Cerium (Ce, atomic number 58) is a metallic element belonging to the lanthanide series, often called rare earth elements. Despite this classification, cerium is the most abundant element in the group. It is a soft, silvery-white metal that is never found in its pure state in nature, instead occurring in minerals like bastnasite and monazite.
Fundamental Characteristics
Cerium is soft and ductile, appearing silvery-white or iron-gray. It tarnishes quickly when exposed to air due to its high chemical reactivity, readily oxidizing to form cerium dioxide on its surface. The metal also reacts with water, slowly in cold water and more rapidly when heated.
Cerium commonly exists in two oxidation states: +3 and +4. While most other lanthanides only exhibit the +3 state, cerium’s ability to easily switch between the Ce³⁺ and Ce⁴⁺ forms is the foundation of its industrial usefulness. This variable electron configuration allows it to participate in redox reactions by accepting or donating electrons, a property highly valued in catalytic applications.
Primary Commercial Uses
Cerium’s ability to cycle between oxidation states is used in catalysis, its primary commercial application. Cerium dioxide (CeO₂) is a component in three-way catalytic converters used in automobiles to manage exhaust emissions. It functions as an oxygen storage material, releasing oxygen when the engine runs fuel-rich and absorbing it when fuel-lean. This helps convert harmful pollutants like carbon monoxide and nitrogen oxides into less harmful substances.
Cerium oxide is used as an abrasive for polishing, sometimes known as “jeweler’s rouge.” It achieves a high-quality finish on glass products, including lenses, mirrors, and television screens. Cerium compounds are also added to glass manufacturing to decolorize the material by neutralizing the greenish tint caused by iron impurities, or to help the glass absorb ultraviolet light.
In metallurgy, cerium is added to various metal alloys. When incorporated into iron and steel, it acts to scavenge unwanted elements like sulfur and oxygen, improving the castability of the final product. It is also alloyed with magnesium to improve the strength and heat resistance of the metal for use in aerospace and high-performance applications.
Safety and Environmental Presence
Cerium is one of the more abundant elements in the Earth’s crust, occurring naturally in various minerals. Humans are exposed to trace amounts through soil and water, but the most common route of industrial exposure is through the inhalation of dust or fumes. Exposure is often localized near mining operations or manufacturing facilities.
The toxicity of stable cerium compounds is considered low. Industrial dust inhalation remains a concern, as repeated exposure can lead to lung irritation and pneumoconiosis, which involves the accumulation of dust in the lungs. Standard industrial safety protocols, such as using protective equipment and minimizing airborne dust, are necessary when handling cerium metal or its compounds.