阅读说明：本技术 天然水菱镁制备六角片状阻燃型氢氧化镁的方法 (Method for preparing hexagonal flaky flame-retardant magnesium hydroxide from natural hydromagnesite ) 是由 刘志启 焦玲丽 赵鹏程 代建国 周自圆 李娜 于 2021-07-22 设计创作，主要内容包括：本发明公开了一种天然水菱镁制备六角片状阻燃型氢氧化镁的方法,包括以下步骤：S1、将天然水菱镁粉碎筛分；S2、将粉碎筛分的天然水菱镁煅烧得到活性氧化镁；S3、对活性氧化镁进行筛分；S4、以活性氧化镁为原料、去离子水为溶剂配置成氧化镁悬浮液；S5、将氧化镁悬浮液置入封闭式加热装置中进行加热反应得到溶液；S6、取出溶液自然冷却至室温得到产物,将产物进行过滤、洗涤、干燥,得到六角片状氢氧化镁。本发明方法过程中无需添加任何其他原料或助剂,即可得到分散性好、形貌规则的六角片状阻燃型氢氧化镁,具有原料成本低、操作简单、产物纯度高等优点。(The invention discloses a method for preparing hexagonal flaky flame-retardant magnesium hydroxide from natural hydromagnesite, which comprises the following steps: s1, smashing and screening the natural hydromagnesite; s2, calcining the crushed and screened natural hydromagnesite to obtain active magnesium oxide; s3, screening the active magnesium oxide; s4, preparing a magnesium oxide suspension by taking active magnesium oxide as a raw material and deionized water as a solvent; s5, putting the magnesium oxide suspension into a closed heating device for heating reaction to obtain a solution; and S6, taking out the solution, naturally cooling to room temperature to obtain a product, and filtering, washing and drying the product to obtain hexagonal flaky magnesium hydroxide. The hexagonal flaky flame-retardant magnesium hydroxide with good dispersibility and regular appearance can be obtained without adding any other raw materials or auxiliary agents in the process of the method, and the method has the advantages of low raw material cost, simplicity in operation, high product purity and the like.)

1. The method for preparing hexagonal flaky flame-retardant magnesium hydroxide from natural hydromagnesite is characterized by comprising the following steps of:

s1, crushing the natural hydromagnesite and then screening;

s2, heating the natural hydromagnesite obtained by crushing and screening in the step S1 to a set temperature, and then carrying out heat preservation and calcination to completely decompose the natural hydromagnesite to obtain active magnesium oxide, wherein:

the heating rate is 5-15 ℃/min, the set temperature to be reached by heating is 300-800 ℃, and the time of heat preservation and calcination is 1-4 h;

s3, screening the active magnesium oxide obtained in the step S2;

s4, preparing a magnesium oxide suspension by taking the active magnesium oxide obtained by screening in the step S3 as a raw material and deionized water as a solvent, and uniformly dispersing the raw material in the magnesium oxide suspension by adopting ultrasonic dispersion, wherein:

the solid-liquid ratio of the raw material to the solvent is 1: 9-1: 4, namely the solid content of the magnesium oxide suspension is 10-20 wt%;

s5, putting the magnesium oxide suspension obtained in the step S4 into a closed heating device with a stirring function for heating reaction to obtain a solution, wherein:

the heating temperature in the closed heating device is 100-200 ℃, the stirring speed is 200-600 rpm, and the reaction time is 1-3 h;

s6, taking out the solution obtained in the step S5, naturally cooling to room temperature to obtain a product in the solution, and filtering, washing and drying the product after the product is taken out to obtain hexagonal flaky magnesium hydroxide.

2. The method for preparing the hexagonal flaky flame-retardant magnesium hydroxide according to claim 1, wherein the volume of the natural hydromagnesite with the particle size of less than 2 μm accounts for 50% of the total volume of the natural hydromagnesite after the natural hydromagnesite is crushed and sieved in step S1.

3. The method for preparing hexagonal flaky flame-retardant magnesium hydroxide according to claim 1, wherein the volume of the activated magnesium oxide with the particle size of less than 2 μm is 50% of the total volume of the activated magnesium oxide after sieving in step S3.

4. The method for preparing hexagonal flaky flame-retardant magnesium hydroxide according to claim 1, wherein in step S4, the power of ultrasonic dispersion is 40-3500W, and the frequency of ultrasonic wave is 10-50 kHz.

5. The method for preparing hexagonal flaky flame-retardant magnesium hydroxide according to claim 1, wherein in step S5, the heating temperature of the closed heating device is 140-160 ℃.

6. The method for preparing the hexagonal flaky flame-retardant magnesium hydroxide according to the natural hydromagnesite of claim 1, wherein in the step S5, the closed heating device is a hydrothermal reaction kettle with a stirring function and a volume of 2L, and the filling rate of the hydrothermal reaction kettle is 50% -80%.

7. The method for preparing hexagonal flaky flame-retardant magnesium hydroxide according to claim 1, wherein in the step S6, vacuum drying is adopted during drying, and the drying temperature is 50-110 ℃.

8. The method for preparing hexagonal flaky flame-retardant magnesium hydroxide according to claim 1, wherein in step S6, the obtained micron-sized hexagonal flaky magnesium hydroxide has a particle size of 0.8-1.2 μm, and the peak intensity ratio I of (001) to (101) crystal faces is₀₀₁/I₁₀₁0.8 to 2.0.

Technical Field

The invention relates to the field of magnesium hydroxide preparation methods, in particular to a method for preparing hexagonal flaky flame-retardant magnesium hydroxide from natural hydromagnesite.

Background

The chemical formula of the natural hydromagnesite is 4MgCO₃·Mg(OH)₂·4H₂O is a carbonate mineral with white texture and low impurity content. Hydromagnesite has the following advantages: (1) the reserves are rich, and a plurality of mineral deposits are formed in the salt lake region of the Qinghai-Tibet plateau in China; (2) the magnesium content is high, and the magnesium content of hydromagnesite is the fourth in the currently proven magnesium-containing nonmetallic ore; (3) the calcined product is environment-friendly, and the calcined product mainly comprises magnesium oxide, carbon dioxide and water, and is an environment-friendly product. Therefore, hydromagnesite is a natural high-quality mineral resource for preparing the magnesium material, has good development and utilization prospects, and is widely applied to the fields of building materials, medicines, refractory materials and the like.

At present, China does not have many relevant theories and application researches on the abundant and unique mineral resources, and Zheng is gentle and moderate (Zheng is gentle, Liu is tall, Jinwenshan. research on salt minerals in Tibet salt lake [ J ]. Proc of academy of China geological sciences-headings of mineral deposit geology research institute, 1981, 2(1): 87-89.) hydromagnesite is found in Tibet salt lake areas in China, and preliminary researches on the mineral characteristics such as appearance, chemical components, mineral properties and the like are carried out, besides, the relevant reports of other scholars on the mineral researches on the mineral resources are rarely seen. Zhang Xinbo et al (Zhang Xinbo, Chen Shunjiang, Li Guoshua, etc.. calcining process research [ J ] of light-burned MgO powder prepared by hydromagnesite [ 2012, 46(05), 353-355.) have studied the calcining process of light-burned MgO powder prepared by hydromagnesite, determined that the optimal process parameter is 900 ℃ heat preservation for 3h, and selected by a 0.425 mm sieve, and the magnesia materials have wide application in the fields of building materials, refractory materials, catalysis, etc.; but the temperature and the heat preservation time of the calcination process are both high, the energy consumption is high, and the production cost is increased. But few reports are made about the method for preparing the magnesium hydroxide flame retardant by natural hydromagnesite.

Magnesium hydroxide is developed rapidly in the field of inorganic flame retardants due to the characteristics of non-toxicity, no smoke and the like, and when hexagonal flaky magnesium hydroxide is used as a flame retardant, the dispersibility and the purity have great influence on the flame retardant performance. The production methods of magnesium hydroxide include a direct precipitation method, a hydrothermal method and the like, wherein in the hydrothermal treatment, in order to obtain a product with regular appearance and uniform particle size distribution, a surfactant, a strong alkali solution and the like are often added as an auxiliary agent, so that the hydrothermal reaction equipment is required to have stronger acid resistance and alkali resistance, and the production cost is increased. Therefore, the preparation of the magnesium hydroxide flame retardant needs to reduce the cost, facilitate the operation and be beneficial to environmental protection.

Chinese patent CN107804863A provides a method for preparing uniform hexagonal flaky nano magnesium hydroxide by a hydration method, which comprises the steps of adding magnesium oxide suspension into distilled water for hydration reaction, filtering, washing and drying after the reaction is finished, thus obtaining uniform hexagonal flaky nano magnesium hydroxide; although the process is simple, solvents such as ethanol and isopropanol are added in the experimental process, the experimental steps become complicated, the experimental cost is increased, and impurity ions may be introduced.

Chinese patent CN201811586790.0 provides a method for obtaining magnesium hydroxide precipitate by reacting organic amine with soluble metal salt solution, which has high product purity, but large particle size and uneven distribution. Zhangyuxing et al (Zhangyuxing, Chenjianming, Song Yun Hua. magnesium oxide two-step method for preparing flame-retardant magnesium hydroxide [ J ]. inorganic chemistry report, 2014, 30(4), 860-866.) use magnesium oxide generated by roasting magnesium chloride as a raw material, prepare hexagonal flaky magnesium hydroxide by adopting a two-step method, namely a method of firstly hydrating and then hydro-heating, and investigate the influence of the hydration time, the hydro-heating time and temperature and the concentration of hydro-heating additive sodium hydroxide on the appearance of a magnesium hydroxide material. The experimental steps are complicated, and the hydrothermal additive sodium hydroxide is added for hydrothermal modification, so that the requirement on reaction equipment is high, the hydrothermal additive sodium hydroxide cannot be recycled, the environmental pollution is caused, and the production cost is increased.

Chinese patent 201110336270.6 provides a method for preparing hexagonal flaky magnesium hydroxide from natural magnesite. In the patent, firstly, natural magnesite is calcined to obtain active magnesium oxide, then suspension liquid consisting of the active magnesium oxide, magnesium salt and water is prepared and subjected to constant-temperature water bath, and magnesium hydroxide crystal seeds are added in the water bath process to finally obtain hexagonal flaky magnesium hydroxide. The raw material magnesite of the patent is an anhydrous magnesium carbonate mineral, and the hydromagnesite is a natural basic magnesium carbonate mineral, so that in the process of preparing active magnesium oxide, compared with hydromagnesite, the raw material magnesite of the patent has the advantages of higher calcination temperature, longer heat preservation time and lower magnesium oxide activity; and magnesium salt is required to be added as an auxiliary raw material, and magnesium hydroxide seed crystal is required to be added during water bath, so that the problems of complicated process, high production cost and difficulty in realizing large-scale industrial production exist.

Disclosure of Invention

The invention aims to provide a method for preparing hexagonal flaky flame-retardant magnesium hydroxide from natural hydromagnesite, so as to solve the problems of complex method, high cost, environmental friendliness and the like in the process of producing a magnesium hydroxide flame retardant in the prior art.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the method for preparing hexagonal flaky flame-retardant magnesium hydroxide from natural hydromagnesite comprises the following steps:

s1, crushing the natural hydromagnesite and then screening;

s2, heating the natural hydromagnesite obtained by crushing and screening in the step S1 to a set temperature, and then carrying out heat preservation and calcination to completely decompose the natural hydromagnesite to obtain active magnesium oxide, wherein:

the heating rate is 5-15 ℃/min, the set temperature to be reached by heating is 300-800 ℃, and the time of heat preservation and calcination is 1-4 h;

s3, screening the active magnesium oxide obtained in the step S2;

s4, preparing a magnesium oxide suspension by taking the active magnesium oxide obtained by screening in the step S3 as a raw material and deionized water as a solvent, and uniformly dispersing the raw material in the magnesium oxide suspension by adopting ultrasonic dispersion, wherein:

the solid-liquid ratio of the raw material to the solvent is 1: 9-1: 4, namely the solid content of the magnesium oxide suspension is 10-20 wt%;

s5, putting the magnesium oxide suspension obtained in the step S4 into a closed heating device with a stirring function for heating reaction to obtain a solution, wherein:

the heating temperature in the closed heating device is 100-200 ℃, the stirring speed is 200-600 rpm, and the reaction time is 1-3 h;

s6, taking out the solution obtained in the step S5, naturally cooling to room temperature to obtain a product in the solution, and filtering, washing and drying the product after the product is taken out to obtain hexagonal flaky magnesium hydroxide.

Furthermore, after the step S1, the natural hydromagnesite with the particle size less than 2 μm accounts for 50% of the total volume of the natural hydromagnesite after being crushed and sieved.

Further, after the sieving in step S3, the volume of the active magnesium oxide with the particle size of less than 2 μm is 50% of the total volume of the active magnesium oxide.

Further, in step S4, the power of ultrasonic dispersion is 40-3500W, and the frequency of ultrasonic is 10-50 kHz.

Further, in step S5, the heating temperature of the closed heating device is 140 ℃ to 160 ℃.

Further, in the step S5, the closed heating device is a 2L hydrothermal reaction kettle with a stirring function, and the filling rate is 50% to 80%.

Further, in step S6, vacuum drying is adopted during drying, and the drying temperature is 50-110 ℃.

Further, in step S6, the particle size of the obtained micron-sized hexagonal flaky magnesium hydroxide is 0.8-1.2 μm, and the peak intensity ratio I of the (001) crystal face to the (101) crystal face is₀₀₁/I₁₀₁0.8 to 2.0.

The principle of the invention is as follows:

the mineral calcining method is one of the commonly used methods for preparing magnesium oxide on a large scale due to abundant raw materials and low cost, but the commonly used mineral is generally magnesite, a complicated pretreatment process is usually required before calcining, and most of the produced magnesium oxide is low-end magnesium oxide. The initial decomposition temperature of hydromagnesite is about 150 ℃, and the complete decomposition temperature is about 670 ℃. In the step S2, as the calcination temperature increases and the holding time is prolonged, the hydromagnesite decomposition tends to be complete, before the inflection point, the hydromagnesite decomposition plays a leading role, and the activity of the obtained magnesia powder tends to increase; after the inflection point, the growth of the active magnesium oxide plays a dominant role, and the activity of the obtained magnesium oxide powder tends to be reduced. The activity of magnesium oxide is determined by its crystallization property, and the active magnesium oxide has many surface defects, high specific surface area and easy reaction with water. And (4) preparing a magnesium oxide suspension by using the active magnesium oxide obtained by screening in the step S3 as a raw material and deionized water as a solvent, and stirring and heating by using the closed heating device mentioned in the step S5 to fully and uniformly mix the raw material and the solvent, so that the method has the advantages of no need of adding auxiliary raw materials, simple process and low cost.

Compared with the prior art, the invention has the advantages that:

the method adopts natural hydromagnesite to directly calcine to obtain magnesium oxide with high purity and high activity, the magnesium oxide is used as a magnesium hydroxide precursor, and the nucleation and crystallization speed of the magnesium hydroxide is changed by controlling the activity of the magnesium oxide to prepare the flame-retardant magnesium hydroxide with high crystallinity and good dispersibility.

The invention adopts unique mineral resource natural hydromagnesite which is abundant in resource and environment-friendly as a raw material, directly calcines the natural hydromagnesite to obtain magnesium oxide with high purity and high activity, prepares magnesium oxide suspension with a certain concentration, takes out the product after hydrothermal reaction for a period of time, and filters, washes and dries the product to obtain hexagonal flaky magnesium hydroxide. In the process, the hexagonal flaky flame-retardant magnesium hydroxide with high crystallinity, good dispersity and regular appearance can be obtained without adding any other raw materials or auxiliary agents except the hydromagnesite. The preparation process is simple, the technical route is reasonable, the raw materials are cheap and easy to obtain, the production cost is low, the production process has no pollution to the environment, and the industrial value is high.

Drawings

Figure 1 is an XRD picture of the product of example 1 of the invention.

FIG. 2 is an SEM photograph of the product of example 1 of the present invention.

Figure 3 is an XRD picture of the product of example 2 of the invention.

FIG. 4 is an SEM photograph of the product of example 2 of the present invention.

Figure 5 is an XRD picture of the product of example 3 of the invention.

FIG. 6 is an SEM photograph of the product of example 3 of the present invention.

Figure 7 is an XRD picture of the comparative example 1 product of the present invention.

Fig. 8 is an SEM picture of the comparative example 1 product of the present invention.

Detailed Description

The preparation method of the present invention will be illustrated below by specific examples, but it will be understood by those skilled in the art that the following examples are only specific examples of the preparation method of the present invention and are not intended to limit the entirety thereof.

Example 1

Crushing natural hydromagnesite, screening, weighing the screened hydromagnesite, calcining for 2 hours at 600 ℃, heating up at 10 ℃/min, screening active magnesium oxide obtained after the hydromagnesite is completely decomposed, taking the active magnesium oxide as a raw material and deionized water as a solvent, preparing magnesium oxide suspension with the concentration of 10% after ultrasonic dispersion for 15 minutes, putting the magnesium oxide suspension into a closed heating device, heating for 4 hours at the constant temperature of 140 ℃, stirring at 300rpm, naturally cooling the product to room temperature after the reaction is finished, and filtering, washing and drying the product to obtain hexagonal flaky magnesium hydroxide. The product 1 is obtained. The XRD and SEM pictures of the product are shown in figures 1 and 2.

Compared with a magnesium hydroxide crystal PDF standard card, the product has high purity, and the product is hexagonal flaky and uniform in particle size distribution as can be seen from an SEM picture. Taking and placing SEM results with the magnification of 10000 times, randomly sampling 50 SEM results in a visual field, and calculating by using a software Nano Measurer to obtain the SEM results with the average diameter of about 0.9-1.0 mu m and the thickness of about 100 nm.

Example 2

Crushing natural hydromagnesite, screening, weighing the screened hydromagnesite, calcining at 800 ℃ for 2h, heating at a speed of 10 ℃/min, screening active magnesium oxide obtained after the hydromagnesite is completely decomposed, taking the active magnesium oxide as a raw material and deionized water as a solvent, ultrasonically dispersing for 15min, preparing a magnesium oxide suspension with a slurry concentration of 10%, placing the magnesium oxide suspension into a closed heating device, heating at a constant temperature of 160 ℃ for 4h, stirring at a speed of 300rpm, naturally cooling a product to room temperature after the reaction is finished, filtering, washing and drying the product to obtain hexagonal flaky magnesium hydroxide. The product 2 is obtained. The XRD and SEM pictures of the product are shown in figures 3 and 4.

Compared with a magnesium hydroxide crystal PDF standard card, the purity of the product is higher, and the product is hexagonal flaky and uniform in particle size distribution as can be seen from an SEM picture. Taking and placing SEM results with the large multiple of 10000 times, randomly sampling 50 SEM results in a visual field, and obtaining the SEM results through calculation of a software Nano Measurer, wherein the diameter of the SEM results is about 0.9-1.2 mu m, and the thickness of the SEM results is about 150 nm.

Example 3

Crushing natural hydromagnesite, screening, weighing the screened hydromagnesite, calcining at 800 ℃ for 2h, heating at a speed of 10 ℃/min, screening active magnesium oxide obtained after the hydromagnesite is completely decomposed, taking the active magnesium oxide as a raw material and deionized water as a solvent, ultrasonically dispersing for 15min, preparing a magnesium oxide suspension with a slurry concentration of 10%, placing the magnesium oxide suspension into a closed heating device, heating at a constant temperature of 180 ℃ for 4h, stirring at a speed of 300rpm, naturally cooling a product to room temperature after the reaction is finished, filtering, washing and drying the product to obtain hexagonal flaky magnesium hydroxide. The product 3 is obtained. The XRD and SEM pictures of the product are shown in FIGS. 5 and 6.

Compared with a magnesium hydroxide crystal PDF standard card, the product has high purity, and the product is hexagonal flaky and uniform in particle size distribution as can be seen from an SEM picture. Taking and placing SEM results with the large multiple of 10000 times, randomly sampling 50 SEM results in a visual field, and obtaining the SEM results through calculation of a software Nano Measurer, wherein the diameter of the SEM results is about 0.8-1.1 mu m, and the thickness of the SEM results is about 200 nm.

Comparative example 1

Crushing natural hydromagnesite, screening, weighing the screened hydromagnesite, calcining at 800 ℃ for 2h, heating at a speed of 10 ℃/min, screening active magnesium oxide obtained after the hydromagnesite is completely decomposed, taking the active magnesium oxide as a raw material, adding 0.5mol/L sodium hydroxide solution as a catalyst, ultrasonically dispersing for 15min, preparing magnesium oxide suspension with a slurry concentration of 10%, placing the magnesium oxide suspension in a closed heating device, heating at a constant temperature of 160 ℃ for 4h, stirring at a speed of 300rpm, after the reaction is finished, naturally cooling the product to room temperature, filtering, washing and drying the product to obtain hexagonal flaky magnesium hydroxide. The product 4 is obtained. The XRD and SEM pictures of the product are shown in FIGS. 7 and 8.

Compared with a magnesium hydroxide crystal PDF standard card, the product has low purity and a plurality of impurity peaks, and the product is hexagonal flaky, but has uneven particle size distribution, poor dispersity and serious agglomeration. Under the same other experimental conditions as example 2, the comparative example added the sodium hydroxide reagent as the catalyst, and in turn caused the agglomeration of magnesium hydroxide to become serious, the purity to be reduced, increased the production cost and easily caused environmental pollution.

The embodiments of the present invention are described only for the preferred embodiments of the present invention, and not for the limitation of the concept and scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the design concept of the present invention shall fall into the protection scope of the present invention, and the technical content of the present invention which is claimed is fully set forth in the claims.