Composition of the extracted species:

On the basis of above results, the composition of the extracted species with propionic, butyric and valeric can be represented as follows:

Aliphatic   Amine                System

Zn (II) -          ZnA₂. 3HA.B

Cd (II) -          CdA₂. 3HA.B

Heterocyclic   Amine           System

Zn (II) -            ZnA₂.            2HA. 2B

Cd (II) -           CdA₂.             2HA. 2B

Eq. 3.65 is used for the calculation of extraction constants at different amine and constant acid concentration. A value of extraction constant reveals that the heterocyclic amines are much better synergists than the aliphatic counterparts because of higher basicity of the former.

It may be interesting to note that there is also a phenomenon known as antisynergism which is the reverse of synergism. It was practically observed in the case of an alkyl phosphoric acid - phosphorus ester (HX - S) and in the HTTA -TBP (HX - S) system, due to the addition of excess of S. It appears which in the first case; the further off excess of solvating molecule (S) reduces the concentration of free chelating agent by increasing interaction between HX and S through hydrogen bonding. As a result of this, the extraction is lowered. Within the second example, the decrease in extraction is supposedly caused due to water content of the organic phase and the destruction of anhydrous synergistic species M(TTA)_xS_y.