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不同成分的铝合金其密度也不同，可采用重介质分选。一般铝镁合 金、铝镁硅合金比铝锌合金、铝铜合金、铝硅合金的密度小。前苏联采用此方法处理废铝料,生产率可达10t/ho铝在低温时能保持原有的性能和塑性，而其它金属和非金属在低温时呈现较大脆性，如低碳钢、锌、塑料及橡胶等。比利时有一条液氮低温处理废铝生产线，处理能力为15000t/a，经济效益可观。破碎废铝便于处理和运输，一般废铝料、废铸件、炉渣、电线及易拉罐等都要经过破碎。破碎设备有剪切机、破碎机及火焰切割等。打包的目的在于将松散的废铝料压缩成具有一定尺寸和密度的包，便于运输和熔炼。尤其是对边角料、卷屑、铝箔、切断的废电缆与电线、易拉罐等都要打包。
废铝在熔炼之前要经过烘干处理，以除去水分、润滑剂、油等。一般可采用回转烘干炉和箱式烘干炉。在现代烘干生产线上都装有废气燃烧室、除尘器,对排出的废气、废水进行净化处理。对于数量大、化学成分单一稳定的废铝采用分类集中处理，可提高生产效率，降低成本，提高经济效益。如法国、日本、美国、英国、德国等都采用分类集中处理废电缆一电线、废易拉罐、废铝渣和炉渣，效果较好。
Most of the waste aluminum recovered at home and abroad is remelted and cast into recycled aluminum ingot, or a small part of the waste aluminum is directly reformed and utilized. The waste aluminum recovered from the society should be carefully pretreated according to the classification standard of recycled waste aluminum before smelting, including sorting, packing and pelleting, drying, purification and dust removal. The waste aluminum material is generally used artificial sorting in our country. When the amount of waste aluminum is large, other methods can be used, such as mechanized selection, magnetic separation, heavy medium separation and cold treatment of waste aluminum. Foreign special sorting table or sorting line for continuous processing, more selection, high efficiency. The main role of magnetic separation is to remove the ferromagnetic material in the waste aluminum, using electromagnet or permanent magnet as the magnet or magnetic wheel, the magnet is suspended above the sorting belt, the magnetic wheel is placed on the transmission roller of the sorting conveyor belt. Britain's magnetic wald test separator is when the aluminium scrap material into sorting machine, the machine on the separator one of about 800, 800 mm steel plate, the tank of cooling water in the copper pipe, copper pipe steel to produce magnetic field, after the power supply of aluminum after cutting lines produce induced current and magnetic field to produce a magnetic field, the interaction of two magnetic field would push aluminium to a certain direction, In this way, aluminum can be separated from waste nonmetals.
The density of aluminum alloy with different composition is also different, and can be sorted by heavy medium. General aluminum magnesium alloy, aluminum magnesium silicon alloy than aluminum zinc alloy, aluminum copper alloy, aluminum silicon alloy density is smaller. The former Soviet Union used this method to treat waste aluminum, the productivity can reach 10T/HO aluminum at low temperature can maintain the original performance and plasticity, while other metals and non-metals at low temperature show greater brittleness, such as mild steel, zinc, plastic and rubber. Belgium has a low temperature liquid nitrogen treatment waste aluminum production line, the processing capacity of 15000T /a, considerable economic benefits. Broken waste aluminum is easy to handle and transport. Generally, waste aluminum materials, waste castings, slag, wires and cans should be broken. The crushing equipment has shear machine, crusher and flame cutting, etc. The purpose of packing is to compress loose waste aluminum into a package of a certain size and density, which is easy to transport and melt. In particular, the scrap material, rolled scraps, aluminum foil, cut waste cables and wires, cans and so on must be packed.
Waste aluminum should be dried before melting to remove moisture, lubricant, oil and so on. Generally, rotary drying oven and box drying oven can be used. In the modern drying production line are equipped with exhaust gas combustion chamber, dust collector, exhaust gas, waste water purification treatment. Classification and centralized treatment of waste aluminum with large quantity and single and stable chemical composition can improve production efficiency, reduce costs and improve economic benefits. For example, France, Japan, the United States, the United Kingdom, Germany and other countries adopt the classification of centralized treatment of waste cables and wires, waste cans, waste aluminum slag and slag, the effect is good.