Chemical formula of TOA-Fe(III) sulfate complex
It can be seen from Fig. 5 that one molar of sulfuric acid reacts
with two molars of TOA to form a complex. However, when Fe(III)
and sulfuric acid is extracted simultaneously, the chemical formula
of the formed complex remains a question to be answered. Therefore,
the saturation capacity of the organic phase is measured by
mixing the fresh feed solution with the organic phase continuously
until the concentrations of the components of the raffinate is
the same as that of the feed solution. The concentrations of Fe(III),
SO4
2− and TOA in the organic phase were calculated by subtraction
method. The experimental results listed in Table 3 indicate that
the saturated concentrations of Fe(III) and sulfuric acid stay almost
constant. It is demonstrated that the molar ratio of Fe(III), SO4
2−
and TOA is 1:2:2 in the saturated organic phase.
The complex, polymeric compound and the species in sulfate
medium are related to the acidity of the solution, the supporting
electrolyte concentration, the concentration of Fe(III) itself and
temperature, et al. The overall concentration of Fe(III) can be calculated
by the mass balance equation as follow,
TFe (III) =
Fe3+
+
FeOH2+
+
Fe(OH)2
+
+2
Fe2(OH)2
4+ (10)
Combining this expression with the hydrolysis constants for the
hydroxyl species listed in Table 2,the species distributions of Fe(III)
in the experimental pH region was plotted in Fig. 6. It is deducible
that the chemical species of Fe(III) occur in the aqueous phase in