Method for preparing metakaolin with high whiteness and high oil absorption value from coal series kaolin

Abstract

The invention relates to the technical field of calcined kaolin, and particularly provides a method for preparing metakaolin with high whiteness and high oil absorption value from coal series kaolin.The method comprises the steps that coal gangue raw ore is subjected to superfine grinding, sieving and grading, and coal gangue powder is obtained; the method comprises the following steps: inputting a material into a high-pressure mixing reaction kettle, introducing high-pressure gas into the high-pressure mixing reaction kettle, stirring at a high speed for a certain time, inputting into a spiral feeder, transporting to a high-pressure furnace tube for calcining and decarburizing, enabling the material to stay in an oxidation section for a period of time, then transporting to a reduction section in the high-pressure furnace tube, and staying for a period of time; and then atomizing and spraying the binder into the material in the reduction section through a high-pressure nozzle to form a secondary structure, performing cyclone separation on the material, and quickly cooling to finally obtain the metakaolin with high whiteness and high oil absorption value. The method has the beneficial effects that the coal gangue is calcined and decarbonized under the conditions of lower temperature and shorter time, and the whiteness, the specific surface area, the oil absorption value and other indexes of a metakaolin product are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of calcined kaolin, in particular to a method for preparing high-whiteness high-oil-absorption-value metakaolin from coal-based kaolin. BACKGROUND

[0002] Metakaolin is a high-activity mineral admixture, which is an amorphous aluminosilicate formed by low-temperature calcination (600-900℃) of kaolin, and has excellent pozzolanic activity. It is widely used in high-performance concrete additives (to improve the strength and structural stability of concrete), petroleum catalytic cracking (FCC) catalysts (to improve the gasoline recovery rate), and color decorative mortar. Generally, metakaolin products with a whiteness of ≥85 are in demand.

[0003] Currently, high-quality metakaolin products on the international market are mainly obtained by fine processing and calcination of water-washed kaolin (US20020088376A1, EP3426730B1, US6379452B1), and have high whiteness and high oil absorption value. Such products have a large market size and high added value. For example, BASF's Satintone5HB product has an oil absorption value of 85 and a price of more than 5000 yuan / t.

[0004] In recent years, the processing technology of coal-based kaolin in China has developed rapidly, and a series of superfine high-whiteness calcined kaolin products have been developed (CN110577225B, CN109748286B, CN107601518A). However, compared with imported calcined kaolin, the oil absorption value of the products is still relatively low, about 75. Studies have shown that calcined kaolin from different regions has significant differences in product performance, especially in oil absorption value, due to differences in raw ore origin and processing technology. Generally, water-washed kaolin is easier to exfoliate, and the product has a good preservation of sheet structure and a low sheet thickness after superfine grinding and calcination, so the porosity of the aggregate structure is high, and the oil absorption value is high. Relatively speaking, coal-based kaolin is affected by mineral deposition and organic carbon components, and the superfine grinding process causes greater damage to the kaolin sheet structure and a higher sheet thickness, making it difficult to improve the large pore structure and porosity, resulting in a bottleneck problem in the improvement of oil absorption value. For coal gangue with an iron content of more than 0.6wt%, the whiteness can be greater than 90 after high-temperature calcination at more than 900 degrees, but the oil absorption value is generally only 65-75. When calcined at a lower temperature of about 850 degrees, the oil absorption value can reach 85, but the whiteness generally cannot be higher than 88.

[0005] Overall, high-whiteness kaolin products produced from coal-based kaolin still have problems such as low whiteness at low temperature and low oil absorption value, and cannot meet the needs of high-end market applications. SUMMARY

[0006] Therefore, in view of the problems in the preparation of metakaolin by the conventional calcination method, in order to greatly improve the whiteness and oil absorption value of the high-whiteness high-oil-absorption metakaolin product prepared from the coal-based kaolin, the embodiment of the present application provides a method for preparing high-whiteness high-oil-absorption metakaolin from coal-based kaolin.

[0007] The embodiment of the present application provides a method for preparing high-whiteness high-oil-absorption metakaolin from coal-based kaolin, which specifically comprises the following steps: Step 1: Ultrafine grinding of coal gangue After the ultrafine grinding, sieving and grading of the raw coal gangue, the coal gangue powder is obtained; Step 2: High-pressure preheating The center temperature of the calcination section and the reduction section of the high-pressure furnace tube of the high-pressure multi-stage calcination rotary kiln is preheated to a specified temperature, and after the temperature of the furnace body reaches equilibrium, high-pressure oxygen is input into the high-pressure furnace tube through the high-pressure oxygen pipeline; Step 3: High-pressure material mixing The coal gangue material is input into the high-pressure mixing reaction kettle, and then high-pressure gas is introduced into the high-pressure mixing reaction kettle through the high-pressure pipeline, and high-speed stirring is carried out for a certain period of time to obtain coal gangue material rich in high-pressure oxygen.

[0008] Step 4: High-pressure oxidation calcination The material in the high-pressure mixing reaction kettle is input into the screw feeder and transported at a uniform speed to the high-pressure furnace tube for calcination and decarburization, and the rotation speed is adjusted to make the material stay in the oxidation section for a period of time to obtain metakaolin.

[0009] Step 5: High-pressure reduction calcination The calcined kaolin is transported to the reduction section of the high-pressure furnace tube, high-pressure reducing gas is introduced, and the material stays for a period of time to obtain high-whiteness metakaolin.

[0010] Step 6: Instant sintering calcination The binder is atomized and sprayed into the material in the reduction section of the high-pressure furnace tube through the high-pressure nozzle, and after staying for a period of time, it enters the kiln tail; Step 7: Discharge and cooling The material is discharged through the cyclone separation equipment and quickly cooled to obtain high-whiteness high-oil-absorption metakaolin.

[0011] Further, the coal gangue contains 0.3-0.9wt% of iron, and the particle size is 200-5000 mesh; Further, the center temperature of the calcination section of the high-pressure furnace tube is 300-800℃, and the center temperature of the reduction section is 200-900℃; Further, the high-pressure oxygen in step 2 is a mixed gas containing oxygen, the gas pressure is 0.5-10.0Mpa, and the oxygen content is 20%-100%.

[0012] Further, the high-pressure gas in step 3 is a mixed gas containing oxygen, the gas pressure is 0.5-10.0 Mpa, the oxygen content is 20%-100%, and the residence time is 0.2-1 min.

[0013] Further, the material in step 4 includes a mixed gas containing oxygen, the gas pressure is 0.5-10.0 Mpa, the oxygen content is 20%-100%, and the residence time is 10-60 min.

[0014] Further, the high-pressure reducing gas in step 5 is carbon monoxide, hydrogen or other mixed gas containing reducing gas, the gas pressure is 0.5-10.0 Mpa, the reducing gas content is 20%-100%, and the residence time is 1-30 min.

[0015] Further, the binder in step 6 is aluminum sol, silica sol, water glass or ultra-fine kaolin binder, the pressure is 0.5-10.0 Mpa, the flow rate is 1-100 m / s, the high-pressure pipeline jet angle is 60°-90°, and the residence time is 1-3 min.

[0016] The technical scheme provided by the embodiment of the present application has the following beneficial effects: 1. The method for preparing high-whiteness high-oil-absorption-value meta-kaolin from coal-based kaolin can accelerate the oxidation of fixed carbon and other non-combustible substances in coal gangue under high-pressure oxygen-rich conditions, so that the calcination and decarburization of coal gangue can be realized at a lower temperature and in a shorter time, thereby greatly reducing the energy consumption of the calcination process and the production cost of the product. 2. The method for preparing high-whiteness high-oil-absorption-value meta-kaolin from coal-based kaolin can realize the low-temperature rapid combustion of fixed carbon, the low-temperature rapid oxidation of impurity minerals and the rapid reduction and passivation of color impurities such as hematite in coal gangue during the calcination process through the control of pressure, temperature and its gradient, atmosphere and its gradient, and rotation speed. 3. The method for preparing high-whiteness high-oil-absorption-value meta-kaolin from coal-based kaolin can further improve the oil absorption value index of kaolin through the transient sintering calcination process, which is helpful for the development of high-oil-absorption-value kaolin products. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The figure is a process flow chart of the method for preparing high-whiteness high-oil-absorption-value meta-kaolin from coal-based kaolin. DETAILED DESCRIPTION

[0018] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the embodiments of the present application with reference to the accompanying drawings. The following describes a preferred one of the multiple possible embodiments of the present application, which is intended to provide a basic understanding of the present application, but is not intended to identify key or decisive elements or limit the scope of protection.

[0019] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of example embodiments can have different values.

[0020] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered as part of the specification where appropriate.

[0021] As shown in Figure 1 The method for preparing high-whiteness high-oil-absorption-value metakaolin from coal gangue according to the present application is as follows: Example 1 (high-whiteness high-oil-absorption-value metakaolin) Step 1: Ultrafine grinding of coal gangue After ultrafine grinding, sieving and grading of raw coal gangue, coal gangue powder is obtained, which has an iron content of 0.65 wt%.

[0022] Step 2: High-pressure preheating The center temperature of the calcination section of the high-pressure furnace tube is preheated to 700°C and the center temperature of the reduction section is preheated to 650°C by an electromagnetic induction heating coil device. After the furnace body temperature reaches equilibrium, high-pressure oxygen is input into the high-pressure furnace tube through a high-pressure oxygen pipeline, with a gas pressure of 5.0 Mpa and an oxygen content of 95%, and the rest being air components.

[0023] Step 3: High-pressure material mixing The coal gangue material in the feed bin is input into the high-pressure mixing reaction kettle. High-pressure gas is passed into the high-pressure mixing reaction kettle through a high-pressure pipeline for high-speed stirring of the material, with a gas pressure of 5.0 Mpa, an oxygen content of 95%, and the rest being air components, to obtain coal gangue material rich in high-pressure oxygen.

[0024] Step 4: High-pressure oxidation calcination The material in the high-pressure mixing reaction kettle is input into the screw feeder and transported at a uniform speed to the high-pressure furnace tube for calcination and decarburization. The rotation speed is adjusted so that the residence time of the material in the oxidation section is 30 min, to obtain metakaolin. At the same time that the material is input into the screw feeder, the valves of the feed bin, high-pressure mixing reaction kettle, high-pressure oxygen pipeline, and screw feeder are sequentially controlled to perform stirring and delivery of the next batch of material.

[0025] Step 5: High-pressure reduction calcination The metakaolin is transported to the reduction section of the high-pressure furnace tube, with a residence time of 5 min, a gas pressure of 3.0 Mpa, a carbon monoxide content of 90%, and the rest being air components.

[0026] Step 6: Instant sintering calcination The binder is atomized and sprayed into the material in the reduction section of the high-pressure furnace tube through the high-pressure nozzle, and after a period of residence, it enters the kiln tail; Step 7: Discharge cooling The material is discharged through the cyclone separation equipment and quickly cooled to obtain metakaolin with high whiteness and high oil absorption value.

[0027] Example 2 (metakaolin with ultra-high whiteness and high oil absorption value) Step 1: Ultrafine grinding of coal gangue After ultrafine grinding, sieving, and grading of the raw coal gangue, a coal gangue powder is obtained, with an iron content of 0.35wt%.

[0028] Step 2: High-pressure preheating The center temperature of the calcination section of the high-pressure furnace tube is preheated to 700℃, and the center temperature of the reduction section is preheated to 650℃ by an electromagnetic induction heating coil device. After the furnace body temperature reaches equilibrium, high-pressure oxygen is input into the high-pressure furnace tube through the high-pressure oxygen pipeline, with a gas pressure of 5.0 Mpa, an oxygen content of 95%, and the rest being air components.

[0029] Step 3: High-pressure material mixing The coal gangue material in the feed bin is input into the high-pressure mixing reaction kettle. High-pressure gas is introduced into the high-pressure mixing reaction kettle through the high-pressure pipeline for high-speed stirring of the material, with a gas pressure of 5.0 Mpa, an oxygen content of 95%, and the rest being air components, to obtain coal gangue material rich in high-pressure oxygen.

[0030] Step 4: High-pressure oxidation calcination The material in the high-pressure mixing reaction kettle is input into the screw feeder and transported at a uniform speed to the high-pressure furnace tube for calcination and decarburization. The rotation speed is adjusted to make the residence time of the material in the oxidation section 30 min, and metakaolin is obtained. At the same time that the material is input into the screw feeder, the valves of the feed bin, high-pressure mixing reaction kettle, high-pressure oxygen pipeline, and screw feeder are sequentially controlled to stir and transport the next batch of material.

[0031] Step 5: High-pressure reduction calcination The metakaolin is transported to the reduction section of the high-pressure furnace tube, with a residence time of 5 min, a gas pressure of 3.0 Mpa, a carbon monoxide content of 90%, and the rest being air components.

[0032] Step 6: Instant sintering calcination The binder is atomized by a high-pressure nozzle and sprayed into the material in the reduction section of the high-pressure furnace tube, and after staying for a period of time, it enters the kiln tail; Step 7: discharging and cooling The material is discharged through a cyclone separation device, and high-whiteness high-oil-absorption-value metakaolin is obtained after rapid cooling.

[0033] Comparative Example 1 (calcination of metakaolin by a conventional rotary kiln) Step 1: superfine grinding of coal gangue After superfine grinding, sieving and grading of the raw coal gangue, a coal gangue powder is obtained, which has an iron content of 0.65wt%.

[0034] Step 2: preheating The center temperature of the calcination section of the high-pressure furnace tube is preheated to 850℃ by an electromagnetic induction heating coil device, and air is introduced, and the temperature of the furnace body reaches equilibrium.

[0035] Step 3: reduction-oxidation calcination The material is input into the screw feeder and transported uniformly to the rotary kiln furnace tube for calcination and decarburization, and the total residence time of the material in the reduction section and the oxidation section is adjusted to 90min, and metakaolin is obtained.

[0036] Step 4: discharging and cooling The material is discharged from the cooling section into the kiln tail, and is discharged through the lower discharge port, and high-whiteness metakaolin is obtained after rapid cooling.

[0037] Comparative Example 2 (calcination of kaolin by a conventional rotary kiln) Step 1: superfine grinding of coal gangue After superfine grinding, sieving and grading of the raw coal gangue, a coal gangue powder is obtained, which has an iron content of 0.65wt%.

[0038] Step 2: preheating The center temperature of the calcination section of the high-pressure furnace tube is preheated to 900℃ by an electromagnetic induction heating coil device, and air is introduced, and the temperature of the furnace body reaches equilibrium.

[0039] Step 3: reduction-oxidation calcination The material is input into the screw feeder and transported uniformly to the rotary kiln furnace tube for calcination and decarburization, and the total residence time of the material in the reduction section and the oxidation section is adjusted to 90min, and calcined kaolin is obtained.

[0040] Step 4: discharging and cooling The material is discharged from the cooling section into the kiln tail, and is discharged through the lower discharge port, and high-whiteness calcined kaolin is obtained after rapid cooling.

[0041] Comparative Example 3 (calcination of metakaolin by a conventional rotary kiln) Step 1: superfine grinding of coal gangue The coal gangue raw ore is ultra-finely ground, sieved and graded to obtain a coal gangue powder with an iron content of 0.35wt%.

[0042] Step 2: preheating The center temperature of the calcination section of the high-pressure furnace tube is preheated to 850°C by an electromagnetic induction heating coil device, air is introduced, and the furnace body temperature reaches equilibrium.

[0043] Step 3: reduction-oxidation calcination The material is input into the screw feeder and uniformly transported to the rotary kiln furnace tube for calcination decarburization, and the rotation speed is adjusted to make the total residence time of the material in the reduction section and the oxidation section 60 min, to obtain metakaolin.

[0044] Step 4: discharging and cooling The material is discharged from the cooling section into the kiln tail, discharged through the lower discharge port, and high-whiteness metakaolin is obtained after rapid cooling.

[0045] Results detection and analysis The whiteness, specific surface area and oil absorption value of the products of Examples 1-2 and Comparative Examples 1-3 are shown in Table 1.

[0046] As can be seen from the data of Comparative Example 1 and Comparative Example 2, the conventional rotary kiln calcined metakaolin, even at 850°C or 900°C for 90 min, cannot obtain high-whiteness metakaolin products. As can be seen from the data of Comparative Example 3, the lower the iron content, the higher the product whiteness when the conventional rotary kiln is at 850°C for 60 min, however, the product activity and specific surface area are still insufficient, and it does not belong to high-quality metakaolin products.

[0047] In contrast, Examples 1-2 using the technology of the present application only need to be heated at 700°C for 35 min to obtain high-whiteness metakaolin products, not only can the whiteness be improved by 3-4 percentage points, but also the calcination temperature is reduced by 150 degrees, the calcination time is halved, and it has high activity and large specific surface area, with a specific surface area of up to 65.4m 2 / g, an oil absorption value of up to 95-120, and product indicators reaching the level of international mainstream high-end metakaolin products, which can meet the needs of high-end application scenarios such as high-end papermaking, high-performance concrete mortar, rubber reinforcing filler, FCC catalyst substrate and heavy metal adsorption material.

[0048] Table 1. Whiteness, specific surface area and oil absorption value of each example and comparative example.

[0049]

[0050] The method for preparing high-whiteness high-oil-absorption-value partial kaolin from coal-based kaolin of the present application can accelerate the oxidation of non-combustible substances such as fixed carbon in coal gangue under high-pressure oxygen-rich conditions, realize the calcination decarburization of coal gangue at lower temperature and shorter time, greatly reduce the energy consumption of the calcination process, and reduce the production cost of the product. Through the control of pressure, temperature and its gradient, atmosphere and its gradient, rotation speed, and the transient sintering calcination process, the oil absorption value index of kaolin is further improved, and the whiteness, specific surface area and oil absorption value and other indexes of the calcined kaolin product are greatly improved.

[0051] In the case of no conflict, the above-mentioned embodiments and features in the embodiments can be combined with each other. The above-mentioned only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin, characterized in that, Includes the following steps: Step 1: Ultrafine grinding of coal gangue Coal gangue ore is ultra-finely ground, sieved, and classified to obtain coal gangue powder; Step 2: High-pressure preheating The calcination section and reduction section center temperature of the high-pressure furnace tube of the high-pressure multi-stage calcination rotary kiln are preheated to the specified temperature. After the furnace body temperature reaches equilibrium, the high-pressure oxygen pipeline is opened to input high-pressure oxygen into the high-pressure furnace tube. Step 3: High-pressure material mixing Coal gangue material is fed into a high-pressure mixing reactor, and then high-pressure gas is introduced into the high-pressure mixing reactor through a high-pressure pipeline for high-speed stirring for a certain period of time to obtain coal gangue material rich in high-pressure oxygen. Step 4: High-pressure oxidation calcination The material in the high-pressure mixing reactor is fed into the screw feeder and transported at a uniform speed to the high-pressure furnace tube for calcination and decarburization. The rotation speed is adjusted so that the material stays in the oxidation section for a period of time to obtain metakaolin. Step 5: High-pressure reduction calcination The calcined kaolin is transferred to the reduction section inside the high-pressure furnace tube, where high-pressure reducing gas is introduced and the mixture is left to stand for a period of time to obtain high-whiteness metakaolin. Step 6: Transient sintering and calcination The binder is atomized and sprayed into the material in the reduction section of the high-pressure furnace tube through a high-pressure nozzle, and after staying for a period of time, it enters the kiln tail. Step 7: Discharge and Cooling The material is discharged through a cyclone separator and rapidly cooled to obtain metakaolin with high whiteness and high oil absorption value.

2. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, The coal gangue mentioned in step 1 has an iron content of 0.3~0.9wt% and a particle size of 200~5000 mesh.

3. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, In step 2, the center temperature of the calcination section of the high-pressure furnace tube is 300~800℃, and the center temperature of the reduction section is 200~900℃.

4. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, The high-pressure oxygen mentioned in step 2 is a mixture of oxygen-containing gases with a gas pressure of 0.5~10.0 MPa and an oxygen content of 20%~100%.

5. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, The high-pressure gas mentioned in step 3 is a mixed gas containing oxygen, with a gas pressure of 0.5~10.0 MPa and an oxygen content of 20%~100%; the residence time is 0.2~1 min.

6. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, The material described in step 4 includes a mixed gas containing oxygen, with a gas pressure of 0.5~10.0 MPa and an oxygen content of 20%~100%; the residence time is 10~60 min.

7. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, The high-pressure reducing gas mentioned in step 5 is a mixed gas containing reducing gas, with a gas pressure of 0.5~10.0 MPa and a reducing gas content of 20%~100%; the residence time is 1~30 min.

8. The method for preparing high-whiteness, high-oil-absorption metakaolin from coal-series kaolin as described in claim 1, characterized in that, The binder mentioned in step 6 is aluminum sol, silica sol, water glass or ultrafine kaolin binder, with a pressure of 0.5~10.0 MPa and a flow rate of 1~100 m / s; the high-pressure pipeline spray angle is 60°~90°; and the residence time is 1~3 min.

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