A method for preparing magnesium hydroxide slurry by hydrating light-burned active magnesium oxide

Abstract

The present application relates to a kind of methods for preparing magnesium hydroxide slurry by light-burned active magnesium oxide hydration, and it relates to the technical field of chemical product preparation, comprising the following steps: step one, raw material preparation, according to the ratio of (0.05-1.5) : (0.1-2.5) : (80-120) : (35-45) in weight fraction, prepare thickening agent, dispersant, water and light-burned active magnesium oxide;Step two, the thickening agent and dispersant are added to water and stirred to dissolve, to obtain a dissolution solution;Step three, heating the dissolution solution;Step four, light-burned active magnesium oxide is added to the dissolution solution obtained in step three in batches, and stirring is carried out to carry out hydration reaction;Step five, after the hydration reaction is completed, continue to stir until the temperature drops to room temperature, to obtain magnesium hydroxide slurry.The present application can avoid the agglomeration of small crystal cells of magnesium hydroxide generated during hydration by adding light-burned active magnesium oxide to the dissolution solution with dispersing and thickening effect in batches to generate magnesium hydroxide, so that magnesium hydroxide slurry with high stability can be prepared.

Description

Technical Field

[0001] This invention relates to the field of chemical product preparation technology, specifically a method for preparing magnesium hydroxide slurry by hydration of lightly calcined active magnesium oxide. Background Technology

[0002] Magnesium hydroxide is an environmentally friendly material with excellent adsorption and reactivity. Although its solubility in water is very low, the dissolved portion is completely ionized, resulting in a saturated aqueous solution with a pH of around 9, making it a common moderately strong alkali. Magnesium hydroxide is widely available, non-toxic to humans and the environment, and can be described as a "mild alkali" and a "green and safe water treatment agent." Due to its excellent physicochemical properties, magnesium hydroxide has significant application needs and development potential in production and daily life, such as in flame retardants, resin fillers, and food additives. It also shows great promise in the environmental protection field, serving as a flue gas desulfurizer, a neutralizer for acidic wastewater, a precipitant for heavy metal wastewater, and a pH adjuster for agricultural water bodies.

[0003] In many applications of magnesium hydroxide, solid magnesium hydroxide is difficult to use. For example, in the most common flue gas desulfurization agent, solid magnesium hydroxide is difficult to react with sulfur- and nitrate-containing flue gas in the absorption tower. Furthermore, in wastewater treatment applications, if solid magnesium hydroxide is directly poured into wastewater, some magnesium hydroxide particles will agglomerate into spheres due to surface wetting, making them difficult to disperse. These agglomerated magnesium hydroxides have low reaction efficiency, resulting in low overall reactivity and resource waste. Therefore, preparing magnesium hydroxide slurry with high solid content and high stability can greatly expand the application range of magnesium hydroxide.

[0004] Because magnesium hydroxide is a sparingly soluble precipitate, it naturally settles when dispersed in water. Therefore, the preparation of magnesium hydroxide suspensions often results in stratification and instability, where the upper part of the suspension contains almost no magnesium hydroxide, while the lower part is filled with accumulated magnesium hydroxide. In practical applications, this stratification makes it difficult to determine the concentration of the magnesium hydroxide suspension used, significantly impacting its effectiveness.

[0005] In the preparation of magnesium hydroxide slurry, to avoid stratification, a certain amount of thickener is usually added when dispersing magnesium hydroxide powder in water. The thickener increases the viscosity of the fluid within a certain range, preventing sedimentation. However, the amount of thickener used is very important. If too little is used, the system viscosity is low, making sedimentation and stratification easy. If too much is used, gelation is very likely to occur, meaning the slurry becomes too viscous, resembling a jelly and losing its fluidity. In actual use, because it lacks fluidity, it is difficult to pour out of the container.

[0006] Because the crystal cells of magnesium hydroxide are hexagonal lamellar layered structures, the exposed layers are OH groups, which can be considered non-polar surfaces, while the side surfaces expose six equal faces containing magnesium ions, which are stress polar surfaces. These small crystal cells are prone to agglomeration under polar influence. It is precisely because of the presence of these agglomerates that they are difficult to disperse. Patent CN114213875A discloses a highly stable magnesium hydroxide suspension and its preparation method. Conventional magnesium hydroxide powder is added to water, and a thickener is added to obtain a slurry. Because the large agglomerates are difficult to disperse and easily settle and separate, obtaining a highly stable slurry is very difficult. The amount of thickener added must be precisely controlled, and the solid content is also limited, greatly affecting the application of magnesium hydroxide slurry. Therefore, the preparation of a highly stable magnesium hydroxide slurry with high solid content, capable of maintaining its properties without separation or gelation for a long time, and maintaining good fluidity has significant application prospects. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing magnesium hydroxide slurry by hydration of lightly calcined active magnesium oxide, which can solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing magnesium hydroxide slurry by hydration of lightly calcined activated magnesium oxide, comprising the following steps:

[0009] Step 1: Raw material preparation. Prepare thickener, dispersant, water and lightly calcined active magnesium oxide in the following weight ratios: (0.05-1.5): (0.1-2.5): (80-120): (35-45).

[0010] Step 2: Add the thickener and dispersant to water and stir to dissolve, obtaining a solution;

[0011] Step 3: Heat the solution;

[0012] Step 4: Add the lightly calcined active magnesium oxide in batches to the solution obtained in Step 3, and stir to carry out the hydration reaction;

[0013] Step 5: After the hydration reaction is complete, continue stirring until the temperature drops to room temperature to obtain magnesium hydroxide slurry.

[0014] This invention involves adding lightly calcined activated magnesium oxide to a solution containing a dispersant and a thickener, causing it to hydrate and form a stable magnesium hydroxide slurry. Due to the presence of the dispersant and thickener, the agglomeration of small magnesium hydroxide particles generated during hydration is prevented, resulting in a stable slurry. Specifically, small magnesium hydroxide particles are generated during hydration. The dispersant adsorbs onto these particles, promoting their dispersion in the water and preventing the small particles from re-contacting and forming large precipitates. Simultaneously, an appropriate amount of thickener increases the viscosity of the fluid, preventing sedimentation.

[0015] Because the lightly calcined activated magnesium oxide is added in batches, the hydration process proceeds slowly, thus avoiding the formation of a large amount of magnesium hydroxide in a short period of time, which is more conducive to the dispersion of the generated magnesium hydroxide particles. The method of this invention can prepare a magnesium hydroxide slurry with high solids content and high stability. Furthermore, the preparation process is simple, produces no emissions, and is environmentally friendly.

[0016] As a preferred embodiment of the above preparation method, the thickener, dispersant, and water are added in the following proportions by weight: (0.1-1.0):(0.5-1.8):(80-120).

[0017] As a preferred embodiment of the above preparation method, the proportion of lightly calcined activated magnesium oxide added per batch is no more than 10, according to the weight ratio of thickener, dispersant, water, and lightly calcined activated magnesium oxide as (0.05-1.5):(0.1-2.5):(80-120):(35-45). As a further preferred embodiment of the above preparation method, the proportion of lightly calcined activated magnesium oxide added per batch is 7-10. By controlling the amount of lightly calcined activated magnesium oxide added per batch, a large amount of magnesium hydroxide can be avoided from being generated in a short period of time, which is beneficial to the dispersion of small magnesium hydroxide particles; at the same time, in order to make full use of the solution, the proportion added per batch should not be too low.

[0018] As a preferred embodiment of the above preparation method, in step four, the temperature of the hydration reaction is controlled between 30-80℃. Since the hydration process releases heat, causing the system temperature to rise, it is necessary to monitor and control the hydration reaction at a suitable temperature.

[0019] As a preferred embodiment of the above preparation method, in step four, after all the lightly calcined active magnesium oxide has been added to the solution, the hydration reaction is continued for 1-4 hours to ensure complete reaction.

[0020] As a preferred embodiment of the above preparation method, the thickener is one or more of sodium polyacrylate, polyvinylpyrrolidone, xanthan gum, polyvinyl alcohol, methylcellulose, sodium carboxymethyl cellulose, gelatin, guar gum, and starch.

[0021] As a preferred embodiment of the above preparation method, the dispersant is one or more of sodium pyrophosphate, sodium hydroxyethylidene diphosphonate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and triethanolamine lauryl sulfate.

[0022] The present invention also provides a magnesium hydroxide slurry, which is prepared by the method described in any of the above schemes for preparing magnesium hydroxide slurry by hydration of lightly calcined active magnesium oxide.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] The method for preparing magnesium hydroxide slurry by hydrating lightly calcined active magnesium oxide provided by this invention involves adding lightly calcined active magnesium oxide in batches to a dispersing and thickening solution to hydrate and generate magnesium hydroxide. Due to the effects of the dispersant and thickener, the agglomeration of small magnesium hydroxide crystals generated during the hydration process can be avoided, thereby obtaining a highly stable magnesium hydroxide slurry. At the same time, by controlling the addition ratio of each raw material, the solid content of the magnesium hydroxide slurry can be increased as much as possible while ensuring high dispersibility and solubility. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the hydration of lightly calcined active magnesium oxide in a dispersant and thickener solution to form magnesium hydroxide slurry in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the magnesium hydroxide slurry prepared in Example 1 of the present invention being left at room temperature for 30 days;

[0027] Figure 3 This is a schematic diagram of the magnesium hydroxide slurry prepared in Comparative Example 1 of the present invention, which was placed at room temperature for 30 days.

[0028] Figure 4 This is a schematic diagram of the magnesium hydroxide slurry prepared in Comparative Example 4 of the present invention, which was left at room temperature for 7 days. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art, and the raw materials used are all commercially available products. Example 1

[0031] A method for preparing magnesium hydroxide slurry by hydration of lightly calcined activated magnesium oxide includes the following steps:

[0032] Step 1: Weigh 0.5 g of sodium polyacrylate (5040) and 0.5 g of xanthan gum and add them to 100 g of water, stirring until completely dissolved; then weigh 1 g of sodium hydroxyethylidene diphosphonate and add it to the solution, stirring until dissolved to obtain the solution.

[0033] Step 2: Heat the above solution until the temperature reaches 40°C;

[0034] Step 3: Under stirring conditions, weigh 40 grams of lightly calcined activated magnesium oxide and add it to the stirred solution in 5 portions of approximately 8 grams each. Continue stirring to carry out the hydration reaction. Since the hydration process releases heat, the system temperature may rise; therefore, the temperature of the hydration reaction needs to be controlled. After hydration for a period of time, wait until the temperature drops to 40°C (when added), maintain this temperature for about 10 minutes, and then continue adding lightly calcined activated magnesium oxide to continue the reaction. Repeat this cycle until all the lightly calcined activated magnesium oxide has been added, and continue the hydration reaction for approximately 3 hours.

[0035] Step 4: After the reaction is complete, stop heating, continue stirring, and stop stirring when the temperature drops to room temperature. The resulting mixed slurry is a magnesium hydroxide slurry with a solid content of approximately 40.8%. Since the solvent in this system is water, its solidification temperature is 0℃. To prevent the water in the slurry from solidifying and becoming ineffective, it needs to be stored at room temperature above 0℃.

[0036] Figure 2 The image shows the magnesium hydroxide slurry prepared in this embodiment after being left at room temperature for 30 days. The magnesium hydroxide slurry did not show stratification, had good suspension, and good storage stability. Example 2

[0037] A method for preparing magnesium hydroxide slurry by hydration of lightly calcined activated magnesium oxide includes the following steps:

[0038] Step 1: Weigh 0.5 g of polyvinyl alcohol (1799) and 0.5 g of sodium carboxymethyl cellulose FH9 and add them to 100 g of water, stirring until completely dissolved; then weigh 2 g of sodium dodecylbenzene sulfonate and add it to the solution, stirring until dissolved to obtain the solution;

[0039] Step 2: Heat the above solution until the temperature reaches 50°C;

[0040] Step 3: Under stirring conditions, weigh 35 grams of lightly calcined activated magnesium oxide and add it to the stirred solution in 5 portions of approximately 7 grams each. Continue stirring to carry out the hydration reaction. Since the hydration process releases heat, the system temperature may rise; therefore, the temperature of the hydration reaction needs to be controlled. After hydration for a period of time, wait until the temperature drops to 50°C (the initial temperature at which the magnesium oxide was added), maintain this temperature for about 5 minutes, and then continue adding lightly calcined activated magnesium oxide to continue the reaction. Repeat this cycle until all the lightly calcined activated magnesium oxide has been added, and continue the hydration reaction for approximately 2 hours.

[0041] Step 4: After the reaction is complete, stop heating, continue stirring, and stop stirring when the temperature drops to room temperature. The resulting mixed slurry is a magnesium hydroxide slurry with a solid content of approximately 37%. Since the solvent in this system is water, its solidification temperature is 0℃. To prevent the water in the slurry from solidifying and becoming ineffective, it needs to be stored at room temperature above 0℃.

[0042] The magnesium hydroxide slurry prepared in this way has similar fluidity and storage stability to that of Example 1, and also has good fluidity and storage stability. Example 3

[0043] A method for preparing magnesium hydroxide slurry by hydration of lightly calcined activated magnesium oxide includes the following steps:

[0044] Step 1: Weigh 0.3 g of polyvinylpyrrolidone (K30) and 0.3 g of gelatin and add them to 100 g of water. Stir until completely dissolved. Then weigh 1 g of sodium dodecyl sulfate and add it to the solution. Stir until dissolved to obtain the solution.

[0045] Step 2: Heat the above solution until the temperature reaches 60°C;

[0046] Step 3: Under stirring conditions, weigh 45 grams of lightly calcined activated magnesium oxide and add it to the stirred solution in 5 portions of approximately 9 grams each. Continue stirring to carry out the hydration reaction. Since the hydration process releases heat, the system temperature may rise; therefore, the temperature of the hydration reaction needs to be controlled. After hydration for a period of time, wait until the temperature drops to 60°C (when added) and maintain this temperature for about 5 minutes. Then, continue adding lightly calcined activated magnesium oxide to continue the reaction. Repeat this cycle until all the lightly calcined activated magnesium oxide has been added, and continue the hydration reaction for approximately 2 hours.

[0047] Step 4: After the reaction is complete, stop heating, continue stirring, and stop stirring when the temperature drops to room temperature. The resulting mixed slurry is a magnesium hydroxide slurry with a solid content of approximately 44.4%. Since the solvent in this system is water, its solidification temperature is 0℃. To prevent the water in the slurry from solidifying and becoming ineffective, it needs to be stored at room temperature above 0℃. Example 4

[0048] A method for preparing magnesium hydroxide slurry by hydration of lightly calcined activated magnesium oxide includes the following steps:

[0049] Step 1: Weigh 0.03 g of sodium polyacrylate (5040) and 0.03 g of xanthan gum and add them to 100 g of water, stirring until completely dissolved; then weigh 1 g of sodium hydroxyethylidene diphosphonate and add it to the solution, stirring until dissolved to obtain the solution;

[0050] Step 2: Heat the above solution until the temperature reaches 40°C;

[0051] Step 3: Under stirring conditions, weigh 40 grams of lightly calcined activated magnesium oxide and add it to the stirred solution in 5 portions of approximately 8 grams each. Continue stirring to carry out the hydration reaction. Since the hydration process releases heat, the system temperature may rise; therefore, the temperature of the hydration reaction needs to be controlled. After hydration for a period of time, wait until the temperature drops to 40°C (when added), maintain this temperature for about 10 minutes, and then continue adding lightly calcined activated magnesium oxide to continue the reaction. Repeat this cycle until all the lightly calcined activated magnesium oxide has been added, and continue the hydration reaction for approximately 3 hours.

[0052] Step 4: After the reaction is complete, stop heating, continue stirring, and stop stirring when the temperature drops to room temperature. The resulting mixed slurry is a magnesium hydroxide slurry with a solid content of approximately 40.8%. Since the solvent in this system is water, its solidification temperature is 0℃. To prevent the water in the slurry from solidifying and becoming ineffective, it needs to be stored at room temperature above 0℃.

[0053] Comparative Example 1

[0054] Step 1: Weigh 40 grams of lightly calcined activated magnesium oxide and add it to 100 grams of water, and mechanically stir at 1000 rpm for 30 minutes.

[0055] Step 2: Weigh 0.5 g of sodium polyacrylate (5040) and 0.5 g of xanthan gum and add them to the above stirring solution; then weigh 1 g of sodium hydroxyethylidene diphosphonate and add it to the solution. Continue mechanical stirring at 3000 rpm for 30 min to obtain magnesium hydroxide slurry.

[0056] Figure 3 The image shows the magnesium hydroxide slurry prepared for this comparative example after being left at room temperature for 30 days. The magnesium hydroxide slurry exhibits obvious stratification.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 1 is that in step three, 40 grams of lightly calcined active magnesium oxide are added to the stirred solution all at once, and the hydration reaction is maintained for about 3 hours.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 1 is that in step three, 40 grams of lightly calcined active magnesium oxide is added to the stirring solution in three portions of about 13 grams each, and the mixture is stirred continuously to carry out the hydration reaction.

[0061] Comparative Example 4

[0062] Weigh 40g of magnesium hydroxide powder and add it to 80g of water. Stir mechanically at 500rpm for 30min until the mixture is homogeneous. Then, adjust the speed to 1500rpm and add 0.5g of 40wt% polyacrylic acid aqueous solution, 1g of sodium pyrophosphate, and 0.5g of xanthan gum in sequence. Stir the mixture for 15min until it is homogeneous.

[0063] Figure 4 The image shows the magnesium hydroxide slurry prepared for this comparative example after being left at room temperature for 7 days. The magnesium hydroxide slurry exhibits obvious stratification.

[0064] Eight magnesium hydroxide slurries prepared in Examples 1, 2, 3, 4, Comparative Examples 1, 2, 3, and 4 were sampled, and their viscosity, flowability, and solid content were measured. The measurement data are shown in Table 1.

[0065] Table 1. Viscosity, flowability, and solid content test data of the examples and comparative examples.

[0066]

[0067] According to the table above, the test data from the examples and comparative examples show that the method for preparing magnesium hydroxide slurry by hydrating lightly calcined active magnesium oxide provided in the various embodiments of the present invention, by adding lightly calcined active magnesium oxide in batches to a dissolving solution with dispersing and thickening effects, hydrates to generate magnesium hydroxide, resulting in a highly stable magnesium hydroxide slurry with good solubility, thus ensuring suitable viscosity and fluidity of the slurry. However, in Comparative Example 1, by adding dispersant and thickener to the magnesium hydroxide solution, obvious sedimentation and stratification occur, leading to increased viscosity and poor fluidity. In Comparative Examples 2 and 3, the batch addition amount of lightly calcined active magnesium oxide was not controlled, resulting in poor dispersion, viscosity, and fluidity. In Comparative Example 4, by adding magnesium hydroxide powder to water, large agglomerates are difficult to disperse and easily settle and stratify, resulting in a low solid content in the magnesium hydroxide slurry to ensure the required viscosity and fluidity.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a magnesium hydroxide slurry from light-burned active magnesium oxide by hydration, characterized in that, The method comprises the following steps: Step one, raw material preparation, the thickening agent, dispersing agent, water and light-burned active magnesium oxide are prepared according to the proportion of (0.05-1.5):(0.1-2.5):(80-120):(35-45) by weight, and the light-burned active magnesium oxide is added in a proportion of 7-10 per batch; Step two, the thickening agent and the dispersing agent are added to water and stirred to dissolve, to obtain a dissolved solution; Step three, the dissolved solution is heated; Step four, the light-burned active magnesium oxide is added to the dissolved solution obtained in step three in batches, and stirring is performed to carry out a hydration reaction; Step five, after the hydration reaction is completed, the stirring is continued until the temperature drops to room temperature, to obtain a magnesium hydroxide slurry; The thickening agent is one or more of sodium polyacrylate, polyvinylpyrrolidone, xanthan gum, polyvinyl alcohol, methyl cellulose, sodium carboxymethyl cellulose, gelatin, guar gum and starch; and the dispersing agent is one or more of sodium pyrophosphate, sodium hydroxyethylidene diphosphonate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate and triethanolamine lauryl sulfate.

2. The method of claim 1, wherein the method is characterized by, The thickening agent, dispersing agent and water are added in a proportion of (0.1-1.0):(0.5-1.8):(80-120) by weight.

3. The method of claim 1, wherein the method is characterized by, In step four, the temperature of the hydration reaction is controlled at 30-80℃.

4. The method of claim 1, wherein the method is characterized by, In step four, after the light-burned active magnesium oxide is completely added to the dissolved solution, the hydration reaction is continued for 1-4h.

5. A magnesium hydroxide slurry characterized in that, The magnesium hydroxide slurry is prepared by the method of any one of claims 1-4.

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