Lanthanum is the f block element or rare-earth metal of the periodic table with atomic number 57 and symbol La. The valence shell electronic configuration of La is [Xe] 5d1 6s2 4f0. The name rare earth was given because they originally extracted from rare earth oxide. It was first discovered by the Swedish chemist Carl Gustaf Mosander in 1839 and the name of lanthanum was given from the Ancient Greek latter lanthanein which means to lie hidden. It is the first f block element and prototype of the lanthanide family.
Properties of lanthanum
It is a soft, silvery-white rare earth metal that rapidly tarnishes in the air and burning easily when heated. Lanthanum is part of the scandium group or group 3 (IIIA) due to the presence of (n-1) d1 ns2 electronic configuration. Due to the lack of common features of d-block elements, it shows a single stable oxidation number or state like +3, and closely resembles lanthanides.
|Properties of lanthanum
|Electron per shell||2-8-18-18-9-2|
|Electronic configuration||[Xe] 5d1 6s2|
|Melting point||920 °C or 1688 °F|
|Boiling point||3464 °C or 6267 °F|
|Molar heat capacity||27.11 J mol-1K-1|
|Electrical resistivity||615 nΩ·m|
|Atomic radius||187 pm|
|Covalent radius||207±8 pm|
|Electronegativity||Pauling scale – 1.10|
|Ionization energy (kJ/mol)||1st||2nd||3rd|
Where is lanthanum found?
Lanthanum is third-most abundant of all the lanthanides. There are 200 minerals known which contain rare earth metals. The two most commercially important minerals are monazite and bastnaesite. Monazite is a mixed phosphate of lanthanum, cerium, thorium, and other rare-earth. Bastnaesite is a fluoride carbonate of lanthanum and other rare earth metals, but the heavier elements are virtually absent on it. Naturally, occurring lanthanum contains two isotopes like 139La and 138La. 139La is most abundant but 138La is rare.
Monazite, which is chemically quite inert and has a high density. It is mostly concentrated in beach sands and river beds through weathering. It is found in southern India, South Africa, Brazil, Australia, and Malaysia. Commonly, we used monazite for the extraction of lanthanum and other rare earth metals.
The main steps involve in the production of lanthanum and other rare earth are as follows:
- Digestion of the concentrated ore by concentrated aqueous sodium hydroxide (NaOH) at 140 °C, followed by extraction with water.
- The slurry of impure hydrous oxides is boiled with hydrochloric acid around a pH scale of 3.5. ThO2 is precipitated and filtered out.
- The filtrate containing LaCl3 and LnCl3 (Ln = lanthanides) is treated with a solution of BaCl2. A stoichiometric amount of Ln2(SO4)3 is used to precipitate the entire barium as BaSO4. BaSO4 carries its traces of RaSO4 which is removed by filtration.
- The filtrate contains LaCl3 and LnCl3 from which La may be separated by fractionation crystallization. However, the most modern method is solvent extraction and the ion exchange process.
Lanthanum is silvery-white, soft, and malleable with high electrical conductance. It is highly electropositive and reactive. The reactivity of higher members of lanthanides is comparable to calcium and scandium to aluminum. The compact metal is quite stable to dry air at ordinary temperatures. It burns in the air to form oxide (La2O3) and nitride (LaN).
Uses of Lanthanum
- The rare earth metal, lanthanum metal has no commercial uses. It is used as an additive of steel to improve strength and workability. It is used for the preparation of mischmetal. But due to the high production cost of lanthanum, we used mixed lanthanide for the preparation of mischmetal.
- Hydrogen sponge alloys can contain lanthanum which is used for storing hydrogen gas in power vehicles. It is also used for manufacturing solid oxide batteries.
- Lanthanum or rare earth metal compounds are widely used in photo studios and projectors. These compounds increase the brightness of the surface.
- Lanthanum trifluoride (LaF3) is used for the production of heavy fluoride glasses. It is used in optical fiber for communication. La(III) oxide (La2O3) is used for the production of optical glasses. It is used in camera and telescope lenses. The optical glass is also used for storing alkali metals due to its high alkali resistance properties.
- Mixed lanthanides contain lanthanum are added to zeolite to enhance the chemical catalyst activity. It is used in the creaking of and petroleum.