What Is Lanthanum?
Lanthanum, with the symbol La, was discovered by Swedish chemist Carl Gustaf Mosander in 1839 as an impurity in cerium nitrate. It is part of group 3 of the periodic table and lends its name to the lanthanide series, which consists of 15 elements from lanthanum to lutetium (Lu).
Though classified as a rare earth element, lanthanides, including lanthanum, are more prevalent in the Earth’s crust than lead, occurring in minerals such as phosphates, carbonates, and silicates.
Uses of Lanthanum
Lanthanum oxide (La2O3), employed in the manufacture of ceramic capacitors and optical lenses, and LaNi5, an alloy with hydrogen storage capabilities, is crucial in the negative electrodes of nickel-hydrogen rechargeable batteries.
The isolation and purification of lanthanum from other lanthanides are challenging and costly. As a result, it is commonly used in a mischmetal form, comprising more than 50% lanthanum, rather than in a pure state.
Furthermore, lanthanum carbonate serves as a phosphorus absorption inhibitor in patients suffering from renal failure by forming non-absorbable phosphorus compounds in the intestinal tract.
Properties of Lanthanum
Lanthanum is a soft, silvery-white metal that tarnishes slowly in the air. It is ductile enough to be cut with a knife. It reacts with halogens to produce trihalides and forms binary compounds with nonmetals like boron, carbon, nitrogen, and phosphorus upon heating. Lanthanum hydroxide, La(OH)3, results from its reaction with water, while dilute sulfuric acid yields a colorless solution of the hydrated tripositive ion [La(H2O)9]3+, due to the absence of f-electrons in La3+.
It is the least volatile among lanthanides, with a melting point of 920°C and a boiling point of 3,464°C.
Structure of Lanthanum
Lanthanum has an atomic weight of 138.91, a density of 6.162 g/cm3 at room temperature, and a liquid density of 5.94 g/cm3 at its melting point. It boasts the largest atomic radius among the lanthanides. Its electron configuration is [Xe] 5d1 6s2, and it usually exhibits a +3 oxidation state in chemical reactions.
At room temperature, lanthanum adopts a hexagonal structure, transitioning to face-centered cubic at 310°C, and becoming body-centered cubic at 865°C.
Other Information on Lanthanum
1. Production of Lanthanum
As the third most abundant lanthanide in the Earth’s crust, lanthanum can be extracted by heating lanthanum oxide with hydrofluoric acid and ammonium chloride or fluoride, then reduced to metallic form with alkali or alkaline earth metals in vacuum or argon atmosphere. Pure lanthanum is also obtainable through the electrolysis of a molten mixture of LaCl3, NaCl, or KCl at elevated temperatures.
2. Lanthanum Isotopes
Lanthanum’s isotopes range in atomic weight from 117 to 155, with naturally occurring stable isotopes being 139La and 138La. 139La, the most prevalent at 99.91%, and 138La, a radioactive isotope with a half-life of 105 x 109 years. In total, thirty-eight radioactive isotopes and three nuclear isomers of lanthanum have been identified.
3. Hazards of Lanthanum
Lanthanum, while low to moderately toxic, requires careful handling. Its injection can lead to adverse effects such as hypotension, hyperglycemia, liver alteration, and spleen degeneration. It also influences human metabolism, potentially lowering cholesterol levels, appetite, blood pressure, and blood clotting risk, and acts as a painkiller when injected into the brain.