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

Abstract

The invention discloses a novel environment-friendly material prepared from ardealite solid waste as a raw material through medium-temperature roasting in a rotary kiln and a preparation method of the novel environment-friendly material. The preparation method comprises the following steps: S1, pretreatment of ardealite; s2, flotation of ardealite; s3, pre-calcining the ardealite; and S4, carrying out medium-temperature roasting on the ardealite. Through the synergistic effect of the steps of pretreatment, flotation, pre-calcination, medium-temperature roasting and the like, the problems of low comprehensive utilization rate of phosphogypsum, high impurity content, unstable product performance and the like are effectively solved; the method is simple in technological process, controllable in parameter and environment-friendly, and the prepared novel environment-friendly material is high in II-type anhydrous gypsum content, regular in crystal form and excellent in performance, can be widely applied to the fields of building materials, molds and the like, realizes efficient resource utilization of phosphogypsum, and has remarkable economic benefits and environmental benefits.

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 medium-temperature roasting in 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 of producing 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, and radioactive substances. Usually, for every 1t of phosphoric acid produced, 4 - 6t of phosphogypsum will be generated. Nearly 300 million tons of new phosphogypsum are generated globally every year. In 2021, about 80 million tons of phosphogypsum were generated in China, and the recovery rate is less than 27%. In China, a small amount of phosphogypsum is used in the production of building materials, and most of it is stored in piles. Long-term large-scale storage may pollute the soil, surface water, and groundwater. In addition, dust pollution will also be generated in the phosphogypsum storage 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 storage 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 solid waste treatment and resource utilization.

[0003] Currently, the treatment method of phosphogypsum is to purify and calcine phosphogypsum to prepare hemihydrate gypsum and type III anhydrous gypsum. Such gypsum is commonly used in the preparation of building materials such as cement, plastering materials, roadbed fillers, wall panels, gypsum boards, and gypsum blocks. Secondly, phosphogypsum is converted into type II anhydrous gypsum. Type II anhydrous gypsum has the characteristics of stable properties, light weight, fire resistance, acid and alkali resistance, etc., and is commonly used as a filler for rubber, paper, plastics, etc. Currently, there are mainly two preparation methods: calcination and wet method. Calcination is to calcine phosphogypsum at a temperature above 600°C to prepare type II anhydrous gypsum. However, due to its high cost, it is difficult to be applied on a large scale and the economic benefit is not high. The wet method is to make phosphogypsum remove the water molecules in its molecules in a certain medium to convert it into type II anhydrous gypsum. However, due to the difficult control of the conversion process parameters, it is difficult to apply.

[0004] A method for preparing micron-sized anhydrous calcium sulfate using phosphogypsum is disclosed in Chinese Patent Application CN114162845A. Using phosphogypsum as raw material, after adding water to make a slurry, sulfuric acid with a concentration of 70-98% is used as the reaction reagent, and micron-sized (with lengths all less than 10 microns) anhydrous calcium sulfate is prepared at 25-80°C. Due to the large amount of sulfuric acid incorporated, the supersaturation increases sharply, the anhydrous gypsum crystal nuclei are fine, and finally the anhydrous gypsum crystal particles are fine, which will cause great difficulties in filtration and separation, resulting in a low content of anhydrous gypsum in the product. Chinese Patent Application CN114436551A discloses a system and method for producing high-purity β-hemihydrate gypsum or type II anhydrous gypsum using industrial by-product gypsum. The system includes a pretreatment subsystem, a calcination subsystem, a cooling subsystem, a water circulation treatment subsystem, and a flue gas treatment subsystem: the pretreatment subsystem washes and removes impurities from the industrial by-product gypsum to obtain pretreated materials; the calcination subsystem preheats and calcines the obtained pretreated materials to obtain high-purity gypsum and high-temperature flue gas, the high-temperature flue gas returns to preheat the pretreated materials, and the high-purity gypsum enters the cooling subsystem for cooling and discharging to obtain high-purity gypsum products; the flue gas treatment subsystem returns the purified ash, and the water circulation treatment subsystem returns the materials and water. The system for producing high-purity gypsum in this invention can accurately convert industrial by-product gypsum into β-hemihydrate gypsum or type II anhydrous gypsum, with the characteristics of impurity removal, high raw material utilization rate, energy conservation and environmental protection, low cost, etc., expanding the application ways of industrial by-product gypsum. However, the process steps involved in this patent are complicated and the requirements for production equipment are high, which is not conducive to industrial production.

[0005] Therefore, it is of great significance to develop a method for preparing type II anhydrous gypsum using phosphogypsum solid waste as raw material, which is economical and environmentally friendly in the field. 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 roasting at medium temperature in a rotary kiln. Through medium-temperature roasting, high-quality type II anhydrous gypsum can be obtained, the purity of type II anhydrous gypsum can be improved, the comprehensive performance of type II anhydrous gypsum can be improved, and it 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 roasting at medium temperature in a rotary kiln, comprising the following steps:

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

[0010] S2. Flotation 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, perform solid - liquid separation to obtain a flotation phosphogypsum slurry;

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

[0012] S4. Medium - temperature roasting of phosphogypsum: Grind the pre - calcined phosphogypsum in step S3, then add it into a rotary kiln or a tunnel kiln for medium - temperature roasting. After the roasting is completed, the novel environmental - friendly material is obtained.

[0013] Preferably, in step S1, the solid - liquid ratio of the phosphogypsum to deionized water is 1:3 - 5, the addition amount of calcium oxide is 2 - 3% of the mass of phosphogypsum, the addition amount of disodium EADA 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. At the same time, calcium oxide and disodium EADA 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 - containing 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 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 type II anhydrous 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 composite additive in step S3 is 5-8% of the mass of the flotation phosphogypsum slurry; the temperature of the pre-calcination treatment is 200-220 °C, and the time is 1.5-2 h.

[0021] Preferably, the preparation method of the composite additive in step S3 is as follows:

[0022] Add sodium aluminate to deionized water, stir evenly, then add sodium sulfate, silica fume, and sodium gluconate, and perform constant-temperature stirring. After the stirring is completed, the composite additive is obtained.

[0023] In the present invention, a specific composite additive is added in the pre-calcination stage. Sodium aluminate promotes the transformation of dihydrate gypsum into type II anhydrous gypsum at a lower temperature. Sodium sulfate can be used as an activator to promote the hydration of type II anhydrous gypsum subsequently. Silica fume improves the strength and durability of the material through pozzolanic reaction. Sodium gluconate plays a role in regulating the hydration activity in the pre-calcination stage and forms amorphous carbon during the subsequent medium-temperature roasting process. A small amount of amorphous carbon may play a role similar to that of fine aggregate, filling the pores, thereby improving the strength of the material; through the synergistic effect of each raw material, the precise control of the calcination and subsequent hydration processes of phosphogypsum is achieved, and the comprehensive performance of the material is significantly improved.

[0024] Preferably, the mass ratio of sodium aluminate, deionized water, sodium sulfate, silica fume, and sodium gluconate is 8-12:90-100:5-8:4-6:3-4, the temperature of the constant-temperature stirring is 50-60 °C, and the time is 30-40 min.

[0025] Preferably, the rotation speed of the ball milling in step S4 is 800-900 r / min, and the time is 20-30 min; the process of the medium-temperature roasting is to rise to 460-500 °C at a heating rate of 7-10 °C / min and keep warm for 3-3.5 h.

[0026] In the present invention, by controlling the heating rate, crystal bursting and structural defects caused by rapid heating are avoided; by holding the temperature in the range of 460 - 500 °C, the full dehydration of gypsum dihydrate into type II anhydrous gypsum is ensured, thereby improving the purity of type II anhydrous gypsum.

[0027] The present invention also protects a new type of environmentally friendly material prepared by the method as described above.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The new type of environmentally friendly material provided by the present invention, which uses phosphogypsum solid waste as raw material and is subjected to medium-temperature roasting in a rotary kiln, effectively solves the problems of low comprehensive utilization rate of phosphogypsum, high impurity content, unstable product performance, etc. through the synergistic effect of steps such as pretreatment, flotation, pre-calcination and medium-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 type II anhydrous gypsum, regular crystal form and excellent performance, and can be widely used in fields such as building materials and molds. By converting and recycling large amounts of solid waste such as phosphogypsum, the utilization value of solid waste is improved on the premise of reducing environmental pollution, realizing the efficient resource utilization of phosphogypsum, and having significant economic and environmental benefits.

[0030] (2) The new type of environmentally friendly material provided by the present invention, which uses phosphogypsum solid waste as raw material and is subjected to medium-temperature roasting in a rotary kiln, uses a 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 flotation 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 the purity and quality of type II anhydrous gypsum.

[0031] (3) The composite additive prepared from the phosphogypsum solid waste as a raw material by medium-temperature roasting in a rotary kiln in the new environmentally friendly material provided by the present invention is composed of sodium metaaluminate, sodium sulfate, silica fume and sodium gluconate. Sodium metaaluminate can reduce the temperature at which dihydrate gypsum dehydrates and transforms into type II anhydrous gypsum, and synergistically with sodium sulfate, it can improve the early strength and hardening rate of gypsum, and more type II anhydrous gypsum crystal nuclei can be generated at the pre-calcination temperature. During the subsequent medium-temperature roasting process, it synergistically acts with sodium sulfate to promote the growth of type II anhydrous gypsum; sodium sulfate is a good activator for type II anhydrous gypsum, which can significantly improve the solubility and hydration rate of type II anhydrous gypsum, enabling the new environmentally friendly material to have good activity during subsequent application; silica fume acts together with sodium metaaluminate and sodium sulfate, which can improve the microstructure of the gypsum hardened body and enhance the mechanical properties of the material; at the same time, the added sodium gluconate plays a role in regulating the hydration activity during the pre-calcination stage, and carbonizes to form amorphous carbon during the subsequent medium-temperature roasting process. A small amount of amorphous carbon may play a role similar to that of fine aggregate, filling the pores, thereby improving the strength of the material; through the synergistic effect of each raw material in the composite additive, the prepared new environmentally friendly material has excellent properties such as fast hydration rate, high strength and good durability.

[0032] (4) The new environmentally friendly material prepared from the phosphogypsum solid waste as a raw material by medium-temperature roasting in a rotary kiln provided by the present invention avoids crystal explosion and structural defects caused by rapid heating by controlling the heating rate; it is kept warm in the temperature range of 460 - 500 °C to ensure that dihydrate gypsum is fully dehydrated and transformed into type II anhydrous gypsum, thereby improving the purity of type II anhydrous gypsum, avoiding overburning or underburning phenomena caused by high-temperature calcination, and ensuring the uniformity and stability of the material; at the same time, medium-temperature roasting is carried out using a rotary kiln or a tunnel kiln, which reduces energy consumption and meets environmental protection requirements. Specific embodiments

[0033] 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 them. 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.

[0034] 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 after preliminary aging treatment by recycling; the content of dihydrate gypsum and the main impurity composition in the phosphogypsum are as follows:

[0035] <![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

[0036] Example 1

[0037] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as raw material and adopting medium-temperature roasting in a rotary kiln, which is characterized by including the following steps:

[0038] 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 2.5% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stir at a rotation speed of 70 r / min and a temperature of 45 °C for 70 min. After stirring, add a sulfuric acid solution with a mass fraction of 5% to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0039] S2. Flotation 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 sodium hydroxide solution 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 carry out flotation treatment. The aeration amount of the flotation treatment is 0.45 L / min, the time is 25 min, and the rotation speed is 1700 r / min. After flotation, carry out solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0040] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 11% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 210 °C for 2 h, and obtain pre-calcined phosphogypsum after the treatment;

[0041] S4. Medium-temperature roasting of phosphogypsum: 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 medium-temperature roasting. The process of medium-temperature roasting is to raise the temperature to 480 °C at a heating rate of 8 °C / min and keep it warm for 3.5 h. After the roasting is completed, the new environmentally friendly material is obtained.

[0042] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0043] Add Tween 80 to deionized water, and obtain an emulsifier solution with a mass fraction of 2.5% after stirring evenly; Add 5 g of dodecylamine to 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 to 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.

[0044] The preparation method of the composite additive described in step S3 is as follows:

[0045] Add 10 g of sodium metaaluminate to 95 g of deionized water. After stirring evenly, add 7 g of sodium sulfate, 5 g of silica fume, and 3.5 g of sodium gluconate. Stir at a constant temperature of 55 °C for 35 min. After the stirring is completed, the composite additive is obtained.

[0046] Example 2

[0047] A preparation method of a new type of environmentally friendly material using phosphogypsum solid waste as a raw material and roasting at medium temperature in a rotary kiln, which is characterized by including the following steps:

[0048] 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 2.5% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.7% of the mass of phosphogypsum. Stir at a rotation speed of 70 r / min and a temperature of 45 °C for 60 min. After the stirring is completed, add a sulfuric acid solution with a mass fraction of 10% to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0049] S2. Flotation 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 sodium hydroxide solution with a mass fraction of 5% to adjust the pH to 9, then add a flotation agent accounting for 1.2% of the mass of the pretreated gypsum, and carry out flotation treatment. The aeration amount of the flotation treatment is 0.45 L / min, the time is 25 min, and the rotation speed is 1600 r / min. After the flotation is completed, carry out solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0050] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 10% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 210 °C for 1.5 h. After the treatment is completed, pre-calcined phosphogypsum is obtained;

[0051] S4. Medium-temperature roasting of phosphogypsum: 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 medium-temperature roasting. The process of medium-temperature roasting is to raise the temperature to 480 °C at a heating rate of 8 °C / min and hold for 3 h. After the roasting is completed, the new type of environmentally friendly material is obtained.

[0052] Among them, the preparation method of the flotation agent described in step S2 is as follows:

[0053] 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 70 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 70 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.

[0054] The preparation method of the composite additive described in step S3 is as follows:

[0055] 10 g of sodium aluminate was added to 95 g of deionized water, and after stirring evenly, 6 g of sodium sulfate, 5 g of silica fume, and 3.5 g of sodium gluconate were added, and stirring was carried out at a constant temperature of 55 °C for 35 min. After the stirring was completed, the said composite additive was obtained.

[0056] Example 3

[0057] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as a raw material and calcined at medium temperature in a rotary kiln, which is characterized by including the following steps:

[0058] 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 1:3. After dispersing evenly, calcium oxide and disodium EADA were added. The addition amount of calcium oxide was 2% of the mass of phosphogypsum, and the addition amount of disodium EADA was 0.5% of the mass of phosphogypsum. Stirring was carried out at a rotation speed of 60 r / min and a temperature of 40 °C for 80 min. After the stirring was completed, a sulfuric acid solution with a mass fraction of 5% was added to adjust the pH to 7, and then centrifugation and filtration were carried out to obtain pretreated phosphogypsum.

[0059] S2. Flotation 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. A sodium hydroxide solution with a mass fraction of 5% was added to adjust the pH to 8, and then a flotation agent accounting for 1% of the mass of the pretreated gypsum was added for flotation treatment. The aeration amount during the flotation treatment was 0.4 L / min, the time was 30 min, and the rotation speed was 1500 r / min. After the flotation was completed, solid-liquid separation was carried out to obtain a flotation phosphogypsum slurry (with a water content of 40%).

[0060] S3. Pre-calcination of phosphogypsum: A composite additive was added to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive was 9% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcination was carried out at 200 °C for 2 h, and pre-calcined phosphogypsum was obtained after the treatment was completed.

[0061] S4. Medium-temperature roasting of phosphogypsum: The pre-roasted phosphogypsum in step S3 is ball-milled at a rotation speed of 800 r / min for 30 min, then added to a rotary kiln for medium-temperature roasting. The process of medium-temperature roasting is to increase the temperature to 460 °C at a heating rate of 7 °C / min and hold for 3.5 h. After the roasting is completed, the new environmentally friendly material is obtained.

[0062] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0063] Tween 80 is added to deionized water, and after stirring evenly, an emulsifier solution with a mass fraction of 2% is obtained; 4 g of dodecylamine is added to 80 g of the emulsifier solution, and emulsification is carried out for 12 min under the conditions of an ultrasonic frequency of 30 kHz and a power of 50 W to obtain a dodecylamine emulsion; 2 g of terpineol is added to 70 g of the emulsifier solution, and emulsification is carried out for 12 min under the conditions of an ultrasonic frequency of 30 kHz and a power of 50 W to obtain a terpineol emulsion; 80 g of the dodecylamine emulsion and 70 g of the terpineol emulsion are mixed evenly, and then 3 g of sodium oleate and 1 g of carboxymethyl cellulose are added and stirred evenly to obtain the flotation agent.

[0064] The preparation method of the composite additive in step S3 is as follows:

[0065] 8 g of sodium meta-aluminate is added to 90 g of deionized water, and after stirring evenly, 5 g of sodium sulfate, 4 g of silica fume, and 3 g of sodium gluconate are added, and stirring is carried out at a constant temperature of 50 °C for 40 min. After the stirring is completed, the composite additive is obtained.

[0066] Example 4

[0067] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as a raw material and medium-temperature roasting in a rotary kiln, which is characterized by including the following steps:

[0068] S1. Pretreatment of phosphogypsum: The phosphogypsum is ground and sieved through a 100-mesh sieve, then added to deionized water. The solid-liquid ratio of phosphogypsum to deionized water is 1:5. 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 1% of the mass of phosphogypsum. Stirring is carried out at a rotation speed of 80 r / min and a temperature of 50 °C for 50 min. After the stirring is completed, 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.

[0069] S2. Flotation of phosphogypsum: Add the pretreated phosphogypsum in step S1 into deionized water. The mass ratio of the pretreated phosphogypsum to deionized water is 1:5. Add a sodium hydroxide solution with a mass fraction of 10% to adjust the pH to 10. Then add a flotation agent accounting for 1.5% of the mass of the pretreated gypsum and conduct flotation treatment. The air inflow rate for the flotation treatment is 0.5 L / min, the time is 30 min, and the rotation speed is 1800 r / min. After the flotation is completed, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 50%);

[0070] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 12% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 220 °C for 1.5 h to obtain pre-calcined phosphogypsum after the treatment is completed;

[0071] S4. Medium-temperature roasting of phosphogypsum: Ball-mill the pre-calcined phosphogypsum in step S3 at a rotation speed of 900 r / min for 20 min, then add it into a rotary kiln for medium-temperature roasting. The process of the medium-temperature roasting is to increase the temperature to 500 °C at a heating rate of 10 °C / min and keep it warm for 3 h. After the roasting is completed, the novel environmental protection material is obtained.

[0072] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0073] Add Tween 80 into deionized water, and after stirring evenly, obtain an emulsifier solution with a mass fraction of 3%; Add 6 g of dodecylamine into 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 into 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, then add 4 g of sodium oleate and 2 g of carboxymethyl cellulose, and stir evenly to obtain the flotation agent.

[0074] The preparation method of the composite additive in step S3 is as follows:

[0075] Add 12 g of sodium meta-aluminate into 100 g of deionized water, stir evenly, then add 8 g of sodium sulfate, 6 g of silica fume, and 4 g of sodium gluconate, and stir at a constant temperature of 60 °C for 30 min. After the stirring is completed, the composite additive is obtained.

[0076] Comparative Example 1

[0077] A preparation method of a novel environmental protection material using phosphogypsum solid waste as a raw material and performing medium-temperature roasting in a rotary kiln, which is characterized by including the following steps:

[0078] 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 1:4. After dispersing evenly, add calcium oxide and disodium EADA. The addition amount of calcium oxide is 2.5% 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, add a sulfuric acid solution with a mass fraction of 5% to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0079] S2. Flotation 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 sodium hydroxide solution 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 flotation treatment is 0.45 L / min, the time is 25 min, and the speed is 1700 r / min. After flotation, perform solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0080] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 11% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 210 °C for 2 h to obtain pre-calcined phosphogypsum after treatment;

[0081] S4. Medium-temperature roasting of phosphogypsum: 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 medium-temperature roasting. The process for medium-temperature roasting is to increase the temperature to 480 °C at a heating rate of 8 °C / min and hold for 3.5 h. After roasting, the novel environmental protection material is obtained.

[0082] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0083] Add Tween 80 to deionized water and stir evenly to obtain an emulsifier solution with a mass fraction of 2.5%. Add 2.5 g of terpineol to 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 75 g of the terpineol emulsion with 3.5 g of sodium oleate and 1.5 g of carboxymethyl cellulose and stir evenly to obtain the flotation agent.

[0084] The preparation method of the composite additive in step S3 is as follows:

[0085] Add 10 g of sodium aluminate to 95 g of deionized water, stir evenly, then add 7 g of sodium sulfate, 5 g of silica fume, and 3.5 g of sodium gluconate, and stir at a constant temperature of 55 °C for 35 min. After stirring, the composite additive is obtained.

[0086] Compared with Example 1, dodecylamine was not added to the flotation agent in this comparative example.

[0087] Comparative Example 2

[0088] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as raw material and medium-temperature roasting in a rotary kiln, characterized by comprising the following steps:

[0089] 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 2.5% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stir at a rotation speed of 70 r / min and a temperature of 45 °C for 70 min. After stirring, add a sulfuric acid solution with a mass fraction of 5% to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0090] S2. Flotation 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 sodium hydroxide solution 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 carry out flotation treatment. The aeration amount of the flotation treatment is 0.45 L / min, the time is 25 min, and the rotation speed is 1700 r / min. After flotation, carry out solid-liquid separation to obtain a flotation phosphogypsum slurry (with a water content of 45%);

[0091] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 11% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 210 °C for 2 h to obtain pre-calcined phosphogypsum after the treatment;

[0092] S4. Medium-temperature roasting of phosphogypsum: 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 medium-temperature roasting. The process of medium-temperature roasting is to raise the temperature to 480 °C at a heating rate of 8 °C / min and keep it warm for 3.5 h. After the roasting is completed, the new environmentally friendly material is obtained.

[0093] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0094] 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 n-decanol 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 an n-decanol emulsion; 90 g of the dodecylamine emulsion and 75 g of the n-decanol 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.

[0095] The preparation method of the composite additive described in step S3 is as follows:

[0096] 10 g of sodium aluminate was added to 95 g of deionized water, and after stirring evenly, 7 g of sodium sulfate, 5 g of silica fume, and 3.5 g of sodium gluconate were added, and stirring was carried out at a constant temperature of 55 °C for 35 min. After the stirring was completed, the said composite additive was obtained.

[0097] Compared with Example 1, in this comparative example, terpineol in the flotation agent was replaced with n-decanol.

[0098] Comparative Example 3

[0099] A preparation method of a new environmentally friendly material using phosphogypsum solid waste as a raw material and roasting at medium temperature in a rotary kiln, which is characterized by including the following steps:

[0100] 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 being dispersed evenly, calcium oxide and disodium EADA were added. The addition amount of calcium oxide was 2.5% 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 the stirring was completed, a sulfuric acid solution with a mass fraction of 5% was added to adjust the pH to 7, and then centrifugation and filtration were carried out to obtain pretreated phosphogypsum;

[0101] S2. Flotation 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. A sodium hydroxide solution 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 during the flotation treatment was 0.45 L / min, the time was 25 min, and the rotation speed was 1700 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%);

[0102] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 11% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 210 °C for 2 h to obtain pre-calcined phosphogypsum after the treatment is completed;

[0103] S4. Medium-temperature roasting of phosphogypsum: 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 medium-temperature roasting. The process of medium-temperature roasting is to increase the temperature to 480 °C at a heating rate of 8 °C / min and keep it warm for 3.5 h. After the roasting is completed, the novel environmental protection material is obtained.

[0104] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0105] Add Tween 80 to deionized water, and stir evenly to obtain an emulsifier solution with a mass fraction of 2.5%; add 5 g of dodecylamine to 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 to 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.

[0106] The preparation method of the composite additive in step S3 is as follows:

[0107] Add 17 g of sodium sulfate to 95 g of deionized water, stir evenly, then add 5 g of silica fume and 3.5 g of sodium gluconate, and stir at a constant temperature of 55 °C for 35 min. After the stirring is completed, the composite additive is obtained.

[0108] Compared with Example 1, sodium meta-aluminate is not added to the composite additive in this comparative example.

[0109] Comparative Example 4

[0110] A preparation method of a novel environmental protection material using phosphogypsum solid waste as a raw material and medium-temperature roasting in a rotary kiln, which is characterized by including the following steps:

[0111] 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 2.5% of the mass of phosphogypsum, and the addition amount of disodium EADA is 0.8% of the mass of phosphogypsum. Stir at a rotation speed of 70 r / min and a temperature of 45 °C for 70 min. After stirring, add a sulfuric acid solution with a mass fraction of 5% to adjust the pH to 7, and then centrifuge and filter to obtain pretreated phosphogypsum;

[0112] S2. Flotation 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 sodium hydroxide solution 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 amount of the 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%);

[0113] S3. Pre-calcination of phosphogypsum: Add a composite additive to the flotation phosphogypsum slurry in step S2. The addition amount of the composite additive is 11% of the mass of the flotation phosphogypsum slurry. After mixing evenly, pre-calcine at 210 °C for 2 h to obtain pre-calcined phosphogypsum after treatment;

[0114] S4. Medium-temperature roasting of phosphogypsum: 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 medium-temperature roasting. The process of medium-temperature roasting is to raise the temperature to 480 °C at a heating rate of 8 °C / min and hold for 3.5 h. After roasting, the novel environmental protection material is obtained.

[0115] Among them, the preparation method of the flotation agent in step S2 is as follows:

[0116] Add Tween 80 to deionized water, and stir evenly to obtain an emulsifier solution with a mass fraction of 2.5%; add 5 g of dodecylamine to 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 to 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.

[0117] The preparation method of the composite additive in step S3 is as follows:

[0118] Add 13.5 g of sodium aluminate to 95 g of deionized water. After stirring evenly, add 12 g of sodium sulfate and stir at a constant temperature of 55 °C for 35 min. After the stirring is completed, the composite additive is obtained.

[0119] Compared with Example 1, silica fume and sodium gluconate were not added to the composite additive in this comparative example.

[0120] Perform performance tests on the new environmentally friendly materials prepared in Examples 1-4 and Comparative Examples 1-4. Among them, use a gypsum three-phase meter to measure the content of β-type hemihydrate gypsum in the new environmentally friendly materials; Standard consistency water consumption: Weigh 250 g of the new 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 new environmentally friendly material into the stirring pot within 10 s so that the water completely wets the new environmentally friendly material. Start timing from the moment the new environmentally friendly material comes into contact with water, and stir quickly for 30 s to form a building gypsum slurry with a certain fluidity. Then, pour the slurry into a gypsum consistency cylinder. At 50 s, lift the consistency cylinder vertically at a constant speed. After the slurry has 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 new environmentally friendly material are all carried out according to this water-to-plaster ratio. Compressive strength and flexural strength: Use the measured standard consistency water consumption to prepare the hardened body of the new environmentally friendly material. Slowly add 900 g of the new environmentally friendly material into the mixing 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 of GB / T 9776-2022 "Building Gypsum", test the flexural and compressive strengths of the hardened body of the new environmentally friendly material. The test results are shown in Tables 1 and 2 below.

[0121] Table 1

[0122]

[0123]

[0124] As can be seen from Table 1 above, the new environmentally friendly material prepared by the present invention has a higher content of type II anhydrous gypsum and higher whiteness, can meet the requirements of the building materials industry for the whiteness of gypsum powder, and can be used for decorative products, interior painting, etc., laying a foundation for the large-scale utilization of phosphogypsum.

[0125] Table 2

[0126]

[0127] As can be seen from Table 2 above, the novel environmentally friendly material prepared by the present invention has a lower standard consistency water demand, and at the same time has excellent mechanical properties, showing good application prospects.

[0128] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. 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 it at medium temperature in a rotary kiln, 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 composite additive 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-burned phosphogypsum in step S3, and then adding it into a rotary kiln or a tunnel kiln for medium-temperature roasting. After the roasting is completed, the novel environmentally friendly material is obtained.

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 2-3% 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: The amount of the composite additive added in step S3 is 9-12% of the mass of the flotation phosphogypsum slurry; the temperature of the pre-calcination treatment is 200-220° C., and the time is 1.5-2 hours.

7. The preparation method according to claim 1, characterized in that: The preparation method of the composite additive in step S3 is as follows: Sodium aluminate is added into deionized water, and after being stirred evenly, sodium sulfate, silica fume and sodium gluconate are added thereto, and the mixture is stirred at a constant temperature. After the stirring is completed, the composite additive is obtained.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the sodium aluminate, deionized water, sodium sulfate, silica fume and sodium gluconate is 8-12:90-100:5-8:4-6:3-4, and the constant temperature stirring temperature is 50-60° C. and the time is 30-40 min.

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 medium-temperature calcination process is to increase the temperature to 460-500°C at a heating rate of 7-10°C / min and keep the temperature for 3-3.5h.

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

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