Understanding the Role of Aluminum

Aluminum could easily win the title of 'most unlikely to thrive.' Although ancient Persian potters incorporated aluminum into their clay to enhance the strength of their pottery, the pure form of aluminum wasn't identified until 1825. By then, humanity had already been using various metals and alloys (like bronze) for millennia.

Even after its discovery, aluminum seemed destined for limited use. Chemists could only extract tiny amounts at a time, making it so rare that it was grouped with gold and silver as a semi-precious metal. In fact, in 1884, the total production of aluminum in the U.S. amounted to only 125 pounds (57 kilograms) [source: Alcoa].

In 1886, Charles Martin Hall of the United States and Paul L. T. Heroult of France, working separately, developed a method to extract aluminum from aluminum oxide. This technique, known as electrolytic reduction, required immense electrical power but allowed for the production of aluminum in substantial amounts. By 1891, aluminum production had surged past 300 tons (272 metric tons) [source: Alcoa], and it began to appear in a wide range of products, from cookware and light bulbs to power lines, cars, and motorcycles.

Over a century later, aluminum is the most plentiful metallic element. The United States now produces more than 5.6 million tons (5.1 million metric tons) annually [source: International Aluminum Institute]. A large portion of this aluminum is used in the creation of beer and soda cans — a staggering 300 million aluminum cans are made every day, totaling 100 billion cans per year [source: Can Manufacturers Institute]. Not bad for an element that was once undiscovered for so long.

In this article, we will dive deeper into aluminum — exploring its properties, where it occurs, and how it behaves. We will also track the aluminum lifecycle, from its creation through the Hall-Heroult process to its reincarnation through recycling. Finally, we will explore the diverse ways aluminum is used today and look at some future applications that may surprise you.

Let’s begin with the fundamentals: aluminum from a chemist’s perspective.

Aluminum 101

Is Two I's Better Than One? In the United States, we use the term "aluminum." However, the rest of the world, including the International Union of Pure and Applied Chemistry, prefers "aluminium." This naming debate traces back to Sir Humphry Davy, who first called the unknown element "alumium." He later revised it to "aluminum," and finally to "aluminium," choosing an ending similar to other metals Davy had discovered, such as potassium and sodium.

Aluminum alloys, aluminum foil, and aluminum oxide are exactly the same as aluminium alloys, aluminium foil, and aluminium oxide. The difference in spelling depends on where you live, with North Americans favoring the version with one less vowel.

Aluminum, like many other elements on the periodic table, is a naturally occurring substance. Like all elements, aluminum is a pure chemical substance that cannot be broken down into simpler materials. Elements are organized on the periodic table based on their atomic number — the number of protons in their nucleus. Aluminum’s atomic number is 13, which means an aluminum atom contains 13 protons and 13 electrons.

The elements positioned above and below aluminum on the periodic table form a family, or group, sharing similar properties. Aluminum is part of group 13, which also includes boron (B), gallium (Ga), indium (In), and thallium (Tl). The table to the right shows how these elements are arranged on the periodic table. Each element is represented by a symbol, with aluminum’s symbol being Al. The number above each symbol represents the element’s atomic weight, measured in atomic mass units (amu), which is the average mass of the element, considering the contribution of each natural isotope. Aluminum’s atomic weight is 26.98 amu, and the number beneath its symbol is its atomic number.

Chemists categorize the elements in group 13 as metals, except for boron, which is not a true metal. Metals are typically shiny, conductive of heat and electricity, and malleable — able to be hammered into different shapes — and ductile — able to be stretched into wires. These qualities certainly apply to aluminum. In fact, aluminum is commonly used in cookware because it transfers heat so well. Only copper conducts electricity better, making aluminum ideal for electrical applications like light bulbs, power lines, and telephone wires. Other notable properties of aluminum are listed below:

These two characteristics make aluminum extremely useful. Its ability to resist corrosion is a result of a chemical reaction between the metal and oxygen. When aluminum comes into contact with oxygen, it forms a protective aluminum oxide layer on its surface. This thin barrier prevents further damage from oxygen, water, and other chemicals. Consequently, aluminum is particularly useful in outdoor environments. Moreover, it doesn’t spark when struck, making it safe to use around flammable or explosive materials.

Aluminum naturally occurs in a variety of compounds. However, to unlock its potential, aluminum must be separated from these compounds, which involves a long and complicated process that begins with a hard mineral known as bauxite.

After undergoing this process, aluminum is soft and lightweight in its purest form. Occasionally, it’s necessary to modify these properties to enhance its strength and hardness. This is achieved by combining aluminum with other metals to form alloys. Aluminum is often alloyed with copper, magnesium, and manganese. Copper and magnesium increase aluminum’s strength, while manganese helps improve its corrosion resistance.

Mining and Refining Aluminum

Aluminum doesn't naturally occur as a pure element. Due to its high chemical reactivity, it readily bonds with other elements to form compounds. More than 270 minerals in Earth's rocks and soils contain aluminum compounds, making aluminum the most abundant metal and the third most abundant element in Earth's crust. Only silicon and oxygen are more prevalent than aluminum. The metals that follow aluminum in abundance are iron, magnesium, titanium, and manganese.

The main source of aluminum is an ore known as bauxite. An ore refers to any naturally occurring material from which a metal or valuable mineral can be extracted. In this case, bauxite is a mixture of hydrated aluminum oxide and hydrated iron oxide. The term 'hydrated' means that water molecules are chemically bonded to these compounds. The chemical formula for aluminum oxide is Al₂O₃, and the formula for iron oxide is Fe₂O₃.

Bauxite deposits are usually found in flat layers near the Earth's surface and can stretch over large areas. Geologists locate these deposits by prospecting—drilling or taking core samples from soils believed to contain the ore. By analyzing the samples, scientists can assess both the quantity and quality of the bauxite.

Once the ore is located, open-pit mines are typically used to extract the bauxite that will be refined into aluminum. First, bulldozers clear the land above the deposit. Then, explosives loosen the soil, bringing the ore to the surface. Large shovels scoop up the bauxite-rich soil and load it into trucks, which transport the ore to a processing plant. France was the first country to mine bauxite on a large scale. In the United States, Arkansas was a major supplier of bauxite during and after World War II, but today, the material is mainly mined in Australia, Africa, South America, and the Caribbean.

The initial stage in producing aluminum commercially involves separating aluminum oxide from iron oxide in bauxite. This separation is achieved using a method created by Karl Joseph Bayer, an Austrian chemist, in 1888. Known as the Bayer process, the technique involves mixing bauxite with caustic soda, or sodium hydroxide, and heating the mixture under pressure. The sodium hydroxide dissolves the aluminum oxide, forming sodium aluminate. The iron oxide remains undissolved and is separated through filtration. Lastly, introducing aluminum hydroxide into the sodium aluminate solution causes the aluminum oxide to precipitate, or crystallize out of the solution as a solid. These crystals are washed and heated to remove any remaining water. The result is pure aluminum oxide, a fine white powder commonly referred to as alumina.

Alumina is valuable in its own right due to its hardness, making it ideal as an abrasive and a component in cutting tools. It is also used in water purification and the manufacturing of ceramics and various building materials. However, its primary role is to serve as the starting material for extracting pure aluminum. In the following section, we will explore the steps involved in converting alumina into aluminum.

Aluminum Smelting

The conversion of alumina (aluminum oxide) into aluminum marked a significant turning point in the industrial revolution. Before modern smelting techniques were developed, only small amounts of aluminum could be produced. Earlier methods involved replacing aluminum with more reactive metals, but the metal remained costly and hard to obtain. This all changed in 1886, when two determined chemists and industrialists developed a new smelting process based on electrolysis.

Electrolysis essentially means 'breaking down with electricity,' and it is used to decompose a compound into its individual components. The conventional setup for electrolysis involves two metal electrodes submerged in a liquid or molten substance that contains both positive and negative ions. Once the electrodes are connected to a battery, one electrode becomes the positive terminal, called the anode, while the other becomes the negative terminal, known as the cathode. Due to their electrical charge, the electrodes attract or repel the ions in the solution. The positively charged anode attracts negative ions, whereas the negatively charged cathode attracts positive ions.

Sir Humphry Davy, the British chemist credited with naming aluminum, made unsuccessful attempts to produce aluminum through electrolysis in the early 1800s. Similarly, French schoolteacher and amateur chemist Henri Saint-Claire Deville also failed in his efforts. However, in February 1886, after years of experimentation, American chemist Charles Martin Hall discovered the right method: applying a direct current to a solution of alumina dissolved in molten cryolite, or sodium aluminum fluoride (Na₃AlF₆). Cryolite was mined from deposits on the west coast of Greenland until 1987, after which it has been synthesized from fluorite, a more commonly available mineral.

The aluminum smelting process is outlined in the following steps:

2Al₂­O₃ + 3C -> 4Al + 3CO₂­

The aluminum smelting method discovered by Hall led to large-scale production of pure aluminum. This marked the shift from aluminum being a rare metal to one that was more widely available. Interestingly, the idea of electrolytically reducing aluminum in cryolite was also independently conceived by a Frenchman, Paul L.T. Heroult, a few months after Hall's discovery. Nevertheless, Hall was granted the patent for the process in 1889, a year after he founded the Pittsburgh Reduction Company, which would eventually become the Aluminum Company of America (Alcoa). By 1891, aluminum production had surpassed 300 tons (272 metric tons) [source: Alcoa].

In the next section, we will explore what happens to the aluminum once it exits the electrolytic cells.

Aluminum Fabricating

In the Hall-Heroult process, the containers used for aluminum production are called pots. A single large pot can generate over 2 tons of aluminum daily. However, this output is often increased by linking multiple pots together to form potlines. A smelting facility may house several potlines, with each line consisting of 200 to 300 pots. Within these pots, aluminum is continuously produced around the clock to keep the metal in its molten state.

Each day, workers extract aluminum from the potlines. A significant portion is reserved for creating fabricating ingots. To produce a fabricating ingot, the molten aluminum is transferred to large furnaces, where it is mixed with other metals to create alloys. The metal then undergoes a purification process known as fluxing, which uses gases like nitrogen or argon to eliminate impurities by bringing them to the surface, where they can be skimmed away. Afterward, the purified aluminum is poured into molds and cooled swiftly by spraying it with cold water.

Not all the aluminum extracted from the potlines is alloyed or purified. Some of it is directly poured into molds where it cools gradually, hardening into foundry (or remelt) ingots. Primary aluminum plants sell these remelt ingots to foundries, which melt the aluminum back into a liquid state. They then continue with alloying and fluxing before transforming the aluminum into various parts, such as those used in appliances, vehicles, and other industries, through various fabricating techniques.

Aluminum is a highly desirable metal that often doesn’t need any finishing. However, it can be polished, painted, or electroplated. For example, beverage manufacturers use printing processes to apply labels to aluminum cans. The most common printing formulations involve lacquer coatings that adhere well to the metal while providing a visually appealing finish. These coatings present challenges in recycling, as they need to be removed before the aluminum can be reused. In the following section, we will dive into the detailed process of aluminum recycling.

Using and Recycling Aluminum

Aluminum is incredibly versatile and is used in a wide array of applications. It's the second most widely used metal after steel, with primary production reaching 24.8 million tons (22.5 million metric tons) annually in 2007 [source: International Aluminum Institute]. A significant portion of this production is dedicated to the 187 billion aluminum cans produced worldwide each year [source: Novelis]. The automotive industry represents aluminum's fastest-growing market, as using aluminum in car parts, such as wheel rims, cylinder heads, pistons, and radiators, helps reduce vehicle weight, which in turn lowers fuel consumption and emissions.

Aluminum is also used in a variety of other crucial sectors. Here are some notable applications.

Aluminum by the Numbers: In the United States, 100 billion aluminum beverage cans are produced each year, and about two-thirds of them are recycled. It takes approximately 7,000 Btu of energy to create one aluminum can, but recycling can save up to 95% of the energy required to produce new metal from raw ore. It only takes about 60 days for an aluminum beverage container to be recycled and returned to store shelves. *Source: Alcoa

Remarkably, almost all the aluminum ever produced is still in use today. This is due to its ability to be recycled repeatedly without any degradation in quality. The majority of recycled aluminum comes from three main sources: used beverage cans, parts from old cars, and scrap material collected during aluminum product manufacturing [source: World Book]. Aluminum can recycling stands as one of the great triumphs of the modern sustainability movement (If you're a dedicated recycler, check out What one thing should I recycle?). The first nationwide can-recycling initiative launched in 1968, and today, around 66 billion cans are recycled annually in the United States alone [source: Alcoa].

Recycling aluminum cans follows a closed-loop process, meaning the recycled product is identical to its original form. This process consists of six key steps:

Much of the innovation within the aluminum sector revolves around enhancing the efficiency of both production and recycling. However, as we will explore in the next section, the demand for aluminum is expected to increase as new and exciting applications continue to emerge.

The Future of Aluminum

The Shiny, Metallic History of Aluminum 1746: Johann Heinrich Pott successfully isolates alumina from alum. 1825: Hans Christian Oersted produces the first sample of aluminum. 1886: Charles Martin Hall and Paul L. T. Heroult independently discover the process of electrolysis for aluminum production. 1888: Hall and his business partners establish what would eventually become the Aluminum Company of America (Alcoa). 1914: Demand for aluminum rises dramatically during World War I. 1947: Reynolds Wrap introduces aluminum foil to the market. 1963: Coors launches the first aluminum beverage can. 1968: The United States initiates its first national aluminum can-recycling program. 2020: The International Aluminum Institute predicts the aluminum industry will achieve carbon neutrality.

The production of aluminum in its primary form requires significant energy and contributes to the emission of greenhouse gases, which influence global warming. According to the International Aluminum Institute, the creation of new aluminum accounts for 1 percent of the total global human-induced greenhouse gas emissions. A major goal for the industry is to reduce these emissions by improving recycling methods and using aluminum in a variety of applications, such as vehicles, aircraft, boats, and trains. In fact, the use of lightweight aluminum parts in cars is one of the most groundbreaking advances in automotive design. Replacing just 1 kilogram (2.2 pounds) of heavier materials with aluminum can eliminate up to 22 kilograms (44 pounds) of carbon dioxide over the vehicle's lifespan [source: International Aluminum Institute].

One exciting new application is aluminum's role in fuel-cell-powered vehicles. Researchers at Purdue University have found that aluminum can be used to generate hydrogen fuel efficiently. The process begins with aluminum pellets mixed into liquid gallium, which forms a substance known as aluminum-gallium. When water is added, the aluminum reacts with the oxygen in the water to create a gel, while simultaneously producing hydrogen gas, which can then be collected and used to fuel a fuel cell.

Such innovations are expected to increase the demand for aluminum. Despite its relatively recent discovery, aluminum is now considered one of the most significant metals in the history of human civilization. In the future, archaeologists and anthropologists may very well look back at the 19th, 20th, and 21st centuries and label them the Aluminum Age, positioning this era alongside the Stone, Bronze, and Iron Ages as one of the defining periods in the development of human culture.