Method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash

Abstract

The invention provides a method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash. The method comprises the following steps: respectively discharging secondary aluminum ash, limestone and bauxite from a raw material bin according to a ratio, and feeding into a stirrer; the preparation method comprises the following steps: uniformly stirring raw materials in a stirrer to obtain a mixture, spraying a liquid binder while stirring, and feeding the mixture into a high-pressure roller mill for treatment to obtain a material cake; feeding the material cake into a vertical mill through a discharging chute for grinding, separating fine powder through a powder concentrator under the driving of airflow, collecting the fine powder through a dust collector to obtain a raw material, and feeding the raw material into a homogenizing silo for storage; and feeding the raw material in the homogenizing silo into a preheater for preheating, feeding into a rotary kiln for calcining to obtain clinker, cooling the clinker, and grinding into powder to obtain the calcium aluminate powder. According to the invention, the homogeneity problem of the raw materials is effectively solved, the operation efficiency and stability of the system are improved, high-value utilization of multiple solid wastes is realized, the production operation environment is improved, the equipment corrosion risk is reduced, and the process adaptability is strong.

Description

Technical Field

[0001] This invention relates to the field of calcium aluminate powder manufacturing technology, specifically to a method for producing calcium aluminate powder by using aluminum ash to replace part of the bauxite. Background Technology

[0002] Calcium aluminate powder is an important raw material for the production of water purification agents, refractory materials, and cement additives. Its traditional production process mainly relies on the high-temperature calcination of bauxite and limestone. In recent years, to promote the resource utilization of solid waste, the technical route of replacing part of the bauxite raw material with secondary aluminum ash (aluminum industry hazardous waste after primary recycling treatment) has received widespread attention. This process typically includes two core steps: raw material grinding and clinker calcination. First, secondary aluminum ash, limestone, and bauxite are mixed in a specific ratio, then ground to the target fineness to form raw material. This raw material is then sintered at high temperature in a rotary kiln to produce calcium aluminate clinker, which is finally ground into the finished product. However, in the raw material grinding stage, existing technologies face the following serious technical bottlenecks that severely restrict product quality stability: The issue of conflicting raw material fineness: Due to pretreatment such as ammonia removal and screening, the particle size of secondary aluminum ash is already close to the target fineness of the raw material (generally requiring ≤12% residue on an 80μm square-hole sieve). However, current mainstream grinding equipment generally uses air-swept mill systems (which transport and classify materials via hot air). This results in fine aluminum ash particles not being fully ground after entering the mill, but instead being directly carried into the classifier by the high-speed airflow, and ultimately collected as "qualified fine powder" in the cyclone dust collector.

[0003] Uncontrolled fluctuations in raw meal composition: Due to the significant differences in hardness and density between aluminum ash and limestone / bauxite, the preferential escape of aluminum ash results in an actual proportion of aluminum ash in the raw meal that is far lower than the designed ratio, while coarse-grained limestone and other materials remain in the mill and are repeatedly ground. This directly causes drastic fluctuations in the effective components of the raw meal (Al2O3, CaO), ultimately leading to a deviation from the expected mineral composition of the clinker (such as CA, CA2 phases) and a decrease in product activity.

[0004] Existing control methods are ineffective: traditional solutions such as reducing system airflow will weaken grinding efficiency and cause blockage inside the mill; although pre-grinding aluminum ash separately can increase particle size, it will increase energy consumption and equipment costs, and it is still difficult to accurately match the grinding kinetics of other raw materials.

[0005] In summary, in the scenario of secondary aluminum ash resource utilization, the deterioration of raw meal homogeneity caused by the selective separation effect of materials in the air-swept mill system has become a common technical problem restricting the large-scale production of calcium aluminate powder. There is an urgent need for an innovative technical solution at the process or equipment level that, while ensuring grinding efficiency, forces the synergistic grinding of aluminum ash and other raw materials to ensure the stability of the raw meal composition. Summary of the Invention

[0006] To address the technical challenge of selective grinding in air-swept mill systems caused by differences in hardness and fineness among raw materials when producing calcium aluminate powder using secondary aluminum ash, leading to drastic fluctuations in raw material composition and a decline in clinker quality, this invention provides a method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash. This method aims to fundamentally solve the problem of raw material homogeneity by forcing the synergistic grinding of different materials through new raw material pretreatment and feeding methods, thereby achieving the resource utilization of solid waste while ensuring the chemical stability and activity of the final product, calcium aluminate powder.

[0007] The objective of this invention is achieved through the following technical solution: A method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash includes the following steps: The secondary aluminum ash, limestone, and bauxite, which have undergone ammonia removal and water washing desalination treatment, are released from the raw material silo and fed into the mixer according to a predetermined ratio.

[0008] The raw materials in the mixer are stirred evenly to obtain a mixture. During the stirring process, 0.5%-1.5% of the total mass of the mixture is sprayed in as a liquid binder. After the moisture content of the mixture is controlled at 1.5-2.5%, it is sent to a high-pressure roller mill with a working pressure of 4.0-6.0 MPa for processing to form a dense cake with a thickness of 20-40 mm. In this process, the fine aluminum ash particles, under the combined action of the binder and water, form a dense agglomerate structure with the coarse limestone and bauxite particles.

[0009] The feed cake is fed into the vertical mill through a specially designed chute for grinding; the fine powder is separated by an airflow classifier and collected by a dust collector to obtain a uniform raw material, which is then sent to a homogenization silo for storage.

[0010] The raw materials in the homogenization silo are sent to the preheater for preheating, and then sent to the rotary kiln for high-temperature calcination to obtain clinker. After cooling, the clinker is sent to the clinker silo for storage.

[0011] The clinker powder in the clinker silo is ground into powder to obtain qualified calcium aluminate powder.

[0012] This invention involves spraying a liquid binder in a specific ratio and then subjecting it to high-pressure roller milling to bind and coat fine aluminum ash onto coarse aggregates, forming agglomerates with uniform physical properties. The liquid binder used is a compound of component A (papermaking black liquor or sugar refining waste molasses) and component B (starch slurry or protein slurry). Component A is papermaking black liquor or sugar refining waste molasses, and component B is added at 2%-8% of the dry weight of component A. The compounded liquid binder not only provides excellent bonding performance, but the macromolecular organic matter (protein / starch) in component B can form a coating film on the surface of the aluminum ash particles. This coating film acts as a coating and isolation layer, significantly reducing the direct contact between the aluminum ash particles and water molecules, thereby effectively inhibiting the pre-hydrolysis reaction of the aluminum ash, reducing ammonia release, and further enhancing the strength and water stability of the agglomerates.

[0013] The liquid binder used in this invention is low-cost. Component A, consisting of black liquor from papermaking and molasses from sugar refining, is itself industrial wastewater requiring treatment, with extremely low acquisition costs (even negative costs, meaning disposal would incur additional costs). It contains abundant lignin, residual sugar, organic acids, and other natural binding substances. Component B, consisting of starch slurry (from starch factory waste) or protein slurry (from food processing and brewing waste), is also an inexpensive industrial byproduct or waste. However, it contains starch polysaccharides or proteins, which are also natural polymers. When dissolved in water, they exhibit excellent viscosity and film-forming properties, effectively enhancing the strength of aggregates. Compared to using pure water as a binder, the cost increase is negligible.

[0014] The liquid binder of this invention utilizes natural binder components such as residual sugar and lignin in papermaking black liquor or sugar refining waste liquor to form a synergistic effect with long-chain polymers such as polysaccharides and proteins in starch slurry or protein slurry. Under the high pressure of a high-pressure roller mill, a more robust bonding network is formed between material particles.

[0015] The small-molecule organic matter (such as sugars) in the black liquor from papermaking or waste molasses from sugar production used in component A has good permeability and can wet the surface of the particles; while the starch residue or protein residue used in component B plays a "bridging" and "flocculation" role, together forming a strong network structure, thus effectively achieving strong binding between aluminum ash and coarse particles.

[0016] The feeding chute of this invention is divided into upper and lower troughs by an arc-shaped partition. The upper trough is equipped with low-speed rotating (20-60 rpm) crushing teeth or hammers to break up the material cake. The broken material is screened through the screen holes on the partition. Fine particles fall into the lower trough through the screen holes, while coarse particles flow along the arc surface at the bottom of the upper trough. Finally, the two material flows merge at the bottom outlet, forming a mixed material flow with coarse material on the outside and fine material on the inside, which enters the middle of the vertical mill grinding disc. The improvement of the feeding chute ensures that coarse and fine materials are fed into the mill simultaneously and mixed, completely eliminating selective grinding (i.e., preventing fine material from being carried away by the air before it falls onto the grinding disc and is subjected to the grinding roller powder) from the feeding mechanism.

[0017] The beneficial effects of this invention are as follows: (1) This invention combines aluminum ash particles with other raw materials in the action of liquid binder and roller press to form agglomerates. At the same time, a feeding chute is used for encapsulation-type coarse and fine mixing feeding, which forces raw materials with different properties to be ground together, ensuring the high homogeneity and stability of raw material composition. This lays a solid foundation for the production of high-activity, stable high-quality calcium aluminate powder and effectively solves the problem of raw material homogeneity.

[0018] (2) The homogenized feed material of the present invention makes the vertical mill run more smoothly, avoiding problems such as mill vibration, blockage and excessive circulating load caused by differences in material properties, thereby improving grinding efficiency, reducing unit product power consumption, and improving the system's operating efficiency and stability.

[0019] (3) In the main raw materials of this invention, secondary aluminum ash is a hazardous waste material of aluminum industry, and liquid binder is industrial waste liquid such as papermaking black liquor, sugar molasses waste, and starch residue slurry, realizing "using waste to treat waste" and "turning waste into treasure", with outstanding environmental protection and economic benefits, and realizing the high-value utilization of multiple solid wastes.

[0020] (4) Aluminum ash contains active aluminum (Al), aluminum nitride (AlN), and other substances, which react with water (pre-hydrolysis), consuming not only the effective components but also releasing ammonia (NH3), resulting in a harsh production environment and equipment corrosion. In contrast, the macromolecular organic matter (protein / starch) in component B (protein slurry or starch slurry) of this invention forms an organic film on the surface of the material particles. This film acts as a coating and isolation layer, significantly reducing the direct contact between aluminum ash particles and water molecules, thereby effectively inhibiting the pre-hydrolysis reaction of aluminum ash, greatly reducing the fugitive emission of ammonia during production, improving the production operating environment, and reducing the risk of equipment corrosion.

[0021] (5) The solution of the present invention does not require major modifications to the existing mainstream grinding and calcining equipment. It mainly solves the problem by optimizing the pretreatment and feeding methods. The investment cost is low, and it is very suitable for the technical transformation and upgrading of existing production lines. It has strong process adaptability. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method described in this invention.

[0023] Figure 2 This is a schematic diagram of the material feeding chute described in this invention.

[0024] Figure 3 for Figure 2 A cross-sectional view along the AA direction.

[0025] The figure shows: 1-feed chute, 11-upper trough, 12-lower trough, 2-partition, 21-screen hole, 3-horizontal shaft. Detailed Implementation

[0026] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings of this specification are merely for illustrative purposes to aid those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0028] In the description of this invention, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" or "linked" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. It should be noted that the terms "comprising," "including," or any other variations are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Example 1

[0029] like Figure 1 As shown, this embodiment provides a method for producing calcium aluminate powder by replacing part of the bauxite with aluminum ash, including the following steps: S1. Ingredients: Secondary aluminum ash (Al2O3 content ≥50%, and treated with deammoniation and water washing desalination), limestone (CaO content ≥52%), and bauxite (Al2O3 content ≥65%) are discharged from the raw material silo in a ratio of 3:10:9 and fed into the mixer by belt conveyor. The mixture is stirred evenly in the mixer to obtain a mixture. The mixer is a horizontal twin-shaft continuous mixer.

[0030] S2. Add liquid binder: Take approximately 10% black liquor from papermaking (component A), and add starch slurry (component B, approximately 5% of the dry weight of component A). Stir and mix thoroughly to prepare a liquid binder. While mixing the mixture in a mixer, spray the prepared liquid binder evenly from the front end (feed end) of the mixer using a spray device. The total amount sprayed should be controlled to be 1.0% of the total mass of the mixture, so that when the mixture is discharged from the discharge end of the mixer, the moisture content is uniform and reaches approximately 2.0%.

[0031] S3. High-pressure roller mill pretreatment: The mixture discharged from the mixer's feed end (after the addition of liquid binder) is fed into a high-pressure roller mill. The working pressure of the roller mill is adjusted to 5.0 MPa, resulting in a dense cake with a thickness of approximately 30 mm. Observation reveals that the fine aluminum ash particles have formed a dense and firm agglomerate structure with the coarse limestone and bauxite particles.

[0032] S4. Raw material grinding: The material cake is fed into a dedicated feeding chute 1 (which can be disassembled and replaced with a conventional feeding chute), such as Figure 2 and Figure 3As shown, the dedicated feeding chute 1 is divided into upper and lower troughs by a partition 2. The upper trough 11 has a square cross-section, and the lower trough 12 has a V-shaped structure that is wider at the top and narrower at the bottom. The partition 2 is an arc-shaped partition with the convex surface facing upward. Multiple screen holes 21 are provided on the partition 2. The screen holes 21 are conical holes with an upper diameter of 10 mm and a lower diameter of 6 mm. The upper trough 11 and the lower trough 12 converge at the bottom discharge port, so that the coarse particle flow in the upper trough 11 and the fine particle flow in the lower trough 12 merge before entering the vertical mill to form a mixed flow with coarse material on the outside and fine material on the inside.

[0033] In the feeding chute 1, a horizontal shaft 3 (i.e., a crushing tooth shaft) is provided through the feeding end of the upper trough 11. Multiple crushing teeth or hammers are installed on the horizontal shaft 3. The horizontal shaft 3 is driven to rotate by a motor installed outside the feeding chute 1 at a speed of 40 rpm, and is used to crush and break up the material cake.

[0034] The dense cake obtained after processing by the high-pressure roller mill enters the upper trough 11 of the feeding chute 1 through the feed inlet, and is broken up by the crushing toothed shaft in the feed end of the upper trough 11. The broken material falls onto the baffle 2 with conical screen holes 21 (upper hole diameter 10mm, lower hole diameter 6mm). Fine particles (<6mm) pass through the screen holes 21 and fall into the V-shaped lower trough 12, while coarse particles flow along the arc surface of the baffle 2. The two material flows merge at the bottom of the feeding chute 1, forming a mixed material flow in which coarse material surrounds fine material, which is naturally fed into the center of the grinding disc of the vertical mill for grinding. The ground raw material is then sent to the homogenization silo after powder selection and dust collection. The test results show that the residue on the 80μm sieve of the raw material is 10.5%, and the fluctuation range of Al2O3 content is controlled within ±0.3%, indicating excellent homogeneity.

[0035] S5. Clinker calcination: The homogenized raw material in the homogenization silo is sent to a five-stage preheater for preheating, and then sent to a rotary kiln for calcination to obtain clinker. After cooling, the clinker is sent to a clinker silo for storage.

[0036] S6. Finished Product Grinding: The clinker in the clinker silo is fed into a ball mill for grinding to obtain calcium aluminate powder. X-ray diffraction (XRD) analysis shows that the total content of the main active mineral phases CA (calcium monoaluminate) and CA2 (calcium disaluminate) in the product exceeds 80%, indicating excellent product activity. Example 2

[0037] The difference between this embodiment and Embodiment 1 is that the liquid binder used in this embodiment is water (i.e., step S2 is not included); and in step S3, while the mixture is being stirred in the mixer, water, which serves as the liquid binder, is uniformly sprayed into the mixer from the front end (feed end) through a spraying device, with the total amount sprayed controlled to be 1.0% of the total mass of the mixture. Apart from this, the remaining steps, raw materials, proportions, and process parameters of this embodiment are exactly the same as those of Embodiment 1.

[0038] Replacing the liquid binder with water allowed for the formation of a cake, but the strength was lower, and it was prone to pulverization during conveying and chute dispersal. The resulting raw material exhibited lower homogeneity (Al2O3 fluctuation range ±0.8%) compared to Example 1. Furthermore, a distinct ammonia odor was detected during production, indicating that the pre-hydrolysis reaction of the aluminum ash was not effectively suppressed.

[0039] Furthermore, in the selection of the liquid binder, 200# asphalt was heated to 160°C and melted into a liquid state, and then sprayed into the mixture at the same mass fraction (1.0%) as the liquid binder in Example 1. However, due to the extremely high viscosity of the asphalt, it was difficult to disperse it evenly, and some of the mixture agglomerated into large asphalt lumps. When touched by hand, they still had a high degree of stickiness. Considering that hot air would be introduced during the vertical mill grinding process, the temperature inside the vertical mill would be high. If the high-viscosity mixture were fed into the feed chute, on the one hand, it would be heated and softened, and would adhere to and block the screen holes and the feed chute. On the other hand, if it was forcibly fed into the vertical mill, it would inevitably soften at the high temperature inside the mill and adhere to the grinding rollers and liners, causing abnormal vibration of the vertical mill and a sharp drop in grinding efficiency. Therefore, subsequent experiments on feeding into the high-pressure roller mill and feeding into the mill were stopped. Obviously, using asphalt as a binder is completely unfeasible.

[0040] Other aspects of this invention that are not detailed herein are all conventional techniques known to those skilled in the art.

[0041] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0042] The scope of protection of this invention is not limited to the technical solutions disclosed in the specific embodiments. Any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of this invention shall fall within the scope of protection of this invention.

Claims

1. A method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash, characterized in that, Includes the following steps: Secondary aluminum ash, limestone, and bauxite are discharged from the raw material silo and fed into the mixer according to the proportions. The raw materials are mixed evenly in a mixer to obtain a mixture. While mixing, a liquid binder is sprayed in. The mixture is then fed into a high-pressure roller mill for processing to obtain a cake. The feed cake is fed into the vertical mill through the feed chute for grinding. The fine powder is separated by the airflow and collected by the dust collector to obtain raw material, which is then sent to the homogenization silo for storage. The raw materials in the homogenization silo are fed into the preheater for preheating and then into the rotary kiln for calcination to obtain clinker. After the clinker is cooled, it is sent to the clinker silo for storage. The clinker powder in the clinker silo is ground into powder to obtain calcium aluminate powder.

2. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 1, characterized in that: The moisture content of the mixture fed into the high-pressure roller mill is 1.5-2.5%.

3. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 1, characterized in that: The liquid binder is water or a solution containing binder; the amount of liquid binder injected is 0.5%-1.5% of the total mass of the mixture; after being processed by a high-pressure roller mill, the fine aluminum ash particles, under the combined action of the binder and water, form a dense agglomerate structure with the coarse limestone and bauxite particles.

4. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 3, characterized in that: The solution containing the binding substance is one or more of the following: papermaking black liquor, sugar refining waste molasses, starch residue, or protein residue, with a concentration of 5%-15%.

5. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 4, characterized in that: The liquid binder is a compound of component A and component B; component A is papermaking black liquor or sugar refining waste molasses; component B is starch slurry or protein slurry, and its addition amount is 2%-8% of the dry basis mass of component A.

6. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 3, characterized in that: The high-pressure roller mill operates at a pressure of 4.0-6.0 MPa, and produces a cake thickness of 20-40 mm.

7. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 1, characterized in that: The feed chute is divided into upper and lower layers by a partition. The upper layer has a square cross-section, while the lower layer has a V-shaped structure that is wider at the top and narrower at the bottom. The partition is an arc-shaped partition with the convex side facing upwards and has multiple sieve holes. The upper and lower layers converge at the bottom outlet, so that the coarse particle flow in the upper layer and the fine particle flow in the lower layer merge before entering the vertical mill, forming a mixed flow with coarse material on the outside and fine material on the inside.

8. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 7, characterized in that: In the feeding chute, a horizontal shaft is provided through the upper trough feed end, and multiple crushing teeth or hammers are installed on the horizontal shaft; the horizontal shaft is driven to rotate by a motor installed outside the feeding chute, with a rotation speed of 20-60 rpm, for crushing and breaking up the material cake.

9. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 8, characterized in that: The sieve holes on the partition plate are conical holes, with an upper hole diameter of 8-12mm and a lower hole diameter of 5-8mm.

10. The method for producing calcium aluminate powder by replacing part of bauxite with aluminum ash according to claim 1, characterized in that: Before the secondary aluminum ash is sent into the raw material silo, it is first subjected to ammonia removal treatment and water washing and desalination treatment.

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