This document discusses methods for separating lanthanide ions using ion exchange and solvent extraction. In ion exchange, lanthanide ions in solution are passed through a resin column and interact differently with the resin based on their size, allowing for separation. Smaller ions interact more strongly and elute first. Solvent extraction involves dissolving lanthanide ions in water and adding an immiscible organic solvent. The partition coefficient determines how ions distribute between the two solvents, allowing separation based on differences in this value for different ions through multiple extractions.

1. Separation of Lanthanides
(ion-exchange & solvent extraction)
D. JIM LIVINGSTON
Asst. Prof. of Chemistry
St. John’s College.

2. Ion-Exchange method

3. Ion-Exchange method
Lanthanide ion mixture (Ln3+) passed through the glass column
Stationary phase - resin
Resin – Positive charge ion
to exchange
Ln3+ + 3 R-H Ln-R3 + 3H+
Lanthanide ions are dissolved in water while
the resin is solid.
Interaction between lanthanides and resin take place

4. Ion-Exchange method
• Consider the following three lanthanide ions,
• La3+ , Gd3+ and Lu3+
• Size variation,
• La3+ > Gd3+ > Lu3+
• Lanthanum – large size, Lutetium – small size.
• Since the ions are dissolved in water, it is surrounded by
water molecule. (hydrated)
• Smaller the ion – greater the hydration.
• Small hydrated ion-
strong binding with resin.
ie, held at the top of the
column

5. Ion-Exchange method
La3+
Gd3+
Lu3+
Eluent – citric acid / ammonium citrate buffer.
La-R3 + 3NH4+ 3 NH4-R + La3+
Lu3+ - comes first, La3+ - comes last

6. Solvent Extraction
"Extraction" refers to transference of compound(s) from a solid or liquid into a
different solvent or phase
Types of extraction
Liquid–liquid extraction (Solvent extraction)
Solid-phase extraction
Acid-base extraction
Supercritical fluid extraction
When a tea bag is added to hot water, the compounds
responsible for the flavor and color of tea are extracted
from the grounds into the water
Liquid-liquid extractions in the
laboratory usually make use of a
separatory funnel, where two immiscible
solvents are combined to separate a solute
from one solvent into the other, according
to the relative solubility in each of the
solvents

7. Example : Gd3+ from La3+
Gd(NO3)3 and La(NO3)3 in water
Organic solvent:
tributylphosphate in kerosene

8. Partition Coefficient
When a solution is placed in a separatory funnel and shaken with an immiscible
solvent, solutes often dissolve in part into both layers. - "partition" or "distribute
themselves" between the two layers. When equilibrium has established, the ratio
of concentration of solute in each layer is constant for each system, and this can be
represented by a value K (called the partition coefficient or distribution
coefficient).
Partition coefficient (K) is the ratio of concentrations of a compound in a
mixture of two immiscible solvents at equilibrium
Concentration of solute in organic solvent
K =
Concentration of solute in water
Credit:
Organic Chemistry Laboratory Techniques, Nichols, 2017
Lisa Nichols (Butte Community College) Oroville, California, United States

9. Value of K is constant for a particular solvent
system

10. Multiple extraction

11. • Partition coefficient of gadolinium and lanthanum
are different.
• By make use of the multiple extraction,
• Gadolinium and lanthanum can be separated.

12. References
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book%3A_
Organic_Chemistry_Lab_Techniques_(Nichols)/04%3A_Extraction