阅读说明：本技术 一种干法制备高强建筑石膏的方法 (Method for preparing high-strength building gypsum by dry method ) 是由 张宜仓 夏举佩 于 2021-07-16 设计创作，主要内容包括：本发明涉及一种干法制备高强建筑石膏的方法,属于工业固体废弃物资源化利用和建筑材料应用技术领域。磷石膏经石灰粉调节PH值后,加入转晶剂和偶联剂进行分散、预热、转晶、排气、干燥、陈化、粉磨制得高强建筑石膏。本发明不需要经过水洗,仅用石灰调整磷石膏pH即可,避免了水资源的浪费和洗液难以回收利用问题,并且符合《GB/T 9776-2008建筑石膏》国家标准3.0级要求。(The invention relates to a method for preparing high-strength building gypsum by a dry method, and belongs to the technical field of resource utilization of industrial solid wastes and application of building materials. After the pH value of the phosphogypsum is adjusted by lime powder, a crystal transformation agent and a coupling agent are added for dispersing, preheating, crystal transformation, exhausting, drying, aging and grinding to prepare the high-strength building gypsum. The method does not need water washing, only needs lime to adjust the pH value of the phosphogypsum, avoids the problems of water resource waste and difficult recycling of washing liquor, and meets the 3.0-level requirement of the national standard GB/T9776-2008 building gypsum.)

1. A method for preparing high-strength building gypsum by a dry method is characterized by comprising the following steps: after the pH value of the phosphogypsum is adjusted by lime powder, adding a crystal transformation agent and a coupling agent for dispersing, preheating, crystal transformation, exhausting, drying, aging and grinding to prepare the high-strength building gypsum, wherein the preparation method comprises the following specific steps:

(1) pretreatment of raw materials: crushing phosphogypsum, and adding lime powder to adjust the pH value to obtain phosphogypsum powder;

(2) dispersing: adding a crystal transfer agent and a coupling agent into the phosphogypsum powder prepared in the step (1) for forced dispersion;

(3) preheating: preheating the phosphogypsum powder treated in the step (2) by using dried tail gas to ensure that the temperature of the phosphogypsum powder is 50-70 ℃ and the moisture content is less than 5 percent;

(4) crystal transformation: introducing steam into the phosphogypsum powder treated in the step (3) for dehydration and crystal transformation to obtain building gypsum powder;

(5) and (3) drying: hot air flow dries the building gypsum powder to the free water content less than 0.5%;

(6) aging: aging the building gypsum powder treated in the step (5) in a normal-temperature, dry and closed environment;

(7) crushing: and (4) grinding the building gypsum powder treated in the step (6) to obtain the high-strength building gypsum powder.

2. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (1), the particle size of the phosphogypsum is less than 5% of the sieve residue of a 1mm square-hole sieve, and the addition amount of the lime powder is 0.6-1% of the mass of the phosphogypsum.

3. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (1), the PH value is 6-9.

4. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (2), the addition amount of the crystal transformation agent is 0.2-0.5 per mill of the mass of the phosphogypsum, and the addition amount of the coupling agent is 0.4-0.8 per mill of the mass of the phosphogypsum; the grain size of the crystal transfer agent and the coupling agent is less than 10 percent of the screen allowance of a square hole screen with the grain size of 45 mu m.

5. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (2), the crystal transformation agent is at least two of cetyl trimethyl quaternary ammonium bromide, triethanolamine oleate soap, sodium acrylate, calcium stearate, sulfamic acid, sodium polycarboxylate and potassium hydrogen phthalate, and the coupling agent is two or three of phthalate coupling agent TMC-201, aluminate coupling agent F-1 and silane coupling agent KH 792.

6. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (3), the temperature of the dried tail gas is 50-70 ℃.

7. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (4), steam with the temperature of 120-130 ℃ is uniformly introduced for 30-40min at the constant speed of 20-30L/min, and is exhausted after heat preservation for 1.5-2 h.

8. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (5), the temperature of the hot gas flow is 500-600 ℃.

9. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (6), aging is carried out for 12-24h in a closed environment at the temperature of 20-25 ℃ and the relative humidity of 40-60%.

10. The dry process for preparing high strength building gypsum according to claim 1, wherein: in the step (7), the high-strength building gypsum powder is sieved by a 80-mesh sieve, and the balance is less than or equal to 10 percent.

Technical Field

The invention relates to a method for preparing high-strength building gypsum by a dry method, and belongs to the technical field of resource utilization of industrial solid wastes and application of building materials.

Background

Phosphogypsum is an industrial byproduct generated in the process of industrial wet-process phosphoric acid and phosphate fertilizer, about 4.5 t-5 t of phosphogypsum is generated per 1 ton of phosphoric acid, and about 2.8 million tons of phosphogypsum are generated every year all over the world. The main component of phosphogypsum is calcium sulfate dihydrate, the content of which is generally more than 80 percent, and in addition, harmful impurities such as phosphorus, fluorine, organic matters and the like are also contained. Because the different processes for industrial production of phosphoric acid lead to different components and impurity types of the phosphogypsum, the comprehensive utilization difficulty of the phosphogypsum is larger.

At present, the phosphogypsum is mainly treated by adopting a stockpiling mode, the treatment mode not only occupies a large amount of land resources, but also contains soluble phosphorus, fluorine and other substances which are corrosive to organisms, and long-term stockpiling can cause harmful substances to be soaked into soil, surface (lower) water bodies and vegetation, thus seriously influencing the ecological environment of the area and simultaneously puzzling the sustainable development of the phosphorus chemical industry.

With the increase of ecological environmental protection pressure, the Yangtze river economy carries on the action of clearing solid wastes, and particularly, the 'implementation scheme of the action of clearing and regulating the three phosphorus special item in Yangtze river' which is printed by the ministry of ecological environment in 4 months in 2019 indicates that the concentrated clearing and regulating treatment is carried out in 7 provinces (cities) such as Hubei, Sichuan, Guizhou, Yunnan, Hunan, Chongqing, Jiangsu and the like, wherein one of the 'three key' is the phosphogypsum reservoir. Strict ecological environment protection requirements and an admission threshold of comprehensive utilization ensure that the comprehensive utilization of the phosphogypsum is imperative and urgent.

The building gypsum is mainly beta-semi-hydrated gypsum, can be used for producing whitewash gypsum, plastering gypsum, gypsum mortar, gypsum wallboards, ceilings, decorative acoustic boards, gypsum blocks, other decorative parts and the like, and is a building material widely applied to building engineering. The building gypsum is prepared by heating and calcining natural dihydrate gypsum or chemical gypsum at a certain temperature to dehydrate and decompose the dihydrate gypsum to obtain a product with hemihydrate gypsum as a main component. The phosphogypsum has similar main components with natural gypsum and can replace the natural gypsum to prepare building gypsum. However, due to the existence of impurities, the strength of the building gypsum prepared by stir-frying the phosphogypsum without washing and impurity removal can hardly meet the requirement of the 3.0 level of the national standard GB/T9776-2008 building gypsum.

For this reason, a large number of researchers have been exploring how to massively utilize phosphogypsum. At present, the production method of the alpha-hemihydrate gypsum mainly comprises the following steps: the steam pressing method, the hydrothermal method, the normal pressure salt dissolving method, the dry steaming method and the like have advantages and disadvantages, but in general, no matter what method is adopted, in order to obtain the alpha-hemihydrate gypsum, dehydration is carried out in high-pressure equipment or in solution, such as: CN201510845093.2 discloses a method for producing PVC profiles by using phosphogypsum to prepare alpha-hemihydrate gypsum, beta-hemihydrate gypsum and anhydrite as fillers, CN201510667340.4 discloses a method for preparing high-strength alpha-hemihydrate gypsum by a dry method, CN201210552607.1 discloses a method for preparing high-strength alpha-hemihydrate gypsum by using calcium carbide sludge modified phosphogypsum in a normal pressure hydrothermal method, cn201110101252.x discloses a process method for producing alpha-hemihydrate gypsum by using industrial by-product gypsum, CN201210226224.5 discloses a process method for producing alpha-hemihydrate gypsum powder at low temperature and low pressure, CN200810121470.8 discloses a method for converting desulfurized gypsum into alpha-hemihydrate gypsum in normal pressure KCl solution, and CN201711303247.0 is a method for preparing alpha-beta composite hemihydrate gypsum by using phosphogypsum.

In conclusion, the process for preparing the beta-hemihydrate gypsum by using the phosphogypsum in the prior art is complex and has weak strength; the cost of the alpha-hemihydrate gypsum prepared with phosphogypsum is too high. A method for preparing building gypsum powder which has simple process and short preparation time and meets the requirement of the 3.0 level of the national standard GB/T9776-2008 building gypsum is needed.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art and provides a method for preparing high-strength building gypsum by a dry method, which adopts phosphogypsum in a phosphogypsum yard as a raw material to prepare building gypsum powder which is not washed and fried and meets the requirement of the 3.0 level of the national standard GB/T9776-plus 2008 building gypsum by dry method production, thereby solving the problem of resource utilization of the phosphogypsum at present.

In order to solve the technical problems, the invention provides a method for preparing high-strength building gypsum by a dry method, phosphogypsum is subjected to pH value adjustment by lime powder, and then is added with a crystal transformation agent and a coupling agent for dispersion, preheating, crystal transformation, exhaust, drying, aging and grinding to prepare the high-strength building gypsum, and the method comprises the following specific preparation steps:

(1) pretreatment of raw materials: and (3) crushing the phosphogypsum, and adding lime powder to adjust the pH value to obtain phosphogypsum powder.

(2) Dispersing: adding a crystal transfer agent and a coupling agent into the phosphogypsum powder prepared in the step (1) and dispersing by using a horizontal rotary vane forced dispersion machine.

(3) Preheating: and (3) preheating the phosphogypsum powder treated in the step (2) by using dried tail gas in a rotary dryer, so that the temperature of the phosphogypsum powder is 50-70 ℃, and the moisture content is less than 5%. Tail gas preheating makes 5-10% of gypsum be removed into semi-hydrated gypsum as seed crystal for subsequent treatment. And introducing tail gas into the dryer at a constant speed of 20-30L/min to uniformly heat the phosphogypsum powder.

(4) Crystal transformation: and (4) filling the phosphogypsum powder treated in the step (3) into a vertical crystal conversion kettle, and introducing steam to carry out dehydration and crystal conversion to obtain the building gypsum powder.

(5) And (3) drying: the building gypsum powder is dried by hot air flow until the free water content is less than 0.5 percent, and the flow rate of the hot air flow is 200 plus 500L/min. Drying may be carried out using a pneumatic dryer.

(6) Aging: and (3) aging the building gypsum powder treated in the step (5) for 12-24h at 20-25 ℃ and under a closed environment with a relative humidity of 40% -60% and normal pressure.

(7) Crushing: and (4) grinding the building gypsum powder treated in the step (6) to obtain the high-strength building gypsum powder.

In the step (1), the particle size of the phosphogypsum is less than 5% of the screen allowance of a 1mm square-hole screen, and the phosphogypsum is sourced from a gypsum yard.

In the step (1), the addition amount of the lime powder is 0.6-1% of the mass of the phosphogypsum.

In the step (1), the PH value is 6-9.

In the step (2), the addition amount of the crystal transformation agent is 0.2-0.5 per mill of the mass of the phosphogypsum, and the addition amount of the coupling agent is 0.4-0.8 per mill of the mass of the phosphogypsum. The grain size of the crystal transfer agent and the coupling agent is less than 10 percent of the screen allowance of a square hole screen with the grain size of 45 mu m.

In the step (2), the crystal modifier is at least two of cetyl trimethyl quaternary ammonium bromide, triethanolamine oleate soap, sodium acrylate, calcium stearate, sulfamic acid, sodium polycarboxylate and potassium hydrogen phthalate, and the substances forming the crystal modifier have no mass ratio requirement, meet the actual requirement and are available in any proportion.

The coupling agent is two or three of phthalate coupling agent TMC-201, aluminate coupling agent F-1 and silane coupling agent KH792, the mass ratio of the substances forming the coupling agent is not required, the actual requirements are met, and any proportion is adopted.

In the step (3), the temperature of the dried tail gas is 50-70 ℃.

In the step (4), steam with the temperature of 120-130 ℃ is uniformly introduced for 30-40min at the constant speed of 20-30L/min, and the steam is exhausted after heat preservation for 1.5-2 h.

In the step (5), the temperature of the hot gas flow is 500-600 ℃.

In the step (7), the high-strength building gypsum powder is sieved by a 80-mesh sieve, and the balance is less than or equal to 10 percent.

The high-strength building gypsum powder prepared by the invention is alpha-beta composite semi-hydrated gypsum, and three components of the alpha-beta composite semi-hydrated gypsum are determined according to GB/T36141-2018 building gypsum phase composition analysis method; according to GB/T17669.4-1999 determination of physical properties of the building gypsum neat paste, the standard thickening time and the initial and final setting time are determined; according to GB/T17699.3-1999 determination of mechanical properties of building gypsum, the 2h flexural strength is more than 3.0MPa, and the compressive strength is more than 6.0 MPa.

Compared with the existing method for preparing the building gypsum meeting the 3.0 grade by taking the phosphogypsum as the raw material, the method does not need to be washed by water, and only needs to adjust the pH value of the phosphogypsum by lime, so that the problems of water resource waste and difficult recycling of washing liquor are solved. In addition, the energy consumption of the invention is equivalent to that of the fried beta powder, the performance is greatly improved, the production process is simple, and the invention has positive significance for the large-scale utilization of the phosphogypsum; the addition of a small amount of the crystal transfer agent and the coupling agent shortens the conversion time and can meet the requirement of large-scale industrial treatment.

Compared with the calcining process in the prior art, the high-strength building gypsum powder prepared by the invention has the advantages that the heating treatment time is greatly shortened, the processing efficiency is improved, and the compressive strength is also stronger than that of the gypsum powder prepared by the prior art. As in the following table:

	calcination process	The invention
			Heating temperature/. degree.C	150-180	120-130
Heating time/h	6-8	1.5-2
			Compressive strength/MPa	≥4.0	7.0-16.0

The invention utilizes solid wastes as raw materials, changes wastes into valuables and realizes the utilization of waste resources. Meanwhile, the invention has low production cost and simple process, and achieves higher economic benefit.

Drawings

FIG. 1 is a schematic process flow diagram of the present invention.

Detailed Description

The following further describes the embodiments of the present invention in detail. The techniques or products not mentioned in the examples are all conventional products which are available in the prior art or can be obtained by purchase.

Example 1: as shown in figure 1, in the method for preparing the high-strength building gypsum by the dry method, after the phosphogypsum is subjected to pH value adjustment by lime powder, a crystal transformation agent and a coupling agent are added for dispersing, preheating, crystal transformation, exhausting, drying, aging and grinding to prepare the high-strength building gypsum, and the preparation method specifically comprises the following steps:

(1) pretreatment of raw materials: crushing the phosphogypsum to 4.5 percent of the screen residue of a square-hole screen with the granularity of 1mm, adding lime powder with the mass of 0.6 percent of the phosphogypsum, and adjusting the pH value to 6 to obtain phosphogypsum powder;

(2) dispersing: adding a crystal transfer agent with the mass of 0.2 per mill of the phosphogypsum and a coupling agent with the mass of 0.4 per mill of the phosphogypsum into the phosphogypsum powder prepared in the step (1) and dispersing by using a horizontal rotary vane forced dispersion machine. The crystal transformation agent consists of hexadecyl trimethyl quaternary ammonium bromide and potassium hydrogen phthalate with the mass ratio of 1:2, and the coupling agent consists of phthalate ester coupling agent TMC-201 and aluminate ester coupling agent F-1 with the mass ratio of 1: 2. The grain size of the crystal transfer agent and the coupling agent is 9 percent of the screen allowance of a square hole screen with the grain size of 45 mu m.

(3) Preheating: and (3) preheating the phosphogypsum powder treated in the step (2) by using tail gas at 50 ℃ in a rotary dryer, so that the temperature of the phosphogypsum powder is 50 ℃ and the moisture content is 3%. Tail gas preheating makes 5-10% of gypsum be removed into semi-hydrated gypsum as seed crystal for subsequent treatment. And introducing tail gas into the dryer at a constant speed of 20L/min to uniformly heat the phosphogypsum powder.

(4) Crystal transformation: filling the phosphogypsum powder treated in the step (3) into a vertical crystal conversion kettle, and introducing steam at 120 ℃ for dehydration and crystal conversion to obtain building gypsum powder; introducing steam at a constant speed of 20L/min for 30min, keeping the temperature for 1.5h, and then dehydrating, crystallizing and exhausting to obtain the building gypsum powder.

(5) And (3) drying: drying with airflow dryer, and drying with 500 deg.C hot air flow until free water content is 0.45% and flow rate of hot air flow is 200L/min.

(6) Aging: aging the building gypsum powder treated in the step (5) for 12 hours at 20 ℃ under a sealed environment with a relative humidity of 40% and a normal pressure;

(7) crushing: and (4) grinding the building gypsum powder treated in the step (6) until the building gypsum powder is sieved by a 80-mesh sieve, and obtaining the high-strength building gypsum powder, wherein the balance is 10%.

The high-strength building gypsum powder prepared by the invention is subjected to physical property detection according to GB/T36141-2018, GB/T17669.4-1999 and GB/T17669.3-1999, and meets the requirement index of GB/T9776-2008 building gypsum, national standard 3.0 grade, as shown in the following table:

attached water/%	Without water/%)	Half water/%	Dihydration/%	Standard consistency/%	Initial setting time/min	Final setting time/min	Bending resistance/MPa	compression/MPa resistance
									0.45	0	70.40	10.91	0.55	10	25	3.12	7.74

Example 2: as shown in figure 1, in the method for preparing the high-strength building gypsum by the dry method, after the phosphogypsum is subjected to pH value adjustment by lime powder, a crystal transformation agent and a coupling agent are added for dispersing, preheating, crystal transformation, exhausting, drying, aging and grinding to prepare the high-strength building gypsum, and the preparation method specifically comprises the following steps:

(1) pretreatment of raw materials: crushing the phosphogypsum to 4.5 percent of the screen allowance of a square-hole screen with the granularity of 1mm, adding lime powder with the mass of 1 percent of the phosphogypsum, and adjusting the pH value to 9 to obtain phosphogypsum powder;

(2) dispersing: adding a crystal transfer agent with the mass of 0.5 per mill of the phosphogypsum and a coupling agent with the mass of 0.6 per mill of the phosphogypsum into the phosphogypsum powder prepared in the step (1) and dispersing by using a horizontal rotary vane forced dispersion machine. The crystal transformation agent consists of triethanolamine oleate soap, sulfamic acid and sodium polycarboxylate in a mass ratio of 1:3:2, and the coupling agent consists of aluminate coupling agent F-1 and silane coupling agent KH792 in a mass ratio of 1: 3. The grain size of the crystal transfer agent and the coupling agent is 5 percent of the screen allowance of a square hole screen with the grain size of 45 mu m.

(3) Preheating: and (3) preheating the phosphogypsum powder treated in the step (2) by using tail gas at 70 ℃ in a rotary dryer, so that the temperature of the phosphogypsum powder is 70 ℃ and the moisture content is 4.5%. Tail gas preheating makes 5-10% of gypsum be removed into semi-hydrated gypsum as seed crystal for subsequent treatment. And introducing tail gas into the dryer at a constant speed of 30L/min to uniformly heat the phosphogypsum powder.

(4) Crystal transformation: filling the phosphogypsum powder treated in the step (3) into a vertical crystal conversion kettle, and introducing steam at 130 ℃ for dehydration and crystal conversion to obtain building gypsum powder; introducing steam at 30L/min for 40min, keeping the temperature for 2h, dewatering, crystallizing, and exhausting to obtain building gypsum powder.

(5) And (3) drying: drying with airflow dryer, drying with 600 deg.C hot air flow until free water content is 0%, and hot air flow rate is 500L/min.

(6) Aging: aging the building gypsum powder treated in the step (5) for 24 hours at 25 ℃ in a closed environment with relative humidity of 60% and normal pressure;

(7) crushing: and (4) grinding the building gypsum powder treated in the step (6) until the building gypsum powder is sieved by a 80-mesh sieve, and obtaining the high-strength building gypsum powder, wherein the balance is 6.3%.

The high-strength building gypsum powder prepared by the invention is subjected to physical property detection according to GB/T36141-2018, GB/T17669.4-1999 and GB/T17669.3-1999, and meets the requirement index of GB/T9776-2008 building gypsum, national standard 3.0 grade, as shown in the following table:

attached water/%	Without water/%)	Half water/%	Dihydration/%	Standard consistency/%	Initial setting time/min	Final setting time/min	Bending resistance/MPa	compression/MPa resistance
									0	1.2	80.35	0.22	0.47	4	12	4.71	10.20

Example 3: as shown in figure 1, in the method for preparing the high-strength building gypsum by the dry method, after the phosphogypsum is subjected to pH value adjustment by lime powder, a crystal transformation agent and a coupling agent are added for dispersing, preheating, crystal transformation, exhausting, drying, aging and grinding to prepare the high-strength building gypsum, and the preparation method specifically comprises the following steps:

(1) pretreatment of raw materials: crushing the phosphogypsum to 3.7 percent of the screen residue of a square-hole screen with the granularity of 1mm, adding lime powder with the mass of 0.8 percent of the phosphogypsum, and adjusting the pH value to 8 to obtain phosphogypsum powder;

(2) dispersing: adding a crystal transfer agent with the mass of 0.3 per mill of the phosphogypsum and a coupling agent with the mass of 0.8 per mill of the phosphogypsum into the phosphogypsum powder prepared in the step (1) and dispersing by using a horizontal rotary vane forced dispersion machine. The crystal transformation agent consists of sodium olefin, calcium stearate and sodium polycarboxylate with the mass ratio of 2:4:1, and the coupling agent consists of phthalate coupling agent TMC-201, aluminate coupling agent F-1 and silane coupling agent KH792 with the mass ratio of 1:2: 5. The grain size of the crystal transfer agent and the coupling agent is 8 percent of the screen allowance of a square hole screen with the grain size of 45 mu m.

(3) Preheating: and (3) preheating the phosphogypsum powder treated in the step (2) by using tail gas at 60 ℃ in a rotary dryer, so that the temperature of the phosphogypsum powder is 60 ℃ and the moisture content is 2%. Tail gas preheating makes 5-10% of gypsum be removed into semi-hydrated gypsum as seed crystal for subsequent treatment. And introducing tail gas into the dryer at a constant speed of 24L/min to uniformly heat the phosphogypsum powder.

(4) Crystal transformation: filling the phosphogypsum powder treated in the step (3) into a vertical crystal conversion kettle, and introducing steam at 125 ℃ for dehydration and crystal conversion to obtain building gypsum powder; introducing steam at a constant speed of 25L/min for 35min, keeping the temperature for 1.6h, and then dehydrating, crystallizing and exhausting to obtain the building gypsum powder.

(5) And (3) drying: drying with airflow dryer, drying with 600 deg.C hot air flow until free water content is 0.25%, and hot air flow is 400L/min.

(6) Aging: aging the building gypsum powder treated in the step (5) for 18h at 23 ℃ in a closed environment with a relative humidity of 50% and normal pressure;

(7) crushing: and (4) grinding the building gypsum powder treated in the step (6) until the building gypsum powder is sieved by a 80-mesh sieve, and obtaining the high-strength building gypsum powder, wherein the balance is 3.8%.

The high-strength building gypsum powder prepared by the invention is subjected to physical property detection according to GB/T36141-2018, GB/T17669.4-1999 and GB/T17669.3-1999, and meets the requirement index of GB/T9776-2008 building gypsum, national standard 3.0 grade, as shown in the following table:

attached water/%	Without water/%)	Half water/%	Dihydration/%	Standard consistency/%	Initial setting time/min	Final setting time/min	Bending resistance/MPa	compression/MPa resistance
									0.25	0	73.52	8.33	0.42	8	15	5.45	12.42

Example 4: as shown in figure 1, in the method for preparing the high-strength building gypsum by the dry method, after the phosphogypsum is subjected to pH value adjustment by lime powder, a crystal transformation agent and a coupling agent are added for dispersing, preheating, crystal transformation, exhausting, drying, aging and grinding to prepare the high-strength building gypsum, and the preparation method specifically comprises the following steps:

(1) pretreatment of raw materials: crushing the phosphogypsum to 3.5 percent of the screen residue of a square-hole screen with the granularity of 1mm, adding lime powder with the mass of 0.71 percent of the phosphogypsum, and adjusting the pH value to 7 to obtain phosphogypsum powder;

(2) dispersing: adding a crystal transfer agent with the mass of 0.4 per mill of the phosphogypsum and a coupling agent with the mass of 0.7 per mill of the phosphogypsum into the phosphogypsum powder prepared in the step (1) and dispersing by using a horizontal rotary vane forced dispersion machine. The crystal transformation agent consists of sulfamic acid, sodium polycarboxylate and potassium hydrogen phthalate with the mass ratio of 1:2:4, and the coupling agent consists of phthalate ester coupling agent TMC-201 and silane coupling agent KH792 with the mass ratio of 1: 5. The grain size of the crystal transfer agent and the coupling agent is 2 percent of the screen allowance of a square hole screen with the grain size of 45 mu m.

(3) Preheating: and (3) preheating the phosphogypsum powder treated in the step (2) by using tail gas at 64 ℃ in a rotary dryer, so that the temperature of the phosphogypsum powder is 65 ℃ and the moisture content is 3.5%. Tail gas preheating makes 5-10% of gypsum be removed into semi-hydrated gypsum as seed crystal for subsequent treatment. And introducing tail gas into the dryer at a constant speed of 28L/min to uniformly heat the phosphogypsum powder.

(4) Crystal transformation: filling the phosphogypsum powder treated in the step (3) into a vertical crystal conversion kettle, and introducing steam at 127 ℃ for dehydration and crystal conversion to obtain building gypsum powder; introducing steam at a constant speed of 28L/min for 37min, keeping the temperature for 1.8h, and then dehydrating, crystallizing and exhausting to obtain the building gypsum powder.

(5) And (3) drying: drying with airflow dryer, drying with 570 deg.C hot air until free water content is 0.17%, and hot air flow rate is 300L/min.

(6) Aging: aging the building gypsum powder treated in the step (5) for 20 hours at the temperature of 22 ℃ and in a sealed environment with the relative humidity of 55% and normal pressure;

(7) crushing: and (4) grinding the building gypsum powder treated in the step (6) until the building gypsum powder is sieved by a 80-mesh sieve, and obtaining the high-strength building gypsum powder, wherein the balance is 5%.

The high-strength building gypsum powder prepared by the invention is subjected to physical property detection according to GB/T36141-2018, GB/T17669.4-1999 and GB/T17669.3-1999, and meets the requirement index of GB/T9776-2008 building gypsum, national standard 3.0 grade, as shown in the following table:

attached water/%	Without water/%)	Half water/%	Dihydration/%	Standard consistency/%	Initial setting time/min	Final setting time/min	Bending resistance/MPa	compression/MPa resistance
									0.17	0	78.12	4.55	0.37	6	13	5.21	15.84

While the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.