Lanthanum – Properties and Applications

Chemical Formula

La

Topics Covered

Background
Basic Information
Occurrence
Isotopes
Production of Lanthanum
Health Aspects
Key Properties
Applications

Background

The word lanthanum was derived from a Greek word lanthaneia. In 1839, a Swedish chemist, Carl Gustaf Mosander discovered lanthanum when he was searching for impurities in cerium samples. He treated cerium nitrate salt (Ce(NO3)3) with dilute nitric acid (HNO3)and isolated a new substance, which was named as lanthana (La2O3). The relatively pure form of lanthanum was obtained in the year 1923.

Basic information

Name Lanthanum
Symbol La
Atomic number 57
Atomic weight 138.90547 (7) amu
Standard state solid at 298 K
CAS Registry ID 7439-91-0
Group name Lanthanoid
Period in periodic table 6 (lanthanoid)
Block in periodic table f-block
Colour silvery white
Classification Metallic
Melting Point 1191 K (918°C or 1684°F)
Boiling Point 3737 K (3464°C or 6267°F)
Density 6.15 g /cm3
Phase at Room Temperature Solid
Ionization Energy 5.577 eV
Oxidation State +3

Occurrence

Lanthanum is widely spread in the Earth's crust and does not occur in a single place like copper or zinc. Lanthanum is a relatively abundant element at about 18 parts per million. Monazite, bastnasite, and cerite are the common ores in which lanthanum occurs. The other rare elements are also present in these minerals.

Isotopes

Although there are only 2 naturally occurring isotopes of lanthanum, more than a dozen radioactive isotopes that have been made artificially. None of the radioactive isotopes of lanthanum have any commercial application.

Production of Lanthanum

The ores containing lanthanum are typically contain a range of other rare earths. Consequently they undergo a series of chemical treatments to remove rare earths such as thorium and cerium to yield lanthanum salts. These salts are heated to yield lanthanum oxide, which is then converted to lanthanum chloride by heating in the presence of ammonium chloride and hydrofluoric acid. The Lanthanum metal can then be produced by reduction with lithium or another alkaline earth, or by electrolysis of molten lanthanum chloride.

Health Aspects

High concentrations of lanthanum and lanthanum compounds are toxic in nature, so that the metal has to be handled carefully. Long-term exposure may cause lung embolisms and increases the chance of lung cancer when inhaled. If lanthanum accumulates in the human body, it can be a threat to the liver.

Key Properties

The key properties of lanthanum are:

  • It is an active metal. It forms compounds with nitrogen, carbon, boron, selenium, phosphorus, silicon, sulfur and with the halogens.
  • It is a soft malleable silvery metal that can be cut with a knife
  • It reacts very quickly with hot water and most of the acids. It reacts slowly with cold water
  • It oxidizes rapidly in air, especially in moist air.

Applications

The major applications of lanthanum are limited and include:

  • An alloying agent for steels and cast irons
  • Hybrid car batteries
  • In cigarette lighter flints in the form of Mischmetal (an alloy primarily consisting of cerium and lanthanum)
  • Carbon arc lighting used in mation pictures, studio lighting and projection

French researchers at the University of Rennes discovered ZBLAN in 1974. ZBLAN is a fluoride glass made of zirconium, barium, lanthanum, aluminum and sodium. It has potential to be used as an optical fiber material for communications and medical applications where it exhibits a broader optical transmission window than more conventional silica-based optical fibre materials.

Source: AZoM.com

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