Method for preparing coal and calcined kaolin from coal gangue through step grinding, step selection, acid leaching and suspension calcination

Abstract

The invention discloses a method for preparing coal and calcined kaolin through coal gangue grinding and grading-acid leaching-suspension calcination, and belongs to the technical field of coal gangue beneficiation. According to the method disclosed by the invention, the three stages of ore grinding flotation, acid leaching purification and fine grinding calcination complement each other, so that fine-grained calcined kaolin of which the content of-7 microns is greater than or equal to 90% and the whiteness is greater than or equal to 90% and ultrafine-grained calcined kaolin of which the content of-2 microns is greater than or equal to 90% and the whiteness is greater than or equal to 90% are prepared. According to the method, effective separation of coarse coal, leaching and purification of impurity iron elements and calcination and purification of fine-grained kaolin are realized through step grinding and step separation; the gas-solid reaction degree is improved and sintering is avoided by utilizing the dispersion and suspension characteristics of fine-particle materials; the dehydroxylation and decarburization reactions can be carried out completely by calcining fine materials and precisely controlling the temperature, so that the whiteness of the calcined kaolin product is remarkably improved. According to the method, the adaptability to coal gangue raw ore is improved, and meanwhile, a new thought is provided for efficiently preparing a calcined kaolin product from the coal gangue and cooperatively recycling coal resources.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal gangue beneficiation, and particularly relates to a method for preparing coal and calcined kaolin through coal gangue step-by-step grinding and beneficiation-acid leaching-suspension calcination. BACKGROUND

[0002] Coal gangue is a solid waste generated in the process of coal mining and washing, mainly composed of kaolinite, quartz and carbonaceous matter. Long-term storage of coal gangue not only occupies a large amount of land, but also pollutes the surrounding environment due to rainwater leaching. At the same time, coal gangue contains rich aluminum resources and a large amount of useful mineral components such as kaolin, and is a solid waste resource with utilization value. Due to the low activity of coal gangue itself, its utilization efficiency is not high. The preparation of kaolin by calcining coal gangue is an important way to realize the high-value utilization of solid waste. In the industrial production process, rotary kiln and tunnel kiln are two mainstream calcining equipment. Rotary kiln relies on the rotation of the inclined cylinder to realize the continuous turnover of the material, so that the coal gangue successively experiences the process stages of preheating, high-temperature reaction and heat preservation; the tunnel kiln adopts the loading mode of the sagger, so that the material passes through different temperature zones in the fixed container, but the static stacking characteristics lead to low heat conduction efficiency and easy sintering and agglomeration. As the key process affecting the whiteness, activity and crystal structure of the product, the performance of the calcining equipment directly determines the quality characteristics of the final product. At present, there are technical bottlenecks such as high sintering rate of the material, insufficient temperature field control precision and the like in the industrial application, especially the problems such as unqualified product whiteness caused by insufficient internal reaction of large particle materials, which seriously restrict the development of the industry. Breaking through the technical limitations of traditional calcining equipment and developing efficient coal gangue resource utilization process have become the key to promoting the resource utilization of solid waste. In addition, the direct acid leaching efficiency of the leaching process of coal gangue is low, and usually needs to be combined with mechanical grinding pretreatment to improve the leaching rate of impurity iron elements, in which process, challenges such as poor leaching selectivity and large acid consumption are faced. In the grinding process, the particle size control of coal gangue directly affects the subsequent acid leaching reaction rate and leaching rate, but the traditional grinding process has problems such as high energy consumption and uneven fineness. SUMMARY

[0003] In view of the problems existing in the current coal gangue preparation coal and calcined kaolin process, including poor adaptability to high-impurity coal gangue, easy ring formation of rotary kiln equipment, incomplete internal reaction due to large material particle size, and poor whiteness, etc., the present application innovatively proposes a coal gangue step-by-step grinding and separation-acid leaching-suspension calcination method for preparing coal and calcined kaolin, which realizes effective separation of coarse-grained coal, impurity iron element leaching and purification, and calcination and purification of fine-grained kaolin through step-by-step grinding and separation, improves the adaptability to coal gangue raw ore, and utilizes the dispersion and suspension characteristics of fine-grained materials in the suspension calcination process to improve the gas-solid reaction degree and avoid sintering; through fine-grained material calcination, combined with precise temperature control, the dehydroxylation and decarburization reactions can be completely performed, and the whiteness of the calcined kaolin product is improved. The present application expects to provide a new method for efficient preparation of calcined kaolin product from coal gangue and simultaneous recovery of coal resources.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0005] A coal gangue step-by-step grinding and separation-acid leaching-suspension calcination method for preparing coal and calcined kaolin, comprising the following steps:

[0006] Step 1, ore grinding operation: the coal gangue raw ore is fed into a ball mill to be ground to a-0.074mm content of 40%~80%, obtaining a finely ground coal gangue product;

[0007] Step 2, flotation operation: the flotation operation can effectively separate coal and kaolin in the coal gangue, and reduce the iron and carbon impurities in the kaolin. The finely ground coal gangue product is fed into a flotation device for roughing, multi-stage cleaning (number of stages≥1) and multi-stage scavenging (number of stages≥1) operations, under the conditions of a flotation collector dosage of 500g / t~800g / t, a water glass dosage of 100g / t~300g / t, a frother dosage of 100g / t~400g / t, and a pulp temperature of room temperature, obtaining a flotation concentrate and a flotation tailings; the flotation concentrate is coal with a carbon content≥45%; the flotation tailings are kaolin primary product with a carbon content≤6% and a Fe2O3 content≤1.5%;

[0008] Step 3, acid leaching operation: the leaching process can selectively dissolve iron elements, reducing their impact on the whiteness of kaolin. The flotation tailings are subjected to acid leaching to obtain a kaolin leaching product; the leaching agent used in the acid leaching process includes HCl, H2SO4, and oxalic acid, the leaching time is 1h~4h, the leaching temperature is 60℃~90℃, and the leaching agent dosage is 5%~15%; the Fe2O3 content in the kaolin leaching product is≤0.35%;

[0009] Step 4, fine grinding operation: a ceramic ball stirring mill is used for fine grinding of the leaching product for preparing fine-grained kaolin; the ceramic ball stirring mill grinding time is 0.7h~1.5h, and the fine-grained kaolin product has a particle size of-7μm with a content≥90%;

[0010] Step 5, dewatering and dispersing operation: the fine particle kaolin is fed into a filter press for dewatering and pressure filtration to obtain a dewatered product, the water content of the dewatered product being ≤10%; the dewatered product is further dewatered in a drying machine, the drying temperature being 160-170 DEG C, and the dispersed product is obtained by dispersing the material in a dispersing machine, the water content being ≤3%;

[0011] Step 6, suspension calcination operation: the calcination and purification process can improve the whiteness of kaolin and obtain high-quality calcined kaolin product. The dispersed product is fed into a suspension calcination and purification furnace, the material is effectively decomposed by calcination, and the surface and interlayer hydroxyl groups are removed, thereby improving the whiteness. The suspension state purification calcination temperature is 850-950 DEG C, the time is 1.5-2.5h, the calcination atmosphere is air, and the calcined product is calcined kaolin.

[0012] Step 7, product grading operation: the calcined kaolin product is cooled and sieved and graded, the product with a content of-7 μm ≥90% is a fine particle calcined kaolin product, and the qualified product with a whiteness ≥90% is obtained; the product with a content of-2 μm ≥90% is an ultra-fine particle calcined kaolin product, and the qualified product with a whiteness ≥90% is obtained.

[0013] The present application mainly comprises three parts of ore grinding and flotation, acid leaching and purification, and fine grinding and calcination. The ore grinding and flotation part comprises ore feeding and grinding operation and flotation operation; the acid leaching and purification part comprises acid leaching operation; and the fine grinding and calcination comprises fine grinding operation, dewatering and dispersing operation, suspension calcination operation, and product grading operation.

[0014] Compared with the existing method for preparing calcined kaolin from coal gangue, the present application has the following characteristics and advantages:

[0015] 1. Compared with the existing crushing-rotary kiln calcination-fine grinding process, the present application proposes a method of step-by-step grinding and step-by-step selection-acid leaching-suspension calcination, adopts two-stage ore grinding, and adds ore grinding-flotation-acid leaching operation before calcination, realizes separation of coal from coal gangue and effective removal of iron impurities, effectively improves the adaptability to coal gangue with high carbon content and iron element content, and also obtains a coal product.

[0016] 2. The invention's stage grinding stage selection operation, acid leaching operation, and suspension calcination are organic as a whole, and they complement each other to achieve efficient impurity removal of kaolinite (ultra-fine particle calcined kaolin whiteness ≥ 90%) and reduce process acid consumption. Only by grinding and flotation operation can a large amount of easily selected coal and kaolin be separated, avoiding coal from entering the subsequent leaching operation to affect acid consumption and leaching efficiency, and avoiding coal from causing local sintering and deteriorating product particle size during calcination; only by leaching can the iron element in the kaolin primary product be removed, significantly improving the whiteness of the product, otherwise the calcination process has limited effect on improving the whiteness of the product; grinding with ceramic balls for grinding and mixing can effectively improve the fineness of the product and the subsequent calcination efficiency of kaolin particles, and the ceramic ball medium can avoid the iron element doping in traditional iron balls; on the basis of the above, the suspension calcination purification operation can directly calcine and purify kaolin in the form of fine ore, which can realize precise temperature control and industrialized continuous feeding and discharging to control the calcination effect. Therefore, these operations complement each other and cannot be separated.

[0017] 3. The suspension calcination process of the present invention utilizes the dispersion and suspension characteristics of fine particles to improve the degree of gas-solid reaction and avoid sintering. By calcining fine particles, combined with precise temperature control at 850℃~950℃, the dehydroxylation and decarburization reactions of kaolinite are complete, significantly improving the whiteness of the calcined kaolin product.

[0018] 4. Compared with the current calcination purification process, the purification process of kaolin in coal gangue of the present invention includes three processes of flotation to remove coal, acid leaching to remove impurities, and calcination to remove carbon-dehydroxylation, which together realize efficient impurity removal and purification of kaolinite. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A flow chart of a method for preparing coal and calcined kaolin from coal gangue by stage grinding and stage selection-acid leaching-suspension calcination;

[0020] Among them, 1 is a ball mill, 2 is a flotation device, 3 is an acid leaching tank, 4 is a ceramic ball stirring mill, 5 is a filter press, 6 is a dryer, 7 is a breaker, and 8 is a suspension calcination purification furnace. DETAILED DESCRIPTION

[0021] The present invention provides a method for preparing coal and calcined kaolin from coal gangue by stage grinding and stage selection-acid leaching-suspension calcination, and the process flow is as follows Figure 1As shown, the coal gangue is fed into the stirred mill 1 for grinding operation, and the obtained finely ground coal gangue is fed into the flotation device 2 for roughing, multi-stage cleaning and multi-stage scavenging, to obtain a flotation concentrate and a flotation tailing. The flotation tailing is fed into the acid leaching tank 3, and the leaching product is obtained after acid leaching. Then, the leaching product is finely ground by using the ceramic ball stirred mill 4, to obtain fine particle kaolin, which is sequentially subjected to pressure filtration by using the filter press 5, drying by using the dryer 6, and dispersion by using the dispersion machine 7. The dispersed product is fed into the suspension calcination purification furnace 8 for suspension calcination, to obtain calcined kaolin. After cooling, the calcined kaolin is classified by screening, to obtain a product with a content of-7 μm≥90% as a fine particle calcined kaolin product, and a product with a content of-2 μm≥90% as a super fine particle calcined kaolin product.

[0022] The present application provides a coal gangue step-by-step grinding and step-by-step separation-acid leaching-suspension calcination method for preparing coal and calcined kaolin, which comprises the following steps:

[0023] Step 1, ore grinding operation: the raw coal gangue is fed into the ball mill for grinding to-0.074 mm content of 40% to 80%, to obtain a finely ground coal gangue product;

[0024] Step 2, flotation operation: the flotation operation can effectively separate the coal and kaolin in the coal gangue, and reduce the iron and carbon impurities in the kaolin. The finely ground coal gangue product is fed into the flotation device for roughing, multi-stage cleaning (≥1 stages) and multi-stage scavenging (≥1 stages). Under the conditions of a flotation collector dosage of 500 g / t to 800 g / t, a water glass dosage of 100 g / t to 300 g / t, a foaming agent dosage of 100 g / t to 400 g / t, and a pulp temperature of room temperature, the flotation concentrate and the flotation tailing are obtained. The flotation concentrate is coal with a carbon content≥45%; and the flotation tailing is a kaolin primary product with a carbon content≤6% and a Fe2O3 content≤1.5%;

[0025] Step 3, acid leaching operation: the leaching process can selectively dissolve the iron element, to reduce its influence on the whiteness of kaolin. The flotation tailing is subjected to acid leaching, to obtain a kaolin leaching product. The leaching agent used in the acid leaching process includes HCl, H2SO4 and oxalic acid, the leaching time is 1 h to 4 h, the leaching temperature is 60℃ to 90℃, and the leaching agent dosage is 5% to 15%. The Fe2O3 content in the kaolin leaching product is≤0.35%;

[0026] Step 4, fine grinding operation: the ceramic ball stirred mill is used for fine grinding of the leaching product, to prepare fine particle kaolin. The grinding time of the ceramic ball stirred mill is 0.7 h to 1.5 h, and the fine grinding product, i.e. the fine particle kaolin, has a content of-7 μm≥90%;

[0027] Step 5, dewatering and dispersing operation: the fine particle kaolin is fed into a filter press for dewatering and pressure filtration to obtain a dewatered product, the water content of the dewatered product being ≤10%; the dewatered product is further dewatered in a drying machine, the drying temperature being 160-170 DEG C, and the product after drying is fed into a dispersing machine to disperse the material to obtain a dispersed product, the water content being ≤3%;

[0028] Step 6, suspension calcination operation: the calcination and purification process can improve the whiteness of kaolin to obtain high-quality calcined kaolin product. The dispersed product is fed into a suspension calcination and purification furnace, the material is effectively decomposed by calcination, and the surface and interlayer hydroxyl groups are removed at the same time, thereby improving the whiteness. The suspension calcination and purification temperature is 850-950 DEG C, the time is 1.5-2.5 h, the calcination atmosphere is air, and the calcined product is calcined kaolin.

[0029] Step 7, product grading operation: the calcined kaolin product is cooled and sieved and graded, the product with a content of-7 μm ≥90% is a fine particle calcined kaolin product, and the qualified product with a whiteness ≥90% is obtained; the product with a content of-2 μm ≥90% is an ultra-fine particle calcined kaolin product, and the qualified product with a whiteness ≥90% is obtained.

[0030] The application will be further described below in combination with the drawings and specific examples.

[0031] Example 1

[0032] In this example, a coal gangue in Shanxi is used as raw material, which mainly includes kaolinite, carbonaceous matter, quartz and the like, wherein the content of Al2O3 is 38.51%, and the content of Fe2O3 is 0.45%, and the specific steps are as follows:

[0033] Step 1, ore feeding and ore grinding operation: the coal gangue raw ore is fed into a ball mill 1 to be ground to a content of-0.074 mm of 45%, to obtain a finely ground coal gangue product;

[0034] Step 2, flotation operation: the finely ground product is fed into a flotation device 2 to perform roughing, two-stage cleaning and one-stage scavenging operation, under the conditions that the dosage of kerosene / diesel oil is 550 g / t, the dosage of water glass is 200 g / t, the dosage of foaming agent methyl alcohol oil is 250 g / t, and the pulp temperature is room temperature, to obtain a flotation concentrate and a flotation tailing; the flotation concentrate is coal, and the carbon content is 52%; the flotation tailing is kaolin concentrate, and the carbon content is 3.5%, and the content of Fe2O3 is 0.30%;

[0035] Step 3, acid leaching operation: the kaolin concentrate is fed into an acid leaching tank 3 for acid leaching, the leaching agent used in the acid leaching process is H2SO4, the leaching time is 2.5 h, the leaching temperature is 75 DEG C, and the acid dosage is 12.50%; the content of Fe2O3 in the kaolin leaching product is 0.08%;

[0036] Step 4, fine grinding operation: the leaching product is subjected to fine grinding operation by using the ceramic ball stirring mill 4 to obtain fine particle kaolin; the grinding time of the ceramic ball stirring mill 4 is 1 h, and the particle size of the fine grinding product, i.e. fine particle kaolin, is -7 μm, and the content thereof is 92%;

[0037] Step 5, dewatering and scattering operation: the fine particle kaolin product is fed into the filter press 5 to perform dewatering pressure filtration to obtain a dewatering product, and the water content of the dewatering product is 10%; the dewatering product enters the dryer 6 for further dewatering, and the drying temperature is 160°C; the dried product enters the scattering machine 7 to scatter the material to obtain a scattering product, and the water content of the scattering product is 2.5%;

[0038] Step 6, suspension calcination operation: the scattering product is fed into the suspension calcination purification furnace 8, and the material is subjected to calcination to effectively decompose the carbon-containing organic matter, and at the same time, the surface and interlayer hydroxyl groups are removed, thereby improving the whiteness. The suspension purification calcination temperature is 950°C, the time is 1.5 h, the calcination atmosphere is air, and the calcined product is calcined kaolin.

[0039] Step 7, product grading operation: after the calcined kaolin product is cooled, it is screened and graded, the product of -7 μm is fine particle calcined kaolin product, and the qualified product with a whiteness of 91% is obtained; the product of -2 μm is ultra-fine particle calcined kaolin product, and the qualified product with a whiteness of 91% is obtained.

[0040] Example 2:

[0041] In this example, a coal gangue in Inner Mongolia is used as raw material, and the composition mainly includes kaolinite, carbon, quartz, etc., wherein the content of Al2O3 is 42.15%, and the content of Fe2O3 is 1.81%, and the specific steps are as follows:

[0042] Step 1, ore feeding and grinding operation: the coal gangue ore is fed into the ball mill 1 to be ground to -0.074 mm content of 78% to obtain fine ground coal gangue product;

[0043] Step 2, flotation operation: the fine ground product enters the flotation equipment 2 to perform roughing, two-stage cleaning and one-stage scavenging operation, under the conditions of flotation collector kerosene / diesel oil dosage of 600 g / t, water glass dosage of 300 g / t, and frother pine oil dosage of 300 g / t, and slurry temperature of room temperature, to obtain flotation concentrate and flotation tailings; the flotation concentrate is coal, and the carbon content is 51.50%; the flotation tailings are kaolin concentrate, and the carbon content is 4.10%, and the Fe2O3 content is 1.40%;

[0044] Step 3, acid leaching operation: the kaolin concentrate enters the acid leaching tank 3 to perform acid leaching, and the leaching agent used in the acid leaching process is oxalic acid, the leaching time is 4 h, the leaching temperature is 60°C, and the acid dosage is 11.50%; the Fe2O3 content in the kaolin leaching product is 0.25%;

[0045] Step 4, fine grinding: The leached product is finely ground using a ceramic ball stirred mill 4 to prepare fine-grained kaolin. The grinding time of the ceramic ball stirred mill 4 is 0.9 h, and the fine-grained kaolin particle size of the fine-ground product is -7 μm and the content is 94%;

[0046] Step 5, dehydration and dispersion operation: the fine-grained kaolin product is fed into the filter press 5 for dehydration and filtration to obtain a dehydrated product, the moisture content of which is 9%; the dehydrated product enters the dryer 6 for further dehydration at a drying temperature of 170°C; the dried product enters the disperser 7 to disperse the material to obtain a dispersed product, the moisture content of which is 2.7%;

[0047] Step 6, Suspension Calcination: This calcination purification process improves the whiteness of the kaolin, resulting in a high-quality calcined kaolin product. The dispersed product is fed into the suspension calcination purification furnace 8. Calcination effectively decomposes carbon-containing organic matter and removes surface and interlayer hydroxyl groups, further improving whiteness. The suspension purification calcination temperature is 900°C for 1.8 hours in an air atmosphere, resulting in calcined kaolin.

[0048] Step 7, product grading operation: the calcined kaolin product is cooled and then screened and graded. The product with a particle size of -7 μm is a fine-grained calcined kaolin product, and a qualified product with a whiteness of 90% is obtained; the product with a particle size of -2 μm is an ultrafine-grained calcined kaolin product, and a qualified product with a whiteness of 90% is obtained.

[0049] Example 3:

[0050] This example uses coal gangue from Liaoning as raw material, which mainly includes kaolinite, carbonaceous materials, etc., wherein the Al2O3 content is 20.51% and the Fe2O3 content is 2.20%. The specific steps are as follows:

[0051] Step 1, ore feeding and grinding operation: feed the gangue ore into ball mill 1 and grind it to -0.074mm content 80%, to obtain finely ground gangue product;

[0052] Step 2, flotation operation: The ground product enters flotation equipment 2 for roughing, three-stage cleaning, and two-stage scavenging operations. Under the conditions of kerosene / diesel collector dosage of 700g / t, water glass dosage of 150g / t, frother pine oil dosage of 250g / t, and slurry temperature of room temperature, flotation concentrate and flotation tailings are obtained; the flotation concentrate is coal with a carbon content of 52%; the flotation tailings is kaolin concentrate with a carbon content of 4.0% and an Fe2O3 content of 1.45%;

[0053] Step 3, acid leaching operation: the kaolin concentrate enters the acid leaching tank 3 for acid leaching. The leaching agent used in the acid leaching process is HCl, the leaching time is 3 hours, the leaching temperature is 65°C, and the acid dosage is 9%. The Fe2O3 content in the kaolin leaching product is 0.21%;

[0054] Step 4, fine grinding operation: the leaching product is subjected to fine grinding operation by using the ceramic ball stirring mill 4 for preparing fine particle kaolin; the grinding time of the ceramic ball stirring mill 4 is 1 h, and the fine grinding product, fine particle kaolin, has a particle size of -7 μm and a content of 95%;

[0055] Step 5, dewatering and scattering operation: the fine particle kaolin product is fed into the filter press 5 for dewatering and pressure filtration to obtain a dewatering product, which has a water content of 10%; the dewatering product is further dewatered in the drying machine 6 at a drying temperature of 170°C; the dried product is fed into the scattering machine 7 to be scattered to obtain a scattered product, which has a water content of 2.5%;

[0056] Step 6, suspension calcination operation: the calcination and purification process can improve the whiteness of kaolin and obtain high-quality calcined kaolin product. The scattered product is fed into the suspension calcination and purification furnace 8, and the material is subjected to calcination to effectively decompose the carbon-containing organic matter and remove the surface and interlayer hydroxyl groups, thereby improving the whiteness. The suspension calcination and purification temperature is 920°C, the time is 2 h, the calcination atmosphere is air, and the calcined product is calcined kaolin.

[0057] Step 7, product grading operation: the calcined kaolin product is cooled and then screened and graded, the product with a particle size of -7 μm is fine particle calcined kaolin product, and the product with a particle size of -2 μm is ultra-fine particle calcined kaolin product, both of which have a whiteness of 92% and are qualified products.

[0058] Comparative Example 1

[0059] The process flow in this example is the same as that in Example 2. The difference is that the coal gangue is not subjected to two-stage grinding, but is directly subjected to fine grinding in the first-stage grinding process by using the ceramic ball stirring mill 4 to grind the particle size of the coal gangue to -7 μm with a content of 90%, and the other conditions remain unchanged.

[0060] The flotation process produces a serious phenomenon of not separating the concentrate and tailings, the carbon content in the flotation concentrate coal is reduced to 44.50%, and the carbon content in the flotation tailings kaolin product is increased to 7.18%. The whiteness of the final calcined kaolin is only 87%, and the whiteness uniformity is poor, which does not meet the product qualification requirements. This is because the suitable particle size for the flotation operation is -0.074 mm with a content of 40% to 80%, and when the direct fine grinding process is used, the fine particle material will reduce the floatability difference between the concentrate and tailings, and worsen the flotation index, so that more carbon enters the subsequent operation with the kaolin concentrate. Therefore, it is necessary to use the step-by-step grinding and step-by-step selection operation.

[0061] Comparative Example 2

[0062] The process flow in this example is same as example 2. The difference is that the coal gangue does not undergo acid leaching operation, and other conditions are unchanged. The final calcined kaolin can also be obtained, but the whiteness is significantly reduced, the whiteness of the product with particle size of-7 μm is reduced to 84%, and the whiteness of the product with particle size of-2 μm is reduced to 84%. This is because the kaolin contains a higher content of iron elements, and after roasting, these iron oxides have color, reducing the whiteness index of the product.

[0063] Comparative example 3:

[0064] The process flow in this example is same as example 1. The difference is that the suspension calcination operation is not performed, and the traditional rotary kiln calcination is used, the calcination temperature is the same, and other conditions are unchanged. The final calcined kaolin can also be obtained, but the whiteness is significantly reduced, the whiteness of the product with particle size of-7 μm is reduced to 85.8%, and the whiteness of the product with particle size of-2 μm is reduced to 86.7%. This is because the calcination effect of the rotary kiln is not as good as that of the suspension purification calcination furnace, reducing the whiteness index of the product, and the total cost per ton of product increases by 10% because the rotary kiln has high energy consumption and low heat utilization efficiency.

[0065] Comparative example 4:

[0066] The process flow in this example is same as example 3. The difference is that the suspension calcination operation is not performed, and the traditional rotary kiln calcination is used, the calcination temperature is the same, and other conditions are unchanged. The final calcined kaolin can also be obtained, but the whiteness is significantly reduced, the whiteness of the product with particle size of-7 μm is reduced to 84.4%, and the whiteness of the product with particle size of-2 μm is reduced to 85.2%. This is because the calcination effect of the rotary kiln is not as good as that of the suspension purification calcination furnace, reducing the whiteness index of the product, and the total cost per ton of product increases by 12% because the rotary kiln has high energy consumption and low heat utilization efficiency.

Claims

1. A method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination, characterized in that: The following steps are involved: Step 1: Feed the gangue ore into the ball mill for ball milling until the particle size is -0.074mm and the content of ore powder is 40%~80%; Step 2, flotation operation: the coal gangue products after ball milling enter the flotation equipment for roughing, cleaning and scavenging operations to obtain flotation concentrate and flotation tailings; Step 3, acid leaching operation: the flotation tailings are acid-leached in a leaching agent to obtain a kaolin leaching product; the leaching agent dosage is 5% to 15%; the Fe2O3 content in the kaolin leaching product is ≤0.35%; Step 4: Fine grinding: The leached product is finely ground using a ceramic ball stirred mill to obtain fine-grained kaolin; Step 5: Dehydration and dispersion: the fine-grained kaolin is sequentially subjected to filter pressing, drying, and dispersion to obtain a dispersed product; Step 6, suspension calcination operation: the dispersed product is fed into a suspension calcination purification furnace for suspension calcination, the carbon-containing organic matter in the dispersed product is effectively decomposed, and the surface and interlayer hydroxyl groups are removed at the same time, to obtain a suspension calcined product, namely calcined kaolin; Step 7, product classification operation: After the calcined kaolin is cooled, it is screened and classified. Products with a -7μm content ≥90% are fine-grained calcined kaolin products, and products with a -2μm content ≥90% are ultrafine-grained calcined kaolin products.

2. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 2, the number of selected segments is ≥1, and the number of scanned segments is ≥1.

3. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 2, flotation concentrate and flotation tailings are obtained under the conditions that the flotation collector dosage is 500g / t~800g / t, the water glass dosage is 100g / t~300g / t, the frother dosage is 100g / t~400g / t, and the slurry temperature is room temperature.

4. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: The flotation concentrate is coal with a carbon content of ≥45%; the flotation tailings are primary kaolin products with a carbon content of ≤6% and a Fe2O3 content of ≤1.5%.

5. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 3, the leaching agents used in the acid leaching process include HCl, H2SO4, and oxalic acid, the leaching time is 1 hour to 4 hours, and the leaching temperature is 60°C to 90°C.

6. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 4, the grinding time of the ceramic ball stirred mill is 0.7h~1.5h, and the content of fine kaolin with a particle size of -7μm is ≥90%.

7. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 5, a dehydrated product with a water content of ≤10% is obtained by filter pressing. The dehydrated product is dried in an environment of 160°C to 170°C and then dispersed. The water content of the dispersed product is ≤3%.

8. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 6, the suspension calcination temperature is 850° C. to 950° C., the time is 1.5 h to 2.5 h, and the calcination atmosphere is air.

9. The method for preparing coal and calcining kaolin by gangue step grinding-acid leaching-suspension calcination according to claim 1, characterized in that: In step 7, the whiteness of the fine-grained calcined kaolin product is ≥90%; The ultrafine calcined kaolin product has a whiteness of ≥90%.

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