HYDROGEN EVOLUTION INHIBITING ADDITIVES FOR ZINC ELECTROWINNING

ADDITIFS INHIBITEURS DE L'EVOLUTION DE L'HYDROGENE POUR L'EXTRACTION ELECTROLYTIQUE DE ZINC

English Abstract

A cetylpyridinium salt, cetylpyridinium chloride (CPC) is used as a hydrogen
evolution inhibitor (a current efficiency improver) in a commercial zinc
electrowinning process. Zinc electrowinning compositions containing a)
antimony and b) antimony and glue were tested. Adding CPC at a 0.05mM
concentration to the electrowinning liquor resulted in increased current
efficiency for both electrolytes.

French Abstract

On utilise une sel de cétylpyridinium, à savoir du chlorure de cétylpyridinium (CPC) comme inhibiteur de l'évolution de l'hydrogène (un agent d'amélioration de l'efficacité du courant) dans un procédé commercial d'extraction électrolytique de zinc. Des compositions d'extraction électrolytique de zinc contenant (a) de l'antimoine et (b) de l'antimoine et de la colle ont été testées. En ajoutant du CPC à une concentration de 0.05mM à la liqueur d'extraction électrolytique de zinc, on a pu obtenir une meilleure efficacité du courant pour les électrolytes.

Claims

WE CLAIM:
1. A method of improved zinc electrowinning, comprising:
adding a cetylpyridinium salt additive to a zinc electrowinning
electrolyte.
2. A method according to claim 1, wherein said cetylpyridinium
salt is a cetylpyridinium halide.
3. A method according to claim 2, wherein said cetylpyridinium
halide is cetylpyridinium chloride.
4. A method according to claim 3, wherein said cetylpyridinium
chloride is at 0.05 millimolar (mM) concentration in said zinc
electrowinning liquor.
5. A method according to claim 1, wherein said zinc
electrowinning electrolyte contains zinc sulfate.
6. A method according to claim 1, wherein said zinc
electrowinning electrolyte contains antimony.
7. A method according to claim 1, wherein said zinc
electrowinning electrolyte contains glue.
8. A method according to claim 7, wherein said glue is animal
glue.
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9. A method according to claim 8, wherein said animal glue is
gelatin.
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Description

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HYDROGEN EVOLUTION INHIBITING ADDITIVES FOR ZINC ELECTROWINNING
FIELD
The invention is related to additives for zinc
electrowinning that inhibit hydrogen evolution and/or improve
current efficiency for zinc electrodeposition, specifically
cetylpyridinium-based additives.
BACKGROUND
Improving the energy efficiency of the zinc electrowinning
process by inhibition of the parasitic hydrogen evolution
reaction, which occurs in parallel with zinc deposition, is of
major technological and commercial interest. One way of
minimizing the cathodic hydrogen evolution is by the use of
additives, generally organic compounds, which selectively
increase the hydrogen evolution overpotential. Mackinnon et a1.
(Journal of Applied Electrochemistry, Volume 20, pages 728-736,
1990) and Scott et al. (Journal of Applied Electrochemistry,
Volume 18, pages 120=127, 1988) describe the use of animal glue
in combination with antimony to improve the current efficiency
for zinc electrowinning when compared to additive-free
electrolytes.
There is a need for improved additives that minimize

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hydrogen evolution during zinc electrowinning while providing
the same or improved performance over traditional additives_
Therefore, it is an object of this invention to provide
improved additives for zinc electrowinning that minimize
hydrogen evolution while providing similar or improved
performance over traditional additives.
S UNWARY
Cetylpyridinium chloride (CPC), a cetylpyridinium salt, was
tested as an additive in a zinc electrowinning process in two
separate zinc electrowinning electrolyte compositions: 1) with
antimony and 2) with both antimony and glue.
The CPC additive had the most significant influence in the
presence of antimony or antimony + glue combination, where it
increased the current efficiency by 23.2% and 7.6%,
respectively.. Moreover, the presence of 0.05 mM CPC did not
increase the overall.cell voltage.
DETAILED DESCRIPTION
Methods And Apparatus
Commercial beaker test cells containing a commercial
electrowinning electrolyte (liquor) were connected to a power
supply and placed in a 37 °C water bath. The anodes and cathodes
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were made of lead and aluminium, respectively. The laboratory
supplied MSDS sheet indicated for the electrolyte the following
composition: zinc sulfate 28 - 34% by weight, magnesium sulfate
9 - 15 g/l (grams/litre) and manganese 1.5 - 2.5 g/1.
After allowing the temperature inside the test cells to
reach the desired value of 37 °C, a constant current of 0.045 A,
representing an electrowinning current density of 450
- amperes/meter2, was applied for either 4 or 20 hours to a non-
agitated electrolyte. After completion of the experiment the
electrode assembly was removed from the glass beaker, rinsed
with distilled water and the cathode deposit carefully scraped
off and weighed with four digits precision using a digital
Mettler AE 100 analytical balance. The test cells were rinsed
between experiments with distilled water and acetone in order to
remove traces of the organic additives. Replicates were also
performed and the standard deviation was estimated.
The zinc electrodeposition current efficiency was
calculated based on Faraday's law:
CE(%) _ ' ~ F ~ nzd .100 ( 1 )
I~t~AZn
where
CE- current efficiency for Zn electrodeposition (o)
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z - no. of electrons exchanged [=2]
F - Faraday's number [=96485.3 C mol-1]
and - amount of zinc deposit (g)
I- applied current [=0.045 A]
t - time (s)
AZ" - atomic weight of zinc [=65.39] .
The cetylpyridinium chloride (CPC) (e. g. Sigma-Aldrich,
U.S.) had the following structure:
CayHas~Cl
C~
~N~(CH2)~4
~CH3
Example 1
Zinc Electrowinning Liquor with antimony present
Antimony (Sb) in 0.04 mg/1 (milligrams/litre) concentration
was added as antimony - potassium tartrate to the zinc
electrowinning electrolyte. Both four and twenty hour runs were
performed. The experimental results of the four-hour runs are
summarized in Table 1.
without the CPC additive present in the electrolyte, Sb had
a detrimental effect on the current efficiency, i.e. between
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65.1% (cell no. 15) and 74.7% (cell no. 14). On average, the
current efficiency without the CPC additive present was 69.9%.
Adding CPC improved the current efficiency on average by 23.2%,
i . e. from 69 . 9 0 to 93 . 1 0 .
Table 1: Effect of CPC on the current efficiency of
zinc electrowinning in the electrolyte containing
0.04 mg/1 Sb (as Sb-tartrate).
Conditions: Current Average
efficiency
(~)
Temperature : 3 7 C per Cell Cs
No .
Time : 4 hours 14 15
No additive ' 74.7 65.1 69.9
+1.0 6.8
CPC 0.05 mM (mM = 93.7 92..7 93.1
millimolar) 2.g 0.9
rn
The effect of CPC in~longer-term (20 hours) experiment is
shown in Table 2. Without the CPC additive, the current
efficiency of cell no. 15 was only 36.6%, whilst with 0.05 mM
CPC present the zinc electrowinning current efficiency was
58.9%. Thus, with the CPC additive the current efficiency was
higher by 22.3%.
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Table 2: Effect of CPC on the zinc electrowinning
current efficiency in 20 hour experiment with 0.04
mg/1 Sb in the electrolyte.
Conditions: Current efficiency
(%)
Temperature : 3 7 per Cel l No .
C
Time: 20 hours 15
No additive 36.6
CPC 0.05 mM 58.9
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Example 2
Zinc E~ectrowinning Liquor with both antimony and glue
Similar experiments to those in Example 1 were performed
with an electrolyte containing 0.04 mg/1 of Sb and 10 mg/1 of
glue (e. g. "pearl glue" supplied by Hudson Industries,
Johnstown, New York). Both 4 and 20 hour runs were carried out.
The effect of the CPC additive on the zinc electrowinning
current efficiency in the 4 hour runs is shown in Table 3.
The presence of glue minimizes to a certain extent the
negative effect of antimony, yielding current efficiencies
between 88.9% and 90%. However, adding 0.05 mM CPC brought
about additional increases of current efficiency, i.e. from
89.4% on average in the absence to 97% in the presence of CPC
(Table 3).
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Table 3: Effect of CPC on the current efficiency of
zinc electrowinning in the electrolyte containing
0.04 mg/1 Sb (as Sb-tartrate) + 10 mg/1 glue.
Conditions: Current Average
efficiency
Temperature: 37 C (%) per CB (~)
Cell No.
Time : 4 hours 13 16
No additive 88.9 90.0 89.4
0.9 0.8
CPC 0.05 mM 98.3 95.8 97.0
1.8
.
The 20 hour experiments (Table 4) showed that CPC in 0.05
mM concentration increased the current efficiency of cell no. 16
from 77_2% to 87.3%.
Table 4: Effect of CPC on the zinc electrowinning
current efficiency in 20 hour experiment with 0.04
mg/1 Sb and 10 mg/1 glue in the electrolyte.
Conditions: Current efficiency (o)
per
Temperature : 3 7 Cel l No .
C
Time: 20 hours 16
No additive 77.2
CPC 0.05 mM 87.3
The cell voltage is another important figure of merit of
the electrowinning process. An increase in the cell voltage
represents an increase in the amount of energy required and,
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therefore, a less efficient electrowinning process. Table 5
shows that using 0.05 mM CPC in conjunction with Sb and glue did
not induce an increase of the cell voltage.
Table 5: Effect of CPC on the average cell voltage
in 4 hour experiments with 0.04 mg/1 Sb and 10 mg/1
glue in the electrolyte.
Conditions: Average cell voltage ~(v)
Temperature: 37 C
Time: 4 hours
No additive 2.83
CPC 0.05 mM 2.83
Accordingly, while this invention has been described with
reference to illustrative embodiments, this description is not
intended to be construed in a limiting sense. Various
modifications of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons
skilled in the art upon reference to this description. It is
therefore contemplated that the appended claims will cover any
such modifications or embodiments as fall within the scope of
the invention.
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