjust the pH to 7, and mixing uniformly to obtain a mixture I; adding a curing agent of 0.3% by mass of the phosphogypsum and process water to the mixture I, and mixing uniformly to obtain a mixture II, wherein the process water is added to ensure that the attachment water content of the granulating balls of the granulator is 21%; (2) feeding the mixed material II into a granulator for granulation to obtain phosphogypsum balls with an attached water content of 21%; (3) placing the phosphogypsum balls into an autoclave at a steam pressure of 0.6 MPa, an autoclave temperature of 160° C., and an autoclave time of 180 min to obtain hemihydrate gypsum; (4) After the hemihydrate gypsum is naturally cooled and hardened for 20 days, dihydrate gypsum is obtained.

[0026] Embodiment 3: A comprehensive utilization and treatment process of phosphogypsum comprises the following steps: (1) adding phosphogypsum and bentonite in a mass ratio of 92:8 into a mixer, adding carbide slag to adjust the pH to 7, and mixing uniformly to obtain a mixture I; adding a curing agent of 0.3% by mass of the phosphogypsum and process water to the mixture I, and mixing uniformly to obtain a mixture II, wherein the process water is added to ensure that the attachment water content of the granulating balls of the granulator is 21%; (2) feeding the mixed material II into a granulator for granulation to obtain phosphogypsum balls with an attachment water content of 21%; (3) placing the phosphogypsum balls into an autoclave at a steam pressure of 0.6 MPa, an autoclave temperature of 140° C., and an autoclave time of 150 min to obtain hemihydrate gypsum; (4) After the hemihydrate gypsum is naturally cooled and hardened for 20 days, dihydrate gypsum is obtained.

[0027] Embodiment 4: A comprehensive utilization and treatment process of phosphogypsum comprises the following steps: (1) adding phosphogypsum and bentonite in a mass ratio of 94:6 into a mixer, adding carbide slag to adjust the pH to 7, and mixing uniformly to obtain a mixture I; adding a curing agent of 0.3% by mass of the phosphogypsum and process water to the mixture I, and mixing uniformly to obtain a mixture II, wherein the process water is added to ensure that the attachment water content of the granulating balls of the granulator is 21%; (2) feeding the mixed material II into a granulator for granulation to obtain phosphogypsum balls with an attachment water content of 21%; (3) placing the phosphogypsum balls into an autoclave at a steam pressure of 0.6 MPa, an autoclave temperature of 150° C., and an autoclave time of 165 min to obtain hemihydrate gypsum; (4) After the hemihydrate gypsum is naturally cooled and hardened for 20 days, dihydrate gypsum is obtained.

[0028] Embodiment 5: A comprehensive utilization and treatment process of phosphogypsum comprises the following steps: (1) adding phosphogypsum and bentonite in a mass ratio of 93:7 to a mixer, adding carbide slag to adjust the pH to 7, and mixing uniformly to obtain a mixture I; adding a curing agent of 0.3% by mass of the phosphogypsum and process water to the mixture I, and mixing uniformly to obtain a mixture II, wherein the process water is added to ensure that the attachment water content of the granulating balls of the granulator is 21%; (2) feeding the mixed material II into a granulator for granulation to obtain phosphogypsum balls with an attachment water content of 21%; (3) placing the phosphogypsum balls into an autoclave at a steam pressure of 0.6 MPa, an autoclave temperature of 155° C., and an autoclave time of 160 min to obtain hemihydrate gypsum; (4) After the hemihydrate gypsum is naturally cooled and hardened for 20 days, dihydrate gypsum is obtained.

[0029] The harmful substances of the dihydrate gypsum prepared in the above Examples 1-5 were detected respectively, and compared with the untreated original phosphogypsum (Comparative Example 1). The detection results are shown in Table 1.

[0030] Table 1

[0031] It can be seen from Table 1 that the contents of water-soluble P2O5 and water-soluble fluorine in the dihydrate gypsum in the embodiment of the present invention are significantly lower than those of the original phosphogypsum; and the obtained dihydrate gypsum exhibits strong alkalinity, which can effectively avoid corrosion to the ball mill when ball-milling cement.

[0032] The comprehensive utilization and treatment method of phosphogypsum of the present invention can effectively remove impurities such as soluble phosphorus and fluorine, and the produced dihydrate gypsum meets the requirements of phosphogypsum cement retarder.

[0033] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A comprehensive utilization and treatment process of phosphogypsum, characterized in that: The following steps are involved: (1) After phosphogypsum, carbide slag and bentonite are fully mixed, process water and a curing agent are added, and the mixture is obtained after continuing to mix uniformly; (2) The mixed material is granulated into balls, autoclaved and hardened to obtain dihydrate gypsum.

2. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: The mass ratio of phosphogypsum to bentonite in step (1) is: (92-95): (5-8).

3. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (1), carbide slag is added to control the pH value to be ≥7.

4. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (1), the mass fraction of water-soluble phosphorus pentoxide in the phosphogypsum is less than 5%, the mass fraction of water-soluble fluorine is less than 5%, the sum of the mass fraction of attached water and the mass fraction of crystallization water is less than 40%, and the pH value is less than 2.

5.

5. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (1), the curing agent is curing agent DST-812, and the mass of the curing agent is 0.3% of the mass of the phosphogypsum.

6. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (1), process water is added to control the attached water content of the granulator during granulation into balls to be 18-24%.

7. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (2), the mixed material I is granulated into balls by a granulator, and the particle size of the balls is controlled to be above 20 mm.

8. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (2), the pressure of the autoclave reaction is 0.3-1.0 MPa, the temperature is 140-160° C., and the time is 150-180 min; the hardening time is 18-22 days.

9. The comprehensive utilization and treatment process of phosphogypsum according to claim 1 is characterized in that: In the step (2), the mass fraction of water-soluble phosphorus pentoxide in the dihydrate gypsum is less than 0.1%, the water-soluble fluorine is less than 0.03%, the attached water is less than 12%, the crystal water is less than 15%, and the pH value is greater than 7.

10. Use of dihydrate gypsum prepared by the comprehensive utilization and treatment process of phosphogypsum according to any one of claims 1 to 9 as a cement retarder.

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