What Is Alumina? Production, Problems, and Mitigation

Aluminum is the most abundant metal in the crust of the Earth—but it doesn't exist in its pure form in nature. Bauxite ore first needs to be mined, then alumina is extracted from the bauxite, then the alumina is smelted into aluminum.

Alumina is aluminum oxide (Al₂O₃). Its hardness, strength, and resistance to corrosion make it valuable as a coating to glass, ceramics, and aluminum itself.

While aluminum is often lauded as a highly recyclable, environmentally friendly product, the process of creating aluminum—from mining to manufacturing—can be environmentally destructive, highly polluting, and carbon-intensive. There are ways to mitigate those impacts, but more needs to be done.

Mining and Extracting Alumina

Given aluminum's abundance in Earth's crust, mining operations are found in many places around the world. Alumina is extracted from bauxite, a sedimentary rock that is strip-mined from open-pit mines. Five of the world's 10 biggest bauxite mines are in Australia, with the other five in Brazil and the Republic of Guinea.

Bauxite mined in the United States is used in the hydraulic fracturing (fracking) of oil and gas. Around the world, bauxite mining is increasingly sited on indigenous-owned land, with little input from the traditional landowners themselves, displacing them from their ancestral homelands.

Most bauxite mines are located in tropical or subtropical zones, regions with a high degree of biodiversity. The operation involves clearing forests and removing topsoil, which have environmental impacts as diverse as humidity and rainfall loss, soil compaction and changes in its chemical composition, erosion, and flooding, as well as the more obvious losses of habitats and reduction of the region's biodiversity.

Forest clearing (usually through burning) releases long-sequestered carbon into the atmosphere. Bauxite mining operations release an estimated 1.4 megatons of carbon dioxide into the atmosphere each year—the equivalent of 3.2 billion miles driven in an average passenger car.

Extracting Alumina

To extract the alumina from bauxite ore, the bauxite is crushed and cooked in caustic soda and alumina hydrate is precipitated out. The separated alumina hydrate is then cooked at 2,000 degrees F to drive off the water, leaving anhydrous alumina crystals, the stuff that aluminum is made from. What's left is "red mud," a toxic mix of water and chemicals produced at an approximate rate of 120 million tons per year. The mud is often held in ponds, which have leaked with disastrous results.

In 2010, a red mud reservoir in Hungary breached, leading up to 1 million square meters of highly alkaline mud that flowed into waterways and flooded agricultural lands. Six years later, mercury concentrations were still at excessive levels in the surrounding region. Other ecotoxic residues in red mud include fluoride, barium, beryllium, copper, nickel, and selenium.

How Aluminum Is Made

Aluminum is made by running electricity through a reduction pot filled with dissolved alumina crystals. Basically, every pound of aluminum is made from about two pounds of alumina.

It takes a lot of energy to break the bond between aluminum and oxygen, about 15 kilowatt-hours per kilogram (2.2 pounds) of aluminum. This is why the great dams of the Tennessee Valley and the Columbia River were built—to generate electricity to make aluminum for airplanes. When that electricity became too valuable because it was needed for cooling and lighting buildings, the aluminum smelting industry followed the cheap hydropower to Canada, Iceland, and Norway. Today, however, China is responsible for the production of 56% of the world's aluminum.

Aluminum production also creates a lot of carbon dioxide, as the oxygen given off when it is separated from the aluminum combines with the carbon from the electrodes. Overall, the aluminum smelting process causes 2% of the world's carbon emissions, largely because of the widespread use of coal to generate electricity—especially in China, where over 80% of its aluminum production relies on coal.

A life-cycle assessment of the entire aluminum production process, from mining to manufacturing, finds smelting to be the most environmentally impactful step in the aluminum production process, contributing to ecotoxicity, human toxicity, climate change, and acidification.

Mitigation

Aluminum's utility as a strong, lightweight, and corrosion-resistant metal means that demand for it is not going to go away any time soon. Finding ways to reduce its environmental impact is urgent, given its role in both biodiversity loss and global warming. A variety of approaches must be taken simultaneously.

Recycling

Aluminum recycling is one of the few commercially successful forms of recycling, and aluminum recycling requires ten times less energy than the production of new aluminum does. But the demand for aluminum far exceeds the supply of recycled aluminum, so recycling is not a panacea, and recycling efforts can only contribute so much.

Aluminum can be recycled indefinitely, and 71% of aluminum from commercial products is recycled, yet only roughly one-third of all aluminum production is from recycled material. Even if 100% of aluminum already in the market was recycled, the majority of aluminum production would still require bauxite mining, alumina extraction, and aluminum smelting.

Cleaner Energy

Since the consumption of electricity in aluminum smelting is the leading contributor to its environmental impacts, switching to cleaner sources of electricity can play a significant role in reducing the entire environmental cost of aluminum production.

Smelting involves high amounts of heat, chemical reactions, and electrolysis to separate the oxygen from the aluminum in alumina. Electrolysis is also used to produce green hydrogen from renewable sources of electricity. As the emerging green hydrogen industry grows in scale, applying the same process to smelting aluminum can reduce its climate change effects and other impacts.

Of course, the cleanest form of energy is energy that is not used in the first place, and efforts to increase the energy efficiency of the extraction and smelting processes have reduced levels of emissions in the aluminum life cycle.

Habitat Restoration

In countries where bauxite mining operations are subject to public pressure and government regulation, such as Australia, habitat restoration efforts have been undertaken with moderate success. By contrast, mining in other parts of the world, such as Brazil or Indonesia, leaves behind a radically different and degraded landscape.

Many mining companies have made “no net loss” pledges, offsetting biodiversity losses from mining operations with restoration projects elsewhere, while government policies requiring biodiversity offsets have increased in the past decade. As with carbon offsets, however, primary efforts should be aimed at avoiding impacts in the first place—and reducing them in the second place—otherwise, an offset merely becomes a “license to trash.”