Aluminum recycling technology and benefits

Aluminum has a number of advantages, but its greatest advantage is its recyclability, which can be recycled over and over again. Compared with the production of primary aluminum, recycled aluminum has no effect on the performance of aluminum. The oxidation loss during re-melting and remelting is only 2% to 3%. Each cycle can save about 95% of energy and reduce the corresponding carbon dioxide emissions. This has great significance for building a low-carbon economy. The recycling of beer cans can explain the problem, from tank production, charging, sales, consumption, waste tank recycling to recycling, each cycle does not exceed 60 days. In the past few years, aluminum recovered from scrapped cars in North America has surpassed recycled aluminum in used beer cans. The increase in the amount of aluminum used in automobiles has, on the one hand, drastically reduced the quality of the car itself, and on the other hand, has improved fuel efficiency and reduced greenhouse gas emissions. The automotive industry is the main application of recycled aluminum alloy.

First, the advantages of aluminum recycling and recycling

In addition to energy conservation and emission reduction, waste aluminum is also a useful resource. For countries and regions that need to import aluminum, the use of some recycled aluminum can reduce aluminum imports, improve trade balance and increase employment opportunities. Manufacturing and processing industries provide sufficient raw materials, with or without solid waste dumping sites, to eliminate climate change caused by industry.

A comprehensive survey and evaluation of the industry shows that the advantages of aluminum recycling are very large. For every ton of primary aluminum produced, the total energy consumption for power generation, transmission loss and fuel transportation is about 45,000 kWh, and about 12 tons of carbon dioxide is emitted. . However, the energy consumption for producing 1 ton of recycled aluminum is only about 2,800 kWh, and the carbon dioxide emitted is only about 600 kilograms, which can save about 95% of electricity, and the temperature of warm air is about 95%. The energy used to produce the primary aluminum or the energy stored in the primary aluminum can be recovered in a single cycle with only minor losses.

In the US Aluminum Association released "Aluminum Industry Overview", the primary aluminum called "Energy Savings Bank", which means that the extraction of primary aluminum in the course of the energy consumed in the subsequent use of the recycling process, It can be "taken out" and returned to the society. Therefore, from the perspective of sustainable development, aluminum recycling has become a conventional raw material “urban mine”, which is a recyclable material for energy conservation and emission reduction. In order to reduce the quality of the car, improve fuel efficiency, improve safety and ride comfort, the automotive industry is increasingly using more aluminum, and the amount of aluminum that can be recycled is increasing year by year. It is worthy of the name, and it is a mine that is "always inexhaustible". In addition, the use of aluminum in the construction industry is also rising, which has led to an increase in the amount of aluminum accumulated in society.

Second, the crushing and classification of aluminum scrap

In North America, there are multiple channels for collecting and recycling waste aluminum parts. Waste cans and similar waste packaging products are usually collected by metal waste bins (MRF) and then sent to aluminum recycling companies through fixed recycling networks. Beer cans are made of alloys such as 3004, 3104, and 5182. The inevitable impurities such as iron and silicon should be strictly controlled during the recycling of waste materials. In recent years, the recycling rate of waste cans in the United States is about 54%, while the recovery rate of aluminum in scrapped cars is as high as 90%. This is because the recycling of waste cans is a voluntary action, but scrapped cars and other durable consumer goods ( Recycling of refrigerators, washing machines, etc. must be carried out in accordance with laws and regulations and is mandatory. If there are mandatory regulations for the recycling of waste cans, the recovery rate will increase. Some states have introduced stimulative measures to encourage people to recycle used cans and have received good results. The recovery rate in these states is significantly higher than in other states. Cane producers such as Alcoa and Nevelis have established separate recycling systems that not only promote recovery, but also play a role in ensuring waste quality.

High strength 2XXX and TXXX alloys used in the aerospace industry are generally not recycled. In the United States, decommissioned aircraft are kept in dry, desolate areas and selectively dismantled as a source of spare parts. After evaluation, the value of qualified aluminum alloy parts is much higher than the economic value of scrap aluminum. Therefore, the broken pieces that enter the aluminum waste distribution channel are usually scrapped cars and discarded durable consumer goods, most of which are 3XXX series, SXXX series and 6XXX series alloys.

In 2003, Jesse et al. said in an article on the basic situation of scrap aluminum recycling in scrapped cars, more than 6,000 scrap aluminum purchase stations in the United States supply raw materials to the crushing plant. Those crushing plants have about 200 crushers , broken. In the scrap, the steel is removed by a magnetic separator. After removing the iron, the scrap is sent to a separation plant of different classifications (by density). There are about 10 such plants in the United States; heavy metals sink below the flotation agent, they are copper , brass, bronze, and lead. , zinc, etc., while low density metals such as aluminum and magnesium are in the upper part. The broken metal fragments in the upper part of the flotation agent contained about 75% of the aluminum alloy and were transported to Huron Valley Steel Corporation (HVSC) in Belleville, Missouri for further final treatment. Of course, the quantity and equipment of these scrap metal acquisition stations, crushing plants and flotation plants are changing with the times. The above is just a brief introduction to the flow of aluminum scrap in the United States.

HVSC is a world leader in the development of waste sorting technology and equipment, some of which are done with large automotive companies and the Alcoa. Some technologies, such as eddy current, coloring classification, X-ray classification, and laser induced classification (LIBS), have been applied in production, and have a good effect in the classification of aluminum alloy waste. The waste can be sorted by alloy system. According to one of the HVSC sorting technologies, the aluminum scrap sorting production line constructed by LIBS technology has been put into operation in 2003 and has performed well and achieved the expected target.

Production proves that the aluminum-magnesium (6XXX) alloy can be sorted from Al-Si-Mg(6XXX) alloy scrap by LIBS technology. They are the two most used alloys in automobiles. This sorting technology will inevitably The classification of aluminum alloy waste has been promoted. Another advantage of LIBS technology is that with the development of laser and computer manufacturing technology, the price of LIBS equipment will be greatly reduced.

At the 2008 Light Metal Recycling Symposium in Detroit, Missouri, USA, Gesing proposed an idea to improve the efficiency of waste sorting. He said that in automotive scrap, aluminum and magnesium scraps are always mixed together, and it is necessary to separate them, which not only improves the quality of aluminum scrap, but also spawns a new industry - the reclaimed magnesium alloy industry.

Third, control impurities in waste aluminum

HVSC has made considerable achievements in the development of aluminum scrap sorting technology and equipment, and has made outstanding contributions to increasing the value of scrap aluminum. For example, the technology developed by the classification of deformed aluminum alloy and cast aluminum alloy has been successfully applied, and has a milestone in the waste aluminum classification technology, so that the content of impurity silicon and iron is effectively controlled. As we all know, when the content of iron and silicon in aluminum alloy exceeds a certain limit, it is extremely detrimental to the mechanical properties, fracture toughness and corrosion behavior of the alloy.

Effective separation of cast aluminum alloy and deformed aluminum alloy allows them to enter their respective circulation fields, recycling, and greatly improving the material value. For example, AA356.0 cast aluminum alloy is an important common alloy, its silicon and iron content are 7.0% and 0.6%, respectively, while the deformed aluminum alloy has much less silicon and iron content, if their waste is mixed. Together, it will reduce the grade and value of the deformed aluminum alloy. Silicon can improve the fluidity of the cast aluminum alloy melt and is beneficial for casting.

On the contrary, the controlled aluminum alloy has a much stricter control range for silicon, iron and other impurities. With the technology and equipment of HVSC, the deformed aluminum alloy can be separated by the alloy grade. The classification developed by the company is technically feasible but has not yet been applied in actual production. By adopting this sorting technology, the iron-containing aluminum pieces in the scrap can be effectively selected as the steel-making deoxidizer, and the value of the aluminum scrap is improved after the crushed aluminum with high iron content is removed.

At present, it is imperative to develop a highly deformable aluminum alloy with strong compatibility with impurities. In addition, automotive designers should minimize the number of alloys when designing automotive aluminum parts, and it is possible to use recycled aluminum alloys. The recovery rate of waste cans is high and the value is high because the tanks are all aluminum, all alloys are 5XXX series and 3XXX series; the tank body is 3004 or 3104 alloy, the can lid and the pull ring are 5182 alloy, their iron, The silicon content is almost the same, except that the magnesium content of the 5182 alloy is higher, and magnesium is not difficult to control in the re-melting smelting, and it can be controlled to a certain level by flux refining. But reducing the type of alloy is a difficult task because different parts have different requirements for material properties. In this respect, Japan Toyota Motor Co., Ltd. produces the same alloy 6022 alloy inside and outside the car. The inner plate is in the O state and has high formability. The outer plate is in the T4 state. Higher strength and anti-concave properties, they have good compatibility with the impurity content of the alloy. In the process of handling and handling of waste materials, impurities should be avoided as much as possible, and wastes of different varieties should be avoided.

Fourth, the conclusion

Since the commercial production of aluminum in 1886, about 70% of the aluminum produced worldwide is still in use today. The reason for this is not the result of government actions, but the result of the value of circular economy. Furthermore, aluminum has a strong reproducibility, and more than 95% of the aluminum used in the structure can be recovered and recycled, and the burning loss during the re-manufacturing will not exceed 5%. However, most of the functions of aluminum, such as packaging aluminum foil, aluminum for steelmaking, aluminum for metallurgical reducing agent, aluminum powder aluminum paste, fuel aluminum powder, etc., cannot enter the circulation system. In order to build a low-carbon economic society and meet the era of “negative” carbon trajectory, relevant Chinese departments should introduce strict vehicle fuel efficiency standards to stimulate the application of aluminum in the transportation industry.

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