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The alumina trihydrate crystals are then classified into size fractions and fed into a rotary or flu-
idized-bed calcination kiln. In the kiln, alumina trihydrate crystals are calcined to remove their
water of crystallization and prepare the alumina for smelting.
The basis for aluminum smelting plants is the Hall-Héroult process. Alumina is dissolved in an
electrolytic bath of molten cryolite (sodium aluminum fluoride) within a large carbon- or graphite-
lined steel container. The bath also contains a small amount of aluminum fluoride and calcium flu-
oride. An electric current is passed through the electrolyte at low voltage, but very high current,
typically 150,000 A. The electric current flows between a carbon anode made up of petroleum coke
and pitch, and a cathode formed by the thick carbon or graphite lining of the pot. Molten aluminum
is deposited at the bottom of the pot and is siphoned off periodically, taken to a holding furnace,
and often alloyed with selected elements to produce required qualities for specific end-uses such as
beverage cans, sheet, transportation uses, and building and construction products.
Few U.S. companies refine bauxite into alumina in the United States. Most import alumina
from Australia, Jamaica, Suriname, Guyana, and Guinea. The United States is the largest aluminum
producer in the world, with containers and packaging accounting for the largest share of shipments.

6.9.2 ALUMINUM RECYCLING

Aluminum waste consists of industrial scrap, which is a by-product of aluminum manufacturing
processes (“new scrap”), and old scrap consisting of postconsumer items such as used aluminum
beverage cans, window frames, building siding, and foil. Nearly 80% of the aluminum in MSW
consists of used beverage containers (UBCs).
Nationwide, aluminum cans constitute less than 1% of MSW; in communities having estab-
lished recycling programs or container deposit laws, the percentage in the local waste stream is neg-
ligible. Table 6.5 presents data on the quantity of aluminum recycled. In 1975, about 25% of
aluminum cans were recycled. This percentage remained relatively constant until about 1980. The
increased rate in the latter half of the 1980s is attributable to additional collection programs and
container deposit legislation. During this period, a number of states passed laws requiring deposits
of $0.05 to $0.10 per container, thus providing an additional incentive for recycling. Aluminum bev-
erage containers were recovered at a rate of 59.5% of generation (0.9 million tons) in 1997, and
48.5% of all aluminum in containers and packaging was recovered for recycling in 1997. The rate
of aluminum recycling has been in decline for a decade, after peaking at 65% in 1992.
There are numerous successful community recycling programs for mixed aluminum scrap and
aluminum cans. These programs are generally self-sufficient and, in some municipal programs, pro-
vide an income to subsidize other recycling activities (Pfeffer, 1992). Used aluminum cans are col-
lected in curbside pickup programs, at buy-back locations, at recycling centers, and by scrap metal
dealers. A number of states have established mandatory deposits for beverage containers and have
installed redemption centers at supermarkets.
Cans brought to collection centers are processed in a number of ways. Small, low-volume
processors normally flatten cans and sell them to a nearby wholesaler. Larger operations will bale,
densify, or shred cans for shipment to aluminum consumers (Figure 6.4). Aluminum manufacturers
have established specific criteria as to how aluminum cans should be prepared. The baled or shred-
ded aluminum is shipped by truck, railcar, or sea container to regional mills or reclamation plants.
At the reclamation plant the bales are unloaded and the cans are tested for quality and moisture
content. After inspection the bales of cans are shredded to reduce volume. The shredded cans are con-
veyed to a delacquering oven to remove coatings and moisture. The hot shredded aluminum is then
passed over a small screen to remove dirt and contaminants and fed directly into a reverberatory fur-
nace. Heated to 1400°F (650°C), the cans melt and blend in with the molten metal already in the fur-
nace. Alloying elements and primary aluminum are added as needed. A mixture of salt and potassium
fluoride is added as a flux to separate any oxides (“dross”) that are skimmed off (CMI, 2002).
Molten aluminum is analyzed for the appropriate chemical properties and then tapped (removed)
from the furnace and poured into large molds that cast sheet ingots. These large rectangular ingots