Novel environment-friendly material prepared from ardealite solid waste through rotary kiln low-temperature roasting and preparation method of novel environment-friendly material

Abstract

The invention discloses a preparation method of a novel environment-friendly material by taking ardealite solid waste as a raw material and adopting rotary kiln low-temperature roasting. The preparation method comprises the following steps: S1, pretreatment of ardealite; s2, flotation treatment of ardealite; s3, pre-calcining the ardealite; and S4, low-temperature roasting. According to the novel environment-friendly material which takes the ardealite solid waste as the raw material and is subjected to low-temperature roasting through the rotary kiln, through the synergistic effect of the steps of pretreatment, flotation, pre-roasting, low-temperature roasting and the like, the problems that the comprehensive utilization rate of ardealite is low, the impurity content is high, and the product performance is unstable are effectively solved; the method is simple in technological process, controllable in parameter and environment-friendly, the prepared novel environment-friendly material is high in beta-type semi-hydrated gypsum content, regular in crystal form and excellent in performance and can be widely applied to the fields of building materials, molds and the like, efficient resource utilization of phosphogypsum is achieved, and remarkable economic benefits and environmental benefits are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a new type of environmentally friendly material prepared by low-temperature roasting of a rotary kiln using phosphogypsum solid waste as a raw material and a preparation method thereof. Background Art

[0002] Phosphogypsum is a solid waste generated in the wet-process production of phosphoric acid. Its main component is calcium sulfate dihydrate, and there are also a small amount of impurities such as phosphorus, fluorine, organic matter, oxides, heavy metals, radioactive substances, etc. Usually, for every 1t of phosphoric acid produced, 4 - 6t of phosphogypsum will be generated. In China, a small amount of phosphogypsum is used in the production of building materials, and most of it is treated by stacking. Long-term large-scale stacking may pollute the soil, surface water and groundwater. In addition, dust pollution will also be generated in the phosphogypsum yard. Phosphogypsum contains harmful impurities such as phosphorus, mercury, cadmium and radioactive elements. If it enters the atmosphere with steam, it may cause harm to human health. Thus, it can be seen that the stacking of phosphogypsum will not only occupy a large amount of land resources, but also pose potential risks to the ecological environment. Therefore, the harmless treatment and comprehensive utilization of phosphogypsum have become key research projects in the treatment and resource utilization of solid waste.

[0003] There are many ways to resourcefully utilize industrial by-product gypsum. Among them, using gypsum raw materials to calcine and prepare building gypsum powder is one of the most effective ways. At present, the process of preparing building gypsum powder from desulfurized gypsum has been relatively mature, and the properties of the prepared β-type hemihydrate gypsum are relatively stable. However, for phosphogypsum, the presence of harmful impurities such as phosphorus, fluorine, and organic matter will seriously affect the properties of the building gypsum powder prepared from phosphogypsum, such as setting time, strength, etc. Since the phosphogypsum raw materials come from different manufacturers and batches, and the components fluctuate greatly, the β-type hemihydrate gypsum powder prepared from phosphogypsum produced by traditional preparation processes has the disadvantages of unstable setting time, large water requirement for standard consistency, and low strength, and cannot meet the basic quality requirements of building gypsum powder in the standard GB / T 9776-2022 "Building Gypsum", and it is difficult to be well utilized.

[0004] Chinese Patent Application CN102390942A discloses a method for producing building gypsum powder from phosphogypsum, which includes the processes of phosphogypsum calcination, sieving, and cooling. The phosphogypsum calcination is carried out continuously in three temperatures, that is, calcining at 500 - 750 °C for 2 - 4 minutes, at 300 - 450 °C for 2 - 4 minutes, and at 140 - 250 °C for 2 - 4 minutes. However, the above method has a high calcination temperature, high energy consumption, and does not achieve a good effect on the modification of phosphogypsum, with insignificant economic benefits and being difficult to be utilized on a large scale. Chinese Patent Application CN115724606A discloses a method for producing gypsum board using phosphogypsum as raw material. In this patent, preliminary calcination is carried out in a hammer dryer to obtain preliminary gypsum powder; the preliminary gypsum powder is subjected to secondary calcination in a fluidized bed furnace, with more uniform calcination and a higher content of effective components in the gypsum powder, to obtain building gypsum powder. The content of hemihydrate gypsum in the obtained building gypsum powder is 81.15%; the content of dihydrate gypsum is 2.16%; the content of soluble anhydrous gypsum is 2.7%; the content of crystal water is 5.4%. However, in the above method, the heat source temperature for preliminary calcination is 500 - 520 °C, with high energy consumption, resulting in a high content of anhydrous gypsum in the building gypsum powder. When anhydrous gypsum is converted into dihydrate gypsum, it is accompanied by volume expansion, which may cause the volume of hardened gypsum to expand too much and lead to cracking problems.

[0005] Therefore, it is necessary to appropriately improve the process for preparing β-type hemihydrate gypsum powder from phosphogypsum to improve the quality of β-type hemihydrate gypsum. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a new environmentally friendly material and its preparation method using phosphogypsum solid waste as raw material and low-temperature roasting in a rotary kiln. This method can obtain high-quality β-hemihydrate gypsum, improve problems such as short initial setting time, loose structure, low strength, and high water demand for standard consistency of β-hemihydrate gypsum, and has a positive promoting effect on the comprehensive utilization of phosphogypsum.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as raw material and low-temperature roasting in a rotary kiln, including the following steps:

[0009] S1. Pretreatment of phosphogypsum: Grind the phosphogypsum and sieve it through a 100-mesh sieve, then add it to deionized water. After dispersing evenly, add calcium oxide and EADA disodium, stir, and after stirring is completed, add sulfuric acid solution to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0010] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 into deionized water, adjust the pH to 8 - 10, then add a flotation agent and conduct flotation treatment. After flotation is completed, perform solid-liquid separation to obtain a flotation phosphogypsum slurry;

[0011] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2, mix evenly and then conduct pre-calcination treatment. After the treatment is completed, obtain pre-calcined phosphogypsum;

[0012] S4. Low-temperature roasting: Grind the pre-calcined phosphogypsum in step S3, then add it into a rotary kiln or a tunnel kiln for low-temperature roasting. After roasting is completed, carry out aging to obtain the novel environmental protection material.

[0013] Preferably, in step S1, the solid-liquid ratio of the phosphogypsum to water is 1:3 - 5, the addition amount of calcium oxide is 3 - 5% of the mass of phosphogypsum, the addition amount of EADA disodium is 0.5 - 1% of the mass of phosphogypsum, the stirring speed is 60 - 80 r / min, the temperature is 40 - 50 °C, the time is 50 - 80 min, and the mass fraction of the sulfuric acid solution is 5 - 10%.

[0014] In the present invention, first, the phosphogypsum is pretreated by washing with water, and at the same time, calcium oxide and EADA disodium are added, which can react with impurities such as soluble phosphates and organic matters in the phosphogypsum, and can remove soluble P 2 O 5 and fluorine impurities in the phosphogypsum, improve the mechanical properties of the phosphogypsum, and create favorable conditions for subsequent flotation.

[0015] Preferably, in step S2, the mass ratio of the pretreated phosphogypsum to deionized water is 1:4 - 5, the addition amount of the flotation agent is 1 - 1.5% of the mass of the pretreated gypsum, the aeration amount of the flotation treatment is 0.4 - 0.5 L / min, the time is 20 - 30 min, and the rotation speed is 1500 - 1800 r / min; control the water content of the flotation phosphogypsum slurry to be 40 - 50%.

[0016] Preferably, the preparation method of the flotation agent in step S2 is as follows:

[0017] Add Tween 80 into deionized water, stir evenly to obtain an emulsifier solution; add dodecylamine into the emulsifier solution and conduct emulsification under ultrasonic conditions to obtain a dodecylamine emulsion; add terpineol into the emulsifier solution and conduct emulsification under ultrasonic conditions to obtain a terpineol emulsion; mix the dodecylamine emulsion and the terpineol emulsion evenly, then add sodium oleate and carboxymethyl cellulose, and stir evenly to obtain the flotation agent.

[0018] In the present invention, by adding a specific flotation agent and performing flotation treatment on phosphogypsum, the content of impurities such as organic matter in the phosphogypsum can be effectively reduced, thereby improving the purity of the phosphogypsum and laying a foundation for the subsequent preparation of high-performance β-hemihydrate gypsum.

[0019] Preferably, the mass fraction of Tween 80 in the emulsifier solution is 2-3%, the mass ratio of dodecylamine to the emulsifier solution is 4-6:80-100, the mass ratio of terpineol to the emulsifier solution is 2-3:70-80, the mass ratio of the dodecylamine emulsion, terpineol emulsion, sodium oleate, and carboxymethyl cellulose is 80-100:70-80:3-4:1-2, the frequency of the ultrasonic wave is 30-40 kHz, the power is 50-100 W, and the time is 8-12 min.

[0020] Preferably, the addition amount of the crystal habit modifier in step S3 is 3-4% of the mass of the flotation phosphogypsum slurry; the temperature of the pre-calcination treatment is 120-130 °C, and the time is 3-4 h.

[0021] In the present invention, by adding a crystal habit modifier, during the pre-calcination process, the formation of β-type hemihydrate gypsum crystals is promoted, the growth of other morphological crystals is inhibited, the β-type hemihydrate gypsum crystals are finer and more uniform, and the purity of β-type hemihydrate gypsum in the subsequent roasting process is improved.

[0022] Preferably, the preparation method of the crystal habit modifier in step S3 is as follows:

[0023] Add fumaric acid to deionized water, then add L-cysteine and calcium chloride, stir evenly, and then add propylene glycol alginate, and perform constant-temperature stirring to obtain the crystal habit modifier.

[0024] In the present invention, the prepared crystal habit modifier uses fumaric acid, L-cysteine, calcium chloride, and propylene glycol alginate as raw materials. Fumarate ions can form a complex with Ca 2+ This complexation will reduce the activity of free Ca in the solution, 2+ Thereby affecting the dissolution equilibrium and crystallization process of calcium sulfate. Moreover, the rigid planar structure of fumaric acid and the flexible side chain of L-cysteine may cooperate with each other in space, better cover the crystal surface, and tend to adsorb on the crystal plane of β-type gypsum, promoting its growth, thereby improving the purity of β-type hemihydrate gypsum in the environmental protection material; the added propylene glycol alginate can be adsorbed on the surface of phosphogypsum particles, prevent particle agglomeration, improve dispersibility, and at the same time reduce the interfacial tension between phosphogypsum and water, promote the wetting of phosphogypsum by water, change the crystal growth rate, thereby changing the crystal morphology and improving the strength of β-type hemihydrate gypsum.

[0025] Preferably, the mass ratio of fumaric acid, deionized water, L-cysteine, calcium chloride, and propylene glycol alginate is 5-8:200-300:7-10:3-5:1-2, and the temperature of the constant-temperature stirring is 40-50°C, and the time is 1-2 h.

[0026] Preferably, in step S4, the rotation speed of the ball milling is 800-900 r / min, and the time is 20-30 min; the process of the low-temperature roasting is to rise to 165-175°C at a heating rate of 7-10°C / min and keep warm for 20-35 min; the process of the aging is to place the roasted gypsum in an environment with a temperature of 40-50°C and a humidity of 60-70% and let it stand for 24-30 h.

[0027] In the present invention, by controlling the heating rate, the crystal burst and structural defects caused by rapid heating are avoided; by keeping warm in the temperature range of 165-175°C, it is ensured that the dihydrate gypsum is fully dehydrated and converted into β-type hemihydrate gypsum, and at the same time, overburning or the formation of anhydrous gypsum caused by too high temperature is avoided, making the surface of the β-type hemihydrate gypsum particles denser, reducing the number of micropores, and the crystal structure more stable, thereby prolonging its initial setting time and improving its strength.

[0028] The present invention also protects a new type of environmentally friendly material prepared by the method as described above.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The new type of environmentally friendly material provided by the present invention, which uses phosphogypsum solid waste as raw material and adopts low-temperature roasting in a rotary kiln, effectively solves the problems of low comprehensive utilization rate of phosphogypsum, high impurity content, and unstable product performance through the synergistic effect of steps such as pretreatment, flotation, pre-calcination, and low-temperature roasting; the process flow of this method is simple, the parameters are controllable, and it is environmentally friendly. The prepared new type of environmentally friendly material has a high content of β-type hemihydrate gypsum, regular crystal form, and excellent performance, and can be widely used in fields such as building materials and molds. It converts and reuses large amounts of phosphogypsum-based solid waste, improves the utilization value of solid waste on the premise of reducing environmental pollution, and realizes the efficient resource utilization of phosphogypsum, with significant economic and environmental benefits.

[0031] (2) The novel environmentally friendly material provided by the present invention, which uses phosphogypsum solid waste as raw material and is prepared by low-temperature roasting in a rotary kiln, and the flotation agent prepared with a specific formula and method. The added dodecylamine and sodium oleate can selectively adsorb on the surface of impurities, and have a good collecting effect on impurities such as silicate under acidic conditions; the added terpineol as a foaming agent can reduce the surface tension of water. Compared with short-chain alcohols and long-chain alcohols, it has better foaming properties, generating a large number of small and stable bubbles, which can not only ensure that the bubbles stay in the pulp for enough time to make the mineral particles fully adhere, but also break on the surface of the flotation cell, which is beneficial to the control of the foam layer, thereby improving the flotation effect and enhancing the purity and quality of β-type hemihydrate gypsum.

[0032] (3) The novel environmentally friendly material provided by the present invention, which uses phosphogypsum solid waste as raw material and is prepared by low-temperature roasting in a rotary kiln, and the crystal habit modifier prepared with a specific formula. Through the synergistic effect of various components, it effectively regulates the growth process of β-type hemihydrate gypsum crystals; fumaric acid and L-cysteine as organic additives can adsorb on specific crystal planes of hemihydrate gypsum crystals to inhibit their growth, thereby changing the crystal habit; the calcium ions provided by calcium chloride can combine with sulfate ions to affect the crystal nucleation rate; propylene glycol alginate as a polymer compound can increase the system viscosity, delay the crystal growth rate, and play a dispersing role to prevent crystal agglomeration; through the synergistic effect of these components, the crystal habit modifier can effectively control the morphology and size of β-type hemihydrate gypsum crystals, making them more regular and uniform, thereby improving the performance of the final product.

[0033] (4) The novel environmentally friendly material provided by the present invention, which uses phosphogypsum solid waste as raw material and is prepared by low-temperature roasting in a rotary kiln or a tunnel kiln. By precisely controlling the roasting temperature and time, it realizes the efficient conversion of phosphogypsum into β-type hemihydrate gypsum; by controlling the heating rate, it avoids the crystal explosion and structural defects caused by rapid heating; by keeping warm in the temperature range of 165 - 175 °C, it ensures that the dihydrate gypsum is fully dehydrated and converted into β-type hemihydrate gypsum, while avoiding overburning or generating anhydrous gypsum due to too high temperature; the use of the rotary kiln ensures uniform heating of the material, improving the conversion efficiency and product quality; the aging process further stabilizes the performance of β-type hemihydrate gypsum, making it more stable and reliable during application. Detailed Embodiments

[0034] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] The phosphogypsum used in the present invention is an industrial solid waste material generated during the wet production of phosphoric acid in the phosphoric acid manufacturing industry and subjected to preliminary aging treatment through recycling; the content of dihydrate gypsum and the main impurity composition in the phosphogypsum are as follows:

[0036] <![CDATA[CaSO 4 ·2H 2 O]]> <![CDATA[Total P 2 O 5 > <![CDATA[Soluble P 2 O 5 > Total F Soluble F <![CDATA[SiO 2 > Mass fraction % 76.88 4.35 3.39 3.92 3.41 7.11

[0037] Example 1

[0038] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as raw material and low-temperature roasting in a rotary kiln, comprising the following steps:

[0039] S1. Pretreatment of phosphogypsum: Grind the phosphogypsum and pass it through a 100-mesh sieve, then add it to deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:4. After dispersing evenly, add calcium oxide and disodium EADA. The addition amount of calcium oxide is 4% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stir for 70 min under the conditions of a rotation speed of 70 r / min and a temperature of 45 °C. After stirring is completed, add a 10% sulfuric acid solution to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0040] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 to deionized water. The mass ratio of pretreated phosphogypsum to deionized water is 1:4.5. Add a 10% sodium hydroxide solution to adjust the pH to 9, then add a flotation agent accounting for 1.3% of the mass of the pretreated gypsum, and carry out flotation treatment. The aeration amount for flotation treatment is 0.45 L / min, the time is 25 min, and the rotation speed is 1700 r / min. After flotation is completed, carry out solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0041] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier is 3.5% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at a temperature of 125 °C for 3.5 h, and obtain pre-calcined phosphogypsum after the treatment is completed;

[0042] S4. Low-temperature roasting: Ball-mill the pre-calcined phosphogypsum in step S3 at a rotation speed of 850 r / min for 25 min, then add it to a rotary kiln for low-temperature roasting. The low-temperature roasting process is to raise the temperature to 170 °C at a heating rate of 8 °C / min and keep it warm for 25 min. After roasting is completed, carry out aging. The aging process is to place the roasted gypsum in an environment with a temperature of 45 °C and a humidity of 65% and let it stand for 27 h to obtain the new environmentally friendly material.

[0043] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0044] Tween 80 was added to deionized water, and after stirring evenly, an emulsifier solution with a mass fraction of 2.5% was obtained; 5 g of dodecylamine was added to 90 g of the emulsifier solution, and emulsification was carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a dodecylamine emulsion; 2.5 g of terpineol was added to 75 g of the emulsifier solution, and emulsification was carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a terpineol emulsion; 90 g of the dodecylamine emulsion and 75 g of the terpineol emulsion were mixed evenly, and then 3.5 g of sodium oleate and 1.5 g of carboxymethyl cellulose were added, and after stirring evenly, the said flotation agent was obtained.

[0045] The preparation method of the crystal habit modifier described in step S3 is as follows:

[0046] 7 g of fumaric acid was added to 250 g of deionized water, then 8 g of L-cysteine and 4 g of calcium chloride were added. After stirring evenly, 1.5 g of propylene glycol alginate was added, and stirring was carried out at a constant temperature of 45 °C for 1.5 h to obtain the said crystal habit modifier.

[0047] Example 2

[0048] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as a raw material and low-temperature roasting in a rotary kiln includes the following steps:

[0049] S1. Pretreatment of phosphogypsum: The phosphogypsum was ground and passed through a 100-mesh sieve, and then added to deionized water. The solid-liquid ratio of phosphogypsum to deionized water was 1:4. After dispersing evenly, calcium oxide and disodium EADA were added. The addition amount of calcium oxide was 4% of the mass of phosphogypsum, and the addition amount of the disodium EADA was 0.7% of the mass of phosphogypsum. Stirring was carried out for 60 min under the conditions of a rotation speed of 70 r / min and a temperature of 45 °C. After stirring was completed, a 5% sulfuric acid solution was added to adjust the pH to 7, and then centrifugation and filtration were carried out to obtain pretreated phosphogypsum;

[0050] S2. Flotation treatment of phosphogypsum: The pretreated phosphogypsum in step S1 was added to deionized water. The mass ratio of pretreated phosphogypsum to deionized water was 1:4. Sodium hydroxide with a mass fraction of 5% was added to adjust the pH to 9, and then a flotation agent accounting for 1.2% of the mass of the pretreated gypsum was added for flotation treatment. The aeration amount during the flotation treatment was 0.45 L / min, the time was 25 min, and the rotation speed was 1600 r / min. After the flotation was completed, solid-liquid separation was carried out to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0051] S3. Pre-calcination of phosphogypsum: A crystal habit modifier was added to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier was 3.5% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcination was carried out at a temperature of 125 °C for 3 h, and pre-calcined phosphogypsum was obtained after the treatment was completed;

[0052] S4, Low-temperature roasting: The pre-roasted phosphogypsum in step S3 is ball-milled at a rotation speed of 850 r / min for 25 min, and then added into a rotary kiln for low-temperature roasting. The low-temperature roasting process is to increase the temperature to 170 °C at a heating rate of 8 °C / min and hold for 30 min. After roasting, aging is carried out. The aging process is to place the roasted gypsum in an environment with a temperature of 45 °C and a humidity of 5% and let it stand for 26 h to obtain the novel environmentally friendly material.

[0053] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0054] Tween 80 is added to deionized water, and after stirring evenly, an emulsifier solution with a mass fraction of 2.5% is obtained; 5 g of dodecylamine is added to 90 g of the emulsifier solution, and emulsification is carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 70 W to obtain a dodecylamine emulsion; 2.5 g of terpineol is added to 75 g of the emulsifier solution, and emulsification is carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 70 W to obtain a terpineol emulsion; 90 g of the dodecylamine emulsion and 75 g of the terpineol emulsion are mixed evenly, and then 3 g of sodium oleate and 2 g of carboxymethyl cellulose are added and stirred evenly to obtain the flotation agent.

[0055] The preparation method of the crystal habit modifier in step S3 is as follows:

[0056] 6 g of fumaric acid is added to 250 g of deionized water, then 9 g of L-cysteine and 4 g of calcium chloride are added. After stirring evenly, 1.5 g of propylene glycol alginate is added, and stirring is carried out at a constant temperature of 45 °C for 1.5 h to obtain the crystal habit modifier.

[0057] Example 3

[0058] A preparation method of a novel environmentally friendly material using phosphogypsum solid waste as a raw material and low-temperature roasting in a rotary kiln, comprising the following steps:

[0059] S1, Pretreatment of phosphogypsum: The phosphogypsum is ground and passed through a 100-mesh sieve, and then added into deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:3. After dispersing evenly, calcium oxide and disodium EADA are added. The addition amount of calcium oxide is 3% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.5% of the mass of phosphogypsum. Stirring is carried out at a rotation speed of 60 r / min and a temperature of 40 °C for 80 min. After stirring, a 5% sulfuric acid solution is added to adjust the pH to 7, and then centrifugation and filtration are carried out to obtain pretreated phosphogypsum;

[0060] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 into deionized water. The mass ratio of the pretreated phosphogypsum to deionized water is 1:4. Add sodium hydroxide with a mass fraction of 5% to adjust the pH to 8. Then add a flotation agent accounting for 1% of the mass of the pretreated gypsum and conduct flotation treatment. The air inflow rate for the flotation treatment is 0.4 L / min, the time is 30 min, and the rotation speed is 1500 r / min. After the flotation is completed, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 40%);

[0061] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier is 3% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at a temperature of 120 °C for 4 h to obtain pre-calcined phosphogypsum after the treatment is completed;

[0062] S4. Low-temperature roasting: Ball-mill the pre-calcined phosphogypsum in step S3 at a rotation speed of 800 r / min for 30 min, then add it into a rotary kiln for low-temperature roasting. The process of the low-temperature roasting is to increase the temperature to 165 °C at a heating rate of 7 °C / min and keep it warm for 35 min. After the roasting is completed, conduct aging. The aging process is to leave the roasted gypsum standing in an environment with a temperature of 40 °C and a humidity of 60% for 30 h to obtain the novel environmentally friendly material.

[0063] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0064] Add Tween 80 into deionized water, and after stirring evenly, obtain an emulsifier solution with a mass fraction of 2%; add 4 g of dodecylamine into 80 g of the emulsifier solution, and emulsify for 12 min under the conditions of an ultrasonic frequency of 30 kHz and a power of 50 W to obtain a dodecylamine emulsion; add 2 g of terpineol into 70 g of the emulsifier solution, and emulsify for 12 min under the conditions of an ultrasonic frequency of 30 kHz and a power of 50 W to obtain a terpineol emulsion; mix 80 g of the dodecylamine emulsion and 70 g of the terpineol emulsion evenly, then add 3 g of sodium oleate and 1 g of carboxymethyl cellulose, and stir evenly to obtain the flotation agent.

[0065] The preparation method of the crystal habit modifier in step S3 is as follows:

[0066] Add 5 g of fumaric acid into 200 g of deionized water, then add 7 g of L-cysteine and 3 g of calcium chloride, stir evenly, add 1 g of propylene glycol alginate, and stir constantly at 40 °C for 2 h to obtain the crystal habit modifier.

[0067] Example 4

[0068] A preparation method of a novel environmentally friendly material using phosphogypsum solid waste as a raw material and conducting low-temperature roasting in a rotary kiln, comprising the following steps:

[0069] S1. Pretreatment of phosphogypsum: Grind the phosphogypsum and sieve it through a 100-mesh sieve. Then add it to deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:5. After dispersing evenly, add calcium oxide and disodium EADA. The addition amount of calcium oxide is 5% of the mass of phosphogypsum, and the addition amount of disodium EADA is 1% of the mass of phosphogypsum. Stir for 50 min under the conditions of a rotation speed of 80 r / min and a temperature of 50 °C. After stirring, add a 10% sulfuric acid solution to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0070] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 to deionized water. The mass ratio of pretreated phosphogypsum to deionized water is 1:5. Add sodium hydroxide with a mass fraction of 10% to adjust the pH to 10. Then add a flotation agent with 1.5% of the mass of the pretreated gypsum and conduct flotation treatment. The aeration rate of the flotation treatment is 0.5 L / min, the time is 20 min, and the rotation speed is 1800 r / min. After flotation, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 50%);

[0071] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier is 4% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 130 °C for 3 h to obtain pre-calcined phosphogypsum after treatment;

[0072] S4. Low-temperature roasting: Ball-mill the pre-calcined phosphogypsum in step S3 at a rotation speed of 900 r / min for 20 min, and then add it to a rotary kiln for low-temperature roasting. The process of low-temperature roasting is to increase the temperature to 175 °C at a heating rate of 10 °C / min and keep it warm for 20 min. After roasting, carry out aging. The aging process is to place the roasted gypsum in an environment with a temperature of 50 °C and a humidity of 70% and let it stand for 24 h to obtain the new environmentally friendly material.

[0073] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0074] Add Tween 80 to deionized water and stir evenly to obtain an emulsifier solution with a mass fraction of 3%. Add 6 g of dodecylamine to 100 g of the emulsifier solution and emulsify for 8 min under the conditions of an ultrasonic frequency of 40 kHz and a power of 100 W to obtain a dodecylamine emulsion. Add 3 g of terpineol to 80 g of the emulsifier solution and emulsify for 8 min under the conditions of an ultrasonic frequency of 40 kHz and a power of 100 W to obtain a terpineol emulsion. Mix 100 g of the dodecylamine emulsion and 80 g of the terpineol emulsion evenly, and then add 4 g of sodium oleate and 2 g of carboxymethyl cellulose and stir evenly to obtain the flotation agent.

[0075] The preparation method of the crystal habit modifier described in step S3 is as follows:

[0076] Add 8 g of fumaric acid to 300 g of deionized water, then add 10 g of L-cysteine and 5 g of calcium chloride. After stirring evenly, add 2 g of propylene glycol alginate and stir at a constant temperature of 50 °C for 1 h to obtain the crystal habit modifier.

[0077] Comparative Example 1

[0078] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as raw material and low-temperature roasting in a rotary kiln includes the following steps:

[0079] S1. Pretreatment of phosphogypsum: Grind phosphogypsum and pass it through a 100-mesh sieve, then add it to deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:4. After dispersing evenly, add calcium oxide and disodium EADA. The addition amount of calcium oxide is 4% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stir at a speed of 70 r / min and a temperature of 45 °C for 70 min. After stirring is completed, add a 10% sulfuric acid solution to adjust the pH to 7, then centrifuge and filter to obtain pretreated phosphogypsum;

[0080] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 to deionized water. The mass ratio of pretreated phosphogypsum to deionized water is 1:4.5. Add a 10% sodium hydroxide solution to adjust the pH to 9, then add a flotation agent accounting for 1.3% of the mass of pretreated gypsum and conduct flotation treatment. The aeration rate of the flotation treatment is 0.45 L / min, the time is 25 min, and the speed is 1700 r / min. After flotation is completed, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0081] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier is 3.5% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at a temperature of 125 °C for 3.5 h. After the treatment is completed, obtain pre-calcined phosphogypsum;

[0082] S4. Low-temperature roasting: Ball-mill the pre-calcined phosphogypsum in step S3 at a speed of 850 r / min for 25 min, then add it to a rotary kiln for low-temperature roasting. The process of low-temperature roasting is to increase the temperature to 170 °C at a heating rate of 8 °C / min and keep it warm for 25 min. After roasting is completed, carry out aging. The aging process is to place the roasted gypsum in an environment with a temperature of 45 °C and a humidity of 65% and let it stand for 27 h to obtain the new environmentally friendly material.

[0083] Among them, the preparation method of the flotation agent described in step S2 is as follows:

[0084] Tween 80 was added to deionized water, and after stirring evenly, an emulsifier solution with a mass fraction of 2.5% was obtained; 2.5 g of terpineol was added to 75 g of the emulsifier solution, and emulsification was carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a terpineol emulsion; 75 g of the terpineol emulsion was mixed with 3.5 g of sodium oleate and 1.5 g of carboxymethyl cellulose, and stirred evenly to obtain the flotation agent.

[0085] The preparation method of the crystal habit modifier described in step S3 is as follows:

[0086] 7 g of fumaric acid was added to 250 g of deionized water, then 8 g of L-cysteine and 4 g of calcium chloride were added. After stirring evenly, 1.5 g of propylene glycol alginate was added, and stirring was carried out at a constant temperature of 45 °C for 1.5 h to obtain the crystal habit modifier.

[0087] Compared with Example 1, dodecylamine was not added to the flotation agent in this comparative example.

[0088] Comparative Example 2

[0089] A preparation method of a new type of environmentally friendly material using phosphogypsum solid waste as a raw material and low-temperature roasting in a rotary kiln includes the following steps:

[0090] S1. Pretreatment of phosphogypsum: The phosphogypsum was ground and passed through a 100-mesh sieve, and then added to deionized water. The solid-liquid ratio of phosphogypsum to deionized water was 1:4. After dispersing evenly, calcium oxide and disodium EADA were added. The addition amount of calcium oxide was 4% of the mass of phosphogypsum, and the addition amount of disodium EADA was 0.8% of the mass of phosphogypsum. Stirring was carried out at a rotation speed of 70 r / min and a temperature of 45 °C for 70 min. After stirring, a 10% sulfuric acid solution was added to adjust the pH to 7, and then centrifugation and filtration were carried out to obtain pretreated phosphogypsum;

[0091] S2. Flotation treatment of phosphogypsum: The pretreated phosphogypsum in step S1 was added to deionized water. The mass ratio of pretreated phosphogypsum to deionized water was 1:4.5. Sodium hydroxide with a mass fraction of 10% was added to adjust the pH to 9, and then a flotation agent accounting for 1.3% of the mass of the pretreated gypsum was added for flotation treatment. The aeration amount of the flotation treatment was 0.45 L / min, the time was 25 min, and the rotation speed was 1700 r / min. After flotation, solid-liquid separation was carried out to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0092] S3. Pre-calcination of phosphogypsum: A crystal habit modifier was added to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier was 3.5% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcination was carried out at a temperature of 125 °C for 3.5 h, and pre-calcined phosphogypsum was obtained after treatment;

[0093] S4. Low-temperature roasting: The pre-roasted phosphogypsum in step S3 is ball-milled at a rotational speed of 850 r / min for 25 min, and then added to a rotary kiln for low-temperature roasting. The low-temperature roasting process is to raise the temperature to 170 °C at a heating rate of 8 °C / min and hold for 25 min. After roasting, aging is carried out. The aging process is to leave the roasted gypsum standing for 27 h in an environment with a temperature of 45 °C and a humidity of 65%, and the novel environmentally friendly material is obtained.

[0094] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0095] Tween 80 is added to deionized water, and after stirring evenly, an emulsifier solution with a mass fraction of 2.5% is obtained; 5 g of dodecylamine is added to 90 g of the emulsifier solution, and emulsification is carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a dodecylamine emulsion; 2.5 g of n-decanol is added to 75 g of the emulsifier solution, and emulsification is carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain an n-decanol emulsion; 90 g of the dodecylamine emulsion and 75 g of the n-decanol emulsion are mixed evenly, and then 3.5 g of sodium oleate and 1.5 g of carboxymethyl cellulose are added, and after stirring evenly, the flotation agent is obtained.

[0096] The preparation method of the crystal habit modifier in step S3 is as follows:

[0097] 7 g of fumaric acid is added to 250 g of deionized water, then 8 g of L-cysteine and 4 g of calcium chloride are added. After stirring evenly, 1.5 g of propylene glycol alginate is added, and stirring is carried out at a constant temperature of 45 °C for 1.5 h, and the crystal habit modifier is obtained.

[0098] Compared with Example 1, in this comparative example, terpineol in the flotation agent is replaced with n-decanol.

[0099] Comparative Example 3

[0100] A preparation method of a novel environmentally friendly material using phosphogypsum solid waste as a raw material and low-temperature roasting in a rotary kiln, comprising the following steps:

[0101] S1. Pretreatment of phosphogypsum: The phosphogypsum is ground and sieved through a 100-mesh sieve, and then added to deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:4. After dispersing evenly, calcium oxide and disodium EADA are added. The addition amount of calcium oxide is 4% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stirring is carried out at a rotational speed of 70 r / min and a temperature of 45 °C for 70 min. After stirring, a 10% sulfuric acid solution is added to adjust the pH to 7, and then centrifugation and filtration are carried out to obtain pretreated phosphogypsum;

[0102] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 into deionized water. The mass ratio of the pretreated phosphogypsum to deionized water is 1:4.5. Add sodium hydroxide with a mass fraction of 10% to adjust the pH to 9. Then add a flotation agent accounting for 1.3% of the mass of the pretreated gypsum and conduct flotation treatment. The aeration rate for the flotation treatment is 0.45 L / min, the time is 25 min, and the rotation speed is 1700 r / min. After the flotation is completed, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0103] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier is 3.5% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at a temperature of 125 °C for 3.5 h to obtain pre-calcined phosphogypsum after the treatment;

[0104] S4. Low-temperature roasting: Ball-mill the pre-calcined phosphogypsum in step S3 at a rotation speed of 850 r / min for 25 min, then add it into a rotary kiln for low-temperature roasting. The process of low-temperature roasting is to raise the temperature to 170 °C at a heating rate of 8 °C / min and keep it warm for 25 min. After the roasting is completed, conduct aging. The aging process is to let the roasted gypsum stand in an environment with a temperature of 45 °C and a humidity of 65% for 27 h to obtain the novel environmental protection material.

[0105] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0106] Add Tween 80 into deionized water, and after stirring evenly, obtain an emulsifier solution with a mass fraction of 2.5%. Add 5 g of dodecylamine into 90 g of the emulsifier solution, and emulsify for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a dodecylamine emulsion. Add 2.5 g of terpineol into 75 g of the emulsifier solution, and emulsify for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a terpineol emulsion. Mix 90 g of the dodecylamine emulsion and 75 g of the terpineol emulsion evenly, then add 3.5 g of sodium oleate and 1.5 g of carboxymethyl cellulose, and stir evenly to obtain the flotation agent.

[0107] The preparation method of the crystal habit modifier in step S3 is as follows:

[0108] Add 15 g of fumaric acid into 250 g of deionized water, then add 4 g of calcium chloride, stir evenly and add 1.5 g of propylene glycol alginate, and stir constantly at 45 °C for 1.5 h to obtain the crystal habit modifier.

[0109] Compared with Example 1, L-cysteine was not added to the crystal habit modifier in this comparative example.

[0110] Comparative Example 4

[0111] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as raw material and low-temperature roasting in a rotary kiln, comprising the following steps:

[0112] S1. Pretreatment of phosphogypsum: Grind phosphogypsum and pass it through a 100-mesh sieve, then add it to deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:4. After dispersing evenly, add calcium oxide and disodium EADA. The addition amount of calcium oxide is 4% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stir for 70 min under the conditions of a rotation speed of 70 r / min and a temperature of 45 °C. After stirring, add a 10% sulfuric acid solution to adjust the pH to 7, then centrifuge and filter to obtain pretreated phosphogypsum;

[0113] S2. Flotation treatment of phosphogypsum: Add the pretreated phosphogypsum in step S1 to deionized water. The mass ratio of pretreated phosphogypsum to deionized water is 1:4.5. Add 10% sodium hydroxide to adjust the pH to 9, then add a flotation agent accounting for 1.3% of the mass of the pretreated gypsum and conduct flotation treatment. The aeration amount for flotation treatment is 0.45 L / min, the time is 25 min, and the rotation speed is 1700 r / min. After flotation, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0114] S3. Pre-calcination of phosphogypsum: Add a crystal habit modifier to the flotation phosphogypsum slurry in step S2. The addition amount of the crystal habit modifier is 3.5% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 125 °C for 3.5 h. After the treatment, obtain pre-calcined phosphogypsum;

[0115] S4. Low-temperature roasting: Ball-mill the pre-calcined phosphogypsum in step S3 at a rotation speed of 850 r / min for 25 min, then add it to a rotary kiln for low-temperature roasting. The process of low-temperature roasting is to increase the temperature to 170 °C at a heating rate of 8 °C / min and keep it warm for 25 min. After roasting, carry out aging. The process of aging is to place the roasted gypsum in an environment with a temperature of 45 °C and a humidity of 65% and let it stand for 27 h to obtain the new environmentally friendly material.

[0116] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0117] Tween 80 was added to deionized water, and after stirring evenly, an emulsifier solution with a mass fraction of 2.5% was obtained; 5 g of dodecylamine was added to 90 g of the emulsifier solution, and emulsification was carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a dodecylamine emulsion; 2.5 g of terpineol was added to 75 g of the emulsifier solution, and emulsification was carried out for 10 min under the conditions of an ultrasonic frequency of 35 kHz and a power of 80 W to obtain a terpineol emulsion; 90 g of the dodecylamine emulsion and 75 g of the terpineol emulsion were mixed evenly, and then 3.5 g of sodium oleate and 1.5 g of carboxymethyl cellulose were added and stirred evenly to obtain the flotation agent.

[0118] The preparation method of the crystal habit modifier described in step S3 is as follows:

[0119] 15 g of L-cysteine was added to 250 g of deionized water, then 8 g of L-cysteine and 4 g of calcium chloride were added, and after stirring evenly, 1.5 g of propylene glycol alginate was added, and stirring was carried out at a constant temperature of 45 °C for 1.5 h to obtain the crystal habit modifier.

[0120] Compared with Example 1, fumaric acid was not added to the crystal habit modifier in this comparative example.

[0121] The novel environmentally friendly materials prepared in Examples 1-4 and Comparative Examples 1-4 were tested. Among them, a gypsum three-phase meter was used to determine the content of β-type hemihydrate gypsum in the novel environmentally friendly materials; Standard consistency water consumption: Weigh 250 g of the novel environmentally friendly material and measure 155 mL of water. First, slowly pour the measured water into the gypsum stirring pot, and then slowly pour the novel environmentally friendly material into the stirring pot within 10 s so that the water completely wets the novel environmentally friendly material. Start timing from the moment the novel environmentally friendly material comes into contact with water, and quickly stir for 30 s to form a building gypsum slurry with a certain fluidity. Then, pour the slurry into a gypsum consistency cylinder, and at 50 s, lift the consistency cylinder vertically at a constant speed. After the slurry is completely spread out, measure the diameter of the round cake-shaped slurry (the national standard requires 180 ± 5 mm). If the diameter is too small, reduce the measured water. If the diameter is too large, vice versa. When the diameter of the round cake-shaped slurry meets the national standard requirements, the measured water is the standard consistency water consumption of the building gypsum powder, and subsequent determination of the setting time and preparation of the hardened body of the environmentally friendly material are all carried out according to this water-to-plaster ratio. Initial setting time and final setting time: According to Standard GB / T 17669.4-1999, use a Vicat apparatus to test. Weigh 200 g of the novel environmentally friendly material, weigh water according to the standard consistency water consumption, pour it into the stirring pot and start timing. After stirring for 30 s, pour it into the ring mold, vibrate up and down 5 times, use a spatula to scrape off the overflowing slurry, and then place it on the base of the Vicat apparatus so that the tip of the steel needle touches the surface of the slurry. Subsequently, loosen the fixing screw of the Vicat apparatus to allow the steel needle to freely insert into the ring mold. The time experienced when the steel needle first cannot contact the glass plate under the ring mold is the initial setting time. The time experienced when the depth of the steel needle inserted into the ring mold for the first time is not greater than 1 mm is the final setting time. Compressive strength and flexural strength: Use the determined standard consistency water consumption to prepare the hardened body of the novel environmentally friendly material. Slowly add 900 g of the environmentally friendly material to the stirring bowl containing water within 10 s, stir evenly for 30 s, and then pour the slurry into the mold. After hardening, take out the specimen from the mold and cure it under the conditions of a temperature of 20 ± 2 °C and a relative humidity of 90 ± 5%. According to the standard GB / T 9776-2022 "Building Gypsum", test the 2-hour flexural and compressive strengths of the hardened body of the novel environmentally friendly material, and the results are shown in Table 1 below.

[0122] Table 1 Performance test results of the novel environmentally friendly materials

[0123]

[0124]

[0125] As can be seen from Table 2 above, the novel environmentally friendly material products prepared by the present invention have relatively better performance, with a longer initial setting time and a lower standard consistency water requirement, improving the purity and quality of β-type hemihydrate gypsum, and having good application prospects.

[0126] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a new type of environmentally friendly material using phosphogypsum solid waste as raw material and roasting in a rotary kiln at low temperature, characterized in that: The following steps are involved: S1, grinding the phosphogypsum powder and passing it through a 100-mesh sieve, then adding it to deionized water, adding calcium oxide and disodium EADA after uniform dispersion, stirring, adding sulfuric acid solution after stirring to adjust the pH to 7, then centrifuging and filtering to obtain pretreated phosphogypsum; S2, adding the pretreated phosphogypsum in step S1 into deionized water, adjusting the pH to 8-10, then adding a flotation agent to perform flotation treatment, and performing solid-liquid separation after flotation to obtain a flotation phosphogypsum slurry; S3, adding a crystal habit modifier to the flotation phosphogypsum slurry in step S2, mixing evenly and then pre-calcining the mixture to obtain pre-calcined phosphogypsum; S4, ball-milling the pre-calcined phosphogypsum in step S3, then adding it into a rotary kiln or a tunnel kiln for low-temperature roasting, and aging after roasting to obtain the novel environmentally friendly material.

2. The preparation method according to claim 1, characterized in that: In step S1, the solid-liquid ratio of the phosphogypsum to deionized water is 1:3-5, the amount of calcium oxide added is 3-5% of the mass of the phosphogypsum, the amount of disodium EADA added is 0.5-1% of the mass of the phosphogypsum, the stirring speed is 60-80r / min, the temperature is 40-50°C, the time is 50-80min, and the mass fraction of the sulfuric acid solution is 5-10%.

3. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of the pretreated phosphogypsum to deionized water is 1:4-5, the amount of the flotation agent added is 1-1.5% of the mass of the pretreated gypsum, the aeration volume of the flotation treatment is 0.4-0.5 L / min, the time is 20-30 min, and the rotation speed is 1500-1800 r / min.

4. The preparation method according to claim 1, characterized in that: The preparation method of the flotation agent in step S2 is as follows: Tween 80 is added into deionized water, and the mixture is stirred evenly to obtain an emulsifier solution; dodecylamine is added into the emulsifier solution, and emulsification is performed under ultrasonic conditions to obtain a dodecylamine emulsion; pineneol is added into the emulsifier solution, and emulsification is performed under ultrasonic conditions to obtain a pineneol emulsion; the dodecylamine emulsion and the pineneol emulsion are mixed evenly, and then sodium oleate and carboxymethyl cellulose are added and stirred evenly to obtain the flotation agent.

5. The preparation method according to claim 4, characterized in that: The mass fraction of Tween 80 in the emulsifier solution is 2-3%, the mass ratio of dodecylamine to the emulsifier solution is 4-6:80-100, the mass ratio of pineol to the emulsifier solution is 2-3:70-80, the mass ratio of dodecylamine emulsion, pineol emulsion, sodium oleate and carboxymethyl cellulose is 80-100:70-80:3-4:1-2, the frequency of the ultrasound is 30-40kHz, the power is 50-100W, and the time is 8-12min.

6. The preparation method according to claim 1, characterized in that: In step S3, the amount of the crystal habit modifier added is 3-4% of the mass of the flotation phosphogypsum slurry; the temperature of the pre-calcination treatment is 120-130° C., and the time is 3-4 hours.

7. The preparation method according to claim 1, characterized in that: The preparation method of the crystal habit modifier in step S3 is as follows: Fumaric acid is added into deionized water, followed by L-cysteine ​​and calcium chloride, and after being stirred evenly, propylene glycol alginate is added and stirred at a constant temperature to obtain the crystal habit modifier.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the fumaric acid, deionized water, L-cysteine, calcium chloride and propylene glycol alginate is 5-8:200-300:7-10:3-5:1-2, and the constant temperature stirring is 40-50° C. for 1-2 hours.

9. The preparation method according to claim 1, characterized in that: The ball milling speed in step S4 is 800-900r / min, and the time is 20-30min; the low-temperature roasting process is to increase the temperature to 165-175°C at a heating rate of 7-10°C / min and keep warm for 20-35min; the aging process is to place the roasted gypsum in an environment with a temperature of 40-50°C and a humidity of 60-70% for 24-30h.

10. A new environmentally friendly material prepared by the method according to any one of claims 1 to 9.

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