The Heavy Weight of Aluminum

The processing of aluminum has harmful byproducts, that if not properly handled, can be deadly.

Why and how is aluminum used?

Aluminum is used a lot because of its non-toxicity, its non-magnetism, and its resistance to corrosion. It’s also lightweight and can withstand extremely low temperatures. Also, aluminum scrap can be recycled over and over again. Due to recycling, about 75% of all aluminum made is still in use. Aluminum is used in a variety of things today. Not only is it used in soda cans and foil, it’s also used in buildings and aircraft components.

Figure 1.1: Due to its properties, Aluminum is often used in beverage cans

What are some harmful byproducts of aluminum manufacturing?

The only harmful byproduct of the use of aluminum in manufacturing is red mud. Red mud is a toxic byproduct of the industrial process that refines bauxite, raw aluminum ore, into aluminum oxide, or alumina (which is then smelted into pure aluminum metal for use). For every ton of alumina produced, the process can leave behind one third of a ton to more than two tons of red mud. This mud has a high pH because of the sodium hydroxide solution used in the refining process. The base is strong enough to kill plant and animal life, and to cause burns and damage to our respiratory system if the fumes are inhaled.

Although it contains useful elements, such as iron, titanium, and residual aluminum, there is no economically viable way to extract them from the mud. Other than some limited use as a pigment in bricks and concrete, the red mud is waste. The only way to neutralize this harmful substance is to treat it with sea water. As of right now, the main way of dealing with the red mud is keeping in reservoirs, so there is the possibility of leaks and floods.

Figure 1.2: Red mud is a harmful product of the Aluminum manufacturing process

How are they produced?

Aluminum originates from the bauxite ore, but the entire process starts with acquiring alumina from that source. The bayer process involves a long series of chemical reactions that depend on the makeup of bauxite ore. First, the crushed and washed bauxite ore must go through a process of removing any silica found in the bauxite to avoid any decrease of quality. Next, the remaining bauxite ore goes through digestion where it is combined with hot caustic soda material in a heated pressure vessel so it dissolves the aluminum-bearing minerals, yielding a sodium aluminate solution:

\(Al_2O_3 + 2NaOH → 2NaAlO_2 + H_2O \)

*For every mole of Aluminum oxide, 2 moles of sodium aluminate are produced alongside water.

After this reaction has occurred, the bauxite residue could be separated from the solution through a sedimentation process whereas the alumina can then be crystallized from the solution through the precipitation process resulting in the following reaction:

\(Al(OH)_4(-) + Na → Al(OH)_3 + Na(+) + OH(-) \)

*Through crystallization, a mole of aluminum hydroxide merged with sodium would yield a mole of aluminum hydroxide, a mole of sodium, and a mole of hydroxide.

Next, the coarse crystals are then extracted through classification, and processed in a rotary kiln or calciner to eliminate bound moisture, yielding alumina in the reaction:

\(2Al(OH)_3 → Al_2O_2 + 3H_2O \)

*For every 2 moles of aluminum hydroxide, the classification step would result in a mole of Aluminum oxide and 3 moles of Hydrogen dioxide.

Of course the entire process doesn't stop there since we need to refine alumina into aluminum. The smelting method, also known as the Hall-Heroult Process--which should take place at temperatures between 940-980°C to result in aluminum of high purity. This process dissolves the alumina in cryolite (molten solvent), and an electrical current is run through the solution, causing the carbon from the carbon anode to attach to the oxygen component of the alumina. Finally, it yields aluminum and carbon dioxide:

\(2Al_2O_3 + 3C → 4Al + 3CO_2 \)

*For every 2 moles of Aluminum Hydroxide merged with 3 moles of carbon, the reaction would yield in 4 moles of Aluminum and 3 moles of Carbon dioxide.

Figure 1.3: The Aluminum extraction process

How has the aluminium industry been hit by the Pandemic?

The aluminum market is quite prone to volatile price fluctuations, as past regional supply disruptions and economic activity have shown. The same is true with the Covid-19 Pandemic, yet maybe even more so. United States aluminum production and mining capacity utilization dropped below 80% for the first time since October 2009. Smelting capacity utilization dropped from 61.1% to 55.9% in 2020. The shutdown of both the aerospace and automobile industrial sectors dropped shipment demand by upwards of 30% to 50% in the second quarter of 2020 alone. Despite the ongoing pandemic, worldwide demand has been strong overall, leading to some forecasting a 3.8% global growth in 2021 over 2020. However, the pace of growth in the U.S. and Canadian markets will be more subdued at 2.3% and 0.9%, respectively. This may be bad for a variety of industries that consume aluminium, which include: transportation (34%), packaging (16%), construction (12%), electrical (9%), consumer durables (8%), machinery (8%), and others (13%). Despite concerns regarding a supply overhang, until some of the restocking-related pandemic supply chain issues are resolved, current market dynamics are very tight.

Although it contains useful elements, such as iron, titanium, and residual aluminum, there is no economically viable way to extract them from the mud. Other than some limited use as a pigment in bricks and concrete, the red mud is waste. The only way to neutralize this harmful substance is to treat it with sea water. As of right now, the main way of dealing with the red mud is keeping in reservoirs, so there is the possibility of leaks and floods.

Figure 1.4: The pandemic has contributed to a decline in the growth of the Aluminum industry

Conclusion

Overall the pandemic has positively impacted the environment in regards to the aluminum industry. With the decline in mining and smelting, there has in turn been less toxic red mud produced. The main result of this is cleaner soil and cleaner water. This is good, but overall there is still a huge problem with this byproduct that needs to be addressed promptly. As of right now there are 3 billion tons of red mud, either in respective ponds or dried up mounds and the industry is set to be producing 150 million tons annually, even with recycling efforts. Most don’t know about this issue, as it doesn’t affect the average person, but in 2010 a red mud pond collapsed in Hungary, killing 10 and chemically burning hundreds. Red mud has long lasting effects and is hard to get rid of, pictured is the town over one year later.

Figure 1.5: The reside of red mud from manufacturing Aluminum is an issue that needs to be brought to attention to the general public