Method for preparing phosphoric acid and mixed-phase phosphogypsum and preparing gypsum building material pressed product by semi-hydrated-anhydrous composite wet-process phosphoric acid process

Abstract

The invention belongs to the field of chemical engineering, and particularly relates to a method for preparing phosphoric acid and mixed-phase phosphogypsum and preparing a gypsum building material pressed product by a semi-hydrated-anhydrous composite wet-process phosphoric acid process. The method for preparing the phosphoric acid and the mixed-phase ardealite comprises the following processes that phosphate concentrate and reaction return slurry are mixed in a dissolving tank, the mixed slurry enters a decomposing tank for continuous reaction, and the reacted slurry enters a crystal transformation tank to be mixed with first sulfuric acid liquid and second sulfuric acid liquid for crystal transformation reaction; one part of the slurry in the crystal transformation tank is used as reaction return slurry, and the other part of the slurry is subjected to solid-liquid separation to obtain phosphoric acid liquor and a mixed-phase ardealite crude product; washing the ardealite crude product by using an inhibitor aqueous solution to obtain a mixed-phase ardealite finished product and washing liquid; and washing liquid is used as reaction return acid. According to the method provided by the invention, the high-concentration wet-process phosphoric acid can be obtained, and meanwhile, the mixed-phase phosphogypsum which takes two high-strength gypsum, namely alpha-semi-hydrated gypsum and II-type anhydrous gypsum, as main components is obtained through in-situ generation.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry, and in particular relates to a method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet phosphoric acid process, and a method for preparing gypsum building material pressed products. Background Art

[0002] When wet-process phosphoric acid is produced by decomposing phosphate rock with sulfuric acid, theoretically, gypsum exists in three hydrated crystalline forms in the wet-process phosphoric acid solution: dihydrate gypsum (CaSO4·2H2O), hemihydrate gypsum (α-CaSO4·0.5H2O), and type II anhydrous gypsum (II-CaSO4). Dihydrate gypsum (CaSO4·2H2O) does not have gelling properties, while hemihydrate gypsum (α-CaSO4·0.5H2O) and anhydrous gypsum (II-CaSO4) are high-strength gypsums with excellent gelling properties.

[0003] According to the classification of calcium sulfate hydrate crystal form, there are five main process flows for using sulfuric acid to decompose phosphate rock to produce wet-process phosphoric acid and obtain phosphogypsum: dihydrate process, semi-hydrate-dihydrate recrystallization process, dihydrate-semi-hydrate process, semi-hydrate process, and anhydrous process.

[0004] (1) Dihydrate wet phosphoric acid process: In mature industrial production, phosphate concentrate and sulfuric acid are usually mixed in a slurry with a solid content of 30-40%, a temperature of 65-85°C, a P2O5 concentration of 12-28%, and a SO4 2- The reaction is carried out under conditions of a concentration of 3-6%, and then after a certain period of crystallization, the dihydrate calcium sulfate crystals become coarse, and then filtered and separated to obtain wet-process phosphoric acid with a P2O5 concentration of usually 12-28%, and dihydrate gypsum (CaSO4·2H2O) is produced.

[0005] (2) Semi-aqueous wet phosphoric acid process: In mature industrial production, phosphate concentrate and sulfuric acid are usually mixed at a slurry solid content of 20-30%, a temperature of 90-100°C, a P2O5 concentration of 40-44%, and a SO4 2- The reaction is carried out under conditions of a concentration of 1-2%, and then after a certain period of crystallization, the calcium sulfate hemihydrate crystals become coarse, and then filtered and separated to obtain wet-process phosphoric acid with a P2O5 concentration of usually 39-43%, and α-hemihydrate gypsum (α-CaSO4·0.5H2O) is produced.

[0006] (3) Semi-hydrate-dihydrate recrystallization wet-process phosphoric acid process: First, wet-process phosphoric acid with a P2O5 concentration of 40-44% is obtained through the semi-hydrate wet-process phosphoric acid process, and semi-hydrate gypsum (α-CaSO4·0.5H2O) is produced at the same time. Then, dihydrate gypsum (CaSO4·2H2O) is obtained through recrystallization.

[0007] (4) Dihydrate-hemihydrate recrystallization wet-process phosphoric acid process: First, wet-process phosphoric acid with a P2O5 concentration of usually 15-25% is produced through the dihydrate process, and dihydrate gypsum (CaSO4·2H2O) is obtained. The dihydrate gypsum (CaSO4·2H2O) is then converted into α-hemihydrate gypsum (α-CaSO4·0.5H2O) through a crystallization method such as autoclaving, pressurized aqueous solution method or atmospheric pressure salt (alcohol) solution method.

[0008] (5) Anhydrous wet phosphoric acid process: The anhydrous process is theoretically to mix phosphate concentrate with sulfuric acid in a slurry with a liquid-to-solid ratio of 20-30%, raise the temperature to above 110°C, control the P2O5 concentration to above 45%, and reduce the SO4 2- By controlling the concentration to above 7%, the reaction produces wet-process phosphoric acid with a P2O5 concentration of 44% or higher, while also producing anhydrous gypsum (II-CaSO4). However, the anhydrous wet-process phosphoric acid process has yet to be industrialized due to issues such as severe corrosion and difficulty in filtration.

[0009] Existing wet-process phosphoric acid production processes using sulfuric acid to decompose phosphate rock are unable to simultaneously produce high-concentration phosphoric acid while also in-situ generating a mixed-phase phosphogypsum primarily composed of α-hemihydrate gypsum (α-CaSO₄·0.5H₂O) and type II anhydrous gypsum (II-CaSO₄). Addressing these challenges presents a pressing technical challenge in this field. Summary of the Invention

[0010] In view of this, the object of the present invention is to provide a method for preparing phosphoric acid and mixed-phase phosphogypsum and preparing gypsum building material pressed products using a semi-aqueous-anhydrous composite wet-process phosphoric acid process. The method provided by the present invention can simultaneously obtain high-concentration wet-process phosphoric acid and in situ generate a mixed-phase phosphogypsum containing two high-strength gypsums, α-hemihydrate gypsum (α-CaSO4·0.5H2O) and type II anhydrous gypsum (II-CaSO4), as the main components. On this basis, the obtained mixed-phase phosphogypsum does not need to be dried and calcined, and can be directly prepared into gypsum blocks, bricks and other building material pressed products using a combination of chemical excitation and physical pressing.

[0011] The present invention provides a method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process, comprising the following steps:

[0012] The phosphate concentrate and the reaction slurry are mixed in a dissolving tank to form a mixed slurry; the phosphoric acid content in the liquid phase of the mixed slurry is 42-45 wt% in terms of P2O5;

[0013] The mixed slurry enters the decomposition tank to continue reacting, and the slurry after the reaction enters the crystallization tank to react with the first sulfuric acid solution and the second sulfuric acid solution added to the crystallization tank respectively; wherein the first sulfuric acid solution is concentrated sulfuric acid, and the second sulfuric acid solution is a mixture of concentrated sulfuric acid and reaction back acid, and the concentration of the concentrated sulfuric acid is ≥98wt%; calculated as concentrated sulfuric acid, the amount of the first sulfuric acid solution added to the crystallization tank is less than that of the second sulfuric acid;

[0014] A portion of the slurry after the mixed reaction in the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other portion is subjected to solid-liquid separation to obtain phosphoric acid solution and crude phosphogypsum;

[0015] Washing the crude phosphogypsum with an inhibitor aqueous solution to obtain a mixed-phase phosphogypsum and a washing solution; wherein the inhibitor in the inhibitor aqueous solution is one or more of glucose, protein, and sodium tripolyphosphate;

[0016] The washing liquid is mixed with concentrated sulfuric acid as reaction return acid and then returned to the crystallization tank.

[0017] Preferably, the operating temperature of the dissolving tank is 100-105°C; the solid content of the mixed slurry is 25-30wt%; the SO4 2- The content is 0.6~1wt%.

[0018] Preferably, the operating temperature of the decomposition tank is 100-105°C; the solid content of the slurry in the decomposition tank is 20-25wt%; the phosphoric acid content in the liquid phase of the slurry in the decomposition tank is 42-45wt% in terms of P2O5, SO4 2- The content is 0.6-1wt%, and the calcium content calculated as CaO is 1-2wt%.

[0019] Preferably, the addition position of the first sulfuric acid solution is located at 1.5 to 2.5 meters below the liquid surface of the crystallization tank slurry and at a distance from the bottom of the tank, and the addition position of the second sulfuric acid solution is located at 0.5 to 1.5 meters below the liquid surface of the crystallization tank slurry and at a distance from the bottom of the tank; calculated as concentrated sulfuric acid, the amount of the first sulfuric acid solution added to the crystallization tank is 30 to 35 wt% of the total amount of the first sulfuric acid solution and the second sulfuric acid solution added; the temperature of the first sulfuric acid solution addition area is 113 to 118°C, and the distance between the temperature measurement position and the first sulfuric acid solution addition area is 3 to 10 cm; the temperature of the second sulfuric acid solution addition area is 110 to 115°C, and the distance between the temperature measurement position and the second sulfuric acid solution addition area is 3 to 10 cm; the average operating temperature of the crystallization tank is 106 to 110°C; the solid phase content of the slurry in the crystallization tank is 20 to 25 wt%; the phosphoric acid content in the liquid phase of the slurry in the crystallization tank is 42 to 45 wt% in terms of P2O5, and SO4 2-The content is 2.0~2.5wt%.

[0020] Preferably, the content of the inhibitor in the inhibitor aqueous solution is 0.1 to 0.3 wt%.

[0021] The present invention provides a method for preparing a gypsum building material pressed product, comprising the following steps:

[0022] The mixed phase phosphogypsum, activator, hydrophobic agent and modifier are mixed, pressed into shape, and naturally cured to obtain a gypsum building material pressed product;

[0023] The mixed-phase phosphogypsum is the mixed-phase phosphogypsum prepared by the method described in the above technical solution;

[0024] The gypsum building material pressed products include gypsum blocks and / or gypsum bricks.

[0025] Preferably, the activator is prepared according to the following steps: mixing aluminum hydroxide, aluminum oxide and magnesium aluminum silicate aqueous solution to obtain a suspension; mixing the suspension with sulfuric acid to react to obtain the activator;

[0026] The amount of the activator used accounts for 3 to 6 wt% of the total mass of the mixed phase phosphogypsum, the activator, the hydrophobic agent and the modifier.

[0027] Preferably, the hydrophobic agent is one or more of sodium methylsiliconate, sodium methyl silicate, hydrogen silicone oil, silane, siloxane and silicone resin; the amount of the hydrophobic agent used accounts for 0.05 to 0.3 wt% of the total mass of the mixed phase phosphogypsum, activator, hydrophobic agent and modifier.

[0028] Preferably, the modifier is one or more of cement, carbide slag and lime; the amount of the modifier is 2 to 5 wt% of the total mass of the mixed phase phosphogypsum, activator, hydrophobic agent and modifier.

[0029] Preferably, the press molding is carried out in a press using a unidirectional or bidirectional static pressure method; the pressing pressure of the press is above 800t, and the molding output pressure intensity is above 10MPa.

[0030] Compared with the prior art, the present invention provides a method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process and a method for preparing gypsum building material pressed products. The method for preparing phosphoric acid and mixed-phase phosphogypsum provided by the present invention includes the following steps: phosphate concentrate and reaction slurry are mixed in a dissolution tank to form a mixed slurry; the phosphoric acid content in the liquid phase of the mixed slurry is 42 to 45 wt% in terms of P2O5; the mixed slurry enters a decomposition tank to continue to react, and the slurry after the reaction enters a crystallization tank to be mixed and reacted with a first sulfuric acid solution and a second sulfuric acid solution added to the crystallization tank; wherein the first sulfuric acid solution is concentrated sulfuric acid, and the second sulfuric acid solution is a mixture of concentrated sulfuric acid and reaction slurry, and the concentration of the concentrated sulfuric acid is ≥ 98wt%; in terms of concentrated sulfuric acid, the amount of the first sulfuric acid solution added to the crystallization tank is less than that of the second sulfuric acid; a part of the slurry after the mixed reaction in the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other part is subjected to solid-liquid separation to obtain phosphoric acid solution and crude phosphogypsum; the crude phosphogypsum is washed with an inhibitor aqueous solution to obtain mixed-phase phosphogypsum and a washing liquid; wherein the inhibitor in the inhibitor aqueous solution is one or more of glucose, protein and sodium tripolyphosphate; the washing liquid is mixed with concentrated sulfuric acid as a reaction back acid and returned to the crystallization tank. The present invention adopts a semi-aqueous-anhydrous wet phosphoric acid composite process, and the phosphate concentrate is decomposed by reacting with a reaction slurry containing phosphoric acid and sulfuric acid. The slurry with a high phosphoric acid content after sufficient decomposition enters the crystallization tank, and the crystallization process adopts the method of adding sulfuric acid to make the crystallization environment SO4 2- The concentration rises. At this time, the SO4 2- The concentration is under certain rich conditions, the Ca in the slurry 2+ With SO4 2- CaSO4 is formed. Sulfuric acid is added by diluting concentrated sulfuric acid and adding concentrated sulfuric acid directly. The large proportion of concentrated sulfuric acid is added by diluting, that is, the added concentrated sulfuric acid is mixed with the reaction acid to make the concentrated sulfuric acid fully diluted and reduce SO4 2- Concentration to avoid local overheating and local SO4 in the crystallization tank 2- Too high a concentration will form too much other forms of gypsum, so that most of the gypsum will be converted into hemihydrate gypsum (α-CaSO4·0.5H2O) in the metastable zone of hemihydrate gypsum; a small proportion of concentrated sulfuric acid is added by direct addition, forming local high temperature and high SO4 in the crystallization tank. 2-The environment causes a small portion of gypsum to form anhydrous gypsum (Ⅱ-CaSO4) in the metastable zone of anhydrous gypsum. Through the above process control, a mixed phase gypsum with a large proportion of hemihydrate gypsum (α-CaSO4·0.5H2O) and a small proportion of anhydrous gypsum (Ⅱ-CaSO4) is formed in the crystallization tank. Afterwards, the slurry produced by the crystallization tank is subjected to solid-liquid separation to obtain high-concentration wet-process phosphoric acid and crude phosphogypsum. Finally, the crude phosphogypsum is washed, and an inhibitor is added to the washing water used for washing to slow down the conversion of α-hemihydrate gypsum to dihydrate gypsum, ultimately obtaining a mixed phase phosphogypsum with two high-strength gypsums, α-hemihydrate gypsum (α-CaSO4·0.5H2O) and type II anhydrous gypsum (Ⅱ-CaSO4), as the main components. This mixed-phase phosphogypsum does not require drying and calcining, and can be directly prepared into gypsum building material pressed products using a combination of chemical excitation and physical pressing. This avoids a series of environmental problems such as sewage, dust, and land occupation that may be caused by the storage of phosphogypsum, and has the advantages of low carbon, energy saving, emission reduction, greenness, environmental protection, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0032] Figure 1 is a process flow chart provided by an embodiment of the present invention;

[0033] Figure 2 is an XRD pattern of the mixed-phase phosphogypsum provided in Example 1 of the present invention;

[0034] Figure 3 This is a composition analysis diagram of the mixed-phase phosphogypsum provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0036] The present invention provides a method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process, comprising the following steps:

[0037] The phosphate concentrate and the reaction slurry are mixed in a dissolving tank to form a mixed slurry; the phosphoric acid content in the liquid phase of the mixed slurry is 42-45 wt% in terms of P2O5;

[0038] The mixed slurry enters the decomposition tank to continue reacting, and the slurry after the reaction enters the crystallization tank to react with the first sulfuric acid solution and the second sulfuric acid solution added to the crystallization tank respectively; wherein the first sulfuric acid solution is concentrated sulfuric acid, and the second sulfuric acid solution is a mixture of concentrated sulfuric acid and reaction back acid, and the concentration of the concentrated sulfuric acid is ≥98wt%; calculated as concentrated sulfuric acid, the amount of the first sulfuric acid added to the crystallization tank is less than that of the second sulfuric acid;

[0039] A portion of the slurry after the mixed reaction in the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other portion is subjected to solid-liquid separation to obtain phosphoric acid solution and crude phosphogypsum;

[0040] Washing the crude phosphogypsum with an inhibitor aqueous solution to obtain a mixed-phase phosphogypsum and a washing solution; wherein the inhibitor in the inhibitor aqueous solution is one or more of glucose, protein, and sodium tripolyphosphate;

[0041] The washing liquid is used as reaction back acid and is returned to the crystallization tank after being mixed with concentrated sulfuric acid.

[0042] In the method provided by the present invention, the main components of the phosphate concentrate are P2O5 and CaO on a dry basis, wherein the content of P2O5 is preferably 30-40wt%, and the content of CaO is preferably 45-55wt%.

[0043] In the method provided by the present invention, the operating temperature of the dissolution tank is preferably 100-105°C, specifically 100°C, 101°C, 102°C, 103°C, 104°C or 105°C.

[0044] In the method provided by the present invention, the phosphoric acid content in the liquid phase of the mixed slurry formed in the dissolution tank as calculated as P2O5 can be specifically 42wt%, 43wt%, 44wt% or 45wt%; the solid phase content of the mixed slurry is preferably 25-30wt%, specifically 25wt%, 26wt%, 27wt%, 28wt%, 29wt% or 30wt%; the SO4 2- The content is preferably 0.6-1 wt%, specifically 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%.

[0045] In the method provided by the present invention, the operating temperature of the decomposition tank is preferably 100-105°C, specifically 100°C, 101°C, 102°C, 103°C, 104°C or 105°C.

[0046] In the method provided by the present invention, the phosphoric acid content in the liquid phase of the slurry in the decomposition tank is preferably 42-45wt% in terms of P2O5, specifically 42wt%, 43wt%, 44wt% or 45wt%; the solid phase content of the slurry in the decomposition tank is preferably 20-25wt%, specifically 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt%; the SO4 content in the liquid phase of the slurry in the decomposition tank is preferably 20-25wt%, specifically 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt%. 2- The content is preferably 0.6-1wt%, specifically 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%; the calcium content in the liquid phase of the slurry in the decomposition tank calculated as CaO is preferably 1-2wt%, specifically 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2wt%.

[0047] In the method provided by the present invention, the concentration of the concentrated sulfuric acid can specifically be 98 wt % or 99 wt %.

[0048] In the method provided by the present invention, the concentration of the second sulfuric acid solution is preferably 10-20wt%, specifically 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%.

[0049] In the method provided by the present invention, the mass ratio of the total concentrated sulfuric acid mass of the first sulfuric acid solution and the second sulfuric acid solution added to the crystallization tank to the mass ratio of the phosphate concentrate added to the dissolution tank is preferably 16.18:(17-20), more preferably 16.18:(18-19), and even more preferably 16.18:(18.7-18.9).

[0050] In the method provided by the present invention, the position for adding the first sulfuric acid solution is preferably located 1.5 to 2.5 m below the liquid level of the slurry in the crystallization tank and away from the bottom of the tank, more preferably 2 m; the position for adding the second sulfuric acid solution is preferably located 0.5 to 1.5 m below the liquid level of the slurry in the crystallization tank and away from the bottom of the tank, more preferably 1 m; the distance between the position for adding the first sulfuric acid solution and the position for adding the second sulfuric acid solution is preferably 3 to 6 m, more preferably 4 to 5 m, and even more preferably 4.8 m.

[0051] In the method provided by the present invention, the amount of the first sulfuric acid solution added to the crystallization tank is preferably 30 to 35 wt% of the total amount of the first sulfuric acid solution and the second sulfuric acid solution added, calculated as concentrated sulfuric acid, and can be specifically 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt% or 35 wt%.

[0052] In the method provided by the present invention, the temperature of the area where the first sulfuric acid solution is added is preferably 113-118°C, specifically 113°C, 114°C, 115°C, 116°C, 117°C or 118°C, and the distance between the position where the temperature is measured and the position where the first sulfuric acid solution is added is preferably 3-10 cm, more preferably 5 cm; the temperature of the area where the second sulfuric acid solution is added is preferably 110-115°C, specifically 110°C, 111°C, 112°C, 113°C, 114°C or 115°C, and the distance between the position where the temperature is measured and the position where the second sulfuric acid solution is added is preferably 3-10 cm, more preferably 5 cm.

[0053] In the method provided by the present invention, the average operating temperature of the crystal transfer tank is preferably 106-110°C, specifically 106°C, 107°C, 108°C, 109°C or 110°C.

[0054] In the method provided by the present invention, the solid content of the slurry in the crystallization tank is preferably 20-25wt%, specifically 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt%; the phosphoric acid content in the liquid phase of the slurry in the crystallization tank as calculated as P2O5 is preferably 42-45wt%, specifically 42wt%, 43wt%, 44wt% or 45wt%; the SO4 2- The content is preferably 2.0-2.5 wt%, specifically 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4% or 2.5 wt%.

[0055] In the method provided by the present invention, the solid-liquid separation method is preferably filtration.

[0056] In the method provided by the present invention, the phosphoric acid (calculated as P2O5) content in the phosphoric acid solution obtained by the solid-liquid separation is preferably 42-45wt%, specifically 42wt%, 43wt%, 44wt% or 45wt%.

[0057] In the method provided by the present invention, the content of the inhibitor in the aqueous inhibitor solution is preferably 0.1-0.3 wt%, specifically 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt% or 0.3 wt%.

[0058] In the method provided by the present invention, in the prepared mixed-phase phosphogypsum, the proportion of α-hemihydrate gypsum (α-CaSO4·0.5H2O) is preferably 45-60wt%, the proportion of type II anhydrous gypsum (Ⅱ-CaSO4) is preferably 15-25wt%, the proportion of dihydrate gypsum is preferably 3-8wt%, the proportion of other solid components such as silicon dioxide is preferably 5-10wt%, the content of crystalline water is preferably 5-7wt% (including crystalline water contained in gypsum and other salts), and the content of free water is preferably 17-27wt%.

[0059] The method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process provided by the present invention can simultaneously obtain high-concentration wet-process phosphoric acid and in-situ generate mixed-phase phosphogypsum with two high-strength gypsums, α-semi-hydrate gypsum (α-CaSO4·0.5H2O) and type II anhydrous gypsum (Ⅱ-CaSO4), as main components, thus filling the technical gap in the relevant field.

[0060] The present invention also provides a method for preparing a gypsum building material pressed product, comprising the following steps:

[0061] The mixed phase phosphogypsum, activator, hydrophobic agent and modifier are mixed, pressed into shape, and naturally cured to obtain a gypsum building material pressed product;

[0062] The mixed-phase phosphogypsum is the mixed-phase phosphogypsum prepared by the method described in the above technical solution;

[0063] The gypsum building material pressed products include gypsum blocks and / or gypsum bricks.

[0064] In the method for preparing gypsum building material pressed products provided by the present invention, the activator can promote the rapid hydration of α-hemihydrate gypsum in the mixed phase, so that the prepared gypsum building material pressed products have a strength of more than 2 MPa within 5 minutes and a strength of more than 5 MPa within 20 minutes. At the same time, the activator can promote the conversion of type II anhydrous gypsum and promote the formation of ettringite phase in the gypsum building material pressed products, thereby increasing the strength, hardness and water resistance of the products.

[0065] In the method for preparing the gypsum building material pressed product provided by the present invention, the activator is preferably prepared according to the following steps:

[0066] Aluminum hydroxide, aluminum oxide and magnesium aluminum silicate aqueous solution are mixed to obtain a suspension; the suspension is mixed with sulfuric acid for reaction to obtain an activator.

[0067] In the above-mentioned activator preparation step provided by the present invention, the mass ratio of aluminum hydroxide to aluminum oxide is preferably 6:(2-6), more preferably 6:4; the concentration of magnesium aluminum silicate in the magnesium aluminum silicate aqueous solution is preferably 0.5-2wt%, more preferably 1wt%; the solute concentration of the suspension is preferably 30-40wt%, more preferably 35.1wt%; the sulfuric acid is preferably concentrated sulfuric acid, and the concentration of the concentrated sulfuric acid is preferably 90-99wt%, more preferably 98wt%; the sulfuric acid preferably accounts for 30-35wt% of the total mass of the suspension and sulfuric acid, more preferably 32.02wt%; the temperature of the mixing reaction is preferably 50-80°C, more preferably 65°C.

[0068] In the method for preparing gypsum building material pressed products provided by the present invention, the amount of the activator preferably accounts for 3 to 6 wt% of the total mass of the mixed phase phosphogypsum, activator, hydrophobic agent and modifier, and can be specifically 3 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, 5 wt%, 5.2 wt%, 5.4 wt%, 5.6 wt%, 5.8 wt% or 6 wt%.

[0069] In the method for preparing gypsum building material pressed products provided by the present invention, the hydrophobic agent can reduce the water absorption rate of the gypsum building material pressed products, increase the softening coefficient, improve the freeze-thaw resistance and increase the water resistance. Since the hardened body of the mixed-phase phosphogypsum after hydration contains some tiny capillaries, it will absorb water in moisture or water, allowing the water to enter the gypsum capillaries, causing the gypsum to slowly dissolve, destroying the microstructure of the gypsum, and affecting the strength and freeze-thaw resistance of the gypsum building material pressed products. After adding a small amount of hydrophobic agent, a film will form on the crystal surface of the gypsum building material pressed products after drying, preventing water molecules from entering the gypsum capillaries, thereby reducing the water absorption rate of the gypsum building material pressed products, improving the softening coefficient and freeze-thaw resistance, and increasing the water resistance of the gypsum.

[0070] In the method for preparing gypsum building material pressed products provided by the present invention, the water repellent is preferably one or more of sodium methylsiliconate, sodium methyl silicate, hydrogen silicone oil, silane, siloxane and silicone resin; the amount of the water repellent is preferably 0.05-0.3wt% of the total mass of the mixed phase phosphogypsum, activator, water repellent and modifier, specifically 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt% %, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%, 0.23wt%, 0.24wt%, 0.25wt%, 0.26wt%, 0.27wt%, 0.28wt%, 0.29wt% or 0.3wt%.

[0071] In the method for preparing gypsum building material pressed products provided by the present invention, the modifier regulates the pH and the amount of water-soluble acidic substances such as phosphorus and fluorine in the solidified mixed phase of phosphogypsum, ensuring that the water-soluble phosphorus and fluorine content meets the technical requirements of the GB / T 23456-2018 "Phosphogypsum" standard. Furthermore, the modifier synergizes with the activator to promote the hydration of α-hemihydrate gypsum and type II anhydrous gypsum, increasing its strength and improving the hardness, softening coefficient, and water resistance of the gypsum blocks.

[0072] In the method for preparing gypsum building material pressed products provided by the present invention, the modifier is preferably one or more of cement, carbide slag and lime; the amount of the modifier is preferably 2-5wt% of the total mass of the mixed phase phosphogypsum, activator, hydrophobic agent and modifier, specifically 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt%, 4wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt%, 4.5wt%, 4.6wt%, 4.7wt%, 4.8wt%, 4.9wt% or 5wt%.

[0073] In the method for preparing gypsum building material pressed products provided by the present invention, the pressing molding is preferably carried out in a press using a unidirectional or bidirectional static pressure method; the pressing pressure of the press is preferably above 800t, more preferably 800-1600t, specifically 800t, 900t, 1000t, 1100t, 1200t, 1300t, 1400t, 1500t or 1600t; the molding output pressure intensity of the press is preferably above 10MPa, more preferably 10-20MPa, specifically 10MPa, 11MPa, 12MPa, 13MPa, 14MPa, 15MPa, 16MPa, 17MPa, 18MPa, 19MPa or 20MPa. In the present invention, pores and air between material particles can be quickly discharged through pressing, the contact area between the activator and the mixed phase gypsum is increased, and the migration distance of ions is shortened, so that various materials are fully contacted, the microstructure of the newly generated dihydrate gypsum is changed during the rapid hydration of the hemihydrate gypsum, crystal defects are reduced, and early strength is generated, thereby achieving continuous and stable production.

[0074] In the method for preparing gypsum building material pressed products provided by the present invention, the natural curing time is preferably 3 to 10 days, specifically 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days or 10 days.

[0075] The method for preparing gypsum building material pressed products provided by the present invention uses the mixed-phase phosphogypsum prepared by the present invention as the gypsum raw material and adopts a combined process of chemical excitation and physical pressing to directly produce the gypsum building material pressed products. The present invention does not require drying and calcining the phosphogypsum, thus avoiding a series of environmental problems such as sewage, dust, and land occupation that may be caused by the storage of phosphogypsum. It has the advantages of low carbon, energy saving, emission reduction, green, environmental protection, and low cost. The resulting gypsum building material pressed products have excellent performance and can be used in various environments such as interior walls, exterior walls, kitchens and bathrooms, roads, squares, slope protection, and ditches.

[0076] For the purpose of greater clarity, the present invention is described in detail with reference to the following examples.

[0077] In the following examples of the present invention, the main indicators of the phosphate concentrate used are shown in Table 1:

[0078] Table 1 Main indicators of phosphate concentrate

[0079]

[0080]

[0081] In the following embodiments of the present invention, the sulfuric acid used is concentrated sulfuric acid with a concentration of 98 wt %. Based on the consumption of phosphate concentrate of 18.8 tons / hour (on a dry basis), the theoretical consumption of sulfuric acid is 16.18 tons / hour.

[0082] In the following embodiments of the present invention, the activator used is prepared according to the following steps: aluminum hydroxide and aluminum oxide are added to a 1wt% magnesium aluminum silicate aqueous solution in a mass ratio of 6:4, and the mixture is stirred and mixed for 30 minutes to prepare a suspension with a solute concentration of 35.1wt%; 32.02wt% concentrated sulfuric acid (98wt%) and 67.98wt% of the suspension are added to a reaction tank, and the mixture is stirred and mixed continuously at 65°C to allow the mixture to react fully to obtain an activator.

[0083] Example 1

[0084] A method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process and directly preparing gypsum building material pressed products, the process flow is as follows Figure 1 The specific process is as follows:

[0085] The phosphate concentrate and the reaction slurry are added to the dissolving tank to form a mixed slurry. The content of phosphoric acid (in terms of P2O5) in the liquid phase of the slurry is controlled to be 45wt%, SO4 2- The content is 0.8wt%, the solid content of the slurry is controlled to be 27wt%, and the reaction temperature of the dissolving tank is controlled to be 105℃;

[0086] The mixed slurry formed in the dissolving tank is transferred to the decomposition tank to continue the reaction, and the content of phosphoric acid (in terms of P2O5) in the liquid phase of the slurry in the decomposition tank is controlled to be 45wt%, SO4 2- The content is 0.8wt%, the solid content is 23wt%, the calcium (calculated as CaO) content is 1.3wt%, and the decomposition tank temperature is controlled at 105°C;

[0087] The slurry in the decomposition tank enters the crystallization tank, and a small proportion of concentrated sulfuric acid is added to the crystallization tank through the first sulfuric acid liquid feeding pipe at a flow rate of about 5.26t / h as the first sulfuric acid liquid. A large proportion of concentrated sulfuric acid is mixed with the reaction back acid in the acid mixer at a flow rate of about 10.92t / h and diluted to a concentration of about 16wt% and then added to the crystallization tank through the second sulfuric acid liquid feeding pipe as the second sulfuric acid liquid; the discharge port of the first sulfuric acid liquid feeding pipe is set below the liquid level of the crystallization tank slurry and about 2m from the bottom of the tank, and the temperature control area of ​​the discharge port is controlled. The temperature of the second sulfuric acid feeding pipe is set at 116 ° C, and the temperature is measured at a distance of 5 cm from the discharge port. The discharge port of the second sulfuric acid feeding pipe is set below the liquid level of the crystallization tank slurry and about 1 m from the bottom of the tank. The temperature of the area where the discharge port is located is controlled at 113 ° C, and the temperature is measured at a distance of 5 cm from the discharge port. The distance between the discharge ports of the two sulfuric acid feeding pipes is 4.8 m. The average operating temperature of the crystallization tank is controlled at 109 ° C. The solid content of the slurry in the crystallization tank is 23 wt%, the phosphoric acid content in the liquid phase of the slurry as P2O5 is 45 wt%, and SO4 2- The content is 2.3wt%;

[0088] Part of the slurry produced by the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other part is filtered and separated to obtain a phosphoric acid solution (finished phosphoric acid) with a concentration (in terms of P2O5) of about 44.52wt% and a crude phosphogypsum (filter cake);

[0089] The crude phosphogypsum is washed with a 0.2 wt% protein aqueous solution to obtain a mixed phase of phosphogypsum and a washing liquid; the washing liquid is mixed with concentrated sulfuric acid as a reaction acid and then returned to the crystallization tank;

[0090] According to the mixed phase ratio of 91.7wt% of phosphogypsum, 5.2wt% of activator, 0.1wt% of hydrogen-based silicone oil, and 3wt% of cement (PO 42.5), each material is weighed and added to a stirring pot in sequence, stirred and mixed evenly, and then sent to a press using a unidirectional or bidirectional static pressure method. The pressing pressure of the press is 1600t and the molding output pressure intensity is 18MPa. Rapid pressing and molding is carried out within 1 minute;

[0091] After pressing and forming, the material is demoulded and transferred to a conveyor belt for slow transportation and natural curing. The compressive strength of the material reaches 3.2MPa within 5 minutes after demoulding, and the compressive strength reaches 6.8MPa within 20 minutes. After being transported on the conveyor belt for 20 minutes, mechanical stacking can be carried out. After the stacking is naturally cured at room temperature in the warehouse for 5 days, the gypsum blocks are obtained.

[0092] The X-ray diffraction (XRD) characterization results of the mixed phase phosphogypsum prepared in this embodiment are as follows: Figure 2 The mixed phase phosphogypsum prepared in this embodiment is characterized by full elemental analysis and thermogravimetric analysis. Figure 3 As shown. Figure 2 and Figure 3 It can be seen that the mixed-phase phosphogypsum (wet basis) prepared in this embodiment contains hemihydrate gypsum, anhydrous gypsum and dihydrate gypsum, α-hemihydrate gypsum (α-CaSO4) accounts for 47.99%, type II anhydrous gypsum (Ⅱ-CaSO4) accounts for 20.53wt%, dihydrate gypsum accounts for 4.91wt%, other solid components such as silicon dioxide account for 5.96wt%, the crystallization water content is 5.04wt% (including the crystallization water contained in gypsum and other salts), and the free water content is 20.60wt%.

[0093] The solid density of the gypsum blocks prepared in this embodiment is 1854 kg / m 3 The absolute dry compressive strength is 20.7MPa, the breaking load is 7.5KN, the 2h water absorption is 1.7wt%, the moisture content is 2.3wt%, the softening coefficient is 0.82, there is no cracking or corner loss after 20 freeze-thaw cycles, and the gypsum hardness tester test is 37.5N / mm2.

[0094] Example 2

[0095] A method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process and directly preparing gypsum building material pressed products, the process flow is as follows Figure 1 As shown, the specific process is as follows:

[0096] The phosphate concentrate and the reaction slurry are added to the dissolving tank to form a mixed slurry. The content of phosphoric acid (in terms of P2O5) in the liquid phase of the slurry is controlled to be 44wt%, SO4 2- The content is 0.8wt%, the solid content of the slurry is controlled to be 27wt%, and the reaction temperature of the dissolving tank is controlled to be 105℃;

[0097] The mixed slurry formed in the dissolving tank is transferred to the decomposition tank to continue the reaction, and the content of phosphoric acid (in terms of P2O5) in the liquid phase of the slurry in the decomposition tank is controlled to be 44wt%, SO4 2- The content is 0.8wt%, the solid content is 23wt%, the calcium (calculated as CaO) content is 1.3wt%, and the decomposition tank temperature is controlled at 104°C;

[0098] The slurry in the decomposition tank enters the crystallization tank, and a small proportion of concentrated sulfuric acid is added to the crystallization tank through the first sulfuric acid liquid feeding pipe at a flow rate of about 5.26t / h as the first sulfuric acid liquid. A large proportion of concentrated sulfuric acid is mixed with the reaction back acid in the acid mixer at a flow rate of about 10.92t / h and diluted to a concentration of about 16wt% and then added to the crystallization tank through the second sulfuric acid liquid feeding pipe as the second sulfuric acid liquid; the discharge port of the first sulfuric acid liquid feeding pipe is set below the liquid level of the crystallization tank slurry and about 2m from the bottom of the tank, and the temperature control area of ​​the discharge port is controlled. The temperature of the second sulfuric acid feeding pipe is set at 115℃, and the temperature is measured at a distance of 5cm from the discharge port. The discharge port of the second sulfuric acid feeding pipe is set at about 1m below the liquid level of the crystallization tank slurry and about 1m from the bottom of the tank. The temperature of the area where the discharge port is located is controlled at 110℃, and the temperature is measured at a distance of 5cm from the discharge port. The distance between the discharge ports of the two sulfuric acid feeding pipes is 4.8m. The average operating temperature of the crystallization tank is controlled at 107℃. The solid content of the slurry in the crystallization tank is 23wt%, the phosphoric acid content in the liquid phase of the slurry as P2O5 is 44wt%, and SO4 2- The content is 2.3wt%;

[0099] Part of the slurry produced by the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other part is filtered and separated to obtain a phosphoric acid solution (finished phosphoric acid) with a concentration (in terms of P2O5) of about 43.71wt% and a crude phosphogypsum (filter cake);

[0100] The crude phosphogypsum is washed with a 0.2 wt% protein aqueous solution to obtain a mixed phase of phosphogypsum and a washing liquid; the washing liquid is mixed with concentrated sulfuric acid as a reaction acid and then returned to the crystallization tank;

[0101] According to the mixed phase ratio of 91.4wt% of phosphogypsum, 4.8wt% of activator, 0.2wt% of hydrogen-based silicone oil, and 3.6wt% of cement (PO 42.5), each material is weighed and added to a stirring pot in sequence, stirred and mixed evenly, and then sent to a press using a unidirectional or bidirectional static pressure method. The pressing pressure of the press is 1400t and the molding output pressure intensity is 15MPa. Rapid pressing and molding is carried out within 1 minute;

[0102] After pressing and forming, the material is demoulded and transferred to a conveyor belt for slow transportation and natural curing. The compressive strength of the material reaches 2.6MPa within 5 minutes after demoulding, and the compressive strength reaches 4.8MPa within 20 minutes. After being transported on the conveyor belt for 20 minutes, mechanical stacking can be carried out. After the stacking is naturally cured at room temperature in the warehouse for 5 days, the gypsum blocks are obtained.

[0103] In the mixed-phase phosphogypsum prepared in this embodiment, α-hemihydrate gypsum (α-CaSO4) accounts for 49.51%, type II anhydrous gypsum (Ⅱ-CaSO4) accounts for 17.05wt%, dihydrate gypsum accounts for 4.97wt%, other solid components such as silicon dioxide account for 5.92wt%, the crystallization water content is 5.30wt% (including the crystallization water contained in gypsum and other salts), and the free water content is 22.55wt%.

[0104] The gypsum blocks prepared in this embodiment have a solid density of 1721 kg / m3, an absolute dry compressive strength of 17.2 MPa, a breaking load of 6.8 KN, a 2h water absorption rate of 2.8 wt%, a moisture content of 3.1 wt%, a softening coefficient of 0.76, and no cracking or chipping after 18 freeze-thaw cycles. The gypsum hardness test result is 34.2 N / mm2.

[0105] Example 3

[0106] A method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process and directly preparing gypsum building material pressed products, the process flow is as follows Figure 1 As shown, the specific process is as follows:

[0107] The phosphate concentrate and the reaction slurry are added to the dissolving tank to form a mixed slurry, and the content of phosphoric acid (in terms of P2O5) in the slurry liquid phase is controlled to be 45wt%, SO4 2- The content is 0.8wt%, the solid content of the slurry is controlled to be 27wt%, and the reaction temperature of the dissolving tank is controlled to be 105℃;

[0108] The mixed slurry formed in the dissolving tank is transferred to the decomposition tank to continue the reaction, and the content of phosphoric acid (in terms of P2O5) in the liquid phase of the slurry in the decomposition tank is controlled to be 45wt%, SO4 2-The content is 0.8wt%, the solid content is 23wt%, the calcium (calculated as CaO) content is 1.4wt%, and the decomposition tank temperature is controlled at 105°C;

[0109] The slurry in the decomposition tank enters the crystallization tank, and a small proportion of concentrated sulfuric acid is added to the crystallization tank through the first sulfuric acid liquid feeding pipe at a flow rate of about 5.26t / h as the first sulfuric acid liquid. A large proportion of concentrated sulfuric acid is mixed with the reaction back acid in the acid mixer at a flow rate of about 10.92t / h and diluted to a concentration of about 16wt% and then added to the crystallization tank through the second sulfuric acid liquid feeding pipe as the second sulfuric acid liquid; the discharge port of the first sulfuric acid liquid feeding pipe is set below the liquid level of the crystallization tank slurry and about 2m from the bottom of the tank, and the temperature control area of ​​the discharge port is controlled. The temperature of the second sulfuric acid feeding pipe is set at 114 ° C, and the temperature is measured at a distance of 5 cm from the discharge port. The discharge port of the second sulfuric acid feeding pipe is set below the liquid level of the crystallization tank slurry and about 1 m from the bottom of the tank. The temperature of the area where the discharge port is located is controlled at 110 ° C, and the temperature is measured at a distance of 5 cm from the discharge port. The distance between the discharge ports of the two sulfuric acid feeding pipes is 4.8 m. The average operating temperature of the crystallization tank is controlled at 107 ° C. The solid content of the slurry in the crystallization tank is 23 wt%, the phosphoric acid content in the liquid phase of the slurry as P2O5 is 45 wt%, and SO4 2- The content is 2.3wt%;

[0110] Part of the slurry produced by the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other part is filtered and separated to obtain a phosphoric acid solution (finished phosphoric acid) with a concentration (in terms of P2O5) of about 44wt% and a crude phosphogypsum (filter cake);

[0111] The crude phosphogypsum is washed with a 0.2 wt% protein aqueous solution to obtain a mixed phase of phosphogypsum and a washing liquid; the washing liquid is mixed with concentrated sulfuric acid as a reaction acid and then returned to the crystallization tank;

[0112] According to the mixed phase ratio of 92.9wt% of phosphogypsum, 4.4wt% of activator, 0.2wt% of hydrogen-based silicone oil, and 2.5wt% of cement (PO 42.5), each material is weighed and added to a stirring pot in sequence, stirred and mixed evenly, and then sent to a press using a unidirectional or bidirectional static pressure method. The pressing pressure of the press is 1200t and the molding output pressure intensity is 14MPa. Rapid pressing and molding is carried out within 1 minute;

[0113] After pressing and forming, the material is demoulded and transferred to a conveyor belt for slow transportation and natural curing. The compressive strength of the material reaches 2.2MPa within 5 minutes after demoulding, and the compressive strength reaches 4.5MPa within 20 minutes. After being transported on the conveyor belt for 20 minutes, mechanical stacking can be carried out. After the stacking is naturally cured at room temperature in the warehouse for 5 days, the gypsum blocks are obtained.

[0114] In the mixed-phase phosphogypsum prepared in this embodiment, α-hemihydrate gypsum (α-CaSO4) accounts for 55.54% by weight, type II anhydrous gypsum (Ⅱ-CaSO4) accounts for 15.59wt%, dihydrate gypsum accounts for 4.34wt%, other solid components such as silicon dioxide account for 5.75wt%, the crystallization water content is 5.36wt% (including the crystallization water contained in gypsum and other salts), and the free water content is 18.78wt%.

[0115] The gypsum blocks prepared in this embodiment have a solid density of 1669 kg / m3, an absolute dry compressive strength of 15.2 MPa, a breaking load of 5.8 KN, a 2h water absorption rate of 3.6 wt%, a moisture content of 2.7 wt%, a softening coefficient of 0.70, and no cracking or chipping after 15 freeze-thaw cycles. The gypsum hardness test result is 31.4 N / mm2.

[0116] Example 4

[0117] Evaluation of energy conservation and emission reduction advantages

[0118] The energy consumption and electricity consumption of the process of preparing gypsum blocks using mixed-phase phosphogypsum in Example 1 are compared with those of the traditional casting method for preparing building gypsum blocks and the semi-dry method for preparing building gypsum blocks, as shown in the following:

[0119] (1) Casting method for building gypsum blocks: dihydrate gypsum is dried to remove free water and calcined to remove crystal water to prepare building gypsum powder (i.e., β-type hemihydrate gypsum). During this process, drying and calcining the dihydrate gypsum consumes natural gas, and running the motor consumes electricity. The building gypsum powder is mixed with water to make a slurry, cast into shape, and demoulded. During this process, running the motor consumes electricity. The demoulded product is dried at low temperature to remove free water. During this process, drying the gypsum product consumes natural gas, and running the motor consumes electricity.

[0120] (2) Semi-dry construction gypsum blocks: Dihydrate gypsum is dried to remove free water and calcined to remove crystal water to prepare construction gypsum powder (i.e., β-type semi-hydrated gypsum). During this process, drying and calcining the dihydrate gypsum consumes natural gas, and running the motor consumes electricity. Adding an appropriate amount of water to the construction gypsum powder, pressing it into shape, and demolding it also consumes electricity. The demolded product does not need to be dried and can be cured naturally at room temperature.

[0121] (3) Example 1 Preparation of gypsum blocks from mixed-phase phosphogypsum: The gypsum raw material does not need to be dried and calcined, but is directly mixed with an appropriate amount of additives, pressed into shape, and demolded. During this process, running the motor consumes electricity; the product after demolding does not need to be dried and can be naturally cured at room temperature.

[0122] The comparison results of energy consumption and electricity consumption are shown in Table 2 and Table 3:

[0123] Table 21 Comparison of energy consumption of 1t phosphogypsum block products (calculated in natural gas)

[0124]

[0125] Table 3.1 Comparison of electricity consumption of 1t phosphogypsum block products (carbon emissions converted to natural gas)

[0126]

[0127] Note: The conversion basis in Table 3 is GB / T 2589-2020 "General Rules for Calculating Comprehensive Energy Consumption", "Guidelines for the Compilation of Provincial Greenhouse Gas Inventories" (Development and Reform Commission Climate

[2011] No. 1041), GB / T 51366-2019 "Building Carbon Emission Calculation Standard" and "Phosphate Fertilizer and Compound Fertilizer".

[0128] It can be seen from Tables 2 and 3 that compared with the preparation of building gypsum blocks, the preparation of mixed-phase phosphogypsum blocks consumes less electricity and natural gas, and the carbon emissions and carbon dioxide emissions are significantly reduced.

[0129] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing phosphoric acid and mixed-phase phosphogypsum by a semi-aqueous-anhydrous composite wet-process phosphoric acid process, characterized in that: The following processes are included: The phosphate concentrate and the reaction slurry are mixed in a dissolving tank to form a mixed slurry; the phosphoric acid content in the liquid phase of the mixed slurry is 42-45 wt% in terms of P2O5; The mixed slurry enters the decomposition tank to continue reacting, and the slurry after the reaction enters the crystallization tank to react with the first sulfuric acid solution and the second sulfuric acid solution added to the crystallization tank respectively; wherein the first sulfuric acid solution is concentrated sulfuric acid, and the second sulfuric acid solution is a mixture of concentrated sulfuric acid and reaction back acid, and the concentration of the concentrated sulfuric acid is ≥98wt%; calculated as concentrated sulfuric acid, the amount of the first sulfuric acid solution added to the crystallization tank is less than that of the second sulfuric acid; A portion of the slurry after the mixed reaction in the crystallization tank is returned to the dissolution tank as a reaction slurry, and the other portion is subjected to solid-liquid separation to obtain phosphoric acid solution and crude phosphogypsum; Washing the crude phosphogypsum with an inhibitor aqueous solution to obtain a mixed-phase phosphogypsum and a washing solution; wherein the inhibitor in the inhibitor aqueous solution is one or more of glucose, protein, and sodium tripolyphosphate; The washing liquid is mixed with concentrated sulfuric acid as reaction return acid and then returned to the crystallization tank.

2. The method according to claim 1, characterized in that The operating temperature of the dissolving tank is 100-105°C; the solid content of the mixed slurry is 25-30wt%; the SO4 2- The content is 0.6~1wt%.

3. The method according to claim 1, characterized in that The operating temperature of the decomposition tank is 100-105°C; the solid content of the slurry in the decomposition tank is 20-25wt%; the phosphoric acid content in the liquid phase of the slurry in the decomposition tank is 42-45wt% in terms of P2O5, SO4 2- The content is 0.6-1wt%, and the calcium content calculated as CaO is 1-2wt%.

4. The method according to claim 1, wherein The addition position of the first sulfuric acid solution is located at 1.5 to 2.5 meters below the liquid surface of the crystallization tank slurry and at a distance from the bottom of the tank, and the addition position of the second sulfuric acid solution is located at 0.5 to 1.5 meters below the liquid surface of the crystallization tank slurry and at a distance from the bottom of the tank; calculated as concentrated sulfuric acid, the amount of the first sulfuric acid solution added to the crystallization tank is 30 to 35 wt% of the total amount of the first sulfuric acid solution and the second sulfuric acid solution added; the temperature of the first sulfuric acid solution addition area is 113 to 118°C, and the distance between the temperature measurement position and the first sulfuric acid solution addition area is 3 to 10 cm; the temperature of the second sulfuric acid solution addition area is 110 to 115°C, and the distance between the temperature measurement position and the second sulfuric acid solution addition area is 3 to 10 cm; the average operating temperature of the crystallization tank is 106 to 110°C; the solid phase content of the slurry in the crystallization tank is 20 to 25 wt%; the phosphoric acid content in the liquid phase of the slurry in the crystallization tank is 42 to 45 wt% in terms of P2O5, and SO4 2- The content is 2.0~2.5wt%.

5. The method according to claim 1, characterized in that The content of the inhibitor in the inhibitor aqueous solution is 0.1-0.3 wt %.

6. A method for preparing a gypsum building material pressed product, characterized in that: The following steps are involved: The mixed phase phosphogypsum, activator, hydrophobic agent and modifier are mixed, pressed into shape, and naturally cured to obtain a gypsum building material pressed product; The mixed-phase phosphogypsum is the mixed-phase phosphogypsum prepared by the method according to any one of claims 1 to 5; The gypsum building material pressed products include gypsum blocks and / or gypsum bricks.

7. The preparation method according to claim 6, characterized in that The excitant is prepared according to the following steps: mixing aluminum hydroxide, aluminum oxide and magnesium aluminum silicate aqueous solution to obtain a suspension; and mixing the suspension with sulfuric acid to react to obtain an activator; The amount of the activator used accounts for 3 to 6 wt% of the total mass of the mixed phase phosphogypsum, the activator, the hydrophobic agent and the modifier.

8. The preparation method according to claim 6, characterized in that The hydrophobic agent is one or more of sodium methylsiliconate, sodium methyl silicate, hydrogen silicone oil, silane, siloxane and silicone resin; the amount of the hydrophobic agent is 0.05-0.3wt% of the total mass of the mixed phase phosphogypsum, activator, hydrophobic agent and modifier.

9. The preparation method according to claim 6, characterized in that The modifier is one or more of cement, carbide slag and lime; the amount of the modifier is 2-5wt% of the total mass of the mixed phase phosphogypsum, activator, hydrophobic agent and modifier.

10. The preparation method according to claim 6, characterized in that The compression molding is carried out in a press using a unidirectional or bidirectional static pressure method; the compression pressure of the press is above 800t, and the molding output pressure intensity is above 10MPa.

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