Separation of lanthanides

Ion exchange method and solvent extraction method are discussed

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 (Ln 3+ ) passed through the glass column Stationary phase - resin Resin – Positive charge ion to exchange Ln 3+ + 3 R-H Ln-R 3 + 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, La 3+ , Gd 3+ and Lu 3+ Size variation, La 3+ > Gd 3+ > Lu 3+ 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 La 3 + Gd 3+ Lu 3+ Eluent – citric acid / ammonium citrate buffer . La-R 3 + 3NH 4+ 3 NH 4 -R + La 3+ Lu 3+ - comes first, La 3+ - 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 : Gd 3+ from La 3+ Gd (NO 3 ) 3 and La(NO 3 ) 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