Method for reducing moisture content and particle size of active calcium silicate

Abstract

The invention belongs to the technical field of solid waste resource utilization and inorganic material synthesis, and relates to a method for reducing the water content and particle size of active calcium silicate. According to the method, powdery quicklime or ground carbide slag is used as a calcium source, the reaction activity of the calcium source is improved through steam activation, then the calcium source is added into desiliconization liquid containing sodium silicate in batches, a reaction is carried out under the temperature control and stirring conditions, and finally, hot water ultrasonic washing and drying are carried out, so that an active calcium silicate product with low water content and fine particle size is prepared. According to the process, the problems of high water content, large particle size, impurity residues and the like in the traditional process are effectively solved by accurately controlling the Ca / Si molar ratio, temperature sectional reaction and ultrasonic-assisted washing. According to the method, the post-treatment burden of the product is remarkably reduced, the whiteness and the purity are improved, high-value utilization of high-calcium solid wastes such as the carbide slag is also realized, and the method has good industrial popularization prospects and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and inorganic material synthesis technology, specifically relating to a method for reducing the moisture content and particle size of active calcium silicate. Background Technology

[0002] Activated calcium silicate, an inorganic material with properties such as adsorption, high whiteness, and large specific surface area, is widely used in environmental protection, building materials, and rubber and plastic additives industries. However, the existing technology for preparing this material typically involves reacting quicklime with water to form lime slurry, followed by reaction with sodium silicate solution. This method has significant technical drawbacks in practice. On the one hand, the activated calcium silicate synthesized by this method generally has a high water content, usually exceeding 70%, which greatly increases the energy consumption of the subsequent drying process, hindering energy conservation, emission reduction, and large-scale production. On the other hand, the reaction products generally have a large particle size, requiring secondary processing through an energy-intensive grinding step, further increasing costs and processing difficulty.

[0003] Furthermore, current technologies often fail to accurately calculate the effective calcium content in raw materials, leading to deviations in the calcium-silicon ratio within the reaction system. This results in higher levels of impurities, such as Na₂O, in the generated calcium silicate, affecting the product's whiteness and stability. Simultaneously, the addition of lime slurry in its slurry form causes a large slurry volume and dilution during the reaction, resulting in loose precipitates and low liquid-solid separation efficiency, further exacerbating the problem of high product moisture content.

[0004] On the other hand, as a representative of high-calcium solid waste, carbide slag has potential resource utilization value due to its high proportion of calcium hydroxide (Ca(OH)2). However, this type of waste has not yet been effectively introduced into the preparation system of activated calcium silicate, and is still mostly disposed of by landfill, which wastes resources and brings serious environmental risks. Therefore, how to introduce carbide slag into the calcium silicate synthesis system and improve the quality of the product has become one of the hot topics in resource utilization research.

[0005] In summary, existing technologies for the preparation of activated calcium silicate suffer from problems such as high water content, large particle size, numerous impurities, and low raw material utilization efficiency. There is an urgent need to develop a high-efficiency, low-consumption, and highly adaptable preparation process to achieve simultaneous control of water content and particle size, reduce post-processing difficulties, and improve product quality and industrialization feasibility. Summary of the Invention

[0006] The purpose of this invention is to provide a method for reducing the moisture content and particle size of activated calcium silicate. This method significantly reduces the moisture content and average particle size of the calcium silicate product by controlling the morphology of raw materials and reaction conditions. The method has the advantages of low energy consumption, good filtration, and stable product performance, and is particularly suitable for the high-value utilization of bulk solid waste resources and large-scale industrial preparation.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for reducing the moisture content and particle size of activated calcium silicate includes the following steps:

[0009] (1) Powdered quicklime or pretreated carbide slag is used as a calcium source. Its effective calcium content is determined. Then, the calcium source is treated with steam to obtain a steam-activated calcium source.

[0010] (2) Add the steam-activated calcium source to the sodium silicate solution in batches and stir to react;

[0011] (3) After the reaction in step (2) is completed, the slurry is filtered and separated, and the solid phase is washed to obtain active calcium silicate with a water content of 45-55% and D50≤10μm.

[0012] The effective calcium content refers to the mass percentage of active CaO or Ca(OH)2 in the calcium source that can participate in the reaction, determined by titration according to the standard titration method of HG / T 4205-2011.

[0013] Furthermore, the sodium silicate-containing solution is a desilication liquid produced after alkali dissolution and aluminum extraction from fly ash or coal gangue, with a SiO2 concentration of 30–200 g / L and an Al2O3 concentration of ≤10 g / L.

[0014] Further, the pretreatment of the carbide slag in step (1) includes grinding the carbide slag to D50≤50μm.

[0015] Further, the powdered quicklime in step (1) is obtained by grinding quicklime to D50≤50μm, or by grinding limestone to D50≤50μm and then calcining it.

[0016] Further, the steam treatment process in step (1) includes: placing the calcium source in a sealed container, introducing steam at 60-80°C, and treating for 8-15 minutes.

[0017] This invention significantly enhances the reactivity and product performance of the calcium source through steam treatment. The steam treatment is conducted at 60-80℃ for 8-15 minutes. This gentle hydrothermal activation process partially hydrolyzes the calcium source surface to form Ca(OH)₂ microcrystals, effectively reducing particle agglomeration and increasing the specific surface area, thereby improving the efficiency of subsequent reactions with sodium silicate. This treatment temperature avoids the sintering and hardening of CaO caused by high-temperature calcination, preserving the high activity of the calcium source, and also prevents the problem of excessively rapid heterogeneous nucleation of calcium silicate due to localized overheating during direct feeding through pre-hydration. Simultaneously, the steam also volatilizes residual organic matter such as acetylene in the calcined carbide slag, reducing the impact of impurities on product purity and creating cleaner conditions for subsequent reactions.

[0018] Furthermore, the molar ratio of effective calcium in the calcium source to silicon dioxide in the sodium silicate solution is 0.8 to 1.2:1.

[0019] Further, the calcium source described in step (2) is added to the sodium silicate solution in 3-5 batches.

[0020] Furthermore, after adding the first batch of calcium source, stir the mixture at 70-85℃ and a speed of 30-50 rpm for 10-20 minutes; after adding the second to fifth batches of calcium source, stir the mixture at 90-95℃ and a speed of 60-80 rpm for 30-60 minutes each time.

[0021] The synergistic effect of batch feeding and gradient temperature control in this invention significantly improves the reaction process and product quality. Adding the calcium source to the sodium silicate solution in 3-5 batches with a Ca / Si molar ratio of 0.8-1.2 effectively avoids localized supersaturation caused by single-batch feeding, which can lead to the formation of coarse calcium silicate particles or colloidal coatings. The first batch of calcium source reacts at a lower temperature of 70-85℃ for 10-20 minutes, which is conducive to the formation of uniform crystal nuclei; subsequent batches react at a higher temperature of 90-95℃ for 30-60 minutes, promoting controlled crystal growth. Combined with increasing the stirring speed from 30-50 rpm to 60-80 rpm, this combination of gradient temperature and enhanced stirring ensures sufficient reaction and effectively controls the product particle size distribution, ultimately achieving the fine particle size requirement of D50 ≤ 10 μm.

[0022] Furthermore, the washing described in step (3) is performed using hot water at 60–90°C with ultrasonic assistance.

[0023] Furthermore, the frequency of the ultrasound is 30-50 kHz, and the washing time is 10-20 minutes.

[0024] Washing with hot water at 60-90℃ effectively dissolves residual soluble salts. Simultaneously, the high-frequency microjets generated by ultrasonic cavitation can penetrate deep into the interparticle spaces, powerfully stripping adsorbed water molecules and impurities. The mechanical vibration of the ultrasound also disrupts the hydration film on the surface of the calcium silicate particles, making it easier to remove encapsulated water. This combined washing method further reduces the water content, ensuring the final product's water content is stably controlled within the range of 45-55%, while significantly improving product purity.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0026] This invention uses powdered quicklime or pretreated carbide slag as the calcium source, achieving both resource utilization of industrial solid waste and ensuring the reactivity of the raw materials by grinding them to D50≤50μm. Using fly ash / coal gangue alkaline desilication solution as the silicon source forms a complete industrial by-product recycling chain. Compared to traditional one-step synthesis processes, this invention solves the common problems of high moisture content and uneven particle size in the production of activated calcium silicate through the synergistic innovation of steam activation, batch reaction, and ultrasonic washing. In particular, by precisely controlling the calcium-silicon molar ratio and reaction temperature gradient, ultrafine and uniformly distributed products can be obtained without the addition of crystal form control agents, significantly reducing production costs and improving product performance indicators. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0028] Example 1

[0029] This embodiment provides a method for reducing the moisture content and particle size of activated calcium silicate, including the following steps:

[0030] (1) Commercially available quicklime blocks were coarsely crushed using a jaw crusher and then ground to a D50 of 42 μm using a ball mill. The effective calcium content (calculated as CaO) was measured to be 84.17%. 500 g of powdered quicklime was placed in a sealed stainless steel activation kettle, and 72°C saturated steam (pressure 0.03 MPa) was introduced and maintained for 12 minutes to obtain a steam-activated calcium source. After activation, the BET specific surface area of ​​the material increased from the original 1.2 m². 2 / g increased to 3.6m 2 / g.

[0031] (2) The desiliconization liquid after alkaline extraction of aluminum from fly ash in a power plant was used as the sodium silicate solution. The SiO2 concentration was 179.2 g / L and the Al2O3 content was 9.62 g / L by ICP. The solution temperature was adjusted to 40℃ for later use. The effective calcium in the calcium source and the silicon dioxide in the sodium silicate solution were mixed according to a molar ratio of 1:1. 10L of desiliconization liquid (containing a total SiO2 of 1792 g) was added to a 20L jacketed reactor. The stirring was started, with an initial speed of 35 rpm, and the temperature was raised to 82℃. Steam-activated calcium source was added to the desiliconization liquid in 4 batches: First batch: 25% of the total calcium source was added, and the reaction was maintained at 82℃ for 15 minutes; Second batch: 25% was added, the temperature was raised to 92℃, the speed was adjusted to 65 rpm, and the reaction was carried out for 40 minutes; Third batch: 30% was added, and the reaction was maintained at 92℃ for 50 minutes; Fourth batch: 20% was added, and the reaction was raised to 94℃ for 55 minutes.

[0032] (3) After the reaction is completed, the reaction slurry is filtered through a plate and frame filter press at a pressure of 0.8 MPa for 25 minutes. The filter cake is then transferred to an ultrasonic washing tank, where 80°C deionized water is added at a solid-liquid ratio of 1:8. The ultrasonic waves are turned on at 45 kHz and the filter cake is washed for 15 minutes. The washing is repeated 3 times. The filter cake is then dried in an oven at 105°C for 2 hours to obtain active calcium silicate.

[0033] Example 2

[0034] This embodiment provides a method for reducing the moisture content and particle size of active calcium silicate. The difference from Embodiment 1 is that the molar ratio of effective calcium in the calcium source to silicon dioxide in the sodium silicate solution is 0.8:1.

[0035] Example 3

[0036] This embodiment provides a method for reducing the moisture content and particle size of active calcium silicate. The difference from Embodiment 1 is that the molar ratio of effective calcium in the calcium source to silicon dioxide in the sodium silicate solution is 1.2:1.

[0037] Example 4

[0038] This embodiment provides a method for reducing the moisture content and particle size of activated calcium silicate, including the following steps:

[0039] (1) Take calcium carbide slag (initial moisture content 38%) from a chemical plant, first centrifuge it to a moisture content of 22%, then wet ball mill it (zirconia balls:material = 5:1) to D50 = 48 μm, and the effective calcium content (calculated as Ca(OH)2) is 65.4%, and the residual acetylene content is ≤50ppm according to GC-MS. Place 800g of the ground calcium carbide slag in a sealed stainless steel activation kettle, and treat it with saturated steam at 68℃ for 10 minutes to obtain a steam-activated calcium source.

[0040] (2) Using the same sodium silicate solution as in Example 1, the effective calcium in the calcium source and the silicon dioxide in the sodium silicate solution were mixed in a 1:1 ratio. 15L of desilication liquid (containing a total of 2688g of SiO2) was added to a 30L reactor. Stirring was started, with an initial stirring speed of 40rpm. The temperature was raised to 83°C. Steam-activated calcium source was added in 5 batches: First batch: 20%, reacted at 73°C for 18 minutes; Second batch: 20%, reacted at 70rpm for 45 minutes; Third batch: 25%, reacted at 91°C for 50 minutes; Fourth batch: 20%, reacted at 93°C for 60 minutes; Fifth batch: 15%, reacted at 94°C for 40 minutes.

[0041] (3) After the reaction is completed, the reaction slurry is filtered by a vacuum drum filter. The filter cake is washed with 75°C hot water under 50kHz ultrasound for 12 minutes each time, for a total of 4 washes. The filter cake is dried in an oven at 105°C for 2 hours to obtain active calcium silicate.

[0042] Comparative Example 1

[0043] The difference between this comparative example and Example 1 is that quicklime is replaced with lime milk, and the lime milk is not treated with steam.

[0044] Comparative Example 2

[0045] The difference between this comparative example and Example 1 is that the quicklime powder is not subjected to steam treatment.

[0046] Comparative Example 3

[0047] The difference between this comparative example and Example 1 is that in step (2), the steam-activated calcium source is added to the sodium silicate solution at once, the temperature is raised to 92°C, the rotation speed is maintained at 65 rpm, and the reaction is carried out for 160 minutes.

[0048] Comparative Example 4

[0049] The difference between this comparative example and Example 1 is that the washing process in step (3) does not involve ultrasonic treatment.

[0050] Performance testing

[0051] The particle size, moisture content, whiteness, and Na2O content of the active calcium silicate prepared in Examples 1-4 and Comparative Examples 1-4 were determined, and the results are shown in Table 1.

[0052] Table 1 Performance Test Results

[0053]

[0054] The above results demonstrate that by using powdered quicklime or pretreated carbide slag as the calcium source, combined with key steps such as steam activation, batch feeding, temperature gradient control, and ultrasonic washing, not only was the uniformity of the reaction process and precipitation behavior effectively controlled, but the moisture content, particle size, and impurity content of the product were also significantly improved. The overall performance was excellent, showcasing the comprehensive advantages of this method in improving product quality, reducing energy consumption, and expanding raw material adaptability. Comparative Example 1, a commonly used method in existing technologies, used lime slurry instead of quicklime and did not undergo steam treatment, resulting in a product with high moisture content and large particle size. Comparative Example 2 used untreated quicklime, leading to a particle size increase to 14.7 μm, possibly due to insufficient calcium source activity and incomplete reaction. In Comparative Example 3, the calcium source was added all at once, causing localized supersaturation precipitation and rapid formation of large particles, increasing the particle size to 15.9 μm and reducing whiteness. Comparative Example 4, without ultrasonic washing, had a high Na2O content, indicating that surface impurities were not effectively removed, affecting purity and verifying the important role of ultrasonic cleaning in improving quality.

[0055] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles 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 reducing the moisture content and particle size of activated calcium silicate, comprising the following steps: (1) Powdered quicklime or pretreated carbide slag is used as a calcium source. Its effective calcium content is determined. Then, the calcium source is treated with steam to obtain a steam-activated calcium source. (2) Add the steam-activated calcium source to the sodium silicate solution in batches and stir to react; (3) After the reaction in step (2) is completed, the slurry is filtered and separated, and the solid phase is washed to obtain active calcium silicate with a water content of 45-55% and D50≤10μm.

2. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, The sodium silicate-containing solution is a desilication liquid produced after alkali dissolution and aluminum extraction of fly ash or coal gangue, with a SiO2 concentration of 30-200 g / L and Al2O3 ≤ 10 g / L.

3. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, The pretreatment of carbide slag in step (1) includes grinding the carbide slag to D50≤50μm.

4. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, The powdered quicklime in step (1) is obtained by grinding quicklime to D50≤50μm or by grinding limestone to D50≤50μm and then calcining it.

5. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, The water vapor treatment process in step (1) includes: placing the calcium source in a sealed container, introducing water vapor at 60-80℃, and treating for 8-15 minutes.

6. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, The molar ratio of effective calcium in the calcium source to silicon dioxide in the sodium silicate solution is 0.8 to 1.2:

1.

7. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, In step (2), the calcium source is added to the sodium silicate solution in 3-5 batches.

8. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 7, characterized in that, After adding the first batch of calcium source, stir the mixture at 70-85℃ and 30-50 rpm for 10-20 minutes. After adding the 2nd to 5th batches of calcium source, stir the mixture at 90-95℃ and 60-80 rpm for 30-60 minutes each time.

9. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 1, characterized in that, The washing described in step (3) is performed using hot water at 60-90°C with ultrasonic assistance.

10. The method for reducing the moisture content and particle size of activated calcium silicate according to claim 9, characterized in that, The frequency of the ultrasound is 30-50kHz, and the washing time is 10-20 minutes.

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