Recycling process of aluminum chips and aluminum scrap

It is very important to consider energy and environmental protection factors, because it can not only save energy, but also reduce energy consumption by 95% compared with electrolytic aluminum production. It can also save landfill costs of aluminum scrap and reduce the waste of scrap aluminum resources. Nowadays, such small aluminum scrap recycling enterprises are still increasing. New progress has also been made in aluminum scrap melt and aluminum ash processing technology. 　　 1. Electromagnetic stirring technology (Electro magnetic stirring Technology) The advantage of electromagnetic stirring technology is to improve labor productivity in the furnace. The Swedish ABB company has this technology, which uses the technical concept of the steel industry. An induction coil is placed outside the furnace, or the induction coil can be placed at the bottom or side wall of the furnace. The only change to the furnace is to add a non-magnetic plate adjacent to the induction coil. 　　This technology was applied to aluminum melts in 1969, and so far 59 furnaces have installed this induction coil. Electromagnetic stirring improves furnace thermal uniformity and chemical consistency, shortens melting time, and reduces aluminum ash formation. Because electromagnetic stirring provides lower surface temperatures, labor productivity is improved due to deeper molten pools and shorter melting cycles, and aluminum ash formation is reduced. For a 25-ton static furnace when melting high-silicon alloys, the melting cycle is shortened by 22%. For a 90-ton melting furnace and alloying furnace, the melting cycle time is shortened from 12 hours to 8 hours, because the flushing effect of circulating aluminum water on solid aluminum scrap accelerates smelting, and electromagnetic stirring promotes alloying and refining. 　 2 New type of ingot and scrap melting farnace The value of remelting aluminum scrap has been generally valued by people because it only requires 5% of the energy of electrolytic aluminum and requires minimal equipment investment. According to relevant data, 30% of the world's aluminum is now produced through aluminum scrap recycling and meets quality requirements. If the right technology is used, the amount of aluminum scrap recycled depends on the market. For example, the recycling rate of aluminum scrap in the transportation industry is 90%, the construction industry is 85%, the recycling rate of aluminum beverage cans is 80%, and only the packaging industry has a lower recycling rate of 10-20%. 　　Thermco, a subsidiary of Outokumpu Group After evaluating various Thermcon furnace designs, Ovens designed a new smelting and refining furnace, which uses a regenerative burner that can capture the heat of the flue gas to preheat the combustion air. The typical energy consumption is 490-560kwh/t. The regenerative burner uses the thermal energy of the flue gas to oxidize it to eliminate volatiles, dioxides and furans, which are especially produced in deep aluminum waste. 　　The emission amount of dioxide and furan from the new smelting furnace is 0.01Ng/Nm3, which is lower than the saturation limit of 0.01Ng/Nm3. 　 3 Processing of ovross in India According to relevant data, about 3.5 million tons of aluminum ash are produced globally every year, and only about half of it is processed into aluminum. The aluminum recycling rate has also increased from 30% a few decades ago to 65% now. This chemical reaction is an exothermic reaction, so in order to prevent the aluminum from oxidizing and turning into smoke after skimming, the aluminum ash must be cooled quickly. Melting aluminum scrap means producing more aluminum ash, generally a 10% aluminum loss, which in India is 120,000 tons of aluminum per year, while in electrolytic aluminum production the aluminum loss is 1-2%, and the annual loss is 15,000 tons. So like India * * Recycling aluminum from aluminum is becoming increasingly important. India is expanding its scrap aluminum recycling industry, with a production capacity of more than 1.2 million tons/year, while India's electrolytic aluminum production capacity is about 1 million tons/year. In the next five years, India's scrap aluminum recycling capacity and electrolytic aluminum production capacity will double. 　 　　Advanced smelting process technology and scrap aluminum reinforcement technology such as packaging and compaction, charging technology, especially dip-dye charging technology, advanced furnace design technology, good furnace door sealing structure and new burner nozzle (to avoid overheating) are adopted to minimize the exposure time of aluminum water to the air and minimize the formation of aluminum ash. 　 　　According to a German company, if the operation of the scrap aluminum remelting furnace is optimized, the smelting cycle time can be reduced by 8%, the energy consumption can be reduced by 8%, and the energy consumption can be reduced by 10%. If the furnace is well fed and controlled and optimized, the formation of aluminum ash can be reduced by 12%.

　　Recycled aluminum plays an increasingly prominent role in the production of aluminum in major developed countries. developed * * The ratio of primary aluminum to recycled aluminum is close to or exceeding 1:1. Because of this, the recycling and regeneration of waste Al has become a matter of great importance to countries around the world and has become an important industry. 　　However, the recycling and regeneration of aluminum alloys is a very complex technical task. Various aluminum products are widely used and scattered. How to collect, classify, and then recycle them is a very complicated and huge project. Secondly, there are hundreds of alloys with different alloy compositions and properties around the world, and the component elements in many of them are mutually exclusive and incompatible. How to use the simplest method, the lowest cost and the most effective process to regenerate waste Al into a composition that meets the ideal alloy requirements, performance that meets the use, and a recycling technology whose quality can reach or be close to the level of virgin materials is the goal pursued by this industry in various countries around the world. 　　Currently developed * * A complete scrap aluminum collection, management and sorting system has been formed to adapt to the expanding market demand. * * New technological innovation measures have been continuously introduced in production, such as low-cost continuous smelting and treatment processes, processes for upgrading low-grade scrap aluminum, etc. Scrap aluminum can be used to produce large quantities of recycled aluminum ingots for casting, die-casting, rolling and master alloys. The largest cast The ingot weighs 13.5 tons, of which remelted secondary alloy ingots (RSI) are used to make special thin plates for cans. The quality of the thin plates has reduced the weight of each can to only about 14 grams. Some recycled aluminum is also used to make the frame of computer floppy disk drives. 　　However, my country’s concept and understanding of the recycling of scrap aluminum has not yet reached the level of developed countries such as the United States and Japan. * * The largest recycled aluminum enterprise in my country and Asia is Shanghai Xinge Nonferrous Metals Co., Ltd. located in the suburbs of Shanghai. Although the company has two sets of 50-ton smelting static furnaces and one set of 40-ton fuel-fired smelting static furnaces ； A 12-ton oil-fired rotary furnace, these 50-ton furnaces are not only the largest recycled aluminum smelting furnace in China, but also among the largest recycled aluminum smelting furnaces in Asia. 　　However, in terms of some environmental measures and process technology levels, even though Xinge Company's level is in a leading position in China, it is still at the level of foreign countries in the 1980s. As for some enterprises with small scale, low output and weak environmental protection measures, they still account for the majority. It can be said that there are many difficulties in the implementation of technological transformation and environmental protection facilities.

(1) The recycling processing of scrap aluminum generally goes through the following four basic processes. (1) Preparation of scrap aluminum materials: First, primary classification of scrap aluminum is carried out and stacked in different grades, such as pure aluminum, deformed aluminum alloy, cast aluminum alloy, mixed materials, etc. For scrap aluminum products, they should be disassembled to remove the steel and other non-ferrous metal parts connected to the aluminum materials, and then processed into cleaning, crushing, magnetic separation, drying and other processes to produce scrap aluminum materials. For thin and loose flake scrap aluminum parts, such as locking arms, speed gear bushings and aluminum chips on automobiles, a hydraulic metal baler should be used to pack them into packages. For steel core aluminum stranded wire, the steel core should be separated first, and then the aluminum wire should be wound into a roll. Iron impurities are very harmful to the smelting of scrap aluminum. When there is too much iron, brittle metal crystals will be formed in the aluminum, thereby reducing its mechanical properties and weakening its corrosion resistance. The iron content should generally be controlled below 1.2%. Scrap lead with an iron content of more than 1.5% can be used as a deoxidizer in the steel industry. Commercial aluminum alloys rarely use scrap aluminum with high iron content for smelting. Currently, there are no very successful methods in the aluminum industry that can satisfactorily remove excess iron from scrap aluminum, especially in the form of stainless steel. Scrap aluminum often contains organic non-metallic impurities such as paint, oil, plastic, and rubber. It must be removed before returning to the furnace for smelting. For wire scrap aluminum, the foreskin can generally be removed by mechanical grinding or shear stripping, heating stripping, chemical stripping and other measures. At present, domestic enterprises commonly use high-temperature ablation to remove insulators. During the ablation process, a large amount of harmful gases will be produced, seriously polluting the air. If a combination of low-temperature baking and mechanical peeling is used, the insulator is first softened by heat energy and the mechanical strength is reduced, and then peeled off by mechanical rubbing. This can not only achieve the purpose of purification, but also recover the insulator material. The coating, oil stains and other pollutants on the surface of scrap aluminum vessels can be cleaned with organic solvents such as acetylene. If it still cannot be removed, a paint stripping furnace should be used to remove the paint. The maximum temperature of the paint stripping furnace should not exceed 566°C. As long as the waste materials stay in the furnace for enough time, general oils and coatings can be removed. For aluminum foil paper, it is difficult to effectively separate the aluminum foil layer and the paper fiber layer using ordinary waste paper pulping equipment. An effective separation method is to first place the aluminum foil paper in an aqueous solution, heat and pressurize it, and then quickly discharge it to a low-pressure environment for decompression and mechanical stirring. This separation method can recycle both fiber pulp and aluminum foil. The liquefaction separation of scrap aluminum is the future development direction of recycling aluminum metal. It combines the pretreatment of scrap aluminum miscellaneous materials with re-melting and casting, which not only shortens the process flow, but also avoids air pollution to the greatest extent, and improves the recovery rate of net metal. * * improve. There is a filter in the device that allows gas particles to pass through. In the liquefied layer, aluminum precipitates at the bottom. Organic matter such as paint attached to the waste aluminum is decomposed into gas, tar and solid carbon at temperatures above 450°C, and is then completely burned through the oxidation device inside the separator. The waste material is stirred by the rotating drum and mixed with the dissolving liquid in the bin. Impurities such as sand and gravel are separated into the sand and gravel separation area. The dissolving material brought out by the waste material returns to the liquefaction bin through the recovery propeller. (2) The ingredients are selected based on the preparation and quality conditions of the scrap aluminum materials and the technical requirements of the recycled products and the dosage of each type of materials is calculated. The ingredients should consider the degree of oxidation burning loss of the metal. The oxidation burning loss of silicon and magnesium is greater than that of other alloying elements. The burning loss rate of various alloying elements should be determined through experiments in advance. The physical specifications and surface cleanliness of scrap aluminum will directly affect the quality of recycled products and the actual metal yield. For scrap aluminum that is not clean of oil, up to 20% of the active ingredients will enter the slag. (3) The deformed aluminum alloys that can be produced from scrap aluminum alloys include 3003, 3105, 3004, 3005, 5050, etc., among which 3105 alloy is mainly produced. In order to ensure that the chemical composition of the alloy material meets the technical requirements and the process needs of pressure processing, a portion of primary aluminum ingots should be added when necessary. (4) The process flow of recycled aluminum alloy is shown in Figure 1-19. Only a small part of the scrap aluminum material is regenerated into deformed aluminum alloy, about 1/4 is regenerated into deoxidizer for steelmaking, and most of it is used to regenerate aluminum alloy for casting. Die-cast aluminum alloys such as A380 and ADCl0, which are widely used in the United States, Japan and other countries, are basically recycled from scrap aluminum. Four basic processes for scrap aluminum recycling processing (2) The main equipment for recycling aluminum is the smelting furnace and the refining and purification furnace. Generally, a special static furnace using fuel or gas is used. my country's largest recycled aluminum enterprise is Shanghai Xinge Nonferrous Metals Co., Ltd. located in the suburbs of Shanghai. The company has two sets of 50t smelting static furnaces and one set of 40t fuel oil smelting static furnaces. ； A 12t oil-fired rotary furnace. Small enterprises can use pool kilns, crucible kilns, etc. for smelting. In recent years, developed * * A series of new technological innovations have been continuously introduced in production, such as low-cost continuous smelting and processing processes, which can upgrade low-grade aluminum scrap and be used to manufacture recycled aluminum ingots for casting, die-casting, rolling and master alloys. The largest ingot weighs 13.5t. Among them, the remelted secondary alloy ingot (RSI) can be used to make special thin plates for cans. The quality of the thin plates has reduced the quality of each can to only about 14g. ； Some recycled aluminum is even used to make the frames for computer floppy drives. In the recycling process of scrap aluminum, the smelting and melt processing of recycled aluminum are key processes to ensure the metallurgical quality of recycled aluminum. The modification, refining and purification of the aluminum melt can not only change the form of silicon in the aluminum-silicon alloy and purify the aluminum melt, but also * * Improve the properties of aluminum alloys. For the refining, deterioration and purification of aluminum melt, chlorine salts and fluorine salts such as Nacl, NaF, KCI and Na3AIF6 are currently used. Some also use C12 or C2C16. for processing. Although the effect of using chlorine-containing substances to refine scrap aluminum melt is good, its by-products such as AICI3, HCl and Cl can cause serious damage to the human body, the environment and equipment. In recent years, people are trying to improve the treatment process and use non-toxic, low-toxic refining and deterioration materials to solve environmental pollution problems, such as using N2, Ar, etc. as refining agents, but the results are not satisfactory. The basic ingredients of the so-called "pollution-free" refining agents on the market are carbonates, nitrates and a small amount of C2C16. Since a small amount of nitrogen oxides and chlorine are still emitted, environmental pollution cannot be completely eliminated. In recent years, the newly developed process of using rare earth alloys to modify, refine and refine recycled aluminum is expected to completely solve the environmental pollution problem in the scrap aluminum recycling and smelting industry. This process makes full use of the interaction characteristics between rare earth elements and aluminum melt, exerts the refining, purifying and deteriorating functions of rare earth elements on aluminum melt, and can realize the integrated treatment of purification, refining and deterioration of aluminum melt. It is not only simple and efficient, but also can effectively improve the metallurgical quality of recycled aluminum. No harmful waste gases and other by-products will be produced during the entire treatment process.