Simplification results:

This simplification results because of the fact that the extent of dissociation is negligible and the terms multiplied by K11 and K12 are unimportant. From Eq. 3.33, we can infer that the extraction increases with the increasing iron concentration.

In the region of low iron concentration where dissociation of the complex remains the only significant organic phase reaction, the terms involving K11 and K12 are important and those multiplied by K10 become insignificant. So Eq.3.32 simplifies to the subsequent expression:

D ≅  K _D′ K₇[HS⁺ ] [1 + K₁₁{K_DK₇K₁₁[HS⁺  ] [Fe] + K₁₂K_D[HS⁺ ][Cl^-]}o ^-1/2 ]]

This display that the extraction rise along with decreasing iron concentration reaching to a value of

D ≅ K_D K₇ [HS+] {1+K₁₂K_D [H+] [Cl-]}^-1/2

From Eq. 3.35, it is clear that the extraction of Fe(III) is favored by increasing acidity. Those equations do not reflect anything on the decrease in the extraction of Fe (III) at very high acidity which is primarily due to the solubility effect.