A method for producing a natural hydraulic lime

Abstract

The application provides a preparation method of natural hydraulic lime, which comprises the following steps: calcining natural hydraulic lime raw material to obtain a calcined product; and mixing the calcined product with digestion water containing a digestion regulator to perform a digestion reaction, so as to obtain natural hydraulic lime, wherein the digestion regulator is selected from hydrochlorides of alkali metals, sulfates of alkali metals and hydrofluorides of alkali metals. The method is simple in process and convenient to operate, and the natural hydraulic lime obtained by using the method has high carbonation activity.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a method for preparing natural hydraulic lime. Background Technology

[0002] Natural hydraulic lime (NHL) is a cementitious material that combines air-hardening and hydraulic properties. Its main components are calcium hydroxide and dicalcium silicate. The raw materials for preparing NHL include limestone and clay. During calcination, calcium carbonate initially decomposes at 600–900℃ to form calcium oxide. When the temperature rises to 900–1200℃, some of the calcium oxide reacts with silicon dioxide to form dicalcium silicate. Early mechanical properties of natural hydraulic lime primarily depended on the hydration rate of dicalcium silicate. Excess calcium oxide is converted into calcium hydroxide through digestion, serving as an air-hardening component. Later, it reacts with carbon dioxide in the air to form calcium carbonate, filling the pores created by hydration within the system, increasing the density of the natural hydraulic lime, and thus improving its mechanical properties.

[0003] The long-term performance of natural hydraulic lime is affected by carbonation. According to BSEN459:1-2010, the standard for the raw material composition of natural hydraulic lime, the calcium hydroxide content corresponding to NHL2 / 3.5 / 5 should not be less than 35 / 25 / 15% of the mass of the digested product, respectively. The digestion process has a significant impact on the carbonation rate and efficiency of NHL; therefore, it is necessary to improve the long-term performance of natural hydraulic lime by optimizing the digestion process. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing natural hydraulic lime. By digesting the product of calcined natural hydraulic lime raw material in the presence of a specific digestion regulator, the digestion time can be adjusted without affecting the final conversion rate of quicklime. This optimizes the hydration and carbonization activity of natural hydraulic lime. The preparation method provided by this invention is simple, easy to operate, and yields natural hydraulic lime with high carbonization activity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing natural hydraulic lime, comprising:

[0007] Natural hydraulic lime raw material is calcined to obtain calcined product;

[0008] The calcined product is mixed with digestion water containing a digestion regulator to carry out a digestion reaction, wherein the digestion regulator is selected from alkali metal hydrochlorides, alkali metal sulfates and alkali metal hydrofluoric acid salts.

[0009] According to some embodiments of the present invention, the natural hydraulic lime raw material is selected from clayey limestone and siliceous limestone. In some embodiments, the raw material is limestone tailings. Preferably, the limestone tailings have the following composition: 65wt%–89wt% CaCO3, 6wt%–28wt% SiO2, with the remainder being one or more of MgCO3, Al2O3, and Fe2O3.

[0010] This invention does not impose special requirements on the preparation conditions, mineral phase composition, or source of the calcined product; conventional calcined products in the art can be used. According to BSEN459:1-2010, the standard for the raw material composition of natural hydraulic lime, the calcined product should be a product obtained by cooling and grinding calcined clayey limestone with varying clay content or siliceous limestone with varying silica content. The phase composition of the calcined product is approximately 11-29% CaO by mass, approximately 71-89% C2S (dicalcium silicate) by mass, and the remainder being one or more of MgO, Al2O3, and Fe2O3. In the method of this invention, the main phases in the calcined product are dicalcium silicate and calcium oxide.

[0011] According to some embodiments of the present invention, the calcination product comprises calcium oxide and dicalcium silicate. In some preferred embodiments, the content of calcium oxide is 5-50 wt%, preferably 10-30 wt%. In some preferred embodiments, the content of dicalcium silicate is 50-95 wt%, preferably 70-90 wt%. Optionally, the calcination product of the present invention further comprises impurities selected from one or more of MgO, Al2O3, and Fe2O3. The mass percentage of the impurity component is the balance.

[0012] According to some embodiments of the present invention, the calcination temperature is 800 to 1200°C, for example 900°C, 1000°C or 1100°C.

[0013] The digestion process in this invention mainly involves the following reactions:

[0014] CaO + H₂O → Ca(OH)₂ (solution)

[0015] Ca(OH)2→Ca 2+ +2OH -

[0016] Ca 2+ +OH (solid surface) → Ca 2+ +OH - (Liquid phase bulk)

[0017] CaO + H₂O → Ca(OH)₂ (solution) → Ca(OH)₂ (crystals)

[0018] When powder containing CaO is mixed with water, Ca is produced. 2+ OH - A Ca(OH)₂ solution is formed, and calcium hydroxide crystals gradually precipitate out after the solution becomes saturated. The above reaction is exothermic; as the reaction proceeds, the temperature gradually increases, which promotes the reaction. Simultaneously, the particle volume increases significantly during the reaction, and the heat and expansion pressure generated during digestion heat some of the digested water to its boiling point, producing a large amount of water vapor.

[0019] In this invention, the main function of the digestion regulator is to affect the Ca ion transport rate by forming salts with high or low solubility with Ca ions or coating the surface of calcium oxide, thereby adjusting the rate at which CaO reacts with water to form Ca(OH)2 in the calcined product, reducing or prolonging the digestion time, preventing C2S from reacting with water during digestion, controlling the particle size of Ca(OH)2, reducing the specific surface area, and improving the carbonization efficiency of Ca(OH)2.

[0020] In this invention, the preferred method of using the digestion regulator is to dissolve the digestion regulator in digestion water and then mix and stir it together with the digestion raw materials to carry out the digestion reaction. Furthermore, in this invention, if the amount of digestion regulator added is too large and the digestion time is too short, the particle size of the natural hydraulic lime decreases, the specific surface area increases, and the carbonization efficiency improves, but the water demand increases significantly, affecting its early / long-term mechanical property development. If the amount added is too small and the digestion time is too long, the Ca(OH)2 crystals become coarser, affecting its further carbonization efficiency. Simultaneously, dicalcium silicate may undergo a hydration reaction, and the hydration rate decreases after drying, resulting in a decline in the mechanical properties of the natural hydraulic lime. Therefore, it is necessary to control the amount of digestion regulator used within a suitable range.

[0021] According to some embodiments of the present invention, the amount of the digestion regulator is 0.5% to 7% of the mass of calcium oxide in the calcined product, for example 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%.

[0022] According to some embodiments of the present invention, the digestive regulator is selected from one or more of NaCl, NaF, and Na2SO4. The present invention does not have special requirements regarding the source of the sodium chloride, sodium fluoride, and sodium sulfate; commercially available raw materials conventionally available in the art can be used. In the present invention, the purity of the sodium chloride, sodium fluoride, and sodium sulfate is preferably ≥98%.

[0023] According to some embodiments of the present invention, the digestion regulator is NaCl. In some embodiments, the amount of NaCl used is 1% to 7% of the mass of calcium oxide in the calcined product, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or 7%. In some embodiments, the amount of NaCl used is 3% to 5% of the mass of calcium oxide in the calcined product, for example, 3.2%, 3.5%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.5%, or 4.8%. In some embodiments, the amount of NaCl used is 3.5% to 4.2% of the mass of calcium oxide in the calcined product.

[0024] According to some embodiments of the present invention, the digestion regulator is NaF. In some embodiments, the amount of NaF used is 1% to 7% of the mass of calcium oxide in the calcined product, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or 7%. In some embodiments, the amount of NaF used is 1% to 5% of the mass of calcium oxide in the calcined product, for example, 1.2%, 1.3%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.7%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.2%, 4.5%, 4.8%, or 5%. In some embodiments, the amount of NaF used is 1.3% to 2.7% of the mass of calcium oxide in the calcined product.

[0025] According to some embodiments of the present invention, the digestion regulator is Na₂SO₄. In some embodiments, the amount of Na₂SO₄ used is 0.5% to 7% of the mass of calcium oxide in the calcined product, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or 7%. In some embodiments, the amount of Na₂SO₄ used is 0.5% to 3% of the mass of calcium oxide in the calcined product, for example, 0.5%, 0.8%, 1.0%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 2.9%, or 3%. In some embodiments, the amount of Na₂SO₄ used is 2% to 3% of the mass of calcium oxide in the calcined product.

[0026] In this invention, the digested water has no special requirements and can be ordinary tap water, with CO3 as the main impurity. 2- SO4 2- Cl - Ca 2+ Mg 2+ Na + Fe 3+One or more of the following. The method of use is to heat to a suitable temperature before use.

[0027] According to some embodiments of the present invention, the suitable temperature of the digested water is 20–100°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C. Preferably, the temperature of the digested water is 40–80°C, more preferably 40–60°C.

[0028] According to some embodiments of the present invention, the amount of digested water is 3 to 5 times, for example 3 times, 4 times or 5 times, the calcium oxide content in the calcined product.

[0029] The digestion reaction in this invention can be carried out at room temperature and pressure. According to some embodiments of the invention, the temperature of the digestion reaction is 20°C to 100°C.

[0030] According to some embodiments of the present invention, the pressure of the digestion reaction is 0.95 atm to 1.05 atm.

[0031] According to some embodiments of the present invention, the digestion reaction takes 10-60 minutes.

[0032] According to some embodiments of the present invention, the calcined product, after cooling, is crushed and ball-milled before being mixed with digested water. In some preferred embodiments, the ball-milled particle size of the calcined product is such that it passes through an 180-mesh sieve with a residue of no more than 2%.

[0033] The present invention does not impose any particular limitation on the cooling method of the calcined product; any cooling method known to those skilled in the art can be selected. In the present invention, air cooling is preferred for cooling.

[0034] This invention does not impose any particular limitation on the crushing method of the calcined products; any crushing method well known to those skilled in the art can be used. In this invention, a jaw crusher is preferably used for crushing.

[0035] The present invention does not impose any particular limitation on the ball milling method of the calcined product; any ball milling method well known to those skilled in the art can be selected.

[0036] According to some embodiments of the present invention, the method further includes: drying and ball milling the digestion product after the digestion reaction to obtain natural hydraulic lime. In some embodiments, the drying temperature is 70°C to 90°C. In some embodiments, the drying time is 20 hours to 30 hours. In some embodiments, the ball milling time is 5 to 20 minutes.

[0037] Secondly, the present invention provides a natural hydraulic lime, which is obtained using the preparation method described in the first aspect of the present invention.

[0038] According to some embodiments of the present invention, the fineness of the natural hydraulic lime is such that the residue on a 0.2 mm sieve does not exceed 2% of the total mass of the sieved material.

[0039] According to some embodiments of the present invention, the fineness of the natural hydraulic lime is such that the residue on a 0.09 mm sieve does not exceed 15% of the total mass of the sieved material.

[0040] The beneficial effects of the present invention are: the preparation method of the present invention uses a specific type and amount of digestion regulator to adjust the digestion time of lime without affecting the final conversion rate of quicklime, thereby optimizing the hydration and carbonization activity of natural hydraulic lime; the natural hydraulic lime prepared by the method of the present invention has high carbonization activity. Attached Figure Description

[0041] Figure 1 The digestion time of natural hydraulic lime prepared at 20°C using different dosages and types of digestion regulators is shown. Detailed Implementation

[0042] To further illustrate the present invention, the following embodiments are provided to further explain the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0043] It should be noted that the "natural hydraulic lime raw material" mentioned in this invention refers to raw materials that can be used to prepare natural hydraulic lime, the main component of which is limestone, such as clayey limestone, siliceous limestone, etc.

[0044] The natural hydraulic lime raw material used in the following embodiments and Comparative Example 1 of the present invention is limestone tailings, which consists of 82 wt% CaCO3, 10 wt% SiO2, and the remainder being one or more of MgCO3, Al2O3 and Fe2O3.

[0045] The purity of the digestive regulators sodium chloride, sodium fluoride, and sodium sulfate used in the following embodiments of the present invention is ≥98%.

[0046] The calcium oxide content in the calcined products obtained in the following embodiments and Comparative Example 1 of this invention was determined by titration using the ethylene glycol method according to GB / T 176-2008 "Chemical Analysis Methods for Cement". The specific method is as follows:

[0047] Weigh approximately 0.5 g of the sample (accurate to 0.0001 g) into a 250 mL dry conical flask, add 30 mL of ethylene glycol-ethanol solution, place a stir bar inside, attach a condenser, and place the flask on a free calcium oxide analyzer. Stir the solution at an appropriate speed while simultaneously heating to boiling. When the condensed ethanol begins to drip continuously, continue heating with stirring until it boils gently for 4 minutes. Remove the conical flask and filter under vacuum using rapid filter paper pre-wetted with anhydrous ethanol or a glass frit funnel pre-washed with anhydrous ethanol. Wash the conical flask and precipitate three times with anhydrous ethanol, waiting for the previous washings to be completely filtered before each subsequent wash. Collect the filtrate and washings in a 250 mL dry vacuum filtration flask and immediately titrate with benzoic acid-anhydrous ethanol standard titration solution until the faint red color disappears.

[0048] mass fraction of free calcium oxide w f-cao Calculate using the following formula:

[0049]

[0050] In the formula:

[0051] w f-cao —Mass fraction of free calcium oxide, %

[0052] T cao The titer of benzoic acid-anhydrous ethanol standard titration solution for calcium oxide is expressed in milligrams per milliliter (mg / mL).

[0053] V—The volume of benzoic acid-anhydrous ethanol standard titrant solution consumed during titration, in milliliters (mL).

[0054] m — the mass of the sample, in grams (g).

[0055] Example 1

[0056] Limestone tailings were calcined at 1200℃ to obtain the calcined product, which was then cooled and crushed. 100g of the calcined product was weighed and ground until it passed through a 180-mesh sieve with a residue of no more than 2%. The content of calcium oxide in the powder was determined to be approximately 11g and the content of dicalcium silicate to be approximately 89g by the ethylene glycol method. 0.33g of NaCl was dissolved in 33g of tap water. The temperature was maintained at 20℃. The stirred solution and powder were placed in a beaker and mixed evenly. The mixture was stirred continuously at a speed of 400rpm. The digestion reaction was considered to have stopped when the exothermic reaction ceased. The digestion time (i.e., the minimum digestion time) was recorded.

[0057] After the digestion reaction is completed, the digestion product is transferred into a drying oven and dried at a temperature of 80°C for 24 hours. Then, the digestion product is ball-milled for 10 minutes to obtain the finished natural hydraulic lime.

[0058] Examples 2-19

[0059] Examples 2-19 follow the same operating steps as Example 1, except that the digestion water temperature, the type of digestion regulator, or the dosage of the digestion regulator (based on the mass of calcium oxide in the calcined product being 100%) are different, as detailed in Table 1.

[0060] Comparative Example 1

[0061] The operation steps of this comparative example are the same as those of Example 1, except that the digestion regulator NaCl is not added, as shown in Table 1.

[0062] Table 1

[0063] Digestion water temperature Types of digestive regulators Dosage / % Example 1 20 NaCl 3 Example 2 40 NaCl 5 Example 3 60 NaCl 1 Example 4 80 NaCl 7 Example 5 100 NaCl 3 Example 6 40 NaCl 3.5 Example 7 40 NaCl 4.2 Example 8 40 NaF 5 Example 9 60 NaF 3 Example 10 80 NaF 2 Example 11 100 NaF 5 Example 12 40 NaF 1 Example 13 20 <![CDATA[Na2SO4]]> 3 Example 14 40 <![CDATA[Na2SO4]]> 5 Example 15 60 <![CDATA[Na2SO4]]> 2 Example 16 80 <![CDATA[Na2SO4]]> 7 Example 17 100 <![CDATA[Na2SO4]]> 1 Example 18 40 <![CDATA[Na2SO4]]> 2 Example 19 40 <![CDATA[Na2SO4]]> 3 Comparative Example 1 20 none 0

[0064] Performance testing

[0065] The slaking time of natural hydraulic lime in Examples 1-19 and Comparative Example 1, as well as the 28-day compressive strength, standard consistency water requirement, and initial setting time of the obtained NHL product, were tested. The results are shown in Table 2.

[0066] (1) Digestion time

[0067] The digestion time of natural hydraulic lime in each embodiment and Comparative Example 1 was recorded using a digital display thermometer, and the end time of the digestion reaction was defined as the time when the reaction stopped releasing heat.

[0068] (2) 28-day compressive strength

[0069] The 28-day compressive strength of NHL neat cement paste was tested using the following method:

[0070] 40*40*40mm cubic specimens were prepared according to a water-cement ratio of 0.5 and the method specified in GB / T1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". The specimens were cured in a standard environment (temperature 23+1)℃, relative humidity 295% for 24 hours before demolding. Mechanical property tests were then performed on the demolded specimens after standard curing for 28 days. A servo universal cement press was used with a loading speed of 0.5 kN / s. Three specimens were grouped together, and the average value was taken.

[0071] (3) Standard consistency water-cement ratio

[0072] The water-cement ratio and initial setting time of NHL standard consistency were determined according to GB / T1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement".

[0073] Use a cement paste mixer. Wipe the mixing pot and mixing blades with a damp cloth first. Pour the mixing water into the mixing pot, and then carefully add 500g of weighed NHL into the water within 5 to 10 seconds to prevent water and cement from splashing out. When mixing, first place the pot on the pot base of the mixer, raise it to the mixing position, start the mixer, mix at low speed for 120 seconds, stop for 15 seconds, and at the same time scrape the cement paste on the blades and the pot wall into the middle of the pot. Then mix at high speed for 120 seconds and stop the machine.

[0074] After mixing, immediately take an appropriate amount of NHL neat cement paste and fill it into the mold already placed on the glass base plate. The paste should extend beyond the top of the mold. Gently tap the excess paste five times with a straight-edged knife (approximately 25mm wide) to remove any pores. Then, at approximately 1 / 3 of the way up the mold surface, slightly tilt the mold and gently saw off the excess paste outwards. Finally, lightly smooth the top edge of the mold to make the paste surface smooth. During the sawing and smoothing process, avoid compacting the paste. After smoothing, quickly move the mold and base plate onto the Vicat apparatus, centering it under the test rod. Lower the test rod until it contacts the cement paste surface, tighten the screw for 1-2 seconds, then suddenly release it, allowing the test rod to sink vertically and freely into the cement paste. Record the distance between the test rod and the base plate 30 seconds after the rod stops sinking or is released. After raising the test rod, wipe it clean immediately. The entire operation should be completed within 1.5 minutes of mixing. The standard consistency of the cement paste is defined as the cement paste in which the test rod sinks to a depth of 6 mm ± 1 mm from the bottom plate. The mixing water content is the standard consistency water content (P) of the NHL, expressed as a percentage by mass.

[0075] (4) Initial setting time

[0076] The initial setting time of natural hydraulic lime was tested using the following method:

[0077] Prepare a standard consistency cement paste using the standard consistency water ratio. After pouring and leveling the paste in a mold, immediately place it in a moisture curing chamber. Record the time when all the cement is added to the water as the starting time for setting.

[0078] The first test was conducted 30 minutes after water was added to the specimens in a moisture curing chamber. During the test, the specimen was removed from the moisture curing chamber and placed under the needle, lowering the needle to contact the cement paste surface. After tightening the screw for 1-2 seconds, it was suddenly released, allowing the needle to sink vertically and freely into the cement paste. The pointer reading was observed when the needle stopped sinking or 30 seconds after release. Measurements were taken every 5 minutes (or less) until the initial setting time approached. When the needle sank to 4mm ± 1mm ​​from the bottom plate, the cement reached its initial setting state. The initial setting time of the cement, expressed in minutes, is the time from when all the cement was added to the water until it reached this initial setting state.

[0079] Table 2

[0080]

[0081]

[0082] As can be seen from Table 2, the digestion time can be adjusted to varying degrees by using a digestion regulator in the method of the present invention. Reducing the digestion time can effectively prevent the hydration of dicalcium silicate and at the same time make the overall particle size of the product finer, which is conducive to the subsequent carbonization reaction. Under the premise of controlling the dosage, the working performance and mechanical properties of NHL in the later stage can be improved. Appropriately extending the digestion time can increase the particle size of the product and reduce the water requirement for standard consistency. Therefore, the method of the present invention can also adjust the compressive strength, initial setting time and water-cement ratio of the final product, natural hydraulic lime.

[0083] Experiment Example 1: Effect of Different Digestion Regulators on Digestion Time of Natural Hydraulic Lime

[0084] Different amounts of NaCl, NaF, and Na₂SO₄ were dissolved in slaked water at 20°C, and the slaked time of natural hydraulic lime was tested (see [link to test results]). Figure 1 The results showed that, under 20℃ conditions, within a certain range, the digestion time of calcium oxide in natural hydraulic lime was linearly related to the amount of digestion regulator added as the dosage of digestion regulator increased. Among them, the more NaCl was added, the shorter the digestion time, which could reach as low as 900s, much lower than the 1840s of the blank control group. However, the more NaF and Na2SO4 were added, the longer the digestion time became, with digestion times reaching 2530s and 2770s respectively, much higher than the 1840s of the blank control group.

[0085] It is evident that different digestion regulators have varying effects on natural hydraulic lime at 20℃. NaCl promotes the digestion process of natural hydraulic lime, while NaF and Na2SO4 reduce digestion efficiency. This may be because the presence of Cl ions helps generate soluble CaCl2, increasing the solubility of Ca ions in solution and promoting Ca ion transport. Conversely, F ions react with Ca ions to form CaF2, which has lower solubility, coating the unreacted CaO surface and preventing further reaction with water and Ca ion transport. The performance test results of Examples 2 and 6 in Table 2 also show that NaF inhibits the digestion process of NHL, prolonging digestion time, coarsening Ca(OH)2 grains, increasing specific surface area, and reducing the standard thickening water requirement. Therefore, high dosages of NaF indirectly affect the hydration effect of C2S, and appropriate use helps improve the early hydration rate. Current research indicates that F ions have no direct effect on the hydration activity of C2S and can regulate the overall particle size distribution of NHL to some extent, thus benefiting the early mechanical property development of NHL.

[0086] Example 2: Model Construction for Optimizing Digestion Time with Different Types of Digestive Regulators

[0087] By fitting the digestion times obtained using different dosages and types of digestion regulators, optimization models for the digestion time of different types of digestion regulators can be obtained. It can be seen that the optimization of digestion time by the three digestion regulators all conforms to a linear structure, and the results are as follows:

[0088] ① Using sodium chloride as a digestion regulator for natural hydraulic lime

[0089] Y = a1 + b1 * X (Equation 1);

[0090] In Equation 1: a1 = 1804 ± 32.58834

[0091] b1 = -318 ± 26.60827

[0092] R 2 =0.97943

[0093] ② Using sodium fluoride as a digestion regulator for natural hydraulic lime

[0094] Y = a² + b² * X (Equation 2);

[0095] In Equation 2: a2 = 1844.8 ± 69.98971

[0096] b2 = 421.6 ± 57.14636

[0097] R 2 =0.94776

[0098] ③ Using sodium sulfate as a digestion regulator for natural hydraulic lime

[0099] Y = a³ + b³ * X (Equation 3);

[0100] In Equation 3: a3 = 1854 ± 37.60319

[0101] b3 = 270 ± 30.70288

[0102] R 2 =0.96266

[0103] In Equations 1 to 3, Y represents digestion time, X represents the dosage of different digestion regulators, and R... 2 The correlation coefficient.

[0104] The correlation coefficients show that the optimization models for digestion time by different types of digestion regulators all conform to a linear structure within a certain range. Furthermore, the dosage and digestion time of different digestion regulators can be calculated, which is beneficial for further research and large-scale production.

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing natural hydraulic lime, comprising: Natural hydraulic lime raw material is calcined to obtain calcined product; The calcined product is mixed with digestion water containing a digestion regulator to carry out a digestion reaction, wherein the digestion regulator is selected from one or more of NaCl, NaF and Na2SO4, and the amount of the digestion regulator is 0.5% to 7% of the mass of calcium oxide in the calcined product.

2. The preparation method according to claim 1, characterized in that, The natural hydraulic lime raw material is selected from clayey limestone and siliceous limestone; and / or the calcination temperature is 800-1200℃; and / or the calcination product includes calcium oxide and dicalcium silicate.

3. The preparation method according to claim 2, characterized in that, The content of calcium oxide is 5-50 wt%, and the content of dicalcium silicate is 50-95 wt%.

4. The preparation method according to claim 2, characterized in that, The content of calcium oxide is 10-30 wt%, and the content of dicalcium silicate is 70-90 wt%.

5. The preparation method according to claim 1, characterized in that, The amount of NaCl used is 1% to 7% of the mass of calcium oxide in the calcined product; and / or the amount of NaF used is 1% to 5% of the mass of calcium oxide in the calcined product; and / or the amount of Na2SO4 used is 1% to 7% of the mass of calcium oxide in the calcined product.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The temperature of the digested water is 20–100°C; and / or the amount of the digested water used is 3–5 times the calcium oxide content in the calcined product.

7. The preparation method according to claim 6, characterized in that, The temperature of the digested water is 40–80°C.

8. The preparation method according to any one of claims 1 to 5, characterized in that, The digestion reaction is carried out at a temperature of 20℃ to 100℃, at a pressure of 0.95 atm to 1.05 atm, and for a time of 10 to 60 minutes.

9. The preparation method according to any one of claims 1 to 5, characterized in that, The ball milling particle size of the calcined product is such that it passes through an 180-mesh sieve with a residue of no more than 2%.

10. The preparation method according to any one of claims 1 to 5, characterized in that, Also includes: The digestion products after the digestion reaction are dried and ball-milled to obtain natural hydraulic lime.

11. The preparation method according to claim 10, characterized in that, The drying temperature is 70℃~90℃, the drying time is 20h~30h; and / or, the ball milling time is 5~20min.

12. The natural hydraulic lime obtained by the preparation method according to any one of claims 1 to 11.

13. The natural hydraulic lime according to claim 12, characterized in that, The fineness of the natural hydraulic lime is such that the residue on a 0.2mm sieve does not exceed 2% of the total mass of the material being sieved; and / or the fineness of the natural hydraulic lime is such that the residue on a 0.09mm sieve does not exceed 15% of the total mass of the material being sieved.

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