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The purpose of pretreatment of scrap aluminum is to remove other metals and impurities contained in the scrap aluminum, and to classify the scrap aluminum according to its components so that the alloy components can be utilized to the maximum extent. The third is to remove oil stains, oxides and coatings on the surface of scrap aluminum. The final result of pretreatment is to process the scrap aluminum into furnace charge that meets the conditions for entering the furnace. Fourth, the aluminum (containing alumina) in the aluminum-containing scrap is used in the most economical and reasonable manner. Domestic scrap aluminum pretreatment technology is still very simple and backward. Even in large-scale recycled aluminum plants, there is no relatively advanced technology for the pretreatment of scrap aluminum. From the current point of view, the following pretreatment technologies are mainly used. ①Scrap aluminum of a single type or basically containing no other impurities generally does not undergo complex pretreatment. It is just classified according to the type and composition of the scrap and stacked separately. When using a single type of scrap aluminum, as long as one component is randomly checked and tested, the composition of the batch can be known. It is a high-quality recycled aluminum raw material and can generally be smelted in the furnace without any pretreatment. When smelting a certain alloy, scrap aluminum of corresponding composition and variety is often directly added to a large reverberatory furnace for smelting, so that it can be easily smelted into an aluminum alloy of the corresponding grade. Some scrap aluminum with high copper and zinc content can also be used as a master alloy for adjusting the composition. For enterprises that use small reverberatory furnaces or crucible furnaces, large scrap aluminum must be broken into pieces that meet the furnace specifications as needed. ②For higher-grade scrap aluminum slices, the main components include cast aluminum alloy, alloy aluminum, pure aluminum, etc. There are many brands of the first two items, and it is currently difficult to classify them by brand. In large-scale recycled aluminum plants, they are generally only screened to remove mixed soil, etc., that is, directly put into the furnace for smelting. In small recycled aluminum plants, this kind of scrap aluminum must be manually divided into cast aluminum alloy, alloy aluminum and pure aluminum, and then used separately. ③Low-grade sliced and incinerated shredded scrap aluminum (the latter is generally not used by large recycled aluminum plants) requires complex sorting because of its complex composition. In addition to scrap aluminum, it also contains scrap copper, scrap steel, scrap lead and other metals, as well as other wastes. The sorting of this type of waste mainly relies on manual labor. First, the soil and garbage are screened out, and then sorted manually. Most of the manual sorting is done on the operating table, and the selection mainly relies on workers' visual inspection and experience. Non-metallic scraps are sorted first, and then the scrap metals are sorted. The selection of scrap copper and pure aluminum scrap is particularly careful, because scrap copper can increase the output value, and pure aluminum scrap such as scrap aluminum wire, etc., are all high-quality raw materials for adjusting the composition in regeneration smelting. The separated scrap aluminum is mixed and generally no longer subdivided. At present, the pretreatment of domestic scrap aluminum has basically not been mechanized and automated. It mainly relies on manual labor. The tools used are magnets and steel files, and it is based on experience. This sorting method has low efficiency, poor quality, and high cost. Moreover, most of the non-ferrous metals such as copper in the scrap aluminum are contaminated. Manual sorting is difficult and has fallen far behind. There is an urgent need to study advanced scrap aluminum pretreatment technology. Advanced scrap aluminum pretreatment technology The purpose of advanced scrap aluminum pretreatment technology is to realize the mechanization and automation of scrap aluminum sorting, remove metallic and non-metallic impurities to the maximum extent, and effectively classify and sort scrap aluminum according to its alloy composition. The most ideal sorting method is to divide scrap aluminum into several categories according to the main alloy composition, such as alloy aluminum, aluminum-magnesium alloy, aluminum-copper alloy, aluminum-zinc alloy, aluminum-silicon alloy, etc. This can reduce the difficulty of impurity removal technology and composition adjustment during the smelting process, and can comprehensively utilize the alloy components in scrap aluminum, especially scrap aluminum containing high zinc, copper, and magnesium, which must be stored separately and can be used as an intermediate alloy raw material for adjusting the composition of smelting aluminum alloys. The current advanced scrap aluminum pretreatment technologies mainly include: ①The air separation method separates waste paper, waste plastic and dust. All kinds of waste aluminum contain more or less waste paper, waste plastic film and dust. The more ideal process is the air separation method. The process of air separation method is simple and can efficiently separate most of the light waste materials. However, the use of air separation method requires a good dust collection system to avoid dust pollution to the environment. The local waste paper and waste plastic film are generally not suitable for further sorting and can be used as fuel. ②Magnetic separation equipment is used to sort out magnetic waste such as scrap steel. Iron is a harmful substance in aluminum and its alloys and has the greatest impact on the mechanical properties of aluminum alloys. Therefore, scrap iron and steel from miscellaneous aluminum should be sorted out as much as possible in the pretreatment process. Slice scrap aluminum and low-grade scrap aluminum materials. The ideal technology for sorting scrap steel is magnetic separation. This method has been widely used abroad. The equipment of the magnetic separation method is relatively simple. The magnetic source comes from electromagnets or permanent magnets. There are various process designs. The one that is easier to implement is the cross method of conveyor belts. The scrap aluminum on the conveyor belt moves transversely. When entering the magnetic field, the scrap steel is sucked up and leaves the transverse belt, and is immediately taken away by the longitudinal belt. After the running longitudinal belt leaves the magnetic field, the scrap steel loses gravity and automatically falls to the ground and is concentrated. The magnetic separation method has a simple process, low investment, and is easily adopted. The volume of aluminum scrap processed by the magnetic separation method should not be too large. General sliced and crushed aluminum scraps are more suitable. Large pieces of scrap must be crushed before entering the magnetic separation process. The scrap iron and steel sorted by magnetic separation method needs to be further processed, because some scrap iron and steel devices contain mechanically combined aluminum-based non-ferrous metal parts, which are difficult to separate, such as nuts, wires, keys, plumbing parts, pinions, etc. on scrap aluminum parts. Sorting of this part is very necessary, because the sorted non-ferrous metals can increase the value and improve the grade of scrap iron and steel. However, the sorting is difficult, and manual disassembly and sorting are generally used, but the efficiency is low. In order to improve production efficiency, the most effective way to deal with the separated aluminum and steel combinations that are difficult to dismantle is to heat them in a special melting furnace to melt the aluminum and scrape out the scrap steel. ③The flotation method using water as the medium can be used to separate light materials such as waste plastics, waste wood, and waste rubber mixed in the light impurity scrap aluminum. The flotation method using water as the medium can be used. The main equipment is a spiral propeller. The scrap aluminum is pushed out with the spiral propeller. During the whole process, most of the soluble substances such as soil and dust remaining in the air separation process are dissolved in water and washed away by the water into the settling tank. After multiple sedimentation and clarification processes, the sewage is returned for recycling and the sludge is removed regularly. This method can separate all light substances with a specific gravity less than water, and is a simple and easy method. ④Technology for sorting heavy non-ferrous metals such as copper from scrap aluminum. Heavy non-ferrous metals such as copper in scrap aluminum are basically contaminated by oil. It is difficult to separate heavy non-ferrous metals from scrap using manual sorting methods. An effective method is parabolic beneficiation. This method utilizes the principle that various objects with basically the same volume will land at different points when thrown by the same force. It can separate various scrap non-ferrous metals with different densities in scrap aluminum. When the same force is used to shoot objects with different densities but basically the same volume along a straight line, various objects move in a parabola direction and land at different points when they land. The simplest test can be carried out on a horizontal conveyor belt. When the mixed waste materials rotate at high speed on the conveyor belt, when the conveyor belt reaches the end, the scrap aluminum is thrown out along a straight line. Due to the different gravity of various wastes, they land at different points respectively, thereby achieving the purpose of sorting. This method can evenly separate scrap aluminum, scrap copper, and other wastes. Equipment designed based on this principle has been used abroad, but the price is prohibitive. It is in the research stage domestically. ⑤Pretreatment of surface coating of scrap aluminum: The surface of many scrap aluminum is coated with protective layers such as paint, especially scrap aluminum packaging containers. The largest quantities are packaging containers such as scrap cans and toothpaste wrappers. In small smelters, the waste is generally smelted directly without any pretreatment, and the patent leather is re-burned during the smelting process. However, such waste materials are thin-walled, and the paint leather will oxidize part of the aluminum during the combustion process, and increase impurities and bubbles in the aluminum. The more advanced recycled aluminum process generally requires pretreatment to remove the coating before smelting. The main technologies include dry method and wet method. The wet method is to soak waste aluminum in a certain solvent to cause the paint layer to fall off or be dissolved by the solvent. The disadvantage of this method is that the waste liquid is large and difficult to handle. Generally not suitable for use. The dry method is the fire method, and the rotary kiln roasting method is generally used. The main equipment of the roasting method is the rotary kiln. Its biggest advantage is its high thermal efficiency, which facilitates the separation of waste aluminum and carbide. The heat source for roasting comes from the hot air from the heating furnace and the heat generated during the carbonization process of the scrap aluminum paint layer. During production, the rotary kiln rotates at a certain speed, and the paint layer on the surface of the scrap aluminum is gradually carbonized at a certain temperature. Due to the rotation of the rotary kiln, the materials collide and vibrate with each other, and finally the carbonized materials fall off from the scrap aluminum. Part of the fallen carbonized material is collected at one end of the rotary kiln, and part of it is recovered in the dust collector. The pretreatment of scrap aluminum is an important part of the scrap aluminum recycling process. With the improvement of recycled aluminum technology, pretreatment technology will become more and more important. Completely separate non-aluminum substances from scrap aluminum and its alloys, and efficiently classify scrap aluminum according to alloy grades to achieve the most effective comprehensive utilization of scrap aluminum. This is the development direction of pretreatment technology research in recycled aluminum technology.