Effect of initial pH on the extraction yield
The initial pH of the DASE is a very important parameter for
the extraction of sulfuric acid and Fe(III). By optimizing the initial
pH, it is convenient to maximize the removal of sulfuric acid and
Fe(III) from the DASE. Therefore, the pH of the DASE was adjusted
by sulfuric acid in the range of 0.28–1.80, which is in accordance
with the pH range of the DASE derived from commercial processes.
The extraction of sulfuric acid and Fe(III) from the DASE with Fe(III)
concentration of 0.0509 mol/L was operated with 35 (v/v)% TOA
and 12 (v/v)% TBP in kerosene. The experiments were performed at
25 ◦C with O/A ratio of 1:1 and the mixture was stirred for 10 min.
The results of the effect of initial pH on the final pH are presented
in Fig. 7.
It can be seen from Fig. 7 that the curves of the extraction yield
and the pH are consisted of three parts. The first part is when the
initial pH ranges from 0.28 to 0.64, during which the extraction
yield jumps from 47.5 to 88.9% and the final pH increases significantly
from 1.62 to 2.41. This phenomenon can be attributed to
the formation of Fe(OH)(SO4)2
2− which is extracted into organic
phase. It is different from the curve of Fe(III) and the curve of the
final pH in the second part. When the initial pH ranges from 0.64 to
1.20 and the final pH falls into the range of 2.40–3.50,the extraction
yield drops dramatically from 88.9 to 2.0%. Ferric ions hydrolyzed as