阅读说明：本技术 一种大粒径氢氧化镁水热法制备阻燃剂用六角片状氢氧化镁的方法 (Method for preparing hexagonal flaky magnesium hydroxide for flame retardant by hydrothermal method of large-particle-size magnesium hydroxide ) 是由 罗仙平 宋学文 曹雨微 梁健 唐学昆 于 2019-10-24 设计创作，主要内容包括：本发明公开了一种大粒径氢氧化镁水热法制备阻燃剂用六角片状氢氧化镁的方法,称量好大粒径氢氧化镁和水氯镁石转入高温高压反应釜中,加入蒸馏水,搅拌进行水热处理,使得大粒径氢氧化镁实现充分的溶解-再结晶；将反应所得产物进行过滤、洗涤、干燥,得到阻燃剂用氢氧化镁。本发明以大粒径氢氧化镁为原料,水氯镁石为添加剂,其工艺流程简单、生产成本低,在未使用碱性添加剂(氢氧化钠、氢氧化钾等)的条件下,解决了氢氧化镁难以溶解的难题,实现了阻燃剂用氢氧化镁低成本、高效的制备；通过本发明制得的产品纯度高、粒径分布窄、粒径小(D<Sub>50</Sub>＝1.86μm,D<Sub>90</Sub>＝4.20μm),形貌呈六角片状,具有极大的应用价值和市场价值。(The invention discloses a method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by a large-particle-size magnesium hydroxide hydrothermal method, weighing large-particle-size magnesium hydroxide and bischofite, transferring the large-particle-size magnesium hydroxide and the bischofite into a high-temperature high-pressure reaction kettle, adding distilled water, stirring and carrying out hydrothermal treatment, so that the large-particle-size magnesium hydroxide is fully dissolved and recrystallized; and filtering, washing and drying a product obtained by the reaction to obtain the magnesium hydroxide for the flame retardant. The invention takes the magnesium hydroxide with large particle size as the raw material and the bischofite as the additive, has simple process flow and low production cost, solves the problem that the magnesium hydroxide is difficult to dissolve under the condition of not using alkaline additives (sodium hydroxide, potassium hydroxide and the like), and realizes the low-cost and high-efficiency preparation of the magnesium hydroxide for the flame retardant; the product prepared by the invention has high purity, narrow particle size distribution and small particle size (D) 50 ＝1.86μm，D 90 4.20 mu m) and the shape is hexagonal sheet, thereby having great application value and market value.)

1. A method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by a large-particle-size magnesium hydroxide hydrothermal method is characterized by comprising the following steps of: the method comprises the following steps of (1),

A. weighing magnesium hydroxide with large particle size and bischofite, transferring the weighed magnesium hydroxide with large particle size and bischofite into a high-temperature high-pressure reaction kettle, and adding distilled water into the high-temperature high-pressure reaction kettle;

B. carrying out hydrothermal treatment on the magnesium hydroxide with large particle size, distilled water and bischofite at a certain temperature and stirring speed for a certain time to ensure that the magnesium hydroxide with large particle size realizes a sufficient dissolving-recrystallization process;

C. and filtering the product obtained by the reaction to obtain a filter cake, and washing and drying the filter cake to obtain hexagonal flaky magnesium hydroxide for the flame retardant.

2. The method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by the large-particle-size magnesium hydroxide hydrothermal method according to claim 1, wherein: in the step A, the amount of the large-particle-size magnesium hydroxide is 75-85 parts, the amount of the bischofite is 77-86 parts, and the addition amount of the distilled water is 1440-1600 parts.

3. The method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by the large-particle-size magnesium hydroxide hydrothermal method according to claim 1 or 2, wherein: in step A, the mass of the large-particle-diameter magnesium hydroxide was 80g, the mass of bischofite was 81.32g, and the amount of distilled water added was 1520 mL.

4. The method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by the large-particle-size magnesium hydroxide hydrothermal method according to claim 1, wherein: in the step A, the mass ratio of the large-particle-size magnesium hydroxide to the distilled water is 1 (18-20), and the amount of the bischofite substance is 0.25 mol/L.

5. The method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by the large-particle-size magnesium hydroxide hydrothermal method according to claim 1, wherein: in the step B, the magnesium hydroxide with large particle size and bischofite are subjected to hydrothermal reaction in a high-temperature high-pressure reaction kettle at the stirring speed of 500r/min and the reaction temperature of 160 ℃ for 6 hours.

6. The method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by the large-particle-size magnesium hydroxide hydrothermal method according to claim 1, wherein: in step C, the prepared filter cake was thoroughly washed five times.

7. The method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by the large-particle-size magnesium hydroxide hydrothermal method according to claim 1, wherein: the particle size of the large-particle-size magnesium hydroxide is 40-60 mu m.

Technical Field

The invention relates to the technical field of preparation of hexagonal flaky magnesium hydroxide for flame retardant grade, in particular to a method for preparing magnesium hydroxide for flame retardant grade by using large-particle-size magnesium hydroxide as a raw material and adopting a hydrothermal method.

Background

The magnesium hydroxide product is an important magnesium inorganic material, has excellent physical and chemical properties such as no toxicity, no pollution, high temperature resistance, corrosion resistance and the like, and is widely used as a filler in the antibacterial, waste water, waste gas and acidic water pollutant treatment, paper industry, electronic and optical devices, a precursor for producing magnesium oxide and a new-generation flame retardant. The characteristics of the magnesium hydroxide such as particle size, particle size distribution, micro morphology and the like have decisive influence on the dispersibility of the magnesium hydroxide in the matrix material and the physical and chemical properties of the matrix material. In order to improve the flame retardant property of magnesium hydroxide added into high molecular materials, a large amount of magnesium hydroxide needs to be added into a base material to reach the flame retardant grade specified by the state, however, the physical and chemical properties of the base material are seriously reduced by adding a large amount of magnesium hydroxide, and the magnesium hydroxide with ordered microstructure arrangement, narrow particle size distribution and small particle size has high flame retardant effect, low addition amount and small influence on the physical and chemical properties of the base material. In order to obtain high-performance magnesium hydroxide with good dispersity, special appearance, small particle size and narrow distribution, a great deal of research is carried out by domestic and foreign science and technology workers. At present, the preparation methods of magnesium hydroxide at home and abroad mainly comprise a simple precipitation method, a hydrothermal method, a sol-gel method, an electrochemical method, a microwave-assisted method, a gas phase method and the like.

The magnesium hydroxide prepared by the conventional method is seriously agglomerated, and the hydrothermal method can realize the optimization of the magnesium hydroxide prepared by the conventional method. The hydrothermal method is a chemical reaction process in a high-temperature high-pressure solvent, and has the main advantages that the reaction conditions are controllable, the size and the shape of the prepared inorganic material crystal and the growth effect of the crystal can be controlled, and therefore the magnesium hydroxide with low agglomeration degree and regular shape is prepared. Therefore, a great deal of research reports are also provided for preparing the magnesium hydroxide by the hydrothermal method, and the research on the influence factors of preparing the magnesium hydroxide by the hydrothermal method mainly focuses on the research on the aspects of reaction temperature, reaction pressure and induction of a mineralizer. The hydrothermal method is adopted to realize the dissolution-recrystallization of the magnesium hydroxide, and usually alkaline additives such as sodium hydroxide, potassium hydroxide, ammonia water and the like are needed to be used, the alkaline additives such as the sodium hydroxide and the potassium hydroxide are high in price and strong in corrosivity, so that the large-scale industrial application of the alkaline additives is severely restricted, and the additive which is cheap and easy to obtain and low in corrosivity is used for promoting the dissolution-recrystallization of the magnesium hydroxide, so that the method has extremely important value and significance.

The Qinghai West magnesium industry Limited company utilizes bischofite in salt lake to successfully produce magnesium hydroxide with large particle size by a precipitation method, the production capacity is 16 ten thousand tons/year, but the magnesium hydroxide product produced by the method has wide particle size distribution, large particle size, large crystal lattice size, irregular crystal arrangement and large specific surface area, thereby seriously restricting the development of enterprises in the industry of magnesium hydroxide for flame retardants. With the development and utilization of potassium resources, a large amount of magnesium chloride hydrate is discharged as waste, and the discharge accumulation for many years causes the unbalance of the components of salt lake brine, which is called as 'magnesium damage', so that the resource waste is caused and the environmental pressure is brought. If the magnesium chloride waste from the salt lake can be used for preparing the magnesium hydroxide product, the magnesium harm in the salt lake can be well treated, a new development opportunity is developed for the modern magnesium industry, and the sustainable development of economy, resources and environment can be realized.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art, and provides a method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by a large-particle-size magnesium hydroxide hydrothermal method, which has the characteristics of simpler process flow, lower production cost and environmental friendliness.

In order to solve the technical problems, the invention adopts the following technical scheme: a method for preparing hexagonal flaky magnesium hydroxide for a flame retardant by a large-particle-size magnesium hydroxide hydrothermal method is characterized by comprising the following steps of: the method comprises the following steps of (1),

A. weighing magnesium hydroxide with large particle size (the particle size is 40-60 mu m) and bischofite, transferring the weighed magnesium hydroxide with large particle size and bischofite into a high-temperature high-pressure reaction kettle, and adding distilled water into the high-temperature high-pressure reaction kettle;

B. carrying out hydrothermal treatment on the magnesium hydroxide with large particle size, distilled water and bischofite at a certain temperature and stirring speed for a certain time to ensure that the magnesium hydroxide with large particle size realizes a sufficient dissolving-recrystallization process;

C. and filtering the product obtained by the reaction to obtain a filter cake, washing and drying the filter cake to obtain hexagonal flaky magnesium hydroxide for the flame retardant, wherein the washing frequency of the filter cake is five times.

In the step A, the amount of the large-particle-size magnesium hydroxide is 75-85 parts, the amount of the bischofite is 77-86 parts, and the addition amount of the distilled water is 1440-1600 parts.

As a preferred example, the mass of the large-particle-size magnesium hydroxide was 80g, the mass of bischofite was 81.32g, and the amount of distilled water added was 1520 mL.

In the step A, the mass ratio of the large-particle-size magnesium hydroxide to the distilled water is 1 (18-20), and the amount of the bischofite substance is 0.25 mol/L.

In the step B, the magnesium hydroxide with large particle size and bischofite are subjected to hydrothermal reaction in a high-temperature high-pressure reaction kettle under the conditions of stirring speed of 500r/min and reaction temperature of 160 ℃ (the temperature difference of several degrees can exist), and the reaction time is 6 h.

As KCl and CaCl are used in the prior art₂The invention adopts bischofite (MgCl) on the basis of the technology of preparing the magnesium hydroxide with large particle size by additives₂·6H₂O) as an additive for promoting the dissolution of magnesium hydroxide with large particle size in bischofite (MgCl) by monitoring the reaction process₂·6H₂O) in the presence of bischofite (MgCl)₂·6H₂O) Mg produced by dissolving in an aqueous solution²⁺And Cl^-Can continuously replace Mg in magnesium hydroxide with large particle size²⁺And the hydrothermal system of the whole reaction is promoted to be in a weak acid environment in a local area to a certain extent, so that the dissolution of magnesium hydroxide is realized, and the aim of preparing the flame-retardant grade magnesium hydroxide by the large-particle-size magnesium hydroxide hydrothermal method is finally realized.

The method takes magnesium hydroxide with large particle size as a raw material, and adds the magnesium hydroxide with large particle size and bischofite in a certain mass proportion into a high-temperature high-pressure reaction kettle device to react at a certain temperature and stirring speed to prepare the magnesium hydroxide for flame retardant grade; the method has simple process flow and low production cost, not only can the raw materials not generate obvious environmental pollution, but also realizes the utilization of the waste bischofite, realizes the preparation of flame-retardant grade magnesium hydroxide, solves the problems of high cost and strong corrosivity of the magnesium hydroxide dissolving-recrystallizing additive, and has good economic benefit, social benefit and environmental benefit; the flame-retardant grade magnesium hydroxide product prepared by the method is hexagonal and flaky, contains high-purity magnesium hydroxide, has narrow particle size distribution and D₅₀1.86 μm, D₉₀4.20 μm, and has great application value and market value.

Drawings

FIG. 1 shows the result of X-ray diffraction analysis (XRD spectrum) of magnesium hydroxide for flame retardant grade;

FIG. 2 is a scanning electron microscope image of flame retardant grade magnesium hydroxide;

FIG. 3 is a graph showing the analysis result (particle size distribution) of the flame retardant grade by a magnesium hydroxide laser particle sizer.

Detailed Description

The following is further described in conjunction with the detailed description: