Lanthanum - La

Lanthanum — chemical properties and water context

Lanthanum is a soft, silvery rare-earth metal. In water-related applications, lanthanum is encountered mainly in compounds or engineered lanthanum-containing materials, rather than as the elemental metal.

Atomic number	57
Standard atomic weight	138.90547 g/mol
Density	6.15 g/cm3
Melting point	920 °C
Boiling point	3464 °C
Electron configuration	[Xe] 5d1 6s2

Chemical properties

Lanthanum is commonly assigned to the lanthanide series and is in Period 6; the Royal Society of Chemistry places it in the d block. It commonly forms La³⁺. The metal tarnishes in air and can react with water. Lanthanum compounds have different solubilities and behaviours, so the specific compound matters in environmental and process assessments.

Uses and applications

Lanthanum is used in optical glass, catalysts, specialty alloys and rechargeable battery materials. Lanthanum-containing solids have also been studied and applied for phosphate capture in water and wastewater. In such systems, phosphate removal can occur through formation of poorly soluble lanthanum phosphate; treatment performance depends on pH and the water matrix.

Lanthanum in water treatment

Research on lanthanum carbonate and other lanthanum-containing materials shows potential for orthophosphate removal, including from wastewater matrices. This is a material-specific treatment approach, not a general recommendation to add lanthanum salts to water. Engineers should assess competing anions, pH, residual lanthanum, solids handling and the intended phosphorus-recovery strategy before selecting a process.

Environmental and health context

Lanthanum is a rare-earth element and may be present in mineral or industrial streams. Its mobility depends on the compound and water chemistry. For process monitoring, measure the relevant dissolved and total fractions and consider co-occurring rare-earth elements and suspended solids.

Back to the periodic table of elements