Tributyl phosphate rare earth complexes

Lanthanum also may be separated from aqueous solutions of rare-earth nitrates by liquid-hquid extraction using a suitable water-immiscible organic hquid such as tributyl phosphate or another complexing agent dissolved in it. 

Neutral extractants constitute the third important class of solvent extraction reagents for the rare-earth elements. Since they have no charge, neutral extractants only extract neutral complexes or charge-balanced ion pairs. They also tend to extract ion-paired acid molecules such as HNO3. Solvating extractants may be dissolved in an organic diluent, or they may be the organic diluent itself (e.g., diethylether, methylisobutylketone, tributyl-phosphate). Phase transfer is accomplished by solvation of the complex by the extractant, and a typical equilibrium can be written as... 

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