Distribution coefficients complexing agent, effect

In addition to the applications in extractive distillation referred to above, there are other industrial examples where electrolytes in mixed solvents occur. In many industrial situations nonvolatile electrolytes are either added to effect the separation of multicomponent process streams (e.g., the complexing agents added to enhance distribution coefficients in solvent extraction) or are present as a result of the process itself. Ex-... 

Complexing agents may be added to an extraction system either to increase or to decrease the distribution coefficient of a metallic component between aqueous solution and kerosene. For example, Zr(N03)4 is not extracted at all from aqueous solution by kerosene. However, when TBP is added to the kerosene, a compound of probable composition [H4] Zr(N03)4 2TBP is formed that is readily extracted. As an example of a complexing agent that reduces extraction, the effect of adding fluoride ion to the above system may be considered. The more stable, inextractable complex ion ZrF is then formed according to the reaction... 

When the distribution equilibrium reaction involves hydrogen ions, changing the hydrogen ion concentration will have a strong effect on the distribution coefficient. An example of this is the extraction of metal complexes of acetyl acetone (HAa) and other weakly acid complexing agents by benzene. The equilibrium reaction for extraction of thorium by this reagent is... 

The complexing agent itself may be a poor solvating medium for the complex, in which case an effective diluent can solvate the complex and thereby encourage hs formation. Very large changes in equilibrium distribution coefficients can be achieved by char ir the diluent. 

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