A method for treating silicon-calcium slag solid waste

Abstract

The application discloses a kind of silicon calcium slag solid waste processing method, belong to coal-based solid waste processing technical field;The application is by the synergistic effect of hydrothermal combination acid environment, the originally stable silicate lattice in silicon calcium slag is destroyed, one of main elements, calcium is dissolved out, and separation with silicon is realized.After being changed into water-soluble calcium ion from stable crystal form, it can be used in regional agricultural economic crops long in nutrition supply, soil improvement and physiological disease prevention and control etc.As another main element, silicon is constructed as high value-added silicon dioxide aerogel material in pure amorphous state.

Description

Technical Field

[0001] This invention relates to the field of coal-based solid waste treatment technology, and in particular to a method for treating silicon-calcium slag solid waste. Background Technology

[0002] Calcium silicate slag is a newly generated bulk solid waste in the post-processing of fly ash, a major coal-based solid waste in the region, to produce high-value-added alumina. Its main components include silicon, calcium, and small amounts of impurities such as aluminum and iron. Existing publicly available technologies involving the resource utilization of calcium silicate slag all have various limitations, which are illustrated below.

[0003] Chinese invention patent CN118290115B discloses a method for producing building materials by carbonizing calcium silicate slag. The specific process involves washing, drying, and mixing the calcium silicate slag produced during the alumina extraction process from fly ash with water. This mixture is then molded into building profiles using a pressure molding machine and finally fed into a reaction vessel for carbonization. While this process achieves the resource utilization of calcium silicate slag, the products are limited to low-value-added building materials such as bricks and aggregates. Furthermore, it suffers from problems such as long carbonization times, reliance on pressurized equipment, and the use of high-concentration carbon dioxide gas, failing to achieve high-purity dissociation of calcium silicate components and the synergistic preparation of high-value-added products.

[0004] Chinese invention patent CN106747205B discloses a method for preparing hard calcium silicate using calcium silicate slag. The specific method involves mixing the calcium silicate slag with siliceous raw materials and then performing a high-temperature dynamic hydrothermal synthesis reaction at 200-260℃ under a liquid-to-solid ratio of (10-40):1 to prepare hard calcium silicate. While this technology shortens the synthesis time of traditional hard calcium silicate, it still has the following drawbacks: to obtain high-performance products, a complex segmented heating and holding process is required (e.g., sequentially heating from 130 to 150℃). o C. 150~180 o C. 180~200 o The segmented residence time (C-stage) and differentiated stirring rate control increase the difficulty of continuous industrial production. The product of this technology is only hard silica-calcium stone particles or slabs, mainly used in building insulation. It fails to deeply dissociate and reconstruct the silicon and calcium components in the silica-calcium slag, limiting its resource enhancement value.

[0005] Chinese invention patent CN108275886B discloses an aerogel insulation felt prepared from industrial solid waste and its preparation method. This technology utilizes slag to prepare high-value-added aerogel insulation felt. The process relies on an energy-intensive electrofusion fiber-forming step and requires impregnating the fiber felt with an external aerogel solution and adding various chemical additives. In this technology, the fiber size in the fiber felt is on the micrometer scale, while the aerogel itself is on the nanometer scale. The significant size difference between the two composite materials limits the composite effect. Furthermore, the resulting composite felt is prone to powder shedding, losing the excellent properties of the aerogel. Therefore, this type of composite material suffers from limited performance and a short lifespan. Summary of the Invention

[0006] The purpose of this invention is to provide a method for treating calcium silicate slag solid waste, which is used to extract high-value-added calcium ion aqueous solution and prepare silica aerogel powder.

[0007] The technical solution adopted in this invention is as follows: This invention provides a method for treating calcium silicate slag solid waste, comprising:

[0008] Step 1: Dry the calcium silicate slag to obtain calcium silicate slag raw material. Then, ball mill the calcium silicate slag raw material and take the calcium silicate slag powder sieved through a 100-mesh standard sieve as the raw material for subsequent reactions.

[0009] Step 2: Mix the calcium silicate slag powder obtained in Step 1 with a 4-8 mol / L nitric acid solution to prepare a suspension. The ratio of calcium silicate slag powder to nitric acid solution is 1:3-7. Then, stir at 100-160 °C. o The hydrothermal reaction was carried out at C for 0.5-10 hours, followed by cooling to room temperature. Then, high-speed centrifugation was performed to dissociate the liquid from the solid particles. After centrifugation, a transparent mother liquor and a solid precipitate were separated. The solid precipitate was washed with deionized water until the washing solution was neutral. The washed solid precipitate was dried to obtain amorphous silica solid. The transparent mother liquor and the washing solution were mixed to obtain a calcium ion aqueous solution.

[0010] Step 3: Dissolve the amorphous silica solid prepared in step 2 in sodium hydroxide solution and stir the reaction; then centrifuge at high speed, take the supernatant, and obtain the sodium silicate precursor.

[0011] Step 4: Add the sodium silicate precursor prepared in step 3 dropwise to a 1.0 mol / L sulfuric acid solution until the pH of the system reaches 7, and let it stand to obtain a silica wet gel; age the silica wet gel at 80℃ for 4 h to obtain a silica wet gel.

[0012] Step 5: Immerse the aged silica wet gel from Step 4 in anhydrous ethanol for complete displacement, then place it in an autoclave using liquid CO2 as the drying medium at a pressure of 15 MPa and a temperature of 60°C.o Under conditions of C, supercritical drying was carried out for 2 hours to obtain silica aerogel powder.

[0013] In a preferred embodiment, the source of the calcium silicate slag is: the large-volume coal-based solid waste fly ash generated by the soda lime sintering method is activated to produce white solid waste calcium silicate slag; the initial moisture content of the calcium silicate slag produced by this process is 70%; the calcium silicate slag is placed in a forced-air drying oven at 80°C. o The raw material of white calcium silicate slag was obtained by constant temperature drying at C for 12 hours. The main chemical components of the raw material of calcium silicate slag were: 25-45 wt% silicon dioxide, 35-55 wt% calcium oxide, and a small amount of impurities such as aluminum oxide and sodium oxide (0-40 wt%). The dried raw material of calcium silicate slag was then transferred into a ball mill jar and the ball mill speed was set to 600 r / min. The grinding was carried out continuously for 1 hour. The ball-milled material was sieved through a 100-mesh standard sieve, and the calcium silicate slag powder under the sieve was collected as raw material for subsequent reaction.

[0014] In a preferred embodiment, in step 2, the silica-calcium slag powder obtained in step 1 is mixed and stirred with a 6 mol / L nitric acid solution to prepare a suspension, wherein the ratio of silica-calcium slag powder to nitric acid solution is 1:5; then, at 160°C... o Hydrothermal reaction under C conditions for 0.5 h.

[0015] In a preferred embodiment, in step 3, the liquid-to-solid ratio of sodium hydroxide solution to amorphous silica solid is 6:1; the mixture is stirred continuously at 200 r / min for 10 min; then, the resulting mixture is placed in a high-speed centrifuge, the speed is set to 10000 r / min, and the mixture is centrifuged continuously for 10 min.

[0016] In a preferred embodiment, in step 5, the aged silica wet gel from step 4 is immersed in anhydrous ethanol for complete displacement, and then placed in an autoclave using liquid CO2 as the drying medium at a pressure of 15 MPa and a temperature of 60°C. o Under conditions of C, supercritical drying was carried out for 2 hours to obtain silica aerogel powder.

[0017] The beneficial effects of this invention are as follows: This invention provides a method for treating calcium silicate slag solid waste. Through the synergistic effect of hydrothermal treatment combined with an acidic environment, the originally stable silicate lattice in the calcium silicate slag is destroyed, dissolving calcium, one of the main elements, and achieving separation from silicon. After transforming from a stable crystalline form into water-soluble calcium ions, it can be used for nutrient supply during the growth of local agricultural economic crops, soil improvement, and the prevention and control of physiological diseases. Meanwhile, silicon, the other main element, is constructed in a pure amorphous form as a high-value-added silica aerogel material. This method avoids the transformation of silica from amorphous to crystalline state, thus ensuring a mild construction process for the subsequent aerogel. Subsequently, through simple and mild pH control, aging, and displacement processes, combined with supercritical drying technology, inexpensive undissolved solids from calcium silicate slag are used to replace expensive tetraethyl orthosilicate (TEOS) as raw material, significantly reducing the production cost of silica aerogel and facilitating industrial-scale promotion. Attached Figure Description

[0018] Figure 1 The image shown is a scanning electron microscope (SEM) image of the silica-calcium slag raw material after treatment in step 1 of Embodiment 1 of the present invention at different magnifications. Among them, Figure 1 a is a scanning electron microscope image of the silica-calcium slag raw material at a magnification of 20μm; Figure 1 b is a scanning electron microscope image of the silica-calcium slag raw material at a magnification of 10μm; Figure 1 c is a scanning electron microscope image of the silica-calcium slag raw material at a magnification of 2μm.

[0019] Figure 2 The image shown is the XRD pattern of the dried calcium silicate slag raw material of the present invention.

[0020] Figure 3 The image shown is a physical photograph of the silicon-calcium slag raw material and the amorphous silica solid powder obtained after activation in Example 1 of this invention. Among them, Figure 3 Image 'a' is a physical picture of the silica-calcium slag raw material; Figure 3 b is a physical image of amorphous silica solid powder.

[0021] Figure 4 The image shown is the XRD pattern of the amorphous silica solid obtained in step 2 of Example 1 of this invention.

[0022] Figure 5 The image shown is a physical picture of the silica wet gel after aging in step 4 of Example 1 of the present invention.

[0023] Figure 6 The image shown is a comparison of the infrared spectra (FT-IR) of the silica aerogel powder and the silica wet gel prepared in Example 1 of this invention.

[0024] Figure 7The figure shown is an N2 adsorption-desorption test curve of the silica aerogel powder prepared in Example 1 of the present invention.

[0025] Figure 8 The figure shown is a pore size distribution curve of the silica aerogel powder prepared in Example 1 of the present invention.

[0026] Figure 9 The figure shown is a water contact angle test diagram of the silica aerogel powder prepared in Example 1 of the present invention. 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] Unless otherwise specified, the methods described in the embodiments of this invention are all conventional experimental methods. All reagents used are commercially available, as summarized in Table 1 below, which lists the main material sources and related parameters of this invention.

[0029] Table 1. Summary of main material sources and related parameters of this invention.

[0030] This invention relates to the efficient separation and extraction of silicon and calcium elements from silica-calcium slag solid waste, addressing a multidimensional parameter space (acid concentration, liquid-to-solid ratio, hydrothermal temperature, and reaction time). Orthogonal experiments, through their mathematically "equilibrium dispersion" characteristic, can directly pinpoint the globally optimal solution in the parameter space (Example 1) while fully covering the scope of the claims (e.g., temperature 100-160℃, acid concentration 4-8 mol / L, etc.) using a relatively small number of representative experiments (9 groups in Table 5). Therefore, this invention first presents the optimal implementation scheme (Example 1), followed by orthogonal experiments.

[0031] Example 1: This example provides a method for treating silicon-calcium slag solid waste, including the following steps.

[0032] Step 1: The calcium silicate slag is dried to obtain calcium silicate slag raw material. The raw material is then ball-milled, and the calcium silicate slag powder sieved through a 100-mesh standard sieve is used as the raw material for subsequent reactions. The specific operation in this embodiment is as follows.

[0033] The calcium silicate slag used in this invention originates from a power plant in Ordos. This plant uses a quicklime sintering method to activate and treat the large quantities of coal-based solid waste, fly ash, producing white solid waste, calcium silicate slag. The initial moisture content of the calcium silicate slag produced by this process is 70%. The process of this invention first places the calcium silicate slag in a forced-air drying oven at 80°C. o After being dried at a constant temperature of C for 12 hours, white calcium silicate slag raw material was obtained.

[0034] like Figure 1 The image shown is a scanning electron microscope (SEM) image of the silica-calcium slag raw material after treatment in step 1 of Embodiment 1 of the present invention at different magnifications. Among them, Figure 1 a is a scanning electron microscope image of the silica-calcium slag raw material at a magnification of 20μm; Figure 1 b is a scanning electron microscope image of the silica-calcium slag raw material at a magnification of 10μm; Figure 1 c is a scanning electron microscope image of the raw silica-calcium slag at 2μm magnification. As can be seen from the image, the dried raw silica-calcium slag has a dense blocky structure.

[0035] This invention analyzes the phase composition of dried calcium silicate slag raw material. For example... Figure 2 The image shown is the XRD pattern of the dried calcium silicate slag raw material of this invention. Analysis revealed that the dried calcium silicate slag raw material is composed of calcium silicate crystals.

[0036] Subsequently, the present invention uses inductively coupled plasma atomic emission spectrometry (ICP) to detect the main element content of the dried calcium silicate slag raw material. Table 2 below shows the ICP analysis of the main element content of the dried calcium silicate slag raw material of the present invention.

[0037] Table 2. Analysis of the main element content (ICP) of the dried silica-calcium slag raw material of the present invention.

[0038] Analysis revealed that the main components of the dried calcium silicate slag raw material are calcium and silicon, with corresponding mass percentages of 25.9% and 16.9%, respectively.

[0039] This invention uses N2 adsorption-desorption tests on dried calcium silicate slag raw materials to determine that its specific surface area is only 5.31 m². 2 / g. Combined with scanning electron microscopy Figure 1 It can be seen that the raw material of calcium silicate slag lacks effective pores and has an extremely dense structure.

[0040] Subsequently, the dried calcium silicate slag raw material was transferred into a ball mill jar, and the ball mill speed was set to 600 r / min. Under the action of high-frequency impact and shear force of the grinding media, the material was continuously ground for 1 hour. The ball-milled material was then sieved through a 100-mesh standard sieve, and the calcium silicate slag powder that passed through the sieve was collected as a raw material for subsequent reactions, ensuring the consistency of material size before the activation reaction.

[0041] Step 2: Mix the calcium silicate slag powder obtained in Step 1 with a 6 mol / L nitric acid solution to prepare a suspension. The liquid-to-solid ratio of the nitric acid solution to the calcium silicate slag powder is 5:1. Then, heat at 160°C... o The hydrothermal reaction was carried out at C for 0.5 h, and then cooled to room temperature. The mixture was then centrifuged at high speed to dissociate the liquid from the solid particles. After centrifugation, a transparent mother liquor and a solid precipitate were separated. The solid precipitate was washed with deionized water until the washing solution was neutral. The washed solid precipitate was dried to obtain amorphous silica solid. The transparent mother liquor and the washing solution were mixed to obtain a calcium ion aqueous solution.

[0042] The specific operation in this embodiment is as follows: First, 50 mL of deionized water is placed in a beaker, and then 37.5 mL of concentrated nitric acid is slowly added along the beaker wall; after the solution cools to room temperature, it is transferred to a 100 mL volumetric flask; the volume is adjusted to the mark with deionized water to obtain a nitric acid solution with a concentration of 6 mol / L for later use.

[0043] Weigh 20g of the calcium silicate slag powder obtained in step 1 and place it in a polytetrafluoroethylene (PTFE) reactor liner. Then add 100mL of a prepared 6mol / L nitric acid solution. Control the liquid-to-solid ratio at 5:1. Set the mechanical stirring speed to 200r / min and stir continuously for 10min to obtain a suspension.

[0044] The resulting suspension was then transferred to a stainless steel hydrothermal reactor, which was placed in a forced-air drying oven, and the reaction temperature was set to 160°C. o C, the reaction time was 0.5 h; after the reaction was completed, it was cooled to room temperature. Next, the obtained hydrothermal reaction product (acidic slurry) was removed from the reactor and transferred to centrifuge tubes; the centrifuge tubes were placed in a high-speed centrifuge, set to a speed of 10000 r / min, and centrifuged continuously for 10 min. This allowed for the dissociation of the liquid and solid particles. After centrifugation, a transparent mother liquor and solid precipitate were separated.

[0045] The solid precipitate was washed with deionized water as follows: 20 mL of deionized water was used to wash the solid precipitate three times, until the washing solution was neutral (pH=7.0). The washed solid was a pure white filter cake. The neutralized solid precipitate was then placed in an 80°C container. oThe sample was dried in a forced-air drying oven at C for 12 hours to obtain 7.1 g of white powdery amorphous silica solid.

[0046] like Figure 3 The image shown is a physical photograph of the silicon-calcium slag raw material and the amorphous silica solid powder obtained after activation in Example 1 of this invention. Among them, Figure 3 Image 'a' is a physical picture of the silica-calcium slag raw material; Figure 3 b is a photograph of amorphous silica solid powder. (e.g.) Figure 3 As shown, compared with the raw silicon-calcium slag, the macroscopic morphology of the activated amorphous silica solid did not change significantly.

[0047] The composition of amorphous silica solids was determined by ICP, as shown in Table 3.

[0048] Table 3. Elemental analysis (ICP) table of the amorphous silica solid obtained in step 2 of Example 1 of the present invention.

[0049] The formula for calculating the residual rate of each element in the undissolved solid is shown in Formula 1. Comparing the data in Table 3 and Table 2, it can be seen that compared with the initial calcium silicate slag containing 25.9% wt% Ca, the Ca content in the solid powder after step 2 is only 1.31 wt%; the residual rate of Si reaches 96.12 wt%.

[0050] (Formula 1).

[0051] like Figure 4 The image shown is the XRD pattern of the amorphous silica solid obtained in step 2 of Example 1 of this invention. (Comparison) Figure 2 The sharp diffraction peaks of calcium silicate in the raw silica-calcium slag, and the absence of sharp peaks in the XRD pattern of the amorphous silica solid after acid dissolution and activation, indicate that the remaining solid mainly exists in an amorphous form. Based on the composition analysis, it is identified as amorphous silica powder.

[0052] In this invention, a transparent mother liquor and a washing liquid are mixed, and then compositional analysis is performed using ICP. Table 4 below shows the elemental content analysis (ICP) of the mixture of transparent mother liquor and washing liquid in step 2 of Example 1 of this invention.

[0053] Table 4. Elemental content analysis (ICP) of the mixture of transparent mother liquor and washing liquid in step 2 of Example 1 of the present invention.

[0054] Table 4 shows that calcium mainly exists in the liquid phase as water-soluble ions. Compared to calcium silicate slag, the recovery rate (solution rate) of calcium in the liquid phase is 86.76%. The recovery rate calculation formula is detailed in Formula 2. The recovery rates of other dissolved elements in the liquid phase can be obtained using the same calculation method. Among them, the silicon recovery rate is only 0.88%, which is extremely low compared to the composition of unactivated calcium silicate slag; this indicates the efficient separation of the two core elements, silicon and calcium, in the calcium silicate slag.

[0055] (Formula 2).

[0056] The method of this invention can efficiently and selectively recover stable calcium from solid crystals and convert it into soluble ionic calcium. This calcium ion aqueous solution can be used for plant nutrient supply, soil improvement and physiological disease control, etc., realizing the efficient extraction and high-value utilization of calcium resources in silicon-calcium slag solid waste.

[0057] Step 3: Dissolve the amorphous silica solid prepared in Step 2 in sodium hydroxide solution and stir the reaction; then centrifuge at high speed, collect the supernatant, and obtain the sodium silicate precursor. The specific operation in this embodiment is as follows.

[0058] First, dissolve 2g of sodium hydroxide solid in 10mL of deionized water. After the sodium hydroxide solid has completely dissolved to form a clear and transparent solution, place it in a fume hood and let it cool naturally to room temperature before use.

[0059] 2g of amorphous silica solid obtained in step 2 was slowly added to a sodium hydroxide solution; the liquid-to-solid ratio of sodium hydroxide solution to amorphous silica solid was 6:1; then the mixture was stirred continuously at 200 rpm for 10 min. The resulting mixture was then placed in a high-speed centrifuge and centrifuged at 10000 rpm for 10 min. After centrifugation, the supernatant was collected; this supernatant was a clear, transparent liquid without any visible suspended matter, which is the sodium silicate precursor.

[0060] Step 4: Add the sodium silicate precursor prepared in step 3 dropwise to a 1.0 mol / L sulfuric acid solution until the pH of the system reaches 7. Let it stand for 10 minutes to obtain a silica wet gel. Aged the silica wet gel at 80℃ for 4 hours to obtain a silica wet gel.

[0061] The specific operation in this embodiment is as follows: First, 5.43 mL of 18.4 mol / L concentrated sulfuric acid was measured using a pipette and slowly poured into water along the wall of a beaker, while continuously stirring with a glass rod. The dilution process was accompanied by a significant exothermic reaction. After the solution had completely cooled to room temperature, it was transferred to a 100 mL volumetric flask and diluted to volume to obtain a 1.0 mol / L sulfuric acid solution.

[0062] Subsequently, under a stirring speed of 200 r / min, sodium silicate precursor was added dropwise to a 9.15 mL sulfuric acid solution with a concentration of 1.0 mol / L using a burette. As the sodium silicate precursor was added, the pH value of the system steadily increased from the initial value of 1. When the pH meter reading reached 7, the titration was immediately stopped and the mechanical stirring was stopped simultaneously, entering the static gelation stage. After standing in situ for 10 min, a silica wet gel was obtained.

[0063] Next, the silica wet gel, along with the reaction vessel, was sealed and placed in a constant temperature water bath or forced-air oven at 80°C. o The mixture was heated at a constant temperature (C) for 4 hours to obtain a wet silica gel. Figure 5 The image shown is a physical picture of the silica wet gel after aging in step 4 of Example 1 of the present invention.

[0064] Step 5: Immerse the aged silica wet gel from Step 4 in anhydrous ethanol for complete displacement, then place it in an autoclave using liquid CO2 as the drying medium at a pressure of 15 MPa and a temperature of 60°C. o Under conditions of C, supercritical drying was carried out for 2 hours to obtain silica aerogel powder.

[0065] The specific operation in this embodiment is as follows: First, the silica wet gel is completely immersed in anhydrous ethanol for displacement, and the anhydrous ethanol is replaced every 12 hours for a total of 48 hours. Then, the displaced wet gel is placed in an autoclave, using liquid CO2 as the drying medium, and subjected to an autoclave at a pressure of 15 MPa and a temperature of 60°C. o The material was dried at temperature C for 2 hours. After drying, the pressure was slowly released to obtain silica aerogel powder.

[0066] Figure 6 The image shows a comparison of the Fourier Transform Infrared (FT-IR) spectra of the silica aerogel powder and the silica wet gel prepared in Example 1 of this invention. As can be seen from the image, the silica aerogel exhibits a high FT-IR intensity at 1080 cm⁻¹. -1 and 800cm -1 The presence of Si-O-Si characteristic peaks confirms that the wet silica gel was transformed into silica through supercritical drying. Furthermore, compared to the wet silica gel, the silica aerogel sample exhibited a wavenumber of 1630 cm⁻¹. -1 and 3400cm -1 The disappearance of the two diffraction peaks attributed to hydroxyl groups indicates that the method of the present invention has removed the water from the gel through supercritical drying.

[0067] The present invention performs N2 adsorption-desorption tests on the silica aerogel powder prepared in Example 1. Figure 7The figure shown is an N2 adsorption-desorption test curve of the silica aerogel powder prepared in Example 1 of the present invention. Figure 8 The figure shown is a pore size distribution curve of the silica aerogel powder prepared in Example 1 of the present invention.

[0068] like Figure 7 As shown, this curve belongs to a typical type IV isotherm, indicating that the silica aerogel powder has a mesoporous structure inside. Figure 8 As shown, the pore size distribution of the silica aerogel powder is mainly between 20 and 40 nm, and the specific surface area of ​​the aerogel powder is approximately 311 m². 2 / g.

[0069] Figure 9 The figure shown is a water contact angle test diagram of the silica aerogel powder prepared in Example 1 of the present invention. Water droplets spread completely and are absorbed instantly upon contact with the surface of the silica aerogel powder, with the contact angle approaching 0°; this demonstrates that the material possesses excellent superhydrophilic properties.

[0070] This invention further employs the graduated cylinder method to determine the bulk density of silica aerogel powder. The specific procedure is as follows: 0.0746 g of the prepared dry aerogel powder is weighed and allowed to fall naturally into a 10 mL dry graduated cylinder. The bulk volume occupied by the powder is read as 1 mL. Based on the bulk density formula (Formula 3), the bulk density of the silica aerogel powder prepared in Example 1 is calculated to be 0.0746 g / cm³. (Formula 3)

[0071] The porosity was calculated using a density conversion algorithm. The bulk density of the aerogel was 0.0746 g / cm³, and the porosity was 96.61% according to the porosity calculation formula (Formula 4). The theoretical density of the amorphous silica framework was 2.2 g / cm³. (Formula 4)

[0072] Furthermore, this invention employs a hot-wire thermal conductivity meter (a testing instrument based on the principle of unsteady-state hot-wire method) to test the thermal conductivity of the silica aerogel powder prepared in Example 1 under ambient temperature and pressure. The sample is placed in the test chamber, ensuring the hot-wire probe is completely embedded in the powder and maintains good contact. The test results show that the thermal conductivity of the silica aerogel powder is 0.0266 W / (m·K).

[0073] Furthermore, this invention studies key conditions through a series of orthogonal experiments. Details are as follows.

[0074] Table 5. Summary table of orthogonal experimental data of the present invention.

[0075] The comparative analysis of Example 1 and Example 1 is as follows.

[0076] Comparative Example 1 follows the same method and steps as Example 1, but differs from Example 1 in the following ways: In step 2, the nitric acid concentration is adjusted to 4 mol / L, and 20 g of calcium silicate slag powder is added to 60 mL of nitric acid solution, with a liquid-to-solid ratio of nitric acid solution to calcium silicate slag powder of 3:1. The hydrothermal reaction temperature is set to 100°C. o C.

[0077] Experimental results showed that the total mass of undissolved solids after the hydrothermal reaction was 11.98 g. The elemental content of this solid was analyzed and is shown in Table 6 below. Compared with the pretreated calcium silicate slag, the residual silicon rate was 79.92 wt%, and the residual calcium rate was 0.81%.

[0078] Table 6. Elemental analysis (ICP) of the solids after washing and drying in Comparative Example 1.

[0079] The present invention analyzed the elemental content of the mixture of transparent mother liquor and washing liquid in step 2 of comparative example 1, as shown in Table 7 below. The solubility rate of calcium in the mixture was 52.79 wt%, and the solubility rate of silicon was 0.49%.

[0080] Table 7. Elemental content analysis (ICP) of the mixture of transparent mother liquor and washing liquid in step 2 of Comparative Example 1.

[0081] The comparative analysis of Example 3 and Example 1 is as follows.

[0082] The comparative example No. 3 follows the same method and steps as in Example 1, but differs from Example 1 in the following ways: the concentration of nitric acid used in step 2 is adjusted to 4 mol / L, 20g of calcium silicate slag powder is added to 140mL of nitric acid solution, and the liquid-solid ratio of nitric acid solution to calcium silicate slag powder is 7:1; the hydrothermal reaction time is increased to 10h.

[0083] Experimental results showed that the final mass after washing was 9.83 g. The elemental content of this solid was analyzed, as shown in Table 8 below. Compared to the pretreated calcium silicate slag, the residual silicon content was 85.87 wt%, and the residual calcium content was 0.95 wt%.

[0084] Table 8. Elemental analysis (ICP) of the solids after washing and drying in Comparative Example No. 3.

[0085] The present invention analyzed the elemental content of the mixture of transparent mother liquor and washing liquid in step 2 of comparative example 3, as shown in Table 9 below. The solubility rate of calcium in the mixture was 69.41 wt%, and the solubility rate of silicon was 0.42 wt%.

[0086] Table 9. Elemental content analysis (ICP) of the mixture of transparent mother liquor and washing liquid in step 2 of comparative example 3.

[0087] The comparative analysis of Example 9 and Example 1 is as follows.

[0088] The comparative example (No. 9) follows the same method and steps as Example 1, but differs from Example 1 in the following ways: In step 2, the nitric acid concentration is adjusted to 8 mol / L, and 20 g of calcium silicate slag powder is added to 140 mL of nitric acid solution, with a liquid-to-solid ratio of 7:1. The hydrothermal reaction temperature is set to 130°C. o C.

[0089] Experimental results showed that the mass of the undissolved solid was 8.20 g. The elemental content of this solid was analyzed, as shown in Table 10. Compared to the pretreated calcium silicate slag, the residual silicon content was 92.53 wt%, and the residual calcium content was 0.80 wt%.

[0090] Table 10, Serial No. 9, shows the elemental analysis (ICP) of the solids after washing and drying.

[0091] The present invention analyzed the elemental content of the mixture of transparent mother liquor and washing liquid in step 2 of comparative example 9, as shown in Table 11 below. The solubility rate of calcium in the mixture was 82.90 wt%, and the solubility rate of silicon was 0.51 wt%.

[0092] Table 11, Elemental content analysis (ICP) of the mixture of transparent mother liquor and washing liquid in step 2 of comparative example 9.

[0093] Although the separation effect of the two core elements in this embodiment is close to that of the optimal embodiment 1, considering that a high acid content will increase reagent costs and increase the operating costs of the production process due to corrosion of equipment, this embodiment is considered inferior to embodiment 1 from an economic perspective.

[0094] The following is additional information.

[0095] The hydrothermal acid dissolution system of this invention is complex: the destruction of the calcium silicate lattice and the dissolution of ions in the calcium silicate slag are not isolated processes. Under the high-pressure hydrothermal environment of 100~160℃, there is a strong synergistic and interactive effect between thermodynamic activation and acid etching. Higher hydrothermal temperatures may significantly reduce dependence on acid concentration or reaction time. Using the controlled variable method severs the coupling between parameters, making it impossible to examine this interaction. Orthogonal experiments (such as the range or variance comparisons shown in Comparative Examples 2, 3, and 4) can not only assess the independent influence weight of individual factors but also scientifically evaluate the tolerance of process conditions.

[0096] The following is additional information.

[0097] When treating bulk solid waste, the core objective is to dissolve as many impurities as possible, such as calcium ions, into the liquid phase, leaving behind a high-purity amorphous silica framework. Therefore, the evaluation index for the orthogonal experiment in Table 5 is the "mass of solids after washing and drying." The lower this value, the more thorough the dissolution and the better the purification effect.

[0098] By analyzing L9(3) in Table 5 4 Range analysis of the data can clearly reveal the actual weight of each process parameter on the reaction system.

[0099] K ij : Represents the sum of all experimental results (solid mass after washing and drying) corresponding to the i-th factor at the j-th level.

[0100] k ij : represents the average experimental result of the i-th factor at the j-th level. Since each factor at each level was tested 3 times, k... ij =k ij / 3

[0101] R (range): The difference between the maximum and minimum values ​​of the average values ​​of different levels of a factor, i.e., R = max(k) - min(k). The larger the range, the greater the influence of the factor on the result.

[0102] 1. The calculation process of Factor A (nitric acid concentration) corresponds to column 1 in Table 5 (nitric acid concentration 4, 6, 8 mol / L).

[0103] Level 1 (4 mol / L): Includes experiment numbers 1, 2, and 3.

[0104] K A1 =11.98+7.50+9.83=29.31.

[0105] k A1 =29.31 / 3=9.77g.

[0106] Level 2 (6 mol / L): Includes experiment numbers 4, 5, and 6.

[0107] K A2 =10.67+7.10+8.47=26.24.

[0108] k A2 =26.24 / 3=8.75g.

[0109] Level 3 (8 mol / L): Includes experiment numbers 7, 8, and 9.

[0110] K A3 =11.30+7.13+8.20=26.63.

[0111] k A3 =26.63 / 3=8.88g.

[0112] Range R: max(9.77,8.75,8.88)-min(9.77,8.75,8.88)=9.77-8.75=1.02.

[0113] 2. Calculation process of factor B (liquid-solid ratio); corresponding to column 2 in Table 5 (liquid-solid ratio 3:1, 5:1, 7:1).

[0114] Level 1 (ratio 3:1): Includes experiments numbered 1, 4, and 7.

[0115] K B1 =11.98+10.67+11.30=33.95.

[0116] k B1 =33.95 / 3=11.32g.

[0117] Level 2 (ratio 5:1): Includes experiments numbered 2, 5, and 8.

[0118] K B2 =7.50+7.10+7.13=21.73.

[0119] k B2 =21.73 / 3=7.24g.

[0120] Level 3 (ratio 7:1): Includes experiments numbered 3, 6, and 9.

[0121] K B3 =9.83+8.47+8.20=26.50.

[0122] k B3 =26.50 / 3=8.83g.

[0123] Range R: max(11.32,7.24,8.83)-min(11.32,7.24,8.83)=11.32-7.24=4.08.

[0124] The calculation process for factor C (hydrothermal temperature) corresponds to column 4 in Table 5 (hydrothermal temperatures 100, 130, and 160℃).

[0125] Level 1 (100℃): Includes experiment numbers 1, 6, and 8.

[0126] K C1 =11.98+8.47+7.13=27.58.

[0127] k C1 =27.58 / 3=9.19g.

[0128] Level 2 (130℃): Includes experiment numbers 2, 4, and 9.

[0129] K C2 =7.50+10.67+8.20=26.37.

[0130] k C2 =26.37 / 3=8.79g.

[0131] Level 3 (160℃): Includes experiment numbers 3, 5, and 7.

[0132] K C3 =9.83+7.10+11.30=28.23.

[0133] k C3 =28.23 / 3=9.41g.

[0134] Range R: max(9.19,8.79,9.41)-min(9.19,8.79,9.41)=9.41-8.79=0.62.

[0135] 4. The calculation process of factor D (time) corresponds to column 5 (0.5, 5, 10h) in Table 5.

[0136] Level 1 (0.5h): Includes experiment numbers 1, 5, and 9.

[0137] K D1 =11.98+7.10+8.20=27.28.

[0138] k D1 =27.28 / 3=9.09g.

[0139] Level 2 (5h): Includes experiments numbered 2, 6, and 7.

[0140] K D2 =7.50+8.47+11.30=27.27.

[0141] k D2 =27.27 / 3=9.09g.

[0142] Level 3 (10h): Includes experiment numbers 3, 4, and 8.

[0143] K D3 =9.83+10.67+7.13=27.63.

[0144] k D3 =27.63 / 3=9.21g.

[0145] Range R: max(9.09,9.09,9.21-min(9.09,9.09,9.21)=9.21-9.09=0.12.

[0146] Liquid-to-solid ratio (4.08) > nitric acid concentration (1.02) > hydrothermal temperature (0.62) > time (0.12).

[0147] Calculations show that in this specific chemical system, blindly extending the reaction time (with an impact of only 0.12) is ineffective, while precisely controlling the liquid-to-solid ratio (with an impact as high as 4.08) is the key to the success or failure of the process. Simple single-factor control variable methods are unlikely to capture the influence weights of these four dimensions simultaneously with such high efficiency.

[0148] Referring to the data in Table 5 of this invention, only 7.10g of solid remained after the reaction in Example 1 of this invention. In contrast, Comparative Example 1 left nearly 12g (11.98g) of solid, which reflects that the calcium silicate lattice was not sufficiently destroyed.

[0149] In Comparative Example 3, 9.83 g of solid remained, and the calcium dissolution rate was only 69.41 wt%, far lower than in Example 1. This indicates that when the nitric acid concentration is low, blindly increasing the liquid volume not only fails to improve efficiency but also dilutes the effective collision concentration at the solid-liquid interface. Although a large amount of liquid increases the theoretical upper limit of calcium ion capacity, it reduces the chemical driving force for disrupting the calcium silicate lattice.

[0150] Furthermore, in Comparative Example 3, under the conditions of the highest reaction temperature of 160℃ and the longest reaction time of 10h, the calcium dissolution rate of 69.41wt% was much lower than that of Example 1. This indicates that during the hydrothermal reaction, the acid concentration has a higher influence on the separation and purification effect than the reaction liquid volume and reaction temperature. In the acid dissolution and separation process of calcium silicate, the breaking of chemical bonds is highly dependent on the concentration of hydrogen ions.

[0151] In Comparative Example 9, the highest concentration of acid (8 mol / L) and the largest volume (liquid-to-solid ratio 7:1) were used, along with a massive amount of chemical reagents. However, the final calcium recovery rate (82.90%) and solid purification amount (8.20 g) still did not surpass those of Example 1. This indicates that the reaction system was already saturated with acid, and adding more acid would not produce any further positive benefits.

[0152] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for treating silicon-calcium slag solid waste, characterized in that, include: Step 1: Dry the calcium silicate slag to obtain calcium silicate slag raw material. Then, ball mill the calcium silicate slag raw material and take the calcium silicate slag powder separated by 100 mesh standard sieve as the raw material for subsequent reaction. Step 2: Mix the calcium silicate slag powder obtained in Step 1 with a 4-8 mol / L nitric acid solution to prepare a suspension. The ratio of calcium silicate slag powder to nitric acid solution is 1:3-7. Then, stir at 100-160 °C. o The hydrothermal reaction was carried out at C for 0.5-10 hours, followed by cooling to room temperature. Then, high-speed centrifugation was performed to dissociate the liquid from the solid particles. After centrifugation, a transparent mother liquor and a solid precipitate were separated. The solid precipitate was washed with deionized water until the washing solution was neutral. The washed solid precipitate was dried to obtain amorphous silica solid. The transparent mother liquor and the washing solution were mixed to obtain a calcium ion aqueous solution. Step 3: Dissolve the amorphous silica solid prepared in step 2 in sodium hydroxide solution and stir the reaction; then centrifuge at high speed, take the supernatant, and obtain the sodium silicate precursor; Step 4: Add the sodium silicate precursor prepared in step 3 dropwise to a 1.0 mol / L sulfuric acid solution until the pH of the system reaches 7, and let it stand to obtain a silica wet gel; age the silica wet gel at 80℃ for 4 h to obtain a silica wet gel. Step 5: Immerse the aged silica wet gel from Step 4 in anhydrous ethanol for complete displacement, then place it in an autoclave using liquid CO2 as the drying medium at a pressure of 15 MPa and a temperature of 60°C. o Under conditions of C, supercritical drying was carried out for 2 hours to obtain silica aerogel powder.

2. The method for treating silicon-calcium slag solid waste according to claim 1, characterized in that, The source of calcium silicate slag is: calcium silicate slag is produced by activating large quantities of coal-based solid waste, fly ash, using a quicklime sintering method; the initial moisture content of the calcium silicate slag produced by this process is 70%; the calcium silicate slag is placed in a forced-air drying oven at 80°C. o The raw material of white calcium silicate slag was obtained by constant temperature drying at C for 12 hours. The main chemical components of the raw material of calcium silicate slag were: 25-45 wt% silicon dioxide, 35-55 wt% calcium oxide, and a small amount of impurities such as aluminum oxide and sodium oxide (0-40 wt%). The dried raw material of calcium silicate slag was then transferred into a ball mill jar and the ball mill speed was set to 600 r / min. The grinding was carried out continuously for 1 hour. The ball-milled material was sieved through a 100-mesh standard sieve, and the calcium silicate slag powder under the sieve was collected as raw material for subsequent reaction.

3. The method for treating silicon-calcium slag solid waste according to claim 1, characterized in that, In step 2, the silica-calcium slag powder obtained in step 1 is mixed and stirred with a 6 mol / L nitric acid solution to prepare a suspension. The ratio of silica-calcium slag powder to nitric acid solution is 1:

5. Then, the suspension is heated at 160°C. o Hydrothermal reaction under C conditions for 0.5 h.

4. The method for treating silicon-calcium slag solid waste according to claim 1, characterized in that, In step 3, the liquid-to-solid ratio of sodium hydroxide solution to amorphous silica solid is 6:1; the mixture is stirred continuously at 200 r / min for 10 min; then, the resulting mixture is placed in a high-speed centrifuge, the speed is set to 10000 r / min, and the mixture is centrifuged continuously for 10 min.

5. The method for treating silicon-calcium slag solid waste according to claim 1, characterized in that, In step 5, the aged silica wet gel from step 4 is immersed in anhydrous ethanol for complete displacement, and then placed in an autoclave using liquid CO2 as the drying medium at a pressure of 15 MPa and a temperature of 60°C. o Under conditions of C, supercritical drying was carried out for 2 hours to obtain silica aerogel powder.

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