A preparation method of hexagonal flaky calcium hydroxide

Abstract

The present invention discloses a method for preparing hexagonal flaky calcium hydroxide, comprising the following steps: step 1: calcining ore to obtain CaO, crushing and removing impurities, sieving, and obtaining CaO powder for standby use; step 2: placing low-temperature digestion water into a reactor, adding sodium dihydrogen phosphate additive to the digestion water, starting stirring, and slowly pouring the CaO powder from step 1 into the reactor for digestion reaction; step 3: drying, crushing, and sieving to obtain hexagonal flaky calcium hydroxide. The present invention can prepare hexagonal flaky calcium hydroxide, provides a new method and idea for the research of calcium hydroxide, and expands the application direction of calcium hydroxide.

Description

Technical Field

[0001] The present invention relates to the technical field of calcium hydroxide preparation, and specifically to a method for preparing hexagonal flaky calcium hydroxide. Background Art

[0002] Calcium hydroxide is a very important chemical raw material. Due to its alkalinity, antibacterial properties, absorption of carbon dioxide, and reinforcing effect in polymers, it is widely used in the construction, food, medicine, plastics, papermaking, petroleum additives and other industries. It is currently a commonly used carbon adsorbent and flue gas treatment material. In industry, quicklime is often used as a raw material to obtain calcium hydroxide products with different properties through dry and wet processes. Due to the property that calcium hydroxide will undergo a carbonization reaction to form calcium carbonate when it comes into contact with carbon dioxide in the air, it is widely used in the restoration of historical and cultural buildings and murals. Due to the alkalinity and low cost of calcium hydroxide, it is widely used for desulfurization and denitrification treatment of waste incineration and factory flue gases. Due to its antibacterial effect, it is also an important filler in current root canal treatment of teeth. "Professional" calcium hydroxide products are usually designed and prepared for different fields of use.

[0003] Calcium hydroxide production methods are categorized into two main methods: dry and wet. The dry digestion process involves adding quicklime of a certain particle size to a digester, where it interacts with a small amount of water to produce a digestion reaction. Because the amount of water added is small, a calcium hydroxide powder with a low water content is directly produced. The reaction is exothermic, and as the temperature gradually rises, it accelerates the reaction, facilitating its completion, releasing more heat and causing a noticeable change in the material's appearance. The heat released during the digestion reaction converts some of the water into steam, generating expansion pressure that fills the interstices between the particles. This increases the pore volume and changes the structure, resulting in a loose powder with a volume that increases by 1-2 times its original volume. The product and raw material exhibit good fluidity. The wet method for producing calcium hydroxide strictly encompasses both double decomposition and digestion of CaO with sufficient water. Industrial calcium hydroxide is a typical example of the wet method, typically produced by digestion of quicklime (CaO) with water. Its low cost and readily available raw materials make it suitable for large-scale production. Usually, calcium hydroxide used in flue gas treatment, building repair, papermaking filler, etc. is made from limestone as raw material. After calcination, crushing and impurity removal, quicklime (CaO) is obtained, and then digested with water to produce it.

[0004] Deng Changzheng et al. pointed out in "Application of Calcium Hydroxide in New Materials Field" that calcium hydroxide is mainly used in various materials such as flue gas treatment materials, flame retardant organic polymers, and biodegradable polymer materials. It can be seen that calcium hydroxide can be used in materials in different fields.

[0005] Chinese patent CN113526536A discloses a method for synthesizing calcium hydroxide with a high specific surface area, belonging to the technical field of calcium hydroxide synthesis. Calcium chloride solution is dropwise added to a mixture of cetyltrimethylammonium bromide and liquid caustic soda to produce calcium hydroxide molecules. Crystallization occurs when the calcium hydroxide concentration in the system exceeds saturation. Cetyltrimethylammonium bromide is added during the synthesis process to perform in-situ modification of the product, thereby preventing particle agglomeration and slowing down Brownian motion to effectively control agglomerates. During the post-treatment of the calcium hydroxide, homemade graphene-modified carboxymethyl-β-cyclodextrin is added. The graphene-modified carboxymethyl-β-cyclodextrin forms a network structure after cross-linking. The calcium hydroxide molecules are dispersed in the network structure, effectively preventing intermolecular agglomeration. In the applied deacidification gas reaction, the binding sites of the calcium hydroxide and the acidic gas are well dispersed, resulting in a more efficient reaction.

[0006] Chinese patent CN 110078389 A discloses a method for preparing calcium hydroxide powder with high reactivity and high specific surface area, comprising the following steps: (1) crushing: crushing calcined quicklime; (2) digestion: digesting the crushed quicklime; first adding chemical additives to the digestion water, then mixing the quicklime and digestion water in a premixer at a water-to-material ratio of 0.55 to 0.70, and then entering the digester; the digester stirring speed is 700-800 rpm, the digester outlet temperature is 90°C, and the digestion time is 9-12 minutes; (3) drying and crushing: drying the digested calcium hydroxide at a temperature of 80-110°C and then crushing; (4) classification: classifying the dried and crushed calcium hydroxide in a classifier at a speed of 1000-1200 rpm to obtain calcium hydroxide powder with high reactivity and high specific surface area. The method obtains calcium hydroxide with high reactivity and high specific surface area by controlling the appropriate digestion process parameters such as water-to-material ratio, digestion temperature, and digestion time.

[0007] It is known from the above-mentioned known patents and literature that most of the research on calcium hydroxide is biased towards application, such as high specific surface area calcium hydroxide, high activity calcium hydroxide, etc., while there is less research on the structural morphology of calcium hydroxide itself. The purpose of the present invention is to provide a method for preparing flaky calcium hydroxide, so as to expand the research scope of calcium hydroxide and develop new application scenarios thereof.

[0008] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above content has been disclosed on the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of this application. Summary of the Invention

[0009] The invention provides a preparation method of hexagonal flaky calcium hydroxide, which can prepare hexagonal flaky calcium hydroxide, provides a new method and idea for the research of calcium hydroxide, and expands the application direction of calcium hydroxide.

[0010] In order to achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0011] A method for preparing hexagonal flaky calcium hydroxide comprises the following steps:

[0012] Step 1: calcining the ore to obtain CaO, crushing and removing impurities, sieving, and obtaining CaO powder for later use;

[0013] Step 2: Put low-temperature digestion water into the reactor, add sodium dihydrogen phosphate additive to the digestion water, start stirring, and slowly pour the CaO powder from step 1 into the reactor for digestion reaction;

[0014] Step 3: drying, crushing and sieving to obtain hexagonal flaky calcium hydroxide.

[0015] Preferably, in step 1, the calcination temperature is 1150° C. to 1300° C., and the calcination time is 280 to 360 minutes.

[0016] Preferably, in step 1, sieving is performed using a 100-300 mesh sieve.

[0017] Preferably, in step 2, the ash-water ratio is 1:6-8.

[0018] Preferably, in step 2, the initial temperature of the digestion water is 5-10°C.

[0019] Preferably, in step 2, the amount of sodium dihydrogen phosphate added is 0.5-1% of the mass of CaO.

[0020] Preferably, in step 2, the stirring speed is 100-200 rpm.

[0021] Preferably, in step 2, the reaction time is 3 to 5 hours.

[0022] Preferably, in step three, the drying is oven forced air drying; the drying temperature is 90-110° C., and the drying time is 8-12 h.

[0023] Preferably, in step three, sieving is performed using a 100-300 mesh sieve.

[0024] The present invention adds calcium dihydrogen phosphate as an inhibitor to the digestion water, which has the following mechanism of action:

[0025] (1) When lime is added for digestion reaction, the phosphate in the solution will inhibit the growth of calcium hydroxide crystals along a specific direction, and the Ca 2+Calcium ions react with phosphoric acid to form calcium phosphate, and the initial consumption of Ca 2+ Calcium ions react to form soluble calcium phosphate, which further inhibits the growth of calcium hydroxide in a certain direction, and the prototype of flaky calcium hydroxide is formed;

[0026] (2) As the reaction continues, when the pH of the solution rises above 8, Ca 2+ Calcium ions react with phosphoric acid to form precipitated calcium phosphate, which coats the larger surface of calcium hydroxide, forming thin flake calcium hydroxide.

[0027] (3) Phosphate makes Ca 2+ It tends to nucleate and grow around calcium phosphate, inhibiting the formation of calcium hydroxide crystals, making the reaction slower and further reducing the thickness of the flakes;

[0028] (4) The lower the digestion starting temperature, the slower the reaction, and the reaction temperature is kept below 20 °C, which makes the crystals grow slowly. The slower the reaction, the thinner the six-layer thickness.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0030] The calcium hydroxide prepared by this method has a morphology different from that of ordinary calcium hydroxide chemical industry. It is a hexagonal thin-plate calcium hydroxide with a special morphology. The method is simple, the flake thickness is small, and it can be produced industrially. It also provides a new method and idea for the research of calcium hydroxide and expands the application direction of calcium hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is an SEM photo of hexagonal flaky calcium hydroxide prepared in Example 1;

[0032] Figure 2 This is an SEM photo of hexagonal flaky calcium hydroxide prepared in Example 2;

[0033] Figure 3 This is an SEM photo of hexagonal flaky calcium hydroxide prepared in Example 3;

[0034] Figure 4 This is a SEM photo of calcium hydroxide prepared in Comparative Example 1;

[0035] Figure 5 This is a SEM photo of calcium hydroxide prepared in Comparative Example 2;

[0036] Figure 6 This is a SEM photo of calcium hydroxide prepared in Comparative Example 3;

[0037] Figure 7 This is the SEM photo of calcium hydroxide prepared in Comparative Example 4. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below in conjunction with specific embodiments. It should be emphasized that the following description is merely illustrative and is not intended to limit the scope of the present invention and its application.

[0039] Example 1

[0040] A method for preparing hexagonal flaky calcium hydroxide comprises the following steps:

[0041] Step 1: calcining the ore to obtain CaO at a calcination temperature of 1150°C for 360 minutes, crushing and removing impurities, and sieving with a 300-mesh sieve to obtain CaO powder for later use;

[0042] Step 2: First, low-temperature digestion water is placed into the reactor with an ash-water ratio of 1:7. The initial temperature of the digestion water is 5°C, and sodium dihydrogen phosphate additive is added to the digestion water. The amount of sodium dihydrogen phosphate added is 0.5% of the mass of CaO. Stirring is started at a stirring speed of 100 rpm. Then, the CaO powder from step 1 is slowly poured into the reactor for digestion reaction. The reaction time is 5 hours.

[0043] Step 3: drying in an oven at 90° C. for 12 h, crushing, and sieving with a 300-mesh sieve to obtain hexagonal flaky calcium hydroxide.

[0044] Example 2

[0045] A method for preparing hexagonal flaky calcium hydroxide comprises the following steps:

[0046] Step 1: calcining the ore to obtain CaO at a temperature of 1300°C for 300 minutes, crushing and removing impurities, and sieving with a 100-mesh sieve to obtain CaO powder for later use;

[0047] Step 2: First, low-temperature digestion water is placed into the reactor with an ash-water ratio of 1:6. The initial temperature of the digestion water is 8°C, and sodium dihydrogen phosphate additive is added to the digestion water. The amount of sodium dihydrogen phosphate added is 0.8% of the mass of CaO. Stirring is started at a stirring speed of 150 rpm. Then, the CaO powder from step 1 is slowly poured into the reactor for digestion reaction. The reaction time is 4 hours.

[0048] Step 3: drying in an oven at 100° C. for 10 h, crushing, and sieving with a 100-mesh sieve to obtain hexagonal flaky calcium hydroxide.

[0049] Example 3

[0050] A method for preparing hexagonal flaky calcium hydroxide comprises the following steps:

[0051] Step 1: calcining the ore to obtain CaO at a temperature of 1200°C for 280 minutes, crushing and removing impurities, and sieving with a 200-mesh sieve to obtain CaO powder for later use;

[0052] Step 2: First, put the low-temperature digestion water into the reactor with an ash-water ratio of 1:8. The initial temperature of the digestion water is 10°C, and sodium dihydrogen phosphate additive is added to the digestion water. The amount of sodium dihydrogen phosphate added is 1% of the mass of CaO. Start stirring at a stirring speed of 200 rpm, and then slowly pour the CaO powder from step 1 into the reactor for digestion reaction. The reaction time is 3 hours;

[0053] Step 3: drying in an oven at 110° C. for 8 h, crushing, and sieving with a 200-mesh sieve to obtain hexagonal flaky calcium hydroxide.

[0054] Comparative Example 1

[0055] A method for preparing calcium hydroxide comprises the following steps:

[0056] Step 1: calcining the ore to obtain CaO at a temperature of 1300°C for 300 minutes, crushing and removing impurities, and sieving with a 100-mesh sieve to obtain CaO powder for later use;

[0057] Step 2: First, put low-temperature digestion water into the reactor with an ash-water ratio of 1:6. The initial temperature of the digestion water is 25°C. Stirring is started at a stirring speed of 150 rpm. Then, the CaO powder from step 1 is slowly poured into the reactor for digestion reaction. The reaction time is 4 hours.

[0058] Step 3: drying in an oven at 100° C. for 10 h, crushing, and sieving with a 100-mesh sieve to obtain calcium hydroxide.

[0059] Comparative Example 2

[0060] A method for preparing calcium hydroxide comprises the following steps:

[0061] Step 1: calcining the ore to obtain CaO at a temperature of 1300°C for 300 minutes, crushing and removing impurities, and sieving with a 100-mesh sieve to obtain CaO powder for later use;

[0062] Step 2: First, low-temperature digestion water is placed into the reactor with an ash-water ratio of 1:6. The initial temperature of the digestion water is 25°C, and sodium dihydrogen phosphate additive is added to the digestion water. The amount of sodium dihydrogen phosphate added is 0.8% of the mass of CaO. Stirring is started at a stirring speed of 150 rpm. Then, the CaO powder from step 1 is slowly poured into the reactor for digestion reaction. The reaction time is 4 hours.

[0063] Step 3: drying in an oven at 100° C. for 10 h, crushing, and sieving with a 100-mesh sieve to obtain calcium hydroxide.

[0064] Comparative Example 3

[0065] A method for preparing calcium hydroxide comprises the following steps:

[0066] Step 1: calcining the ore to obtain CaO at a temperature of 1300°C for 300 minutes, crushing and removing impurities, and sieving with a 100-mesh sieve to obtain CaO powder for later use;

[0067] Step 2: Put low-temperature digestion water into the reactor with an ash-water ratio of 1:6. The initial temperature of the digestion water is 8°C. Start stirring at a stirring speed of 150 rpm. Then slowly pour the CaO powder from step 1 into the reactor for digestion reaction. The reaction time is 4 hours.

[0068] Step 3: drying in an oven at 100° C. for 10 h, crushing, and sieving with a 100-mesh sieve to obtain calcium hydroxide.

[0069] Comparative Example 4

[0070] A method for preparing calcium hydroxide comprises the following steps:

[0071] Step 1: calcining the ore to obtain CaO at a temperature of 1300°C for 300 minutes, crushing and removing impurities, and sieving with a 100-mesh sieve to obtain CaO powder for later use;

[0072] Step 2: First, low-temperature digestion water is placed into the reactor at an ash-water ratio of 1:6. The initial temperature of the digestion water is 15°C, and sodium dihydrogen phosphate additive is added to the digestion water. The amount of sodium dihydrogen phosphate added is 0.8% of the mass of CaO. Stirring is started at a stirring speed of 150 rpm. Then, the CaO powder from step 1 is slowly poured into the reactor for digestion reaction. The reaction time is 4 hours.

[0073] Step 3: drying in an oven at 100° C. for 10 h, crushing, and sieving with a 100-mesh sieve to obtain calcium hydroxide.

[0074] Comparative experiment

[0075] The high specific surface area nano calcium carbonate powders prepared in Examples 1 to 3 and the nano calcium carbonate powders prepared in Comparative Examples 1 to 4 were examined by scanning electron microscopy. The test results are as follows: Figures 1 to 7 shown.

[0076] Depend on Figures 1 to 3It can be seen that Examples 1 to 3 of the present invention can all prepare hexagonal flaky calcium hydroxide. However, to prepare hexagonal flaky calcium hydroxide, it is necessary to inhibit the growth of its crystals. Only under the control of low temperature and inhibitors can thin hexagonal flaky calcium hydroxide be successfully prepared.

[0077] Depend on Figures 4 to 7 It can be seen that in Comparative Example 1, the digestion water was at room temperature and no inhibitor was added, and thin hexagonal flaky calcium hydroxide could not be prepared; in Comparative Example 2, the digestion water was also at room temperature, and an inhibitor was added, but thin hexagonal flaky calcium hydroxide could not be prepared; in Comparative Example 3, although the initial temperature of the digestion water was lowered, no inhibitor was added, and hexagonal flaky calcium hydroxide still could not be prepared; it can be seen that low temperature reaction conditions and inhibitors are both indispensable. In Comparative Example 4, an inhibitor was added, and the initial temperature of the digestion water was also lowered, but it was still above the temperature range of the present invention, and hexagonal flaky calcium hydroxide still could not be prepared. It can be seen that controlling the initial temperature of the digestion water is crucial to the final formation of hexagonal flaky calcium hydroxide.

[0078] The above description is a further detailed description of the present invention in conjunction with specific / preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. Those skilled in the art of the present invention may make various substitutions or modifications to the described embodiments without departing from the scope of the present invention, and such substitutions or modifications should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing hexagonal flaky calcium hydroxide, characterized in that: The following steps are involved: Step 1: calcining the ore to obtain CaO, crushing and removing impurities, sieving, and obtaining CaO powder for later use; Step 2: Put low-temperature digestion water with an initial temperature of 5-10°C into the reactor, add sodium dihydrogen phosphate additive to the digestion water, start stirring, and slowly pour the CaO powder from step 1 into the reactor for digestion reaction; Step 3: drying, crushing and sieving to obtain hexagonal flaky calcium hydroxide.

2. The preparation method of hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 1, the calcination temperature is 1150° C. to 1300° C., and the calcination time is 280 to 360 minutes.

3. The preparation method of hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 1, sieve with a 100-300 mesh sieve.

4. The preparation method of hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 2, the gray-water ratio is 1:6-8.

5. The preparation method of hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 2, the amount of sodium dihydrogen phosphate added is 0.5-1% of the mass of CaO.

6. The method for preparing hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 2, the stirring speed is 100-200 rpm.

7. The method for preparing hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 2, the reaction time is 3 to 5 hours.

8. The method for preparing hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 3, the drying is oven drying with forced air; the drying temperature is 90-110° C., and the drying time is 8-12 hours.

9. The method for preparing hexagonal flaky calcium hydroxide according to claim 1, wherein: In step 3, 100-300 mesh sieve is used for sieving.

Images