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Show 4.6.1 About the Industry . . 'YJUle aluminum was not produced for commercial use until the 20th century, it is now one of the world's most cntIcal pnmary m~tals, supplying manufacturing, construction, automotive, aerospace, beverage, and other industries. It h~s many a~actIve features, including a high strength to weight ratio, high corrosion resistance, alloyability for vano~s properties, ~d recyclability. Although aluminum is very common in its oxide fonn (comprising 7% of the earth.s cru~t), alunu.ntnll metal ~as not produced in a relatively pure state until the 1820s (Williams 1993). The ~lummum mdustry IS separated mto a primary industry (conversion of bauxite ore to basic metal) and a secondary mdustry (metal recycling, shaping, fabrication, finishing, and treating). Aluminum production did not become a major industry until the 1900s, following the development of the HallHero~ 1t and Baye~ processes, and the establislunent of a market for the aluminum. By the end of World War II, a!ummum pn;>duchon had peaked at two million tons per year. Following the post war slump caused by reduced a~c~aft alummum demand, aluminunl production continued to increase to four million tons per year by 1960 and 25 Dllihon to.ns ,Per year today. Current aluminum production is second only to steel (which is over 700 million tons per year) (Telssler-duCros 1995). . . ~ost im,?ortant, of all current industrial metals, aluminum has the strongest growth potential, since it is an mdus.~ahzed natIon's metal. For example, the world alwninum consumption would increase to 140 million tons per year if It matched Japan's per capital consumption. However there is a significant shift between primary and secondary aluminum production and national dominance in these industries. The U. S. market dominance in worldwide primary aluminum production has decreased from 41 % in 1960 to 21 % today. The primary causes for this shift are locations of bauxite resources (primarily outside the United States), energy costs, oversupply, and increased use of recycled or secondary aluminum. Between 1987 and 1992, about 1.1 million tons of high-cost U.S. aluminum capacity (nearly 25% of the U.S. total) were closed. Lower power costs in competing countries make it unlikely that new primary aluminum smelters will be built in the United States. Domestic aluminum firms are more likely to retrofit existing plants with incrementally improved technologies. Increased investment in the U.S. aluminwn fabrication and recycling facilities (secondary aluminum industry) has also occurred and is expected to continue. Energy savings and waste disposal concerns boosted aluminum recycling from 0.4 million tons in 1960 to 2.8 million tons in 1992. Primary aluminum smelting is one of the most energy-intensive manufacturing processes. Even with efficiency improvements in recent decades, smelters require about 7 kWhllb of aluminum produced, and account for 70% of energy use for primary aluminum production. The annual primary aluminum energy consumption is about one quad. Recycled aluminunl production is much more energy efficient (because the smelting step is eliminated) and requires only about 50/0 of the energy needed to make primary alwninum. The aluminum industry spends about $2 billion on energy, about 8.6% of the value of shipments. For primary production, the costs were $1.55 billion, or 220/0 of its value of shipments. 4.6.1.1 Primary Aluminum Industry. Ore, most commonly bauxite, is processed to high purity AI in the primary industry. Limestone is processed to hydrate in a rotary kiln, and then combined with ore and caustic soda. This mixture is fed to steam-heated digesters that convert the Al to a hydrate. The weak caustic solution for this process is also concentrated in ste~m-~eated evapor.ators for chemical.recovery. The s~parated and dried alll?1ina trihydrate is then calcined to a]u!llm~ m a second, ~Irect-fir~d rotary kiln. !'1atw:al gas IS the preferred fuel, SInce the hydrate is susceptible to contamm~tlOn. ElectrolytIc re?uctlOn of the .alumma WI.th carbon electrodes c.onv~rts the feed to high purity Al in the final smeltmg pr<:>cess. !'v10s~ pnmary processmg .to a.lumma for U.S. cons~ptIon IS done offshore at the ore mines and is not conSidered In thiS report. Most alumma IS transported to locatIOns of low power cost (usually hydro derived) such as t~e ~orth Western stat~s as the smel~ing process is very .electrically energy intensive. Carbon electrodes are sacnficIally consumed durmg the reductIOn process, producmg CO2 and molten aluminum. Electrodes are fabricated on-site in bake ovens, the major combustion process at U.S. smelters. Hazardous wastes from the smelting process are significant. These wastes include aluminum dross and spent pot lining material (pot li~er). Pot .liner consists of a.nthracite coal. and graphite, wit.h alwl1~na and re~ac.tory brick insulation. During operatIOn, the ~mer absorb~ fluondes and cyanIdes from ~arbon l~ the lIner, fluonne. In the process materials and nitrogen from the aIr. The pot llller may also become contanunated With heavy metal OXIdes and salts from the petroleum coke powder of the anode as it is conswned during electrolysis. The pot must be relined every 18 |