LANTHANUM CHLORIDE 447

LANTHANUM CHLORIDE

[10099-58-8]

Formula: LaCl3; MW 245.26; forms a stable heptahydrate, LaCl3•7H2O, [20211-76-1], MW 371.37.

Uses

Lanthanum chloride is used to prepare other lanthanum salts. The anhydrous chloride is employed to produce lanthanum metal.

Physical Properties

The anhydrous chloride is a white hexagonal crystal; hygroscopic; density 3.84 g/cm3; melts at 850°C; soluble in water. The heptahydrate is a white triclinic crystal; decomposes at 91°C; soluble in water and ethanol.

Preparation

The heptahydrate is formed by dissolving the oxide, hydroxide or carbonate in hydrochloric acid, followed by crystallization. The anhydrous chloride is obtained by heating oxide, hydroxide, or carbonate in an atmosphere of dry hydrogen chloride.

La2(CO3)3 + 6HCl → 2LnCl3 + 3CO2 + 3H2O

Another method involves heating lanthanum oxide with excess ammonium chloride at 300°C:

Reactions

When heated in the presence of water vapor, lanthanum oxochloride is formed:

high

LaCl3 + H2O temperature→ LaOCl + 2HCl

Heating with glass at elevated temperatures also forms oxochloride:

elevated

LaCl3 + SiO2 temperature→ 2LaOCl + SiCl4

Lanthanum chloride reacts with hydrogen sulfide when heated at 1100°C, forming lanthanum sulfide:

o

2LaCl3 + 3H2S 1100 C → La2S3 + 3H2S

Reactions with ammonia and phosphine at elevated temperatures yield

448 LANTHANUM FLUORIDE

lanthanum nitride and phosphide, respectively:

elevated

LaCl3 + PH3 temperature→ LaP + 3HCl

The addition of hydrofluoric acid to an aqueous solution of lanthanum chloride precipitates out lanthanum fluoride, LaF3:

LaCl2 + 3HF → LaF3 + 3HCl

Lanthanum chloride is reduced to lanthanum metal when heated with an alkali or alkaline earth metal at temperatures above 1000°C:

LaCl3 + 3Li >1000o C→ La + 3LiCl

Analysis

Elemental composition: La 56.63%, Cl 43.36%. The salt and its hydrate may be characterized by x-ray methods. Water of crystallization may be determined by gravimetry. Lanthanum may be analyzed by flame or furnace AA or by ICP-AES methods (See Lanthanum). Chloride ion in an aqueous solution of the salt may be measured by titration with a standard solution of silver nitrate or mercuric nitrate or by ion chromatography following appropriate dilution.

LANTHANUM FLUORIDE

[13709-38-1]

Formula: LaF3; MW 195.90

Uses

Lanthanum fluoride is used in phosphor lamp coating. Mixed with other rare earths, it is used in carbon arc electrodes and lasers. Also, the fluoride is used in the production of lanthanum metal, an intermediate step in the manufacture of high purity metal.

Physical Properties

White hexagonal crystal; hygroscopic; density 5.9 g/cm3; melts at 1,493°C; insoluble in water and acids.

Preparation

Lanthanum fluoride may be precipitated by adding hydrofluoric acid to an aqueous solution of lanthanum nitrate or chloride:

La(NO3)3 + 3HF → LaF3 + 3HNO3

The compound also can be made by heating lanthanum oxide with ammoni-

LANTHANUM HYDROXIDE 449

um fluoride in hydrofluoric acid at 300 to 400°C. Ammonium fluoride released in the reaction sublimes at this temperature:

La2O3 + 6NH4F•6HF 300−400o C → 2LaF3 + 6NH4F↑ + 3H2O↑

Anhydrous lanthanum fluoride also may be made by passing dry hydrogen fluoride over lanthanum oxide. This process, however, produces trace amounts of lanthanum oxyfluoride, LaOF. Highly purified material may be obtained by passing dry purified HF over molten fluoride in a platinum crucible.

Analysis

Elemental composition: La 70.91%, F 29.01%. The compound may be characterized by x-ray methods. Lanthanum may be analyzed by AA or ICP technique following digestion in nitric acid and appropriate dilution of acid extract.

LANTHANUM HYDROXIDE

[14507-19-8]

Formula: La(OH)3; MW 189.93

Uses

Lanthanum hydroxide is used to prepare other lanthanum salts.

Physical Properties

White amorphous solid; decomposes on heating; insoluble in water.

Preparation

Lanthanum hydroxide is precipitated by adding excess of caustic soda, caustic potash or ammonia to an aqueous solution of a La3+ salt, such as LaCl3, La(NO3)3 or La(SO4)3:

La3+ + 3OH¯ → La(OH)3

Reactions

The hydroxide is strongly basic. It reacts with acids undergoing neutralization reactions; i.e., reaction with HCl or HNO3 yields hydrated salt of lanthanum chloride or nitrate on evaporation and crystallization of the solution.

It reacts with ammonium salts displacing ammonia:

La(OH)3 + 3NH4Cl → LaCl3 + 3NH3 + 3H2O

The hydroxide absorbs CO2 from air forming lanthanum carbonate:

2La(OH)3 + 3CO2 → La2(CO3)3 + 3H2O

450 LANTHANUM NITRATE

Lanthinum hydroxide on dehydration produces lanthanum oxide monohydrate, La2O3•H2O:

Analysis

Elemental composition: La 73.13%; O 25.27%, H 1.59%. Lanthanum may be analyzed in the acidified extract of the compound by AA or ICP technique (See Lanthanum). Dehydration at 100°C produces La2O3•H2O, releasing one mole of water of crystallization per mole of hydroxide (9.5%) loss, which may be measured by gravimetry.

LANTHANUM NITRATE

[10277-43-7]

Formula: La(NO3)3•6H2O; MW 433.01; stable as hexahydrate Synonym: lanthanum nitrate hexahydrate

Uses

The nitrate is used as an analytical standard; as a matrix modifier in furnace AA analysis; and for preparing other lanthanum salts.

Physical Properties

White crystalline solid; hygroscopic; decomposes around 40°C; very soluble in water and alcohol.

Preparation

The salt is prepared by dissolution of lanthanum oxide, hydroxide or carbonate in nitric acid, followed by crystallization, and obtained as a hexahydrate. The general reactions are as follows:

La2O3 + 6HNO3 → 2La(NO3)3 + 3H2O

La (OH)3 + 3HNO3 → La(NO3)3 + 3H2O

La2 (CO3)3 + 6HNO3 → 2La(NO3)3 + 3CO2 + 3H2O

Reactions

Thermal dissociation yields lanthanum oxide, La2O3. Its reactions in aqueous solutions are those of La3+ ion. It forms double salts with magnesium, calcium and ammonium nitrates and many other salts when mixed in stoichiometic amounts. Such double salts are obtained from solution mixtures on crystallization and may vary in their compositions.

Analysis

Elemental composition (for hexahydrate): La 32.08%, N 9.70%, H 2.79%, O