Because there are many impurities in the aluminum liquid in the electrolytic cell, it must be filtered before casting the aluminum ingot. Common methods include fluxes, gases, and clarification purification methods. The main methods are:
Fluxes purification method and gas purification method
1. The fluxes purification method is to use the refining flux added to the solution, which has the characteristics of low density, high activity, and strong adsorption capacity. By adsorbing the oxides in the solution, new droplets are formed and rise to the surface. Scum forms after cooling. The aluminum ingot can be cast by removing the scum.
2. Gas purification, commonly used chlorine, nitrogen or chlorine-nitrogen mixed gas, is a main primary aluminum purification method.
The chlorine gas in the molten aluminum generates many small bubbles, which are fully mixed in the molten aluminum, and the hydrogen dissolved in it, as well as some mechanical inclusions, can be adsorbed on the small bubbles. As the bubbles rise to the surface of the molten aluminum, they are discharged.
Nitrogen purification method
Because chlorine is toxic and costly, nitrogen purification has emerged. Use alumina balls as filter media. N2 is directly passed into the molten aluminum. The molten aluminum is continuously fed into the purification furnace, passes through the alumina ball filter layer, and is flushed by nitrogen, so the non-metallic inclusions and dissolved hydrogen in the molten aluminum are removed, and then continuously discharged, so that the fine nitrogen bubbles are evenly distributed Play a purifying effect in the treated aluminum liquid.
Mixed gas purification method
A mixture of chlorine and nitrogen is used to purify molten aluminum. Its role is to remove hydrogen and separate oxides on the one hand, and to remove certain metal impurities (such as magnesium) in aluminum on the other. The commonly used composition is 90% nitrogen + 10% chlorine . There are also 10% chlorine + 10% carbon dioxide + 80% nitrogen. This effect is better, carbon dioxide can diffuse chlorine and nitrogen well, which can shorten the operation time.