LANTHANIDES

Separation

²/₃ of world production is actually used mixed in the proportions occuring naturally in the ore

1. Cerium & Europium may be extracted Chemically:

• Oxidize only Ce to M⁴⁺ by HClO or KMnO₄, then precipitate as CeO₂ or Ce(IO₃)₄
• On action of Zn/Hg only Eu forms a stable M²⁺ that doesn't reduce H₂O, then isolate by precipitation as EuSO₄

2. Separation by Fractionation:

Small Scale methods used originally:

• Fractional Crystallization of e.g. Ln(NO₃)₃^.2NH₄NO₃^.4H₂O or Ln(BrO₃)₃

• Fractional Thermal Decomposition of e.g. Ln(NO₃)₃

Current Small Scale Lab. Separation:

• Ion-Exchange Displacement Column

• Ln³⁺(aq) are strongly adsorbed by a cation-exchange resin
• add an eluant ligand

  typically chelating ligands

  e.g. EDTA , or 2-hydroxy-EDTA

  e.g. HIB{[[alpha]]-hydroxyisobutyric acid}

• Ligand binds most strongly to smallest ion

• Elution order is Lu Æ La
• The process of separation is indicated graphically

greater detail on these columns may be found in:-

• Greenwood & Earnshaw, p. 1427-1428
• Open University S304 Unit 27, p. 20-22

Current Large Scale Industrial Separation:

Solvent Extraction

• Ln³⁺(aq) is extracted in a continuous counter-current process into a non-polar organic liquid (e.g. kerosene)
• the kerosene contains ca. 10% of
  • bis(2-ethylhexyl)phosphinic acid (DEHPA)

  or

  • tri-n-butylphosphine oxide (TBPO) (ⁿBu₃O)₃PO

1. solubility of Ln³⁺ in organic solvent increases with its RAM
2. separation factor for adjacent rare earths = 2.5
3. automatic multistep, counter-current conditions Æ 99.9% purity Ln