Method for producing aluminum oxide by using carbide slag instead of lime

Abstract

The invention discloses a method for producing aluminum oxide by using carbide slag instead of lime, which comprises the following steps: in the process of dissolving out bauxite by a Bayer process, adding carbide slag into circulating mother liquor, and carrying out dissolution treatment. According to the method for producing the aluminum oxide by using the carbide slag instead of the lime, the dissolution effect of the bauxite is equivalent to that of the traditional lime. The calcium-containing characteristic of the carbide slag is utilized, the effect of lime in the Bayer process dissolution process is ingeniously replaced, the effects of turning waste into wealth and recycling waste are achieved, and remarkable economic and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to a method for producing alumina using carbide slag as a substitute for lime, belonging to the field of alumina preparation technology. Background Technology

[0002] The Bayer process is a conventional method for producing alumina, involving two main processes: decomposition and leaching. The first process involves seed crystal decomposition of sodium aluminate solution: at room temperature, aluminum hydroxide is added as a seed crystal to a sodium aluminate solution with a low molecular weight. With continuous stirring, Al₂O₃ in the solution slowly precipitates as aluminum hydroxide. Simultaneously, the molecular ratio of the solution (the ratio of sodium oxide to aluminum oxide molecules in the sodium aluminate solution, characterizing the alumina-dissolving ability of the sodium aluminate solution) continuously increases. The second process involves leaching: the solution after most of the aluminum hydroxide has precipitated is called the mother liquor. After heating and concentration, it can dissolve alumina hydrates from bauxite. This is the process of leaching bauxite using the mother liquor.

[0003] my country's bauxite is characterized by high silica, high aluminum, and a low aluminum-silicon ratio. Most of it is monohydrate gibbsite, which is more difficult to leach than trihydrate gibbsite, requiring stringent leaching techniques and making it unsuitable for direct Bayer process processing. To address the characteristics of my country's low- to medium-grade monohydrate gibbsite ore, domestic alumina companies have adopted the lime-Bayer process. The lime-Bayer process involves adding an excess of lime compared to the conventional Bayer process during leaching to process low- to medium-grade bauxite. By adding excess lime, some of the hydrated sodium aluminosilicate in the red mud (alumina production waste) is converted into hydrated calcium aluminosilicate, reducing alkali consumption. The lime-Bayer process is simple, energy-efficient, and requires low investment, making it a primary method for producing alumina from domestic bauxite. However, it also has drawbacks such as high bauxite consumption and low recovery rate, as well as high lime consumption, leaving room for further optimization.

[0004] Calcium carbide slag is a waste residue produced during the production of acetylene from calcium carbide (calcium carbide). Its main components include calcium oxide, silicon dioxide, aluminosilicates, magnesium oxide, and ferric oxide. Calcium oxide has the highest content, typically exceeding 60%. This high calcium content makes it a potential substitute for lime in my country's lime-Bayer process. However, its chemical properties differ significantly from lime. First, the main component of calcium carbide slag is Ca(OH)₂, while the main component of limestone is CaCO₃. Second, their decomposition characteristics differ. Ca(OH)₂ in calcium carbide slag begins to decompose at 550℃, while limestone only begins to decompose at 750℃. Furthermore, during heating, some of the Ca(OH)₂ in calcium carbide slag absorbs CO₂ from the gas to form CaCO₃. Above 900℃, the CaCO₃ formed from both parts decomposes again. Finally, the heat changes during the reaction process also differ.

[0005] The application of calcium carbide slag as a substitute for lime in my country's Bayer process for alumina production presents both advantages and challenges. Using calcium carbide slag to replace lime in alumina production has several potential advantages. First, calcium carbide slag is an industrial waste, widely available and inexpensive, thus reducing the raw material cost of alumina production. Second, the high calcium oxide content in calcium carbide slag can replace some lime, reducing lime usage and energy consumption in the production process. The main challenge lies in the potential impact of silicon, iron, and magnesium compounds present in calcium carbide slag on the alumina production system. Summary of the Invention

[0006] In view of the above-mentioned prior art, the present invention provides a method for producing alumina by using carbide slag to replace lime.

[0007] This invention is achieved through the following technical solution: A method for producing alumina using calcium carbide slag as a substitute for lime is as follows: the calcium carbide slag is pretreated to improve its purity and chemical activity; then, during the Bayer process for leaching bauxite, the pretreated calcium carbide slag is added to the circulating mother liquor for leaching treatment.

[0008] Furthermore, the pretreatment involves washing and dehydrating the carbide slag with boiling water, followed by calcination, and then crushing and screening.

[0009] Furthermore, the boiling water washing is performed twice; the dehydration process involves removing most of the water by filtration and then drying at 108°C for 1 hour.

[0010] Furthermore, the calcination treatment is carried out at a temperature of 750°C for 1 hour. Calcination removes impurities such as water of crystallization and organic carbon from the carbide slag, while simultaneously decomposing Ca(OH)₂ into CaO, thereby improving the purity and activity of the carbide slag.

[0011] Furthermore, the crushing and screening process involves passing the crushed material through a 200-mesh sieve.

[0012] Furthermore, the amount of carbide slag added is: 1 to 5 g of carbide slag per 100 ml of circulating mother liquor.

[0013] Furthermore, the dissolution temperature is 260–270°C.

[0014] Furthermore, the dissolution reaction time is 1 hour.

[0015] In practical applications, advanced detection technologies and data analysis models can be used to accurately calculate and control the amount of calcium carbide slag added, based on the specific silicon content and other impurities in the bauxite. Different calcium-silicon ratios can be determined according to the calcium and silicon content in the calcium carbide slag and bauxite to analyze the optimal amount of calcium carbide slag to add. Simultaneously, different leaching reaction temperatures can be determined to analyze the optimal leaching conditions.

[0016] This invention discloses a method for producing alumina using calcium carbide slag as a substitute for lime, achieving bauxite leaching effects comparable to those using traditional lime. This invention cleverly utilizes the calcium content of calcium carbide slag to replace lime in the Bayer process leaching, achieving the effect of turning waste into treasure and recycling waste, resulting in significant economic and social benefits. Compared to lime, calcium carbide slag is more economically advantageous. Calcium carbide slag itself is a production waste with low price, while lime requires purchase or processing by enterprises and is expensive. Based on a Bayer process production system with an annual lime production of 1 million tons, approximately 250,000 tons of lime are consumed annually. Using calcium carbide slag as a substitute yields considerable economic benefits. Detailed Implementation

[0017] The present invention will be further described below with reference to embodiments. However, the scope of the present invention is not limited to the following embodiments. Those skilled in the art will understand that various changes and modifications can be made to the present invention without departing from the spirit and scope thereof.

[0018] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0019] Experiment 1: Production of alumina using carbide slag as a substitute for lime Pretreatment of carbide slag: (1) Take carbide slag and wash it with boiling water twice. Then remove most of the water by filtration and place it in an oven to dry at 108°C for 1 hour.

[0020] (2) Place it in a muffle furnace and calcine at 750°C for 1 hour, remove it, and let it cool naturally to room temperature.

[0021] (3) The calcined carbide slag may clump together. It should be crushed and sieved through a 200-mesh sieve.

[0022] Domestic bauxite (specific composition shown in Table 1) was selected. 31 g of bauxite, 100 mL of circulating mother liquor (specific composition shown in Table 2), and 1–5 g of the pretreated calcium carbide slag (the specific amount added was determined according to different calcium-silicon ratios) were mixed evenly in a steel ball and then placed in a lava furnace for a leaching experiment (experimental temperature 260–270℃, reaction time 1 hour). After the leaching reaction was completed, the leaching slurry was collected and filtered. The filtrate was retained for testing (test results shown in Table 3). The filter residue was washed with hot water to obtain leached red mud. Simultaneously, lime was added as a control; the test results are shown in Table 4.

[0023] As can be seen from Tables 3 and 4, under the same leaching reaction conditions, the relative leaching rate of ore leached by carbide slag is slightly worse than that leached by lime. However, overall, the effect of carbide slag replacing lime in ore leaching can meet production needs. The ore leaching efficiency can be improved by appropriately increasing the amount of carbide slag added.

[0024] The above embodiments are provided to those skilled in the art to fully disclose and describe how the claimed implementations can be carried out and used, and are not intended to limit the scope of the disclosure herein. Modifications that will be obvious to those skilled in the art will be within the scope of the appended claims.

Claims

1. A method for producing alumina using carbide slag instead of lime, characterized by: The carbide slag is pretreated; and the pretreated carbide slag is added into the circulating mother liquor in the process of dissolving bauxite by the Bayer method to perform a dissolving treatment.

2. The method for producing alumina by replacing lime with carbide slag according to claim 1, characterized by, The pretreatment is that the carbide slag is washed by boiling water, dewatered, calcined, and then crushed and sieved.

3. The method for producing alumina by replacing lime with carbide slag according to claim 2, characterized in that: The washing by boiling water is performed twice; the dewatering treatment is that most of the water is removed by suction filtration, and then the dewatered carbide slag is dried at 108 ℃ for 1 hour.

4. The method for producing alumina by replacing lime with carbide slag according to claim 2, characterized in that: The calcination treatment is performed at 750 ℃ for 1 hour.

5. The method for producing alumina by replacing lime with carbide slag according to claim 2, characterized in that: The crushing and sieving is that the calcined carbide slag is crushed and then sieved through a 200-mesh sieve.

6. The method for producing alumina by replacing lime with carbide slag according to claim 1, wherein The addition amount of the carbide slag is 1-5 g per 100 ml of the circulating mother liquor.

7. The method for producing alumina by replacing lime with carbide slag according to claim 1, characterized in that: The dissolving temperature is 260-270 ℃.

8. The method for producing alumina by replacing lime with carbide slag according to claim 1, characterized in that: The reaction time of the dissolving is 1 hour.

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