Production of recycled aluminum

Due to the excellent properties of aluminum, is hardly etched in the course of normal use, failure to use aluminum products for a long period, so the aluminum with a high rate of industrial production since 1886 since the metal aluminum, the production of human Of the approximately 680 million tons of aluminum, approximately 440 million tons are still in use. Aluminum is most likely to be recyclable and recyclable in all non-ferrous metals. Secondary aluminum resources only need to undergo a relatively simple processing process to return to their various properties before failure, and can be recycled well. Aluminum is a true metal that can be used for a long time.

The energy consumed to produce recycled aluminum from secondary aluminum resources is only 5% of the energy consumption of the whole process of primary aluminum production. The recycling rate of metal during the cycle is very high. In general, the metal loss rate per cycle is only 3.5%. ~ 8.5%. The investment in the recycled aluminum plant is only 12.5% ​​of the total investment from the aluminum mine to the primary aluminum process, and the production cost is only 10% to 15% of the original aluminum. It also greatly reduces greenhouse gas emissions and environmental pollution.

The use of secondary aluminum resources has attracted the attention of all countries in the world. After the first human environmental conference in the 1970s and the emergence of the oil crisis, industrial developed countries have examined the high-energy industries and vigorously strengthened the production of recycled metals. Major Japanese companies have shut down alumina and electrolytic aluminum production lines and switched to recycling aluminum resources to produce recycled aluminum. The production of primary aluminum decreased from 1.1 million tons in the 1970s to 0.66 tons in 2001, while the output of recycled aluminum has grown to around 1.2 million tons. Today, nearly 12 million tons of waste aluminum is processed into recycled aluminum and aluminum alloy each year, which accounts for about 40% of the total global aluminum market demand.

In recent years, the annual growth rate of recycled aluminum in the world is about 5.65%, and the average growth rate of primary aluminum production in the same period is 1.93%. In 2002, the total amount of recycled aluminum in the world was 8,885,900 tons (excluding the “process waste aluminum material” that directly returned to the smelting and processing process), accounting for 25.35% of the world's total aluminum production and 33.96% of the total primary aluminum production. The output of recycled aluminum in developed countries is 7,873,900 tons, including 2.98 million tons in the United States, 1,238,800 tons in Japan, 668,800 tons in Germany, and 609,900 tons in Italy. The total output of recycled aluminum in the top 13 countries of world recycled aluminum production is 7,484,900 tons, accounting for the world. 95% of the total amount of recycled aluminum. According to a recent report by Austrian University of Austria, Professor Peter Paschen, it is estimated that by 2030 the world's total aluminum consumption will reach 50 million tons, of which 22 to 24 million tons are recycled aluminum, accounting for 44% to 48% of total consumption.

China's waste aluminum recycling began relatively late. In the 1980s, driven by the reform and opening up policy, downstream industries developed rapidly and domestic aluminum consumption increased substantially. In addition to the import of primary aluminum, in order to make up for the shortage of supply, the recycling aluminum industry has developed rapidly. The output of recycled aluminum, which was included in the statistics in 1990, was 0.72 million tons, which was 0.84% ​​of the total aluminum production in that year. In 1995, it was 193,600 tons, accounting for 10.35% of the total output. The annual growth rate of recycled aluminum reached 193.16%, which is 1.65 times of the growth rate of total aluminum production. "Nine Five" period, each geothermal keen on expanding primary aluminum production, aluminum production is almost standing still, in 2000 recycled aluminum production 145 200 t, accounting for the proportion of total output of aluminum fell to 4.86%. Table 1 lists the production of recycled aluminum in China.

Table 1 Production and proportion of recycled aluminum in China

In recent years, China's aluminum production and consumption demand has grown rapidly, and has become a major producer and consumer of aluminum. However, China's recycled aluminum production and scrap aluminum recycling rate are very different from those in developed countries. According to preliminary statistics, in 2001, China's various aluminum and aluminum alloy scraps and scraps were 1.2 million tons, and waste aluminum beverage cans were about 108,000 tons. However, the amount of scrap aluminum recovered was only 420,000 tons, and the recovery rate was 32%. At the same time, the consumption of recycled aluminum in China is also growing rapidly, especially in the Pearl River Delta, the Yangtze River Delta and the Bohai Rim region. In order to meet the demand, a large number of small-scale recycled aluminum plants have been built and imported aluminum is imported from abroad. Generally, these small-scale recycled aluminum plants are attached to the processing plants, and recycled aluminum is directly used for processing materials to enter the market. Did not enter the national statistical channel. These large number of small aluminum recycling processing plants have poor overall technology, low equipment level, high energy consumption, and metal burning loss of more than 30%. The waste aluminum deposits in the process are seriously harmful to the environment. Table 2 lists the imports of recycled aluminum and scrap aluminum in China in recent years.

Table 2 China's recycled aluminum consumption and aluminum imports (10,000 t)

The main source of primary and secondary aluminum resources

About 20% of the secondary aluminum resources come from the packaging industry, 40% from the transportation industry, and more than 30% from the construction industry.

About 80% of the aluminum alloys produced worldwide are used in the manufacture of castings and castings for automotive parts. The highest recovery rate of scrap aluminum in scrapped automobiles has reached 95%. With the gradual increase in the amount of aluminum used in automobiles and the development of automobile production and the increase in the number of social vehicles, the amount of aluminum scrap obtained from scrapped automobiles will be related to the product of the growth rate of aluminum used in automobiles and the growth rate of automobile production. The transportation sector, including the automotive industry, is the industry with the fastest growth in aluminum demand and the largest share of the aluminum consumer market, and has now surpassed the packaging and construction industries. According to the World Aluminum Association (IPAI) report, aluminum consumption in the world's transportation industry accounted for 32.5% of total consumption in 2000, and the United States has reached 34%. Waste aluminum produced by the transportation industry is the main source of secondary aluminum resources.

The construction industry is another important source of secondary aluminum resources. Aluminum consumed by the construction industry accounts for about 25% of the total aluminum consumption. Since the aluminum alloy has a relatively long period of failure (generally 30 years), which is about 2.5 times the failure period of automotive aluminum products, the aluminum in the construction industry is The amount is quite large. Over time, the absolute amount of secondary aluminum resources formed by the construction industry will be a huge number. At present, the recycling rate of waste aluminum in the construction industry is about 85%.

About 80% of the world's beverage cans are made of aluminum. The market share of beverage cans (bottles) in aluminum cans is about 50% in Europe, and more than 90% in the US, Brazil and Japan. The United States is the largest consumer of aluminum cans. In 2001, the sales volume was about 100 billion. In the fiscal year 2001-2002, Japan consumed 17.44 billion aluminum cans; Brazil: 10.96 billion; Western Europe 5.6 billion. The production of waste aluminum beverage cans is extremely dispersed, and the recovery is very difficult. If it is not concentrated, it is impossible to form resources. Countries have made tremendous and lasting efforts in collecting aluminum cans, and the average recovery rate of aluminum cans in the world is currently over 50%. In 2001, the United States was 55%. Japan is 38%, Europe is 45%, Brazil is 85%, Switzerland is 91%, and Sweden is 88%.

Second, the production of recycled aluminum with secondary aluminum resources

The effective use of secondary aluminum resources is based on a well-established recycling organization network and a strict classification management system.

Among the recovered aluminum scraps, the main impurities are Si, Ti, Fe, Mn, etc., and various alloying elements incorporated into the base metal aluminum. Until now, there has not been an industrially efficient, economically and economically viable industrial process that removes impurities from waste aluminum. Therefore, it is only possible to carry out a strict sorting classification of the waste aluminum material before re-dissolving. Then, the smelting is carried out separately, and the uniformity of the product components of the regeneration rate is maintained as much as possible, and the contamination of impurities is reduced. At present, these impurities are generally produced as a part of an alloying element by adjusting a component to form an aluminum alloy. That is, from pure to impure, from alloy components to alloy components, from the content of components to the content of components, such a step by step, in order to make reasonable use of all effective components. Nowadays, the technology for recycling aluminum has been developed to the extent that recycled aluminum, which is the same quality as primary aluminum, can be produced from carefully classified waste. But most of it is converted to cast aluminum.

The production technology of recycled aluminum is mainly focused on solving the problems of improving the efficiency of the re-dissolution process, reducing energy consumption, reducing burning loss and eliminating pollution. Foreign countries also attach great importance to the pretreatment technology of waste aluminum materials and the mechanization and automation of the pretreatment process.