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Aluminum Electrolysis Production Knowledge Q & A
- Dec 26, 2018 -

1. Which two major categories of metal elements are usually classified, and which one of them belongs to?


A: Usually metal elements are divided into two categories: black and colored. Except for iron, manganese and chrome ferrous metals, the rest are non-ferrous metals, and aluminum is a non-ferrous metal.


2. What kinds of non-ferrous metals can be classified according to their characteristics?


A: Non-ferrous metals can be classified into heavy metals, light metals, precious metals, rare metals, and semi-metals according to their characteristics. Aluminum is a metal of colored light metals.


3. What are the properties and uses of aluminum?


A: Nature: Aluminum is a light metal with a silvery white metallic luster that is hailed as a versatile metal in the industry. Aluminum has a specific gravity of 2.7/cm3 and a melting point of 660 °C. Aluminum has good electrical conductivity, thermal conductivity and corrosion resistance, and also has good ductility and plasticity, while aluminum alloy has high mechanical strength.


Uses: Due to the low specific gravity of aluminum and the high strength of aluminum and its alloys, aluminum can be used as lightweight structural materials and construction industry materials, such as aircraft, ships, profiles, etc., as well as electrical materials, thermal materials and corrosion-resistant materials, food packaging. Materials, etc.


4. What are the two stages in the history of aluminum smelting?


A: Two stages of chemical aluminum smelting and electrolytic aluminum smelting.


5. What is electrolytic aluminum?


Answer: Electrolytic aluminum smelting is a cryolite-alumina melting salt electrolysis method. It uses cryolite as a solvent and alumina as a melting material. A strong direct current is passed into the electrolytic cell to electrochemically react on the cathode and the anode. Electrolytic product, aluminum liquid on the cathode, CO2 and CO gas on the anode (carbon as anode), this method is electrolytic aluminum.


6. What is the raw material for aluminum electrolysis?


Answer: The raw materials used in aluminum electrolysis are roughly divided into three categories: raw materials - alumina; flux - fluoride salts (including cryolite, aluminum fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, lithium fluoride, etc.) Anode material - pre-baked carbon block (prebaked trough).


7. What is the purpose of aluminum electrolysis to DC?


Answer: The direct current is supplied to the electrolytic cell. On the one hand, the thermal energy is used to melt the cryolite into a molten state and maintain a certain electrolysis temperature; on the other hand, the main thing is to achieve an electrochemical reaction at the two poles, that is, to make the electrolyte The aluminum ions in the electrolyte are precipitated from the cathode to obtain aluminum, and the oxygen ions are discharged on the anode to form a mixed gas of CO2 and CO with the carbon.


8. What are the hazards of impurities in alumina raw materials?


Answer: Aluminum bismuth production requires relatively high purity of alumina. General industrial alumina has a purity of over 98% and usually contains a small amount of silica, ferric oxide, sodium oxide, calcium oxide, and moisture. These impurities have an adverse effect on aluminum electrolysis. Oxide impurities of elements whose potential is positive to aluminum, such as silicon oxide, and iron oxide, titanium dioxide, are reduced by aluminum during electrolysis, and the reduced Si and Fe enter the aluminum, thereby lowering the grade of aluminum, and those potentials Oxide impurities of elements that are negative to aluminum, such as Na20 and CaO, decompose cryolite, altering electrolyte composition and increasing fluoride salt consumption. Moisture decomposes the cryolite and increases the hydrogen content of the aluminum liquid. If there is too much water, it will cause electrolyte explosion and endanger the safe production of workers. P205 and SO2 will reduce current efficiency. Therefore, the aluminum industry places strict requirements on the purity of alumina.


9. What are the requirements for industrial aluminum electrolysis for the physical properties of A1203?


A: The physical properties of industrial alumina have a great relationship to ensure the normal progress of the electrolysis process and improve the efficiency of gas purification. It is generally required to have a small water absorption property, can dissolve in the molten cryolite more quickly, has less flying loss during processing, and can better block the carbon anode, prevent it from oxidizing in the air, and has good heat preservation performance, and at the same time It is also required for gas purification to have good activity and a sufficient specific surface area to be able to efficiently absorb HF gas. These physical properties depend on the crystal form, particle size and shape of the alumina crystals.


10. According to the physical properties of Al2O3, which three types of alumina can be divided into three types? Which one is better for production?


A: According to the physical properties of alumina, alumina can be divided into three types: sand type, intermediate type and powder type. Among them, sand type alumina is better for production.


11. What is the role of cryolite flux?


A: Cryolite is used as a flux for electrolytic aluminum; its function is: firstly, it can dissolve aluminum oxide well, and the formed melt can be electrolyzed below the melting point of pure cryolite, and the fluidity is better; At the electrolysis temperature, the density of the cryolite-alumina melt is 10% lower than that of the aluminum liquid, so the electrolyzed aluminum liquid can be deposited on the cathode below the electrolyte, which can reduce the oxidation loss of the aluminum and greatly simplify the The structure of the aluminum electrolysis cell; third, the cryolite has good conductivity; fourth, the cryolite does not contain metal impurities whose potential order is more positive than aluminum, which can ensure the quality of the product aluminum. Currently, cryolite or aluminum electrolysis The most ideal flux in production.


12. Why is aluminum anode used in aluminum electrolysis?


Answer: During the aluminum electrolysis process, the high temperature and highly aggressive cryolite melt is in direct contact with the electrode. Among the various materials of the conductive yin and yang poles, only the carbon material is good in electrical conductivity, high temperature resistance, corrosion resistance, and low cost. Therefore, the aluminum industry uses carbon materials as the two poles.


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