Method for preparing silicon carbide from coal gasification coarse slag and fine slag

Abstract

The invention provides a method for preparing silicon carbide from coal gasification coarse slag and fine slag, and belongs to the technical field of coal slag resource recycling. Comprising the following steps: S1, carrying out acid pickling and ball-milling mixing pretreatment; s2, transferring the carbon-rich and silicon-source powder into a graphite boat carrier, introducing nitrogen as a shielding gas, balancing the pressure in the reactor to 0.015 Mp, and enabling the mixture in the graphite boat to react in a high-temperature air-isolated state; s3, calcining a reaction product in the graphite boat in a muffle furnace; and performing ultrasonic pickling to remove impurities, and then performing suction filtration to obtain high-crystallinity silicon carbide. According to the method, the coal gasification coarse slag is reasonably compounded into the fine slag, the traditional way of classified utilization of the coal gasification slag is broken, the energy loss is reduced by a short-time and efficient method, the high-crystallinity silicon carbide is prepared, and the method has positive significance in the solid waste resource recycling direction.

Description

Technical Field

[0001] This invention provides a method for preparing silicon carbide from coal gasification coarse slag and fine slag, belonging to the field of coal slag resource recycling technology. Background Technology

[0002] Coal gasification technology is one of the core technologies for the efficient and clean conversion and utilization of coal. However, the coal gasification process generates a large amount of coarse and fine coal gasification slag, with fine slag accounting for 20%-40% of the total slag and coarse slag accounting for 60%-80%. Currently, most coal gasification slag is simply disposed of through open-air stockpiling or burial, which not only occupies land resources but also pollutes the environment with harmful substances, posing a significant potential hazard. A small portion of the slag is used for agricultural soil improvement, recycling, and the preparation of high-value-added products and insulation materials after carbon and ash separation and upgrading, but the utilization rate remains low, and due to technological and cost limitations, industrial application remains a significant challenge. Therefore, the resource utilization of gasification slag remains one of the urgent problems to be solved.

[0003] Coal gasification fine ash mainly consists of a large amount of amorphous substances and a small amount of crystalline minerals, primarily SiO2, Al2O3, CaO, and residual carbon. It has a high fixed carbon content, with SiO2 being the dominant component in the ash, making it a valuable source of carbon and silicon and possessing the potential for in-situ silicon carbide production. However, the process of preparing silicon carbide solely from coal gasification fine ash often results in excessive residual carbon, wasting resources. Coal gasification coarse ash typically has less residual carbon and a higher SiO2 content than fine ash, and can be used in conjunction with fine ash for silicon carbide production.

[0004] The direct carbon-silicon reaction method utilizes refined carbon (purity > 99.999%) and silica powder / quartz sand (purity > 99.999%), resulting in high raw material costs. Conventional furnaces that perform carbothermic reduction reactions at high temperatures require long reaction times and consume significant energy. Joule heating technology, however, utilizes the characteristic of short-duration high-temperature reduction to extract oxygen from silica through the reducing properties of carbon. This method rapidly transforms low-reactivity residual carbon and silica ash into high-value silicon carbide materials, showing potential for industrial application and representing a route for the resource utilization of coal gasification slag.

[0005] Patent CN108046265A discloses a method for preparing silicon carbide from coal gangue and waste activated carbon. The method involves pulverizing and drying the coal gangue, mixing it with waste activated carbon treated at a certain temperature in a certain proportion, removing acidic soluble impurities with a strong acid solution, washing with hot water until neutral, drying, heating to a certain temperature in a protective atmosphere and holding for a period of time to obtain silicon carbide powder. The powder is then oxidized and burned in an oxidizing atmosphere to remove residual carbon powder, dispersed in a mixed acid to remove residual silicon dioxide and other impurities, and finally washed and dried to obtain silicon carbide powder. However, this method has the following disadvantages: (1) it requires the supplementation of another carbon-containing solid waste as a carbon source; (2) the energy consumption required for the experiment is large, resulting in high cost; (3) there is an excess of carbon source resources, and sintering wastes resources.

[0006] Patent CN119409195A discloses a method for preparing silicon carbide materials using coal gasification slag. First, the coal gasification slag is pretreated, then acid-leached, washed, filtered, and dried. Next, it undergoes Joule heating treatment, followed by calcination to obtain silicon carbide. In the Joule heating treatment, the discharge voltage is set to 120V-150V, and the number of discharges is 1-5 times. This invention, by subjecting the coal gasification slag to Joule heating treatment, achieves extremely short reaction times for each Joule heating, significantly reducing energy consumption and drastically shortening the reaction time. This solves the technical problem of high energy consumption due to long reaction times in traditional carbothermal reduction for silicon carbide material preparation. However, this method suffers from excess carbon source resources in the coal gasification slag, leading to resource waste during sintering. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing silicon carbide using coarse coal gasification slag in conjunction with fine coal gasification slag. The process of preparing silicon carbide using only fine coal gasification slag typically suffers from excessive residual carbon, wasting residual carbon resources. Coarse coal gasification slag usually has a lower residual carbon content and a higher SiO2 content than fine coal gasification slag, and can supplement the silicon source for silicon carbide preparation by working with the fine coal gasification slag.

[0008] The specific technical solution is as follows:

[0009] A method for preparing silicon carbide from coal gasification co-processing slag and fine slag includes the following steps:

[0010] S1. Pickling and ball milling pretreatment;

[0011] The impurity removal treatment using an acid leaching solution with a molar concentration of 3 mol / L specifically includes the following sub-steps:

[0012] S1.1. After thoroughly drying the coal gasification fine slag and coarse slag in a 105°C oven, seal and store for later use;

[0013] S1.2. Prepare a 3 mol / L HCl solution. Add the dried coal gasification fine slag and coarse slag to the prepared HCl solution at a solid-liquid mass ratio of 1:10. Heat and stir at 60°C for 5 hours in a magnetic stirrer to obtain a black slurry.

[0014] S1.3. The black slurry is filtered and washed with water until neutral. The solid filter cake after filtration is placed in an oven at 105°C and dried to obtain acid-washed coal gasification fine slag and coarse slag.

[0015] S1.4. The fine and coarse slags from the acid-washed coal gasification were placed in a zirconia ball mill jar and a uniformly mixed carbon-rich and silicon-based powder was obtained in a planetary ball mill. The volume ratio of the mixed slag to the zirconia balls during the ball milling process was 1:1, the ball milling speed was 700 r / min, and the time was 2 h.

[0016] S2. Joule heating thermal shock treatment;

[0017] Carbon-rich and silicon source powders were transferred into a graphite boat carrier, and then the graphite boat was placed in a Joule heating device. Nitrogen gas was introduced as a protective gas, and the pressure in the reactor was balanced to 0.015 MPa. The current of the Joule heating device was set to 461.53 A, the reaction temperature to 2000℃, and the residence time to 45 s, so that the mixture in the graphite boat could react under high temperature and air-isolated conditions.

[0018] S3. Calcination and purification treatment;

[0019] The reaction products in the graphite boat were heated to 1000°C at a heating rate of 10°C / min and calcined in a muffle furnace.

[0020] The calcined product was mixed with a mixed acid at a solid-liquid ratio of 1:20, with the volume ratio of HF and 3 mol / L HCl in the mixed acid being 1:1. The mixture was ultrasonically washed at 50 °C for 120 min to remove impurities, and then filtered to obtain highly crystalline silicon carbide.

[0021] The method of this invention rationally blends coarse coal gasification slag into fine slag, breaking the traditional approach of classifying and utilizing coal gasification slag. It reduces energy consumption in a short and efficient manner and produces highly crystalline silicon carbide, which has positive significance for the recycling and utilization of solid waste resources. Attached Figure Description

[0022] Figure 1 The XRD patterns of the silicon carbide material before and after impurity removal prepared in Example 1 of this invention;

[0023] Figure 2 The XRD patterns of silicon carbide materials before and after impurity removal prepared in Example 2 of this invention;

[0024] Figure 3 The XRD patterns of the silicon carbide material before and after impurity removal prepared in Example 3 of this invention;

[0025] Figure 4 The XRD patterns of the silicon carbide material before and after impurity removal prepared in Example 4 of this invention;

[0026] Figure 5 The XRD patterns of the silicon carbide material before and after impurity removal prepared in Example 5 of this invention are shown. Detailed Implementation

[0027] The specific technical solutions of the present invention will be described with reference to the embodiments.

[0028] (a) Raw material acid leaching pretreatment

[0029] Acid leaching treatment using an acid leaching solution with a molar concentration of 3 mol / L specifically includes the following steps:

[0030] (1) After thoroughly drying the fine and coarse coal gasification slag in a 105°C oven, seal and store for later use;

[0031] (2) Prepare a 3 mol / L HCl solution, and add the dried coal gasification fine slag and coarse slag to the prepared HCl solution at a solid-liquid mass ratio of 1:10. Heat and stir at 60°C for 5 hours in a magnetic stirrer to obtain a black slurry.

[0032] (3) The black slurry was filtered and washed with water until neutral. The solid filter cake after filtration was placed in an oven at 105°C and dried to obtain fine and coarse slag from acid-washed coal gasification.

[0033] The phase composition of the fine and coarse coal gasification slags before and after acid washing was analyzed by elemental analysis and X-ray fluorescence spectrometry. The results are shown in Table 1.

[0034] Table 1. Composition and distribution of coal gasification slag and pickling slag

[0035]

[0036] (II) Design of the blending ratio of pickling fine slag and coarse slag

[0037] 1) Theoretical amount of SiO2 and C used in the synthesis of silicon carbide

[0038] Main reaction: SiO2 (s) + 3C (s) = SiC + 2CO (g) (1)

[0039] Molar ratio: 1 3 1 2

[0040] Theoretical dosage: 60.09g 36.03g 40.09g

[0041] 1g 0.60g 0.67g

[0042] 2) Design of the blending ratio of fine and coarse pickling residue

[0043] When HCGFS is used alone for Joule heating to prepare materials, the SiO2 / C (mass ratio) in HCGFS is approximately 1, resulting in excessive residual carbon content from the consumption of silica. This requires sintering in a muffle furnace to remove the remaining residual carbon. Therefore, HCGFS is compounded with HCGCS, and the SiO2 / C mass ratio in the compounded raw materials is designed to be 1.68, 2, 3, and 4 to completely consume the residual carbon resources in the coal gasification slag.

[0044] Based on 1g HCGFS, the following compounding was performed:

[0045]

[0046] in 1g 43.42%, 65.42%, 41.40%, : 12.52%.

[0047] Substituting into the formula, we can deduce m. HCGCS Dosage.

[0048] (III) Preparation of silicon carbide by Joule heating of compound slag

[0049] Example 1:

[0050] Step 1: Place 1g of acid-washed coal gasification fine slag in a zirconia ball mill jar and obtain a uniformly mixed carbon-rich silicon source powder in a planetary ball mill; the volume ratio of the mixed slag to the zirconia balls during the ball milling process is 1:1, the ball milling speed is 700 r / min, and the time is 2h.

[0051] Step 2: Transfer the carbon-rich silicon source powder into the graphite boat carrier, then place the graphite boat in the Joule heating device, introduce nitrogen as a protective gas, balance the pressure in the reactor to 0.015 MPa, set the current of the Joule heating device to 461.53 A, the reaction temperature to 2000℃, and the residence time to 45 s, so that the mixture in the graphite boat reacts under high temperature and air-isolated conditions.

[0052] Step 3: The reaction products in the graphite boat from Step 2 are heated to 1000°C in a muffle furnace at a heating rate of 10°C / min.

[0053] Step 4: The calcined product from Step 3 was mixed with a mixture of acids (HF and 3 mol / L HCl in a volume ratio of 1:1) at a solid-liquid ratio of 1:20. The mixture was then ultrasonically washed at 50 °C for 120 min to remove impurities. Following this, the mixture was filtered to obtain silicon carbide with a crystallinity of 32.64%. The XRD patterns of the silicon carbide material before and after impurity removal are shown below. Figure 1 As shown.

[0054] Example 2:

[0055] Step 1: Mix 1g of acid-washed coal gasification fine slag and 0.5886g of coarse slag in a zirconia ball mill jar and obtain a uniformly mixed carbon-rich silicon source powder in a planetary ball mill; the volume ratio of the mixed slag to the zirconia balls during the ball milling process is 1:1, the ball milling speed is 700 r / min, and the time is 2h.

[0056] Step 2: Transfer the carbon-rich silicon source powder into the graphite boat carrier, then place the graphite boat in the Joule heating device, introduce nitrogen as a protective gas, balance the pressure in the reactor to 0.015 MPa, set the current of the Joule heating device to 461.53 A, the reaction temperature to 2000℃, and the residence time to 45 s, so that the mixture in the graphite boat reacts under high temperature and air-isolated conditions.

[0057] Step 3: The reaction products in the graphite boat from Step 2 are heated to 1000°C in a muffle furnace at a heating rate of 10°C / min.

[0058] Step 4: The calcined product from Step 3 was mixed with a mixture of acids (HF and 3 mol / L HCl in a volume ratio of 1:1) at a solid-liquid ratio of 1:20. The mixture was then ultrasonically washed at 50 °C for 120 min to remove impurities. Following this, it was filtered to obtain highly crystalline silicon carbide with a crystallinity of 62.81%. The XRD patterns of the silicon carbide material before and after impurity removal are shown below. Figure 2 As shown.

[0059] Example 3:

[0060] Step 1: Mix 1g of acid-washed coal gasification fine slag and 0.9752g of coarse slag in a zirconia ball mill jar and obtain a uniformly mixed carbon-rich silicon source powder in a planetary ball mill; the volume ratio of the mixed slag to the zirconia balls during the ball milling process is 1:1, the ball milling speed is 700 r / min, and the time is 2h.

[0061] Step 2: Transfer the carbon-rich silicon source powder into the graphite boat carrier, then place the graphite boat in the Joule heating device, introduce nitrogen as a protective gas, balance the pressure in the reactor to 0.015 MPa, set the current of the Joule heating device to 461.53 A, the reaction temperature to 2000℃, and the residence time to 45 s, so that the mixture in the graphite boat reacts under high temperature and air-isolated conditions.

[0062] Step 3: The reaction products in the graphite boat from Step 2 are heated to 1000°C in a muffle furnace at a heating rate of 10°C / min.

[0063] Step 4: The calcined product from Step 3 was mixed with a mixture of acids (HF and 3 mol / L HCl in a volume ratio of 1:1) at a solid-liquid ratio of 1:20. The mixture was then ultrasonically washed at 50 °C for 120 min to remove impurities. Following this, it was filtered to obtain highly crystalline silicon carbide with a crystallinity of 62.86%. The XRD patterns of the silicon carbide material before and after impurity removal are shown below. Figure 3 As shown.

[0064] Example 4:

[0065] Step 1: Mix 1g of acid-washed coal gasification fine slag and 3.0072g of coarse slag in a zirconia ball mill jar and obtain a uniformly mixed carbon-rich silicon source powder in a planetary ball mill; the volume ratio of the mixed slag to the zirconia balls during the ball milling process is 1:1, the ball milling speed is 700 r / min, and the time is 2h.

[0066] Step 2: Transfer the carbon-rich silicon source powder into the graphite boat carrier, then place the graphite boat in the Joule heating device, introduce nitrogen as a protective gas, balance the pressure in the reactor to 0.015 MPa, set the current of the Joule heating device to 461.53 A, the reaction temperature to 2000℃, and the residence time to 45 s, so that the mixture in the graphite boat reacts under high temperature and air-isolated conditions.

[0067] Step 3: The reaction products in the graphite boat from Step 2 are heated to 1000°C in a muffle furnace at a heating rate of 10°C / min.

[0068] Step 4: The calcined product from Step 3 was mixed with a mixture of acids (HF and 3 mol / L HCl in a volume ratio of 1:1) at a solid-liquid ratio of 1:20. The mixture was then ultrasonically washed at 50 °C for 120 min to remove impurities. Following this, it was filtered to obtain highly crystalline silicon carbide with a crystallinity of 67.66%. The XRD patterns of the silicon carbide material before and after impurity removal are shown below. Figure 4 As shown.

[0069] Example 5:

[0070] Step 1: Mix 1g of acid-washed coal gasification fine slag and 7.9648g of coarse slag in a zirconia ball mill jar and obtain a uniformly mixed carbon-rich silicon source powder in a planetary ball mill; the volume ratio of the mixed slag to the zirconia balls during the ball milling process is 1:1, the ball milling speed is 700 r / min, and the time is 2h.

[0071] Step 2: Transfer the carbon-rich silicon source powder into the graphite boat carrier, then place the graphite boat in the Joule heating device, introduce nitrogen as a protective gas, balance the pressure in the reactor to 0.015 MPa, set the current of the Joule heating device to 461.53 A, the reaction temperature to 2000℃, and the residence time to 45 s, so that the mixture in the graphite boat reacts under high temperature and air-isolated conditions.

[0072] Step 3: The reaction products in the graphite boat from Step 2 are heated to 1000°C in a muffle furnace at a heating rate of 10°C / min.

[0073] Step 4: The calcined product from Step 3 was mixed with a mixture of acids (HF and 3 mol / L HCl in a volume ratio of 1:1) at a solid-liquid ratio of 1:20. The mixture was then ultrasonically washed at 50 °C for 120 min to remove impurities. Following this, the mixture was filtered to obtain highly crystalline silicon carbide with a crystallinity of 63.24%. The XRD patterns of the silicon carbide material before and after impurity removal are shown below. Figure 5 As shown.

Claims

1. A method for producing silicon carbide from coal gasification coarse slag in cooperation with fine slag, characterized by, The method comprises the following steps: S1. acid washing and ball milling mixing pretreatment; The impurity removal treatment is performed by using an acid immersion solution with a molar concentration of 3 mol / L, and specifically comprises the following sub-steps: S1.

1. The coal gasification fine slag and coarse slag are dried in a 105°C oven and then sealed and stored for standby; S1.

2. A 3 mol / L HCl solution is prepared, and the dried coal gasification fine slag and coarse slag are respectively added into the prepared HCl solution at a solid-liquid mass ratio of 1:10, heated and stirred in a magnetic stirrer at 60°C for 5h to obtain a black slurry; S1.

3. The black slurry is filtered and washed to neutral, and the solid filter cake after suction filtration is dried in a 105°C oven to obtain acid-washed coal gasification fine slag and coarse slag; S1.

4. The acid-washed coal gasification fine slag and coarse slag are placed in a zirconia ball milling tank, and a uniformly mixed carbon-rich and silicon source powder is obtained in a planetary ball mill; S2. Joule heating thermal shock treatment; The carbon-rich and silicon source powder is transferred into a graphite boat carrier, and then the graphite boat is placed in a Joule heating device, nitrogen gas is introduced as a protective gas, the pressure in the reactor is balanced to 0.015 MPa, and the mixture in the graphite boat is reacted in a high-temperature air-tight state; S3. Calcination purification treatment; The reaction product in the graphite boat is calcined in a muffle furnace; The calcined product is mixed with mixed acid, ultrasonically washed at 50°C for 120 min to remove impurities, and then suction filtered to obtain high-crystallinity silicon carbide.

2. The method according to claim 1, wherein the method is characterized by, In S2, the current of the Joule heating device is set to 461.53 A, the reaction temperature is 2000°C, and the residence time is 45s.

3. The method according to claim 1, wherein the method is characterized by, In S3, the reaction product in the graphite boat is heated to 1000°C at a temperature rising speed of 10°C / min in a muffle furnace.

4. The method according to claim 1, wherein the method is characterized by, The volume ratio of HF to 3 mol / L HCl in the mixed acid is 1:1.

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