- Lanthanum (La) is a soft, silvery-white metallic element with atomic number 57, marking the beginning of the lanthanide series in the periodic table.
- It is located in period 6 and is often grouped with the rare earth elements, although it is relatively abundant in the Earth’s crust.
- Lanthanum has an electron configuration of [Xe] 5d¹ 6s², with three valence electrons that it readily loses to form the La³⁺ ion. Its atomic structure consists of fifty-seven protons, typically eighty-two neutrons, and fifty-seven electrons arranged in six shells.
- Naturally occurring lanthanum is composed primarily of the stable isotope lanthanum-139 (¹³⁹La), which makes up 99.91% of its natural abundance, along with trace amounts of radioactive lanthanum-138 (¹³⁸La) that has an extremely long half-life.
- Lanthanum is never found in nature as a free metal due to its reactivity; instead, it occurs in a variety of rare earth minerals, most notably monazite ((Ce,La,Nd,Th)PO₄) and bastnäsite ((Ce,La)(CO₃)F). These minerals are mined primarily in China, the United States, Brazil, and India. The extraction of lanthanum involves complex separation processes, as it is chemically similar to other rare earth elements and often found mixed with them.
- The element was discovered in 1839 by Swedish chemist Carl Gustaf Mosander, who isolated it from a sample of cerium nitrate. He noticed that the cerium compound he was working with contained a previously unknown element, which he named “lanthanum” from the Greek lanthanein, meaning “to lie hidden,” reflecting the element’s subtle presence within cerium minerals.
- In modern applications, lanthanum plays a role in various high-technology and industrial processes. It is used in the production of specialized optical glasses, including camera and telescope lenses, because lanthanum oxide increases the refractive index while reducing dispersion. Lanthanum is also used in nickel–metal hydride (NiMH) rechargeable batteries, which are common in hybrid vehicles. Lanthanum-containing catalysts are important in petroleum refining, particularly in fluid catalytic cracking to produce high-octane gasoline. Additionally, lanthanum compounds are employed in hydrogen storage materials, carbon arc lamps for studio lighting, and water treatment to remove phosphates from drinking water.
- Chemically, lanthanum is a reactive metal that tarnishes rapidly in air, forming an oxide layer. It reacts readily with water to produce lanthanum hydroxide and hydrogen gas, and with halogens to form lanthanum halides. As a lanthanide, it exhibits strong electropositivity and forms primarily ionic compounds in the +3 oxidation state.
- Biologically, lanthanum has no known essential role in human metabolism. Most lanthanum compounds are of low toxicity when insoluble, but soluble salts can pose health risks. A notable medical application is lanthanum carbonate, used as a phosphate binder to treat hyperphosphatemia in patients with chronic kidney disease.
- From an environmental standpoint, lanthanum is relatively benign in its naturally occurring mineral forms, but mining and refining rare earth elements can have significant ecological impacts due to chemical waste and radioactive by-products. The management of such waste is an important consideration in lanthanum production.
