A method for preparing porous hydrated calcium silicate by using high-silicon coal gasification slag

Abstract

The application provides a method for preparing porous hydrated calcium silicate by using high-silicon coal gasification slag, comprising the following steps: 1) screening high-silicon coal gasification slag; 2) adding NaOH solution according to the content of SiO2 and Al2O3 in the coal gasification slag to prepare a coarse material slurry; 3) grinding the coarse material slurry to obtain a fine material slurry; 4) high-temperature roasting the fine material slurry to obtain a blocky clinker; 5) grinding the blocky clinker to obtain a powdery clinker; 6) mixing the powdery clinker with lime milk to obtain a slurry; 7) filtering, washing and drying the slurry to obtain a product; and 8) mixing the washing liquid and the filtrate of step 7) and then evaporating and concentrating, and recycling the concentrated liquid for preparing the coal gasification slag slurry. The application not only realizes the high-value utilization of the whole component of the coal gasification slag, but also has no secondary discharge of three wastes. The process is simple, the flow is short, no special requirement is needed for the equipment, the cost is low, the product has a wide application range, the added value is high, and the NaOH alkali liquor can be recycled.

Description

Technical Field

[0001] This invention relates to a method for preparing porous hydrated calcium silicate using high-silica coal gasification slag, which belongs to the interdisciplinary field of chemical engineering and materials science. Background Technology

[0002] Although coal has long been a primary energy source, it is imperative to pursue clean and efficient utilization methods. Against this backdrop, coal chemical industries such as coal-to-oil, methanol, olefins, and ethylene glycol have developed rapidly. However, the use of coal in these chemical processes generates large quantities of coal gasification slag (including coarse and fine slag). As a novel type of bulk solid waste composed of unburned carbon and inorganic components, the treatment and utilization of coal gasification slag has become an urgent problem to be solved.

[0003] Currently, coal gasification slag is mainly treated through stockpiling, while its utilization is still in the research and development stage. Research focuses primarily on using unburned carbon as an adsorbent or chemical filler after decarbonization, while the inorganic components are mainly used as building material raw materials. However, due to the significant differences in the composition and structure of unburned carbon in coal gasification slag compared to conventional coal, traditional coal preparation technologies struggle to achieve efficient separation of unburned carbon and inorganic components, hindering large-scale application. Furthermore, the high moisture content (over 40%) in coal gasification slag leads to high drying costs during its utilization. Therefore, the utilization of coal gasification slag needs to pursue a high-value-added approach.

[0004] Research on the high-value utilization of coal gasification slag mainly involves acid leaching to remove inorganic components, followed by the synthesis of zeolites or flocculants from the leachate. The main problem with this technology is that after acid leaching, unburned carbon needs to be removed by filtration. However, due to the extremely small particle size of some unburned carbon particles, solid-liquid separation through filtration is difficult. Furthermore, the acid used is highly volatile, creating a harsh working environment, and places extremely high demands on the corrosion resistance of the equipment. Therefore, it is difficult to move beyond the laboratory and achieve industrial application. Summary of the Invention

[0005] The purpose of this invention is to utilize high-silicon coal gasification slag for high-value production, and to provide a method for preparing porous hydrated calcium silicate from high-silicon coal gasification slag, comprising the following steps:

[0006] 1) The moisture content and dry basis chemical composition content of the coal gasification slag were tested and screened to obtain high-silicon coal gasification slag with a moisture content of ≤38% and a SiO2 content of ≥40% in the dry basis of the high-silicon coal gasification slag.

[0007] The dry basis of coal gasification slag is a product obtained by drying coal gasification slag. The main chemical components of the dry basis of coal gasification slag include SiO2, CaO, Al2O3, Fe2O3, Na2O, MgO, and loss on ignition. The main mineral components are amorphous minerals and a small amount of zeolite. Loss on ignition refers to the unburned carbon in the dry basis of coal gasification slag.

[0008] This invention limits the moisture content of high-silicon coal gasification slag to ≤38%. If the moisture content in the coal gasification slag is too high, the solid content in the prepared coarse and fine slurries will be low. This results in not only a lower clinker yield during the later roasting stage, but also higher energy consumption. Production tests show that for every 1% increase in the liquid phase content of the fine slurry, the energy consumption in the roasting stage will increase by approximately 4.8%.

[0009] Furthermore, the SiO2 content in the coal gasification slag used in this invention must be above 40% by mass. This is because the target product of this invention is porous hydrated calcium silicate. Generally, the main components of coal gasification slag, besides SiO2, are mainly Al2O3 and CaO. If the Al2O3 and CaO content is too high, a large amount of NaAlO2 and β-2CaO·SiO2 will be generated during the roasting stage. When synthesizing porous calcium silicate with lime slurry, a large amount of NaAlO2 cannot participate in the synthesis of porous hydrated calcium silicate in the form of AlO4, but instead precipitates as Al(OH)3 solid phase, affecting the quality of porous hydrated calcium silicate. β-2CaO·SiO2 is a mineral with a relatively slow hydration rate. If the amount of β-2CaO·SiO2 in the clinker is small, it can fully hydrate to form porous calcium silicate hydrate. However, if the amount of β-2CaO·SiO2 is large, the synthesized porous calcium silicate hydrate will contain a large amount of unhydrated β-2CaO·SiO2, leading to a decrease in the quality of the porous calcium silicate hydrate. Therefore, it is preferable that the Al2O3 mass percentage in the dry basis of coal gasification slag is ≤15% and the CaO mass percentage is ≤13%.

[0010] 2) Based on the content of SiO2 and Al2O3 in the dry chemical composition of coal gasification slag, add NaOH solution to make the Na / (Si+Al) molar ratio 1.5 to 2.2 to prepare a coarse slurry. The preferred concentration of NaOH solution used is 4.5 to 5.5 mol / L.

[0011] This invention limits the Na / (Si+Al) molar ratio in the coarse slurry to 1.5–2.2 to ensure that the reactions in steps 4) and 6) occur according to the stoichiometric ratio; otherwise, the reaction will be incomplete or an undesirable phase will be formed. Additionally, the NaOH solution concentration is limited to 4.5–5.5 mol / L. If the NaOH solution concentration is too low, the solid content in the slurry will be low, and the solids will not dissolve sufficiently; if the concentration is too high, it will be detrimental to the calcination reaction in step 4), and step 8) requires evaporation and concentration, which also requires concentrating the sodium hydroxide solution to this concentration, resulting in excessive energy consumption during the concentration process.

[0012] 3) Grind the prepared coarse slurry using a wet mill, preferably with a maximum solid particle size ≤ 0.045 μm, to obtain a fine slurry;

[0013] The coarse slurry must be ground; otherwise, it will be difficult to react fully during the roasting process, and a longer roasting time will be required. If the solid particles in the fine slurry are too large, the rate and extent of the roasting reaction in step 4) will decrease, and a homogeneous product cannot be obtained. If the solid particles in the fine slurry are too fine, although the reaction rate and extent will be improved, the requirements for the grinding equipment will be higher, and the energy consumption of the grinding process will be increased.

[0014] 4) The finely ground slurry is roasted in a wet rotary kiln. The preferred roasting temperature is 760-810℃ and the roasting time is 15-30 min. After cooling, block clinker is obtained.

[0015] During coal gasification, high-temperature ash is rapidly cooled to form coal gasification slag, which is mainly in an amorphous state. During high-temperature roasting of the fine slurry, reactions shown in equations (1) to (3) mainly occur, with equation (1) being the main reaction. The main mineral in the coal gasification slag, amorphous SiO2, reacts with NaOH to form Na2O·xSiO2. A small amount of amorphous Al2O3 mineral in the coal gasification slag reacts with NaOH to form NaAlO2, as shown in reaction (2). A small amount of CaO-containing mineral in the coal gasification slag reacts with amorphous SiO2 and further crystallizes to form β-2CaO·SiO2, as shown in reaction (3).

[0016] xSiO2 (amorphous) + 2NaOH → Na2O·xSiO2 + H2O (1)

[0017] Al₂O₃ (amorphous) + 2NaOH → 2NaAlO₂ + H₂O (2)

[0018] SiO2 (amorphous) + 2CaO → β-2CaO·SiO2 (3)

[0019] 5) Grind the blocky clinker, preferably to a maximum particle size ≤0.045μm, to obtain powdered clinker;

[0020] 6) Mix the powdered clinker with lime milk (Ca(OH)2) at a CaO / SiO2 molar ratio of 0.90 to 1.10 to obtain a slurry. Preferably, after obtaining the slurry, heat it at 75 to 100°C for 45 to 80 minutes while stirring at a speed of 40 to 80 r / min.

[0021] The CaO / SiO2 molar ratio is limited to 0.90–1.10 to ensure the reaction shown in equation (4) occurs. The amount of lime slurry added needs to be determined based on the SiO2 content in the clinker. The above heating temperature is the suitable temperature for the clinker and lime slurry to react and generate porous hydrated calcium silicate.

[0022] Preferably, the CaO in lime milk 有效 >150g / L, whiteness ≥75%. CaO in lime milk. 有效 This refers to the effective Ca(OH)2 content in lime slurry that can react with clinker; in the industry, it is generally expressed as CaO. 有效 Characterization. The main reason for requiring whiteness is that the prepared porous hydrated calcium silicate may be used in papermaking, and papermaking has whiteness requirements for raw materials, so the whiteness of lime milk is limited.

[0023] The main reactions occurring in this process are shown in equation (4). The main mineral Na2O·xSiO2 in the roasted clinker reacts with lime slurry to form porous calcium silicate. A small amount of NaAlO2 reacts with Na2O·xSiO2 together with lime slurry to form porous hydrated calcium silicate doped with aluminum oxide tetrahedra, as shown in reaction equation (5). In essence, aluminum oxide tetrahedra participate in the network structure of silicon oxide tetrahedra. An even smaller amount of β-2CaO·SiO2, as a self-hydrated mineral, can form porous calcium silicate mineral and Ca(OH)2 at high temperature, as shown in reaction equation (6). The generated Ca(OH)2 participates in the reaction according to equations (4) and (5).

[0024] The reactions shown in equations (5) and (6) are unavoidable. If the Al2O3 and CaO content in the coal gasification slag is within the specified range, a small amount of aluminum and silicon minerals will react in the above manner. If the Al2O3 and CaO content exceeds the specified range, as mentioned above, some aluminum and silicon minerals will generate a large amount of NaAlO2 and β-2CaO·SiO2 during the roasting stage, which will subsequently precipitate as Al(OH)3 solid phase, affecting the quality of porous hydrated calcium silicate.

[0025] Na2O·xSiO2+Ca(OH)2+H2O→CSH(porous)+NaOH (4)

[0026] NaAlO2 + Na2O·xSiO2 + Ca(OH)2 + H2O → CS(A)-H (porous) + NaOH (5)

[0027] β-2CaO·SiO2+H2O→CSH(porous)+Ca(OH)2 (6)

[0028] 7) Filter and dehydrate the slurry after the reaction in step 6), and wash the dehydrated porous calcium silicate minerals, preferably with clean water at 80-100°C for 1-2 times to remove the NaOH adsorbed on the porous hydrated calcium silicate minerals.

[0029] 8) The washing liquid and filtrate from step 7) are mixed and then evaporated and concentrated, preferably until the NaOH concentration reaches 4.5 to 5.5 mol / L. The NaOH solution can be recycled for the preparation of coal gasification slag slurry in step 2).

[0030] 9) The porous hydrated calcium silicate material after filtration and washing is dried. The preferred drying temperature is 150-200℃, and the moisture content after drying is controlled below 3% to obtain the porous hydrated calcium silicate.

[0031] The present invention also provides porous hydrated calcium silicate prepared by the method, having an average pore diameter ≥35 nm and a specific surface area ≥300 m². 2 / g.

[0032] This invention targets coal gasification slag with high silicon content. It primarily employs an alkaline fusion process, adding NaOH solution to the slag and allowing it to fully react with the amorphous SiO2 and Al2O3 within the slag at high temperature. The clinker, after high-temperature calcination, is ground and then reacted with lime slurry to synthesize porous hydrated calcium silicate minerals. Compared to other coal gasification slag utilization technologies under development, this technology eliminates the need for decarbonization and fully utilizes the unburned carbon in the slag. Furthermore, compared to acid dissolution processes, the alkaline fusion process offers a safer and healthier working environment with no corrosive effect on equipment. Simultaneously, the synthesized porous hydrated calcium silicate minerals, being uncrystalline CSH with a large specific surface area, can be used as a high-value-added material, not only as a reinforcing agent for high-strength concrete but also as a filler in papermaking, plastics, and rubber, as well as a highly efficient adsorbent. This technology not only comprehensively solves the problem of coal gasification slag treatment with significant environmental benefits but also possesses substantial economic benefits and has the potential for large-scale promotion.

[0033] This technology has the following advantages:

[0034] (1) The high-value utilization of all components of high-silicon coal gasification slag has been realized;

[0035] (2) The NaOH solution was recycled throughout the system;

[0036] (3) The overall production process is very environmentally friendly, and no wastewater, waste gas, solid waste or other waste is generated in the entire system;

[0037] (4) The process is simple, the investment cost is low, and it is conducive to industrialization and promotion;

[0038] (5) The prepared porous hydrated calcium silicate products not only have a wide range of applications, but also have high added value and significant economic benefits. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a process flow diagram of the present invention for preparing porous hydrated calcium silicate using high-silica coal gasification slag;

[0041] Figure 2 The image shows the XRD pattern of the high-silicon coal gasification slag used in Example 1.

[0042] Figure 3 SEM image of porous hydrated calcium silicate prepared from high-silica coal gasification slag in Example 1;

[0043] Figure 4 XRD pattern of porous calcium silicate prepared in Example 1;

[0044] Figure 5 The image shows the XRD pattern of the high-silicon coal gasification slag used in Example 2.

[0045] Figure 6 SEM image of porous hydrated calcium silicate prepared from high-silica coal gasification slag in Example 2;

[0046] Figure 7 The image shows the XRD pattern of the porous calcium silicate prepared in Example 2.

[0047] Figure 8 The XRD pattern of the coal gasification slag used in Comparative Example 1;

[0048] Figure 9 SEM image of the final product of Comparative Example 1;

[0049] Figure 10 The XRD pattern of the final product of Comparative Example 1;

[0050] Figure 11 SEM image of the final product of Comparative Example 2;

[0051] Figure 12 The XRD pattern of the final product of Comparative Example 2;

[0052] Figure 13 SEM image of the final product of Comparative Example 3;

[0053] Figure 14The image shows the XRD pattern of the final product of Comparative Example 3. Detailed Implementation

[0054] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0055] Example 1:

[0056] (1) The chemical composition of the high-silicon coal gasification slag used in this embodiment is shown in Table 1, and its mineral composition is as follows: Figure 2 As shown. The main component of this coal gasification slag is SiO2, and the main mineral component is amorphous mineral, with only a very small amount of clinoptilolite.

[0057] Table 1. Chemical composition (wt%) of dry-based high-silica coal gasification slag used in Example 1

[0058] chemical composition <![CDATA[SiO2]]> CaO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> MgO Loss on ignition content 47.0 11.4 10.6 2.8 2.16 1.79 24.25

[0059] (2) Add a 5.0 mol / L NaOH solution to the high-silicon coal gasification slag and adjust the Na / (Si+Al) molar ratio in the slurry to 1.8 to obtain a coarse slurry;

[0060] (3) Grind the prepared coarse slurry using a wet mill to make the maximum particle size of the solid particles in the coal gasification slag slurry no higher than 0.045μm, and obtain fine slurry;

[0061] (4) The above wet-milled fine slurry was calcined at 780°C for 20 minutes and then cooled to obtain block clinker.

[0062] (5) Grind the block clinker to a maximum particle size of less than 0.045 μm to obtain powdered clinker;

[0063] (6) Add CaO to the powdered clinker 有效 A lime slurry with a concentration of 180 g / L and a whiteness of 76 was used to synthesize a slurry with a CaO / SiO2 molar ratio of 1.0. The slurry was then heated at 90°C for 50 minutes while being stirred at 60 r / min.

[0064] (7) The synthetic slurry was filtered and dehydrated, and the filter cake was washed twice with fresh water at 98°C. The filtrate and washing liquid were mixed and then evaporated and concentrated by heating until the NaOH concentration reached 5.0 mol / L.

[0065] (8) The filter cake is dried at 180℃ to reduce the moisture content of the hydrated porous calcium silicate to below 3%, thus obtaining a qualified porous hydrated calcium silicate product with the following morphology. Figure 3As shown. Its average pore diameter was measured to be 36.11 nm, and its specific surface area was 321 m². 2 / g. Figure 4 The image shows the XRD pattern of the product prepared in Example 1, indicating that its main component is porous calcium silicate.

[0066] Example 2:

[0067] (1) The chemical composition of the high-silicon coal gasification slag used in this embodiment is shown in Table 2, and the mineral composition is as follows: Figure 4 As shown. The main component of this coal gasification slag is SiO2, and the main mineral component is amorphous mineral, with only a very small amount of clinoptilolite.

[0068] Table 2. Chemical composition (wt%) of dry-based high-silica coal gasification slag used in Example 2.

[0069] chemical composition <![CDATA[SiO2]]> CaO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> MgO Loss on ignition content 43.6 9.7 9.6 1.9 1.98 2.04 31.18

[0070] (2) Add a 5.5 mol / L NaOH solution to the high-silicon coal gasification slag and adjust the Na / (Si+Al) molar ratio in the slurry to 2.0 to obtain a coarse slurry;

[0071] (3) Grind the prepared coarse slurry using a wet mill to make the maximum particle size of the solid particles in the coal gasification slag slurry no higher than 0.045μm, and obtain fine slurry;

[0072] (4) The above wet-milled fine slurry was calcined at 800°C for 15 minutes and cooled to obtain block clinker.

[0073] (5) Grind the block clinker to a maximum particle size of less than 0.045 μm to obtain powdered clinker;

[0074] (6) Add CaO to the powdered clinker 有效 A lime slurry with a concentration of 170 g / L and a whiteness of 75 was used to synthesize a slurry with a CaO / SiO2 molar ratio of 1.05. The slurry was then heated at 90°C for 60 min while being stirred at 80 r / min.

[0075] (7) The synthetic slurry is filtered and dehydrated, and then the filter cake is washed twice with fresh water at 100°C. The filtrate and washing liquid are mixed and then evaporated and concentrated by heating until the NaOH concentration reaches 5.5 mol / L;

[0076] (8) The filter cake is dried at 200℃ to reduce the moisture content of the hydrated porous calcium silicate to below 3%, thus obtaining a qualified porous hydrated calcium silicate product, such as... Figure 5 As shown. Its average pore diameter was measured to be 40.25 nm, and its specific surface area was 308 m². 2 / g. Figure 7The XRD pattern of the porous calcium silicate prepared in Example 2 shows that the product phase is basically the same as that in Example 1.

[0077] Comparative Example 1:

[0078] (1) The chemical composition of the coal gasification slag used in this comparative example is shown in Table 3, and the mineral composition is as follows: Figure 8 As shown. The main components of this coal gasification slag are SiO2 and Al2O3, the main mineral components are amorphous minerals, and there is also some mullite.

[0079] Table 3. Chemical composition (wt%) of dry-based coal gasification slag used in Comparative Example 1

[0080] chemical composition <![CDATA[SiO2]]> CaO <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[Na2O]]> MgO Loss on ignition content 23.5 7.3 32.7 0.8 0.98 3.6 31.12

[0081] (2) Add a 5.5 mol / L NaOH solution to the high-silicon coal gasification slag and adjust the Na / (Si+Al) molar ratio in the slurry to 2.0 to obtain a coarse slurry;

[0082] (3) Grind the prepared coarse slurry using a wet mill to make the maximum particle size of the solid particles in the coal gasification slag slurry no higher than 0.045μm, and obtain fine slurry;

[0083] (4) The above wet-milled fine slurry was calcined at 805°C for 15 minutes and cooled to obtain block clinker.

[0084] (5) Grind the block clinker to a maximum particle size of less than 0.045 μm to obtain powdered clinker;

[0085] (6) Add CaO to the powdered clinker 有效 A lime slurry with a concentration of 170 g / L and a whiteness of 75 was used to synthesize a slurry with a CaO / SiO2 molar ratio of 1.05. The slurry was then heated at 90°C for 60 min while being stirred at 80 r / min.

[0086] (7) The synthetic slurry is filtered and dehydrated, and then the filter cake is washed twice with fresh water at 100°C. The filtrate and washing liquid are mixed and then evaporated and concentrated by heating until the NaOH concentration reaches 5.5 mol / L;

[0087] (8) The filter cake is dried at 200℃ to reduce its moisture content to below 3%, and its microstructure is as follows. Figure 9 As shown, the pore structure of the product is completely different from that of Examples 1 and 2. Its average pore diameter was measured to be 72.46 nm, and its specific surface area was 146 m². 2 / g, and perform XRD analysis as follows Figure 10 As shown, the product contains not only hydrated calcium silicate, but also a large amount of Al(OH)3.

[0088] This comparative example confirms that the raw material used in this invention must be high-silicon coal gasification slag, and the mass percentage of Al2O3 therein must be ≤15%.

[0089] Comparative Example 2:

[0090] (1) The chemical composition of the high-silicon coal gasification slag used in this comparative example is shown in Table 1, and its mineral composition is as follows: Figure 2 As shown. The main component of this coal gasification slag is SiO2, and the main mineral component is amorphous mineral, with only a very small amount of clinoptilolite.

[0091] (2) Add a 5.0 mol / L NaOH solution to the high-silicon coal gasification slag and adjust the Na / (Si+Al) molar ratio in the slurry to 1.2 to obtain a coarse slurry;

[0092] (3) Grind the prepared coarse slurry using a wet mill to make the maximum particle size of the solid particles in the coal gasification slag slurry no higher than 0.045μm, and obtain fine slurry;

[0093] (4) The above wet-milled fine slurry was calcined at 780°C for 20 minutes and then cooled to obtain block clinker.

[0094] (5) Grind the block clinker to a maximum particle size of less than 0.045 μm to obtain powdered clinker;

[0095] (6) Add CaO to the powdered clinker 有效 A lime slurry with a concentration of 180 g / L and a whiteness of 76 was used to synthesize a slurry with a CaO / SiO2 molar ratio of 1.0. The slurry was then heated at 90°C for 50 minutes while being stirred at 60 r / min.

[0096] (7) The synthetic slurry was filtered and dehydrated, and the filter cake was washed twice with fresh water at 98°C. The filtrate and washing liquid were mixed and then evaporated and concentrated by heating until the NaOH concentration reached 5.0 mol / L.

[0097] (8) The filter cake is dried at 180℃ to reduce its moisture content to below 3%, and its microstructure is as follows. Figure 11 As shown, its structure is sheet-like rather than porous, completely different from the microstructure of Examples 1 and 2. Its specific surface area was measured to be 58 m². 2 / g, and perform XRD analysis as follows Figure 12As shown, this indicates that in addition to a small amount of CSH, it also contains a large amount of Ca(OH)2 and small amounts of mullite and calcite. This suggests that when the amount of NaOH added is insufficient, the silicon and aluminum minerals in the high-silicon coal gasification slag cannot completely generate Na2O·xSiO2 and NaAlO2 during the roasting stage. Instead, the amorphous silicon and aluminum minerals undergo a crystallization reaction at high temperatures to generate mullite. Mullite is a relatively stable mineral and hardly reacts with lime milk, thus leading to an excess of lime milk. A large amount of unreacted Ca(OH)2 remains in the product, and a small amount of Ca(OH)2 is carbonized during the filtration and drying stages to generate calcite (CaCO3).

[0098] Therefore, this comparative example confirms that when the Na / (Si+Al) molar ratio in the slurry is less than 1.5, porous hydrated calcium silicate cannot be produced using high-silica coal gasification slag. Furthermore, if the Na / (Si+Al) molar ratio is greater than 2.2, although excess NaOH can completely react the silica-alumina minerals in the coal gasification slag and produce porous hydrated calcium silicate, it will result in NaOH waste and increase the system's material flow rate and energy consumption.

[0099] Comparative Example 3:

[0100] (1) The chemical composition of the high-silicon coal gasification slag used in this comparative example is shown in Table 2, and the mineral composition is as follows: Figure 4 As shown. The main component of this coal gasification slag is SiO2, and the main mineral component is amorphous mineral, with only a very small amount of clinoptilolite.

[0101] (2) Add a 5.5 mol / L NaOH solution to the high-silicon coal gasification slag and adjust the Na / (Si+Al) molar ratio in the slurry to 2.0 to obtain a coarse slurry;

[0102] (3) Grind the prepared coarse slurry using a wet mill to make the maximum particle size of the solid particles in the coal gasification slag slurry no higher than 0.045μm, and obtain fine slurry;

[0103] (4) The above wet-milled fine slurry was calcined at 800°C for 15 minutes and cooled to obtain block clinker.

[0104] (5) Grind the block clinker to a maximum particle size of less than 0.045 μm to obtain powdered clinker;

[0105] (6) Add CaO to the powdered clinker 有效 A lime slurry with a concentration of 170 g / L and a whiteness of 75 was used to synthesize a slurry with a CaO / SiO2 molar ratio of 0.7. The slurry was then heated at 90°C for 60 min while being stirred at 80 r / min.

[0106] (7) The synthetic slurry is filtered and dehydrated, and then the filter cake is washed twice with fresh water at 100°C. The filtrate and washing liquid are mixed and then evaporated and concentrated by heating until the NaOH concentration reaches 5.5 mol / L;

[0107] (8) The filter cake was dried at 200℃ to reduce the moisture content of the product to less than 3%, and the microstructure was as follows. Figure 13 As shown, its structure is strip-like rather than porous, completely different from the microstructure of Examples 1 and 2. Its specific surface area was measured to be 73 m². 2 / g, and perform XRD analysis as follows Figure 14 As shown, its main mineral is tobermorite, rather than porous hydrated calcium silicate.

[0108] This comparative example confirms that the CaO / SiO2 molar ratio of the present invention needs to be controlled within the range of 0.90 to 1.10; otherwise, it is difficult to generate porous hydrated calcium silicate.

[0109] This invention provides a method for preparing porous hydrated calcium silicate using high-silica coal gasification slag. This invention offers a novel approach to the treatment of high-silica coal gasification slag, compared to other methods such as decarbonization, use as building material raw materials, and acid dissolution. This invention not only achieves high-value utilization of all components of the coal gasification slag but also eliminates secondary emissions of waste. Furthermore, the process is simple, has a short flow, requires no special equipment, is low-cost, has a wide range of applications, and high added value. The key NaOH alkaline solution in this invention can be recycled. Therefore, this invention has significant environmental, economic, and social benefits and possesses the potential for large-scale industrial application.

[0110] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing porous hydrated calcium silicate using high-silica coal gasification slag, characterized in that, Includes the following steps: 1) The moisture content and dry basis chemical composition of the coal gasification slag were tested and screened to obtain high-silicon coal gasification slag with a moisture content of ≤38% by mass and a SiO2 content of ≥40% by mass on a dry basis. 2) Based on the content of SiO2 and Al2O3 in the dry chemical composition of coal gasification slag, add NaOH solution to make the Na / (Si+Al) molar ratio 1.5~2.2 to prepare a coarse slurry; 3) Grind the prepared coarse slurry using a wet mill to obtain a fine slurry; 4) The finely ground slurry is roasted in a wet rotary kiln and then cooled to obtain block clinker; 5) Grind the block clinker into powdered clinker; 6) Mix the powdered clinker with lime slurry at a CaO / SiO2 molar ratio of 0.90~1.10 to obtain a slurry; 7) Filter and dewater the slurry from step 6), and wash the dewatered porous calcium silicate minerals. 8) The washing liquid and filtrate from step 7) are mixed and then evaporated and concentrated. The concentrated liquid is then recycled for the preparation of coal gasification slag slurry in step 2). 9) The porous hydrated calcium silicate material after filtration and washing is dried to obtain the porous hydrated calcium silicate.

2. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 1), the mass percentage of Al2O3 in the dry basis of the high-silicon coal gasification slag is ≤15%, and the mass percentage of CaO is ≤13%.

3. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 2), the concentration of the NaOH solution used is 4.5~5.5 mol / L.

4. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 3), the maximum particle size of the solid particles in the fine slurry is ≤0.045μm.

5. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 4), the roasting temperature is 760~810℃ and the roasting time is 15~30min.

6. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 5), the maximum particle size of the powdered clinker is ≤0.045 μm.

7. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 6), after obtaining the slurry, the slurry is heated at 75~100℃ for 45~80 minutes while being stirred at a speed of 40~80 r / min.

8. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 6), the CaO in the lime slurry 有效 >150g / L, whiteness ≥75%.

9. The method for preparing porous hydrated calcium silicate using high-silica coal gasification slag according to claim 1, characterized in that, In step 8), the NaOH concentration is evaporated and concentrated until it reaches 4.5~5.5 mol / L. The concentrated liquid is then recycled for the preparation of coal gasification slag slurry in step 2).

10. Porous hydrated calcium silicate prepared by the method according to any one of claims 1 to 9.

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