The recycling of waste aluminum is generally carried out through the following four basic processes.
(1) Preparation of waste aluminum materials
First of all, the primary classification of waste aluminum, hierarchical stacking, such as pure aluminum, deformed aluminum alloy, cast aluminum alloy, mixed materials. For scrap aluminum products, it shall be dismantled to remove steel and other non-ferrous metal parts connected with aluminum materials, and then made into waste aluminum materials through washing, crushing, magnetic separation and drying. For thin and loose sheet-like scrap aluminum parts, such as locking arms on the car, speed gear bushings and aluminum chips, they should be pressed into a bag with a hydraulic metal baler. For steel core aluminum stranded wire, the steel core should be separated first;
The aluminum wire is then wound into a roll. Iron impurities are very harmful to the smelting of scrap aluminum. When iron is too much, brittle metal crystals are formed in the aluminum, thereby reducing its mechanical properties and reducing its corrosion resistance. The iron content should generally be controlled below 1.2%. For waste lead containing more than 1.5% of iron, it can be used as a deoxidizer for the steel industry. Commercial aluminum alloys are rarely smelted with waste aluminum with high iron content.
At present, there is no very 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 paint, oil, plastic and rubber. It must be removed before it can be smelted. For wire-like waste aluminum, mechanical coating or shear stripping, heat stripping, chemical stripping, etc. are generally used to remove the foreskin. At present, domestic enterprises often use high-temperature ablation to remove insulators. During the ablation process, a large amount of harmful gases will be generated, which will seriously pollute the air. If a combination of low-temperature baking and mechanical peeling is adopted, the insulator can be softened by heat, the mechanical strength is lowered, and then peeled off by mechanical boring, thereby achieving the purpose of purification and at the same time recovering the insulator material.
Coatings, oil stains and other contaminants on the surface of waste aluminum vessels may be cleaned with an organic solvent such as acetone. If they cannot be removed, they should be stripped in a paint stripping furnace. The maximum temperature of the paint stripping furnace should not exceed 566 ° C. As long as the waste material stays in the furnace for a sufficient period of time, the general oil and coating can be removed. For aluminum foil paper, it is difficult to effectively separate the aluminum foil layer and the paper fiber layer by ordinary waste paper pulping equipment. The effective separation method is to first heat and press the aluminum foil paper in an aqueous solution, and then quickly discharge it to a low pressure environment. And mechanical agitation. This separation method can recover both fiber pulp and aluminum foil.
The liquefaction separation of waste aluminum is the development direction of recycling aluminum metal in the future. It combines the pretreatment of reclaimed aluminum scrap with remelting, which not only shortens the process, but also avoids air pollution to the utmost extent, and makes the recovery of net metal. The rate has been greatly improved. The waste aluminum liquefaction separation device has a filter for allowing gas particles to pass through. In the liquefaction layer, aluminum is precipitated at the bottom, and organic substances such as paint adhered to the waste aluminum are decomposed into gas, tar and solid carbon at 450 ° C or higher, and then passed through a separator. The internal oxidation unit is completely burned. The waste is stirred by a rotating drum, mixed with the dissolved liquid in the silo, and impurities such as sand and gravel are separated into the gravel separation zone, and the dissolved ferrite is taken out by the recovery propeller and returned to the liquefaction chamber.
(2) Ingredients
According to the preparation and quality of waste aluminum materials, according to the technical requirements of recycled products, select and calculate the amount of various materials. The oxidative burning loss of the metal should be considered in the batching. The oxidative burning loss of silicon and magnesium is larger than that of other alloying elements, and the burning rate of various alloying elements should be determined experimentally in advance. The physical specifications and surface cleanliness of the waste aluminum material will directly affect the quality of the recycled product and the metal yield. The waste aluminum with unclean oil will have up to 20% of the active ingredient entering the slag.
(3) Regenerated deformation aluminum alloy
The deformed aluminum alloys that can be produced from waste aluminum alloys are 3003, 3105, 3004, 3005, 5050, etc., mainly producing 3105 alloy. In order to ensure that the chemical composition of the alloy material meets the technical requirements and the process requirements of the pressure processing, a part of the original aluminum ingot should be added if necessary.
(4) Recycled cast aluminum alloy
Only a small part of the waste aluminum material is regenerated into a deformed aluminum alloy, and about 1/4 of the deoxidizer for steelmaking is produced, and most of it is used for reclaiming aluminum alloy for casting. Die-casting aluminum alloys a380, adcl0, etc., which are widely used in the United States and Japan, are basically regenerated from waste aluminum. The main equipment for reclaimed aluminum is a melting furnace and a refining and purifying furnace, and a special static furnace for fuel or gas is generally used. China's largest recycled aluminum enterprise is Shanghai Xinge Nonferrous Metal Co., Ltd. located in the suburbs of Shanghai. The company has two sets of 50t smelting static furnaces, a 40t fuel smelting static furnace and a 12t fuel rotary kiln. Small enterprises can use smelting such as pool kiln and kiln.
In recent years, 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 waste aluminum for manufacturing, die casting, rolling and Recycled aluminum ingot for use as a master alloy. The largest ingot weight is 13.5t. Among them, the remelted secondary alloy ingot (rsi) can be used to manufacture 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, even used The framework for making computer floppy drives. In the process of regeneration of waste aluminum, the smelting of reclaimed aluminum and the treatment of the melt are the key processes to ensure the quality of recycled aluminum metallurgy. The modification and refining of aluminum melt can not only change the shape of silicon in the aluminum-silicon alloy, but also purify the aluminum melt and greatly improve the performance of the aluminum alloy. The refining and purification of aluminum melts are currently treated with chlorine and fluoride salts such as nacl, naf, kci and na3aif6, and some are c12 or c2c16. Process it. The use of chlorine-containing materials to refine the waste aluminum melt, although the effect is better, but its by-products aici3, hcl and cl, etc. will cause serious damage to the human body, the environment and equipment.
In recent years, people are trying to improve the treatment process, using non-toxic, low-toxic refining and metamorphic materials to solve environmental pollution problems, such as the use of n2, ar, etc. as a refining agent, but the effect is not satisfactory. The so-called "non-polluting" refining agent commercially available, the basic components of which are carbonates, nitrates and a small amount of c2c16, can not completely eliminate environmental pollution because a small amount of nitrogen oxides and chlorine gas are still discharged.
In recent years, the newly developed process of metamorphism, refinement and refining of reclaimed aluminum with rare earth alloys is expected to completely solve the environmental pollution problem of the waste aluminum recycling and smelting industry. The process fully utilizes the characteristics of the interaction between the rare earth element and the aluminum melt, and exerts the refining, purifying and deteriorating function of the rare earth element on the aluminum melt, and can realize the integrated treatment of purification, refining and deterioration of the aluminum melt, which is not only simple and efficient. And can effectively improve the metallurgical quality of recycled aluminum. No harmful exhaust gases and other by-products are produced throughout the process.
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