Resource utilization method of fly ash
By grading fly ash and alkali leach desilicate treatment, combined with aluminum thermal reduction and plasma smelting, the problems of high cost and low utilization in the high value-added utilization of fly ash are solved, efficient and environmentally friendly resource utilization is achieved, and the added value and purity of the product are improved.
Patent Information
- Application Number
- CN202510681182.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-26
- Publication Date
- 2025-08-22
AI Technical Summary
In the prior art, the high added value utilization of fly ash has problems such as high cost, large energy consumption and complex process, especially in the process of extracting alumina to produce electrolytic aluminum, and the utilization rate of high-alumina fly ash is relatively low.
By grading fly ash, large and small-grain fly ash were obtained respectively. Large-grain fly ash was treated by alkali leach desiliconization method, and mixed with carbonaceous reducing agent and binder to granulate and heat reduction was carried out. Smelting was performed using a plasma smelting furnace to obtain aluminum-silicon alloy products. At the same time, magnetic separation and solid-liquid separation were performed simultaneously to prepare water glass and aerogel products.
The full-component resource utilization of fly ash has been achieved, with a utilization rate of more than 95%, which reduces treatment costs, increases product profits, reduces secondary pollution, and improves the purity and added value of the target product.
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Figure CN120519699A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of industrial solid waste resource utilization, and in particular to a method for resource utilization of fly ash. Background Art
[0002] Fly ash, a solid waste generated by coal-fired power plants, primarily consists of oxides such as silicon, aluminum, calcium, iron, titanium, and gallium. The national standard "GB / T 39201-2020" defines fly ash from coal-fired power plants as high-alumina fly ash if its Al2O3 content is ≥40% and its aluminum-silicon ratio is greater than 1.0; and as semi-high-alumina fly ash if its Al2O3+SiO2+Fe2O3 content is ≥80% and its Al2O3 content is ≥38%.
[0003] At present, more than 90% of fly ash is mainly concentrated in low-value-added utilization in the building materials field, such as serving as cement additives, used in concrete and wall materials, etc., while high-value-added utilization, such as extracting valuable metals and producing high-performance materials, is relatively lagging behind.
[0004] The high value-added utilization route of fly ash in related technologies is mainly: first desiliconize the high-aluminum fly ash to extract Al2O3, and then electrolyze Al2O3 to extract metallic aluminum.
[0005] Conventional alkaline leaching desiliconization procedures are as follows: High-aluminum fly ash is first finely ground to a particle size of 0.5 to 75 μm (the particle size range for fly ash is 0.5 to 300 μm). The ground fly ash is then immersed in an alkaline solution, heated and stirred for desiliconization. The solid-liquid separation results in a crude water glass solution, achieving desiliconization and increasing the aluminum content in the solid slag, making it easier to process and utilize in the next step. This step requires fine grinding and consumes a large amount of alkaline solution, resulting in high desiliconization costs.
[0006] In addition, the above-mentioned process of producing electrolytic aluminum using alumina is complex and also has the problems of high cost and huge energy consumption. Summary of the Invention
[0007] In view of this, the object of the present invention is to provide a method for resource utilization of fly ash. The method of the present invention not only realizes resource utilization of fly ash, but also has the advantages of simple process, low processing cost and high product profit, further increasing the added value of fly ash.
[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:
[0009] The present invention provides a method for resource utilization of fly ash, comprising the following steps:
[0010] Classifying fly ash to obtain large-particle fly ash and small-particle fly ash; the particle size boundary of the classification is 30 to 45 μm; the mass content of Al2O3 and SiO2 in the fly ash is ≥70%, and the mass content of Al2O3 is ≥30%;
[0011] Desiliconizing the large-particle fly ash by alkali leaching, and obtaining desiliconized fly ash after solid-liquid separation;
[0012] The desiliconized fly ash, the small-particle fly ash, a carbonaceous reducing agent and a binder are mixed, the obtained mixture is granulated, and the granules are obtained by drying;
[0013] The pellets are smelted to undergo aluminothermic reduction, and the resulting melt is gravity-separated to obtain an aluminum-silicon alloy liquid in the upper layer and a multi-component alloy liquid in the lower layer; the smelting temperature is 2250-2450° C.;
[0014] Aluminum powder and / or silicon powder are added to the aluminum-silicon alloy liquid to adjust the chemical composition to obtain an aluminum-silicon alloy product.
[0015] Preferably, the smelting is carried out in a plasma smelting furnace.
[0016] Preferably, magnetic separation is performed simultaneously with the classification to collect the iron oxide powder.
[0017] Preferably, the alkali solution used in the alkali leaching desiliconization is a sodium hydroxide solution, and the mass concentration of the sodium hydroxide solution is 30-50%.
[0018] Preferably, the solid-liquid separation further obtains a solution containing sodium silicate, and the solution containing sodium silicate is used to prepare a water glass product and / or an aerogel product.
[0019] Preferably, after obtaining the multicomponent alloy liquid, the method further comprises: solidifying the multicomponent alloy liquid and using it as a deoxidizer for steelmaking.
[0020] Preferably, the binder comprises high alumina clay and water glass;
[0021] The mass content of Al2O3 in the high-alumina clay is 30-50%; the mass content of high-alumina clay in the mixture is 8-13%;
[0022] The modulus of the water glass is 1.5 to 3.5, and the Baume concentration is 30 to 60 degrees Bé; the mass content of the water glass in the mixture is 2 to 3%.
[0023] Preferably, the carbonaceous reducing agent comprises bituminous coal powder; the mass content of C in the bituminous coal powder is greater than 85%.
[0024] Preferably, the mass ratio of the total mass of the desiliconized fly ash and the small-particle fly ash to the carbonaceous reducing agent is 1.2 to 2.3:1.
[0025] Preferably, the smelting process also produces fly ash, which is used as a filler for rubber or plastic.
[0026] The applicant's research has found that small fly ash particles, with a particle size of 30 to 45 μm as the demarcation point, have a lower silicon dissolution rate. Based on this, the present invention separates fly ash into two fractions (i.e., coarse and fine particles)—large and small. The small particles are not subjected to fine grinding or alkali leaching. Large particles, however, do not require fine grinding due to their higher silicon dissolution rate. Alkaline leaching results in solid-liquid separation, and the aluminum in the core remains in the solid slag (i.e., desiliconized fly ash) for further utilization. The present invention replaces the full alkali leaching desiliconization process with a graded treatment based on particle size, eliminating fine grinding. Separating small particles reduces desiliconization by 40 to 50%, lowering processing costs.
[0027] Furthermore, the present invention innovatively utilizes fly ash in the smelting of aluminum-silicon alloys, offering advantages over existing electrolytic aluminum production processes that extract alumina, resulting in lower processing costs and higher product profits. By controlling the smelting temperature, the present invention ensures that the aluminothermic reduction reaction proceeds fully, yielding a qualified aluminum-silicon alloy product.
[0028] Furthermore, the present invention simultaneously performs magnetic separation during grading, collecting iron oxide powder that can be used as raw material for ironmaking in ironworks; after alkaline leaching and desiliconization, a sodium silicate solution is obtained, which can be used to prepare water glass products or higher value-added aerogel products; the multi-component alloy liquid produced by smelting is used as a deoxidizer for steelmaking after solidification, and the fly ash produced is used as a filler for rubber or plastic. The present invention almost achieves resource utilization of all components of fly ash, with a utilization rate exceeding 95%, reaching a maximum of 98%, far exceeding the previous fly ash utilization rate (50-60%). In addition, the present invention does not emit secondary pollution, which is a problem with the process of extracting alumina to produce electrolytic aluminum.
[0029] In addition, the present invention simultaneously performs magnetic separation during classification, which can remove iron oxide impurities and improve the purity of a series of subsequent target products (including aluminum silicon alloy, aerogel products, and water glass products). BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 Schematic diagram of a fly ash resource utilization method in a specific embodiment;
[0031] Figure 2 This is a comparison chart of silicon dissolution rates of large-particle fly ash and small-particle fly ash. DETAILED DESCRIPTION
[0032] The present invention provides a method for resource utilization of fly ash, comprising the following steps:
[0033] Classifying fly ash to obtain large-particle fly ash and small-particle fly ash; the particle size boundary of the classification is 30 to 45 μm; the mass content of Al2O3 and SiO2 in the fly ash is ≥70%, and the mass content of Al2O3 is ≥30%;
[0034] Desiliconizing the large-particle fly ash by alkali leaching, and obtaining desiliconized fly ash after solid-liquid separation;
[0035] The desiliconized fly ash, the small-particle fly ash, a carbonaceous reducing agent and a binder are mixed, the obtained mixture is granulated, and the granules are obtained by drying;
[0036] The pellets are smelted to undergo aluminothermic reduction, and the resulting melt is gravity-separated to obtain an aluminum-silicon alloy liquid in the upper layer and a multi-component alloy liquid in the lower layer; the smelting temperature is 2250-2450° C.;
[0037] Aluminum powder and / or silicon powder are added to the aluminum-silicon alloy liquid to adjust the chemical composition to obtain an aluminum-silicon alloy product.
[0038] In the present invention, unless otherwise specified, the raw materials and equipment used are commercially available products well known in the art.
[0039] The invention classifies fly ash to obtain large-particle fly ash and small-particle fly ash.
[0040] In the present invention, the mass content of Al2O3 and SiO2 in the fly ash is ≥70%, preferably 70-95%; and the mass content of Al2O3 is ≥30%. The present invention does not require the aluminum-silicon ratio of the fly ash, and it only needs to meet the above content requirements. The fly ash of the present invention is different from the high-aluminum fly ash defined in the national standard. The mass content of Al2O3 can be ≥30%, which is lower than the national standard requirement of Al2O3 mass content ≥40%. The method of the present invention can increase the processing capacity of fly ash and is more universal. In the present invention, the particle size of the fly ash is preferably 0.5-300μm. In the present invention, the total mass content of oxides of elements such as silicon, aluminum, calcium, titanium, gallium, and iron in the fly ash is preferably greater than 90%.
[0041] In the present invention, the classification is preferably airflow classification; the present invention preferably performs the classification in a multi-stage airflow classifier. In the present invention, the classification divides the fly ash into two parts, namely large-particle fly ash and small-particle fly ash. In the present invention, the particle size boundary of the classification is 30 to 45 μm. In an embodiment of the present invention, the particle size boundary of the classification can specifically be 30 μm, 35 μm, 40 μm or 45 μm. The present invention controls the particle size of the classification to be 30 to 45 μm, and the mass of the small-particle fly ash obtained will not exceed 50% of the total mass of the fly ash, which can reduce the total amount of silicon in the small-particle fly ash, thereby reducing the amount of aluminum powder used in the subsequent chemical composition preparation of the aluminum-silicon alloy liquid, and reducing the production cost of the aluminum-silicon alloy.
[0042] In the present invention, the small-particle fly ash is mainly composed of Al2O3, and the mass content of Al2O3 in the small-particle fly ash is preferably ≥45%; the large-particle fly ash is mainly composed of amorphous SiO2, and the mass content of SiO2 in the large-particle fly ash is preferably 60-90%.
[0043] The applicant's research found that the Al2O3 content in small-particle fly ash is higher than that in large-particle fly ash. The main reasons are as follows: First, it is caused by different formation mechanisms. Specifically, during coal combustion, high temperature causes a series of complex changes in minerals such as melting and gasification. Aluminum compounds have certain volatility and will appear in gaseous form during the combustion process. As the temperature gradually decreases, gaseous aluminum compounds will first condense and deposit on small-particle crystal nuclei, causing the aluminum content of smaller particles to increase; on the other hand, it is caused by the sorting effect. Specifically, in the natural sedimentation or wind sorting after the formation of fly ash, small-particle aluminum-containing particles are more easily entrained by airflow and gathered in specific areas due to their lighter weight and larger specific surface area, while large-particle particles are more inclined to settle. Therefore, after sorting, the aluminum content in the small-particle fly ash is relatively high.
[0044] In the present invention, the small-particle fly ash has stable chemical properties and a dense crystal structure, is not easily reacted or destroyed under alkali leaching conditions, and can exist in a pure small particle form. By classifying the fly ash and separating the small-particle fly ash, the present invention can reduce the amount of alkali leaching by 40-50%, thereby lowering processing costs.
[0045] In the present invention, magnetic separation is preferably performed simultaneously with the classification to collect iron oxide powder; the magnetic field strength of the magnetic separation is preferably greater than 1.5 T. In the present invention, a neodymium iron boron dry magnetic separator is preferably used for magnetic separation. The magnetic separation performed during the classification process can remove the iron oxide component without increasing costs, reducing the impact of iron oxide as an impurity. The collected iron oxide powder can be used as raw material for ironmaking in ironworks.
[0046] Conventional iron removal uses chemical methods. For example, by adding a flux containing boron compounds (such as boric acid or boron carbide) to a high-aluminum alloy melt, the boron reacts with iron to form high-melting-point ferroboron compounds (such as FeB). These compounds have high density and are easily separable from the melt, allowing them to be removed through scum. The present invention uses a physical method for iron removal, which is both simple and economical.
[0047] After obtaining the large-particle fly ash, the present invention performs alkaline leaching on the large-particle fly ash to desiliconize, and obtains desiliconized fly ash after solid-liquid separation.
[0048] In the present invention, the alkali solution used for alkali leaching and desiliconization is preferably sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 30-50% (at this time, the pH value of the alkali leaching system is maintained at 10-12), and in specific embodiments, it can be 30%, 35%, 40%, 45%, or 50%; in the present invention, the temperature of the alkali leaching and desiliconization is preferably 80-110°C, and in specific embodiments, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, or 110°C; the time of the alkali leaching and desiliconization is preferably 1.5-3 hours, and in specific embodiments, it can be 1.5 hours, 2 hours, 2.5 hours, or 3 hours. In the present invention, the volume ratio of the sodium hydroxide solution to the mass of the large-particle fly ash (i.e., the liquid-to-solid ratio) is preferably (3-10) L:1 kg, and in specific embodiments, it can be 3 L:1 kg, 5 L:1 kg, 7 L:1 kg, or 10 L:1 kg. In the present invention, the alkali leaching and desiliconization is preferably carried out under stirring conditions. In the alkali leaching process of the present invention, SiO2 reacts with NaOH to generate sodium silicate and water.
[0049] The applicant's research has found that fly ash with a small particle size of 30-45 μm has a low silicon dissolution rate. Therefore, fine grinding and alkaline leaching are not required for small fly ash particles. The present invention eliminates fine grinding and alkaline leaching for small fly ash particles, saving costs while still maintaining a high alumina content in the small fly ash particles.
[0050] Large-particle fly ash does not need fine grinding due to its high silicon dissolution rate. The present invention directly leaches the silicon element on the outer layer of the large-particle fly ash into the alkaline solution to remove it, while the aluminum element remains in the core for further use.
[0051] The present invention has no special limitation on the solid-liquid separation, and any solid-liquid separation method well known in the art may be used, such as filtration.
[0052] After completing the solid-liquid separation, the present invention obtains desiliconized fly ash, which is used to prepare silicon-aluminum alloy together with the aforementioned small-particle fly ash; when the alkali solution used for alkali leaching desiliconization is sodium hydroxide solution, a solution containing sodium silicate is also obtained after solid-liquid separation.
[0053] In the present invention, the sodium silicate-containing solution can be sold directly, or used to prepare water glass products and / or aerogel products.
[0054] Desiliconized fly ash is obtained above. In the present invention, the desiliconized fly ash, the small-particle fly ash, a carbonaceous reducing agent and a binder are mixed, the obtained mixture is granulated, and granules are obtained by drying.
[0055] The present invention has no special requirements on the ratio of the desiliconized fly ash and the small-particle fly ash, and any ratio is acceptable.
[0056] In the present invention, the carbonaceous reducing agent preferably comprises bituminous coal powder; the carbon content of the bituminous coal powder is preferably greater than 85% by mass; and the mass ratio of the total mass of the desiliconized fly ash and small-particle fly ash to the carbonaceous reducing agent is preferably 1.2 to 2.3:1. In specific embodiments, the ratio may be 1.2:1, 1.8:1, or 2.3:1.
[0057] In the present invention, the binder preferably includes high-alumina clay and water glass; the mass content of Al2O3 in the high-alumina clay is preferably 30-50%, and in specific embodiments, it can be 30%, 35%, 40%, 45%, or 50%; the mass content of the high-alumina clay in the mixture is preferably 8-13%, and in specific embodiments, it can be 8%, 9%, 10%, 11%, 12%, or 13%. In the present invention, the high-alumina clay can promote the shaping of the raw materials.
[0058] In the present invention, the water glass preferably has a modulus of 1.5 to 3.5 and a Baume concentration of 30 to 60°Bé. The water glass content in the mixture is preferably 2 to 3% by weight. In the present invention, the water glass is preferably the homemade water glass product described above. Using homemade water glass reduces costs. The water glass exhibits excellent bonding properties as a binder.
[0059] In the present invention, the mixing preferably includes: subjecting desiliconized fly ash, small-particle fly ash, a carbonaceous reducing agent, and high-alumina clay to a primary strong stirring and mixing to obtain a primary mixture; and subjecting the primary mixture to a secondary strong stirring and mixing with water glass. The present invention achieves preliminary blending of the raw materials through primary strong stirring, and promotes thorough mixing of the raw materials and water glass through secondary strong stirring to achieve a uniform dispersion effect, thereby laying a good foundation for subsequent granulation. In the present invention, the primary strong stirring and the secondary strong stirring are preferably carried out in different strong stirring machines; the primary strong stirring and the secondary strong stirring are preferably kneading.
[0060] In the present invention, the granulation preferably includes: agglomerating the mixed material to obtain wet pellets. In the present invention, the wet pellets are preferably dried and then sieved to obtain granules.
[0061] In the present invention, the agglomeration is preferably performed by pressing the mixture into agglomerates, and the agglomeration is preferably performed in a pellet press. The pellet press press presses the mixture into wet pellets by means of strong pressure, and these wet pellets are conveyed to the subsequent pellet drying process via a belt conveyor.
[0062] The present invention does not impose any particular restrictions on the drying conditions; drying conditions well known in the art may be employed. In the present invention, the moisture content of the pellets is preferably 1-3%. In the present invention, the pellet size is not particularly limited; any size well known in the art may be employed, and in a specific embodiment, the pellet size may be 50 mm ± 5 mm.
[0063] In the present invention, the screening is preferably performed using a vibrating screen. In the present invention, the undersize material produced by the screening, as well as the crushed powder produced for various reasons during the drying process, are preferably mixed with newly added raw materials and reintroduced into the mixing and granulation process. By reintroducing the undersize material and crushed powder into the mixing and granulation process, the present invention achieves material recycling and improves resource utilization.
[0064] After obtaining the pellets, the present invention smelts the pellets to obtain a melt.
[0065] In the present invention, the smelting temperature is 2250-2450°C. In specific embodiments, the smelting temperature can be 2250°C, 2300°C, 2350°C, 2400°C, or 2450°C. The smelting time is preferably 1-1.5 hours. The smelting is preferably carried out in a semi-enclosed environment and in air. In the present invention, the semi-enclosed environment refers to the organized collection and discharge of smoke generated by the smelting.
[0066] In the related art, coal gangue is generally used to smelt aluminum silicon alloys, and the smelting equipment used is a reduction ore-fired furnace (DC arc). There are no reports on the use of fly ash to smelt aluminum silicon alloys. It is particularly important to note that although high-aluminum coal gangue and high-aluminum fly ash have some similarities, there are still great differences in the processing process, and improvements are needed before they can be used for high-aluminum fly ash processing. In addition, the use of a reduction ore-fired furnace and fly ash as raw material to smelt aluminum silicon alloys will result in a large amount of residual impurities in the target product, aluminum silicon alloy. The applicant's research found that this is because the average bond energy of Al2O3 is higher than that of other metal oxides, so the melting temperature is higher (2051.6°C), and it can be fully decomposed into aluminum and oxygen ions above 2250°C. However, the temperature of the reduction furnace cannot meet the corresponding redox conditions of alumina (the operating temperature of the reduction furnace body is 1600-1800°C, and the maximum temperature is only about 2200°C), resulting in insufficient redox reaction during the smelting process. In particular, it is easy to form a false furnace bottom. After the false furnace bottom reaches a certain thickness, the furnace needs to be stopped to cool down and manually cleaned. Frequent cleaning of the false furnace bottom affects production efficiency and increases production costs. The present invention preferably uses a plasma melting furnace for smelting, which overcomes the above technical obstacles and can meet the temperature requirements of smelting.
[0067] From a kinetic perspective, the high-temperature environment created by the plasma melting furnace acts as a powerful catalyst for the reaction, significantly increasing its rate. Under high temperatures, the thermal motion of the carbonaceous reducing agent and Al₂O₃ particles becomes more intense, significantly increasing the frequency and energy of collisions between them. This allows the reactant molecules to more easily cross the activation energy barrier, further accelerating the reaction.
[0068] From the perspective of plasma properties: plasma possesses the remarkable characteristics of high energy and high activity. Within the plasma melting furnace, plasma interacts with Al2O3 and the carbonaceous reducing agent. On the one hand, plasma further promotes the decomposition of Al2O3, reducing its reduction difficulty and making it easier to reduce. On the other hand, plasma significantly increases the chemical activity of the carbonaceous reducing agent, significantly enhancing its reducing ability, thereby effectively promoting the reduction reaction and significantly improving reaction efficiency.
[0069] Furthermore, the overall temperature inside a plasma smelting furnace is much higher than that of a reduction furnace, and the furnace bottom temperature also rises significantly. This greatly improves the fluidity of the furnace bottom deposits, making furnace bottom cleaning easier and effectively solving the problem of a false furnace bottom. The so-called false furnace bottom of a reduction furnace refers to a layer of material or special state with furnace bottom properties that gradually forms above the actual furnace bottom due to the interaction of multiple complex factors. Because it lacks fluidity, the reduction furnace must be shut down and cooled before cleaning, which is a tedious task and affects processing efficiency.
[0070] In the present invention, the granular material is preferably delivered to a top hopper of a plasma smelting furnace, and then put into the plasma smelting furnace from the top hopper.
[0071] In the smelting process of the present invention, the aluminothermic reduction reaction is fully generated, the carbonaceous reducing agent reacts with Al2O3 to reduce Al from its oxide, and finally form an aluminum silicon alloy.
[0072] After the smelting is completed, the present invention preferably cools the resulting melt from the smelting temperature to 600° C. and allows it to stand, and then heats it to 650° C. for gravity separation.
[0073] In the present invention, the cooling rate is preferably 5-7°C / min; the heating rate is preferably 5-7°C / min. In a specific embodiment, the melt is transferred to a cooling tunnel kiln via a ferry ladle for cooling. After cooling to 600°C and allowing to stand, the melt is transferred to a heating tunnel kiln for heating. In the present invention, the standing time is preferably 20-60 minutes.
[0074] The present invention has the following effects through cooling and standing: (1) Improving gas precipitation: Slow cooling and standing is conducive to giving gas more time to precipitate from the alloy liquid before solidification, reducing the internal porosity defects of the casting, thereby improving the density of the alloy and being beneficial to the improvement of mechanical properties. (2) Promoting composition homogenization: During the cooling and standing process, the elements in the alloy have more time to diffuse, which helps to improve the composition segregation phenomenon that may be caused by excessive temperature, making the alloy composition more uniform and improving the consistency of performance. (3) Refining grains: Although high temperature has caused the grains to grow, slow cooling can slow down the grain growth rate and may promote the formation of some new crystal nuclei, thereby refining the grains to a certain extent and restoring the strength and toughness of the alloy.
[0075] In addition, since some organizational forms that are not conducive to performance or internal stress may be formed during the cooling process, the present invention can recrystallize the aluminum-silicon alloy melt by reheating, so that dislocations are reorganized and annihilated, and the hardness of the aluminum-silicon alloy is reduced, and the ductility and toughness are improved, which is convenient for subsequent processing or meeting the requirements for soft products. At the same time, it can eliminate the internal stress generated during the cooling process, stabilize the size and performance of the alloy, and prevent problems such as deformation or cracking during subsequent use.
[0076] In the present invention, the gravity separation is preferably carried out in a gravity separation device. After gravity separation, an aluminum-silicon alloy liquid (55-65% by mass) is obtained in the upper layer, and a multi-component alloy liquid is obtained in the lower layer.
[0077] The present invention does not impose any special requirements on the gravity separation device, and any gravity separation device well known in the art can be used, such as a centrifuge.
[0078] In the present invention, the mass content of Si in the aluminum-silicon alloy liquid is preferably 8-13%, the mass content of Al is preferably ≥85%, and the mass content of iron is preferably ≤0.7%; the aluminum-silicon alloy liquid fully meets the quality requirements of casting aluminum-silicon alloys and successfully achieves the goal of producing high value-added products.
[0079] In the present invention, the composition of the multi-component alloy liquid is preferably such that the aluminum content is less than 15% by mass.
[0080] After obtaining the aluminum-silicon alloy liquid, the present invention adds aluminum powder and / or silicon powder to the aluminum-silicon alloy liquid to adjust the chemical composition to obtain an aluminum-silicon alloy product.
[0081] The present invention preferably places the aluminum-silicon alloy liquid in a medium frequency melting furnace for chemical composition preparation. In the medium frequency melting furnace, the aluminum-silicon alloy liquid can maintain its liquid heat preservation state.
[0082] The present invention adjusts the chemical composition according to actual needs to meet the market demand for aluminum-silicon alloys of different specifications. Specifically, the alloy can be adjusted according to the chemical composition of the ZL102 alloy, and then cast to obtain ZL102 alloy ingots that meet market specifications for sale.
[0083] The obtained multi-component alloy liquid is preferably solidified and used as a deoxidizer for steelmaking in the present invention; specifically, it can be sold to steel mills for use to exert its deoxidation effect in the steelmaking process.
[0084] In the present invention, fly ash is also generated during the smelting process, and the fly ash is preferably used as a filler for rubber or plastic. In the present invention, the fly ash comprises a significant proportion of metal oxides, primarily SiO2 and Al2O3, with possible inclusions of CaO, Fe2O3, and MgO. These metal oxides form the primary material basis of the fly ash, with SiO2 and Al2O3 enhancing the hardness, wear resistance, and heat resistance of rubber and plastic materials. The present invention sells fly ash as a filler for rubber and plastic, achieving resourceful waste utilization and further enhancing the economic and environmental benefits of the entire production process.
[0085] Figure 1 FIG. 1 is a flow chart of a method for resource utilization of fly ash in a specific embodiment. Figure 1As shown, the present invention first classifies fly ash to obtain large-particle fly ash and small-particle fly ash respectively; the large-particle fly ash is subjected to alkali leaching for desiliconization, and desiliconized fly ash and a sodium silicate-containing solution are obtained after solid-liquid separation; the sodium silicate-containing solution (crude water glass) can be used to prepare aerogel products after impurities are removed; the desiliconized fly ash, the small-particle fly ash, a carbonaceous reducing agent and a binder are mixed, and the obtained mixture is granulated to obtain pellets; the pellets are smelted, and the obtained melt is gravity-separated to obtain aluminum-silicon alloy liquid in the upper layer and multi-component alloy liquid in the lower layer; aluminum powder and / or silicon powder are added to the aluminum-silicon alloy liquid to adjust the chemical composition to obtain an aluminum-silicon alloy product; the multi-component alloy liquid is solidified and sold as a deoxidizer for steelmaking; fly ash is also generated during the smelting process, and the fly ash is used as a filler for rubber or plastic.
[0086] The present invention realizes resource utilization of almost all components of fly ash, with a utilization rate exceeding 95% and reaching 98% at the highest. Only a small amount of slag produced during the smelting process cannot be utilized.
[0087] The fly ash resource utilization method provided by the present invention is described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0088] Example 1
[0089] The particle size of fly ash is 0.5-300 μm, and the composition is: Al2O3+SiO2+Fe2O3≥80%, and Al2O3≥30%;
[0090] Fly ash is classified using a multi-stage airflow classifier to separate the fly ash into two parts: small-particle fly ash and large-particle fly ash. The small-particle fly ash has a particle size of less than 45 μm, and the remainder is large-particle fly ash. During the classification process, a NdFeB dry magnetic separator is used for magnetic separation with a magnetic field strength of 2 T. Iron oxide powder is collected and sold as raw material for ironmaking in ironworks.
[0091] The large-particle fly ash is placed in a sodium hydroxide solution with a mass concentration of 40%, and alkali leaching is performed under stirring at a temperature of 80° C., a time of 1.5 hours, and a liquid-to-solid ratio of 5:1. The solution is filtered to obtain desiliconized fly ash and a solution containing sodium silicate;
[0092] The modulus of the sodium silicate-containing solution is adjusted to 2, and the solution is concentrated and then impurities are removed to obtain a water glass product with a Baume concentration of 40°Bé; part of the water glass product is used in the subsequent kneading and agglomeration process, and part can be used to prepare an aerogel product;
[0093] Desiliconized fly ash, small-particle fly ash, high-aluminum bituminous coal powder (C content >85% by mass), and high-aluminum clay (Al2O3 content of 35% by mass) are collected together via a weighing screw conveyor and then conveyed to a closed belt conveyor. The kneading process is equipped with a two-stage high-pressure stirring device. The measured raw materials first enter the first-stage high-pressure stirring device for preliminary mixing to allow the various components to initially blend. The materials then enter the second-stage high-pressure mixer. At this stage, water glass (with a modulus of 2 and a Baume concentration of 40°Bé, obtained in-house) is added to obtain a mixture. The mass ratio of the total mass of the desiliconized fly ash and small-particle fly ash to the bituminous coal powder is 1.7:1. The mass content of water glass in the mixture is 3%, and the mass content of high-aluminum clay is 12%.
[0094] The kneaded mixture enters the agglomeration process. In this process, the raw materials are evenly transported by a quantitative feeder to a pelletizer, which presses the materials into elliptical wet pellets. These wet pellets are then sent to a dryer for drying. The dried pellets (with a moisture content of 2%) are screened by a vibrating screen. The qualified pellets on the screen (size 50mm±5mm) are sent to the finished pellet bin via a belt conveyor, ready to be fed into the aluminum-silicon alloy smelting process as granular material. The undersize material from the vibrating screens before and after the dryer, as well as the broken powder generated by various reasons during the drying process, are collected together on the return conveyor, mixed with the newly added raw materials, and once again participate in the kneading and agglomeration process, realizing material recycling.
[0095] The qualified pellets prepared through the previous process are transported to the top hopper of the plasma melting furnace. Subsequently, the pellets are put into the plasma melting furnace from the top hopper. The plasma melting furnace power is set to 500kW. The melting is carried out at a high temperature of 2350℃ for 1.5 hours. The produced molten liquid is smoothly transported to the cooling tunnel kiln through the ferry casting bag. The temperature is gradually reduced from 2350℃ to 600℃ (cooling rate is 6℃ / min) in the cooling tunnel kiln and allowed to stand for 30 minutes. The molten liquid that has completed the cooling is sent to the heating tunnel kiln. The temperature is increased to 650℃ at a rate of 6℃ / min in the heating tunnel kiln. The obtained molten liquid is centrifuged. After separation, the upper layer obtains aluminum-silicon alloy liquid and the lower layer obtains multi-component alloy liquid, whose aluminum content is ≤15% and other components are ≥85%;
[0096] The aluminum-silicon alloy liquid is transported to a medium frequency melting furnace, where aluminum powder is added to accurately adjust its chemical composition. After adjustment, the iron content is controlled to be ≤0.7%, the silicon content is ≤13%, and the aluminum content is ≥85%. The aluminum-silicon alloy liquid is cast into ZL102 alloy ingots that meet market specifications and are sold to the market.
[0097] The separated multi-component alloy liquid solidifies into a block form, and after shaping, it is sold to steel mills as a deoxidizer to play its deoxidation role in the steelmaking process;
[0098] In addition, fly ash collected during the smelting process is sold as filler for rubber and plastics.
[0099] The resource utilization rate of the fly ash in Example 1 is 98% (resource utilization rate=(amount of fly ash used-amount of slag) / amount of fly ash used*100%).
[0100] Test Example 1
[0101] Dissolution experiment of fly ash with different particle sizes:
[0102] The fly ash has a particle size of 0.5 to 300 μm and a composition of Al2O3+SiO2+Fe2O3≥80%, with Al2O3≥30%. The fly ash is sieved using a 45 μm standard sieve to separate into fine particle components of <45 μm and coarse particle components of ≥45 μm.
[0103] The test conditions are shown in Table 1; a total of 9 parallel experiments were set up, namely: alkaline leaching was carried out in sodium hydroxide solutions with mass concentrations of 30%, 40% and 50% at 85°C, 95°C and 105°C, respectively.
[0104] Table 1 Alkali leaching conditions
[0105] Parameter Category Specific settings Types of lye Sodium hydroxide (NaOH) solution, mass concentration gradient: 30%, 40%, 50% Reaction temperature Temperature gradient: 85℃, 95℃, 105℃ Reaction time Fixed value: 2.5h Liquid-to-solid ratio (L / S) Fixed value: 5:1 (volume to mass ratio) Stirring rate Fixed value: 10r / min Leachate detection time 1.0h, 1.5h, 2.0h, 2.5h (corresponding to real-time sampling during the reaction process)
[0106] The test steps are as follows:
[0107] 1. Sample weighing and loading: Accurately weigh 50.0 g of fly ash samples <45 μm and ≥45 μm respectively and place them in a 1000 mL reactor with heating and stirring function.
[0108] 2. Alkali leaching reaction operation: Add NaOH solution of corresponding concentration according to the set liquid-solid ratio, adjust the reaction system to the target temperature and stirring rate, and start the timing to carry out the alkali leaching reaction.
[0109] 3. Leachate Analysis: Leachate was rapidly extracted at preset time points (1.0 h, 1.5 h, 2.0 h, and 2.5 h). The Na2SiO3 concentration in the solution was determined by spectrophotometry, and the desiliconization rate was calculated. The test results are shown in Table 2.
[0110] Table 2 Test results
[0111] Particle size Desiliconization rate range (%) Typical characteristics <45μm 20～35％ The desiliconization efficiency is low and increases slowly with the extension of reaction time. ≥45μm 50～85％ Desiliconization efficiency is significantly higher than fine particles
[0112] Table 3 shows the desiliconization of small-particle fly ash (<45μm) and large-particle fly ash (≥45μm) when the mass concentration of sodium hydroxide is 40% and the reaction temperature is 85°C. Table 4 shows the chemical composition of small-particle fly ash and large-particle fly ash.
[0113] Table 3 Desiliconization of small-particle fly ash and large-particle fly ash
[0114]
[0115] Table 4 Composition of small particle fly ash and large particle fly ash
[0116] quality <45μm ≥45μm Original ash 100g 50g 50g Alumina 40g 23g 17g Silicon oxide 35g 15.75g 19g other 25g 11.25g 14g
[0117] The results in Table 3 are plotted as a graph. Figure 2 From Table 3 and Figure 2 It can be seen that the silicon dissolution rate of small-particle fly ash is lower, while the silicon dissolution rate of large-particle fly ash is higher.
[0118] Result Analysis
[0119] 1. Influence of particle size: The desiliconization rate of coarse particles (>45μm) is significantly higher than that of fine particles (<45μm), which is presumably related to the more developed internal pore structure of coarse particles and the smoother diffusion path of alkali solution.
[0120] 2. Process parameter correlation:
[0121] Alkali solution concentration: Increasing the concentration (30%→50%) significantly accelerates the desiliconization rate, and high-concentration alkali solution enhances the solubility of silicate minerals in fly ash.
[0122] Reaction temperature: The desiliconization efficiency increases linearly with increasing temperature (85°C → 105°C), which is consistent with the Arrhenius equation describing the effect of temperature on the chemical reaction rate.
[0123] Leaching time: The desiliconization rate continued to increase with the extension of reaction time, and at 2.5h, the reaction was close to equilibrium under all conditions.
[0124] Examples 2-3 and Comparative Example 1
[0125] The only difference from Example 1 is that the melting temperatures are 2250° C., 2450° C., and 2150° C. The furnace bottom production conditions of the various examples and comparative examples are summarized in Table 5.
[0126] Table 5 Furnace bottom production of the embodiment and the comparative example
[0127] Example 1 Example 2 Example 3 Comparative Example 1 2350℃ 2250℃ 2450℃ 2150℃ No false furnace bottom There is a slight false bottom No false furnace bottom There is an obvious false furnace bottom
[0128] Note: Method for judging the condition of furnace bottom: After smelting, pour out the melt and use a metal rod to detect the furnace bottom (the specific condition can be judged by the depth of the scratches). The thicker the thickness, the deeper the scratches, and the more serious the false furnace bottom.
[0129] Systematic testing at gradient temperatures of 2150°C, 2250°C, 2350°C, and 2450°C demonstrated that the chemical composition and mechanical properties of the silicon-aluminum alloy products remained highly consistent, meeting quality standards. However, as the temperature gradually increased, the kinetics of the redox reaction significantly enhanced, the reaction progressed more completely, and the melting cycle was effectively shortened. The fluidity of the melt was significantly improved, facilitating subsequent process operations. At a melting temperature of 2150°C, a noticeable false bottom remained. However, as the temperature increased, this problem was essentially eliminated, significantly reducing the constraints on production efficiency.
[0130] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.
Claims
1. A method for resource utilization of fly ash, characterized in that: The following steps are involved: Classifying fly ash to obtain large-particle fly ash and small-particle fly ash; the particle size boundary of the classification is 30 to 45 μm; the mass content of Al2O3 and SiO2 in the fly ash is ≥70%, and the mass content of Al2O3 is ≥30%; Desiliconizing the large-particle fly ash by alkali leaching, and obtaining desiliconized fly ash after solid-liquid separation; The desiliconized fly ash, the small-particle fly ash, a carbonaceous reducing agent and a binder are mixed, the obtained mixture is granulated, and the granules are obtained by drying; The pellets are smelted to undergo aluminothermic reduction, and the resulting melt is gravity-separated to obtain an aluminum-silicon alloy liquid in the upper layer and a multi-component alloy liquid in the lower layer; the smelting temperature is 2250-2450° C.; Aluminum powder and / or silicon powder are added to the aluminum-silicon alloy liquid to adjust the chemical composition to obtain an aluminum-silicon alloy product.
2. The resource utilization method according to claim 1, characterized in that: The smelting is carried out in a plasma melting furnace.
3. The resource utilization method according to claim 1, characterized in that: During the classification, magnetic separation is performed simultaneously to collect the iron oxide powder.
4. The resource utilization method according to claim 1, characterized in that: The alkali solution used in the alkali leaching desiliconization is a sodium hydroxide solution, and the mass concentration of the sodium hydroxide solution is 30-50%.
5. The resource utilization method according to claim 4, characterized in that: The solid-liquid separation also produces a sodium silicate-containing solution, which is used to prepare water glass products and / or aerogel products.
6. The resource utilization method according to claim 1, characterized in that: After obtaining the multicomponent alloy liquid, the method further comprises: solidifying the multicomponent alloy liquid and using it as a deoxidizer for steelmaking.
7. The resource utilization method according to claim 1, characterized in that: The binder includes high-alumina clay and water glass; The mass content of Al2O3 in the high-alumina clay is 30-50%; the mass content of high-alumina clay in the mixture is 8-13%; The modulus of the water glass is 1.5 to 3.5, and the Baume concentration is 30 to 60 degrees Bé; the mass content of the water glass in the mixture is 2 to 3%.
8. The resource utilization method according to claim 1, characterized in that: The carbonaceous reducing agent includes bituminous coal powder; the mass content of C in the bituminous coal powder is greater than 85%.
9. The resource utilization method according to claim 1 or 8, characterized in that: The mass ratio of the total mass of the desiliconized fly ash and the small-particle fly ash to the carbonaceous reducing agent is 1.2-2.3:
1.
10. The resource utilization method according to claim 1 or 2, characterized in that: The smelting process also produces fly ash, which is used as a filler for rubber or plastic.