Process for preparing high-strength alpha gypsum powder from phosphogypsum

Abstract

The application discloses a process for preparing high-strength alpha gypsum powder from phosphogypsum. The process comprises the following steps: preparing a solution of a crystal transformation agent, adding the solution into a reaction kettle, setting a reaction temperature and a stirring speed, adding a small amount of calcium chloride after the solution reaches the set reaction temperature, stirring for 10-20 min, adding pretreated bagged phosphogypsum, continuously reacting for 5-10 h, obtaining a hemihydrate gypsum slurry, filtering and washing the hemihydrate gypsum slurry, drying the hemihydrate gypsum slurry at 60-120 DEG C, and grinding the hemihydrate gypsum slurry to obtain high-strength gypsum powder. The application prepares high-strength gypsum with a strength higher than that of the alpha 40 grade in the standard JC / T2038-2010 and a blue light whiteness higher than 60, and the quality of the high-strength gypsum is stable. The application solves the increasingly serious storage problem of phosphogypsum and realizes high-value utilization of the phosphogypsum.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building materials, and particularly relates to a process for preparing high-strength alpha gypsum powder from phosphogypsum as raw material. BACKGROUND

[0002] Phosphogypsum is a by-product of industrial production of wet-process phosphoric acid. Its composition is affected by many factors such as the composition of raw ore, phosphoric acid production process and equipment. For example, the main component of phosphogypsum produced by the dihydrate process is calcium sulfate dihydrate, and the main component of phosphogypsum produced by the hemihydrate process is calcium sulfate hemihydrate. At present, the dihydrate process still occupies a dominant position. About 5 tons of phosphogypsum are produced for every ton of phosphoric acid (calculated by phosphorus pentoxide) produced by this process. The phosphogypsum contains many harmful impurities such as phosphorus, fluorine and organic matter, which makes it difficult to apply and has a low comprehensive utilization rate. The long-term storage of phosphogypsum not only occupies a large amount of land resources, but also causes the water-soluble impurities such as soluble phosphorus and soluble fluorine in the phosphogypsum to leach into surface water, soil and groundwater, thereby damaging the ecological environment.

[0003] At present, there are many studies on the comprehensive utilization of phosphogypsum. For example, phosphogypsum is used for producing sulfuric acid at high temperature, absorbing and mineralizing carbon dioxide under alkaline conditions, soil improvement in saline-alkali land, production of cement retarder, artificial aggregate or production of gypsum blocks and self-leveling mortar, and has applications in many fields such as industry, agriculture and construction. However, many of the current researches are still at the laboratory stage. At present, the production of cement retarder and building gypsum is mainly relied on to consume phosphogypsum. However, these products not only have a low economic added value, but also have a gradually saturated market. Therefore, it is urgent to find a way to utilize phosphogypsum with a high economic added value and a large consumption. The production of high-strength alpha gypsum powder from phosphogypsum as raw material is an important way to realize the high-value utilization of phosphogypsum. High-strength gypsum, i.e. alpha-hemihydrate gypsum, has a more regular crystal shape, a smaller specific surface area, a lower water consumption at standard consistency, a smaller hydration heat, a slower hydration rate, a higher mechanical strength after hardening and a better biocompatibility. Compared with beta-hemihydrate gypsum, i.e. building gypsum, high-strength gypsum can not only be used to replace beta-hemihydrate gypsum to produce traditional gypsum products such as self-leveling, fire door core plate, mortar and gypsum block, but also be widely applied in high-end ceramics, precision casting, medical dental superhard materials and art crafts, and is a more superior gypsum cementing material.

[0004] Patent CN114956624A invented a method for preparing ultra-high strength alpha-hemihydrate gypsum from industrial by-product phosphogypsum using autoclaving method. The phosphogypsum doped with defluorination residue water washed and purified is stirred uniformly with a crystal transformation agent solution, then transferred to an autoclave, reacted at constant temperature for 20-120 min, discharged after pressure relief, dried at 80-130℃, and ground to obtain ultra-high strength gypsum with strength standard higher than JC / T2038-2010 alpha 50 grade. The preparation method of this patent is autoclaving method, which requires special equipment such as autoclave, has high requirements for equipment, high energy consumption, and the prepared high-strength gypsum powder has poor whiteness and narrow application range.

[0005] Patent CN114538811A proposes a method for preparing high-strength gypsum from phosphogypsum. The dried phosphogypsum is divided into two parts, one part is calcined to prepare anhydrous gypsum, and the other part is added with adjusting agent and crystal modifier and reacted in a crystal transformation tank at 110-140℃ for 6-10h, then dried and dehydrated to obtain alpha-beta composite hemihydrate gypsum with crystal water content of 5%-7%. The anhydrous gypsum and alpha-beta composite hemihydrate gypsum are ground separately and mixed to obtain high-strength gypsum. The prepared gypsum has initial setting time not earlier than 3min, final setting time not later than 30min, 2h flexural strength ≥3.5MPa, and absolute dry compressive strength ≥25MPa. The process energy consumption of this patent for preparing high-strength gypsum powder is extremely high, the process is complex, it needs to be prepared in two steps and mixed and ground, and the strength of the prepared gypsum powder is relatively low, so the application range is narrow.

[0006] Currently, the processes for producing alpha-hemihydrate gypsum include autoclaving method, pressurized hydrothermal method, chemical synthesis method and atmospheric salt solution method, among which only autoclaving method has realized large-scale industrialization. However, autoclaving method has high requirements for raw materials and equipment, and the raw materials used for production are usually block-shaped high-purity natural gypsum, while phosphogypsum is a powder-like industrial by-product gypsum. The pressurized hydrothermal method and semi-dry method have high requirements for equipment, and this patent attempts to use a new atmospheric salt solution method to produce alpha-hemihydrate gypsum powder, which not only solves the phenomenon of hydration and hardening of hemihydrate gypsum during the filtration, washing and drying process, but also has the effect of further purifying phosphogypsum, increasing the whiteness of the product, and providing certain reference value for the industrialization of atmospheric salt solution method. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art and provide a process for preparing high-strength alpha gypsum powder using phosphogypsum as raw material.

[0008] The technical scheme of the present application is as follows:

[0009] A method for preparing high-strength alpha gypsum powder from phosphogypsum, comprising the following steps:

[0010] (1) Phosphogypsum is washed and floated to obtain purified phosphogypsum;

[0011] (2) Preparation of bagged phosphogypsum precursor: filter cloth wrapped purified phosphogypsum is tied with a string to form spherical bagged phosphogypsum for standby;

[0012] (3) Configuration of crystal transformation agent solution: magnesium chloride hexahydrate, magnesium sulfate heptahydrate, trisodium citrate, maleic acid are dissolved in water to configure a crystal transformation agent solution;

[0013] (4) Crystal transformation reaction: the crystal transformation agent solution configured in step (3) is added to a normal pressure reaction kettle, the rotation speed is set, heated to the set temperature, calcium chloride is added, and after stirring for a certain time, the bagged phosphogypsum obtained in step (2) is added to the reaction kettle, and constant temperature normal pressure reaction is carried out for a period of time to obtain hemihydrate gypsum slurry;

[0014] (5) Filtration, washing, drying and grinding: the hemihydrate gypsum slurry obtained in step (4) is filtered and washed to obtain filter cake A, which is dried and ground to obtain high-strength α-gypsum product;

[0015] Preferably, the purified phosphogypsum in step (1) contains ≥96% calcium sulfate dihydrate, ≤3% silicon dioxide, ≤0.3% organic matter, and pH = 6-7.

[0016] Preferably, the filter cloth aperture in step (2) is 10-20 μm, and the filter cloth and the string are both nylon materials.

[0017] Preferably, the spherical bagged phosphogypsum prepared in step (2) has a diameter of 1-3 cm.

[0018] Preferably, the crystal transformation agent solution in step (3) is configured as follows: magnesium chloride accounts for 25%-40% of the total mass of the solution; magnesium sulfate accounts for 0.42%-0.84% of the total mass of the solution; trisodium citrate accounts for 0-0.5% of the total mass of the solution; and maleic acid accounts for 0-0.5% of the total mass of the solution.

[0019] Preferably, the mass of calcium chloride in step (4) accounts for 0.2%-0.4% of the total mass of the solution, and the stirring time after adding calcium chloride is 10-20 min.

[0020] Preferably, the mass ratio of phosphogypsum to crystal transformation agent solution in step (4) is 1: (3-8).

[0021] Preferably, the rotation speed in step (4) is 150-300 rpm, the reaction temperature is 90-98 ℃, and the reaction time is 5-10 h.

[0022] Preferably, the reaction kettle in step (4) has an iron mesh at the bottom to filter the bagged phosphogypsum after reaction.

[0023] Preferably, the washing water in step (5) is boiling water, the washing times are 3 times, and the drying temperature of the filter cake is 60-120℃; the powdering machine is a FW-100 type high-speed universal pulverizer, and the powdering time is 10-30s.

[0024] The present application has the following advantages:

[0025] 1. In the process for preparing α-hemihydrate gypsum according to the present application, no autoclave or hydrothermal kettle and other high-temperature and high-pressure special equipment is used, and the process can be carried out in a normal-pressure reaction kettle, which has a lower requirement for equipment and a relatively lower production temperature, thereby reducing the energy consumption in the production process. The powder-like phosphogypsum is prepared into bagged phosphogypsum, and the dihydrate gypsum dissolution zone and the hemihydrate gypsum crystallization zone in the process for preparing high-strength gypsum by the normal-pressure salt solution method are separated, thereby reducing the heterogeneous nucleation rate and reaction rate in the crystal transformation process. Therefore, the prepared α-hemihydrate gypsum has a larger particle size, is easy to filter, has a slower hydration, has a lower water requirement for standard consistency after being pulverized, has a higher strength, and has an absolute dry compressive strength of more than 40 MPa. The bagged filter cloth can achieve a certain impurity separation effect, further increase the whiteness of the high-strength gypsum powder product, and the slurry is relatively large, the production efficiency is relatively high, and the crystal transformation agent solution can be recycled.

[0026] 2. The present application prepares high-strength gypsum with a strength higher than that of the standard JC / T2038-2010 α40 grade and a blue light whiteness of more than 60, which has stable quality, a low requirement for equipment in the preparation process, a low energy consumption, a larger crystal particle size of the prepared high-strength gypsum, a good filtering performance, a slow hydration, and basically no hardening phenomenon in the filtering and drying process. The phosphogypsum is further purified, the whiteness of the high-strength α-gypsum powder product is increased, the economic added value is improved, the problems of high energy consumption, unstable quality, low whiteness, and low strength in the preparation of high-strength gypsum from phosphogypsum are solved, the phosphogypsum is helpful for consumption, the increasingly serious stacking problem of phosphogypsum is solved, and the high-value utilization of phosphogypsum is realized. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 the hemihydrate gypsum obtained in Example 7 (without being pulverized);

[0028] Figure 2 the high-strength α-gypsum product after being pulverized in Example 7;

[0029] The present application is further described below in conjunction with examples, but is not limited to the basis of the examples. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with specific embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0031] Embodiment 1

[0032] A process for preparing high-strength alpha gypsum powder from phosphogypsum, comprising the following steps:

[0033] 1) Purification and purification of phosphogypsum: take the phosphogypsum by-produced in the production process of wet-process phosphoric acid by the dihydrate process, remove the soluble phosphorus, soluble fluorine, silicon dioxide, Al2O3, Fe2O3 and organic matter and other impurities in the phosphogypsum by water washing-flotation to obtain purified phosphogypsum for standby.

[0034] 2) Preparation of high-strength gypsum: take 4140g industrial-grade magnesium chloride hexahydrate and 1860g H2O to configure a crystal transformation agent solution, add it into a 5L reaction kettle, heat to 95℃, start stirring, the stirring speed is 170rpm, add 1.2Kg purified phosphogypsum, after 2h of reaction, long rod-shaped alpha-hemihydrate gypsum is obtained.

[0035] 3) Post-treatment: filter the slurry, wash it with boiling water for 3 times, then dry the filter cake in an 80℃ oven for 4h, and then use a pulverizer to grind the long rod-shaped alpha-hemihydrate gypsum for 10s to reduce its aspect ratio, so as to reduce the water requirement for standard consistency and improve the mechanical strength of the product.

[0036] 4) According to the standard JC / T2038-2010, the water requirement for standard consistency of the alpha-hemihydrate gypsum prepared in this embodiment is 36%, the initial setting time is 5min, the final setting time is 13min, the 2h flexural strength is 5.3MPa, the dry compressive strength is 31.4MPa, and the blue light whiteness is 48.2.

[0037] Embodiment 2

[0038] A process for preparing high-strength alpha gypsum powder from phosphogypsum, comprising the following steps

[0039] 1) Purification and purification of phosphogypsum: take the phosphogypsum by-produced in the production process of wet-process phosphoric acid by the dihydrate process, remove the soluble phosphorus, soluble fluorine, silicon dioxide, Al2O3, Fe2O3 and organic matter and other impurities in the phosphogypsum by water washing-flotation to obtain purified phosphogypsum for standby.

[0040] 2) Preparation of bagged phosphogypsum precursor: take the purified phosphogypsum, wrap it with 15μm nylon filter cloth to prepare bagged phosphogypsum with a diameter of about 1cm.

[0041] 3) High-strength gypsum preparation: Take 4140g of industrial-grade magnesium chloride hexahydrate, 1860g of H2O to prepare a crystal transformation agent solution, add it to a 5L reaction kettle, heat to 95°C, start stirring at 170rpm, add 1.2Kg (not including bag weight) of bagged phosphogypsum, after 6h of reaction, long rod-shaped α-hemihydrate gypsum is obtained.

[0042] 4) Post-treatment: filter the slurry, wash it quickly with boiling water for 3 times, then place the filter cake in a 90°C oven to dry for 2h, and α-high-strength gypsum product is obtained.

[0043] 5) According to standard JC / T2038-2010, the water requirement for standard consistency of the α-hemihydrate gypsum prepared in this example is 32%, the initial setting time is 8min, the final setting time is 19.5min, the 2h flexural strength is 5.5MPa, the absolute dry compressive strength is 41.7MPa, and the blue light whiteness is 64.5.

[0044] Example 3

[0045] A process for preparing high-strength α-gypsum powder from phosphogypsum, comprising the following steps

[0046] 1) Phosphogypsum purification and purification: Take the phosphogypsum produced by the wet-process phosphoric acid production process, remove the soluble phosphorus, soluble fluorine, silicon dioxide, Al2O3, Fe2O3 and organic matter and other impurities in the phosphogypsum by water washing-flotation to obtain purified phosphogypsum for standby use.

[0047] 2) Preparation of bagged phosphogypsum precursor: Take the purified phosphogypsum, wrap it with 15μm nylon filter cloth to prepare bagged phosphogypsum with a diameter of about 2cm.

[0048] 2) Take 4580g of industrial-grade magnesium chloride hexahydrate, 1420g of H2O, 6g of trisodium citrate, and prepare a crystal transformation agent solution, add it to a 5L reaction kettle, heat to 98°C, start stirring at 200rpm, add 1.2Kg of bagged phosphogypsum, and after 10h of reaction, short rod-shaped phosphogypsum is obtained.

[0049] 3) Post-treatment: filter the slurry, wash it quickly with boiling water for 3 times, then place the filter cake in a 80°C oven to dry for 4h, and α-high-strength gypsum product is obtained.

[0050] 4) According to standard JC / T2038-2010, the water requirement for standard consistency of the α-hemihydrate gypsum prepared in this example is 32.5%, the initial setting time is 25min, the final setting time is 63.5min, the 2h flexural strength is 4.1MPa, the absolute dry compressive strength is 30.3MPa, and the blue light whiteness is 62.1.

[0051] Example 4

[0052] A process for preparing high-strength alpha gypsum powder from phosphogypsum

[0053] 1) Purification and purification of phosphogypsum: phosphogypsum by-produced in the process of wet-process phosphoric acid production by the dihydrate method is subjected to water washing-flotation to remove soluble phosphorus, soluble fluorine, silicon dioxide, Al203, Fe203and organic matter and other impurities in the phosphogypsum to obtain purified phosphogypsum for standby use.

[0054] 2) Preparation of bagged phosphogypsum precursor: the purified phosphogypsum is wrapped with 15 μm nylon filter cloth to prepare bagged phosphogypsum with a diameter of about 2 cm.

[0055] 3) 5610g of the filtrate after reaction in Example 3 is taken, 390g of industrial-grade magnesium chloride hexahydrate is added to prepare a crystal transformation agent solution, which is added into a 5L reaction kettle, heated to 98℃, then stirring is started with a speed of 180rpm, 1.2Kg of bagged phosphogypsum is added, and reaction is carried out for 8h to obtain long rod-shaped alpha-hemihydrate gypsum.

[0056] 4) Post-treatment: the slurry is filtered, washed quickly with boiling water for 3 times, the filter cake is dried in a 90℃ oven for 2h, then the long rod-shaped alpha-hemihydrate gypsum is ground for 10s by a grinding machine to reduce its aspect ratio, thereby reducing the water requirement for standard consistency and improving the mechanical strength of the product, to obtain alpha-high-strength gypsum product.

[0057] 5) The alpha-hemihydrate gypsum prepared in this example is measured according to the standard JC / T2038-2010, and the water requirement for standard consistency is 33%, the initial setting time is 28min, the final setting time is 58min, the 2h flexural strength is 4.5MPa, the dry compressive strength is 34.1MPa, and the blue light whiteness is 62.6.

[0058] Example 5

[0059] A process for preparing high-strength alpha gypsum powder from phosphogypsum, comprising the following steps

[0060] 1) Purification and purification of phosphogypsum: phosphogypsum by-produced in the process of wet-process phosphoric acid production by the dihydrate method is subjected to water washing-flotation to remove soluble phosphorus, soluble fluorine, silicon dioxide, Al203, Fe203and organic matter and other impurities in the phosphogypsum to obtain purified phosphogypsum for standby use.

[0061] 2) Preparation of bagged phosphogypsum precursor: the purified phosphogypsum is wrapped with 15 μm nylon filter cloth to prepare bagged phosphogypsum with a diameter of about 1 cm.

[0062] 3) High-strength gypsum preparation: Take 4140g of industrial-grade magnesium chloride hexahydrate, 1860g of H2O, and 0.5g of trisodium citrate, and configure them into a crystal modifier solution. Add them into a 5L reaction kettle, heat to 96°C, start stirring at 180rpm, add 1.2Kg of bagged phosphogypsum, and after 6h of reaction, obtain long rod-shaped α-hemihydrate gypsum.

[0063] 4) Post-processing: Filter the slurry, quickly wash it with boiling water for 3 times, then place the filter cake in a 90°C oven for drying for 2h, obtain α-high-strength gypsum product, then use a pulverizer to pulverize the long rod-shaped α-hemihydrate gypsum for 15s to reduce its aspect ratio, thereby reducing its water requirement for standard consistency and improving the mechanical strength of the product, and obtain α-high-strength gypsum product.

[0064] 5) According to the reference standard JC / T2038-2010, the water requirement for standard consistency of the α-hemihydrate gypsum prepared in this embodiment is 33.5%, the initial setting time is 13min, the final setting time is 25min, the 2h flexural strength is 5.1MPa, the dry compressive strength is 42.8MPa, and the blue light whiteness is 64.3.

[0065] Example 6

[0066] A process for preparing high-strength α-gypsum powder from phosphogypsum, comprising the following steps

[0067] 1) Phosphogypsum purification and purification: Take the phosphogypsum byproduct of the wet-process phosphoric acid production process by the dihydrate process, remove the soluble phosphorus, soluble fluorine, silicon dioxide, Al2O3, Fe2O3, and organic matter impurities in the phosphogypsum by water washing-flotation to obtain purified phosphogypsum for standby use.

[0068] 2) Preparation of bagged phosphogypsum precursor: Take the purified phosphogypsum, wrap it with 15μm nylon filter cloth to make bagged phosphogypsum with a diameter of about 1cm.

[0069] 3) High-strength gypsum preparation: Take 4140g of industrial-grade magnesium chloride hexahydrate, 1860g of H2O, and 0.5g of trisodium citrate, and configure them into a crystal modifier solution. Add them into a 5L reaction kettle, heat to 96°C, start stirring at 180rpm, add 1.2Kg of bagged phosphogypsum, and after 6h of reaction, obtain long rod-shaped α-hemihydrate gypsum.

[0070] 4) Post-processing: Filter the slurry, quickly wash it with boiling water for 3 times, then place the filter cake in a 90°C oven for drying for 2h, obtain α-high-strength gypsum product, then use a pulverizer to pulverize the long rod-shaped α-hemihydrate gypsum for 15s to reduce its aspect ratio, thereby reducing its water requirement for standard consistency and improving the mechanical strength of the product, and obtain α-high-strength gypsum product.

[0071] 5) The α-hemihydrate gypsum prepared in this example has a water requirement of 32% for standard consistency, an initial setting time of 11.5 min, a final setting time of 20 min, a 2h flexural strength of 5.4 MPa, an absolute dry compressive strength of 45.6 MPa, and a blue light whiteness of 62.9, as measured according to the standard JC / T2038-2010.

[0072] Example 7

[0073] A process for preparing high-strength α-gypsum powder from phosphogypsum, comprising the following steps

[0074] 1) Purification of phosphogypsum: Take the phosphogypsum byproduct from the wet-process phosphoric acid production process using the dihydrate method, and remove the soluble phosphorus, soluble fluorine, silicon dioxide, Al203, Fe203, and organic matter and other impurities in the phosphogypsum by water washing-flotation to obtain purified phosphogypsum for standby use.

[0075] 2) Preparation of bagged phosphogypsum precursor: Take the purified phosphogypsum, and use 15 μm nylon filter cloth to wrap it to form bagged phosphogypsum with a diameter of about 1 cm.

[0076] 3) Preparation of high-strength gypsum: Take 4140 g of industrial-grade magnesium chloride hexahydrate, 1860 g of H20, 0.5 g of trisodium citrate, 0.3 g of maleic acid, and 12.3 g of magnesium sulfate heptahydrate to configure a crystal transformation agent solution, add it to a 5 L reaction kettle, heat it to 98°C, start stirring at a speed of 160 rpm, add 5.5 g of calcium chloride, stir for 15 min, then add 1.0 kg of bagged phosphogypsum, and react for 6 h to obtain long rod-shaped α-hemihydrate gypsum.

[0077] 4) Post-treatment: Filter the slurry, wash it quickly with boiling water for 3 times, then place the filter cake in an 80°C oven for drying for 4 h to obtain α-high-strength gypsum products, and then use a pulverizer to pulverize the long rod-shaped α-hemihydrate gypsum for 10 s to reduce its aspect ratio, thereby reducing its water requirement for standard consistency and improving the mechanical strength of the product, to obtain α-high-strength gypsum products.

[0078] 5) The α-hemihydrate gypsum prepared in this example has a water requirement of 32% for standard consistency, an initial setting time of 11.5 min, a final setting time of 20 min, a 2h flexural strength of 5.4 MPa, an absolute dry compressive strength of 45.6 MPa, and a blue light whiteness of 62.9, as measured according to the standard JC / T2038-2010.

[0079] Example 8

[0080] A process for preparing high-strength α-gypsum powder from phosphogypsum, comprising the following steps

[0081] 1) Phosphogypsum purification and purification: take the by-product phosphogypsum of the wet-process phosphoric acid production process of the dihydrate process, remove the soluble phosphorus, soluble fluorine, silicon dioxide, Al203, Fe203and organic matter and other impurities in the phosphogypsum by water washing-flotation to obtain purified phosphogypsum for standby.

[0082] 2) Preparation of bagged phosphogypsum precursor: take the purified phosphogypsum, wrap it with 15 μm nylon filter cloth to make bagged phosphogypsum with a diameter of about 1 cm.

[0083] 3) High-strength gypsum preparation: take 5610g filtrate in Example 7, 390g industrial-grade magnesium chloride hexahydrate, 0.5g trisodium citrate, 13.5g magnesium sulfate heptahydrate to configure into a crystal modifier solution, add it into a 5L reaction kettle, heat it to 98℃, start stirring at a speed of 160rpm, add 6g calcium chloride, stir for 20min, then add 1.5Kg bagged phosphogypsum, react for 6h to obtain long rod-shaped α-hemihydrate gypsum.

[0084] 4) Post-treatment: filter the slurry, wash it quickly with boiling water for 3 times, then place the filter cake in a 90℃ oven to dry for 2h to obtain α-high-strength gypsum product, then use a pulverizer to pulverize the long rod-shaped α-hemihydrate gypsum for 10s to reduce its aspect ratio, thereby reducing its water requirement for standard consistency and improving the mechanical strength of the product, to obtain α-high-strength gypsum product.

[0085] 5) According to the standard JC / T2038-2010, the water requirement for standard consistency of the α-hemihydrate gypsum prepared in this example is 32.5%, the initial setting time is 11.5min, the final setting time is 18min, the 2h flexural strength is 5.4MPa, the absolute dry compressive strength is 44.8MPa, and the blue light whiteness is 63.7.

[0086] Table 1 Test results of high-strength gypsum products obtained under different examples

[0087]

[0088] As can be seen from Table 1, by comparing Example 1 with Example 2, it can be seen that by reacting the phosphogypsum into a bagged phosphogypsum precursor, the mechanical strength of the product can be significantly improved, and the whiteness of the product can also be improved; by comparing Example 2 with Example 3, Example 5 and Example 6, it can be seen that too high an amount of trisodium citrate will reduce the strength of the product, and trisodium citrate at about 0.008% can improve the strength of the product to a certain extent, and will increase the initial and final setting time of the product, and can have a certain synergistic effect with maleic acid; by comparing Example 6 with Example 7, it can be seen that the addition of magnesium sulfate heptahydrate can react with calcium chloride in the solution to quickly reach the saturation degree of the crystal modifier solution and produce crystal seeds, thereby reducing the reaction time; by comparing Example 7 with Example 8, it can be seen that the crystal modifier solution can be recycled.

[0089] The above merely provides the relatively optimal embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing high-strength α-gypsum powder using phosphogypsum, characterized in that the steps include... include: (1) The purified phosphogypsum was obtained by washing and flotation with water; (2) Preparation of bagged phosphogypsum precursor: The purified phosphogypsum is wrapped in filter cloth and tied tightly with rope to form spherical bags of phosphogypsum with a diameter of 1~3cm for later use; (3) Preparation of crystal-converting agent solution: Take magnesium chloride hexahydrate, magnesium sulfate heptahydrate, trisodium citrate, and maleic acid, add water and dissolve to prepare crystal-converting agent solution; (4) Crystallization reaction: Take the crystallization agent solution prepared in step (3) and add it into the atmospheric pressure reactor. Set the rotation speed and heat it to the set temperature. Add calcium chloride and stir for a certain time. Then add the bagged phosphogypsum obtained in step (2) into the reactor and react at constant temperature and atmospheric pressure for a period of time to obtain hemihydrate gypsum slurry. (5) Filtration, washing, drying and grinding: After filtering and washing the hemihydrate gypsum slurry obtained in step (4), filter cake A is obtained. After drying, it is ground to obtain high-strength α-gypsum product.

2. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, In step (1), the purified phosphogypsum has a calcium sulfate dihydrate content of ≥96%, a silica content of ≤3%, an organic matter content of ≤0.3%, and a pH of 6~7.

3. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, The filter cloth in step (2) has a pore size of 10~20μm, and both the filter cloth and the string are made of nylon.

4. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, The crystallizing agent solution in step (3) is prepared as follows: magnesium chloride accounts for 25% to 40% of the total mass of the solution; magnesium sulfate accounts for 0.42% to 0.84% ​​of the total mass of the solution; trisodium citrate accounts for 0 to 0.5% of the total mass of the solution; and maleic acid accounts for 0 to 0.5% of the total mass of the solution.

5. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, In step (4), the mass of calcium chloride accounts for 0.2% to 0.4% of the total mass of the solution, and the stirring time after adding calcium chloride is 10 to 20 minutes.

6. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, In step (4), the mass ratio of phosphogypsum to crystallizing agent solution is 1:(3~8).

7. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, The rotation speed in step (4) is 150~300 rpm, the reaction temperature is 90~98℃, and the reaction time is 5~10h.

8. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, In step (4), there is a wire mesh at the bottom of the reactor to filter the phosphogypsum bag after the reaction.

9. The method for preparing high-strength α-gypsum powder using phosphogypsum according to claim 1, characterized in that, In step (5), the washing water is boiling water, the washing is performed 3 times, and the filter cake drying temperature is 60~120℃. 5) The grinding machine is the FW-100 high-speed universal pulverizer, and the grinding time is 10~30s.

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