Slag treatment method for reducing aluminum loss
[China Aluminum Network] During the smelting of aluminum alloys, a portion of non-recoverable metal loss occurs due to oxidation of aluminum and its interaction with furnace walls and refining agents. This loss is known as burnout, and the metals contained in both the burnout and slag are collectively referred to as melt loss. When using a flame reverberatory furnace for melting aluminum alloys, the amount of slag generated can range from 2% to 5% of the charge weight, with approximately 40-60% of that being aluminum. Proper treatment of aluminum slag and recovery of aluminum from it play a crucial role in reducing melting losses. The practice of using a 5-ton flame reverberatory furnace for smelting aluminum alloys includes several effective methods for managing and reducing melt loss through slag treatment.
To minimize the formation of aluminum slag, various measures can be taken during the melting process. As slag increases, so does the melting loss, which is influenced by factors such as smelting temperature, charge condition, and production techniques. Here are some key strategies:
(1) Designing the furnace geometry properly and adding materials in the right order;
(2) Controlling the smelting temperature carefully to avoid overheating. The flame should be directed at an appropriate angle to speed up melting and reduce time;
(3) Using the right flux and refining time, ensuring stable stirring without breaking the oxide layer on the surface of the melt, and covering the melt promptly;
(4) Sorting and cleaning scrap aluminum, comparing the surface area of finely divided materials with a press;
(5) Pre-treating the slag before removal.
After refining, the slag floating on the surface of the melt has good wettability with the molten aluminum, with a wetting angle less than 90 degrees. A significant amount of melt becomes mixed with the slag, with some aluminum droplets dispersed throughout. At lower temperatures, the wettability between the two is better, and if slag is removed at this stage, about 60% of the slag's weight may consist of lost melt. Adding a slagging agent at a rate of 1‰ to 2‰ evenly across the melt surface helps reduce the aluminum content in the slag. The chemical reactions involved include: Na₂SiF₆ → 2NaF + SiF₄; 2NaF + Al₂O₃ → NaAlO₂ + NaAlOF₂; 4NaF + 2Al₂O₃ → 3NaAlO₂ + NaAlF₄; 6NaF + Al₂O₃ → 2AlF₃ + 3Na₂O. The resulting AlF₃ reacts exothermically with aluminum and oxygen, turning viscous slag into dry, powdery material. This reduces the wettability between the melt and slag, allowing aluminum droplets to separate and return to the melt.
After tapping, the slag still contains small aluminum droplets. To recover them, the slag is first poured into a perforated iron box, allowing some aluminum to drain out. Then, the slag is placed in a prepared pit, where more slagging agent is added and stirred for 5–10 minutes. The slagging agent rapidly heats the slag to around 950°C, causing the oxide layers around the aluminum droplets to crack. The droplets then fall to the bottom under gravity. After secondary treatment, the remaining slag contains only minimal aluminum particles, which can be manually picked out after cooling. This method is simple, practical, and effective. Currently, the melting loss in aluminum alloy production has been reduced to 1.6%, sometimes even reaching 1.4%. For a plant producing 5,000 tons annually, this could save up to 400,000 yuan in losses, offering significant economic benefits.
Garden Street Light,Solar Power Garden Lights,Garden Solar Light Outdoor,Solar Powered Garden Street Light
Yantai LUHAO Lighting CO.,Ltd , https://www.luhaosolar.com