Method for recovering and treating decomposition tank scabs
By treating the scale in the decomposition tank through wet crushing and causticization reaction, the problems of organic matter and resource waste in the scale were solved, and the efficient recovery of aluminum hydroxide and sodium hydroxide was achieved, improving resource utilization and decomposition tank operating efficiency, and reducing production costs.
Patent Information
- Application Number
- CN202610366029.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-24
- Publication Date
- 2026-07-31
AI Technical Summary
In existing technologies, there is a lack of effective recovery and treatment of Na2CO3, Na2C2O4, NaOH, NaAl(OH)4 and organic matter in the scale of the decomposition tank, which leads to the accumulation of organic matter and waste of resources, affecting the operating efficiency of the decomposition tank and increasing production costs.
After solid-liquid separation by wet crushing and decomposition of scale in the tank, calcium hydroxide is added to the liquid separator for causticization reaction. Sodium hydroxide overflow is obtained by sedimentation separation, and aluminum hydroxide and sodium hydroxide are recycled. The amount of feed for causticization reaction is controlled to improve accuracy and reduce the accumulation of organic matter.
It achieves efficient recovery of aluminum hydroxide and sodium hydroxide, inhibits the accumulation of organic matter, improves resource utilization, reduces production costs, and improves the operating efficiency of the decomposition tank.
Smart Images
Figure CN122480073A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of alumina production via the Bayer process, and more specifically to a method for recovering and treating scale buildup in a decomposition tank. Background Technology
[0002] During the Bayer process for alumina production, scale gradually accumulates on the bottom and inner walls of the decomposition tank. As production time increases, the scale thickens, which not only reduces the effective volume of the decomposition tank but also affects the flow of the slurry and the heat transfer effect. In severe cases, it may even affect the normal operation of the decomposition tank. Therefore, it is necessary to clean the decomposition tank regularly to remove the scale.
[0003] On September 6, 2012, Aluminum Corporation of China Limited (Chalco) applied for a Chinese invention patent entitled "A Method for Treating Scale in a Decomposition Tank" with authorization announcement number CN102826578B. This patent proposes a technical solution to crush and separate the scale in the decomposition tank, thereby recovering aluminum hydroxide from the scale as a seed crystal for reuse in the decomposition process, which to a certain extent realizes the recycling of aluminum hydroxide from the scale.
[0004] However, the above-mentioned technical solutions lack effective recycling and treatment measures for Na2CO3, Na2C2O4, NaOH, NaAl(OH)4 and organic matter contained in the scale. In particular, the scale contains a certain amount of organic matter. If it is directly reused in the production system without treatment, it will easily cause the concentration of organic matter in the solution to increase. In addition, if the sodium carbonate and sodium oxalate contained in the scale cannot be effectively converted or recycled, it will also cause waste of resources. Summary of the Invention
[0005] The purpose of this invention is to provide a method for recycling and treating scale from a decomposition tank. This method involves wet-milling the scale to obtain a slurry, followed by solid-liquid separation. Calcium hydroxide is then added to the liquid separator for a causticizing reaction, and sodium hydroxide overflow is obtained through sedimentation separation. This method solves the technical problems in existing technologies regarding insufficient recycling and treatment of sodium carbonate, sodium oxalate, sodium tetrahydroxyaluminate, and organic matter within the scale, which easily leads to the accumulation of organic matter and resource waste. It achieves the beneficial effects of efficiently recovering aluminum hydroxide and sodium hydroxide, improving the operating efficiency of the decomposition tank, and reducing production costs.
[0006] To achieve the aforementioned objectives, the technical solution adopted by the present invention is as follows:
[0007] A method for recycling and treating scale buildup in a decomposition tank includes the following steps:
[0008] S1: Clean the decomposition tank to obtain decomposition tank scale, and wet-crush the decomposition tank scale to obtain crushed slurry.
[0009] S2: The pulverized slurry is subjected to solid-liquid separation to obtain a liquid separator and a solid separator, wherein the main component of the solid separator is aluminum hydroxide;
[0010] S3: Determine the amount of sodium carbonate, sodium oxalate and sodium tetrahydroxyaluminate in the liquid separator, and add calcium hydroxide to the liquid separator to carry out a causticizing reaction to obtain a causticized slurry;
[0011] The causticization reaction is carried out at a temperature of 50-70℃ and a time of 50-80 min. The amount of calcium hydroxide added, i.e., n[Ca(OH)2], satisfies the following relationship:
[0012] n[Ca(OH)2]=A[n(Na2CO3)+n(Na2C2O4)+1.5n(NaAl(OH)4)]
[0013] In the formula, A is the proportionality coefficient A, which ranges from 1.1 to 1.6; n(Na2CO3), n(Na2C2O4) and n(NaAl(OH)4) are the amounts of sodium carbonate, sodium oxalate and sodium tetrahydroxyaluminate in the liquid separator, respectively.
[0014] S4: The causticized slurry is subjected to sedimentation separation to obtain overflow and underflow, wherein the main component of the overflow is sodium hydroxide.
[0015] Preferably, in S1, a ball mill is used to wet-mill the scale in the decomposition tank, and the grinding fluid used for wet milling is hot water at 80-100°C.
[0016] Preferably, in S2, a flat plate filter or a vacuum filter flask is used to perform solid-liquid separation on the pulverized slurry.
[0017] Preferably, in step S2, the solid separator is washed with hot water at 80-100°C, and the decomposition mother liquor and the washed solid separator are mixed and fed into the decomposition tank of the alumina production system.
[0018] Preferably, in S3, the proportionality coefficient A is determined by the following method:
[0019] S3.1: Acquire an image of the pulverized slurry and extract the RGB color feature values of the image;
[0020] S3.2: A preset RGB color space model, wherein the RGB color space model contains multiple non-overlapping color sub-regions, and each color sub-region is associated with a preset scaling factor;
[0021] S3.3: Map the RGB color feature values to the RGB color space model, and take the color sub-region to which the RGB feature values belong as the target color region;
[0022] S3.4: The preset scaling factor associated with the target color region is used as the scaling factor A.
[0023] Preferably, in S3.1, after homogenizing the pulverized slurry using a stirring device, an image of the pulverized slurry is acquired.
[0024] Preferably, in step S3, calcium hydroxide is added to the liquid separator in two separate steps to carry out a causticizing reaction;
[0025] The initial addition of calcium hydroxide accounts for 40-50% of the total mass of calcium hydroxide added. The causticizing reaction temperature is controlled at 50-60℃, and the causticizing reaction is carried out for 15-20 minutes. Subsequently, the remaining calcium hydroxide is added, and the causticizing reaction temperature is controlled at 60-70℃. The causticizing reaction is then continued for 35-60 minutes.
[0026] Preferably, in S4, the causticized slurry settles and separates in a settling tank, the overflow obtained from the separation flows into the secondary settling tank of the alumina production system, and the underflow obtained from the separation is discharged from the alumina production system.
[0027] The beneficial effects of this invention are:
[0028] Efficient recovery of aluminum hydroxide and sodium hydroxide, improving resource utilization: Wet crushing loosens and breaks down the scale in the decomposition tank, and solid-liquid separation is performed on the crushed slurry. The solid separated product is mainly aluminum hydroxide, achieving effective recovery of aluminum hydroxide. At the same time, calcium hydroxide is added to the liquid separated product to carry out a causticization reaction to obtain a causticized slurry. The overflow with sodium hydroxide as the main component is obtained through sedimentation separation, thereby achieving the recycling of sodium hydroxide.
[0029] Suppressing the accumulation of organic matter in the Bayer process: Wet pulverization fully exposes the organic matter encapsulated in the scale. After solid-liquid separation, the organic matter enters the causticization reaction system along with the liquid separation. During the causticization reaction, some of the organic matter is converted into insoluble substances and discharged from the alumina production system with the underflow, thereby reducing the accumulation of organic matter in the decomposition tank and mitigating the adverse effects caused by the accumulation of organic matter.
[0030] Improving the accuracy of causticization reaction feed control: Due to the different organic matter content in the scale, the crushed slurry exhibits different color characteristics. By identifying the color of the crushed slurry, the organic matter content can be indirectly reflected, thereby determining the amount of calcium hydroxide to be fed, improving the accuracy of causticization reaction feed control, and avoiding incomplete organic matter conversion due to insufficient calcium hydroxide addition, or resource waste due to excessive addition. Attached Figure Description
[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some examples or embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort, and this application can be applied to other similar scenarios based on the provided drawings. Unless obvious from the linguistic context or otherwise stated, the same reference numerals in the drawings represent the same structure or operation.
[0032] Figure 1 This is a flowchart of the method for recycling and treating scale buildup in the decomposition tank in this application;
[0033] Figure 2 This is a flowchart of the method for determining the proportionality coefficient A described in S3;
[0034] Figure 3 Line graph showing the oxalate concentration in the alumina production system over several months;
[0035] Figure 4 Line graph showing TOC concentration in the alumina production system over several months. Detailed Implementation
[0036] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining the relevant application and are not intended to limit the application. The described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.
[0037] Example 1:
[0038] See appendix Figure 1 This embodiment provides a method for recycling and treating scale buildup in a decomposition tank, the method comprising the following steps:
[0039] S1: Clean the decomposition tank to obtain decomposition tank scale, and wet-crush the decomposition tank scale to obtain a pulverized slurry; the cleaning of the decomposition tank can be done manually or mechanically to obtain blocky or flaky decomposition tank scale. Specifically, a ball mill can be used to wet-crush the decomposition tank scale to obtain a pulverized slurry. During the wet crushing process, hot water at a temperature of 80℃ to 100℃ is added as a grinding fluid to fully loosen and disintegrate the scale and fully expose the organic matter therein, ultimately obtaining a pulverized slurry.
[0040] S2: The pulverized slurry obtained in S1 is transported to a solid-liquid separation device for solid-liquid separation. The solid-liquid separation device can be a flat plate filter or a vacuum filtration flask used in the laboratory. Through solid-liquid separation, liquid and solid products are obtained. The main component of the solid product is aluminum hydroxide. The solid product is washed with hot water at 80-100℃ to wash away the organic matter attached to the surface of the solid product. Then, the washed solid product and the decomposition mother liquor are mixed and fed into the decomposition tank of the alumina production system as seed crystals for reuse, so as to achieve effective recovery of aluminum resources.
[0041] S3: Perform chemical analysis on the liquid separator obtained in step S2, and determine the amounts of sodium carbonate, sodium oxalate, and sodium tetrahydroxyaluminate in the liquid separator, denoted as n(Na2CO3), n(Na2C2O4), and n[NaAl(OH)4], respectively; based on the determination results, calculate the amount of calcium hydroxide to be added, n[Ca(OH)2]. n[Ca(OH)2] is calculated using the formula... It is determined that A is the proportionality coefficient A, which ranges from 1.1 to 1.6.
[0042] Calcium hydroxide is added to the liquid separator in one or several batches to carry out a causticization reaction, resulting in a causticized slurry. The reaction temperature during the entire causticization process is controlled at 50-70°C, preferably 60°C, and the reaction time is 50-80 min, preferably 60 min. When adding calcium hydroxide to the liquid separator in two batches for causticization, the mass of the first batch of calcium hydroxide added is 40% to 50% of the total mass of calcium hydroxide added, preferably 40%. The reaction temperature is controlled between 50°C and 60°C, preferably 55°C, and the reaction is stirred for 15 to 20 min, preferably 20 min. Subsequently, the remaining mass of calcium hydroxide is added, and the reaction temperature is raised to 60°C to 70°C, preferably 65°C, and the reaction is continued with stirring for 35 to 60 min, preferably 40 min. Adding a smaller proportion of calcium hydroxide initially and reacting at a lower temperature can prevent calcium carbonate or calcium oxalate crystals from rapidly coating the surface of the calcium hydroxide particles to form a dense product layer.
[0043] S4: The causticized slurry obtained in S3 is pumped into a settling tank for settling and separation, resulting in overflow and underflow. The main component of the overflow is sodium hydroxide, which can be transported to the secondary washing settling tank of the alumina production system to realize the recycling of alkali resources. The underflow mainly consists of solid impurities such as calcium carbonate and calcium oxalate generated in the reaction, as well as organic matter. The underflow can be discharged from the alumina production system as waste residue, thereby effectively avoiding the accumulation of organic matter in the production system.
[0044] The range of values for the proportionality coefficient A was determined through the following experiment:
[0045] First, since the liquid separator contains not only Na2CO3, Na2C2O4 and NaAl(OH)4, but also some complex and diverse organic compounds, some of which can react with calcium hydroxide to produce insoluble substances, thus removing these organic compounds, the proportion coefficient A should be greater than 1.
[0046] In addition, five groups of different decomposition tank scales (A, B, C, D, and E) were collected. These scales were subjected to wet pulverization and solid-liquid separation to obtain the corresponding liquid precipitates. The TOC (Total Organic Carbon) concentration before the causticization reaction was measured. The liquid precipitates corresponding to each group of decomposition tank scales were divided into six portions. The amount of calcium hydroxide added to these six portions was calculated sequentially according to the proportionality coefficient A of 1.1, 1.2…1.5, 1.6. After the causticization reaction, the TOC concentration was measured sequentially, and the TOC removal rate was calculated. The experimental data are shown in the table below.
[0047]
[0048] Experimental data clearly shows that when the proportionality coefficient A ≥ 1.5, the TOC removal rate remains almost unchanged with increasing proportionality coefficient. Further increasing the proportionality coefficient A not only fails to improve the removal of organic matter but also leads to excessive residual calcium hydroxide in the underflow sludge, wasting chemical reagents. It should also be noted that, in addition to the scaling in the five different decomposition tanks (A, B, C, D, and E) mentioned above, this invention has conducted numerous experiments, all of which yielded conclusions satisfying the aforementioned relationship: the optimal range for the proportionality coefficient A is 1.1-1.6. Therefore, setting the proportionality coefficient A within the range of 1.1-1.6 ensures effective removal of organic matter while avoiding excessive addition of calcium hydroxide.
[0049] Example 2:
[0050] See Figure 2 Based on Example 1, this example elaborates on the method for determining the proportionality coefficient A described in S3. The proportionality coefficient A is determined by the following method:
[0051] S3.1: Acquire images of the pulverized slurry and extract the RGB color feature values of the images. Specifically, before acquiring images of the pulverized slurry, it is best to use a stirring device to homogenize the pulverized slurry. For example, use a stirrer to stir the pulverized slurry in a transparent container at a speed of 200-400 rpm for 3-5 minutes to achieve a visually uniform color. Use an industrial camera or a high-resolution digital camera to acquire digital images of the homogenized pulverized slurry under standard light source and preset pulverized slurry temperature conditions. After acquiring the images, extract the RGB color feature values of the images. Specifically, after removing the area after 10% of the image edges, calculate the average value of R (red), G (green), and B (blue) of all pixels in the image, and use this as the RGB color feature value of the pulverized slurry.
[0052] S3.2: Preset RGB color space model. The RGB color space model contains multiple non-overlapping color sub-regions, and each color sub-region is associated with a preset scaling factor. The value range of the preset scaling factor is 1.1-1.6. The preset scaling factor associated with each color sub-region is determined based on a large amount of historical experimental data.
[0053] In fact, during the Bayer process of alumina production, the organic matter content in the scale of the decomposition tank will affect the color of the pulverized slurry. When the organic matter content in the scale is high, the slurry formed after wet pulverization usually appears as a dark brown or dark gray; while when the organic matter content is low, the slurry is mostly light gray or yellowish-white. Therefore, the color characteristics of the pulverized slurry can reflect its internal organic matter content to a certain extent. In addition, for pulverized slurries containing more organic matter, a larger proportion coefficient A should be set, but the proportion coefficient A should not exceed 1.6.
[0054] S3.3: Map RGB color feature values to the RGB color space model, and use the color sub-region to which the RGB color feature values belong as the target color region;
[0055] S3.4: Use the preset scaling factor associated with the target color area as the scaling factor A.
[0056] When the RGB color characteristic value of the pulverized slurry falls into a certain color sub-region, the preset ratio coefficient associated with that color sub-region can be directly called as the feeding ratio coefficient A of calcium hydroxide in the causticization reaction, thereby realizing the rapid determination of the feeding amount of the causticization reaction.
[0057] Experimental verification:
[0058] To verify the effectiveness of this invention in removing organic matter from the Bayer process alumina production system, different scaling treatment strategies were implemented in three stages within a Bayer process alumina production system. From January to February 2.5 months, the scaling from the regularly cleaned decomposition tanks was sold externally without recycling. From February 2.5 to June, the scaling from the regularly cleaned decomposition tanks was ground and used as seed crystals. From June to November, the method described in this invention was used for treatment. The TOC and oxalate concentrations in the alumina production system were monitored to obtain... Figure 3 and Figure 4 .
[0059] From January to February 5th, the scale from the regularly cleaned decomposition tanks is sold directly without recycling. During this period, the total organic carbon and oxalate concentrations in the alumina production system remain relatively stable, indicating that the input and output of organic matter in the alumina production system are roughly balanced.
[0060] From 2.5 to 6 months, the scale from the regularly cleaned decomposition tanks was ground and crushed before being returned to the decomposition tanks as seed crystals. During this period, the total organic carbon and oxalate concentrations in the alumina production system increased sharply, indicating that simple physical crushing and reuse would lead to the continuous accumulation of organic matter in the alumina production system.
[0061] From June to November, the TOC and oxalate content in the alumina production system showed a downward trend. This was mainly because, using the method employed in this application, the scale removed from the decomposition tank was washed and causticized, resulting in a higher TOC and oxalate content in the discharged alumina production system compared to the inlet alumina production system. This reduced the TOC and oxalate content in the system's liquid phase and also enabled the recovery of aluminum and alkali resources.
[0062] In the description of the embodiments of this application, unless otherwise stated, "、" means "or". For example, A and B can mean A or B. "And" and "or" in this article are merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and or B can mean: A exists alone, A and B exist simultaneously, and B exists alone.
[0063] It should be noted that, for ease of description, only the parts relevant to the application are shown in the accompanying drawings; unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.
[0064] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed, and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art; the scope of this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described application concept; for example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.
Claims
1. A recovery process for decomposing a scab of a ladle, characterized by: Includes the following steps: S1: Clean the decomposition tank to obtain decomposition tank scale, and wet-crush the decomposition tank scale to obtain crushed slurry. S2: The pulverized slurry is subjected to solid-liquid separation to obtain a liquid separator and a solid separator, wherein the main component of the solid separator is aluminum hydroxide; S3: Determine the amount of sodium carbonate, sodium oxalate and sodium tetrahydroxyaluminate in the liquid separator, and add calcium hydroxide to the liquid separator to carry out a causticizing reaction to obtain a causticized slurry; In the causticization reaction, the reaction temperature is 50-70°C, the reaction time is 50-80 min, the amount of substance of the calcium hydroxide added is 0.1-0.3 mol per 1 mol of the sulfuric acid, and the amount of water added is 0.5-1.5 mol per 1 mol of the sulfuric acid. satisfies the following relationship: n[Ca(OH)2]=A[n(Na2CO3)+n(Na2C2O4)+1.5n(NaAl(OH)4)] In the formula, A is the proportionality coefficient A, which ranges from 1.1 to 1.6; n(Na2CO3), n(Na2C2O4) and n(NaAl(OH)4) are the amounts of sodium carbonate, sodium oxalate and sodium tetrahydroxyaluminate in the liquid separator, respectively. S4: The causticized slurry is subjected to sedimentation separation to obtain overflow and underflow, wherein the main component of the overflow is sodium hydroxide.
2. The method for recycling and treating scale buildup in a decomposition tank as described in claim 1, characterized in that: In S1, a ball mill is used to wet-mill the scale in the decomposition tank. The grinding fluid used for wet milling is hot water at 80-100℃.
3. The method for recycling and treating scale buildup in a decomposition tank as described in claim 1, characterized in that: In S2, a flat plate filter or a vacuum filter flask is used to perform solid-liquid separation on the pulverized slurry.
4. The method for recycling and treating scale buildup in a decomposition tank as described in claim 1, characterized in that: In step S2, the solid separated material is washed with hot water at 80-100°C, and the decomposition mother liquor and the washed solid separated material are mixed and fed into the decomposition tank of the alumina production system.
5. The method for recycling and treating scale buildup in a decomposition tank as described in claim 1, characterized in that: In S3, the proportionality coefficient A is determined by the following method: S3.1: Acquire an image of the pulverized slurry and extract the RGB color feature values of the image; S3.2: A preset RGB color space model, wherein the RGB color space model contains multiple non-overlapping color sub-regions, and each color sub-region is associated with a preset scaling factor; S3.3: Map the RGB color feature values to the RGB color space model, and take the color sub-region to which the RGB feature values belong as the target color region; S3.4: The preset scaling factor associated with the target color region is used as the scaling factor A.
6. The method for recycling and treating scale buildup in a decomposition tank as described in claim 5, characterized in that: In step S3.1, after homogenizing the pulverized slurry using a stirring device, an image of the pulverized slurry is acquired.
7. The method for recycling and treating scale buildup in a decomposition tank as described in claim 1, characterized in that: In S3, calcium hydroxide is added to the liquid separator in two separate steps to carry out a causticizing reaction; The initial addition of calcium hydroxide accounts for 40-50% of the total mass of calcium hydroxide added. The causticizing reaction temperature is controlled at 50-60℃, and the causticizing reaction is carried out for 15-20 minutes. Subsequently, the remaining calcium hydroxide is added, and the causticizing reaction temperature is controlled at 60-70℃. The causticizing reaction is then continued for 35-60 minutes.
8. The method for recycling and treating scale buildup in a decomposition tank as described in claim 1, characterized in that: In S4, the causticized slurry settles and separates in a settling tank, and the overflow obtained from the separation flows into the secondary settling tank of the alumina production system, while the underflow obtained from the separation is discharged from the alumina production system.