La - Lanthanum

Properties

Lanthanum is a soft, silvery-white, ductile and malleable metal. Lanthanum is the first member of the Lanthanoid Group (Rare Earths) of the Periodic Table and is the 28th most abundant element within the Earth’s crust. It is soft enough to be cut with a knife and when exposed to air will tarnish rapidly. When ignited, it will burn easily. Lanthanum is one of the most reactive elements within this group and will react even with water to give off hydrogen gas.

Lanthanum salts are often very insoluble, such as the oxide, hydroxide, carbonate, fluoride, phosphate and oxalate. The chloride, bromide, and nitrate are readibly soluble. The difference in properties as you go down this group of elements is not great, as the added electrons, which make them differ are concealed in inner orbitals rather than their outermost orbital, which is the most influential, and therefore, as these elements are all chemically similar, they are often found together.

History

Lanthanum was discovered in 1839 by the Swedish chemist, Carl Gustav Mosander, who was able to extract it from a sample of cerium nitrate, an element that had been discovered in 1803. Mosander was able to produce the nitrate of this new element, and shared his new discovery with his friend J Berzelius. It was Berzelius who suggested the name lanthanum, which he derived from the Greek word lanthanein, meaning “to lie hidden”. Mosander agreed with this name, but then fell strangely silent about his discovery, not even publishing an account announcing what he had found. The delay was explained a few years later, as Mosander had been silently working on extracting yet another new earth from his lanthanum oxide. This new earth he called didymium, from the Greek word didumos, meaning “twin”. Didimium was ultimately discovered to be a mixture, and in 1885 it was separated into praseodymium and neodymium.

Sources

The main ores from which it is extracted today are Monazite and Bastnäsite, where Lanthanum makes up 25% and 38% of the minerals, respectively.  Allanite and Cerite also contain Lanthanum, but these ores are not mined for their lanthanum content in particular.

The main mining regions of the aforementioned ores are USA, Brazil, India, Sri Lanka and Australia, making up the world production of lanthanum at 12,500 mt/year.  The reserves of this element are thought to be in the region of 6 million mt.  Despite being one of the ‘rare earths’, Lanthanum is probably one of the least rare, occurring in a tonnage similar to that of lead and tin combined!  Lanthanum metal itself is produced by reacting lanthanum fluoride and calcium metal, however lanthanum is only commercial in its other forms such as, lanthanum oxide, carbonate, chloride, fluoride, nitrate and sulphate.

Uses

Despite there being no commercial uses of lanthanum alone, it is often utilised once alloyed with other elements.  For example, lanthanum nickel is a good absorber of hydrogen gas, and as a powder can absorb up to 400 times its own volume.  This could prove useful for future use in hydrogen fuelled cars, as a way of storing the hydrogen gas. However today, it is mainly used as an addition to glass.  It is used as a core material in carbon arc electrodes for film/photographic studio lighting and floodlighting, as it produces an emission spectrum similar to that of sunlight.  When lanthanum oxide is added to glass for lens making it improves the refractive index, where up to 40% of lanthanum oxide is consumed by optical glass manufacture.  In these applications, in addition to increasing the refractive index, it improves low colour dispersion and renders it more resistant to attack by alkalis. Finally lanthanum salts included in zeolite crystals are used in petroleum refining, helping to stabilise the zeolite at high temperatures.