Process suitable for roasting activation of coal gangue

Abstract

The invention belongs to the technical field of solid waste resource utilization, and particularly relates to a process suitable for roasting activation of coal gangue. The process comprises the following steps: crushing and screening coal gangue to obtain a raw material; preheating at the temperature of 200-750 DEG C to extract volatile components; an inert or micro-reducing atmosphere is introduced at the temperature of 400-600 DEG C for phase control treatment; roasting and activating at 900-1200 DEG C in a mixed atmosphere of nitrogen, carbon dioxide and water vapor in a segmented heating manner; after roasting, slowly cooling and stabilizing in an atmosphere containing CO2 and water vapor; and finally, alkali leaching is adopted for desilicication, so that the aluminum-silicon ratio of the coal gangue is increased to 4-8. Through the process, local overburning and unfavorable crystal phase transformation can be effectively avoided, excessive generation of mullite is inhibited, and the separation state of aluminum oxide and silicon dioxide is kept, so that the desilicication efficiency and the dissolution rate of aluminum oxide are remarkably improved, and a feasible path is provided 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 improved 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 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: 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) sending the coal gangue raw materials into a preheating system and preheating at 200-750℃ to extract the volatile components, to obtain preheated coal gangue; (3) introducing inert gas or micro-reducing atmosphere into the preheated coal gangue at 400-600℃ to obtain phase-controlled treated coal gangue; (4) sending 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; (5) introducing CO2 and / or water vapor containing atmosphere into the roasted coal gangue 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.

[0009] Further, the preheating time of step (2) is 0.1-6 h.

[0010] The role of the preheating stage is to heat the coal gangue to 200-750℃, so that the volatile components are extracted before entering the high temperature roasting zone. In this way, the spontaneous combustion of volatile components under high temperature conditions can be avoided, so as to effectively prevent local overburning and abnormal crystal phase transformation. At the same time, the preheating process also creates a more stable mineral foundation structure for subsequent roasting, ensuring the controllability of mineral phase transformation. In addition, this step realizes the recycling of energy, the heat required in the preheating stage can be derived from the waste heat of the roasting section, and the extracted volatile components can be used as fuel to provide external heat source for the roasting process, greatly reducing energy consumption and improving the energy utilization efficiency of the overall process.

[0011] Further, the treatment time of step (3) is 0.1-2 h.

[0012] 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%.

[0013] Step (3) controls the phase of coal gangue under a medium temperature condition of 400-600°C, and an inert or micro-reducing atmosphere is introduced to decompose and effectively remove the organic matter and pyrite impurities in the coal gangue. This can significantly reduce the side reactions of impurities in the high-temperature roasting process and avoid the generation of side-phase minerals that are difficult to remove. At the same time, the micro-reducing atmosphere can inhibit the premature reaction of part of the silicon dioxide and alumina, so that the mineral structure remains in a more favorable state for subsequent activation and desiliconization. Through this intermediate phase control adjustment step, the pre-control of the mineral phase transformation path of coal gangue can be realized, the possibility of forming mullite and other insoluble phases in the roasting process is reduced, and the separation efficiency of aluminum and silicon is improved.

[0014] Further, the roasting time in step (4) is 0.1-16 h.

[0015] Further, the roasting atmosphere 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%.

[0016] Further, the roasting in step (4) adopts a staged heating mode, first heated to 900-1000°C at a rate of 3-8°C / min and kept for 0.1-2 h, and then heated to 1000-1200°C at a rate of 1-5°C / min and kept for 0.1-16 h.

[0017] Further, the volatile matter removed in step (2) is recovered and used as a 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).

[0018] The roasting stage causes the crystal transformation and activation reaction of kaolinite and other aluminum-silicon-containing minerals in the coal gangue. The staged heating mode can avoid the non-uniform damage to the structure caused by rapid heating and ensure 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 roasting 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 alumina. As a result, the product after roasting has a high activation degree and dispersion, providing a more easily reactive structure basis for subsequent desiliconization, and greatly improving the separation efficiency of aluminum and silicon and the dissolution rate of alumina.

[0019] 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.

[0020] The introduction of the mixed atmosphere containing CO2 and water vapor during the cooling process after roasting can significantly improve the stability of the coal gangue mineral phase. CO2 and water vapor can weakly react with the surface of the roasting product in the cooling stage, delaying and inhibiting the further formation of mullite, thereby maintaining the relatively independent dispersed state of alumina and silica. 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 roasting product in the microstructure. Through this stabilization treatment, not only the reaction selectivity and efficiency of subsequent alkali desilication 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.

[0021] Further, the alkali desilication in step (6) is specifically: the coal gangue after stabilization treatment is leached with a sodium hydroxide solution with a mass fraction of 10-40 wt% at 50-180℃ for 1-10 h.

[0022] Compared with the prior art, the advantages and beneficial effects of the present application are: Compared with the prior art, the present application avoids temperature loss of control and impurity side reactions caused by volatilization combustion by preheating and volatilization fraction separation before roasting and medium temperature phase control, so that the coal gangue has a relatively optimal mineral structure before entering the high-temperature roasting stage; a mixed atmosphere of nitrogen, carbon dioxide and water vapor is used in the roasting process, and uniform crystal phase transformation is achieved by stepwise heating, which not only inhibits the excessive formation of mullite, but also avoids adverse solid phase reactions between aluminum and silicon; a slow cooling atmosphere containing CO2 and water vapor is introduced in the cooling stage to further maintain the separated state of alumina and silica, reduce structural stress and crystal phase reconstruction; finally, combined with alkali leaching desilication treatment, 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 terms of energy utilization, aluminum-silicon separation efficiency and environmental friendliness, and has good industrial application prospect. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0024] Example 1 The embodiment provides a process suitable for coal gangue roasting activation, comprising the following steps: (1) Coal gangue in a mining area of Ordos City, Inner Mongolia is first crushed by a jaw crusher and then screened 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.

[0025] (2) The coal gangue raw materials are sent into a tubular preheating furnace, heated to 500 DEG C in an air atmosphere, and kept for 1 h, so that volatile components in the coal gangue are extracted, and preheated coal gangue is obtained. The volatile gas discharged in the process is collected and then introduced into a combustion chamber as external fuel in the subsequent roasting stage.

[0026] (3) The preheated coal gangue obtained in step (2) is transferred to a medium-temperature reaction furnace, treated in a mixed atmosphere of nitrogen and carbon monoxide at 500 DEG 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 the process, organic matter and pyrite impurities in the coal gangue are decomposed, and side reactions in the subsequent roasting are avoided, and the coal gangue after phase control treatment is obtained.

[0027] (4) The coal gangue obtained in step (3) is sent into a high-temperature rotary kiln and roasted 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 DEG C at a rate of 5 DEG C / min and kept for 1 h, and then the temperature is raised to 1150 DEG C at a rate of 2 DEG C / min and kept for 4 h. External fuel is used for heating in the roasting process, part of the heat is provided by the combustion of the volatile components extracted in step (2), and the waste heat of roasting is recovered as a heat source of the preheating furnace. The roasting-activated coal gangue is obtained after roasting.

[0028] (5) In the cooling stage after roasting, 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 is reduced to below 200 DEG C. After cooling, the coal gangue after stabilization treatment is obtained.

[0029] (6) The coal gangue obtained in step (5) is ground to a particle size of less than 75 μm, added into a 20 wt% sodium hydroxide solution, the liquid-solid ratio is 5:1, and the temperature is kept at 120 DEG C for 6 h. After filtration, washing and drying, the desiliconized coal gangue solid product is obtained.

[0030] Example 2 The embodiment provides a process suitable for coal gangue roasting activation, comprising the following steps: (1) Coal gangue from a certain mining area in Ordos City, Inner Mongolia, was 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 was 1.0.

[0031] (2) The coal gangue raw material was sent into a tubular preheating furnace and heated to 200°C in an air atmosphere for 4 h to remove the volatile matter therefrom, thereby obtaining preheated coal gangue. The volatile gas discharged in this process was collected and introduced into a combustion chamber as external fuel for the subsequent roasting stage.

[0032] (3) The preheated coal gangue obtained in step (2) was 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 was 95:5, the total flow rate was 2 L / min, and the treatment time was 1 h. In this process, the organic matter and pyrite impurities in the coal gangue were decomposed, avoiding side reactions in the subsequent roasting, thereby obtaining phase-controlled treated coal gangue.

[0033] (4) The coal gangue obtained in step (3) was sent into a high-temperature rotary kiln and roasted in a mixed atmosphere of nitrogen, carbon dioxide, and water vapor. The volume fraction of nitrogen was 70%, the volume fraction of carbon dioxide was 20%, and the volume fraction of water vapor was 10% in the atmosphere, and the total flow rate was 5 L / min. The temperature program was as follows: heating to 950°C at a rate of 5°C / min and maintaining for 1 h, and then heating to 1150°C at a rate of 2°C / min and maintaining for 4 h. External fuel was used for heating during the roasting process, and part of the heat was provided by the combustion of the volatile matter removed in step (2), and the waste heat from the roasting was recovered as a heat source for the preheating furnace. After roasting, the activated coal gangue was obtained.

[0034] (5) During the cooling stage after roasting, a mixed gas containing 15% carbon dioxide, 15% water vapor, and the balance nitrogen was continuously introduced into the rotary kiln at a flow rate of 3 L / min until the temperature dropped to below 200°C. After cooling, the stabilized treated coal gangue was obtained.

[0035] (6) The coal gangue obtained in step (5) was ground to a particle size of less than 75 μm and added to a 30 wt% sodium hydroxide solution with a liquid-solid ratio of 8:1. The mixture was stirred and leached at 100°C for 3 h. After filtration, washing, and drying, the desilicated coal gangue solid product was obtained.

[0036] Example 3 This example provides a process suitable for the roasting and activation of coal gangue, comprising the following steps: (1) Coal gangue from a certain mining area in Ordos City, Inner Mongolia, was 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 was 0.96.

[0037] (2) The coal gangue raw material is sent into a tubular preheating furnace, heated to 700°C in an air atmosphere, and kept for 1 h, so that the volatile components are extracted, and preheated coal gangue is obtained. The volatile gas discharged in this process is collected and enters the combustion chamber as external fuel for the subsequent roasting stage.

[0038] (3) The preheated coal gangue obtained in step (2) is transferred to a medium-temperature reaction furnace, and nitrogen gas is introduced at 400°C for treatment, with a flow rate of 2 L / min, and a treatment time of 2 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.

[0039] (4) The coal gangue obtained in step (3) is sent into a high-temperature rotary kiln and roasted 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%, with a total flow rate of 5 L / min. The temperature rising program is as follows: heating to 950°C at a rate of 5°C / min and keeping for 1 h, and then heating to 1150°C at a rate of 2°C / min and keeping for 4 h. External fuel heating is used during the roasting process, and part of the heat is provided by the combustion of the volatile components extracted in step (2), and the waste heat from the roasting is recovered as a heat source for the preheating furnace. After roasting, the roasting-activated coal gangue is obtained.

[0040] (5) During the cooling stage after roasting, 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, the stabilized treated coal gangue is obtained.

[0041] (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 with a liquid-solid ratio of 3:1, and stirred at 50°C for 10 h. After filtration, washing, and drying, the desilicated coal gangue solid product is obtained.

[0042] Comparative Example 1 This comparative example provides a process suitable for coal gangue roasting activation, which is different from Example 1 in that the coal gangue does not undergo step (2) of volatile component extraction and step (3) of phase control treatment, and the coal gangue is directly roasted.

[0043] Comparative Example 2 This comparative example provides a process suitable for coal gangue roasting activation, which is different from Example 1 in that the coal gangue does not undergo step (3) of phase control treatment.

[0044] Comparative Example 3 The comparative example provides a process suitable for coal gangue roasting activation, which is different from example 1 in that the atmosphere for roasting in step (4) is air.

[0045] Comparative example 4 The comparative example provides a process suitable for coal gangue roasting activation, which is different from example 1 in that the roasting process in step (4) uses a single temperature rising program, i.e. directly rising to 1150℃ at a rate of 5℃ / min and maintaining for 5h without segmented temperature rising.

[0046] Comparative example 5 The comparative example provides a process suitable for coal gangue roasting activation, which is different from example 1 in that the cooling stage in step (5) uses natural cooling method, directly cooling to below 200℃ in air.

[0047] Performance test The products of examples 1-3 and comparative examples 1-5 are respectively tested for aluminum-silicon ratio, and the results are shown in Table 1.

[0048] Table 1 Performance test results

[0049] 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 comparison, comparative example 1 does not perform preheating and phase control treatment, resulting in volatile interfering with roasting and generating adverse by-phase, with extremely poor desiliconization effect. Comparative example 2 is preheated but not phase controlled, with impurities not completely decomposed, and the aluminum-silicon ratio is significantly low. Comparative example 3 uses air roasting, with excessive generation of mullite, limiting the dissolution of aluminum. Comparative example 4 does not use segmented temperature rising, with uneven crystal phase conversion, resulting in insufficient separation degree. Comparative example 5 does not use CO2 / water vapor slow cooling, with serious crystal phase reconstruction during cooling process, and obvious performance decline.

[0050] 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, which should also be considered within the protection scope 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 material; (2) feeding the coal gangue raw material into a preheating system, preheating at 200-750°C to remove volatile matter therefrom, to obtain preheated coal gangue; (3) passing the preheated coal gangue into an inert gas or a slightly reducing atmosphere at 400-600°C to obtain phase-controlled treated coal gangue; (4) feeding the phase-controlled treated coal gangue into a roasting system, roasting at 900-1200°C using external heat source to obtain roasted coal gangue; (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 for coal rejects torrefaction activation as claimed in claim 1 wherein, The inert gas in step (3) is nitrogen or argon; the slightly reducing atmosphere is a mixture of nitrogen or argon and carbon monoxide, wherein the volume fraction of carbon monoxide is 1-10%.

5. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The roasting time in step (4) is 0.1-16 h.

6. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The roasting atmosphere 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%.

7. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The roasting in step (4) adopts a staged temperature rising mode, first rising at a rate of 3-8°C / min to 900-1000°C and holding for 0.1-2 h, and then rising at a rate of 1-5°C / min to 1000-1200°C and holding for 0.1-16 h.

8. The process as claimed in claim 1, wherein the process is suitable for coal gangue roasting activation, characterized by, The volatile matter removed in step (2) is 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).

9. 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.

10. 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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