Lanthanum was one of the earlier Lanthanides to be discovered, by the Swedish scientist Carl Gustav Mosander, working at the famous Karolinska Institute in 1839, though it was 1923 before the pure metal was produced.
One of the most reactive of the Lanthanides, readily oxidising and bubbling away in water, Lanthanum turned up unexpectedly in a Cerium salt sample Mosander was working on. It was because of its sneakily unexpected appearance in the sample that Mosander called it Lanthanum, from the Greek word ‘lanthano’, meaning to escape notice. A soft, silvery-white metal, Lanthanum rapidly tarnishes in air and burns easily when ignited.
It will come as quite a surprise to discover just how many ways Lanthanum is used, although much of the Lanthanum we experience is invisible. When it comes to using Lanthanum, it generally plays a secondary, supporting role. Although essential in a range of material compositions, its properties are commonly overlooked.
It is mostly added to glass used in some camera lenses to improve the clarity of the images it can produce. For many years, lead has been added to glass to give it an increased refractive index, producing an extra-shiny crystal effect. As the refractive index goes up, light travels more slowly in the material and the light is bent more as it travels from air into the glass. Lanthanum is much better than lead at pushing up the refractive index without dispersing the light too much; this extra clarity means that Lanthanum oxide is now used widely in lenses for cameras and telescopes. They increase the brightness and give an emission spectrum similar to sunlight.
One of the many chemicals likely to be added to the water in a swimming pool is a Lanthanum salt, aimed at latching onto phosphates that would otherwise act as in-water fertiliser, encouraging green algae to discolour the pool.
Lanthanum salts are used in catalysts for petroleum refining. It is often added in small quantities to metals like Iron and Steel to make them less brittle, or to Tungsten to improve the quality of electrodes used in arc welding.
The ion La3+ is used as a biological tracer for Ca2+, and radioactive Lanthanum has been tested for use in treating cancer.
In a work setting, Lanthanum can be dangerous because gasses can be inhaled; long-term exposure causes lung embolisms. In humans, exposure to Lanthanum can cause cancer, especially if inhaled. Large amounts of Lanthanum in the body are a threat to the proper functioning of the liver.