A method for reducing the calcium content of a product alumina

Abstract

The application discloses a method for reducing the content of impurity calcium in product alumina, which comprises the following steps: step 1: in the crude liquid refining step, when the filtering effect of the leaf filter is good, i.e. the floating matter of the refined liquid is less than 20 mg / L, the amount of lime milk is added at 1 ‰ of the volume of the crude liquid; when the filtering effect of the leaf filter is poor, i.e. the floating matter of the refined liquid is more than 20 mg / L, the amount of lime milk is added at 3 ‰ of the volume of the crude liquid; step 2: in the seed decomposition step, the feed amount and the rotating speed of the seed vertical disk filter are adjusted, so that the solid content of the first decomposition tank is in the range of 600-800 g / L and close to the lower limit; step 3: in the seed decomposition step, the temperature of the first decomposition tank is adjusted to be in the range of 60±2 DEG C and close to the lower limit; and step 4: in the seed decomposition step, the stirring speed of the agitator of the decomposition tank is adjusted to be in the range of 10-20 r / min and close to the upper limit; the method can make the content of impurity calcium in the produced product alumina be 0.006-0.009 %, and the content of impurity calcium in the product alumina is reduced.

Description

Technical Field

[0001] This invention relates to the field of alumina production, and in particular to a method for reducing the calcium content of impurities in alumina products. Background Technology

[0002] Calcium oxide is an impurity in industrially produced alumina products, and its content is one of the important technical indicators for evaluating alumina quality. In metallurgical-grade alumina, excessive calcium oxide content will cause a continuous increase in the CaF2 content in the electrolyte of aluminum electrolysis, leading to a decrease in electrolyte conductivity, an increase in density, and a decrease in alumina solubility, thus deteriorating electrolysis indicators and causing a series of negative impacts on electrolytic aluminum. Therefore, controlling the calcium oxide content in alumina products is extremely important.

[0003] Currently, there is limited research in the alumina production industry on how to reduce the calcium oxide content in alumina products, especially regarding the control of calcium oxide content in the crude liquid refining and seed crystal decomposition steps of alumina production processes. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for reducing the calcium content of impurities in alumina products, by controlling the conditions of the crude liquid refining and seed crystal decomposition steps in the alumina production process to reduce the calcium content of impurities in the alumina products.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for reducing the calcium impurity content in alumina products includes the following steps:

[0007] Step 1: In the crude liquid refining step, when the leaf filter has a good filtration effect (i.e., the suspended solids in the seminal liquid are less than 20 mg / L), the amount of lime milk added is 1‰ of the crude liquid volume; when the leaf filter has a poor filtration effect (i.e., the suspended solids in the seminal liquid are greater than 20 mg / L), the amount of lime milk added is 3‰ of the crude liquid volume.

[0008] Step 2: In the seed crystal decomposition step, adjust the feed rate and rotation speed of the seed vertical plate filter to keep the solid content in the first decomposition tank within the range of 600-800g / L and close to the high line;

[0009] Step 3: In the seed crystal decomposition step, adjust the temperature of the first decomposition tank to be within the range of 60±2℃ and close to the lower limit. The methods for adjusting the temperature of the first decomposition tank are: (1) When the temperature of the first decomposition tank is high, i.e. greater than 62℃, with a fixed amount of semen, increase the amount of heat exchange stock solution, or, with a fixed amount of stock solution, decrease the amount of heat exchange semen; (2) When the temperature of the first decomposition tank is low, i.e. less than 58℃, with a fixed amount of semen, decrease the amount of heat exchange stock solution; or, with a fixed amount of stock solution, increase the amount of heat exchange semen.

[0010] Step 4: In the seed crystal decomposition step, adjust the stirring speed of the decomposition tank agitator to a range of 10-20 r / min and close to the high line.

[0011] Furthermore, in step 1: when the leaf filter is functioning normally and the suspended matter in the semen is far above 20 mg / L, open the discharge nozzle of the leaf filter to check. If the outflowing semen is turbid, remove the leaf filter in time and replace the filter cloth of the leaf filter.

[0012] Furthermore, in step 3, if the temperature of the first decomposition tank is high, i.e., greater than 62°C, and the semen plate heat exchanger forms scale, then the currently operating semen plate heat exchanger is removed and replaced with a cleaned semen plate heat exchanger.

[0013] The beneficial effects of this invention are:

[0014] This invention discloses a method for reducing the calcium impurity content in alumina products. By adjusting the amount of lime slurry added in the crude liquor refining step of the alumina production process, and controlling the solid content, temperature, and stirring speed of the agitator in the first decomposition tank of the seed crystal decomposition step, the calcium impurity content of the produced alumina is reduced to 0.006-0.009%, thereby improving the quality of the alumina products.

[0015] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained from the following description and claims. Detailed Implementation

[0016] The preferred embodiments of the present invention will now be described in detail. It should be understood that the preferred embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0017] A method for reducing the calcium impurity content in alumina products includes the following steps:

[0018] Step 1: In the crude liquid refining step, adjust the amount of lime slurry added. When the leaf filter has a good filtration effect (i.e., the suspended solids in the liquid are less than 20 mg / L), add lime slurry at 1‰ of the crude liquid volume. When the leaf filter has a poor filtration effect (i.e., the suspended solids in the liquid are greater than 20 mg / L), add lime slurry at 3‰ of the crude liquid volume. When the leaf filter has a normal material flow effect and the suspended solids in the liquid are far greater than 20 mg / L, open the leaf filter outlet to check. If the outflowing liquid is turbid, remove the leaf filter in time and replace the filter cloth to prevent the leaf filter from operating with a damaged filter cloth.

[0019] Table 1 shows the effect of different lime milk addition amounts on the calcium content of alumina impurities in the product:

[0020]

[0021] The table above shows that the amount of lime slurry added has a significant impact on the calcium impurity in the alumina of the product. Therefore, in the crude liquor refining step, the amount of lime slurry added should be 1‰ and 3‰, provided that the leaf filter is operating normally.

[0022] Step 2: In the seed crystal decomposition step, adjust the feed rate and rotation speed of the seed vertical plate filter to keep the solid content in the first decomposition cell within the range of 600-800 g / L and close to the upper limit. The adjustment method is as follows: when the solid content in the first decomposition cell is greater than 800 g / L, appropriately reduce the feed rate and rotation speed of the seed vertical plate filter and reduce the amount of seed added; when the solid content in the first decomposition cell is less than 800 g / L, appropriately increase the feed rate and rotation speed of the seed vertical plate filter and increase the amount of seed added. By adjusting in the above two ways, maintain the solid content in the first decomposition cell at 600 g / L-800 g / L and control it towards the upper limit.

[0023] Table 2 shows the effect of solid content in the first decomposition cell on the calcium content of alumina impurities in the product:

[0024]

[0025] The table above shows that increasing the solids content in the first decomposition tank can reduce the calcium content of alumina impurities in the product. In actual production, the solids content in the first decomposition tank can be increased by increasing the capacity of the seed vertical disc filter, thereby reducing the calcium content of alumina impurities in the product. The solids content in the first decomposition tank should be controlled within the range of 600g / L-800g / L% and should be increased towards the higher end.

[0026] Step 3: In the seed crystal decomposition step, adjust the temperature of the first decomposition cell to be within the range of 60±2℃ and close to the lower limit;

[0027] The methods to adjust the temperature of the first decomposition tank are as follows: (1) When the temperature of the first decomposition tank is high, i.e. greater than 62°C, the temperature of the first decomposition tank can be reduced by lowering the semen temperature. The methods to lower the semen temperature are as follows: First, if the semen plate is crusted and the heat exchange effect of the semen is poor, resulting in a high temperature of the first decomposition tank, i.e. greater than 62°C, then the operating semen plate heat exchanger should be removed and replaced with a cleaned semen plate heat exchanger to increase the heat exchange effect and lower the semen temperature; Second, if the semen volume is constant, increase the amount of heat exchanged original liquid; Third, if the original liquid volume is constant, reduce the amount of heat exchanged semen to increase the heat exchange effect and lower the semen temperature; (2) When the temperature of the first decomposition tank is low, i.e. less than 58°C, the temperature of the first decomposition tank can be increased by raising the semen temperature. The methods to raise the semen temperature are as follows: First, if the semen volume is constant, reduce the amount of heat exchanged original liquid; Second, if the original liquid volume is constant, increase the amount of heat exchanged semen.

[0028] Table 3 shows the effect of the initial decomposition tank temperature on the calcium impurity content in the alumina product:

[0029]

[0030] The table above shows that lowering the temperature of the first decomposition tank can reduce the calcium content of alumina impurities in the product. During production, the temperature of the first decomposition tank should be controlled within the range of 60±2℃. While ensuring the particle size of the product, the temperature of the first decomposition tank should be controlled at a lower limit.

[0031] Step 4: In the seed crystal decomposition step, the agitator in the decomposition tank is set to a stirring speed of 10-20 r / min and close to the high line.

[0032] Table 4 shows the effect of the stirring speed of the decomposition tank agitator on the calcium impurity content in the alumina of the product:

[0033]

[0034] The table above shows that increasing the stirring speed of the decomposition tank agitator can reduce the calcium content of alumina impurities in the product. During production, the stirring speed of the decomposition tank agitator should be controlled within the range of 10-20 r / min. While ensuring the product strength and particle size, the stirring speed of the decomposition tank should be controlled at the higher limit.

[0035] Table 5 shows the calcium impurity content of alumina in Examples 1-4 of the present invention and the products produced therefrom:

[0036]

[0037] As shown in the table above, by improving the crude liquid refining and seed crystal decomposition steps of the alumina production process in this invention, the calcium impurity content of the produced alumina is controlled at 0.006-0.009%, thereby reducing the calcium impurity content in the alumina and improving the quality of the alumina.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for reducing the calcium impurity content in alumina products, characterized in that: Includes the following steps: Step 1: In the crude liquid refining step, when the leaf filter has a good filtration effect (i.e., the suspended solids in the seminal liquid are less than 20 mg / L), the amount of lime milk added is 1‰ of the crude liquid volume; when the leaf filter has a poor filtration effect (i.e., the suspended solids in the seminal liquid are greater than 20 mg / L), the amount of lime milk added is 3‰ of the crude liquid volume. Step 2: In the seed crystal decomposition step, adjust the feed rate and rotation speed of the seed vertical plate filter to keep the solid content in the first decomposition tank within the range of 700-800g / L; Step 3: In the seed crystal decomposition step, adjust the temperature of the first decomposition tank to be within the range of 60℃. The methods for adjusting the temperature of the first decomposition tank are: (1) When the temperature of the first decomposition tank is high, i.e. greater than 60℃, with a certain amount of semen, increase the amount of heat exchange stock solution, or, with a certain amount of stock solution, decrease the amount of heat exchange semen; (2) When the temperature of the first decomposition tank is low, i.e. less than 60℃, with a certain amount of semen, decrease the amount of heat exchange stock solution; or, with a certain amount of stock solution, increase the amount of heat exchange semen. Step 4: In the seed crystal decomposition step, adjust the stirring speed of the decomposition tank agitator to a range of 15-20 r / min. In step 1: When the leaf filter is working properly and the suspended matter in the semen is far above 20mg / L, open the outlet of the leaf filter to check. If the semen that flows out is turbid, remove the leaf filter in time and replace the filter cloth of the leaf filter.

2. The method for reducing the calcium content of impurities in alumina products according to claim 1, characterized in that: In step 3, if the temperature of the first decomposition tank is high, i.e., greater than 62°C, and the semen plate heat exchanger forms scale, then the currently operating semen plate heat exchanger should be removed and replaced with a cleaned semen plate heat exchanger.

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