A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material

Abstract

The invention discloses a method for preparing flower-spherical magnesium hydroxide using magnesium oxide as a raw material, and belongs to the technical field of inorganic functional crystal material preparation. The method for preparing flower-spherical magnesium hydroxide comprises the following steps: mixing magnesium oxide and a soluble crystal shaping agent solution and then slurrying to obtain a raw material slurry, subjecting the raw material slurry to a hydrothermal synthesis reaction and then solid-liquid separation, and the solid phase is the flower-spherical magnesium hydroxide. The invention uses magnesium oxide as a raw material, adds a soluble crystal shaping agent to the reaction system, and synthesizes a flower-spherical magnesium hydroxide product with a regular morphology through a one-step hydrothermal synthesis method, which can be used as an inorganic flame retardant, a precious metal / heavy metal ion adsorbent, and a decolorizing agent, etc.

Description

Technical Field

[0001] The invention relates to the technical field of functional crystal material preparation, in particular to a method for preparing flower-spherical magnesium hydroxide using magnesium oxide as a raw material. Background Art

[0002] Magnesium hydroxide (Mg(OH) 2 ) has the advantages of wide raw material sources, non-toxicity, antibacterial and high thermal stability. As a crystalline product, its crystal form is diverse, mainly including needle-shaped, flake-shaped, rod-shaped and flower-shaped crystal morphologies. It plays an important role in the production and preparation of various high-end materials. It can be used as a flame retardant, heavy metal precipitant, acid wastewater neutralizer, antibacterial agent, chemical sensor and raw material for drug production. Compared with magnesium hydroxide with other crystal morphologies, flower-shaped magnesium hydroxide has a larger specific surface area to improve the adsorption capacity of precious metals / heavy metals, and a higher decomposition temperature for use as a polymer flame retardant. Therefore, its synthesis mechanism and method have received more and more attention and increasing importance in recent years.

[0003] At present, the synthesis method of flower ball-shaped magnesium hydroxide is mainly a precipitation method using soluble salt as raw material, such as invention patent CN201310698274.8, invention patent CN201611112000.6 and invention patent CN202111152371.8. Invention patent CN201310698274.8 uses a certain concentration of magnesium salt aqueous solution and a certain concentration of alkaline solution, accompanied by the addition of an organic auxiliary solvent, to carry out a precipitation reaction at a certain stirring speed and then complete the aging reaction. The product is separated, washed and dried to be a lightweight, high specific surface area, flower ball-shaped nano magnesium hydroxide, but its reaction process is a two-step intermittent reaction of "precipitation-aging", and the overall reaction time is relatively long (precipitation reaction stirring time 5 to 48 hours, preferably 10 to 24 hours; aging time 1 to 8 hours, preferably 2 to 6 hours). After the reaction is completed, the waste liquid is a salt solution containing an organic auxiliary solvent, which cannot be reused as a raw material for the next stage. If it is scaled up to an industrial scale, a large amount of mother liquor needs to be properly treated before discharge and disposal, otherwise it will cause environmental problems. Invention patent CN201611112000.6 uses magnesium chloride solution and ammonia water to carry out precipitation reaction at a temperature of 80-100°C. The reaction product is a petal-shaped magnesium hydroxide product with regular morphology. However, since its core reaction is an ammonia precipitation method, the by-product waste liquid contains a high level of ammonia salt compounds, and its discharge will cause environmental problems. In addition, due to the volatility of ammonia water, it will produce a pungent odor, which is easy to cause ammonia pollution to the atmosphere during large-scale production, affecting the safety of life and property. Invention patent CN202111152371.8 utilizes the volatility of ammonia water, and places open containers containing high sodium-magnesium ratio sodium sulfate industrial wastewater and ammonia water in a sealed reactor. Within 12 to 48 hours, ammonia gas evaporates from the ammonia water container and enters the high sodium-magnesium ratio sodium sulfate industrial wastewater container to dissolve and react, producing magnesium hydroxide with a flower ball morphology. However, this reaction is still a precipitation reaction using ammonia as a precipitant, and there are similar problems as invention patent CN201611112000.6; and the entire process needs to be completed in a completely closed environment to volatilize, dissolve, and precipitate, which are all spontaneous reactions, with a long reaction time. The process conditions cannot be effectively controlled, and it is not easy to achieve industrialization.

[0004] In summary, the problems existing in the prior art are:

[0005] (1) Existing technologies mainly use precipitation methods, with precipitants being alkali solution or ammonia. Some technologies require the addition of organic auxiliary solvents to adjust the product morphology, thus producing a large amount of wastewater containing low-value inorganic salts or a mixture of inorganic salts and organic solvents. Under large-scale production conditions, effective disposal is required to avoid direct discharge and environmental impact.

[0006] (2) The existing technology requires a long time. In order to ensure product quality, a two-step intermittent process of "precipitation-aging" at a certain temperature is often adopted. The production cycle is long, and the production efficiency under large-scale production conditions needs to be improved.

[0007] (3) The precipitation used in the prior art is a spontaneous reaction, which has the advantage of being simple and easy to operate, but also has the disadvantages of relatively low product purity and crystal development integrity, relatively uneven distribution of crystal particles, and difficulty in controlling the crystal form. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing flower-ball-shaped magnesium hydroxide using magnesium oxide as a raw material, so as to solve the problems existing in the above-mentioned prior art. The present invention aims at the defects and shortcomings of the existing flower-ball-shaped magnesium hydroxide preparation process, such as large amount of by-product of salt-containing mother liquor, long production cycle, and inability to achieve continuous production after industrialization, and provides a method for preparing flower-ball-shaped magnesium hydroxide using magnesium oxide as a raw material. Compared with the precipitation method, the hydrothermal method adopted in the present invention provides a crystallization environment with stable energy supply and reaction process parameters. The higher reaction temperature is conducive to overcoming the energy barrier, and cheaper raw materials can be used to produce crystalline products with higher value and special morphology. The output product crystals have the advantages of more complete grain development, more uniform particle size distribution, lower particle agglomeration, etc., which is convenient for large-scale production. In addition, unlike the traditional precipitation process in which the reaction is completed and the mother liquor is mostly a low-value inorganic salt solution, the present invention uses magnesium oxide solid raw material to be converted into a magnesium hydroxide product through a hydration reaction under hydrothermal conditions, and the added soluble crystal shaping agent is used as a morphology conversion catalyst. The anions and cations generated by the ionization in the mother liquor play a role in changing the surface characteristics of the crystal nucleus, affecting the growth direction of the grains, and inducing orderly self-assembly of the grains during the hydration process, so as to promote the hydration growth of magnesium oxide into a flower ball-shaped magnesium hydroxide. After the hydrothermal reaction is completed and the solid-liquid separation is carried out, the soluble crystal shaping agent exists in the mother liquor, which can be completely reused. While saving a large amount of water resources, it reduces the impact of the discharge of salt-containing waste liquid on the environment, reduces the processing cost, and improves the economic benefits of the product.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] One of the technical solutions of the present invention is a method for preparing flower-spherical magnesium hydroxide using magnesium oxide as a raw material, comprising the following steps: mixing magnesium oxide and a soluble crystal shaping agent solution and adding the mixture to a homogenizer for slurrying to obtain a raw material slurry, subjecting the raw material slurry to a hydrothermal synthesis reaction (a hydrothermal reactor with stirring), performing solid-liquid separation after the reaction is completed, washing the solid phase with a washing liquid (deionized water) and then drying at a high temperature to obtain the flower-spherical magnesium hydroxide.

[0011] The mechanism equation for preparing spherical magnesium hydroxide by hydrothermal synthesis of magnesium oxide is as follows:

[0012] MgO+H 2 O→Mg(OH) 2

[0013] In the process of preparing spherical magnesium hydroxide by hydrothermal synthesis of magnesium oxide, the anions and cations generated by the ionization of the soluble crystal shaping agent in the reaction system play a role in changing the surface characteristics of the crystal nucleus, affecting the growth direction of the grains, and inducing orderly self-assembly of the grains during the hydrothermal synthesis process. Under the conditions of hydrothermal synthesis, the growth and self-assembly of magnesium hydroxide crystals into spherical crystals are promoted.

[0014] After the hydrothermal synthesis reaction is completed, the magnesium oxide is hydrated to form magnesium hydroxide crystals with a flower ball shape, and the added soluble crystal former still exists in the system in its original form. After solid-liquid separation, the solid phase product is washed and dried to become a flower ball-shaped magnesium hydroxide product, and the liquid phase mother liquor is a solution containing the soluble crystal former, which can be used as a raw material "soluble crystal former solution" back in the first pulping step of the method of the present invention.

[0015] Furthermore, the magnesium oxide is industrial magnesium oxide with a purity of 75-99%.

[0016] Furthermore, the soluble crystal shaping agent solution is a magnesium chloride solution or a magnesium sulfate solution.

[0017] Furthermore, the concentrations of the magnesium chloride solution and the magnesium sulfate solution are both 0.3-3 mol / L.

[0018] Furthermore, the concentrations of the magnesium chloride solution and the magnesium sulfate solution are both 0.5-2 mol / L.

[0019] Furthermore, the solid content of the raw material slurry is 5-12% (solid mass / total slurry volume).

[0020] Furthermore, the solid content of the raw material slurry is 6-10%.

[0021] Furthermore, the temperature of the hydrothermal synthesis reaction is 120-180° C., the time is 2-8 hours, and the stirring speed is 120-600 r / min.

[0022] Furthermore, the temperature of the hydrothermal synthesis reaction is 140-160° C., the time is 4-6 hours, and the stirring speed is 120-600 r / min.

[0023] Furthermore, the mass ratio of the washing liquid to the solid phase is (3-5):1.

[0024] Furthermore, the washing is performed 3 to 5 times.

[0025] Furthermore, the high temperature drying temperature is 80-120° C., and the time is 48-72 hours.

[0026] The second technical solution of the present invention is a flower-spherical magnesium hydroxide prepared by the above-mentioned preparation method.

[0027] The third technical solution of the present invention: an application of the above-mentioned flower ball-shaped magnesium hydroxide in flame retardants, heavy metal precipitants, and decolorizers.

[0028] The effect of the specific process of the present invention is as follows:

[0029] (1) At the beginning of the process, magnesium oxide is added to a solution containing a soluble crystal shaping agent and then placed in a homogenizer for slurrying to obtain a raw material slurry with a certain solid content. During this process, large particles or agglomerated particles in the raw material magnesium oxide solid particles are broken up into small particles with uniform particle size, which are evenly dispersed in the solution containing the soluble crystal shaping agent to form a raw material slurry with good fluidity. This process helps to improve the uniform distribution of heat and mass of the material system during the hydrothermal process and improve the efficiency of the hydrothermal reaction. In addition, before the hydrothermal reaction, the product obtained by hydrothermal treatment of the untreated raw material is different from the product obtained by hydrothermal treatment of the raw material after slurrying. The particle size distribution of the products was compared, and the SD values ​​(i.e., variance values, the smaller the variance values, the more uniform the distribution of the data series) that characterize the uniformity of the particle size distribution were 1.157-1.459 and 0.480-0.808, respectively, indicating that the particle size uniformity of the solid raw materials in the hydrothermal process is positively correlated with the particle size uniformity of the hydrothermal products. Therefore, in the subsequent solid-liquid separation process, the mother liquor entrainment can be effectively reduced, the product washing efficiency can be improved (the number of washing times or the amount of washing water can be reduced), and the discharge of washing water can be reduced. Therefore, the effect of the raw material homogenization process in the present invention can have a key influence on the subsequent hydrothermal effect and the washing and separation effect.

[0030] (2) The raw material slurry is placed in a hydrothermal reactor with stirring to carry out a hydrothermal synthesis reaction. Since magnesium oxide can only undergo hydration reaction at high temperature, its reaction with water at room temperature is very slow and weak. In addition, the particles on the weak polar crystal surface of the magnesium hydroxide crystal with special morphology are connected by ionic bonds. In the process of hydration of magnesium oxide to magnesium hydroxide, the formation of new bonds between particles on its weak polar crystal surface requires better activation energy, and certain potential energy barriers need to be overcome during the growth process. Therefore, the present invention proposes a method for hydrothermal synthesis reaction (the temperature of the hydrothermal synthesis reaction is 140-160°C, the time is 4-6h, and the stirring speed is 120-600r / min), which can be used for the synthesis, transformation and crystallization of magnesium oxide hydration to prepare flower-shaped magnesium hydroxide. The morphology control process provides a stable and sufficient energy supply, but insufficient reaction time will affect the completeness of crystal development. Low reaction temperature cannot provide sufficient energy to overcome the potential energy barrier for the growth of specific crystal faces. Too high reaction temperature increases energy consumption and is not conducive to the formation of flower ball-like morphology. In addition, an appropriate stirring speed (120-600r / min) can make the heat and mass of the material system evenly distributed during the hydrothermal process, promote the nucleation and growth of crystals. When the stirring speed is too low, the material system is prone to solid sedimentation at the bottom of the reactor, affecting the product quality. Too high a stirring speed not only increases the process energy consumption, but also too high a shear rate will destroy the integrity of the product crystal morphology.

[0031] (3) After the solid-liquid separation of the material is completed, a solid phase filter cake and a mother liquor are formed. After washing and drying, the solid phase filter cake is obtained to obtain a magnesium hydroxide product with a flower ball morphology. The liquid phase mother liquor is reused in the pulping process as a liquid raw material. Deionized water is used to wash the solid phase filter cake. Since the magnesium hydroxide crystals with flower ball morphology have lower agglomeration than other one-dimensional and two-dimensional magnesium hydroxide crystals, when the particle sizes of crystals with different morphologies are close, the solid-liquid separation speed and efficiency of the magnesium hydroxide slurry with flower ball morphology are higher. However, the specific surface area of ​​magnesium hydroxide crystals with flower ball morphology is larger, and the BET test results are usually within 60m 2 / g or more (correspondingly, the specific surface areas of one-dimensional whisker-like magnesium hydroxide and two-dimensional flake magnesium hydroxide are usually <20 and 8-10m after BET test. 2 / g or so), and its ability to absorb impurities in the mother liquor is stronger, so a certain amount of deionized water is needed to fully wash it a certain number of times. Compared with magnesium hydroxide with no fixed morphology or hexagonal plate morphology, the flower ball-shaped magnesium hydroxide particles of the present invention are uniform in shape, not easy to agglomerate, and more convenient for solid-liquid separation and washing, which solves the problem that impurities are difficult to simply remove due to agglomeration in the production process of magnesium hydroxide with no fixed morphology or hexagonal plate morphology. Therefore, the present invention can effectively utilize magnesium oxide raw materials with high impurities, and the solid phase filter cake is fully washed and dried to obtain a flower ball-shaped magnesium hydroxide product with a regular morphology.

[0032] (4) The general method for synthesizing flower-ball-shaped magnesium hydroxide is a one-step / step-by-step precipitation method for liquid raw materials, and the mother liquor is mostly a salt-containing waste liquid that cannot be directly reused. The method of the present invention adopts a one-step hydrothermal method for solid raw materials. The soluble crystal shaper added to the reaction system serves as a morphology transformation catalyst. The anions and cations generated by ionization in the mother liquor play a role in changing the surface characteristics of the crystal nucleus, affecting the growth direction of the grains, and inducing orderly self-assembly of the grains during the hydration process. After the reaction is completed, they still exist in the system in their original form. Therefore, after solid-liquid separation, the liquid mother liquor is a solution containing a soluble crystal shaper, which can be reused as a raw material "soluble crystal shaper solution" in the pulping process.

[0033] The present invention discloses the following technical effects:

[0034] (1) The present invention aims at the defects and shortcomings of the existing polycrystalline magnesium hydroxide synthesis process (such as poor controllability of product morphology in precipitation synthesis method and high disposal cost of by-product salt-containing mother liquor), and provides a method for preparing flower-ball-shaped magnesium hydroxide using magnesium oxide as raw material. Magnesium oxide is used as raw material, and a soluble crystal shaping agent is added to the reaction system. Then, a one-step hydrothermal synthesis method is used (the reaction process is stable and easy to control, solid-liquid separation is performed after the reaction is completed, and the mother liquor containing the soluble crystal shaping agent can be completely recycled, without wastewater discharge, and is environmentally friendly) to synthesize a flower-ball-shaped magnesium hydroxide product with regular morphology, which can be used as an inorganic flame retardant, a precious metal / heavy metal ion adsorbent, and a decolorizing agent.

[0035] (2) The preparation method of the present invention adopts solid raw materials and inorganic crystal-changing agents (soluble crystal-forming agents) to control certain hydrothermal conditions to synthesize flower-shaped magnesium hydroxide products. Compared with the precipitation method used in the past, it has great advantages in terms of controllable product preparation, improved product quality and reduced wastewater discharge.

[0036] (3) The mother liquor produced in the process of preparing the flower ball-shaped magnesium hydroxide of the present invention can be recycled, which overcomes the disadvantages of the previous precipitation process that the mother liquor produces a large amount of salt solution that cannot be reused and needs to be treated, and the process water consumption and mother liquor treatment volume are greatly reduced.

[0037] (4) The core process of the preparation method of the present invention is the hydrothermal synthesis process, the process conditions are stable and controllable, the required equipment is simple, and it is easy to realize industrialization.

[0038] (5) Compared with magnesium hydroxide with no fixed morphology or hexagonal plate morphology, the flower ball-shaped magnesium hydroxide particles of the present invention are uniform in shape, not easy to agglomerate, and more convenient for solid-liquid separation and washing, thereby avoiding the problem of difficulty in simply removing impurities due to agglomeration during the production of magnesium hydroxide with no fixed morphology or hexagonal plate morphology. Therefore, the present invention can effectively utilize magnesium oxide raw materials with higher impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 This is a process flow chart for preparing flower-shaped magnesium hydroxide in Example 1 of the present invention;

[0041] Figure 2 The SEM images of the flower-shaped magnesium hydroxide prepared in Examples 1 to 6 of the present invention, wherein A is Example 1, B is Example 2, C is Example 3, D is Example 4, E is Example 5, and F is Example 6;

[0042] Figure 3 XRD patterns of the flower-shaped magnesium hydroxide prepared in Examples 1 to 6 of the present invention, wherein A is Example 1, B is Example 2, C is Example 3, D is Example 4, E is Example 5, and F is Example 6;

[0043] Figure 4 This is a SEM image of the flower-shaped magnesium hydroxide prepared in Comparative Example 1 of the present invention;

[0044] Figure 5 The XRD diffraction peak diagram of the flower-shaped magnesium hydroxide prepared in Comparative Example 1 of the present invention;

[0045] Figure 6 This is a SEM image of the crystal product prepared in Comparative Example 2 of the present invention;

[0046] Figure 7 The XRD diffraction peak diagram of the crystal product prepared in Comparative Example 2 of the present invention;

[0047] Figure 8 This is a SEM image of the crystal product prepared in Comparative Example 3 of the present invention;

[0048] Fig. 9 The XRD diffraction peak diagram of the crystal product prepared in Comparative Example 3 of the present invention;

[0049] Fig.10 This is a SEM image of the crystal product prepared in Comparative Example 4 of the present invention;

[0050] Fig.11 The XRD diffraction peak diagram of the crystal product prepared in Comparative Example 4 of the present invention;

[0051] Fig.12 Particle size distribution diagram of raw material, unpulped material, and product prepared by hydrothermal reaction after pulping. DETAILED DESCRIPTION

[0052] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0053] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0054] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0055] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0056] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0057] Example 1

[0058] A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material:

[0059] (1) Preparation of raw material slurry: Magnesium oxide (industrial magnesium oxide, purity 99%) and a soluble crystal shaping agent solution (1 mol / L magnesium chloride solution) are mixed to prepare a mixed slurry with a solid content of 5%. After mixing, the mixed slurry is placed in a homogenizer for slurrying (homogenization speed is about 1800 r / min, time is about 8 min) to obtain a raw material slurry.

[0060] (2) Hydrothermal synthesis reaction: The raw material slurry was placed in a hydrothermal reactor with stirring, the stirring speed was set to 120 r / min, and the hydrothermal reaction was carried out at a hydrothermal reaction temperature of 180° C. for 4 h to obtain the finished material.

[0061] (3) Completing material processing: After the material is cooled, solid-liquid separation is performed by suction filtration to form a solid phase filter cake and a mother liquor; the solid phase filter cake is washed with deionized water as a washing liquid, and the mass ratio of the washing liquid to the solid phase filter cake is 4:1. The solid phase filter cake is washed three times and dried at 120° C. for 72 hours to obtain a white powder product, i.e., a flower ball-shaped magnesium hydroxide (see the process flow chart). Figure 1 , SEM images are shown in Figure 2 A, XRD diffraction peak diagram Figure 3 A). The concentration of magnesium chloride in the mother liquor is 1.02 mol / L. Add appropriate amount of water to make the concentration 1 mol / L, which can be reused in "raw material slurry preparation".

[0062] from Figure 2 As can be seen from A, the flower ball-shaped magnesium hydroxide prepared in this example is in a relatively regular flower ball shape, and the petals of the flower ball are uniform in shape and have distinct edges.

[0063] from Figure 3 It can be seen from A that the diffraction peaks of the flower ball-shaped magnesium hydroxide prepared in this example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn], and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0064] The above results show that the process of this embodiment can achieve the technical effect of preparing a flower-shaped magnesium hydroxide product with good quality and regular morphology.

[0065] Example 2

[0066] A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material:

[0067] (1) Preparation of raw material slurry: Magnesium oxide (industrial magnesium oxide, purity 85%) and a soluble crystal shaping agent solution (3 mol / L magnesium chloride solution) are mixed to prepare a mixed slurry with a solid content of 12%. After mixing, the mixed slurry is placed in a homogenizer for slurrying to obtain a raw material slurry.

[0068] (2) Hydrothermal synthesis reaction: The raw material slurry was placed in a hydrothermal reactor with stirring, the stirring speed was set to 480 r / min, and the hydrothermal reaction was carried out at a hydrothermal reaction temperature of 140° C. for 6 h to obtain the finished material.

[0069] (3) Completing material processing: After the material is cooled, solid-liquid separation is performed by suction filtration to form a solid phase filter cake and a mother liquor; the solid phase filter cake is washed with deionized water as a washing liquid, and the mass ratio of the washing liquid to the solid phase filter cake is 5:1. The solid phase filter cake is washed 5 times and dried at 120° C. for 72 h to obtain a white powder product, i.e., a flower ball-shaped magnesium hydroxide (SEM image is shown in FIG. Figure 2 B, XRD diffraction peak diagram see Figure 3 B). The concentration of magnesium chloride in the mother liquor is 3.2 mol / L. An appropriate amount of water is added to make the concentration 3 mol / L, which can be reused in the "raw material slurry preparation".

[0070] from Figure 2 It can be seen from B that the flower ball-shaped magnesium hydroxide prepared in this example is in a relatively regular flower ball shape, and the petals of the flower ball are uniform in shape and have distinct edges.

[0071] from Figure 3 It can be seen from B that the diffraction peaks of the flower-shaped magnesium hydroxide prepared in this example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn] and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0072] The above results show that the process of this embodiment can achieve the technical effect of preparing a flower-shaped magnesium hydroxide product with good quality and regular morphology.

[0073] Example 3

[0074] A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material:

[0075] (1) Preparation of raw material slurry: Magnesium oxide (industrial magnesium oxide, purity 75%) and a soluble crystal shaping agent solution (0.5 mol / L magnesium chloride solution) are mixed to prepare a mixed slurry with a solid content of 8%. After mixing, the mixed slurry is placed in a homogenizer for slurrying to obtain a raw material slurry.

[0076] (2) Hydrothermal synthesis reaction: The raw material slurry was placed in a hydrothermal reactor with stirring, the stirring speed was set to 600 r / min, and the hydrothermal reaction was carried out at a hydrothermal reaction temperature of 160° C. for 2 h to obtain the finished material.

[0077] (3) Completing material processing: After the material is cooled, solid-liquid separation is performed by suction filtration to form a solid phase filter cake and a mother liquor; the solid phase filter cake is washed with deionized water as a washing liquid, and the mass ratio of the washing liquid to the solid phase filter cake is 5:1. The solid phase filter cake is washed 5 times and dried at 80°C for 72 hours to obtain a white powder product, i.e., a flower ball-shaped magnesium hydroxide (SEM image is shown in Figure 2 C, XRD diffraction peak pattern see Figure 3C). The concentration of magnesium chloride in the mother liquor is about 0.5 mol / L, which can be reused in the "raw material slurry preparation".

[0078] from Figure 2 It can be seen from C that the flower ball-shaped magnesium hydroxide prepared in this example is in a relatively regular flower ball shape, and the petals of the flower ball are uniform in shape and have distinct edges.

[0079] from Figure 3 It can be seen from Figure C that the diffraction peaks of the flower-shaped magnesium hydroxide prepared in this example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn], and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0080] The above results show that the process of this embodiment can achieve the technical effect of preparing a flower-shaped magnesium hydroxide product with good quality and regular morphology.

[0081] Example 4

[0082] A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material:

[0083] (1) Preparation of raw material slurry: Magnesium oxide (industrial magnesium oxide, purity 80%) and a soluble crystal shaping agent solution (0.3 mol / L magnesium sulfate solution) are mixed to prepare a mixed slurry with a solid content of 10%. After mixing, the mixed slurry is placed in a homogenizer for slurrying to obtain a raw material slurry.

[0084] (2) Hydrothermal synthesis reaction: The raw material slurry was placed in a hydrothermal reactor with stirring, the stirring speed was set to 240 r / min, and the hydrothermal reaction was carried out at a hydrothermal reaction temperature of 120° C. for 2 h to obtain the finished material.

[0085] (3) Completing material processing: After the material is cooled, solid-liquid separation is performed by suction filtration to form a solid phase filter cake and a mother liquor; the solid phase filter cake is washed with deionized water as a washing liquid, and the mass ratio of the washing liquid to the solid phase filter cake is 4:1. The solid phase filter cake is washed 4 times and dried at 120° C. for 48 hours to obtain a white powder product, i.e., a flower ball-shaped magnesium hydroxide (SEM image is shown in FIG. Figure 2 D, XRD diffraction peak diagram see Figure 3 D). The concentration of magnesium sulfate in the mother liquor is 0.3 mol / L, which can be reused in the "raw material slurry preparation".

[0086] from Figure 2 As can be seen from D, the flower ball-shaped magnesium hydroxide prepared in this example is in a relatively regular flower ball shape, and the petals of the flower ball are uniform in shape and have distinct edges.

[0087] from Figure 3It can be seen from D that the diffraction peaks of the flower-shaped magnesium hydroxide prepared in this example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn] and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0088] The above results show that the process of this embodiment can achieve the technical effect of preparing a flower-shaped magnesium hydroxide product with good quality and regular morphology.

[0089] Example 5

[0090] A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material:

[0091] (1) Preparation of raw material slurry: Magnesium oxide (industrial magnesium oxide, purity 99%) and a soluble crystal shaping agent solution (2 mol / L magnesium sulfate solution) are mixed to prepare a mixed slurry with a solid content of 5%. After mixing, the mixed slurry is placed in a homogenizer for slurrying to obtain a raw material slurry.

[0092] (2) Hydrothermal synthesis reaction: The raw material slurry was placed in a hydrothermal reactor with stirring, the stirring speed was set to 200 r / min, and the hydrothermal reaction was carried out at a hydrothermal reaction temperature of 160° C. for 6 h to obtain the finished material.

[0093] (3) Completion of material processing: After the material is cooled, solid-liquid separation is performed by suction filtration to form a solid phase filter cake and a mother liquor; the solid phase filter cake is washed with deionized water as a washing liquid, the mass ratio of the washing liquid to the solid phase filter cake is 3:1, washed 4 times, and dried at 80°C for 72 hours to obtain a white powder product, i.e., flower ball-shaped magnesium hydroxide (SEM image see Figure 2 E, XRD diffraction peak pattern see Figure 3 E). The concentration of magnesium sulfate in the mother liquor is 2.05 mol / L. An appropriate amount of water is added to make the concentration 2 mol / L, which can be reused in the "raw material slurry preparation".

[0094] from Figure 2 It can be seen from E that the flower ball-shaped magnesium hydroxide prepared in this example is in a relatively regular flower ball shape, and the petals of the flower ball are uniform in shape and have distinct edges.

[0095] from Figure 3 It can be seen from E that the diffraction peaks of the flower-shaped magnesium hydroxide prepared in this example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn] and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0096] The above results show that the process of this embodiment can achieve the technical effect of preparing a flower-shaped magnesium hydroxide product with good quality and regular morphology.

[0097] Example 6

[0098] A method for preparing spherical magnesium hydroxide using magnesium oxide as raw material:

[0099] (1) Preparation of raw material slurry: Magnesium oxide (industrial magnesium oxide, purity 90%) and a soluble crystal shaping agent solution (1.5 mol / L magnesium sulfate solution) are mixed to prepare a mixed slurry with a solid content of 12%. After mixing, the mixed slurry is placed in a homogenizer for slurrying to obtain a raw material slurry.

[0100] (2) Hydrothermal synthesis reaction: The raw material slurry was placed in a hydrothermal reactor with stirring, the stirring speed was set to 300 r / min, and the hydrothermal reaction was carried out at a hydrothermal reaction temperature of 140° C. for 6 h to obtain the finished material.

[0101] (3) Completion of material processing: After the material is cooled, solid-liquid separation is performed by suction filtration to form a solid phase filter cake and a mother liquor; the solid phase filter cake is washed with deionized water as a washing liquid, the mass ratio of the washing liquid to the solid phase filter cake is 5:1, washed 5 times, and dried at 80°C for 60h to obtain a white powder product, i.e., flower ball-shaped magnesium hydroxide (SEM image see Figure 2 F, XRD diffraction peak pattern see Figure 3 F). The concentration of magnesium sulfate in the mother liquor is 1.56 mol / L. An appropriate amount of water is added to make the concentration 1.5 mol / L, which can be reused in the "raw material slurry preparation".

[0102] from Figure 2 It can be seen from F that the flower ball-shaped magnesium hydroxide prepared in this example is in a relatively regular flower ball shape, and the petals of the flower ball are uniform in shape and have distinct edges.

[0103] from Figure 3 It can be seen from F that the diffraction peaks of the flower-shaped magnesium hydroxide prepared in this example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn] and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0104] The above results show that the process of this embodiment can achieve the technical effect of preparing a flower-shaped magnesium hydroxide product with good quality and regular morphology.

[0105] Comparative Example 1

[0106] Same as Example 2, except that the stirring speed in step (2) is 1000 r / min, and the spherical magnesium hydroxide is produced (see SEM image Figure 4, XRD diffraction peak pattern see Figure 5 ).

[0107] from Figure 4 It can be seen that the relatively high stirring speed causes a certain degree of damage to the product morphology. The flower ball-shaped magnesium hydroxide prepared in this comparative example has a poor spherical shape, and part of it is an accumulation of fragments after the flower ball is broken. The petals of the spherical crystal product are less regular and are mixed with a large amount of fragments.

[0108] from Figure 5 It can be seen that the diffraction peaks of the flower-shaped magnesium hydroxide prepared in this comparative example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn] and the product diffraction peaks are relatively obvious and sharp, proving that it is a magnesium hydroxide product with high crystal quality.

[0109] Comparative Example 2

[0110] Same as Example 2, except that the hydrothermal reaction time in step (2) is 1 h. The resulting crystalline product (SEM image is shown in Figure 6 , XRD diffraction peak pattern see Figure 7 ).

[0111] from Figure 6 It can be seen that due to insufficient reaction time, the raw materials were not completely converted, the product and raw materials were mixed, and the regular morphology could not be reflected.

[0112] from Figure 7 It can be seen that the diffraction peaks of the product prepared in this comparative example overlap with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn] and the diffraction characteristic peaks 200, 220 and 311 of the physical phase standard diffraction card #45-0946 [Periclase, syn], proving that it is a mixture of magnesium oxide and magnesium hydroxide crystals.

[0113] Comparative Example 3

[0114] Same as Example 2, except that the magnesium chloride solution was replaced with a sodium hydroxide solution of the same concentration. The crystalline product was obtained (see SEM image). Figure 8 , XRD diffraction peak pattern see Fig. 9 ).

[0115] Figure 8 It can be seen that after magnesium chloride is replaced by sodium hydroxide, the product is in the form of two-dimensional flakes, and the crystal morphology has clear boundaries and neat edges, proving that the main effect of sodium hydroxide on crystal growth and assembly direction under the reaction conditions is the two-dimensional growth direction, which is different from the effect of magnesium chloride used in the present invention.

[0116] from Fig. 9 It can be seen that the diffraction peaks of the product prepared in this comparative example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn], which proves that magnesium hydroxide crystal products can be generated when sodium hydroxide is used as a crystal conversion promoter.

[0117] In summary, under the same other conditions, magnesium hydroxide crystal products can also be prepared by replacing magnesium chloride with sodium hydroxide, but their morphology is regular two-dimensional flakes.

[0118] Comparative Example 4

[0119] Same as Example 6, except that the magnesium sulfate solution was replaced with a sodium hydroxide solution of the same concentration. The crystalline product was obtained (see SEM image). Fig.10 , XRD diffraction peak pattern see Fig.11 ).

[0120] from Fig.10 It can be seen that after magnesium sulfate is replaced by sodium hydroxide, the product is in the form of two-dimensional flakes, and the crystal morphology has clear boundaries and neat edges, proving that the main effect of sodium hydroxide on crystal growth and assembly direction under the reaction conditions is the two-dimensional growth direction, which is different from the effect of magnesium sulfate used in the present invention.

[0121] from Fig.11 It can be seen that the diffraction peaks of the product prepared in this comparative example are consistent with the diffraction characteristic peaks 001, 101, 102 and 110 of the physical phase standard diffraction card #07-0239 [Brucite, syn], which proves that magnesium hydroxide crystal products can be generated when sodium hydroxide is used as a crystal conversion promoter.

[0122] In summary, under the same other conditions, magnesium hydroxide crystal products can also be prepared by replacing magnesium sulfate with sodium hydroxide, but their morphology is regular two-dimensional flakes.

[0123] Effect Example 1

[0124] As a method for preparing inorganic crystal functional materials, the hydrothermal method provides a crystallization environment with stable energy supply and reaction process parameters. The higher reaction temperature is conducive to overcoming the energy barrier, and cheaper raw materials can be used to produce high-value and special-shaped crystalline products. The output product crystals have the advantages of more complete grain development and more uniform particle size distribution. At the same time, in addition to the hydrothermal process, the pre-treatment process can also have a certain degree of influence on the particle distribution of the product crystals. The particle size distribution data D of the raw materials, the unpulped product (after hydrothermal treatment), and the pulped product (after hydrothermal treatment) 50 , D 90 The standard deviation SD is shown in Table 1. Fig.12as shown in .

[0125] The method of pulping and hydrothermal treatment is the same as that of Comparative Example 1.

[0126] Table 1

[0127]

[0128] In Table 1, N represents the product obtained by hydrothermal treatment without pulping, and the three samples are referred to as N1, N2, and N3 respectively; D represents the product obtained by hydrothermal treatment after pulping, and the four samples are referred to as D1, D2, D3, and D4 respectively.

[0129] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing spherical magnesium hydroxide using magnesium oxide as a raw material, characterized in that: The following steps are involved: The magnesium oxide and the soluble crystal shaping agent solution are mixed and slurried to obtain a raw material slurry, and the raw material slurry is subjected to a hydrothermal synthesis reaction and then solid-liquid separation, and the solid phase is the flower ball-shaped magnesium hydroxide; The soluble crystal shaping agent solution is a magnesium chloride solution; The temperature of the hydrothermal synthesis reaction is 120-180° C., the time is 2-8 hours, and the stirring speed is 120-600 r / min.

2. The method for preparing the spherical magnesium hydroxide according to claim 1, wherein The magnesium oxide is industrial magnesium oxide with a purity of 75-99%.

3. The method for preparing the spherical magnesium hydroxide according to claim 1, wherein The concentration of the magnesium chloride solution is 0.3-3 mol / L.

4. The method for preparing the spherical magnesium hydroxide according to claim 3, wherein The concentration of the magnesium chloride solution is 0.5-2 mol / L.

5. The method for preparing the flower ball-shaped magnesium hydroxide according to claim 1, characterized in that: The solid content of the raw material slurry is 5-12%.

6. The method for preparing the flower-spherical magnesium hydroxide according to claim 1, wherein The temperature of the hydrothermal synthesis reaction is 140-160° C., the time is 4-6 hours, and the stirring speed is 120-600 r / min.

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