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[China Aluminum Industry Network] 1. Outline the quality of primary aluminum produced in aluminum electrolytic cells. In addition, it also contains some metal impurities, gas and non-metallic solid inclusions. The task of aluminum ingot casting is to increase the utilization of low-grade aluminum liquids and remove as much impurities as possible. The impurities in the primary aluminum can be divided into the following three categories: the former are metal elements such as iron, silicon, copper, calcium, magnesium, titanium, vanadium, boron, nickel, zinc, antimony, tin, lead, phosphorus, etc. The main elements are iron and silicon; the second is non-gold solid inclusions, Al2O3, AlN and Al4C3; the third is gas, H2, CO2, CO, CH4, N2, of which the main one is H2. At 660C, approximately 0.2 cm3 of hydrogen was dissolved in 100 g of aluminum liquid. The solubility of gas in aluminum liquid increases with temperature. The aluminum liquid sucked from the electrolytic cell is subjected to a purification process to remove some of the impurities and cast into a commercial aluminum ingot (99.85% A1). With 99.996% Al pure aluminum (aluminum wire φ2mm, hard puller), the resistivity is 2.668×10-8Ω·m. If there is an impurity element in pure aluminum, the resistivity increases. The larger ones are chromium, vanadium, manganese, lithium, and titanium. The less affected are indium, lead, zinc, cadmium, tin, antimony, and iron.
1. The balance of impurity elements in aluminum The amount of impurities in industrial alumina produced from bauxite using the Bayer process is greatly reduced compared to the raw material bauxite. In addition to the bases brought from the lye, the total amount of analysis of the impurity elements is usually less than 1%. The main impurities are SiO2 and Fe2O3. In addition to impurities in the electrolytic bath caused by alumina, carbon anodes and flux cryolite also cause a lot of impurities. Impurities caused by carbon anodes are mainly iron and silicon, as are cryolites.
If all of the impurity elements of the raw material are precipitated in the primary aluminum, the resulting grade of aluminum is only 99.7% Al. However, the actual production of aluminum has a higher grade of 99.8% Al. This difference is mainly due to the evaporation of impurity elements. Iron, titanium, phosphorus, zinc, and bismuth are the majority of aluminum oxide, while silicon and vanadium are the majority of carbon anodes. The impurity element from the flux is phosphorus, which accounts for about 20% of the total phosphorus. The rest of silicon, iron, titanium, and vanadium are rare.
In the balance sheet, silicon and iron exceeded the amount brought by raw materials, of which silicon exceeded 60% and iron exceeded 37%. The lining materials of the electrolyzers, such as high ash bottomed carbon blocks and carbon paste and refractories, are another important source of these impurity elements. In addition, due to the erosion of the operating tool and the cathode steel bar, the iron is also balanced. The rest of the elements are close to balance.
Expenditure allocation is different in the amount of impurity elements in primary aluminum and exhaust gas. Phosphorus, which accounts for the largest amount of evaporation, accounted for 72% of the total income. Vanadium accounted for 64.4%, iron accounted for 62.4%, titanium accounted for 57.7%, thorium accounted for 49.6%, and zinc accounted for 19.7%. The smaller is silicon, which only accounts for 13.3% of total revenue. The reason for this is that: 1 silicon and zinc exist in the electrolyte in the form of compounds that are more difficult to evaporate or even evaporate, such as SiO2, ZnO, or ZnF2. Silicon and zinc clearly accumulate in the liquid aluminum. The extent to which aluminum liquid is contaminated with silicon and zinc is mainly determined by the total amount of silicon compounds and zinc compounds fed into the material balance. In this case, the collection efficiency of the slot hood does not matter. 2 Iron, ruthenium, titanium and nickel are present in the system at least partly in the form of volatile compounds. These compounds are probably produced after entering the electrolyte. Possible compounds are Fe(CO)5, Ni(CO)4, TiF3, TiF4 and GaF3. If the collection efficiency of the tank cover increases, the quality of aluminum will be affected to some extent. 3 Vanadium and phosphorus exist only in the form of volatile compounds. The possible compounds are first fluoride (VF3 and PF3) and phosphorus pentoxide (P2O5). Since the increase of the phosphorus content in the electrolyte will affect the current efficiency, the increase in the amount of vanadium in aluminum will reduce the conductivity of aluminum, so it can be expected to improve the collection efficiency of the tank cover will bring about the quality of primary aluminum and better production results damage.
2. Classification of Aluminum Ingots Aluminum ingots are divided into aluminum ingots, high-purity aluminum ingots, and aluminum alloy ingots according to their composition. They can be classified into strips, round ingots, slab ingots, and T-shaped ingots according to shapes and sizes. Several, following are several common aluminum ingots;
Remelting aluminum ingot -15kg, 20kg (≤99.80% Al):
T-shaped aluminum ingot - 500kg, 1000kg (≤ 99.80% Al):
High-purity aluminum ingots - l0kg, 15kg (99.90% to 99.999% Al);
Aluminum alloy ingot --10kg, 15kg (Al--Si, Al--Cu, Al--Mg);
Plate ingots - 500 ~ 1000kg (for plate making);
Ingot - 30~60kg (for drawing).
3. Aluminum ingot casting process aluminum - slag dregs - test kiln - Ingredients - Furnace - scouring - casting - remelting aluminum ingots - finished product inspection - finished product inspection jin - storage out of aluminum - slag residue - test jin - ingredients - Furnace installation - refining - Casting - Alloy ingots - Casting alloy ingots - Finished product inspection - Finished product inspection - Storage II. Primary aluminum purification The aluminum liquid extracted from the electrolytic cell contains various impurities, so it needs to be purified before casting. In the industry, clarification, flux, gas, and other purification methods are mainly used, and some methods of directional solidification and filtration are used for purification.
1. flux purification flux purification is the use of flux added to the aluminum liquid to form a large number of fine droplets, so that the oxides in the aluminum liquid are wetted by the droplets to adsorb and dissolve, forming new droplets to the surface and cooling to form a float Slag removed.
The flux used for purification is composed of salt with low melting point, low density, small surface tension, high activity, and strong adsorption capacity for oxidized slag. When using, firstly put a small amount of flux into the iron cage, and then insert it into the bottom of the mixing furnace to stir it. After the flux is finished, remove the iron cage and let it rest for 5 to 10 minutes. Remove surface scum and cast. The flux can also be withdrawn on the surface as needed to provide coverage.
2. Gas Purification Gas purification is a major primary aluminum purification method. The gas used is a mixture of chlorine, nitrogen, or chlorine and nitrogen.