ZINC(II) EXTRACTION-STRIPPING WITH

XVIII-th ARS SEPARATORIA – Zloty Potok, Poland 2003
ZINC(II) EXTRACTION-STRIPPING
WITH TRIBUTYL PHOSPHATE
Magdalena REGEL-ROSOCKA, Joanna STELMASZYK,
Ana Maria SASTRE*) and Jan SZYMANOWSKI
Institute of Chemical Technology and Engineering, Poznan University of
Technology, Poznan, Poland,
*)
Departament d’Enginyeria Quimica, Universitat Politecnica de Catalunya,
E.T.S.E.I.B., Barcelona, Spain
Hot-dip galvanizing in 96.5-99% purity zinc, carried out at 445-465°C
[1], needs the pure surface of iron goods. The rust is removed by the pickling
with 20% HCl carried out at room temperature. As a result, the concentration
of hydrochloric acid decreases and accumulation of iron ions (90% as Fe(II))
occurs. When pickled goods are housed on recycled hooks, i.e., covered in
previous process with zinc, an accumulation of zinc(II) in the pickling
solution is also observed. Chloride concentration is constant due to
accumulation of metal as chlorides [1]. Spent pickling solution contains 911% HCl, 60-90 g/L Fe (mainly Fe(II)), 5 g/L Zn(II).
In high HCl concentration anionic chlorocomplexes of zinc are
formed (Fig. 1). They are extracted with solvating and basic reagents very
well.
1.0
0.9
2-
ZnCl4
Molar fraction
0.8
0.7
0.6
2+
Fe
+
FeCl2
+
FeCl
0.5
0.4
2+
FeCl
0.3
0.2
FeCl3
-
ZnCl3
0.1
ZnCl2
0.0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-
Cl , M
Fig. 1. Theoretical distribution of chlorocomplexes of Zn(II), Fe(II), Fe(III)
in HCl solution
93
XVIII-th ARS SEPARATORIA – Zloty Potok, Poland 2003
(O
Bu
)
3
P=
O
.....
HC
l
(OBu)3 P = O ..... HCl
) 3P
Bu
(O
=O
l
HC
Water
pool
ClH ..... O=P (OBu)3
.
....
ClH ..... O=P (OBu)3
The extraction isotherms and studies on zinc(II) recovery by
extraction with various solvating and basic extractants, including tributyl
phosphate (TBP), trialkylphosphine oxides and alkylamines were described
in our recent works [2-[6]. The effective stripping was only possible when
TBP was used. TBP was used as zinc(II) extractant in a mixer-settler system
(MSU 0.5, MEAB, Sweden). Mass transfer was observed not only in the
mixer but also in the settler. The model taking into account the ideal mixing
in the mixer and combination of perfect mixing and plug flow in the settler
was proposed and positively verified [7].
The transfer of HCl and H2 O from the aqueous phase to the organic
phase is observed. The water transfer to the organic phase is responsible for
third phase formation. This phase is rich of metal, HCl and extractant. There
is possibility of reversed micelle formation and the transfer of Fe(II) to the
organic phase in hydrophilic micelle core. Hypothetical reversed micelle of
tributyl phosphate is shown in the Fig. 2.
.....
u )3
OB
(
P
O=
ClH
ClH ..... O=P (OBu)3
ClH
.....
O=
P(
OB
u)
3
Fig. 2. Hypothetical reversed micelle
Moreover, emulsion formation causes problems in extraction-stripping
process carried out in mixer-settler system. That is why the attempts of
determination of reversed micelle formation during zinc(II) extractionstripping with tributyl phosphate were undertaken. Conductivity
measurements were chosen as one of the key methods for the study of
microemulsions.
94
XVIII-th ARS SEPARATORIA – Zloty Potok, Poland 2003
ACKNOWLEDGEMENT
The work was supported by the Science for Peace NATO grant SfP 972398
Hydrochloric Acid and by the Polish State Committee for Scientific
Research grant No. 1473/TO9/2001/2.
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[1]
[2]
[3]
[4]
[5]
[6]
[7]
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