Beneficiation Technology
After mining, the next step in traditional metal extraction is minerals processing,
in which the valuable minerals are liberated from the gangue material in the ore.
Following this, the minerals are sorted into a separate stream, using differences
between their physical properties and those of the gangue. In some cases, chemical
or thermal processes may be used to remove impurities from the concentrated min-
erals. As a nal step, the concentrated minerals may be agglomerated to make them
easier to ship and easier to handle in subsequent smelting processes.
In Chapter 3, the mining (collecting) of scrap aluminum was described. Over
the next two chapters, the equivalent mineral processing (beneciation or upgrad-
ing) of this ore will be introduced. In this chapter, the techniques and equipment
used to separate scrap aluminum from contaminants will be introduced. This will
be followed by a description in Chapter 6 of how this technology is put into practice.
As with the processing of traditional minerals, the beneciation of scrap can be
divided into four types of unit process. These include comminution, sorting, thermal
processing, and agglomeration.
Aluminum scrap comes in a wide variety of size and conditions. Pieces can be as small
as the aluminum wires used in electronic equipment or as large as a jet airliner. Scrap
is sometimes liberated, free of any attached pieces of other materials. However, it is
often found bolted, welded, or otherwise attached to other parts. To be remelted, the
scrap will have to be separated from these other materials. The dismantling of auto-
mobiles and other large assemblies described in Chapter 3 accomplishes this to some
degree. However, in many cases, the value of the scrap recovered by dismantling is
insufcient to justify the expense of this labor-intensive process.
Many sorting processes require scrap pieces of a given size to be effective.
In addition, furnaces have maximum sizes of scrap that can be successfully fed.
Consistent particle size is also essential to the proper functioning of some sorting
devices. Some scrap already has the proper size for automated sorting, but most of
it does not. Comminution is the process by which oversize material is reduced to the
proper size for further processing. The comminution of naturally occurring miner-
als is usually done by crushing it into smaller rocks. However, metal scrap cannot
be turned into smaller separate pieces in this fashion. Instead, it must be torn apart.
Numerous devices have been invented for tearing apart metal scrap. Here, they will
be separated into three categories—shears, impact shredders, and rotary shredders.
Most of the shears in operation are either alligator or guillotine shears. Figure 5.1
shows a typical alligator shear (Fowler, 2003), so named because the hinged cut-
ting motion is similar to that of an alligator. Only the top portion of the jaw moves
68 Aluminum Recycling
during operation. The cutting blade is made of hardened tool steel and can be
resharpened when it gets dull. Sizes and power ratings vary, according to the size and
type of material to be cut. Most alligator shears use electric power, although gasoline
and diesel engines are available.
Alligator shears have been available since the early 1900s. Major changes in the
basic design include the following:
The use of hydraulic rather than mechanical ywheel drives. Hydraulic
drives allow the machine to be stopped immediately to prevent damage to
the machine or injury to the operator, a feature not available in ywheel-
driven shears.
The addition of a hold-down clamp to keep scrap pieces still while being
The addition of guards around the machine to prevent injury to the opera-
tors. Alligator shears were notorious safety hazards before the introduction
of these guards, which are now mandatory in most countries.
One of the advantages of the alligator shear is its versatility (A-Ward, 2005). This is
particularly important in the processing of aluminum scrap, which takes a variety of
forms. Figure 5.2 shows a crane-mounted shear used for recovering scrap that cannot
be brought to a processing plant. Crane-mounted shears remove aluminum and other
scrap metals from aircrafts, ships, rail cars, and other large objects. Another special
type of alligator shear is the nibbling or metal cleaning shear used for detaching
small metal attachments such as bolts or collars. Metal-cleaning shears are espe-
cially popular for separating steel parts from cable scrap (American Recycler, 2003).
FIGURE 5.1 An alligator shear. (From Ohio Baler Co., http://www.ohiobaler.com/
alligatorshear.htm. With permission.)

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