Question

What are the sources for the production of krypton and xenon?

Short answer

Krypton and xenon are primarily produced by fractional distillation of liquefied air, and they can also be obtained as byproducts of nuclear fission in nuclear reactors.

Step-by-step solution

Understand the Origin

Krypton (Kr) and xenon (Xe) are noble gases found in the Earth's atmosphere in trace amounts. The primary source for these gases is the extraction from air. Air is liquefied and then fractionally distilled to separate its components, including the noble gases.

Recognize Other Sources

Krypton and xenon can also be produced during the fission of uranium and other heavy elements in nuclear reactors. These gases can be released during nuclear fission and collected from the byproducts of nuclear reactions.

Identify Commercial Production

Commercially, while the extraction from air remains the primary method, special attention is given to the collection and purification during nuclear fuel reprocessing, which may become an additional source of these noble gases.

Key concepts

Fractional Distillation of Air

Fractional distillation of air is the process by which air is converted into a liquid form and then separated into its individual components. The air is first cooled to extremely low temperatures until it liquefies. This liquid air is then placed in a distillation column where it's gradually heated. As different gases have different boiling points, they vaporize at different stages and can be collected separately.

For instance, nitrogen boils off first followed by oxygen, argon, and other gases. Noble gases like krypton and xenon, being present in very small amounts, are among the last to be separated. This efficient method ensures a reliable supply of these rare gases which are used in various industries for lighting, electronics, and medical applications.

Nuclear Fission Byproducts

When a heavy nucleus like uranium-235 undergoes fission, it splits into smaller nuclei releasing a significant amount of energy and additional byproducts – including noble gases such as krypton and xenon.

Nuclear reactors, where fission reactions are controlled to produce energy, also become sources of noble gases as these are produced in fission reactions of the fuel. The gases formed are contained within the fuel rods but can be released and recovered during the reprocessing of spent nuclear fuel. The reclamation of these noble gases provides an alternate source to the fractional distillation of air, especially given their relative scarcity and valuable properties.

Uranium Fission

Uranium fission occurs when the nucleus of an uranium atom absorbs a neutron and becomes unstable, eventually splitting into smaller atoms, a reaction that releases a significant amount of energy. This process is utilized in nuclear reactors to generate power.

In addition to energy, fission produces a range of fission products, including noble gases. These can accumulate in the fuel rods over time. Retrieving noble gases from fission processes requires sophisticated filtration and containment techniques to ensure that only the desired inert gases are captured without any harmful byproducts.

Commercial Noble Gas Purification

After the initial recovery of noble gases through methods like fractional distillation and collection from nuclear byproducts, further purification is often necessary to meet commercial standards.

This purification typically involves the removal of any residual gases and impurities. Techniques like adsorption, where impurities are trapped on solid surfaces, and cryogenic distillation, which employs extreme cold to further refine the gases, are commonly used. These processes are crucial to ensure that the noble gases such as krypton and xenon are of a high enough purity for their specialized uses in high-performance lighting, electronics, and space exploration technology.