阅读说明：本技术 一种常压下微波辐照磷石膏制备半水硫酸钙晶须的方法 (Method for preparing calcium sulfate hemihydrate crystal whiskers by irradiating phosphogypsum with microwaves under normal pressure ) 是由 郭荣鑫 林志伟 张绍奇 夏海廷 杨洋 颜峰 于 2019-11-05 设计创作，主要内容包括：本发明涉及一种以微波辐照为热源,常压下以磷石膏为原料在醇水-硫酸盐溶液中制备半水硫酸钙晶须的方法,属于无机功能材料制备技术领域。本发明是以微波辐照取代水浴、油浴、蒸压等常规加热方式,利用磷石膏中存在的高介电常数杂质及醇水溶液中的醇、水吸收电磁波,常压下以磷石膏为原料在醇水-硫酸盐溶液中制备半水硫酸钙晶须。与现有的以磷石膏为原料制备半水硫酸钙晶须技术相比,本发明具有转化效率高,生产时间短,反应条件温和,无需高压反应设施,对设备无腐蚀性,醇类溶液可以循环再利用等优点,具有显著的社会、经济及环保效益。(The invention relates to a method for preparing calcium sulfate hemihydrate whiskers in an alcohol water-sulfate solution by taking microwave irradiation as a heat source and phosphogypsum as a raw material under normal pressure, belonging to the technical field of preparation of inorganic functional materials. The invention uses microwave irradiation to replace conventional heating modes such as water bath, oil bath, steam pressure and the like, utilizes high dielectric constant impurities in phosphogypsum and alcohol and water in alcohol-water solution to absorb electromagnetic waves, and uses the phosphogypsum as a raw material to prepare the calcium sulfate hemihydrate crystal whisker in the alcohol-water sulfate solution under normal pressure. Compared with the prior art for preparing the calcium sulfate hemihydrate crystal whisker by taking the phosphogypsum as the raw material, the method has the advantages of high conversion efficiency, short production time, mild reaction condition, no need of high-pressure reaction facilities, no corrosivity on equipment, capability of recycling alcohol solution and the like, and has remarkable social, economic and environmental benefits.)

1. A method for preparing calcium sulfate hemihydrate crystal whiskers by microwave irradiation of phosphogypsum under normal pressure is characterized by comprising the following steps: washing the original phosphogypsum with water, and irradiating the original phosphogypsum with microwave until the original phosphogypsum is constant in weight; adding the phosphogypsum subjected to microwave irradiation into an alcohol water-sulfate solution in proportion, putting the mixed solution into a microwave irradiation device, setting temperature parameters, connecting and starting an external steam condensing device, starting microwave irradiation, and heating to a control temperature under normal pressure; pouring the mixed solution into a sand core filter for filtering after the irradiation is finished, and adding absolute ethyl alcohol into the filtered substance to stop the reaction; and finally, placing the filtered substance under microwave irradiation for drying to constant weight to obtain a calcium sulfate hemihydrate whisker finished product.

2. The method for preparing calcium sulfate hemihydrate whiskers by microwave irradiation of phosphogypsum under normal pressure according to claim 1, is characterized in that: the method comprises the following specific steps:

(1) washing the original phosphogypsum with water, and drying the original phosphogypsum to constant weight by microwave irradiation;

(2) preparing an alcohol-water solution from one or more of glycerol, ethanol and glycol, adding 5-20% of microwave-irradiated phosphogypsum into the solution, and uniformly stirring;

(3) taking out sulfate Na₂SO₄、K₂SO₄、MgSO₄、Li₂SO₄Adding 1-20% of the phosphogypsum in the step (2) into the solution, and uniformly stirring to form a mixed solution;

(4) pouring the mixed solution into a closed reaction container, placing the closed reaction container in a microwave reaction device, connecting a condenser pipe of the closed container with an external steam condensing device, starting equipment at normal pressure to start microwave irradiation, and heating to 85-110 ℃;

(5) after the irradiation is carried out for 20min to 60min, the microwave irradiation equipment is closed, the solution in the closed reaction container is poured into a sand core filter for filtration, and the filtered substance is added with absolute ethyl alcohol to terminate the hydration reaction;

(6) and (4) placing the filtered substance in microwave irradiation at 50 ℃ for drying to constant weight to obtain the calcium sulfate hemihydrate crystal whisker.

3. The method for preparing calcium sulfate hemihydrate whiskers by microwave irradiation of phosphogypsum under normal pressure according to claim 2, is characterized in that: the mass fraction of the alcohol-water solution is 50-90%.

4. The method for preparing calcium sulfate hemihydrate whiskers by microwave irradiation of phosphogypsum under normal pressure according to claim 2, is characterized in that: the original phosphogypsum is powdery solid waste generated in the production of phosphoric acid by phosphorus chemical enterprises, and the main component of the original phosphogypsum is CaSO₄·2H₂O, containing F, SiO₂、Al₂O₃、MgO、Fe₂O₃、P₂O₅And organic impurities.

5. The method for preparing calcium sulfate hemihydrate whiskers by microwave irradiation of phosphogypsum under normal pressure according to claim 2, is characterized in that: the mixed solution does not need to be stirred in the microwave irradiation reaction process.

Technical Field

The invention relates to a method for preparing calcium sulfate hemihydrate whiskers by microwave irradiation of phosphogypsum under normal pressure, belonging to the technical field of preparation of inorganic functional materials.

Background

The phosphogypsum is a solid waste generated in the production of phosphoric acid by phosphorus chemical enterprises, and 4-5t of phosphogypsum is generated every 1t of phosphoric acid. According to statistics, the phosphogypsum production in 2015 in China is about 8000 ten thousand tons, and the resource utilization rate is about 33%. The large amount of stockpiling of the phosphogypsum not only occupies land, pollutes environment and wastes resources, but also restricts the sustainable development of phosphorus chemical enterprises in China. The calcium sulfate hemihydrate crystal whisker is a fine fibrous sub-nanometer material formed by taking gypsum, limestone, calcite and the like as main raw materials and growing in a single crystal form through certain process control, has the advantages of high strength, wear resistance, corrosion resistance, no toxicity, easiness in compounding with polymers and the like, and is widely applied to industries of building materials, plastics, resins, rubber, papermaking, asphalt and the like. CaSO in phosphogypsum₄·2H₂The content of O reaches more than 85 percent, and the calcium sulfate hemihydrate crystal whisker is an ideal raw material for preparing the calcium sulfate hemihydrate crystal whisker. The conventional preparation method of the calcium sulfate hemihydrate crystal whisker mainly comprises an evaporation method and a salt solution method. The steam pressure method is to let CaSO₄·2H₂The O is dehydrated and converted into the calcium sulfate hemihydrate crystal whisker in saturated steam generated at high temperature and high pressure, and has higher requirements on the performance of equipment and energy consumption. The salt solution method requires a high-concentration salt solution as a reaction medium, has high corrosion to equipment, and is not beneficial to industrial production.

Microwave irradiation is an efficient heating means. Compared with the conventional heating mode, the microwave irradiation is integral heating, and the method has the advantages of high temperature rise speed, low heat loss, low energy consumption, cleanness, no pollution and the like. Water and alcohol have the characteristic of high dielectric constant, and microwave energy can be converted into heat energy under microwave irradiation. The invention replaces the conventional heating mode with microwave irradiation, and prepares the calcium sulfate hemihydrate crystal whisker in an alcohol-water-sulfate solution reaction system by taking phosphogypsum as a raw material.

Through the research of literature, the patent of a method for preparing gypsum whisker under normal pressure (application publication No. CN 107059134A) discloses a method for preparing gypsum whisker in salt solution and organic solvent by using dihydrate gypsum as raw material. The differences of the patent compared with the invention are as follows: the method is a conventional heating mode, sodium chloride is used, a PH regulator is required to be added for equipment with strong corrosivity, the solution is required to be stirred in the reaction process, the reaction time is 4-6 h, and after the reaction is finished, the reaction product is required to be dried in an oven for 1-8 h; the method takes microwave irradiation as a heat source, uses sulfate, has no corrosion to equipment, does not need to use a pH regulator, does not need stirring in the reaction process, has the reaction time of 20-60 min, and after the reaction is finished, the reaction product is irradiated to constant weight (about 20 min) by microwave.

A method for preparing gypsum whiskers in alcohol water under conventional heating is disclosed in an integrated method for preparing and modifying gypsum special-shaped powder in an atmospheric pressure open system (an authorization publication No. CN 103523814B). The heating of the patent is a conventional heating mode, gypsum needs to be subjected to crushing, screening, ball milling and water washing pretreatment, stirring is needed in the heating process, the reaction time is 20-180 min, the reaction temperature is 90-140 ℃, the added modifying agent is one or more of titanate coupling agent series, silane coupling agent series and stearic acid series, and the product is dried conventionally; the method takes microwave irradiation as a heat source, stirring is not needed in the reaction process, the reaction time is 20-60 min, and the added sulfate is Na₂SO₄、K₂SO₄、MgSO₄、Li₂SO₄One or more of the above, and the drying method of the product is microwave irradiation.

A control method for the directional growth of semi-hydrated gypsum single crystal is disclosed in the patent of a control method for the directional growth of semi-hydrated gypsum single crystal (No. CN 105624772B), which is completely different from the invention in that an acidity regulator is added into phosphogypsum, the phosphogypsum is aged for 24h for pretreatment, a reaction device is a reaction kettle with a condensation reflux device, impurity stabilizers are sorbitol, mannitol and glycerol, a crystal face selection adsorbent is one of maleic acid, polycarboxylic acid and succinic acid, an ion motion controller is added into a reaction system at the same time, the reaction is carried out for 0.5 h-2 h, and the product is dried to be conventional drying.

A method for preparing α -hemihydrate gypsum (application publication No. CN 108483957A) discloses a method for preparing α -type high-strength gypsum by using microwave irradiation as a heat source and gypsum as a raw material, wherein a product prepared by the method is α -hemihydrate gypsum, belongs to the technical field of inorganic cementing materials, the length-diameter ratio of crystals of the α -type high-strength gypsum is about 1: 1, necessary pretreatment such as crushing and screening of phosphogypsum is needed during preparation, a reactor is needed to be a pressure-resistant reaction kettle or a kiln with a stirring or rotating function in the reaction preparation process, the reaction temperature is 110-400 ℃, cooling and aging are needed after the reaction is finished, the product prepared by the method is calcium sulfate hemihydrate whisker, belongs to the technical field of inorganic functional materials, the length-diameter ratio of the crystals of the phosphogypsum is not less than 10: 1, crushing and screening of the phosphogypsum are not needed during preparation, the reaction process is normal pressure and stirring are not needed, the reaction temperature is 85-110 ℃.

The patent "method for microwave-assisted synthesis of calcium sulfate whiskers in inorganic salt solution" (application publication No. CN 107723800 a) discloses a method for synthesizing calcium sulfate whiskers in salt solution under microwave irradiation. The raw material of the patent is desulfurized gypsum with CaSO4 & 2H₂The content of O is high (90-95%), the gypsum crystal has good crystallization form and low impurity content, the impurities do not need to be pretreated in the resource utilization, the resource utilization difficulty is low, the reaction solution is inorganic salt water solution, the mass concentration of the inorganic salt water solution is 4-45 g/mL, the salt is any one or mixture of sodium chloride, ammonium sulfate, potassium chloride and calcium chloride, a crystal form control agent needs to be added in the reaction process, stirring is needed, aging is carried out for 2-6 hours, and water is added to wash the mixture to be neutral; the raw material used by the invention is phosphogypsum except CaSO₄·2H₂The O also contains various harmful impurities, which can seriously affect the crystal structure and the physical and mechanical properties of the gypsum and have larger difficulty in resource utilization. The reaction solution of the invention is alcohol water-sulfate solution, and the sulfate is Na₂SO₄、K₂SO₄、MgSO₄、Li₂SO₄One or more of the components are added without adding a crystal form control agent, and stirring and ageing are not needed.

Through comparison of the above literature data, it can be found that the method for preparing calcium sulfate hemihydrate whiskers in an alcohol-water-sulfate solution reaction system under normal pressure by using microwave irradiation as a heat source and phosphogypsum as a raw material has not been reported in the literature.

Disclosure of Invention

The invention provides a method for preparing calcium sulfate hemihydrate whiskers by microwave irradiation of phosphogypsum under normal pressure, which is characterized in that conventional heating modes such as water bath, oil bath, steam pressure and the like are replaced by microwave irradiation, high dielectric constant impurities in the phosphogypsum and alcohol and water in an alcohol-water solution are utilized to absorb electromagnetic waves to generate heat, and the phosphogypsum is used as a raw material to prepare the calcium sulfate hemihydrate whiskers in the alcohol-water-sulfate solution under the normal pressure.

The technical scheme of the invention is as follows:

washing the original phosphogypsum with water, and irradiating the original phosphogypsum with microwave until the original phosphogypsum is constant in weight; adding the phosphogypsum subjected to microwave irradiation into an alcohol water-sulfate solution in proportion, putting the mixed solution into a microwave irradiation device, connecting and starting an external steam condensing device, setting temperature parameters, starting microwave irradiation, and heating to a control temperature under normal pressure; pouring the mixed solution into a sand core filter for filtering after the irradiation is finished, and adding absolute ethyl alcohol into the filtered substance to stop the reaction; and finally, placing the filtered substance under microwave irradiation for drying to constant weight to obtain a calcium sulfate hemihydrate whisker finished product.

The method comprises the following specific steps:

(1) washing the original phosphogypsum with water, and drying the original phosphogypsum to constant weight by microwave irradiation;

(2) preparing an alcohol-water solution from one or more of glycerol, ethanol and glycol, adding 5-20% of microwave-irradiated phosphogypsum into the solution, and uniformly stirring;

(3) taking out sulfate Na₂SO₄、K₂SO₄、MgSO₄、Li₂SO₄Adding one or more of the above into a solution with the mass of 1-20% of the phosphogypsum, and uniformly stirring to form a mixed solution;

(4) pouring the mixed solution into a closed reaction container, placing the closed reaction container in a microwave reaction device, connecting a condenser pipe of the closed container with an external steam condensing device, starting equipment at normal pressure to start microwave irradiation, and heating to 85-110 ℃;

(5) after the irradiation is carried out for 20min to 60min, the microwave irradiation equipment is closed, the solution in the closed reaction container is poured into a sand core filter for filtration, and the filtered substance is added with absolute ethyl alcohol to terminate the hydration reaction;

(6) and (4) placing the filtered substance in microwave irradiation at 50 ℃ for drying to constant weight to obtain the calcium sulfate hemihydrate crystal whisker.

The mass fraction of the alcohol-water solution is 50-90%.

The original phosphogypsum is powdery solid waste generated in the production of phosphoric acid by phosphorus chemical enterprises, and the main component of the original phosphogypsum is CaSO₄·2H₂O, containing F, SiO₂、Al₂O₃、MgO、Fe₂O₃、P₂O₅And organic matter and the like.

The working principle of the invention is as follows: the invention replaces the conventional heating mode with microwave irradiation, utilizes high dielectric constant impurities in phosphogypsum and alcohol aqueous solution to absorb and convert microwave energy to generate heat, and prepares the calcium sulfate hemihydrate crystal whisker in the alcohol water-sulfate solution by taking the phosphogypsum as a raw material under normal pressure. The invention uses alcohols to adjust the activity of water and reduce the reaction temperature; the dissolution of calcium sulfate dihydrate and the precipitation of calcium sulfate hemihydrate are accelerated by the oscillation effect of microwaves, so that the reaction speed is accelerated; and alcohol hydroxyl is adsorbed on the side surface of the calcium sulfate hemihydrate crystal to form a hydrogen bond layered structure to hinder the lateral growth of the calcium sulfate hemihydrate crystal, and meanwhile, cations precipitated by sulfuric acid salt and anions precipitated by phosphogypsum form ion pairs to enable calcium ions to migrate to a crystal (111) surface to promote the calcium sulfate hemihydrate crystal to grow on a C axis to form the calcium sulfate hemihydrate crystal whisker with a high length-diameter ratio.

The invention has the beneficial effects that: the method can complete the conversion of the main component calcium sulfate dihydrate of the phosphogypsum into the calcium sulfate hemihydrate crystal whisker within 20-60 min, has the advantages of short production time, high conversion efficiency, mild reaction conditions, no need of high-pressure reaction facilities, no corrosivity to equipment, capability of recycling alcohol solution and the like, and has remarkable social, economic and environmental benefits, and the conversion rate reaches more than 99%.

Drawings

FIG. 1 is an SEM image of fibrous calcium sulfate hemihydrate whiskers prepared in example 1;

FIG. 2 is an SEM image of fibrous calcium sulfate hemihydrate whiskers prepared in example 2;

FIG. 3 is an SEM image of fibrous calcium sulfate hemihydrate whiskers prepared in example 3;

FIG. 4 is an SEM image of fibrous calcium sulfate hemihydrate whiskers prepared in example 4;

figure 5 is an XRD pattern of phosphogypsum and fibrous calcium sulphate hemihydrate whiskers prepared in the examples.

Detailed Description

The invention is further described with reference to the following figures and specific examples.