A process for coal gangue roasting activation

Abstract

The present application belongs to the technical field of solid waste resource utilization, and particularly relates to a process suitable for coal gangue roasting activation. The process comprises: crushing and screening coal gangue to obtain raw materials; preheating at 200-750 DEG C to remove volatile matter; introducing inert or slightly reducing atmosphere for phase control treatment at 400-600 DEG C; roasting and activating in a mixed atmosphere of nitrogen, carbon dioxide and water vapor by using a staged heating method at 900-1200 DEG C; after roasting, slowly cooling and stabilizing treatment in an atmosphere containing CO2 and water vapor; finally, desiliconizing by alkali leaching to improve the aluminum-silicon ratio of coal gangue to 4-8. By the process, local overburning and unfavorable phase transformation can be effectively avoided, the excessive generation of mullite is inhibited, and the separation state of alumina and silicon dioxide is maintained, thereby significantly improving the desiliconization efficiency and alumina dissolution rate, and providing a feasible path for efficient utilization of coal gangue resources.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid waste resource utilization, and particularly relates to a process suitable for coal gangue roasting activation. BACKGROUND

[0002] Coal gangue is a large amount of solid waste generated in the process of coal mining and washing, which contains a high proportion of silicon dioxide and aluminum oxide. Due to its abundant reserves and relatively stable composition, coal gangue has been widely studied as an important raw material for extracting aluminum oxide and other valuable elements. However, in the process of coal gangue resource utilization, how to efficiently separate silicon and aluminum components and improve the aluminum-silicon ratio has always been a key technical problem that limits its industrial application.

[0003] In the prior art, coal gangue is usually treated by direct roasting or acid-base leaching. In the traditional roasting process, the volatile components in coal gangue often participate in combustion during the heating process, which can easily cause local temperature to be too high, resulting in inaccurate control of the roasting temperature. This temperature fluctuation can cause over-burning of coal gangue, leading to unfavorable transformation of the crystal structure, and thus affecting the subsequent activation effect and desiliconization efficiency. Especially during the high-temperature roasting stage of 900-1200℃, the kaolinite in coal gangue gradually transforms into mullite, and a large amount of amorphous silicon dioxide is emitted. If the temperature is not properly controlled, the emitted silicon dioxide will react with free aluminum oxide to form mullite, thereby reducing the extractability of aluminum oxide and increasing the difficulty of aluminum-silicon separation.

[0004] In addition, the combustion of volatile components during roasting can also cause uneven temperature distribution, increase the formation of local hot spots, and affect the controllability and consistency of the crystal transformation. Due to the complex mineral composition of coal gangue, it contains a certain amount of carbonaceous matter, pyrite and other impurities. When these components undergo incomplete reactions under temperature fluctuations, they can generate by-products that are difficult to remove, further reducing the reactivity of the roasting products. Under the traditional roasting method, even after subsequent alkali desiliconization treatment, the aluminum-silicon ratio of coal gangue can only be increased to 1.5-3, which is far lower than the actual industrial demand, severely restricting the improvement of the extraction rate of aluminum oxide.

[0005] On the other hand, atmosphere control is also a major problem in existing processes. Most traditional roasting processes only rely on air or simple reducing atmosphere, and cannot dynamically adjust according to the stage characteristics of coal gangue mineral decomposition and transformation, resulting in a lack of targeted regulation of the crystal phase transformation process. For example, under different atmospheres, the volatilization of silicon dioxide and the aluminum-silicon separation behavior differ significantly. If the atmosphere environment is not reasonably designed, it is easy to cause the generation of silicon-aluminum intergrowth, reducing the selectivity of desiliconization.

[0006] Therefore, how to effectively extract the volatile components in coal gangue during the roasting process, so that they do not participate in combustion, while using external heat source to accurately control the temperature, combined with suitable atmosphere adjustment, to ensure the reasonable conversion and separation of silicon and aluminum components in the roasting product, has become a key problem to be solved in the field. SUMMARY

[0007] The purpose of the present application is to provide a process suitable for coal gangue roasting and activation, to solve the problems of difficult accurate control of roasting temperature, serious overburning, insufficient activation degree and limited improvement of aluminum-silicon ratio in the prior art.

[0008] In order to achieve the above purpose, the present application provides the following technical solutions:

[0009] A process suitable for coal gangue roasting and activation, comprising the following steps:

[0010] (1) crushing and screening the coal gangue to obtain coal gangue raw materials;

[0011] (2) feeding the coal gangue raw materials into a preheating system and preheating at 200-750℃ to extract the volatile components therein, to obtain preheated coal gangue;

[0012] (3) passing the preheated coal gangue into an inert gas or a slightly reducing atmosphere at 400-600℃ to obtain phase-controlled treated coal gangue;

[0013] (4) feeding the phase-controlled treated coal gangue into a roasting system and roasting at 900-1200℃, using external heat source to heat, to obtain roasted coal gangue;

[0014] (5) passing the roasted coal gangue into an atmosphere containing CO2 and / or water vapor for cooling to obtain stabilized treated coal gangue;

[0015] (6) alkali desiliconizing the stabilized treated coal gangue to make the aluminum-silicon ratio of the coal gangue reach 4-8.

[0016] Further, the preheating time of step (2) is 0.1-6 h.

[0017] The preheating stage is to heat the coal gangue to 200-750℃, so that the volatile matter is removed before entering the high-temperature roasting zone. In this way, the spontaneous combustion of volatile matter under high-temperature conditions can be avoided, thereby effectively preventing local overburning and abnormal crystal phase transformation. At the same time, the preheating process also creates a more stable mineral structure for subsequent roasting, ensuring the controllability of mineral phase transformation. In addition, this step realizes the recycling of energy, and the heat required in the preheating stage can be obtained from the waste heat of the roasting section, while the removed volatile matter can be used as fuel to provide external heat for the roasting process, greatly reducing energy consumption and improving the energy utilization efficiency of the overall process.

[0018] Further, the treatment time in step (3) is 0.1-2 h.

[0019] Further, the inert gas in step (3) is nitrogen or argon; and the micro-reducing atmosphere is a mixture of nitrogen or argon and carbon monoxide, wherein the volume fraction of carbon monoxide is 1-10%.

[0020] Step (3) controls the phase of the coal gangue, which is carried out at a medium temperature of 400-600℃ and an inert or micro-reducing atmosphere is introduced, so that the organic matter and pyrite impurities in the coal gangue are decomposed and effectively removed. This can significantly reduce the side reactions of impurities during high-temperature roasting and avoid the formation of difficult-to-remove side phase minerals. At the same time, the micro-reducing atmosphere can inhibit the premature reaction of part of the silicon dioxide and aluminum oxide, so that the mineral structure remains in a more favorable state for subsequent activation and desiliconization. Through this intermediate phase control step, the phase transformation path of the coal gangue can be controlled in advance, reducing the possibility of forming mullite and other insoluble phases during roasting, thereby improving the separation efficiency of aluminum and silicon.

[0021] Further, the roasting time in step (4) is 0.1-16 h.

[0022] Further, the atmosphere for roasting in step (4) is a mixture of nitrogen, carbon dioxide and water vapor, wherein the volume fraction of nitrogen is 70-90%, the volume fraction of carbon dioxide is 5-20%, and the volume fraction of water vapor is 2-15%.

[0023] Further, the roasting in step (4) adopts a staged heating mode, first heated to 900-1000℃ at a rate of 3-8℃ / min and held for 0.1-2 h, and then heated to 1000-1200℃ at a rate of 1-5℃ / min and held for 0.1-16 h.

[0024] Further, the heat generated by the recovered volatile matter in step (2) is used as an external heat source for step (4); and the waste heat after roasting in step (4) is used as a heat source for the preheating stage in step (2).

[0025] The calcination stage causes the crystalline transformation and activation reaction of kaolinite and other aluminum-silicon-containing minerals in coal gangue. The use of a staged temperature rise mode can avoid the uneven destruction of the structure caused by rapid temperature rise, ensuring the stable progress of the activation process. At the same time, the introduction of a mixed atmosphere of nitrogen, carbon dioxide and water vapor makes the calcination environment inert and moderately oxidizing / acidifying, which not only effectively inhibits the excessive generation of mullite, but also to some extent prevents the solid-phase reaction of silicon dioxide and aluminum oxide. Thus, the product after calcination maintains a high degree of activation and dispersion, providing a more easily reactive structural basis for subsequent desiliconization, greatly improving the efficiency of aluminum-silicon separation and the dissolution rate of alumina.

[0026] Further, the volume fraction of carbon dioxide in the atmosphere in step (5) is 10-40%, the volume fraction of water vapor is 5-20%, and the balance is nitrogen or argon.

[0027] The introduction of a mixed atmosphere containing CO2 and water vapor during the cooling process after calcination can significantly improve the stability of the mineral phase of coal gangue. CO2 and water vapor can weakly react with the surface of the calcined product during the cooling stage, delaying and inhibiting the further generation of mullite, thereby maintaining the relative independence of the dispersion state of alumina and silicon dioxide. This slow cooling atmosphere can also reduce the structural stress caused by the cooling rate, avoid the occurrence of cracks or excessive crystallization, and ensure the integrity of the calcined product in the microstructure. Through this stabilization treatment, not only the reaction selectivity and efficiency of subsequent alkali desiliconization are improved, but also the control effect of the entire process on the improvement of the aluminum-silicon ratio is ensured, significantly enhancing the feasibility of alumina resource utilization.

[0028] Further, the alkali desiliconization in step (6) is specifically: immersing the stabilized coal gangue in a sodium hydroxide solution with a mass fraction of 10-40 wt% at 50-180℃ for 1-10 h.

[0029] Compared with the prior art, the advantages and beneficial effects of the present application are:

[0030] Compared with the prior art, the present application avoids temperature loss of control and impurity side reaction caused by volatile combustion by preheating and removing volatile and adjusting phase at medium temperature before roasting, so that the coal gangue has a better mineral structure basis before entering the high-temperature roasting stage; the mixed atmosphere of nitrogen, carbon dioxide and water vapor is used in the roasting process, and the uniform phase transformation is realized by the staged heating mode, which not only inhibits the excessive generation of mullite, but also avoids the adverse solid phase reaction between aluminum and silicon; the slow cooling atmosphere containing CO2 and water vapor is introduced in the cooling stage, which further maintains the separation state of alumina and silica, reduces the structural stress and phase reconstruction; finally, combined with the desiliconization treatment by alkali leaching, the aluminum-silicon ratio of the coal gangue can be significantly improved from about 1.0 to 4-8, and the alumina dissolution rate is more than 70%. The implementation results show that the process of the present application is superior to the traditional roasting or acid leaching method in energy utilization, aluminum-silicon separation efficiency and environmental friendliness, and has good industrial application prospect. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0032] Embodiment 1

[0033] The present embodiment provides a process suitable for coal gangue roasting and activation, comprising the following steps:

[0034] (1) Coal gangue in the mining area of Ordos City, Inner Mongolia, is first crushed by a jaw crusher, and then sieved by a vibrating screen to obtain coal gangue raw materials with a particle size of 5-20 mm; the initial aluminum-silicon ratio of the coal gangue is 1.04.

[0035] (2) The above coal gangue raw materials are sent into a tubular preheating furnace, heated to 500℃ in an air atmosphere, and kept for 1 h, so that the volatile components therein are removed, and preheated coal gangue is obtained. The volatile gas discharged in this process is collected and then enters a combustion chamber as external fuel for the subsequent roasting stage.

[0036] (3) The preheated coal gangue obtained in step (2) is transferred to a medium temperature reaction furnace, and a mixed atmosphere of nitrogen and carbon monoxide is introduced at 500℃ for treatment, the volume fraction ratio of nitrogen to carbon monoxide is 95:5, the total flow rate is 2 L / min, and the treatment time is 1 h. In this process, the organic matter and pyrite impurities in the coal gangue are decomposed, avoiding side reactions in the subsequent roasting, and obtaining phase-controlled treated coal gangue.

[0037] (4) The coal gangue obtained in step (3) is sent into a high-temperature rotary kiln and calcined in a mixed atmosphere of nitrogen, carbon dioxide and water vapor. The volume fraction of nitrogen in the atmosphere is 80%, the volume fraction of carbon dioxide is 12%, and the volume fraction of water vapor is 8%, and the total flow rate is 5 L / min. The temperature rising program is as follows: the temperature is raised to 950°C at a rate of 5°C / min and kept for 1 h, and then the temperature is raised to 1150°C at a rate of 2°C / min and kept for 4 h. External fuel heating is adopted during the calcination process, and part of the heat is provided by the combustion of the volatiles removed in step (2), and the waste heat of the calcination is recovered as a heat source for the preheating furnace. After the calcination is completed, the calcined and activated coal gangue is obtained.

[0038] (5) During the cooling stage after calcination, a mixed gas containing 30% carbon dioxide, 10% water vapor and the balance nitrogen is continuously introduced into the rotary kiln at a flow rate of 3 L / min until the temperature drops to below 200°C. After cooling is completed, the coal gangue after stabilization treatment is obtained.

[0039] (6) The coal gangue obtained in step (5) is ground to a particle size of less than 75 μm and added to a 20 wt% sodium hydroxide solution with a liquid-solid ratio of 5:1. The mixture is stirred and leached at 120°C for 6 h. After filtration, washing and drying, the desiliconized coal gangue solid product is obtained.

[0040] Example 2

[0041] The present embodiment provides a process suitable for the calcination and activation of coal gangue, comprising the following steps:

[0042] (1) Coal gangue from a certain mining area in Ordos City, Inner Mongolia, is first crushed by a jaw crusher and then sieved by a vibrating screen to obtain coal gangue raw material with a particle size of 5-20 mm. The initial aluminum-silicon ratio of the coal gangue is 1.0.

[0043] (2) The coal gangue raw material is sent into a tubular preheating furnace and heated to 200°C in an air atmosphere for 4 h to remove the volatiles therein, thereby obtaining preheated coal gangue. The volatilized gas discharged in this process is collected and introduced into a combustion chamber as external fuel for the subsequent calcination stage.

[0044] (3) The preheated coal gangue obtained in step (2) is transferred to a medium-temperature reaction furnace and treated in a mixed atmosphere of nitrogen and carbon monoxide at 500°C. The volume fraction ratio of nitrogen to carbon monoxide is 95:5, the total flow rate is 2 L / min, and the treatment time is 1 h. In this process, the organic matter and pyrite impurities in the coal gangue are decomposed, avoiding side reactions in the subsequent calcination, thereby obtaining coal gangue after phase control treatment.

[0045] (4) The coal gangue obtained in step (3) is sent into a high-temperature rotary kiln and calcined in a mixed atmosphere of nitrogen, carbon dioxide and water vapor. The volume fraction of nitrogen in the atmosphere is 70%, the volume fraction of carbon dioxide is 20%, and the volume fraction of water vapor is 10%. The total flow rate is 5 L / min. The temperature rising program is as follows: the temperature is raised to 950°C at a rate of 5°C / min and kept for 1 h, and then the temperature is raised to 1150°C at a rate of 2°C / min and kept for 4 h. External fuel heating is adopted during the calcination process, and part of the heat is provided by the combustion of the volatiles removed in step (2). At the same time, the waste heat from the calcination is recovered as a heat source for the preheating furnace. After the calcination is completed, the calcined and activated coal gangue is obtained.

[0046] (5) During the cooling stage after calcination, a mixed gas containing 15% carbon dioxide, 15% water vapor and the balance nitrogen is continuously introduced into the rotary kiln at a flow rate of 3 L / min until the temperature drops to below 200°C. After cooling is completed, the coal gangue after stabilization treatment is obtained.

[0047] (6) The coal gangue obtained in step (5) is ground to a particle size of less than 75 μm and added to a 30 wt% sodium hydroxide solution. The liquid-solid ratio is 8:1, and the leaching is carried out at 100°C for 3 h with constant temperature stirring. After filtration, washing and drying, the desilicated coal gangue solid product is obtained.

[0048] Example 3

[0049] This example provides a process suitable for the calcination and activation of coal gangue, comprising the following steps:

[0050] (1) Coal gangue from a certain mining area in Ordos City, Inner Mongolia, is first crushed by a jaw crusher and then sieved by a vibrating screen to obtain coal gangue raw material with a particle size of 5-20 mm. The initial aluminum-silicon ratio of the coal gangue is 0.96.

[0051] (2) The coal gangue raw material is sent into a tubular preheating furnace and heated to 700°C in an air atmosphere for 1 h to remove the volatiles therein, thereby obtaining preheated coal gangue. The volatilized gas discharged in this process is collected and introduced into a combustion chamber as external fuel for the subsequent calcination stage.

[0052] (3) The preheated coal gangue obtained in step (2) is transferred to a medium-temperature reaction furnace and treated by introducing nitrogen at a flow rate of 2 L / min at 400°C for 2 h. In this process, the organic matter and pyrite impurities in the coal gangue are decomposed, avoiding side reactions in the subsequent calcination, thereby obtaining coal gangue after phase control treatment.

[0053] (4) The coal gangue obtained in step (3) is sent into a high-temperature rotary kiln and calcined in a mixed atmosphere of nitrogen, carbon dioxide and water vapor. The volume fraction of nitrogen in the atmosphere is 80%, the volume fraction of carbon dioxide is 12%, and the volume fraction of water vapor is 8%, and the total flow rate is 5 L / min. The temperature rising program is as follows: the temperature is raised to 950°C at a rate of 5°C / min and kept for 1 h, and then the temperature is raised to 1150°C at a rate of 2°C / min and kept for 4 h. External fuel heating is adopted during the calcination process, and part of the heat is provided by the combustion of the volatiles removed in step (2), and the waste heat of the calcination is recovered as a heat source for the preheating furnace. After the calcination is completed, the calcined and activated coal gangue is obtained.

[0054] (5) During the cooling stage after calcination, a mixed gas containing 40% carbon dioxide, 5% water vapor and the balance nitrogen is continuously introduced into the rotary kiln at a flow rate of 3 L / min until the temperature drops to below 200°C. After cooling is completed, the coal gangue after stabilization treatment is obtained.

[0055] (6) The coal gangue obtained in step (5) is ground to a particle size of less than 75 μm and added to a 40 wt% sodium hydroxide solution, and the liquid-solid ratio is 3:1. The mixture is stirred and leached at 50°C for 10 h. After filtration, washing and drying, the desilicated coal gangue solid product is obtained.

[0056] Comparative Example 1

[0057] This comparative example provides a process suitable for calcination and activation of coal gangue, which is different from Example 1 in that the coal gangue is not subjected to the volatiles removal in step (2) and the phase control treatment in step (3), but is directly calcined.

[0058] Comparative Example 2

[0059] This comparative example provides a process suitable for calcination and activation of coal gangue, which is different from Example 1 in that the coal gangue is not subjected to the phase control treatment in step (3).

[0060] Comparative Example 3

[0061] This comparative example provides a process suitable for calcination and activation of coal gangue, which is different from Example 1 in that the atmosphere for calcination in step (4) is air.

[0062] Comparative Example 4

[0063] This comparative example provides a process suitable for calcination and activation of coal gangue, which is different from Example 1 in that the calcination process in step (4) adopts a single temperature rising program, i.e. the temperature is directly raised to 1150°C at a rate of 5°C / min and kept for 5 h without sub-stage temperature rising.

[0064] Comparative Example 5

[0065] The comparative example provides a process suitable for coal gangue roasting activation, which is different from example 1 in that: in step (5), the cooling stage adopts natural cooling, and is directly cooled to below 200°C in air.

[0066] Performance test

[0067] The products of examples 1-3 and comparative examples 1-5 are respectively tested for the aluminum-silicon ratio, and the results are shown in Table 1.

[0068] Table 1: Performance test results

[0069]

[0070] As can be seen from the test results in Table 1, examples 1-3 of the present application all show significantly better desiliconization effect than the comparative examples. In contrast, comparative example 1 does not perform preheating and phase control treatment, resulting in volatile interference with roasting and the generation of adverse secondary phases, and the desiliconization effect is extremely poor. Comparative example 2 is preheated but not phase-controlled, and the impurities are not completely decomposed, so the aluminum-silicon ratio is significantly low. Comparative example 3 uses air roasting, and excessive mullite is generated, which limits the dissolution of aluminum. Comparative example 4 does not perform staged temperature rising, and the crystal phase conversion is not uniform, resulting in insufficient resolution. Comparative example 5 does not use CO2 / water vapor slow cooling, and the crystal phase is severely reconstructed during the cooling process, and the performance is significantly reduced.

[0071] The above describes preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A process suitable for coal gangue roasting activation, comprising the following steps: (1) crushing and screening the coal gangue to obtain coal gangue raw materials; (2) feeding the coal gangue raw materials into a preheating system, preheating at 200-750°C to remove volatile components therefrom, to obtain preheated coal gangue; (3) passing the preheated coal gangue into an inert gas or a micro-reducing atmosphere at 400-600°C to obtain phase-controlled treated coal gangue; the inert gas is nitrogen or argon; the micro-reducing atmosphere is a mixture of nitrogen or argon and carbon monoxide, wherein the volume fraction of carbon monoxide is 1-10%; (4) feeding the phase-controlled treated coal gangue into a roasting system, roasting at 900-1200°C using an external heat source, to obtain roasted coal gangue; the roasting atmosphere is a mixture of nitrogen, carbon dioxide and water vapor, wherein the volume fraction of nitrogen is 70-90%, the volume fraction of carbon dioxide is 5-20%, and the volume fraction of water vapor is 2-15%; the roasting adopts a staged temperature rising mode, first rising at a rate of 3-8°C / min to 900-1000°C and maintaining for 0.1-2 h, and then rising at a rate of 1-5°C / min to 1000-1200°C and maintaining for 0.1-16 h; (5) passing the roasted coal gangue into an atmosphere containing CO2 and / or water vapor for cooling to obtain stabilized treated coal gangue; (6) alkali desiliconizing the stabilized treated coal gangue to make the aluminum-silicon ratio of the coal gangue reach 4-8.

2. The process suitable for coal gangue roasting activation according to claim 1, characterized by, The preheating time in step (2) is 0.1-6 h.

3. The process suitable for coal gangue roasting activation as claimed in claim 1 wherein, The treatment time in step (3) is 0.1-2 h.

4. The process as claimed in claim 1, wherein, The roasting time in step (4) is 0.1-16 h.

5. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The volatile components removed in step (2) are recovered and used as heat generated by fuel as the external heat source in step (4); the residual heat after roasting in step (4) is used as the heat source in the preheating stage in step (2).

6. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The volume fraction of carbon dioxide in the atmosphere in step (5) is 10-40%, the volume fraction of water vapor is 5-20%, and the balance is nitrogen or argon.

7. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The alkali desiliconization in step (6) is specifically: immersing the stabilized treated coal gangue in a sodium hydroxide solution with a mass fraction of 10-40 wt% at 50-180°C for 1-10 h.

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