The four basic processes for waste aluminum recycling

According to the large-scale non-ferrous net reprint: attention to recycled aluminum - recycled aluminum is scrap aluminum and aluminum scrap aluminum or scrap aluminum, remelted and refined aluminum or aluminum metal, is an important source of metal aluminum. China is a big country in aluminum production, but compared with other developed countries, the entire industry structure is unreasonable, and the scale of the recycled aluminum industry is lagging behind. The development of recycled aluminum industry is in line with the development trend of the aluminum industry in the world today and meets the needs of China's sustainable development related policies. Therefore, China's aluminum industry structure urgently needs to increase the development ratio of the recycled aluminum industry.

Today, let's take a look at how scrap aluminum is processed in the industry.

The recycling of scrap aluminum generally goes through the following four basic processes.

1. Preparation of waste aluminum material

First of all, the primary classification of waste aluminum, graded stacking, such as pure aluminum, deformed aluminum alloy, cast aluminum alloy, mixed materials. For waste aluminum products, dismantling shall be carried out, steel and other non-ferrous metal parts connected with aluminum materials shall be removed, and waste aluminum materials shall be made through the processes of cleaning, crushing, magnetic separation, and drying. For thin, loose, flake-shaped scrap aluminum parts, such as locking arms, speed gear bushings, and aluminum shavings on automobiles, hydraulic metal balers are used to apply pressure. For ACSR, the steel core should be separated first; then the aluminum wire is wound into a roll. Iron impurities are very harmful to the smelting of aluminum scrap. When the iron is too much, brittle metal crystals are formed in the aluminum, thereby reducing its mechanical properties and weakening its corrosion resistance. Iron content should generally be controlled below 1.2%. For lead with an iron content of 1.5% or more, it can be used as a deoxidizer for the iron and steel industry, and commercial aluminum alloys are rarely used for smelting scrap aluminum with high iron content. At present, there is no successful method in the aluminum industry to satisfactorily remove excess iron in scrap aluminum, especially in the form of stainless steel. Waste aluminum often contains organic non-metallic impurities such as paints, oils, plastics, and rubber. Before smelting, you must try to remove it. For wire type scrap aluminum, mechanical abrasion or shear peeling, heat stripping, chemical stripping, etc. can generally be used to remove the wrapper. At present, domestic companies commonly use high-temperature ablation methods to remove insulators, and a large amount of harmful gases will be generated during the ablation process, which will seriously pollute the air. If the combination of low-temperature baking and mechanical peeling is used, the insulator is first softened by heat, the mechanical strength is reduced, and then it is peeled off by mechanical rubbing so that both the purpose of purification can be achieved and the insulator material can be recovered.

The coating, oil, and other contaminants on the surface of aluminum waste containers can be cleaned with acetone and other organic solvents. If they cannot be removed, paint stripping ovens should be used for paint stripping. The maximum temperature of the stripping furnace should not exceed 566 °C. As long as the waste material stays in the furnace for a sufficient period of time, general oils and coatings can be removed. For aluminum foil paper, it is difficult to effectively separate the aluminum foil layer from the paper fiber layer by ordinary waste paper pulping equipment. The effective separation method is to first heat the aluminum foil paper in an aqueous solution, pressurize it, and then quickly discharge it to a low pressure environment. , And mechanical stirring. This separation method can recover both fiber pulp and aluminum foil. The liquefaction and separation of aluminum scrap is the development direction of metal aluminum recovery in the future. It combines the pretreatment of aluminum scrap with remelting, which not only shortens the process flow, but also avoids air pollution to the maximum extent, and it also makes net metal recovery. The rate has greatly increased. The aluminum liquefaction separation device has a filter that allows gas particles to pass through. In the liquefaction layer, aluminum is precipitated at the bottom, and organic substances such as paint attached to the aluminum scrap are decomposed into gas, tar, and solid char at 450° C. and then passed through the separator. The internal oxidizer completely burns. The waste is stirred by a rotating drum, mixed with the dissolving liquid in the bunker, the impurities such as sand and gravel are separated into the gravel separation area, and the dissolved fertilization brought out by the waste is returned to the liquefaction tank through the recovery propeller.

2 ingredients

According to the preparation and quality conditions of waste aluminum materials, according to the technical requirements of recycled products, choose and match and calculate the amount of various materials. Ingredients should consider the degree of oxidation of the metal burned, silicon, magnesium oxide burning than other alloying elements to large, the burning rate of various alloying elements should be determined in advance through experiments. The physical specifications and surface cleanliness of waste aluminum materials will directly affect the quality of recycled products and the metal yield. With the exception of waste aluminum that is not clean, up to 20% of the active ingredients will enter the slag.

3. Regeneration aluminum alloy

The deformed aluminum alloys that can be produced from scrap aluminum alloys are 3003, 3105, 3004, 3005, 5050, etc., of which the main production is 3105 alloys. In order to ensure that the chemical composition of the alloy material meets the technical requirements and the pressure processing process needs, a part of the original aluminum ingot should be added when necessary.

4. Recycled casting aluminum alloy

Only a small part of the waste aluminum material is regenerated into deformed aluminum alloy, about 1/4 of which is regenerated into deoxidizer for steelmaking, and most of it is used for regenerating casting aluminum alloys. The die-cast aluminum alloys a380, adcl0, etc. that are widely used in the United States, Japan, and other countries are basically recycled with scrap aluminum. The main equipments for reclaimed aluminum are smelting furnaces and refining and purifying furnaces, and generally use dedicated static furnaces for fuel or gas.

Developed countries have continuously introduced a series of new technological innovations in production, such as low-cost continuous smelting and treatment processes, which can upgrade low-grade scrap aluminum for manufacturing, casting, rolling and master alloys. Used recycled aluminum ingots. The largest ingot weight is 13.5t, in which the remelted secondary alloy ingot can be used for the manufacture of special plates for cans. The quality of the sheet has reduced the quality of each can to only about 14g; some recycled aluminum, even for the manufacture of computers Floppy disk drive frame. In the regeneration process of waste aluminum, the smelting of regenerated aluminum and the treatment of the melt are the key processes to ensure the quality of regenerated aluminum metallurgy. The metamorphism and refining of aluminum melt can not only change the shape of silicon in aluminum-silicon alloys, purify the aluminum melt, but also greatly improve the performance of aluminum alloys. The refinement and purification of aluminum melts are currently treated with chloride salts and fluoride salts such as nacl, naf, kci, and na3aif6. Others use c12 or c2c16. Processing. The use of chlorine-containing substances for the refining of waste aluminum melts, although effective, has caused the byproducts aici3, hcl and cl to cause serious damage to the human body, the environment and equipment. People are trying to improve the treatment process and use non-toxic, low-toxic refined metamorphic materials to solve environmental pollution problems, such as the use of n2, ar as refining agents, but the effect is not satisfactory. The so-called “pollution-free” refining agents on the market are based on carbonates, nitrates, and small amounts of c2c16. Since there is still a small amount of nitrogen oxides and chlorine emissions, environmental pollution cannot be completely eliminated.

In recent years, newly developed processes for modifying, refining, and refining recycled aluminum with rare earth alloys are expected to completely solve the problem of environmental pollution in the scrap aluminum recovery and smelting industry. The process fully utilizes the interaction of rare earth elements with aluminum melts, performs the refining and purification and metamorphism of rare earth elements on aluminum melts, and can realize integrated treatment of purification, refining, and deterioration of aluminum melts. And can effectively improve the metallurgical quality of recycled aluminum. No harmful exhaust gas and other by-products are generated during the entire process.