Waste aluminum recycling technology

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

(1) Preparation of Waste Aluminum Materials

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 prepared 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 and then the aluminum wire 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, which contains more than 1.5 % iron , it can be used as a deoxidizer in the iron and steel industry. Commercial aluminum alloys rarely use aluminum scrap 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.

There is a filter in the device that allows gas particles to pass through. In the liquefaction layer, aluminum precipitates at the bottom, and organic substances such as paint attached to the scrap aluminum decompose at 450°C into gas, tar, and solid char, and then pass through the oxidizer inside the separator. Completely burned. 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) Recycled deformed aluminum alloy

Deformed aluminum alloys that can be produced from scrap aluminum alloys include 3003, 3105, 3004, 3005, and 5050 , among which 3105 alloys are mainly produced. 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 Cast 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 and ADCl0 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. The largest reclaimed aluminum enterprise in China is Shanghai Xinge Nonferrous Metals Co., Ltd., located in the suburbs of Shanghai. The company has two 50t smelting and standing furnaces, a group of 40t fuel smelting and standing furnaces, and a 12t fuel rotary kiln. Small enterprises can use kiln such as tank kiln and kiln.

In recent years, developed countries have continuously introduced a series of new technological innovations in their production, such as low-cost continuous smelting and processing technologies, which can upgrade low-grade scrap aluminum for manufacturing for casting, die-casting, rolling and Recycled aluminum ingots for master alloys. The largest ingot weight is 13.5t, in which the remelted secondary alloy ingot (RSI) can be used to make special plates for cans. The quality of the thin plates has reduced the quality of each can to only 14g.

Left and right; some recycled aluminum, even for the manufacture of computer 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 and fluoride salts such as Nacl, NaF, KCI, and Na3AIF6, while others use C12 or C2C16. Processing.

The use of chlorine-containing substances to refine waste aluminum melts, although effective, is a by-product of AICI3, HCl, and Cl that 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 refined metamorphic materials to solve environmental pollution problems, such as the use of N2, Ar as a refining agent, but the effect is not satisfactory. The so-called “pollution-free” refining agents on the market are based on carbonates, nitrates, and a small amount 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 characteristics of rare earth elements and aluminum melts, and exerts the function of rarer elements on the refining and metamorphism of aluminum melts, and can realize integrated treatment of purification, refining, and deterioration of aluminum melts, and is not only simple and efficient. , And can effectively improve the quality of recycled aluminum metallurgy. No harmful exhaust gas and other by-products are generated during the entire process.